The most recent thing I read (or saw in a youtube video, more likely) is that you want the obscenely powerful fluoro tubes for UVB, but pulse them on/off for "short" intervals. By short, I got the impression they were talking about 5-10 minute periods, but it wasn't explicitly defined.
The powerful fluoros will burn the living fuck out of a plant, if left on for, oh, say about 4 hours. So don't "pulse" them that long. I think I'll try this method next.
I've seen this mentioned too, not tried it. I can kinda see it tho. You need X amount of UVR8 stimulation in a given day to create the response, but if you give it all at once, plants respond negatively and tissue burns.
I have burned the fuck out of my plants with 2X 40W floros in a 4x4 area. I'm sure I gave them skin cancer.
The other thing that I learned from Dennis - founder of
Solacure - UVB is not a thing. It is a spectrum. There is no such thing as a UVB light that produces only UVB at a specific wavelength. You get some above, and some below, including UVA. So the UVB bulbs all produce UVA too, but YMMV based on manufacturer, phospors and pigments used, etc. Any directions that say "Turn on UVB for X amount of time at X distance" should be taken with skepticism and perhaps used as a starting point, but the grower will have to adjust based on how the plants respond. These instructions may be wildly off for your genetics / growspace.
When it comes down to it, seems to me this is only for advanced growers that have everything else dialed in perfectly and plenty of experience to fall back on. New growers will probably only get frustrated, and there is no step by step manual on how to use this stuff.
From what I have read, studies have shown a max increase of 4% THC boost. Others show none or negative. It's a lot of work and risk for 4% IMO, and should be attempted after all the other normal grow improvements like CO2 are in place. I'd much rather have 20% more weed guaranteed than a chance at a THC boost.