Visual Comfort for Motorists

Visual comfort is a subjective aspect related to road-lighting quality. If the degree of visual comfort is not good enough, a motorist’s level of fatigue will increase and as a consequence, his visual performance and alertness will decrease. So both visual comfort and visual performance are important for road safety. Subjective appraisal studies have shown that the lighting level, the uniformity of the roadsurface luminance pattern and glare have an influence on visual comfort. The same type of studies have been the basis for definitions of visual comfort metrics such as longitudinal uniformity, luminance gradient and discomfort glare marks. The spectrum of the light source used has an influence on the last mentioned. LEDs may sometimes have a special influence on visual comfort because they are available in a much wider range of spectra than are the conventional light sources. Their small light-emitting surfaces enable more pronounced beams to be produced, that in turn may influence visual comfort or discomfort. Most LED luminaires consist of a multiple array of small LEDs resulting in a non-uniform luminance distribution of the light-emitting surface, which may have an influence on their discomfort glare aspect.