Luminescence emission is the result of a chemical or biochemical reaction. Luminescence detection is simpler optically than fluorescence detection because luminescence does not require a light source for excitation or optics for selecting discrete excitation wavelengths. A typical luminescence optical system consists of a light-tight reading chamber and a [[Photomultiplier|PMT]] detector. Some plate readers use an Analog PMT detector while others have a [[photon counting]] PMT detector. Photon Counting is widely accepted as the most sensitive means of detecting luminescence. Some plate readers offer filter wheel or tunable wavelength monochromator optical systems for selecting specific luminescent wavelengths. The ability to select multiple wavelengths, or even wavelength ranges, allows for detection of assays that contain multiple luminescent reporter enzymes, the development of new luminescence assays, as well as a means to optimize signal to noise.
Common applications include [[luciferase]] -based gene expression assays, as well as cell viability, cytotoxicity, and biorhythm assays based on the luminescent detection of [[Adenosine triphosphate|ATP]].
