Not really sure, right now im useing 2 flourescent lightbulbs made for growing, but they arent the tubes, they screw in a normal socket, and also 2 60w incandescent grow lights higher up. I may just wait and see what i can get out of what i have, but i keep hearing how much better yield u get off the HPS bulb. What wattage of a HPS would be best for 4-5 plants in a closet.
I once spent about 5 times what a regular hps bulb costs($65), for a fancy enhanced spectrum hortilux bulb ($300) and absolutely did NOT see a huge(if any) improvement.
"IMHO"...certainly not worth the extra bucks.