Legibility Investigations of the Binem Display for E-Reader Applications

UPTEC IT 10 009 Examensarbete 30 hp Mars 2010

Legibility Investigations of the BiNem Display for e-Reader Applications

Robert Nordström

Abstract Legibility Investigations of the BiNem Display for e-Reader Applications Robert Nordström

Teknisk- naturvetenskaplig fakultet UTH-enheten The electronic reader (e-reader) application is a new device that recently has entered the commercial market. The device is thin, light weighted and portable Besöksadress: with a display that is developed for longtime reading books. Since the display Ångströmlaboratoriet Lägerhyddsvägen 1 technology used in e-readers differs from conventional displays used in e.g. Hus 4, Plan 0 computer monitors and TV-screens, it is not fully known how the optical properties of this new display technology are translated into legibility and reading Postadress: comfort. Box 536 751 21 Uppsala The BiNem® display is a bistable reflective liquid crystal display. The purpose of Telefon: this thesis is to investigate and optimize the legibility of the BiNem display for e- 018 – 471 30 03 reader applications. BiNem displays with various optical properties have been

Telefax: investigated and also benchmarked against an E-Ink Vizplex display present in the 018 – 471 30 00 Amazon Kindle 2 e-reader device. Real users have performed various tasks such as visual letter recognition, preference ranking, and long time reading along with Hemsida: subjective measures to evaluate the legibility and reading experience of the http://www.teknat.uu.se/student different displays.

The results show no statistic difference between the BiNem and E-Ink Vizplex display in terms of legibility. Further, higher contrast displays were preferred over higher brightness and sharp and well-defined letters were requested.

We have found that the BiNem e-reader display is competitive to the E-Ink Vizplex display present in Amazon Kindle 2 device in terms of legibility. An optimized optical stack for the BiNem display for e-reader applications is presented.

Handledare: Jesper Osterman Ämnesgranskare: Bengt Sandblad Examinator: Anders Jansson ISSN: 1401-5749, UPTEC IT 10 009 Tryckt av: Reprocentralen ITC

Svensk sammanfattning

Den elektroniska läsaren (e-läsare) är en ny uppﬁnning som nyligen har kommit ut på den allmänna marknaden. Apparaten är tunn, lätt och portabel med en display som är speciellt utvecklad för att läsa böcker på. Eftersom displayens teknik skiljer sig mot konventionella displayer, som används tex. i datorer och TV-apparater, så är det inte fullt känt hur de optiska egenskaperna hos denna nya displayteknik översätts till läsbarhet.

BiNem R är en bistabil reflektiv liquid crystal display. Syftet med denna uppsats är att undersöka och optimera läsbarheten av BiNem-displayen för e-läsare. Flera BiNem displaykonfigurationer med olika optiska egenskaper har undersökts och jämförts mot en E-Ink Vizplex display som används i Amazon Kindle 2 e-läsaren. Riktiga användare har utfört olika typer av tester som korta betygssättning, visuell bokstavsletning och längre läs uppgifter med subjektiva utvärderingar för att betygsätta läsbarheten och läsupplevelsen av de olika displayerna. Ingen statistisk skillnad mellan BiNem och E-Ink Vizplex displayen när det gäller läsbarhet kunde hittas. Vidare så föredrog användarna hög kontrast över hög brightness. Skarpa och väldefinerade bokstäver var en annan egenskap som efterfrågades. Slutsatsen av rapporten är att BiNem displayen är en utmärkt kandidat för e-läsare och är konkurrenskraftig mot E-Ink Vizplex displayen när det gäller läsbarhet. Vidare så presenteras en optimerad BiNem display för e-läsare.

Contents

1 Introduction 9 1.1 Background...... 9 1.2 NEMOPTIC...... 10 1.3 Aim...... 10 1.4 Delimitations...... 11

2 Theory 12 2.1 Optical properties of displays...... 12 2.1.1 Light...... 12 2.1.2 Brightness...... 13 2.1.3 Contrast...... 14 2.1.4 Bright state color...... 15 2.1.5 Gray scales and anti-alaising...... 15 2.1.6 Diffuse and specular reflection...... 16 2.1.7 Viewing angles...... 17 2.1.8 Inter pixel...... 18 2.2 Paper as a display...... 19 2.3 LCD...... 20 2.3.1 Liquid crystal...... 20 2.3.2 Polarizer...... 21 2.3.3 Two polarizer...... 22 2.3.4 One polarizer...... 23 2.3.5 Mono-/bi-stable...... 23 2.3.6 Parallax effect in 1- and 2-polarizer...... 23 2.4 Electrophoretic...... 24 2.4.1 E-Ink...... 26

1 2.5 BiNem...... 26 2.5.1 Top coating...... 26 2.5.2 Top polarizer...... 26 2.5.3 Retardation compensation...... 26 2.5.4 Diffuse adhesive...... 26 2.5.5 White balancing film...... 27 2.5.6 BiNem cell...... 28 2.5.7 Reflector...... 28 2.5.8 Optical stack...... 28 2.6 Legibility research...... 28

3 Experimental design 30 3.1 Method...... 30 3.2 Overview design...... 30 3.2.1 Selection...... 31 3.2.2 Ethic consideration...... 31 3.3 Phase 1: Legibility benchmarking of current 2-polarizer BiNem configuration vs. E-Ink Vizplex display and printed paper...... 32 3.3.1 Aim...... 32 3.3.2 Investigated displays...... 32 3.3.3 Test description...... 32 3.4 Phase 2: Top coating and diffuse adhesive optimization of 1-polarizer BiNem configuration 35 3.4.1 Aim...... 35 3.4.2 Investigated displays...... 35 3.4.3 Test description...... 36 3.5 Phase 3: Reading comfort evaluation of optimized 1-polarizer BiNem configuration.... 37 3.5.1 Aim...... 37 3.5.2 Investigated displays...... 37 3.5.3 Test description...... 38 3.6 Phase 4: User preference evaluation including latest viewing angle enhanced 1-polarizer BiNem configuration...... 39 3.6.1 Aim...... 39 3.6.2 Investigated displays...... 40 3.6.3 Test description...... 41

2 4 Results and conclusions 42 4.1 Phase 1...... 42 4.1.1 Results...... 42 4.1.2 Discussion...... 43 4.1.3 Conclusions...... 44 4.2 Phase 2...... 45 4.2.1 Results...... 45 4.2.2 Discussion...... 46 4.2.3 Conclusions...... 47 4.3 Phase 3...... 47 4.3.1 Results...... 47 4.3.2 Discussion...... 48 4.3.3 Conclusions...... 48 4.4 Phase 4...... 48 4.4.1 Results...... 48 4.4.2 Discussion...... 49 4.4.3 Conclusions...... 49

5 Overall conclusions 51 5.1 Conclusions...... 51 5.2 Evaluation...... 52

References 53

A Consent letter in phase 1 55

B Subjective questionnaire from phase 1 56

C Images used for ranking task 59

D Raw data 61

3 List of Tables

2.1 The performance of the diﬀerent light modes in various lighting...... 21 2.2 Optical stack for the BiNem 2-polarizer...... 28 2.3 Optical stack for the BiNem 1-polarizer...... 28

3.1 Thesis phases with tested displays and type of test...... 31 3.2 Main characteristics of BiNem BF700, Amazon Kindle 2 and High graded printed paper. 33 3.3 Optical properties and main characteristics of configurations used in phase 2...... 36 3.4 Specifications of top coatings used in phase 2...... 36 3.5 E-reader properties used in phase 3...... 38 3.6 Optical properties of configurations used in phase 4...... 40

4.1 Results of letter recognition task...... 42 4.2 Comments from interviews in phase 3...... 50

D.1 Raw data phase 1...... 62 D.2 Raw data phase 2...... 64 D.3 Raw data phase 4...... 66

4 List of Figures

1.1 Forecasted e-paper market revenues from NanoMarkets[1]...... 9

2.1 Color spectrum of white light along with the luminosity function (graph)...... 13 2.2 A polar plot of the measured brightness of a display...... 14 2.3 Three LCDs with different text- and background colors. The upper and middle display has dark state characters and the lower display has bright state characters...... 15 2.4 CIE 1976 color space...... 16 2.5 Three different grayscale levels...... 16 2.6 From left to right: 16-level, 4-level, 2-level with dithering, and 2-level grayscale without dithering...... 17 2.7 Light gets a specular reflection from various materials such as a mirror...... 17 2.8 Light gets a diffuse reflection from various materials such as paper...... 17 2.9 In the right image the pixels are in the same bright state as the inter pixel. To the left the pixels are in dark state and the inter pixel bright state inter pixel degrades the black level of that area. The pointers pointing at the interpixel...... 19 2.10 Geometrical contrast ratio as a function of the inter pixel ratio area...... 19 2.11 Transmissive mode...... 21 2.12 Reflective mode...... 21 2.13 In the solid phase are the cigar-like molecules oriented the same way and they can not move around. In the liquid phase have the molecules no particular orientation and they are completely free to move around. The liquid crystal phase is in between, the molecules have an orientation but can move around some...... 22 2.14 Two polarizing filters and two light beams (red and green). The red light beam is absorbed in the first polarizer and the blue gets absorbed in the second...... 22 2.15 2-polarizer reflective display...... 22 2.16 1-polarizer reflective display...... 23 2.17 From the two viewpoints the same object can be viewed but the backgrounds are different. 24

5 2.18 The upper image shows a magnification of a 2-polarizer display, the parallax effect is clearly apparent. The lower image shows an 1-polarizer display with inner reflector with no parallax effect. Both photos are taken in the same angle with a spot light source from the left up. Both displays are reflective LCDs but the 2-polarizer is thicker than the 1-polarizer display...... 24 2.19 Three containers in an electrophoretic display. The surface of the middle container will appear bright white for the viewer and the other two will appear dark...... 25 2.20 When the diffuse adhesive is placed on top of the BiNem cell the light gets scattered one time on its way in and one time on its way out of the display...... 27 2.21 When diffuse adhesive is placed at the bottom of the BiNem cell the light gets scattered only once...... 27

3.1 Displays used in legibility investigations phase 1...... 32 3.2 A part of pseudo text block used in letter recognition task...... 33 3.3 Statement from subjective questionnaire used in phase 1...... 34 3.4 Lighting conditions in phase 1...... 35 3.5 Displays used in phase 2...... 36 3.6 E-readers used in legibility investigations phase 3. From left to right: BiNem BF700 in SYLEN, Amazon Kindle 2 and Apple iPhone...... 39 3.7 The four displays used in phase 4...... 40 3.8 The biaxial ﬁlm keeps the contrast and color even when viewed in angle compared to the uniaxial ﬁlm. This results in a more uniform display appearance...... 41

4.1 Results of letter recognition task...... 42 4.2 Results of reading speed task...... 42 4.3 The main important results from subjective questionnaire. The highlighted green scores are the most significant ones...... 43 4.4 Results from phase 2. The diagrams show how the different configurations were rated at each position. See Table 3.3 for configuration explanation...... 44 4.5 Results from phase 2. Average ranking score for all displays. See Table 3.3 for configuration explanation...... 45 4.6 Average ranking score of different age groups...... 46 4.7 Average ranking score of different lighting conditions. Green: Bright indirect illumination, Yellow: Dark indirect illumination, and Red: Specular illumination...... 46 4.8 Results from phase 3. Diagrams show how the different configurations was rated at each position. See Table 3.5 for configuration explanation...... 49

6 4.9 Results from phase 3. Average ranking score for all displays. See Table 3.5 for conﬁguration explanation...... 49

C.1 Phase 2 ranking image. The black outer borders are not part of the image...... 59 C.2 Phase 3 ranking image. The black outer borders are not part of the image...... 60

7 8 Chapter 1

Introduction

1.1 Background effects of paper manufacturing and they can also be implemented in office environment for Electronic readers (e-readers) are a new improved ergonomics at work. These type of application that entered the commercial market displays are called electronic paper (e-paper) and in 2004. An e-reader is portable pocket book like are developed to be as paper-like as possible. device that is intended to read books on, but it Many e-reader applications use e-paper displays. can display many types of information. The main One advantage of e-paper displays compared to difference between e-readers and other portable conventional displays is that the e-paper display display-devices is that the e-reader is mainly does not require constant power supply, power is developed to have superior legibility for a good only required when updating the content of the reading experience. The type of display used in display which makes the battery life of portable computer monitors can display text, color-images, applications such as e-reader, that uses this type video and other information, and when the of displays, very long. The e-reader application is computer became a standard in every office it was today (May 3, 2010) still a relative new product, believed to be the start of the paperless office. but the market is growing and the future looks However, instead of reading documents on the promising, as shown in Figure 1.1. monitor, people prefer to print out the documents on paper because they find the paper more legible and less visual fatigue than the computer monitor. Therefore paper is still used at daily basis in offices [2]. Numerous reports indicate that the continuous use of computer causes occupational problems and a high level of discomfort to the human eye [3][4]. A dynamic display with similar optics to normal paper would lower the Figure 1.1: Forecasted e-paper market revenues from needs for paper that decreases the environmental NanoMarkets[1]

9 Contrast ratio, brightness and viewing angles e-paper display for reading applications. are some of the display properties that are known to be very important for the human eye to be 1.3 Aim able to read and have a nice reading experience from conventional display monitors. Since the Knowledge about optical properties such as the e-paper display-technology is new and works in contrast, brightness and viewing angles is known a different manner, it is not fully known which in NEMOPTIC and these properties can easily optical properties and in which way they are be measured with optical instruments. But important for the legibility. E-paper displays have how are these properties translated into legibility an extremely low power consumption which results for humans? How are different age groups in more challenging to achieve superior optical experiencing the display? And how will the properties. Normally there is a trade-off between display performance vary under different lighting the optical properties, for example if the brightness conditions? The aim for this thesis is to is enhanced it is for the cost of some other property evaluating different e-paper displays focusing on such as the contrast ratio of the display. NEMOPTICs BiNem technology to understand which display properties that are important 1.2 NEMOPTIC for e-paper display to achieve high legibility. Different BiNem display configurations will be NEMOPTIC is a display company developing tested on real users with user-oriented tasks and and licensing its patented bistable liquid crystal subjective measures, these configurations will also based e-paper BiNem R technology for various be compared to e-paper display available on applications, such as electronic shelf labels the market to see if the BiNem displays are a (ELSs) and e-readers, in which low power competitive alternative for the e-paper market. consumption and at the same time excellent optical Since the display is meant to be used in an e- properties of the display are required. The reader application it is also important to adjust the company’s head quarter is located in Paris, France, display properties in order to meet the application while mass-production is realized together with features. The outcome of this thesis is an large multi-national Asian display manufacturers. optimized cost-effective BiNem displays solution NEMOPTIC has also access to a pilot line at LC- for reading applications. TEC DISPLAYS AB located in Borlänge, Sweden. The aim for the thesis is summarized in these At these facilities the company has a small group four bullets: working on the optics development of the BiNem • Optimize the legibility of the BiNem e-reader display. As a part of NEMOPTIC’s research display for reading books this thesis will provide data about how real users experience their specific display and these results • Understand which display properties that are will be a guide for further developing of the BiNem important for e-reader applications

10 • Benchmark the BiNem display versus various e-reader competitors

• Propose a cost-eﬀective optical stack solution for e-reader applications

1.4 Delimitations

To develop and produce an e-reader device with high legibility and usability is it not only the display that need to be optimized. How the information is presented on the display is as least important as the optical properties for a proper reading experience. Further if the graphical user interface is poorly developed for the actual users will nobody in the end use the device. Other important factors are the design and price of the product. This thesis focus on how the optical properties aﬀects the legibility of the display. No further investigations of these areas, all important for e- reader devices, have been performed:

• Text layout (font style, font size, line space, etc.)

