Dirty Headlights - Frequency and Visibility Effects

To investigate the problem of dirty headlamps, three experiments have been carried out. In the first, dirt layers were systematically collected under various road conditions. The wetness of the road was found markedly to influence the amount of dirt deposited. In the second, light reduction caused by dirt on cars in traffic was measured. It was found that even in dry weather on seemingly clean roads light reduction due to headlamp dirt is normally 10-20%. In bed (slushy) road conditions few cars have light reduction below 50%. Drivers normally do not react to light reduction below 60% In the third experiment, reduction in visibility during night driving was measured as a function of light reduction. Light reduction of 60% causes a 20% reduction of high beam visibility and a 15% reduction of low beam visibility.