Mine are setup in a track lighting rail. I have 4 50 watt GU10 floods on gooseneck fixtures so that I can adjust the distance & direction to the basking spot. In the case of my enclosure, it does heat the entire enclosure. My temps range from 130F basking surface temp. to 85F-ish ambient in the middle, to 75F-ish ambient on the cool end.
If you're going to use full size (PAR38 or so) flood lights, they do make full size bulb fixtures for track lighting still, but you may have to do some looking. The only ones I've found recently are discontinued models at Menards.