• Graphical user interface

• Device design (color, buttons, size, etc.)

11 Chapter 2

Theory

2.1 Optical properties of the wavelengths correspond to different colors for displays humans. Humans are more and less sensitive to different wavelengths. The luminosity function 2.1.1 Light (the graph in Figure 2.1) defines the average visual sensitivity of the human eye to light of different Displays are used to show text, images and other wavelengths. The highest sensitivity is at 555 nm. information, humans perceive the information on The intensity of light is the amplitude of the the displays by interpreting the light coming from electromagnetic wave. The more intense it is, the the display surface. Some amount of light is always brighter the light. There are several units for needed to be able to read from a display. Light can measuring the intensity of light: be described as tiny packets called photons that behaves as a transverse electromagnetic wave[5]. • Lumens is the unit of total light output The three major properties of an electromagnetic from a light source in all directions. Lumens wave are intensity, wavelength and polarization. indicate a rate of energy flow. Thus, it The wavelength is defined by the frequency of is a power unit, like watt or horsepower. the lightwave. Electromagnetic waves wavelengths A typically indoor lamp has light outputs spans from 1 pico meter to 100 millions of ranging from 50 to 10,000 lumens. meters. However, all these wavelengths can not • Lux is an unit that indicates the density of be perceived by humans, we can only visually light that falls on a surface. This is measured "see" wavelengths between 380 and 780 nano with a light meter. Average indoor lighting meters (nm) [6]. The range of wavelengths are ranges from 100 to 1000 lux, and outdoor called visible light. Shorter wavelengths than 380 sunlight is about 50000 lux. nm down to 330 nm is called ultraviolet light. Wavelengths over 780 nm are called infrared light • Luminance is the light that gets reflected and is not visible for humans, but we can feel from a surface. The luminance is dependent them as heat. In Figure 2.1 can we see how on which angle you look at the surface. It is

12 measured in candelas/m2. 2.1.2 Brightness

Polarization is a property of waves that In general, brightness is not an official term, but describes the orientation of their oscillations. The is widely used when describing the visual quality polarization of light is perpendicular to the waves of displays. Brightness is the perceived amount direction of travel, normal light coming from a light of light coming from an area of light-source or a source can have various polarization, this is called surface reflecting light from a light-source (same unpolarized light. There is no visually difference as luminance as describe above). The brightness between light with different polarization but when of a display is used to describe how much light a light travels through special materials the light display can emit and it is normally computed by can, depending on its polarization, be transmitted, measure the luminance of the brightest part of the absorbed or reflected and this feature can be used display. Luminance is measured in candela/m2. in visual display units. Not all displays are emitting light, instead they reflects the presence surrounding luminance. The brightness of these types of displays are instead measured in how many percent of the incoming light that can be reflected back to the viewer. Most of the displays investigated in this thesis are of this type. Brightness of reflective displays is measured by the reflected luminance of the bright state of the display is divided with the corresponding measured reflectance of a white lambertian surface standard1. The luminosity function of the human Figure 2.1: Color spectrum of white light along with eye is also taken into the calculation. The the luminosity function (graph) function to calculate the luminosity reflectance or brightness is:

D65 light R 780 RBright(λ)P (λ)D(λ) dλ Brightn. = 380 (2.1) D65 is a standard illuminant defined by the R 780 RLmbStd(λ)P (λ)D(λ) dλ International Commission on Illumination (CIE). 380 It is a blend of light waves of different wavelengths where that corresponds to an average mid-day sun in Western Europe, and therefore it is also called • RBright is the reflectance of the bright state daylight illumination. This standard light is • RDark is the reflectance of the dark state used in optical measurements applications when 1The brightness of a lambertian surface is constant measuring optical display properties. regardless of the angle it is viewed

13 • P (λ) is the luminosity function of the human 2.1.3 Contrast eye Contrast is another important factor when describing the optical performance of any display. • D(λ) is the illuminant spectral distribution The contrast is defined by the difference in (D65 light) appearance of two parts of an area, normally the brightest and the darkest parts of a display. The luminance contrast is one of the ways to compute The display is illuminated with D65 light the contrast and it is simply the ratio between from all incident angles and the reflected light the brightest and darkest luminance, this is often intensity is measured. Since all reflected angles called the contrast ratio (CR) defined by: are measured the result is presented as a polar plot, see Figure 2.2. The polar plot shows the R 780 brightness of the measured display when viewed RBright(λ)P (λ)D(λ) dλ Contrast = 380 (2.2) R 780 from different angles. The center of the polar 380 RDark(λ)P (λ)D(λ) dλ plot is the brightness when viewed at 0◦ angle, the longer away from the center of the polar plot, where the larger angle. It is desirable to have a high • RBright is the reflectance of the bright state constant brightness in all angles, like a lambertian surface. When the brightness of the display is • RDark is the reflectance of the dark state given as only one value number it is the measured • P (λ) is the luminosity function of the human reflectance in center of the plot, at 0◦ angle. This eye is a NEMOPTICs standard for measuring the brightness. • D(λ) is the illuminant spectral distribution (D65 light)

For example the contrast ratio of a pocket book is the ratio between the paper brightness and the black printed text brightness. The CR function has been used when measuring all displays in this report. The contrast is very important for humans to easily distinguish diﬀerences in the content of a display, light grey letters printed on dark grey background will be diﬃcult to perceive Figure 2.2: A polar plot of the measured brightness while stressing the eyes. The International of a display Standards Organizations (ISO 9241, part 3) recommends a minimum 3:1 luminance contrast

14 ratio of text (lower luminance) and background (higher luminance), but 10:1 is preferred. This recommendation can be applied to any display where ﬁne-detail resolution is desirable.

2.1.4 Bright state color

Color is a visual perceptual property in humans that corresponds to red, green, blue and others. We perceive the light and interpreters the wavelength, intensity and purity that together correspond to a color. Individual perceive colors individually and some are not even able to see all colors. Advanced LCDs used in computers and TVs can show millions of various colors by mixing the three ground colors red, green and blue. However Figure 2.3: Three LCDs with different text- and simpler LCDs can normally only show two different background colors. The upper and middle display has colors, one bright and one dark color. The bright dark state characters and the lower display has bright color is called the bright state and the dark is state characters called the dark state color. In Figure 2.3 are three different LCDs shown with various bright and dark value in the CIE 1976 L*a*b color space [7], see state colors. E-paper displays should resemble the Figure 2.4. appearance of normal paper and therefore is the two states normally black and white. However it 2.1.5 Gray scales and anti-alaising can be difficult to achieve a neutral bright state color without degrading the blackness of the dark As described before, some e-reader displays can state. only show the two colors, black and white, but To get a display as attractive and readable as some of them can also show a blend of black and possible it is desirable to have such a white neutral white, gray. A display that can only show black color as possible of the bright state and at the same and white is called a two level gray scale display, time a deep black level dark state. if it can show black, white and two gray shades The color is measured by illuminating the bright between the black and white it is called a four level state of the display with a controlled D65 light and gray scales, see Figure 2.5. by analyzing the wavelength of the reflecting light. A two-level grayscale display can show text The result of the measurement corresponds to a efficiently, but high detail images and other Figures

15 with higher details. The problem with this is that it takes several pixels to render the same detail as on a display that can show grayscale, and thus the resolution of the image is reduced. Another advantage of grayscale is that text can be rendered with anti-aliasing. Anti-aliasing is a technique used to minimize the distortion artifacts when representing a high-resolution image at a lower resolution.

Figure 2.4: CIE 1976 color space

Figure 2.5: Three different grayscale levels will be rendered poorly. The use of gray scales significantly increases the quality of the rendered image, in Figure 2.6 can you see how the same 2.1.6 Diffuse and specular reflection image under different gray scale levels is rendered. The 16-level grayscale image shows higher details When light strikes an object, a number of things and the image looks much better than the 4-level could happen. The light wave could be absorbed and 2-level grayscale images. by the object, in which case its energy is converted Dithering is the process of combining 2 (or more to heat. The light wave could also be reflected or colors) together in a pattern to deceive the eye be transmitted by the object. Depending on the into thinking there is 3rd color. This technique surface material of the object the type of reflection can be used to enhance the details in an image on can vary between a more or less specular or diffuse a 2-level grayscale display. The display can not reflection. show gray on a single pixel, but if one pixel is In a specular reflection the direction of the black and one pixel next to it is white it will be incoming light and the outgoing reflected light has perceived by the human eye as gray because the the same angle in respect to the surface normal, see eye can not see each pixel thus it is too small. Figure 2.7. A mirror is one type of material that For example will 5 black pixel next to 2 white has a mainly specular reflection, a total specular pixels will be perceived as dark gray. A dithering reflection however is difficult to achieve, some light algorithm calculates where to render the black and is always scattered in other angles. The advantage white pixels on the display to achieve an image of having specular reflection in displays is that the

16 Figure 2.6: From left to right: 16-level, 4-level, 2-level with dithering, and 2-level grayscale without dithering incoming light can be reﬂected in a special angle to of which angle the user looks at it. Therefore, it is achieve a very high brightness in that angle, with desirable to have diﬀuse light coming from e-reader a cost of less brightness in other angles. displays.

Figure 2.7: Light gets a specular reflection from Figure 2.8: Light gets a diffuse reflection from various materials such as a mirror various materials such as paper

In a diffuse reflection on the other hand the 2.1.7 Viewing angles incoming light get scattered in all angles when it hits the surface, see Figure 2.8. Materials that are Many displays do not have an even appearance gibbous have this property, like paper. A material when viewed from different angles. The optical with a total diffuse reflection is called a lambertian. properties such as the contrast ratio, brightness Diffuse light is perceived to be more natural white and color can get distorted or worsen when the than specular light. display is viewed from large angles compared to If the light coming from a display is highly when viewed. The term viewing angles describes diffuse it is perceived more neutral white and the from which angles you can view the display without display will have the same brightness independent worsen the optical properties of it.

17 To achieve the same brightness in all viewing In many applications it would be desirable to angles must the light coming from the display be have a total even display appearance of the display distributed in all angles. Materials that scatter and this can partly be achieved with optical films the light traveling through the display and make that compensate for the light distortion inside the it more diffuse are used to improve the brightness display. viewing angles. But even if the light coming from the display is 2.1.8 Inter pixel diffuse, which makes it bright in all angles, the light can be distorted in specific angles which can for A display is made up by several small areas that example lower the contrast and invert colors. This can be individually controlled i.e. change from is a common problem and it is difficult to produce a black to white for example. These are called display that has an even display appearance for all pixels or segments. A pixel is normally square or angles. Instead the producers try to understand rectangle shaped and the resolution of a display is how the display will be used in the end product measured in how many pixels per area the it has, when designing it. The display is turned so the pixels per inch (ppi). The smallest area in low "best" viewing angles are where the users looking resolution displays such as car radios and alarm at the display. clocks displays are instead called segments. A A normal notebook computer display can be segment is a larger area and can have the shape of used to explain this solution. The display have a digit for example. The pixels in a high-resolution very good optics when viewed straight ahead, display are made by printing a layer on the display. like when you are sitting alone and working at The layer is a square or rectangle grid over the your computer. But it is common to be several entire display. The borders of the grid cannot users sitting beside each other looking at the change state like the pixels can, they can only be computer screen and therefore has the display in one of the states. A black and white display been optimized to have good optics also when where you mainly showing black images and you the display is viewed from large angles from left want to increase the contrast the grid should to be and right. This is how the display is used in the in the black state color. For an e-reader display end product, viewed straight ahead, from the left application where only the text is black and the and form the right and therefore the optics must rest is white, a grid in the bright state color is be superior in these angles. However, it is not preferred. This increases the brightness of the total common to view the notebook computer screen display and it will appear more white paper-like from the top, and therefore is this angle not as instead of gray. But at the same time it decreases important. When the display is viewed from above the contrast because the black part of the display the information on the display is hard to perceive, is not completely black. When measuring contrast the contrast and brightness is lowered and the a measuring-spot that is larger than one pixel is colors are distorted. being used, see Figure 2.9. In the same way as

18 dithering can be used to achieve gray colors in an image make the white borders of the grid the dark As we can see, if RDark = 0 the contrast is only state less deep black. dependent of the inter pixel area. The relation can be seen in Figure 2.10. To achieve a contrast ratio of 10:1 or more, the inter pixel area must be no more than 10% of the total display area.

