Your other problem is 400w 4' away will make the plants stretch for light. At that distant the lumens are wasting away. Look for some glass you can install as a heat shield. You can also install a fan to remove the heat from the light and that may save you around 10 deg or better and allow you to get the light closer.
Zandor Reviewed by Zandor on . Major heat prob!! HELP!! I have a kinda growing problem with heat building up in my grow room, since its like a walk in closet i have a 400watt hps about 4 feet from the plants and after the light has been on for about 4-5hours you open the door and get quite a considerable bit heat that heats you in the face...i have no obvios way of getting rd of the heat except opening the door and have a fan blowing full tilt through the door for bout an hour before it cools down...anyone have any ideas of a cheap but effective Rating: 5