http://boards.cannabis.com/indoor-gr...-lighting.html

I searched for "400 halide top height" and found that. Don't expect everyone to do your searching for you though I just want to set you on the right track. Topics such as that have been discussed thoroughly and you'll probably find a better answer searching for a previous discussion than asking for a quick one-liner here.

Apparently about 3 ft is a good height for a 400W light, but I have no personal experience which is why I didn't answer before. Hope you figure it out soon!

-canuck :jointsmile:

edit: I should read both pages next time before I post! I hope that lighting FAQ by LIP will help you anyway.