Latest UVA vs UVB cannabinoid test results

Grow Lights Australia said:

We've done a bit of UV testing. In fact, LED Teknik has done a lot of real-world testing of UV diodes and the tested efficiencies have ranged from 40% up to more than 70%. Efficiency has almost as much to do with the wavelength as it does the manufacturer. For example wavelengths around 395-405nm tend to be most efficient and then drop off as you get to higher wavelengths until you hit about 450nm. They also drop off below 395nm.

The most efficient UV diodes LED Teknik has tested are the new Nichia 405s (3535 format) which came in at around 71-72%. We looked at including these on our High Light 420 boards, but to include one high-power UV diode we'd need to remove one of the 660s. We'd also need to include a Seoul Semiconductor or another type of purple pump white phosphor mid-popwer (3030) LED to get the 405-430nm range up. After we did all that, board efficiency was still about the same as it is now, but with less red and a heavier UV rating. We may still produce a few boards in this configuration for those who want extra UV, but what we're learning is that when it comes to UV, a little goes a long way so you don't need that much.

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Have y’all ever tested higher uva and noticed undesirable or negligible results?

budman410 said:

Have y’all ever tested higher uva and noticed undesirable or negligible results?

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We haven't tested larger percentages of UVA so haven't really seen any undesirable results, although we have read reports of too much UVA stunting growth and too much UVB causing significant tissue damage.

One disadvantage to running a lot of high UVA is the loss of photon efficiency. If you know a bit about Planck's Law you will know that even if you use a UV light (400nm) of 70% energy efficiency, the photon count will be lower than a 660nm red light of the same energy efficiency.

Grow Lights Australia said:

We haven't tested larger percentages of UVA so haven't really seen any undesirable results, although we have read reports of too much UVA stunting growth and too much UVB causing significant tissue damage.

One disadvantage to running a lot of high UVA is the loss of photon efficiency. If you know a bit about Planck's Law you will know that even if you use a UV light (400nm) of 70% energy efficiency, the photon count will be lower than a 660nm red light of the same energy efficiency.

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I think I’ve read something similar. Keep up the great work. I’ve been trying to balance efficiency, purpose, and balancing what’s enough or to much. Most respites of what uva can do have been hearsay with no basis in research. I could say under the reds and uva I have running now my plants look more frosty then the last run without uva but it’s hard to gauge. So I’m sure we are all grateful for y’all sharing your info your getting and it’s surely great for your company

Grow Lights Australia said:

Thanks for the link. It is unfortunate that Professor Bugbee does not go into much detail in that video and seems more interested in promoting Apogee Instruments than actually explaining what UVB and UVA do to plants.

One thing that is not always taken into account is the fact that while UVB does stress the plant into producing secondary metabolites, it also destroys them. This is in addition to causing DNA damage to plants with large doses.

The most interesting thing we've noted in these experiments is that in all cases the UVB plants have higher levels of CBG and CBGa, which are the precursors to other cannabinoids. However the UVB plants also all had lower levels of overall cannabinoids including THC and CBD which leads us to believe that UVB may be effective in increasing cannabinoids, but it is also destroying them at the same time. Perhaps that is what Professor Bugbee meant when he said it was "tricky" – that there is a fine balance between stressing a plant into producing more secondary metabolites and breaking down those same secondary metabolites once produced.

The other conclusion we are starting to draw is that while UVA, near-UV and deep blue are less effective at producing cannabinoid precursors, they don't break down the final product as fast, which means more cannabinoids remain after harvest. In other words UVA and near-UV stress the plant into producing more cannabinoids than they can break down, unlike UVB which breaks down them down at a much faster rate.

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Hey mate, nice write-up as usual. I was just looking at those figures and I think you'll find that in the Afghan-Skunk samples, the CBG levels were lower in the UVB grown buds. You're right about the other samples, but that particular A1 sample was lower across the board. It surprised me a bit as I collected all those samples and delivered them for testing. I also grew the first sample A and was surprised that my sample was almost identical to the other grower's. Maybe I shouldn't be that surprised, because he modelled his grow on mine, but it's still interesting that the same strain grown under the same lights – even by different growers – can be so close in results. I think my sample was a little bit older, but that was about the only difference.

The big surprise was that there wasn't much difference between the Cheesecake samples grown under UVB and the High LIght 420 boards with UVA, as this sort of goes against the other tests we've done. When I picked the samples, I tried to make sure they were as close to their respective lights as I could find, but I'm now wondering if there was a bit too much overlap betwen the lights. Having different lights in the same tent divided by tall plants is not the most scientific test so I might have a chat with the grower to see if we can come up with something better, like a divider film or something between the two grows. At least we know the UVA isn't losing out to the UVB.

