Light flicker

from Wikipedia, the free encyclopedia

The light flicker describes fluctuations in the luminance of an electrically operated light source , which is caused by the structure and construction of the light source. It is to be distinguished from the term flicker , the change in luminance of which is caused by usually unwanted fluctuations in the mains voltage in the power grid . In English there is no such term separation, flicker is often referred to as stroboscopic flicker .

General

After the invention of the first electrical lighting in the form of the carbon filament lamp in the second half of the 19th century and its operation with alternating current , the issue of freedom from flicker and temporal uniformity of light was discussed in the “Manual of Lighting Technology” in 1938. Electric light sources such as incandescent lamps or fluorescent tubes , which are operated directly with the mains AC voltage , flicker at twice the mains frequency . Due to the thermal inertia, the flicker with incandescent lamps is less than with fluorescent lamps and compact fluorescent lamps . In the case of LED lamps , the optical flicker is determined by the type of power supply usually integrated in the lamp base: Technically more complex switched-mode power supplies allow flicker-free operation of the light-emitting diodes, whereas a noticeable flicker can occur with the inexpensive capacitor power supplies .

Effect on the organism

Sunlight as a natural light source does not represent flickering light, which is why living beings have not developed any measures to compensate for flickering light in the course of evolution . The flickering of light stresses the nervous system to the extent that in extreme cases ( stroboscope ) the individual images perceived in rapid succession have to be converted by the brain into a continuous process sequence. Deceptions to the effect that continuously moving objects are not perceived as such are also possible, which is why strongly flickering light according to DIN EN 12464-1 must be avoided or classified as dangerous at corresponding machine workplaces and must therefore be prevented or compensated. The perceptual sluggishness of the seeing organism is in turn related to the speed of information processing in the retina and the brain, which in turn depends on how strongly these organisms are dependent on perceiving fast movements.

The flicker fusion frequency "is the frequency at which a sequence of light flashes is perceived as a continuous light." It applies to the state of rest of the sighted being in relation to the light source and depends on other factors, such as the amplitude of the light modulation, the mean light intensity, Wavelength, the position on the retina at which the stimulation takes place and the degree of light-dark adaptation.

1 in 4,000 people are at risk of epilepsy attacks in the frequency range from 3 Hz to 70 Hz, especially 15 to 20 Hz. Photosensitivity is much more common .

In the literature a distinction is made between:

  • the stroboscopic effect , in which the eye is at rest and the object moves in the stroboscopic light (cartwheel effect)
  • the pearl cord effect or phantom array effect, in which the moving eye observes a stroboscopic light source or an object illuminated by stroboscopic light.

With rapid eye or object movements, light flickering up to a frequency of approx. 2000 Hz can lead to so-called pearl-string effects (in which a retinal image of a light source is perceived as a broken line) or stroboscopic effects. There is a research gap with regard to “dynamic” pearl cord fusion frequencies, which must be further scientifically investigated in detail. According to DIN 12464-1, flicker causes disturbances and can cause physiological effects such as headaches. Strobe effects can create dangerous situations by changing the perception of rotating or moving machine parts.

Measurement method

Measurement series via hardware

The following recommendation applies to the structure of the measuring device in order to record the optical influences on the organism:

  • Use of a V-lambda photodiode to suppress the infrared light component and limit it to the visible light component of an incandescent lamp
  • Transimpedance amplifier with variable transimpedance for optimal use of the vertical measuring range
  • Antialiasing - low-pass filter to comply with the sampling theorem , depending on the sampling frequency . In practice, due to the use of switching regulators, light also flickers at frequencies of 80 kHz or more.
  • Analog-digital converter with a sampling frequency of min. 10 kHz (for sufficient display and calculation)
  • Dynamic of 12 bits for sufficient vertical resolution
  • Depending on the calculation method, a recording of at least five periods of up to one second duration

Calculation method

There are various efforts to measure light flicker, whereby various details must be taken into account for a meaningful measured value (taking into account the above-mentioned effects on the organism):

  • Change amplitude relative to the constant component of light
  • Fundamental flicker frequency
  • Waveform (frequency components)
  • Light-dark adaptation (contrast from darkest to lightest value)
  • Stroboscopic effect (parts of complete darkness), (phantom array effect), pearl effect
  • Human perception threshold depending on amplitudes and flicker frequencies
  • Operating modes according to classic retrofit use (dimmed, undimmed, 12 V ~)

The approaches are divided into the two categories “time-based” and “frequency-based”.

Time-based calculation methods

A measured value for the flicker over this path results mainly from amplitude ratios. Frequencies are not taken into account, which limits the suitability as a measurement method for flicker.

