A photographic technique for assessing the viewing‐angle performance of liquid‐crystal displays

Abstract— Liquid‐crystal displays (LCDs) have notable variation in luminance and perceived contrast as a function of the angle from which they are viewed. Though this is an important performance issue for LCDs, most evaluation techniques for assessing this variation have been limited to laboratory settings. This study demonstrates the use of a photographic technique for such an evaluation. The technique is based on an actively cooled charge‐coupled‐device (CCD) detector in combination with a macro lens covering a circular angular range (θ) of ±42.5°. The camera was used to evaluate the luminance and perceived contrast properties of an LCD. Uniform field images corresponding to 17 equally spaced gray‐scale values in the digital driving level (DDL) range of the display system were acquired. The 12‐bit gray‐scale digital images produced by the camera were converted to luminance units (cd/m²) via the measured luminance vs. DDL response function of the camera. The changes in perceived contrast as a function of viewing angle were derived from the Barten model of the gray‐scale response of the human‐visual system using the methods proposed by the AAPM TG18 Report. The results of this photographic technique were compared to measurements acquired from a similar display using a Fourier‐optics‐based luminance meter. The results of the two methods generally agreed to within 5%. The photographic methods used were found to be accurate and robust for in‐field assessment of the angular response of LCDs over the FOV of the camera.     

Modulation of viewing angle on an LCD surface through backlight optics

Abstract— A backlight unit (BLU) that varies the viewing angle from the top to the bottom surface of a transmissive LCD screen has been developed through the design and fabrication of microstructures on a light‐guide plate (LGP). An array of taper prisms has been designed and fabricated on the back surface of the LGP, which resulted in the variation of 29° in the angular distribution of the luminance of the backlight from the top sector to the bottom sector of its surface. This characteristic is employed to modulate the viewing angle of the LCD from the top of the screen to the bottom of the screen for special applications.     

Visual effects of the luminance surrounding a computer display

The luminance surrounding a computer display can potentially reduce visibility of the display (disability glare), result in sensations of discomfort (discomfort glare) and result in transient adaptation effects from fixating back and forth between the two luminance levels. The study objective was to measure the effects of surround luminance levels upon these functions in younger and older adults to determine recommended surround luminance levels. The younger age group comprised 20 subjects (mean age 27.9 years, range 23 – 39) and the older group 17 subjects (mean age 55.5 years, range 47 – 63). The central task was presented with luminance of 91 cd/M², tested surround luminance levels were 1.4, 2.4, 8.9, 25.5, 50, 91, 175, 317, and 600 cd/M². Disability glare was tested with low contrast (20%) visual acuity charts, transient adaptation was tested with a task that required regular fixation between the two luminance levels, discomfort was measured with a questionnaire after reading stories with different surround luminance levels, and preferred luminance was measured by method of adjustment. The surround luminance significantly affected transient adaptation (p < 0.0001), optimal performance occurred at 50 cd/M² and above for the young group and at 91 cd/M² and above for the older group. Neither low contrast acuity (disability glare) nor symptoms when reading were significantly affected by surround luminance. There was wide variation in preferred surround luminance; however, average preferred surround luminance was 86.9 cd/M² for the young group and 62.2 cd/M² for the older group, slightly below the central luminance of 91 cd/M². The effects of the surround luminance within the tested range are not large; however, the data show that the lowest surround luminance levels should be avoided and that surround luminance levels at or slightly below that of the central task are preferred.     

Angular dependence of the performance of stereoscopic liquid‐crystal‐display (LCD) television using shutter glasses (SG)

Abstract— 3‐D cross‐talk typically represents the ratio of image overlap between the left and right views. For stereoscopic LCDs using shutter‐glasses technology, 3‐D cross‐talk for stereoscopic LCD TV with a diagonal size of 46 in. and vertical alignment (VA) mode was measured to change from 1% to 10% when the stereoscopic display is rotated around the vertical axis. Input signals consist of the left and right images that include patterns of different amounts of binocular disparity and various gray levels. Ghost‐like artifacts are observed. Furthermore, intensities of these artifacts are observed to change as the stereoscopic display is rotated about the vertical axis. The temporal luminance of the LCD used in stereoscopic TV was found to be dependent on the viewing direction and can be considered as one cause of the phenomenon of angular dependence of performance for stereoscopic displays.     

