Taken from Gwen Gibson's site. I bought some of her photoEz stuff.
Build a light table
What you’ll need to make the light table
Light fixture: Two 20-watt double fluorescent light tube fixtures measuring 24" long with cords and plugs. (If you don’t want to re-wire the fixtures yourself, ask if the store will re-wire up them for you).
Bulbs: All of the following tubes will work, but the exposure times vary.
Fluorescent Light Table Exposure Times
using two 20-watt bulbs approximately 1.5"-2" from PhotoEZTM
Full Spectrum tubes Transparency 4 minutes
20-lb white paper 14 minutes
Daylight tubes Transparency 6 minutes
20-lb white paper 24 minutes
Cool White tubes Transparency 14 minutes
20-lb white paper 40 minutes
Clear Top: Plexiglass (1/4" thick) for top measuring 14” x 28”
PVC pipe framework: Two 12.5" lengths 3/4" pipe for short sides of table
Two 25” lengths 3/4" pipe for long sides sides of table
Four 3/4" x 3/4" x 1/2" side outlet elbows with a 1/2" threaded opening for corners
Four 4" lengths of 1/2" threaded nipples for legs
PVC piping comes in various lengths and will probably require cutting. If your hardware store won’t cut it for you, you can purchase a ratchet action PVC pipe cutter that cuts up to 1” diameter pipe for under $10.
Total cost of materials to construct the frame is approximately $21.
Light fixtures and bulbs are additional.
Assemble the light table
Insert 2 long pipes in outlet elbows.
Insert 2 short pipes in remaining openings of outlet elbows.
Insert threaded nipples into threaded holes in outlet elbows.
Place over top of PVC frame.
Place the clear plexiglas sheet on top of the PVC frame.
There should be approximatly 2" between the plexiglass and the bulbs.
You can modifiy to fit your needs.