Contrast method (alternating portion)

The companies Admesy BV and CHROMA ATE INC thus describe a process which puts the alternating component (Max − Min or RMS after subtracting the direct component) of the light emission into relation to the direct component (mean or ½Max + ½Min). This ratio is sometimes given in decibels. The level of the base frequency is sometimes taken into account, e.g. B. minus 12 dB at 50 Hz.

Calculation according to IESNA

The somewhat widespread measuring method according to IES: RP-16-10 results in 2 measured values: 1. The flicker in percent (Percent Flicker;% Flicker) and 2. The flicker index (Flicker Index). The correlation of% Flicker with the Flicker Index changes with the waveform. The stroboscopic effect can be determined when the% flicker has reached 100%, but this does not allow any statement about its intensity ( duty cycle ). How the two values, which are only used in combination, ultimately lead to a flicker value is not transparent for the user. A smartphone app from Viso Systems uses this calculation, but it has decisive disadvantages that can lead to incorrect measurements and thus to wrong decisions:

  • Lamps with high-frequency switching regulators are sampled too low (violation of the sampling theorem )
  • How the two values ​​together lead to a good / bad decision is not documented

In addition, when calculating according to IES: RP-16-10, neither the fundamental flicker frequency, which is important for perceptibility, nor the operating modes are taken into account.

Frequency-based calculation method

For the calculation, the measurement signal is broken down into its frequency components using Fourier transformation . Periodic signals can thus be described as a discrete spectrum of individual frequency components, the basic flicker frequency and other frequency components in the case of a non-sinusoidal course are included in the calculation.

JEITA and VESA method

For the JEITA method, the companies Admesy BV and CHROMA ATE INC apply a frequency-dependent evaluation characteristic after breaking down the curve into its frequency components, which evaluates all frequencies ≥ 65 Hz with 0. The resulting highest individual amplitude determines the flicker frequency and the flicker amplitude.

The VESA value is 3.01 dB higher due to the squaring of the individual FFT amplitudes. By including only one frequency of max. 65 Hz, curve shapes and the main problem of flickering with twice the mains frequency, the stroboscopic effect (phantom array effect), and the pearl line effect are not taken into account.

Calculation according to LRC

The ASSIST group of the Lighting Research Center applies the discrete Fourier transform to the values ​​sampled at 2 kHz . The frequency components obtained are evaluated according to a characteristic curve that is based on the flicker fusion frequency . A so-called “metric value” arises from the formation of the effective value (square mean value) of the evaluated frequency components. This in turn is subjected to a further evaluation formula, from which the detection probability of the flicker is given in percent. By choosing the upwardly limited flicker fusion frequency of 70 Hz, the main problem of flickering with twice the mains frequency, the stroboscopic effect (phantom array effect), and the pearl line effect are not taken into account.

Calculation as CFD

The compact flicker degree CFD (Compact Flicker Degree) applies to those with min. 20 kHz for 1 s sampled individual values ​​on the discrete Fourier transformation and evaluates the frequency components depending on the frequency. The root mean square of all evaluated frequency components forms the CFD measured value as a percentage unit. Dimmable lamps are measured a second time with 25% of the maximum light emission and the higher (worse) of the two (dimmed, undimmed) is considered the final value. Due to the large frequency range for the frequency-dependent evaluation, all known effects effective on humans are taken into account (e.g. stroboscopic light with 2 kHz is not considered to be flicker-free for a long time). A 5-stage categorization according to the traffic light procedure enables identification and assessment.

Calculation as P st LM and SVM

The CIE ( International Commission on Illumination ) coined the term Temporal Light Artifacts (TLA), the calculation of which is made up of two components:

  • the frequency range up to 80 Hz is covered by the P st LM based on IEC / TR 61547-1, IEC 61000-4-15 and IEC / EN 61000-3-3.
  • The SVM covers the frequency range from 80 Hz to 2 kHz according to CIE TN 006: 2016 ( discrete Fourier transformation and frequency-dependent weighting).

The SVM measurement method also detects flicker at twice the line frequency. A disadvantage is the need to communicate two values ​​in order to arrive at an overall statement about the flickering of a light source.

