I got a fluorescent clipboard a while back. I love the effect.

The edge is much, much brighter than the rest, though it’s a little easier to see this in person. The clipboard is acting as a waveguide for the emitted fluorescence; any light emitted within the total internal reflectance angle is being transported to the edge, and any light entering through the edge is likewise guided. Except for the places where there is clear tape (holding a Dilbert cartoon on a transparency) where you can see some of the light coupling out through the tape, because the light isn’t totally contained in a waveguide. There is an evanescent wave that can couple to a material of a different index, resulting in frustrated total internal reflection.