4 foot of total height?...that's gonna be a problem. You need 7-8 feet. IMO.

Bottomline: you need to keep a 400 watt HPS at least 12-15 inches from the top of the plants. Even more during the veg cycle.
Dutch Pimp Reviewed by Dutch Pimp on . how many plants hey, how many plants could i grow in a space of 2.5foot x 3.5 foot x 4 foot tall growing with a 400w hps Rating: 5