Limit values

On December 5, 2019, the EU published the new Regulation (EU) No. 2019/2020 with requirements for the environmentally friendly design of lighting products based on a decision of the EU member states of December 17, 2018. According to this regulation, which will come into force in September 2021, LED light sources - both inorganic (ALED) and organic (OLED) - must meet the following requirements at full load: P st LM ≤ 1.0 and SVM ≤ 0.4. Until then, no normative measurement procedure for light flicker has been specified; accordingly, there are no numerical limit values ​​that have to be defined depending on the application. According to DIN EN 12464-1, lighting systems should be designed in such a way that flickering and stroboscopic effects are avoided. The Energy Star standard, which came into force on September 30, 2014, specifies, for example, that the maximum flicker rate and flicker index must be specified. The Alliance for Solid-State Illumination Systems and Technologies (ASSIST), on the other hand, regards a flicker content of more than 20% as no longer acceptable at 100 Hz and more than 30% at 120 Hz. In a single percentage value, the CFD rates light flickering below 1% as "flicker-free", up to 12.5% ​​as "low-flicker" (like the light bulb), up to 25% as "acceptable" and above 50% you are outside of the recommendation DIN EN 12464-1.

Causes and Actions

The causes of light flickering and remedial measures differ for the individual light source technologies. The light flicker can be completely eliminated by supplying the light element with direct voltage. It can be reduced by choosing the frequency of the light flicker so high (greater than approx. 30 kHz) that the nervous system of the seeing living being, which is either at rest or in motion relative to the light source, does not flicker due to its physical properties can perceive. There are fundamentally three different technologies for generating artificial light.

Lightbulb

In the case of an incandescent lamp, the thermal inertia of the filament dampens its temperature and, depending on it, the emitted light. A flicker is also present in the incandescent lamp, but it is comparatively low and soft. During operation, the filament is heated to incandescence at approx. 2500 ° C, and in the area of ​​the zero crossing (no power supply) it cools down slightly, which results in a light flicker amplitude of about 5 ... 20% (the higher the power consumption, the lower the flicker) and results in a sinusoidal shape. Experience has shown that this has no effect on human health - incandescent lamps are generally suitable for workplaces on moving machines.

Fluorescent lamps

Fluorescent lamps can be divided into:

  • Energy-saving lamp or compact fluorescent lamp : the electronic ballast works with switching frequencies of around 40 kHz. Depending on the interior design, the lamps flicker more or less at 100 Hz.
  • Fluorescent lamps with conventional ballast (KVG): strong 100 Hz flicker. In the zero crossings, the yellow fluorescent material continues to glow and somewhat reduces the flicker. Older lamps can show 50 Hz flicker components.
  • Fluorescent lamps with electronic ballast (EVG) are mostly flicker-free, as they often work with a frequency of> 30000 Hz. Compact fluorescent lamps are excluded from this, as there is usually not enough space in their base for such high-quality power supplies. Nevertheless, compact fluorescent lamps usually have less flicker than fluorescent lamps with conventional ballasts.
  • Cold cathode lamps are partially to the backlight (backlight) of LCD -Fernsehern and monitors used and flicker there principle not (high transducer frequency), but using pulse width modulation dimming with frequencies above 100 Hz. In the case of neon signs , the flicker depends on whether an electronic transverter or a stray field transformer is used. The latter lead to strong flicker, the former not.

see also:

Laptop display with LED backlight, the brightness of which has been dimmed or works in energy-saving flicker mode. A hand moved in front of the screen illustrates the flicker frequency of around 167 Hz

High pressure lamps

Sodium vapor lamps , high pressure mercury vapor lamps and metal halide lamps flicker heavily or slightly, depending on the ballast - depending on whether they are operated on a conventional ballast or an electronic ballast. Ultra-high pressure lamps ( xenon arc lamps in film projectors and headlights, high-pressure mercury vapor lamps) are operated with direct current. If there is no battery operation, the flicker depends on the quality of the smoothing in the power supply unit.

LED bulbs

The light produced by an LED follows very quickly and proportionally the current flowing through it. Only the fluorescent substance of white LEDs is a little dampening. In order to avoid flickering, operation with constant voltage direct current or sufficiently high-frequency modulated is therefore necessary. Initially, it does not matter whether the ballast is a simple or complicated electronic circuit - flicker-free operation requires a smoothing capacitor that can bridge the zero points of the mains voltage with the energy stored in it. Such electrolytic capacitors are expensive, heat sensitive and large.

Depending on the ballast, light modulations with degrees of modulation of <1… 100% occur with retrofit lamps . The relevant base frequency is twice the network frequency , which is 100 Hz in the European electricity network.

