Triboluminescence

Triboluminescence is an optical phenomenon in which light is generated through the breaking of chemical bonds in a material when it is pulled apart, ripped, scratched, crushed, or rubbed (see tribology). The phenomenon is not fully understood, but appears to be caused by the separation and reunification of electrical charges. The term comes from the Greek τρίβειν ("to rub"; see tribology) and the Latin lumen (light). Triboluminescence can be observed when breaking sugar crystals and peeling adhesive tapes.