Hmmm Interesting. I just gutted a 70W and 150W (ok, small grow room) and looking at the wiring, I think it can be done. Separate, matched to bulb, igniters might be needed. Think I'm gonna inquire to manufacturers. I *think* 2 400's over a larger area might work better. (just thinking of a BIG grow room, but mainly peppers, tomatoes, etc.)
What 'guy' did you ask? (I have corrected a lot of floor sales people helping other customers on stuff. a few of the salesman actually thanked me, but not many)