The conclusion of the Planck radiation law is proposed, which does not require the involvement of non-thermodynamic considerations. The conclusion is based on the concept of the wave nature of the radiation process and the existence of harmonics in oscillators. It is shown that the true radiation quantum is a wave that is discrete both in time and in space, and the Planck constant plays the role of the proportionality coefficient between the fluxes of radiant energy and traveling waves. The de Broglie relation is obtained as a consequence of the identity of the oscillation frequency of the oscillators to the flow of emitted waves. The proposed approach removes a number of contradictions of quantum theory with classical physics.