I've posted this before, but some people here might be interested to know that my Afghan-Skunk sample came from this particular plant:

MidnightSun72 said:

First let me say thank you.
I absolutely love these posts.

This video is relevant as the researchers found it difficult to get the amount of UV correct. 1 UVB photon has 100X the energy of a UVA photon. Basically what I understood is you can use UVA UVB or UVC. But you have to adjust the dose. In the video he says they run UVB for a few hours and UVC for only seconds and still burns plants.

UVA is a lot easier on plants and humans and you can run them long/bright enough to achieve a similar effect in dose.

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I haven't got anything against Bugbee spruiking Apogee PAR meters, but I agree with GLA that he doesn't go into a lot of detail in his videos. They seem to be more directed towards novice growers who may not know the basics. I can't say I've learned that much from watching his videos . . . except how to use the 1.5x speed function on YouTube, lol! Sometimes I crank his videos up to 2x just so I can sit through them. I wonder if he's smoked a lot of pot like me, lol! But at least I don't talk that slow!

Prawn Connery said:

Hey mate, nice write-up as usual. I was just looking at those figures and I think you'll find that in the Afghan-Skunk samples, the CBG levels were lower in the UVB grown buds. You're right about the other samples, but that particular A1 sample was lower across the board. It surprised me a bit as I collected all those samples and delivered them for testing. I also grew the first sample A and was surprised that my sample was almost identical to the other grower's. Maybe I shouldn't be that surprised, because he modelled his grow on mine, but it's still interesting that the same strain grown under the same lights – even by different growers – can be so close in results. I think my sample was a little bit older, but that was about the only difference.

The big surprise was that there wasn't much difference between the Cheesecake samples grown under UVB and the High LIght 420 boards with UVA, as this sort of goes against the other tests we've done. When I picked the samples, I tried to make sure they were as close to their respective lights as I could find, but I'm now wondering if there was a bit too much overlap betwen the lights. Having different lights in the same tent divided by tall plants is not the most scientific test so I might have a chat with the grower to see if we can come up with something better, like a divider film or something between the two grows. At least we know the UVA isn't losing out to the UVB.

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You're right but I think it might be an anomoly as it is the only UVB sample we've teted so far that had lower CBG levels than the UVA samples.

The purple's nice but I noticed the sampled wasn't purple. Did you hide the good stuff?

Grow Lights Australia said:

You're right but I think it might be an anomoly as it is the only UVB sample we've teted so far that had lower CBG levels than the UVA samples.

The purple's nice but I noticed the sampled wasn't purple. Did you hide the good stuff?

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LOL! They were purple when harvested but as you know, they lost their colour in the cure. I can assure you it was the same sample.

Little update on the highlights with the arcadia uvb bulb. Sorry for the blurry pic of the whole tent, snapped em right before lights went out on me. Figured I'd just throw a couple updates on it in case anyone was interested.

The top of the bigger plant definitely stressed a little bit more than any lowers, but really liking how they are finishing. Hopefully not too much longer.

loco41 said:

Little update on the highlights with the arcadia uvb bulb. Sorry for the blurry pic of the whole tent, snapped em right before lights went out on me. Figured I'd just throw a couple updates on it in case anyone was interested.

The top of the bigger plant definitely stressed a little bit more than any lowers, but really liking how they are finishing. Hopefully not too much longer.

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Wow, nice colours! They might give Prawn's a run for their money

Hey guys, loving the experiments and the data they're producing!

How come the tests are being done with the Arcadia 6% UVB Bulb? Surely something designed for horticulture with a better spectrum including more UVB would be more appropriate? I've had what I think is some pretty good success with running the Migro UVB-310 for a couple hours a day in late flowering.

Also, if your hypothesis that higher levels of UVB are encouraging the production of cannabinoids but then destroying those cannabinoids; do you think that it would be possible to find the exact right amount of UVB radiation to subject your plants to before turning them off in order to maximize cannabinoid production but minimize destruction? Or perhaps even stop running the UVB in the last week of flowering?

plebschmo said:

Hey guys, loving the experiments and the data they're producing!

How come the tests are being done with the Arcadia 6% UVB Bulb? Surely something designed for horticulture with a better spectrum including more UVB would be more appropriate? I've had what I think is some pretty good success with running the Migro UVB-310 for a couple hours a day in late flowering.

