Well I have seen this debate on several forums as why even bother using a MH light at all. I think alot depends on your pocket book an HPS light well do just fine for veg but MH is optimum. Just like you can do w/o a Co2 setup but its optimum. So if you haven't the money to buy both kinds of light setups you don't really have to and still get decent weed.

SaH