/ˌlo͞oməˈnesəns/
Noun
1. Emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a substance as a result of heating. (wikipedia.org)
2. Any emission of light that cannot be attributed merely to the temperature of the emitting body. (wiktionary.org)
3. The emission of light by a substance that has not been heated, as in fluorescence and phosphorescence. (Google Dictionary)