That could very well be an issue. I don't have personal experience with that, but halogen bulbs do throw a lot of heat. An LED would be far better.
I actually bought this one in December: http://www.brushymountainbeefarm.com...oductinfo/239/
It seems okay, but not super great quality - it appears to be built in Russia. I'll give it a go this spring. My son tried it and said he could see the bottom of the cells better without it - but of course 10 year old eyes can count the hairs on a flea.