a lot. they are very very very picky about lighting, as it is their "diet".
you'll have to post the number of gallons of your tank as well as depth and any other useful info. someone should be around to give you a safe recommendation.
i don't know how much you know about lighting basics so i'll just go ahead and rule out fluorescents. no anemone can live under that. it's just a matter of how many watts of power compact, vho, t-5, mh, or etc etc etc you'll need. these special lighting setups don't normally come standard on tanks.