for a good sized closet setup, You are gonna need ~160-400 watts of White light(blue spectrum) Either use a 250-400 watt Metal Halide or Cool white Fluorescent tubes or CFLs. Thats just for Vegging your plants.... Then to yield any buds your going to need either a 250-400 watt High pressure sodium Light(red spectrum) or some Warm white fluro tubes or the compact fluros.
More light = more buds.
HPS can be used for both stages of growth But they use a lot of energy and they get really hot. Save your electric bill and go with CLFs they work! Then save the HPS for the flowering stages thats when it will be needed.
You also should know that using HID lights requires a special ballast in order to ignite the gases inside the bulb. And also the fixture is called a mogul socket, its much bigger than standard fixtures.