Flicker fusion threshold

Last updated

The flicker fusion threshold, also known as critical flicker frequency or flicker fusion rate, is the frequency at which a flickering light appears steady to the average human observer. It is a concept studied in vision science, more specifically in the psychophysics of visual perception. A traditional term for "flicker fusion" is "persistence of vision", but this has also been used to describe positive afterimages or motion blur. Although flicker can be detected for many waveforms representing time-variant fluctuations of intensity, it is conventionally, and most easily, studied in terms of sinusoidal modulation of intensity.

Contents

There are seven parameters that determine the ability to detect the flicker:

  1. the frequency of the modulation;
  2. the amplitude or depth of the modulation (i.e., what is the maximum percent decrease in the illumination intensity from its peak value);
  3. the average (or maximum—these can be inter-converted if modulation depth is known) illumination intensity;
  4. the wavelength (or wavelength range) of the illumination (this parameter and the illumination intensity can be combined into a single parameter for humans or other animals for which the sensitivities of rods and cones are known as a function of wavelength using the luminous flux function);
  5. the position on the retina at which the stimulation occurs (due to the different distribution of photoreceptor types at different positions);
  6. the degree of light or dark adaptation, i.e., the duration and intensity of previous exposure to background light, which affects both the intensity sensitivity and the time resolution of vision;
  7. physiological factors such as age and fatigue. [1]

Explanation

As long as the modulation frequency is kept above the fusion threshold, the perceived intensity can be changed by changing the relative periods of light and darkness. One can prolong the dark periods and thus darken the image; therefore the effective and average brightness are equal. This is known as the Talbot-Plateau law. [2] Like all psychophysical thresholds, the flicker fusion threshold is a statistical rather than an absolute quantity. There is a range of frequencies within which flicker sometimes will be seen and sometimes will not be seen, and the threshold is the frequency at which flicker is detected on 50% of trials.

Different points in the visual system have very different critical flicker fusion rate (CFF) sensitivities; the overall threshold frequency for perception cannot exceed the slowest of these for a given modulation amplitude. Each cell type integrates signals differently. For example, rod photoreceptor cells, which are exquisitely sensitive and capable of single-photon detection, are very sluggish, with time constants in mammals of about 200 ms. Cones, in contrast, while having much lower intensity sensitivity, have much better time resolution than rods do. For both rod- and cone-mediated vision, the fusion frequency increases as a function of illumination intensity, until it reaches a plateau corresponding to the maximal time resolution for each type of vision. The maximal fusion frequency for rod-mediated vision reaches a plateau at about 15  hertz (Hz), whereas cones reach a plateau, observable only at very high illumination intensities, of about 60 Hz. [3] [4]

In addition to increasing with average illumination intensity, the fusion frequency also increases with the extent of modulation (the maximal relative decrease in light intensity presented); for each frequency and average illumination, there is a characteristic modulation threshold, below which the flicker cannot be detected, and for each modulation depth and average illumination, there is a characteristic frequency threshold. These values vary with the wavelength of illumination, because of the wavelength dependence of photoreceptor sensitivity, and they vary with the position of the illumination within the retina, because of the concentration of cones in central regions including the fovea and the macula, and the dominance of rods in the peripheral regions of the retina.

Technological considerations

Display frame rate

Flicker fusion is important in all technologies for presenting moving images, nearly all of which depend on presenting a rapid succession of static images (e.g. the frames in a cinema film, TV show, or a digital video file). If the frame rate falls below the flicker fusion threshold for the given viewing conditions, flicker will be apparent to the observer, and movements of objects on the film will appear jerky. For the purposes of presenting moving images, the human flicker fusion threshold is usually taken between 60 and 90 Hz, though in certain cases it can be higher by an order of magnitude. [5] In practice, movies since the silent era are recorded at 24 frames per second and displayed by interrupting each frame two or three times for a flicker of 48 or 72 Hz. Television typically originates at 50 or 60 frames or interlaced fields per second.

