When refracted light is bent back into the incident material, it's called total internal reflection.

Here's why:

* Refraction: Light bends as it passes from one medium to another (like air to water) because the speed of light changes in different mediums.

* Angle of incidence: The angle at which light strikes the surface is called the angle of incidence.

* Critical angle: There's a specific angle of incidence (called the critical angle) where the refracted light ray grazes along the boundary between the two mediums.

* Total internal reflection: If the angle of incidence is greater than the critical angle, the light ray cannot pass into the second medium and is instead reflected back into the first medium. This phenomenon is known as total internal reflection.

Let me know if you'd like a more detailed explanation or have any other questions!