AbstractThe fluctuation theory of light scattering for moderately concentrated polymer solutions is extended in a phenomenological fashion to include angle‐dependent terms up to sin2(θ/2). The treatment is based on an uncoupling of the center of mass and segment contributions to the free enthalpy. In particular, equations are derived for three‐component mixtures containing two polymer and one solvent component. These are applied near the region of incompatibility. The results are compared with Debye's theory of critical opalescence. It is found that the Debyelparameter should be of the order of magnitude of the radii of gyration of the polymer molecules. This is confirmed by some experim