Editing Stroboscopic effect (section)

=== Root causes ===
Light emitted from [[lighting]] equipment such as luminaires and lamps may vary in strength as function of time, either intentionally or unintentionally. Intentional light variations are applied for warning, signalling (e.g. [[Traffic-light signalling and operation|traffic-light signalling]], flashing aviation light signals), entertainment (like [[stage lighting]]) with the purpose that flicker is perceived by people. Generally, the light output of lighting equipment may also have residual unintentional light level modulations due to the lighting equipment technology in connection with the type of electrical mains connection. For example, lighting equipment connected to a single-phase mains supply will typically have residual TLMs of twice the mains frequency, either at 100 or 120&nbsp;Hz (depending on country).

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). If the modulation frequency is below the [[flicker fusion threshold]] and if the magnitude of the TLM exceeds a certain level, then such TLMs are perceived as [[Flicker (light)|flicker]]. Light modulations with modulation frequencies beyond the flicker fusion threshold are not directly perceived, but illusions in the form of stroboscopic effect may become visible (example see Figure 1).
[[File:Photo4Wiki strobo effect screwdriver.jpg|thumb|563x563px|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'']]
[[Light-emitting diode|LEDs]] do not intrinsically produce temporal modulations; they just reproduce the input current waveform very well, and any ripple in the current waveform is reproduced by a light ripple because LEDs have a fast response; therefore, compared to conventional lighting technologies (incandescent, fluorescent), for LED lighting more variety in the TLA properties is seen. Many types and topologies of [[LED circuit|LED driver]] circuits are applied; simpler electronics and limited or no buffer capacitors often result in larger residual current ripple and thus larger temporal light modulation.

Dimming technologies of either externally applied [[dimmer]]s (incompatible dimmers) or internal light-level regulators may have additional impact on the level of stroboscopic effect; the level of temporal light modulation generally increases at lower light levels.

''NOTE – The root cause temporal light modulation is often referred to as flicker. Also, stroboscopic effect is often referred to as flicker. Flicker is however a directly visible effect resulting from light modulations at relatively low modulation frequencies, typically below 80 Hz, whereas stroboscopic effect in common (residential) applications may become visible if light modulations are present with modulation frequencies, typically above 80 Hz.''