i dunno man, i can only say what works for me specifically...ive researched this topic immensely and cfls put out an average of 1,600 lumens on one of those 23-27 watt bulbs that ive seen in all the pics in this thread...and they lose lumen output DRASTICALLY every inch u get farther from the plant, i personally run just a 400 watt hps system, i purchased a metal halide conversion bulb from HTGsupply.com, u dont need to do anything except unscrew your HPS bulb and screw in the MH conversion bulb, its called a MH conversion bulb cause it works in the hps ballast, my bulb was like 35 bux from them and its puts out 38,000 lumens,lol, do u know how many CFL bulbs that is???...look into it atleast, im sure a 600 watt mh conversion bulb cant be more than 40-50 bux max...CFLs are weak man, not to mention i ran the 400 watt mh conv bulb 24 hours a day during my veg and the bill barely went up...