Field study on discomfort glare from headlamps with small light-emitting areas

The use of LEDs as a light source combined with innovative optical concepts offers increasingly free design possibilities for headlamps. The design trend is moving towards narrow contours, resulting in smaller light-emitting areas. As the light-emitting area decreases, the average luminance of the surface increases if the same luminous flux is to be emitted. This raises the question of whether the higher luminance of headlamps lead to an increase of discomfort glare for the oncoming traffic. Various research studies have been conducted on this topic. While some laboratory studies show an influence of luminance on discomfort glare, this effect was not found when using real headlamps as glare sources. To further strengthen the understanding of the influence of the size of the light-emitting area and the average luminance on discomfort glare, a field study was conducted in a real traffic scenario. Five types of headlamps with varying light-emitting surface areas were mounted on two test vehicles. The test subjects were driving with a third car on a straight, dry road at a speed of 80 km/h when one of the test vehicles was oncoming with one pair of headlamps activated. After the oncoming situation was over, the subjects had to rate the discomfort glare on the De Boer scale. 17 participants took part in the study. Depending on the size of the light emitting area, there were only slight differences in the discomfort glare ratings. Thus, the average luminance of the headlamps had no relevant effect on discomfort glare. A significant increase of discomfort glare could only be observed when the headlamps were misaligned and thus produced a higher illuminance at the eye of the observers.