Influence of ambient-tablet PC luminance ratio on legibility and visual fatigue during long-term reading in low lighting environment

We examine the effect of the (luminance) ratio of ambient luminance to tablet surface luminance on text legibility and fatigue over 1 h of long-term reading with a tablet PC in low-ambient-luminance environments limited to 45 cd/m² (illuminance ~230 lx). Four reading-pattern subject experiments are carried out at ambient-luminance-to-tablet-surface-luminance ratios of 1:1, 1:3, 1:6, and 1:9 at 15 and 45 cd/m². As per legibility tests based on the semantic differential (SD) method, we find that subjects experience glare at luminance ratios of 1:6 and 1:9, and it is difficult to read text at the luminance ratio of 1:9 under ambient luminances of 15 and 45 cd/m². Based on subject fatigue (determined by subjective symptom survey), we find that the feeling of fatigue, according to the change in the luminance ratio, most affects the Fuzziness group among the five subjective fatigue groups. Based on physical fatigue determined using the critical flicker fusion frequency (CFF) value, we observe significant CFF differences before and after reading for luminance ratios of 1:1 and 1:9 at the ambient luminance of 45 cd/m² and for the ratio of 1:9 when the ambient luminance is 15 cd/m². A larger difference between the ambient and surface luminances corresponds to higher CFF variation rates and more fatigue.     

Effects of ambient illuminance and electronic displays on users' visual performance for young and elderly users

Abstract— This study investigated the effects of age (young participants aged 20–30 and elderly participants older than 60), ambient illuminance (50, 500, 1 500, 3000, 6000, and 9000 lx) on participants' visual performance when using various electronic displays (conventional transmissive LCD, Ch‐LC display, and E‐ink display). Overall, the results indicated that participants' visual performance showed sign if icant difference among various ambient il luminance cond itions, electronic displays, and between two groups of participants. Significantly different visual performance was observed between young and elderly participants. The interaction among ambient illuminance, type of electronic display, and age had a significant effect on participants' visual performance. When participants used the E‐ink display, both young and elderly participants had significantly worse visual performance under an ambient illuminance of 50 lx compared to other illuminance settings. When participants used the Ch‐LC display, young participants had significantly worse visual performance under an ambient illuminance of 50 lx compared to other illuminance settings, but elderly participants had significantly better visual performance under an ambient illuminance higher than 1500 lx. When young participants used a conventional transmissive LCD, the ambient illuminance had no significant effect on their visual performance. When elderly participants use a conventional transmissive LCD, an illuminance of 50 and 6000 lx seem to have a detrimental effect on their visual performance.     

Effects of ambient illuminance on users' visual performance using various electronic displays

Abstract— This study investigated the effect of ambient illuminance (50, 500, 1500, 3000, 6000, and 9000 lx) on participants' visual performance using four electronic displays (conventional LCD under transmissive mode, conventional LCD under reflective mode, Ch‐LC display, and E‐ink display). Analysis results indicate that participants' visual performance shows significant difference under various ambient illuminance and electronic displays. The interaction between ambient illuminance and electronic display also has significant effect on participants' visual performance. When participants use the conventional LCD under transmissive mode, ambient luminance has no significant effect on participants' visual performance. However, participants' visual performance is significantly different under various ambient illuminances using the conventional LCD under reflective mode, Ch‐LC display, and E‐ink display. The conventional LCD under transmissive mode is the only choice at a lower illuminance of 50 lx. Higher illuminance (500 lx) for E‐ink displays may result in as good a performance as the conventional LCD under transmissive mode; nevertheless, much higher illuminance (1500 lx) for the conventional LCD under reflectance mode and Ch‐LC display may achieve better performance.     