Figure 2.9: In the right image the pixels are in the same bright state as the inter pixel. To the left the pixels are in dark state and the inter pixel bright state inter pixel degrades the black level of that area. The Figure 2.10: Geometrical contrast ratio as a pointers pointing at the interpixel function of the inter pixel ratio area

The grid borders are usually called the inter pixel, a part of a pixel in a display will always 2.2 Paper as a display contain inter pixel. Of course, producers are trying to produce displays with as small grid border Paper in any form has been the most common (less inter pixel area) as possible to increase the medium for documenting text and images for the contrast. The geometrical contrast ratio function, last millennium. Paper is a thin, ﬂat and ﬂexible Equation 2.3, describes how the inter pixel ratio is material and by writing ink-color on it information linked to the contrast: can be stored for as long as the paper stays intact. This technique goes back to the Egyptian papyrus,

RBright where the name paper comes from. Paper is Cgeo = IP IP (2.3) RBright 100 + RDark(1 − 100 ) produced by pressing together moist fibers from cellulose pulp derived mainly from trees and drying where RBright is the reflectance of the brightest them into flexible sheets. The daily consumption part, RDark is the darkest and IP is the inter pixel of paper is huge and the paper industry is a ratio. If we assume RDark = 0, then the function worldwide industry which devastates trees on a is simplified to: large scale. This has led to a debate about using less paper and trying to recycling paper. Today 100 Cgeo = (2.4) are fiction books, literature, brochures and news IP

19 paper all printed on newspaper. produce any light itself, instead it modulate the Seeing paper as a display, paper has several optic light passing through the unit. The light comes key properties that makes paper a superior unit for from some kind of external light source and it can reading on. At first the paper itself is very bright be any of transmissive, reflective and transflective white and reflects, depending of the quality of the light modes. In transmissive light mode, the paper, between 60 and 95% of the surrounding external light source is placed behind the LCD unit luminance. Paper does not emit any light itself to illuminate it, see Figure 2.11. The light passes and thus can not be read in dark illumination. through the unit only once and the brightness can The surface of a paper is curved which makes the easily be changed by adjusting the light source. reflection almost completely diffuse (lambertian), Transmissive displays are perfect for indoor usage because of this, paper has superior viewing angles. such as computer and television monitors. But if Another key property of paper is the high contrast, a transmissive display is used outdoors in bright black ink printed into the paper reflects only about sunlight the ambient light is stronger than the 4% which give a contrast ratio of over 20:1. backlight and the image gets washed out and Paper has the advantages that it is very legible, impossible to read. low cost, robust and requires no power, but after In sunlight the reflective light mode is preferred, printing information on a paper it is impossible a reflector is placed behind the unit and the to change that information unless you recycle the ambient surrounding light is used as light source, whole paper and print something new on it. see Figure 2.12. The advantage of this type is lower power consumption due to the use of the 2.3 LCD external light source. A transflective LCD is a combination of a reflective and transmissive LCD, A liquid crystal display (LCD) is a thin, flat panel it has both a reflector and a backlight. In Table used for electronically showing text, images, and 2.1 is the displays performance for different light moving pictures. The applications range from modes under various light levels shown. simple small displays used in e.g. calculators, and clocks to high performance computers, televisions, 2.3.1 Liquid crystal gaming devices and video players. This new display technology has several benefits to older A normal substance can have several different display technologies such as the cathode ray tube phases, for example water is solid below 0◦ C (CRT) that has been the standard computer screen degrees, is liquid between 0◦ and 100◦ C degrees choice the past decades. The main advantages of and is in gas form over 100◦ C degrees. What a LCD are the light weighted, thin profile, low differs these states is how the molecules are aligned power consumption and the ability to produce and if they are able to move around. When water much larger screen size with higher resolution. freezes the molecules align in certain positions, ice A LCD can be seen as an unit that does not crystals. If the ice is melted down to liquid water

20 Table 2.1: The performance of the diﬀerent light modes in various lighting

Sun light Normal oﬃce light Dark low light

Transmissive mode Poor Very good Excellent Reﬂective mode Very good Good Unusable Transﬂective mode Very good Good Very good

LCs are composed of several organic molecules, see Figure 2.13, this illustration is very simplified but it works to explain the technology. When the LC is in its normal state the molecules are floating around and the substance will appear clear and fluid like normal water. The light passes through the liquid and gets scattered by the molecules becoming more diffuse. When an electric field is applied in the LC the molecules arrange after the field. In this state the molecules are affecting Figure 2.11: Transmissive mode the light by changing the polarization of the light wave. While light travel through the crystal the polarization of the light is turned. If the distance that the light travels through LC is fixed a 90◦ degrees polarization turn can be achieved for all wavelengths.

2.3.2 Polarizer Figure 2.12: Reflective mode A linear polarizer is a device that converts the molecules can move around and change places unpolarized beams of electromagnetic waves, while they still have a certain position to each such as normal light, into beams with a single other. If water is heated above 100◦ C degrees polarization called polarized light. This can the liquid is turned into gas and the positions is be achieved in four types of ways: selective completely lost and the molecules can move away absorption, reflection, scattering or double from each other. Liquid crystal (LC) is a substance refraction. The polarizer type mainly used in that is in a state that is between the solid and the LCDs uses selective absorption, which can be liquid phase, it has the ability to be in one solid- illustrated as a grid. Light that has parallel like phase and at the same time flow like liquid. polarization to the grid can pass through the

21 Figure 2.13: In the solid phase are the cigar-like molecules oriented the same way and they can not move around. In the liquid phase have the molecules no particular orientation and they are completely free Figure 2.14: Two polarizing ﬁlters and two light to move around. The liquid crystal phase is in beams (red and green). The red light beam is absorbed between, the molecules have an orientation but can in the ﬁrst polarizer and the blue gets absorbed in the move around some second

2.3.3 Two polarizer polarizer as seen in the Figure 2.14. All light In a two-polarizer reflective display a polarizer is with perpendicular polarization to the polarizer placed on the top and bottom of the liquid crystal gets absorbed and stays in the polarizer. If two cell as seen in Figure 2.15. polarizers are placed after each other with the grids parallel, all light coming from the first polarizer will also pass the second because the light has the right polarization. But if the second polarizer is turned 90 degrees all light coming from the first polarizer will be absorbed in the second.

Polarizers are used in several applications. When light strikes a surface with a large incident angle it gets reflected as polarized light. For Figure 2.15: 2-polarizer reflective display example reflections from the road while driving car, from water while fishing or from the snow while The incident light will pass through a polarizer skiing can be polarized light. These unwanted four times before it is observed by by the viewer. reflections can be removed with a pair of glasses The disadvantage with this configuration is that that has a polarizer film. Polarizer is used in each time the light passes through a polarizer several other devices such as LCDs. some of the light is absorbed in the polarizer

22 which decreases the total brightness. Another second polarizer is removed. The brightness of a disadvantage is the polarizer between the LC cell BiNem 1-polarizer display is about 42-44% that and reﬂector, which causes a parallax eﬀect. The can be compared to a BiNem 2-polarizer which has amount of parallax is proportional to the resolution about 34-38% brightness. and therefor is 2-polarizer displays not suitable for high-resolution devices. But for simpler displays 2.3.5 Mono-/bi-stable used in for example wristwatches, the 2-polarizer A conventional display such as a TV- or a works excellent. computer-display is normally a monostable display. Monostable means that the pixels on the display 2.3.4 One polarizer have one stable state when no power is applied.

An 1-polarizer LCD has only one polarizer that is When a TV-display is turned off it becomes placed on the top of the LC cell, see Figure 2.16. completely black, this is the stable state for that The main advantage with this type of configuration display. To be able to change the state of of the is that the height of the LCD is thinner and the pixels power is required. parallax effect is reduced or if the reflector is placed In a bistable display has the pixels two stable inside the LC cell can the parallax be completely states, power is only required when switching the removed. Figure 2.18 shows a magnification of pixels between the two states. Since the pixels an 1-polarizer and a 2-polarizer display, both the can be in either of the two states it is possible to images are taken at the same distance and in the maintain information (text, image) on the display same lighting condition. without any applied voltage. The pixels stays in their stable states forever, just like printing something on paper, this results in an extremely low power consumption compared to conventional LCDs which needs a constant voltage applied to remain the pixels in desired positions.

2.3.6 Parallax eﬀect in 1- and 2- polarizer

Parallax is the apparent displacement of an object Figure 2.16: 1-polarizer reflective display viewed from two different viewpoints. Imaging two people standing at different locations in a room Another advantage is that the light only passes looking at the same object in the room. Both see through a polarizer twice compared to four times the object but they may see different background in the 2-polarizer configuration. This increases the behind the object, see Figure 2.17. brightness and reduces the parallax effect as the The parallax is depending on the angle between

23 the two viewpoints, if they move away from each height and in this way can the parallax effect other the parallax effect increases and if they move be reduced. 1-polarizer displays is significantly closer to each other they will eventually see the thinner than 2-polarizer since they only have one same background. The distance to the background polarizer and the reflector can be moved inside the from the object also affects the parallax effect, LC-cell and therefore the parallax effect is almost as the object moves closer to the background the eliminated as seen in image 2.18. This type of parallax effects gets less apparent. display works much better for displaying fine detail text and other small pixel information.

Figure 2.17: From the two viewpoints the same object can be viewed but the backgrounds are diﬀerent.

For reflective type LCDs the parallax effect can result in a double image on the display. The Figure 2.18: The upper image shows a image is formed at the top of the display, but magnification of a 2-polarizer display, the parallax if the distance of the top to the reflector is long effect is clearly apparent. The lower image shows an and a light source is pointing at the display in 1-polarizer display with inner reflector with no a large angle a shadow of the top image appears parallax effect. Both photos are taken in the same at the bottom. The shadow image will make the angle with a spot light source from the left up. Both text blurry and more difficult to read. Since it displays are reflective LCDs but the 2-polarizer is is difficult to control where the light sources are, thicker than the 1-polarizer display the only way to decrease this parallax effect is to decrease the height between top and bottom in the display. 2.4 Electrophoretic Reflective 2-polarizer displays have parallax problems but some improvements can be done An electrophoretic display (EPD) is a type of by slimming down components in the display, for low-power thin display that is considered a prime example the glass substrate. This decreases the example of e-paper. EPDs are widely used in e-

24 book devices such as the iLiad, Sony Reader and Amazon Kindle [8][9][10]. EPDs uses another technology compared to LCDs to create images for viewer. It uses millions of tiny particles, each about a micrometer in diameter suspended in a carrier. The particles have two different colors, normally it is black and white particles. These Figure 2.19: Three containers in an electrophoretic are covered with different charging agents to give display. The surface of the middle container will them an electronic field, which gives the name appear bright white for the viewer and the other two will appear dark. electronic ink. The particles are held between two parallel conductive plates that are connected to circuitry that allows external signals to manipulate diffuse similar to paper. EPDs can be produced at the electric charge at different precise points on high resolution and at various display size. This the display. When the charge is manipulated the makes the electrophoretic displays an excellent particles, depending on its current charge, moves choice for the e-paper market with low power to the surface or the bottom of the display. The consumption, high diffuse reflectance and with particles stays at their position even when the high resolution. Another key feature is that the voltage is removed, only when the particles are position of the two different particles inside the moving to another position voltage is required. container does not necessary need to separate, a This effect is called electrophoresis which these mix of white and black particles can be moved types of displays are named. to the surface resulting in perceived gray color, When the white particles are at the top of the this feature enable the use of grayscale. Black and display, and the black particles at the bottom, the white EPDs have usually 4 or 16 gray scale levels. white particles reflects and scatters the incident One drawback with this technology is the low light which will appear bright white. If the refresh rate and low contrast. When voltage is conductive plates change its charge the particles applied the particles will travel through the color changes position and the black particles will be container to desired position, this takes some time at the top absorbing the incident light which will and the user perceives the refresh. This drawback make it appear black. By manipulating small areas limits the use of interactive graphical interfaces over the entire display, images can be created for and fast page turning. the viewer, see Figure 2.19. The other drawback is the contrast. The bright The main advantages of this types of display white state of the display is very good with is that no polarizer is used, the light is reflected high reflectance but the dark state mode lacks of direct at the top of the display which enhances insufficient level of blacks. The black particles are the brightness compared to LCDs. The particles not absorbing enough of the incident light and the scattering the incident light and the reflection is light gets reflected back to the viewer which sees a

25 grayish dark state. scattered away from the display which lowers the brightness. An anti-reflection coating also reduces 2.4.1 E-Ink unwanted reflections but instead of scattering away the light it reduces the differences between the E-Ink is a Korean company that develops and incident lights medium and the displays medium produces electrophoretic displays, the name stands which increases the absorption of the light down for electronic ink. E-Ink is the leading company in the stack. A normal glass-plate reflects about producing electrophoretic displays that are used in 4% when light travels through air to the glass- most e-reader applications on market today. Their plate, but when used with an anti-reflection film current product is named E-Ink Vizplex. the reflection can be reduced to about 0.5% and lower. 2.5 BiNem A combination of these types of top coatings are used in the BiNem 1-polarizer optical stack, BiNem BiNem R is a patented technology based on 2-polarizer uses only an anti-glare top coating. bistable LCDs. The name BiNem stands for Bistable Nematic were bistable is the technique with two stable states described above and nematic 2.5.2 Top polarizer means that it uses nematic types of liquid crystal The top-polarizer turn the incident unpolarized materials. These materials are cheap, robust and light into polarized light that can interacts with standard in LCD production. Many LCDs uses the liquid crystal. The top-polarizer is placed as nematic materials. the second layer in the optical stack. The problem when using polarizers is that so much light gets 2.5.1 Top coating absorbed and only about 45% of all incoming light

