Red–eye reduction functions emit short flashes of light in quick succession before the camera actually takes the picture. The burst of light beforehand makes the subject's pupils constrict, and there's not enough time between flashes for them to re-dilate, thereby reducing the red–eye effect in photos.
Red eye occurs because when you take a flash photograph – the camera produces a big burst of light to illuminate the subject and that burst of light goes in
. eyes in some flash photographs? Take a look at the science behind why red eyes happen.. If a flash is bright enough, it can cause reflection off of the retina.