https://www.solacure.com/exuvandca.html
"When a plant is outside, they get a fair amount of UVA and UVB, typically in a ratio that is around 5% UVB and 95% UVA"
"It takes more than just random UVB. We have found certain frequencies of UVB make the plant react more vigorously than others.
We have reason to believe that UVA is also beneficial. While it doesn't stimulate THC production, it penetrates much more deeply than UVB and may stimulated trichome production, which makes THC possible. This is why we have UVB lights with multiple "soft" peaks at the right frequencies, as well as strong UVA output in exactly the same part of the spectrum that the sun is strongest at. This gives you a sun-like glass tube that you control."