Electro‐optical transfer function preferences for LCD TVs: The effect of display brightness and surround illumination on preferred gamma

Abstract— Recent commercial liquid‐crystal‐display (LCD) televisions are larger and brighter than traditional televisions, thus impacting the viewing conditions in which they are viewed. These changes in viewing conditions may require different electro‐optical transfer functions (EOTFs) for LCD TVs than those for conventional TVs. Here, the way various EOTFs affect the preferred image quality of test images with changes in brightness and surround illumination conditions are examined. The first method used a gain, offset, and gamma (GOG) function with a range of gamma values, and the second method altered the intrinsic EOTFs. Image preference for the simulated EOTFs was determined using a paired‐comparison experiment for ten images. The first experiment took place in a darkened room at two display luminance levels. The results indicated that a gamma of 1.6 was most preferred overall although more so at a lower screen luminance level. In a second experiment, the procedure was repeated with a dim surround of 10% of the display's white point. With this surround, preference for a gamma value of around 1.6 at both screen luminance levels was more enhanced. These results indicated that image preference for different EOTFs is dependent on display luminance and that this dependence is maintained with a dim surround.     

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.     

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.     

Visual effects of the luminance surrounding a computer display

The luminance surrounding a computer display can potentially reduce visibility of the display (disability glare), result in sensations of discomfort (discomfort glare) and result in transient adaptation effects from fixating back and forth between the two luminance levels. The study objective was to measure the effects of surround luminance levels upon these functions in younger and older adults to determine recommended surround luminance levels. The younger age group comprised 20 subjects (mean age 27.9 years, range 23 - 39) and the older group 17 subjects (mean age 55.5 years, range 47 - 63). The central task was presented with luminance of 91 cd/M(2), tested surround luminance levels were 1.4, 2.4, 8.9, 25.5, 50, 91, 175, 317, and 600 cd/M(2). Disability glare was tested with low contrast (20%) visual acuity charts, transient adaptation was tested with a task that required regular fixation between the two luminance levels, discomfort was measured with a questionnaire after reading stories with different surround luminance levels, and preferred luminance was measured by method of adjustment. The surround luminance significantly affected transient adaptation (p < 0.0001), optimal performance occurred at 50 cd/M(2) and above for the young group and at 91 cd/M(2) and above for the older group. Neither low contrast acuity (disability glare) nor symptoms when reading were significantly affected by surround luminance. There was wide variation in preferred surround luminance; however, average preferred surround luminance was 86.9 cd/M(2) for the young group and 62.2 cd/M(2) for the older group, slightly below the central luminance of 91 cd/M(2). The effects of the surround luminance within the tested range are not large; however, the data show that the lowest surround luminance levels should be avoided and that surround luminance levels at or slightly below that of the central task are preferred.     

Effects of illumination conditions on preferred viewing distance of portable liquid‐crystal television

This study explored the effect of TV size, light source, and ambient illumination on the preferred viewing distance of portable liquid‐crystal‐display televisions. Results showed that the mean preferred viewing distance was 1389 mm. TV size had significant effects on preferred viewing distance. The larger the screen size, the greater the preferred viewing distance, at around 6.7–14.7 times the width of the screen (W). Light sources revealed no significant effect on preferred viewing distance. The effect of ambient illumination on preferred viewing distance was significant. The higher the ambient illumination was, the longer the preferred viewing distance.     

LCD backlights: with or without Hg?

High luminance and efficacy vs. temperature independence and environmental protection: these are the determining factors for the choice of Hg or Xe for LCD backlights. A capacity‐coupled cylindrical Hg discharge lamp attains a luminance of 114,000 cd/m² and an efficacy of 35 lm/W when driven at 5 MHz. On the other hand, a mercury‐free Xe flat discharge backlight produces 11,000 cd/m² and 30 lm/W, with fast luminance response. This paper discusses the underlying limitations assessed to the Hg and Xe backlights, considering application to LC TVs.     

