If you go to any outdoor, nighttime event these days, you're likely to see people wearing glowing plastic necklaces.These necklaces seem to glow magically, as though they were made from cool, flexible neon lights, but how do they work?

Each necklace is a hollow, plastic tube filled with chemicals which are undergoing a slow reaction to create chemiluminescence, or light from chemicals. This reaction is essentially oxidation, the same thing as burning, but the energy released by a chemiluminescent reaction comes out as light, not heat. Indeed, the cool chemistry that takes place inside one of those glowing necklaces is very similar to the chemistry that lets fireflies glow.

You start the reaction by bending the flexible tube. This breaks a miniature glass vial inside, and allows two different chemical solutions to mix. These solutions are like the fuel for the chemical reaction, as soon as they mix, they begin to give off energy. The energy doesn't escape the tube as heat, though. Instead, it is passed to a fluorescent dye, also present inside the tube, which turns the chemical energy into a cool, colorful glow. The reaction continues for several hours, and your necklace will glow until all the fuel is used up.

Chemical reactions tend to be slowed by cold, and this one's no exception. You can test this by buying two glowing necklaces, and putting one in your cooler. The colder one will keep glowing longer, because its chemical reaction is taking place more slowly.