Display Luminance Research Articles

44.3: Effect of Luminance on Visual Comfort under Different Illuminations

The effect of luminance and illuminance on visual comfort was explored on TV screen with subjective and physiological measurements. The results condensed by information utility value and principal component analysis revealed that 250 cd/m2 and 400 cd/m2 were the optimum display luminance levels under <1 lx and 500 lx respectively and the illuminance of 500 lx induced less physiological discomfort than <1 lx.

Display Characterization for Contrast Sensitivity Testing

Contrast sensitivity measurements using a computer display have been reported to lack accuracy when displaying small contrasts. This report investigates if the characterization/calibration of display luminance may contribute substantively to these kinds of described inaccuracies. This study aimed to investigate what errors in contrast sensitivity may result from characterizing a display by fitting a gamma curve through physical or psychophysical luminance measurement data. The luminance functions of four different in-plane switching liquid crystal displays (IPS LCDs) have been measured for all 256 gray levels (the actual luminance function). This has been compared with a gamma-fitted luminance curve (the gamma luminance function). Calculated are the errors in displayed contrast that may arise when assuming the gamma luminance function instead of the actual luminance function. The amount of error differs considerably between the displays. In general, for large contrasts (Michelson log CS <1.2), the error is acceptable (<<0.15 log unit). However, for smaller contrasts (Michelson log CS >1.5), the error may become unacceptably high (>0.15 log unit). To improve the accuracy of testing contrast sensitivity with an LCD, it is necessary to fully characterize the display, measuring the luminance of each gray level instead of fitting a smooth gamma function through limited luminance data.

Melanopic irradiance defines the impact of evening display light on sleep latency, melatonin and alertness

Evening light-emitting visual displays may disrupt sleep, suppress melatonin and increase alertness. Here, we control melanopic irradiance independent of display luminance and colour, in 72 healthy males 4 h before habitual bedtime and expose each of them to one of four luminance levels (i.e., dim light, smartphone, tablet or computer screen illuminance) at a low and a high melanopic irradiance setting. Low melanopic light shortens the time to fall asleep, attenuates evening melatonin suppression, reduces morning melatonin, advances evening melatonin onset and decreases alertness compared to high melanopic light. In addition, we observe dose-dependent increases in sleep latency, reductions in melatonin concentration and delays in melatonin onset as a function of melanopic irradiance—not so for subjective alertness. We identify melanopic irradiance as an appropriate parameter to mitigate the unwanted effects of screen use at night. Our results may help the many people who sit in front of screens in the evening or at night to fall asleep faster, feel sleepier, and have a more stable melatonin phase by spectrally tuning the visual display light without compromising the visual appearance.

Paper] Autostereoscopic Display Based on Time-Division Multiplexing Parallax Barrier Using a Monochrome LCD Panel

This paper presents a full-HD autostereoscopic display with a pair of monochrome and color panels based on time-division multiplexing parallax barrier. In the conventional system, usage of two color LCD panels with limited transmittance decreased the display luminance. In the proposed method, a monochrome panel is used in place of a color panel to generate an active barrier pattern, which is expected to increase transmittance. A prototype system is made, where moire is removed without using a diffuser. The maximum luminance given by the proposed method is measured and compared with that given by the conventional method. It is confirmed that the prototype system based on the proposed method has approximately 2.5 times higher luminance than the conventional system. It is also confirmed that the proposed method slightly decreases stereoscopic crosstalk, which is further reduced by widening the slit from 3 subpixels to 5 subpixels to alleviate diffraction.

Optimum display luminance under a wide range of ambient light for cockpit displays.

