Uvb is a part of thc production. It influences most plants that use a similar defense to uvb and environment. Anecdotally, its noticeable when you add uvb to just hps(and probably more so with led). We're not totally sure of plant mechanisms, but we're reasonably certain that trichomes and thc and
terpenes specifically are part of cannabis' defense to heat, water loss, uvb damage from the sun, insect and herbivore defense, and potentially even part of affecting the surrounding soil and plants. It seems likely to me that uvb exposure could be a limiting factor to thc production. Theoretically, a certain amount of uvb exposure is required to allow the genetics to express their full genetic cannabinoid and terpene content. Anecdotally, people do comment often about quality increase just from switching to cmh from old hid bulbs and i believe this is due to greater uvb exposure.
I have studied about this for a couple of years now and I have compared quality of my favorite plants grown under 600w
Hortilux super hps and the Phillips 315 lec and at first I thought the quality was higher with the 315. Looked frostier and seemed to have a “special” high.
When I went back to hps only the quality actually seemed higher. Patients were picking the hps bud blind 3 to 1.
We don’t lab test anymore but ed rosenthal already proved uv increases thc in his book years ago. But he was growing outdoor land race strains indoors.
But he also proved higher wattage produced more potent marijuana.
I think it may not as positively effect strains bred indoors under hps as much. The breeder of my seeds has grown and bred under hps since the early 90’s or even earlier.
And I also think many hyped up reports of cmh only may be due to cooler temps and better plant health due to the full spectrum. And also some hype due to growing under the more natural light. The first time I moved a plant from under the hps to the cmh I was like “whoa” it looks so much frostier.
I also got almost a half pound more yield with the 600 hps every test.
Also the depth of quality buds is much deeper with hps over the 315. Almost have to use sog or scrog to keep the buds in range.
Also the more blue in the spectrum limits stretch and grows much leafier plants.
My best results were using 2 600’s to 1 315 cmh. Very much the same results as 2 hps to 1 metal halide.
When I rebuild I plan to include both.
