Optical rain sensor testing method for determining humidity amount on glass surface of windscreen of motor vehicle, involves changing optical characteristics of optical element by applying electric voltage at element

摘要

The method involves arranging an optical element e.g. lens (7) with variable focal length, in a measuring range of a rain sensor at a glass surface using a silicone foil (8). Optical characteristics of the element are changed by applying electric voltage at the element. A portion of light reflected from a glass surface of a windscreen (1) is determined based on the optical characteristics. A boundary surface (18) between two-non mixable fluids (12, 13), is provided in the lens, where position and shape of the surface are changed by electric field.