Observations and theoretical principles indicate that electromagnetic waves, including light, propagate more slowly in dielectric media than in a vacuum. This behavior is elegantly described by Maxwell's equations, which account for material‐specific permittivity and permeability. According to the principle of superposition, the net electromagnetic wave within a dielectric medium results from the combination of the incident wave and secondary waves generated by the medium's interaction with the incident wave. Notably, both the incident wave and the secondary waves propagate at the speed of light in a vacuum. The Ewald‐Oseen extinction theorem explains that secondary waves, emitted by atoms in the dielectric medium, interfere with the incident wave in such a way that they cancel the original wave and produce a resultant wave propagating at a reduced speed determined by the dielectric constant of the medium. In this paper, we extend the application of the Ewald‐Oseen theorem to electromagnetic wave propagation in transmission lines and demonstrate that the principles used to model lightning return strokes align closely with those predicted by the theorem.