Optimization of Chinese interface design in motion environments

The Taguchi method has been successfully applied in engineering fields to deal with a single performance quality problem, but it is not often used in interface design and the handling of multiple performance quality problems. This study investigated a multi-response problem in terms of searching time, number of missing characters/buttons (NMCB), and visual fatigue by integrating the Taguchi method and the weighting method to optimize the Chinese interface design parameters such as display type, character size, font type, and text/background color combination in motion environments. The results indicated that subjects’ visual performance was improved when using the optimum interface setting (LCD, 7.5 * 7.5 mm, Kai font and white/blue color combination) rather than the current interface setting.     

Effects of text/background color combination,ambient illuminance,and display type on discriminating performance for young and elderly users

Abstract— This study examined the effects of text/background color combinations (black‐on‐white, red‐on‐white, green‐on‐white, and blue‐on‐white), ambient illuminance (50, 500, and 12,000 lx), and display type (color electronic‐paper displays and conventional transmissive liquid‐crystal displays) on the discriminating performance of young and elderly users. The results showed that when participants used the color e‐paper display, young participants had significantly better discriminating performance than elderly participants under the text/background color combinations of black‐on‐white, green‐on‐white, and blue‐on‐white, whereas no significant difference was present between young and elderly participants under red‐on‐white. When participants used a conventional transmissive LCD, however, there was no significant difference between young and elderly participants under all text/background color‐combination settings. Young participants had substantially better discriminating performance under 500 and 12,000 lx than under 50 lx, whereas elderly participants had the best discriminating performance under 12,000 lx, followed by that under 500 lx, and the worst performance under 50 lx. Participants who used a conventional transmissive LCD had substantially better discriminating performance under 500 and 12,000 lx than under 50 lx. Participants who used the color e‐paper display had the best discriminating performance under 12,000 lx, followed by that under 500 lx, and the worst performance under 50 lx. The results can be the guild for the designers of color e‐paper displays.     

Survey of actual viewing conditions at home and appropriate luminance of LCD‐TV screens

Abstract— To understand actual viewing conditions at home is important for TV design. And the preferred luminance level of LCD TVs under actual viewing conditions is also important in order to obtain both good picture quality and low power consumption. The actual viewing conditions of households and the preferred luminance levels was investigated. In a field test of 83 households, the display luminance, screen illuminance, and viewing locations were measured on site. In laboratory experiments, young and elderly subjects adjusted the luminance of an LCD‐TV screen to their preferred levels under different screen illuminance levels, angular screen sizes, and average luminance levels (ALL) of the images. As a result, two equations, which represent the preferred luminance level of LCD‐TV screens corresponding to different viewing conditions for young and elderly subjects were obtained. When the ALL of the images was 25% and the screen illuminance and angular screen size were set at 100 lx and 20°, respectively, the preferred luminance was 1 60 cd/m² for the young subjects and 248 cd/m² for the elderly subjects. By using the setting of the preferred luminance of an LCD TV under actual viewing conditions, it is possible to conserve energy consumption.     

Visual methods for determining ambient illumination conditions when viewing medical images in mobile display devices

Abstract— The quality of the displayed image on mobile devices is affected by the varying ambient illumination conditions. Determining appropriate viewing conditions for particular visual tasks requires time and the appropriate instrumentation. To this end, the usefulness of more practical visual tests for use in clinical environments were explored. Experiments to determine the limitations of mobile displays in terms of the visibility of subtle targets for different background luminance and ambient illumination with two mobile devices were conducted. A noise‐embedded text detection task and a threshold estimation staircase technique for a range of illuminance between 1 and 80,000 lx encompassing conditions found in dark reading rooms, office spaces, and outdoor scenarios has been compared. It was found that the text detection method holds promise as a surrogate for more complicated tests in the framework of a clinically practical implementation.     

