3' x 4', roughly, for a 600-watt light. For a 4' x 4' space, one 1000-watt light is good, or two 600-watt lights. For a 2' x 3' space or a 3' x 3' space, a 400-watt light works. For a 2' x 4' space, a 400 watt light works okay, a 600-watt light is better (if you can handle the heat), or a 400-watt light plus some accent CFLs at the far edges works well.

I think your plan to go with a 400-watt light makes the most sense for your (2' x 3') area. Better to use a 400-watt light and find out you need a few cheap accent CFLs to go with it than to use a bigger light and find out you can't use it at all because of the heat.
jamstigator Reviewed by jamstigator on . Amount of CFL vs Higher Wattage. Is it worth it to drop the extra money on the big CFLS (105-125 watt 30-50$ a light) Or use multiple low wattage? What do you guys with experience think, because I'm considering using all CFLs to save money but still would like to attempt a sea of green grow in a 4X4 organic soil bed (for 16 clone SOG). Rating: 5