In a retroreflector the wavefront of the radiation is reflected straight back to the
wave's source.
This works at a wide range of angle of incidence, unlike a planar mirror, which does this only if the mirror is
exactly perpendicular to the wave front, having a zero angle of incidence. Being directed, the retroflector's reflection isbrighter than that of a diffuse reflector. Corner reflectors, and cat eye reflectors are the most used kinds.