I rigged up 4 regular screw base lamp holders, like $1.50 each at Lowes, and am using the spirally compact fluorescents, not too difficult and i can find all different wattages or colour temperatures to use, the lid is white inside so that reflects the lights back, the lamps have ballasts in them and they get a little warm but it just means my heater pretty much only runs at night.
Rav