At the last Maker Faire I had a bunch of interactive gizmos for people to play with, but one question I was asked more than any other was "How did you make those displays?" On the Rock Paper Scissors Playing Glove one small display showed three different images and text while on the Secret Knock Detecting Gumball Machine the light just seemed to float in the clear plastic without an obvious source. The answer is edge lighting.
Edge lighting exploits a fun property of light called internal reflection where light can get trapped inside a transparent material. It's the same concept that makes both a diamond sparkle and optical fibers work. But we’re going to use it to make light come out of a sheet of plastic.
Simply put we shine a light in the edge* of a clear piece of plastic and etch it where we want the light to come out. With this simple, cheap method you can use a single LED to display words or images. Because it's etched into a transparent surface the images can seem to float in mid air or you can layer several of them to make a single display with more than one image or color.
Keep reading to see how easy and quick it is to get this effect.
*And thus the name "Edge Lighting"