Your best bet for adding blue light is 2 to 4 CFL's, however another good method is to take some traditional fluorescent fixtures, single bulb 24" or 18", and place them around the grow room about 2' apart on the walls. Use actinic blue bulbs, you can get them from an aquarium supply store, and switch them on! These were great at preventing my first crop from stretching under my 400w hps and the bulbs last a long time while every watt used is producing usable light for the plants, and only usable light. They look like blue neon they are so blue. Each bulb is about 20 watts so there is an increase in your electric bill but light gets to the lower branches and the blue light is so effective it prevents stretching while creating dense compact growth. I know it's an odd way of doing things but that way the spectrum of your grow room will be a huge spike in the blue and red, the best spectrum for plant growth, hell your space may look purple! Third option, get a metal halide conversion bulb, makes a lot more heat, costs a good bit (but less then the fluorescence, I think) and puts out less light. But in my opinion, you want a bumper crop, go with the fluorescence, they gave me gold from bag seed.
