For a thorough discussion both of the limitations of imaging a`#S|'oatC
optical systems in the collection of radiant energy and of the O - G1})$
nonimaging collectors which can be used to collect energy TfJL+a0
efficiently, see W.T. Welford and R. Winston, High Collection J"-_{)0lD
Nonimaging Optics, Academic Press (San Diego), 1989.
