Estimating the legibility of a single letter E viewed at different display angles
Authors: Hongyi Cai, Paul A. Green, Jong-Jin Kim.
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 lette E's using 20 young human subjects.