Luminous efficacy of global solar radiation on a horizontal surface for overcast and intermediate skies

In the first part of this research two models for the luminous efficacy of global solar radiation on horizontal surfaces and overcast skies have been developed. The first of these models is developed using a method similar to that proposed by Littlefair (1988). The second model has been obtained fro m the corresponding illuminance and irradiance models in an, apparently, ne w approach to the subject. In the second part of this research, a model for the luminous efficacy of global solar radiation for intermediate skies and horizontal surfaces is developed from the corresponding illuminance and ir radiance models. The model for intermediate skies is given by the same math ematical function as that of the analogous model for overcast skies, and on ly the empirical constants change. In all the cases the only independent va riables used are the solar altitude and the brightness index. The models pr oposed in the present paper have been statistically tested, and their predi ction accuracy compared with other models available in the scientific liter ature.