The flicker fusion threshold does not prevent indirect detection of a high frame rate, such as the phantom array effect or wagon-wheel effect, as human-visible side effects of a finite frame rate were still seen on an experimental 480 Hz display. [6]

Display refresh rate

Cathode-ray tube (CRT) displays typically operated at a vertical scan rate of 60 Hz, the same as SDTV content they displayed, which resulted in noticeable flicker. The same was true of other impulsed technologies such as plasma displays. Some systems could increase refresh rate to higher values such as 72, 75, 100, or 120 Hz to ease this problem, though even if the faster refresh is an integer multiple of the source material framerate to eliminate judder, without higher framerate source material this causes the perception of duplicate images. [7] Any flicker on sample and hold technologies such as LCD or OLED, is unrelated to refresh rate and far less conspicuous, instead coming from incidental design compromises such as fluorescent backlights, PWM dimming, or temporal dithering, all of which are eliminated on some devices that do not flicker at all. Because of the resulting display motion blur inherent to sample and hold screens, in applications where accurate motion perception is prioritized over user fatigue, the correct type of flicker can be reintroduced through techniques such as backlight strobing or black frame insertion.

Lighting

Flicker is also important in the field of domestic (alternating current) lighting, where noticeable flicker can be caused by varying electrical loads, and hence can be very disturbing to electric utility customers. Most electricity providers have maximum flicker limits that they try to meet for domestic customers.

Fluorescent lamps using conventional magnetic ballasts flicker at twice the supply frequency. Electronic ballasts do not produce light flicker since the phosphor persistence is longer than a half cycle of the higher operation frequency of 20 kHz. The 100–120 Hz flicker produced by magnetic ballasts is associated with headaches and eyestrain. [8] Individuals with high critical flicker fusion threshold are particularly affected by light from fluorescent fixtures that have magnetic ballasts: their EEG alpha waves are markedly attenuated and they perform office tasks with greater speed and decreased accuracy. The problems are not observed with electronic ballasts. [9] Ordinary people have better reading performance using high-frequency (20–60 kHz) electronic ballasts than magnetic ballasts, [10] although the effect was small except at high contrast ratio.

The flicker of fluorescent lamps, even with magnetic ballasts, is so rapid that it is unlikely to present a hazard to individuals with epilepsy. [11] Early studies suspected a relationship between the flickering of fluorescent lamps with magnetic ballasts and repetitive movement in autistic children. [12] However, these studies had interpretive problems [13] and have not been replicated.

LED lamps generally do not benefit from flicker attenuation through phosphor persistence, the notable exception being white LEDs. Flicker at frequencies as high as 2000 Hz (2 kHz) can be perceived by humans during saccades, [14] and frequencies above 3000 Hz (3 kHz) have been recommended to avoid human biological effects. [15]

Visual phenomena

In some cases, it is possible to see flicker at rates beyond 2000 Hz (2 kHz) in the case of high-speed eye movements (saccades) or object motion, via the "phantom array" effect. [16] [17] Fast-moving flickering objects zooming across view (either by object motion, or by eye motion such as rolling eyes), can cause a dotted or multicolored blur instead of a continuous blur, as if they were multiple objects. [18] Stroboscopes are sometimes used to induce this effect intentionally. Some special effects, such as certain kinds of electronic glowsticks commonly seen at outdoor events, have the appearance of a solid color when motionless but produce a multicolored or dotted blur when waved about in motion. These are typically LED-based glow sticks. The variation of the duty cycle upon the LED(s), results in usage of less power while by the properties of flicker fusion having the direct effect of varying the brightness.[ citation needed ] When moved, if the frequency of duty cycle of the driven LED(s) is below the flicker fusion threshold timing differences between the on/off state of the LED(s) becomes evident, and the color(s) appear as evenly spaced points in the peripheral vision.

A related phenomenon is the rainbow effect, where different colors are displayed in different places on the screen for the same object due to fast motion.

Flicker

Flicker is the perception of visual fluctuations in intensity and unsteadiness in the presence of a light stimulus, that is seen by a static observer within a static environment. Flicker that is visible to the human eye will operate at a frequency of up to 80 Hz. [19]

Stroboscopic effect

The stroboscopic effect is sometimes used to "stop motion" or to study small differences in repetitive motions. The stroboscopic effect refers to the phenomenon that occurs when there is a change in perception of motion, caused by a light stimulus that is seen by a static observer within a dynamic environment. The stroboscopic effect will typically occur within a frequency range between 80 and 2000 Hz, [19] though can go well beyond to 10,000 Hz for a percentage of population. [20]

Phantom array

Phantom array, also known as the ghosting effect, occurs when there is a change in perception of shapes and spatial positions of objects. The phenomenon is caused by a light stimulus in combination with rapid eye movements (saccades) of an observer in a static environment. Similar to the stroboscopic effect, the phantom effect will also occur at similar frequency ranges. The mouse arrow is a common example [21] of the phantom array effect.