The self-luminous cockpit displays need to be adaptive to a wide range of ambient light levels, which changes from very low illuminance to very high levels. Yet, current studies on evaluation and luminance setting of displays in bright surroundings are still limited. In this study, a three-dimensional visual ergonomic experiment was carried out to investigate how bright a cockpit display should be to meet aircrew operational requirements under different illuminance. A lab study with a within-subjects (N = 12) design was conducted in a simulated cockpit. According to the Weber-Fechner's Law, human observers evaluated five display luminance conditions (101, 101.5, 102, 102.5, 103 cd/m2) under five ambient illuminance conditions (10°, 101, 102, 103, 104 lx). Visual performance, visual fatigue and visual comfort were used as evaluation bases, which were measured by d2 task, subjective fatigue questionnaire and visual perception semantic scales. Nonlinear function fitting was used to calculate the optimal luminance under a certain illuminance. Finally, curvilinear regression was used to analyze the illuminance and its corresponding optimal luminance. Based on Silverstein luminance power function, a luminance adjustment model with the form of power function was obtained. The proposed three-dimensional model fits the experimental data well and is consistent with the existing studies. It can be regarded as a supplement and optimization of the previous model under high ambient illuminance. This study can contribute not only to the pleasing luminance setting of panel displays in aircraft cockpits but also to other self-luminous devices, such as tablet devices, outdoor monitoring equipment and advertising screens.

18‐2: Assessment of Image Quality in Augmented Reality Displays Using a Computational Model of Target Detectability

We characterized augmented reality (AR) displays and developed a computational task‐based model to evaluate their image quality. The model enables fast assessment of image quality and evaluation of tradeoffs between display configurations such as display luminance response, uniformity, resolution, and noise. This work supports the development and optimization of AR displays without extensive measurements or resource‐intensive perception studies.

Perceived contrast on displays with different luminance ranges.

PurposeMedical displays are fundamental in today's healthcare since they provide the link between digitally stored data and the human clinician, and it is thus important that the transfer of information is as effective and reliable as possible. Contrast perception in viewed images is complex due to the nature of the human visual system, and the luminance distribution in the viewed scene plays a major role. Standards and guidelines concerning medical displays are important as they set a baseline image quality. However, as the number of imaging applications as well as display technology has evolved rapidly during the past decades, there may be possible uses not foreseen in the current guidelines. Bright screens may perform as good in bright rooms as less bright displays do in dark rooms, but current guidelines are likely to favor dark rooms due to historical reasons. The purpose of this study was to determine the limits of contrast perception in three very different lighting conditions and relate the outcome to guideline recommendations.MethodsThree different display luminance settings were studied, 1–250, 6–500, and 12–750 cd/m2 with luminance ratios of 250, 85, and 62, respectively. Although the luminance ratios, black levels, and white levels were different, they all covered the same number of just noticeable differences (JNDs). By using a two‐alternative forced‐choice method, contrast thresholds were determined at dark, mid‐gray, and bright pixel values for all luminance settings using bar patterns with two different spatial frequencies. In total, 18 contrast thresholds were determined by each of the 10 observers.ResultsThe contrast thresholds for the low‐frequency patterns were close to 0.5 JNDs and there were no systematic differences between the three luminance conditions at any of the pixel values. The high‐frequency patterns required almost 10 times higher contrast where the highest contrast threshold (worst visibility) was obtained for the luminance setting 1–250 cd/m2 at the dark pixel value.ConclusionsThe differences between the three luminance conditions were mostly minor, which indicate that display settings with low luminance ratios and high minimum luminance levels can be used without compromising displayed image contrast. The number of JNDs enclosed by the luminance range of a display is a reliable metric for global perceived contrast. Luminance ratios are limited regarding the ability to detect low contrast objects when there are large differences in luminance, although they can still be used within a relatively small range of luminance levels. Low luminance levels may cause a loss of visibility, especially for fine details, and should be avoided.

Deep convolutional neural network‐based quantitative evaluation of display non‐uniformity

AbstractWe developed a quantitative method for evaluation of display luminance and color non‐uniformity (which we call mura) using a deep convolutional neural network (DCNN). In previous research, quantitative evaluation methods using DCNN were studied. From among a wide variety of DCNN models, these methods have used a convolutional autoencoder (CAE) for abnormality detection. A CAE trained with only non‐defective data was then used to evaluate the degree of mura. However, there is a problem with these methods in that they have not been able to evaluate properly when there are multiple mura defects on a single screen. Consequently, the correlation between these methods and human visual evaluation was low. Therefore, we improved the previous method to handle multiple mura defects on the same screen. We confirmed the accuracy of the proposed method by comparing the quantitative evaluation and human visual evaluation. As a result, we obtained a higher correlation than the previous methods.

