What is a photon in terms of EM waves?

[k9b4]

Is it one wavelength of EM wave? I have googled for this and I can't find an explanation for what a photon is in terms of EM waves.

 

[Orodruin]

This is a complicated issue. The photon is the smallest possible excitation of the quantized electromagnetic field. It really does not make much sense to think of it as a classical EM wave, because it is not. Classical EM fields are better described by coherent quantum states.

 

[Dale]

Is it one wavelength of EM wave? I have googled for this and I can't find an explanation for what a photon is in terms of EM waves.

It is most definitely not one wavelength of an EM wave.

Quantum electrodynamics (the theory of photons) is a more general theory than classical electrodynamics (the theory of EM waves). Thus, you can explain what classical EM waves are in terms of photons, but not the other way around.

There simply is no classical EM analog of a photon, but there is a quantum analog of a classical EM wave, the coherent state that Orodruin mentioned.