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.
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,
so the lamp has a dim violet glow when operating.
Black light bulbs which have this filter have a lighting industry designation that includes the letters "BLB".
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.
These are made for use in "bug zapper
" insect traps and are identified by the industry designation "BL".
Black light sources may be specially designed fluorescent lamps
, mercury vapor
lamps, light-emitting diodes
, or incandescent lamps
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
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,
the detection of substances tagged with fluorescent dyes
, the detection of counterfeit money
, the curing of plastic resins, and attracting insects.
Strong sources of long-wave ultraviolet light are used in tanning beds
. 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.