A laboratory study was conducted for evaluating the effect of size of High-Intensity Discharge (HID) headlamps and the separation from the direction indicator on discomfort glare and direction indicator conspicuity, respectively. The discomfort glare was subjectively rated on the nine-point De Boer scale. In addition to the expected effects of glare illuminance and glare angle on the discomfort rating, a small but statistically significant effect of headlamp size was found. Reducing lamp dimensions by a factor two (a factor four in area) increases the discomfort glare by only 0.1 points. This effect can be compensated for by an 11% reduction in the luminous intensity of the headlamps. The conspicuity of the front direction indicator as a function of its separation from the HID headlamp was measured by determining the maximum eccentricity of the line of sight at which the direction indicator was just perceptible. A strong effect of separation was only found for low indicator intensities. When the separation is defined as the distance between the lamp centres, there was no effect of lamp size. A minimum centre-to-centre distance of 22 cm is recommended, based on the criterion of a minimum conspicuity angle of 25 degrees. (A)
Abstract