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Bicycle reflector

This animation shows how a bicycle reflector (or indeed any other multiple reflector) works. Bike reflectors are not plane. They are made of a large number of small tetrahedrons set together so that there are dips in between in the shape of a corner of a right angled cube. This is difficult to draw in 3D so we will look at the 2D version where a beam of light hits the corner of a square. Whatever angle the light beam hits the corners it will reflect back along its original path. (You can show this by dragging the small disc at the end of the ray using the mouse.) This means that it does not matter where the car headlights are if any light hits the reflector it will be reflected back towards the car and the cyclist will be seen no matter where they are.

© Keith Gibbs/John Bourne 2016