The speed of an
electromagnetic wave in
free space, precisely 299,792,458 m/s.
Note 1: The preceding figure is precise because by international agreement the meter is now defined in terms of the speed of
light.
Note 2: The speed of an electromagnetic wave,
e.g. , light, is equal to the product of the
wavelength and the
frequency.
Note 3: In any physical
medium, the speed of light is lower than in free space. Since the frequency is not changed, the wavelength is also decreased. [After
FAA]