Establishes how the yield of photoluminescence depends on the wavelength of the exciting light. According to Vavilov's law, the quantum yield of photoluminescence is constant over a wide range of wavelengths of the exciting light and falls off sharply at wavelengths greater than the one at which the maximum of the luminescence spectrum is observed (anti-Stokes excitation). It is connected with the quantum nature of light and is analogous to Einstein's law for the quantum yield of photochemical reactions. Established by S. I. Vavilov in 1924.