Efficient Interfacial Upconversion Enabling Bright Emission at an Extremely Low Driving Voltage in Organic Light‐Emitting Diodes (Advanced Optical Materials 4/2022)

In article number 2101710, Seiichiro Izawa, Masahiro Morimoto, Shigeki Naka, and Masahiro Hiramoto report an efficient organic light-emitting diode (OLED), operable by a 1.5-V battery, that produces bright emission equivalent to the luminance of a typical display. The OLED is based on an upconversion transition through triplet–triplet annihilation near its donor/acceptor interface. The efficient upconversion is realized by controlling the character of an interfacial charge transfer state, which is a key intermediate.

Efficient Interfacial Upconversion Enabling Bright Emission at an Extremely Low Driving Voltage in Organic Light‐Emitting Diodes

AbstractA remaining frontier in the field of organic light‐emitting diodes (OLEDs) is reducing their operating voltage. Herein, an efficient OLED is reported, operable by a 1.5 V battery, that produces bright emission equivalent to the luminance of a typical display. The OLED has a smaller turn‐on voltage at 0.97 V than an optical energy of emitted photons at 2.04 eV (608 nm), because the OLED is based on an upconversion (UC) transition associated with triplet–triplet annihilation that doubles the energy of excited states. The characteristics of charge transfer (CT) state at the interface have been revealed, which are key to efficient UC, and the percentage of excited states deactivated by parasitic loss processes during the UC transition is significantly reduced from over 90% to approximately 10% by introducing a highly crystalline acceptor material and an emissive dopant. Consequently, the UC‐OLED achieves a quantum efficiency that is two orders of magnitude higher than that in the previous report.

A Display-Independent Quality Assessment for HDR Images

High Dynamic Range (HDR) images improve visual quality by representing a wide range of luminance in real world. HDR Image Quality Assessment (IQA) is essential in HDR processing technologies. This work focus on the IQA for the HDR applications represented by HDR compression. Towards designing IQA for these tasks, user-end display information should not be considered, given that these tasks only focus on the media intrinsic features. However, most existing HDR metrics are associated with display luminance, hence they can not handle IQA during HDR processing. In this work, we find that it is possible to evaluate HDR image quality without prior knowledge of luminance for display. Based on this, we proposed a low complexity Display-Independent Gradient Magnitude Similarity (DIGMS) metric. Experimental results demonstrate that the proposed DIGMS outperforms the state-of-the-arts in HDR IQA. This work opens up a new perspective for designing IQA algorithms for HDR images.

Effect of Luminance and Contrast Variation on Stereoacuity Measurements Using Smartphone Technology.

Owing to the limitations of printed stereoacuity tests, the effects of luminance and contrast on stereopsis have not yet been sufficiently investigated, despite its important implications in designing stereoacuity measuring instruments, particularly for electronic devices. A stereopsis measurement system was established using two 4 K smartphones and a phoropter to evaluate the effects of luminance and contrast variations on the stereoacuity test. Seventeen young subjects with normal visual acuity and stereopsis were recruited. Two types of test symbols, contour-based and random-dot-based, were used in the experiment. Four series tests were established with different maximum brightness values, including 240 lux, 120 lux, 60 lux, and 30 lux. Each series test contained 19 pages with different contrasts between 95% and 5% and was calculated using the Michelson contrast formula. No significant difference was found for both contour-based and random-dot-based stereograms in any of the contrast groups with different maximum brightness. Similarly, no significant difference was found between contour-based and random-dot-based patterns under different contrasts of above 35%. As the contrast decreased below 30%, the stereopsis was significantly better in the contour-based pattern than in the random-dot-based pattern for some degrees of contrast. The luminance and contrast of the digital display are not critical factors for stereoacuity under normal circumstances. This implies that a standard monitor with a certain 3D technology can be used to measure the stereoacuity threshold without calibrating the luminance and contrast.

