It is a challenge work to render natural lighting phenomena in real-time. A major reason is due to high computational expense to simulate the physical model of atmosphere scattering. Another is due to the lack of power and programmability in the graphic hardware. In this paper, we propose unified volumes representation for light shaft and shadow, which is an efficient method of simulating natural light shafts and shadows with atmospheric scattering effect. We give the analytic formula of light shaft without numerical integration and then make use of the current graphic hardware to implement the integral computation on each volume surface for scattering. Our approach can not only simulate the lighting effect with single light source but also multiple parallel light sources according to the physical model of skylight and sunlight. With acceleration of the GPU, we can generate realistic appearance with high frame rate satisfying real time application. It can possibly be used in current commercial game or other virtual reality systems.