A glow stick is made up of two tubes: an outer, flexible plastic tube and an inner, smaller tube made of brittle glass. Both tubes contain liquid compounds that create the glowing effect when mixed together.
The outer plastic tube contains phenyl oxalate ester and fluorescent dye solution, while the inner glass tube contains hydrogen peroxide solution. To activate the glowing effect, the inner glass tube is broken by bending. When the glow stick is shaken vigorously, the hydrogen peroxide oxidizes the phenyl oxalate ester in a reaction called chemiluminescence, which releases energy in the form of light.
The duration and intensity of the light emitted by the glow stick can be determined by the concentrations of the compounds contained in the two tubes. Heating an already activated glow stick intensifies the brightness of the light but shortens its duration, while cooling it dims the light but extends its duration.