There is quite a bit of evidence that "more" UV-B produces more resin - but resin isn't THC, and THC is what gets you high (resin just makes you cough)! Resin is made up of many compounds, a few of these are cannabinoids, one of these cannabinoids is THC (Delta-9, Tetra-hydo-cannabinol).
There is no conclusive evidence or reliable research source that states "More UV-B will produce more THC or more potent Marijuana". I say this because I know, I tried to find this evidence - but it ain't there!!! There is an abundance of anecdotal evidence by "questionable people" who would have you believe they are experts, people who have no real expertise at stake. Most of the real experts tred lightly on this subject and suggest something wimpy like "it's commonly believed -blah-blah-blah!".
Cannibis is the only plant that produces THC in reasonable amounts, and nobody knows why! Of course there are theories, but nobody knows for sure! There are also a lot of theories about how to maximize the potency of cannibis, but it all comes down to 2 things:
1. Genetics.
2. Allowing the plant to reach it's full potential. In other words, big, strong, healthy plants produce big, strong, potent yields!
The Controversy goes on!