Regarding a few comments above about scenes that should be completely black in which the actors (and often the viewers) see "too well," it might be noted that for some time many "dark of night" scenes have been shot in broad daylight, using an infrared or similar "dark" filter on the camera.

One photographer explained the popularity of the method as "most professional actors are so incredibly clumsy they'd kill themselves floundering around in actual darkness."

One might suspect that it's also handy for the crews working the scene to be able to see ... maybe. The real incentive probably is to get the work done without waiting for "the right light" - or the right lack of same.

John