Non-human species

The flicker fusion threshold also varies between species. A 2014 survey of the critical fusion frequency in animals found the lowest value (6.7 Hz) in the cane toad (Bufo marinus) and the highest value (400 Hz) in the black fire beetle (Melanophila acuminate). [22] Estimates for different species of bird vary from 40 Hz to 140 Hz, with higher values tending to be associated with faster-moving species. [23] Many mammals have a higher proportion of rods in their retina than humans do, and it is likely that they would also have higher flicker fusion thresholds. This has been confirmed in dogs. [24]

If artificial lighting is perceived as flickering by some animals, the aversive effect might be an issue for animal welfare and conservation. However, those animals most liable to perceive flicker tend to be diurnal species active in bright light, and thus least likely to be exposed to artificial lighting outside of captivity. [22] Size and metabolic rate are two further factors associated with the variation in flicker fusion thresholds: small animals with a high metabolic rate tend to have high values. [25] [26]

See also

Related Research Articles

<span class="mw-page-title-main">Persistence of vision</span> Optical illusion

Persistence of vision is the optical illusion that occurs when the visual perception of an object does not cease for some time after the rays of light proceeding from it have ceased to enter the eye. The illusion has also been described as "retinal persistence", "persistence of impressions", simply "persistence" and other variations. A very commonly given example of the phenomenon is the apparent fiery trail of a glowing coal or burning stick while it is whirled around in the dark.

Frame rate, most commonly expressed in frames per second or FPS, is typically the frequency (rate) at which consecutive images (frames) are captured or displayed. This definition applies to film and video cameras, computer animation, and motion capture systems. In these contexts, frame rate may be used interchangeably with frame frequency and refresh rate, which are expressed in hertz. Additionally, in the context of computer graphics performance, FPS is the rate at which a system, particularly a GPU, is able to generate frames, and refresh rate is the frequency at which a display shows completed frames. In electronic camera specifications frame rate refers to the maximum possible rate frames could be captured, but in practice, other settings may reduce the actual frequency to a lower number than the frame rate.

<span class="mw-page-title-main">Fluorescent lamp</span> Lamp using fluorescence to produce light

A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, to produce ultraviolet and make a phosphor coating in the lamp glow. Fluorescent lamps convert electrical energy into useful light much more efficiently than incandescent lamps, but are less efficient than most LED lamps. The typical luminous efficacy of fluorescent lamps is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output.

<span class="mw-page-title-main">Strobe light</span> Device producing regular flashes of 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 στρόβος (stróbos), meaning "act of whirling".

Flicker is a visible change in brightness between cycles displayed on video displays. It applies to the refresh interval on cathode-ray tube (CRT) televisions and computer monitors, as well as plasma computer displays and televisions.

<span class="mw-page-title-main">Stroboscope</span> Instrument used to make a cyclically moving object appear to be slow-moving, or stationary

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.

<span class="mw-page-title-main">Stroboscopic effect</span> Visual phenomenon

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.

<span class="mw-page-title-main">Compact fluorescent lamp</span> Fluorescent lamps with folded tubes, often with built-in ballast

A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent light bulb; some types fit into light fixtures designed for incandescent bulbs. The lamps use a tube that is curved or folded to fit into the space of an incandescent bulb, and a compact electronic ballast in the base of the lamp.

<span class="mw-page-title-main">Wagon-wheel effect</span> Optical illusion

The wagon-wheel effect is an optical illusion in which a spoked wheel appears to rotate differently from its true rotation. The wheel can appear to rotate more slowly than the true rotation, it can appear stationary, or it can appear to rotate in the opposite direction from the true rotation.

Flicker-free is a term given to video displays, primarily cathode ray tubes, operating at a high refresh rate to reduce or eliminate the perception of screen flicker. For televisions, this involves operating at a 100 Hz or 120 Hz hertz field rate to eliminate flicker, compared to standard televisions that operate at 50 Hz or 60 Hz (NTSC), most simply done by displaying each field twice, rather than once. For computer displays, this is usually a refresh rate of 70–90 Hz, sometimes 100 Hz or higher. This should not be confused with motion interpolation, though they may be combined – see implementation, below.

<span class="mw-page-title-main">Electrical ballast</span> Device to limit the current in lamps

An electrical ballast is a device placed in series with a load to limit the amount of current in an electrical circuit.