Luminance effects influencing perception of 3‐D TV imagery

Abstract— This study investigates whether screen luminance or ambient illumination has a significant effect on the perception of 3‐D TV imagery for static images and dynamic films. Two types of stimuli were shown on a multi‐view stereoscopic display: the static image, which included computer‐generated and photographic images, and dynamic film, which contained real‐life and animation images. In each treatment with a different level of screen luminance, subjects completed psychophysical and physiological measurements and subjective comfort evaluations. The results showed that when subjects viewed 3‐D static images, the ambient illumination affected psychophysical visual fatigue and screen luminance had a significant effect on subjective comfort evaluation and visual discrimination performance. However, when subjects viewed 3‐D dynamic films, screen luminance was the major factor causing psychophysical visual fatigue, and ambient illumination significantly affected subjective comfort evaluation. The outcomes contribute to knowledge concerning the suitable viewing conditions for the 3‐D viewing experience. Future work will explore the intolerance threshold of the lowest display luminance or the effect of decomposition of the screen on other physiological measurements.     

Viewers’ optimization of preferred viewing distance by spatial resolution of TV display

We have shown in a previous paper that preferred viewing distance (PVD)—a viewer’s favored distance from which to watch TV in the home viewing environment—is shorter when watching a high spatial resolution 4k TV than on a high-definition TV (HDTV). PVD depends on (1) the spatial resolution of the viewer’s object of interest in the relevant scene, (2) whether viewers have sufficient time to optimize their PVD, as with still images, and (3) whether they are appropriately encouraged to pay attention to the object at hand on the screen, by, for example, narrative instructions. In this paper, we demonstrate that an analogous result is obtained in a comparison between high spatial resolution 8k TV and HDTV: The PVD of viewers for 8k TV is shorter than that for HDTV. This result suggests new possibilities for high spatial resolution TV, such as novel applications and TV programs that are especially developed for 8k TV systems.     

Fabrication and cathodoluminescent properties of the ZnO‐Cu,Ga and ZnS‐Cu,Ga film phosphors

Abstract— A novel technique for cathodoluminescent screen fabrication using a new method of film phosphor doping has been developed. The crystalline structure and morphology of the films were investigated. Cathodoluminescence spectra were measured at different excitation levels and temperatures (300 and 77 K). The luminance is 200 cd/m² for ZnS:Cu, Ga and 1100 cd/m² for ZnO:Cu, Ga films at a temperature of 300 K and 3700 cd/m² for ZnO:Cu, Ga film at a temperature of 77 K. The films show more saturated green color than commercial phosphors.     

Advanced IPS technology for mobile applications

Abstract— In‐plane‐switching LCD (IPS‐LCD) technologies originally developed for LCD monitors and TV applications are applied to mobile applications. Advantages of the IPS mode over other optical modes for mobile applications are quantitatively clarified. The panel achieves stable color reproduction and chromaticity in the viewing‐angle range for mobile displays. Superiority of the IPS mode over other optical modes is discussed also from the viewpoints of stability in chromaticity during the brightness change and the driving power consumption. A transflective IPS mode with good performance is accomplished by the use of a proper optical design. A new structure, IPS‐Pro, which enables sunlight readability by increasing the transmittance, i.e., the brightness of the panel, without additional cost and power consumption in contrast to additional fabrication processes required to fabricate the transflective mode is realized. Furthermore, to improve the users' convenience, an automatic luminance control system and a controllable viewing‐angle device are developed. The panels developed fulfill the market requirements of increasing the function and performance variations and will be the most appropriate ones to be applied to mobile appliances, such as cellular phones, digital still cameras, music players, GPS, mobile TV sets, etc.     

Effects of bending curvature and text/background color-combinations of e-paper on subjects’ visual performance and subjective preferences under various ambient illuminance conditions

The study used the simulated e-paper to investigate how the bending radius of curvature (−10 cm, plane, and 10 cm) and 12 text/background color-combinations of e-paper affect subjects’ visual performance and subjective preference under various ambient illuminance conditions (200 and 500 lx). Analysis results indicated that the bending curvature and ambient illuminance did not significantly affect subjects’ visual performance. However, subjects visual performance differed significantly for different text/background color combinations of the simulated e-paper. When the background color of the simulated e-paper was set to yellow-like condition and the luminance of the text was low (2.2 and 4.6 cd/m²), subjects’ visual performance was best. Regarding the subjective preferences of subjects, the results of this research also demonstrated that the bending curvature, text/background color combinations and ambient illuminance all significantly affected the subjective preferences of subjects. Subjects exhibited the best preference under the following settings: bending curvature of the simulated e-paper set to plane; background color of the simulated e-paper set to yellow-like condition and low text luminance (2.2 or 4.6 cd/m²); high ambient illuminance (500 lx).     

