OSL is a cold light and a generic term for the electromagnetic radiation (usually in the form of visible light) emitted as a consequence of an atomic or molecular optical excitation. Luminescent materials are able to absorb energy, store part of it and convert it into light; these materials usually have a crystalline structure. OSL is based on the estimation of the impact of radiation on the crystalline structure of materials while they are shielded from light.
OSL is applied in personal environmental and retrospective dosimetry. Retrospective dosimetry can be divided into archaeological & geological dating and accident dosimetry. In dating applications the goal is to determine the dose absorbed by natural materials resulting from exposure to naturally occurring radio nuclides in the environment. If the dose rate in the media is known (or can be determined separately) and is assumed to be constant throughout time, the absorbed dose can be converted into an age, since the size of the absorbed dose is proportional to the age of the sample. In accident dosimetry the goal is to reconstruct doses absorbed as a consequence of a radiation accident. A radiation accident is an unintended or unexpected event occurring with a radiation source, or during a practice involving ionising radiation, which may result in significant human exposure and/or material damage. The techniques used in accident dosimetry and dating applications are identical.