Speed of light in matter

Description

The speed of light in vacuum is the speed at which all massless particles and changes of the associated fields (including electromagnetic radiation such as light and gravitational waves) travel in vacuum. The speed of light – as electromagnetic wave that propagates through the vacuum- is related to the electric constant and the magnetic constant. In a medium, light usually does not propagate at a speed equal to the speed of light in vacuum and is related to the permittivity and permmeability of the medium.