Optimal Brightness of Passing Beam for Wet Road Conditions
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At the Laboratory of Lighting Technology of the Technical University of Darmstadt, a field test was carried out to determine the optimal brightness of the passing beam for wet road surfaces. The passing beam of two encountering vehicles was varied and the brightness impression, glare and visibility on both dry and wet road surfaces were compared. From the results an adverse weather light distribution was derived, which reduces the glare level to values of a dry road, while increasing the visibility of the driver.
Depending on the degree of wetness, the reflection properties of the road surface change, resulting in increased forward reflection and reduced backward reflection. This can dazzle other road users and can lead to dark appearing roads. In order to counteract this effect, some vehicle manufacturers reduce the brightness of low beam for wet road conditions. This raises the question of what the optimum brightness is and which areas of the passing beam should be...