This paper proposes a method for estimating the illuminant spectral power distributions and their relative positional relationship of multiple light sources under a complex illumination environment. A multiband camera system is used for capturing spectral images of dielectric objects in a scene. First, dielectric object surfaces are segmented into regions with different object colors, by using the hue angle of the diffuse reflection component. Specular highlights are used as a clue for estimating the light source information, which are detected on curved object surfaces with the different object colors. The illuminant spectra of light sources are estimated from the camera data for highlight areas detected on each surface region. Then, the illuminant spectral estimates are obtained for a different set of light sources. Next, the geometric information, such as the number of light sources and their relative positional relationship is predicted based on the set of estimated illuminant spectra on the segmented surface regions. The algorithm of probabilistic relaxation labeling is used for classification of the detected highlights and the estimated spectra. The feasibility of the proposed method is examined in experiments on real scenes.