The impact of display angles on the legibility of Sans-Serif 5 × 5 capitalized letters

This paper introduced a laboratory study on quantifying the impact of display angles 0.0°-90.0° on the legibility of Sans-Serif 5 × 5 Capitalized Letters C, D, E, F, H, K, N, P, R, U, V, and Z, commonly used for acuity tests. This study addressed three issues not tackled in the previous studies, including (a) extremely large incident angles 82.8°-90°, (b) multiple letters other than a single letter E previously used, and (c) the interference of people's normal reading habit on legibility evaluation. A total of 20 young college students with Snellen acuity 20/20 or better and normal color vision participated in this experiment. They were asked to read viewing materials presented at 15 display angles. This study derived two equations and modified an existing legibility index to correct the interference of people's normal reading habit on legibility evaluation at extreme oblique display angles.