E-reading devices are becoming more and more common in our daily life, and they are used under a wide range of ambient light levels, from completely dark to extremely bright conditions. In this study, a psychophysical experiment is carried out to investigate how ambient light level affects the visual comfort of an e-reading device. Human observers compare the visual comfort of pairs of different text-background lightness combinations on a tablet device under three ambient light levels (i.e., 150, 1500, and 15,000 lx). With our previous work, the experimental results show that the trend of visual comfort interval scales below 1500 lx (i.e., Dark, 150, 300, and 1500 lx) are similar to each other but not for those under illuminance above the 1500 lx (i.e., 3000 and 15,000 lx). For the same lightness difference between text and background, the observers tend to read the text with a white background compared to a black background, especially for 3000 and 15,000 lx. Moreover, a black text on a light-gray background is the most comfortable combination under these two illuminance levels. An evaluation model is proposed based on ambient illuminance, screen parameters, and visual estimation to design an optimal viewing condition when reading on the tablet display.

Up until now, head-up displays (HUDs) have been installed in front of the driver’s seat to provide drivers with auxiliary information. It may be used in various surroundings, ranging from very dark to very bright environments, such as daylight. A suitable text-background lightness combination can improve the driver’s visual clarity and efficiency when identifying displayed information to raise driving safety. Although many kinds of HUDs are designed to improve visual clarity by adjusting brightness, few studies have investigated the influence of the text-background lightness combination of a HUD on visibility, especially as the lighting level of the driving condition changes dramatically. In the study, 60 observers, comprising 20 young, 20 middle-aged, and 20 older participants, evaluated the visual clarity of 20 text-background lightness combinations on a HUD using paired comparison methods under dark and daylight surroundings (i.e., 300, 1500, and 9000 lx conditions). As a result, the combination of white text on a black background and black text on a white background presented the most significant preference and the best visual clarity under dark and daylight surroundings, respectively, improving visual safety when driving.

The appearance of white significantly impacts display image quality, requiring a neutral white point for optimal performance. This study explores how perceived whiteness changes under ambient illumination levels (150, 300, 600, and 1200 lx) and correlated color temperatures (3500 K and 6500 K). As a result, the adapted white points of light sources with different correlated color temperatures are similar at lower ambient illuminance levels. In comparison, their adaptation trends exhibit significant differences at higher illuminance levels. At 150 lx, adapted white points for 3500 K and 6500 K light sources shift toward higher color temperatures and converge. With increased illumination, the 3500 K white point shifts toward its light source, while the 6500 K white point shifts to a higher correlated color temperature. The neural network-based prediction model developed in this study accurately forecasts perceived whiteness across conditions, offering valuable design guidance for the display and lighting industries.