For a thorough discussion both of the limitations of imaging Kc
r)W
optical systems in the collection of radiant energy and of the Z{(Gib~{N
nonimaging collectors which can be used to collect energy IA1O]i
S
efficiently, see W.T. Welford and R. Winston, High Collection xF) .S@
Nonimaging Optics, Academic Press (San Diego), 1989.