how far from top of plant 250watt HPS?

I was woundering how far i should keep my 250w hps away from my plant?

20 inchs good luck and happy growing

you should not have to have your light 20 inches away unless you have major heat problems. I keep my 400 watter that isn't in a cool tube about 8 eight inches from the tops of my plants. Use your hand to tell if you put your hands over your plants and the heat from the light makes your hand uncomfortable move the light up two inches and try again until you get as close as you can without discomfort.

ok i will do that when i get my light