Patent ID: 9063264
Filing Date: 2015-06-23
Classification: G02B,G02F

Abstract:
1. A backlight system having an optical axis, comprising: an extended area light guide having an output surface and a side surface; one or more light sources disposed to emit light into the light guide through the side surface, the light guide providing a first light distribution from the output surface, the first light distribution having a maximum luminance at a first polar angle relative to the optical axis; and a first and second prismatic recycling film, each having an input surface and an output surface, the first prismatic recycling film being disposed between the second prismatic recycling film and the light guide, the first and second recycling films being rotated azimuthally with respect to each other in a substantially crossed orientation, and the first and second prismatic recycling films providing a second light distribution from the output surface of the second recycling film; wherein light is specularly transmitted from the output surface of the light guide to the input surface of first recycling film; wherein the first prismatic recycling film comprises first prisms and the second prismatic recycling film comprises second prisms, the first and second prisms having refractive indices tailored to provide the second light distribution with a maximum luminance at a second polar angle relative to the optical axis, the second polar angle being no more than 10 degrees; wherein the first polar angle is at least 60 degrees; and wherein the first and second prisms have refractive indices at a wavelength of 550 nm in a range from 1.63 to 1.76.