UV light

A black light, also referred to as a UV light, ultraviolet light, or Wood's lamp, is a lamp that emits ultraviolet radiation (UV) in the long-wave (near ultraviolet, UVA) range, and little visible light. Other types of ultraviolet lamp emit large amounts of visible light along with the ultraviolet; however, a "black light" usually refers to a lamp that has a dark blue optical filtering material in the glass envelope of the bulb (or the lamp housing) which blocks most of the visible light, so the lamp emits mostly ultraviolet. Ultraviolet radiation is invisible, but a small fraction of visible light passes through the filtering material, with wavelengths no longer than 400-410 nm, and as a result, when operating the lamp emits a dim purple or violet glow. Wood's glass is one type of filtering material which is used in black lights.

Black light sources may be made from specially designed fluorescent lamps, mercury vapor lamps, light-emitting diodes, or incandescent lamps. In most black lights the blue optical filter material to block visible light is in the glass envelope of the light bulb, but in some types there is a separate filter glass in the lamp housing. 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).

Ultraviolet lights have many uses, but black lights are essential when UV 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. Most artificial ultraviolet sources are low power. Powerful ultraviolet sources present a hazard to eyes and skin; apparatus using these sources requires personal protective equipment.