The present invention provides a composite light guiding plate comprising a light guiding layer comprising an incident face for receiving light from at least one light source, a light guiding output surface that is also generally orthogonal to the incident face, a featured surface, opposite the light-guiding output surface and generally orthogonal to the input face for redirecting light through the light guiding output surface. Further, the featured surface comprises a plurality of rows of linear prismatic structures extended in a length direction that is substantially perpendicular to the incident face and having height and width dimensions of 10 to 200 microns and wherein the length-to-width aspect ratio of the linear prismatic structures is greater than 100:1 the thickness of the light guiding layer is less than 1 mm. Further, the plate is formed from polymeric materials comprising polyesters, amorphous polyesters, polyarylates, polycarbonates, polyamides, polyether-amides, polyamide-imides, polyimides, polyetherimides, cyclic olefin polymers, impact-modified polymethacrylates, polyacrylates, polyacrylonitrile, polystyrenes, polyethers, cellulosics, sulfur-containing polymers and blends or alloys of two or more polymers or copolymers thereof. Additionally, the plate comprises a light extraction layer comprising an input surface having a plurality of protruding light extraction features that have tips that are bonded to the light-guiding output surface of the light guiding layer and provide optical contact between the light guiding and light extraction layers and an illumination output surface for providing light output from the composite illumination plate. Further, the thickness of the light extraction layer is less than 1 mm and wherein one or more channels of air or other gas are sandwiched between the light guiding layer and the light extraction layer.