I think a good test is the hand test...

Place your hand under the light, and move it closer until it starts burning... then place your plants just a little bit lower.

You should have air circulation over your 'canopy' and/or over your plants. You might consider a sealed reflector housing... or a cool tube.
turtle420 Reviewed by turtle420 on . quick question? How far/close should my400 hps light be to the tops of me plants ? any help welcome thnx. :) Rating: 5