Light plate for examination of material surfaces using an evanescent light field, e.g. for an optical reader, has a radiating surface with a layer of light conducting material of different optical density and a colored pattern

摘要

Light plate (17), made from light conducting material has a coupling point (16) for coupling of a light beam (12) to it and a radiating surface (18) for the output of an evanescent light field (19). The radiating surface has a layer (21) of a light conducting material with a different optical density to that of the light plate and is provided with a coloring that is distributed in a known pattern. An independent claim is made for a method for calibrating an optical reader with a light plate for evanescent field excitation of an examination surface (20).