distance

I am currently using the ZooMed 10.0 T8 18" tube light for my baby Russian tortoise's enclosure. It is about 15" away from him, which is as close as I can get due to the size of the tank. Is that an ok distance or too far? Would a reflector help if it's too far? Thanks!

So I came back from NYC last night to find Rusky's heat lamp dead. He had not eaten and had buried himself deep underground. It was a special reptile Exo Terra one, and now I realize that I only need a regular incandescent flood. This is the second time my heat lamp has gone in two months. What...