Well... once ive read (dont remember where... possibly in erowid.org) that the THC was meant to protect the cannabis plant from the heat... and that was the reason because weed from hotter climates had a higher percentage of THC in it. But as heat and UV radiation are both from the sun, maybe its the UV radiation which increases the THC production... i dont know... anyway, your experiment is very interesting... when you have conclusive results, i think it would be nice to post the results on the cultivation sub-forums, so everybody would benefit from your discovery.