last update: 19 July 2024

• Far red primer

• main papers link page

• Far-red: The Forgotten Photons ---YouTube vid by Bruce Bugbee, Utah State (those yield claims and results are for lettuce and not cannabis)

• [Far-red photons have equivalent efficiency to traditional photosynthetic photons:

implications for re-defining photosynthetically active radiation](https://onlinelibrary.wiley.com/doi/am-pdf/10.1111/pce.13730) --this is Bruce Bugbee's argument for including far red light in PAR measurements

• Photosynthetic activity of far-red light in green plants

• The effect of far-red light on the productivity and photosynthetic activity of tomato

• The long-wavelength limit of plant photosynthesis

• Far‐red radiation stimulates dry mass partitioning to fruits by increasing fruit sink strength in tomato

• Plant responses to red and far-red lights, applications in horticulture

• Growth and Cell Division of Lettuce Plants under Various Ratios of Red to Far-red Light-emitting Diodes

• Supplemental Far-Red Light Stimulates Lettuce Growth: Disentangling Morphological and Physiological Effects

• Effects of the red:far-red light ratio on photosynthetic characteristics of greenhouse cut Chrysanthemum

• Disentangling the effects of photosynthetically active radiation and red to far-red ratio on plant photosynthesis under canopy shading: a simulation study using a functional–structural plant model

• Dissecting the Genotypic Variation of Growth Responses to Far-Red Radiation in Tomato

• The photosynthetic parameters of cucumber as affected by irradiances with different red:far-red ratios

• Growth and nutritional properties of lettuce affected by mixed irradiation of white and supplemental light provided by light-emitting diode

• Promotion of Flowering from Far-red Radiation Depends on the Photosynthetic Daily Light Integral

• Increase in Biomass and Bioactive Compounds in Lettuce under Various Ratios of Red to Far-red LED Light Supplemented with Blue LED Light

• Effects of Continuous or End-of-Day Far-Red Light on Tomato Plant Growth, Morphology, Light Absorption, and Fruit Production

• Effect of supplemental far-red light with blue and red LED lamps on leaf photosynthesis, stomatal regulation and plant development of protected cultivated tomato

• Far-red light is needed for efficient photochemistry and photosynthesis

• Far-Red Light Accelerates Photosynthesis in the Low-Light Phases of Fluctuating Light

• Effect of interactions between light intensity and red-to- far-red ratio on the photosynthesis of soybean leaves under shade condition

• The role of far-red light (FR) in photomorphogenesis and its use in greenhouse plant production

• [Action spectra of photosystems II and I and quantum yield of

photosynthesis in leaves in State 1](https://www.sciencedirect.com/science/article/pii/S0005272813002144)

• Far-Red Spectrum of Second Emerson Effect: A Study Using Dual-Wavelength Pulse Amplitude Modulation Fluorometry

• Defining the Far-Red Limit of Photosystem II in Spinach

• Far-red radiation promotes growth of seedlings by increasing leaf expansion and whole-plant net assimilation

• Fast cyclic electron transport around photosystem I in leaves under far-red light: a proton-uncoupled pathway?

• The phytochrome red/far-red photoreceptor superfamily

• A Moderate to High Red to Far-red Light Ratio from Light-emitting Diodes Controls Flowering of Short-day Plants

• Overhead supplemental far-red light stimulates tomato growth under intra-canopy lighting with LEDs

• Morphological and physiological properties of indoor cultivated lettuce in response to additional far-red light

• Far-red light enhances photochemical efficiency in a wavelength-dependent manner

• Far-red light during cultivation induces post harvest cold tolerance in tomato fruit

• Supplemental intracanopy far-red radiation to red LED light improves fruit quality attributes of greenhouse tomatoes

• End-of-day Lighting with Different Red/Far-red Ratios Using Light-emitting Diodes Affects Plant Growth of Chrysanthemum × morifolium Ramat. ‘Coral Charm’

• Blue radiation attenuates the effects of the red to far-red ratio on extension growth but not on flowering

• Supplemental Far-red Light-emitting Diode Light Increases Growth of Foxglove Seedlings Under Sole-source Lighting

• The effect of far-red light on the productivity and photosynthetic activity of tomato

• The Effect of Supplemental Blue, Red and Far-Red Light on the Growth and the Nutritional Quality of Red and Green Leaf Lettuce

• Substituting green or far-red radiation for blue radiation induces shade avoidance and promotes growth in lettuce and kale

• A Mathematical Model of Photosynthetic Electron Transport in Response to the Light Spectrum Based on Excitation Energy Distributed to Photosystems

• Duration of light-emitting diode (LED) supplemental lighting providing far-red radiation during seedling production influences subsequent time to flower of long-day annuals

• Improvement of Growth and Morphology of Vegetable Seedlings with Supplemental Far-Red Enriched LED Lights in a Plant Factory

• Effect of Extended Photoperiod with a Fixed Mixture of Light Wavelengths on Tomato Seedlings

• Leaf morphology, optical characteristics and phytochemical traits of butterhead lettuce affected by increasing the far-red photon flux

• Low Red to Far-Red Light Ratio Promoted Growth and Fruit Quality in Salt-Stressed Tomato Plants Based on Metabolomic Analysis

• Spectral-conversion film potential for greenhouses: Utility of green-to-red photons conversion and far-red filtration for plant growth

• Far-red light enrichment affects gene expression and architecture as well as growth and photosynthesis in rice

• Far-red light modulates grapevine growth by increasing leaf photosynthesis efficiency and triggering organ-specific transcriptome remodelling

• Supplemental far-red light influences flowering traits and interactions with a pollinator in tomato crops

• End-of-day Far-red Lighting with a Low Daily Light Integral Increases Stem Length But Does Not Promote Early Leaf Expansion for Petunia ×hybrida Seedlings

• Improved chilling tolerance in glasshouse-grown potted sweet basil by end-of-production, short-duration supplementary far red light

• Cucumber leaf necrosis caused by radiation with abrupt increase of far-red component

• Far-red Light in Sole-source Lighting Can Enhance the Growth and Fruit Production of Indoor Strawberries

• Far-red Light and Nitrogen Concentration Elicit Crop-specific Responses in Baby Greens under Superelevated CO2 and Continuous Light

• Hypsochromic shift of phyC complements the inhibition of hypocotyl elongation under moderate red/far-red light

• Florigen-producing cells express FPF1-LIKE PROTEIN 1 that accelerates flowering and stem growth in long days with sunlight red/far-red ratio in Arabidopsis

• Brassinosteroid and gibberellin signaling are required for Tomato internode elongation in response to low red: far-red light

• Characterizing the expression patterns of short-day flowering genes, the manipulation of their expression using red-far red wavelengths, and the resulting phenotype/ chemotype in Cannabis sativa

• Day-extension Blue Light Inhibits Flowering of Chrysanthemum When the Short Main Photoperiod Includes Far-red Light

• Photosynthesis under a red Sun: predicting the absorption characteristics of an extraterrestrial light-harvesting antenna

• The Power of Far-Red Light at Night: Photomorphogenic, Physiological, and Yield Response in Pepper During Dynamic 24 Hour Lighting

• Photosynthesis in sun and shade: the surprising importance of far-red photons

• The structure of Photosystem I acclimated to far-red light illuminates an ecologically important acclimation process in photosynthesis

• Regulation of lateral root development by shoot-sensed far-red light via HY5 is nitrate-dependent and involves the NRT2.1 nitrate transporter

• Far-Red Light Effects on Lettuce Growth and Morphology in Indoor Production Are Cultivar Specific -good read

• Far-red light: A regulator of plant morphology and photosynthetic capacity

• Far-red light and temperature interactively regulate plant growth and morphology of lettuce and basil

• Far-red Fraction: An Improved Metric for Characterizing Phytochrome Effects on Morphology

• Exposure to lower red to far-red light ratios improve tomato tolerance to salt stress

• Low red: Far-red light ratio causes faster in vitro flowering in lentil

• Evaluation of Growth and Photosynthetic Rate of Cucumber Seedlings Affected by Far-Red Light Using a Semi-Open Chamber and Imaging System

• Adding Far-Red to Red-Blue Light-Emitting Diode Light Promotes Yield of Lettuce at Different Planting Densities

• Far-red photography for measuring plant growth: a novel approach

• [USING FAR-RED LIGHT TO PROMOTE LEAF EXPANSION FOR YOUNG PLANT

PRODUCTION](https://api.mountainscholar.org/server/api/core/bitstreams/e2ce892e-21ec-42f4-b402-7021d58ecc70/content) -master thesis

• Effects of Supplemental Far-Red Light on Leafy Green Crops for Space

• The Phytochrome System – Why Use Far-Red? - application note

• How gibberellin-related compounds shape far-red light responses in Marchantia polymorpha

• Far-red radiation stimulates dry mass partitioning to fruits by increasing fruit sink strength in tomato

• [Far-Red Light Reflection from Green Leaves and Effects on Phytochrome-Mediated Assimilate Partitioning under

Field Conditions](https://www.semanticscholar.org/paper/Far-Red-Light-Reflection-from-Green-Leaves-and-on-Kasperbauer/135567932368846ca9ca07bdbffe0b1de99643ad)

• Young watermelon plant growth responses to end-of-day red and far-red light are affected by direction of exposure and plant part exposed

• Far-red light is needed for efficient photochemistry and photosynthesis

last update: 19 july 2024

• part of SAG's Lighting Guide

• links to 2024 far red papers

TL;DR: You likely do not want to add far red light in the most common indoor grow situations like with cannabis. I went through some of the peer reviewed literature, have done my own testing, read through the misinformation that is ever present on cannabis forums, read up on what industry professionals are thinking, and came up with this primer. Far red likely benefits some crops like lettuce.

David Hawley Ph.D of Fluence has a solid primer on far red light that you should read through before reading this primer. He articulates how there is a lot of confusion when it comes to far red light and plant growth.

• FAR-RED: INTRODUCTION AND YIELD

Quick far red light facts

• Far red light is defined as light from 700-750 nm or 700-800 nm depending on the source. PAR (photosynthetic active radiation) is light from 400-700 nm only. ePAR (extended PAR) is a definition being popularized by Bruce Bugbee (one of the world's foremost plant lighting researcher) which is light from 400-750 nm and is not recognized by ANSI/ASABE S640 which are the standardized definitions for the "quantities and units of electromagnetic radiation for plants". ANSI/ASABE S640 defines light with a wavelength of 700-800 nm as far red light and in most situations is the correct answer.

• According to Bruce Bugbee et al, far red photons are equal to PAR photons in photosynthetic capacity, however, things are a little more complex than this blanket statement and far red photons with a wavelength longer than 750 nm have little photosynthetic capacity, and why ePAR is defined as 400-750 nm only. Far red light must be used in conjunction with PAR light for efficient photosynthesis and far red light is very inefficient on its own for photosynthesis.

• The older past claims of adding far red light to PAR light with plants to significantly boost photosynthesis rates above normal are not being backed by the modern peer reviewed literature although there may still be some synergistic effect. This is commonly called the "Emerson effect" or "Emerson enhancement effect". The Emerson effect must use light that has a wavelength of less than 680 nm (deep red) and greater than 680 nm, and these longer wavelengths of far red light can be used instead of PAR photons to a certain point for photosynthesis. The Emerson effect has nothing to do with flowering nor does it have to do with combining multiple wavelengths of light other than with far red light.

• Far red light causes increased acid growth which will result in leaves to be larger (but thinner) and stems to be more elongated. This will increase the LAI (leaf area index) of a plant for greater photon capture but you may not want the additional elongation in the stems or inflorescence (flowers/buds). Plants are sensitive to far red radiation through the phytochrome protein group out to about 800 nm and this is why far red is defined as 700-800 nm. But, even longer wavelengths can elicit some responses in plants which is important because many video cameras use 850 nm LEDs for night/dark time illumination.

• Close to 50% of far red light is reflected off healthy green leaves, depending on chlorophyll levels, and far red also transmits through leaves at a greater rate than PAR light. For reference, perhaps 6-10% of red/blue and 15-20% green light is reflected off a healthy green leaf.

• Far red LEDs (735 nm) have a higher theoretical maximum PPE (photosynthetic photon efficacy) of 6.14 uMol/joule at 100% efficiency and there are far red LEDs on the market that are >4 uMol/joule. For reference, a 100% efficient 450 nm blue/white LED would be 3.76 uMol/joule. Far red LEDs can be more energy efficient than PAR LEDs.

• 1-2% of light intercepted by a leaf is readmitted as far red light. This is known as chlorophyll fluorescence and the levels at a particular PPFD roughly tells us about how well the photosynthesis systems in the plant are performing in real time, with lower amounts meaning the plant is doing better. Plants are always exposed to tiny amounts of far red light whenever the plant receives light even from a pure blue light source, as an example, due to the chlorophyll fluorescence from the leaves.

• Far red generally promotes flowering in long day plants but can be variable in short day or day neutral plants. There may be a difference in far red light on continuously during normal daylight hours versus end of day far red light treatment only.

• In cannabis, the latest limited research so far is showing that far red light may lower final yields, cannabinoid levels, terpene levels and anthocyanins (purple pigmentation). There are only a few studies on far red light and cannabis and there needs to be more studies before hard claims can be made, but there's a good reason most lights don't have far red LEDs.

• Far red light can improve yields in some plants other than cannabis such as lettuce by making larger leaves. Far red generally lowers anthocyanin and phenolic compounds in microgreens which is undesirable.

• If you read about red to far red ratios, it's often the amount of red light specifically at 660 nm and far red light at 730 or 735 nm, rather than all red light and all far red light. It's important to understand what the author means.

Far red photosynthesis and the Emerson effect

Far red light increases photochemical efficiency in photosynthesis and most far red photons are not actually absorbed by a leaf (perhaps 10-20% of far red photons are absorbed in a stand alone leaf depending on leaf thickness).

Far red light must be used with PAR light for efficient photosynthesis, and far red light on its own is very inefficient known as the "red drop effect" (see the McCree curve which is only for monochromatic light). The red drop off effect starts to happen at 680-685 nm so the common 660 nm deep red LEDs are the longest wavelength and the lowest energy photons compared to other PAR photons that can drive photosynthesis efficiently on its own.

PAR (up to 680 nm) and far red (specifically >680 nm in this case to about 750 nm) working together is known as the Emerson effect. There are some papers that claim that red and far red working together can give a significantly greater photosynthetic capacity than normal, and one might find this claim in botany textbooks. However, Zhen/Bugbee claims that red and far red have an equal net photosynthesis, not a greater net photosynthesis, with up to 40% far red light able to be used with PAR and have a linear response, but with longer wavelengths of far red being less efficient:

• Far-red photons have equivalent efficiency to traditional photosynthetic photons: Implications for redefining photosynthetically active radiation --this study used the single leaf model and CO2 gas exchange to measure net photosynthesis with 14 different plants

What's going on with the Emerson effect?

In plants there are two photosystems that operate in series that are involved with photosynthesis: PSII (photosystem 2- named in order of discovery) which is the first step is mostly only sensitive to PAR light and can be over excited by PAR light and not very far red sensitive, while PSI (photosystem 1) works with PAR and far red but can be under excited by PAR light.

• wiki link to photosystem

To simplify what happens with far red photosynthesis, there are electrons that get transported from the PSII to PSI when illuminated, but the PSI is not quite as efficient at processing these electrons as the PSII with PAR light alone, so we can get a bit of an electron "traffic jam" between the PSII and the PSI (through a few mobile electron transport carriers particularly plastoquinone). By adding enough far red light, we make the PSI act as efficiently as the PSII that clears up this electron "traffic jam". Adding far red increases photochemical efficiency in the leaf and that in a nutshell is how the Emerson enhancement effect works.

But, the PSII (unlike the PSI) is not very far red sensitive, and that's why we can't efficiently drive photosynthesis with far red light alone. This is the "red drop effect" and why PAR has always been defined as light from a wavelength of 400-700 nm. Wavelengths longer than 700 nm (actually starting at about 680 nm) take a nose dive in its photosynthesis efficiency unless that far red light is added to PAR light.

• PAR alone- good photosynthesis but PSI is not optimal

• Far red alone- not much photosynthesis because PSII is not working well

• PAR and far red- the Emerson effect with both PSI and PSII working at maximum efficiently

This all gets into electron transport found in the "z scheme" that is part of light dependent reactions in photosynthesis:

• wiki link to light dependent reactions

I really want to emphasize this point: PAR as a PPFD measurement is not going away despite new metrics like by Bruce Bugbee promoting 400-750 nm ePAR because far red light really does not work on its own efficiently. Both metrics have their uses and given a personal choice I'd buy an ePAR meter rather than a PAR meter. I elaborate further on this post on /r/budscience on issues with ePAR:

• How Bruce Bugbee's ePAR has been rejected as an industrial standard

This book chapter below really gets into the fine details of how the Emerson enhancement effect really works:

• The Red Drop and the Emerson Effect --from the book "Photosynthesis" chapter 13, 1969 (note that green and red algae are used in this chapter)

It's important to understand that there is a difference between net photosynthesis in a leaf and the final yield in a plant. They are closely correlated but not necessarily completely correlated.

This below is a paper stating the far red lower yields in cannabis. As a caution, look at the pics and you'll see that no training is being used which likely affected the results in the study. There needs to be more studies before strong claims can be made.

• The morphology, inflorescence yield, and secondary metabolite accumulation in hemp type Cannabis sativa can be influenced by the R:FR ratio or the amount of short wavelength radiation in a spectrum

Efficacy of far red LEDs

TL:DR- Far red LEDs can make engineering sense and have the potential to be more energy efficient than PAR LEDs. Don't get "efficacy" confused with "efficiency".

PPE is the "photosynthetic photon efficacy" of the LED and is a metric pertaining to the amount of photons that are generated compared to the energy input to the LED in joules (watt-seconds). The best white LEDs are currently around 3.1 uMol/joule (micromoles of photons generated per joule) and the best red are a little above 4 uMol/joule.

Far red photons have less energy than PAR photons therefore we can theoretically create more photons per energy input to the LED. To calculate the energy of a photon in electron-volts (eV), take 1240 and divide it by the wavelength to get the energy. Then use 10.37 and divide by the photon eV to get the maximum PPE.

Example for a 735 nm far red LED:

• 1240 / 735 nm = 1.69 eV <---energy of the photon in eV

• 10.37 / 1.69 eV = 6.14 uMol/joule <---maximum possible PPE

• A 100% efficient 735 nm far red LED will have a PPE of 6.14 uMol/joule

Because far red LEDs can have a higher theoretical PPE than red LEDs, due to far red photons having less energy than PAR photons, this means that far red LEDs could be more energy efficient. The maximum efficacy of a 100% efficient 735 nm far red LED is 6.14 uMol/joule, while for 660 nm red it's 5.51 uMol/joule, so a far red LED can put out about 11% more photons than a red LED at the same electrical efficiency.

By comparison, a 450 nm blue/white 100% efficient LED would only be 3.76 uMol/joule.

Of course we don't have 100% efficient LEDs and the best LEDs today have efficiency in the lower 80s% (Samsung LM301B/H). The Samsung LM301 EVO is 86% efficient for the top bin at nominal current levels but uses a 437 nm LED as a phosphor pump rather than more traditional 450 nm LEDs and is rated at 3.14 uMol/joule.

White LEDs aren't going to get much more efficient because it's more than just the electrical efficiency of the LED chip to consider, it's also the quantum efficiency of the phosphors used and the efficiency of the optical extraction of the photons from the LED itself. That 86% efficiency for the Samsung LM301 EVO is close to as high as it's going to go (Ledestar claims white LEDs that are about 89% efficient).

The best far red LEDs are now close to 4 uMol/joule which would be about 65% efficient so there is still room for improvement and there's not a phosphor efficiency hit. The phosphor used in white LEDs also causes some of those photons to scatter and far red (and red) LEDs don't have that issue. The very best 660 nm red LEDs are about 4.4 uMol/joule or 83% efficient under driven a little so there is still a little room for improvement, but not as much as far red LEDs.

Photomorphogenesis

Far red light is a plant morphology (shape) regulator and promotes the shade avoidance response. Far red light will increase the amount of "acid growth" in a plant which causes additional stem/petiole stretching and larger but thinner leaves. These larger leaves can capture more photons and the longer petioles can space the leaves out further both which can increase the canopy LAI (leaf area index).

What happens with acid growth, which is different from growth through photosynthesis, is that the plant cell walls loosen and swell up with water becoming larger than normal that is regulated through the plant hormone auxin (and gibberellins). This is what causes stretching in plants.

• wiki link to shade avoidance

• wiki link to acid growth

• wiki link to acid growth hypothesis

If far red LEDs can have a higher theoretical efficacy, and if according to Zhen/Bugbee we can use up to 40% far red light, then why don't we just use 40% far red light in LED grow lights?

Because it's going to hyper elongate your plants if you do, and we may not want that except perhaps in some crops like lettuce. Even then 40% far red is likely excessive even in lettuce which is why Bugbee says to use 10-20% far red instead (source- his YouTube videos). You may read that the sun has a around a 1:1 ratio of far red light, but that is only compared to red light, not the additional green or blue light. 700-750 nm far red makes up around 19% of sunlight as measured as solar 400-750 nm ePAR (but full sunlight has a significantly higher PPFD of around 2000 uMol/m2/sec than what we normally grow at indoors).

Far red increases acid growth mediated through the phytochrome protein group. There are five identified forms of phytochrome (A-E) that play different roles in plants that are in two states: far red light changes phytochrome to Pr and red changes phytochrome to Pfr. It's these two states that determine how phytochrome is expressed.

• wiki link to phytochrome

Photoperiodism

Photoperiod cannabis is a short day plant and the autoflowers are day neutral. Many far red light studies are for long day plants that can react the opposite to short day plants with photoperiodism.

There is evidence that NIR photons can delay photoperiod flowering in cannabis by 3-12 days. The study below has to do with 850 nm photons often used in night time security cameras but the NIR lighting levels are pretty high (Bugbee is 3rd author):

• Photons from NIR LEDs can delay flowering in short-day soybean and Cannabis: Implications for phytochrome activity

This study claimed no difference in far red light and flowering time but the far red PPFD was pretty low:

• • The Effect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L.

Leaf Optical Characteristics

While dark green leaves reflect 6-10% blue/red and perhaps 15-20% green, about 40-50% of far red light is reflected off a green leaf. Far red also has a high transmission through leaves.

The following pics are spectral shots taken with my spectroradiometer:

• spectral profile shot of a very high nitrogen cannabis leaf --I used this photo starting in 2012 to illustrate that most all green light is being absorbed in a very high nitrogen leaf yet far red is still highly reflective.

• spectral shot of sunlight through a green leaf --this really illustrates how transparent a leaf can be to far red light. Much more far red light is being transmitted than green light.

• solar spectral reflectance from a dark green tree --keep in mind that this is a relative chart and not an absolute chart. About 85% of green was absorbed by that fir tree.

• leaf thickness scanner using red and far red LEDs --because red light is well absorbed but far red is not, I can use this idea to make a leaf thickness scanner. I can actually use a digital oscilloscope to chart the thickness of a leaf.

Far red fluorescence

Any time that a leaf or any part of a plant that contains chlorophyll is being illuminated with PAR light then that plant part is also radiating far red light. Roughly 1-2% of the light absorbed by a leaf is being re-radiated as far red light. This is known as chlorophyll fluorescence (CF) and higher amounts of CF at a particular PPFD means that photosynthesis is less efficient. For example, we can measure the amount of CF to see how well a plant is photosynthesizing like if the plant's roots are dry then the stomata (gas exchange pores) in the leaves close to prevent moisture from escaping. This also cuts off the plant from receiving CO2 shutting down photosynthesis and increasing the CF.

Here is a direct shot of a leaf glowing with far red light. The leaf was illuminated with a 405 nm UV laser. One can use this technique to see leaf damage not normally visible to the naked eye:

• leaf glowing far red --the green is dead leaf tissue and the blue is some cotton fibers.

• same leaf as above buy color saturated --I saturated the above pic in Photoshop to help see the details.

• different leaf with pH burn --pH burn really shows up using far red CF techniques particularly if I were to then saturate the pic.

• relative spectral chart of green and far red --I adjust my spectroradiometer to only show green and far red. That far red hump is all CF.

SAG's personal thoughts on far red light

Look at what the high end science driven LED manufacturers are doing like Fluence LED. Are they adding far red LEDs to the vast majority of their lights? Nope, just red LEDs. Are there any papers showing that adding far red has a total positive efficacy in cannabis? Not that I've seen so far.

Are there papers showing a positive efficacy with other plants? Yes, but not with cannabis and it can be financially tricky to grow other plants with LEDs as the sole source light (so many commercial vertical lettuce grow ops have gone out of business because they had no realistic business model in the first place, particularly in Europe where energy prices are higher). Microgreens can be grown under LEDs with financial success but far red generally lowers red/purple anthocyanin pigmentation and lowers aromatic phenolic compounds which we don't want.

To me, far red light is that nonsense that causes my plants to start to elongate, and as a tiny grower in particular, that last thing I want is extra elongation in my plants. I would add far red to lettuce, though, to get bigger leaves.

Full sunlight is around a PPFD of 2000-2200 uMol/m2/sec. Such intense light will cause your plants to be very compact, perhaps more than you want. That's where you might want to add far red light and natural sunlight is right around 10-20% far red compared to 400-700 nm PAR light (not compared to the whole solar spectrum). Plants generally have a significantly lower photosynthesis rate at full sunlight levels. Can adding a bunch of far red light change this indoors?

I've seen far red photosynthesis "boosters" for sale such as small far red pucks that are only a few watts. I've seen threads on cannabis forums about "ZOMG!!!" my plants are growing so much better with the far red puck. It's all BS.

Far red lasers are particularly dangerous because you'll see the reflection from the dim beam but might get fooled into thinking that there is not much power in that dim far red beam because our eyes have low far red sensitivity but not zero sensitivity. In 2009 I had a close call with a 20 watt far red laser that I wanted to use with a beam spreader as a far red light source. I looked at the diffuse reflection of the far red beam when first setting it up and took my googles off briefly to help align things (but...but...but...just a quick look! The beam is pointed the other way!). I had a headache for a few days and my eyes felt like they had sand in them. I never use lasers as general light sources anymore, even if using a beam spreader. The conservation of etendue also means that the laser can be focused down to a tiny very intense point which can make wrinkled foil side reflectors in a grow chamber safety problematic unlike with LEDs.

part of SAG's Plant Lighting Guide

last update: 21 April 2024

TL;DR- you may want to experiment using low color temperature white lights rather than high color temperature white lights for growing some microgreens and try having the lights on 24 hours per day with the lower color temperature. A lower color temperature may allow you to run your microgreens at high lighting levels for greater photosynthesis. 200-400 uMol/m2/sec is the norm for most microgreens, but some of the papers below show mixed results and promote using a lower PPFD and I've seen commercial growers promote around 100 uMol/m2/sec. Most people's hobby grow ops I see online are likely growing at a lower PPFD.

Although I'm only an amateur grower and experimenter when it comes to microgreens (I have far more experience with cannabis), I did take the time to skim over about 30 peer reviewed papers on the subject of microgreen lighting that are linked below, and I do know the technical aspects of the theory along with almost three decades of indoor growing experience. I'm merely offering some opinions here as it pertains to microgreens.

This YouTube channel has done far more light testing with microgreens than I have done:

• On The Grow YouTube channel --he points out very well how light geometry makes a difference.

Be careful of assumptions

A major issue with making broad statements about very optimal microgreen lighting is that you're dealing with a variety of different plant species: radish, basil, pea etc. With cannabis for example, you're dealing with a single species, and even then different cultivars can have different optimal results in light quantity (the PPFD) and light quality (the SPD or spectral power distribution i.e. the specific wavelengths). Even the optimal photoperiod can be different with different cannabis cultivars according to the very latest research.

This higher variety notion can be magnified even further with microgreens because the same species of a microgreen can have different cultivars with very different optical characteristics in their leaves e.g.- sweet basil with green leaves and purple basil with purple leaves due to the very high anthocyanin content. Another example would be the red radish cultivars versus the green ones. Different cultivars can also have different specific light sensitive protein expressions (although not a microgreen, different tomato cultivars can have very different reactions to light particularly the photoperiod, as an example).

Don't assume that all microgreens have the same optimal lighting conditions.

Don't make assumptions about your light intensity- get a light meter down at canopy levels using a light meter that is cosine corrected and that has a remote sensor head, and not a potentially unreliable phone app.

Don't assume that you can grow hemp microgreens which can be legally problematic without a license in many states in the US like Nevada, even with the Agriculture Improvement Act of 2018. It costs several thousand dollars to get fully licensed to grow hemp in Nevada and I don't know how the state mandated harvest report would work with hemp microgreens. I believe Arizona has a maximum 14 day old hemp seedling standard for microgreens.

Don't assume a commercial grower actually understands lighting theory. I have yet to meet anyone IRL outside a plant growth lab and very few people online who understand the technical aspects of the theory. I have seen "experts" promote certain wavelengths for plants of pigments only found in algae, for example.

Light intensity and measurement

In horticulture the light intensity is the PPFD (photosynthetic photon flux density) measured in micromoles of photons per square meter per second. I write it as uMol/m2/sec although it's often written as µmol m-2 s-1. With white light, and white light only, we can use lux instead of uMol/m2/sec (1) <---read the notes below. For a white light with a CRI of 70 or 80 we can use 70 lux = 1 uMol/m2/sec and be within 10% true all of the time of a quantum light meter (assuming both meters are properly calibrated). With modern phosphors using 73 lux = 1 uMol/m2/sec and be within 5% most of the time.

For a CRI 90 white light we can use 63 lux = 1 uMol/m2/sec and be within 10% all of the time and 65 lux = 1 uMol/m2/sec to be within 5% most of the time. For the sun we use 55 lux = 1 uMol/m2/sec. To be noted, most professional quantum meters claim no better than 5% absolute accuracy although the good ones I've measured were closer to within 1% as measured with my spectroradiometer. Cheap quantum light meters like the $150 one by Hydrofarm can be a crapshoot due to the sensor used (horrible design!), and the cheap LightScout meters can be problematic from an even different type of sensor used although they will be good enough for white light for non-scientific use. Based on my testing, I would not trust cheap quantum light meters for color LEDs or blurple lights.

For common measurements I use the Apogee SQ-520 for PPFD and the Extech 401025 for lux. For complex measurements I use a Stellarnet Greenwave spectroradiometer.

I have an article on using lux meters instead of quantum light meters for white light with the theory of why we can do this accurately enough:

• Using a lux meter as a plant light meter

Due to cosine correction errors, unknown sensor errors depending on the specific phone, and the way that people tend to tilt their phone back when taking a reading, I do not recommend using your phone as a light meter no matter what app you may be using. You can get proper lux meters with a remote sensor head starting at $20-$30, and particularly as a professional or heading in that direction, it's irrational not to have a proper light meter when growing plants. Know your PPFD! Don't use lux meters with the red/blue "blurple" lights- that is a case where you want to use a proper quantum light meter unless you know the lux to uMol/m2/sec conversion value.

I have been generically using 200 uMol/m2/sec (around 15,000 lux) with microgreens but a review of the literature below shows that a higher PPFD may be more optimal for both yield and phenolic content. A lot of those papers below are showing around 300 uMol/m2/sec (around 22,000 lux) may be more optimal depending on the microgreen or even around 400 uMol/m2/sec for some microgreens like basil. Few if any papers promote 500 uMol/m2/sec and above for any microgreen and some promote in the 100 uMol/m2/sec range.

To me it never made sense to have any periods of darkness when growing any vegetative plant but in most plants we are not trying to grow with elongated stems so microgreens are a special case. With some microgreens we want a very elongated stem with very small and immature leaves.

For the 24/7 in vegetative growth argument, generally speaking crop plants don't get "tired" and need to "sleep" in a vegetative state unless perhaps grown at a very high PPFD. This can be demonstrated by measuring the net photosynthesis rate by measuring the amount of chlorophyll fluorescence a plant gives off (1-2% of the light absorbed by a plant is readmitted as far red light, the amount depends on the PPFD and how efficient photosynthesis is working in the plant). I can measure the amount of chlorophyll fluorescence using my spectroradiometer or by using a large area silicon photodiode with a far red filter with a high precision, high sensitivity bench top multimeter (Rigol 3068).

Below is an example of a shot off my spectroradiometer measuring far red chlorophyll fluorescence to measure photosynthesis efficiency. In this case I was seeing how long it takes radish microgreen to "wake up" (30-60 seconds from darkness) and "go to sleep" (3-5 minutes from lights on). Different lighting spectra can give a slightly different signature depending how far the light penetrates the sample leaf. I can use this technique to see how much light a plant can "handle" short and long term (there are also other techniques like measuring the photochemical reflectance index).

• chlorophyll fluorescence over a few minute period --this is the far red light being emitted by a plant and is radish microgreens "waking up" in this case. Each line represents 2 seconds. The greater the chlorophyll fluorescence at a given PPFD the lower the photosynthesis efficiency. It takes time for certain enzymes involved with photosynthesis to be activated when the lights first turn on.

So generally speaking, running the lights 24/7 is fine for most plants we grow as far as photosynthesis.

To be noted, it is important that microgreen trays have an even PPFD so there is even stem stretching which is a compelling reason to use tube style lights.

SAG tip: if you see people throw around specific wavelengths for photosynthesis, they probably are not understanding how photosynthesis works by wavelength. If you see someone saying you need certain wavelengths for specifically chlorophyll A and B then that is most definitely a red flag and they are likely misunderstanding relative absorption charts for chlorophyll dissolved in a solvent at a relatively low chlorophyll density, rather than how leaves actually work that have a very significantly higher chlorophyll density. The notion that certain wavelengths are needed for photosynthesis simply is not true and all of PAR (400-700 nm) can drive photosynthesis. See this article for the theory:

• Green leaves and green light: what's really going on

Here is an example "technical" article where the author very clearly does not understand the theory and there are many, many mistakes in it:

• https://hightimes.com/grow/from-the-archives-light-through-the-eyes-of-cannabis-2011/

The lighting spectrum

One of the grow goals of many microgreens is long stems. What many people will do is have a period of etiolation (complete darkness) in the beginning of the grow cycle or long periods of darkness each day which encourages acid growth (cellular elongation or stem "stretching") which is different from growth through photosynthesis. Acid growth is basically where the cell walls loosen up and are able to fill up with water. A lower PPFD and lower levels of blue light as a ratio of light also causes this stretching. We don't neccessarily gain any dry yield with increased acid growth beyond increased acid growth also cause leaves to be bigger (and thinner) and thus have a greater light capture area for greater photosynthesis in the individual microgreen, but we will gain a lot more wet yield and that's important with microgreens, particularly if the focus is on having longer stems.

Blue light typically has the greatest effect on plants as it pertains to acid growth through the cryptochrome and phototropin protein groups. Far red light can cause additional acid growth through the phytochrome protein group.

• wiki link to "acid growth hypothesis"

Any discussion on the shape of the plant brought on by light like extra stretching/acid growth gets into photomorphogenesis and how the above mentioned light sensitive proteins are being expressed.

• wiki link to "photomorphogenesis" --I'm so glad this wiki entry was cleaned up and made more accurate

This is what a typical blue action response chart looks like for blue light by the specific wavelength. It's sometimes called the "three finger action response" response in botany. Remember, this is not a photosynthesis chart:

• blue three finger response

An issue is that most people are using lights with a very high CCT which has a high amount of blue light (2). Blue light generally suppresses acid growth the most and suppresses overall photosynthesis rates a bit in most, but not all, modern peer reviewed articles on photosynthesis rates by different wavelengths. We can see this in the McCree curve where blue light has a lower photosynthesis rate than red light or even 550 nm middle green light (3).

To me it never made sense to use a very high color temperature like 6500K to grow most microgreens because the relatively high 30% or so blue light component may be working against your goal of having longer stems and larger leaves (4). Higher lighting levels also decrease acid growth/stem elongation which is the argument that by having a lower color temperature light that increases stem elongation, we can negate the effects of the higher lighting levels i.e. lower color temperature with less blue at a higher PPFD may be optimal for greater yield while still keeping the stems longer.

To illustrate this point I have some pictures below of radish and peas grown at a PPFD of 200 uMol/m2/sec with the lights on 24/7 for maximum daily photosynthesis rates (a DLI of about 17 mol/m2/day).

If you grow with red/blue "blurple" light instead of white light, you may want to choose a blurple light that has lower amounts of blue light if you want longer stems. Blurple has no green light and green light acts the opposite way than blue light on plants, so it may be worthwhile to use lower amounts of blue to get more stretching (some academics have speculated of unknown green light receptors in plants but I think the blue light proteins are simply reversible like the red/far red phytochrome proteins are).

I've seen a lot of people promote 6500K because it's closer to natural sunlight. That's a bad argument known as "appeal to nature". For example, natural sunlight also has a lot of far red light which will lower anthocyanins and phenolic compounds. A lot of studies coming out show that far red will also reduce yields in some plants. If one wants to appeal to nature then why aren't they also using high amounts of far red light at a red to far red ratio close to 1:1 like it is in nature? There is nothing natural about indoor growing under artificial light sources.

BTW, all white lights are "full spectrum" by definition of having adequate red, green and blue light components. Blurple lights are not "full spectrum" because they don't have green light. It could be the case that people who use the term "full spectrum" are also including some far red and a bit of UV. It's not a recognized industrial term as per ANSI/ASABE S640 and more of a marketing term, so take it for what it is.

pics of some results

To be clear, this is not exactly a peer reviewed study I'm doing, and I'm only showing a few pics to illustrate a point, not to make hard claims. My plant count is not high enough to make hard claims nor would I make hard claims using single small grow containers, nor do I have proper climate controlled grow chambers.

All microgreens I grow are normally at a PPFD of 200 uMol/m2/sec. They are grown with the lights on 24 hours per day with an ambient temperature of 75-80 degrees F and a relative humidity of around 20% in the Mojave Desert (you absolutely can grow microgreens in low humidity environments with experience and proper technique). My CO2 levels tend to be around 700-800 ppm when I'm home.

This is what the grow setup looks like with six, 2 gallon "space buckets" that each have a unique LED configuration (the dark one lower right is actually pure UV-A). Different wavelengths, different color temperatures, some can be pulsed. This allows me to brute force the problem in a relatively tiny area:

• six buckets on a shelf

I have found that you can get a fairly straight line in the results for peas at 2000K, 3000K, 5000K and pure blue. 2000K had the longest stems and the largest leaves.

• peas at various CCT and blue

Radish was a little different in that 2000K gave the longest stems and the largest leaves but the difference between 3000K and 5000K was not as large. But 2000K is the way that I'd grow radish with how I grow. I let these get a little larger than radish microgreens should be.

• radish at various CCT --microgreen radish is not normally grown this big and you would not want to eat those shown

I prefer to grow microgreens with a lower CCT and there can be a significant difference between 2000K and 3000K white light in the microgreens I've played with. I prefer to have the lights on 24 hours per day. Your results may vary.

What about adding far red light?

Far red is tricky when it comes to plants. High amounts of far red light will definitely increase acid growth so you will get longer stems. Far red will also easily penetrate through leaves to hit the stems even when leaves block other light (far red is also highly reflected by leaves and ~10% far red is actually being absorbed in a single pass depending on leaf thickness). Far red may help drive photosynthesis in a phenomenon called the Emerson effect (5).

Far red is well known to trigger the "shade avoidance" response in plants by increased acid growth through the phytochrome protein group. The shade avoidance response is simply additional acid growth.

• [wiki link to "shade avoidance"](https://en.wikipedia.org/wiki/Shade_avoidance#:~:text=Shade%20avoidance%20is%20a%20set,%2Davoidance%20syndrome%20(SAS)

The issue is that you need a lot of far red light to really trigger this response to get the extra elongation, and in some of my personal experiments, far red light may reduce the amount of anthocyanins and this is supported in the literature below. It's almost never the case that we want reduced anthocyanins and "purple" is its own selling point (particularly in cannabis and not just microgreens).

• tomato seedlings example with and without far red --far red suppressed anthocyanins from forming in this case. We don't grow tomato microgreens due to the high alkaloid content in the leaves.

In this study below adding far red light decreased yields and phenolic levels. A lot of studies in plants are showing that far red has no effect on yields or reduces yields:

• Adding UVA and Far-Red Light to White LED Affects Growth, Morphology, and Phytochemicals of Indoor-Grown Microgreens

Far red LEDs do have the potential to have a much higher efficacy than other LEDs and a theoretical 100% efficient 735 nm far red LED would have an efficacy of 6.14 uMol/joule.

As an aside, far red has been a bust so far for cannabis in the literature with lower yields, lower cannabinoid levels, and potential delayed flowering. It could be the case that the benefit of far red is at extremely high, outdoor sunlight PPFD levels.

