Quote Originally Posted by Dutch Pimp
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.
That true, you need to keep space from the top of the plants and the light, you have to think about the containers you're going to use, 5 gallon containers are quite tall. Plus the plant may be growing a lot, all depends on the veg. time and they will stretch in the first 3 weeks of flowering. This is all some little things you have to consider before you make this setup. If you get some place with more height you could make a nice 6 plants there !