Ghost light (theatre)-
The superstitious have various justifications for the ghost light in relation to the supernatural. A popular theatrical superstition holds that every theater has a ghost, and some theaters have traditions to appease ghosts that reach far back into their history. Similar superstitions hold that ghost lights provide opportunities for ghosts to perform onstage, thus appeasing them and preventing them from cursing the theater or sabotaging the set or production. This is also used to explain the traditional one day a week that theaters are closed.
The practical use of a ghost light is mainly for safety. A ghost light enables one to navigate the theater to find the lighting control console and to avoid accidents such as falling into the orchestra pit and stepping on or tripping over set pieces.
— Wikipedia (via upstagetraveler)
In the theater I work at our ghost light is nicknamed ghosty and we use it to appease the grey lady who wonders the basement and the forgetful man who likes to turn the bathroom sinks on.