A lightstick, also called a glowstick, is a transparent plastic tube which contains chemical fluids held apart in two compartments. The outer plastic tube contains one part of the chemical mixture, and the inner compartment is a glass or brittle plastic tube containing the second mixture. If the lightstick is bent, the inner tube breaks and the chemicals mix, resulting in a reaction that emits light but not necessarily heat. This phenomenon is called chemoluminescence.
Lightsticks have various purposes: they are used in the military, by recreational divers doing night diving, by marching band conductors for night time performances, and also used for entertainment at parties (especially raves), concerts, and dance clubs. Glowsticking refers to the use of glowsticks in dancing. A further application are light effects, especially Balloon-carried light effects.
By adjusting the concentrations of the two chemicals, manufacturers can produce lightsticks that either glow brightly for a short amount of time, or glow more dimly for a much longer amount of time. At maximum concentration (typically only found in laboratory settings), mixing the chemicals results in a furious reaction, producing large amounts of light for only a few seconds.
Heating a lightstick causes the reaction to proceed faster and the lightstick to glow brighter, but for a shorter period of time. Cooling a lightstick slows the reaction and causes it to last longer, but the light is dimmer. This can be demonstrated by refrigerating or freezing an active glowstick; when it warms up again, it will resume glowing.