Why we don't know that (half the time) we are in the dark in the movie theater

As Eric Williams (2018) has pointed out, if a film is shown on a traditional projector, "you are sitting in darkness half the time."

To understand why we don't realize this, let's start with the obvious: At the movies,  you are not seeing moving pictures. Instead, you are seeing a series of photos.

Between each photo, a shutter blocks the light from hitting the screen while the film advances to the next photo.

Traditionally, the pattern has been: (1) Show the first picture for about 1/24 of a second, (2) then use the shutter to block the light for 1/24 of a second to give time to position the next picture, and (3) tthen show the next picture.

Technical notes:

  1. Often, the same picture is shown 2 to 3 X before changing to a different picture.
  2. Most digital projectors display images at a faster frame rate than 1/24 of a second.

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