2 1 5 high reflectivity at the front surface does not become a problem until the angle of incidence exceeds 56 u00b0 these losses can be reduced by application of an anti reflective coating to the front surface the general performance characteristics of both metallic and total internal reflecting sunlight concentrators are determined by the shape and texture of the sidewalls in the case of total internal reflectance however rays which are insufficiently oblique to the walls are only partially reflected and energy is lost from the concentrator by the portion of the rays passing through this can be avoided by designing the wall shape so that this situation seldom arises or by metallizing certain zones of the wall where partial internal reflection is likely to occur the use of solid dielectric sunlight concentrators poses special problems in transferring the radiant energy flux from the dielectric to the photoelectric cell should air or any medium having an index of refraction less than that of the collector dielectric partially or wholly fill the spacing between the refractive collector dielectric and the photoelectric cell then instead of refracting and transmitting the light to the surface of the photoelectric cell the surface of the collector dielectric which is adjacent the photoelectric cell may become an additional reflecting surface similar to the sides of the collector and a substantial portion of the light which enters the collector may be reflected away from the photoelectric cell rather than transmitted to it greatly reducing the efficience of the collector when the collector is formed from a solid block as shown in fig5 and 6 an additional layer of a refractive material must fill the space.