The acceptance angle is a concept in optical systems and solar concentrators. It refers to the maximum angle at which incoming light can be captured by the system or concentrator

. In the context of optical fibers, the acceptance angle is the maximum incidence angle of a light ray that can be used for injecting light into a fiber core or waveguide

. The acceptance angle is determined by the refractive index contrast between the core and cladding materials of the fiber

. In the context of solar concentrators, the acceptance angle is the maximum angle at which incoming sunlight can be captured by the concentrator

. The value of the acceptance angle depends on the concentration of the optic and the refractive index in which the receiver is located

. Maximizing the acceptance angle of a concentrator is desirable in practical systems, as it affects the efficiency of the system

. In summary, the acceptance angle is an important parameter in both optical systems and solar concentrators, as it determines the maximum angle at which incoming light can be captured by the system.