Visual Fatigue and Performances for the 40-min Mixed Visual Work with a Projected Screen

Objective: The main purpose of this study is to evaluate the visual angle and ambient illumination effects on visual fatigue and performances while viewing from a projected screen for 40 minutes. Methods: Visual angle (16, 24 and 48 min arc of Chinese character height) and ambient illumination (200 and 750 lux) were the independent variables in this study. Change in critical flicker frequency (c_CFF), subjective visual fatigue, proofreading accuracy, and film-watching performance in the experimental trials were obtained from 30 young adults. Each experimental trial took 40 minutes, including a 10-min proofreading test and a 30-min film watching task. Results: Visual angle had a significant effect on proofreading accuracy. An increased proofreading accuracy tendency was found with increasing visual angle. Higher ambient illumination (750 lux) had a positive effect on c_CFF. A significantly higher film-watching performance was also found at the higher ambient illumination (750 lux) compared to that of the lower one (200 lux). Conclusion: We suggest that (a) the ambient illumination should be controlled at about 750 lux for better audiences’ attention and visual comfort; (b) a greater visual angle (24 ~ 48 min arc of character height) is more suitable for Chinese text-reading on a projected screen as compared with 16 min arc; and (c) if the visual tasks with a projected screen mostly contain video and voice, the visual angle of character height will have little effect on performance.