Stage lighting?

Question

When a stage is lit with a blue light during a theater performance, how do the audience associate it with being a dream?

Answer 1

I believe the reason is traditional. Television, cinema and theatre have long had to deal with the problem of presenting night scenes without having them look empty due to an absence of light (try doing a comedy scene at night and the problem is magnified). Blue, by simply being a dark color, allows one to fill out the image. Over time, we as audience members have simply grown to accept it as meaning night or, similarly, a dream state. It could just as easily have been purple though it was a more difficult color to produce with older technology lamps. A more moderm equivalent for night in television is to put a single HMI fresnel on a tower or crane and let it represent moonlight or a streetlight though it might not work for dreams.

Answer 2

There might be an "official" answer or reason, but personally the blue light provides a ghostly quality and almost takes the third dimension out of the people and objects on stage. The lighting subject will look more ethereal.