150w HPS bulbs usually give off about 15,000 lumens. That's good enough for 3 sq. ft.--which will easily take care of two decent sized plants. One of the things about the 150w HPS systems is that almost all of them have built-in ballasts...and the ballasts generate some pretty serious heat. If you have a 250w with a separate ballast, you won't get much if any more heat from just the bulb than you will from the bulb/ballast of a 150w.

I got my 250w system at discount-hydro.com...switchable remote ballast for about $179 with bulb.