When light hits a surface or moves from one passes through it. medium to another some of the light gets absorbed and some get reflected. In a reflective type LCD 2.5.3 Retardation compensation it is desirable to absorb as much ambient light Retardation compensation films are key optical as possible but at the same time reduce specular components used in a LCD to improve the viewing reflections from ambient light sources. This is angles by preventing light distortion. The film is done by introducing an optical film at the top in placed in the top of the stack and modulates the the optical stack. The optical film can either be light passing through it. an anti-reflective coating, anti-glare coating or a combination of these. 2.5.4 Diffuse adhesive An anti-glare coating has a rough surface which reflects the incident light in a diffuse manner, When the light leaves the optical stack on its the unwanted reflections are reduced but light is way out it should be scattered in all angles for

26 improving the viewing angles. For this purpose a diffuse adhesive is being used. It can be placed on top of the retardation compensation film, and also if the display configuration is using outer reflector it can be placed between the BiNem cell and the reflector. The adhesive is compound of tiny particles that scatters the light passing through it. The diffuse adhesive can be adjusted to preferred level by adjusting the density of particles in the film. Figure 2.20: When the diffuse adhesive is placed on The level of how much the light gets scattered top of the BiNem cell the light gets scattered one time is measured in % haze according to JSA JIS K on its way in and one time on its way out of the 7105 (Testing Methods for Optical Properties of display Plastics). Higher level of haze results in more scattered diffuse light. Depending on where in the stack, top or bottom, the diffuse adhesive is placed different result is achieved. If the diffuse adhesive is placed on top the light will travels through it two times and scattering the light each time if passes the adhesive. If it is placed on the bottom close to the reflector the light will only scatters once and hence less than the top adhesive. Therefore, is it important to distinguish between top and bottom diffuse adhesive, in this thesis they are referred as Figure 2.21: When diffuse adhesive is placed at the top haze and bottom haze. bottom of the BiNem cell the light gets scattered only once 2.5.5 White balancing film

The BiNem display uses a white balancing film two different paints with different hues are mixed in order to achieve a neutral bright state color. (and both mixing ratio and total concentration are Without it the BiNem display shows a slightly controlled). yellowish bright state. The white balancing Of course the brightness of a white balanced film has a purple hue and hence absorbs part configuration is slightly lower compared to a non- of the yellowish light resulting in a neutral balanced one, but the neutral bright state color bright state color. The exact color can be well is usually perceived as more appealing and even controlled by using a two-paint system in which brighter compared to a slightly yellowish one.

27 2.5.6 BiNem cell reflective display can be seen in Table 2.2 and Table 2.3. The BiNem cell contains liquid crystal. The special with the BiNem cell compared to normal liquid Table 2.2: Optical stack for the BiNem 2-polarizer crystal cells is that the liquid crystal is bistable, Top coating it can be in two stable states without any applied Polarizer voltage. Retardation compensation Top haze 2.5.7 Reflector Ink In the bottom of the optical stack is a reflector BiNem cell placed which purpose is to reflect all incident light Bottom haze back to the viewer. Any substrate that reflects Polarizer light can work as a reflector, such as normal paper, Reflector a glass mirror or a metal plate, and it is important to have a substrate that reflects as much as possible to achieve higher brightness of the display. Table 2.3: Optical stack for the BiNem 1-polarizer A high quality paper reflects about 90 % of the Top coating incident light and the reflection will be diffuse and Polarizer the needs for the diffuse adhesive will be lowered. Retardation compensation Higher reflecting reflectors can be achieved by Top haze putting a thin layer of aluminum, tin or silver Ink on a substrate, it can also be a blend of these BiNem cell metals. This type of reflector will have a mirror- like specular reflection. Reflector

2.5.8 Optical stack 2.6 Legibility research An LCD display is made up of several components that modulate the light that passes through it. One of the consequences of the computerized world Each component can be seen as a layer in a stack, we live in is that people increasingly rely on called the optical stack. To understand how the computers to do a variety of everyday tasks such different displays that are used in this thesis works as browsing webpages, writing reports, sending e- and differs, understanding of the optical stack and mail and processing images and other information. the different layers are important. The optical The visual unit is the medium that the human stack is seen from top to bottom having the top mainly interacts through the computer. In the closest to the viewer. An optical stack for a 90’s was the CRT the standard VDT, however the

28 size of it and other disadvantages have lead to development of e-paper displays attracted a the development of the flat panel display (FPD) great deal of public attention. As pointed out which has overcome many of the disadvantages earlier, compared to conventional VDUs like CRTs of the CRT. The most popular FPD is the LCD and transmissive type LCDs which self emits light, that can be used in thin portable devices such e-paper display uses the ambient illumination as as notebooks. Several studies concerning the its reading source. Hence, this previous research usability of CRTs and LCDs have been performed cannot be directly applied to this new types of the past years. There are mainly three classes of displays. The e-paper research is still at an early methods for evaluating VDT affects, each with its age and independent studies are relatively few. advantages and disadvantages [11]. Some methods Some studies of e-paper displays have found that measure change in the functioning visual acuity ambient illuminance does not have a significant systems, such as accommodation, convergence and effect on visual performance [14][15][16]. critical fusion frequency. These methods are However, even though a significant relation not often intrusive and require various constraints could be found the subjects preferred a higher on the subjects. Other methods use more ambient illuminance (500 lux). Other studies general visual task performance such as visual have shown that users legibility for using e-book character search and reading tasks to assessing displays under higher illuminance (1500 lux) is the VDT’s performance. The disadvantages with better than that under lower illuminance (200- these methods is that it can be difficult for the 800 lux) [17]. It has been shown that the subject to maintain the same attention to all contrast ratio affects the human performance in tasks during the study. A decline in performance the context of acquiring information from VDTs over time may reflect factors such as boredom [18][19]. The reading speed increases with that are unrelated to VDT design. The third increasing contrast at low contrast ratio levels, but type of methods involves the use of subjective at higher contrast ratio levels is the reading speed measures based on questionnaires, interviews and almost independent of the contrast ratio [20]. other informal discussions. This method can be easier to perform and more economical but are likely to be biased by topical misconceptions and popular beliefs. Several studies of the legibility of different displays such as CRTs and LCDs compared to normal paper have been performed the past years [12]. They have found that properties such as contrast, viewing angle and brightness are important for reading on electronic displays [13]. In recent years have the research and

29 Chapter 3

Experimental design

3.1 Method little test group. Since the time was limited shorter visual tasks were generally chosen. More powerful The aim of this study is to optimize the BiNem methods such as long time usage could have been BF700 display for e-reader applications. To used but due to the time and resources available achieve this, several methods and procedures have for this thesis it was not possible to realize. been used. At first a literature study was performed to gather information about previous legibility research. Both research reports about 3.2 Overview design the legibility of e-reader displays and normal paper was studied. Since the display technology of the Several display-types and a variety of BiNem display differs from any other display on configurations of them has been used during the market, further investigations with real users this study. The first part, called phase 1, was was needed. about benchmarking the BiNem BF700 2-polarizer The visual performance of any display can be configuration display and compare it to an E-Ink tested in several ways. The methods used in this Vizplex display and normal printed paper. The thesis have been chosen from the literature study participants performed user-oriented tasks and and to be suitable for the displays that have been filled out a subjective questionnaire regarding available and how they could be used. For example the reading experience of the displays. At the in the beginning the only BiNem displays available same time as phase 1 was proceeding, a BiNem was static, which means that the content of the 1-polarizer optical stack was being developed. display was difficult to update. Because of this The results from phase 1 worked as the basis for long time reading could not be realized and the the new 1-polarizer configurations. These new visual tasks was modified to suit one page content. configurations where evaluated in phase 2 of this Another limitation was the time. It was assumed study. that it is more important to get brief feedback from In phase 2 we wanted to optimize the 1-polarizer a large test group rather than more feedback from a optical stack by evaluating different top coatings,

30 Table 3.1: Thesis phases with tested displays and type of test

Phase 1 Phase 2 Phase 3 Phase 4 Displays -2-pol ref (A) -2-pol ref (A) -1-pol (phase 2) (A) -2-pol ref (A) -E-Ink (Amazon) (B) -5 different 1-pol -E-Ink (Amazon) (B) -E-Ink (Amazon) (B) -Printed paper (C) configs (B,C,D,E,F) -TFT-LCD (iPhone) (C) -1-pol (Phase 2) (C) -1-pol biaxial (D) Type of test Task-oriented Preference ranking Long-time reading Preference ranking Time 8 weeks 5 weeks 4 weeks 3 weeks top- and bottom-haze levels, and if white balancing The study phases and the displays used in each film (ink) is increasing the legibility of the displays. phase are summarized in Table 3.1. Each phase is The BiNem 2-polarizer configuration used in phase described in detail later in this chapter. 1 was included in phase 2 to work as a baseline. Five new 1-polarizer configuration and together 3.2.1 Selection with the baseline BiNem display was tested in phase 2. These were evaluated by letting users To get a statistic result that can be applied to rank all displays from the one they preferred the a large population it was desirable to get as most to read on to the one they preferred the least much variation among the participant as possible. by looking at the same static image on each display. The idea was that it would vary between the participants sex, age, educational level, visual The most preferred 1-polarizer from phase 2 was weakness and technical habits. But due to the then used in phase 3, the aim of phase 3 was short time, the recruit process was limited and to collect user experience from a more natural a wide population was not possible to recruit long time reading compared to the relative short to any of the phases. Mainly students and reading tasks that where used in phase 1 and 2. teachers at the Uppsala University, Sweden, were Two other displays was also included: the E-Ink used in the study. The participants must speak Vizplex display used in phase 1, and a transmissive and understand Swedish language to be able to TFT-LCD. complete the tasks. Since e-reader devices are a In the last part of the study, phase 4, we wanted new application the test subjects had no previous to investigate if all optical improvements of the 1- information about the tested displays. polarizer configuration is perceived by the user. A new 1-polarizer configuration with a biaxial optical 3.2.2 Ethic consideration film was compared to the 1-polarizer configuration with a uniaxial film used in phase 3, the 2-polarizer Participants were informed that it was completely used in phase 1 and 2, and also compared to the voluntary to participate in any of the parts E-Ink Vizplex display used in phase 1 and 3. of the study. Each participant was given

31 information about study purpose, how the tasks and E-Ink Vizplex display was masked with black and interviews would proceed and information plastic so all three displays had similar casings, no about confidentiality. By signing a consent letter, buttons or brands were visible at all. The three the participant agreed that he understood the displays in their casings can be seen in figure 3.1. given information, see appendixA. The optical properties of the displays are The names of the persons participating in the summarized in Table 3.2. With a resolution of study are not presented, all data are stored and 600 dpi, contrast of 17:1 and brightness of 89% are inaccessible to others than the author of this the printed paper have superior optics compared to study and his supervisors. The data will not be both the BiNem and E-Ink Vizplex display. When used to any purpose other than this study. comparing BiNem to the E-Ink Vizplex BiNem has higher contrast, 8:1 compared to 5:1 in E-Ink. 3.3 Phase 1: Legibility The E-Ink Vizplex display have higher brightness with 44% compared to 38% on BiNem. All three benchmarking of current displays were 6" in size. 2-polarizer BiNem configuration vs. E-Ink Vizplex display and printed paper

3.3.1 Aim Figure 3.1: Displays used in legibility investigations • Compare the legibility and reading comfort phase 1 of the BiNem BF700 prototype display with the E-Ink Vizplex EPD display used in the Amazon Kindle 2 e-reader, and with 3.3.3 Test description conventional printed paper Task-oriented test • Understand which display characteristics that Letter recognition In the letter recognition are important for e-reading applications task the test subject is instructed to search for 3.3.2 Investigated displays a deﬁned letter on each display inside a block of randomly generated letters and spaces. The Three displays have been used in phase 1: BiNem block was generated by a small script with these 2-polarizer, E-Ink Vizplex EPD (Amazon Kindle constraints: 2) and normal printed paper. The printed paper was inserted in similar casing as the BiNem display • a block contains of 26 lines of words

32 Table 3.2: Main characteristics of BiNem BF700, Amazon Kindle 2 and High graded printed paper

BiNem BF700 - (A) E-Ink Vizplex - (B) Printed paper - (C)

Technology Reﬂective PM 2-pol Reﬂective TFT E-Ink EPD High graded printed paper Display size 6" 6" 6" Resolution 200 dpi (960x720) 167 dpi (800x600) 600 dpi Brightness 37 % 44 % 89 % Contrast 8:1 5:1 17:1

• a line contains 9-11 words Three different pseudo-texts were used, so the test subject read a new pseudo text on each • a word contains 2-11 characters (only lower displays. Between test subjects were the pseudo case letters) texts switched between the displays and also the text density were chosen to fit as much the order the displays gets presented is changed information as possible on the 6 inch displays while between test subjects. the character size is still large enough for normal reading. After generating the block of text, the target letter is randomly inserted at between 18 and 26 places in the text. A part of the text-block can be seen in Figure 3.2. The test subject does not Figure 3.2: A part of pseudo text block used in letter know how many target letters there are, therefore, recognition task both the accuracy and total time can be measured. Test subject was told to search from the top left corner of the text block, just like normal reading, Reading speed The letter recognition task is as accurate as possible, but also as fast as possible. good for determine how easy it is to find a specific One problem was to define what target character character on a display, but it has been shown to search for, if the character is very easy to that while reading, we do not look at every single recognize like the Swedish letters å, ä and ö or character. Reading is a complex perceptual task, y, t and k the test subject will use some other we learn to see patterns in words and text and searching technique instead of "reading" through people that are very used to read can read very the text. If the target character is very similar to fast by traversing the text. This is why a task another character like a i similar to o and u, the where the user reads a normal text was included. test subject will count the wrong character and the The task was to read a normal article text as data will be difficult to analyze. We decide to use fast as possible but still understand the content. s as the target character. s is not outstanding but The articles were chosen from a standard Swedish is hard to confuse with some other character. "reading test" (Högskoleprovet [21]). When

33 instructed, the test subject start to read from Font the display and after a defined time the subject Due to the optical differences of the displays, a is instructed to stop and show how far he read. font style that suits on for example high resolution By counting the words read e subject a word-per- display could be chosen, but the font will look minute (WPM) value can be calculated. bad on a low resolution display and it will be less Text from three different articles was used, so legible. Instead we tried to choose a font style that the test subject read a new text on each and size so the text would be equally legible on display. Between test subjects the texts were each display. After evaluating each display the switched between the displays and also the order chosen font was Georgia. Georgia is a serif font of the displays were changed between the test designed for clarity on computer monitors even at subjects. small sizes, it is similar to normal pocket book text, and is widely used (for example by the New York Subjective questionnaire The first two tasks Times website [22]). The size was chosen as small measured the reading performance of the displays. as possible, approximately 12 px. However, the user may experience the displays widely different but still get the same results. Test subjects To find out what subjective feelings the test To get objective results, the test subject has not subjects felt about each display, they filled out been given any information about the displays or a questionnaire. The questionnaire contained 15 the study in advance. Students from Uppsala statements, for each of them the test subject rate University, Sweden, were asked to join the phase each display by circle any of the integers on a 6- 1 legibility investigation study and a total of 27 point scale, one of the statement can be seen in person participated. The average age was 25,1 Figure 3.3. The complete questionnaire can be years old with a standard deviation of 2,2 years found in appendixB. and all participants are used to read on various displays on daily basis.

