4 NONIMAGING OPTICAL SYSTEMS
4.1 LIMITS TO CONCENTRATION
The relationship between the concentration ratio and the angular field of view is a fundamental one that merits more than one demonstration. We shall give a thermodynamic argument in the context of solar energy concentration. Imagine the sun itself as a spherically symmetric source of radiant energy (Figure 4.1). The flux falls off as the inverse square of the distance R from the center, as follows from the conservation of power through successive spheres of area 4πR2. Therefore, the flux on the earth’s surface, say, is smaller than the solar surface flux by a factor (r/R)2, where r is the radius of the sun and R is the distance from the earth to the sun. By simple geometry, r/R = sin ...
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