How does a black light work? — JLM, Kettering, OH
I think that most black lights are gas discharge lamps that resemble normal fluorescent lamps. However, while a normal fluorescent light uses fluorescent phosphors to convert the ultraviolet light produced by its mercury discharge into visible light, a black light allows that ultraviolet light to emerge from the lamp unchanged. The ultraviolet light from a mercury discharge has too short a wavelength to be useful or safe as artistic black light, so other gases are likely to be used. The lamps are probably filtered so that they emit relatively little visible light or short wavelength ultraviolet light.