Brightness enhancement film with improved view angle

Abstract

A structural shape on the surface of an optical substrate is such that the brightness of diffuse light departing from the surface of the optical substrate at certain off axis angles is reduced, at the expense of a small reduction in peak brightness measured near the viewing axis. The net result is an overall increase in useful illumination. A cross section of a prism as the structural shape has a curved sidewall or facet. A material with a relatively high index of refraction combined with a prismatic structure having a modified prism geometry improves brightness.

1 . An optical substrate comprising: 
 a surface comprising a prism structure characterized by a cross section having a plurality of facets described by linear segments approximating a polynomial, wherein adjacent ones of the linear segments intersect at one side of a centerline of the prism, and    wherein a peak angle of the prism structure is greater than 100 degrees and less than 105 degrees, and the refractive index of the substrate is between approximately 1.65 and 1.8.    
     
     
         2 . The optical substrate as set forth in  claim 1 , wherein the prism structure comprises a plurality of prisms having a prescribed peak angle, α, a height, h, a length, 1, and a pitch, p.  
     
     
         3 . The optical substrate as set forth in  claim 2 , wherein the plurality of prisms include at least a pseudorandom peak angle, α, height, h, length, 1, and pitch, p.  
     
     
         4 . The optical substrate as set forth in  claim 1 , wherein the prism structure is an ultraviolet curable organic or inorganic material.  
     
     
         5 . A backlight display device comprising: 
 an optical source for generating light;    a light guide for guiding the light therealong including a reflective device positioned along the light guide for reflecting the light out of the light guide;    an optical substrate receptive of the light from the reflective device, the optical substrate comprising:    a surface comprising a prism structure characterized by a cross section having a plurality of facets described by linear segments approximating a polynomial, wherein adjacent ones of the linear segments intersect at one side of a centerline of the prism, and wherein a peak angle of the prism structure is greater than 100 degrees and less than 105 degrees, and the refractive index of the substrate is between approximately 1.65 and 1.8.    
     
     
         6 . The backlight display device as set forth in  claim 5 , wherein the prism structure comprises a plurality of prisms having a prescribed peak angle, α, a height, h, a length, 1, and a pitch, p.  
     
     
         7 . The backlight display device as set forth in  claim 6 , wherein the plurality of prisms include at least a pseudorandom peak angle, a, height, h, length, 1, and pitch, p.  
     
     
         8 . The backlight display device as set forth in  claim 5 , wherein the prism structure is an ultraviolet curable organic or inorganic material.  
     
     
         9 . A backlight display device comprising: 
 an optical source for generating light;    a light guide for guiding the light therealong including a reflective device positioned along the light guide for reflecting the light out of the light guide;    an optical substrate receptive of the light from the reflective device, the optical substrate comprising:    a surface comprising a prism structure characterized by a cross section having a plurality of facets including a first facet oriented at a first angle with respect to the surface of the prism and a second facet oriented at a second angle with respect to the surface of the prism, wherein the first and second facets intersect at one side of a centerline of the prism and the first and second angles are different, and wherein a peak angle of the prism structure is greater than 100 degrees and less than 105 degrees, and the refractive index of the substrate is between approximately 1.65 and 1.8.    
     
     
         10 . The backlight display device as set forth in  claim 9 , wherein the prism structure comprises a plurality of prisms having a prescribed peak angle, α, a height, h, a length, 1, and a pitch, p.  
     
     
         11 . The backlight display device as set forth in  claim 10 , wherein the plurality of prisms include at least a pseudorandom peak angle, a, height, h, length, 1, and pitch, p.  
     
     
         12 . The backlight display device as set forth in  claim 9 , wherein the prism structure is an ultraviolet curable organic or inorganic material.