Retroreflectance

Retroreflectance is a phenomenon where light is reflected directly back towards the source, regardless of the angle of incidence. This is distinct from diffuse reflection, where light scatters in many directions, or specular reflection, where light reflects at an angle equal to the angle of incidence. The most common examples of retroreflective materials are those found on safety vests, road signs, and bicycle reflectors. These materials are designed to efficiently return incident light to the observer, making them highly visible in low-light conditions when illuminated by a light source.

The principle behind retroreflectance often involves a specific geometric arrangement of reflective elements. One common design uses a series of small, precisely oriented corner cubes or prisms. Each of these elements reflects light back in three perpendicular directions. When arranged in a material, they collectively send a significant portion of the incoming light back to its origin. Another method employs a layer of tiny glass beads. These beads act as miniature lenses and reflectors, focusing light onto a reflective backing and then directing it back along the path from which it came. The effectiveness of a retroreflective material is measured by its retroreflective coefficient, which quantifies the amount of light returned to the source. This property is crucial for safety applications where increased visibility is paramount.