Quote Originally Posted by drdettroilet
the let the plant grow up too 3'',4'' from top of plant. 400w , you can just about touch the plant with the bulb, they dont get real hot.
And the Darwin award of the week goes to you my friend. I invite you to come touch my HPS's and tell me how hot they aren't.

The real answer is you have to play with it a little. Some people won't let their plants come within 12" some 16". Like Horseman said, don't let it get much over 84 degrees at the canopy or you will probably have some heat stress issues. With my current setup i'm in the 6" to 8" neighborhood, no pun intended. Obviously if you have an open reflector or an air cooled one it will also make a difference. 12" to 18" should be a decent safe zone for a relatively mature plant, seedlings should be stay about double that distance away. Let us know what you end up with:thumbsup: