Good question. But, I think all that you would grow with a hallogen would be massive amounts of algae. A hallogen would probably be good for macro algae, but the bulbs get extremely hot.
I doubt that, halogen lights are very inefficient. You would be wasting a ton of wattage (and not be able to grow much) if you were to use them on a reef tank.
hummm.... okay. i wasnt thinking of using halogens it was just a curosity question as i was looking at my living room fixture and thought ... hummmmmmmmmm?????