A black light, also referred to as a UV-A light, ultraviolet light, is a lamp that emits ultraviolet radiation (UV) in the long-wave (near ultraviolet, UVA) range. Unfiltered lamps appear white when turned off and are designated BL; filtered lamps use the same phosphors but use Wood's glass to filter out visible light, and appear black when turned off.

Black light sources may be specially designed fluorescent lamps, mercury vapor lamps, light-emitting diodes, or incandescent lamps. A filter to block visible light may be part of the bulb, or built into the light fixture. In medicine, forensics, and some other scientific fields, such a light source is referred to as a Wood's lamp (named after Robert Williams Wood).