The working mechanisms of a luminescent concentrator. (1) When a photon enters the luminescent material, (2) it will undergo absorption if it is within the absorption spectrum. When spontaneous emission occurs, the photon will be emitted isotropically, which means the radiation has the same intensity in all directions. (3) If the angle of incidence is smaller than the critical angle, the photon will refract out of the material through the escape cone as a loss. (4) Otherwise, the photon will undergo total internal reflection (TIR). (5) After a number of TIR, the photon will reach the output surface and be coupled out. Some of the loss mechanisms include (6) transmission through the LSC without absorption, (7) surface reflection, (8) self-absorption, (9) host matrix absorption, (10) host scattering, (11) surface scattering and (12) non-radiative decay due to η□_QY < 1.