How close to the water can the light sit without a lid?

[jassz]

Hi all. Not sure what forum to post this in, but as I have a FOWLR I'll try it here.

I have a six foot aquarium with a ballast that holds 2 30 inch lights that rests on the edges of the tank. At the moment there is a glass lid, but I hate the thing and most of the time the light is trying to shine through 2 layers of salt covered glass (as I usually have it slid open because it doesn't slide all that well). I thought there'd be a standard mounting leg for the light, but there seems to be no such thing, which means custom making one. But I wonder if it wouldn't be okay to just have it sitting on the edge without the glass (it sits about 2 inches from the water level). Or, if I do make a stand for it, how high should it sit?

Thanks,