Importance

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Abstract

An optical sheet (25) for spreading light has a substantially smooth surface (27), and a structured surface (28) comprising an array of prisms (30, 31). A beam of light that is to be spread is directed through the film from the smooth surface. Some of the prisms (termed 'refraction prisms') deviate normally-incident light only by refraction at a prism facet as the light leaves the film while others (termed 'reflection prisms') deviates normally-incident light by total internal reflection within the prism before the light leaves the film. There are a plurality of reflection prisms (30) selected to deviate normally-incident light through different angles and a plurality of refraction prisms (31) selected to deviate the normally-incident light through different angles, and they are arranged, preferably in a non-ordered manner, so that successive reflection prisms are separated by at least one refraction prism. In alternative embodiments, the structured surface comprises a non-ordered arrangement of a plurality of reflection prisms selected to deviate normally-incident light through different angles, or a non-ordered arrangement of a plurality of refraction prisms selected to deviate normally-incident light through different angles.

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First Claim