To establish a minimum luminance level, a psychophysical procedure was used to establish the 95% correctness threshold for 95% of older drivers (ages ranged from 45 to 67). The correctness threshold and subject response times were obtained over eight letter luminance levels, four letter sizes, and three contrast ratios. The results showed that letters must be at least 0.64 cm high (at an 81.3-cm viewing distance) in order to be visible to 95% of the older drivers when letter luminance is set at 1.71 cd/m2. Response times declined as letter size, contrast ratio, and letter luminance increased beyond their threshold values. Although older drivers' visual acuity losses may be compensated by the use of corrective lenses, their losses in brightness and contrast sensitivity simply mean that they need about 10 times as much light as younger drivers. (Author/publisher)
Abstract