1995 Volume 79 Issue 11 Pages 620-627
The Sky can be classified according to the amount of cloud as clear sky, overcast sky or intermediate sky (where clouds are scattered), and the skylight that comes to a horizontal plane of the ground from all sky components is respectively called clear skylight, overcast skylight or intermediate skylight. This paper discusses the correlated color temperatures (CCTs) of the clear skylight, the overcast skylight and the global light that is composed of the clear skylight and direct sunlight. Consequently, the mean CCTs of clear skylight and global light for atmosphere of annual mean atmospheric transmittance in Japan, 0.70, based on visible radiation rather than on the amount of direct solar radiation, are respectively estimated to be 8000K and 5900K. The CCT of covercast skylight is similarly estimated to be 6200K, which is almost the CCT of extraterrestrial sunlight.