Luminous efficacy of solar radiation and evaluation of natural illumination—A review

This review is mainly based on work carried out by the author earlier [Ind. J. Met. Hydrol. Geophys. 29 667 (1978); Ind. J. Pure Appl. Phys. 18 413 (1980); and Ph.D. Thesis, Univ. of Roorkee (1981)] and presents computed and measured values of the luminous efficacy of solar radiation over varied solar altitudes and atmospheric turbidity conditions. Based on the analysis of theoretical and experimental data, values of luminous efficacy for the direct and diffuse components of solar radiation are recommended for practical use under clear (cloudless) atmospheric conditions in India. The utility of the recommended values has been illustrated by deriving the natural illumination for four major Indian cities.