Modelling visibility of temporal light artefacts Citation for published version (APA): Perz, M. (2019). Modelling visibility of temporal light artefacts. Technische Universiteit Eindhoven. Document status and date: Published: 05/02/2019 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. 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A catalogue record is available from the Eindhoven University of Technology Library ISBN: 978-90-386-4681-7. Keywords: Visual perception, Temporal Light Artefacts, Flicker, Stroboscopic Effect Printed by: Proefschriftmaken || www.proefschriftmaken.nl Modelling visibility of temporal light artefacts PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de rector magnificus prof.dr.ir. F.P.T. Baaijens, voor een commissie aangewezen door het College voor Promoties, in het openbaar te verdedigen op dinsdag 5 februari 2019 om 13:30 uur. door Małgorzata Perz geboren te Jelenia Góra, Polen Dit proefschrift is goedgekeurd door de promotoren en de samenstelling van de promotiecommissie is als volgt: Voorzitter: prof. dr. ir. A.W.M. Meijers 1e promotor: prof. dr. I.E.J. Heynderickx copromotor: dr. I.M.L.C. Vogels copromotor: dr. D. Sekulovski (Signify) leden: prof. dr. P. Hanselaer (KU Leuven) prof. dr. ir. W.L. IJzerman prof. dr. S.C. Pont (TUD) prof. dr. ir. Y.A.W. de Kort Het onderzoek of ontwerp dat in dit proefschrift wordt beschreven is uitgevoerd in overeenstemming met de TU/e Gedragscode Wetenschapsbeoefening. Contents 1 Introduction 1 1.1 Light and visual perception . 3 1.2 Visual aspects of time-modulated lighting systems . 13 1.3 Objective . 21 1.4 Outline . 21 2 Modeling flicker visibility in the frequency domain 23 2.1 Introduction . 24 2.2 Temporal Contrast Sensitivity Function . 27 2.3 Flicker Visibility Measure . 31 2.4 Flicker visibility of realistic waveforms . 41 2.5 Discussion . 45 2.6 Conclusions . 48 3 Modeling flicker visibility in the time domain 51 3.1 Introduction . 52 3.2 Temporal processing of the HVS . 56 3.3 Derivation of the Time domain Flicker Visibility Measure . 58 3.4 Determining single-order statistic . 63 3.5 Time domain Flicker Visibility Measure . 68 3.6 Validation of the TFVM and other measures . 69 3.7 Discussion . 75 3.8 Conclusions . 77 4 Modeling visibility of the stroboscopic effect 79 4.1 Introduction . 80 4.2 Literature on temporal artefacts . 81 4.3 Testing methodology . 84 4.4 Sinusoidal and square waveforms . 88 4.5 Stroboscopic Visibility Measure . 92 4.6 General discussion and conclusions . 97 v 5 Stroboscopic effect: contrast threshold function and dependence on illumination 103 5.1 Introduction . 104 5.2 Literature overview . 106 5.3 Goal of the current study . 107 5.4 Effect of frequency . 108 5.5 Stroboscopic effect contrast threshold function . 115 5.6 Effect of illumination level . 117 5.7 Comparison of results from different experiments . 120 5.8 General Discussion . 122 6 General discussion 125 6.1 Applicability of the proposed measures . 126 6.2 Probability of detection . 129 6.3 Acceptability . 131 6.4 Phantom array effect . 134 6.5 Biological effects . 135 6.6 Outlook for the future . 138 Bibliography 141 Summary 155 List of publications 157 Curriculum Vitae 159 vi Introduction 1 As I write this page, it is already dark outside, and I sit in front of my laptop. The brightness of the display is almost fully on, creating a high luminous contrast with the background: my rather dark living room. When I look around I see that the light emitted by my fancy lamp is subtly changing colors, and I can see the headlights of cars, which are rapidly passing by in the street outside. Indeed, my visual field encompasses scenes of a substantial complexity, but despite that, I can clearly see the shapes and colors of different objects. This rather incredible perceptual ability is enabled by the intricate structure and processing of our visual system, one of the most complex systems in the human body [110]. Then again, I could hardly see anything at all, once the sun is down, if not for the artificial lighting, which for decades has been readily available to illuminate our homes, offices, and cities [23]. The natural lighting comes from the Sun, and presumably the performance of our visual system is optimal under conditions of such natural illumination. An artificial lighting comes from electric light sources, and since it can differ from natural lighting in many aspects, it can also have an impact on our visual perception. How the artificial lighting differs from the natural one largely depends on the technology, and over the last century the most commonly used conventional lighting technologies included hot and highly inefficient incandescent bulbs, and different types of gas-discharge lamps, best-known of which are fluorescent lamps [23, 120]. As lighting quality of these sources is defined by their limited technological capabilities, their impact on visual perception is also easily defined. However, the same cannot be said about light emitting diodes (LEDs), the rapidly-evolving semiconductor technology, which is currently transforming the world of artificial lighting. One indication of just how valuable LEDs are, is the fact that in 2014 the Nobel Prize in physics was awarded to three scientists: Isamu Akasaki, Hiroshi Amano and Shuji Nakamura, for the invention of “efficient blue light-emitting diodes leading to bright and energy-saving white light sources” [3]. Making the announcement, the Nobel jury stated that “[. ] the Prize awards an invention of greatest benefit to mankind”. The superiority of LEDs over conventional sources is underpinned by, next to energy-efficiency, a flexible control of properties of their illumination, which can be tailored to different applications and specific needs. LEDs, which can be very small sources, have bright luminous output, the spectrum of which can be almost arbitrary, and which can be changed at a very fast rate. These versatile qualities of LED lighting can have a huge impact on our visual perception. 1 The topic of this thesis is derived from one property of luminous output of LEDs, namely its rapid change rate. It occurs because LEDs respond almost instantaneously to the changes of the driving current, meaning that a modulation of the current is converted into modulation of the luminous output. On one hand, this is advantageous as it allows for unique functionalities, that are not possible with conventional light sources, for instance one can transfer data via LED light output, a method known as LiFi [53]. On the other hand, modulated luminous output can result in unwanted changes in the perception of our environment, called temporal light artefacts (TLAs) [41]. The modulation is most commonly induced by mains power, which is an alternating current (AC) supply, delivered at a frequency of 50 Hz or 60 Hz. Additionally, modulation can be induced by mains voltage fluctuations typically caused by overloading on the network or it can result from interactions between the (incompatible) driving and dimming electronics. Exposure to such modulated lighting, that gives rise to TLAs, not only impacts our percep- tion of lighting quality, leading to annoyance and irritation, but studies in this area suggest that it can also have a negative impact on our physiology, for instance, it can trigger migraines [52] and epileptic seizures [175]. It is known that TLAs can be prevented by suppressing the modulation in the light output of LEDs, however this typically requires a trade-off with other aspects of the sources, like cost, size, lifetime or efficiency [8, 137]. The challenge is to find such modulation of the luminous output, that does not give rise to visible TLAs, and at the same time, that does not compromise on the other aspects.