# speed of light (c)

The speed of light (c) is a primary physical constant for the propagation speed of light and electromagnetic waves.

The speed of light (c0) is exactly 299,792.458 km/s in a vacuum. In calculations, 300,000 km/s is used. In denser media such as metals or glass, this speed is reduced to the signal propagation time "c". This is calculated from the shortening factor, the Nominal Velocity of Propagation( NVP), which is multiplied by the speed of light.