well there's an equation that goes like this....

5000 lumens per square foot = optimal growth

with three bulbs on each, you're not quite at that level . also keep in mind that lumens diminish rapidly with distance. so if you have 4800 lumens 6" away from your plant, its getting about 2400 lumens. i'd get more bulbs. or maybe finish this grow out and see if that satisfies your need. for an example, with 12 CFLs on one plant grown to about 18" before harvest, i got just over a 1/2 oz.