The chemical process used in a glow stick is not that far from the chemical process that occurs inside a lightning bug.
When you open the glow stick package, you find a stick with yellow liquid inside (generally, a chemical called luciferin).
Inside the yellow liquid is a glass tube that contains a chemical enzyme (generally, luciferase). When you break the glass tube by bending the stick, per the directions, the two chemicals mix, creating a lot of energy and giving you a good glow.
A lightning bug creates a glow in the same waymixing the two chemical enzymes luciferin and luciferase.