More THC testing – UVA vs UVB vs near-UV

end_of_the_tunnel said:

Interesting.

Mold Reduction with UVB+A — AgricUltra™ Advancements

UV lighting allows facilities to operate with a greater margin of safety, reducing intervention costs, and, in some cases, avoiding the need to replace poorly designed HVAC systems. UV extended curing times allow growers to elevate the art of Cannabis curing to the same level as a coveted cigar, o

www.agricultra.com

Seems like the quote comes from their pest control page. A possibility is that 295 might not reverse flowering? As you read on, they give references to literature. But near end of page mention that experimentation on effects on various types of insects. Leaves a lot open for interpretation, and suggests it is a speculative comment based off of research from others work.

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Flowering in short-day plants is triggered by the Pr : Pfr ratio at the end of the dark period. If there is more Pr – which has been converted from Pfr during the dark period – then that indicates a long night and triggers flowering as a photomorphogenic response.

I would think that, looking at the following graph, both Pr and Pfr receptors absorb UVR8 equally, but if you look at the UVA spectrum, then it appears Pfr aborption peaks at 405nm whilst Pr peaks at around 375nm. So for flowering 405nm would compliment Pfr – which is converted to Pr overnight and would promote flowering – whereas 375nm (in the absense of 405nm) would inhibit it.

That would be my initial conclusion, but I would have to read more into it to be convinced.

Grow Lights Australia said:

Hi, sorry for not replying to you earlier but we've had a busy couple of weeks and I haven't been posting much lately.

We would recommend using it full cycle. 390-410nm is pretty much in the visible spectrum and does not carry as much energy as deep UVA or UVB, so we'd expect it to have similar results to the small amount of 400-430nm we have in our High Light boards. In fact, we're trialling some new LEDs at the moment and in one of the trials we've added about double the dose of 400-430nm compared to the current High Lights to see how it impacts cannabinoid yields. The trial is being conducted using the same strain and under the same conditions as those used at the start of this thread.

So far there does not appear to be any damage to the plants or any real down side. The same boards were used to veg the plants prior to flower, and the grower said they were the healthiest he had ever grown under LED. We suspected the vegging plants could take a good amout of UV, as there is more UV present in sunlight during the summer months when cannabis grows outside prior to flowering. We note some growers follow nature in adding UV to their vegging plants also.

As soon as we get the test results we'll let you know.

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Much appreciated! Please do keep us updated! Awesome work you guys are doing!

Grow Lights Australia said:

Flowering in short-day plants is triggered by the Pr : Pfr ratio at the end of the dark period. If there is more Pr – which has been converted from Pfr during the dark period – then that indicates a long night and triggers flowering as a photomorphogenic response.

I would think that, looking at the following graph, both Pr and Pfr receptors absorb UVR8 equally, but if you look at the UVA spectrum, then it appears Pfr aborption peaks at 405nm whilst Pr peaks at around 375nm. So for flowering 405nm would compliment Pfr – which is converted to Pr overnight and would promote flowering – whereas 375nm (in the absense of 405nm) would inhibit it.

That would be my initial conclusion, but I would have to read more into it to be convinced.

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I was replying this quote originally. "the UV effect can be had for up to 20 hours crossing the visible cycle and night cycles." Kassiopeija first referenced it. I was surprised so went and found where he got it from and posted a link to page. It is from their pest control page info page. Which means they are talking about duration of effects on insects.

Not the plants. I think Kassiopeija might have misinterpreted the statement he read on their webpage? Hence my mentioning 285 (tongue in cheek) with a question mark, to query his thinking. I do not think using any wavelengths during lights out makes any sense.

Interesting image. Seen it before. I have never considered what you propose. If what you meant to say was UVB, rather than UVR8. (UVR8 is a receptor.) Certainly food for thought.

end_of_the_tunnel said:

I was replying this quote originally. "the UV effect can be had for up to 20 hours crossing the visible cycle and night cycles." Kassiopeija first referenced it. I was surprised so went and found where he got it from and posted a link to page. It is from their pest control page info page. Which means they are talking about duration of effects on insects.

Not the plants. I think Kassiopeija might have misinterpreted the statement he read on their webpage? Hence my mentioning 285 (tongue in cheek) with a question mark, to query his thinking. I do not think using any wavelengths during lights out makes any sense.

Interesting image. Seen it before. I have never considered what you propose. If what you meant to say was UVB, rather than UVR8. (UVR8 is a receptor.) Certainly food for thought.

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If you look at the UVR8 receptor peak, it appears Pfr and Pr both follow it. I'm not sure if they peak at the same wavelength as the UVR8 receptor, and the lines cut out because that's the limit of measurement, but that's what I was alluding to (285nm). Poor choice of language on my part.

