For a thorough discussion both of the limitations of imaging #T
Cz$_=t
optical systems in the collection of radiant energy and of the owZj Q
nonimaging collectors which can be used to collect energy NuI9"I/
efficiently, see W.T. Welford and R. Winston, High Collection :k8>)x]
)
Nonimaging Optics, Academic Press (San Diego), 1989.
