Abstract: A light directing film and an optical system incorporating same are disclosed. The light directing film includes a first major surface and a microstructured second major surface. The microstructured second major surface has a periodic microstructured pattern. A plurality of extended microstructures form each period. The period is in the range from about 200 microns to about 400 microns. About 15 to 25 percent of the plurality of extended microstructures that form each period form a first group. A planar film that is placed adjacent the second major surface makes contact with substantially all the extended microstructures in the first group, but does not make contact with substantially all extended microstructures that are not in the first group.