nice and specific........
a 600w digital HPS would be great in a closet for one plant
as would a 400w, as would a 250, as would a 300w cfl, as would a 125w cfl, as would 10 45w cfl's, as would a 1000w watercooled hps.
you wont get any reply of use unless you are specific about what you want, can afford, would like to yield, the size. details details details