Actually, I just had a 100w equivalent CFL kicking around and it does fit... barely. It actually sticks out a tiny bit, but with the exo-terra the screen is indented a little bit so it fits great and it nice and bright. And I still have the other bulb that actually is 6500k in there so the plants will be happy? Lol I don't know if it actually works that way or not but it looks a thousand times better.