High dynamic range (HDR) displays are designed to simulate the range of perceived brightness afforded by the real world. To study how visual performance and visual comfort are affected by luminance level, 34 participants with normal vision were first asked to discriminate the brightness of two circles presented on LCD and OLED screens to determine the luminance threshold for brightness discrimination. They then judge the orientation of a circular grating target alternating with a luminance circle while their visually-evoked potentials and viewing discomfort was assessed. Results show contrast ratio is more important than luminance difference in brightness discrimination. Regression model based on behavioral outcomes suggest the maximal OLED luminance (647 cd/m2) was perceived as bright as 1035 cd/m2 on LCD screen. In discerning grating orientation, the VEP signals associated with the luminance level increased along with viewing discomfort and the signals associated with the grating target decreased along the reduced accuracy of orientation discrimination. The threshold luminance for visual discrimination and discomfort is 695 cd/m2. The OLED is visually more comfortable and affords better visual performance than LCD when the screen luminance is high due to its higher contrast and more moderate luminance. These findings suggest higher contrast ratio rather than greater luminance difference is important for brightness discrimination. To reduce visual discomfort while achieving better visual performance in dynamic images, better contrast ratio and black level are more important than greater screen luminance.
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