I messed up the space would be 8.5 cubic feet and heres this:
Originally Posted by stealthy44
i would go with the hps if i were you. look at the 150 watt hps thread on here, i believe the OP used a 150 hps in ONE 25 gallon rubbermaid- with only computer fans as an outtake. in my opinion, it should work as long as you are smart about it. meaning dont let anything extremely hot (which the light and socket will be) touch rubber, or your plant for that matter. also make sure you have a fan or two blowing directly on the hps, for obvious reasons. and good ventilation in general. if you are planning two stacked on one another id say a 6 inch duct booster will be enough, provided you still have an intake and circulation on the inside.

are you really thinking of getting 500 watts of cfl's instead of ONE 150 hps? im pretty damn sure those cfls will put out more heat.