Back light unit for backlit displays
A BLU includes a 2D array of LEDs producing light with an angular distribution of nominally ±90 degrees around a center. A transparent solid material layer is positioned with a bottom surface over the 2D array of LEDs and configured to transform the light produced by the 2D array into light having an angular distribution of nominally less than ±90 degrees around the at a top surface of the transparent solid material layer. A diffuser film is positioned over the top surface of the transparent solid material layer configured to provide a FWHM of greater than 60 degrees and configured to diffuse the light produced at the top surface of the transparent solid material layer to produce diffused light at a top surface of the diffuser film. A BEF positioned over the top surface of the diffuser film and comprising a plurality of prism microstructures, where at least some prism microstructures have an apex angle of approximately ninety degrees. The BEF configured to narrow an angular optical distribution of the diffused light produced at the top surface of the diffuser film, thereby providing uniform and high brightness light output from the back light unit.
1 . A back light unit comprising:
a) a two-dimensional array of light emitting diodes (LEDs), at least one LED in the two-dimensional array generating light with an angular distribution of nominally ±90 degrees around a center of the at least one LED;
b) a diffuser film positioned adjacent to the two-dimensional array of LEDs in a direction of propagation of light generated by the two-dimensional array of LEDs and spaced apart from the two-dimensional array of LEDs with an air gap, the diffuser film configured to provide light with a full width at half max of greater than 60 degrees and configured to diffuse the light generated by the two-dimensional array of LEDs;
c) a brightness enhancement film positioned in a path of light generated by the two-dimensional array of LEDs, and comprising a plurality of prism microstructures on at least one surface, wherein at least some prism microstructures have an apex angle of approximately ninety degrees; and
d) a polarizer reflector film positioned in the path of light generated by the two-dimensional array of LEDs and configured to transmit one polarization and to reflect another polarization to improve uniformity of light output from the back light unit.
2 . The back light unit of claim 1 , further comprising a second diffuser film positioned in the path of light generated by the two-dimensional array of LEDs.
3 . The back light unit of claim 1 , further comprising a second brightness enhancement film positioned in the path of light generated by the two-dimensional array of LEDs.
4 . The back light unit of claim 3 , further comprising a second polarizer reflector film positioned in the path of light generated by the two-dimensional array of LEDs.
5 . The back light unit of claim 1 , further comprising a prismatic angle bend film positioned over the polarizer reflector film and configured to tilt a light distribution of the light output from the back light unit.
6 . The back light unit of claim 1 , further comprising an elliptical diffuser film positioned over the polarizer reflector film, the elliptical diffuser film being configured to broaden a light distribution of the light output from the back light unit in one direction.
7 . The back light unit of claim 1 , wherein the polarizer reflector film is positioned over the brightness enhancement film, the polarizer reflector film being configured to improve uniformity of the light output from the back light unit.
8 . The back light unit of claim 1 , wherein the brightness enhancement film comprises a pair of cross brightness enhancement films.
9 . The back light unit of claim 1 , further comprising at least one additional film positioned above the brightness enhancement films.
10 . The back light unit of claim 9 , wherein the at least one additional film is configured to further shape the light from the back light unit.
11 . The back light unit of claim 9 , wherein the at least one additional film is configured to redirect the light from the back light unit.
12 . The back light unit of claim 1 , wherein a number of rows in the two-dimensional array of LEDs is less than a number of columns in the two-dimensional array.
13 . The back light unit of claim 1 , wherein the two-dimensional array of LEDs comprises a row spacing of 8 mm and a column spacing of 8 mm.
14 . The back light unit of claim 1 , wherein the two-dimensional array of LEDs comprises ten rows and eight columns.
15 . The back light unit of claim 1 , wherein the two-dimensional array of LEDs comprises less than or equal to fifteen rows and greater than or equal to fifteen columns.
16 . The back light unit of claim 1 , wherein a number of rows in the two-dimensional array of LEDs is less than or equal to fifteen.
17 . The back light unit of claim 1 , wherein the two-dimensional array of LEDs comprises less than or equal to ten rows and greater than or equal to ten columns.
18 . The back light unit of claim 1 , wherein the diffuser film comprises the full width at half max of greater than 80 degrees.
19 . The back light unit of claim 1 , wherein the diffuser film comprises the full width at half max of greater than 100 degrees.