This research presents a practical method to estimate the positions of light sources in real environment, using a mirror sphere placed on a known natural marker. For the stable results of static lighting, we take the multiple images around a sphere and estimate the principal light directions of the vector clusters for each light source in running-time. We also estimate the moving illuminant for changes of the scene illumination, and augment the virtual objects onto the real image with the proper shading and shadows. Some experimental results show that the proposed method produces plausible AR visualization in real time.