Considering Planck's assumption of quantized energy, was this idea proved later in quantum electrodynamics or any other theory of electromagnetic radiation? I have seen at places that Max Planck had an intuition about this idea, along with extensive research on the problem. Is intuition thing true? And the final part, since classical electrodynamics suggests the energy density for a radiation to be proportional to square of frequency, if I have to study the motion of radiation along null geodesic in curved space, should I use energy to be proportional to frequency or square of frequency? Of course quantum nature is used in Minkowski space-time, still for complete classical nature, which of the two is correct form?