Reflection:

While a radiation travelling within a medium is incident on a medium of variant refractive index, the fraction of the radiation bounces back at an angle equivalent to the angle of incidence of the radiation. This is known as reflection of light. Greater the difference within refractive index the greater is the fraction of reflected radiation. The fraction of the reflected light is providing as below:

P_r/ P_o = (η₂  - η₁ )²/(η₂ + η₁ )²

Where P₀ and P_r are the radiant powers of the incident and reflected beams, correspondingly; η₁ and η₂   are the refractive indices of the two media. Figure displays the reflection and the refraction of radiation.

Figure: Diagrammatical representation of reflection and refraction