as I've researched light sources, and prices, I was put off by the prices I found of the 600-watt ... the 600w bulbs were price MUCH higher than the 400s, and pretty close to the 1000w ... the 400w seems to be the best bang for the buck ... if I was to go bigger than 400w, I would go to 1000w, not the 600w ... :smokin: