For a thorough discussion both of the limitations of imaging =0ZRG p
optical systems in the collection of radiant energy and of the [H}>
2Q
nonimaging collectors which can be used to collect energy V" YeF:I
efficiently, see W.T. Welford and R. Winston, High Collection [:y:_ECs6
Nonimaging Optics, Academic Press (San Diego), 1989.
