D2 is a general light source for UV range spectroscopic applications. D2 lamps produce intense ultraviolet radiation by maintaining a stable electric arc in a deuterium atmosphere. The spectral power distribution of this radiation has a continuous range that extends from 160 to 400 nm (D2 spectrum). This continuous and stable characteristic of the arc makes deuterium lamps the most useful source of UV for analytical instruments, including spectrophotometers, liquid chromatography detectors, medical analyzers, pollution analyzers, colorimeters, and densitometers. Because of the stability and reproducibility of deuterium lamps, they are suitable as secondary calibration standards in the ultraviolet region.