Chemiluminescence (chemoluminescence) is the production of light and heat from a chemical reaction.
Given reactants A and B, with an excited intermediate ◊,
[A] + [B] → [◊] → [Products] + light

The decay of the excited state [◊] to a lower energy level is responsible for the emission of light. In theory, one photon of light should be given off for each molecule of reactant, or Avogadro's number of photons per mole. In actual practice, non-enzymatic reactions seldom exceed 1% QC, quantum efficiency.

An example of chemiluminescence in the laboratory is found in the luminol test- where evidence of blood is taken when the sample glows on its contact with iron.

When chemiluminescence takes place in living organisms,it is refered to as  bioluminescence. A lightstick emits a form of light by chemiluminescence.