The term 'luminescenz' was introduced by German physicist Eilhardt Wiedemann in 1888, as meaning "all those phenomena of light which are not solely conditioned by the rise in temperature." This was in contrast to the incandescence or 'hot light' that is emitted by any material heated to the temperatures at which they become 'red hot.' Classification of different types of luminescence according to the method of excitation was proposed by Wiedemann and remains valid today. He recognized photoluminescence, thermoluminescence, electroluminescence, crystalloluminescence, triboluminescence, and chemiluminescence. Although currently many new types of luminescence have been discovered and investigated, they all belong to the original six categories of Wiedemann. The designations are indicated by prefix: photoluminescence is excited by the energy of light itself and is subdivided into fluorescence and phosphorescence; thermoluminescence is the emission of light due to moderate heating; electroluminescence occurs due to the energy of electrical fields; triboluminescence and crystalloluminescence occur when crystals are shattered or when solutions crystallize, and chemiluminescence obtains its energy from chemical reactions. Bioluminescence-the emission of cold light by living organisms-is an example of chemiluminescence that derives excitation energy from a biochemical reaction. Emission of light from living organisms can be either specific or non-specific in nature.
Nonspecific biochemiluminescence results from the inadvertent release of reactive oxygen species (O2- ; H2O2, or O2) and its subsequent reactions with suitable molecules in their vicinity, which generates energy in the form of a light photon. This ultraweak luminescence was first observed in 1961 by Tarusov et al. Since then, a wealth of experimental data has accumulated on the application of ultraweak photon emission for monitoring oxidative status in human subjects under both physiological and pathophysiological conditions. However, much more basic research and clinical studies are needed for ultraweak bioluminescence to be employed as an analytical tool.
A specific (though non-functional and presumably low quantum yield) biochemiluminescence can be observed in peroxidative reactions, in oxidative decarboxylation, in dioxygenase reactions that involve dioxetane intermediates, and in epoxidative reactions, where rearrangements of perepoxides to dioxetane is possible. These reactions are specific because they involve oxygenation of a substrate molecule belonging to a specific biochemical pathway; they do not, however, carry any specific function in the organism.