For a thorough discussion both of the limitations of imaging so;
]&
optical systems in the collection of radiant energy and of the @d_M@\r=j
nonimaging collectors which can be used to collect energy RNL9>7xV
efficiently, see W.T. Welford and R. Winston, High Collection "N;EL0=
Nonimaging Optics, Academic Press (San Diego), 1989.
