Ergonomic requirements for reflective liquid-crystal displays

Abstract

We investigated the ergonomic requirements for lightness, contrast and character size of reflective liquid-crystal displays (LCDs) for young and aged users. The 30 young subjects (mean age: 21.3 yr) and 24 older subjects (mean age: 58.6 yr) subjectively rated 25 combinations of lightness and contrast for five character sizes displayed on hard copies that simulated reflective LCDs. The results indicate that the character size should be 15 point (pt) when the characters are viewed at a distance of 40 to 50 cm and at an inclination angle of about 40°. The required contrast depends on the background lightness. When the background lightness L* is 70, the required contrast ( L max/ L min) is about 4 for 15 pt characters, whereas a contrast of 6 or 7 is required when L* is 50. These requirements for the 15 pt characters are common to both the young and older subjects. When the character size is smaller than 15 pt, however, the older subjects required a very high lightness and contrast compared with the younger subjects.