The bulb is a few inches away from the translucent plastic folder. You can see the colored cellophane sandwiched between the folder and the plexiglas rods (the rods aren't visible in this shot). A curved piece of mat board reflects the light, and another piece of white mat board is screwed behind the bulb, a few inches away from it for more reflectivity. The edges were painted black to cut down any light leak that may occur from the sides.

It works for me.