Temporal light effects (TLEs) is the general term for all possible effects resulting from temporal light modulations (TLMs).

Root cause

Light emitted from

lighting Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylig ...

equipment such as luminaires and lamps may vary in strength as function of time, either intentionally or unintentionally. Intentional light variations are applied amongst others for warning, signalling (e.g. traffic-light signalling, flashing aviation light signals), entertainment (like stage lighting), metrology (

strobe light A strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of light. It is one of a number of devices that can be used as a stroboscope. The word originated from the Ancient Greek ('), meaning ...

for measurement of rotation speed), navigation (like optical beacons, lighthouses) or for communication (

Li-Fi Li-Fi (also written as LiFi) is a wireless communication technology which utilizes light to transmit data and position between devices. The term was first introduced by Harald Haas during a 2011 TEDGlobal talk in Edinburgh. Li-Fi is a light comm ...

). Generally, the light output of lighting equipment may also have unintentional light level modulations due to the lighting equipment itself. The magnitude, shape, periodicity and frequency of the TLM 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). These TLM properties may vary over time due to aging effects, component failure or end-of-life behavior. Furthermore external factors such as incompatibility with dimmers or presence of mains-supply voltage fluctuations (

power-line flicker Power-line flicker is a visible change in brightness of a lamp due to rapid fluctuations in the voltage of the power supply. The voltage drop is generated over the source Electrical impedance, impedance of the grid by the changing load current of a ...

) play a role. TLMs are also known from non-electrical lighting sources like candle light or they may be experienced while driving along a row of trees lit by the sun or by driving through a tunnel lit by luminaires having a certain spacing.See flicker problems in the Queensway Tunnel

Categories of temporal light effects

Obviously, the intentional TLMs listed under 'Root cause' above result into wanted effects. In many cases TLMs may cause unacceptable annoying effects such as flicker or stroboscopic effect that can directly be perceived by humans. These effects are categorized as

temporal light artefacts Temporal Light Artefacts (TLAs) are undesired effects in the visual perception of a human observer induced by temporal light modulations. Two well-known examples of such unwanted effects are flicker and stroboscopic effect. The term 'flicker' refers ...

(TLAs). Apart from annoyance, flicker may induce epileptic reactions in susceptible people (

photosensitive epilepsy Photosensitive epilepsy (PSE) is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights; bold, regular patterns; or regular moving patterns. PSE affects approximately o ...

). Temporal light modulations may also induce disturbance or malfunction of equipment that applies light as input signal. Examples are barcode scanners, cameras and medical test equipment. Interference of photo, film and video cameras may become visible by humans after displaying the image or replaying the recorded video or projection of a film.Flicker-free vide
tutorial
Typical unwanted artefacts that can be seen on a display or projection screen are flickering of the image and banding (still or rolling) through the image. Unwanted temporal light effects of equipment are categorized as temporal light interference (TLI).

References

Other references

* CIE technical committe
TC 1-83
on VISUAL ASPECTS OF TIME-MODULATED LIGHTING SYSTEMS. * CIE technical committe
TC 2-89
on MEASUREMENT OF TEMPORAL LIGHT MODULATION OF LIGHT SOURCES AND LIGHTING SYSTEMS Film and video technology Lighting Optical illusions

Root cause

Categories of temporal light effects

See also

References

Other references