Highly efficient styrylamine-doped blue and white organic electroluminescent devices

We have developed highly efficient blue and white organic electroluminescent devices based on a blue fluorescent styrylamine dopant EBDP. The blue and white organic light emitting diodes (OLEDs) with the structures: Indium–tin oxide (ITO)/copper phthalocyanine(CuPc)/N,N′-bis-(1-naphenyl)-N,N′-biphenyl-1,1′-bipheny1-4-4′-diamine (NPB)/2-t-butyl-9,10-di-(2-naphthyl)anthracene (TBADN):EBDP/tris(8-hydroxyquinoline)aluminum(Alq₃)/LiF/Al and ITO/CuPc/NPB/TBADN:EBDP: 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)/Alq₃/LiF/Al were studied by using EBDP as blue dopant. For the blue device, the maximum luminance and maximum efficiency were 26961 cd/m² and 8.29 cd/A, respectively, the luminance at a current density 20 mA/cm² was 1597 cd/m². For the white device, the maximum luminance of 32,291 cd/m², maximum efficiency 8.31 cd/A and the luminance of 1413 cd/m² at a current density 20 mA/cm² were obtained. The slow decrease of efficiency with the increase of current density indicates weak exciton–exciton annihilation, which is resulted from the large steric hindrance due to the non-planar structure of the fluorescence dye EBDP.     

Visual comfort in 2D/3D modes of glasses‐type stereoscopic displays

In this study, we compared visual comfort in 2D/3D modes of the pattern retarder (PR) and shutter glasses (SG) stereoscopic displays by changing viewing factors and image contents. The viewing factors include ambient illuminance/monitor luminance/background luminance and image contents mainly are determined with different disparity limits. The degrees of 2D/3D visual comfort were investigated by using various combinations of ambient illuminance, monitor luminance, background luminance, and disparity limit. A series of psychological experiments were also performed to compare 2D and 3D viewing experiences for the passive PR and active SG stereoscopic displays and to discover more comfortable conditions under various variable combinations. The experiment results show that the various variable combinations affecting visual comfort in the passive PR and active SG stereoscopic displays were significantly different. Finally, we suggest more comfortable conditions of viewing 2D and 3D images for the PR and SG stereoscopic displays.     

Legibility and subjective preference for color combinations in text

This study examined legibility performance and subjective preference for text/background color combinations displayed on a video monitor. Luminance contrast was fixed at two preoptimized levels, either with text brighter than the background (10:1) or vice versa (1:6.5). In Experiment 1, 32 subjects rated about 800 color combinations. No evidence suggested differential effects of luminance polarity or hue, with the only exception that cool background colors (blue and bluish cyan) tended to be preferred for the light-on-dark polarity. Saturation had the most important influence on ratings. Any desaturated color combination appears to be satisfactory for text presentation. In Experiment 2 a reduced set of 18 color combinations was investigated with a new sample of 18 subjects. Reading and search times as well as multidimensional ratings were evaluated. There was no evidence for an influence of luminance polarity or chromaticity on performance. Subjective ratings corresponded well with the results of Experiment 1.     

Influence of the ambient illuminance on the subjective brightness measurements

The subjective brightness is determined by not only the display screen luminance but also the light surrounding the display. A metric for space brightness named “Feu” is adopted to consider the effect of luminance distribution. The relation between the pupil diameter and the space brightness is applied to obtain the subjective brightness. The measured subjective brightness is obtained both for direct‐view display and augmented reality (AR) display. The results indicate that the measured subjective brightness is much closer to the perceived result. The subjective brightness increases along with the increase of the screen luminance under the same ambient illuminance. While under the same screen luminance, the subjective brightness decreases with the increase of the ambient illuminance in most cases.     

Physiological effects of intermittently illuminated textual displays

Optical equipment was developed to simulate visual display terminals (VDTs) with reversed presentation (bright background and dark characters). The decay time and mean luminance were kept constant, while the oscillating frequency varied. During one experiment subjects had to read text aloud for 60min. Before and after the reading, near point distance, critical flicker fusion frequency (CFF), visual acuity, stereo depth perception, lateral heterophoria and contrast sensitivity were measured. The 30 subjects had then to report their subjective reactions on a questionnaire. The following frequencies were used: 0, 30, 60, 90, 180 Hz. In addition subjects read a normally printed text with a luminance of 75 or 150 cd/m². The main finding was that of a strong decrease of the CFF after exposure to 30 and 60 Hz. It is suggested that for reversed presentation the refresh rate should be higher than 90 Hz.     

