Effect of character contrast ratio of tablet PC and ambient device luminance ratio on readability in low ambient illuminance

This study examined the relationship between the ambient and surface luminances needed to obtain optimal and minimum allowable device (paper and tablet) readability in low ambient illumination environments (illuminance of less than 300 lx). In addition, the optimum and minimum allowable surface luminances were evaluated according to ambient luminance based on the tablet character contrast ratio. Experiments were conducted based on a method in which the subject directly adjusts the surface brightness of the device, and revealed that the contrast ratio does not influence the surface luminance of a tablet. In cases with a set contrast ratio of 70%, paper and tablet were found to produce different results. We propose a model for obtaining optimal and minimum allowable paper and tablet surface luminances in low ambient illuminance environments. The optimal and minimal allowable surface luminances of a tablet are respectively higher and lower than the ambient luminance. In the case of paper, if a surface luminance of at least 27 cd/m2 can be obtained, the surface luminance can be lower than the ambient luminance.