Nonimaging Optics

14 MANUFACTURING TOLERANCES

14.1 INTRODUCTION

When a series of concentrators is manufactured, they necessarily differ from the theoretical design model in several aspects. In the first place, the optical surfaces have microscopic roughness, which causes some scattering of the incident light. Second, the surfaces profiles have contour errors—that is, they do not fit perfectly the theoretical ones. This results in slope variations between the two and thus angular deviations of the exiting rays. Third, the relative positions of source, receiver, and optical surfaces involve a certain tolerance. All of these errors affect the performance of the concentrators, and for each application they should be kept below a certain level to guarantee a specified ...