Markings in trade

On December 5, 2019, the EU published the new Regulation (EU) No. 2019/2015 with requirements for the energy consumption labeling of light sources. According to this regulation, the two values ​​P st LM and SVM must be entered in the product database from March 2021. Until then, it is not possible for the end user, dealer or distributor to distinguish between flicker-free and extremely flickering lamps when they are switched off. Only after the purchase does the end consumer determine whether the product is flickering or not. Since, as shown above, the flicker of light at 100 Hz is perceived very differently by individuals, there are very different statements about the products in online reviews.

literature

  • Arnold Wilkins, Jennifer Veitch, Brad Lehman: LED Lighting Flicker and Potential Health Concerns: IEEE Standard PAR1789 Update . Conference contribution: Energy Conversion Congress and Exposition (ECCE) 2010, IEEE, doi: 10.1109 / ECCE.2010.5618050 ( online )

Individual evidence

  1. ↑ Ethan Biery: Understand the lighting flicker frustration. December 4, 2015, accessed November 5, 2017 .
  2. ↑ Rudolf Sewig: Handbook of lighting technology. First part, Springer-Verlag 1938, reprint: ISBN 978-3-642-50384-9 .
  3. ↑ Sarina: The reptilian eye
  4. ^ Holger Luczak: Ergonomics. 2., completely reworked. Edition. Springer, Berlin et al. 1998, ISBN 3-540-59138-9 .
  5. ^ IEEE Standards Association (IEEE-SA): A Review of the Literature on Light Flicker. ( PDF; 682 kB )
  6. ↑ a b c d Naomi J. Miller, Michael Poplawski: SSL Flicker Fundamentals and Why We Care. ( PDF; 33.9 MB )
  7. ↑ a b c d e f Jens Mühlstedt, Patrick Roßner, Angelika C. Bullinger: The dark side of light - discomfort due to flicker in (LED) lights in road traffic in relation to peripheral flicker fusion frequencies . In: Brandenburg, Doria, Gross, Günzler, Smieszek (ed.): Basics and applications of human-machine interaction . University Press of the TU Berlin, Berlin 2013, p. 408-416 ( qucosa.de [PDF] 757 kB, lecture documents of the 10th BWMMS, ISBN 978-3-7983-2626-2 online version).
  8. ↑ Mühlstedt, Roßner, Bullinger: The dark side of light - discomfort due to flicker in (LED) lights in road traffic in relation to peripheral flicker fusion frequencies. ( PDF; 797 kB )
  9. ↑ a b c d e f DIN EN 12464-1: Light and lighting - Lighting of workplaces - Part 1: Workplaces indoors , issue date: August 2011, http://www.beuth.de/de/norm/din-en -12464-1 / 136885861
  10. ↑ a b admesy.nl
  11. ↑ a b go-gddq.com
  12. ^ Illuminating Engineering Society of North America - IES (Ed.): The IESNA Lighting Handbook: Reference & Applications . 9th edition. New York 2000, ISBN 0-87995-150-8 .
  13. ↑ Viso Systems: flicker-tester, http://www.visosystems.com/products/flicker-tester/
  14. ^ Lighting Research Center; Rensselaer Polytechnic Institute (ASSIST): Recommended metric for assessing the direct perception of light source flicker. Volume 11, Issue 3, ( PDF; 1.2 MB )
  15. ↑ a b Peter Erwin: Light flicker: cause and measurement: an overview of the measurement process . In: Smarthouse electronics exchange . December 2016. ISSN  1613-9992 . "Online publication on Feb. 13, 2017"
  16. ↑ Peter Erwin, Peter Shackle: Understand a new flicker metric and its application to AC-LED light engines . In: LEDs Magazine . No. 96, April 2017, pp. 55–62. ISSN  2156-633X .
  17. ^ ZVEI, Central Association of the Electrical and Electronics Industry eV: Temporal Light Artefacts - TLA. Retrieved December 5, 2019 .
  18. ↑ IEC: Equipment for general lighting purposes - EMC immunity requirements - Part 1: An objective light flickermeter and voltage fluctuation immunity test method. Retrieved December 5, 2019 .
  19. ↑ CIE: Visual Aspects of Time-Modulated Lighting Systems - Definitions and Measurement Models. Retrieved December 5, 2019 .
  20. ↑ EU Commission: Regulation (EU) 2019/2020 of the Commission of October 1, 2019 laying down ecodesign requirements for light sources and separate control gear. Open forum EU lighting regulations, December 5, 2019, accessed on December 8, 2019 .
  21. ↑ Paul Scheidt: Flickering in LED lights: Does that really have to be? In: elektronikpraxis.vogel.de. Vogel Communications Group, January 7, 2015, accessed August 21, 2018 .
  22. ↑ EU Commission: Commission Regulation (EU) 2019/2015 of March 11, 2019 to supplement Regulation (EU) 2017/1369 with regard to the energy consumption labeling of light sources. Open forum EU lighting regulations, December 5, 2019, accessed on December 8, 2019 .