Rejecting small! Accepting larger? Optimizing the font size of Chinese characters basing legibility and visual fatigue in OST-HMDs

Font size is highly related to the legibility and visual fatigue in OST-HMDs, but the effects of font size on these factors remain further explored. An experiment was conducted to investigate the effects of a wider range of Chinese character font size (0.32°–1°) on legibility and visual fatigue, as well as to determine the optimal font size. Results showed that 0.32° had the worst legibility, but there was no continuous improvement as font size increased. A larger font size was found to be beneficial in reducing visual fatigue until it reached 0.95°, beyond which visual fatigue would relatively increase. Font size smaller than 0.32° should be rejected while a larger font size does not always provide more benefits. Considering legibility, visual fatigue and efficiency of text presentation, 0.84° is a relatively optimal Chinese character font size.