A
black light, also referred to as a
UV-A light,
Wood's light, or simply
ultraviolet light, is a
lamp that emits long wave (
UV-A)
ultraviolet light and not much visible light.
[1][2][3][4] The lamp has a violet filter material, either on the bulb or in a separate glass filter in the lamp housing, which blocks most visible light and allows through UV,
[3] so the lamp has a dim violet glow when operating.
[5][6] Black light bulbs which have this filter have a lighting industry designation that includes the letters "BLB".
[3][5]
A second type of bulb, which is also called a black light, produces ultraviolet but does not have the filter material, so it produces more visible light and has a blue color when operating.
[3][4][5] These are made for use in "
bug zapper" insect traps and are identified by the industry designation "BL".
[5][6]
Black light sources may be specially designed
fluorescent lamps,
mercury vapor lamps,
light-emitting diodes,
lasers, or
incandescent lamps.
[5][6] 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).
Although many other types of lamp emit ultraviolet light with visible light, black lights are essential when UV-A light without visible light is needed, particularly in observing
fluorescence,
[4][5] the colored glow that many substances emit when exposed to UV. Black lights are employed for decorative and artistic lighting effects, diagnostic and therapeutic uses in medicine,
[3] the detection of substances tagged with
fluorescent dyes,
rock-hunting, the detection of
counterfeit money, the curing of plastic resins, and attracting insects.
[4] Strong sources of long-wave ultraviolet light are used in
tanning beds.
[4] Although the low power UV-A emitted by black lights is not a hazard to skin or eyes and can be viewed without protection, powerful ultraviolet sources present dangers and require personal protective equipment such as goggles and gloves.