every one says the repti sun needs to cover half the tank and needs to be 6-8 inches away to work. I believe though that if it is a on the basking spot 6-8 inches away it can be any size you want. Cause most of the majority of the membors here have one thing 6-8 inches away from the uvb which is the basking spot. so why waste money on a bigger bulb if it will not be used for its full use? how would it do any thing 6-8 inches away if nothing is that close to it?