The clear sky light is generated through the process that the direct sunlight is successively scattered by the air and aerosol in the turbid atmosphere and repeatedly reflected by the earth's surface.
The scattering-transmitting functions of the direct sunlight and the reflected light from the earth's surface were set up theoretically and the spectral power distributions of the clear sky light were estimeted.
It became clear how following factors effect the change of the clear sky light respectively.
(1) The scattering light by the air and that by the aerosol.
(2) The first scattering light and the higher order scattering light than the first.
(3) The reflected light from the earth's surface.
