A review of the literature indicates that a luminance value of 3.2 cd/m2 should be the absolute minimum acceptable sign legend luminance value for proper legibility of overhead guide signs. Although a limited laboratory study, conducted as part of this investigation, suggests a minimum sign luminance of 13 cd/m2, the sample was small and the data varied considerably. Other researchers recommend higher values, including one who suggests 75 cd/m2 as an optimum. In view of these different opinions, we felt that a sign legend luminance (white letters) of 3.2 cd/m2 is a reasonably conservative value for signs located in areas with little or no ambient lighting and no oncoming traffic. Based on this minimum sign legend luminance of 3.2 cd/m2 and commonly used retroreflective signing materials, several cars evaluated in this study did not provide sufficient light toward overhead and left shoulder-mounted signs to produce minimal sign luminance unless type III material was used. One of the cars, using an HID lamp in a composite headlamp, did not provide sufficient sign illumination for the overhead and left shoulder-mounted signs, even if the signing material were of type III.
A field evaluation of retroreflective signs illuminated by headlights
1999
16 Seiten, 4 Bilder, 5 Tabellen, 7 Quellen
Aufsatz (Konferenz)
Englisch
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