I'll post it if I cant find it again, but in one of my grow books (or online ugh i cant recall -- too many sources) theres a really nice chart that goes over wattage, kwph, lumen/lux, to compare incandesant vs floresent tubes vs CFL vs MH vs HPS.

HPS produces the most lumens per watt. If you want 2 48 watt CFLs (96 watts) each bulb gives ~2700 lumens your getting 5200 lumens when a Home Depot 70w outdoor garage lamp modified will shed like 8 or 9k lumens on 70 watts

Till I find it I usually refer people to this link on Greenmans's site, pretty good and goes over ALOT from temps to wattage to lumen vs lux etc.

Marijuana Lighting Types and Intensities