i've got my 400watt mh (4 wks into 12/12) 6-8 inches from my tops, no cool tube, or glass... i do have an ac unit in the room, with a fan blowing the cooled air up at the light, and when i place my hand at the same level as the tops of my plants, it doesn't feel uncomfortable. i'm sure your hps puts out more heat than my mh, but mine are loving the light they're getting!