I'm using a 400w HPS and I red in a grow book by Mel Frank that the light should be 18" to 24" in early stage of vegative growth and I have mine at 18" and they seem to be growing fin with no stretching but at 24" it seemed to slow down growth for a week until I lowered it again.
Hope this help
Ali
amckean Reviewed by amckean on . quick question? How far/close should my400 hps light be to the tops of me plants ? any help welcome thnx. :) Rating: 5