Multi-layer led-illuminated light redirecting structures

An LED-based illumination system comprising:

• a light source comprising a plurality of LEDs;
• and
• a layered optical sheet-form structure comprising:
• a first optically transmissive sheet having a first major surface, an opposing second major surface, a first edge, an opposing second edge extending parallel to the first edge, a third edge extending perpendicular to the first and second edges, and an opposing fourth edge extending parallel to the third edge,
• a plurality of parallel channels formed in at least the first major surface of the first optically transmissive sheet and longitudinally extending from the first edge to the second edge,
• a second optically transmissive sheet substantially coextensive in size with the first optically transmissive sheet and bonded to the first major surface using an optically transmissive adhesive material so as to at least partially encapsulate the plurality of parallel channels,
• and an optically transmissive light diffusing sheet substantially coextensive in size with the first and second optically transmissive sheets,
• wherein the light source is configured to directly or indirectly illuminate the layered optical sheet-form structure at a range of incidence angles from 0 degrees to at least 75 degrees,
• wherein each of the parallel channels has a triangular cross-section and defines a pair of opposing planar walls disposed at an angle with respect to one another and configured to reflect light using total internal reflection, and
• wherein a surface of the second optically transmissive sheet facing away from the first optically transmissive sheet comprises a plurality of light deflecting microstructures.