Lighting conditions

Figure 3.3: Statement from subjective questionnaire To keep the illumination constant under the whole used in phase 1 phase, all tasks were performed in a small office room with bright indirect light. The 18m2 room Designing the questionnaire in this way helps the had one window but with both the blinds and test subject to perceives the differences between curtains closed the outdoor illumination did not the displays. While answering to the statements affect the room illumination, see Figure 3.4. The the test subject can look, hold and compare the average illumination measured on the Table in the displays to each other. room was 583 lux. Test subject was instructed to

34 sit at a desk in a normal office chair but could alone 3.4 Phase 2: Top coating chose how to sit in the chair and how to position and diffuse adhesive and hold the display. optimization of 1-polarizer BiNem configuration

3.4.1 Aim

• Select optimized top coating for 1-polarizer conﬁguration

• Evaluate haze level of diﬀuse adhesive

• Investigate ink

Figure 3.4: Lighting conditions in phase 1 • Compare new 1-polarizer conﬁgurations to current 2-polarizer ref

Other 3.4.2 Investigated displays

Webcam During the whole study a webcam, Five different BiNem 1-polarizer configurations pointed to the front right of test subject, taped along with one BiNem 2-polarizer display was how the test subjects uses and handle the displays. used in phase 2. Three display properties were Small details that are hard to notice while tested in this phase: top coating, haze level watching the test subject live can be analyzed and with or without ink. The optical properties afterwards. For ethic reasons, each test subject of each configuration can be seen in Table 3.3. filled out a paper before the test agreeing to be Configuration B, C and D have the same top filmed. The movie clips are a part of this research coating and ink level but different haze level and will not be available for anybody else except (middle, low and high). the author of this thesis and his supervisors. Configuration C and E have the same haze and ink level but different top coatings (Type1 and Fatigue and learning effects The total time Type2). The two new top coatings were picked for one test subject was less than 30 minutes. That after visual inspection of 5 different top coating time is considered to be just enough to perform including anti-glare type and anti-reflecting type profound tests without tire the test subject. The top coatings. None of the anti-glare top coatings test subject was asked to execute all tasks with the reduced enough front reflections compared to the same level of concentration. anti-reflecting type and therefore only the two best

35 Table 3.3: Optical properties and main characteristics of conﬁgurations used in phase 2

ABCDEF

Top coat Typ0 Type1 Type1 Type1 Type0 Type1 Top haze 0% 88% 0% 88% 0% 0% Ink 2% 1% 1% 1% 1% 0% Bottom haze 88% 40% 88% 88% 88% 88%

Contrast 8:1 7:1 6:1 8:1 7:1 6:1 Brightness 38% 40% 41% 39% 41% 44%

Haze eval Middle Low High Top coat eval Type1 Type2 Ink eval 1% ink No ink anti-reﬂecting top coatings were included in this phase. Speciﬁcations of the three top coatings used can be seen in Table 3.4.

Table 3.4: Speciﬁcations of top coatings used in phase 2

Type0 Type1 Type2

Type Anti-glare Anti- Anti- reflecting reflecting Figure 3.5: Displays used in phase 2 Reflectance - 2.5% 1.8% Haze 7.5% 42% 11% 3.4.3 Test description

Ranking task Configuration C and F have the same top coating and haze level but different ink level Because of the large number of displays, with very (1% ink and no ink). Configuration A worked little differences, reading based tasks were not an as a reference to be compared to all other option, users experience will be the same after configurations. All displays were placed in similar reading just one page on each display. But if casing and masked so only the display was visible they are allowed to view all the displays at the to the user. Each display was named with a same time with the same content on all displays letter (A-F) on the lower parts of the casings. All and compering them to each other will make them displays can be seen in Figure 3.5. see what differ between them and then they can

36 judge which one the prefer most. All displays were 2. Dark diﬀuse (indirect) illumination, placed on a table and the task for the test subject several light sources combine together a is to rank all displays from the one the prefer most diﬀuse illumination under 300 lux. to read on to the one the prefer least. The test 3. Mainly (bright) specular (direct) subjects were told to carefully pick up and view all illumination, one or two spotlights displays in their hands. illuminate the displays.

A flux-meter was used to measure the Image illumination on each test location. The same image was written to each display. The image was a text in Swedish, about Swedish 3.5 Phase 3: Reading weather and a graph of the yearly rainfalls since 1960. The graph in the image showed fine pixel comfort evaluation of details. Since the configurations have exactly the optimized 1-polarizer same resolution the image gets rendered the same on each configuration. BiNem configuration

3.5.1 Aim Test subject • Deeper understanding of user reading A total of 100 persons participated in this phase. experience on the BiNem 1-polarizer The age of test subject varied from 19 to 63 years configuration with an average age of 26,3 years with a standard deviation of 9,3 years. Test subjects were not given • Compare the reading experience of the any information about the differences about the BiNem 1-polarizer configuration integrated in displays. a ”SYLEN kit”, compared to E-Ink Vizplex EPD (Amazon Kindle 2), and transmissive TFT-LCD (iPhone) Lighting conditions The aim of phase 3 was to point out the pros and To evaluate if different haze-levels and top coatings cons with long time reading on e-readers compared are differently preferred in different lighting to a normal printed book and also what main conditions, all tasks where performed at different differences people experience with three different locations (only indoor) and categorized into three e-readers. groups of lighting condition:

3.5.2 Investigated displays 1. Bright diffuse (indirect) illumination, several light sources combine together a Three different types of displays was used in this diffuse illumination over 300 lux. phase, a BiNem 1-polarizer configuration, E-Ink

37 Table 3.5: E-reader properties used in phase 3

BiNem BF700 - (A) E-Ink Vizplex - (B) TFT-LCD - (C)

Technology Reﬂective PM 1-pol Reﬂective TFT E-Ink EPD Transmissive TFT-LCD Device SYLEN kit Amazon Kindle 2 iPhone Display size 6" 6" 3.5" Page turn time1 Slow (≈ 2 sec) Medium Very fast (instant) Resolution 200 dpi (960x720) 167 dpi (800x600) 163 dpi (480x320) Brightness 40% 44% Transmissive, no data Contrast 5:1 5:1 Transmissive, no data

Vizplex, and TFT-LCD. Each display was used The second was the Amazon Kindle 2 e-reader in an e-reader device. The BiNem display was same as used in phase 1. integrated in a SYLEN2 kit, the E-Ink display was The third was the Apple iPhone mobile phone, in the Amazon Kindle 2 e-reader and the TFT- this phone may not be considered as an e-reader LCD was in the iPhone3 mobile phone. but with its 3.5 inch display and the ability In this phase the displays was not masked to to display text files, pdf’s and e-book format remove application feeling as in previous phases. files it can be used as an e-reader. The main An image of all three e-reader applications can difference with iPhone compared to BiNem and be seen in Figure 3.6. The SYLEN kit and the Amazon Kindle 2 is that the display is not Amazon Kindle 2 uses buttons for input (page bistable, power supply is required continuos during navigation) while the iPhone uses touch screen. usage which gives continuos reduce the battery The first e-reader was the BiNem BF700 life drastic and long time reading can be a developed to meet the requirements pointed out problem. The advantage with the iPhone display in phase 1 and 2, the BiNem display is integrated is that brightness and contrast can be adjusted in a prototype e-reader module called SYLEN. As to preferred levels and fast page turning which a prototype e-reader, SYLEN have the drawbacks increases the usability. to be less user-friendly with a simple graphical The e-reader applications used in phase 3 are interface and less battery life, but have the ability shown in Figure 3.6, and the display properties of to load e-book files, navigating through the books each display in Table 3.5. and has a few display settings.

2SYLEN kit is a prototype e-reader device which easily 3.5.3 Test description can change the integrated display. As a prototype e-reader device the SYLEN e-reader has limited features compared Long-time reading to more advanced e-readers on the market 3Mobile phone from Apple that can be used as an e- The task was to read one chapter from a Swedish reader application book, the same chapter on each display. The book

38 in portrait and landscape mode, colors could be inverted and brightness adjusted to preferred level.

Test subject

9 persons participated in this phase and it was the ﬁrst contact with e-reader devices for all of them.

Lighting conditions Figure 3.6: E-readers used in legibility investigations Test subject was free to choose his own lighting phase 3. From left to right: BiNem BF700 in SYLEN, Amazon Kindle 2 and Apple iPhone condition. Some users prefer to read with a reading lamp in bed or on the couch while other prefer reading when they are traveling or are outdoors. is named Hemsöborna and written by the Swedish However, the test subject was instructed to read author August Strindberg. The first three chapters indoors and in the same lighting conditions with are about 20 pocket-book sides each. Reading one all e-readers. Thus, it is easier for the test subject chapter takes approximately 20-30 minutes total. to perceive differences between the displays. The devices were not masked as in previous phases, because of this the user gets influenced by the device design and interface. 3.6 Phase 4: User preference After reading on all three displays an interview evaluation including were held where questions about how the user felt about reading on an e-reader compared to a latest viewing angle traditional printed book and positive and negative enhanced 1-polarizer experience of each display and e-reader device. Also a general open discussion was held. BiNem configuration

Font 3.6.1 Aim

Each e-reader device has its own text renderer In order to see if all improvements have increased and thus different fonts have been used on the the reading experience of the displays the study different displays in this phase. The font size was finished with ranking preference task. was fixed and at similar size on the SYLEN and • Confirmation of improvement of optimized 1- in the Amazon Kindle 2 device, on the iPhone polarizer configuration the user could change the font size to preferred size. The iPhone have some other display settings • Investigate user preference of BiNem display to enhance the reading experience on the relative compared to E-Ink Vizplex (Amazon Kindle small display: the display could be used both 2)

39 Table 3.6: Optical properties of conﬁgurations used in phase 4

BiNem BF700 - (A) E-Ink Vizplex - (B) BiNem BF700 - (C) BiNem BF700 - (D)

Technology Reflective PM 2-pol Reflective TFT E- Reflective PM 1-pol Reflective PM 1-pol LCD Ink EPD LCD LCD Display size 6" 6" 6" 6" Resolution 200 dpi (960x720) 167 dpi (800x600) 200 dpi (960x720) 200 dpi (960x720) Top coating Type0 "Type0-like" Type2 Type2 Haze Bottom 88% EPD Bottom 88% Bottom 88% Retardation comp No EPD Uniaxial Biaxial Ink 2% EPD 1% 2% Contrast 8:1 5:1 5:1 5:1 Brightness 38% 44% 41% 39% Viewing angles Ref EPD Limited Increased

3.6.2 Investigated displays The main difference between the BiNem 1- polarizer configurations (configurations C and D) Four displays were used in this phase: the same E- is that configuration D has a biaxial retardation Ink Vizplex display used in phase 1 and 3, the same compensation film while configuration C has an BiNem 2-polarizer configurations used in phase 1 uniaxial retardation compensation film. The and 2, the same BiNem 1-polarizer configuration uniaxial film enhances the contrast ratio when used in phase 2 and 3 and also a new BiNem viewed in front but when the display is tilted 1-polarizer configurations with enhanced viewing in special angles the contrast and color of the angles. The BiNem displays was inserted into display are distorted. The biaxial film enhances similar casings and the Amazon Kindle 2 device the contrast and keeps the color even when viewed was masked to similar appearance (masked in the in angle. In Figure 3.8 you can see how the biaxial same way as in phase 1). In Figure 3.7 can all four film keeps the contrast and color when the display displays be seen and in Table 3.6 are the optical is tilted and viewed from the lower right corner. properties shown.

Another difference of configuration C and D was that C had 1% ink and D had 2%. This results in a more neutral white bright state but the brightness is lower (39% brightness of configuration D compared to 41% of configuration Figure 3.7: The four displays used in phase 4. C).

40 Lighting conditions

This part of the study was performed at various locations (only indoor), all test locations had bright diﬀuse (indirect) illumination, over 300 lux.

Figure 3.8: The biaxial ﬁlm keeps the contrast and color even when viewed in angle compared to the uniaxial ﬁlm. This results in a more uniform display appearance

3.6.3 Test description

Rankings task

The same image was written to each display and showed for the test subjects which ranked the displays from the one they most preferred to use as e-book reader to the one the preferred least. Test subjects were told to carefully pick up and compare the displays to each other. The displays were masked so only the display was visible.

