thats a very good question:hi mate i would be a touch worried about a metal halide underneath but i would try it anyway!!! lol. if it looks like its not beneficial take it out. have you seen the envirolites? i ask because in danthebull's journal he using them for additional lighting and i think they are pretty decent. very economical and they kick off no extra heat. oh inked are you in any way worried about electricity? i am using 1400 watts of light and all the extra's (fans,pumps etc) and im a little paranoid about how much we can use before the bacon knock on the door. do you know whats seen as legit? i want to start using 2400 watts but im wondering wether its wise. what do you reckon?