woods\' lamp

A blacklight (or often black light), also referred to as a UV-A light, Wood's lamp, or simply ultraviolet light, is a lamp that emits long-wave (UV-A) ultraviolet light and not much visible light.^[1][2][3][4]

One type of 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] Blacklight lamps which have this filter have a lighting industry designation