HPS seems to be the gold standard around here. some folks are having success with just using compact flourescents. not the same as a hardy HPS, but if you have a small space, and heat is an issue, or you need to use little power, it's a thought. i'm definitely considering it just because it would use less electricity and have less heat issues.

you'll also want a fan inside your closet oscillating, creating a breeze. strengthenes the plants