Why not grow with no blue light?

This may work but you need to experiment with the specific cultivar to make sure that you get the results that you want. Blue and UV can trigger increased anthocyanin production to make the microgreens more red or purple which can be a desirable aesthetic characteristic. Blue and UV can also trigger chemicals to increase the aroma in many plants (increased phenolic compounds) which can be an argument against using lower CCT lights that have less blue light.

Furthermore, in many types of leaves you will not get normal growth without some blue light, and have unequal cellular expansion in the leaf veins and the rest of the leaf material, resulting in leaves that are "crinkled" and unnatural looking. You can see this if you grow many (all?) lettuce cultivars under pure green or pure red light and is sometimes called "red light syndrome" as used in botany.

Although I've done pure green grows, a problem with green is that green LEDs themselves have a relatively low efficacy and efficiency known as the "green gap" in semiconductor physics. Nitride (blue) and phosphide (red) LEDs can be 80% and higher efficiency, but green lies in between those so the best efficiency right now is about 40% for some Cree LEDs and most are significantly lower. This translates to an efficacy of about 1.7 uMol/joule at best (remember that efficacy and efficiency conversion values are wavelength dependent).

• Mind the (green) gap --University Of Illinois Grainger College Of Engineering

Green light generally has the opposite effect on plants than blue light from a photomorphogenesis perspective such as increasing stretching rather than reducing stretching. Green may also reduce anthocyanin and other photochemical byproducts but this gets into how you define green. In many papers, "green" is defined as 500 nm (cyan) to 600 nm (amber) and 501 nm "green" may have different results from 599 nm "green" particularly with anthocyanins. We can actually run into the same definition problem to a lesser degree with "blue" in papers.

The latest Samsung white LM301H EVO LEDs have an efficacy of 3.14 uMol/joule (about 2.9 uMol/joule system efficacy depending on the LED driver) and an efficiency of 86% for the highest bin, so it doesn't make engineering sense to use green LEDs for horticulture when it's better from an energy use perspective to use a blue LED with a phosphor for the green light component. T8 non-LED fluorescent lights, by comparison, have an efficacy closer to 1 uMol/joule and T5 tubes are only a little better. Just say no to old style mercury vapor tube fluorescent lights!

Should you grow with very high CRI lighting?

No.

Very high (above 90) CRI lights have an additional deeper red phosphor(s) in the 660 nm range and a flatter lighting spectrum with shallower spectral dips that is closer to an ideal black body radiation source (which would be CRI 100). Most white LEDs use a 450 nm or so blue LED as the phosphor pump and all the rest of the light generated is through fluorescence of the phosphors. Very high CRI lights are less energy efficient.

If you want this deeper 660 nm or so red then you are better off from an energy consumption perspective to just use lower CRI lights and add 660 nm LEDs to the light source. The latest 660 nm red LEDs can have an efficacy of over 4 uMol/joules (low 80s% efficiency).

Having additional deeper red phosphors lowers the energy efficiency of the white LED by increasing the total Stokes shift (the difference between the 450 nm LED and the wavelength of the emitted light) in the white LED which is why higher CRI LEDs tend to run a bit hotter and have a lower efficacy.

You may want to use higher CRI lights where you prepare and serve food, though, because that extra deeper red will make colors look more natural and get red meats and red fruits/vegetables to "pop" in their appearance. Lower CRI makes colors appear dull and lifeless. Personally I think that low CCT but ultra high CRI lights can look a bit weird for general use (I have a 3000K CRI 97 DIY light by my bed).

I generally recommend CRI 80 grow lights with additional red LEDs as needed.

Gimmick lighting

I have enough experience to be very skeptical with any gimmick lighting and plants. Anything outside normal upper light and side or intracanopy lighting I consider gimmick lighting.

One type of gimmick lighting that might be worth exploring for microgreens is having far red only lights on during the dark period if using a more traditional dark period rather than lights on 24/7. The idea here would be to try to boost acid growth greater than etiolation for more stem stretching. Far red may be able to drive low levels of photosynthesis on its own (the photosynthetic drop off with far red light is called "red drop" in botany).

Pure UV-A is really a no-go. I've experimented with pure UV-A and microgreens and you'll get less photosynthesis using LEDs that are less efficient and end up with dwarfed plants that give a lower yield. You'd have to experiment if you get a significant anthocyanin or phenolic compound boost. UV-A LEDs are also less electrically efficient than PAR (400-700 nm) LEDs.

UV is pretty well known for increasing phenolic compounds. One idea may be to grow with very low blue light and then add UV light in the last 24 hours to try to boost phenolic compound and anthocyanin levels.

Pulsed light is supported in some literature to boost yields 10-15% in some plants although the results in literature are mixed. Instead of say 200 uMol/m2/sec of continuous light, you may use 400 uMol/m2/sec of light at a 50% duty cycle switched at perhaps 500 Hz. They will give the identical DLI (mol/m2/day) but the higher pulsed PPFD could trigger a boost in some photochemical reactions in addition to greater potential yield....maybe.

Pulsed light could be taken a step further and maybe pulse blurple light during one part of the 50% duty cycle, and pulse far red during the other part of the 50% duty cycle, as an example. I have no idea what that would do and just throwing out ideas. I would do this at a much higher frequency like 100 KHz (even most COBs I've pulsed work at >300 KHz and would be junction capacitance limited).

Conclusion

In conclusion, I don't know what's best for you and your particular setup. A trend in the literature below supports around 300 uMol/m2/sec may be best for many types of microgreens. Yield per energy consumption may be best at a lower PPFD, though. For me to completely light profile a specific microgreen would take a few months in my setup because I more than have to try a bunch of spectral combinations, I also have to try various PPFD combinations, and I can only do six combinations at once at a lower plant count.

If I optimal light profile a particular microgreen how much greater yield or greater phenolic compound levels am I really getting? At what point is one just being pedantic? What are the established professionals doing?

But, it may be worth it to try experimenting using lower CCT lights like 2000K at a higher PPFD to get the stems to stretch more and to have larger leaves. This may allow you to run the lights 24/7 for greater photosynthesis and faster harvesting times. You have to weigh this against the possibility of lower anthocyanin and phenolic compound levels than higher CCT lights. You would have to experiment.

I do know that there is some dogma (an authoritative opinion or belief presented as a fact) when it comes to microgreen lighting and vegetative plant lighting in general that may not be true.

Finally, in my opinion there is nothing special about 6500K lights for vegetative plant growth although this narrative is commonly pushed online.

notes

(1)

What is white light is its own article and actually a complicated subject. My definition is not going to be that same as another person's definition and different industries have their own standards. I loosely define a white light source as a light source that collectively emits light that is on or near the Planckian locus of the CIE 1931 chromaticity diagram within a certain color temperature range, such as 2700K to 7000K.

• wiki link to Planckian locus

For the purpose of this article, I also define white as 2000K although many people would agree that 2000K would be an amber light source, but to me amber is a specific wavelength range. Bridgelux has a "white" LED with a CCT of 1750K that I would not consider white.

Correlated color temperature (CCT) is essentially the red to blue ratio of a white light source with a lower CCT having more red light and a higher CCT having more blue light (green light has nothing to do with CCT). "Correlated" is used because the color temperature of the artificial light source is correlated to the temperature of a light emitting black body radiation source like an incandescent light bulb or the sun in the temperature unit of Kelvin. We normally don't use "degrees" with Kelvin like Celsius or Fahrenheit because it's an absolute temperature scale. It's a "3000 Kelvin" light and not a "3000 degree Kelvin" light, for example.

Color rendering index (CRI) is how well a light source makes colors look compared to a black body radiation source like the sun. Plants don't care about the CRI. The important thing to know, however, is that higher CRI lights have additional deep red light being emitted.

You can look at very high versus lower CRI and CCT charts here:

• Bridgelux phosphor guide

(2)

The whole idea of 6500K for veg growth gets down to what is the highest color temperature that can be tolerated to be used in shop lights, warehouse lights and the like because the higher amounts of blue light helps with dynamic visual acuity and alertness. It's also close to an illuminant standard used in photometry (standard D) and about where red/green/blue have the same ratio.

6500K lights can be a little more efficient due to the lower amount of Stokes shift in the phosphor (less light is being emitted through fluorescence rather than be directly from the blue LED that is used as the phosphor pump).

There's nothing special about 6500K in growing plants. Quartz metal halides used to be used as HID lighting for plants that had a color temperature of around 4000K.

As an aside, there's nothing particularly special about specifically 2700K lights in flowering other than we may want the reduced blue. 2700K is close to what incandescent bulbs are and why they are popular. HPS is around 2100K.

For modern cannabis growing, around 3500K is fairly typical as both a veg and flowering light, and 3500K CRI 80 is what I use as a standard control light.

(SAG tip for cannabis: if you have a separate higher CCT veg light and a lower CCT flowering light for cannabis, using the higher CCT light for the first two weeks of flowering will greatly help keep the cannabis plants more compact which can be important for tight growing spaces. In the HPS days, I'd encourage people to use metal halides for the first two weeks of flowering for cannabis)

(3)

The McCree curve is only valid from a PPFD of 18-150 uMol/m2/sec and only for monochromatic light. There are papers to support that at a higher PPFD that green can drive photosynthesis greater than even red light due to red light becoming saturated on a leaf's surface while green light can penetrate and drive photosynthesis deeper in a leaf. In most leaves 80-90% of green light is being absorbed.

• The McCree Curve Demystified --Tessa Pocock, Photonics Magazine article

• Green Light Drives Leaf Photosynthesis More Efficiently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are Green --Terashima et al, 2009

(4)

This is close to the amount of blue light in a white light source:

• 2000K is about 3 or 4% blue

• 2700K is about 10% blue

• 3500K is about 15% blue

• 4200K is about 20% blue

• 6500K is about 30% blue

(5)

Far red (700-750 nm) light "may" increase photosynthesis rates by increasing photochemical efficiency. There are two photosynthetic reaction centers, photosystems 1 and 2. PS2 comes first in the reactions and electrons can get "jammed" up when going from the PS2 to the PS1. PS1 can be driven by far red light so a little far red light can help clear up this electron "traffic jam". This is essentially how the Emerson effect works if adding far red to PAR light. But, the question is how well does it actually work and there are mixed results in actual modern testing.

• wiki link to "Emerson effect" --take the "far higher" photosynthesis claim with a big grain of salt

There has been a push to add far red in normal PAR (400-700 nm) measurements but this has not been adapted as an industry standard. I discuss this here:

• How Bruce Bugbee's ePAR has been rejected as an industrial standard.

links to open access literature

Remember that just because there are optimal conditions in a lab does not necessarily mean those results are optimal for a commercial grow operation.

• Intensity of Sole-source Light-emitting Diodes Affects Growth, Yield, and Quality of Brassicaceae Microgreens --blasting microgreens with high amounts of light may be a bad idea

• Light Intensity and Quality from Sole-source Light-emitting Diodes Impact Growth, Morphology, and Nutrient Content of Brassica Microgreens --mentions the role of gibberellins and not just auxins in acid growth. More light means smaller leaves.

• Effects of Light-Emitting Diode Light Irradiance Levels on Yield, Antioxidants and Antioxidant Capacities of Indigenous Vegetable Microgreens --you really have to look at the plant type to determine the optimal PPFD for stuff like phenolic compound levels. Highest yield per energy consumption is not neccessarily at a higher PPFD.

• [Exploration on Using Light-Emitting Diode Spectra to Improve the Quality and

Yield of Microgreens in Controlled Environments](https://atrium.lib.uoguelph.ca/server/api/core/bitstreams/33aebdc2-e247-4e21-b6dd-ce7c827e57f6/content) ---Ph.D thesis. TL;DR- greater blue decreases stem length and makes leaves smaller

• Growth and Appearance Quality of Four Microgreen Species under Light-emitting Diode Lights with Different Spectral Combinations

• Blue and Red LED Illumination Improves Growth and Bioactive Compounds Contents in Acyanic and Cyanic Ocimum basilicum L. Microgreens --there are some contradictions here with other research

• Continuous LED Lighting Enhances Yield and Nutritional Value of Four Genotypes of Brassicaceae Microgreens --continuous light generally increased anthocyanins and yield went up

• Hemp microgreens as an innovative functional food: Variation in the organic acids, amino acids, polyphenols, and cannabinoids composition of six hemp cultivars

• Continuous lighting can improve yield and reduce energy costs while increasing or maintaining nutritional contents of microgreens --uses low PPFD for a longer period

• LED irradiance level affects growth and nutritional quality of Brassica microgreens --330 and 440 uMol/m2/sec did best

• Updates on Microgreens Grown under Artificial Lighting: Scientific Advances in the Last Two Decades --meta study

• Effect of Different Ratios of Blue and Red LED Light on Brassicaceae Microgreens under a Controlled Environment

• Effect of end-of production continuous lighting on yield and nutritional value of Brassicaceae microgreens

• Blue versus Red Light Can Promote Elongation Growth Independent of Photoperiod: A Study in Four Brassica Microgreens Species

• Consumer Preference for Microgreens in the Presence of LED Lights and Information Treatments

• Adding UVA and Far-Red Light to White LED Affects Growth, Morphology, and Phytochemicals of Indoor-Grown Microgreens --adding far red increases elongation and reduced yields. This is why the notion that far red drives photosynthesis better should be taken with a grain of salt.

• Response of Mustard Microgreens to Different Wavelengths and Durations of UV-A LEDs

• Applying Blue Light Alone, or in Combination with Far-red Light, during Nighttime Increases Elongation without Compromising Yield and Quality of Indoor-grown Microgreens --I'd want to see other people duplicate this paper before putting too much stock into it

• Effects of Different Light Spectra on Final Biomass Production and Nutritional Quality of Two Microgreens --this paper contradicts other papers

• The growth and morphology of microgreens is associated with modified ascorbate and anthocyanin profiles in response to the intensity of sole-source light-emitting diodes --phenolic and anthocyanin content increased with increased PPFD

• Differential Effects of Low Light Intensity on Broccoli Microgreens Growth and Phytochemicals --50 uMol/m2/sec gave the greatest yields

• The Effect of Blue Light Dosage on Growth and Antioxidant Properties of Microgreens

• Can Light Spectrum Composition Increase Growth and Nutritional Quality of Linum usitatissimum L. Sprouts and Microgreens?

• Light Intensity and Photoperiod Affect Growth and Nutritional Quality of Brassica Microgreens

• Influence of the radiation intensity of LED light sources of the red-blue spectrum on the yield and energy consumption of microgreens

• The Inclusion of Green Light in a Red and Blue Light Background Impact the Growth and Functional Quality of Vegetable and Flower Microgreen Species --high PPFD is better

• The Response of Egyptian Spinach and Vegetable Amaranth Microgreens to Different Light Regimes --blue could reduce yields

• Effects of Greenhouse vs. Growth Chamber and Different Blue-Light Percentages on the Growth Performance and Quality of Broccoli Microgreens --blue reduced yields

part of SAG's Lighting Guide

last update: 28MAR2024

/r/Budscience actually contains a lot of quality information and I encourage you to join. These are some of the posts I've done and many of the links have discussions.

• How Bruce Bugbee's ePAR has been rejected as an industrial standard.

This gets into why ePAR has been rejected as an industry standard, so far.

• Longer Photoperiod Substantially Increases Indoor-Grown Cannabis’ Yield and Quality: A Study of Two High-THC Cultivars Grown under 12 h vs. 13 h Days

By switching to 13/11 instead of 12/12, this study found 35-50% greater yields. But what about total flowering times?

• The morphology, inflorescence yield, and secondary metabolite accumulation in hemp type Cannabis sativa can be influenced by the R:FR ratio or the amount of short wavelength radiation in a spectrum

Far red is being busted with lots of elongation, lower yields, lower terpenes, and lower cannabinoid levels.

UVA lowers things a bit.

UVB elevates some terpenes and lowers others. Total terpenes are lowered.

• Evaluating Propagation Techniques for Cannabis Sativa L. Cultivation: A Comparitive Analysis of Soilless Methods and Aeroponic Parameters

I also give some tips from my experience with designing and using aeroponic systems.

• Effect of far-red and blue light on rooting in medicinal cannabis cuttings and related changes in endogenous auxin and carbohydrates

Light quality (specific wavelengths) really doesn't affect rooting that much.

• Elevated UV photon fluxes minimally affected cannabinoid concentration in a high-CBD cultivar (Bugbee et al)

UV light keeps getting busted!

• Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids

Bugbee et al. Blue light lowers yields.

• Light Quality Impacts Vertical Growth Rate, Phytochemical Yield and Cannabinoid Production Efficiency in Cannabis sativa

A weak study but supports that blue light lowers yields.

• Light Spectra Have Minimal Effects on Rooting and Vegetative Growth Responses of Clonal Cannabis Cuttings

Another paper showing the type of light isn't that important for cloning.

• Impact of Far-red Light Supplementation On Yield and Growth of Cannabis sativa (master thesis)

SAG gets into more pissing matches! If you make a claim, you need to back it up with evidence. If you say that you have done far red experiments or have grown at 3000 uMol/m2/sec of light (lol...), and if you can't back it up, you're completely and utterly full of shit.

A flawed paper that shoots down far red, yet again.

• Optimisation of Nitrogen, Phosphorus, and Potassium for Soilless Production of Cannabis sativa in the Flowering Stage Using Response Surface Analysis

Study that shows nitrogen is more important than phosphorus for flowering.

• Characterization of Nutrient Disorders of Cannabis sativa

Pics of nute disorders.

• Pot size matters: a meta-analysis of the effects of rooting volume on plant growth

Every doubling of containers size gives around 43% greater yield in this paper.

update: 21 July 2023

• part of SAG's Lighting Guide

• all scientific papers link page

This was sourced from Google Scholar. Around Jan 2024 I'll do another scrape to get all the 2023 papers on a different thread (there's a character limit).

Interesting paper:

• Light Spectra Have Minimal Effects on Rooting and Vegetative Growth Responses of Clonal Cannabis Cuttings

• [A Survey of Modern Greenhouse Technologies

and Practices for Commercial Cannabis Cultivation](https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=10149009)

• Foliar Symptomology, Nutrient Content, Yield, and Secondary Metabolite Variability of Cannabis Grown Hydroponically with Different Single-Element Nutrient Deficiencies
• Cadmium Bioconcentration and Translocation Potential in Day Neutral and Photoperiod Sensitive Hemp Grown Hydroponically for the Medicinal Market
• [Constructing Cannabis:

A Foucauldian Genealogy (critical history) of Western Cannabis discourse and knowledge](https://mro.massey.ac.nz/bitstream/handle/10179/18857/ShoreMScThesis.pdf?sequence=1&isAllowed=y) --master thesis

• Light Spectra Have Minimal Effects on Rooting and Vegetative Growth Responses of Clonal Cannabis Cuttings
• Thermal, energy, economic, and environmental analysis of a smart wastewater recovery system for indoor Cannabis production
• [Towards dsRNA-integrated protection of

medical Cannabis crops: considering human safety, recent- and developing RNAi methods, and research inroads](https://orca.cardiff.ac.uk/id/eprint/155338/1/ps.7323.pdf)

• [THE EFFECTS OF REFLECTIVE PLASTICS ON

FLOWER AND CANNABINOID YIELDS IN DAYNEUTRAL CANNABIS SATIVA L. IN A GREENHOUSE ENVIRONMENT UNDER SUPPLEMENTAL LIGHT](https://ecommons.cornell.edu/bitstream/handle/1813/113296/Rice_Howard_Reflective_Mulch_Project.pdf?sequence=1)

• Diniconazole Promotes the Yield of Female Hemp (Cannabis sativa) Inflorescence and Cannabinoids in a Vertical Farming System
• Is Twelve Hours Really the Optimum Photoperiod for Promoting Flowering in Indoor-Grown Cultivars of Cannabis sativa?

• Effects of Different N, P, and K Rates on the Growth and Cannabinoid Content of Industrial Hemp
• Comprehensive Transcriptome and Metabolome Analysis of Hemp (Cannabis Sativa L.) in Soil Under NaCl Stress
• [Understanding bud rot development, caused by Botrytis

cinerea, on cannabis (Cannabis sativa L.) plants grown under greenhouse conditions](https://cdnsciencepub.com/doi/pdf/10.1139/cjb-2022-0139?download=true)

• Hydroponic Cultivation of Medicinal Plants—Plant Organs and Hydroponic Systems: Techniques and Trends
• [Silicon Reduces Zinc Absorption and Trigger

Oxidative Tolerance Processes Without Impacting Growth in Young Plants of Hemp (Cannabis Sativa L.)](https://assets.researchsquare.com/files/rs-1347314/v1/d1b05050-e2a5-4f1f-851a-61f7176738b1.pdf?c=1647868917)

• [EFFECTIVENESS OF MYCORRHIZAE AND VERMICULTURE SEED

INOCULATION FOR GERMINATION, VEGETATIVE GROWTH, CANNABINOID CONTENT, AND CURED FLOWER WEIGHT OF CBD-RICH HEMP (Cannabis sativa L.)](https://digital.library.txstate.edu/bitstream/handle/10877/16715/BOYER-THESIS-2023.pdf?sequence=1) --master thesis

• [Varying light intensity can alter metabolic profile and cannabispiradienone

content of industrial hemp](https://www.researchgate.net/profile/Muhammad-Roman-5/publication/371834150_Varying_light_intensity_can_alter_metabolic_profile_and_cannabispiradienone_content_of_industrial_hemp/links/6497bf51b9ed6874a5d737af/Varying-light-intensity-can-alter-metabolic-profile-and-cannabispiradienone-content-of-industrial-hemp.pdf)

• Hemp Agronomy: Current Advances, Questions, Challenges, and Opportunities
• [Mycorrhizal-based inoculants in the root microbiome

enhanced phytocannabinoid production in medical Cannabis cultivars](https://assets.researchsquare.com/files/rs-2670871/v1/7b944344-3092-4ee8-bc2a-39cb525eb5fb.pdf?c=1678950880)

• Combined ambient ionization mass spectrometric and chemometric approach for the differentiation of hemp and marijuana varieties of Cannabis sativa

• Flowering Response of Cannabis sativa L. ‘Suver Haze’ under Varying Daylength-Extension Light Intensities and Durations
• A protocol for rapid generation cycling (speed breeding) of hemp (Cannabis sativa) for research and agriculture --9 weeks seed to seed
• Comparison of the Cannabinoid and Terpene Profiles in Commercial Cannabis from Natural and Artificial Cultivation
• Varying light intensity can alter metabolic profile and cannabispiradienone content of industrial hemp
• A comprehensive review of the production technology ofCannabis sativaL. with its current legal status and botanicalfeatures
• Total yeast and mold levels in high THC-containing cannabis (Cannabis sativa L.) inflorescences are influenced by genotype, environment, and pre-and post-harvest handling practices
• Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences
• Effectiveness of Mycorrhizae and Vermiculture Seed Inoculation for Germination, Vegetative Growth, Cannabinoid Content, and Cured Flower Weight of CBD-Rich Hemp (Cannabis sativa L.)
• [Plant Growth-Promoting Rhizobacteria (PGPR) with Microbial

Growth Broth Improve Biomass and Secondary Metabolite Accumulation of Cannabis sativa L.](https://pubs.acs.org/doi/pdf/10.1021/acs.jafc.2c06961)

• [Cannabis sativa: Applications of Artificial Intelligence (AI) and

Plant Tissue Culture for Micropropagation](https://www.researchgate.net/profile/Ravindra-Malabadi/publication/372335345_Cannabis_sativa_Applications_of_Artificial_Intelligence_AI_and_Plant_Tissue_Culture_for_Micropropagation/links/64aff4e38de7ed28ba95e7c5/Cannabis-sativa-Applications-of-Artificial-Intelligence-AI-and-Plant-Tissue-Culture-for-Micropropagation.pdf)

• [Maximizing medical cannabis growth and quality: An evaluation of the effects of

ecological water regeneration in greenhouse cultivation ](https://gsconlinepress.com/journals/gscbps/sites/default/files/GSCBPS-2023-0164.pdf)

• Agronomic evaluation of Cannabis sativa (L.) cultivars in northern Colombia
• LED Technology Applied to Plant Development for Promoting the Accumulation of Bioactive Compounds: A Review --wide range of plants
• When Cannabis sativa L. Turns Purple: Biosynthesis and Accumulation of Anthocyanins
• Cannabis: a multifaceted plant with endless potentials
• CANNABIS SATIVA: ETHNOBOTANY AND PHYTOCHEMISTRY
• Cannabis sativaL.: ORIGIN, DISTRIBUTION, TAXONOMY AND BIOLOGY
• Phytochemical Composition and Antioxidant Activity of Various Extracts of Fibre Hemp (Cannabis sativa L.) Cultivated in Lithuania
• [MEDICAL CANNABIS SATIVA (MARIJUANA OR DRUG TYPE): THE STORY OF DISCOVERY OF

Δ9-TETRAHYDROCANNABINOL (THC)](https://www.journalijisr.com/sites/default/files/issues-pdf/IJISRR-1167.pdf)

• Industrial Hemp (Cannabis sativa L.) Agronomy and Utilization: A Review

• Uncovering the Potential and Handicaps of Non-drug Hemp Cultivation in South and Southeast Asia
• [CURRENT TRENDS AND FUTURE PROSPECTS OF

MEDICINAL CANNABIS: AN UNDERUTILIZED ANCIENT ETHNOMEDICINAL PLANT FOR HUMAN WELLBEING](https://www.xisdxjxsu.asia/V19I02-84.pdf)

• [Efficacies of Biological Control Agents for Controlling

Fusarium spp. in Soilless Cannabis Cultivation](https://atrium.lib.uoguelph.ca/server/api/core/bitstreams/15726c2f-3822-42d0-93e1-b3ec6843a535/content) --master thesis

• A BRIEF INTRODUCTION TO HEMP CULTIVATION, PROCESSING, TRADE, AND PUBLICATION IN THE OTTOMAN ERA

• [Monitoring of Cannabis Cultivar Technological Maturity by

Trichome Morphology Analysis and HPLC Phytocannabinoid Content](https://repository.ukim.mk/handle/20.500.12188/25120)

• Determining Antioxidant Activity of Cannabis Leaves Extracts from Different Varieties—Unveiling Nature’s Treasure Trove
• CANNABIS SATIVA: Industrial hemp (fiber type) - An Ayurvedic Traditional Herbal Medicine
• The Cannabis Plant as a Complex System: Interrelationships between Cannabinoid Compositions, Morphological, Physiological and Phenological Traits
• [Δ9-TETRAHYDROCANNABINOL (THC): THE MAJOR PSYCHOACTIVE COMPONENT IS OF

BOTANICAL ORIGIN](http://www.journalijisr.com/sites/default/files/issues-pdf/IJISRR-1178_0.pdf)

• Cannabis Extraction Technologies: Impact of Research and Value Addition in Latin America

• Correlations among morphological and biochemical traits in high-cannabidiol hemp (Cannabis sativa L.)
• Water demands of permitted and unpermitted cannabis cultivation in Northern California
• Characterization of trichome phenotypes to assess maturation and flower development in Cannabis sativa L. (cannabis) by automatic trichome gland analysis
• Developing Prediction Models Using Near-Infrared Spectroscopy to Quantify Cannabinoid Content in Cannabis Sativa
• Temporal cannabinoids profile and biomass yield in cannabigerol dominant industrial hemp under different planting dates in southern Florida
• [Quantitative Analysis of Cannabidiol and

Δ9-Tetrahydrocannabinol Contents in Different Tissues of Four Cannabis Cultivars using Gas Chromatography-Mass Spectrometry](https://www.hst-j.org/articles/pdf/KYVd/kshs-2023-041-03-10.pdf)

• [Combined Effect of Biocompost and Biostimulant on Root

Characteristics of Cannabis sativa L.](https://www.researchgate.net/profile/Ioannis-Roussis-2/publication/371732759_Combined_Effect_of_Biocompost_and_Biostimulant_on_Root_Characteristics_of_Cannabis_sativa_L/links/6492ca78b9ed6874a5c40c25/Combined-Effect-of-Biocompost-and-Biostimulant-on-Root-Characteristics-of-Cannabis-sativa-L.pdf)

• Crown gall development on cannabis (Cannabis sativa L., marijuana) plants caused by Agrobacterium tumefaciens species-complex
• Nitrogen fertilization impact on hemp (Cannabis sativa L.) crop production: A review
• The Use of Silicon Substrate Amendments to Decrease Micronutrient Concentrations at Varying Micronutrient Fertility Rates with Cannabis sativa ‘Auto CBG’

• Extraction techniques for bioactive compounds of cannabis
• Floral hemp (Cannabis sativa L.) responses to nitrogen fertilization under field conditions in the high desert
• Alternative Rooting Methods for Medicinal Cannabis Cultivation in Denmark—Preliminary Results
• Biological control of Fusarium oxysporum causing damping-off and Pythium myriotylum causing root and crown rot on cannabis (Cannabis sativa L.) plants
• [Formation of the Quality Indicators of Hemp (Cannabis sativa L.)

Seeds Sown under Organic Growing Technology](http://www.jeeng.net/Formation-of-the-Quality-Indicators-of-Hemp-Cannabis-Sativa-L-Seeds-Sown-under-Organic,166388,0,2.html)

• Organically grown cannabis (Cannabis sativa L.) plants contain a diverse range of culturable epiphytic and endophytic fungi in inflorescences and stem tissues
• Identification of Characteristic Parameters in Seed Yielding of Selected Varieties of Industrial Hemp (Cannabis sativa L.) Using Artificial Intelligence Methods
• [The responses of Cannabis sativa to environmental stress: a

balancing act](https://cdnsciencepub.com/doi/pdf/10.1139/cjb-2023-0056?download=true)

• [Micropropagation of Hemp (Cannabis sativa L.)

](https://journals.ashs.org/hortsci/view/journals/hortsci/58/3/article-p307.xml)

• [Study on the Effects of Light Intensity on the Growth and Metabolites of Industrial

Hemp](https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4456899)

• The Response of Cannabis Sativa Plants to Three Novel Plant Growth-Promoting Rhizobacteria: Yield and Cannabinoid and Terpene Profile
• Effect of Explant Source on Phenotypic Changes of In Vitro Grown Cannabis Plantlets over Multiple Subcultures
• [Minimum Wage Pass-through to Wholesale and Retail

Prices: Evidence from Cannabis Scanner Data](https://arxiv.org/pdf/2303.10367.pdf)

• Assessing the impact of piercing-sucking pests on greenhouse-grown industrial hemp (Cannabis sativa L.)
• [Physiological and cannabinoid responses of hemp (Cannabis sativa) to rock phosphate dust under tropical conditions

](https://www.publish.csiro.au/fp/Fulltext/FP22264)

• Controlled Environment Horticulture --99 pages, California codes and standards
• Loss of day length sensitivity by splice site mutation in Cannabis --what causes an auto flower to be an auto flower
• Characterization of Three Fusarium spp. Causing Wilt Disease of Cannabis sativa L. in Korea
• Variation in Hydric Response of Two Industrial Hemp Varieties (Cannabis sativa) to Induced Water Stress
• [Optimizing in vitro germination of primed industrial hemp (Cannabis

sativa L.) seeds](https://dergipark.org.tr/en/download/article-file/3098519)

• [The role of cannabis (Cannabis sativa) cultivation growth

as a driving force in land use and cover change (LUCC) in the upstream part of the Laou river catchment area (Northern Morocco)](https://ddd.uab.cat/pub/dag/dag_a2023v69n2/dag_a2023v69n2p333.pdf)

• [Using a global diversity panel of Cannabis sativa L. to develop a near InfraRed-based chemometric application for cannabinoid quantification

](https://www.nature.com/articles/s41598-023-29148-0)

• Investigation of the Effect of the Auxin Antagonist PEO-IAA on Cannabinoid Gene Expression and Content in Cannabis sativa L. Plants under In Vitro Conditions
• Challenges and potentials of new breeding techniques in Cannabis sativa
• Genomics-based taxonomy to clarify cannabis classification
• Genetic Mapping of SNP Markers and Candidate Genes Associated with Day-Neutral Flowering in Cannabis sativa L
• Effects of chitin and chitosan on root growth, biochemical defense response and exudate proteome of Cannabis sativa
• [Performance Evaluation of a Commercial Greenhouse in Canada Using Dehumidification Technologies and LED Lighting: A Modeling Study

](https://www.mdpi.com/1996-1073/16/3/1015) --math models for green houses

• [Effect of silicon on some growth, physiological and phytochemical properties

of Cannabis sativa L. in soil and soilless culture](https://ecophytochemical.gorgan.iau.ir/article_699775_5c9ec829774ab0787f6398b740557d20.pdf)

• [Biomass and Nutrient Accumulation by Dual-Purpose Hemp and

Concurrent Soil Profile Water Depletion at Three Locations in Kansas in 2022 ](https://newprairiepress.org/kaesrr/vol9/iss3/4/)

last update: 10 JUNE 2024

part of SAGs Lighting Guide

Latest:

• Measurements of the new GE dual CCT 3000/5000K "150W" PAR38

• Lights not to buy and a few you should buy

• Bridgelux Vero gen 9 COBs are coming out. Preliminary data sheets

• measurements of a 25 watt par38 in a five gallon bucket

• A community discussion on trolling

• Notes on building your own quantum board and wiring up the Mean Well XLG LED driver

TL;DR- white UFO or PAR38

Lighting level measurements for the white dimming UFO with a five gallon bucket:

• An analysis of and how to mod the FECiDA UFO LED dimmable grow light --I get into how to flip the fan and why you may not want to do it

Lighting level measurements for the PAR38 build:

• A low cost, no hassle lighting setup for a five gallon Space Bucket --this is the origianl PAR38 post

bucket cooler/warmer project

This is a current project to come up with a cheap and easy way to cool and warm a bucket.

• bucket cooler proof of concept

a discussion on defoliation

If you don't know what you are doing then don't defoliate.

• PSA: stop defoliating your plant- some of you are killing your yields

don't underwater your plant!

• How to water a plant part 2

As a beginner, use the second knuckle rule. Stick your finger in the soil down to the second knuckle and if it feels dry then do a complete and thorough watering (not just around the stem). Experienced growers typically just go off weight of the soil container.

how to do full color fluorescent imaging

This is a great DIY project. If you have a cheap UV laser, go out at night and point it at the grass. The red dot you see is chlorophyll fluorescence. It can help to use a yellow/orange/red filter to look through to block the UV.

• cheap and easy chlorophyll fluorescence imaging of a leaf

FAQ I'm working on

• Bugbee, UV light, aluminum foil/white paint

• top 5 yield killers, green light, roots, phones, CO2, temperature

a few examples of bucket builds

• Far red COB with a Vero 18 --I'm giving a lot of details on working with far red LED

• Vero 29, dimming Mean Well, dimming fan how-to bucket build

• A low cost, no hassle lighting setup for a five gallon Space Bucket --this is the OG PAR38 build brought to you by being bored in a Walmart and Covid-19

• Safety tips on the PAR38 build --how to wire up a dual PAR38 build

• PAR20 build guide --kind of a pain, I get into the safety of this particular build and why it's a problem

• 2 gallon isolation bucket day 28 --pothos plant and shows some Vero 10 under lighitng

• 5 gallon pea microgreen setup --this is the first try with microgreens at 10-15% humdity

• 5 gallon pea microgreen day 18 --this is microgreens optimized in shape to a single COB with a five gallon bucket. This is the torus or torodial pattern I sometimes mention.

• 2 gallon isolation buckets and why to use one --LOL...don't take a plant from the hardware store and put it in your grow chamber. Isolate it for three weeks first.

• 2 gallon mini buckets and showing a technique I call a "folded torus". Tomato plants --I'm showing a variety of lighting techniques

• 1st try with the Ekrof Space Bucket ---2013, note- modding LED bulbs was safe(r) back then because they still had ingress protection over the LEDs when the cover was removed and the LEDs were isolated. You should never do this with a modern LED bulb and you should use much better PAR38 bulbs instead.

testing lights

I tested seven different cheap quantum boards and they all failed. Three were quite deadly. I talk about safety testing and standards in some of the posts.

A quick tip on how to tell if the light is dangerous- look for plastic washers used anywhere in the lights construction. The light maker is playing games with the grounding and it's likely a dangerous light. Lights on Amazon, eBay and the like don't actually need safety testing to be sold (lights bought in store at a Walmart or a big box hardware store will be safe).

• I am testing cheaper "quantum boards" to UL 1598 standards. The first four failed.

• Another cheap "quantum board" failed. Very rough draft of an article. Help me pick the next light to test --I'm getting in depth on safety testing

• Found another stupid dangerous quantum board not to buy.

• MarsHydro TS 600 "quantum board" failed very badly in my testing

• Review of a $15 sixty watt garage light

• Line voltage COBs and a discussion on electrical safety --we've had people getting bad shocks by using line voltage COBs.

• Quick safety note on the very cheapest eBay line voltage LED power supplies

SAG's Light Guide linked together

• Amazon link to the light we are discussing

edit- THIS LIGHT HAS BEEN SUBJECT TO A SAFETY RECALL AND CAN NO LONGER RECOMMEND THIS LIGHT

• https://www.gov.uk/product-safety-alerts-reports-recalls/product-safety-report-fecida-led-grow-light-cruiser-series-ufo600-2305-0074

I discuss this issue here:

• https://www.reddit.com/r/SpaceBuckets/comments/1ci0as9/the_fecida_dimming_ufo_light_has_a_do_not_buy/

This is an analysis and how to hack the generic white dimming UFO grow light that is popular on the /r/spacebuckets subreddit. At $40 it's a pretty ideal solution for lighting up a five gallon space bucket but understand that it is what I commonly call a "junk light" due to the lower quality LEDs and LED driver. I would not use this light for more than a one square foot grow and don't use it normally myself (I DIY most of my lights).

I like the light because there is low voltage on the LEDs that is isolated from ground with the MCPCB (the aluminum plate that the LEDs are soldered to) also being directly grounded. The 13-100% power dimming function is very convenient. It will totally rock a 5 gallon bucket and the current best options now for the 5 gallon bucket is this light or the dual PAR38 setup.

What I don't like is the LED driver itself that has no safety markings. The light fixture itself has a CE mark but I don't trust CE with cheaper Chinese products. Without cracking the LED driver open and reverse engineering it while examining the PCB (eg checking the distance between PCB traces on the line voltage side known as "creepage" and that appropriate line voltage circuit protection is used) I can't truly attest to its safety but it would easily pass a basic electrical safety test. I don't know if it would pass a full UL 1598 (luminaires) test.

This light also blows hot air down through the light and into the bucket and we really don't want that. Below I discuss how to flip the fan so it sucks air out of the bucket instead and if you should do this mod.

PPFD (light intensity in the bucket)

Test conditions: inside a 5 gallon bucket, aluminum foil liner, Apogee SQ-520 quantum PAR sensor, the light placed on a lid with a hole cut in it. "medium power" is an estimate and may differ a bit from the measurements.

10 inches below the light:

• full power: 1354 µMol/m2/sec

• medium power: 780 µMol/m2/sec

• lowest power: 173 µMol/m2/sec

6 inches below the light:

• full power: 1570 µMol/m2/sec

• medium power: 925 µMol/m2/sec

• lowest power: 196 µMol/m2/sec

3 inches below the light:

• full power: 2950 µMol/m2/sec

• medium power: 1630 µMol/m2/sec

• lowest power: 382 µMol/m2/sec

electrical characteristics

Gear used: Rigol DM3068, Fluke 287, Siglent SDS1202X-E, TinySA

• imgur pic of LED driver ripple --sigh...

