This research examines the ease of reading text on a car navigation screen as a visual display when the luminance of the driver's eye-fixation point differs from that of the screen while driving. To conduct this research, an experiment was performed to determine how such variation in luminance affects the time taken for a driver to read text displayed on a car navigation screen during driving operations. Evaluation indexes in this experiment were locus of eye-fixation point during movement of line of sight, duration of stationary viewpoint, and time taken to read text. Results of this experiment revealed the following.(1) Reading time for a screen luminance of 100cd/m
2 was short under nighttime luminance conditions of 2.5cd/m
2 exhibiting a difference of about 0.314s compared to 500cd/m
2.(2) Reading time for a driving environment of 50Ocd/m
2with screen luminance lower at 25cd/ m
2 was short exhibiting a difference of about 0.13s.(3) Reading time shortens as the ratio of monitor luminance to luminance while driving increases.
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