Chapter 21 How to Make and Use Retroreflectors

A retroreflector is an optical device that returns an oncoming beam of light back to its source. It can be as simple as a tiny glass sphere or a type of prism formed from glass or plastic.

While ordinary flat mirrors also reflect light, the light isn’t reflected back to the source but off to the side at the same angle the beam arrived. Only if the light beam is perfectly perpendicular to the surface of a flat mirror does it act like a retroreflector.

Retroreflectors are so much a part of everyday life that typically they don’t attract much attention. But they attract plenty of attention while driving at night, when they seem to be almost everywhere. They’re incorporated into the taillights of ...

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