Stroboscopic effect
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 (as opposed to a continuous view) 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 (such as on horse-drawn wagons) sometimes appear to be turning backwards.
[1] Simon Stampfer, who coined the term in his 1833 patent application for his stroboscopische Scheiben (better known as the "phenakistiscope"), explained how the illusion of motion occurs when during unnoticed regular and very short interruptions of light, one figure gets replaced by a similar figure in a slightly different position.
Sixty-one flashes will occur before the object is seen in the same position again, and the series of images will be perceived as if it is rotating backwards once per second.
The same could be applied at other frequencies like the 50 Hz characteristic of electric distribution grids of most of countries in the world.
In the case of motion pictures, action is captured as a rapid series of still images and the same stroboscopic effect can occur.
Stroboscopic principles, and their ability to create an illusion of motion, underlie the theory behind animation, film, and other moving pictures.
For instance, a stroboscope is tool that produces short repetitive flashes of light that can be used for measurement of movement frequencies or for analysis or timing of moving objects.
Various scientific committees have assessed the potential health, performance and safety-related aspects resulting from temporal light modulations (TLMs) including stroboscopic effect.
[4][5][6] Adverse effects in common lighting application areas include annoyance, reduced task performance, visual fatigue and headache.
[8][9] Stroboscopic effects may also lead to unsafe situations in workplaces with fast moving or rotating machinery.
Further background and explanations on the different TLA phenomena including stroboscopic effect is given in a recorded webinar “Is it all just flicker?”.
[10] Possible stroboscopic induced medical issues in some people include migraines & headaches, autistic repetitive behaviors, eye strain & fatigue, reduced visual task performance, anxiety and (rarer) epileptic seizures.
The magnitude, shape, periodicity and frequency of the TLMs will depend on many factors such as the type of light source, the electrical mains-supply frequency, the driver or ballast technology and type of light regulation technology applied (e.g. pulse-width modulation).
However, use of such capacitors significantly shortens the lifetime of the LED, as they are found to have the highest failure rate among all components.
Detailed explanations on the visibility of stroboscopic effect and other temporal light artefacts are also given in CIE TN 006:2016[7] and in a recorded webinar “Is it all just flicker?”.
[12] SVM is calculated using the following summation formula: where Cm is the relative amplitude of the m-th Fourier component (trigonometric Fourier series representation) of the relative illuminance (relative to the DC-level); Tm is the stroboscopic effect contrast threshold function for visibility of stroboscopic effect of a sine wave at the frequency of the m-th Fourier component (see § Visibility).
None of these metrics are suitable to predict actual human perception because human perception is impacted by modulation depth, modulation frequency, wave shape and if applicable the duty cycle of the TLM.
[citation needed] Because of the illusion that the stroboscopic effect can give to moving machinery, it is advised that single-phase lighting is avoided.
[citation needed] The 100/120 Hertz stroboscopic effect in commercial lighting may lead to disruptive issues and non-productive results in workspaces such as hospitals & medical facilities, industrial facilities, offices, schools or video conferencing rooms.
