they get hot to so make sure there about 1foot-1.5feet above the tank, my tank i have a glass top and a plastic support beam on top it cracked the glass top and started to melt the beam when i fist put it on lol
If your tank is open top and large enough the heat generated won't really be that much of a problem. On my 75 I've got 2 250w MH only about 4-5 inches above the water and my temp doesn't go up at all during the day.