Image

The image that was written to each display was an article text in Swedish, taken from a Swedish standard reading test (Högskoleprovet [21]).

Test subjects

All test subjects were gathered from Uppsala University with the average age of 26,5 years old with a standard deviation of 9,5 years. Since the task is quite easy and does not take long time to perform a total of 78 persons could be recruited.

41 Chapter 4

Results and conclusions

4.1 Phase 1 Table 4.1: Results of letter recognition task

4.1.1 Results BiNem E-Ink Printed BF700 Vizplex paper Letter recognition Search 97.8s 97.0s 98.2s The results of the letter recognition task are shown time in fig 4.1. The accuracy is slightly higher for the Accuracy 83.9% 81.1% 81.3% BiNem BF700 compared to the E-Ink display and printed paper, and the searching time is almost speed of 283 word per minute (WPM). Also in identical for all three displays. The standard this result the standard deviation was high, so deviation was high so there was no significant no word per minute-mean significantly differ from difference between results. each other.

Figure 4.1: Results of letter recognition task Figure 4.2: Results of reading speed task

Reading speed Subjective questionnaire

In the reading speed task results we can see that The results from the subjective questionnaire the BiNem BF700 scored highest with a reading proved to be more useful to point out the weak

42 Figure 4.3: The main important results from subjective questionnaire. The highlighted green scores are the most significant ones and strengthens of each display. Table 4.3 show a were pointed out in statement 5,6 and 7, it was summary of the most important statements along perceived to be darker than the others and also the with average score of each display. A score of viewing angles and diffuse reflection was not good 0 means that the user does not agree and a enough on BiNem. But still, when users comparing score of 5 means that they totally agreeing on BiNem to the on the market Amazon Kindle 2 e- that statement. The most significant scores are reader by only looking at the display, they prefer highlighted green. both equally as an e-book reader.

On statement 1, which is about the contrast, 4.1.2 Discussion BiNem scored significant higher than Amazon Kindle but similar to paper. The perceived The BiNem 2-polarizer configuration shows higher contrast level is increasing much more when contrast than the E-Ink Vizplex display, 8:1 increasing the contrast from 5:1 (as in the Amazon compared to 5:1. The BiNem display has less Kindle) to 8:1 (as in BiNem), than increasing the brightness with 38% compared to 44% for E-Ink contrast from 8:1 to 17:1 (as in the printed paper). Vizplex display. Several studies has pointed out On statement 2 scored the 600 dpi laser printed that both the contrast and brightness is important paper highest. The scores of statement 3 shows for high legible e-paper displays. The significant a little difference betweens the scores, the results lower brightness on the BiNem was predicted are consistence with the optical properties of the to result in worse scores in the visual tasks in displays. Some problems of the BiNem display phase 1. However, both the BiNem 2-polarizer

43 Figure 4.4: Results from phase 2. The diagrams show how the different configurations were rated at each position. See Table 3.3 for configuration explanation configuration and the E-Ink Vizplex display had the human eye. The paper used in phase 1 had 17:1 similar search time and accuracy in the letter in contrast ratio but it was only pointed out to be recognition task, and no significant difference was slightly better than the BiNem display with 8:1 found in the reading speed task. In the subjective in contrast ratio in the subjective questionnaire. questionnaire on the statement I could imagine However, on the same question had the BiNem myself having this display as an e-book (electronic display much better score than the E-Ink Vizplex book) scored the BiNem and E-Ink Vizplex display display which has 5:1 in contrast ratio. the same. On other statements pointed test It is very important to achieve a contrast ratio subjects out the sharp and well-defined characters of at least 8:1 but it is not necessary to increase it as an advantage of the BiNem display, the subjects over 15:1 of the cost of other display properties. found them much easier to perceive which lead to a nice reading experience even though the 4.1.3 Conclusions display itself has lower brightness than the E- • No significant difference in legibility between Ink. It is believed that a low brightness can be BiNem 2-polarizer reference, E-Ink Vizplex compensated with higher contrast for the same and normal printed paper reading experience. The contrast level is an important factor, the • People could imagine themselves having both recommended contrast ratio for text is at least BiNem 2-polarizer reference and the E-Ink 3:1, but 10:1 is preferred, see 2.1.3. Over 10:1 in Vizplex display equally as an e-book reader contrast is changes in contrast less perceivable for display

44 • Areas of improvement could be identified from configurations. The three other configurations A, the subjective questionnaire, all important for E, and F are also low haze configurations but further enhancing the reading experience and with other top coatings and ink level, all of these comfort of the BiNem display had lower average ranking score compared to the middle and high haze configurations. – Increase brightness

– Reduce front reﬂection

– Increase diﬀuse reﬂection (viewing angles)

• A contrast ratio ratio of 8:1 is a suﬃcient contrast ratio for e-reader displays

4.2 Phase 2 Figure 4.5: Results from phase 2. Average ranking 4.2.1 Results score for all displays. See Table 3.3 for conﬁguration explanation The results from the haze evaluation can be seen in Figure 4.4. Out of 100 rankings was conﬁguration

A most preferred 73 times. Configuration E was Top coating evaluation most preferred 15 times and second preferred 45 Configuration E with Type2 top coating was times. The D configuration was ranked at fifth clearly preferred over configuration C with Type1 place 39 times and as the least preferred 43 times. top coating. Configuration E had an average The average calculated score of each configuration ranking score of 2.58 and configuration C 3.69. can be seen in Figure 4.5. The score corresponds to Configuration E was the configuration that scored the average ranking order where 1 is most preferred best of the 1-polarizer displays with the Type2 top and 6 is least preferred (lower score is better). The coating, low haze and no ink. high-contrast configuration A is clearly the most preferred. Ink evaluation Diffuse adhesive evaluation No significantly difference could be found between Low haze configuration C show significant better the ink- and no ink-configuration. Configuration results than middle haze configuration B and high C (ink) scored 3.68 and configuration F (no ink) haze configuration D. Configuration C had an 3.41. The 1% ink concentration did not balance average ranking score of 3.69 compared to 4.53 the yellowish color of the bright state enough, for configuration B and 5.14 for configuration the differences between the two configurations was D which had the highest average ranking of all very little.

45 Ages

The test subjects was divided into three age- groups:

• Group 1: 0-22 years old

• Group 2: 23-27 years old

• Group 3: 28-63 years old

Group 1 contained 38 test subjects, group 2 had Figure 4.7: Average ranking score of different 37, and group 3 had 25 test subjects. No significant lighting conditions. Green: Bright indirect difference could be found between the groups. The illumination, Yellow: Dark indirect illumination, and average ranking score of all ages along with each Red: Specular illumination age group can be seen in Figure 4.6.

top haze blurs the text and made it much difficult to read. Less sharpness of the text is not preferred to the cost of better viewing angles. The Type2 top coating was preferred over the Type1 but it may not only be because it is reducing front reflections better than the Type1, the two top coatings has their own haze except the diffuse haze that are on the display. The Type2 has only 11% haze and the Type1 has 42% haze, see Table 3.4. The high haze in the Type1 increases the top haze effect and the Figure 4.6: Average ranking score of different age text blurs more. groups The slimmed 2-polarizer BiNem shows a little parallax effect, but not so much so the shadow

Lighting conditions effect is present (double image). The effect of this is that the parallax shadows a part of the No significant difference could be found in the bright inter pixel, hence, the contrast is enhanced. different lighting conditions. The results can be Without the parallax the inter pixel around each seen in Figure 4.7. pixel becomes more visible and the black-level is decreased. This is one of the reasons why the new 4.2.2 Discussion 1-polarizer configurations have less contrast ratio The high- and middle-haze configuration was than the 2-polarizer. believed to be of its good viewing angles but the Even though the new 1-polarizer displays shows

46 higher brightness with 39-44% than the 2-polarizer On the BiNem 1-polarizer configuration was with 38%, subjects still prefer the 2-polarizer sharp letters pointed out as a pro. The cons configuration with its higher contrast 8:1 compared were narrow viewing angles and that 1-pixel width to 5:1 in the 1-polarizer configurations. details were hard to perceive. The SYLEN kit was preferred for its size and the design makes it easy to 4.2.3 Conclusions hold. However, the software and buttons are very slow and not working properly. The very slow page • Type2 top coating is preferred over Type1 on turn time was the biggest issue with the BiNem 1- 1-polarizer configuration polarizer in SYLEN kit. • Diffuse reflection should be as high as possible without starting to blur the image The E-Ink Vizplex display had better viewing • Location of diffuse adhesive effects diffuse angles compared to the BiNem 1-polarizer reflection properties and image sharpness configuration. People found that the letters were • 1% ink is not enough to achieve the preferred thin and grayish colored which makes them harder bright state color (both no ink and 1% ink are to perceive. The Amazon Kindle 2 device got yellowish) very good feedback with its nice design, graphical interface, easy buttons for page navigation and fast • Individual optimization for different age- page turning. The page turn time was perceived to groups is not needed be very fast because they mainly compared to the • Lighting conditions do not effect the preferred SYLEN kit which have very slow page turn time. configuration

• High contrast ratio is more important than The advantages of the TFT-LCD were its high optimized top coating and diffuse level contrast and adjustable high brightness which can be used even in dark illumination. No 4.3 Phase 3 direct disadvantages could be found. The iPhone was liked of its portability, configurable display 4.3.1 Results properties and e-reader software preferences, and The comments from the interviews were analyzed extra features such as camera, music player, by picking out the most recurring. Since calendar, and internet browsing etc. However, both the display properties and the e-reader people thought that the display size was too small device (buttons, graphical interface etc.) are for long time reading. The small display size evaluated comments of the displays and devices results in smaller font size to fit enough text was separated. The pros and cons for each display content on one page. This resulted in closer and its device can be seen in Table 4.2. viewing distance.

47 4.3.2 Discussion 2 can not be increased without loosing its portability The outcome from the interviews in phase 3 shows different interesting results. The test subjects • Maximize area on display for showing text found e-book reading interesting and they see the possibilities with the application. Most thought • Ineffective font style for BiNem 1-polarizer in it was not quite the same feeling as reading a SYLEN traditionally book but they did not think it was more difficult to read on the e-reader compared to • Display with adjustable/configurable the traditionally book. This shows that e-reader properties are preferred devices can today be used as a complement to normal printed paper. However, the 3.5" display • Improved viewing angles (diffuse reflection) on the iPhone is not big enough for long-time 1-polarizer configuration has still to narrow reading and viewing angles Since it was the first time the test subjects used an e-reader device they found the page- turning annoying especially on the SYLEN e- reader. Feedback regarding the displays was less 4.4 Phase 4 than about the devices, the display itself is not as important than design and the user interface of the 4.4.1 Results device. The results from phase 4 can be seen in Figure 4.8, the diagram shows how many times each 4.3.3 Conclusions display configuration has been ranked at each • Graphical interface and design are more position. Of a total of 78 performed rankings, important than optical properties of the 38 choose configuration A as the most preferred. display such as contrast and brightness Configuration A was picked as the second preferred 22 times and as the least preferred only 4 times • Reading on e-readers are competitive to of 78 total. Configuration was the second best reading in normal books with 23 most preferred and 39 second preferred • Graphical interface and design are more rankings. Configuration B was ranked as the least important than optical properties of the preferred of the four displays as it was ranked last display 53 of 78 times total. The average calculated score of each • 3.5” display is not large enough for long time configuration can be seen in Figure 4.9. The reading score corresponds to the average ranking order • Device size of SYLEN and Amazon Kindle where 1 is most preferred (lower score is better).

48 test subjects are comparing BiNem to the E-Ink Vizplex by only looking at the same static image, they prefer the BiNem displays. This result is very important because it shows what the ﬁrst impressions about these displays are.

4.4.3 Conclusions

• Contrast enhancement improves the legibility

Figure 4.8: Results from phase 3. Diagrams show • High contrast is important for e-reader display how the different configurations was rated at each (2-polarizer BiNem most preferred) position. See Table 3.5 for configuration explanation

Figure 4.9: Results from phase 3. Average ranking score for all displays. See Table 3.5 for conﬁguration explanation

4.4.2 Discussion

The high contrast BiNem 2-polarizer configuration is still more preferred than the new improved BiNem 1-polarizer configuration with enhanced viewing angles and a neutral white bright state. Remarkable is that all BiNem displays was preferred over the E-Ink Vizplex display. In the previous phases was the reading performance of the E-Ink Vizplex display compared to BiNem display and no difference could be found between them. The results from this phase shows that when the

49 Table 4.2: Comments from interviews in phase 3

Pros Cons BiNem 1-polarizer - Sharp letters - Narrow viewing angles - Fine pixel details such as dots over the letters i, ä and ö are hard to perceive - Optics non conﬁgurable (contrast, brightness) SYLEN device - Device size - Slow page turning - Non-curved and easy to hold - Slow graphical interface - Loose and diﬃcult buttons

E-Ink Vizplex - Wide viewing angles (especially - Grayish letter color when compared to A) - Thin letters - Optics non-conﬁgurable (brightness, contrast) Amazon Kindle 2 - Device size - Fast page turning (compared to A) - Appealing design

TFT-LCD - High contrast - Adjustable brightness - No glare - Independent of presence lighting condition iPhone - Easy to hold - Small display size - Very portable - Small font size - Conﬁgurable - Very little content on each page - Extra features (phone, music, - Shorter viewing distance necessary camera, calendar, internet browsing etc.)

