NOVELTY - A Fresnel lens (100) comprises: a transparent substrate (110); and a structured polyurethane layer (120), where the structured polyurethane layer comprises: an at least partially cured reaction mixture where the reaction mixture comprises: a polyol; a polyisocyanate; a catalyst; and at least one UV stabilizer.    USE - The Fresnel lens is useful in an optical array, and in a solar power generation device (claimed).    ADVANTAGE - The Fresnel lens effectively converts a light beam from a point light source into a parallel beam of light, such as the lens used with a backlight in a liquid crystal display, or conversely to concentrate a parallel beam of light into a defined beam, such as a condensing lens used in a solar power generating system. Additionally, the Fresnel lenses can be used as light spreaders.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are:    (1) a method of preparing a Fresnel lens comprising: providing a transparent substrate with a first surface and a second surface; providing a curable reaction mixture comprising: a polyol; a polyisocyanate; a catalyst; and at least one UV stabilizer; providing a structuring tool; preparing a transparent substrate, curable reaction mixture laminate construction; treating the reaction mixture; and removing the structuring tool;    (2) an optical array comprising: a set of Fresnel lenses, where at least one Fresnel lens comprises: a transparent substrate; and a structured polyurethane layer, where the structured polyurethane layer comprises: an at least partially cured reaction mixture where the reaction mixture comprises: a polyol; a polyisocyanate; a catalyst; and at least one UV stabilizer; and    (3) a solar power generation device comprising: a Fresnel lens comprising: a transparent substrate; and a structured polyurethane layer, where the structured polyurethane layer comprises: an at least partially cured reaction mixture where the reaction mixture comprises: a polyol; a polyisocyanate; a catalyst; and at least one UV stabilizer; and a solar light convertor.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross sectional view of a Fresnel lens.    Fresnel lens (100)    Transparent substrate (110)    Structured polyurethane layer (120)