Fresnel equations

Fresnel equations show how light is reflected or refracted when it travels from one material to another. They are used to explain how light behaves when it passes from air into a material like glass or water, or when it moves from one material to another like from glass to water.

Think about a pool of water. If you took a flashlight and shone it directly into the water, the light would bend and go in different directions because it's entering a different material. The Fresnel equations help us explain how this bending happens. The equations tell us the amount of light that will be reflected back off the surface of the water, and the amount of light that will pass through and into the water.