A "black light" or "UV light" is a lamp emitting electromagnetic radiation that is almost exclusively in the soft near ultraviolet range, and emits very little visible light. In medicine, forensics, and some other scientific fields, such a light source is referred to as a Wood's lamp.

Black light sources may be made from especially designed fluorescent lamps, mercury vapor lamps, light-emitting diodes, or incandescent lamps, with a lamp enclosure designed to reduce emission of visible light and pass desired parts of the ultraviolet spectrum.

Black light sources may be used for decorative and artistic lighting effects, for diagnostic and therapeutic uses in medicine, for eradication of microorganisms, for observation or detection of substances that exhibit the fluorescent effect, curing of plastic resins, and for attraction of insects for eradication. Strong sources of long-wave ultraviolet light are used in tanning beds. Black light lamps are used for detection of counterfeit money.

Powerful ultraviolet sources present a hazard to eyes and skin and apparatus using these sources requires personal protective equipment.

Black light fluorescent tubes are typically made in the same fashion as normal fluorescent lights except that only one phosphor is used and the normally clear glass envelope of the bulb may be replaced by a deep-bluish-purple glass called Wood's glass, a nickel-oxide–doped glass, which blocks almost all visible light above 400 nanometers. In practice, partly due to cost but mainly because Wood's glass does not make a satisfactory material for lamp manufacture, the lamp will be made from normal glass and a relatively thin coating of a UV filtering material is applied to the exterior. The color of such lamps is often referred to in the trade as "blacklight blue" or "BLB." This is to distinguish these lamps from "bug zapper" black light ("BL") lamps that don't have the filter material