One of the larger lighting companies - I think it's Sun - now sells a dual 600 watt light that uses two bulbs. I'm pretty sure that the intended use is one MH and one HPS. Probably if you went to SunlightSupply.com you can find their research on why they think the combo light is better. (At lest you'd think they would do some research before marketing the product.) Also, there was a recent thread here on CanCom that discusses this same subject. ...something about "what's better a 400w or 600w light" I don't remember the exact title of the thread but it was something to that effect.

PC :smokin: