Also called a strobe, an instrument that
produces regular brief flashes of intense light, used to study periodic
motion, to test machinery, and in high-speed photography. Stroboscopes usually
have a calibrated scale from which the number of flashes per minute can
be read. When the flash frequency exactly matches that of the rotation or
vibration, the object is illuminated in the same position during each cycle,
and appears stationary. A gas discharge lamp is used, with flash duration
about 1 microsecond and frequency from 2 to 3,000 hertz.