Black lights look just like normal fluorescent lamps or incandescent light bulbs, but they do something completely different. Switch one on, and white clothes, teeth and various other things glow in the dark, while the bulb itself only emits faint purple light.

These devices are all around us -- in clubs, science museums, amusement parks and teenagers' bedrooms, among other places -- but to most people, they're a total mystery.

In this article, we'll find out exactly what's going on here. We'll also see why black lights make some objects glow but not others, and we'll look at some interesting black light applications.