Citation

Finch DM, Howard J. Highw. Res. Board bull. 1958; 191: 1-6.

Copyright

(Copyright © 1958, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

In city driving conditions there exists the problem of advertising signs of the same or nearly the same color and in close proximity with traffic signals causing the driver to confuse the two. An instrument designed to be used in the comparison of the colors of distracting lights with established color limits is discussed. The color limits, suggested by the national bureau of standards, delineate those which are considered unlikely to be confused with traffic signal colors, red and green. The device utilizes an optical system that contains neutral density wedges, a field splitting prism and a standard reference source consisting of a tungsten source operated at a specific color temperature and selected glass filters. In use, a light source such as a neon advertising sign, in close proximity with a traffic light is selected. It is then to be determined whether the source is within the range of allowable colors. The instrument is aimed at the source and the nearest matching color from the reference source is selected by means of a rotating filter holder. Then the field brightness or the reference source brightness is adjusted by means of the density wedge associated with it until a brightness match is obtained in the split image field. The reference source impinges upon two semicircles separated by a small distance and the remainder of the circular field contains the source to be measured. It is then determined whether the external source is within the range of allowable colors. In the case of the green limit, for example, it is determined whether the external source is bluer or greener than the reference source. Relating this to the standard ici color triangle, the green limit is a line given by y equals x plus 0.040 and the red limit is a line given by 6 equals x minus 0.240. These lines are established by three filters for each line. If the color to be measured falls in between any two reference colors, the observer must use his experienced judgement to make a determination.