Also, if your hypothesis that higher levels of UVB are encouraging the production of cannabinoids but then destroying those cannabinoids; do you think that it would be possible to find the exact right amount of UVB radiation to subject your plants to before turning them off in order to maximize cannabinoid production but minimize destruction? Or perhaps even stop running the UVB in the last week of flowering?

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This would be very strain dependent, probably impossible to find a general limit.
The 6% is usually used for longer hours and lower hanging height than the pure uvb tube. Maybe repeated shorter bursts of uvb could be a way forward.

Rocket Soul said:

This would be very strain dependent, probably impossible to find a general limit.

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Possibly with regards to the production of cannabinoids but certainly not with regards to the degredation of already produced cannabinoids as one is a biological process and the other a chemical process. Do you have any evidence to back this claim up or is this just a hypothesis?

Rocket Soul said:

The 6% is usually used for longer hours and lower hanging height than the pure uvb tube. Maybe repeated shorter bursts of uvb could be a way forward.

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I'm using a 310UVB globe and I run it for between 2 - 2.5 hours in the first 3 of the last 4 weeks of flower. AFAIK the most common theory as to why UVB increasaes cannabinoid production is that the plant is producing it as a form of sunscreen to protect itself from the UVB radiation - this is allegedly why cannabis grown at higher alitutudes is more potent and may suggest why it is a good idea to run high UVB for only a couple of hours a day - to mimmic the sun's increase in UVB as it is directly above us in the sky.

So what I don't understand is why a 6% UVB being used all day? Is there a different theory/thought behind this and why not just use a 310nm UVB globe instead?

plebschmo said:

Hey guys, loving the experiments and the data they're producing!

How come the tests are being done with the Arcadia 6% UVB Bulb? Surely something designed for horticulture with a better spectrum including more UVB would be more appropriate? I've had what I think is some pretty good success with running the Migro UVB-310 for a couple hours a day in late flowering.

Also, if your hypothesis that higher levels of UVB are encouraging the production of cannabinoids but then destroying those cannabinoids; do you think that it would be possible to find the exact right amount of UVB radiation to subject your plants to before turning them off in order to maximize cannabinoid production but minimize destruction? Or perhaps even stop running the UVB in the last week of flowering?

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Rocket Soul said:

This would be very strain dependent, probably impossible to find a general limit.
The 6% is usually used for longer hours and lower hanging height than the pure uvb tube. Maybe repeated shorter bursts of uvb could be a way forward.

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Hi guys I'm sorry I missed this earlier. @Rocket Soul is correct: the grower has his lights lower and he uses the fluros as supplemental light for longer periods. He thought it better to err on the side of caution with UVB because he figured he could always run them a bit longer if the UVB component was not as strong. Also, he was trying to match the percetange of UVB found in sunlight when it reaches the earth. I can't remember the calulation, but it was pretty close. I think it is documented in one of the other UVB threads we have running.

It's also worth remembering that fluro reptile bulbs have some other useful spectra, which can supplement LED, including UVA (365nm), near-UV (405nm) and chlorophyl abosorbed 430nm – which most LEDs do not have. Looking at the whole picture, its's not a bad supplement when paired with our original High Red boards that have alot of red and far red in them but lack UV and light below 440nm. Here is the Arcadia spectrum I am talking about.

plebschmo said:

Possibly with regards to the production of cannabinoids but certainly not with regards to the degredation of already produced cannabinoids as one is a biological process and the other a chemical process. Do you have any evidence to back this claim up or is this just a hypothesis?



I'm using a 310UVB globe and I run it for between 2 - 2.5 hours in the first 3 of the last 4 weeks of flower. AFAIK the most common theory as to why UVB increasaes cannabinoid production is that the plant is producing it as a form of sunscreen to protect itself from the UVB radiation - this is allegedly why cannabis grown at higher alitutudes is more potent and may suggest why it is a good idea to run high UVB for only a couple of hours a day - to mimmic the sun's increase in UVB as it is directly above us in the sky.

So what I don't understand is why a 6% UVB being used all day? Is there a different theory/thought behind this and why not just use a 310nm UVB globe instead?

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You may be correct that the best way to utilise UVB is to run it for short periods to stress the plant into producing secondary metabilites, and then turn it off or dim it to prevet those same metabolites from degrading. I still think @Rocket Soul has a good point, because while cannabis originally evolved as an equatorial species in the tropics, it was transported around the world and grown in different places where it evolved into other sub-species.