You are giving them too much Blue wavelength and why these results are showing. The plant only needs a maximum of 15% Blue. Studies show this to be true.

twistedwords said:

You are giving them too much Blue wavelength and why these results are showing. The plant only needs a maximum of 15% Blue. Studies show this to be true.

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Hi, our High Light UV boards are 14.3% blue. Is that what you were talking about? I take it you are referring to "maximum 15% blue" in flower? We also tend to agree that 10-15% blue is optimal for flowering based on some of the studies we have seen.

Grow Lights Australia said:

Hi, our High Light UV boards are 14.3% blue. Is that what you were talking about? I take it you are referring to "maximum 15% blue" in flower? We also tend to agree that 10-15% blue is optimal for flowering based on some of the studies we have seen.

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You have it backwards...During VEG you go 15% blue. Then the last half of flower you turn up the blue.

Here is a study for you to look at!

twistedwords said:

You are giving them too much Blue wavelength and why these results are showing. The plant only needs a maximum of 15% Blue. Studies show this to be true.

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twistedwords said:

You have it backwards...During VEG you go 15% blue. Then the last half of flower you turn up the blue.

Here is a study for you to look at!

Leaf photosynthetic rate, growth, and morphology of lettuce under different fractions of red, blue, and green light from light-emitting diodes (LEDs) | Semantic Scholar

Current LED-based artificial lights for crop cultivation consist of red and blue lights because these spectra effectively promote leaf photosynthesis. However, the absence of green light could be disadvantageous for crop production, as green light plays an important role in plant development...

www.semanticscholar.org

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You mentioned 15% blue max in your first post. I don't understand what you mean about their results? Their results and tests are pretty clear. What seems to be wrong?

Then, you said to turn up the blue during last half of flower? Aren't you contradicting yourself?

Just trying to understand what you really mean. No offense intended.

twistedwords said:

You have it backwards...During VEG you go 15% blue. Then the last half of flower you turn up the blue.

Here is a study for you to look at!

Leaf photosynthetic rate, growth, and morphology of lettuce under different fractions of red, blue, and green light from light-emitting diodes (LEDs) | Semantic Scholar

Current LED-based artificial lights for crop cultivation consist of red and blue lights because these spectra effectively promote leaf photosynthesis. However, the absence of green light could be disadvantageous for crop production, as green light plays an important role in plant development...

www.semanticscholar.org

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Interesting article, but unfortunately most of the growers here are not growing lettuce – they are flowering cannabis.

What is the point of adding more blue during flower and what advantage does it have over near-UV (400-430nm)?

Have you done any cannabinoid testing to confirm your theory?

How does the above study into RGB lighting of lettuce correspond with full-spectrum lighitng of cannabis? We're always open to discussion and learning new things so would love to hear your theories.

twistedwords said:

You have it backwards...During VEG you go 15% blue. Then the last half of flower you turn up the blue.

Here is a study for you to look at!

Leaf photosynthetic rate, growth, and morphology of lettuce under different fractions of red, blue, and green light from light-emitting diodes (LEDs) | Semantic Scholar

Current LED-based artificial lights for crop cultivation consist of red and blue lights because these spectra effectively promote leaf photosynthesis. However, the absence of green light could be disadvantageous for crop production, as green light plays an important role in plant development...

www.semanticscholar.org

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one of the "results" of this study is funny:

" the addition of green light (...) reduced the leaf photosynthetic rate, it did not reduce plant growth."

Its bc of the photomorphogenetic response, where lettuce reacts differently than hemp, a lot.
Also, look at the ppfd used...

Kassiopeija said:

one of the "results" of this study is funny:

" the addition of green light (...) reduced the leaf photosynthetic rate, it did not reduce plant growth."

Its bc of the photomorphogenetic response, where lettuce reacts differently than hemp, a lot.
Also, look at the ppfd used...

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Yes, we noticed that study was done at 150 PPFD vs 800-1000 PPFD typically used for growing cannabis.

Also, lettuce is a Long Day plant and cannabis is a Short Day plant, so their flowering cycles are manifestly different.

Still, I would like to hear @twistedwords theory as he says he has read many studies. We're all for sharing knowledge.

twistedwords said:

You have it backwards...During VEG you go 15% blue. Then the last half of flower you turn up the blue.

Here is a study for you to look at!

Leaf photosynthetic rate, growth, and morphology of lettuce under different fractions of red, blue, and green light from light-emitting diodes (LEDs) | Semantic Scholar

Current LED-based artificial lights for crop cultivation consist of red and blue lights because these spectra effectively promote leaf photosynthesis. However, the absence of green light could be disadvantageous for crop production, as green light plays an important role in plant development...

www.semanticscholar.org

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not everyone here grows lettuce...

