If you don't need a whole lot of light, you might consider going with an LED light that's made to be a 'moonlight' for a fish tank. I don't have them on my fish tank, but as I understand it, they put out no heat at all and use very little power. Here's a link to one in red. They also come in white and blue too.
Red LED light
You might use white for daytime viewing and red for nighttime.
Hope that helps!
-Janel