I found the explanation of the radiation here, in the document of the Purcell Simplified: http://physics.weber.edu/schroeder/mrr/MRRtalk.html I like it, however I'm ucertain how to fit this to the light, as photon. Am I thinking correctly, that this figure fits also the case when a photon is emitted by an atom? I assumed that the "jump" in the center may be a jump of the electron in an atom, so the radiation is the light. In this case how can I calculate the frequency of the light (the energy of the photon)? Can it be calculated from the size of the jump? Is there a formula for it? Thank you!