Cat's eye (road)

Cat eyes, Eng. cat's eyes are small cylindrical glass body diameter of about 10 to 20 mm with a curved, mirrored back and curved front. Much like the eyes of a cat or other nocturnal animals they reflect the light largely independent of their orientation back in the direction from which it comes. It thus is retroreflectors.

In German, it is often also called planar reflectors and retroreflectors on the principle of corner cube arrays cat eyes.

" True ," that is rotationally symmetric cat's eyes go back to an invention of the Irish Percy Shaw of 1934.

Design and function

Real " Cat's Eye " work with rotationally symmetrical glass bodies that are shaped much like the middle part of the eye and work equally. The back ( " retina " ) is coated and is located at the focal point of the front curved surface constituting a focusing lens. Front and back have the same center of curvature, so that the cat's eye works just when the light is incident at an angle (upper diagram).

Because of the spherical aberration of the light is not reflected for each incident angle exactly in the direction of incidence. The further out a light beam is incident, the larger the deviation. Only by such a deviation, the cat's eye (or any other reflector ) work at all, because if the light is to be thrown back exactly in the direction of incidence, then it goes back to the light source, but not in the eye of an observer.

It 's not a big " retina " area or not so great " point of view " just like a real eye required, therefore the missing to form a real eye edge areas can be eliminated.

Mode of action and application areas

Natural and artificial cat's eyes appear much brighter than diffusely reflecting body when illuminated from the direction of the viewer. Persons who consider such a scenery from a different angle, be able to recognize any special luminous effect of the cat's eye, because the light is reflected only in the direction of incidence. A cat's eye does not appear brighter than the surrounding area for an observer without its own light source.

Rotationally symmetrical " cat eyes " made ​​of glass are still used today in sublime road markings and site closures and in highway emergency telephones.

Only very old bikes have sometimes even such a " real" cat's eye as a reflector.