• imgur pic of RFI/EMI --damn...out to 80 MHz

LED driver frequency: about 63 KHz

max voltage on LEDs: 40.292 volts DC

average current : 1.294897 amps (5 minute average after 10 minute warm up, 74 F ambient)

current standard deviation: 377.6441 µA (as above conditions)

ave current / std dev = 3429 (ENOB = 11.7) --this is a figure of merit

true power on the LEDs: 52.174 watts

fan power draw: 0.81 watts (70 mA at 11.5 VDC)

power draw light fixture: 61.0 watts

minimum power draw light fixture: 6.4 watts

power supply electrical efficiency: 86.9%

Take a look at the RFI (radio frequency interference) pic above with the tiny spectrum analyzer. That's all noise being generated. As a ham radio operator/geek I can't have such a light around and it will also interfere with some of my high gain amplifiers. From almost DC to 80 MHz I'm getting interference. I've tested worse lights but this is pretty bad.

optical characteristics

Gear used: Stellarnet Greenwave spectroradiometer

• imgur pic light spectral plot --I got lazy and took a pic of the screen

• imgur pic of 1931 CIE chromaticity diagram

CCT: 4631K

lux to PPFD ratio: 68 lux = 1 uMol/m2/sec

chromaticity coordinates: x = 0.340, y = 0.318

DUV = -0.0158 --this is how far off from an ideal white light source we are (black body radiation source and it's that line in the middle of the 1931 chromaticity diagram also called the "Planckian locus"). For normal light bulbs we want +/- 0.006

SAG tip: I want people to see a close up pic of a red LED on this light:

• imgur pic of red LED

That's not really a red LED but rather a blue LED with a red phosphor. Normally we would never buy a light that has these sorts of very low performing LEDs on a light. That's a red flag to normally never buy the light. Actual red LEDs will have a clear package and if you get in close you should be able to see a real red LED's die. Blue LEDs, also used in white LEDs, are so cheap due to economy of scale, that this is a way for low end light makers to advertise that they have red LEDs when they really don't (but they still put out red light). Lots of the really cheap lights on Amazon use this trick but not all of them do.

how to open the light up

• 4 imgur pics of the light opened up

Obviously when you modify a line voltage device that you assume full liability when doing so. This light is fairly safe because all of the internal parts are insulated and the aluminum heat sink for the LEDs is directly grounded. I wouldn't do more than flip the fan because that's still a cheap power supply with no safety markings.

You need to drill out the heads of the rivets. Put the light on a folded heavy towel or something to protect the light's dimmer knob and take a 1/4 inch drill bit and just drill down into the center divot in the rivet. The head should pop off and the rivet's pin should fall out. If the pin does not fall out you may need to take an awl of something with a hammer and pop it out. In the worst case you can drill the pin out and retap the hole.

I bought an assorted pack of stainless steel machine screws, found the right size, and forced them in the holes causing them to be rethreaded. You have to be careful doing this because it's easy to strip the holes.

• imgur pic light closed with machine screw closeup

Ideally you get in there and scrape some of the paint/enamel off so that the head of the screw makes a better ground bond contact. You need a dremel tool or something similar. The enamel is tough and did not want to come off:

• imgur pic trying to scrape enamel

An issue is the ground bond and how the rivets and now the screws are part of the light's grounding system. The aluminum heat sink is directly grounded but the rest of the light is grounded through the rivets/screws. A solution/hack is to drill/tap a ground point on the light fixture and tie all of the grounds together (this is what I would do). I don't know how legal the grounding is because the ground bond should be on the same metal as the power input to the light but "same location" could be interpreted differently (I doubt it):

• UL 1598: *6.14.2.2 The grounding means shall be in the same location as the power supply connection means and

shall be a pigtail lead grounding conductor, a pressure terminal connector, a wire binding screw, or the equivalent*

I can measure a good ground bond using the screws with a muiltimeter but that's not how ground bond points are tested. It requires high current then you measure the voltage drop across the junction. The ground bond point and system has to handle 30 amps for 2 minutes:

• UL 1598: *17.2.3 The test of impedance shall be performed by passing a 30 A current from a part to be grounded

to the grounding terminal means for a period of 2 min and measuring the potential drop between them at the end of the period* --(no more than 4 volts drop after 2 minutes)

But to be clear, that sort of ground bond testing is done at the manufacturer level and electricians don't normally do ground bond testing because we only work with certified products in the first place and have been well trained in their use (no product safety marking means no install which in the US is covered under state electrical codes rather than the National Electrical Code).

The fan mod

The 0.8 watt fan in the light really sucks and is not pushing a lot of air. I partially damaged the power supply when I shorted the fan wires. Now when the power light switch is in the off position but still plugged in, the light will quickly strobe on and off at minimum power. When power supplies strobe like this it typically is responding to a shorted condition or the short circuit circuitry has been damaged. Don't do this.

When I flipped the fan and put everything back together the light stayed cool and at 75 degree F ambient I can press the palm of my hand into the LEDs at full power and keep it there for at least for seconds (I strive for 4 seconds, if I have to remove my hand after an honest one second then it is getting too hot).

But, when I had the now modded light on a bucket and measured the temps I was getting a 10 degree F rise over ambient inside the bucket. That's ok if your temps are low but we normally do not want such a temp rise.

By simply putting another cheap fan on top of the existing fan I was able to draw enough air through the bucket to have less than a 3 degree F rise. That's more like it and it's ready to grow some cannabis. I used a cheap 60 mm fan as the additional fan and shows just how bad of a fan that came with the light is.

• imgur pic of fan hack

• 2 imgur pics thermal camera after mod --took a pic of the thermal camera with my phone

Can you just swap out the fan with a better fan? Maybe....I did for about 10 minutes and it worked but the new fan was drawing about 200 mA while the original fan draws 70 mA. 130 mA seems small but that's triple the current draw and with such a cheap power supply I would not do this. I would have to open up the LED driver and take a hard look before I could recommend triple the current even at these smaller current levels. The fan power supply itself is not well regulated and drifts above 15 volts in an open condition and dropped from 11.5 to 11 volts with the better fan.

Is it worth modding this light?

You should know what you are doing. This isn't really dangerous like removing the cover from a light bulb and everything is insulated...or is it? I have to test the insulation to close to 1700 volts DC to make that claim in this case and my insulation tester only goes to 1000 volts. I need (1000 volts * 1.41) + twice the supply voltage and that illustrates the problem with making electrical safety claims. It tested safe for me but I don't have the gear to actually do the needed test and high voltage testing is often destructive testing.

I personally like the fan flip mod using the external fan but at the end of the day I would be recommending a mod with a no safety marking LED driver and modification to the grounding system. The existing rivets actually give a pretty good ground bond (not legit but just using a multimeter in a 4 wire Kelvin setup their junction point is less than 0.1 ohms).

Another mod would be to just remove the LED driver with a better driver and run a better fan off a separate 12 volt power supply. You could flip the aluminum heat sink around and mount your own LEDs.

So I'm torn- if you have experience then modding appears somewhat safe and it will improve the performance of your bucket system. If you have no experience you'll likely mess up drilling out the rivets and/or stripping out the holes when you try to self-tap the screws and have a poor grounding system (or more poor as the case may be).

Think before you drill and don't blame me if things go wrong.

What is ENOB? (going down the rabbit hole with power supplies)

ENOB means "effective number of bits" and used with ADC/DAC circuitry and their circuitry (op amp, voltage references etc).

• https://en.wikipedia.org/wiki/Effective_number_of_bits

I use this as a figure of merit with power supplies to test how stable and how much noise there is in the power supply. It's usually for voltage but in this case I tested for current since the light has a constant current power supply. I want to know just how constant the constant current is and have a simple figure of merit.

You need high resolution to get this number and the multimeter itself always needs a higher ENOB than the power supply being tested.

What I do is use a 6.5 digit, 2 million count multimeter (Rigol DM3068) and let the multimeter and the light warm up for at least 10 minutes. With high resolution multimeters you have temperature considerations and in the first 10 minutes my multimeter can drift as much as 40 ppm or 0.004% which is way too much for good accuracy and precision. I let my multimeter warm up and then compare it to a precision voltage reference that I never turn off and that is how I try to get closer to a few ppm error very short term (the resolution is actually 0.5 ppm true or 0.035 ppm with 100 times over sampling).

I'm likely closer to perhaps 3-5 ppm off if not more depending on how my voltage reference is feeling that day and what the room temperature is. Even the best 8.5 digit multimeters on the market can only guarantee 7-8 ppm (4 ppm ultra high accuracy option) over a one year period but they tend to perform better than that.

Anyways, then I hook the light up to read current and let the meter do a running average over a 5 minute or so period. While the meter is doing that it's also precisely measuring the standard deviation of the current or how much noise and drift there is. I divide the current numbers, take the base 2 log of that number, and that's how I get my ENOB.

For example from above:

• average current: 1.294897 amps

• current standard deviation: 377.6441 µA

• average current / std dev = 3429 (1294897 / .0003776441)

• Log2(3429) = 11.7 and this is how I get the bits.

So if this were a voltage reference I know it's stable enough for a 11.7 bit system (ignoring decimation techniques). I may be able to get away with using it with a 12 bit ADC but 8 or 10 bits is a better idea.

An ENOB of 11.7 is not good but when you consider the price point of the light and consider the application of the LED driver it's not bad either. It's an RF noise generator but at least it's a consistent RF noise generator.

What is the ENOB of my multimeter? Well it's 2 million count and Log2(2 million) is about 21. With 100 times over sampling I'm theoretically at closer to an ENOB of 25 very short term (as per data sheet of 0.035 ppm resolution over sampled). That 100 times over sampling is actually 100 NPLC or "number of power line cycles" because with higher resolution multimeters you have to take instabilities that the power line causes into account and by precisely integrating over power line cycles there is a lot of noise that we can get to drop out. I doubt I'm truly seeing these numbers.

What calibrates the calibrator?

Quantum mechanics and liquid helium.

• https://en.wikipedia.org/wiki/Josephson_voltage_standard

Once we used to use special batteries called a Weston cell that would put out 1.018638 volts but that's not really good enough for the 7.5 and the 8.5 digit multimeters and the Wetson cell has some tiny temperature drift.

• https://en.wikipedia.org/wiki/Weston_cell

With the Josephson voltage standard we can use a microwave frequency to control the voltage output and microwave frequencies can be ultra precise using small atomic clocks (rubidium or cesium frequency standards). I don't pretend to understand how it all works. But there are government and commercial labs (eg NIST, Fluke) that have these voltage standards and what people can do is ship in their 8.5 digit multimeters to be calibrated "against the stack" or use a traveling standard with a precision temperature controlled buried Zener diode calibrated to multiple stacks that can calibrate the 8.5 digit multimeters:

https://us.flukecal.com/products/electrical-calibration/electrical-standards/732c-734c-dc-voltage-reference-standards

I only have 6.5 digits so I can use low cost calibration standards that have been calibrated to an 8.5 digit multimeter.

https://voltagestandard.com/001%25-10v-reference --(initial calibration is 0.5 ppm with a 2000 hour burn in and calibrated to your choice of temperature)

If you really want to go down the rabbit hole then there is a YouTuber named Marco Reps where you'll learn about the "precious PPMs" with dry German humor:

https://www.youtube.com/watch?v=GZxJR3C0N0c

11 NOV 2022

Part of SAG's Lighting Guide

I ran in to the 40,000 character limit with part 1

• cannabis links part 1

I still have to take time to organize everything! I have over 250 papers to go over and reorganize. This is less than half of all cannabis papers that have now been published.

Most interesting and contradicts Bruce Bugbee:

• Impact of Far-red Light Supplementation On Yield and Growth of Cannabis sativa (master thesis- will be made public May 2023. "Results showed a decrease in yield and an increase in height as far-red light intensity increased")

• A Comprehensive Review on the Techniques for Extraction of Bioactive Compounds from Medicinal Cannabis

• Light Quality Impacts Vertical Growth Rate, Phytochemical Yield and Cannabinoid Production Efficiency in Cannabis sativa

• Performance Evaluation of a Commercial Greenhouse in Canada Using Dehumidification Technologies and Led Lighting: A Modeling Study

• Impacts of Different Light Spectra on CBD, CBDA and Terpene Concentrations in Relation to the Flower Positions of Different Cannabis Sativa L. Strains

• Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content

• Cannabis sativa L.: Crop Management and Abiotic Factors That Affect Phytocannabinoid Production

• Multi-Omics Approaches to Study Molecular Mechanisms in Cannabis sativa

• Industrial Hemp Clone Selection Method under LED Smart Farm Condition Based on CBD Production per Cubic Meter

• Effect of Prolonged Photoperiod on Light-Dependent Photosynthetic Reactions in Cannabis

• Several Pythium species cause crown and root rot on cannabis (Cannabis sativa L., marijuana) plants grown under commercial greenhouse conditions

• Diseases of Cannabis sativa Caused by Diverse Fusarium Species

• Characterization of the Volatile Profiles of Six Industrial Hemp (Cannabis sativa L.) Cultivars

• [Effects of intermittent-direct-electric-current (IDC) on growth

and content on photosynthetic pigments in hemp (Cannabis sativa L.)](https://www.researchgate.net/profile/Tomas-Vyhnanek/publication/361585129_Effects_of_intermittent-direct-electric-current_IDC_on_growth_and_content_on_photosynthetic_pigments_in_hemp_Cannabis_sativa_L/links/62bad80b5e258e67e10bd772/Effects-of-intermittent-direct-electric-current-IDC-on-growth-and-content-on-photosynthetic-pigments-in-hemp-Cannabis-sativa-L.pdf) (I'm highly skeptical of this stuff)

• Genome-wide polymorphism and genic selection in feral and domesticated lineages of Cannabis sativa

• Research and development of cultivation methods of Cannabis sativa L. to maximize the yield of non-THC bioactive compounds of nutraceutical, cosmeceutical and pharmaceutical interest

• Simple Extraction of Cannabinoids from Female Inflorescences of Hemp (Cannabis sativa L.)

• Understanding Sources of Heavy Metals in Cannabis and Hemp: Benefits of a Risk Assessment Strategy (corperate white paper)

• Hemp microgreens as an innovative functional food: Variation in the organic acids, amino acids, polyphenols, and cannabinoids composition of six hemp cultivars

• Characterization of trichome phenotypes to assess maturation and flower development in Cannabis sativa L. (cannabis) by automatic trichome gland analysis

• Effects of short-term environmental stresses on the onset of cannabinoid production in young immature flowers of industrial hemp (Cannabis sativa L.)

• [Effects of chitin and chitosan on root growth, biochemical defense response1

and exudate proteome of Cannabis sativa](https://www.biorxiv.org/content/10.1101/2022.10.27.514128v1.full.pdf)

• [An Uncertain Middle Ground: Burford Abstention in Federal Cannabis ContractAn Uncertain Middle Ground: Burford Abstention in Federal Cannabis Contract

Enforcement Actions Enforcement Actions](https://ecommons.udayton.edu/cgi/viewcontent.cgi?article=1741&context=udlr) (legal)

• Amino Acid Supplementation as a Biostimulant in Medical Cannabis (Cannabis sativa L.) Plant Nutrition

• [Biocontrol Activity of Bacillus spp. and Pseudomonas spp. Against

Botrytis cinerea and Other Cannabis Fungal Pathogens](https://drive.google.com/file/d/1falLDyyv4vmPg2FM4cCgbnzentajb-qL/view)

• A Comprehensive Phytochemical Analysis of Terpenes, Polyphenols and Cannabinoids, and Micromorphological Characterization of 9 Commercial Varieties of Cannabis sativa L.

• [IMPROVEMENTS TOWARDS DURABLE MANAGEMENT STRATEGIES OF

HEMP POWDERY MILDEW THROUGH HOST RANGE DETERMINATION, FUNGICIDE USE, AND GENETIC HOST SUSCEPTIBILITY](https://ecommons.cornell.edu/bitstream/handle/1813/111926/Cala_cornellgrad_0058F_13268.pdf?sequence=1) (PhD thesis)

• How does legalising cannabis influence the purchasing choices of cannabis consumers and the modus operandi of illicit cannabis suppliers? (PhD thesis)

• Effect of Potassium (K) Supply on Cannabinoids, Terpenoids and Plant Function in Medical Cannabis

• Impact of Harvest Time and Pruning Technique on Total CBD Concentration and Yield of Medicinal Cannabis

• Effects of Harpin and Flg22 on Growth Enhancement and Pathogen Defense in Cannabis sativa Seedlings

• Nitrogen Source Matters: High NH4/NO3 Ratio Reduces Cannabinoids, Terpenoids, and Yield in Medical Cannabis

• Differentiating Cannabis Products: Drugs, Food, and Supplements

• Chemical profiling of Cannabis varieties cultivated for medical purposes in southeastern Brazil

• An analysis of cannabis home cultivation and associated risks in Canada, before and after legalization

• Recent advances in electrochemical sensor technologies for THC detection—a narrative review

• Whole-genome resequencing of wild and cultivated cannabis reveals the genetic structure and adaptive selection of important traits

• Variation among hemp (Cannabis sativus L.) analytical testing laboratories evinces regulatory and quality control issues for the industry

• CULTIVATING DEVIANCE IN THE MARIJUANA INDUSTRY (legal)

• The Effect of Harvest Date on Temporal Cannabinoid and Biomass Production in the Floral Hemp (Cannabis sativa L.) Cultivars BaOx and Cherry Wine

• [Benefits of Cultivating Industrial Hemp (Cannabis sativa ssp. sativa) - A versatile plant for

a sustainable future.](https://sciforum.net/manuscripts/12359/manuscript.pdf) (India)

• [Horticultural Management and Environment Control Strategies for Cannabis

(Cannabis sativa L.) Cultivation](https://atrium.lib.uoguelph.ca/xmlui/bitstream/handle/10214/26674/Hoogenboom_Jennifer_202201_MSc.pdf?sequence=3&isAllowed=y) (master thesis)

• Adapting the cultivation of industrial hemp (Cannabis sativa L.) to marginal lands: A review

• Ghana’s preparedness to exploit the medicinal value of industrial hemp

• A One-Step Grafting Methodology Can Adjust Stem Morphology and Increase THCA Yield in Medicinal Cannabis

• Analytical Techniques for Phytocannabinoid Profiling of Cannabis and Cannabis-Based Products—A Comprehensive Review

• Facing the Forensic Challenge of Cannabis Regulation: A Methodology for the Differentiation between Hemp and Marijuana Samples

• The Effect of Transplant Date and Plant Spacing on Biomass Production for Floral Hemp (Cannabis sativa L.)

• Characterization of the Biological Activity of the Ethanolic Extract from the Roots of Cannabis sativa L. Grown in Aeroponics

• Delineating genetic regulation of cannabinoid biosynthesis during female flower development in Cannabis sativa

• Effects of Cold Temperature and Acclimation on Cold Tolerance and Cannabinoid Profiles of Cannabis sativa L. (Hemp)

• Effect of harvest time on the compositional changes in essential oils, cannabinoids, and waxes of hemp (Cannabis sativa L.)

• Genetic Evaluation of In Vitro Micropropagated and Regenerated Plants of Cannabis sativa L. Using SSR Molecular Markers

• Analysis of Morphological Traits, Cannabinoid Profiles, THCAS Gene Sequences, and Photosynthesis in Wide and Narrow Leaflet High-Cannabidiol Breeding Populations of Medical Cannabis

• Post-Harvest Operations to Generate High-Quality Medicinal Cannabis Products: A Systemic Review

• Overlooked Influence of Indian Hemp (Cannabis sativa) Cultivation on Soil Physicochemical Fertility of Humid Tropical Agroecosystems: Lowland Soils (Nigeria)

• The Effect of Rotational Cropping of Industrial Hemp (Cannabis sativa L.) on Rhizosphere Soil Microbial Communities

• Enhancement of growth and Cannabinoids content of hemp (Cannabis sativa) using arbuscular mycorrhizal fungi

• Morpho-physiology and cannabinoid concentrations of hemp (Cannabis sativa L.) are affected by potassium fertilisers and microbes under tropical conditions

• Releasing the Full Potential of Cannabis through Biotechnology

• Different Fertility Approaches in Organic Hemp (Cannabis sativa L.) Production Alter Floral Biomass Yield but Not CBD:THC Ratio

• New Insight into Ornamental Applications of Cannabis: Perspectives and Challenges

• Cannabis Seedlings Inherit Seed-Borne Bioactive and Anti-Fungal Endophytic Bacilli

• Proceedings of the 3rd Australian Industrial Hemp Conference Launceston, 22-25 March 2022 (153 pages, bunch of presentations)

• Suppression of Hemp Powdery Mildew Using Root-Applied Silicon

• [THE ROLE AND IMPORTANCE OF THE DECARBOXYLATION PROCESS IN

THE PRODUCTION OF QUALITY FULL-SPECTRUM CANNABIS EXTRACT FOR MEDICINAL PURPOSES](https://eprints.unite.edu.mk/963/1/Acta%20Medica%20Balkanica%20FINAL%20FINAL-119-128.pdf)

• Impact of Harvest Time and Pruning Technique on Total CBD Concentration and Yield of Medicinal Cannabis

• Empirical Evaluation of Inflorescences’ Morphological Attributes for Yield Optimization of Medicinal Cannabis Cultivars

• Non-Invasive and Confirmatory Differentiation of Hermaphrodite from Both Male and Female Cannabis Plants Using a Hand-Held Raman Spectrometer

• Studying the Effects of Waterhemp Competition on Yield and Phytochemical Content of High-cannabidiol Hemp in Plasticulture (using plasticulture for weed control)

• [RAMAN SPECTROSCOPY ENABLES HIGHLY ACCURATE

DIFFERENTIATION BETWEEN YOUNG MALE AND FEMALE HEMP PLANTS](https://oaktrust.library.tamu.edu/bitstream/handle/1969.1/196502/HIGGINS-FINALTHESIS-2022.pdf?sequence=1&isAllowed=y) (senior thesis)

• Terpenes and Cannabinoids in Supercritical CO2 Extracts of Industrial Hemp Inflorescences: Optimization of Extraction, Antiradical and Antibacterial Activity

• [Growth and dry matter accumulation of three hemp (Cannabis

sativa L.) cultivars sown on three dates in Canterbury](https://www.agronomysociety.org.nz/files/ASNZ_2021_07._3_hemp_cvs_growth_effects_Canterbury.pdf) (New Zealand)

• Physiological and morphological responses of industrial hemp (Cannabis sativa L.) to water deficit

• Far-Red Photography for Measuring Plant Growth: A Novel Approach (cannabis was used in study)

• Low-cost Prototype for Automating of Greenhouse Medicinal Cannabis Production Supported by IoT

• Agricultural traceability model based on IoT and Blockchain: Application in industrial hemp production

• Self-Supervised Leaf Segmentation under Complex Lighting Conditions (cannabis growth monitoring system)

• Research on Monitoring Technology of Industrial Cannabis Based on Blockchain and SM Series Cryptographic Algorithm

• [Kinetics of CBD, D9 -THC Degradation

and Cannabinol Formation in Cannabis Resin at Various Temperature and pH Conditions](https://www.researchgate.net/profile/Wuttichai-Jaidee/publication/352206874_Kinetics_of_CBD_D_9_-THC_Degradation_and_Cannabinol_Formation_in_Cannabis_Resin_at_Various_Temperature_and_pH_Conditions/links/619c9701d7d1af224b1a1a72/Kinetics-of-CBD-D-9-THC-Degradation-and-Cannabinol-Formation-in-Cannabis-Resin-at-Various-Temperature-and-pH-Conditions.pdf)

• [Optimization of the Decarboxylation of Cannabis

for Commercial Applications](https://pubs.acs.org/doi/full/10.1021/acs.iecr.2c00826) (free download at bottom of page)

80 ________________________________________________________

• Extraction of Cannabinoids from CBD-Dominant Cannabis Flowers by Supercritical Carbon Dioxide

• Germination of Industrial Hemp (Cannabis sativa L.) at Different Level of Sodium Chloride and Temperatures

• [Postharvest Operations of Cannabis and Their Effect on

Cannabinoid Content: A Review](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9404914/)

• Methods for characterizing pollen fitness in Cannabis sativa L.

• [THC and CBD Fingerprinting of an Elite Cannabis Collection

from Iran: Quantifying Diversity to Underpin Future Cannabis Breeding](https://www.researchgate.net/publication/357704283_THC_and_CBD_Fingerprinting_of_an_Elite_Cannabis_Collection_from_Iran_Quantifying_Diversity_to_Underpin_Future_Cannabis_Breeding)

• Simultaneous Quantification of 17 Cannabinoids in Cannabis Inflorescence by Liquid Chromatography-Mass Spectrometry

• Quality control of cannabis inflorescence and oil products: Response factors for the cost-efficient determination of ten cannabinoids by HPLC

• Understanding Cannabis sativa L.: Current Status of Propagation, Use, Legalization, and Haploid-Inducer-Mediated Genetic Engineering

• An Alternative In Vitro Propagation Protocol of Cannabis sativa L. (Cannabaceae) Presenting Efficient Rooting, for Commercial Production

• A Temporary Immersion System to Improve Cannabis sativa Micropropagation

90 _____________________________________________

• Impact of Indole-3-butyric Acid Concentration and Formulation and Propagation Environment on Rooting Success of ‘I3’ Hemp by Stem Cuttings

• Glandular trichomes affect mobility and predatory behavior of two aphid predators on medicinal cannabis

• Production of Novel Medicinal Cannabis Using Genome Editing Technology (PhD thesis)

• Response of cannabidiol hemp (Cannabis sativa L.) varieties grown in the southeastern United States to nitrogen fertilization

• [Semi-quantitative analysis of cannabinoids

in hemp (Cannabis sativa L.) using gas chromatography coupled to mass spectrometry](https://link.springer.com/content/pdf/10.1186/s42238-022-00161-w.pdf)

• Cannabis entrepreneurship: A guide to core concepts, resources, and research strategies

• [Root-TRAPR: a modular plant growth device

to visualize root development and monitor growth parameters, as applied to an elicitor response of Cannabis sativa](https://link.springer.com/content/pdf/10.1186/s13007-022-00875-1.pdf)

• Cannabis sativa L. Spectral Discrimination and Classification Using Satellite Imagery and Machine Learning

• Machine Learning-Mediated Development and Optimization of Disinfection Protocol and Scarification Method for Improved In Vitro Germination of Cannabis Seeds

SAG's Open Access Cannabis Links

last update: 11 NOV 2022 (added 100 papers in part 2)

• this is part 2 with 100 papers

• SAG's Plant Lighting Guide

• Main open access page -many hundreds more papers

• Most links are for THC cannabis but some are for hemp or CBD and found primarily using Google Scholar. At the very bottom is a recently added section which will likely be every few months.

• Please report dead links! You sometimes have to look around a bit to find the actual PDF download in the page linked to.

Highlights

• Characterization of Nutrient Disorders of Cannabis sativa -this is for vegetative hemp and the only broad study I know of with nute issues and any cannabis

• Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids "As percent blue increased from 4 to 20%, flower yield decreased by 12.3%. This means that flower yield increased by 0.77% per 1% decrease in blue photons."

• Optimisation of Nitrogen, Phosphorus, and Potassium for Soilless Production of Cannabis sativa in the Flowering Stage Using Response Surface Analysis

Cannabis spectral and lighting

--THESIS

• The Impact of LED Spectra on Cannabis sativa Production master thesis

• SPECTRAL DIFFERENTIATION OF CANNABIS SATIVAL FROM MAIZE USING HYPERSPECTRAL INDICES master thesis

--ULTRAVIOLET

• Cannabis Yield Increased Proportionally With Light Intensity, but Additional Ultraviolet Radiation Did Not Affect Yield or Cannabinoid Content

• Cannabis Inflorescence Yield and Cannabinoid Concentration Are Not Improved with Long-Term Exposure to Short-Wavelength Ultraviolet-B Radiation

• Cannabis sativa L. Response to Narrow Bandwidth UV and the Combination of Blue and Red Light during the Final Stages of Flowering on Leaf Level Gas-Exchange Parameters, Secondary Metabolite Production, and Yield

• UV-B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH AND CANNABINOID PRODUCTION OF TWO Cannabis sativa CHEMOTYPES (note, the Lydon, 1987 paper was using relatively low THC plants and the results of this paper are not being duplicated with modern cannabis strains and testing)

• Cannabinoids and Terpenes: How Production of Photo-Protectants Can Be Manipulated to Enhance Cannabis sativa L. Phytochemistry

--SPECTRUM AND LIGHTING LEVELS

• Photons from NIR LEDs can delay flowering in short-day soybean and Cannabis: Implications for phytochrome activity

• Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids

• The Effect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L

• Beyond vegetables: effects of indoor LED light on specialized metabolite biosynthesis in medicinal and aromatic plants, edible flowers, and microgreens

• THE EFFECTS OF RED, BLUE AND WHITE LIGHT ON THE GROWTH AND DEVELOPMENT OF CANNABIS SATIVA L.

• LED lighting affects the composition and biological activity of Cannabis sativa secondary metabolites

• Influence of Light Spectra on the Production of Cannabinoids

• LED lighting affects the composition and biological activity of Cannabis sativa secondary metabolites

• Cannabinoids accumulation in hemp (Cannabis sativa L) plants under LED light spectra and their discrete role as a stress marker

• THE EFFECTS OF LIGHT SPECTRA ON THE GROWTH AND DEVELOPMENT OF GREENHOUSE CBD HEMP

• Wavelengths of LED light affect the growth and cannabidiol content in Cannabis sativa L

• An Update on Plant Photobiology and Implications for Cannabis Production

• Identification of Cannabis plantations using hyperspectral technology

• Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment

• Optimization of Cannabis Grows Using Fourier Transform Mid-Infrared Spectroscopy

• The Effect of Electrical Lighting Power and Irradiance on Indoor-Grown Cannabis Potency and Yield

• Light matters: Effect of light spectra on cannabinoid profile and plant development of medical cannabis (Cannabis sativa L.)

• Photoperiodic Response of In Vitro Cannabis sativa Plants

• Improving Cannabis Bud Quality and Yield with Subcanopy Lighting

• Light dependence of photosynthesis and water vapor exchange characteristics in different high Δ9-THC yielding varieties of Cannabis sativa L.

• Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment

• Photoperiodic Response of In Vitro Cannabis sativa Plants

• Comparative Growth, Photosynthetic Pigments, and Osmolytes Analysis of Hemp (Cannabis sativa L.) Seedlings under an Aeroponics System with Different LED Light Sources

• [Influence of Light Spectra on

the Production of Cannabinoids](https://www.karger.com/Article/Pdf/510146)

• High Light Intensities Can Be Used to Grow Healthy and Robust Cannabis Plants During the Vegetative Stage of Indoor Production

• Impact of Different Phytohormones on Morphology, Yield and Cannabinoid Content of Cannabis sativa L.

• A Principal Components Analysis-Based Method for the Detection of Cannabis Plants Using Representation Data by Remote Sensing

Commercial Cultivation

--THESIS

• ENERGY CONSUMPTION AND ENVIRONMENTAL IMPACTS ASSOCIATED WITH CANNABIS CULTIVATION master thesis

• Improving Aquaponics for Indoor Drug-type Cannabis sativa L. Cultivation master thesis

• The blunt truth: Industrial safety in cannabis growing facilities master thesis

• From Seed to Sale master thesis (real estate)

• [Health Effects of Exposure to Cannabis in Workers in

an Indoor Growing Facility](https://digital.lib.washington.edu/researchworks/bitstream/handle/1773/44222/Ghodsian_washington_0250O_20433.pdf?sequence=1&isAllowed=y) master thesis

• [An Environmental Analysis of Recreational

Cannabis Cultivation & Processing](https://digital.wpi.edu/downloads/gx41mm39x) senior thesis

--ENERGY

• Energy Use by the Indoor Cannabis Industry: Inconvenient Truths for Producers, Consumers, and Policymakers

• Factors determining yield and quality of illicit indoor cannabis (Cannabis spp.) production

• Energy Consumption Model for Indoor Cannabis Cultivation Facility

• Cannabis Indoor Growing Conditions, Management Practices, and Post-Harvest Treatment: A Review

--BUSINESS

• Closing the Yield Gap for Cannabis: A Meta-Analysis of Factors Determining Cannabis Yield

• Yield of Illicit Indoor Cannabis Cultivation in The Netherlands

• Equity in Cannabis Agriculture

• Why comply? Farmer motivations and barriers in cannabis agriculture

• Coming out of the closet:Risk management strategies of illegal cannabis growers United Kingdom

• Trends in intellectual property rights protection for medical cannabis and related products

• The Cannabinoid Content of Legal Cannabis in Washington State Varies Systematically Across Testing Facilities and Popular Consumer Products

• [CANNABIS WASTE MANAGEMENT

IN METRO VANCOUVER](http://www.metrovancouver.org/services/solid-waste/SolidWastePublications/CannabisReport.pdf)

--ENVIRONMENT AND SAFETY

• Hotboxing the Polar Bear: The Energy and Climate Impacts of Indoor Marijuana Cultivation

• [Potential regional air quality impacts of cannabis

cultivation facilities in Denver, Colorado](https://acp.copernicus.org/articles/19/13973/2019/acp-19-13973-2019.pdf)

• [Growing practices and the use of potentially harmful chemical

additives among a sample of small-scale cannabis growers in three countries](https://eprints.lancs.ac.uk/id/eprint/126618/1/DAD_GCCRC_Chemicals_paper_ACCEPTED_PROOF.pdf)

• Application of the Environmental Relative Moldiness Index in Indoor Marijuana Grow Operations

• Allergic and Respiratory Symptoms in Employees of Indoor Cannabis Grow Facilities

• Review of NIOSH Cannabis-Related Health Hazard Evaluations and Research

• Application of the Environmental Relative Moldiness Index in Indoor Marijuana Grow Operations

• Allergic and Respiratory Symptoms in Employees of Indoor Cannabis Grow Facilities

• [The greenhouse gas emissions of indoor cannabis

production in the United States](https://ewscripps.brightspotcdn.com/e2/60/e295ff9744eab576ce7fa326b729/cannabis-nature-1.pdf)

• A narrative review on environmental impacts of cannabis cultivation

• [Growing practices and the use of potentially harmful chemical

additives among a sample of small-scale cannabis growers in three countries](https://eprints.lancs.ac.uk/id/eprint/126618/1/DAD_GCCRC_Chemicals_paper_ACCEPTED_PROOF.pdf)

--CULTIVATION

• Aquaponic and Hydroponic Solutions Modulate NaCl-Induced Stress in Drug-Type Cannabis sativa L.

• Impact of Harvest Time and Pruning Technique on Total CBD Concentration and Yield of Medicinal Cannabis

• Novel Solventless Extraction Technique to Preserve Cannabinoid and Terpenoid Profiles of Fresh Cannabis Inflorescence

• Evaluation of disease management approaches for powdery mildew on Cannabis sativa L. (marijuana) plants

• Early topping: an alternative to standard topping increases yield in cannabis production

• Cannabis sativa L. Inflorescences from Monoecious Cultivars Grown in Central Italy: An Untargeted Chemical Characterization from Early Flowering to Ripening

• Epidemiology of Fusarium oxysporum causing root and crown rot of cannabis (Cannabis sativa L., marijuana) plants in commercial greenhouse production

• Increasing Inflorescence Dry Weight and Cannabinoid Content in Medical Cannabis Using Controlled Drought Stress

• Several Pythium species cause crown and root rot on cannabis (Cannabis sativa L., marijuana) plants grown under commercial greenhouse conditions

)

• Pathogens and Molds Affecting Production and Quality of Cannabis sativa L.

• Yield, Characterization and Possible Exploitation of Cannabis Sativa L. Roots Grown Under Aeroponics Cultivation

• Cannabis Indoor Growing Conditions, Management Practices, and Post-Harvest Treatment: A Review

• Processing and extraction methods of medicinal cannabis: a narrative review

• Growing Mediums for Medical Cannabis Production in North America

Root zone

• Potential impacts of soil microbiota manipulation on secondary metabolites production in cannabis

• Fusarium and Pythium species infecting roots of hydroponically grown marijuana (Cannabis sativa L.) plants

• [Plant-Growth Promoting Rhizobacteria

in Soilless Cannabis Cropping Systems: Implications for Growth Promotion and Disease Suppression](https://stud.epsilon.slu.se/16079/11/soderstrom_l_200923.pdf)

• Impact of Different Growing Substrates on Growth, Yield and Cannabinoid Content of Two Cannabis sativa L. Genotypes in a Pot Culture

• Plant Growth-Promoting Rhizobacteria for Cannabis Production: Yield, Cannabinoid Profile and Disease Resistance

• Comparing hydroponic and aquaponic rootzones on the growth of two drug-type Cannabis sativa L. cultivars during the flowering stage

• [Can manipulation of soil microbiota enhance, stabilize and sustain cannabinoid

production?](https://www.preprints.org/manuscript/202012.0736/v1)

Propagation and genetics

• Propagation and Root Zone Management for Controlled Environment Cannabis Production PhD Thesis

• Recent advances in Cannabis sativa genomics research

• The Past, Present and Future of Cannabis sativa Tissue Culture

• [Large-scale whole-genome resequencing unravels

the domestication history of Cannabis sativa](https://www.science.org/doi/pdf/10.1126/sciadv.abg2286)

• Effect of Rhizophagus irregularis on Growth and Quality of Cannabis sativa Seedlings

• Shape Matters: Plant Architecture Affects Chemical Uniformity in Large-Size Medical Cannabis Plants

• Cryopreservation of 13 Commercial Cannabis sativa Genotypes Using In Vitro Nodal Explants

• Comparative Analysis of Machine Learning and Evolutionary Optimization Algorithms for Precision Micropropagation of Cannabis sativa: Prediction and Validation of in vitro Shoot Growth and Development Based on the Optimization of Light and Carbohydrate Sources

• Advances and Perspectives in Tissue Culture and Genetic Engineering of Cannabis

• The characterization of key physiological traits of medicinal cannabis (Cannabis sativa L.) as a tool for precision breeding

• The genetics of Cannabis—genomic variations of key synthases and their effect on cannabinoid content

• The Past, Present and Future of Cannabis sativa Tissue Culture

• Regeneration of shoots from immature and mature inflorescences of Cannabis sativa

• Polyploidization for the Genetic Improvement of Cannabis sativa

• Flower power: floral reversion as a viable alternative to nodal micropropagation in Cannabis sativa

• Phenotypic plasticity influences the success of clonal propagation in industrial pharmaceutical Cannabis sativa

• Hermaphroditism in Marijuana (Cannabis sativa L.) Inflorescences – Impact on Floral Morphology, Seed Formation, Progeny Sex Ratios, and Genetic Variation

• Propagation of Cannabis for Clinical Research: An Approach Towards a Modern Herbal Medicinal Products Development

• Medical Cannabis and Industrial Hemp Tissue Culture: Present Status and Future Potential

• Development of a Direct in vitro Plant Regeneration Protocol From Cannabis sativa L. Seedling Explants: Developmental Morphology of Shoot Regeneration and Ploidy Level of Regenerated Plants

• The Effect of TIBA and NPA on Shoot Regeneration of Cannabis sativa L. Epicotyl Explants

• Back to the roots: protocol for the photoautotrophic micropropagation of medicinal Cannabis

• [TITANIUM DIOXIDE NANOPARTICLES

AND MAGNETIC FIELD STIMULATE SEED GERMINATION AND SEEDLING GROWTH OF Cannabis sativa L.](https://www.researchgate.net/profile/Hassan-Feizi/publication/344868325_TITANIUM_DIOXIDE_NANOPARTICLES_AND_MAGNETIC_FIELD_STIMULATE_SEED_GERMINATION_AND_SEEDLING_GROWTH_OF_Cannabis_sativa_L/links/5f94fd27299bf1b53e4392d2/TITANIUM-DIOXIDE-NANOPARTICLES-AND-MAGNETIC-FIELD-STIMULATE-SEED-GERMINATION-AND-SEEDLING-GROWTH-OF-Cannabis-sativa-L.pdf)

Biochemistry

• Nitrogen supply affects cannabinoid and terpenoid profile in medical cannabis (Cannabis sativa L.)

