I made these from 1/2 inch box steel . I put a bolt in the top and used the Lowes cheapo work lamp to clamp onto the bolt. Put some 5000k bulbs in it and works like a champ !
If you go to Wal-Mart and muck around the lighting you may find a light that looks just like that called a "daylight" bulb, look for the 6500K rating. It looks even nicer than a 5000K. You just can't beat a compact flourescent in color and light-watt ratio.
I've got to remember to get some of these. I have close to the same setup but incandescent bulbs make things so yellow! And the slightly green tint in my light box sheet doesn't help any!