The refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is "v" = "c"/"n", and similarly the wavelength in that medium is "λ" = "λ"0/"n", where "λ"0 is the wavelength of that light in vacuum. This implies that vacuum has a refractive index of 1, and that the frequency ("f" = "v"/"λ") of the wave is not affected by the refractive index. As a result, the perceived color of the refracted light to a human eye which depends on the frequency is not affected by the refraction or the refractive index of the medium.