The production of light is achieved in two primary ways. Incandescent objects give off light due to their high temperature. If temperature is not involved, the production of light is known as luminescence. Luminescence itself can come about in different ways, but in the lab, one of the primary phenomena of interest is chemiluminescence, the production of light due to a chemical reaction. A subset of chemiluminescence is bioluminescence, in which the chemical reaction is biochemical in nature, often involving enzymatic reactions, such as those produced by luciferase, a class of enzymes derived from fireflies. Since the light is produced by chemical reactions, the intensity of light is proportional to the reaction rate, which can sometimes provide more information than related techniques, such as fluorescence.

One specific application for luminescence is adenosine triphosphate (ATP) testing. ATP is used by living cells as a method of transferring energy, and when it reacts with luciferase, bioluminescence results. ATP serves as a proxy for bacteria or other cells. Thus, one of the main applications of ATP testing is to gauge the efficacy of hygiene procedures. This is commonly used in the food industry, pharmaceutical production and by water utilities to ensure that the proper regulations for purity and safety are being followed. The instruments are typically marketed as ATP hygiene instruments rather than as luminometers.

Luminometers are relatively simple instruments. The sample is placed in a cuvette, centrifuge tube or other holder, which is introduced into a light-tight chamber in the instrument. Some systems will use mirrors and other optics to try to catch as much of the light emitted by the sample as possible and direct it to the detector. Detectors are typically photomultiplier tubes, allowing these instruments to detect trace concentrations of ATP and other compounds. Because there is little to no interference as with related techniques, like fluorescence, luminometers are usually several orders of magnitude more sensitive.

The most common application for luminometers is measuring the presence of microbiological organisms in samples, primarily for hygiene applications in the food industry. Water and sewage utilities use the instruments for detecting biological activity. The pharmaceutical industry uses luminescence for hygiene purposes and to measure the effectiveness of antibiotics, and biochemical effects of other pharmaceutical agents on samples. Environmental applications also exist in quantifying the total biomass present in soil or marine samples, and the effect of pollutants on living organisms in different environments.

This profile considers only single-sample luminometers and thus excludes microplate readers. The total market for luminometers in 2013 was about $60 million, the majority of which was for ATP hygiene applications. Providers of general-purpose lab luminometers include Hach (Danaher) and Promega/Turner Designs.