| quotient of the speed of light in vacuum and the speed of light in a medium
Note 1 to entry: The value of the refractive index can depend on the frequency, polarization, and direction.
Note 2 to entry: The refractive index is expressed by n = c0/c, where c0 is the speed of light in vacuum and c is the speed of light in the medium.
Note 3 to entry: See also "complex refractive index.
Note 4 to entry: The refractivity is expressed by n − 1, where n is refractive index.
Note 5 to entry: The refractive index has unit one.
Note 6 to entry: This entry was numbered 845-04-101 in IEC 60050-845:1987.