Refraction use – bicycle reflectors

Wherever the bicycle rider is on the road, light will be reflected back to the car from the bicycle's rear reflector.

If the back of the bicycle had a mirror instead of a reflector then the car may not see the cyclist at all.

How this reflector works is by using total internal reflection.

Whatever the direction of light, the ray of light incident on the reflector is sent back in the same direction.

Light from the car headlamps hits the front of the red reflector at a small angle of incidence. The back of the red plastic is angled so that light hits this surface at a high angle of incidence greater than the critical angle. Total internal reflection occurs twice. All the light bounces back and is returned in the direction it came. No matter in which direction the light enters the red plastic, it will always return in the opposite direction. The car driver can therefore see the reflection of their own headlamps.