Those critter keepers are too small to be heated with an overhead light, it is going to get very warm and dry in there. You are better off heating one end (1/4-1/3 of the enclosure) with an under tank heater (such as a 3 or 4 inch heat tape on a thermostat set to (88-91F) so he can thermoregulate. Good luck.

-T.J.