In short, the ideal leaf surface temperature depends on the species / variety of the plant, overall environmental conditions, as well as what the plant is being grown for. Only experimentation can determine an ideal range for LST for a specific plant variety in a specific set of conditions."
Re: What distance should my light be from my plants?
That is a complicated Question you should check with the manufacture of your lights. But the guy above me is wrong the optumum leaf temperature is no where close as a matter of fact if you take that advice and keep your leaf temps at 70...