Retroreflection device

A retroreflective device in which a large number of complex cube-corner retroreflective elements are arranged in closest-packed state, each of said complex cube-corner retroreflective elements having a first and second triangular-pyramidal retroreflective units and at least one tetrahedral retroreflective unit, characterized in that

• the three reflective lateral faces (a1, b1, c1 and a2, b2, c2) of each of the first and second triangular-pyramidal retroreflective units form mutually perpendicular cube-corner reflective surfaces, respectively,
• the first reflective lateral face (f11), the second reflective lateral face (e11) and the third reflective lateral face (g11) of said at least one tetrahedral retroreflective unit form a mutually perpendicular cube-corner reflective surfaces,
• said first reflective lateral face (a1) of the first triangular-pyramidal retroreflective unit is on the same plane with the first lateral face (f11) of said tetrahedral retroreflective unit,
• said second reflective lateral face (b1) of the first triangular-pyramidal retroreflective unit is on the same plane with the second lateral face (e11) of said tetrahedral retroreflective unit,
• said complex cube-corner retroreflective element has a quadrangular circumference defined by mutually parallel y-lines and mutually parallel z-lines,
• said complex cube-corner retroreflective element has a substantially symmetrical V-shaped groove with its center line x-x′ passing through the points of intersection of said parallel y-lines and parallel z-lines,
• the third reflective lateral face (c1) of said first triangular-pyramidal retroreflective unit is parallel to one of the two lateral faces (g11) forming said V-shaped groove,
• the third reflective lateral face (c2) of said second triangular-pyramidal retroreflective unit is identical with, or parallel to, the other (g21) of the two faces forming said V-shaped groove, and
• the third reflective lateral face (g11) of said tetrahedral retroreflective unit is same as one of the two faces forming said V-shaped groove.