page_title: Stroboscopic effect
section_title: Acceptance criterion
hierarchical_section_title: Stroboscopic effect / Unwanted effects in common lighting / Objective assessment of stroboscopic effect / Acceptance criterion
caption_attribution_description: English: A typical test setup for stroboscopic effect testing.
context_page_description: The stroboscopic effect is a visual phenomenon caused by aliasing that occurs when continuous motion is represented by a series of short or instantaneous samples. It occurs when the view of a moving object is represented by a series of short samples as distinct from a continuous view, and the moving object is in rotational or other cyclic motion at a rate close to the sampling rate. It also accounts for the "wagon-wheel effect", so-called because in video, spoked wheels sometimes appear to be turning backwards.
  A strobe fountain, a stream of water droplets falling at regular intervals lit with a strobe light, is an example of the stroboscopic effect being applied to a cyclic motion that is not rotational. When viewed under normal light, this is a normal water fountain. When viewed under a strobe light with its frequency tuned to the rate at which the droplets fall, the droplets appear to be suspended in mid-air. Adjusting the strobe frequency can make the droplets seemingly move slowly up or down.
context_section_description: If the value of SVM equals one, the input modulation of the light waveform produces a stroboscopic effect that is just visible, i.e. at the visibility threshold. This means that an average observer will be able to detect the artefact with a probability of 50 %. If the value of the visibility measure is above unity, the effect has a probability of detection of more than 50 %. If the value of the visibility measure is smaller than unity, the probability of detection is less than 50 %. These visibility thresholds show the average detection of an average human observer in a population. This does not, however, guarantee acceptability. For some less critical applications, the acceptability level of an artefact might be well above the visibility threshold. For other applications, the acceptable levels might be below the visibility threshold. NEMA 77-2017 amongst others gives guidance for acceptance criteria in different applications.
caption: Figure 3: Generic setup to test lighting equipment for its stroboscopic effect performance.
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