Computational Assessment of Text Legibility in Lecture Halls

Text presented in lecture halls often simultaneously appears on multiple visual displays (e.g., blackboards, projection screens, video monitors), which should be legible to the entire audience seated in an ideal viewing area. Existing guidelines identify this area as fanshaped, but the origin of those guidelines and the data on which they are based are not specified. To supplement the guidelines, this paper describes the development of a computer program (available online) to compute locations in which all displays are legible to the audience, which considers the height, width, location and orientation of each display, text geometries (height, height-to-stroke width ratio) and its lighting conditions (background luminance, luminance contrast percent), as well as the observer’s visual acuity. This program was validated in a small experiment involving 21 subjects looking at text in a lecture hall, and further examined for two other test cases.