Backlight Using High-Powered Corner LED

Abstract

Various embodiments of corner-coupled backlights are described, where one or more LEDs are optically coupled to a truncated corner of a solid rectangular light guide backlight. In one embodiment, a high-power, white light LED is mounted in a small reflective cavity, which is then coupled to a flattened corner of the light guide. The reflective cavity provides a more uniform light distribution at a wide variety of angles to the face of the truncated corner to better distribute light throughout the entire light guide volume. This creates a more uniform light guide emission into the liquid crystal layers. In other embodiments, an LED is mounted in a small cavity near a corner of the light guide, and a reflector is mounted on the corner of the light guide. Various techniques for removing heat from the LED without adding additional area requirements are also disclosed.

1 . A light emitting device comprising:
 a light emitting diode (LED) die;   a reflective cavity housing the LED die, the cavity having an opening for light to exit, the opening having a cross-sectional area of at least 4 mm 2 ; and   a substantially rectangular light guide formed of a solid material having at least a first truncated corner, the truncated corner having a face, the light guide adapted for supplying light as a backlight;   the opening of the reflective cavity opposing the face of the truncated corner such that light exiting the opening of the reflective cavity is coupled into the light guide through the face of the corner,   where the LED die is at least 1 mm from the face of the truncated corner.   
     
     
         2 . The device of  claim 1  wherein an angle of a surface of the LED die to a far edge of the cavity opposing the face of the truncated corner is approximately 30-60 degrees. 
     
     
         3 . The device of  claim 1  wherein the opening of the cavity covers at least 75% of the face of the truncated corner. 
     
     
         4 . The device of  claim 1  wherein the opening of the cavity covers at least 90% of the face of the truncated corner. 
     
     
         5 . The device of  claim 1  wherein the LED die is at a distance d from the face of the truncated corner, and the truncated corner has a width of w, the LED die being a distance of at least d=w/5 from the face of the truncated corner. 
     
     
         6 . The device of  claim 1  wherein the LED die is at a distance d from the face of the truncated corner, and the truncated corner has a width of w, the LED die being a distance of at least d=w/3.5 from the face of the truncated corner. 
     
     
         7 . The device of  claim 1  wherein the LED die is at a distance d from the face of the truncated corner, and the truncated corner has a width of w, the LED die being a distance between w/2 and w/3.5 from the face of the truncated corner. 
     
     
         8 . The device of  claim 1  wherein the reflective cavity comprises a rectangular cavity. 
     
     
         9 . The device of  claim 1  wherein the reflective cavity comprises a rounded cavity. 
     
     
         10 . The device of  claim 1  wherein the reflective cavity comprises an elliptical cavity. 
     
     
         11 . The device of  claim 1  wherein the reflective cavity comprises a parabolic cavity. 
     
     
         12 . The device of  claim 1  wherein the LED die has a major surface facing the face of the truncated corner. 
     
     
         13 . The device of  claim 1  wherein the LED die has a side surface facing the face of the truncated corner. 
     
     
         14 . The device of  claim 1  wherein the LED is encapsulated by a lens. 
     
     
         15 . The device of  claim 1  wherein the face of the truncated corner is rounded. 
     
     
         16 . The device of  claim 1  wherein the face of the truncated corner is scalloped. 
     
     
         17 . The device of  claim 1  wherein the reflective cavity has reflective walls, wherein at least one wall extends over a surface of the light guide. 
     
     
         18 . The device of  claim 1  wherein the reflective cavity has reflective walls that taper towards the face of the truncated corner. 
     
     
         19 . The device of  claim 1  wherein the reflective cavity has walls that are specular. 
     
     
         20 . The device of  claim 1  wherein the reflective cavity has walls that are diffusing. 
     
     
         21 . The device of  claim 1  wherein the reflective cavity is substantially filled with an encapsulant. 
     
     
         22 . The device of  claim 1  wherein the reflective cavity has walls that provide a heat sink for the LED die. 
     
     
         23 . The device of  claim 22  wherein at least one wall of the reflective cavity extends over a portion of the light guide for conducting heat away from the LED die. 
     
     
         24 . The device of  claim 23  wherein the at least one wall of the reflective cavity that extends over a portion of the light guide acts as a reflector for reflecting light in the light guide towards an opposing surface of the light guide. 
     
     
         25 . The device of  claim 1  further comprising a heat conductive submount on which the LED die is mounted, the submount being thermally coupled to a back surface of the light guide. 
     
     
         26 . The device of  claim 1  further comprising a heat conductive submount on which the LED die is mounted, the submount being thermally coupled to a reflector on a back surface of the light guide. 
     
     
         27 . The device of  claim 1  further comprising liquid crystal layers overlying the light guide. 
     
     
         28 . The device of  claim 1  further comprising a phosphor in the reflective cavity for color conversion of light emitted by the LED die. 
     
     
         29 . The device of  claim 28  wherein the phosphor comprises at least one layer over the LED die for generating a white light into the light guide. 
     
     
         30 . The device of  claim 28  wherein the phosphor comprises a phosphor plate located closer to the face of the truncated corner than to the LED die for generating a white light into the light guide. 
     
     
         31 . The device of  claim 1  further comprising a diffuser between the LED die and the face of the truncated corner. 
     
     
         32 . The device of  claim 1  further comprising a plurality of LED dies in the reflective cavity. 
     
     
         33 . The device of  claim 32  wherein the LED dies comprise at least a blue LED die and an LED die that emits a different color. 
     
     
         34 . The device of  claim 32  further comprising an optical feedback sensor in the reflective cavity for detecting a color of light generated in the reflective cavity. 
     
     
         35 . A light emitting device comprising:
 a light emitting diode (LED) die;   a substantially rectangular light guide formed of a solid material having at least a first corner; and   the light guide having a cavity proximate to the first corner, the light guide adapted for supplying light as a backlight,   the LED die being mounted so as to emit light into the cavity formed in the light guide.   
     
     
         36 . The device of  claim 35  further comprising a side-emitting lens over the LED die such that light emitted from the lens is substantially directed toward a wall of the cavity. 
     
     
         37 . The device of  claim 35  further comprising a reflector around the first corner for reflecting light back into the light guide. 
     
     
         38 . The device of  claim 35  wherein the first corner is cusp shaped to redirect light. 
     
     
         39 . The device of  claim 35  further comprising a reflector over an end of the cavity to reflect light back into the cavity. 
     
     
         40 . The device of  claim 39  wherein the reflector is cone shaped. 
     
     
         41 . The device of  claim 39  wherein the reflector is cusp shaped. 
     
     
         42 . The device of  claim 39  wherein the reflector is patterned. 
     
     
         43 . The device of  claim 35  wherein the LED die is mounted within 15 mm from the first corner. 
     
     
         44 . The device of  claim 35  further comprising a phosphor in the cavity for color conversion of light emitted by the LED die. 
     
     
         45 . The device of  claim 35  further comprising additional LED dies in the light guide proximate to the first corner. 
     
     
         46 . The device of  claim 35  further comprising a heat conductive submount on which the LED die is mounted, the submount being thermally coupled to a back surface of the light guide. 
     
     
         47 . The device of  claim 35  further comprising a heat conductive submount on which the LED die is mounted, the submount being thermally coupled to a reflector on a back surface of the light guide. 
     
     
         48 . The device of  claim 35  further comprising liquid crystal layers overlying the light guide.