A somewhat inaccurate term for a form of illumination containing short-wavelength ultraviolet light (radiation just beyond the blue end of the visible spectrum). Although "black light" is technically invisible, it tends to cause some substances to fluoresce upon exposure. Photographic emulsions (especially those that use photopolymers), are susceptible to black light. Sun lamps, plant "grow" lights, lights used in discotheques, etc., are all forms of black light. Black light is also used to read "invisible" inks, such as nightclub hand stamps.
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