How do glow sticks glow?

A glow stick is a plastic tube containing a solution of hydrogen peroxide and, inside it, a thin glass vial holding a chemical called a phenyl oxalate ester along with a fluorescent dye. Bending the stick snaps the glass vial, letting the two liquids mix. The resulting reaction releases energy, which is passed to the dye molecules; they then give off that energy as visible light. The colour of the glow depends on which dye is used. Because the reaction speeds up when warm and slows down when cold, a glow stick shines more brightly but for less time in hot water, and lasts longer if kept in a freezer.