• The Highs and Lows of P Supply in Medical Cannabis: Effects on Cannabinoids, the Ionome, and Morpho-Physiology

• Recent applications of chromatography for analysis of contaminants in cannabis products: a review

• The impact of extraction protocol on the chemical profile of cannabis extracts from a single cultivar

• Improvement of the antioxidant activity, phytochemicals, and cannabinoid compounds of Cannabis sativa by salicylic acid elicitor

• Characterization of the Cannabis sativa glandular trichome proteome

• Cannabis Glandular Trichomes: A Cellular Metabolite Factory

• [Cannabis Cultivator Phenotype and Attribute

Preferences in Legal Recreational and Medical Cannabis Cultivation Operations in Oregon and Colorado](https://assets.researchsquare.com/files/rs-1045029/v1/c94b423f-223a-4223-ac83-2fb3d01c104c.pdf?c=1636577854)

• Extraction of Phenolic Compounds and Terpenes from Cannabis sativa L. By-Products: From Conventional to Intensified Processes

• [Yielding Morphological Characteristics and Biochemical Analysis of

“Karma Lemon” Cannabis Producing Cannabinoids in Thessaloniki-Greece](https://www.researchgate.net/profile/Dani-Fadel-2/publication/342267867_Yielding_Morphological_Characteristics_and_Biochemical_Analysis_of_Karma_lemon_Cannabis_Producing_Cannabinoids_in_Thessaloniki-Greece/links/5eec4721299bf1faac627fc0/Yielding-Morphological-Characteristics-and-Biochemical-Analysis-of-Karma-lemon-Cannabis-Producing-Cannabinoids-in-Thessaloniki-Greece.pdf)

• The preservation and augmentation of volatile terpenes in cannabis inflorescence* Chemical and physical variations of cannabis smoke from a variety of cannabis samples in New Zealand

• [Qualitative terpene profiling of Cannabis varieties cultivated

for medical purposes](https://www.scielo.br/j/rod/a/k69ddvqc5cgCTmKmRfBGqmS/?format=pdf&lang=en)

• Optimisation of Nitrogen, Phosphorus, and Potassium for Soilless Production of Cannabis sativa in the Flowering Stage Using Response Surface Analysis

• Cannabis glandular trichomes alter morphology and metabolite content during flower maturation

• The diverse mycoflora present on dried cannabis (Cannabis sativa L., marijuana) inflorescences in commercial production

• Dominant volatile organic compounds (VOCs) measured at four Cannabis growing facilities: Pilot study results

• Potassium and micronutrients fertilizer addition in aquaponic solution for drug-type Cannabis sativa L. cultivation

Recently added

39 papers added 20may22

• [Technological surveillance of medical Cannabis

horticultural production](https://www.researchgate.net/profile/Claudia-Jimenez-Hernandez/publication/360247058_Technological_surveillance_of_medical_Cannabis_horticultural_production/links/626b15a7bfd24037e9dd0523/Technological-surveillance-of-medical-Cannabis-horticultural-production.pdf) -gets in to keywords for research searching

• [Horticultural Management and Environment Control Strategies for Cannabis

(Cannabis sativa L.) Cultivation](https://atrium.lib.uoguelph.ca/xmlui/bitstream/handle/10214/26674/Hoogenboom_Jennifer_202201_MSc.pdf?sequence=3) -master thesis

• [Expanding Research Initiatives Relating to Micropropagated

Cannabis sativa L. Through Integration of Multidisciplinary Methods](https://atrium.lib.uoguelph.ca/xmlui/bitstream/handle/10214/26872/Pepe_Marco_202204_MSc.pdf?sequence=1&isAllowed=y) -master thesis

• [Beyond vegetables: effects of indoor LED light on specialized metabolite biosynthesis in

medicinal and aromatic plants, edible flowers, and microgreens](https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/jsfa.11513) -spectral manipulation

• Light intensity can be used to modify the growth and morphological characteristics of cannabis during the vegetative stage of indoor production -claims 600-900 umol/m2/sec is optimal for plant morphology

• History of Controlled Environment Horticulture: Indoor Farming and Its Key Technologies

• [A One-Step Grafting Methodology Can Adjust Stem

Morphology and Increase THCA Yield in Medicinal Cannabis](https://mdpi-res.com/d_attachment/agronomy/agronomy-12-00852/article_deploy/agronomy-12-00852-v3.pdf?version=1650433838) -mix and match scion and rootstock

• Accumulation of somatic mutations leads to genetic mosaicism in cannabis -do clones lose vigor over time?

• Shaping and Tuning Lighting Conditions in Controlled Environment Agriculture: A Review

• Beyond Δ9-tetrahydrocannabinol and cannabidiol: chemical differentiation of cannabis varieties applying targeted and untargeted analysis

• [A Comprehensive Review on the Techniques for Extraction of

Bioactive Compounds from Medicinal Cannabis](https://mdpi-res.com/d_attachment/molecules/molecules-27-00604/article_deploy/molecules-27-00604.pdf?version=1642505610)

• Cannabis Cultivation Facilities: A Review of Their Air Quality Impacts from the Occupational to Community Scale

• Home cultivation across Canadian provinces after cannabis legalization

• [Chemical profiling of Cannabis varieties cultivated for medical purposes

in southeastern Brazil](https://www.researchgate.net/profile/Virginia-Carvalho-4/publication/359970580_Chemical_profiling_of_Cannabis_varieties_cultivated_for_medical_purposes_in_southeastern_Brazil/links/626803dbbca601538b6a83e3/Chemical-profiling-of-Cannabis-varieties-cultivated-for-medical-purposes-in-southeastern-Brazil.pdf)

• Legalization of Cannabis Cultivation a Comparative Study -Iraq

• Origin, early expansion, domestication and anthropogenic diffusion of Cannabis, with emphasis on Europe and the Iberian Peninsula

• ILLEGAL CANNABIS GROWERS IN SERBIA

• Why the concept of terroir matters for drug cannabis production -fucking wine snobs...

• Farmability and pharmability: Transforming the drug market to a health-and human rights-centred approach from self-cultivation to safe supply of controlled substances

• 30 Shades of Green:Land Use Regulation of Adult-Use Cannabis in the United States -this gets in to zoning issues, 65 pages

• Evolution, genetics and biochemistry of plant cannabinoid synthesis: a challenge for biotechnology in the years ahead

• How do pinching and plant density affect industrial hemp produced for cannabinoids in open field conditions?

• Growing ganja permission: a real gate-way for Thailand’s promising industrial crop?

• Understanding Cannabis sativa L.: Current Status of Propagation, Use, Legalization, and Haploid-Inducer-Mediated Genetic Engineering

• Converting Sugars into Cannabinoids—The State-of-the-Art of Heterologous Production in Microorganisms

• [Production du cannabis médical (Cannabis sativa L.)

cultivé en hydroponie : impact de N, P et K sur la croissance, productivité et qualité](https://corpus.ulaval.ca/jspui/bitstream/20.500.11794/73208/1/37951.pdf) -French and English, Concentrations above 25 ppm P and 175 ppm K, however, did not improve the productivity and the quality of the inflorescences

• [Analytical Techniques for Phytocannabinoid Profiling

of Cannabis and Cannabis-Based Products—A Comprehensive Review](https://mdpi-res.com/d_attachment/molecules/molecules-27-00975/article_deploy/molecules-27-00975.pdf?version=1643709174) -42 pages

• The Regulatabilization of Cannabis -tax and law issues

• Exploiting Beneficial Pseudomonas spp. for Cannabis Production -adding bacteria to soil

• [Facing the Forensic Challenge of Cannabis Regulation:

A Methodology for the Differentiation between Hemp and Marijuana Samples](https://www.researchgate.net/profile/Virginia-Carvalho-4/publication/352699641_Facing_the_Forensic_Challenge_of_Cannabis_Regulation_A_Methodology_for_the_Differentiation_between_Hemp_and_Marijuana_Samples_Presumptive_and_confirmatory_methods_for_hemp_and_marijuana_analysis/links/613fc9246c61e2367c79866a/Facing-the-Forensic-Challenge-of-Cannabis-Regulation-A-Methodology-for-the-Differentiation-between-Hemp-and-Marijuana-Samples-Presumptive-and-confirmatory-methods-for-hemp-and-marijuana-analysis.pdf) -High-performance liquid chromatography

• [Empirical Evaluation of

Inflorescences’ Morphological Attributes for Yield Optimization of Medicinal Cannabis Cultivars](https://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC9063709&blobtype=pdf)

• [Post-Harvest Operations to Generate High-Quality Medicinal

Cannabis Products: A Systemic Review](https://mdpi-res.com/d_attachment/molecules/molecules-27-01719/article_deploy/molecules-27-01719.pdf?version=1646558142)

• [Industry-Based Misconceptions

Regarding Cross-Pollination of Cannabis spp](https://fjfsdata01prod.blob.core.windows.net/articles/files/793264/pubmed-zip/.versions/1/.package-entries/fpls-13-793264/fpls-13-793264.pdf?sv=2018-03-28&sr=b&sig=CXXYYZNpxKylburRHjpV8SUv%2FKIjJP4RiGlql2EWJ2o%3D&se=2022-05-20T04%3A12%3A13Z&sp=r&rscd=attachment%3B%20filename%2A%3DUTF-8%27%27fpls-13-793264.pdf)

• [Cannabis for Medical Use: Versatile

Plant Rather Than a Single Drug](https://www.researchgate.net/profile/Paula-Berman-2/publication/360165558_Cannabis_for_Medical_Use_Versatile_Plant_Rather_Than_a_Single_Drug/links/626623328cb84a40ac889101/Cannabis-for-Medical-Use-Versatile-Plant-Rather-Than-a-Single-Drug.pdf) -biochem

• [Post-Harvest Operations to Generate High-Quality Medicinal

Cannabis Products: A Systemic Review](https://mdpi-res.com/d_attachment/molecules/molecules-27-01719/article_deploy/molecules-27-01719.pdf?version=1646558142)

• [What do we know about opportunities and

challenges for localities from Cannabis legalization?](https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/ropr.12460)

• [Weeding out the Dealers?

The Economics of Cannabis Legalization](https://deliverypdf.ssrn.com/delivery.php?ID=783031087103096101022070111097121074031015063050001069009037027033120068020026109077071004017090030117029029075068068118080104006077028086015072041099041088099046095097085123098005095120125028055107046054063120094095123006088004027024101071121029008085091127001118082000023098015025111&EXT=pdf&INDEX=TRUE) -69 pages

• A Noninvasive Gas Exchange Method to Test and Model Photosynthetic Proficiency and Growth Rates of In Vitro Plant Cultures: Preliminary Implication for Cannabis sativa L -good paper on measuring photosynthesis rates

Bruce Bugbee AMA highlights and commentary

part of SAG's Lighting Guide

Bugbee AMA <<<link to the AMA

last update: 13 SEP 2021

Organic vs synthetic fertilizers

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha66mu4/

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha6ate2/

I think "organic" is non-sense and stopped using it in the late 1990's (I'll go ahead and put that flame suit on now!). For me and cannabis, it was/is a consistency issue. I knew a lot of growers (Seattle area) who would use hot organic soils, and in many instances get leaves all curled up due to phosphorus levels being way too high affecting taste and how the pot smokes (I thought this was a huge problem in Amsterdam in the late 1990's). Or the lower leaves may start yellowing much too early. I prefer everything dialed in perfectly from start to finish and expect all leaves to be green when harvested.

But, fertilizers and "organic" are outside my specialty, and I do not engage in debates over it. My mantra has always been, "find what works for you and stick with it". I use General Hydroponics 3 part flora with the same 1:1:1 ratio (NPK of 7/6/11) for everything and every plant. The nitrogen and phosphorus levels are about the same with very high potassium levels (all protein/enzyme synthesis relies on potassium, and plays a role in many other plant processes like photosynthesis and carbohydrate metabolism). I use the same fertilizer ratios for radish seedlings as I do for flowering cannabis, with the same pH for hydro and soil (around 6.5), but at different strengths. I need consistency so my motivations may be different than yours because I enjoy researching plant lighting, not plant fertilizers.

Because I use potassium hydroxide for pH control, my potassium levels are even higher than what's mentioned above.

Even outdoors I avoid organic fertilizers. I have seen nitrifying bacterial inoculations perform very well outdoors, and I'm sure it works well indoors, too.

I would like to say that I'm quite pleasantly amused that Bugbee is not a fan of organic! Take that, hippies. /s

"find what works for you and stick with it"

Veg vs flowering fertilizers

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha64ihk/

I use the same for everything.

Fertilizer strength

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha6du4n/

TL;DR- EC of 1.4

This is in the ballpark of what I run cannabis at.

pH with lime

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha6328a/

Lime is a pH buffer in that it stays in the soil. I personally use potassium hydroxide, and I do tend to run my pH a bit higher than most people.

Container size

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha6f985/

TL;DR- the bigger the better. There is a good meta-study below. It likely has to do with cytokinin levels which is a hormone responsible for cellular division, and higher cytokinin levels in the roots means higher cytokinin levels throughout the plant. Bonsai plants have small leaves due to small root mass. Not all plants can be turned in to a true small bonsai plant, though.

• https://www.publish.csiro.au/fp/pdf/FP12049 (meta-analysis of 65 studies shows 43% increase when doubling pot size)

A case for smaller containers may be the sea of green style of growing. But, taller containers that are narrow stills means one can have a larger container size. BTW, legal reasons and plant count is a compelling reason not to do sea of green.

Flushing

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha69aqr/

TL;DR- don't bother in most cases. Below is what he's referring to.

• https://www.rxgreentechnologies.com/rxgt_trials/flushing-trial/

I can honestly say that no one can ever tell if I flushed a plant or not.

Pruning

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha65974/

TL;DR- minimal

This is another amusing response because I tend not to prune, either. I prefer to light up the lower leaves rather than prune. Airflow issues may be a good reason to prune, though. People often over prune and a photon that is absorbed by the soil is a wasted photon.

Mediums

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha6dzmq/

Don't ask too many question in a single post!

Powdery mildew

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha6gamw/

TIL about silicon levels in the soil and PM (powdery mildew). For me, I use strains not prone to PM, and use a half teaspoon of baking soda and a drop of liquid soap in a standard size spray bottle to spray on the leaves for PM. This raises the pH of the leaf surface so PM can't grow. I'm highly allergic to PM and know if it's there before it becomes visible.

Heirloom strains

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha67xj0/

I think a lot of heirloom strains suck. I've grown original strains that were around in Seattle in the 1980's, and the Dutch did wonders in correcting their many flaws in the 1990's. Original Big Bud from the 1980's is very prone to botrytis (gray mold) and "banana hermies", the Dutch version does not have these issues.

These newer strains out are superior to most heirlooms in most every way. An heirloom that I am very fond of is Durban Poison which is a South African pure sativa that is an 8 week plant with very high yields. Durban Poison x Northern Lights #5 is also a favorite and another huge yielder.

Spectrum tuning

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha6c3mi/

Spectrum shapes the plant, but high light increases yield- Bugbee. This is perfectly written.

....

High efficacy (the technical term for efficiency) is more important than spectrum- Bugee. This is horribly written.

NO, just NO! Efficacy is absolutely not the technical term for efficiency, particularly in lighting, and I don't know why he wrote this. There are many instances where efficacy and efficiency will be the same, but I've never seen them the same in lighting. Never.

I would have wrote it as, "in general, light quantity is more important than light quality".

Say I have a 450 nm blue LED that is 2.8 umol/joule and a 660 nm red LED that is 2.8 umol/joule. Those are identical efficacies, right? That is the PPE or "photosynthetic photon efficacy". But that blue LED has an electrical efficiency of 74% and the red LED has an efficiency of 51%. Refer to my cheat sheet under the Energy and efficacy of photons for the math, and why I'm right.

But SAG, he has a PhD and you barely graduated high school with a GPA of 2.3 and never even took high school biology! I don't care, he's wrong here.

Luminous efficacy and luminous efficiency are also no where close to being the same. Not even the same ballpark. I talk about this in my cheat sheet linked to above under "Luminous efficiency and lux meters", and show a luminous efficiency chart. Luminous efficiency is in percentage sensitivity for a certain wavelength of light relative to 555 nm and the spectral response of the human eye, luminous efficacy is lumens per watt. Those are not close to being the same. It mixes things up but I can also have a red 660 nm LED that will have a luminous efficiency of about 6%, could have an electrical efficiency of 60%, and this gets us a photosynthetic photon efficacy of 3.3 uMol/joule that would have a luminous efficacy of about 25 lumens per watt.

• Luminous efficiency chart from the book, "Introduction to Radiometry and Photometry" and an example of "fair use" under 17 USC part 107.

He's actually been wrong on other stuff like claiming UV photons are "hundreds or thousands of times more powerful" than PAR (source- 4 minute mark on video, How Ultraviolet Radiation Affects Plants with Dr. Bruce Bugbee). Photons of those energy levels would be x-rays or soft gamma rays (depending how they are generated- x-rays are emitted from electrons, gamma rays are from atomic nucleus but can have the same energy levels), and this will quickly kill the plant.

Even if he's talking about a UV beibg thousands of times more powerful for a photomorphogenesis effect, he still has to prove the claim and the claim has not been proven in the literature.

He used to also conflate PPF with PPFD (he explained why in a couple videos, and why he does not anymore). When I see papers conflating PPF and PPFD, I look to see if Bugbee is being referenced.

My points being, just because it's Dr Bruce Bugbee does not mean everything he's saying is correct although it nearly always is. I've corrected my share of PhDs IRL and online, and the title "Dr" does not confer infallibility. But, most PhDs will readily stand corrected if actually demonstrated to be incorrect because that's being a good scientist, and it's easy to make mistakes just typing or talking away in an AMA. I go back and do edits as needed in my lighting guide to fix my mistakes or to add clarifications.

Also, don't confuse some slight criticism and scientific corrections for lack of respect.

My questions- overdriving light, chlorophyll fluorescence, spectral sensors

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha63jmi/

I wanted his opinion on overdriving plants and he did not actually answer. But, saying "We are doing additional studies o this now" is honest which should be respected. "I don't know" is always acceptable in this case and it means the person has credibility because they are not BSing you. Red has has a higher theoretical (and currently practical) maximum efficacy over blue although the efficiency may never reach that of blue. Did I mention don't get efficacy and efficiency confused!

He did say that he also uses chlorophyll fluorescence techniques but preferred other techniques (it allows me to see what individual proteins are up to). His alluding to chlorophyll fluorescence not being able to be used on single leaf and whole canopies models is actually wrong (see the work by David Kramer). NASA also uses chlorophyll fluorescence imaging in some satellites.

• https://www.nasa.gov/topics/earth/features/fluorescence-map.html

• Chlorophyll fluorescence of a leaf taken by me. I can see leaf damage before it's visible to the naked eye using this technique.

He ignored the question about using $5 spectral sensors instead of using silicon diodes with a fairly cheap interference band pass filter and a rather expensive response flattening filter (that one linked to is larger and more expensive than needed), for making a full spectrum PAR meter. As a businessman, I completely understand why he would not answer this question and I would not have answered either if I were in his shoes. There are technical advantages of using the silicon diode instead of the spectral sensor such a faster response time which means a running average can be done to give a smoother response that won't bounce around. The reason the cheap Hydrofarm quantum light meter readings bounce around is because it uses a four channel spectral sensor that uses no averaging. Here's a picture of that spectral sensor. I hooked it up to an oscilloscope and it takes three readings per second (100KHz I2C).

I strongly recommend against cheap quantum light meters like the Hydrofarm meter and Apogee is going to be your best deal for calibrated scientific equipment. Only use full spectrum PAR meters with LED lighting otherwise 660 nm LEDs aren't going to read accurately.

Get something like an Apogee SQ-520 for lab work (this is what I use), get something like an MQ-500 for more field or mobile work.

• 11 channel spectral sensor I was talking about. This is the future of light meters because spectral sensors can be so versatile. It's literally turning your light meter in to a very low cost spectrometer that can be used for full spectrum PAR, lux, CCT, red/far red ratio, chlorophyll meter etc all in one device.

BTW, "570/531 nm photochemical reflectance index" (PRI) I mentioned is a way to tell if a plant is going in to light saturation by monitoring small changes in xanthophyll. It can be measured with a spectrometer or one can build a PRI camera using a couple of bandpass filters.

• https://en.wikipedia.org/wiki/Photochemical_Reflectance_Index

IR cameras

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha649b5/

This can mean NDVI cameras or thermal imaging cameras. NDVI can measure chlorophyll levels, thermal imaging can give ideas about transpiration rates. I use thermal imaging myself.

• https://en.wikipedia.org/wiki/Normalized_difference_vegetation_index

Thermal imaging picture of cannabis leaves:

• https://imgur.com/a/BZge9so (healthy leaves can be below ambient temperatures due to transpiration)

DLI (daily light integral)

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha65vuf/

That answer is for top light, and a total plant DLI can run higher if using side or intracanopy lighting.

• DLI = ((PPFD/100) * 8.6) * (% hours light on time per 24 hours)

Far red light

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha66kq3/

Far red triggers the shade avoidance responses which increases acid growth (plant cells get larger). When Bugbee talks about greater light capture he means that leaves can be made larger than normal with far red light. Very high amounts of far red light could cause foxtailing in buds in some cases.

Green light also triggers the shade avoidance responses.

• https://en.wikipedia.org/wiki/Shade_avoidance

Far red can cause excess stem elongation which is why he mentions he uses it during veging and not flowering. Far red may also increase photosynthesis efficiency through the Emerson effect.

• https://en.wikipedia.org/wiki/Emerson_effect

UV light

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha6jc88/

TL;DR- UV to increase THC is an urban legend. To note, the only UV light sensitive protein known is the UVR8 protein which is UVB sensitive, not UVA sensitive. Keep that in mind.

• https://en.wikipedia.org/wiki/UVR8

There are studies from the 1980's that may show increase in THC from UV but those strains back then had lower THC levels in the first place compared to modern strains.

This is another answer from Bugbee that amuses me because I've been saying for a long time that the UV light question has not been demonstrated to increase THC. Perhaps there's a study out there I'm missing.

Green light

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha6ia29/

I would be willing to bet that he meant cryptochrome and not phytochrome. I'm happy he mentioned Terashima et al and green photons (I think he got the dates confused because it's 2009 that the green photons work was published, not 2005).

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha63xm5/

• https://academic.oup.com/pcp/article/50/4/684/1908367 (Terashima et al 2009)

Photoperiod

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha67xd9/

TL;RD- shorter photoperiods do not accelerate flowering, longer photoperiods may increase yield

QWERTY or DVORAK

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha64cwk/

IMO, DVORAK is basically like kicking a puppy, and that is wrong. You're not a filthy puppy kicker, are you?

• link to cute puppies pics

Don't ask way too many questions at once!

https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha635by/

Don't do this and you should post the questions separately in blocks of two or three. A person doing an AMA will typically not spend too much time with a single person, and most of the questions will be ignored.

Testing the most dangerous light so far and some strong criticism

part of SAG's Lighting Guide

This is the light tested:

https://www.amazon.com/dp/B082Y1PMWF?psc=1&ref=ppx_yo2_dt_b_product_details

As a disclaimer, as always, I bought this light myself so there is no conflict of interest.

edit- spelling and just a bit of wordwmithing

The electrical safety test

Click the link on the light above and look at the one star ratings. What do you see? A bunch of people getting electrical shocks and the light overheating. When I first examined the light the first thing I noticed was some plastic insulators like this that immediately raised a red flag.

https://imgur.com/a/ZBKR8E3

Upon really close inspection I noticed that there was a thermal pad between the heat sink and the MCPCB (metal core printed circuit board and where all the parts are mounted). A thermal pad provides electrical insulation.

https://imgur.com/a/Azrfxdc

Hmmm....what's going on here? To confirm my suspicion I tested for continuity between the MCPCB and the heat sink and found them to be electrically isolated. So we have an energized circuit board that is not grounded although most people who don't know how to properly test lights would not notice, with a very thin plastic film over the energized components that does not provide adequate ingress protection, creating a situation that will get people killed although the light does appear grounded.

It's bullshit like this that is going to get people killed, and why I have an issue with people who have no idea what they are doing performing light "tests". How many of these YouTubers, who look like they know what they are doing by waving a light meter under a light, do you think would actually catch this fatal flaw in this light? None of them would because as far as I know none of them are properly trained or understand electrical safety.

You want to see a YouTuber who gets electrical safety? Check out the fellow electrician Big Clive.

https://www.youtube.com/channel/UCtM5z2gkrGRuWd0JQMx76qA

I didn't even need to do a light meter test because what's the point if I'd never recommend the light in the first place. I did, though, and about eight inches away from the center is the 1000 umol/m2/sec point.

Thermal imaging pics

Here's some thermal shots of the light tested:

https://imgur.com/a/nkfLHb2 (2 thermal pics)

It's important to note that on the backside of the light, in the pic with my thermal imaging camera, the light appears to be fairly cool with a hot spot on the label. What's going on? The heat sink has a very low emissivity while that label has a very high emissivity that gives a true temperature reading. This is the problem with using cheap non-contact thermometers.

The light measures 70 degrees F above ambient and my rule is that a grow light should never run above 145 degrees F. This is a partial failure and why people are getting burns off the light beyond electrical shocks. I say partial failure because a small fan could keep the temperature down. Heat kills LEDs faster.

Spectroradiometer pics

https://imgur.com/a/FUrXAn8 (2 spectrometer pics)

The first pic is my spectroradiometer in "scope" mode which gives me a raw output. The second pic is what's called a "second order derivative" which is used in analytical chemistry and really allows me to get in close and analyze the phosphors used. Every major downward dip is a different phosphor so these modern white LEDs have a lot more going on that what is shown in the data sheets. I use the same technique to analyze pigments and some proteins in plant leaves.

I'm not aware of anyone on the internet outside academia that gets into actually analyzing the phosphors in LEDs, let alone analyzing pigments and proteins.

What's under the hood

https://imgur.com/a/fBEVeHA (4 under the hood pics)

The line and neutral are going through power resistors, which is then rectified, smoothed out with a capacitor, and this higher voltage DC is then fed to the LEDs though linear current regulators in parallel. If you want to make something cheap and dangerous then this is the way to do it. The capacitor is going to be a major fail point particularly at higher temperatures.

MY RANT (and why I'm such a cynic)

The layman gets so impressed with people waving a light meter under a light, maybe doing a grid test, but none of them are doing a safety test to see if the light is going to kill people. I could probably train a monkey to wave a light meter under a light. That's hyperbole of course, but I could train someone in an hour or two to do most any test that you see on YouTube because waving around a light meter is trivial. Right?

Additionally, when I first get a light I'm not making non-sense shills posts on /r/spacebuckets about "herp-a-derp I got this free light, anyone else have this one? I'm going to put a plant under it and keep making a bunch more posts of this free light. Because it's free advertisement for this person who gave me a free light, and I'm too corrupt to get it. I'm even going to do shout outs to the person who gave it to me for free because fuck it, I got a free light and everyone has a price, mine just happens to be low". It's hard to be unbiased when receiving free stuff, and non-sense to compare lights when the lighting levels are not known, right?

This shilling problem was so bad on /r/microgrowery, at one point around 2016 with the mods receiving free lights, posts were being removed and people banned for promoting other lights. There are good reasons I'm proudly banned from /r/microgrowery for calling out non-sense. /r/microgrowery was quite literally founded on corruption, and the original mod was given the boot when publicly called out. When I started making waves about direct sidebar links to pirated grow books, a practice that Reddit admins would not allow today, the current head mod (Codine) threatened to sabotage my lighting guide with misinformation, which is why I made my own subreddit to protect the integrity of my lighting guide (PMs are forever archived!). This all sounds pretty corrupt, right?

The mods of /r/hydroponics were allowing stickied posts by MarsHydro, and MarsHydro was deleting posts on their own subreddit about people getting electrical shocks off their lights which others have confirmed to me about the electrical shock issue. It's very fair to ask, what's in it for the mods? MarsHydro also plays the non-sense "600w" game which is highly misleading. That sounds pretty corrupt, right?

In 2007 I was active with GreenPineLane, the first forum dedicated solely to LED grow lights. The head mod received a free 100 true watt light that had LEDs that were 15% efficient. The person who gave him the light claimed it would perform as well as a 400 watt HPS that would be around 30% efficient. The mod claimed this seemed right after trying to grow a single tomato plant. But I did some severe call outs because we all know that this would be utter non-sense and therefore corrupt, right?

The first grow light on the market was the LGM5 by Solaroasis that used 5 mm low power LEDs and cost well over $30 per watt. source. The person was claiming this 6-9 watt low power light could compete with HPS. When put to the test it could barely grow a tomato seedling without sever elongation. Complete and utter bullshit, right?

Eric Biksa, a public figure so there is no Reddit TOS violation, was writing in Maximum Grow magazine in early 2008 that LED lights were 10-20 times better than HPS while also claiming to be a world class hydro expert at age 24 despite no training. In summer 2008 in response to his non-sense, I wrote a 3000 word essay calling him and the whole LED grow light industry out for being founded on fraud at the time which can be seen here (a huge mistake was saying little light energy was converted to mass when I really meant that photosynthesis itself was very inefficient). The editor loved the essay because she wanted balance in the claims, the publisher hated it because he did not want to upset the LED grow light manufactures who bought advertisement space, so instead of an article it was published as a letter to the editor (it only meant I would not be paid $500 for the essay which was not the point). That would have been pretty corrupt of the publisher, right?

LEDGirl of HydroGrowLED fame was claiming in 2009 that she could get 2 grams per watt and in 2015 that she could get 4 times the yield per watt over HPS. I called her out in real life and believe me, LEDGirl is just as much as an unstable nutcase IRL as she is online. Four times the yield per watt over HPS is a corrupt non-sense claim even by today's standards, right?

I've seen MIGRO straight up grab energized circuit boards without a ground and handle it carelessly. That's either suicidal or a person who is utterly clueless on safety (people in the comments were trying to warn him). He'll also tell people to remove the covers from LED light bulbs which is very dangerous. He's first and foremost a salesman and acting grossly irresponsible, right? (I have many critiques of MIGRO, including having a weak grasp on actual theory, such as making up his own units like PPFD/W(???) and not understanding efficacy vs efficiency as well as being a bit naive on science in general, but I believe he basically operates in good faith for a salesman- he's also good at waving light meters around).

LEDTonic sells a cheap generic light that is twice the price per watt than any other light, and says 12 watts of cheap LEDs per square foot is adequate. source. This is one of the worst deals I've ever seen in all of LED grow lighting. Don't do business with people, who in my opinion, are scammers. Once a scammer always a scammer, right?

MostlySafe is such bullshit that he claims he created the whole concept of space buckets and used to sell homemade shoddy quality $600 space buckets! archived. He literally doxxed me when I called him out. That's pretty fucking cowardly, right?

If you're publicly shilling a free light then you are fair game for criticism, and I will publicly call you out on it, because you made it public. I've been calling people out for ten years on Reddit, have been doxxed three times for it so far, I've literally lawyered up when legal threats were made by MostlySafe against me and three other people including the head mod on /r/spacebuckets, and I'm not going to change. Nobody is going to control my or anybody else's hobby, right?

I have never accepted a free light, I'm not trying to sell anything, never done affiliate links, don't make any money off my guide, back my claims with links to hundreds of sources, back my claims with calibrated lab gear if I don't have another source, and I'm guessing I'm doing something right with over 5,000 subscribers. When I first wrote my lighting guide I was telling people not to use LED grow lights for commercial purposes because back then LEDs could not compete with HPS, which I received a lot of criticism for, and it would have been corrupt to say otherwise. Right...?

Affiliate links

You'll see people promoting lights with affiliate links. Most of the time they have never tested those lights and it's all bullshit if that's the case. They are less interested in the truth, and are more interested in a sale. Not all of them, but most of them. I understand some affiliate links keeps some websites going. But if people are writing lighting guides full of affiliate links then how can they truly be unbiased? Enough said.

N=1 and how not to do a test

N=1 means the plant count (population number) used in a test. It's complete non-sense to only use a single plant because you are not going to catch false positives and false negatives known as type 1 and type 2 errors.

Here is a YouTube video that uses an N=1 test that has over 800,000 views by Albo Pepper:

https://www.youtube.com/watch?v=sfihE4IuFuU

It's such non-sense that the plant under the CFL light was allowed to dry out. How is this even remotely a legitimate test? What does this say about the person performing the test? You'll see stuff like this all the time on YouTube. IS THIS THE BEST GROW LIGHT OF <insert year here>!!!! Non-sense. What does best grow light even mean?

Even in academia, I was once volunteering at a plant growth lab to get some hands on lab experience. I open up a $300,000 plant growth chamber, picked up a tray of arabidopsis thaliana (a model plant used in botany), and they were all dried out. Photosynthesis shuts down before wilting happens. How can this be a legitimate test with such sloppy procedures? Non-sense.

Bruce Bugbee discusses this problem and how hard it can be to do a legitimate test. I've never seen a legitimate test done in the hobby community. The conditions must be identical, and Bugbee himself articulates this and how hard large scale cannabis testing can be. Almost always seedlings are used in tests because clones, being genetically identical, can hide type one and two errors if they have specific mutations. Seedlings provide a little bit of genetic variability so your test does not get stuck in some type one or type two error.

How many plants do you need for a test? N=7 would be the absolute minimum for p<0.05 at power = 0.8 for a SN = 1.6. This is what I was taught at the plant growth lab I volunteered at. Most tests are done with dozens of plants if not hundreds of plants, though. This applies for lighting tests, root tests, or any other type of grow chamber plant test. Arabidopsis thaliana is a tiny long day plant with an eight week life cycle, which is one reason why it's used as a model plant beyond having many variants available with specific genes knocked out. It's also why seedlings are sometimes used in studies, and you can get N>100 in even small containers that will fit in a space bucket.

N>100 microgreen radish seedlings in two gallon space buckets under a table at 2000K, 3000K, and 5000K. 215 uMol/m2/sec, DLI 17 mol/m2/day.

https://en.wikipedia.org/wiki/P-value

https://en.wikipedia.org/wiki/Power_of_a_test

http://www.3rs-reduction.co.uk/html/6__power_and_sample_size.html

In conclusion

The light above sucks, YouTubers mostly suck, LEDTonic sucks, the doxxer MostlySafe sucks, shills promoting free stuff suck, affiliate link people suck if they have not at least used the lights, corrupt people in general suck, Star Wars episode eight power sucks, auto-tune music sucks, the US army (infantry) sucked, jumping out of a C-130 with a partial parachute malfunction sucked, covid sucks, white supremacists suck, legalizing pot in WA state but not allowing small private recreational grows sucks, the other people who have doxxed me suck, the deer who keep jumping in front of my car suck, the IMF sucks, Star Wars episode eight power sucks again, Jesus cult door knockers suck, that time I did four hits of LSD by myself sucked, that time pepper spray went off in my pocket sucked, the time I had a gout attack and then stubbed my gout swollen toe sucked, and Star Wars episodes one and nine also sucked (but not as bad as episode eight, it's a scientific fact that episode five was the best).

SAG's Plant Lighting Guide linked together

last update: 17 JAN 2022 (changed lux numbers per latest research)

Using a lux meter for plants

• Using a lux meter as a plant light meter article -You only use a lux meter with white LED grow lights. You should use a proper $20 and up stand alone lux meter preferably with a remote sensor head. Your phone is likely not an accurate lux meter due to cosine errors in real life conditions. This is a hardware issue that can not be corrected for in software, and the white translucent plastic over a proper light meter's sensor is the cosine correction.

• You should not use a lux meter with red/blue dominate "blurple" grow lights. The theory why is in the above article and some below. Only the more expensive $500 range "full spectrum" quantum light meters should be used with blurple LED grow lights to get accurate readings. Less expensive quantum light meters can work well with white LED grow lights, HPS, and sunlight but not necessarily with blurple LED grow lights.

Rough lux lighting levels for cannabis

White light CRI 80, 70 lux = 1 µmol/m2/sec:

• 5,000 lux_____ unrooted cuttings (many people go higher)

• 15,000 lux____ lower end seedlings (microgreens)

• 30,000 lux____ lower end vegetative growth (cannabis seedlings)

• 40,000 lux____ lower end flowering, rapid veg (tomato, pepper)

• 75,000 lux____ safer maximum beginner level

• 100,000 lux___cannabis starts light saturation

• Keep in mind that with higher lighting levels that things go bad much faster and the fertilizers and all other growing parameters need to be dialed in. The 100klx number is based on the latest 2021 university level research on cannabis and linear growth rates.

• I've grown various seedlings just fine at 35klx and many people on /r/spacebuckets are running their plants at >75klk or equivalent. You really want to stay above 40klx for flowering and many professionals are going to be closer to 75-90klx. I tend to grow plants at higher lighting levels myself.

• If your seedlings or veg plants are "stretching" too much then you need more total light or a higher color temperature light.

• I've seen research papers where cannabis is being rooted at 15,000 lux.

lux to PPFD conversions

The below will get you within 10% for white light.

• 55 lux = 1 µmol/m2/sec sunlight CRI 100

• 63 lux = 1 µmol/m2/sec white light CRI 90

• 70 lux = 1 µmol/m2/sec white light CRI 80

• 80 lux = 1 µmol/m2/sec HPS CRI 40

Higher CRI lights have a higher concentration of deeper red light (around 660 nm) which does not read as well with a lux meter. CRI has a bigger impact on lux to umol/m2/sec conversion values than CCT (color temp).

I've tested dozens of LEDs with my spectroradiometer (Stellarnet Greenwave) to get these numbers to always be within 10%. These are true measurements and not based off any specific lux meter which may be different. The claims are also backed by peer reviewed literature that uses 67 lux = 1 µmol/m2/sec as a generalization for all white LEDs and not taking CRI into account. (source).

Specific conversion values and spectrum shots for a dozen different Bridgelux LEDs can be found here.

DLI (daily lighting integral) calculations

• DLI is the amount of light that the plant receives in a 24 hour period. The unit of measurement is mol/m2/day or "moles per square meter per day".

• (PPFD/100) * 8.6 --this will give the DLI for a 24 hour photoperiod.

• Multiply the result with the percentage of light on time per day. ((PPFD/100) * 8.6) * (% hours on per 24 hours)

• Example: 200 µmol/m2/sec on 18 hours per day. (200/100=2) (2 * 8.6=17.2) (17.2 * 0.75=12.9 mol/m2/day)

• Example: 1200 µmol/m2/sec on 12 hours per day. (1200/100=12) (12 * 8.6=103.2) (103.2 * 0.50=51.6 mol/m2/day)

This usually only counts the top light, and intracanopy or side lighting can greatly increase these numbers.

The basic definitions

• PAR = "photosynthetic active radiation" or light from 400-700 nm by standard definition. PAR is what we measure and not a unit of measurement e.g. "300 PAR" makes no sense because the person could be talking about PAR watts. Around 4.6 µmol/m2/sec is one PAR watt/m2 for white light CRI 80. (source table 2) -great source

• PPFD = "photosynthetic photon flux density" in units of µmol/m2/sec or "micromoles per square meter per second" also written as µmol m-2 s-1. This is the light intensity at the point of measurement. Lux is a close white light equivalent.

• PPF = "photosynthetic photon flux" in µmol/sec or "micromoles per second" also written as µmol s-1. The is the total light given off by a light source. Lumens is a close white light equivalent.

• PPE = "photosynthetic photon efficacy" in µmol/joule or "micromoles per joule" also written as µmol/J. This is how many photons of light are generated per joule (watt * second) of energy input. PPF/Watts will give the PPE. Lumens per watt is a close white light equivalent.

• CCT = "correlated color temperature" is basically the red-blue ratio of a white light source and correlates to (i.e. appears to us as) the color temperature of a black body radiation source in degrees kelvin. Higher CCT, having more blue light, will keep plants more compact at a given lighting level. 3000K and 3500K are pretty common for all around use. Roughly speaking, 2700K is 10% blue, 4200K is 20% blue, and 6500K is 30% blue. (source, fig 1)

• CRI = "color rendering index" is how well the reflected light of different colors look. For our purposes, the thing to know is that CRI 90 and above light will have deeper reds that will read lower with a lux meter, although the true PPFD levels may be the same. The deeper reds is why CRI 80 and 90 have different lux to PPFD conversion values. Roughly speaking, a CRI 100 light has a luminous efficacy of 250 LPW (lumens per watt) at 100% efficiency, CRI 95 is 280 LPW, CRI 90 is 300 LPW, and CRI 80 is 320 LPW. In the real world, these numbers can vary by up to 10% or so. (source 1, fig 2) (source 2, table 1)

• Photomorphogenesis /"photo-morpho-genesis"/ or "light, change, life". These are light sensitive protein (phytochromes, phototropins, cryptochromes, UVR8) reactions that can be wavelength specific. For example, blue light up to about 470 nm has a powerful photomorphogenesis effect by keeping plants more compact, while 500 nm cyan light may do the opposite. (source for phototropins) (source for cryptochromes)

The McCree curve

• Picture of the McCree curve for photosynthesis rates

• Link to the McCree curve paper (fig 14)

• The McCree Curve Demystified -good article on the McCree curve by a Ph.D senior research scientist

• The McCree curve is a quantum efficiency lighting curve used in botany and should be used only as an initial foundation for understanding photosynthesis rates by wavelength. It is far more accurate than charts for chlorophyll dissolved in a solvent or charts for green algae, and it is common for these charts to get mixed up.

• It was developed in the early 1970's by Keith McCree, a Ph.D physicist that was a professor of Soil and Crop Sciences at Texas A&M University. He tested 22 different crop plant types for photosynthesis rates with a PPFD of 18-150 µmol/m2/sec, in monochromatic light at 25 nm intervals from 350 nm to 750 nm, and using the single leaf model. The McCree curve is only valid for these conditions. Monitoring CO2 uptake was used to measure photosynthesis rates.

• The McCree curve illustrates that all of 400-700 nm is useful for photosynthesis including green light, and not just red and blue light.

• The McCree curve should not be used for very high lighting levels.

• The McCree curve does not take in to account the whole plant model, or multi-wavelength lights including mixing in far red to try to increase photosynthesis efficiency (Emerson enhancement effect).

• The work of McCree demonstrated that both sides of a leaf can be used efficiently for photosynthesis. Dicotyledons may reflect more green light on the abaxial (underside) of a leaf, while monocotyledons will have the same green reflectance on both sides of a leaf.

