Supplemental UV light questions

I am serious. Elucidating the pathway by which UV-B would increase THC in individual trichomes is the missing link and could lend much weight to the hypothesis that UV-B increases THC.

You suggestion isn’t without merit, but cryptochromes (CRYs) photoreceptors aren’t activated by (don’t perceive) UV-B spectrum; their action spectrum is primarily UV-A and blue-violet (315–500 nm). While UV RESISTANCE LOCUS 8 (UVR8) photoreceptors are activated by (perceive) UB-V (280-315 nm). And UVR8 is mainly used by plants to reduce damage to plant tissue and DNA by UV-B, not to increase secondary metabolite biosynthesis.

Cryptochrome = primarily UV-A and blue
UVR8 = primarily UV-B


Interesting paper.

Cryptochromes (CRYs) and UV RESISTANCE LOCUS 8 (UVR8) photoreceptors perceive UV-A/blue (315–500 nm) and UV-B (280–315 nm) radiation in plants, respectively. While the roles of CRYs and UVR8 have been studied in separate controlled-environment experiments, little is known about the interaction between these photoreceptors. Here, Arabidopsis wild-type Ler , CRYs and UVR8 photoreceptor mutants (uvr8-2 , cry1cry2 and cry1cry2uvr8-2 ), and a flavonoid biosynthesis-defective mutant (tt4 ) were grown in a sun simulator. Plants were exposed to filtered radiation for 17 d or for 6 h, to study the effects of blue, UV-A, and UV-B radiation. Both CRYs and UVR8 independently enabled growth and survival of plants under solar levels of UV, while their joint absence was lethal under UV-B. CRYs mediated gene expression under blue light. UVR8 mediated gene expression under UV-B radiation, and in the absence of CRYs, also under UV-A. This negative regulation of UVR8-mediated gene expression by CRYs was also observed for UV-B. The accumulation of flavonoids was also consistent with this interaction between CRYs and UVR8. In conclusion, we provide evidence for an antagonistic interaction between CRYs and UVR8 and a role of UVR8 in UV-A perception.


UV makes frost and thus bag appeal. In my experience smoking that flower, it seems to burn longer. I have no idea of the answer to your question about thc, but from just a consumer perspective, UV makes a better product.

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Nothing scientific to my results other than the results themselves. After several cycles and getting to a place that I consider dialed in, I like the increased yield and what visually appears to be increased trichome production. Next time around I will actually send a sample out to the lab for testing to see the difference (if any) from previous tests of that exact same pheno

Here is another benefit I would suggest people take into consideration. My old Kind K3 L600 had a 3 year warranty and I needed to utilize that often. Once the warranty ran out I started purchasing the LED Cluster Plates on line and repairing the lights myself. What I noticed was that almost all of the same diodes in the same location on the plates were what were burnt out and caused the entire plate to go out. Upon research I found that those particular diodes were the UV diodes on the plate.

My GC ROI e720’s have a 5 year warranty for the light but the UV bar only has 2… or maybe 3 year warranty. So when the UV bar burns out, it will not knock out the entire fixture… only the bar. Much cheaper to replace the bar (I think &180.00 for 2) than the entire fixture


We have tried a uvb 10.0 26 watt lamp for reptiles. Test results for checking flower shoots from the same tree The left side is exposed to uvb light and the right side is not exposed to uvb light. The examined flowers were both peaks.


It’s great you tried testing lamps. Unfortunately, your testing adds no value to this discussion and doesn’t show anything about UV-B effects on production of THC or other cannabinoids. Here are a few reasons why these data aren’t useful:

  1. That lamp you’re using provides UV-B, UV-A, and PAR range photons. It’s not a UV-B lamp.
  2. You used the same plant as the single test subject for both treatments.
  3. You didn’t use the scientific method.
  4. You didn’t use a control.
  5. You didn’t use a large enough sample size (i.e., n =1 gives us no statistical significance no matter what the result was).
  6. You only tested two apical inflorescence (not whole plant inflorescence)
  7. You didn’t report other environmental and cultivation conditions.
  8. You didn’t quantify instantaneous or diurnal net irradiance for UV-B, UV-A, and PAR; nor did you report irradiance uniformity. And if you used on the of the SolarMeter UV-B sensors you still didn’t quantify UV-B due to how that sensor weights UV-B and that its spectral response includes UV-A.
  9. And more…

Also, why aren’t the reports dated and signed? That’s odd.


It’s great you fell that way, but your claims (I’m assuming you mean UV-B and not UV-A), and the claims of others using UV-B, are not proven. Humans are terrible at trying to quantify differences in sample groups - our inherent (and unconscious) biases and an inability to use observation to accurately quantify differences are well known.

Assuming you meant UV-B, I would amend your post to say:

From my observation, UV-B might increase frost directly or indirectly (by reducing biomass), which, if true, can increase bag appeal based on visual trichomes. In my experience smoking that flower, it seems to burn longer. I have no idea of the answer to your question about thc, but from just a consumer perspective, I believe UV-B can make a better product even though it will reduce biomass yield, plant size, and growth rate; and causes many deleterious affects on cannabis growth if over applied.

@ralf won’t be a believer till Bugbee admits it. I promise you man, it’s more than par photons that contribute to cannabinoids production. PAR is very important, but it ain’t going to take you all the way…

Also what if I told you in my own personal experiments, you get the most out of a synergistic UV-a and UV-b.

The uvr8 cryptochrome, phytochrome have been my focus for a few years now, I even started writing something on accident and decided not to share my findings. You can simply search gene expression and what I started writing will come up.

