depends on the size of the plants/pots when you put them into flower and the overall size of the light footprint/grow area...like how many watts per sq foot, and how many plants can be crammed into that sq foot or whatever. shoot fer about 6-8000 lumens per sq foot or around 90-110 watts per sq foot and you should be good.
there's also alot of other factors to consider like canopy depth and density, cfls have low penetration and are best utilized with a shallow canopy grow such as lst or scrog
.keep in mind it's not so much about the light being "enough" it's about being able to properly utilize that light, no matter how many watts you run cfls simply wont penetrate deep enough into the canopy to grow plants (efficiantly)over about a foot and a half tall..the bottom buds simply wont get enough light to develop properly and will result in a waste of space.