Principles and design graphs for obtaining uniform illumination in automated visual inspection

This paper is concerned with the inspection of flat materials on which blemishes are to be found. In many such cases, inspection is facilitated by arranging the illumination to make an ideal surface appear uniformly bright. It is found that this can be achieved by several convenient configurations of tubular lights having a close analogy both with Helmholtz coils and with Butterworth filters. The paper presents principles and design graphs for three configurations in which some 'pass-band ripple' is allowed. It is intended that the paper will stimulate further discussion on the optimal design of lighting systems for inspection applications.