Curling leaves and discoloration/dried out leaves. It all depends on what kind of lights you have. T5s and cfls can be inches from a plant whereas you must keep higher wattage metal halide and hps much further away that that.
Your leaves curling/shriveling up. I dont let my HID lamp get any closer then 10"-12" from the top of my plants and thats with my fan blowing on the lamp to keep air moving around.