A survey is given of the results of (a) stationary (indoor and outdoor) and dynamic (outdoor) visibility tests, (b) subjective appraisals of road surface luminance in lighted streets, and (c) recordings on the use of headlights under several lighting conditions. From these results it can be concluded that the road surface luminance should be at least 0.6 foot-lambert, fl, (2 cd/m square) in order to make dense road traffic safe and comfortable. Investigations on glare in lighting for road traffic show that visual comfort of drivers is a graver criterion for glare limitation than the impedance of seeing ability. This means that in installations where glare stays within the borders of visual comfort, disability glare will be negligible. The paper gives a survey of results on this matter providing basic data for the necessary limitation of glare in lighting installations for road traffic. The luminance of the road surface and its distribution determines to a large extent the quality of the installation from a viewpoint of safety and comfort of traffic. The possibility of practical application of the luminance concept in public lighting is, therefore, a matter of high importance. This possibility depends on the availability of convenient methods for computing and measuring road surface luminances. A brief description is given of a simple method of calculation as well as of a photoelectric luminance meter for street lighting purposes both intended for use in everyday practice. /author/
Abstract