Light-emitting diodes (LEDs) are commonly used to backlight text indicators in vehicles, among other uses. It is desirable that such text indicators are both easily legible and have low fatigue-inducing qualities. Suitable spectral distributions for text presentation in vehicles have not yet been clarified. This study examined the legibility and fatigue experienced by participants when reading sentences presented through backlight emission for 10 min in a dark room. The backlight indicators employed both colored and white LEDs. The participants were asked to answer questionnaires to evaluate the LEDs’ legibility and fatigue. Moreover, the participants’ critical fusion frequency and brain activity were measured to objectively evaluate fatigue. The questionnaire results show that all of the colored backlighting displayed an almost equal legibility. The overall results suggest that participants were most (least) fatigued when viewing text illuminated by high color-rending (greenish white backlighting). Thus, fatigue can be reduced by using LEDs with different spectral distributions.
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