UVB levels seem to greatly differ and are not always highest around the equator due to the thicker atmosphere. Remember also that in the highlands of Central Asia at higher lattitudes, daylight hours (and UVB exposure) can be greater (summer) or less (winter) than those around the Equator, which are very close to 12/12 (12.5/11.5 actually) for most of the year.

Grow Lights Australia said:

You may be correct that the best way to utilise UVB is to run it for short periods to stress the plant into producing secondary metabilites, and then turn it off or dim it to prevet those same metabolites from degrading. I still think @Rocket Soul has a good point, because while cannabis originally evolved as an equatorial species in the tropics, it was transported around the world and grown in different places where it evolved into other sub-species.

UVB levels seem to greatly differ and are not always highest around the equator due to the thicker atmosphere. Remember also that in the highlands of Central Asia at higher lattitudes, daylight hours (and UVB exposure) can be greater (summer) or less (winter) than those around the Equator, which are very close to 12/12 (12.5/11.5 actually) for most of the year.

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More than "where" geographically I'm thinking about jungle (under canopy, low uv situation) and southern facing mountain side at high altitude.

Re "short bursts" of uvb: fluros lose output, as do all lights, but like many bulbs they are especially susceptible to being fired up and turned on. With a short bursts regiment it maybe be better to run uvb leds in the long run: no turn on decay. Covid has changed the market quite a bit for uv leds (although mainly for uvc) and prices have dropped quite a bit for those who've been thinking about adding uvb thru leds. @nachooo runs uvb leds, 4x15mw over a meter, with good results.

@Grow Lights Australia and @Prawn Connery (why is tagging not working standard today???) :
I remember someone, probably one of you, who posted something on one of the uv threads: a study in uvb supp done by growers on another forum, I wanna say German or Chech; IIRC the results was 5mw per square foot was the ideal amount of uvb per square foot. Ring any bells anyone? Please repost

Yes I can't remember the thread and I think it was @Prawn Connery who posted it, but it rings a bell and is the post I was talking about.

For "short bursts" they could maybe be for 2-3 hours a day continuous, which is the same as turning the on/off once a day.

If we can find someone running UVB like @plebschmo we'd be happy to run a side-by-side test. UVB does seem to impact yields so that is another consideration.

This is purely anecdotal based on personal experience but I started out with UVB only and had some burn trying to figure everything out. I added 4 x 10k+UVA bulbs for the next cycle and it allowed me to burst UVB at a higher clip. I'm guessing there is some synergy going on with UVA + UVB. I'm currently running clones in another tent to compare at the end of this cycle.

magnetik said:

This is purely anecdotal based on personal experience but I started out with UVB only and had some burn trying to figure everything out. I added 4 x 10k+UVA bulbs for the next cycle and it allowed me to burst UVB at a higher clip. I'm guessing there is some synergy going on with UVA + UVB. I'm currently running clones in another tent to compare at the end of this cycle.

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We'd love to hear your results if you can post them up. It may be that UVA "hardens" the plant in preparation for UVB exposure as natural sunlight contains both. We also have to remember that cannabis has been selectively bred under HPS for 30 years or more, and that those genetics may not have been exposed to UVA or UVB as HPS has almost no UV at all. Ourdoor genetics might be the secret here.

We have some new results for our High Light 420 Gen2 panels. These panels have twice as much UVA in them as the original High Light 420 boards used in the first test of this thread. The results are very interesting. The old panels had a slight higher level of THCA compared to the double-UV boards, and they also had a higher level of CBD. But the old boards had no d9THC whereas the new boards had over 2.5%.

THCA is a precursor to d9THC so there is a conversion factor of .877 to calculate the total amount of d9THC in any sample. Once this conversion factor is done (THCA x .877 + d9THC = TOTAL d9THC), then it appears the new boards produced about 15% more d9THC, although they were down about 10% in terms of CBD.

I have extrapolated the sample results into a table below, but the originals are attached. The first report is the UV1 (original) sample and the second one is the UV2 (Gen2) sample. Both samples were grown in the same room under the same conditions at the same time with the same strain. The only difference was the light. The strain was "Big Bud" and I've attached some photos below. It is a high yielding strain with average potency.


SAMPLE.............CBD...........d9THC...........THCa............Total d9THC (after decarboxylation)

HL420.................1.21%........0.0%..............17.52%........15.37%


HL420 Gen2........1.08%........2.54%............17.36%........17.76%







The Original sample came from the plant on the left at the very back, while the Gen2 sample came from the plant on the right in the middle.