This is my design for a Flat Field Light Box. The main structure is made of 1/4" Foam Core and all joints are bonded with low heat hot glue except for the top and back. I attached these with tape to allow me to get back inside to replace LEDs, dust off the mylar, etc. The 2 diffuser elements are double sided mylar. The light sources are 4 Radio Shack white LEDs wired in parallel. The power supply is a 9VDC battery
I have a parts list and schematic available Email me if you would like a copy.