  We want to study the influence of the quantum vacuum on the light
propagation. At first, by working in the standard linear quantum theory of the
electromagnetic fields, it is shown that the electric permittivity and the
magnetic permeability of the vacuum medium are changed; but, the resulting
speed of light isn't modified. Then, taking into account nonlinear effects by
considering the Euler-Heisenberg Lagrangian, the corresponding zero point
(vacuum) energy and the resulting modification of the speed of light are found
up to the first non-vanishing correction.