Utilizing FR and UV you most deffinitly can control gene expression, specifically and most notably around morphology. Which in turns leads to more resin per/g without a substantial loss in total harvested biomass.

If you havent realized this yet, you haven’t done enough “scientific tests”

Sometimes I feel like Bugbee and the likes just can’t quantify the process so they say it’s “bro science” which is fine, because it is true, but there becomes a point where imperical evidence can’t be ignored.

Not sure why you’re dragging Bugbee into this when he hasn’t published any work on UV-B. I will believe there is an effect when enough scientific evidence and results show it is true.

Right now the science is strongly pointing to no effect on THC production from UV-B irradiation. There is a single study from 1987, which is extremely flawed, which found an increase in THC, but there are at least 3 studies from the past 5 years finding no benefit to THC production from UV-B.

You can promise all you want. And that may be good enough for you and others. I call that the “Cervantes Effect,” wherein someone makes factual claims based on their beliefs and opinions without scientific findings to support those claims. But for me, I want statistical proof before I make any definitive claims. To do otherwise is scientific malpractice and helps no one.

I get that you don’t want your strongly held belief to be challenged, but what you’re claiming is akin to what religious people claim: they don’t need proof because they just ‘know.’

Also, you once told me you never grow the same strain twice, and you grow from seed. Which means you have nothing to compare a UV-B treatment to (no control). And without a control we’re back to your strongly held belief.

What you’re providing isn’t useful empirical evidence, it’s just biased and uncontrolled observational opinion. There’s a HUGE difference.

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I would say this has been well known by scientists for decades, myself included. Heck, I’m the one who pointed out here that you need considerably more UV-A (and blue range photons) than UV-B to offset the negative effects of UV-B.

When I say I don’t grow the same thing twice. I mean I do not have a commercial schedule to pump out the “hottest new shit” to death.

This dosent mean I don’t grow the same thing twice, or grow the genetic in my environment and see it grown in dozens of other environments.

Imperical evidence becomes imperical evidence when an action causes an effect, and the result is observed over a broad spectrum of people.

Some people do science, and others follow it. Call me jesus

Fixed that for ya. <3

That’s true as well.

Also that was just my retort to his religion thing. I don’t have a complex or anything


Noted re: your strains.

All empirical evidence isn’t created equal. Empirical evidence through observation ≠ empirical evidence through measurement and quantification.

Why do you think your biased, unscientific observational empirical evidence is of more value than unbiased, peer-reviewed scientific method empirical evidence? It’s not. It’s just not.

Let me fix that for ya :wink:

Some people do science, some follow it, and others ignore it.

I am in the “do” and “follow” buckets.

But all that said, I love ya, @vortal. None of this is meant as a slight against you. It’s just a discussion of these topics.

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I try not to ever claim fact.

I offer as much factual info as I possibly can, and suggest serious experimentation based off my results.

When those actions are repeated, and the result is similar. It becomes strong imperical evidence in my mind.

No I can not quantify the metabolic pathway, or the biologic reactions that cause the increase in resin density, but it does increase resin density in all my experience, and when used in tandem with FR does not really effect the total harvest weight.


Well, whether it increased thc/cbd/cbn/cbg/etc or not i have no idea, but I have buds that have significantly higher trichome coverage from the same exact cuts that I just ran.

Whether or not they are more/less potent, i notice a visible difference with UV-A (no B added at all).

I also supplement with pr/fr diodes (approximately 7.5% additional pr/fr).

I suppose if I really wanted to I could test and see the difference.

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My supplements are UV-A, according to gavita and rapidled.

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As noted earlier, UV-A has many beneficial effects on cannabis, including likely increasing THC (although why such increase would occur is still to be elucidated). It’s absolutely worth adding UV-A if possible.

For example:
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

The way to figure out if UV-A range photons are causing what you’re perceiving as an increase trichrome density (rather than that increase caused by an increase photosynthetic photons from UV-A) is to repeat what you’re doing without UV-A. BUT, make sure the PPFD without UV-A treatment is equal to the PPFD + UV-A umol/s/m2 for the UV-A treatment. That way you’re accounting for the proven effect of increased PPFD (up to point) on increasing trichome density.

This is simple test and pretty inexpensive (less than $500-800). That’s why I keep going on about measurement being so important and visual observation alone being of much less value. Many methods of quantification can be done at home for relatively low cost by anyone…so, why aren’t more people doing this?

Just get a stereo microscope and a metal micrometer or compound microscope (with top lighting; when using a compound high power microscope an eyepiece reticle is used to make measurements).

Then, figure out your field of view (FOV) diameter (millimeter) and count the number of trichomes from your samples from a few flowers and sugar leafs. Then, covert the trichrome count to mm2 so you’re using the accepted definition of trichrome density. You can also use this method to measure the size of the trichrome heads, which may another useful measurement.



That makes sense and good to know :+1:

What models are you using? And have you had photomeric modeling of your space to estimate the UV-A intensity (umol/s/m2)?

I’m considering adding the UV-A LED bars from Fluence for 50 or 100 umol/s/m2 UV-A at >92% min/avg uniformity to a new commercial grow I’m about to fire up. I emailed Fluence to request a photometric model the other day.

Right now, in phase 1, the grow has two identical flowering rooms with 1000 DE HPS at 1200 PPFD with 96% min/avg uniformity over the entire room at final canopy plane. So I would add UV-A to one room and other identical room wouldn’t get UV-A, but, it would have the same PPFD as the UV-A room as PPFD + UV-A.

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Adding UV-A throughout the entire grow = good
Adding UV-B throughout the entire grow = not good (add it near the end of flowering phase)