Abstract
Three experiments were conducted to investigate the effects of adult aging upon the legibility of simulated symbol highway signs. Each experiment employed a different set of lighting conditions: (1) daytime luminance, (2) nighttime luminance, and (3) nighttime luminance with glare. Young (ages 18-25) and middle-aged (ages 40-55) observers demonstrated small reductions in legibility when luminance was reduced from daytime to nighttime levels. However, older (ages 65-79) observers demonstrated marked losses in legibility distance with reductions in sign luminance. The introduction of a glare source (equivalent to approaching automobile headlights at 30 m) reduced sign legibility distance for the older observers but had no deleterious effects upon their young and middle-aged counterparts. The relative magnitude of the observed age, luminance and glare effects appeared to be equivalent across all signs examined.
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