The Brightness and Legibility at Night of Road Traffic Signs

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Abstract
An investigation to determine the most satisfactory brightness of lettered signs seen against different background brightness levels is described. “Ideal” sign brightnesses are suggested, lying between the minimum for threshold legibility and the maximum acceptable without ill effects from glare. The ideal brightness for legibility was found to be unaffected by the colour of the sign, and was the same for black on white or white on black signs. The effect of disturbing factors such as glare from automobile headlights, and dirt collection on the sign are considered; such handicaps do not affect legibility distance very greatly, tout may seriously reduce the conspicuity of the sign. The second part of the paper gives an account of a study of reflex reflecting lensed symbols used on traffic signs: methods of fitting lenses, and small modifications to some symbols are suggested to make recognition easier. The work described was carried out by a technical committee, called toy the Illuminating Engineering Society at the request of the Ministry of Transport. The results have led to some recommendations made in the Departmental Report on Traffic Signs, 1944.

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