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The Effects of Internally Illuminated On-Premise Sign Brightness on Nighttime Sign Visibility and Traffic Safety (Full Text)

Authors: Philip M. Garvey, Martin T. Pietrucha and Ivette Cruzado

EXECUTIVE SUMMARY

A substantial body of research has established that illuminated, on-premise commercial signs play a critical role in providing both wayfinding information and more general situational awareness to motorists at night. Documented research shows most on-premise sign lighting to be within reasonable bounds of legibility distance; however, at night, dimly illuminated on-premise signs can be very difficult or impossible to read at appropriate distances. On most roadways in commercial, industrial, and office building environments, the method of sign illumination is internal. Previous studies have demonstrated that internally illuminated signs provide significantly longer visibility distances and longer available reading times than externally illuminated signs. The present research concentrated on internally illuminated signs. The objectives of this research were to compare the daytime and nighttime visibility of on-premise, internally illuminated signs; evaluate the impact of varying sign brightness level on the nighttime visibility of these signs; and quantify the safety effect of varying sign brightness levels in terms of viewer reaction distance. Overall, the findings were consistent with previous research in that the subjects in this study were better at reading signs in the daytime than they were at night. However, the quality of sign lighting had a large impact on how much closer the subjects had to be to read the signs at night. Daytime signs were 43 percent more legible and 40 percent more recognizable than the most poorly lit nighttime signs. However, compared to the best nighttime lighting, daytime signs were only 13 percent more legible and 20 percent more recognizable.