50 Chapter 5

Overall conclusions

5.1 Conclusions e-reader devices the optical display properties are not as important as the device design and user The BiNem e-paper display have been interface. The display must be developed to meet benchmarked against the E-Ink Vizplex display the device features but it is the device functionality which can be found in a number of e-reader and design that attracts the user to buy it in devices currently on the commercial market. the end, not the display. Legibility investigations In terms of legibility and reading comfort no with real users are needed to fully understand difference was found between the BiNem and how the performance of a display configuration E-Ink Vizplex display. The display technology is. This thesis has identified an optimized optical and optical properties slightly differs between solution for the BiNem display. The Type2 top the two displays but users can read fast and coating reduces the front reflection and glare and accurate on both without any visual fatigue. the biaxial retardation compensation film keeps However, when comparing the BiNem to the the contrast and color of the display even when E-Ink Vizplex displays by judging the same static viewed in angle. 2% ink should be used to achieve image the users prefer the BiNem displays with a more neutral white bright state and the diffuse its high contrast and sharp letters. A number adhesive should be as high as possible without of key optical properties have been identified starting to blur the image, depending where it is as important for e-paper displays: brightness placed in the optical stack. is always needed to be able to read but lower Conclusions: brightness can be compensated with a higher 1. In terms of reading experience, the BiNem contrast ratio. A contrast ratio of at least 8:1 is display is comparable to the E-Ink Vizplex a sufficient level compared to displays with 5:1 in display contrast ratio. Reducing front reflection and glare and wide viewing angles with an uniform display • No noticeable difference in legibility appearance enhances the reading experiences of • No noticeable difference in reading the display. When e-paper displays are used in comfort

51 2. The BiNem display is preferred over the E-Ink 5.2 Evaluation Vizplex display when judging the displays by The outcome of this thesis has been successful. a static image The purpose have been fulfilled while numerous 3. The following display properties are interesting data about the BiNem display have important for e-reader applications been collected. Many of the difficulties that arose during the • High brightness, but alone is it not work has been primarily how the various tests were enough designed. Because there are differences between

• Contrast ratio the various displays in addition to the tested optical properties (contrast, brightness etc.), the • Front reflections and glare should be tests must be adjusted so that none of the display minimized is more favorable. The resolution, the possibility • Uniform display appearance of using gray scales, and the page-turn time are some characteristics of the display that may affect 4. Legibility investigations with real users is the legibility. However, by for example choosing needed for understanding and optimizing the font style and font size so its perceived similar on BiNem display for e-reader applications a high resolution as on a low resolution display removes this factor and only the optical properties 5. The graphical interface and design are very will affect the legibility. important for the e-reader device, only In three of the four phases static displays have considering the optical properties of the been used. Because of this only relative short display is not enough reading tests have been possible to perform, longer

6. An optimized BiNem 1-polarizer configuration reading test could result in more distinct results. for e-reader applications could be identified: In afterwards you can always ask yourself whether your methods were the best, other • Typ2 top coating reduces front methods could been used but I think that the reflections and glare experimental design well satisfy the goals and purpose of this study. I believe that the • The biaxial retardation compensation bistable LCD has a promising future for several film enhances the contrast, also when applications, not only as an electronic shelf label viewed in angle or in the e-reader application. The low energy • 2% purple ink to achieve a neutral bright consumption and paper-like appearance are strong state color arguments to continue developing this type of

• Maximize the diﬀuse reﬂection without display. starting to blur the image

52 References

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[2] Abigail J. Sellen and Richard H.R. Harper. The myth of the paperless oﬃce. MIT Press, Cambridge, MA, USA, 2003.

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[4] Z Zhu and J Wu. On the line standardization on vdt’s proper and optimal contrast range. Ergonomics, 33(7):925–935, 1990.

[5] M. Born and E. Wolf. Principles of optics. Cambridge University Press, (Seventh Edition), 1999.

[6] Anonymous. Visible spectrum [online], undated. Accessed 12 January 2010, http://en.wikipedia. org/wiki/Visible_spectrum.

[7] Hunter Labs. Insight on Color [online], 2008. http://www.hunterlab.com/appnotes/an02_01.pdf.

[8] IREX Corporate Website. What is the iLiad? [online]. Accessed 12 January 2010, http://www. irextechnologies.com/products/iliad.

[9] Anonymous. Amazon Kindle [online], undated. Accessed 12 January 2010, http://en.wikipedia. org/wiki/Amazon_Kindle.

[10] SONY. Reader Digital Book [online]. Accessed 12 January 2010, http://www.sonystyle. com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10551&storeId=10151&langId= -1&productId=8198552921665562069#specifications.

[11] T. Megaw. The deﬁnition and measurement of visual fatigue. in: Wilson, j.r., corlett, e.n. (eds.), evaluation of human work: A practical ergonomic methodology. Taylor and Francis, London, 22, 1990.

[12] Martin C. Boschman et al. Text quality metrics for visual display units: Ii. an experimental survey. Displays, 18, 1997.

53 [13] Zulquernain Mallick et al. Optimization of operating parameters of video display units in text reading task: Luminance contrast, viewing distance, and character size. SID Symposium Digest Tech. Papers, 15(9), 2007.

[14] K. K. Shie and C. C. Lin. Eﬀect on screen type, ambient illumination, and color combination on vdt visual performance and subjective preference. Intl. J. Ind. Ergonomics, 26:223–228, 2000.

[15] C. C. Shi A. H. Wang and Y.C. Hu. Effects of symbol- and wording-color of three hazardous material labels, surround color, and training on users’ visual identification performance under different ambient illuminance. J. Chinese Inst. Ind. Eng, 21:597–605, 2004.

[16] A. H. Wang et al. Eﬀects of bending curvature and text/background color-combination of simulated e-paper on users’ visual performance and subjective preference under diﬀerent ambient illumination conditions. Displays, 28:161–166, 2007.

[17] S. C. Jeng et al. Ambient illumination inﬂuences on legibility of electronic paper. Proc. IDW/AD ’05, pages 1839–11842, 2005.

[18] Martin C. Boschman et al. Text quality metrics for visual display units: Methodological aspects. Displays, 18:37–43, 1997.

[19] Risto Näsänen et al. Display quality and the speed of visual letter search. Displays, 22, 2001.

[20] T S Klitz G E Legge, T S Ahn and A Luebker. Psychophysics of visual reading: Xvi. the visual span in normal and low vision. Vision Res, 37:1999–2010, 1997.

[21] Högskoleprovet. http://hogskoleprovet.se/.

[22] New york times. http://www.nytimes.com/.

54 Appendix A

Consent letter in phase 1

Welcome and thank you for your participation in this study!

This is a study that I perform within my master thesis in collaboration with the company Nemoptic. The study aims to understand which diﬀerences there exist between various types of displays. In this test 3 diﬀerent types of displays will be used.

The study will be filmed with a webcam in order to enable further analysis after the test. After the analysis the film will be erased. The film will not shown to anyone else than the test manager and the supervisor at Nemoptic.

The test consists of 3 parts

1. Letter recognition in text

2. Reading speed

3. Questionnaire

The test will take approximately 20 to 30 minutes. Please turn oﬀ your mobile phone during the test.

I hereby authorize that I will be ﬁlmed during the tests and I understand that this is completely voluntary and I may at any time choose to end my participation.

55 Appendix B

Subjective questionnaire from phase 1

Questions

For each statement you will rate how you have experienced the properties of the displays and the reading comfort by circling any of the integers (0-5) which ﬁts the best where 0 = do not agree 5 = totally agree Please do not spend too much time on each question.

1. The text on the display is diﬃcult to read

Display A Do not agree at all 0 —– 1—– 2 —– 3 —– 4 —– 5 Totally agree

Display B Do not agree at all 0 —– 1—– 2 —– 3 —– 4 —– 5 Totally agree

Display C Do not agree at all 0 —– 1—– 2 —– 3 —– 4 —– 5 Totally agree

2. The contrast (diﬀerence between black text and background) is acceptable

Display A Do not agree at all 0 —– 1—– 2 —– 3 —– 4 —– 5 Totally agree

Display B Do not agree at all 0 —– 1—– 2 —– 3 —– 4 —– 5 Totally agree

Display C Do not agree at all 0 —– 1—– 2 —– 3 —– 4 —– 5 Totally agree

3. I have to focus my eyes thoroughly in order to read from the display

Display A Do not agree at all 0 —– 1—– 2 —– 3 —– 4 —– 5 Totally agree

Display B Do not agree at all 0 —– 1—– 2 —– 3 —– 4 —– 5 Totally agree

Display C Do not agree at all 0 —– 1—– 2 —– 3 —– 4 —– 5 Totally agree

4. I feel dizzy after reading from the display

56 5. The display quality feels good

6. The letters are dark enough in order to be easy to read

7. The resolution of the display is good

8. The display requires strong illumination in order to be easy to read from

9. The display is equivalent to a pocket book

10. The displays is too dark

11. The display has too much surface glare

12. I have to adjust how I hold the display in respect to the illumination in the room

13. The background color disturbs the reading experience

14. I could imagine myself having this display as an e-book (electronic book)

15. The letters are sharp and well-deﬁned

16. Other experience concerning the display quality, legibility, overall feeling, etc

———————————————————————————————————–

Questions regarding reading habits, circle the alternative that ﬁts best (several alternatives can be chosen)

17. How many books do you read per year?

a 0-1

b 2-3

c 4-9

d 10 or more

18. Where do you read?

57 a Indoors

i. In the couch ii. In the bed iii. At the dinner Table iv. At the desk b During travel

i. In the train/plane ii. In the car iii. In the waiting room/lounge c Outdoors

i. In the park ii. At the cafe iii. In the garden/balcony iv. At the sea/beach

Thank you very much for your participation!

58 Appendix C

Images used for ranking task

Figure C.1: Phase 2 ranking image. The black outer borders are not part of the image.

59 Figure C.2: Phase 3 ranking image. The black outer borders are not part of the image.

60 Appendix D

Raw data

In the tables below are the raw data from phase 1, phase 2, and phase 4 stated.

61 Table D.1: Raw data phase 1

# Time of Age Gender Mother Illuminance Display Pseudu- Time Found Error # Error % Article- Words/m 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 test tongue text (s) letters text

A p1 73,4 14 -4 -0,22222 a1 228 1 4 0 1 4 5 5 4 4 4 2 2 1 4 5 1 13.31 25 M SWE 540 B p2 74,8 18 -6 -0,25 a2 234 2 3 1 1 3 4 4 4 3 3 1 1 1 3 3 C p3 64,2 13 -8 -0,38095 a3 252 0 5 0 1 3 5 5 3 5 1 0 0 1 5 5

A p1 102,9 17 -1 -0,05556 a1 322 0 5 0 0 5 5 4 0 5 1 2 1 0 5 5 2 14.35 25 M SWE 545 B p2 88,3 18 -6 -0,25 a2 382 1 3 1 0 3 3 3 0 3 0 0 0 0 3 3 C p3 90,9 17 -4 -0,19048 a3 372 0 3 3 3 4 5 5 0 5 0 0 0 3 1 5

A p1 71,3 12 -6 -0,33333 a1 162 4 0 4 2 4 4 5 4 2 5 5 5 5 0 4 3 16.45 27 M SWE 535 B p2 77,5 15 -9 -0,375 a2 234 2 3 3 1 2 2 2 2 3 1 2 3 1 2 2 C p3 76,5 15 -6 -0,28571 a3 242 1 5 1 0 5 5 5 1 5 0 0 0 0 5 5

A p1 95,8 15 -3 -0,16667 a1 260 0 5 0 0 5 5 5 3 5 0 0 0 0 5 5 4 09.24 24 M SWE 540 B p2 104,6 20 -4 -0,16667 a2 306 1 4 1 0 5 3 4 2 4 0 0 0 1 5 4 C p3 104,6 17 -4 -0,19048 a3 274 0 5 0 0 5 5 5 1 5 0 0 0 0 5 5

A p1 125,2 14 -4 -0,22222 a1 112 2 4 2 1 3 4 5 3 5 0 2 1 0 5 5 5 13.13 24 M SWE 542 B p2 131,7 22 -2 -0,08333 a2 144 3 3 3 2 2 3 3 2 4 0 4 3 1 4 3 C p3 118,1 15 -6 -0,28571 a3 138 0 5 1 0 3 5 4 1 5 0 0 0 0 4 4

A p1 59,5 16 -2 -0,11111 a1 260 4 1 4 0 2 2 1 4 0 4 1 1 3 2 0 6 14.20 24 M SWE 530 B p2 71,2 22 -2 -0,08333 a2 246 2 3 3 0 3 1 2 3 1 3 2 1 3 2 2

62 C p3 63,3 18 -3 -0,14286 a3 310 0 5 1 0 3 4 4 1 2 2 1 1 1 4 4

A p1 77,8 14 -4 -0,22222 a1 222 1 3 0 0 4 5 5 2 4 2 2 3 2 5 5 7 15.12 26 M ARAB 561 B p2 82,4 19 -5 -0,20833 a2 144 2 4 0 0 3 3 3 2 3 0 3 4 1 3 3 C p3 75,2 14 -7 -0,33333 a3 190 0 5 0 0 5 5 5 2 5 0 0 0 0 5 5

A p1 53,7 14 -4 -0,22222 a1 260 3 3 2 0 3 3 5 1 4 4 0 0 0 4 5 8 16.42 26 M SWE 574 B p2 55,7 18 -6 -0,25 a2 306 2 4 1 0 4 4 4 1 4 2 0 0 0 4 4 C p3 48,8 16 -5 -0,2381 a3 292 1 5 0 0 5 5 5 0 5 1 0 0 0 5 5

A p1 89,9 14 -4 -0,22222 a1 120 3 3 4 3 3 4 4 3 2 4 3 3 5 4 4 9 11.44 26 M BOSN 586 B p2 100,9 18 -6 -0,25 a2 182 1 2 3 3 2 2 4 3 5 3 3 3 3 5 4 C p3 89,3 14 -7 -0,33333 a3 168 2 3 4 3 2 4 4 3 3 1 3 3 5 2 4

