In the present paper, the earlier developed model for wall window has been modified for rooftop window. The model has been validated for dynamic behavior by considering the hourly measured both direct and diffuse components of the sunlight and skylight under clear sky conditions. It can be used to predict the Daylight Illuminance Ratio (DIR) and daylight at a given point in living space. The annual energy saving from rooftop window has been estimated for different climatic locations in India. It has been observed that highest DIR was always along the line normal to the rooftop window and decreases as we go away from the normal line in all directions. It was found that, for increasing aperture to floor area ratio, the energy saving potential increases. The minimum annual energy saving was found to be 65.74 kW h/m(2) for Srinagar whereas the maximum was 77.10 kW h/m(2) for Bengaluru. The monthly average value of model exponent (p) has been computed as 1.25. Hence, the present model can be used to design building for optimum daylighting at a given point inside living space. (C) 2015 Elsevier Ltd. All rights reserved.