The reason I call my blog Photons and Electrons is because of the importance of the relationship between the two in our everyday lives. I even named one of our labs Photon - much to the dismay of my three sons and wife :-) What I really like about this article is how clearly it explains the key aspects of electrons moving to and from the different levels or shells (K, L, M, N, O, P, and Q) inside the atom and what the photons are doing as these moves occur.
Below is from the Post article (note that I highlighted the key aspects):
Zap a few atoms with the right amount of energy -- including energy from light itself -- and their electrons will absorb the energy and jump up to excited levels, the original "quantum leap."
But they won't stay there. That's because, as the parent of any teenager can tell you, it is the natural tendency of things in this universe to preferentially seek the lowest energy condition, which is why water always flows downhill, shoelaces never re-tie themselves and your check is still in the mail. So the excited electrons soon drop back to lower levels; in the process, they spontaneously shed the surplus energy in the form of photons, the smallest individual units, or quanta, of light. The size of the drop determines the wavelength of the emitted photon. That's how light emerges from a flickering campfire, the surface of the sun, the bulb in a lamp or the screen of your TV.
If you google LASER, you will get 126 MILLION hits. The uses of LASERS are simply amazing and it all comes down to electrons and photons.