Photon equation of motion with application to the Lamb shift

A photon equation of motion is proposed which is the scalar product of four-vectors and therefore a Lorentz invariant. A photon equation of motion captures the quantum nature of light but yet does not have the standard field-operator form, thereby making practical calculations easier to perform. The equation of motion proposed here is applied to the Lamb shift. No divergences exist, and the result agrees with the observed Lamb shift for the 1S1/2 state of hydrogen within experimental error.