Effect of Ambient Illumination on Legibility of Displays of Liquid-Crystals and Light-Emitting Diodes

Abstract

Two liquid-crystal (LC) and three light-emitting diode (LED) electronic digital displays were evaluated at 1.5, 15, and 45 fc on the display using five criteria: 1) recognition time of single digits, 2) no-error viewing distance, 3) preferred viewing distance, 4) preferred illumination, and 5) subject vote. Recognition time (at a constant viewing angle of 31 min. of arc for the display character height) of the two seven-segment LED displays did not change significantly in the selected range of illumination. For the hexadecimal LED display, recognition time increased significantly from 1.5 to 15 and 45 fc. Recognition time of the reflective LC display decreased significantly from 1.5 to 15 and 45 fc. For the transmissive LC display, recognition time increased significantly from 15 to 45 fc. The no-error viewing distance of the .77″ LED display decreased significantly from 1.5 and 15 to 45 fc but increased significantly from 1.5 to 15 and 45 fc for the reflective LC display. No-error and preferred viewing distances were predicted with multiple regression equations; using just display character height and stroke width/ height gave a multiple R = .91 for no-error viewing distance. The character height viewing angle obtained for no-error viewing distance was 5 min. of arc, but was 17 for preferred viewing distance. Mean preferred illumination was 62 fc for the reflective LC display, 27 for the transmissive LC display, 21 for the .27″, seven-segment LED display, 18 for the .77″, seven-segment LED display, and 10 for the .27″, hexadecimal LED; any difference greater than 9 fc was significant. Preference for the liquid-crystal displays increased at the expense of the light-emitting diode displays as ambient illumination increased from 1.5 to 45 fc.