Although methods of evaluating the effect of glare on the ability of an observer to detect objects in terms of an equivalent veiling luminance (e.v.l.) were developed by Holladay and Stiles prior to 1930 their results have usually been interpreted in Britain as indicating that disability glare is negligible in lighted streets. A re-examination of this question indicates that disability glare is important and that erroneous conclusions may be reached if disability glare is neglected when calculating revealing power. For example the revealing power of non-cut-off and semi-cut-off lighting installations may be rated higher than that of cut-off installations, though the opposite is usually the case in the critical darker regions of the installations. New work has shown that the e.v.l. is markedly dependent on the age of the observer, and has indicated a need for further work to obtain more precise knowledge of the way the e.v.l. varies with changes in the position of the glare source in relation to the observer's point of regard over the range of conditions important in the street lighting problem.
Abstract