Fresnel lenses

A method of manufacturing a mould for producing a Fresnel lens optical film said method comprising rotating a mould blank, and forming a plurality of different prismatic features on said mould blank by repeatedly advancing a cutting tool onto and then withdrawing the tool away from a surface of the mould blank, wherein said prismatic features are arranged so that the mould is able to produce an optical film comprising a plurality of prismatic features together forming a Fresnel lens when the film is curved, said prismatic features being arranged into at least two segments, wherein the prismatic features in each segment all have a common apex angle, the common apex angle differing between adjacent segments.

An optical concentrator film comprising a plurality of prismatic features together forming a lens arrangement when the film is curved, said prismatic features being arranged into at least two segments, wherein the prismatic features in each segment all have a common apex angle, the common apex angle differing between adjacent segments.

An optical film comprising a plurality of prismatic features together forming a Fresnel lens when the film is curved, said prismatic features being arranged into at least two segments, wherein the prismatic features in each segment all have a common apex angle, the common apex angle differing between adjacent segments.