Black light

A black light, also referred to as a UV-A light, Wood's light, or simply ultraviolet light, is a lamp that emits short 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, lasers, 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).