Effects of Display and Ambient Illuminance on Visual Comfort for Reading on a Mobile Device

A psychophysical experiment was carried out to investigate visual comfort when reading on three OPPO Find X3s displays at three luminance levels (100, 250 and 500 cd/m2) at five illuminance levels (0, 10, 100, 500 and 1000 lx). Twenty young observers evaluated visual comfort using a 6-category points method. The results showed that observers felt most comfortable at the illuminance of 500 lx or display luminance of 500 cd/m2. There was an interaction between ambient illuminance and display luminance. High ambient light and display brightness levels provide a more pleasant visual experience. In low ambient light, however, the lower the brightness level, the more comfortable it is to see. Regarding the influence of background colour on visual comfort, the observers felt more comfortable having a grey background than white or black colour. When at dim illuminance, the background colour would have a great influence on visual comfort for negative contrast conditions, but when at higher illuminance, different background lightness levels had a great impact on visual comfort for positive contrast conditions. The above findings are very similar to the display luminance levels of 100 and 250 cd/m2.

Time course chromatic adaptation under highly saturated illuminants

The goal of this study was to investigate the time course characteristics of chromatic adaptation under highly saturated illuminants. A psychophysical experiment with neutral matching method was conducted on a mobile display at different luminance levels. Models of chromatic adaptation degree against duration of time were fitted using a proportional rate growth function. The upper limit and growth rate of adaptation degree were studied. It was found that higher adapting luminance and lower display luminance led to higher degree and faster speed of chromatic adaptation. This study also proposed the time to achieve stable chromatic adaptation.

An intrinsically eye safe approach to high apparent brightness augmented reality displays using computer‐generated holography

AbstractAchieving the luminance of real‐world scenes is a challenge for many display technologies. Computer‐generated holography offers a number of advantages, due to both the high optical efficiency and the ability to redistribute available luminous flux to individual points. This is important while displaying sparse content that needs to be clearly perceived against a bright background in augmented reality. In this work, we consider a range of optical architectures and analyze the impact of each element on the overall display luminance. We conclude that the range of holographic projector efficiencies can vary from 50% to 0.05%, with the average of 3%. An example holographic projector with 2% efficiency is built to evaluate the analysis. Using a low‐power RGB laser module, outputting 1.78 mW, a mean luminance of 30,000 cd/m2 has been attained. In the presence of sparse content, peak luminance exceeding 300,000 cd/m2 is demonstrated. Both the calculation and the measurements confirm that by using holography, it is possible to achieve a display that is sufficiently bright to be clearly viewable in daylight, in a manner that can be intrinsically eye safe. The image is projected against daytime sky and appears several times brighter, hence adding visual validation to the analysis.

5.1: Invited Paper: Preferred LCD and OLED Luminance In Daily Tasks Is Affected By Ambient Lighting and Age

Preferred display luminance varies in relation to visual demand, image contrast, and ambient illumination. OLED is known to have a higher contrast ratio at a lower luminance output, and is more energy efficient at a lower luminance compared to LCD. To assess the preferred luminance in OLED and LCD in varied ambient lighting conditions, 48 young and older subjects were asked to perform reading, spreadsheet search, and videos viewing. They pre‐selected a preferred luminance level and then reassessed it after a 2‐min session for these tasks to arrive at a preferred luminance. Results show OLED has a lower preferred luminance compared to LCD, especially in bright viewing. Older viewers maintained a similarly higher luminance preference in dark and bright conditions, whereas young viewers preferred a lower luminance in dark viewing but not bright viewing. Conversely, pupil size was smaller in older viewers and in the bright condition. Image qualities were also better for the OLED, except brightness range and color vividness. These outcomes suggest lower OLED luminance is beneficial across age groups, ambient lighting, and task types, and can reduce energy consumption.

