We present here a new parametrization of the radiative properties of broken clouds, which uses the effective cloud fraction as a parameter. We have shown that quite a simple and single valued ratio exists between the effective cloud fraction in the visible, Nevis, and short-wave spectral regions, Nesw = f(Nevis). We also present in this paper a study of the effects due to random geometry of clouds on the effective cloud amount in the visible region. It is also shown that small variations of the atmospheric aerosol optical thickness (0 ≤ τa ≤ 0.22) and of the cloud microstructure may be neglected in the calculations of Nevis at a fixed value of the cloud optical thickness. Among the advantages of the parametrization proposed there are the possibility of accurately taking into account the effects due to random geometry of clouds and the fact that the development of a numerical model of Nevis does not require long computer time, and, finally, there is no need in making serious changes into the GCM radiation codes currently in use.