(eng): Environment illumination is a key to achieving a realistic visualization of material appearance. One way to achieve such an illumination is an approximation by rendering of the material surface lit by a finite set of point light sources. In this paper we employed visual psychophysics to identify a minimal number of point light sources approximating realistic illumination. Furthermore, we analyzed stimuli images and correlation of their statistics with obtained psychophysical data. Finally, image statistics were identified which can predict such a minimal environment representation for three tested materials, depending on the visual properties of the illumination environment.