This paper presents a description of an interference pattern produced by refracted laser rays propagating along a transparent prism. The high contrast of bands in the pattern is explained. The refracted light rays are separated into the edge rays and rays that obey the ordinary laws of refraction. It is shown that the intensity of the edge rays is quite sufficient to produce the observed interference pattern in combination with the rays refracted at the critical refraction angle. Based on the interference of the edge rays and rays refracted at the critical angle, an empirical formula has been derived that describes well the experimentally observed interference patterns.