Just curious to see if anybody knows what would happen, or if the 600 would be brighter... I've thought about (and even purchased several) cfls to increase light, but this is my last grow and I don't want to buy another ballast... I have 12 girls (hopefully) vegging in a 3'x4' closet, excellent exhaust (temps stay around 70). and i'm hoping to have @ least half female once flowering starts. I want to have a max yeild with what i've got, b/c my girls are 10 white widow, and 2 bubble gum and since it's my last grow.....etc... I understand that the ballast will only produce 400W, but with the bigger bulb will it be brighter? idk...