Methods for Providing Uniform Diffuse Illumination
Original Publication Date: 1985-Apr-01
Included in the Prior Art Database: 2005-Feb-18
Although lighting from all directions is often desirable for optical inspection, at present there is no efficient method to illuminate uniformly over an entire hemisphere. Several methods are presented here for providing illumination from all directions using a variety of light sources and a compound parabolic light concentrator (CPC). Because of the properties of the CPC, incoming light that is Lambertian over the CPC's acceptance angle results in outgoing light which is Lambertian over a full 2f steradians. The output irradiance is also uniform. The CPC was devised for concentration of solar energy. Its in ternal parabolic curves depend on the ratio of the radius of its large opening to that of the small opening (r1/r2). The device has an acceptance angle (r) given by: r = sin-1(r2/r1). As shown in Fig.