i think this is most ideal setup, not considering money

start seedlings under fluorescent lighting,

after 2 weeks move to metal halide, remembering to have the light very far away from them at first and gradually move closer each day (getting them used to the strong light)

when you switch to flowering, use HPS (high pressure sodium).

the metal halide has more of a blue spectrum which is good for the vegetative stage, while the HPS has a red spectrum which is needed for flowering.

if you don't have a lot of money and can't afford both metal halide and hps, or conversion bulbs, its completely fine and generally accepted and common for people to just use HPS throughout the entire grow. but you should always start seeds with fluorescents IMHO