From what I can remember when I used tubes, they don't get very hot at all, nothing like the CFL's do. I know I used to get mine almost right up to them. And there were times that I'd come home and find the plants into the lights, and they didn't seem to be burnt nearly as bad as the CFL's burn. But in general, keep them about an inch or two away, just keep an eye on them till you know a good spot.