Retroreflection helps the eye perceive light in low-light conditions. It occurs when light rays are returned in the direction from which they came.

A retroreflector is a device that sends light or other radiation back where it came from regardless of the angle of incidence, unlike a mirror, which does that only if the mirror is exactly perpendicular to the light beam. This effect can be commonly obtained in two ways:
with a set of three perpendicular mirrors which form a corner (a corner reflector or corner cube), and with a transparent sphere of material with refractive index 2.

A retroreflector may consist of many very small versions of these structures incorporated in a thin sheet or in paint. In the case of paint containing glass beads, the paint glues the beads to the surface where retroreflection is required, and the beads protrude, their diameter being about twice the thickness of the paint.

Retroreflection is used on road surfaces, road signs, vehicles and clothing (large parts of the surface of special safety clothing, less on regular coats). When the headlights of a car illuminate a retroflective surface, the reflected light is directed towards the car and its driver, and not wasted by going in all directions as with diffuse reflection. However, a pedestrian can see a retroreflective surface in the dark only if there is a light source directly between them and the reflector, e.g. a torch they carry, or directly behind them, e.g. a car approaching from behind.

Standards applicable:
- CIE Publication No. 54.2-2001
- DIN 67520
- EN 471 High-visibility Clothing
- ECE Regulations R 3, R 27, R 69, R 70, R 104 (at 10 m or 30.5 m measuring distance)
- SAE regulations J 594, J 774, J 943, J 2041 and similar regulations at 30.5 m distance
- DIN 5032, section 6 and 7

Retro-Reflectometer rms10
Measuring system designed to determine retro-reflectance values according to ECE as well as SAE regulations.

Online Retro-Reflectometer "Reflex Checker" rmm 10
for fast measurement of the characteristics of retroreflectors, especially for automotive applications and pavement marking.