Highly efficient and stable white organic light emitting diode with triply doped structure

A triply doped white organic light emitting diode with red and blue dyes in the light emitting layer and a green dye in another layer is proposed. The device structure was CuPc(12 nm)/NPB(40 nm)/ADN:DCJTB(0.2%):TBPe(1%)(50 nm)/Alq:C545(0.5%)(12 nm)/LiF(4 nm)/Al. Here copper phthalocyanine (CuPc) is a buffer layer, N,N′-di(naphthalene-1-y1)-N,N′-dipheyl-benzidine (NPB) is a hole transporting layer, 9,10-di-(2-naphthyl) anthracene (ADN) is blue emitting layer, tris (8-quinolinolato)aluminium complex (Alq) is an electron transporting layer, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidy1-9-enyl)-4H- pyran (DCJTB), 2,5,8,11-tetra-butylperylene (TBPe), Coumarin6 and deveriative (C545) are red, blue and green dyes, respectively. This device shows a luminance of 21200 cd/m² at driving current of 400 mA/cm² and 1026 cd/m² at 20 mA/cm². Its efficiency is 6 cd/A and 3.11 Lm/W. It also shows a higher operating stability: the half lifetime is 22,245 h at an initial luminance of 100 cd/m², while the driving voltage increased only 0.3 V.     

Effects of refresh rates of a simulated CRT display with bright characters on a dark screen

Twenty-nine subjects carried out a 3 hour reading task at a simulated CRT. In the apparatus chopper discs generated oscillating luminances of bright characters of 30, 60, 90, 180 and 0 Hz. A further control experiment was conducted with a printed text. The oscillating luminances had an approximate decay time of 4 ms (to 10% of peak luminance). The character luminance was kept constant (75 cd/m²). In the simulated CRT all characters oscillated simultaneously.Before, during and after each reading task, the following parameters were determined: Near point distance, critical flicker frequency (CFF), visual acuity, heterophorias, contrast sensitivity, eye blinking rate, and subjective symptoms of discomfort. The reading speed was continuously recorded. Furthermore the CFF at the simulated CRT was determined.The range of individual CFF at the simulated CRT was found between 40 and 56 Hz. It is concluded that most models of VDTs have today refresh rates lying in a critical range of CFF. In every condition the reading task was found to have an effect on visual functions and caused visual discomfort. Differentiated results among the six conditions were only observed for CFF and visual discomfort. The visible flicker (30 Hz) produced the strongest effects while 180 Hz, 0 Hz and the printed text were associated with relatively small effects.     

Adaptive luminance difference between text and background for comfortable reading on a smartphone

This study proposes a model of adaptive luminance difference between text and background for comfortable reading on a smartphone display. The study is composed of two experiments. In Experiment I, the optimal luminance difference is identified in accordance with reading speed and preference. On the basis of the experimental results, the gradual decrease of luminance difference between text and background is developed. The change occurs while reading the text, and the model is applied to various illuminance levels. In Experiment II, the effect of adaptive luminance difference is validated in terms of reading speed, preference, and brainwave analysis using an electroencephalogram. Empirical evidence confirms that the developed model improves physiological comfort and psychological satisfaction, thereby it has a potential to be applied to the visual display industry.     

Luminance and luminance contrast requirements for legibility of self-luminous displays in aircraft cockpits

A series of studies was conducted to investigate the effects of display background luminance, display contrast ratio and adaptation luminance on the legibility of self-luminous displays in aircraft cockpits. The studies were designed to avoid the typical confounding of these three variables, and employed luminance levels that are representative of operational conditions. The data show that with typical display symbols and luminances under low and moderate ambient illumination, contrast ratio is the major determinant of legibility; that increasing contrast ratios beyond as little as 1·4:1 may provide no significant improvements in legibility; and that, beyond their contribution to contrast ratio, the absolute luminances of the symbol and the background have no significant effect on legibility. Given the high ambient illumination typical of a sunny day, however, the pilot is adapted to luminances of up to 32 264 cd/m² (10 000 fL). Under these conditions, increases in contrast ratio of up to 30:1 are shown to improve legibility. When the adaptation luminance is more than 100 times that of the display background luminance, symbols on the display cannot be immediately identified, and the absolute luminances of the adapting field and the display background contribute to recovery time apart from their ratio relationship. Hyperbolic functions are applied to describe the multiplicative effects of these variables on legibility.     

