The correlated color temperature (CCT) of total skylight, which comes to a horizontal plane from all sky components, varies hourly with atmospheric transmittance pv and the amount of cloud m. The parameter pvcaused by visible solar radiation is calculated from the atmospheric transmittance based on direct solar radiation. A new practical formula for estimating the CCT of the total skylight is proposed. Using the formula, the CCTs of the total skylight at 14 areas in Japan are calculated from the parameter pv and the number of days that is calculated from the parameter m. Consequently, it is estimated that variation in the CCT of daylight is 5900K to 8000K. The mean CCT of total skylight is 6800K, where the mean CCT of global light is 5900K and that of the total skylight for the parameter m=0 is 8000K.
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