The physical optics method occupies a leading position in solving the problem of light scattering by atmospheric ice particles for active remote sensing problems. At the same time, insufficient attention has been paid to the study of the lower limit of applicability of this method. In this report, the limit of applicability of the method of physical optics is studied on the example of five Platonic solids. For the validation of the method of physical optics developed at the Institute of Atmospheric Optics of the Siberian Branch of the Russian Academy of Sciences, the invariant imbedding Tmatrix method (IITM), the physical geometric optics method (PGOM), the discrete dipole approximation (ADDA) were used.