what u need is VENTILATION....when the plants are still seedlings its ok to leave the light so distant but as the plants get older and bigger u should be able to get that bulb as close as 12" (HPS even closer cause it produces far less heat)...the main issue is, like i said, ventilation, u need to get a fan blowing right into the bulb (more ventilation better)...or else ur not getting the bulbs juice into the plants (a bulb looses half of the lummens at each foot distance)