Safety Hazard of Tinted Automobile Windshields at Night

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Abstract
The effects of tinted optical media, particularly of heat-absorbing automobile windshields, upon visibility distances on the highway at night are analyzed theoretically. The loss percentages in visibility distances caused by replacing clear windshields with tinted ones are calculated as functions of the variables involved, viz., transmittance of the tinted optical medium, isocandle profile of the headlamp, angular size and reflectance of the target. It is found that the loss percentages in visibility distances are further dependent upon the distance of the target itself, with the losses increasing with decreasing distances. Losses in visibility distances caused by commercial brands of tinted windshields amount to between 9 and 15 percent at visibility distances ranging between 1000 and 200 feet. These results agree fairly well with the data of Blackwell and with data obtained experimentally in the field by other authors. The analysis shows further that the losses in visibility distances are greatest for targets so nearly matched to the background that they may be seen even with clear windshields only at short distances. Under these conditions the losses may be as high as 30 to 45 percent. A reconsideration of the 70 percent minimum transmittance requirement for windshields in the American Standard Safety Code Z26.1–1950 is recommended.

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