I've had up to 9 under mine. I think 4 is about right. All depends on how you set things up. I try to keep mine under 3'. you have a little over a 3x3 foot print for the 400w
im growing a mix ive got 4 barneys farm blue cheese 4 greenhouse church 6 royal queen special , 7 x ak47 and 10 big bang so gonna need a few lights but 4 per plant will be sweet thanks agin peeps
ive got them vegging under a t5 8 bulb and im getting a metal halide 400 watt for veg ive got 1 x 600 watt hps so if i get another 6 x 400 watt hps should be well enough and ill put some pics up when its finished cos im paranoid enough lol thanks again