The glowstick is a common thing nowadays found where light is needed, but it can't be
exothermic (situations such as lighting for car accidents instead of
flares,
camping,
trick-or-treating, and
raves). The fact that a glow stick is a sealed system and doesn't consume
oxygen and can't be extinguished makes it superb for
diving.
The glowstick itself is a slightly bendable plastic tube with a small glass vial in it. Bending the plastic allows the person to break the glass in it and mix the chemicals.
Within a glowstick there are three chemicals involved. Within the glass vial is hydrogen peroxide (H2O2). Upon breaking the vial, this mixes with an ester (phenyl oxalate). Mixing hydrogen peroxide with anything tends to oxidize it, as is the case with the ester - creating
phenol (C6H5OH)
and a peroxyacid (H2S2O8)
ester which is unstable. When the peroxacid ester decomposes it produces phenol and a cyclic peroxy compound that then further decomposes into carbon dioxide. Each one of these decompositions releases energy and causes a fluorescent dye to fluoresce. The color of the dye is the color of the glow. This process is known as chemiluminescence and was borrowed from the firefly.
The intensity of the light produced is directly proportional to the rate at which the reaction takes place. Realize, however, that there is a fixed amount of reactants in the system - the brighter the glowstick, the faster the reaction, the shorter the duration. This reaction is
also affected by the temperature of the surroundings. Typically, these glowsticks are either 30 minute long or 4-8 hours (depending on the brand and purpose). However, changing the ambient temperature will speed up or slowdown the rate of reaction - a classic grade-school science lab is to measure the duration of a glowstick. By immersing the glowstick in a hot water bath the intensity of the light
produced goes up significantly. Likewise tossing the glowstick in the freezer overnight drastically reduces the rate of reaction.
http://chemistry.about.com/
http://howstuffworks.com/light%2Dstick.htm