Ergonomic Requirements for Character Legibility of Reflective Liquid Crystal Displays

Age-Related Differences

Abstract

We investigate the ergonomic requirements for lightness, contrast and character size of reflective liquid crystal displays (LCDs) for young and old users. The 30 young subjects (mean age : 21.3) and 24 old subjects (mean age : 58.6) rated 25 lightness and contrast combinations for five character sizes displayed on hard copies that simulated reflective LCDs. The results indicate that the character size required is 15 point when the characters are viewing at a distance of 40 or 50 cm and an inclination angle of about 40 degrees. The required contrast ratio depends on the background lightness. When the background lightness L^* is 70, the required contrast ratio is about 4 for the 15-point characters. When the background lightness is 50, however, the contrast required is 6 or 7. These requirements are almost the same for young and old subjects. When the character size is smaller than 15 point, however, old subjects require very high lightness and contrast compared to young subjects. This difference may be due to age-related differences in the visual acuity for close targets.