Somebody say Lettuce?

Grow Lights Australia said:

Yes, we noticed that study was done at 150 PPFD vs 800-1000 PPFD typically used for growing cannabis.

Also, lettuce is a Long Day plant and cannabis is a Short Day plant, so their flowering cycles are manifestly different.

Still, I would like to hear @twistedwords theory as he says he has read many studies. We're all for sharing knowledge.

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Personal grow knowledge (30 years) as it works. I struggled with much more blue and short stumpy plants. One day later dialing it down to 15% and it works.

Rosenthal didn't have what we know know.

800-1000 PPFD can be too much during flowering it depends on which light cycle you are using...Which one are you using? How far are your lights from the canopy top and bottom?

Also what is your light intensity reading?

Much more than PPFD...

Lastly have been doing it this way for 20 years. I add a reptile light the last 3 weeks for UVB for only 3 hours at a time as that is all that is needed for the flowering and only during the light cycle. I have heard people leaving it on 24/7 and not needed, still do not understand that.

UVB is a response from the plant to defend itself against the UVB and it produces more resin to coat itself, like what we do with sunscreen. Although too much can diminish the results as it will spend its time defending and not flowering/fruiting...

IR is where it is at and we are learning more about it every year.

For the lettuce comment, here is a study for tomatoes using blue...

twistedwords said:

Personal grow knowledge (30 years) as it works. I struggled with much more blue and short stumpy plants. One day later dialing it down to 15% and it works.

Rosenthal didn't have what we know know.

800-1000 PPFD can be too much during flowering it depends on which light cycle you are using...Which one are you using? How far are your lights from the canopy top and bottom?

Also what is your light intensity reading?

Much more than PPFD...

[3 Easy Tips] How to Fix your LED Spectrum for Flowering Plants – The Green Sunshine Company

Welcome! My name is Dan, and I’m excited you’re here. I study the science of photobiology and let me tell you, not many grow lights out there are giving your ...

thegreensunshineco.com

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Hi, 800-1000 PPFD at 12/12 is typically what a lot of growers here are using, although it should be noted that spot readings of around 1000 PPFD often translate to an average 800 (more or less) PPFD across the entire canopy depending on light spread and uniformity.

Now are you referring to DLI (typically around 40+ for cannabis) and if so what light cycle do you use? Some of our customers do use 11/13 for sativas and may adjust their lights accordingly up to 1100-1200 PPFD. We also understand that sativas can handle more light than indicas but many things are strain dependent and supplementary CO2 can also facilitate a significant increase in PAR up to 1400-1500 PPFD.

What instruments do you use to measure your spectrum? I'm assuming you haven't been growing with LED for 30 years, so how do you "dial down" blue? You must be measuring it somehow.

twistedwords said:

One day later dialing it down to 15% and it works.

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When you say "it works" do you mean it increases cannabinoid content as we have shown earlier in this thread? Did you measure it before and after with a baseline measurement similar to what we have been doing?

PPFD is measured at the canopy and is a function of light output, distance and reflection etc so I'm also trying to understand what you mean by the following.

twistedwords said:

How far are your lights from the canopy top and bottom?

Also what is your light intensity reading?


Much more than PPFD...

Click to expand...

How do you measure your light if not in PPFD? What metric do you use? Whatever distance your lights, PPFD is still PPFD.

If you are referring to Biological Photon Flux then perhaps it's just a matter of semantics. We understand that plants use light outside the normal 400-700nm range and some PAR meters also read YPFD (Yield Photon Flux Density) with typical ranges from 380-780nm. We do measure this and point out that our lights actually have a higher YPFD than other white-phosphor LEDs, as our High Light UV spectrum has about 5% far red as well as a small amount of 400-430nm not typically found in white phosphors. (Far red is generally defined as 700-800nm, which you have referred to as infrared)

On that note, the link you provided is interesting:
It is for a company that produces LED lights. I have copied the spectrum on their website and noticed that the light spectrum (nm) scale may have been modified slightly. I've drawn a line through 450nm, which is where most blue pumps peak (445-455nm). It may just be an error. Otherwise it is a nice looking spectrum and appears to have an interesting mix of phosphor coated red (PC Red) LEDs with possibly 2700K CRI90 and 3000K CRI80 white. I am just guessing.

It is not that different to our own spectrum – the main difference being their lack of near-UV but addition of more red and slightly more far red. But otherwise we appear to be going down similar paths.

twistedwords said:

Lastly have been doing it this way for 20 years. I add a reptile light the last 3 weeks for UVB for only 3 hours at a time as that is all that is needed for the flowering and only during the light cycle. I have heard people leaving it on 24/7 and not needed, still do not understand that.