Psychophysical research on switching between light emitting and reflecting modes of light adaptable display considering equal visibility

Viewing high-luminance displays such as liquid crystal displays or organic light emitting diode displays under low-light conditions causes an unbearable glare, while viewing them with low luminance under bright-light conditions reduces visibility. Recently, several research groups have reported light adaptable displays (LADs) to extend display visibility over a wide range of light conditions. Here, we present a psychophysical study on how to effectively utilize the LAD using two different display types for the first time. LAD features two switchable display types: light emitting mode (LEM) and light reflecting mode (LRM). To maintain visibility and prevent visual artifacts, we investigate when to switch modes between LEM and LRM. We conduct psychophysical experiments involving seventy subjects. They are asked to select illuminance levels under which they perceive that the LEM and LRM look the same depending on luminance of the LEM. We propose a mode-switching condition by combining our previous results on the comfortable luminance of LEM display according to the ambient illuminance and the selected illuminance results providing equal visibility of both LEM and LRM displays.     

Effects of heat on visual acuity

Visual acuity of nine subjects was measured with Landolt ‘C’s during 3 hours of exposure to either (i) a neutral control, (ii) a warm humid or (iii) a hot dry atmosphere. The luminance of the background was either 450cd/m² or 5cd/m². Simultaneously, rectal temperature and heart rate were recorded as indicators of thermal strain. A significant loss of visual acuity, linearly correlated with thermal strain, was found in both lighting conditions.     

Combined effects of working environmental conditions in VDT work

The combined effects of city noise and luminance of the computer display were evaluated from the changes in lymphocytes and mental activities of participants. Healthy male students were tested under the following four experimental conditions: (1) a calculating task on a video display terminal (VDT) with luminance of 90 cd m^-2 without city noise; (2) a calculating task on a VDT with luminance of 20 cd m^-2 without city noise; (3) a calculating task on a VDT with luminance of 90 cd m^-2 with city noise of 70 dB(A); and (4) a calculating task on a VDT with luminance of 20 cd m^-2 with city noise of 70 dB(A). A visual reaction test (VRT) was performed, and critical flicker fusion frequency (CFF), heart rate (HR), numbers of circulating white blood cells (WBCs), lymphocyte subsets and subjective symptoms of fatigue were measured (1) before; (2) just after; and (3) 30 min after each 60 min test. Subjective symptoms of fatigue significantly increased just after experiments conducted under the two noisy conditions. VRT and CFF showed significant changes in the case of the highluminance display with noise. WBCs and neutrophils showed significant increases in the two quiet conditions. These results suggested that high luminance with noise had the most effect on subjective fatigue and mental activities.     

Preferred viewing distance of liquid crystal high-definition television

This study explored the effect of TV size, illumination, and viewing angle on preferred viewing distance in high-definition liquid crystal display televisions (HDTV). Results showed that the mean preferred viewing distance was 2856 mm. TV size and illumination significantly affected preferred viewing distance. The larger the screen size, the greater the preferred viewing distance, at around 3-4 times the width of the screen (W). The greater the illumination, the greater the preferred viewing distance. Viewing angle also correlated significantly with preferred viewing distance. The more deflected from direct frontal view, the shorter the preferred viewing distance seemed to be.     

Inorganic EL devices with high‐performance blue phosphor and application to 34‐in. flat‐panel televisions

Abstract— A high‐performance inorganic electroluminescence (EL) device has been successfully developed by using an EL structure with a thick dielectric layer (TDEL) and sputtered BaAl₂S₄:Eu blue phosphor. The luminance and efficacy were higher than 2300 cd/m² and 2.5 lm/W at L⁶⁰, 120 Hz, respectively. Furthermore, the luminance at L⁶⁰, 1.2 kHz was more than 23,000 cd/m². The phosphor layer has a single‐phase and a highly oriented crystalline structure. The phosphor also shows high stability in air. A 34‐in. high‐definition television (HDTV) has been developed by combining a TDEL structure and color‐conversion materials. The panels with an optimized color filter demonstrated a peak luminance of 350 cd/m², a color gamut of more than 100% NTSC, and a wide viewing angle similar to that of plasma‐display panels. The high reproducibility of the 34‐in. panels using our pilot line has been confirmed.