The perception of flashing lights is influenced by a phenomenon known as persistence of vision, which is the tendency of the visual system to retain an image for a short period of time even after the original stimulus has been removed. This persistence allows us to perceive motion and continuous visual stimuli.
When lights are turned on and off slowly, the duration of each individual light phase is longer, and the persistence of vision enables us to perceive the transitions between light and dark. Our visual system integrates these transitions, resulting in the perception of flashing lights.
However, when lights are turned on and off very fast, the duration of each light phase becomes very short, often below the threshold of perception for most individuals. The rapid alternation between light and dark does not allow enough time for the visual system to register each individual transition. As a result, the flashing effect is not perceived, and the light appears to be continuously on.
This phenomenon is utilized in various technologies such as television and cinema, where a rapid succession of still images creates the illusion of motion. By presenting a sequence of static frames in quick succession, persistence of vision allows us to perceive smooth motion rather than a series of discrete images.