• YPF (YPFD) or "yield photon flux (density)" is PPFD that has been weighed to the McCree curve. It is fortunately rarely used in botany but you do sometimes see it. There are special PAR sensors that give measurements in YPFD instead of PPFD, as well as spectroradiometers that can do this.

What different colors of light do to plants

• BLUE. Blue light decreases acid growth which is different than growth through photosynthesis. Excess acid growth, or "stretching", in seedlings/veg is all about greater cell expansion in the stem that we get from lower lighting levels or not enough blue light. We typically only want as much blue in a light source to help prevent any excess stem elongation. Blue photons have much more energy needed for photosynthesis, and this extra energy is wasted as heat that the plant has to dissipate. The associated blue light sensitive proteins are the phototropins and cryptochromes.

• GREEN. In healthy cannabis, 80-90% of green light is being absorbed and available for photosynthesis. Green is the opposite of blue in photomorphogenesis responses in that green causes stretching also called the shade avoidance responses. Pretty much anything blue does, green does the opposite. Green can help make leaves larger and increase the LAI (leaf area index) for greater light capture.

• article on green light and plants

• RED. Red can help keep a plant more compact but not nearly to the degree of blue. Red should be thought of as a lower energy photosynthesis driver and red LEDs can have a PPE that's greater than theoretically possible with white LEDs (blue LEDs with a phosphor). There are red LEDs on the market that are >4.0 µmol/joule. The associated red/far red light sensitive proteins are the phytochromes.

• FAR RED. Far red causes greater stretching like green light and contributes to the shade avoidance responses. It "may" help put short day plants "to sleep" faster. Far red may in some plants may be able to drive photosynthesis efficiently though the Emerson enhancement effect. About 50% of far red light is reflected off plant leaves, and also transmits easily though leaves. For photomorphogenesis responses, red and far red are opposites like blue and green are opposites.

• UV. Ultraviolet is a wild card and I can make no rhyme or reason of it working with a variety of plants. It tends to cause dwarfing when used as an only light source (UVA). For cannabis, the idea is to try to increase trichome and THC levels by adding UV, but some researchers including Bruce Bugbee are saying this does not happen. source. The only identified UV protein is the UVR8 protein, which is only UVB sensitive, not UVA sensitive (285 nm peak sensitivity).

• Anecdotally, certain selective photomorphogenesis experiments I've done with UVA compared to blue, leads me to believe that there may be at least one unknown UVA light sensitive protein either as a primary receptor, or my SWAG (scientific wild-ass guess) is a UVA light sensitive protein that can express itself differently in different plant parts, affecting the protein phototropin/cryptochrome signal transduction pathways locally. For example the hypocotyl (the stem before the first set of true leaves) can react much differently than the epicotyl (the stem after the first set of true leaves) in some plants like pole beans in my 470 nm vs 405 nm experiments.

Energy and efficacy of photons

Knowing this helps us make LED efficiency calculations and understand why red LEDs are used in grow lights. It's easy to get "efficacy" (how well something works) and "efficiency" (ratio of useful work) confused.

• 1240/wavelength of light in nm = energy of a photon in eV (electron volts).

• 10.37/eV of photon = µmol/joule or the maximum possible PPE (photosynthetic photon efficacy).

• max possible PPE * LED efficiency = the PPE for the specific LED.

• Example: 660 nm photon. (1240/660=1.88eV) (10.37/1.88=5.52 µmol/joule). At 100% efficiency, a red 660 nm LED would have a PPE of 5.52 µmol/joule.

• Example: 450 nm photon. (1240/450=2.76eV) (10.37/2.76=3.76 µmol/joule). At 100% efficiency, a blue 450 nm LED would have a PPE of 3.76 µmol/joule.

• Question: what is the electrical efficiency of a 660 nm LED with a PPE of 2.8 µmol/joule? (1240/660=1.88eV) (10.37/1.88=5.52 µmol/joule) (2.8 µmol/joule/5.52 µmol/joule=50.7% efficient)

• Question: what is the electrical efficiency of a 450 nm LED with a PPE of 2.8 µmol/joule? (1240/450=2.76eV) (10.37/2.76=3.76 µmol/joule) (2.8 µmol/joule/3.76 µmol/joule=74% efficient)

• The above means that we can theoretically get about 47% more light for the energy input with 660 nm LEDs versus 450 nm LEDs. It explains why red LEDs are breaking the 4 µmol/joule barrier, and white LEDs based on blue LEDs with a phosphor never will.

• Green LEDs are electrically inefficient and is a physics/semiconductor issue. Our eyes are most sensitive to green light so we don't notice.

Luminous efficiency and lux meters

• Luminous efficiency chart -these are correction factors

• Luminous efficiency is not the same as luminous efficacy (lumens per watt).

• Luminous efficiency is a percentage correction factor for wavelengths of light relative to 555 nm that takes in to account the spectral sensitivity of the human eye. 555 nm is what our eyes are most sensitive to and has a luminous efficiency of 1.0002 (it had to be corrected once which is why it's not 1.0000- that's good science).

• LEDs have a binning tolerance, and a 660 nm LED could actually be 650 nm or 670 nm. A 650 nm LED has a luminous efficiency of 0.107, while a 670 nm LED has a luminous efficiency of 0.032. That means with a lux meter the 650 nm LEDs with give a lux reading three times higher than 670 nm LED although the PPFD may be the same. This is why we don't use lux meters with color LEDs for absolute measurements, and why knowing about luminous efficiency is important.

• A cheap $10 spectroscope can help you identify that actual dominate wavelength of an LED so you can determine the needed correction factor.

• A lux meter with cosine correction can be used accurately with any visible lighting spectrum for relative measurements. The cheap $20 lux meters I examined where using silicon diodes with an appropriate short pass filter. Here is the transmission characteristics of the filter for a Dr.meter LX1010B lux meter.. This, combined with the response curve of a generic silicon photodiode, gets fairly close to a true lux curve response that a spectroradiometer can give that takes into account the luminous efficiency by wavelength.

Watts equivalent for common CFL/LED light bulbs

This is equivalent to an incandescent light bulb.

• 40 watts equivalent is about 450 lumens

• 60 watts equivalent is about 800 lumens

• 75 watts equivalent is about 1200 lumens

• 100 watts equivalent is about 1600 lumens

• greater than 100 watts equivalent is not necessarily very well defined

• Spot and flood lights may be a little different if the manufacturer is using equivalent to halogen lighting.

• The watts equivalent does not ever change although the true wattage does as LEDs become more efficient. This is to help lower the confusion among consumers about what size light bulb they should get as LEDs become more electrically efficient.

• Be wary of any "watts equivalent" to HPS light. A lot of low end LED sellers will use "600w" or "1000w" as a deceptive marketing practice, and you need to go off actual wattage.

Spectrometer shot of a green leaf

• GREEN LEAF -This is showing 83% green absorption. High nitrogen cannabis can be closer to 90% green absorption.

• Pigments listed below the line are absorption points, above the line are reflectance peaks.

• You'll notice that chlorophyll B has very little effect on the red side, and using 630 nm LEDs to try to target it makes no sense.

• Carotenoids (specifically xanthophylls) are dominating the blue side. Carotenoids are an accessory pigment that are 30-70% efficient at transferring absorbed energy to chlorophyll. Only through chlorophyll A can photosynthesis take place.

• Carotenoids help prevent damage to leaves from too much blue light known as the xanthophyll cycle.

• Measuring the 531 nm to 570 nm carotenoid reflectance ratio is one way to determine photosynthesis efficiency and known as the Photochemical Reflectance Index.

• As far as known, chlorophyll to chlorophyll energy transfer is 100% efficient through Förster (fluorescent) resonance energy transfer and coherent resonance energy transfer (source page 5)

Emerson (enhancement) effect

• The Emerson effect is about driving photosynthesis with part of the light PAR (400-680 nm in this case), and part of the light far red (700 nm-740 nm or so), combined can result in photosynthesis rates higher than normal.

• Robert Emerson used his work with red and far red light to deduce that there must be two photosystems, called photosystem I (PSI) and photosystem II (PSII), named in the order of discovery but for photosynthesis, the process starts with the PSII first.

• Monochromatic light has a sharp drop off in photosynthesis at 680 nm or so (red drop effect), but this does not happen if far red light is added with about 720 nm being most efficient in driving additional photosynthesis. (source 1 fig 1) (source 2 Bugbee)

• Far red light can drive the PSI independently of the PSII, and PAR is more efficient with the PSII while not as well excited with the PSI. Basically how the Emerson effect works is freeing up electrons between the PSI and PSII by driving them more efficiently in parallel, and photosynthesis becomes more efficient as a result.

• You can see this jamming of electrons in this chlorophyll fluorescence shot with proteins associated with the PSII and much less fluorescence associated with the PSI (the single 750 nm hump). Higher fluorescence means lower photosynthesis efficiency. (that shot was just turning on the lights)

• I think most far red driver boards are gimmicks because they are likely not putting out enough far red light to make a noticeable difference.

Lighting tips

• You generally want the light meter or the sensor head pointing up and down, not at the light source, to get a cosine correct reading. This is a huge mistake I see people make and the white piece of plastic over the sensor gives the proper cosine correction, not tilting the sensor towards the light which will give false readings. This is also why I recommend meters with remote sensor heads for ease of taking a reading and scanning around.

• Your phone is a poor light meter if it has no cosine correction (highly likely does not), and I can set up conditions where my Samsung A51 (and Samsung S7) are ten times off a true reading and where they read the same as true. This is a hardware limitation that can not be corrected with in software. Phones are basically worthless for color LEDs due to the luminous efficiency issue. Based on hands-on experience, I automatically discount all lux measurements done with phones.

• The harder you push your plants the easier it is to mess things up. If you are having health issues with your plant the first thing to do is to lessen the lighting levels on the plant to slow things down.

• I generally run all plants 24/0 that can handle that lighting schedule in veging. Many long day and day neutral plants can not handle a 24/0 schedule in flowering due to blossom drop. At high levels at 24/0 this can cause photosynthesis rates to lower a bit per amount of light due to some damage being done to certain proteins in the photosystem, and the time needed for these repairs to take place (hours).

• Light quantity (how much light) is generally more important than light quality (the lighting spectrum).

• It can be a bit naive to use PPF to try to calculate actual PPFD numbers. If you do then be sure that you over estimate by perhaps 30-50%.

• I have more success with cuttings at 18/6 rather than 24/0. As a wild guess, it could be because auxins are being produced at their maximum levels in darkness, and auxins help with rooting.

• You can calibrate any light meter for PPFD as long as the meter has cosine correction. Most light meters are highly linear i.e. a light meter based on a light dependent resistor would likely not be linear, but the silicon diodes found in most lux meters are linear to within 1% over 7-10 orders of magnitude.

• It takes about 30-60 seconds for a dark adapted leaf to fully "turn on" for photosynthesis. This can be seen in these chlorophyll fluorescence over time pic off my spectrometer. In many scientific papers the researchers may wait 60-90 minutes for a leaf to become fully light adapted.

Theory and tips on white LEDs and grow lights

last update: 8 July 2021

I wanted to try writing stuff a bit different so I used bullet points with short and direct statements. There's a bit of theory below but actual white light theory would require its own article due to the 40,000 character limit in a post.

• part of SAG's plant lighting guide

• Using a lux meter as a plant light meter -if you don't know the conversion value, use 70 lux = 1 umol/m2/sec for white LEDs

• Core Concepts in Horticulture Lighting Theory -there is theory here that might make some stuff on this post more understandable

Good paper and the basic definitions

• From physics to fixtures to food: current and potential LED efficacy -Must read. When I write "above paper" with a page number, this is it. Note that this paper covers a lot of 2020 LED efficiency numbers while also discussing maximum theoretical efficacy in this paper, and it can be easy to confuse the two.

• PAR -"photosynthetic active radiation" or light from 400-700 nm by standardized definition. PAR is what we measure, and not a unit of measurement. Saying "300 PAR" would be like saying "300 water".

• PPFD- "photosynthetic photon flux density" or light intensity at the point of measurement. The unit is umol/m2/sec (µmol m-2 s-1) or "micromoles per square meter per second". The close white light analogy is lux.

• PPF- "photosynthetic photon flux" or the total amount of 400-700 nm photons per second given off by an LED/grow light. The unit is umol/sec (µmol s-1) or "micromoles per second". The close white light analogy is lumens (e.g a 100 watt incandescent bulb (true or equivalent) puts out about 1600 lumens of light).

• PPE- "photosynthetic photon efficacy" or the amount of photons produced by a light source per amount of energy input. The unit is umol/joule (µmol j-1) or "micromoles per joule". The somewhat close(ish) white light analogy is LPW (lumens per watt). You will sometimes see PPE written as PPF/W.

• Efficiency is the ratio of useful work (e.g an LED is 50% efficient if half the consumed energy is radiated away as the light). Efficacy, as how I'm using it, is how well something works (e.g that white 50% efficient LED at CRI 80 has a luminous efficacy of around 160 lumens per watt, give or take a bit).

The ultimate efficacy limits of fixtures

"The upper limit of LED fixture efficacy is determined by the LED package efficacy multiplied by four factors inherent to all fixtures: current droop, thermal droop, driver (power supply) inefficiencies, and optical losses" -above paper, page 1

• To maximize an LED grow light's idealized efficacy, we want the LED current as low as possible (throw more LEDs at the problem as they become cheaper and underdrive them), keep them as cool as possible (a little airflow goes a long ways, maybe 2-10 times so), get the most efficient driver (you want to look up the efficiency by current level curves in the data sheet), and don't use lenses or a glass cover. But, by not using a cover means we lose ingress protection leaving exposed voltages so there are potential safety concerns, and exposing the LEDs directly to the environment can potentially lower their longevity and the grow light's longer term reliability.

• Current droop -The greater the current though an LED, the less efficient it becomes. This is one reason why medium power LEDs in large series/parallel arrays (e.g quantum boards^® ) have become common at least in the hobby community, and how COBs work by having a large series/parallel array of LEDs in a smaller common package. LED makers typical rate their LED at a "nominal" or "sorting" current that may be significantly lower than what the LED is actually being driven at in real life. The Samsung LM301H has their specs listed for 65 mA, but is rated for 200 mA continuous, for example.

• Thermal droop -The higher the temperature of the LED, the less efficient it becomes. LED data sheets typically give bin numbers for 25 degrees C (77 F) or 85 C (185 F), and most LEDs are specified to operate at 85-125 C. Higher temperatures also means that the LED degrades more quickly, particularly red LEDs. The difference between 25 C and 85 C is about a 5% efficiency loss for most LEDs. Some 125 C continuous rated red LEDs can take a >20% efficiency hit at 125 C. Higher temperatures will also degrade LEDs faster, and cheap light bulbs are going to run their cheap LEDs very hot. Don't buy the cheapest light bulbs if you want them to last- you get what you pay for.

• Driver (power supply) inefficiencies -Some low voltage DC drivers can hit about 98% efficiency depending on drive current. There are AC LED drivers on the market that can peak at 97% efficiency. Some Mean Well LED drivers can hit the mid 90s% efficient. Most of the AC LED drivers you find in products are going to be in the low 90s or upper 80's percent efficient, which can depend on specific LED current levels. Drivers with a lower power factor also contribute to greater inefficiencies. Cheap capacitors in cheap lights (particularly cheap light bulbs) is a major failure mode particularly with poor thermal management.

• Optical losses -Using secondary optics (i.e a lens) over an LED can focus the light so an LED grow light maker can post some impressive PPFD (intensity) numbers right below the light, but the PPF number (total light output) is going to drop, too. There will always be optical losses with a lens of perhaps 7-9%. This same loss applies to grow lights that have a glass/plastic/silicon cover over the LEDs for splash proofing the light. If you grow hydroponically, and a prone to splashing hydro nute solution around, it may be worth it to take this inefficiency hit to keep the salt solution away from the electronics. Electrical safety is another very important reason glass covers are used for the ingress protection they provide.

Keep in mind on LED grow light specs, some low end sellers may give specs (e.g PPF umol/sec numbers) for data sheet temperature and current ideal efficacy (i.e 25 C, lower nominal current), or may not take in to account LED driver losses when posting a umol/joule number, and not how the light actually performs in real world grow conditions. If low end Amazon/eBay style lights are giving specs better than high end lights, then don't don't do business with that seller.

Some basic facts on LEDs, light, and lights

• The "K" in "color temperature" stands for "degrees Kelvin", not to mean "thousand". For example, it's a 2700K light, not a 2.7K light which is deep outer space cold. It's also a correlated color temperature (CCT), and not an actual approximate black body radiator color temperature like with a 2700-2800K incandescent light bulb.

• I define "white" as any light source whose spectral output is on or fairly close to the plankian locus in the CIE 1931 color space chromaticity diagram within a certain color temperature range (2700k-6500K or so). There are many types of white light (i.e different CCT, CRI, TM-30-15 Rf, spectral power distributions), and many ways to create white, so my definition is a bit vague. Bridgelux has 1750K LEDs they call white, for example, but I certainly don't perceive them as white.

• White LEDs (blue LEDs with a phosphor(s) for this discussion) are mass produced very well beyond any other LED lighting, which can make them cheaper through scale of economy, particularly the surface mount medium power LEDs like by Samsung. The amount of R&D into LED technology has resulted in some white LEDs having a PPE of greater than 3 uMol/joule at nominal (lower) current levels and at room temperature. They will max out at about 3.3-3.4ish uMol/joule depending on CCT and CRI, maybe slightly higher if underdriven.

• A 450 nm blue LED will likely have a maximum practical PPE of about 3.5-3.6 umol/joule, with a maximum theoretical PPE of 3.76 umol/joule. The 3.76 umol/joule number is the ultimate barrier to white LEDs based off a 450 nm blue LED with a phosphor, and the only current way to get a higher PPE for grow lights is to add actual red LEDs to white LEDs, or if appropriate for your plant, use red and blue LEDs only (perhaps with some white thrown in).

• There are white LEDs that use the phosphor pump from violet or ultraviolet-A LEDs. Our visibility extends down to about 400 nm, not 450 nm. They use additional broader blue phosphors instead of blue LEDs. But, violet and UV-A LEDs can never have the efficacy of blue LEDs because they have more energy in their photons. We generally wouldn't want to use these types of LEDs in grow light. Seoul Semiconductor Sunlike LEDs use violet LEDs.

• In most cases it's one photon per photochemical reaction also known as the second law of photochemistry. This applies to photosynthesis and to phosphors. You can have multiple down conversions with phosphors and not break the second law (i.e in a white LED, a photon can be absorbed and emitted multiple times always at lower energy levels), but this does not happen with photosynthesis. This means for photosynthesis that a blue photon does not drive photosynthesis better because blue photons have more energy than green and red photons, and the extra energy in the blue photons is wasted as heat in the photosynthesis process.

• 2700K has about 10% blue light, 4200K has about 20% blue light, 6500K has about 30% blue light. The greater the blue light content, the more compact the plant will be by reducing acid growth due to lower auxin levels. This is why people will say to use a higher color temperature in veging to suppress growth like stretching, and use lower color temperature in flowering to promote acid growth in flowering. Most higher end white LED grow lights are 3000K to 4000K.

• Higher color temperature white LEDs will have a higher electrical efficiency, all else being equal, because less blue light is being captured by the phosphors, and the blue light emitted by the LED does not take a phosphor conversion loss hit. The total phosphor conversion loss for a white LED can be 5-20% (page 3, above paper). Because there is a higher conversion loss with lower color temperature LEDs, they will run a bit hotter than higher color temperature LEDs. Lower color temperature (and higher CRI) LEDs will also have greater total Stokes shift heating (the energy difference between the blue photon emitted from the blue LED and the other down converted photon from the phosphor is wasted as heat).

• Some modern white LEDs may use five or more different phosphors or phosphors with multiple peaks, and I didn't really realize this until doing 1st and 2nd order derivative spectroscopic analysis on a dozen different types of Bridgelux white LEDs. The results can be seen here.. Early white LEDs were using a single yellow phosphor with blue LEDs and some still do.

• A "perfect" white light source would be right around 4.6 uMol/joule (it can vary a bit depending on the type of white). If you had a hypothetical 100% efficient array of color LEDs and a 100% LED driver to make white light, then you'll be around 4.6 uMol/joule, give or take a little. This is a theoretical limitation for white light no matter the white light source.

• Mixing warm white and cool white LEDs in a grow light makes no sense, and I consider it a marketing gimmick at best. An exception is if you want a variable color temperature grow light, then it makes sense to to mix warm white and cool white dimmable separately, or use dimmable warm white and blue LEDs to control the color temperature. I go with 3000K or 3500K for all around use for plant growing, but experiment with various 1750K to 6500K COBs, also (1750K is about what candle light is).

• I consider mixing red LEDs like 630 nm and 660 nm, or 450 nm and 470 nm, to also be a marketing gimmick, unless a clear demonstration as to their combined efficacy can be demonstrated in controlled grows (temp, humidity, CO2, and lighting levels consistent and does not significantly fluctuate to remove as many variables as possible). My first non-controlled experiments were in 2008 where I found no significant difference in 450-660, 450-630, 450-630-660 nm, and white light for a leafy lettuce cultivar. I soldered up a few thousand low power 5 mm LEDs to do these early experiments.

• There is nothing special about 6500K light for plants that may be used in veging and don't normally use it. Higher color temperature light usually have a higher luminous efficacy, and 6500K is about the highest color temperature that is tolerated for the consumer before appearing too blue. It's more often found in work spaces. 6500K is also the color temperature of the standard illuminate D65 used in photometry. 6500K has very little to do with professional grow lighting, and traditional (non-ceramic) metal halide is 4200K.

• There is nothing special about 2700K light for plants that may be used for flowering. It's about what incandescent bulbs roughly are and is close to the color temperature for the illuminate standard A used in photometry. You typically want to use this color temperature range or a bit higher for living spaces. Traditional HPS is 2100K.

• Although we tend to use higher color temperature white light for veging and a lower color temperature for flowering, I've gotten great veg growth with 2100K HPS for cannabis when LST (low stress training) techniques and higher lighting levels were used (500 umol/m2/sec). I've found greater growth at higher lighting levels but at lower color temperatures with various microgreens testing 2000K, 3000K, and 5000K light. If longer stems is what want (and what you get with lower lighting levels), but still want aggressive growth with larger leaves, play around with 2000K white LEDs at higher lighting levels for microgreens.

• CRI (color rendering index) tells us how well a light source does at accurately reproducing colors in an object relative to a natural or black body radiation source (e.g sun, incandescent bulb). It really falls flat, though, and a different standard has come out called TM-30. TM-30 doesn't actually replace CRI because they are standards from two different organizations, the CIE (International Commission on Illumination) for CRI, and ANSI/IES (American National Standards Institute/Illuminating Engineering Society) for TM-30.

• A major problem with CRI Ra is that it only measures eight pastel, non-saturated samples in their measurement. Not included are R9 (saturated red), R10 (saturated yellow), R11 (saturated green), R12 (saturated blue), R13 (white skin tone), R14 (leaf green), and sometimes R15 (south east Asian skin tone), which had to be added over time. Most CRI 80 lights have as R9 (red) value of 0, and CRI 90 lights are an R9 value of around 50. This is why you want to use high CRI lighting around food and for photography- CRI 80 is going to give you bland looking reds because of lower red chroma (saturation).

• CRI plays a larger role in lux to PPFD (umol/m2/sec) conversions than color temperature. Higher CRI lighting will have a greater amount of deeper reds, and deeper reds naturally have a lower luminous flux at the same radiant flux because luminous flux takes into account the sensitivity of our eyes by wavelength. In other words, the deeper reds have a lower luminous efficiency. You can see the differences in my spectroradiometer SPD charts here.

• You should consider using higher CRI lighting with plants that are also being used for display purposes (like orchids), particularly with plants that have red or purple colors. You should also be using high CRI lighting in your kitchen and dining room or wherever food is served, particularly for red colors like a medium rare steak. You can buy CRI +90 LED light bulbs and a quick google search shows a seller with CRI +95 (Cri 98 in their photometric data sheet).

• 100% efficient white LEDs would be fairly close to 260 lumens per watt for CRI 100, 280 lumens per watt for CRI 95, 300 lumens per watt for CRI 90, and about 320 lumens per watt for CRI 80. This can vary a bit by up to 10%.

• Red, green, and blue LEDs to make white light looks awful for general lighting because the CRI is around 40ish. The "rendering" part in CRI is about reflected light, and a RBG white light has relatively narrow spectral power distribution rather than a broader distribution, and the accurate colors of an object won't happen.

• What I said about objects having colors above is a lie. Objects don't have colors, light has colors and objects have specific absorption and reflection characteristics. Even that's a partial lie because color is a perception only, and we do not all perceive colors the same (e.g red-green color blind). "Color" is so much about our perception, the specific light, the specific subject, camera sensor characteristics, and different display characteristics which is why there are a multitude of different professional color standards.

• Fidelity Index (Rf) is used with TM-30 measurements and is sort of like CRI (0-100 scale with higher being better, but CRI can also have a negative number), but there's 99 color evaluation samples with a wide range of hue (base color), chroma (amount of saturation), and lightness. It is the average amount of "color smearing" in the 99 color samples, or the average of how far off one is from the color samples. That ultra high CRI bulb above has a TM-30-15 Rf of 94, and around 60 should be the minimum for indoor lighting (higher for living areas). A US Dept of Energy TM-30 tutorial can be found here.

• Gamut Index (Gf) with TM-30 ranges from 80-120 and is basically the amount of saturation with 100 being a neutral saturation. It is the color gamut area. Lower Gf white lights will make objects appear duller with higher Gf having colors more saturated.

• You can have a light with the same CCT, CRI, Rf, and still be different because the simpler numbers don't tell us the spectral power distribution. There's a good reason for high end studio photographers to keep gelling their lights as needed (professional videographers have their own standards on white coming out that takes into account the sensors in their cameras).

• Green LEDs are relatively electrically inefficient which is why they are not commonly used in grow lights. In physics/engineering this is known as the green gap (graph). We do, however, perceive green light much higher than red or blue light, so for display purposes this inefficiency matters less.

• Red photons have a lower energy with a higher theoretical PPE of about 5.51 uMol/joule (660 nm) compared to blue of 3.76 uMol/joule (450 nm). The higher efficacy is one reason why red LEDs are being added to white LEDs, what's held them back a bit is their electrical efficiency (red and blue LEDs use different semiconductor material).

• A red 660 nm LED that is 50% efficient would have a PPE of 2.76 umol/joule. A blue 450 nm LED that is 50% efficient would have a PPE of 1.88 umol/joule. A 450 nm blue LED can never be higher than 100% for 3.76 umol/joule, which is 68% efficient for a 660 nm red LED.

• Red LEDs have now broken the 4 umol/joule barrier in 2020 such as the Oslon Square Hyper Red by Osram (V9 bin 4.42 umol/joule at 350 mA for 80% efficient, and 4.04 umol/joule at 700 mA for 73% efficient). Currently, most red LEDs are significantly less.

• Osram is taking an interesting approach by having 4000K white horticulture LEDs that contain 15% less red than CRI 70 LEDs. This LED is then combined with their very efficient >4 umol/joule red LEDs.

• In some cases far red LEDs could be added depending on your design goals. For instance, far red could potentially help drive photosynthesis more efficiently as per the Emerson effect, but also tends to cause more acid growth (stretching in stems and petioles, larger leaves), which we may or may not want. Far red can also be used to control the photoperiod in some plants. High amounts of far red may encourage "foxtailing" in cannabis, and your specific cultivar would have to be tested.

• Adding UV LEDs are typically only used for light sensitive protein reactions effects, not as photosynthesis drivers per se. The pure UV-A grows I've done did result in slow grow and stunted plants. If I wanted to keep a tiny, important plant alive for a long duration I would be using pure UV-A. But, the effects of UV-A on a plant can be unpredictable and needs to be tested by cultivar. The theoretical maximum PPE of a 375 nm UV-A LED is 3.13 umol/joule, and the relative low photosynthesis rate is going to make them a no-go in LED lighting except for photomorphogenesis effects. Making red lettuce cultivars more red by increasing anthocyanin production, or trying to increase trichome and cannabinoid production in cannabis plants, may be reasons to use UV light.

• UV-A light is fairly safe (it can be dangerous when you stick your eye close to a light source that appears dim yet has a high radiant flux) and at the time of this writing, only UV-A LEDs are used in LED grow lights if UV light is used. The UV-B light sources I've seen in grow lights are still tube based because UV-B LEDs are still inefficient (5-10% range). UV-C should be considered dangerous, and in testing I have damaged a number of plants with higher amounts of UV-C.

• The main UV light sensitive protein known about currently is the UVR8 protein which is a 280-315 nm UV-B receptor, not a UV-A receptor.

• Apogee Instruments (Bruce Bugbee's company) have come out with a SQ-610 USB sensor for "ePAR" (enhanced photosynthetic active radiation) which counts light out to 750 nm far red, and also some UV-A at decreased sensitivity. With a long pass filter it may be possible to turn this into a red/far red light meter. They also have a new SQ-640 Quantum Light Pollution USB sensor that measures from 340-1040 nm. With the right filters, this sensor could have a lot of applications beyond light pollution measurements.

• "Hot swapping" LEDs is generally a bad practice with constant current or constant power supplies. This is where you change out an LED with the power supply still on. By lifting the load, a much higher voltage may be found in constant current power supplies. When the LED is applied, it's possible to get a very quick and short high current pulse causing damage which is accumulative. There are LED drivers where you can dial in both the maximum current and maximum voltage to make hot swapping safer. I've blown LEDs on lab power supplies because of of hot swapping and being careless.

• A silver mirror is fundamentally different than white although they can have the same reflectivity. The the main difference is that the mirror has a specular reflection where the phase information of the photons is preserved if the mirror surface is very smooth, and white has a diffuse reflection with photons being scattered. A mirror, being made out of a conductor, has a bunch of free electrons. These free electrons can oscillate when the photon strikes them, and this oscillation itself creates another photon i.e an opposing oscillating electric field is created that cancels out the original electromagnetic wave. Because these free electrons are not bound and have no discrete energy states, they have a broad range of energy levels they can oscillate at and a broad range of wavelengths of light that they'll reflect. This electric field interference also prevents photons from penetrating more than a few nanometers into the mirror's surface. I'm greatly simplifying all of this.

• If you have issues with cheap LED light bulbs burning out then stop buying such cheap light bulbs. Like most everything in life, you get what you pay for, and buy cheap buy twice.

Heat sink tips

• Only the energy input not radiated as light needs to be taken in to account for LED heat sink calculations. This is called thermal wattage. For example, a 100 watt COB that is 50% efficient would need a heat sink good for 50 watts of heat. A 100 watt COB that is 80% efficient would need a heat sink good for 20 watts of heat.

• A heat sink has a thermal rating or heat dissipation in units of °C/W, or the rise of the heat sink in degrees C per watt of heat on the heat sink. If I have a 100 watt COB that is 50% efficient (so 50 watts of heat) and want the heat sink to rise no more than 10 degrees C, I would need a heat sink with a heat dissipation of 0.2 °C/W. If I use a fan it may be 0.4 to 2 °C/W, depending on how much air the fan pushes and the particular heat sink geometry.

• I often size heat sinks that prevent the LEDs from going above 85-125 C for safety, and then use a quite fan to keep them at a temperature I want them to be. This provides an inherent fail-safe feature when experimenting.

• Rule of thumb I use: I try not to go above 125 degrees F (52 C), or where I can keep my finger on the heat sink for 4 seconds. My personal do not go over temperature is 145 degrees F (63 C), or where I can keep my finger on the heat sink for an honest one second. I've had second degree burns from electronics more than once.

• Temperature measuring tip: When working with a heat sink and a constant current power supply, you can monitor the voltage on the LEDs to see very tiny temperature variations that might not normally be measured with a temperature probe. With a constant voltage power supply, you can monitor the current to see very tiny temperature variations. This is because the I/V curves for LEDs are temperature dependent, and strings of LEDs make very high resolution temperature sensors. I use a 50,000 count data logging Fluke 287 for this purpose (I recommend a 6000 count multimeter for lower cost DIY. Every low cost meter I've ever tested reads within their listed specs when referenced to my Fluke 287, except for the occasional generic $5 meter that companies like Harbor Freight give away for free).

• 6063 aluminum alloy is the alloy with the highest thermal conductivity (around 210 W/m⋅K), and most common in heat sinks. The trade off is that 6063 is a softer alloy so common 6061 alloy (around 167 W/m⋅K) may be used instead in some cases. I've seen sellers advertise about using "aircraft grade aluminum" like 7075 alloy for metal core PCBs for LEDs, which is inferior for our uses (around 140 W/m⋅K). For comparison, copper is closer to 400 W/m⋅K, and steel is closer to 45 W/m⋅K.

• For a Vero 29 running at 120 watts I use a generic $30 CPU cooler with a fan and call it good. I've seen coolers half that price that should also work.

• I can run a Bridgelux gen 7 Vero 29 at 50 watts on the COB on a 40 mm heat sink with a 40 mm fan mounted about 1 cm above the heat sink to improve airflow. To be clear, I'm saying I "can" do this, and not I "should" do this! In these sort of experimental setups I'll use a bimetalic normally closed thermal cutout switch on the heat sink that trips at 70 C (158 F). I don't recommend beginners push DIY setups this hard.

• It is critically important that a thermal compound paste or thermal adhesive is used between the LED and the heat sink. You only want a thin layer, and I always twist the LED around a bit to get rid of air bubbles and get better overall thermal contact. If it's a heat sink/LED I'll never reuse then I'll use a thermal adhesive and just glue the LED down. Thermal pads can work at lower power levels but won't work as well as a compound/adhesive.

• When making mounting holes in a heat sink you can use a stainless steel screw as a tap. Drill a whole just smaller than the diameter of the screw, force the screw in to the much softer aluminum cutting the threads in the process (I use a ratcheting screwdriver for this), back the screw out, take a fine file and smooth out the burs completely, and you have a drilled and tapped mounting hole.

Power supply tips

• Get a Mean Well LED driver for DIY. The XLG are constant power and one work quite well with a Vero 18 or a Vero 29. A Vero 18 or 29 can be quickly interchanged at the same power level so you can rapidly measure the differences between the two if needed.

• I often use lab power supplies as LED drivers. If you only get one lab power supply make sure it's a linear power supply and not a noisy switching power supply. Lower cost linear power supplies typically have a fan that will turn on at certain current levels while more expensive and much heavier ones are entirely passive cooled.

• Power supplies have historically been the weak link in an LED grow light system and cheap capacitors are the main issue.

• The cheap boost converters you can buy on Amazon and eBay will work, but don't expect more than about 6 months use out of them. Again, it's the capacitors that tend to fail.

MacAdam ellipses and steps

The MacAdam ellipses, or SDCM (standard deviation of color matching), as used here are standard deviations of perceived color differences in LED binning including white LEDs. The higher the step or standard deviation, the lower the binning tolerances which lowers LED costs. Sylvania has a good, simple write up on this concept with a convenient graph below.

• MacAdam Ellipses: What are MacAdam Ellipses or color ovals?

• To make it simple and practical, only in a 1-step MacAdam ellipse for white LEDs are any variations in the white light unperceived to most all people with a trained person. In a 2-step MacAdam ellipse variations may just be perceivable to a trained eye, and in a 3-step MacAdam ellipse variations may be just perceivable to an untrained eye. Common quality white LED lighting for residential use tend to be two or three step, but can be 4-step and still be withing ANSI (American National Standards Institute) tolerances, which was causing issues in the past (a relative of mine is a commercial/industrial electrical contractor, and didn't understand why not all the thousand plus LED bulbs installed appeared the same. He didn't understand how white LED binning worked at the time).

• With LED grow lights we don't really care about minor variations in light, and the Samsung LM301H (horticulture) series of medium power LEDs use a 5-step MacAdam ellipse binning, while the LM301B (general illumination) uses a 3-step MacAdam ellipse binning. In other words, the LM301H has a lot more binning slop that is basically irrelevant to plant growth, but could be relevant for general illumination. The highest MacAdam step number used with LEDs is seven.

Don't worry if you can perceive slight color differences in the LEDs of LED grow lights! Your plants don't care.

main links page

SAG's lighting guide

wildlife tracking and monitoring

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• Lessons and Experiences from the Design, Implementation, and Deployment of a Wildlife Tracking System

• Small Unmanned Aerial Vehicle System for Wildlife Radio Collar Tracking

• Radio Receiver Design for Unmanned Aerial Wildlife Tracking

• Recovery Target Tracking in Wildlife

• Movement-Aware Relay Selection for Delay-Tolerant Information Dissemination in Wildlife Tracking and Monitoring Applications

• LIGHTWEIGHT LOW-COST WILDLIFE TRACKING TAGS USING INTEGRATED TRANSCEIVERS

• A Low-Cost RSSI-Based Localization System for Wildlife Tracking

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• Rapid Prototyping for Wildlife and Ecological Monitoring

• Intelligent Wildlife Tracking Using Ubiquitous Technological Suite

• On Using BOC Modulation in Ultra-Low Power Sensor Networks for Wildlife Tracking

• A Low-Cost RSSI Based Localization System Design for Wildlife Tracking

• A low-cost technique for radio-tracking wildlife using a small standard unmanned aerial vehicle

• Implementing a Distance Estimator for a Wildlife Tracking System Based on 802.15.4 -17 MB file

• Aerial Radio-based Telemetry for Tracking Wildlife

• Internet of Things for Wildlife Monitoring

• Open-source, low-cost modular GPS collars for monitoring and tracking wildlife

• AN APPROACH FOR TRACKING WILDLIFE USING WIRELESS SENSOR NETWORKS

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• Tracking Wildlife with Multiple UAVs:System Design, Safety and Field Experiments

• EcoLocate: A heterogeneous wireless network system for wildlife tracking

• Unmanned Aerial Vehicles (UAVs) and Artificial Intelligence Revolutionizing Wildlife Monitoring and Conservation

• Wildlife research and management methods in the 21st century: Where do unmanned aircraft fit in?

• Online Localization of Radio-Tagged Wildlife with an Autonomous Aerial Robot System

• Precision wildlife monitoring using unmanned aerial vehicles

• UAV wildlife radio telemetry:System and methods of localization -very thorough

• WILDLIFE MULTI SPECIES REMOTE SENSING USING VISIBLE AND THERMAL INFRARED IMAGERY ACQUIRED FROM AN UNMANNED AERIAL VEHICLE (UAV)

• Integrating UAV Technology in an Ecological Monitoring System for Community Wildlife Management Areas in Tanzania

• Best practice for minimising unmanned aerial vehicle disturbance to wildlife in biological field research

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• When a few clicks make all the difference: Improving weakly-supervised wildlife detection in UAV images -machine vision

• Autonomous UAVs Wildlife Detection Using Thermal Imaging, Predictive Navigation and Computer Vision -RPi, machine vision

• Efficient and Low-cost Localization of Radio Signals with a Multirotor UAV -very extensive

• Detection, Tracking, and Geolocation of Moving Vehicle From UAV Using Monocular Camera -when tech gets scary

• Quadcopter applications for wildlife monitoring

• Online UAV Path Planning for Joint Detection and Tracking of Multiple Radio-tagged Objects

• Searching for nests of the invasive Asian hornet (Vespa velutina) using radio-telemetry -very detailed on how tiny active radio trackers work

• C-Band Telemetry of Insect Pollinators Using a Miniature Transmitter and a Self-Piloted Drone -phased array, energy harvesting, next level stuff

• The Motus Wildlife Tracking System: a collaborative research network to enhance the understanding of wildlife movement

• Estimating Wildlife Tag Location Errors from a VHF Receiver Mounted on a Drone

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• Fifteen Years of Satellite Tracking Development and Application to Wildlife Research and Conservation

• A Transmitter for Tracking Wildlife -1968, schematics for two crystal pulsing transmitters

• Wildlife tracking technology options and cost considerations

• On a wildlife tracking and telemetry system : a wireless network approach

• VHF Transmitter Development For Wildlife Tracking -master theses

• Radio direction finding using pseudo-Doppler for UAV-based Animal Tracking Animal Tracking -master theses

• Challenges and prospects in the telemetry of insects -good read

harmonic radar (insect tracking including flight patterns)

The basic idea of harmonic radar is to broadcast a radio signal at one frequency and a tiny diode downrange will rebroadcast the signal's second harmonic. This allows very tiny (around 30 mg) passive tracking tags that can be mounted on larger flying insects like bees. The same idea is used in technical surveillance countermeasures and mine/IED countermeasures to find electronics, powered on or off, and are also known as non-linear junction detectors. You can get the special "zero bias diodes", like the Agilent HSMS-2855, on eBay that are needed as powerless tags at around $0.60 each.

