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Retroreflectors reflect light back to its source and can be made of glass, mirrors, paint, tape, or arrays. They have many road and non-road applications, including lunar missions and boat safety. Corner cube retroreflectors are commonly used on highways.
A retroreflector reflects incoming light back to its source. The light is reflected parallel to the direction from which it comes, but in a completely opposite direction. Common types include the corner cube retroreflector, which can send light long distances and is useful on highways. Other common types are mirrors, paint, tape, and retroreflective arrays, such as those that have been placed on the moon or satellites. Retroreflection can be achieved with angled or spherical shaped elements, as well as with phase conjugation, an optical phenomenon that can precisely direct light in lasers and optical transmission lines.
Corner retroreflectors are most commonly made of clear optical glass. The light is completely reflected by the internal optics or by a coating on the external surface. Another type of this type of retroreflector has perpendicular mirrors that delimit an open space. These corner reflectors are sometimes used on roads, although spherical reflectors return the light at a slightly different angle. This prevents the bright headlights of other vehicles from shining into the driver’s eyes and blinding them.
There are many road applications for a reflector. Such devices can be embedded, so that they are flush with the road surface, or installed as raised devices. Those that are lifted are rarely seen in places where it snows, because the plows would tear them up. Retroreflective paint does not cause accelerated wear and tear on the road surface, as do embedded devices, although the paint is worn away by the weather and by passing vehicles.
On several lunar missions, an array of retroreflectors was placed aboard the equipment to track the lunar rotation and position, as well as to refute theories that such landings were hoaxes. Such devices were used on some Apollo and Russian missions. The laser beam retroreflector was, and still is, used for this purpose and can be monitored periodically using ground-based telescopes.
Reflective products are also used on boats, life rafts and other flotation systems. There are also reflectors used on clothing for some photographic applications and others used for sensing and disabling digital cameras. The glowing effect of the eye is an example of retroreflection, as the reflection of light from the lens, ocular fluid, and behind the retina causes an effect that any retroreflector provides, regardless of its type.
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