buy a 400 w hps light for better yield than fluoro,but then you get heat .
i use 2 250 w hps for a 4by6 floor and 6 ft high and don't have prob with heat at all,and the power bill only went up about 60 a month but you get what you pay for.this includes the clone fluoro light and all fans and humidifier.
you should go with at least 8 or six fill er up nothing to looose lots to gain.ha ha
good luck