Light scattering on worn windscreens : development of technique for quantitative measurement of visibility degradation

Abstract: The wear of the windscreens as one important traffic safety problem has been observed in many studies. Transmission loss of windscreen could play an important role in a person‟s possibilities to detect objects on the road. It has been estimated that up to 90% of the information used by drivers to drive their cars is visual. When driving with a worn windscreen, the risk of dazzling increases. It can lead to the consequence that the driver does not discover objects or people in the driving environment.The goal with this thesis is to propose a method for quantitative measurement of the visibility degradation on worn windscreens. It should correlate with customer expectations which require a quick and easy method. This test should be possible to apply at the annual quality check of automobiles at motor vehicle inspection. The thesis work was carried out at Industrial metrology and optics, of the school of Industrial Engineering and Management, Kungliga Tekniska högskolan with support of Svenska Glaskontroll AB.The transparency degradation of a windscreen mainly caused by the incident light beam diffusion due to scattering at small surface defects such as scratches and impact sites. As worn windscreens have more surface defects, the scattering of incident light would be stronger than the new ones, which could cause more windscreen transmission loss. In this thesis we measured the light scattering on four windscreens with different mileages by digital photography techniques. The test was undergoing at a fixed light angle, which is according to the test done in the Swedish Road and Traffic Safety Institute (VTI).Four windscreens were investigated with mileages of 0km, 26000km, 107945km, 170000km. The results are shown by data of the brightness of the pictures of the windscreens which indicate how strong the light scattering on the windscreens was. Also a comparison was made by overlap the pictures of the scattering sites of different windscreens with road scenes to see how the light scattering affects driving. Moreover, we use a software Fiji to analyze the number and area of the scattering sites on the windscreens.