Switching Heat lamp to UTH

[MandyGurl]

So I have always heard to use a heat lamp for leopard geckos. The guy at the pet store who is suppose to be an expert told me that. After reading on here, I have decided to switch to a UTH. But do I put it on just one side of the tank or under the whole tank?

 

[Russ S]

you want it to cover about 1/3 of the tank on one end of the bottom.