I don't want to contradict anyone because I am new at this but Mold does not need light. That is why it can grow on sheet rock behind wall paper, in your attic, on the 2x4's in your wall etc...
Light actually helps kill mold from what I have heard and read.
As for degrading your THC. I just read somewhere that light can degrade your THC up to 15%. Even indirect light. The examle I read was light shining through the jar you store your weed in will degrade the THC. However, you should do your own research cause Im drunk and for some reason my my memory is not what it once was.