Wu, Jintong2014-10-212014-10-2119901467-8659https://doi.org/10.1111/j.1467-8659.1990.tb00426.xSimulating natural light is an interesting subject in computer graphics. Using the principles of meteorology, we build a sphere cap light source model. Unlike existing illumination or light source models, we consider the effects of both the ratio of direct light to diffuse light and the position of the sun under different weather conditions. We use an area light source to generate shadows and a point light source to generate the other effects. The ratio of the two types of light is adjusted by a brightness factor b while the position of the sun is determined by giving the light direction. In addition. a modifiable sphere cap is used to obtain modified penumbra which vary with illumination.10.1111/j.1467-8659.1990.tb00426.x349-353