Glowsticks are chemo-luminescent sticks that usually contain one chemical in the pain tube with a small glass vial that contains a reactant chemical. When the vial is broke by bending and shaking the tube the chemicals react and generate light.
Cyalume or chemical light sticks come in various colors, intensities and time durations. The most common are 6, 8 and 12 hour durations. Additionally there are intense 30 minute lights and very short duration blinding tactical light sticks that are used where flash bang grenades are not able to be safely used.
One concern when using glowsticks is that the glass vial is easily broken by being jarred or during violent movement, for this reason many individuals choose to carry either more batteries or an extra flashlight instead.