It's all about space. My computer tower is about 7" x 17"--small. That's about .8 of a square foot.

Four 23/26w CFLs will put out around 6500-7000 lumens. You need 5000 lumens per sq. ft. for best results, so that's enough to do a good job in up to about 1.35 square feet. That's an area of about, say, 9.5" x 20". Good luck!