• Tracking Insects with Harmonic Radar: a Case Study

• A landscape-scale study of bumble bee foraging range and constancy, using harmonic radar

• Tracking butterfly flight paths across the landscape with harmonic radar

• The Design of a Harmonic Radar System -outstanding senior thesis, gets into tag design

• Ontogeny of orientation flight in the honeybee revealed by harmonic radar

• Recent Developments and Recommendations for Improving Harmonic Radar Tracking Systems

• A High-Range-Accuracy and High-Sensitivity Harmonic Radar Using Pulse Pseudorandom Code for Bee Searching

• A Portable Low-Power Harmonic Radar System and Conformal Tag for Insect Tracking

• Tracking butterfly movements with harmonic radar reveals an effect of population age on movement distance

• HARMONIC RADAR - A METHOD USING INEXPENSIVE TAGS TO STUDY INVERTEBRATE MOVEMENT ON LAND

• An Innovative Harmonic Radar to Track Flying Insects: the Case of Vespa velutina

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• Recent upgrades of the harmonic radar for the tracking of the Asian yellow- legged hornet

• So Near and Yet So Far: Harmonic Radar Reveals Reduced Homing Ability of Nosema Infected Honeybees

• Quasi‐chipless wireless temperature sensor based on harmonic radar

• Application of harmonic radar technology to monitor tree snail dispersal

• Parasitic Harmonic Cancellation for Reliable Tag Detection with Pulsed Harmonic Radar

• Transponder Designs for Harmonic Radar Applications

• Harmonic radar tracking reveals random dispersal pattern of bumblebee (Bombus terrestris) queens after hibernation

• Signal processing for harmonic pulse radar based on spread spectrum technology

• Adaptable Bandwidth for Harmonic Step-Frequency Radar

• Compact Low-cost FMCW Harmonic Radar for Short Range Insect Tracking

• Techniques for tracking amphibians: The effects of tag attachment,and harmonic direction finding versus radio telemetry

• A Review of Insect Monitoring Approaches with Special Reference to Radar Techniques

• HARMONIC DIRECTION FINDING: A NOVEL TOOL TO MONITOR THE DISPERSAL OF SMALL-SIZED ANURANS

• Tracking bees with radar -earlier work

• Life-Long Radar Tracking of Bumblebees

• Autonomous Swarm of UAVs for Tracking of Flying Insects with Harmonic Radar -One UAV transmits, four other UAVs receive

• Autonomous Tracking of Micro-Sized Flying Insects Using UAV: A Preliminary Results

• 1950's CIA work on harmonic radar for audio surveillance

• Wideband Harmonic Radar Detection -master thesis, NLJD design

• HARMONIC RADAR: THEORY AND APPLICATIONS TO NONLINEAR TARGET DETECTION, TRACKING, IMAGING AND CLASSIFICATION -PhD theses, 175 pages

• Back-to-Back Diplexers for Nonlinear Junction Detection -Army Research Lab

• The rationale and concept for collecting signatures of IED, UXO and landmines -other applications of harmonic radar

• Intermodulation Radar for P-N Junction Detection

• Miniaturization of a Low Power Harmonic Radar for UAV use

• 5.8-GHz ISM Band Intermodulation Radar for High-Sensitivity Motion-Sensing Applications -NLJD

• Multitone harmonic radar and method of use -NLJD patent

• Device and method for detecting non-linear electronic components or circuits especially of a booby trap or the like -NLJD patent

• Radar system and method -NLJD patent

• System and method of radar detection of non linear interfaces

• Orion Non-Linear Junction Evaluator -NLJD manual

• Microstrip Antenna Array Design for Harmonic Radar Applications -master theses

• A Software Defined Radio Interrogator for Passive Harmonic Transponders -master theses

• Towards The Development of Millimeter Wave Harmonic Sensors for Tracking Small Insects

radio direction finding (note- most papers on this subject tend to be IEEE papers which are mostly not open access)

Look up amateur radio fox hunt for information on DIY.

protip- the cheap 1N4007 silicon diode can be used as a PIN diode. This makes the TDOA (timed direction of arrival) switched antennas more accessible for DIY like in this well explained KA7OEI's blog. Actual PIN diodes are cheap on eBay (US).

• REVIEW OF CONVENTIONAL TACTICAL RADIO DIRECTION FINDING SYSTEMS -1989, Canadian military

• The radio direction finder and its application to navigation -1922 book

• Exploitation of Radio Direction Finder in the design of a UHF Transmitter Locator System

• The Radio Direction Finding with Advantage of the Software Defined Radio

• RADIO DIRECTION FINDING NETWORK RECEIVER DESIGN FOR LOW-COST PUBLIC SERVICE APPLICATIONS -master theses

• Design of a radio direction finder for search and rescue operations : estimation, sonification, and virtual prototyping -PhD theses

• Design of Wideband Radio Direction Finder Based On Amplitude Comparison

• Analysis of Radio Direction Finder Bearings in the Search for Amelia Earhart

• AN INNOVATIVE PORTABLE ULTRA WIDE BANDS TEREOPHONIC RADIO DIRECTION FINDER

• The Accuracy of Radio Direction Finding in the Extremely Low Frequency Range

• Polarization Direction Finding Method of Interfering Radio Emission Sources

energy harvesting (powering ultra low power sensors nodes and communication systems)

• Honey-Bee Localization Using an Energy Harvesting Device and Power Based Angle of Arrival Estimation

• Advances in Energy Harvesting Communications: Past, Present, and Future Challenges

• Designing intelligent energy harvesting communication systems

• Micropower energy harvesting

• Energy Harvesting Sensor Nodes: Survey and Implications

• Energy harvesting vibration sources for micro systems applications

• On the energy harvesting potential of piezoaeroelastic systems

• Power Management in Energy Harvesting Sensor Networks

• Wireless Networks with RF Energy Harvesting: A Contemporary Survey

• A Survey of Energy Harvesting Sources for Embedded Systems

• MICROSYSTEMS FOR ENERGY HARVESTING

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• Energy Harvesting Wireless Communications: A Review of Recent Advances

• Materials for energy harvesting: At the forefront of a new wave

• Two-hop Communication with Energy Harvesting

• Energy Cooperation in Energy Harvesting Communications

• Networking Low-Power Energy Harvesting Devices:Measurements and Algorithms

• Fundamental Limits of Energy Harvesting Communications

• Efficient Design of Micro-Scale Energy Harvesting Systems

• Implantable Energy-Harvesting Devices

• A review of energy harvesting using piezoelectric materials: state-of-the-art a decade later(2008–2018) -63 pages

• Optimal Energy Allocation for Wireless Communications with Energy Harvesting Constraints

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• Design Optimization and Implementation for RF Energy Harvesting Circuits

• Efficient Far-Field Radio Frequency Energy Harvesting for Passively Powered Sensor Networks

• Ambient RF Energy Harvesting in Urban and Semi-Urban Environments

• RF Energy Harvesting System and Circuits for Charging of Mobile Devices

• All-in-one energy harvesting and storage devices

• Ambient RF Energy Harvesting

• Radio Frequency Energy Harvesting and Management for Wireless Sensor Networks

• DESIGN OF RF ENERGY HARVESTING SYSTEM FOR ENERGIZING LOW POWER DEVICES

• Design architectures for energy harvesting in the Internet of Things

• A Fully Autonomous Ultra-low Power Hybrid RF/Photovoltaic Energy Harvesting System with -25 dBm Sensitivity

• Hybrid Energy Harvesters: Toward Sustainable Energy Harvesting

part of SAG's Plant Lighting Guide

last update: 4 mar 2023 --added green light canopy section and safe light discussion

TL;DR - This is challenging the claim "plants can't use green light", "plants are green because they reflect all green light", or some close iteration that is so often found in biology. My counterclaim is the McCree curve is used in botany, and every paper on photosynthesis studies by wavelength when the test was actually done demonstrates most plants use green light efficiently, particularly compared to blue light and at higher lighting levels.

There are many links to open access papers supporting my claims below. quick link to the McCree (1972) paper

Please point out any mistakes or needed clarifications! I often go back and do edits for mistakes or to add more.

The claim and my problem with it

There is a lot of confusion about how green plants absorb light in biology, and the notion that "plants can't use green light" or "plants are green because they reflect all green light". It comes from biology books that are likely showing you a chart for pigments in a solvent or photosynthetic bacteria/algae, not how higher green land plants actually respond to light. Even with botany books sometimes the wrong charts are used ("Botany for Dummies", written by a PhD botanist, gets it bizarrely wrong by showing pigments that are not even in plants!).

The issue I have with the claim, coming from a horticulture lighting perspective, is that it has been used by many low end predatory LED grow light sellers, such as making outrages claims about the photosynthetic performance of red/blue only LED grow lights compared to some other grow light like HPS (high pressure sodium), by hitting some "magical wavelengths" based off misused science. I've seen a lot of people get taken advantage off (particularity early-mid 2010's) as well as a lot of disappointment.

There were claims about red/blue LED grow lights being better than HPS, by as high as ten to twenty times better growth per watt in the late 2000's, that was overpriced junk (my first LED grow lights were thousands of 5mm low power LEDs that were hand soldered). Even magazine writers were parroting the claim because of a lack of basic due diligence and not testing the lights.

These non-sense claims are where the "600w" and "1000w" "equivalent" Amazon/eBay scammy LED grow lights get their name and their reputation, and it continues to this day with shysters claiming 50 watts of low end LEDs as "600w". Don't ever do business with these type of people, because if they BS you once they'll BS you again. Don't believe their square footage claims needed for growing cannabis.

So from my niche perspective, I have seen the claim collectively cause a lot of financial harm to people, and consumers may not be making good choices by thinking the spectral output of a lower wattage red/blue LED grow light is somehow going to make up for the low lighting levels; It absolutely will not. This is particularly important as indoor growing becomes more popular. It also hurts the "good guys" in the LED grow light business because the shysters give the industry as a whole a bad name. Their hyperbolic claims are a failure every time because science.

The counterclaim and what's really going on

TL;DR- most green light is absorbed and is used for photosynthesis

• THE ACTION SPECTRUM, ABSORPTANCE AND QUANTUM YIELD OF PHOTOSYNTHESIS IN CROP PLANTS -PDF McCree (1972) and the McCree curve used in botany, cited nearly 1,000 times, absorption/net photosynthesis/action spectrum on fig 14.

Every scientific paper on plant lighting by wavelength for photosynthesis backs the claim that plants use green light, and you will never find a paper where the test was actually done say anything differently. But why this is can be very counterintuitive at first, and having so many YouTube videos and even more respectable forums (such as on researchgate.net) show so much misinformation just causes more confusion. I've seen faulty appeal to authority style arguments from even biologist PhD's who are not understanding the science.

...

"plants are green because they reflect all green light or "plants can't use green light"- reflectance, absorption, and transmittance

You are likely going off the pigments dissolved in a solvent chart if you believe this, and that's a relative absorption chart in vitro (e.g cuvette), not the McCree curve that is an absolute chart of how plant leaves respond to light by wavelength for photosynthesis in vivo (living leaf). There is a pretty big difference here. Also, at no point is chlorophyll in a solvent truly at zero percent absorption of green light in higher resolution charts.

Unlike chlorophyll in a solvent, in a green plant leaf we have relatively dense chloroplasts, containing thylakoid membranes stacked as disks (grana), that holds the chlorophyll in a 3D structure called a quantasome (basic photosynthesis unit with around 230 chlorophyll, perhaps 50 carotenoid molecules, and the PSI/PSII). There is a much higher density level of chlorophyll in a leaf than chlorophyll in a solvent extract.

So in vitro, with just relatively loose pigments suspended in a solvents, there is going to be a different measurement and spectral characteristics than in a green leaf in vivo, that is in a dense solid lattice that changes optical characteristics such as broadening the adsorption bands. (BTW, ionized gases do the same broadening under higher pressure/density, and a white xenon strobe tube may be at 10's of atmospheres of pressure (3-4 more typical) giving a broad white and very high CRI light instead of narrow spectral bands (current density also plays a role here)).

You may also be going off an algae chart (first done in the late 1800's!) or some bacteria, which will show a significant dip in the green area, rather than a green terrestrial plant leaf. Hoover (1937) was the first to demonstrate green light photosynthesis in plants (he used wheat that was likely a little bit chlorotic based off the specific shape of his curve).

For absorption, here is an example of a "medium darker green" leaf showing 83% absorption (17% reflectance with how it's set up but that does not matter) from my spectroradiometer, and more typical of what's really going on. Here is a spectral reflectivity profile of a high nitrogen marijuana leaf (Jack Herer). About 90% of the green light is being absorbed although in the cannabis pic. Refer to the McCree paper above to see many more examples (I have my charts flipped because it's easier for me to work with).

The experiment on green leaf absorption with your phone

Don't take my word for it, test it yourself with your three channel spectrometer that's in your phone.

With a color balance adjusted camera (or in post processing), you can take a piece of printer paper and declare that an 88% reflective white reference standard (you want common "88 brightness" paper but can get up to 97 which is based off a 457 nm measurement). Make sure that the paper is "true white', and not "cream white" or "blue white". You can also preferably take an 18% gray card used in photography/video that may have a white side that is typically 90% reflective.

I only use paper or cloth color reference cards to insure near perfect diffused cosine response, not plastic smooth ones which may have a bit of specular reflection (ie glare). The smooth plastic ones are fine in most situations but not in spectrometer. If working with a waxy leaf it's often best to remove the wax layer with very fine steel wool to prevent specular reflections.

Now take a picture of the leaf on the paper. Try to use a more diffuse light source but most any white light source can be used with the color balance adjusted. You want to make sure that you have even lighting on the subject and the white standard.

In your camera's histogram (quick how-to), get the camera's exposure so that the white paper is as high as it goes on the graph without clipping/saturating. We want as much usable dynamic range as possible.

When you have the picture, open it up in GIMP/Photoshop, and we are going to examine a section of white paper right next to the leaf. Adjust the levels to 100% (255 for red/green/blue). Now examine the color of the leaf, taking into account that the levels had to be raised a bit, and you'll see that most of the green light is being absorbed by the leaf and can roughly measure it.

An easily falsifiable experiment is a credible experiment, and the experiment is easy enough to perform to be a good school lesson (if you measure ratios then you can get a good idea of chlorophyll content). I'm sure that there is an app that can easily automatically measure the green levels in leaves.

The McCree curve and its limitations

• The McCree Curve Demystified -this article discusses the McCree curve from a horticulture lighting scientist's perspective. The "relative action" takes in to account the energy of the photon which is why the blue side takes such a hard dip. Blue photons have more energy than red/green photons, but it's one photon per photochemical reaction as per the Stark-Einstein law, also known as the second law of photochemistry (there are exceptions to the second law).

McCree was a physicist who in the early 1970's tested 22 different types of plants for their photosynthesis response rates by lighting level, and by specific monochromatic lighting spectrum. He took what are called leaf disks, about one inch in diameter leaf cutouts in this case, but 20mm x 20mm was being illumined, in to a machine that was able to measure how much carbon dioxide the illuminated leaf disc was uptaking. That's an accurate way to measure photosynthesis rates. BTW, the light sensor was not any sort of full spectrum quantum light sensor like we'd use today, but rather a thermopile pyranometer painted black that measured the heat generated with the illumined area, with a separate thermocouple as a temperature reference. Pyranometers are still used in agriculture.

The light wavelength was measured in 25 nm intervals, from 350 nm to 725 nm, achieved using a high power arc lamp and water cooled filters. This light gave the leaf discs an illumination level at five test points from 18-150 uMol/m2/sec. This mean was taken for all 22 plants, and the mean totality is how McCree curve was created. So, the McCree curve is a good starting point for learning about photosynthesis rates by wavelength, but the results are limited to lighting conditions that most people will never use because most people don't grow plants with monochromatic light at relatively low levels.

The McCree curve also only looks at the single leaf model of plant growth, not the whole plant model. For example, the McCree curve does not take into account that green (and far red) light can make leaves larger which increases the LAI (leaf area index) capturing more light, but can also cause excess stem elongation from a type of growth called acid growth.

McCree also tested the underside (abaxial) of leaves, and found that they were also performing photosynthesis. In many cases the underside of a leaf will have a lower chlorophyll density, and may reflect more green light than the topside (adaxial) of a leaf, which may lower green light photosynthesis. Monocotyledons (e.g grain crops) tend to have the same photosynthesis rates on both sides of a leaf.

He also found that adding white light to monochromatic light can lower absolute (but not relative) photosynthesis rates at lower lighting levels, saying he found no Emerson effect, but I believe he may have misunderstood what the Emerson effect is. The Emerson effect has to do with light that can drive the photosystem one and two separately, basically freeing up electrons between the PSII and the PSI to increase photosynthesis efficiency. This was discover in 1957 by Robert Emerson, and demonstrated that there were two separate photosystems in plants.

It's my guess that the above white light lowering photosynthesis, may be why the below paper is named the way it is.

Terashima et al has entered the chat

TL;DR- green beat red at about 300 uMol/m2/sec

• Green Light Drives Leaf Photosynthesis More Efficiently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are Green -PDF Terashima et al (2009), cited about 500 times so far

When I see people mentioning this is only for higher white light conditions mentioned in the title, then I can tell they have not read the paper.

What's going on above? Well first, we are looking at net photosynthesis rates in the above paper and that is what really counts, not absolute absorption. Also, the absorbed green light can also transmit deeper through leaf material more effectively and potentially used for photosynthesis more efficiently.

This is because the top layers of chloroplasts that contains chlorophyll becomes saturated, as per PI curves, while green light can penetrate deeper into leaf tissue (sieve effect) and reflected around until absorbed by a chlorophyll molecule (scattering) or by an accessory pigment.

This efficiency can be measure through the amount of chlorophyll fluorescence or a gas exchange chamber.

Terashima et al were using chlorophyll florescence techniques to measure net photosynthesis rates. Everything you need to know about chlorophyll fluorescence to measure photosynthesis rates can be found here.

What the team found was the green light started outperforming red light at about 300 uMol/m2/sec as measure with a pulse amplitude modulated fluorometer.

You can see this going on in this pic below of light penetration for red, green, and blue light. Red and blue light gets quickly absorb by the chlorophyll near the leaf surface, but green is able to drive photosynthesis deeper.

• Leaf penetration by light color -pic

So what really high intensity light source has a lot of green light that plants evolved to? The sun and at a full sunlight PPFD (photosynthetic photon flux density) of around 2000 uMol/m2/sec would be considered very, very intense light compared to what the average indoor grower would use. With thin leaves (e.g. apple) I can measure perhaps 150 uMol/m2/sec of sunlight through an upper leaf that will illuminate a lower leaf with nearly all green light which is a very efficient lighting level for photosynthesis.

Ironically, it could be the case that plants evolved to be green because of the high green light component in sunlight makes green leaves more efficient, by absorbing most of the green light, and using the absorbed green light more efficiently throughout the leaf.

• Why are higher plants green? Evolution of the higher plant photosynthetic synthetic pigment complement -PDF Nishio (2000)

It's more than just photosynthesis- photomorphogenesis

Photomorphogenesis has to do with light sensitive proteins, and unlike photosynthesis, can be very wavelength dependent in a plant's response. The phytochromes are predominately red and far red with Pr peaking around 660 nm, the blue sensitive proteins are the crytochromes and phototropins have what's known as the "three finger blue action response" with peaks at roughly 430, 450, and 470 nm depending on the specific protein. 470 nm light can be very different than 490 nm light when it comes to light sensitive proteins and how plants respond to light. source 1 source 2

Green light used alone tends to elicit a lot of elongation (stretching) due to triggering the shade avoidance response causing more acid growth which is different than growth though photosynthesis. This is the opposite of blue light. High pressure sodium lights have a lot of green/yellow/amber light which is why they do so well and are still the most widely used in large scale horticulture even at the time of this writing.

The above means that we can get larger leaves with green (and far red) light due to the reversibility of blue light sensitive proteins. Larger leaves means a greater leaf area index which means more potential for photosynthesis from greater light capture.

Green light can also cause the stomata (gaseous exchange pores) of plants to close a bit more than normal, which is the opposite of blue light. Basically to plants, blue light is the opposite of green light, and red light is the opposite to far red light for light sensitive protein reactions (not completely accurate but fairly close).

You eyes can deceive you, don't trust them -Obi-Wan Kenobi, Jedi master

With plants there's also perceptual differences and our eyes have a combined sensitivity curve where the peak of our sensitivity is also were the peak reflectivity is going to be for a green plant. (The individual sensitivity of our 3 color sensitive cone cells in our eyes is this.).

So, it's true plants do reflect more green light than red or blue, but the way we perceive light is naturally much higher biased for green light with a 555 nm sensitivity peak, which is the same as a green plant's reflectivity peak. This allows use to notice very tiny variations of green which can be use to more precisely diagnose a plant if a gatherer. Coincidence? It's also why in cameras there's a ratio of one red, one blue, and two green pixels.

It should be noted that the maximum absorption wavelength for chlorophyll in leaves in vivo is 675-680 nm (chlorophyll A), and not 660 nm as often cited (chlorophyll B is about 645 nm). This can be seen in this spectrometer shot of a chlorotic (yellow) leaf as a dip in the 675-680 nm range from small amounts of chlorophyll A left over. The blue absorption seen are carotenoids which have perhaps a 30-70% efficiency at transferring the absorbed light energy to a photosynthetic reaction center through chlorophyll A. Chlorophyll B is an accessory pigment and higher land plants do not contain chlorophyll C, D, or F (there is no E type). Depending on the plant, there may be 2.5ish-7 or so chlorophyll A molecules for every chlorophyll B molecule but mostly around a 3:1 ratio.

The 30-70% efficiency claim (depending on type and the paper) about carotenoids is why I've always thought it odd that any grow light seller would brag about targeting carotenoids. Carotenoids are there to help the plant with intense lighting and shunting some of the higher energy blue photons absorbed away from chlorophyll through non-photochemical quenching. From a thermodynamics perspective this makes perfect sense for plants to have evolved carotenoids, and we can measure their activity to high light through the photochemical reflectance index by taking ratiometric measurements with a spectrometer.

And that is what's really going on with green light and green plants, and how you perceive them.

Why not use green LEDs?

Green LEDs are electrically inefficient compared to red and blue LEDs, and this problem is known as the "green gap" (google image link) in physics/engineering. The most efficient green LEDs that I known of are actually blue LEDs with a green phosphor.

The above is why white LEDs, blue LEDs with phosphors, are used instead that have a strong green light component. I've done pure green grows, but was using green COBs in a small space, and just to prove a point.

• Space Bucket with a high power green LED and a pole bean

But the above, with our enhanced green light sensitivity, is why we can use green LEDs in red, green, blue lighting strips, for example, and we won't notice the inefficiency in the green LEDs.

green light penetrates deep into the plant canopy?

Many research papers or online sources will say stuff like an advantage of green light is that it can penetrate deep in the plant canopy and drive photosynthesis in lower leaves. The reality is that green light usually doesn't penetrate through cannabis leaves, but green light can penetrate deeper into individual leaves and drive more photosynthesis in that specific leaf.

Outdoors in many plants there will be much more green and far red light in the lower canopy because leaves from nearby plants reflect higher amounts of green and particularly far red light from sunlight. This is likely where the myth comes from and is true for certain growing conditions.

• solar spectra of reflected light off a leaf

A thin leaf like an apple tree leaf will have about 100-150 uMol/m2/sec of green light penetration through the leaf under full sunlight (2000 uMol/m2/sec) but we're not going to get this with a higher nitrogen and thicker cannabis leaf to any significant degree.

• solar spectra through a leaf --notice the high amounts of far red

• solar spectra through leaf up close --notice how blue penetrates poorly due to carotenoids

So yes, green light can penetrate deeper into a plant canopy, but that's not really going to happen in a typical cannabis grow chamber like a grow tent to any significant degree. We may use green light for multiple reasons but it has nothing to do with canopy penetration in nearly all indoor grow setups.

green light as a safe light <----not necessarily as safe as thought

We might use green as a safe light (a light for inspecting cannabis photoperiod plants in darkness) due to our eyes being more sensitive to green light and the lower sensitivity of the cryptochrome proteins involved with photoperiodism to green light.

• https://www.reddit.com/r/IAmA/comments/paoigz/im_dr_bruce_bugbee_professor_of_crop_physiology/ha6ia29/ ---"Green headlamps should be used with caution."

• https://www.youtube.com/watch?v=HPsb10tHaeE ---15 minute area--- "it's not the case that a green light is a safe light"

The point that Bugbee makes about cryptochrome (light sensitive protein that plays a role in photoperiodism) is that green light has the potential to trigger more of the cryptochrome proteins deeper in the leaf since green light can penetrate deeper in leaf tissue. But, a point he may not be stressing enough is that cryptochrome also has much lower sensitivity to green light so it could be a combination of the two which allows low levels of green light to be used for short periods in the dark period of photoperiod cannabis plants.

• cryptochrome wavelength sensitivity charts

• wikipedia cryptochrome

Links to open access papers on green light and plants

• The action spectrum absorptance and quantum yield of photosynthesis in crop plants

• Green Light Drives Leaf Photosynthesis More Efficiently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are Green-- Terashima et al

• Green Light Drives CO2 Fixation Deep within Leaves-- Sun et al

• Nitrogen-improved photosynthesis quantum yield is driven by increased thylakoid density, enhancing green light absorption

• [Why are higher plants green? Evolution of the higher plant

photosynthetic pigment complement-- Nishio 2000](https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3040.2000.00563.x)

• [Effect of green light wavelength and intensity on photomorphogenesis and

photosynthesis in Lactuca sativa-- Johkan et al](https://www.plantgrower.org/uploads/6/5/5/4/65545169/1-s2.0-s0098847211001924-main.pdf)

• Contributions of green light to plant growth and development- Wang, Folta

• Cost and Color of Photosynthesis -Why plants evolved green.

• Effects of Blue and Green Light on Plant Growth and Development at Low and High Photosynthetic Photon Flux -Master Thesis

• [Sensitivity of Seven Diverse Species to Blue and

Green Light: Interactions With Photon Flux](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0163121)

• Green light augments far-red-light-induced shade response

• Green light signaling and adaptive response

• Green light drives photosynthesis in mosses

• Cryptochromes integrate green light signals into the circadian system

• Photosynthetic Physiology of Blue, Green, and Red Light: Light Intensity Effects and Underlying Mechanisms

• Photosynthesis, Morphology, Yield, and Phytochemical Accumulation in Basil Plants Influenced by Substituting Green Light for Partial Red and/or Blue Light

• [Green light enhances growth, photosynthetic pigments and CO2

assimilation efficiency of lettuce as revealed by 'knock out' of the 480–560 nm spectral waveband](https://www.researchgate.net/profile/Hui-Liu-106/publication/301719010_Green_light_enhances_growth_photosynthetic_pigments_and_CO2_assimilation_efficiency_of_lettuce_as_revealed_by_%27knock-out%27_of_the_480-560_nm_spectral_waveband/links/5a2e2533aca2728e05e2fc64/Green-light-enhances-growth-photosynthetic-pigments-and-CO2-assimilation-efficiency-of-lettuce-as-revealed-by-knock-out-of-the-480-560-nm-spectral-waveband.pdf)

• Partial replacement of red and blue by green light increases biomass and yield in tomato

• The Inclusion of Green Light in a Red and Blue Light Background Impact the Growth and Functional Quality of Vegetable and Flower Microgreen Species

• Shades of Green: Untying the Knots of Green Photoperception -the role green light plays in photomorphogenesis

• Photosynthetic Physiology of Blue, Green, and Red Light: Light Intensity Effects and Underlying Mechanisms --in lettuce green did worse at low ppfd and best at a higher PPFD

• Don’t ignore the green light: exploring diverse roles in plant processes

Directed energy weapons links

main links page

SAG's plant lighting guide

high power microwave

• The E-Bomb - a Weapon of Electrical Mass Destruction -classic essay

• E-BOMB: THE KEY ELEMENT OF THE CONTEMPORARY MILITARY-TECHNICAL REVOLUTION -master theses, 213 pages

• E–BOMB

• Microwave Pulse Generator -shows damage

• High energy microwave weapon-еlectromagnetic bomb

• Ultra Wideband Antennas for High Pulsed Power Applications

• Review of high-power microwave source research

• High Power Microwave Sources and Applications

• Survey of Pulse Shortening in High-Power Microwave Sources

• Design and optimization of a compact, repetitive, high-power microwave system

• All solid-state high power microwave source with high repetition frequency

• High-Power Microwave Radiation as an Alternative Insect Control Method for Stored Products

• High Altitude Electromagnetic Pulse (HEMP) and High Power Microwave (HPM) Devices: Threat Assessments

• reflector antennas for HPM

• Research on High Power Microwave Weapons

• Overview of Four European High-Power Microwave Narrow-Band Test Facilities

• Evolution of Pulse Shortening Research in Narrow Band, High Power Microwave Sources

• Intense Microwave Pulses IV -few dozen conference papers

• A 10 GW PULSED POWER SUPPLY FOR HPM SOURCES

• Preliminary Considerations for HPM Radiating Systems -77 pages

• A Compact Modular 5 GW Pulse PFN-Marx Generator for Driving HPM Source

• The History and Use of Electromagnetic Weapons

vircator

• Axial Vircator for Electronic Warfare Applications

• Investigations of a Double-Gap Vircator at Submicrosecond Pulse Durations

• Enhancement in the power of microwaves by the interference with a cone-shaped reflector in an axial vircator

• The dependence of vircator oscillation mode on cathode material

• Experimental Study of a Triode Reflex GeometryVircator

• S-Band Vircator With Electron Beam Premodulation Based on Compact Pulse Driver With Inductive Energy Storage

• Role of the rise rate of beam current in the microwave radiation of vircator

• HIGH-POWER, COAXIAL VIRCATOR GEOMETRIES -PhD thesis

• A Frequency Stable Vacuum-Sealed Tube High-Power Microwave Vircator Operated at 500 Hz

• HIGH POWER MICROWAVE GENERATION BY A COAXIAL VIRCATOR

• A Low-cost Metallic Cathode for a Vircator HPM Source

• Pulsewidth Variation of an Axial Vircator

• Influence of electron-beam diode voltage and current on coaxial vircator

• Design and Experiments with High Power Microwave Sources -PhD theses

• High-power single-mode microwave generation by coaxial vircator

• A 160 J, 100 Hz rep rate, compact Marx generator for driving and HPM source

• Design and Experiments with High Power Microwave Sources: The Virtual Cathode Oscillator -PhD theses

• Hybrid systems with virtual cathode for high power microwaves generation

• Theoretical analysis and simulation of microwave-generation from a coaxial vircator -62 pages

• Virtual Cathode Oscillator for Repeated Generation HPM

marx generator

• MARX GENERATOR DESIGN AND PERFORMANCE

• High-voltage high-frequency Marx-bank type pulse generator using integrated power semiconductor half-bridges

• A Solid State Marx Generator with a Novel Configuration

• MARX GENERATOR USING PSEUDOSPARK SWITCHES

• COMPACT MARX GENERATOR FOR REPETITIVE APPLICATIONS

• Fast Marx Generator for Directly Driving a Virtual Cathode Oscillator

• Development of a stereo-symmetrical nanosecond pulsed power generator composed of modularized avalanche transistor Marx circuits

• PERFORMANCE CHARACTERISTICS OF A 1 MV MINIATURE MARX BANK

• A Compact MW-Class Short Pulse Generator -pocket size

• COMPACT, REPETITIVE MARX GENERATOR AND HPM GENERATION WITH THE VIRCATOR

• Solid-state Marx generator design with an energy recovery reset circuit for output transformer association

• A Marx Generator for Exploding Wire Experiments

• Study of an Ultra-Compact, Repetitive Marx Generator for High-Power Microwave Applications

• A 60 Joule, 600 kV, 500 ps risetime, 60 ns pulse width Marx generator

• MULTI GAP SWITCH FOR MARX GENERATORS

• Ignition of a Deuterium Micro-Detonation with a Gigavolt Super Marx Generator

flux compression generator

• An introduction to Explosive Magnetic Flux Compression Generators -1975, Los Alamos

• Magnetic Flux Compression Generators: a Tutorial and Survey

• Magnetic Flux Compression Generators

• Electrical Behavior of a Simple Helical Flux Compression Generator for Code Benchmarking

• HELICAL EXPLOSIVE FLUX COMPRESSION GENERATOR RESEARCH AT THE AIR FORCE RESEARCH LABORATORY

• EXPLOSIVELY FORMED FUSE OPENING SWITCHES FOR USE IN FLUX-COMPRESSION GENERATOR CIRCUIT

• AN ECONOMICAL, 2 STAGE FLUX COMPRESSION GENERATOR SYSTEM

• Electric discharge caused by expanding armatures in flux compression generators

• HIGH-PERFORMANCE,HIGH-CURRENT FUSES FOR l-LUX COMPRESSION GENERATOR DRIVEN INDUCTIVE STORE POWER CONDITIONING

• The flux compression generator load parameters selection

• INVESTIGATION OF A HIGH VOLTAGE, HIGH FREQUENCY POWER CONDITIONING SYSTEM FOR USE WITH FLUX COMPRESSION GENERATORS

• DESIGN OF THE MARK 101 MAGNETIC FLUX COMPRESSION GENERATOR

• EXPLOSIVE FLUX COMPRESSION GENERATORS FOR RAIL GUN POWER SOURCES

• IMPROVED MODELING OF ELECTRICALLY EXPLODED FUSE OPENING SWITCHES INFLUX COMPRESSION GENERATOR EXPERIMENTS

• ON THE RESULTS OF AN EXPERIMENT WITH A MEGAJOULE CLASS HELICAL FLUX COMPRESSION GENERATOR OPERATING AT ABOVE-NOMINAL LEVELS OFC URRENT AND VOLTAGE STRESS

• 2D simulation of helical flux compression generator

• Explosive Flux Compression Generators at LLNL

• small helical flux compression amplifiers

pulse power

• ANALYSIS OF A FEASIBLE PULSED-POWER SUPPLY SYSTEM FOR AN UNMANNED AERIAL VEHICLE

• Compact Solid-State Switched Pulsed Power and Its Applications

• REPETITIVE PULSED-POWER GENERATOR "ETIGO-IV"

• Modern Pulsed Power: Charlie Martin and Beyond

• A Novel High Frequency Bipolar Pulsed Power Generator for Biological Applications

• An All-Solid-State Pulsed Power Generator Using a High-Speed Gate-Turn-Off Thyristor and a Saturable Transformer

• Pulsed corona generation using a diode-based pulsed power generator

• PERFORMANCE OF PULSED POWER GENERATOR USING HIGH VOLTAGE STATIC INDUCTION THYRISTOR

• Inductive Pulsed Power Supply Consisting of Superconducting Pulsed Power Transformers With Marx Generator Methodology

• Capacitor Evaluation for Compact Pulsed Power

• An Efficient, Repetitive Nanosecond Pulsed Power Generator with Ten Synchronized Spark Gap Switches

• Review of Inductive Pulsed Power Generators for Railguns

• High Pulsed Power Sources for Broadband Radiation

• PRESENT AND FUTURE NAVAL APPLICATIONS FOR PULSED POWER

• DEVELOPMENT OF REPETITIVE PULSED POWER GENERATORS USING POWER SEMICONDUCTOR DEVICES

• DRILLING AND DEMOLITION OF ROCKS BY PULSED POWER

nanosecond pulsers

• A Compact High Voltage Nanosecond Pulse Generator

• Simple MOSFET-Based High-Voltage Nanosecond Pulse Circuit

• Sub-nanosecond avalanche transistor drivers for low impedance pulsed power applications

• Self-triggering high-frequency nanosecond pulse generator -big file

• 250 kV sub-nanosecond pulse generator with adjustable pulse-width

• A discrete fully logical and low-cost sub-nanosecond UWB pulse generator

• Performances of Nanosecond Pulsed Discharge

• Solid-state high voltage nanosecond pulse generator

• A two-stage DSRD-based high-power nanosecond pulse generator

• An Implementation of a Sub-nanosecond UWB Pulse Generator

• Nanosecond plasmas in water: ignition,cavitation and plasma parameters

• Compact Nanosecond Pulse Generator

• A simple sub-nanosecond ultraviolet light pulse generator with high repetition rate and peak power

• An avalanche transistor-based nanosecond pulse generator with 25 MHz repetition rate

• A compact UWB sub-nanosecond pulse generator for microwave radar sensor with ringing miniaturization

• A high-power nanosecond pulse generator based on solid-state switches

• A 7.8 kV nanosecond pulse generator with a 500 Hz repetition rate

• A sub-nanosecond rise time intense electron beam source

• Traveling-wave Marx circuit for generating repetitive sub-nanosecond pulses

• A 500 V nanosecond pulse generator using cascode-connected power MOSFETS

• Nanosecond EMP simulator using a new high voltage pulse generator

• Nanosecond Marx pulsed generator with semiconductor switches

• High-voltage and High-stability Nanosecond Pulser Based on Avalanche Transistors

• A nanosecond pulse generator of amplitude of 200 KV

• Designing nanosecond high voltage pulse generators using power MOSFETs

electromagnetic pulses

• Effect of the FAST NUCLEAR ELECTROMAGNETIC PULSE on the Electric Power Grid Nationwide: A Different View

• Nuclear Electromagnetic Pulse and Surprise Attack -1983

• Electromagnetic Pulse Threats in 2010

• Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack

• High Altitude Electromagnetic Pulse (HEMP) and High Power Microwave (HPM) Devices: Threat Assessments

• high power ultrawide band electromagnetic pulse radiation

• Power Grid Resilience to Electromagnetic Pulse(EMP) Disturbances: A Literature Review

• Study of UWB Electromagnetic Pulse Impact on Commercial Unmanned Aerial Vehicle

• ELECTROMAGNETIC PULSE EFFECTS AND DAMAGE MECHANISM ON THE SEMICONDUCTOR ELECTRONICS

• Simulation of the Destruction Effects in CMOS-Devices caused by Impact of Fast Transient Electromagnetic Pulses

• EMP handbook -1976, airforce

• Effects of and Responses to Electromagnetic Pulses (EMP) -72 page powerpoint

• Electromagnetic Pulse Weapons as an Emergent Technology and Their Place on Battlefields of the Future

• Dawn of the E-Bomb

• ELECTROMAGNETIC TERRORISM: NEW HAZARDS

• A Study of Electromagnetic Pulse Based Weapon Systems

• China: EMP Threat

• Electromagnetic Defense Task Force 2018 Report -69 pages

• Hypothetical electromagnetic bomb -95 pages, beginner friendly

• The Early-Time (E1) High-Altitude Electromagnetic Pulse (HEMP) and Its Impact on the U.S. Power Grid -168 pages

• The Threat of RF Weapons to Infrastructure

• EMP Knots Untied: Some Common Misconceptions about Nuclear EMP

• NUCLEAR EMP ATTACK SCENARIOS AND COMBINED-ARMS CYBER WARFARE

• Impact of Severe Solar Flares, Nuclear EMP and Intentional EMI on Electric Grids -powerpoint

• A 500KV PULSER WITH FAST RISE TIME FOR EMP SIMULATION

• EMP and Its Impact on Electrical Power System: Standards and Reports

• Collateral Damage to Satellites from an EMP Attack -165 pages

• Black starting the North American power grid after a nuclear electromagnetic pulse (EMP) event or major solar storm -master theses

• RUSSIA:EMP THREAT- The Russian Federation’s Military Doctrine, Plans, and Capabilities for Electromagnetic Pulse (EMP) Attack

• Research on fast rise time EMP radiating-wavesimulator

laser weapons

• History of Laser Weapon Research

• ANALYSIS OF HIGH ENERGY LASER WEAPON EMPLOYMENT FROM A NAVY SHIP -master theses, navy post grad school

• Directed Energy Past, Present, and Future

• High Energy Laser Weapon Systems: Evolution, Analysis and Perspectives

• Navy Shipboard Lasers for Surface, Air, and Missile Defense: Background and Issues for Congress -2014 report

• EXPERIMENTAL DESIGN OF A UCAV-BASED HIGH- ENERGY LASER WEAPON -master theses, navy post grad school

• Laser Weapons for Naval Applications -powerpoint

• U.S.Navy efforts towards development of future naval weapons and integration into an All Electric Warship (AEW)

• Design and Analysis the Fiber Laser Weapon System FLWS

• Laser Beam Energy as Weapon

• U.S. Army Weapons-Related Directed Energy(DE)Programs: Background and Potential Issues for Congress -2018 congress report

• High-Energy Laser Weapons: Overpromising Readiness

• THE HIGH-ENERGY LASER: TOMORROW’S WEAPON TO IMPROVE FORCE PROTECTION

• High Power Laser Weapons and Operational Implications

• Modeling and Analysis of High Energy Laser Weapon System Performance in Varying Atmospheric Conditions -master theses, air force

• Protection Against the Threat of Laser Beams

• 1High Power Lasers –Systems & Weapons -powerpoint

• Applications of Lasers for Tactical Military Operations

• DESIGN AND ANALYSIS OF MEGAWATT CLASS FREE ELECTRON LASER WEAPONS -master theses, navy post grad school

• A FREE ELECTRON LASER WEAPON FOR SEA ARCHER -master theses, navy post grad school

• HIGH POWER OPTICAL CAVITY DESIGN AND CONCEPT OF OPERATIONS FOR A SHIPBOARD FREE ELECTRON LASER WEAPON SYSTEM -master theses, navy post grad school

• THE SHIBOARD EMPLOYMENT OF A FREE ELECTRON LASER WEAPON SYSTEM -master theses, navy post grad school

• EXPERIMENTS ON LASER BEAM JITTER CONTROL WITH APPLICATIONS TO A SHIPBOARD FREE ELECTRON LASER -master theses, navy post grad school

• EXPERIMENTAL DAMAGE STUDIES FOR A FREE ELECTRON LASER WEAPON -master theses, navy post grad school

• ANTI-SHIP MISSILE DEFENSE AND THE FREE ELECTRON LASER -master theses, navy post grad school

• DAMAGE PRODUCED BY THE FREE ELECTRON LASER -master theses, navy post grad school

railgun and coilgun

• Power Supply Options for a Naval Railgun

• Analysis and discussion on launching mechanism and tactical electromagnetic railgun technology

• Navy Lasers, Railgun, and Gun-Launched Guided Projectile: Background and Issues for Congress -2020 Congress report

• Method of ballistic control and projectile rotation in a novel railgun

• A Scenario for a Future European Shipboard Railgun

• A low voltage “railgun”

• Design considerations for an electromagnetic railgun firing intelligent bursts to be used against anti-ship missiles

• Electromagnetic Coil Gun Launcher System

• Electromagnetic coil gun–construction and basic simulation

• Capacitor-Driven Coil-Gun Scaling Relationships

• Design and experiments of multi-stage coil gun system

• Review of Inductive Pulsed Power Generators for Railguns

• DESIGN AND OPTIMIZATION OF A 600-KJ RAILGUN POWER SUPPLY -master theses, naval post grad school

• Test and Evaluation of Electromagnetic Railguns -powerpoint

• Electromagnetic coil gun–design and construction

• Experiments to increase the used Energy with the PEGASUS Railgun

• Effect of Projectile Design on Coil Gun Performance

• A Measuring Method About the Bullet Velocity in Electromagnetic Rail Gun

• COMPARISON OF TWO RAILGUN POWER SUPPLY ARCHITECTURES TO QUANTIFY THE ENERGY DISSIPATED AFTER THE PROJECTILE LEAVES THE RAILGUN -master theses, navy post grad school

• A new advanced railgun system for debris impact study

• Electromagnetic Launcher : Review of Various Structures

• COMPULSATOR DESIGN FOR ELECTROMAGNETIC RAILGUN SYSTEM -senior project

• Research on a novel integral projectile combining of warhead and armature for the railgun

• The summary of missile electromagnetic catapult technology

• Optimization of parameters acting on a projectile velocity within a four stage induction coil-gun

• Investigation on Electromagnetic Launching for Single Stage Coilgun

• Demonstration of Electromagnetic Phenomenon for Point Object Launching

• Use Of Diode As A Crowbar For Electromagnetic Launcher

• KEY FEATURES OF RAILGUN FOR NAVY PLATFORM

main links page

SAGs lighting guide

• RTL-SDR TEMPEST project

• Electromagnetic Eavesdropping -open access book chapter

• Introduction to Electromagnetic Information Security

• Enhancing Electromagnetic Side-Channel Analysis in an Operational Environment -PhD theses

• Compromising Electromagnetic Emanations of Wired and Wireless Keyboards

• Compromising Electromagnetic Emanations of USB Mass Storage Devices

• Assessing the Security of TEMPEST Fonts against Electromagnetic Eavesdropping by Using Different Specialized Receivers -big file

• Soft Tempest- An Opportunity for NATO

• Soft Tempest: Hidden Data Transmission Using Electromagnetic Emanations

• Considerations on estimating the minimal level of attenuation in TEMPEST filtering for IT equipments

• TEMPEST font counteracting a noninvasive acquisition of text data

• Laser printers and TEMPEST

• automatic tempest test and analysis system design

• CONSIDERATIONS ON TEMPEST MEASUREMENTS

....

