LUMINANCE AND CONTRAST REQUIREMENTS FOR LEGIBILITY AND VISIBILITY OF HIGHWAY SIGNS

The study reported on in this paper took place in 2 parts: laboratory tests and outdoor observations. In the laboratorty tests, which were conducted in a darkroom, 51 series of test signs were projected from color slides against 5 backgrounds simulating rural, suburban, and lighted city conditions. Luminances ranged from 0.37 to 4.45 ft-L (1.3 to 15.1 cd/sq m). Legibilities ranged from 20 to 60 ft/in. (2.4 to 7.2 m/cm) and increased approximately linearly with log luminance. Legibility was impaired when contrast was below 50 to 60 percent and was maximum when contrast was between the ratios of 6 and 13 to 1. Optimum stroke width appeared to be narrower for white than for black letter combinations. Color recognition fell below 75 percent correct at lower luminances except for red. The reverse was true for small targets. Outdoor observations of 12-in. (30.5cm) reflective letters (2 color combinations) under headlights confirmed the lower contrast limits for legibility and effects of stroke width. High-beam outdoor legibility curves and laboratory-corrected trends were similar. Apparently, glance legibiilty, which was measured by the laboratory procedure, requires higher luminance. In a previous visibility study, luminance contrasts of sign to background and legend to sign were critical. These results suggest minimum requirements for both legibility and visibility.

• Record URL:
  • http://onlinepubs.trb.org/Onlinepubs/trr/1976/562/562-006.pdf
• Summary URL:
  • https://scholar.google.com/scholar_lookup?title=LUMINANCE+AND+CONTRAST+REQUIREMENTS+FOR+LEGIBILITY+AND+VISIBILITY+OF+HIGHWAY+SIGNS&author=T.+Forbes&author=B.+Saari&author=W.+Greenwood&author=J.+Goldblatt&author=T.+Hill&publication_year=1976
• Availability:
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• Supplemental Notes:
  • Publication of this paper sponsored by Committee on Visibility. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Authors:
  • Forbes, T W
  • Saari, B B
  • Greenwood, W H
  • Goldblatt, J G
  • Hill, T E
• Conference:
  • 54th Annual Meeting of the Transportation Research Board
  • Location: Washington District of Columbia
  • Date: 1975-1-13 to 1975-1-17
• Publication Date: 1976

Media Info

• Media Type: Print
• Features: Figures; References; Tables;
• Pagination: pp 59-72
• Monograph Title: Measures of Effectiveness, Railroad-Highway Grade Crossings, and Visibility
• Serial:
  • Transportation Research Record
  • Issue Number: 562
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Brightness; Color vision; Contrast; Laboratory tests; Legibility; Simulation; Traffic signs; Visibility
• Subject Areas: Highways; Safety and Human Factors;

Filing Info

• Accession Number: 00134869
• Record Type: Publication
• ISBN: 0309024722
• Files: TRIS, TRB
• Created Date: Sep 4 1976 12:00AM