The details of the study of spectral distribution and colour of the daytime north sky at Bombay are presented. The results are discussed in relation to the results at Delhi and other places outside India. Individual measured curves for Bombay are compared with the typical distributions derived from Delhi data and are found to agree fairly well though there are still differences at both ends of the spectrum. The possible reasons for the disagreement in the ultraviolet noticed between Bombay and Delhi curves and in the curves of other workers are also discussed.

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Data on zenith luminance and total horizontal illuminance obtained for tropical clear sky at Delhi showed strong turbidity-related seasonal dependance. A comparison of the variability of these parameters with solar height for the Delhi sky with variabilities for other locations, as given by data-based empirical equations and as calculated theorectically, revealed significant differences. The best approximation to zenith luminance and its variability for different locations was obtained with the formula of Dogniaux. A similar approximation was obtained for the total horizontal illuminance of different locations with the values and variabilities as derived, combining Dogniaux's formula for zenith luminance with the luminance distribution of Kittler. Exceptions to this type of approximation may be noticed for locations with special atmospheric conditions and ground reflectance.

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