Black Light

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).

Filtered black lights are essential when UV-A light without visible light is needed, particularly in observing fluorescence, the colored glow that many substances emit when exposed to UV. Black lights are employed for decorative and artistic lighting effects, for diagnostic and therapeutic uses in medicine, for the detection of substances tagged with fluorescent dyes, rock-hunting, for the curing of plastic resins and for attracting insects. Strong sources of long-wave ultraviolet light are used in tanning beds. Black light lamps are also used for the detection of counterfeit money. Many artificial ultraviolet sources are low power. Powerful ultraviolet sources present a hazard to eyes and skin; maintenance or adjustment of apparatus using these sources requires personal protective equipment such as goggles and gloves.