• Emission Security

• TEMPEST Font Protects Text Data against RF Electromagnetic Attack

• TEMPEST Attacks and Cybersecurity

• Development of an Automatic TEMPEST Test and Analysis System

• Second Order Soft Tempest:from Internal Cascaded Electromagnetic Interactions to Long Haul Covert Channels

• Tempest: A Surveillance Technology in the Service of Humanity

• Study of shielding effectiveness on spurious emissions of information systems by means of metallic and carbon powder screens

• Method of Colors and Secure Fonts Used for Source Shaping of Valuable Emissions from Projector in Electromagnetic Eavesdropping Process

• USBee: Air-Gap Covert-Channel via Electromagnetic Emission from USB

• LED Arrays of Laser Printers as Sources of Valuable Emissions for Electromagnetic Penetration Process

.....

• Data Interception Through Electromagnetic Emanation Monitoring -power point

• Compromising Emanations of LCD TV Sets

• Security Limits for Compromising Emanations

• Electromagnetic Eavesdropping Risks of Flat-Panel Displays

• REALISTIC EAVESDROPPING ATTACKS ON COMPUTER DISPLAYS WITH LOW-COST AND MOBILE RECEIVER SYSTEM

• MEASUREMENT OF COMPUTER RGB SIGNALS IN CONDUCTED EMISSION ON POWER LEADS

• considerations for emission security from the perspective of signal processing techniques

• STUDY OF COMPROMISING EMISSIONS OF PS/2 KEYBOARDS BY CORRELATIVE METHODS

• AirHopper: Bridging the Air-Gap between Isolated Networks and Mobile Phones using Radio Frequencies

• Side Channels

........

• Investigation of the Risk of Electromagnetic Security on Computer Systems

• Optical Time-Domain Eavesdropping Risks of CRT Displays

• COMPROMISING EMANATIONS: OVERVIEW AND SYSTEM ANALYSIS

• On Physical-Layer Identification of Wireless Devices

• Fansmitter: Acoustic Data Exfiltration from (Speakerless) Air-Gapped Computers

• Can Portable Electronic Devices (PEDs) Interfere with Aircraft Systems?

• Electromagnetic Safety of Remote Communication Devices—Video conference

• A Threat for Tablet PCs in Public Space: Remote Visualization of Screen Images Using EM Emanation

• Exploring Radiation Intelligence from Handheld Smartphones and Tablets

• Compromising Radiated Emission from a Power Line Communication Cable

.....

• Reconstruction of Leaked Signal from USB Keyboards

• Is Your Mobile Device Radiating Keys? -power point

• Measurement of shielding effectiveness of different types of wire meshes in a large frequency range

• Synchronization Retrieval and Image Reconstruction of a Video Display Unit Exploiting its Compromising Emanations

• ClearShot: Eavesdropping on Keyboard Input from Video

• Characterization of the Electromagnetic Side Channel in Frequency Domain

• Printed Circuit Board Design Techniques for EMC Compliance

• SIGNAL PROCESSING APPLICATIONS FOR INFORMATION EXTRACTION FROM THE RADIATION OF VDUs

• INFLUENCE OF THE INTERCONNECTING CABLES ON EQUIPMENTS ELECTROMAGNETIC EMISSIONS SPECTRUM

• Electromagnetic Side-Channel Attacks:Potential for Progressing Hindered Digital Forensic Analysis

......

• Radiated Emission From Handheld Devices with Touch-Screen LCD

• EMISSION SECURITY LIMITS FOR COMPROMISING EMANATION AND ITS RECONSTRUCTION -big file

• Security evaluation of Tree Parity Re-keying Machine implementations utilizing side-channel emissions

• PROCESSING GAIN CONSIDERATIONS ON COMPROMISING EMISSIONS -power point

• REALISTIC EAVES DROPPING ATTACKS ON COMPUTER DISPLAYS WITH LOW-COST AND MOBILE RECEIVER SYSTEM

• LED-it-GO Leaking (a lot of) Data from Air-Gapped Computers via the (small) Hard Drive LED

• Standardization Works for Security regarding the Electromagnetic Environment -power point

• Compromising Emissions from a High Speed Cryptographic Embedded System -master theses

• The Search and Reconstruction of Compromising Emanations of Laser Printers in Three Media

• BitWhisper:Covert Signaling Channel be-tween Air-Gapped Computers using Thermal Manipulations

........

• Analysis of Information Leakages on Laser Printers in the Media of Electromagnetic Radiation and Line Conductions

• PowerHammer:Exfiltrating Data from Air-Gapped Computers through Power Lines

• Power line Compromising Emanations Analysis

• ELECTRO-MAGNETIC SIDE-CHANNEL ATTACK THROUGH LEARNED DENOISING AND CLASSIFICATION

• DiskFiltration: Data Exfiltration from Speakerless Air-Gapped Computers via Covert Hard Drive Noise

• Your Noise, My Signal: Exploiting Switching Noise for Stealthy Data Exfiltration from Desktop Computers

• Model for Electromagnetic Information Leakage

• A Trial of the Interception of Display Image using Emanation of Electromagnetic Wave

• Electromagnetic Security

• CTRL-ALT-LED: Leaking Data from Air-Gapped Computers via Keyboard LEDs

.....

• Estimation of Receivable Distance for Radiated Disturbance Containing Information Signal from Information Technology Equipment

• State-of-the-art research on electromagnetic information security

• Possibilities of Electromagnetic Penetration of Displays of Multifunction Devices

• Whispering devices: A survey on how side-channels lead to compromised information

• xLED: Covert Data Exfiltration from Air-Gapped Networks via Router LEDs

• Measurement of Electromagnetic Noise Coupling and Signal Mode Conversion in Data Cabling -PhD theses

• Development of Synchronization System for Signal Reception and Recovery from USB-Keyboard Compromising Emanations

• MEASUREMENT OF RADIATED COMPUTER RGB SIGNALS

• HE INVESTIGATION OF EMBEDDED SYSTEM ELECTROMAGNETIC RADIATION BY USING AUTOMATIC NEAR-FIELD MEASUREMENTS

• Data Exfiltration from Air-Gapped Computers based on ARM CPU

.............

• A SUPPORT VECTOR MACHINE FOR IDENTIFICATION OF MONITORS BASED ON THEIR UNINTENDED ELECTROMAGNETIC EMANATION

• BRIGHTNESS: Leaking Sensitive Data from Air-Gapped Workstations via Screen Brightness

• Secret data embedding scheme modifying the frequency of occurrence of image brightness values

• Optical, Acoustic and Electromagnetic Vulnerability Detection for Information Security

• Aircraft-sized anechoic chambers for electronic warfare, radar and other electromagnetic engineering evaluation

• Trust The Wire, They Always Told Me!On Practical Non-Destructive Wire-Tap Attacks Against Ethernet

• Analysis of the State of Information Security on the Basis of Surious Emission Electronic Components

• Electromagnetic Considerations for Computer Considerations for Computer System Design System Design -power point

• Radio communications Agency Study AY4364 Research to Scope Any EMC Implications of Software Radio Technology

• Aiming to Detect a malware of GSM frequency

........

• Experimental Demonstration of Electromagnetic Information Leakage from Modern Processor-Memory Systems

• A Wireless Covert Channel on Smart Cards

• Enhancement of Simple Electro-Magnetic Attacks by Pre-characterization in Frequency Domain and Demodulation Techniques

• Screaming Channels:When Electromagnetic Side Channels Meet Radio Transceivers

• aIR-Jumper: Covert Air-Gap Exfiltration/Infiltration via Security Cameras & Infrared (IR)

• MAGNETO: Covert Channel between Air-Gapped Systemsand Nearby Smartphones via CPU-Generated Magnetic Fields

• Powermitter: Data Exfiltration from Air-Gapped Computer through Switching Power Supply

• Active Countermeasure using EMI Honeypot against TEMPEST Eavesdropping in High-Speed Signalling

• A Survey of Electromagnetic Side-Channel Attacks and Discussion on their Case-Progressing Potential for Digital Forensics

• TEMPEST Attacks -Using a simple radio receiver

• WIRELESS SECURITY

last update: May 2021

main links page

Part of SAG's Plant Lighting Guide

this will be edited as needed

quick notes on sensors

Don't use resistive moisture sensors for soil like shown in many of the papers below. You want to use capacitive moisture sensors instead. Resistive sensors tend to not last long due to damage from electrolysis. If you do use a resistive moisture sensor then power on the sensor through a digital pin as needed, wait perhaps 1 mSec for everything to stabilize, do your A/D measurement, and then power down the sensor again until the next measurement is needed. This will minimize electrolysis damage long term and you will quickly kill a resistive sensor that is left powered on.

Capacitive soil moisture sensors can be left on all the time and do not have the above electrolysis issue assuming they are properly sealed including the all of electronics. They are not affected by soil (fertilizer) salts content unlike resistive sensors. The orientation and placement of a capacitive sensor will make a difference in their output in soil containers so you may have to play around a bit to get the more ideal reading range you want. I've seen this cause issues and you generally want the circuit board side facing inwards with the common generic capacitive v1.2 soil moisture sensor.

I would avoid the DHT11 humidity/temperature sensor shown in many papers below. I prefer the BME280 because I can set a bunch up and actually have them read the same under the same conditions consistently, which can be a problem with very low cost humidity sensors like the DHT11. The BME280 on protoboards are pretty cheap out of China, if in the US then check out eBay for US sellers at a pretty low cost (around $4 and you get an air pressure sensor in addition). The MCP9808 is one of the better lower cost temperature sensors that I also tested.

The Arduino type lux sensors that I've tested are pretty close to cosine correct (this is so, so important and why your phone makes a poor light meter). Assuming you know the lux to µmol m-2 s-1 PPFD conversion value for your light source, then a lux sensor can be used for plant lighting. I discuss this more in my article on using a lux meter as a plant light meter with links to supporting literature. Be sure that you can verify the lux measurement readings with a calibrated full spectrum quantum light meter for higher academic use. The TSL2591 can also be used for ultra high dynamic range two channel spectrophotometry.

Most of the latest spectral sensors like the $16 10-channel AS7341 spectrometer are not cosine correct so may need a secondary optic depending on your application (probably not as a general purpose spectrophotometer). The AS7341 could be made in to a full spectrum quantum light meter saving you >$500, when cosine corrected with a thin piece of white opaque plastic spaced properly, and a great sign of where lower cost spectrometry and light measurement is headed. The AS72652 can be used as a low cost red/far red light sensor also saving you >$500. The TCS3200 color sensor is being used as a SPAD meter replacement in some papers saving >$1,000. The TCS34725 color sensor is cosine correct and can fairly accurately measure color temperature with the AdaFruit library.

For carbon dioxide measurements, you ideally want to use dual channel NDIR type sensors although most of the lower cost ones are single channel. When first working around CO2 sensors, you need to be aware that you are constantly breathing out about 45,000 ppm CO2 and this is going to affect the sensor on the lab bench. It's a good idea to give lower cost NDIR sensors a several day burn-in period before relying on them. The MH-Z14A is an example of a lower cost but fairly accurate CO2 sensor with official library support.

The $7 VL53L0X laser range finder can be used to monitor plant growth or for cheap 3D scanning with a small tube over the sensor reduce the FOV. You may want to do some averaging with the sensor output.

grow related systems

• Design And Realization Of Fuzzy Logic Control For Ebb And Flow Hydroponic System -Arduino

• Fully Automated Hydroponic System for Indoor Plant Growth -Arduino, RPi

• A Survey of Smart Hydroponic Systems -Arduino, RPi,

• Automated hydroponics nutrition plants systems using arduino uno microcontroller based on android

• Designing and Implementing the Arduino-based Nutrition Feeding Automation System of a Prototype Scaled Nutrient Film Technique (NFT)Hydroponics using Total Dissolved Solids (TDS) Sensor -Arduino

• Red onion growth monitoring system in hydroponics environment -Arduino

• Mock up as Internet of Things Application for Hydroponics Plant Monitoring System -Arduino

• Hydroponic system with automatic water level control based on Arduino

• Enhanced Hydroponic Agriculture Environmental Monitoring: An Internet of Things Approach -Arduino

• Automatic Watering System in Plant House - Using Arduino

• Tools for Detecting and Control of Hydroponic Nutrition Flows with Esp8266 Circuit Module

• THE DESIGN AND IMPLEMENTATION OF A HYDROPONICS CONTROL SYSTEM -Arduino, master thesis

• Prototype Automatic Maintenance System on Hydroponic Plants Using Fuzzy and Arduino Uno Methods

• Development of an Indoor Hydroponic Tower for Urban Farming -Arduino

• Human Interaction Reduction in Hydroponics Systems -Arduino

• Internet of Things for Planting in Smart Farm Hydroponics Style -Arduino, esp8266, Blynk

• Smart green house’s hydroponic with arduino uno

• Automatic pH and Humidity Control System for Hydroponics Using Fuzzy Logic -Arduino

• Design of a hydroponic monitoring system with deep flow technique (DFT) -Arduino

• Intelligent Monitoring and Controlling System for Hydroponics Precision Agriculture -Arduino

• Automation and Robotics Used in Hydroponic System -Arduino, professional grow chamber

• A Hydroponic Planter System to enable an Urban Agriculture Service Industry -Arduino

• Analysis of Deep Water Culture (DWC) hydroponic nutrient solution level control systems -Arduino

• Development and Evaluation of Solar-Powered Instrument for Hydroponic System in Limapuluh Kota, Indonesia -Arduino

• AUTOMATION SYSTEM HYDROPONIC USING SMART SOLAR POWER PLANT UNIT -Arduino

• Enhanced Plant Monitoring System for Hydroponics Farming Ecosystem using IOT -Arduino

• Automation and Control System of EC and pH for Indoor Hydroponics System -Arduino, RPi

• Smart Hydroponic System with Hybrid Power Source -Arduino

• Sliding Modes Strategy Implementation for Controlling Nutrition in Hydroponics Based IoT -Arduino, fuzzy logic

• ACHPA: A sensor based system for automatic environmental control in hydroponics -Arduino

• Development of a Control System for Lettuce Cultivation in Floating Raft Hydroponics

• The control system for the nutrition concentration of hydroponic using web server -Arduino

• The prototype of the Greenhouse Smart Control and Monitoring System in Hydroponic Plants -Arduino

• COMPUTER AIDED HYDROPONICS WITH REINFORCEMENT LEARNING -Arduino, RPi, capstone project

• IoTs Hydroponics System: Effect of light condition towards plant growth -Arduino

• Performance evaluation of a small backyard hydroponics greenhouse using automatic evaporative cooling system -Arduino

• Open Source Automation for Hydroponics: Design, Construction, Programming and Testing -Arduino, senior thesis

• Design of aquaponics water monitoring system using Arduino microcontroller

• Hydroponics System for Soilless Farming Integrated with Android Application by Internet of Things and MQTT Broker -Arduino, esp8266

• Automated Vertical Hydroponic Farming -Arduino, esp8266

• Automation of Greenhouse Using Arduino and GSM Module

• Development of Solar Operated Hydroponic Fodder Production System -Arduino

• Automated Hydroponic system -Arduino, senior thesis

• Mock up as Internet of Things Application for Hydroponics Plant Monitoring System -Arduino, esp8266

• IoT based Hydroponic Temperature and Humidity Control System using Fuzzy Logic -Arduino

• Nutrient Film Technique (NFT) hydroponic nutrition controlling system using linear regression method -Arduino

• Valve Controlled Automatic Opto-Hydroponics System -Arduino

• Control System for Nutrient Solution of Nutrient Film Technique Using Fuzzy Logic -Arduino

• Implementation of Real-Time Fuzzy Logic Control for NFT-Based Hydroponic System on Internet of Things Environment -Arduino

• A novel low-cost open-source LED system for micro algae cultivation -Arduino, APA102, source code

• Design and Implementation of Artificial Grow Light for Germination and Vegetative Growth -Arduino, esp8266, six LED channels

• Effect of Supplementary Cyan Light to Deep Red and Royal Blue Range Wavelengths on the Seedling Period of Iceberg Lettuces -Arduino, extensive grow chamber

farming and agriculture

• Smart Farming: IoT Based Smart Sensors Agriculture Stick for Live Temprature and Moisture Monitoring using Arduino, Cloud Computing & Solar Technology -Arduino, esp8266

• Arduino Board in the Automation of Agriculture in Mexico, A Review

• Iot Based Smart Poultry Farming using Commodity Hardware and Software -Arduino, RPi

• Soil moisture monitoring using IoT enabled arduino sensors with neural networks for improving soil management for farmers and predict seasonal rainfall for planning future harvest in North Karnataka - India

• Smart Aquaponics System for Urban Farming -Arduino

• Smart Farming using IoT, a solution for optimally monitoring farming conditions -Arduino, esp32

• WATER MONITORING IOT SYSTEM FOR FISH FARMING PONDS -Arduino

• A Comprehensive IoT Node Proposal Using Open Hardware. A Smart Farming Use Case to Monitor Vineyards -Arduino

• IoT-based Water Quality Monitoring System for Soft-Shell Crab Farming

• Cave Pearl Data Logger: A Flexible Arduino-Based Logging Platform for Long-Term Monitoring in Harsh Environments -Arduino

• IoT based smart agrotech system for verification of Urban farming parameters -Arduino, esp8266

• Implementation of smart monitoring system in vertical farming -Arduino, esp32

• A Wirelessly Controlled Robot-based Smart Irrigation System by Exploiting Arduino

• AN ANDROID-ARDUINO SYSTEM TO ASSIST FARMERS IN AGRICULTURAL OPERATIONS -Arduino, internet back end

• Design of Fish Feeder Robot based on Arduino-Android with Fuzzy Logic Controller

• Real time fish pond monitoring and automation using Arduino

• Improved premixing in-line injection system for variable-rate orchard sprayers with Arduino platform

measurements and lab gear

• Handheld arduino-based near infrared spectrometer for non-destructive quality evaluation of siamese oranges -Arduino, AS7263 sensor

• Nitrogen Deficiency Level Assessment Device for Rice (Oryza sativa L.) and Maize (Zea mays L.) using Classification Algorithm-based Spectrophotometry -Arduino, TCS3200 color sensor, DIY SPAD meter

• A guide to Open‑JIP, a low‑cost open‑source chlorophyll fluorometer -Ardiuno

• An Arduino-based low cost device for the measurement of the respiration rates of fruits and vegetables -CO2 gas analyzer chamber

• Application of a low-cost RGB sensor to detect basil (Ocimum basilicum L.) nutritional status at pilot scale level -Arduino

• In situ Measurements of Phytoplankton Fluorescence Using Low Cost Electronics -Ardiuno, this can be used on a plant leaf

• LOW COST AND LABORATORY SCALE NIR SPECTROSCOPY FOR QUALITY EVALUATION OF FRUITS AND VEGETABLES -Arduino, Hamamatsu spectrometer sensor (C11708MA)

• Ultra-portable, wireless smartphone spectrometer for rapid, non-destructive testing of fruit ripeness -Arduino, Hamamatsu spectrometer

• Design and Development of a Shortwave near Infrared Spectroscopy using NIR LEDs and Regression Model -Arduino

• Construction of a Photometer as an Instructional Tool for Electronics and Instrumentation -Arduino

• Development of an Economical, Linear CCD Based Spectrometer -Arduino

• A Simple, Rapid Analysis, Portable, Low-cost, and Arduino-based Spectrophotometer with White LED as a Light Source for Analyzing Solution Concentration

• Seawater pH measurements in the field: A DIY photometer with 0.01 unit pH accuracy -Arduino, brutally detailed

• Measuring CO2 with an Arduino: Creating a Low-Cost, Pocket-Sized Device with Flexible Applications That Yields Benefits for Students and Schools -Arduino

• Preparation and Evaluation of Carbon Synthesized by Chemical Activation of Mango Seeds -Arduino

• Arduino Uno-based water turbidity meter using LDR and LED sensors

• Light Meter for Measuring Photosynthetically Active Radiation -Arduino

• Arduino Based Weather Monitoring Telemetry System Using NRF24L01+

• Arduino Based Weather Monitoring System

• Solar Energy Measurement Using Arduino

• Design and Implementation of Portable Outdoor Air Quality Measurement System using Arduino

• A low-cost fluorescence reader for in vitro transcription and nucleic acid detection with Cas13a -Arduino, this same concept can be used on a plant

• Performance evaluation of low-cost IoT based chlorophyll meter -Arduino, SPAD meter replacement

• Non-destructive method for monitoring tomato ripening based on chlorophyll fluorescence induction -Arduino

• A Low-cost Sensor for Measuring and Mapping Chlorophyll Content in Cassava Leaves -Arduino

• An RGB Sensor –Based Chlorophyll Estimation in Carabao Mango Leaves by Multiple Regression Analysis of Hue Saturation Value Color Components -Arduino, TCS3200 color sensor

• Lyco-Frequency: A Development of Lycopersicon Esculentum Fruit Classification for Tomato Catsup Production Using Frequency Sensing Effect -Arduino, ripeness and suitability of tomatoes using a novel low cost resistive technique

• Non-Destructive Oil Palm Fresh Fruit Bunch (FFB) Grading Technique Using Optical Sensor -Arduino

• Portable Water Color Monitoring System Using Microcontroller for Phytoplankton Bloom Measurement in Japanese Lake -Arduino

• Nitrogen Fertilizer Prediction of Maize Plant with TCS3200 Sensor Based on Digital Image Processing -Arduino

• Development of color detector using colorimetry system with photo diode sensor for food dye determination application -Arduino

• Prediction of tomatoes maturity using TCS3200 color sensor -Arduino

• SPECTROPHOTOMETER ON-THE-GO:THE DEVELOPMENT OF A2-IN-1 UV-VIS PORTABLE ARDUINO-BASED SPECTROPHOTOMETER

misc

• NON-INTRUSIVE LOAD MANAGEMENT SYSTEM FOR RESIDENTIAL LOADS USING ARTIFICIAL NEURAL NETWORK BASED ARDUINO MICROCONTROLLER -PhD thesis

• IMPLEMENTING GENETIC ALGORITHMS ON ARDUINO MICRO-CONTROLLERS -source code

• Development of Arduino Microcontroller Based Non-Intrusive Appliances Monitoring System using Artificial Neural Network

• FastGRNN: A Fast, Accurate, Stable and Tiny Kilobyte Sized Gated Recurrent Neural Network

• A Wirelessly Controlled Robot-based Smart Irrigation System by Exploiting Arduino -genetic algorithm

• Fish Quality Recognition using Electrochemical Gas Sensor Array and Neural Network -Arduino Due

• Design of PID controller for DC Motor Speed Control Using Arduino Microcontroller

• Implementation of a Fuzzy Logic Speed Controller For a Permanent Magnet DC Motor Using a Low-Cost Arduino Platform

• Genetic Algorithm based Internet of Precision Agricultural Things (IopaT) for Agriculture 4.0

• The Application of Fuzzy Control in Water Tank Level Using Arduino

Misc papers

last update: April 2021 -added aeroponics section

main papers link page

SAG's Plant Lighting Guide main page

• AQUAPONICS Production Manual

• Prototype of Control and Monitor System with Fuzzy Logic Method for Smart Greenhouse Arduino

• Development of an Integrated IoT-Based Greenhouse Control Three-Device Robotic System

• Design and Implementation of Automated Greenhouse Management System

• Automated smart hydroponics system using internet of things

• AUTOMATED HYDROPONIC PLANT GROWTH SYSTEM USING IOT

• Raman Spectroscopy Study of Delta-9-Tetrahydrocannabinol and Cannabidiol and their Hydrogen-Bonding Activities Cannabidiol and their Hydrogen-Bonding Act master thesis

• Future food-production systems: vertical farming and controlled-environment agriculture

• Review of energy efficiency in controlled environment agriculture

• Cannabis Domestication, Breeding History, Present-day Genetic Diversity,and Future Prospects

• Adaptive grow light robot arm master thesis

• Botanical Internet of Things: Toward Smart Indoor Farming by Connecting People, Plant, Data and Clouds

aeroponics

• Automated Aeroponics System for Indoor Farming using Arduino

• Aeroponics Soilless Cultivation System for Vegetable Crops

• Modern plant cultivation technologies in agriculture under controlled environment: are view on aeroponics

• Getting to the roots of aeroponic indoor farming

• Potato minituber production using aeroponics: Effect of plant density and harvesting intervals

• Potential of aeroponics system in the production of quality potato (Solanum tuberosum l.) seed in developing countries

• Growth Responses and Root Characteristics of Lettuce Grown in Aeroponics, Hydroponics, and Substrate Culture

• Yam Propagation Using ‘Aeroponics’ Technology

• IOT-Based Automated Aeroponics System

• Scaling up quantitative phenotyping of root system architecture using a combination of aeroponics and image analysis

• A fuzzy micro-climate controller for small indoor aeroponics systems

• NUTRITIONAL STUDIES WITH PROCESSING TOMATO GROWN IN AEROPONICS

• Monitoring and Control Systems in Agriculture Using Intelligent Sensor Techniques: A Review of the Aeroponic System

• Yield of Potato Minitubers under Aeroponics, Optimized for Nozzle Type and Spray Direction

• Water and Energy Conservation Grow System: Aquaponics and Aeroponics with a Cycle Timer -senior project on making timers

• Temperature Distribution in Aeroponics System with Root Zone Cooling for the Production of Potato Seed in Tropical Lowland

• Influence of Atomization Nozzles and Spraying Intervals on Growth, Biomass Yield, and Nutrient Uptake of Butter-Head Lettuce under Aeroponics System

• Aeroponics System for Production of Horticultural Crops

• Garduino: A Cyber-Physical Aeroponics System

• Effects of intercropping on growth and nitrate accumulation of lettuce in aeroponics

• nfluence of Atomization Nozzles and Spraying Intervals onGrowth, Biomass Yield, and Nutrient Uptake of Butter-HeadLettuce under Aeroponics System

• YIELD AND NUTRIENT STATUS OF GREENHOUSE TOMATO (LYCOPERSICON ESCULENTUM MILL.) GROWN IN NEW AND RE-USED ROCKWOOL, POLYURETHANE, NFT AND AEROPONICS

• Dry-fog Aeroponics Affects the Root Growth of Leaf Lettuce (Lactuca sativaL. cv.Greenspan) by Changing the Flow Rate of Spray Fertigation

• Technological Modernization and Its Influence on Agriculture Sustainability, Aeroponics Systems in Belt and Road Countries

• Evaluation of different nutrient solution in aeroponics for performance of tomato (Solanum lycopersicum L.)

• Method for Growing Plants Aeroponically -this is from 1977

• A Method to Measure Low Drainage Flow and to Control Nutrient Solution Supply in Aeroponics Systems

• Aeroponic Based Controlled Environment Based Farming System

• Effects of elevated root zone CO2 and air temperature on photosynthetic gas exchange, nitrate uptake, and total reduced nitrogen content in aeroponically grown lettuce plants

• Root-zone CO2 and root-zone temperature effects on photosynthesis and nitrogen metabolism of aeroponically grown lettuce (Lactuca sativa L.) in the tropics

• Manipulating Aeroponically Grown Potatoes with Gibberellins and Calcium Nitrate

• Performance Of Irish Potato Varieties Under Aeroponic Conditions In Rwanda

• Effect of different day and night nutrient solution concentrations on growth, photosynthesis, and leaf NO3- content of aeroponically grown lettuce

• Aeroponic Greenhouse as an Autonomous System Using Intelligent Space for Agriculture Robotics

• Effects of Root-Zone Temperature on Photosynthesis, Productivity and Nutritional Quality of Aeroponically Grown Salad Rocket (Eruca sativa) Vegetable

• Astro GardenTM Aeroponic Plant Growth System Design Evolution

• AEROPONIC BASED SMART INCUBATOR FOR AGRICULTURE USING MICROCONTROLLER

• Effect of ground heat exchanger for root-zone cooling on the growth and yield of aeroponically-grown strawberry plant under tropical greenhouse condition

• Automatic aeroponic irrigation system based on Arduino's platform

• DROPLET SIZE ANALYSIS OF HIGH PRESSURE AEROPONIC SYSTEM -master thesis

• Automated Aeroponics System for Indoor Farming using Arduino

• Automation of pesticide-free cilantro aeroponic crops

• Ultrasonic atomizer application for Low Cost Aeroponic Chambers (LCAC): a review

• Production of Some Medicinal Plants in Aeroponic System

• Design, Development and Evaluation of Solar Powered Aeroponic system –A Case Study

• Hydro-Aeroponic Design -senior group paper

• Design of a Sprout Layer-rack Aeroponic Cultivation Device

• Experiment design to investigate the possibility of using grey water in aeroponic cultivation of various crops for future long-term space missions

• LOW EFFORT MANAGEMENT OF BASIL(OCIMUM BASILICUM) GROWTH IN AN AEROPONIC SYSTEM -senior thesis

• Effects of short light/dark cycles on photosynthetic pathway switching and growth of medicinal Dendrobium officinale in aeroponic cultivation

• Development and Performance of a Fuzzy Logic Control System for Temperature and Carbon Dioxide for Red Chili Cultivation in an Aeroponic Greenhouse System

• 3D printed aeroponic tray nutrient delivery system for bioregenerative life support systems

• Aeroponic/Hydroponic Growth Module -good final design report

• Growing arugula plants using aeroponic culture with an automated irrigation system

• EFFECT OF ELECTRICAL CONDUCTIVITY ON GROWTH AND YIELD OF STRAWBERRY CULTIVATED IN AEROPONIC SYSTEM

Machine vision/learning and plants

last update: March 2021

main papers link page

SAG's Plant Lighting Guide main page

Machine vision (also check out the NDVI links)

• Introduction to remote sensing of environment

• Deep Learning Application in Plant Stress Imaging: A Review

• Multispectral Imaging for Plant Food Quality Analysis and Visualization

• Plant Disease Detection by Imaging Sensors – Parallels and Specific Demands for Precision Agriculture and Plant Phenotyping

• Advanced imaging techniques for the study of plant growth and development

• 3D lidar imaging for detecting and understanding plant responses and canopy structure

• Discrimination of nitrogen fertilizer levelsof tea plant (Camellia sinensis) basedvon hyperspectral imaging

• An automated, high-throughput plant phenotyping system using machine learning-based plant segmentation and image analysis

• Machine Learning and Computer Vision System for Phenotype Data Acquisition and Analysis in Plants

• Temporal dynamics of maize plant growth, water use, and leaf water content using automated high throughput RGB and hyperspectral imaging

• Nondestructive Determination of Nitrogen, Phosphorus and Potassium Contents in Greenhouse Tomato Plants Based on Multispectral Three-Dimensional Imaging

• Verification of color vegetation indices for automated crop imaging applications

• A Review on the Use of Unmanned Aerial Vehicles and Imaging Sensors for Monitoring and Assessing Plant Stresses

• High Throughput In vivo Analysis of Plant Leaf Chemical Properties Using Hyperspectral Imaging

• Lettuce calcium deficiency detection with machine vision computed plant features in controlled environments

• Multispectral imaging and unmanned aerial systems for cotton plant phenotyping

• Hyperspectral imaging and 3D technologies for plant phenotyping: From satellite to close-range sensing

• Chlorophyll estimation in soybean leaves infield with smartphone digital imaging and machine learning

• Optical imaging spectroscopy for plant research: more than a colorful picture

• UAV-Based High Throughput Phenotyping in Citrus Utilizing Multispectral Imaging and Artificial Intelligence

• Computer vision and artificial intelligence in precision agriculture for grain crops: A systematic review

• Determination of Green Leaves Density Using Normalized Difference Vegetation Index via Image Processing of In-Field Drone-Captured Image

• Design and implementation of a computer vision-guided green house crop diagnostics system

Machine learning

• Hyperspectral Leaf Reflectance as Proxy for Photosynthetic Capacities: An Ensemble Approach Based on Multiple Machine Learning Algorithms

• Machine Learning Techniques for Predicting Crop Photosynthetic Capacity from Leaf Reflectance Spectra

• Predicting learning outputs and retention through neural network artificial intelligence in photosynthesis, transpiration and translocation

• Improvement of photosynthetic rate evaluation by plant bioelectric potential using illuminating information and a neural network

• Photosynthetic rate prediction model of newborn leaves verified by core fluorescence parameters

• Training artificial neural networks using APPM photosynthesis modeling

• The Analysis of Plants Image Recognition Based on Deep Learning and Artificial Neural Network

• A Leaf Recognition Algorithm for Plant Classification Using Probabilistic Neural Network

• DEEP-PLANT: PLANT IDENTIFICATION WITH CONVOLUTIONAL NEURAL NETWORKS

• From Parallel Plants to Smart Plants: Intelligent Control and Management for Plant Growth

• Plants meet machines: Prospects in machine learning for plant biology

• Development and evaluation of a low-cost and smart technology for precision weed management utilizing artificial intelligence

• Predicting Lettuce Canopy Photosynthesis with Statistical and Neural Network Models

Chlorophyll fluorescence and NDVI

last update: March 2021

main papers link page

SAG's Plant Lighting Guide main page

Chlorophyll fluorescence

• Frequently asked questions about in vivo chlorophyll fluorescence: practical issues -This is the basics.

• [Frequently asked questions about chlorophyll fluorescence,

the sequel](https://www.semanticscholar.org/paper/Frequently-asked-questions-about-chlorophyll-the-Kalaji-Schansker/a05e0ee7d0d9c1f0bee60d996415dfb227b8161d) -This goes a bit beyond the basics including specific protein profiles.