UVB is a response from the plant to defend itself against the UVB and it produces more resin to coat itself, like what we do with sunscreen. Although too much can diminish the results as it will spend its time defending and not flowering/fruiting...

IR is where it is at and we are learning more about it every year.

For the lettuce comment, here is a study for tomatoes using blue...

Frontiers | Adding Blue to Red Supplemental Light Increases Biomass and Yield of Greenhouse-Grown Tomatoes, but Only to an Optimum

Greenhouse crop production in northern countries often relies heavily on supplemental lighting for year-round yield and product quality. Among the different ...

www.frontiersin.org

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It is not just UVB that stresses the plant, but also UVA, near-UV and blue light. Studies have shown that all these spectra have the ability to increase cannabinoid content, which is what we are exloring in this thread. I am not sure if you have read the entire thread but we have covered some of these areas already.

Did you notice on Page 1 that we compared the same strain grown under different lights including reptile bulbs? Have you done any cannabinoid testing to compare your results? Sorry I think I asked you this already.

I'm not sure about that tomato study as it appears to be based on supplementary LED light with sunlight. I could not find overall figures for combined sunlight and LED (maybe I missed it). Sunlight changes throughout the day, weather, altitude and seasons.

I hope it does not appear that I am picking on your posts, I am just trying to learn anything that we have not already covered as it is a very broad subject and all information and opinions are welcome. Our understanding of science is constantly changing and we hope threads like this can help us achieve new outcomes.

Grow Lights Australia said:

We understand that plants use light outside the normal 400-700nm range and some PAR meters also read YPFD (Yield Photon Flux Density) with typical ranges from 380-780nm.

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Hey GLA thanks for pointing this out, I've not heard of this before but spent the mourning with reading... actually the link @twistedwords provided held some really good & well-researched articles, esp. on some of the physical aspects of light & spectrum. Unfortunately the guy doesn't differentiate between the different "buildplans" prevalent in todays plants, as the response to spectra may alter.... but that could be the only thing I've found so far on that...

Do you perhaps know more about what happens with 360-400nm photons when they hit the plant? Do they reach specific (which?) antennae-complexes and are able to participate to exzitate an electron in PS II? We know that FR is able to do this in PS I, and because these photons do actually partake in photosynthesis they actually are a part of "PAR". I wonder if the same could be said from violett rays?

BTW how do you manage to have the green spike in your spectrum? I've looked at lots of LED spectras lately, and there exists basically 2 different "types", one that basically has a huge gap between 490-580, and those that fill that at least with 30-50% of the max. But yours is actually even a bit more pronounced, you have a green mono there in the mix?

Is there much information out there, separating UVA and UVB? It seems most of the time the two are intermixed in some level, but being as there is more damage potential with UVB, what about just running UVA vs UVA+UVB?

I know there is a lot of research into Far Red right now (Seems to have a lot of shaping ability), been reading up a lot on what Dr. Bruce Bugbee has to say on the topic, but in my limited experience it seems any time someone talks about UV spectrums in general it seems to be nearUV-UVB. Obviously noone wants any 100-290 C in there.

Grow Lights Australia said:

It is not just UVB that stresses the plant, but also UVA, near-UV and blue light. Studies have shown that all these spectra have the ability to increase cannabinoid content, which is what we are exloring in this thread. I am not sure if you have read the entire thread but we have covered some of these areas already.

Did you notice on Page 1 that we compared the same strain grown under different lights including reptile bulbs? Have you done any cannabinoid testing to compare your results? Sorry I think I asked you this already.

I'm not sure about that tomato study as it appears to be based on supplementary LED light with sunlight. I could not find overall figures for combined sunlight and LED (maybe I missed it). Sunlight changes throughout the day, weather, altitude and seasons.

I hope it does not appear that I am picking on your posts, I am just trying to learn anything that we have not already covered as it is a very broad subject and all information and opinions are welcome. Our understanding of science is constantly changing and we hope threads like this can help us achieve new outcomes.

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Not a problem. IMHO I keep seeing everyone trying to use a very old study on plant spectrum done in the 1970's. No one knows if that old graph is even correct. It was theoretical and not done with applied lighting because it doesn't exist. I am not picking on your lights, I am going by many years of experience.

Yes I did read your thread and your results from the analysis, but as you pointed out the grower said that it could have been from too much UV which I have seen as well with experience.

Have you tried a different spectrum of your own? One that you came up with instead up journals? Sometimes outside the box works.