Here’s the design and construction details for the edge lit badge I showed in this post; I didn’t include the Halloween image since it came from a paid clip art program. You’ll want to use your own designs anyway.
Here is the finished badge:
The design is based on a more complex design by Solarbotics I found on Instructables. His design called for four LEDs (two of them scrolling RGBs), two layers of acrylic and two batteries. It’s really really cool and you should check it out.
My design is way simpler, just one battery, one LED, and one layer of acrylic (either 1/8" or 1/4" can be used. I built my design from scratch but it is based on Solarbotics’ design as much as I can tell (couldn’t access his design files).
Couple of notes: There’s no switch on this, so you should assemble the badges just before using them. Don’t worry, it’s a quick assembly. Also, be aware that the current draw for LEDs is different depending on the color (there’s a great discussion of that in this article) so you should avoid red, yellow and orange for that reason.
Here is the file: 
Construction:
Step 1– Materials: laser cut acrylic badge, 3V LED, CR2025 or CR2032 coin battery, duct tape, optional embellishments and ribbon.
Step 2– Cut the legs of the bulb shorter so they will fit on the battery without bending. The longer leg is the positive side.
Step 3– Slide the bulb onto the battery with the longer leg touching the plus side.
Step 4– Cut a piece of duct tape about as wide as the battery and twice as long.
Step 5– Slide the bulb up close to the battery and ensure that it fits in the badge.
Step 6– Wrap the duct tape piece around the battery so both legs of the bulb are making good contact with the battery.
Step 7– Place the battery and bulb assembly (“throwie”) into the badge.
Step 8– Wrap duct tape around the top of the badge to hold the battery in and conceal the bare bulb. Be careful not to cover the holes near the top edge.
Step 9– Wrap the top with ribbon, mummy style, to conceal the duct tape (optional).
Step 10– Top with a leaf embellishment and string ribbon or cord through the holes.
