Estimating the legibility of a single letter E viewed at different display angles.pdfVIP

Applied Ergonomics 44 (2013) 575e587 Contents lists available at SciVerse ScienceDirect Applied Ergonomics journal homepage: /locate/apergo Estimating the legibility of a single letter E viewed at different display angles Hongyi Cai a,*, Paul A. Green b, Jong-Jin Kim a a Taubman College of Architecture and Urban Planning, University of Michigan, 2000 Bonisteel Boulevard, Ann Arbor, MI 48109-2069, USA b University of Michigan Transportation Research Institute, 2901 Baxter Road, Ann Arbor, MI 48109-2150, USA article info Article history: Received 16 January 2012 Accepted 27 November 2012 Keywords: Legibility equation Incident angle Display abstract Text is often viewed not perpendicularly to its display. With nine assumptions, this study developed a new equation for estimating the legibility of a single letter E viewed at different display angles. This equation examines viewing distance, text height, strokewidth, Snellen acuity, background luminance, luminance contrast, and incident angle. This equation was derived from the existing Howett’s equation based on a constant-solid-angle hypothesis tested in a lighting laboratory by reading letter ‘E’s using 20 young human subjects. The hypothesis holds when the incident angle 0 x 65.7, but fails when 65.7 x 82.8 (the maximum angle tested). Another ambient-light hypothesis was also tested in the same laboratory using 20 young subjects to verify the negligible in?uence (less than 9%) of ambient light on legibility of text. The new equation was accordingly improved to help ergonomists and other professionals create and maintain legible displays. ó 2012 Elsevier Ltd and The Ergonomics Society. All rights reserved. 1. Introduction Legibility of text and graphics is critical for people to extract information from their surroundings (e.g., way?nding) or perform individual tasks (e.g., typing). Characters presented on various types of displays, such as signs, blackboards, computer screens, instrument panels, books, and newspa