Patent ID: 8441735

Claim:
As an article of manufacture, an optical element comprising: a body having first and second opposed, substantially planar, major surfaces thereon, the first surface defining a light incident surface, the second surface defining a light output surface, the light output surface having a plurality of grooves formed therein, each groove having a mouth opening on the light output surface, the mouth having a predetermined width dimension “b” measured in the plane of the light output surface, each groove having opposed, substantially planar boundary walls that extend into the body and terminate therewithin at a closed apex, the closed apex having an included apex angle α, the optical element being improved in that it is operative to collect light incident upon the light incident surface thereof at an incident angle β up to a maximum operating angle β Max measured with respect to a normal to the incident surface and to convey that light to the light output surface without retro-reflection toward the incident surface, the improved optical element being characterized in that: the body is formed from a material having an index of refraction n C of at least 1.3 and an induced absorbance rate ΔAbs/Dose less than or equal to about 0.4, and wherein the angle α is defined in accordance with the relationship: α ≤ α Retro = 60 ⁢ ° - 2 3 ⁢ sin - 1 ⁡ ( sin ⁢ ⁢ β Max n C ) for any maximum operating angle β Max within the range from about 1°<β Max <90°.