1987-10-01

Improved Solar Control Car Glazing in the Rearward Field of View-An Approach to Update Regulations 872000

People often modify their vehicles with dark tints on the side windows behind the B-pillar and in the backlite even though this can be against the law. Passenger comfort is the motivating factor for these actions.
Although luminous transmittance of automotive glazing is regulated in many countries, the rearward field of view is not as clearly defined as the 180° forward field of view. The minimum legally allowed limit for the reflectance of a rearview mirror is 35% according to FMVSS 111. A combination of a backlite of 40% luminous transmittance together with a rearview mirror of 70% reflectance is not permitted, although in terms of visibility it renders the same result as a backlite of 70% transmittance together with a rearview mirror of 40% reflectance.
Normally tinted glazing is offered by manufacturers as solar control glazing. The effectiveness of tinted glazing especially green glazing and coated green glazing is discussed. A proposal to increase the thermal comfort in the car is made by recommending darker tints than normally used or the application of printed ceramic dots, on the glazing.
An investigation was carried out by means of a driving simulator to determine how drivers react when looking through windshields with various degrees of luminous transmittance in the range of 90% to 40%. A windshield with scattered light produced by surface damages was also investigated.
Results obtained with the driving simulator show that a small amount of scattered light impairs the driver's vision much more than windows with a normal depth of tint. Dark windows can be tolerated in locations in the car where the images normally observed are of high contrast levels.

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