The speed of light in a vacuum is a physical constant used in many areas of science. It is represented most commonly by the letter "c". The value of the speed of light in 299 792 458 m/s. The speed of light is the maximum speed which all energy or matter can travel.
The speed of light is also the speed of gravity. Particles and waves travel at the speed of light regardless of there motion of the source or the inertial frame of reference of the observer. Light can go through transparent materials, such as glass or air.. The ration between the speed of light and the speed at which light travels through the transparent material is called the refractive index, n, of the material. The equation of for refrctive index is N = c/v.