I'm gonna say do 4 plants at a time, to give space, roughly 1 square foot per plant...and even then their leaves may touch a little, but i don't think it'll matter...you're working with 4 square feet there, and you want about 30 or 40 watts of light per square foot, so according to my calculations you need roughly 120 to 160 watts of light for an optimal light scenario...though lumens is more accurate than watts since it is an actual measure of light intensity and not power output...but 140 watts of light should do you just fine if you use flourescents...don't ask me about any hps or mh...all i know beyond flourescents is DO NOT USE halogen....