A p2 132,1 24 0 0 a2 370 0 4 2 0 4 5 5 4 3 3 0 5 3 2 4 10 15.45 24 M SWE 610 B p3 119,6 21 0 0 a3 356 0 5 2 0 5 5 5 2 5 1 0 4 0 5 4 C p1 128,0 17 -1 -0,05556 a1 282 1 3 3 1 3 5 5 3 5 0 5 4 0 3 5

A p2 69,4 22 -2 -0,08333 a2 298 1 4 2 0 3 4 3 4 1 5 2 1 4 0 3 11 08.04 25 M SWE 630 B p3 63,6 20 -1 -0,04762 a3 254 0 5 0 0 5 4 3 1 4 0 4 3 0 5 5 C p1 63,0 16 -2 -0,11111 a1 246 3 2 4 2 1 4 3 1 5 0 0 0 3 2 3

A p2 129,4 22 -2 -0,08333 a2 376 0 4 1 1 4 5 4 1 1 2 4 4 2 4 4 12 10.13 23 M SWE 621 B p3 137,0 21 0 0 a3 320 0 3 0 0 2 3 4 2 4 0 3 3 1 4 2 C p1 137,2 15 -3 -0,16667 a1 310 1 3 4 5 2 5 4 1 3 0 0 0 1 4 4

A p2 115,2 22 -2 -0,08333 a2 280 0 3 1 1 3 4 4 3 4 1 1 0 0 4 4 13 10.54 25 M SWE 611 B p3 113,4 18 -3 -0,14286 a3 294 0 4 2 2 2 3 4 2 4 1 0 0 1 3 3 C p1 106,3 16 -2 -0,11111 a1 164 1 2 3 2 1 5 4 2 5 0 0 0 1 4 5 A p2 101,3 21 -3 -0,125 a2 326 0 5 3 0 4 5 4 1 2 1 3 4 0 4 4 14 11.26 24 M SWE 617 B p3 87,5 12 -9 -0,42857 a3 280 3 2 4 0 0 1 3 4 1 3 4 4 3 2 2 C p1 88,1 15 -3 -0,16667 a1 282 3 3 4 0 1 2 3 2 2 0 1 0 3 3 4

A p2 103,0 17 -7 -0,29167 a2 400 2 4 4 2 3 4 3 5 2 4 0 1 1 3 3 15 14.24 23 M SWE 636 B p3 105,3 18 -3 -0,14286 a3 368 3 4 4 3 3 3 3 4 2 2 0 3 3 3 1 C p1 87,8 13 -5 -0,27778 a1 350 4 4 5 4 4 4 5 1 1 0 4 1 5 0 4

A p2 115,0 20 -4 -0,16667 a2 352 0 5 2 0 5 5 5 1 4 1 1 4 0 4 5 16 16.17 25 M SWE 625 B p3 106,1 17 -4 -0,19048 a3 288 2 3 4 2 2 2 2 2 2 2 3 1 1 2 3 C p1 110,5 15 -3 -0,16667 a1 306 1 4 3 1 5 5 5 1 5 0 0 0 1 3 5

A p2 168,3 21 -3 -0,125 a2 294 1 5 2 0 4 4 4 4 4 3 1 1 1 4 4 17 16.50 25 M SWE 635 B p3 156,4 17 -4 -0,19048 a3 206 2 2 4 2 3 2 2 3 2 4 2 1 2 3 2 C p1 140,3 14 -4 -0,22222 a1 252 2 4 3 1 4 5 3 4 4 4 2 1 2 4 4

A p2 62,0 21 -3 -0,125 a2 310 1 5 1 1 4 4 5 1 4 1 0 1 1 5 1 18 13.40 23 M ERIT 630 B p3 59,0 18 -3 -0,14286 a3 266 2 3 2 3 3 3 3 2 4 0 1 1 1 4 1 C p1 50,8 16 -2 -0,11111 a1 204 5 0 4 4 1 1 0 3 0 0 4 3 2 0 5

A p3 71,6 17 -4 -0,19048 a3 274 3 1 3 2 3 2 4 2 3 1 1 2 1 4 4 19 10.23 24 F SWE 529 B p1 70,9 15 -3 -0,16667 a1 224 4 3 4 3 3 3 2 1 3 0 1 1 3 1 1 C p2 67,0 18 -6 -0,25 a2 344 0 5 1 0 5 5 5 0 5 0 0 0 0 5 5

A p3 71,6 17 -4 -0,19048 a3 216 3 3 3 0 3 4 4 4 1 3 4 4 4 4 5 20 12.33 31 M SWE 596 B p1 67,0 15 -3 -0,16667 a1 224 2 5 1 0 3 3 3 0 4 0 0 2 0 5 3 C p2 70,9 18 -6 -0,25 a2 250 0 5 0 0 3 5 5 0 5 0 0 0 0 5 5

63 A p3 132,9 19 -2 -0,09524 a3 274 2 2 4 0 1 1 1 2 0 4 3 2 3 0 0 21 14.12 32 M SWE 632 B p1 120,1 15 -3 -0,16667 a1 242 1 5 3 0 5 4 5 2 4 0 0 0 0 5 5 C p2 151,3 20 -4 -0,16667 a2 290 1 3 4 0 5 5 5 2 4 0 0 0 5 4 5

A p3 107,1 16 -5 -0,2381 a3 222 0 2 2 0 3 4 4 4 0 4 3 2 4 1 4 22 08.45 27 M SWE 608 B p1 98,6 15 -3 -0,16667 a1 166 0 3 2 0 2 1 4 1 4 2 3 3 1 3 2 C p2 122,9 21 -3 -0,125 a2 218 0 0 0 0 2 5 5 0 4 0 0 0 1 5 5

A p3 130,5 20 -1 -0,04762 a3 236 1 2 3 3 3 4 4 4 1 5 2 2 0 1 2 23 10.27 25 M SWE 583 B p1 135,0 15 -3 -0,16667 a1 238 2 3 2 1 2 2 2 3 2 2 3 3 1 3 3 C p2 153,0 24 0 0 a2 244 0 5 0 0 4 4 4 3 5 0 0 0 0 5 4

A p3 128,2 20 -1 -0,04762 a3 224 2 4 4 1 4 4 4 4 3 4 3 2 3 4 4 24 12.57 22 M SWE 564 B p1 137,6 14 -4 -0,22222 a1 168 3 3 2 5 2 1 4 3 2 3 4 2 5 1 4 C p2 145,2 21 -3 -0,125 a2 244 0 5 3 3 5 5 4 2 5 0 1 2 1 5 5

A p3 78,7 17 -4 -0,19048 a3 174 1 1 1 0 5 4 5 5 2 5 4 1 3 3 3 25 14.12 25 M SWE 556 B p1 84,3 16 -2 -0,11111 a1 188 3 3 5 1 3 3 4 4 4 3 0 5 5 0 0 C p2 86,8 21 -3 -0,125 a2 276 0 0 0 0 5 5 5 0 5 0 0 0 0 5 5

A p3 105,6 17 -4 -0,19048 a3 302 3 3 4 1 4 4 4 4 3 2 5 5 5 1 2 26 09.49 25 M SWE 545 B p1 100,9 12 -6 -0,33333 a1 226 1 4 2 0 3 4 4 3 5 4 1 1 1 4 4 C p2 112,5 24 0 0 a2 340 0 5 1 0 2 4 5 2 5 5 0 1 0 5 5

A p3 81,6 15 -6 -0,28571 a3 372 0 5 0 0 3 5 5 3 1 2 0 0 0 4 5 27 14.33 23 M SWE 569 B p1 70,7 11 -7 -0,38889 a1 352 1 4 1 1 3 3 5 2 3 1 0 0 1 3 3 C p2 97,7 18 -6 -0,25 a2 316 3 1 4 5 3 5 5 2 5 0 0 0 3 2 5 Table D.2: Raw data phase 2

# Age Gender Illuminance Illuminance Rank: #1 #2 #3 #4 #5 #6 type (ﬂux)

1 25 M 1 170 A E F C B D 2 25 M 1 170 A E C F B D 3 22 M 1 170 A C B E F D 4 21 M 1 170 E A F C D B 5 29 M 1 170 E A C B D F 6 25 M 1 170 A E B F D C 7 32 F 1 170 E C B F D A 8 42 M 1 170 B E A D C F 9 19 M 1 170 A F E B C D 10 22 M 1 170 A B C E D F 11 20 F 1 170 A F C E B D 12 35 M 1 170 A C E B D F 13 23 M 1 170 A F E B C D 14 21 F 1 170 D E B F A C 15 22 F 1 170 E F A C D B 16 19 F 1 170 A E C B D F 17 18 M 1 170 A B E F D C 18 18 M 1 170 A E F D C B 19 21 F 1 170 A E F C B D 20 24 M 1 170 A C E B F D 21 40 M 1 170 A E F B C D 22 25 M 1 170 A F E B D C 23 24 M 1 170 A F B D E C 24 32 M 1 170 E F C D A B 25 24 F 1 170 F B D C E A 26 23 F 1 170 A E F C B D 27 24 M 1 170 A F C E D B 28 31 F 1 170 C F D E A B 29 20 F 1 130 A F E C D B 30 22 F 1 130 A C E B D F 31 21 F 1 130 A E F C B D 32 22 F 1 130 A E C B D F 33 25 M 1 130 A E F B C D 34 19 F 1 130 A E F C B D 35 19 F 1 130 A F E C D B 36 21 M 1 130 F C E D B A 37 20 M 1 130 A B D E F C 38 20 M 1 130 A F E B C D 39 24 F 1 130 A B C E F D 40 20 M 1 130 A E C F B D 41 19 M 1 130 E A C F B D 42 46 F 1 130 A B E C D F 43 28 M 1 130 E A F C B D 44 20 F 1 130 A F B C E D 45 24 M 1 130 A E F C D B 46 26 M 1 130 A E F D B C 47 22 M 1 130 A E C F D B 48 45 F 1 130 C F A D B E 49 25 F 1 130 A E C F B D 50 19 M 1 130 A F B E C D 51 21 F 1 130 A E B F C D 52 20 M 1 130 A E F C B D 53 24 M 1 130 A E B F D C 54 30 M 3 - A E F C B D 55 19 M 3 - A E F C B D 56 26 M 3 - E C A F B D 57 22 F 3 - A E C F D B 58 28 F 3 - C A B F D E 59 23 F 3 - A C B D E F 60 23 M 3 - A C F E B D 61 35 M 2 305 A E F C B D 62 8 M 2 305 A D C E B F 63 63 F 2 305 A C D E F B 64 23 M 2 305 F E A C D B 65 23 M 2 305 A E F D B C

64 66 36 F 2 305 A C E F B D 67 33 M 2 305 F B A E C D 68 24 F 2 305 E A C B F D 69 28 M 2 305 B C F A E D 70 24 F 2 305 E B A F D C 71 52 F 2 305 E A F C D B 72 62 M 2 305 A E F C D B 73 24 M 2 310 A E F C D B 74 31 M 2 310 A E F C D B 75 30 M 2 310 A E F C D B 76 20 M 2 310 A E C B D F 77 24 M 2 310 E B F C D A 78 19 M 2 310 E A F C B D 79 22 F 2 310 A C E B F D 80 22 M 2 310 A E F C B D 81 24 M 2 310 A F C B E D 82 29 M 2 310 F E A C D B 83 23 F 2 310 E A F C B D 84 24 F 2 310 A E F C B D 85 23 F 2 310 A C E D B F 86 21 M 2 310 A E F C D B 87 21 F 3 - A E C F D B 88 24 M 3 - A E C F B D 89 20 M 3 - C F E D A B 90 24 M 3 - A E C F B D 91 21 M 3 - A D F C B E 92 25 M 3 - A F E C B D 93 25 M 3 - A F E C B D 94 23 F 3 - A E F C D B 95 57 F 3 - A E F C D B 96 52 M 3 - A E F C D B 97 26 M 3 - A F E B D C 98 42 M 3 - E A C F B D 99 25 M 3 - A E F C D B 100 24 F 3 - A E C F D B

65 Table D.3: Raw data phase 4

# Age Gender Rank: #1 #2 #3 #4

1 25 M B A D C 2 28 M D B C A 3 25 M B D A C 4 24 M B C D A 5 25 M A D C B 6 23 M A D C B 7 28 M A B D C 8 27 M D A B C 9 25 M D A C B 10 23 M B C A D 11 21 M D A C B 12 22 M A D C B 13 23 F A D C B 14 53 M D A C B 15 61 M D C A B 16 19 F C A B D 17 20 M A D C B 18 64 M D A C B 19 27 M A D C B 20 27 F A D C B 21 19 M B C D A 22 22 M A D C B 23 21 F D A B C 24 19 M D A C B 25 55 M A C D B 26 22 M A D C B 27 22 M A D C B 28 23 M D A C B 29 25 M A D C B 30 24 F B D C A 31 31 M A D C B 32 23 F A D C B 33 24 F A D C B 34 22 M D A C B 35 24 M C A D B 36 19 M A D B C 37 21 M B A D C 38 25 M D C A B 39 27 M D B C A 40 55 F D A C B 41 25 M D A C B 42 27 M A D B C 43 22 F A D C B 44 23 F A D C B 45 41 M A D C B 46 46 M A D C B 47 23 M A D C B 48 24 M D A C B 49 20 M A B D C 50 21 M A D C B 51 20 M D A C B 52 22 M A D C B 53 21 F A D C B 54 19 M D C A B 55 22 M D A C B 56 23 M C B A D 57 21 M C D A B 58 29 M A C D B 59 24 M A D C B 60 35 F C A B D 61 25 M B D A C 62 22 M A D C B 63 25 F A D C B 64 23 F B D A C 65 23 M A B C D 66 42 M C D A B

66 67 22 M D A C B 68 25 M A D C B 69 27 M A D C B 70 25 F D A C B 71 26 F B D A C 72 23 M A C B D 73 23 M A C D B 74 24 F D B A C 75 24 M A D C B 76 23 F C D A B 77 25 M D A C B 78 20 M A D B C