Replacing the screen with glass or plexi glass is really the way to go though, if you can swing it. The screen will eventually rust and get nasty from all the humidity.

Those led's Paul directed you to are good for cheapies. I have been using them about 4 months and I like them. They could have a better color spectrum, IMHO.

Just a note on Paul's comment. Incandescent and some cfl's will drain the tank of humidity, but true florescents won't. The lights don't throw off much heat, maybe a few degrees. The red heating bulb will definitely heat the air up and kill off humidity.