<span class="mw-page-title-main">Chubb illusion</span> Optical illusion

The Chubb illusion is an optical illusion or error in visual perception in which the apparent contrast of an object varies substantially to most viewers depending on its relative contrast to the field on which it is displayed. These visual illusions are of particular interest to researchers because they may provide valuable insights in regard to the workings of human visual systems.

<span class="mw-page-title-main">Underwater vision</span> The ability to see objects underwater

Underwater vision is the ability to see objects underwater, and this is significantly affected by several factors. Underwater, objects are less visible because of lower levels of natural illumination caused by rapid attenuation of light with distance passed through the water. They are also blurred by scattering of light between the object and the viewer, also resulting in lower contrast. These effects vary with wavelength of the light, and color and turbidity of the water. The vertebrate eye is usually either optimised for underwater vision or air vision, as is the case in the human eye. The visual acuity of the air-optimised eye is severely adversely affected by the difference in refractive index between air and water when immersed in direct contact. Provision of an airspace between the cornea and the water can compensate, but has the side effect of scale and distance distortion. The diver learns to compensate for these distortions. Artificial illumination is effective to improve illumination at short range.

Chronostasis is a type of temporal illusion in which the first impression following the introduction of a new event or task-demand to the brain can appear to be extended in time. For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade. This elicits an overestimation in the temporal duration for which that target stimulus was perceived. This effect can extend apparent durations by up to half a second and is consistent with the idea that the visual system models events prior to perception.

<span class="mw-page-title-main">Fluorescent lamps and health</span>

Fluorescent lamps have been suggested to affect human health in various ways.

A phantom contour is a type of illusory contour. Most illusory contours are seen in still images, such as the Kanizsa triangle and the Ehrenstein illusion. A phantom contour, however, is perceived in the presence of moving or flickering images with contrast reversal. The rapid, continuous alternation between opposing, but correlated, adjacent images creates the perception of a contour that is not physically present in the still images. Quaid et al. have also authored a PhD thesis on the phantom contour illusion and its spatiotemporal limits which maps out limits and proposes mechanisms for its perception centering around magnocellularly driven visual area MT.

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

<span class="mw-page-title-main">Temporal light interference</span>

Temporal light interference (TLI) is an unacceptable degradation of the performance of an equipment or system that has an optical input for its intended functioning and is caused by a temporal light modulation disturbance. A temporal light modulation (TLM) disturbance may be either an intentional or unintentional temporal light modulation (TLM) of lighting equipment such as luminaires or lamps. Examples of equipment that can be interfered are barcode scanners, cameras and test equipment.

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. Flicker is a directly visible light modulation at relatively low frequencies and small intensity modulation levels. Stroboscopic effect may become visible for a person when a moving object is illuminated by modulated light at somewhat higher frequencies (>80 Hz) and larger intensity variations.

In visual perception, flicker is a human-visible change in luminance of an illuminated surface or light source which can be due to fluctuations of the light source itself, or due to external causes such as due to rapid fluctuations in the voltage of the power supply or incompatibility with an external dimmer.

