From what I am learing with CFL's you cannot get too much light in a small space, meaning if its crowded with 4 bulbs say in 18" sq. then its probably good for finishing a main cola. The CFL's suck at penetrating below the upper fan leaves. Currently I am experimenting with them vertical on 1 side of the plant. You have to get them really close and have good reflective surroundings.

Just like with any grow light you must keep the ambient temperature down around the plants, it will always be warm above the lights.