it is working perfectly. its not hot enough to melt. its sitting on the black plastic top of the light fixture. which that is plastic so I'm sure its made for the heat of the bulb. there is a little vent that the heat comes out of on top of the fixture and I have it on that. there is another one on the other side. I don't have that one covered. it is working perfectlY! I think I'll start my tomatoes this way too when the peppers are done sprouting
Sheila, gardening on the zone 4b/5a line.