• Chlorophyll Fluorescence Terminology: An Introduction

• [Chlorophyll Fluorescence: A Probe of Photosynthesis

In Vivo](https://pdfs.semanticscholar.org/32dc/109c20cbaf1ac4055eecbb25f110119d0d82.pdf)

• Chlorophyll fluorescence—a practical guide

• Chlorophyll fluorescence emission spectrum inside a leaf

• [Red and far red Sun-induced chlorophyll fluorescence

as a measure of plant photosynthesis](https://www.zora.uzh.ch/id/eprint/113186/1/2015_Rossini_red_and_far.pdf)

• Chlorophyll fluorescence at 680 and 730 nm and leaf photosynthesis

• The Chlorophyll Fluorescence Ratio F735/F700 as an Accurate Measure of the Chlorophyll Content in Plants

• Chlorophyll fluorescence emission of tomato plants as a response to pulsed light based LEDs

• Chlorophyll fluorescence as a tool in plant physiology

• Applications of chlorophyll fluorescence can improve crop production strategies: an examination of future possibilities

• The use of fluorescence nomenclature in plant stress physiology

• Chlorophyll fluorescence analysis: a guide to good practice and understanding some new applications

• Chlorophyll Fluorescence Parameters: The Definitions, Photosynthetic Meaning, and Mutual Relationships

• How to correctly determine the different chlorophyll fluorescence parameters and the chlorophyll fluorescence decrease ratio RFd of leaves with the PAM fluorometer

• Continuous recording of photochemical and non-photochemical chlorophyll fluorescence quenching with a new type of modulation fluorometer

• First observations of global and seasonal terrestrial chlorophyllfluorescence from space

• Global and time-resolved monitoring of crop photosynthesis with chlorophyll fluorescence

• Linking chlorophyll a fluorescence to photosynthesis for remote sensing applications: mechanisms and challenges

• Remote sensing of solar-induced chlorophyll fluorescence: Review of methods and applications

• Measurements of variable chlorophyll fluorescence using fast repetition rate techniques: defining methodology and experimental protocols

• Nonphotochemical Chlorophyll Fluorescence Quenching:Mechanism and Effectiveness in ProtectingPlants from Photodamage

• Chlorophyll Fluorescence in Plant Biology

• Applications of chlorophyll fluorescence imaging technique in horticultural research: A review

• Rapid, Noninvasive Screening for Perturbations of Metabolism and Plant Growth Using Chlorophyll Fluorescence Imaging

• Chlorophyll fluorescence imaging of photosynthetic activity with the flash-lamp fluorescence imaging system

• Chlorophyll fluorescence: A wonderful tool to study plant physiology and plant stress

• Remote Sensing of the Xanthophyll Cycle and Chlorophyll Fluorescence in Sunflower Leaves and Canopies

• A model for chlorophyll fluorescence and photosynthesis at leaf scale

• Profiles of light absorption and chlorophyll within spinach leaves from chlorophyll fluorescence

• A Simple Alternative Approach to Assessing the Fate of Absorbed Light Energy Using Chlorophyll Fluorescence

• Chlorophyll fluorescence quenching by xanthophylls

• Remote sensing of solar-induced chlorophyll fluorescence (SIF) in vegetation: 50 years of progress

• Models of fluorescence and photosynthesis for interpreting measurements of solar‐induced chlorophyll fluorescence

• On the relation between the Kautsky effect (chlorophyll a fluorescence induction) and Photosystem II: Basics and applications of the OJIP fluorescence transient

• Chlorophyll fluorescence emission spectrum inside a leaf

• Monitoring and screening plant populations with combined thermal and chlorophyll fluorescence imaging

• Chlorophyll Fluorescence Imaging of Leaves and Fruits

• Applications of chlorophyll fluorescence imaging technique in horticultural research: A review

• Chlorophyll Fluorescence Effects on Vegetation Apparent Reflectance: I. Leaf-Level Measurements and Model Simulation

• Leaf level detection of solar induced chlorophyll fluorescence by means of a subnanometer resolution spectroradiometer

• Effects of different light intensities on chlorophyll fluorescence characteristics and yield in lettuce

• Contribution of chlorophyll fluorescence to the apparent vegetation reflectance

• A new instrument for passive remote sensing: 1. Measurements of sunlight-induced chlorophyll fluorescence

• A practical approach for estimating the escape ratio of near-infrared solar-induced chlorophyll fluorescence

• The Relation between Laser-Induced Chlorophyll Fluorescence and Photosynthesis

• The Chlorophyll Fluorescence Imaging Spectrometer (CFIS), mapping far red fluorescence from aircraft

• Closing in on maximum yield of chlorophyll fluorescence using a single multiphase flash of sub-saturating intensity

NDVI (normalized difference vegetation index)

• On the Relation between NDVI, Fractional Vegetation Cover, and Leaf Area Index

• Analysis of NDVI and scaled difference vegetation index retrievals of vegetation fraction

• The impact of soil reflectance on the quantification of the green vegetation fraction from NDVI

• Comparing RGB-Based Vegetation Indices With NDVI For Drone Based Agricultural Sensing

• Drones for Normalized Difference Vegetation Index (NDVI), to Estimate Crop Health for Precision Agriculture: A Cheaper Alternative for Spatial Satellite Sensors

• Review on Application of Drone Systems in Precision Agriculture

• Optimization of Agricultural Smart System using Remote Sensible NDVI and NIR Thermal Image Analysis Techniques

• Multi-Scale Evaluation of Drone-Based Multispectral Surface Reflectance and Vegetation Indices in Operational Conditions

• A commentary review on the use of normalized difference vegetation index (NDVI) in the era of popular remote sensing

• Dynamics of the Indices NDVI and GNDVI in a Rice Growing in Its Reproduction Phase from Multi-spectral Aerial Images Taken by Drones

• Crop reflectance monitoring as a tool for water stress detection in greenhouses: A review

• NDVI imaging within space exploration plant growth modules – A case study from EDEN ISS Antarctica

• Experimental Analysis of IoT Based Camera SI-NDVI Values for Tomato Plant Health Monitoring Application

• Utilization of single- image normalized difference vegetation index (SI- NDVI) for early plant stress detection

• Crop reflectance indices for mapping water stress in greenhouse grown bell pepper

Far red, blue, green, and photosynthesis studies

last update: May 2021

main papers link page

SAG's Plant Lighting Guide main page

note- in most papers, blue is counted as 400-500 nm, green is 500-600 nm, red is 600-700 nm, and far red is 700-750 nm (or so). This means in many papers that cyan and yellow/amber will count as green light although their photosynthesis rates are different. Cyan has lower photosynthesis rates compared to green/yellow/amber due to the higher absorption of cyan light by carotenoids, which is only 30-70% efficient at transferring energy to chlorophyll, and only through chlorophyll can absorbed energy be transferred to a photosynthetic reaction center. You'll see in the McCree curve that yellow/amber light is very efficient.

• Do changes in light direction affect absorption profiles in leaves? -TL;DR red and blue very little, green yes

Far red

• The Power of Far-Red Light at Night: Photomorphogenic, Physiological, and Yield Response in Pepper During Dynamic 24 Hour Lighting -pepper

• Far-red: The Forgotten Photons YouTube vid by Bruce Bugbee, Utah State

• [Far-red photons have equivalent efficiency to traditional photosynthetic photons:

implications for re-defining photosynthetically active radiation.](https://onlinelibrary.wiley.com/doi/am-pdf/10.1111/pce.13730)

• Why Far-Red Photons Should Be Included in the Definition of Photosynthetic Photons and the Measurement of Horticultural Fixture Efficacy

• Photosynthetic activity of far-red light in green plants

• The effect of far-red light on the productivity and photosynthetic activity of tomato

• The long-wavelength limit of plant photosynthesis

• Far‐red radiation stimulates dry mass partitioning to fruits by increasing fruit sink strength in tomato

• Plant responses to red and far-red lights, applications in horticulture

• Growth and Cell Division of Lettuce Plants under Various Ratios of Red to Far-red Light-emitting Diodes

• Supplemental Far-Red Light Stimulates Lettuce Growth: Disentangling Morphological and Physiological Effects

• Effects of the red:far-red light ratio on photosynthetic characteristics of greenhouse cut Chrysanthemum

• Disentangling the effects of photosynthetically active radiation and red to far-red ratio on plant photosynthesis under canopy shading: a simulation study using a functional–structural plant model

• Dissecting the Genotypic Variation of Growth Responses to Far-Red Radiation in Tomato

• The photosynthetic parameters of cucumber as affected by irradiances with different red:far-red ratios

• Growth and nutritional properties of lettuce affected by mixed irradiation of white and supplemental light provided by light-emitting diode

• Promotion of Flowering from Far-red Radiation Depends on the Photosynthetic Daily Light Integral

• Increase in Biomass and Bioactive Compounds in Lettuce under Various Ratios of Red to Far-red LED Light Supplemented with Blue LED Light

• Effects of Continuous or End-of-Day Far-Red Light on Tomato Plant Growth, Morphology, Light Absorption, and Fruit Production

• Effect of supplemental far-red light with blue and red LED lamps on leaf photosynthesis, stomatal regulation and plant development of protected cultivated tomato

• Far-red light is needed for efficient photochemistry and photosynthesis

• Far-Red Light Accelerates Photosynthesis in the Low-Light Phases of Fluctuating Light

• Effect of interactions between light intensity and red-to- far-red ratio on the photosynthesis of soybean leaves under shade condition

• The role of far-red light (FR) in photomorphogenesis and its use in greenhouse plant production

• [Action spectra of photosystems II and I and quantum yield of

photosynthesis in leaves in State 1](https://www.sciencedirect.com/science/article/pii/S0005272813002144)

• Far-Red Spectrum of Second Emerson Effect: A Study Using Dual-Wavelength Pulse Amplitude Modulation Fluorometry

• Defining the Far-Red Limit of Photosystem II in Spinach

• Far-red radiation promotes growth of seedlings by increasing leaf expansion and whole-plant net assimilation

• Fast cyclic electron transport around photosystem I in leaves under far-red light: a proton-uncoupled pathway?

• The phytochrome red/far-red photoreceptor superfamily

• A Moderate to High Red to Far-red Light Ratio from Light-emitting Diodes Controls Flowering of Short-day Plants

• Overhead supplemental far-red light stimulates tomato growth under intra-canopy lighting with LEDs

• Morphological and physiological properties of indoor cultivated lettuce in response to additional far-red light

• Far-red light enhances photochemical efficiency in a wavelength-dependent manner

• Far-red light during cultivation induces post harvest cold tolerance in tomato fruit

• Supplemental intracanopy far-red radiation to red LED light improves fruit quality attributes of greenhouse tomatoes

• Plant responses to red and far-red lights, applications in horticulture

• Blue radiation attenuates the effects of the red to far-red ratio on extension growth but not on flowering

• Supplemental Far-red Light-emitting Diode Light Increases Growth of Foxglove Seedlings Under Sole-source Lighting

• The effect of far-red light on the productivity and photosynthetic activity of tomato

• The Effect of Supplemental Blue, Red and Far-Red Light on the Growth and the Nutritional Quality of Red and Green Leaf Lettuce

• Substituting green or far-red radiation for blue radiation induces shade avoidance and promotes growth in lettuce and kale

• A Mathematical Model of Photosynthetic Electron Transport in Response to the Light Spectrum Based on Excitation Energy Distributed to Photosystems

• Duration of light-emitting diode (LED) supplemental lighting providing far-red radiation during seedling production influences subsequent time to flower of long-day annuals

• Improvement of Growth and Morphology of Vegetable Seedlings with Supplemental Far-Red Enriched LED Lights in a Plant Factory

• Effect of Extended Photoperiod with a Fixed Mixture of Light Wavelengths on Tomato Seedlings

Blue

• Spectral Effects of Three Types of White Light-emitting Diodes on Plant Growth and Development: Absolute versus Relative Amounts of Blue Light

• Photosynthesis and leaf development of cherry tomato seedlings under different LED-based blue and red photon flux ratios

• Spectral effects of light-emitting diodes on plant growth, visual color quality, and photosynthetic photon efficacy: White versus blue plus red radiation

• Comparison of Growth, Development, and Photosynthesis of Petunia Grown Under White or Red-blue LED lights

• Effects of varying light quality from single-peak blue and red light-emitting diodes during nursery period on flowering, photosynthesis, growth, and fruit yield of everbearing strawberry

• Effects of environment lighting on the growth, photosynthesis, and quality of hydroponic lettuce in a plant factory

• Photosynthesis, Morphology, Yield, and Phytochemical Accumulation in Basil Plants Influenced by Substituting Green Light for Partial Red and/or Blue Light

• Plant Growth and Photosynthetic Characteristics of Mesembryanthemum crystallinum Grown Aeroponically under Different Blue- and Red-LEDs

• [COP1-Mediated Ubiquitination of CONSTANS Is Implicated in

Cryptochrome Regulation of Flowering in Arabidopsis](http://www.plantcell.org/content/plantcell/20/2/292.full.pdf)

Green

• Green Light Drives Leaf Photosynthesis More Efficiently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are Green-- Terashima et al

• Green Light Drives CO2 Fixation Deep within Leaves-- Sun et al

• Nitrogen-improved photosynthesis quantum yield is driven by increased thylakoid density, enhancing green light absorption

• [Why are higher plants green? Evolution of the higher plant

photosynthetic pigment complement-- Nishio 2000](https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3040.2000.00563.x)

• [Effect of green light wavelength and intensity on photomorphogenesis and

photosynthesis in Lactuca sativa-- Johkan et al](https://www.plantgrower.org/uploads/6/5/5/4/65545169/1-s2.0-s0098847211001924-main.pdf)

• Contributions of green light to plant growth and development- Wang, Folta

• Cost and Color of Photosynthesis -Why plants evolved green.

• Effects of Blue and Green Light on Plant Growth and Development at Low and High Photosynthetic Photon Flux -Master Thesis

• [Sensitivity of Seven Diverse Species to Blue and

Green Light: Interactions With Photon Flux](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0163121)

• Green light augments far-red-light-induced shade response

• Green light signaling and adaptive response

• Green light drives photosynthesis in mosses

• Cryptochromes integrate green light signals into the circadian system

• Don’t ignore the green light: exploring diverse roles in plant processes

Photosynthesis

• Why is photosynthesis interesting? -Some of the basics.

• [THE ACTION SPECTRUM, ABSORPTANCE AND QUANTUM YIELD

OF PHOTOSYNTHESIS IN CROP PLANTS-- McCree](https://www.vegenaut.com/pl/wp-content/uploads/sites/2/2017/07/PPFD_essential_article.pdf) -This is the McCree curve!

• The McCree Curve Demystified -This is what the McCree curve means

• Modelling and Remote Sensing of Canopy Light Interception and Plant Stress in Greenhouses -PhD thesis

• Leaf optical properties and dynamics of photosynthetic activity -PhD thesis

• [Significance of Enhancement for Calculations Based on the

Action Spectrum for Photosynthesis- McCree 1971](http://www.plantphysiol.org/content/plantphysiol/49/5/704.full.pdf) Note- the action spectrum is different than quantum yield

• When there is too much light

• [Toward an optimal spectral quality for plant growth and

development: The importance of radiation capture](https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1765&context=psc_facpub)

• [Photosynthetic response of Cannabis sativa L. to variations in

photosynthetic photon flux densities, temperature and CO2 conditions](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3550641/pdf/12298_2008_Article_27.pdf)

• The Guiding Force of Photons

• A paper on why DLI is important with charts for different plants

• [Leaf and Plant Age Affects Photosynthetic

Performance and Photoprotective Capacity](http://www.plantphysiol.org/content/plantphysiol/175/4/1634.full.pdf)

• Growth and Photosynthesis under Pulsed Lighting

• Measuring fluorescence and photosynthesis

• [Comparison of Lettuce Growth under Continuous

and Pulsed Irradiation Using Light-Emitting Diodes](https://www.hst-j.org/articles/pdf/R91O/kshs-2018-036-04-9.pdf)

• A kinetic model for estimating net photosynthetic rates of cos lettuce leaves under pulsed light

• Response of photosynthetic capacity of tomato leaves to different LED light wavelength

• [Pathways for Energy Transfer in the Core Light-Harvesting Complexes

CP43 and CP47 of Photosystem II](https://core.ac.uk/download/pdf/82683784.pdf)

• Conceptual Developments in Photosynthesis,1924-1974

• Exploring the Limits of Crop Productivity

• [What is the maximum efficiency with which photosynthesis can

convert solar energy into biomass?](http://sippe.ac.cn/gh/2008%20Annual%20Report/Zhu%20X-G.pdf)

• Photosynthesis and high light stress

• Emerging approaches to measure photosynthesis from the leaf to the ecosystem

• A comparison of methods to estimate photosynthetic light absorption in leaves with contrasting morphology

• Chlorophyll excitation energies and structural stability of the CP47 antenna of photosystem II: a case study in the first-principles simulation of light-harvesting complexes

the below gets in to quantum photosynthesis

• Photosynthetic light harvesting: excitons and coherence

• Photosynthetic Quantum Yield Dynamics: From Photosystems to Leaves

• From Förster resonance energy transfer to coherent resonance energy transfer and back

• Does coherence enhance transport in photosynthesis?

• Quieting a noisy antenna reproduces photosynthetic light harvesting spectra

Cannabis, basil, lettuce, tomato, pepper lighting links

last update: March 2021

main papers link page

SAG's Plant Lighting Guide main page

Cannabis lighting

• Temperature response of photosynthesis in different drug and fiber varieties of Cannabis sativa L.

• UV-B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH AND CANNABINOID PRODUCTION OF TWO Cannabis sativa CHEMOTYPES

• An Update on Plant Photobiology and Implications for Cannabis Production

• The Effect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L

• Closing the Yield Gap for Cannabis: A Meta-Analysis of Factors Determining Cannabis Yield

• THE EFFECTS OF RED, BLUE AND WHITE LIGHT ON THE GROWTH AND DEVELOPMENT OF CANNABIS SATIVA L.

• Identification of Cannabis plantations using hyperspectral technology

• The results of an experimental indoor hydroponic Cannabis growing study, using the ‘Screen of Green’ (ScrOG) method—Yield, tetrahydrocannabinol (THC) and DNA analysis

• LED lighting affects the composition and biological activity of Cannabis sativa secondary metabolites

• Energy Consumption Model for Indoor Cannabis Cultivation Facility

• Cannabis Indoor Growing Conditions, Management Practices, and Post-Harvest Treatment: A Review

• Yield of Illicit Indoor Cannabis Cultivation in The Netherlands

• The Profitability of Growing Cannabis Under High Intensity Light

• ENERGY CONSUMPTION AND ENVIRONMENTAL IMPACTS ASSOCIATED WITH CANNABIS CULTIVATION master thesis

• The influence of spectral quality of light on plant secondary metabolism and photosynthetic acclimation to light quality PhD thesis

• Comparing hydroponic and aquaponic rootzones on the growth of two drug-type Cannabis sativa L. cultivars during the flowering stage

• SPECTRAL DIFFERENTIATION OF CANNABIS SATIVAL FROM MAIZE USING HYPERSPECTRAL INDICES master thesis

• Influence of Light Spectra on the Production of Cannabinoids

• Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment

• Influence of Light Spectra on the Production of Cannabinoids

• LED lighting affects the composition and biological activity of Cannabis sativa secondary metabolites

• Cannabinoids accumulation in hemp (Cannabis sativa L) plants under LED light spectra and their discrete role as a stress marker

• Optimization of Cannabis Grows Using Fourier Transform Mid-Infrared Spectroscopy

• Energy Use by the Indoor Cannabis Industry: Inconvenient Truths for Producers, Consumers, and Policymakers

• Cannabis cultivation: Methodological issues for obtaining medical-grade product

• Vegetative propagation of cannabis by stem cuttings:effects of leaf number, cutting position, rooting hormone, and leaf tip removal

• THE EFFECTS OF LIGHT SPECTRA ON THE GROWTH AND DEVELOPMENT OF GREENHOUSE CBD HEMP

• Factors determining yield and quality of illicit indoor cannabis (Cannabis spp.) production

• The Effect of Electrical Lighting Power and Irradiance on Indoor-Grown Cannabis Potency and Yield

• Photoperiodic Response of In Vitro Cannabis sativa Plants

• Improving Cannabis Bud Quality and Yield with Subcanopy Lighting

• Light dependence of photosynthesis and water vapor exchange characteristics in different high Δ9-THC yielding varieties of Cannabis sativa L.

• The Genetic Structure of Marijuana and Hemp Canadian study on cannabis.

Basil lighting

• Unraveling the Role of Red:Blue LED Lights on Resource Use Efficiency and Nutritional Properties of Indoor Grown Sweet Basil

• The Growth and Development of Sweet Basil (Ocimum basilicum) and Bush Basil (Ocimum minimum) Grown under Three Light Regimes in a Controlled Environment

• Morphological and physiological response in green and purple basil plants (Ocimum basilicum) under different proportions of red, green, and blue LED lightings

• Response of Basil Growth and Morphology to Light Intensity and Spectrum in a Vertical Farm

• Optimal light intensity for sustainable water and energy use in indoor cultivation of lettuce and basil under red and blue LEDs

• Comparative Analysis of Horizontal and Vertical Decoupled Aquaponic Systems for Basil Production and Effect of Light Supplementation by LED

• Growth and Photosynthetic Capacity of Basil Grown for Indoor Gardening under Constant or Increasing Daily Light Integrals

• Morphological and Physiological Responses in Basil and Brassica Species to Different Proportions of Red, Blue, and Green Wavelengths in Indoor Vertical Farming

• Far-red radiation interacts with relative and absolute blue and red photon flux densities to regulate growth, morphology, and pigmentation of lettuce and basil seedlings

• The Impact of Blue and Red LED Lighting on Biomass Accumulation, Flavor Volatile Production, and Nutrient Uptake in Accumulation, Flavor Volatile Production, and Nutrient Uptake in Hydroponically Grown Genovese Basil Hydroponically Grown Genovese Basil Master thesis

• Basil plants grown under intermittent light stress in a small-scale indoor environment: Introducing energy demand reduction intelligent technologies

Lettuce lighting

• Increasing Growth of Lettuce and Mizuna under Sole-Source LED Lighting Using Longer Photoperiods with the Same Daily Light Integral

• TEN YEARS OF HYDROPONIC LETTUCE RESEARCH

• Resource use efficiency of indoor lettuce (Lactuca sativa L.) cultivation as affected by red:blue ratio provided by LED lighting

• Spectral Quality of Light Can Affect Energy Consumption and Energy-use Efficiency of Electrical Lighting in Indoor Lettuce Farming

• LED lighting and seasonality effects antioxidant properties of baby leaf lettuce

• Blue Light-emitting Diode Light Irradiation of Seedlings Improves Seedling Quality and Growth after Transplanting in Red Leaf Lettuce

• The effects of red, blue, and white light-emitting diodes on the growth, development, and edible quality of hydroponically grown lettuce (Lactuca sativa L. var. capitata)

• Growth and nutritional properties of lettuce affected by mixed irradiation of white and supplemental light provided by light-emitting diode

• Optimal light intensity for sustainable water and energy use in indoor cultivation of lettuce and basil under red and blue LEDs

• Horticulture of lettuce (Lactuvasativa L.) using red and blue led with pulse lighting treatment and temperature control in SNAP hydroponics setup

• Metabolic Reprogramming in Leaf Lettuce Grown Under Different Light Quality and Intensity Conditions Using Narrow-Band LEDs

• LED pre-exposure shines a new light on drought tolerance complexity in lettuce (Lactuca sativa) and rocket (Eruca sativa)

• The Evaluation of Growth Performance, Photosynthetic Capacity, and Primary and Secondary Metabolite Content of Leaf Lettuce Grown under Limited Irradiation of Blue and Red LED Light in an Urban Plant Factory

• Application of supplementary white and pulsed light-emitting diodes to lettuce grown in a plant factory with artificial lighting

• Impact of sun-simulated white light and varied blue:red spectrums on the growth, morphology, development, and phytochemical content of green- and red-leaf lettuce at different growth stages

• Growing lettuce under multispectral light-emitting diodes lamps with adjustable light intensity

• The Effect of Red & Blue Rich LEDs vs Fluorescent Light on Lollo Rosso Lettuce Morphology and Physiology

• Only Extreme Fluctuations in Light Levels Reduce Lettuce Growth Under Sole Source Lighting

• Growth and Bioactive Compound Synthesis in Cultivated Lettuce Subject to Light-quality Changes

• Effects of intermittent light exposure with red and blue light emitting diodes on growth and carbohydrate accumulation of lettuce

• Effect of green light wavelength and intensity on photomorphogenesis and photosynthesis in Lactuca sativa

• Adding Far-Red to Red-Blue Light-Emitting Diode Light Promotes Yield of Lettuce at Different Planting Densities

• LIGHT SPECTRAL QUALITY ON PRODUCTION OF LETTUCE, CUCUMBER AND SWEET PEPPER SEEDLINGS

• PRODUCTIVITY AND COST PERFORMANCE OF LETTUCE PRODUCTION IN A PLANT FACTORY USING VARIOUS LIGHT-EMITTING-DIODES OF DIFFERENT SPECTRA

• Photoperiod and light intensity influence on hydroponically grown leaf lettuce

• Impact of a shift in the light spectrum on lettuce growth. Simulation of sunrise/sunset using adjustable monochromatic LED light Bachelor thesis

• Effect of End-of-production High-energy Radiation on Nutritional Quality of Indoor-grown Red-leaf Lettuce

• Minimum Light Requirements for Indoor Gardening of Lettuce

• Predicting Lettuce Canopy Photosynthesis with Statistical and Neural Network Models

Tomato lighting

• Response of photosynthetic capacity of tomato leaves to different LED light wavelength

• Effects of Continuous or End-of-Day Far-Red Light on Tomato Plant Growth, Morphology, Light Absorption, and Fruit Production

• Growth of Impatiens, Petunia, Salvia, and Tomato Seedlings under Blue, Green, and Red Light-emitting Diodes

• Adding Blue to Red Supplemental Light Increases Biomass and Yield of Greenhouse-Grown Tomatoes, but Only to an Optimum

• The role of monochromatic red and blue light in tomato early photomorphogenesis and photosynthetic traits

• The Effect of Spectral Quality on Daily Patterns of Gas Exchange, Biomass Gain, and Water-Use-Efficiency in Tomatoes and Lisianthus: An Assessment of Whole Plant Measurements

• Far-red radiation increases dry mass partitioning to fruits but reduces Botrytis cinerea resistance in tomato

• Effect of monochromatic UV-A LED irradiation on the growth of tomato seedlings

• Supplementary Far-Red Light Did Not Affect Tomato Plant Growth or Yield under Mediterranean Greenhouse Conditions

• Ultraviolet-A Radiation Stimulates Growth of Indoor Cultivated Tomato (Solanum lycopersicum) Seedlings

• Effects of Red Light Night Break Treatment on Growth and Flowering of Tomato Plants

• Mixed red and blue light promotes ripening and improves quality of tomato fruit by influencing melatonin content

Pepper lighting

• Physiological responses of pepper seedlings to various ratios of blue, green, and red light using LED lamps

• Alternating high and low intensity of blue light affects PSII photochemistry and raises the contents of carotenoids and anthocyanins in pepper leaves

• Comparative Study of Color, Pungency, and Biochemical Composition in Chili Pepper (Capsicum annuum) Under Different Light-emitting Diode Treatments

• Effects of red and blue light on leaf anatomy, CO2 assimilation and the photosynthetic electron transport capacity of sweet pepper (Capsicum annuum L.) seedlings

• Physiological responses of cucumber seedlings under different blue and red photon flux ratios using LEDs

Light Measurement, LED Grow Light Systems, and Spectral Characteristics

last update: March 2021

main papers link page

SAG's Plant Lighting Guide main page

light meters and measurement

• Measuring Daily Light Integral in a Greenhouse-- Torres, Lopez

• Using a Simple Leaf Color Chart to Estimate Leaf and Canopy Chlorophyll a Content in Maize (Zeamays) -discussion on a low cost calibration standard.

• Maximum Spectral Luminous Efficacy of White Light-- Murphy 2013 -efficiency, efficacy, and how CRI and CCT plays a role

• Light Meter for Measuring Photosynthetically Active Radiation-- Kutschera, Lamb 2018

• Accuracy of quantum sensors measuring yield photon flux and photosynthetic photon flux-- Barnes et al 1993

• Sources of errors in measurements of PAR-- Ross, Sulev 1999

• Accurate PAR Measurement: Comparison of Eight Quantum Sensor Models

• Effects of radiation quality, intensity, and duration on photosynthesis and growth

• An easy estimate of the PPFD for a plant illuminated with white LEDs: 1000 lx = 15 μmol/s/m2-- Sharakshane ‎2018

• Design of Photosynthetically Active Radiation Sensor-- Dilip et al 2018

• Construction and Testing of an Inexpensive PAR Sensor-- Fielder, Comeau 2000

• Comparison of Quantum Sensors with Different Spectral Sensitivities

• Light Meter for Measuring Photosynthetically Active Radiation Arduino

• Development of Simple Band-Spectral Pyranometer and Quantum Meter Using Photovoltaic Cells and Bandpass Filters

• Instruments for the Measurement of Photosynthetically Active Radiation and Red, Far-Red and Blue Light

• A cheap quantum sensor using a gallium arsenide photodiode

• Photometric, Radiometric, and Quantum Light Units of Measure A Review of Procedures for Interconversion

LED grow lights and systems

• From physics to fixtures to food: current and potential LED efficacy

• LED Lighting Systems for Horticulture: Business Growth and Global Distribution PhD thesis

• Exploration on Using Light-Emitting Diode Spectra to Improve the Quality and Yield of Micro greens in Controlled Environments PhD thesis

• Influence of Light-Emitting Diodes (LEDs) on Light Sensing and Signaling Networks in Plants

• Light-Emitting Diodes for Horticulture

• Current status and recent achievements in the field of horticulture with the use of light-emitting diodes (LEDs) 2018

• Comparison and perspective of conventional and LED lighting for photobiology and industry applications

• A Numerical and Experimental Study of a Novel Heat Sink Design for Natural Convection Cooling of LED Grow Lights

• Design of a Scalable and Optimized LED Grow-light System Driven by a High Efficiency DC-DC Power Converter master thesis

• Polychromatic Supplemental Lighting from underneath Canopy Is More Effective to Enhance Tomato Plant Development by Improving Leaf Photosynthesis and Stomatal Regulation

• Plant Productivity in Response to LED Lighting

• Efficiency of an alternative LED-based grow light system

• Design and Implementation of Artificial Grow Light for Germination and Vegetative Growth six channel wireless

• A whole-plant chamber system for parallel gas exchange measurements of Arabidopsis and other herbaceous species

• Analysis of the Uniformity of Light in a Plant Growth Chamber

• Analyses of multi-color plant-growth light sources in achieving maximum photosynthesis efficiencies with enhanced color qualities

• Improving “color rendering” of LED lighting for the growth of lettuce

• Optimization of LED Lighting and Quality Evaluation of Romaine Lettuce Grown in An Innovative Indoor Cultivation System

• Vertical Production of ‘Konstancin’ Rose Cuttings in the Growth Chamber Under Led Light

• Effects of HPS and LED lighting on cucumber leaf photosynthesis, light quality penetration and temperature in the canopy, plant morphology and yield

• Impacts of LED spectral quality on leafy vegetables: Productivity closely linked to photosynthetic performance or associated with leaf traits?

• Leaf Morphology, Photosynthetic Performance, Chlorophyll Fluorescence, Stomatal Development of Lettuce (Lactuca sativa L.) Exposed to Different Ratios of Red Light to Blue Light

• Nighttime Supplemental LED Inter-lighting Improves Growth and Yield of Single-Truss Tomatoes by Enhancing Photosynthesis in Both Winter and Summer

• LED lighting efficacy: Status and directions

• Photosynthetic and growth responses of green and purple basil plants under different spectral compositions

• Morphological and physiological response in green and purple basil plants (Ocimum basilicum) under different proportions of red, green, and blue LED lightings

• Reaching Natural Growth: Light Quality Effects on Plant Performance in Indoor Growth Facilities

• Optimizing LED lighting for space plant growth unit: Joint effects of photon flux density, red to white ratios and intermittent light pulses

• White, blue and red LED lighting on growth, morphology and accumulation of flavonoid compounds in leafy greens

• Alternating Red and Blue Light-Emitting Diodes Allows for Injury-Free Tomato Production With Continuous Lighting

• Combination of Red and Blue Lights Improved the Growth and Development of Eggplant (Solanum melongena L.) Seedlings by Regulating Photosynthesis

• Supplemental LED inter-lighting compensates for a shortage of light for plant growth and yield under the lack of sunshine

• Uncovering LED light effects on plant growth: new angles and perspectives – LED light for improving plant growth, nutrition and energy-use efficiency

• Light-emitting Diode Light Transmission through Leaf Tissue of Seven Different Crops

• Continuous white LED lighting increases chlorophyll content (SPAD), green LED light reduces the infection rate of lettuce during storage and shelf-life conditions

• Effect of the Spectral Quality and Intensity of Light-emitting Diodes on Several Horticultural Crops

• Improving Winter Growth in the Citrus Nursery with LED and HPS Supplemental Lighting

• Analysis of Environmental Effects on Leaf Temperature under Sunlight, High Pressure Sodium and Light Emitting Diodes

• Comparison and perspective of conventional and LED lighting for photobiology and industry applications

• Effect of the Intensity and Spectral Quality of LED Light on Yield and Nitrate Accumulation in Vegetables

• Almost everything you want to know about LEDs

• LED and HID Horticultural Luminaire Testing Report

• Horticultural lighting system optimalization: A review

• Artificial-Light Culture in Protected Ground Plant Growing: Photosynthesis, Photomorphogenesis, and Prospects of LED Application

• Seeing the lights for leafy greens in indoor vertical farming

• Modelling Environmental Burdens of Indoor-Grown Vegetables and Herbs as Affected by Red and Blue LED Lighting

• Optimal light intensity for sustainable water and energy use in indoor cultivation of lettuce and basil under red and blue LEDs

• Energy savings in greenhouses by transition from high-pressure sodium to LED lighting

• Estimating the quantum requirements for plant growth and related electricity demand for LED lighting systems

• UV Lighting in Horticulture: A Sustainable Tool for Improving Production Quality and Food Safety

• Minimizing Electricity Cost through Smart Lighting Control for Indoor Plant Factories

• 2014 Paper analyzing the cost benefit of LED horticultural lighting

Spectral measurements and characteristics

• Spectral Effects of Artificial Light on Plant Physiology and Secondary Metabolism: A Review

• Application of a low-cost RGB sensor to detect basil (Ocimum basilicum L.) nutritional status at pilot scale level Arduino

• Nitrogen Deficiency Level Assessment Device for Rice (Oryza sativa L.) and Maize (Zea mays L.) using Classification Algorithm-based Spectrophotometry Arduino

• [The Photochemical Reflectance Index

(PRI) – a measure of photosynthetic light-use efficiency](https://hyspiri.jpl.nasa.gov/downloads/2010_Symposium/09-Gamon-PRI.pdf)

• Photochemical reflectance index (PRI) and remote sensing of plant CO2 uptake

• Radiation measurement for plant ecophysiology

• Relationships between leaf pigment content and spectral reflectance across a wide range of species, leaf structures and developmental stages

• Application of Spectral Remote Sensing for Agronomic Decisions

• [Neural-network model for estimating leaf chlorophyll

concentration in rice under stress from heavy metals using four spectral indices](https://www.researchgate.net/publication/221088946_Estimating_leaf_chlorophyll_content_of_rice_under_heavy_metal_stress_using_neural_network_model)

• Biophysical & physicochemical methods for analyzing plants in vivo and in situ

• [Chlorophyll a: b Ratio Increases Under Low-light in ‘Shade-tolerant’

Euglena gracilis](https://www.researchgate.net/publication/285634885_Chlorophyll_a_b_Ratio_Increases_Under_Low-light_in_'Shade-tolerant'_Euglena_gracilis)

• [Nondestructive Estimation of Anthocyanin

Content in Grapevine Leaves](https://calmit.unl.edu/people/agitelson2/pdf/2009/2009-AJEV.pdf)

• [Reflectance spectral features and non-destructive estimation of

chlorophyll, carotenoid and anthocyanin content in apple fruit](https://www.researchgate.net/publication/222515624_Reflectance_spectral_features_and_non-destructive_estimation_of_chlorophyll_carotenoid_and_anhocyanin_content_in_apple_fruit)

• [In situ measurement of leaf chlorophyll concentration:

analysis of the optical/absolute relationship](https://onlinelibrary.wiley.com/doi/pdf/10.1111/pce.12324)

• Spectral signatures of photosynthesis I: Review of Earth organisms

• The Secret Beauty of Ultraviolet Radiation in Plants

• Higher plants and UV-B radiation: balancing damage, repair and acclimation

Open Access Scientific Literature (more than just plant lighting)

part of SAG's Plant Lighting Guide

last update: 19 july 2024- added far red 2024 page

• far red papers 2024

Links by subject and video series

• cannabis links

• cannabis links part 2 all from 2022

• cannabis links part 3 first half of 2023

• Light meters, LED grow lights systems, and spectral characteristics

• Cannabis, lettuce, basil, tomato, and pepper plant specific lighting

• Arduino links for the botanist

• Far red light, blue light, green light, and photosynthesis studies

• Machine vision and learning

• Miscellaneous links (50 aeroponics papers added)

• Chlorophyll fluorescence and NDVI -measure photosynthesis rates in real time and monitor plant health

• Bruce Bugbee's (Utah State) YouTube channel -This is one of the few scientifically credible plant lighting resources on YouTube.

• Apogee Instruments YouTube channel -This is also one of the few scientifically credible plant lighting resources on YouTube.

Non-lighting open access papers

• TEMPEST and compromised emissions >100 papers

• Directed energy weapons >200 papers

• wildlife tracking, harmonic radar, energy harvesting >120 papers

Quick links to some favorite papers/videos

• Toward an Optimal Spectral Quality for Plant Growth and Development -YouTube. This is the very basics by Bruce Bugbee, Utah State

• Cannabis Grow Lighting Myths and FAQs with Dr. Bruce Bugbee -YouTube.

• From physics to fixtures to food: current and potential LED efficacy -This paper clearly articulates the theoretical limits of LED grow lights and a great read for anyone into building them. From paper: *"With current LED technology, the calculations indicate efficacy limits of

3.4 µmol J−1 for white + red fixtures, and 4.1 µmol J−1 for blue + red fixtures"*

• [THE ACTION SPECTRUM, ABSORPTANCE AND QUANTUM YIELD

OF PHOTOSYNTHESIS IN CROP PLANTS](http://www.esalq.usp.br/lepse/imgs/conteudo_thumb/mini/The-action-spectrum-absorptance-and-quantum-yield-of-photosynthesis-in-crop-plants.pdf). This is the McCree curve used in botany (fig 14). It's the average CO2 uptake (quantum yield) by wavelength for 22 different plant type leaf samples at lower PPFD levels (15-150 µmol/m2/sec or so) and in monochromatic light, not multiwavelength or white light. This paper is only the starting point on understanding photosynthesis rates by wavelength, however, anyone that has anything to do with plant lighting should at least know what the McCree curve is.

• [Why are higher plants green? Evolution of the higher plant

photosynthetic pigment complement](https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3040.2000.00563.x) -This is a fairly easy read and very thorough.

• Green Light Drives Leaf Photosynthesis More Efficiently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are Green -This paper gets in to why green light can have a higher photosynthesis rate at high lighting levels due to green light being able to penetrate deeper in to leaf tissue.

• When there is too much light -This is what's going on with the photosystems at too high of lighting levels.

• Optics of sunlit water drops on leaves: conditions under which sunburn is possible -most non-waxy hair plants like cannabis are not going to burn from water droplets on a leaf

• Florigen in cannabis -flowering at a protein level is still an active area of research

• Shape Matters: Plant Architecture Affects Chemical Uniformity in Large-Size Medical Cannabis Plants -topping the plant and the like for greater yield. Some of these concepts may not apply to really tiny plant growth chambers like with space buckets.

• Pot size matters: A meta-analysis of the effects of rooting volume on plant growth -for every doubling of soil container size/root mass, we get 40-50% greater yield all else being the same.

• Debunking a myth: plant consciousness -plants are not conscious and we should not anthropomorphize them. "Plant neurobiology" is pseudoscience.

Spectrum charts, conversion factors, and color ratios of the Bridgelux COB array LEDs

updated 11 June 2020

part of SAG's Plant Lighting Guide

Using a lux meter as a plant light meter (only use a lux meter with white light sources)

The conversion factor is luminous flux (lux) to photosynthetic photon flux density (PPFD) in uMol/m2/sec (micro moles per square meter per second) of PAR (photosynthetic active radiation 400-700 nm). This is so that low cost lux meters can be used as plant lighting meters.

The color ratios will not add up to 100. Blue is 400-499 nm, green is 500-599 nm, red is 600-699nm, far red is 700-799nm.

This is the second order derivative of the Bridgelux phosphors. This was specifically a CRI 97 COB. Each of the major downward dips is a different phosphor and is way more complex than I thought it would be. The saturated one on the far left is the phosphor pump blue LED (the wavelength is downshifted or shifted to the right slightly with this technique). Derivative spectroscopy is a powerful analytical chemistry technique that allows one to look at chlorophyll A and B separately in living leaves in vivo, for example, that may not show up very well if at all with more traditional spectroscopy techniques in vivo.

The average wavelength of phosphor pump blue LEDs in my samples was about 453.5 nm.

Vero 10's, Vero 18's and Vero 29's were tested here. In many cases multiple samples of the same phosphor type were tested.

The below backs my claim that you can use 70 lux = 1 umol/m2/sec for CRI 80, and 63 lux = 1 umol/m2/sec for CRI 90 and be within 10%. That 1750K LED is an exception.

1750K cri 80 -This is an oddball LED

lux to PPFD conversion factor: 49 lux = 1 uMol/m2/sec

blue:08....green:25....red:57....far red:06

2000K cri 65

lux to PPFD conversion factor: 70 lux = 1 uMol/m2/sec

blue:05....green:41....red:49....far red:02

2700K cri 80

lux to PPFD conversion factor: 72 lux = 1 uMol/m2/sec

blue:11....green:42....red:36....far red:02

2700K cri 90

lux to PPFD conversion factor: 63 lux = 1 uMol/m2/sec

blue:06....green:19....red:22....far red:02

3000K cri 80

lux to PPFD conversion factor: 73 lux = 1 uMol/m2/sec

blue:16....green:45....red:37....far red:02

3000K cri 90

lux to PPFD conversion factor: 65 lux = 1 uMol/m2/sec

blue:09....green:22....red:23....far red:02

3000K cri 97

lux to PPFD conversion factor: 59 lux = 1 uMol/m2/sec

blue:14....green:36....red:41....far red:04

3500K cri 80

lux to PPFD conversion factor: 74 lux = 1 uMol/m2/sec

blue:20....green:47....red:31....far red:01

4000K cri 80

lux to PPFD conversion factor: 74 lux = 1 uMol/m2/sec

blue:11....green:24....red:14....far red:01

4000K cri 90

lux to PPFD conversion factor: 68 lux = 1 uMol/m2/sec

blue:20....green:40....red:31....far red:02

5000k cri 70

lux to PPFD conversion factor: 75 lux = 1 uMol/m2/sec

blue:13....green:22....red:09....far red:01

5000K cri 80

lux to PPFD conversion factor: 76 lux = 1 uMol/m2/sec

blue:26....green:50....red:21....far red:01

A strong warning about removing the domes from LED light bulbs by an actual electrician.