In preparing excerpts for my video students, I found this lovely passage from “In the Blink of an Eye” by Walter Murch.
… It would be fascinating to take an infrared film of an audience and find out when and in what patterns people blink when they are watching a movie. My hunch is that if an audience is really in the grip of a film, they are going to be thinking (and therefore blinking) with the rhythm of the film.
There is a wonderful effect that you can produce if you shine infrared light directly out in line with the lens of a camera. All animal eyes (including human eyes) will bounce a portion of that light directly back into the camera, and you will see bright glowing dots where the eyes are: It is a version of the “red-eye” effect in family snapshots taken with flashbulbs.
If you took a high-contrast infrared motion picture of an audience watching a film… you would see a galaxy of these dots against a field of black. And when someone in the audience blinked, you would see a momentary interruption in a pair of those dots. (pg. 70)