(a) Dependence of optical efficiency and (b) concentration factor c on the coverage fraction, for an ideal system with and without PSB, obtained by simulations with our Monte Carlo code. Internal values take into consideration only internal losses whereas effective ones account for both internal and external losses. The two horizontal lines in part (a) represent the external efficiency with and without PSB. It does not depend on the coverage fraction. Effective efficiency is the product of the internal and external efficiency.