Citation

Maghsoudi A, Jung FW. Transp. Res. Rec. 1980; 773: 17-20.

Copyright

(Copyright © 1980, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

Considerable energy savings can be achieved by changing overhead-sign illumination from 125-W mercury-vapor (MV) to 70-W high-pressure-sodium (HPS) luminaires. Studies (which included measurements) were carried out to show the technical viability of such a change. The average illumination levels remained sufficiently high, and uniformity did not change significantly. The results were evaluated by comparison with various standards; they are discussed with respect to two aspects of visibility--attention value and legibility of messages. With regard to legibility, a new concept is introduced--the relative local gradient of illuminance or of luminance, i.e., the percentage of change in these values in any direction per unit of length. Since the extreme values of these gradients along distances of the order of the size of a letter interfere with legibility, it is suggested that uniformity standards be based on this concept rather than on the traditional ratios of maximum to minimum or average to minimum values. Luminance contrasts were investigated for various common color combinations of letters and background for both light sources. It was found that luminance contrasts generally increase when a change is made from MV to HPS luminaires. The change from MV to HPS luminaires in sign lighting does not decrease technical performance.