"refractive index" or index of refraction n of a substance (optical medium) is a dimensionless number that describes how light, or any other radiation, propagates through that medium.
$n = \frac{c_0}{c}$, where $c_0$ is the speed of light in vacuum, and $c$ is the speed of light in the medium.
Applicable units are those of quantitykind:RefractiveIndex
Brechzahl
Indeks biasan
Index lomu
Indice de refracție
Refractive Index
Współczynnik załamania
indice de réfraction
indice di rifrazione
kırılma indeksi
índice de refracción
índice refrativo
Показатель преломления
ضریب شکست
معامل الانكسار
अपवर्तनांक
屈折率
折射率
Brechungsindex