A stroboscope, also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving, or stationary. It consists of either a rotating disk with slots or holes or a lamp such as a flashtube which produces brief repetitive flashes of light. Usually, the rate of the stroboscope is adjustable to different frequencies. When a rotating or vibrating object is observed with the stroboscope at its vibration frequency, it appears stationary. Thus stroboscopes are also used to measure frequency.
A bouncing ball captured with a stroboscopic flash at 25 images per second.
1540 Strobolume, a professional grade stroboscope produced by General Radio
Close-up view of the 1540 Strobolume control box
Stroboscope on a gramophone turntable
The stroboscopic effect is a visual phenomenon caused by aliasing that occurs when continuous rotational or other cyclic motion is represented by a series of short or instantaneous samples at a sampling rate close to the period of the motion. It accounts for the "wagon-wheel effect", so-called because in video, spoked wheels sometimes appear to be turning backwards.
Figure 1: Stroboscopic effect resulting from a moving screwdriver lit with a square-waveform modulated light source with a modulation frequency of 100 Hz, duty cycle of 50 % and 100 % modulation (SVM = 4,9); small photo inset shows absence of stroboscopic effect if screwdriver is not moved
Figure 2: Stroboscopic effect contrast threshold function (see Visibility)
Figure 3: Generic setup to test lighting equipment for its stroboscopic effect performance
