Clearness index
Measure of atmosphere clearness
From Wikipedia, the free encyclopedia
The clearness index is a measure of atmosphere clearness. It is calculated as the fraction of the actual total solar radiation on the surface of the Earth during a certain period over the theoretical maximum (i.e., clear sky) radiation during the same period.[1][2] The clearness index is a dimensionless quantity and can vary from 0 (sky is completely covered) to 1 (perfectly sunny).[3]
