A lighting apparatus is broadly disclosed and embodied herein. A series of images of a scene is acquired with the polarizer whose orientation is changed in a in a systematic sequence from 0 degrees to 180 degrees. The microstructures are particularly useful for use in assays and reactions in the relating to biological assays, including applications in medical diagnostics. In order to form the positive connection, the other connector part has a projection with a positive fit engagement in the wall opening of the retainer element when in the plugged position.