Automobile windscreen rake, spectacle lenses, and effective transmittance

To investigate the effect of windscreen rake angle on effective transmittance and the contribution of spectacle lenses to the total transmittance of the system.

Theoretical analysis has been carried out using the Fresnel reflectance equations.

Windscreen rake can reduce effective transmittance significantly at angles present on modern aerodynamic vehicles. Spectacle lenses reduce the total transmittance still further, often to below the minimum level permissible in current international standards for windscreens.

Drivers should always be supplied antireflection-coated lenses where there is a chance of their spectacles being used for night-time driving, if current International standards for windscreen transmittance are to be met by the spectacle-windscreen combination. Windscreen rake angle should be accounted for both in the International Organization for Standardization transmittance standards and in roadside testing devices.