References

  1. ↑ Davis S. W. (1955). "Auditory and visual flickerfusion as measures of fatigue". The American Journal of Psychology. 68 (4): 654–657. doi:10.2307/1418795. JSTOR   1418795. PMID   13275613.
  2. ↑ "eye, human." Encyclopædia Britannica. 2008. Encyclopædia Britannica 2006 Ultimate Reference Suite DVD
  3. ↑ Hecht, Selig; Shlaer, Simon (1936). "Intermittent Stimulation by Light". Journal of General Physiology. 19 (6): 965–977. doi:10.1085/jgp.19.6.965. PMC   2141480 . PMID   19872976.
  4. ↑ "[Neuroscience] Re: Flicker Fusion Threshold Examples". Bio.net. Retrieved 2013-05-05.
  5. ↑ Davis, James (2015), "Humans perceive flicker artefacts at 500 Hz", Sci Rep, 5: 7861, Bibcode:2015NatSR...5E7861D, doi:10.1038/srep07861, PMC   4314649 , PMID   25644611
  6. ↑ Rejhon, Mark (August 16, 2017). "Test Results of an Experimental 480 Hz Display". Blur Busters.
  7. ↑ "Strobe Crosstalk: Blur Reduction Double-Images". Blur Busters. Retrieved 2024-02-01.
  8. ↑ l. Mccoll, Shelley; a. Veitch, Jennifer (2001). "Full-spectrum Fluorescent lighting : A review of its effects on physiology and health". Psychological Medicine. 31 (6): 949–964. doi:10.1017/S0033291701004251. PMID   11513381. S2CID   1105717 . Retrieved 2008-04-23.
  9. ↑ Küller R, Laike T (1998). "The impact of flicker from fluorescent lighting on well-being, performance and physiological arousal". Ergonomics. 41 (4): 433–47. doi:10.1080/001401398186928. PMID   9557586.
  10. ↑ Veitch JA, McColl SL (1995). "Modulation of fluorescent light: flicker rate and light source effects on visual performance and visual comfort" (PDF). Light Res Tech. 27 (4): 243–256. doi:10.1177/14771535950270040301. S2CID   36983942 . Retrieved 2012-06-28.
  11. ↑ Binnie CD, de Korte RA, Wisman T (1979). "Fluorescent lighting and epilepsy". Epilepsia. 20 (6): 725–7. doi:10.1111/j.1528-1157.1979.tb04856.x. PMID   499117. S2CID   26527159.
  12. ↑ Colman RS, Frankel F, Ritvo E, Freeman BJ (1976). "The effects of fluorescent and incandescent illumination upon repetitive behaviors in autistic children". J Autism Child Schizophr. 6 (2): 157–62. doi:10.1007/BF01538059. PMID   989489. S2CID   41749390.
  13. ↑ Turner M (1999). "Annotation: Repetitive behaviour in autism: a review of psychological research". J Child Psychol Psychiatry. 40 (6): 839–49. doi:10.1017/S0021963099004278. PMID   10509879.
  14. ↑ Roberts JE, Wilkins AJ (2013). "Flicker can be perceived during saccades at frequencies in excess of 1 kHz". Lighting Research & Technology . 45 (1): 124–132. doi:10.1177/1477153512436367. S2CID   51247933.
  15. ↑ Lehman B, Wilkins AJ (2014). "Designing to Mitigate Effects of Flicker in LED Lighting: Reducing risks to health and safety". IEEE Power Electronics Magazine. 2014 (9): 18–26. doi:10.1109/MPEL.2014.2330442. S2CID   2503129.
  16. ↑ Wilkins, A. J. (2014) Energy - Docket Optical System. energy.ca.gov
  17. ↑ Roberts, JE; Wilkins, AJ (2013). "Flicker can be perceived during saccades at frequencies in excess of 1 k Hz". Lighting Research & Technology. 45: 124–132. doi:10.1177/1477153512436367. S2CID   51247933.
  18. ↑ Why do LED tail lights trail to me and not to the rest of my family? The Naked Scientists (August 2012)
  19. 1 2 "Driving the Flicker-Free Effect" (PDF). Unios Australia. 2019-02-05. Retrieved 2019-02-08.
  20. ↑ "Flicker Parameters for Reducing Stroboscopic Effects from Solid-state Lighting Systems" (PDF). Alliance for Solid-State Illumination Systems and Technologies (ASSIST). 11 (1). Lighting Research Center: 6. 2012.
  21. ↑ "TestUFO: Animation Of Phantom Array Effect With Mouse Arrow". www.testufo.com. Retrieved 2019-05-20.
  22. 1 2 Inger, R.; Bennie, J.; Davies, T.W.; Gaston, K.J. (29 May 2014). "Potential Biological and ecological effects of flickering artificial light". PLOS ONE. 9 (5): e98631. Bibcode:2014PLoSO...998631I. doi: 10.1371/journal.pone.0098631 . hdl: 10871/21221 .
  23. ↑ Potier, S.; Lieuvin, M.; Pfaff, M.; Kelber, A. (1 January 2019). "How fast can raptors see?". Journal of Experimental Biology. 223 (Pt 1). doi:10.1242/jeb.209031. PMID   31822552.
  24. ↑ "A Dog's Eye View | On Point with Tom Ashbrook". Onpoint.wbur.org. Archived from the original on October 20, 2013. Retrieved 2013-05-05.
  25. ↑ Healy, Kevin; McNally, Luke; Ruxton, Graeme D.; Cooper, Natalie; Jackson, Andrew L. (2013-10-01). "Metabolic rate and body size linked with perception of temporal information". Animal Behaviour. 86 (4). Elsevier: 685–696. doi:10.1016/j.anbehav.2013.06.018. PMC   3791410 . PMID   24109147.
  26. ↑ "Slo-mo mojo: How animals perceive time". The Economist. London. 2013-09-21. Retrieved 2013-10-20.

(Wayback Machine copies)

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.