I have one 15-watt cool-white Sylvania flourescant tube. It is placed almost directly on top of a transparent plastic cover. The cover is scratched up a bit. I let the light run from about 8 am to 10 pm? I have the VFT in a ten-gallon terrarium that is placed near a westward-facing window, but it gets very few, if any, direct sunlight. I live in the suburbs of Chicago. As any more information needed? Any help and advice is very much appreciated.