Stroboscopic Effect

The stroboscopic effect is a visual phenomenon caused by aliasing, occurring when continuous rotational or other cyclic motion is represented by a series of short or instantaneous samples rather than a continuous view, at a sampling rate close to the period of the motion itself. It accounts for the well-known wagon-wheel effect, in which spoked wheels, such as those on horse-drawn wagons filmed on camera, sometimes appear to be turning backwards. A strobe fountain, a stream of water droplets falling at regular intervals and lit by a strobe light, illustrates the same effect applied to non-rotational cyclic motion: under ordinary light it looks like an ordinary fountain, but under a strobe light tuned to the droplets' falling rate, the droplets appear frozen in mid-air, and adjusting the strobe's frequency can make them seem to drift slowly upward or downward. Simon Stampfer coined the term in his 1833 patent application for the stroboscopische Scheiben, better known as the phenakistiscope, explaining that the illusion of motion arises when, during brief, unnoticed interruptions of light, one figure is replaced by a similar figure in a slightly different position, a principle that can be used to make any series of images appear to move in any desired direction.