Well, if a 42w CFL puts out about 2780 lumens, and we need 5k lumens per sq ft, then, with a 1 sq ft space for grow, we'll need about 2, 42w CFL cool whites. I would imagine that doubling that would be acceptable, so probably 4, 42w (5000 lumens) would work in the flowering half of the cab.
Hmm??