Abstract
The temperature formally assigned to spectral electromagnetic radiance Lν by solving Planck’s equation for T permits the application of the Second Law of Thermodynamics to passive concentrating systems. (1) Concentrators operating within the limits of geometrical optics, (2) concentrators changing the frequency of the radiation but conserving the total radiant flux, and (3) systems in which the frequency is changed and part of the absorbed power transferred to the surroundings as heat are discussed. The attainable concentration ratios are given. Particularly for systems of category (3), perspectives are encouraging for further development and application. Such systems resemble, in certain respects, heat pumps. High concentration ratios are allowed by thermodynamics. In this category concentrators that use Stokes fluorescence are discussed.
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