Abstract
Various combinations of black and white letters and backgrounds were night-tested in the field, using an internally illuminated sign, to collect data on the relationship between sign luminance and legibility over a wide range of ambient lighting conditions. Observers in three age groups were pretested for visual acuity and daylight sign legibility before the night tests. Contrast level and direction were controlled, and the sign legend and background luminance were monitored photometrically. Minimum and optimum brightness values over a sign face are suggested for typical rural, suburban, and urban ambient illumination conditions.