retroreflectors

Retroreflectors are devices or surface features that reflect light back toward its source with minimal angular deviation. They are designed to produce bright reflections when illuminated by approaching headlights, flash bulbs, or lasers, and to do so over a wide range of incident angles.

Most retroreflectors rely on a geometry that reverses the light’s path. The most common is the cube-corner (trihedral) reflector, formed by three mutually perpendicular planar facets that create a corner. Light entering the assembly is reflected by the faces and exits parallel to the incoming ray. Other types include cat’s-eye retroreflectors, which use a transparent sphere or lens with a reflective backing, and microprismatic or bead-based sheets that redirect light back toward the source via numerous small prisms or beads.

Applications are diverse. In road safety, retroreflective signs, delineators, and markings improve nighttime visibility for drivers and pedestrians. Safety garments and equipment use retroreflective tapes and films to increase conspicuity. In science and space, passive retroreflectors such as corner-cube arrays are placed on the Moon (for lunar laser ranging) and on satellites to enable precise distance measurements from Earth. Surveying and calibration targets also employ retroreflective materials.

Performance depends on geometry, material, cleanliness, and viewing geometry. Corner-cube reflectors provide near-ideal retroreflection over wide angles, while bead- and prism-based sheets offer high brightness at common incident angles but can vary with dirt or wear. Materials range from glass to durable polymers, chosen for weather resistance and longevity.