I have (2) 150's and 3 plants in a space of 8 sq ft, they do the job pretty well, ive personally never witnessed the handy work of a 400, 600 or 1000 but im sure it belittles my setup....always get more than you think u need, i almost got a 400 twice and should have both times (space is a tent, 2x4x5) temps went from 72 with cfl's to 83 with 1 and 92 with 2, ive since invsted in 2 4" exhaust fans for the top and that got me back around 82-85 throughout the day... good luck man