I've always had trouble with black lights dying on me, whether they're used for tanks or just decoration around the house they tend not to last long. I've tried the fluorescent and cfl black lights and they do seem to last a lot longer but tend not to be as bright. So instead when I want some kind of at-night lighting I use the green or blue colored cfl's. They're plenty bright enough for dark lighting. Green has been my favorite so far
I do miss it having since tinfoiled the top of the tank.
If your concern is keeping the tank hot enough, what have you done to insulate it? I thought about lining the sides & back of my tank with natural cork tile this past winter but ultimately didn't need to. Insulating the sides, doing the tin foil treatment, and having under tank heating should do a lot to keep things ok at night.