For protection purposes, coverslips, such as glass, plastic or fused silica, usually are applied to optically coated cells. The short-circuit current of the coated cells with covers is reported to decrease, compared with the short-circuit current for coated cells without covers. The loss in short-circuit current is generally attributed to the fact that the optical matching between the coating and the cover is not optimized. However, recent work on silicon solar cells with optical coatings (SiO, Si3N4) and plastic covers (FEP Teflon) at NASA-LEWIS shows no decrease in short-circuit current under air mass zero simulated sunlight conditions; in fact, short-circuit current shows an increase in Si3N4 coated cells with plastic covers. The measured covering factor, defined as the ratio of short-circuit current of FEP covered cells to the bare coated cells, is consistent with the calculated covering factor based on single-layer coating theory.