Abstract Experimental data are presented showing effects on the polarized reflection spectrum, from the (001) face of crystalline anthracene which arise upon cooling from room temperature to 80°K. Different crystal mounting methods and different crystal thicknesses are considered. The band profile of only the b-polarized (0—0) region is distorted and a new resonance detected near 25290 cm− 1 at crystal temperatures below 120°K with an intensity dependent on the method of crystal mounting and rate of cooling. This resonance disappears with time. The results ate explained using a theory of submicroscopic voids in the crystal if the crystal has 10 −4 of its volume in the form of extremely thin planar dislocations almost to the direction of light propagation in the crystal.