The aim of this scientific study was to obtain a new physical formula for determining the refractive indices of light as a function of wavelength, which can be applied to the widest range of transparent substances. This study was based on the hypothesis of the dependence of the speed of propagation of photons inside matter on the density of electron clouds of atoms of matter. In the course of research on the basis of Einstein's relativistic formula, this dispersion formula was obtained. The new physical formula was used to calculate 26 refractive indices of light in 5 transparent substances in three states of aggregation. Comparison of the obtained indicators with laboratory indicators showed the high accuracy of the new dispersion formula, which amounted to T10 -7h10 -5 in the calculated wavelength ranges of more than 100 nm.
The successful application of the relativistic formula to processes occurring at the atomic level allows us to look at the nature of the interaction of light and matter from a new angle.