When light is incident upon the interface between two dielectric media with different refraction coefficients, there is refraction and reflection at the interface. If the indices of refraction are equal, the light "passes through" without reflection, and all of the light is transmitted.
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When n(1) is greater than n(2), the angle of refraction is always smaller than the angle of incidence. Alternatively, when n(2) is greater than n(1) the angle of refraction is always greater than the angle of incidence. When the two refractive indices are equal (n(1) = n(2)), then the light is passed through without refraction.
https://micro.magnet.fsu.edu/optics/lightandcolor/refraction...