FovVideoVDP

FovVideoVDP is a video difference metric that models the spatial, temporal, and peripheral aspects of perception. While many other metrics are available, our work provides the first practical treatment of these three central aspects of vision simultaneously. The complex interplay between spatial and temporal sensitivity across retinal locations is especially important for displays that cover a large field-of-view, such as Virtual and Augmented Reality displays, and associated methods, such as foveated rendering. Our metric is derived from psychophysical studies of the early visual system, which model spatio-temporal contrast sensitivity, cortical magnification and contrast masking. It accounts for physical specification of the display (luminance, size, resolution) and viewing distance. To validate the metric, we collected a novel foveated rendering dataset which captures quality degradation due to sampling and reconstruction. To demonstrate our algorithm's generality, we test it on 3 independent foveated video datasets, and on a large image quality dataset, achieving the best performance across all datasets when compared to the state-of-the-art.

Laptop displays performance: Compliance assessment with visual ergonomics requirements

The use of display devices such as smartphones, tablets, laptops is now massive and continuous in everyday life. It, therefore, becomes increasingly important to be aware of the performance of these devices, not only in terms of the tasks to be performed but also in terms of interaction with humans and therefore knows any possible effect on the ergonomics of vision. Following previous research activities conducted by the authors on the assessment of the visual ergonomics at video display terminal workstations, the aim of this study is to evaluate the ergonomics of human-system interaction of laptop displays. In details, a sample of 57 laptop displays is analyzed in accordance with the requirements of the EN ISO 9241-3xx series of international standards related to the display luminance, luminance ratio, contrast non-uniformity. An extensive luminance measurement campaign was carried out using a special pattern that allowed to measure the luminance in 13 different areas of the displays. The results obtained with this activity showed a great luminance variability between different displays. Almost all the displays are able to emit high levels of display luminance, and almost all the displays meet the requirement of contrast non-uniformity. However, several devices did not meet the recommended values of luminance ratio. Furthermore, the authors created a simplified graph to allow a rapid evaluation of the performance of the displays. This method could be periodically used in practice in order to evaluate the residual performance level.

Investigation of the Optimum Display Luminance of an LCD Screen under Different Ambient Illuminances in the Evening

Ambient illuminance and screen luminance have a significant influence on the visual fatigue and visual performance associated with the use of computers. The current study was conducted to investigate optimal screen luminance under different ambient illuminances and fit a curve of the optimum luminance of LCD screens under evening illumination. Thirty-three participants were assigned to rate screen brightness, visual comfort with screen luminance, satisfaction with ambient illuminance and visual fatigue under six screen luminance levels (3.87, 21.47, 42.74, 64.12, 84.77 and 106.7 cd/m2) combined with five ambient illuminance levels (0, 25, 50, 75 and 100 lx) in the evening. The results showed that optimum LCD screen luminance increased with increasing ambient illuminance. Moreover, ambient illuminance and screen luminance levels should be in the range of 13.08–62.16 lx and 20.63–75.15 cd/m2, respectively, to obtain the optimal subjective feelings of visual fatigue and visual comfort during the evening.

Display dimming model characterized by three-dimensional ergonomic study

Self-luminous display devices are essential in various working environments, such as aircraft cockpits and the driver cab of vehicles and trains, where the external light environment varies drastically. Owing to the significant illumination changes, auto-adjusted display luminance based on ambient lighting is necessary for drivers to work efficiently and comfortably. This study proposes a display dimming model based on three dimensions of ergonomic testing, consisting of visual performance (VP), visual comfort (VC), and visual fatigue (VF). Five ambient illuminances, each combined with five display luminance levels, form a total of 25 conditions demonstrated in this experiment. Using a within-subject design, ten observers experienced all the combination conditions. The experiment employs the Anfimov table to test the VP, VC scale to evaluate VC, and VF scale to assess VF. Based on the experimental results, sub-models are constructed to clarify the characteristics of each dimension (VP, VC, and VF). Subsequently, the analytic hierarchy process is employed to construct an evaluation system by calculating the weight of each dimension in the total score. Finally, exponential fitting is utilized to build a wide-range display dimming model, which explicitly describes the inherent connection of complex light environment matching.