US Patent 7528945 Method to determine the optical quality of a glazing

A method of determining the optical quality of a glazing which includes at least one area having a reduced light transmission, involves producing a shadowgraph image of the glazing and measuring the illumination of the glazing at a plurality of measurement points arranged in an array extending over the glazing. The deviation in illumination from a desired value at each measurement point is determined and the at least one area of reduced light transmission is omitted from the array of measurement points.