General purpose of this lecture is to present on Light Refraction and Lenses. Refraction fact 1: As light goes from one medium to another, the velocity changes! Refraction Fact 2: As light goes from one medium to another, the path changes! Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media.