I think he is referring to a university study:
"UV-B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH AND CANNABINOID PRODUCTION OF TWO Cannabis Sativa CHEMOTYPES."
What they forget to mention is that that test used a very high dose of UV to reach that maximum result. 72W/m2 of UV bulb. With a pretty much linear relation between UV light intensity and THC delta (pun intended). So if you use a lot less then the effect is a lot less too.
Now what would happen if you add 72W of regular light per m2? You might get say 20% more yield. Not sure I'd take a THC increase over a yield increase.
Plus I wonder if the plants don't yield less because of the UV. If you make them struggle to survive the UV for a THC response, wont that detract from actual yields. Don't remember if the article mentioned something about that.
See, now that does not sound like something "beneficial" to me. Its obvious that UV is damaging to plants - and as Wietefras points out, gains in potency would likely be offset by yield loss. I've said before, the evidence *is* compelling, but IMO, it falls short of being convincing.
See below, buddies! UVB cause nothing bad as long as you don't use too much and burn them their ass off.
The highest ever measured UVB radiation was measured in the Andes below an ozone hole, over 580μW / cm². It's probably too much but 300-400μW / cm² with 15 / 45min cycles should be safe.
Each and every outdoor plants gets some UVB. Let's take a mexican sativa grow near Mexico City, 2000m above zero, UV-Index is 12-14 in summer, that's ~300-350μW/cm²(factor 25) or 35mW/m² for 4-5h evey day. In Miami Florida they can get the same level. Even fiber hemp is not badly affected by UVB and there is no trichome layer filtering UVB on such strains.
The test are done with a UVB dose of 6,7 and 13,4kJ/m2, that's ~155 and ~310μW/s/cm² for 12h. That's a lot! My current reptile bulb is ~120-180μW/cm² at 1' distance and the only thing that was different than usual was more foxtailing and higher trichome density.
Test results Bluedream with and without UVB are done with Indagro Pontoon (2x 4ft bulbs per 4x 4', running for 15min/hour) and their latest LED fixture. Sorry, no link! But I've found them when I inquired about the UVB pontoons.
One of the old dutch guru's, I believe Jack Herer*), told in one of his books about fiber hemp that they brought fiber hemp to Jamaica. After a few generations trichomes began to form again and they adapt to the new enviroment. He assumed that at latitudes with low UV radiation each hemp species loses potency over time and the opposite happens when it gets more UV light. I still tend to believe that as the more I think of it the more sense does it make.
I had my 39w tube running about 50% of the time, say 6h per day, that's about 15kw / h in 9 weeks. I could have used 20w more white but my 440w fixture is anyway too strong for my small 2x 4' area. So in my situation it makes no sense to add more light but adding UVB does make sense. When you consistently pull good results and max yield per area the only thing left is to add some UVB to get a better product.
*)The Emperor's New Clothes or Why the Hemp Cultivation Should Be Legalized. At least that's the title when translated from my language
BTW, the test were done 1987, todays UVB bulbs like the PureUV from Agromax are much stronger. With 54w you got 440μW/cm² above a 2x 4' area(0,84m²) that would be 370μW/cm² above 1m2. For a dose of 13,4kJ/m²(higher dose in the test) you need ~310μW/s/cm² for ~12h. With 12h á 370μW/s/cm² the dose would be 16kJ/m².
