Citation

Finch DM. Highw. Res. Board bull. 1951; 34: 21-40.

Copyright

(Copyright © 1951, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

Reflex reflectors are special types of mirrors which have the characteristic of returning a substantial fraction of the incident light toward the source from which it originates regardless of the incident angle. Because of their peculiar optical characteristics, reflex reflectors appear very much brighter than even the best of white paints when illuminated under similar conditions and are thus very useful in marking roadway obstacles. A review of the visual methods of appraisal has been prepared together with typical data showing the variations found when the human eye is used as a measuring instrument. A photo-electric photometer is described which permits the physical measurement of the light flux from reflex reflectors when they are used under conditions which approximate field usage. Data are shown for the changes in specific intensity when the different types of reflectors are used under varying conditions of divergence angle, entrance angle, orientation angle, test distance, size of light source, size of reflector, size of receiver and color of light source. A recommended test procedure based upon standardized conditions is outlined.