Effects of ambient illumination conditions and background color on visual performance with TFT-LCD screens

This study investigated the effects of ambient illumination conditions (illumination color and illumination intensity) and background color on visual performance (character identification and reading comprehension) with TFT-LCD screens.Results of Experiment 1 indicated that all the three independent variables had significant effects on mean percentage of character identification. Mean character identification performance was best under white light, 500 lux, and blue background. In general, the backgrounds with primary colors had better mean character identification performance than the middle-point colors and gray. Results of Experiment 2 indicated that the illumination intensity and background color had significant effects on mean text comprehension performance for reading comprehension. Mean text comprehension performance were higher under 500 lux and blue background. The backgrounds with primary colors had better mean correct answers than the gray background. According to the results, white light, normal ambient illumination and a background with primal colors seemed to be the optimal conditions. If the yellow ambient light is necessary, using blue as the TFT-LCD background color of will provide better performance.The Pearson product-moment correlation coefficient indicated that short-term visual task measurement might be suitable to evaluate the visual performance.     

Investigation of top-emitting organic light-emitting devices with highly saturated color employing metal-mirror structure

In this work, characteristics of top-emitting organic light-emitting devices (TEOLEDs) having Ag and Au as anode had been investigated. When using the same emitting materials, the performance of TEOLEDs employing Ag as anode was superior to that of the device using Au as anode. Finally, by using the appropriate dopant instead of Alq as emitter, a TEOLED with high power efficiency (8.7 lm/w with luminance of 640 cd/m²), almost independent on viewing angle had been reported.     

Lighting,font style,and polarity on visual performance and visual fatigue with electronic paper displays

Visual performance and visual fatigue of electronic paper displays (electrophoretic display and cholesteric liquid crystal display) under ambient illuminances and light sources were studied and compared with paper. Forty-eight participants participated in a character-search task in the experiment. The results showed that search speed depends on the illuminance but not light source. Search speed increased as illumination increased from 300 lx (45.6 sec), 700 lx (44.18 sec) to 1500 lx (43.24 sec). The effect of medium display and polarity on accuracy was also significant. Accuracy was greater for electrophoretic display and positive polarity. However, the effect of illuminance and light source on visual fatigue was not statistically significant. Based on the results of this study, it seems that E-paper displays may need greater illumination (700 lx or higher).     

The effect of LED lighting on color discrimination and preference of elderly people

The purpose of this study is to find out the effects of light‐emitting diode (LED) lighting on elderly people's color discrimination and preference, to improve the lighting environment for elderly people. In this study, experiments were conducted under LED lighting with two different spectra (with color‐correlated temperature [CCT] of 2800K and 6000K), and three different illuminance levels (30lx; 100lx; 1000lx). Six elderly observers (aged 55–65 years) participated in the experiments and were exposed to each lighting condition to finish one trial of a color discrimination test (Farnsworth–Munsell 100‐Hue Test) and a 7‐scale, 6‐item preference evaluation test. We conclude that elderly people perform better in color discrimination with higher CCT of LED light sources, which compensate for their decreased lens transmission at short wavelength. Their performance also increases with higher illuminance (30lx‐1000lx) of LED lighting. Meanwhile, they prefer higher illuminance, which makes them find the lighting environment more comfortable, brighter, and better for reading; but for CCT, although they feel a higher CCT is better for reading, they still have different tastes regarding CCT of light sources. © 2011 Wiley Periodicals, Inc.