Are you referring to UVA or UVB?

UVB puts out very little heat. I doubt it would damage your frog in any way...might actually be good for him as long as you don't use one as strong as a 10.0!

UVA found in regular incandescent light bulbs again is not harmful but will produce a lot of heat. This could be a problem if it dries out your substrate.

If you must use a nightlight then black/purple are best because frogs can see the red lights.

Honestly I think heat pads attached to the side of the tank are the safest form of heating a frog enclosure...maybe add a second one for additional heat?