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Photometric Requirements for Arrow Panel Visibility

Laboratory and field studies were conducted using older drivers to identify the minimum lamp intensity needed for legibility of arrows and chevrons on Type C arrow panels (APs). A field study was also conducted to determine the maximum intensity required to control disability and discomfort glare at night. Ninety-fifth-percentile data were used to represent worst-case conditions. These data were combined with the results of an analytic study to identify the angularity required for the APs to perform in all geometric situations that conform to accepted standards. The results of the research provide a specification for AP lamps that will result in the proper identification of the AP message by drivers of all ages under most conditions, at distances of up to 467 m (1,500 ft) or greater at all angles that may be anticipated, and at distances of more than ½ mi on-axis. Further, the specification developed sets of minimum and maximum intensity levels for nighttime operations.