There is no question that you must use HPS or the sun for the flowering stage. Oh sure, other lights will keep the plants alive, but do you want any weed for your investments of time and money? The only other possible alternative would be MH with a red as possible bulb, but you wont get near the yeild of HPS, and you'll still have to aggressively ventalate.

For flowering I have tried everything except LED, and my understanding is that although LED's may kind of work they are no where near cost effective yet. EVERYTHING that I have tried for flowering except HPS and the sun, was a complete waste of time and money. Oh sure I got buds, but literally about 1 or 2 percent of what I would have got using HPS. I'ld say this is a good number for the flouros, window sill, and incandescants that I have tried.

The good news is anything will work pretty well for the veg. stage. Of course MH works the best, but if I could not use this I would use flourecsents. They run so cool you can put them almost right on the plants.

The important part is the flowering stage.

Hope this helps a little.