Antonym of refractive index Moving light has two indices that determine its exit angle when it comes into contact with a surface. In this sense we could, very far-fetchedly, consider antonyms refraction and reflection, and, in turn, refractive and reflection indices. The refractive index is the ratio of the speed of light in a vacuum to the same in another medium ( n=c/v ). In other words, it indicates the angle that the beam takes when penetrating the new medium. The reflection index, on the other hand, is the angle at which light bounces off a hard, polished surface. It determines the extent to which a light of a particular wavelength can penetrate the material before being absorbed. In a material with a low absorption coefficient, light is poorly absorbed, and if the material is thin enough, it will appear transparent at that wavelength (lamda). This absorption rate varies with L and gives rise to the colors of the objects. So we have the possibility of another antonym of the refractive index and it would be the coefficient of light absorption. This considering one as it moves andvitro as it is absorbed.