Joseph Plateau of Belgium, inventor of the stroboscope, a device that employs bright pulses of light to illuminate a vibrating or rotating object and to make it appear motionless or moving very slowly. The stroboscope works by permitting the eye only a brief glimpse of the object or a portion of it at time intervals that correspond to the object's rate of vibration or rotation. The rate of movement and the light pulses can be adjusted to match.
Plateau used a disk with radial slits that he turned while viewing a rotating wheel; when the rotational speed of the disk and the wheel matched exactly, the wheel appeared motionless. Other pioneers employed rotating or vibrating mirrors to produce light pulses. By the later 19th century the camera was being used to capture stroboscopic images for motion studies, and stroboscopic photography has since become the major application for these devices. The use of stroboscopic photographs to produce the illusion of motion also led to the development of motion pictures.
The modern stroboscope, an electronic device, was brought to perfection in 1931 by the American scientist Harold Edgerton. Such devices can produce flashes equivalent to 50,000 watts of incandescent light. A typical flash lasts roughly five millionths of a second, and 100 such flashes may be produced each second. Stroboscopes are commonly available for setting the ignition timing of motor vehicle engines. They are also used industrially when moving machines must be checked for quality, and in the laboratory for studying mechanical systems in motion. Simple stroboscopes are sometimes used for stage-lighting effects.