How Retroreflectors Really Work

Stephen R. Wilk

Retroreflectors, which reflect light from automobile headlamps back in the same direction from which the light originated, are invaluable safety devices. They are entirely passive, requiring no power supply or maintenance. They make street signs, lane dividers, bicyclists, joggers, and road crews highly visible. Although less than 100 years old, the devices are now ubiquitous and indispensable. Even so, most people do not know how they work, and those who think they do are probably wrong. Certainly the explanation I was given when I began my study of optics (and which I have heard from others as well) was demonstrably incorrect.

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