Chemiluminescence is a luminescence which arises from exothermic chemical reactions. Such a reaction can produce certain molecules in excited electronic states, which subsequently decay to the ground states (or other lower-lying states) with emission of photons (→ luminescence). However, the quantum efficiency for light emission is in many cases small.
The phrase “light without heat” is not literally correct, since the heat generated normally takes away most of the energy provided by the chemical reaction, even if for a slow reaction the heat power is too small to cause a significant temperature rise. However, the light emission is not a consequence of heating, and in that sense chemiluminescence produces “cold light”.
Chemiluminescence is applied in lightsticks, as are contained in disaster kits.
If chemiluminescence occurs in living organisms, it is called bioluminescence.