Solid State Bidirectional Light Sheet for General Illumination

Abstract

A solid state light sheet and method of fabricating the sheet are disclosed. In one embodiment, bare LED chips have top and bottom electrodes, where the bottom electrode is a large reflective electrode. The bottom electrodes of an array of LEDs (e.g., 500 LEDs) are bonded to an array of electrodes formed on a flexible bottom substrate. Conductive traces are formed on the bottom substrate connected to the electrodes. A transparent top substrate having conductors is then laminated over the bottom substrate. Various ways to connect the LEDs in series are described along with many embodiments. The light sheets may be formed to emit light from opposite surfaces of the light sheet, enabling it to be used in a hanging fixture to illuminate the ceiling as well as the floor. The light sheet provides a practical substitute for a standard 2×4 foot fluorescent ceiling fixture.

1 - 18 . (canceled) 
     
     
         19 . A bidirectional lighting device comprising:
 a sheet comprising a first sheet surface and a second sheet surface;   a first base substrate comprising a first indented surface and a first base surface opposing the first indented surface, wherein the first base surface is adjacent to the first sheet surface and the first indented surface comprises a plurality of first indentations, the first indentations being spaced apart from one another;   a second base substrate comprising a second indented surface and a second base surface opposing the second indented surface, wherein the second base surface is adjacent to the second sheet surface such that the sheet is sandwiched between the first and second base substrates, and the second indented surface comprises a plurality of second indentations, the second indentations being spaced apart from one another;   a first substrate comprising a first light emitting surface and a first cover surface, the first cover surface of the first substrate being in contact with the first indented surface of the first base substrate between the spaced apart first indentations;   a plurality of first non-packaged light emitting diode (LED) dies being disposed between the first base substrate and the first substrate in respective first indentations such that during operation of the bidirectional lighting device a peak intensity of light emitted by the first non-packaged LED dies is output from the first light emitting surface in a first direction;   a plurality of first conductors configured to provide power to the first non-packaged LED dies, where the first non-packaged LED dies are connected to the first conductors without wires, and the first conductors are formed on the first indented surface of the first base substrate and on the first cover surface of the first substrate;   a second substrate comprising a second light emitting surface and a second cover surface, the second cover surface of the second substrate being in contact with the second indented surface of the second base substrate between the spaced apart second indentations;   a plurality of second non-packaged light emitting diode (LED) dies being disposed between the second base substrate and the second substrate in respective second indentations such that during operation of the bidirectional lighting device a peak intensity of light emitted by the second non-packaged LED dies is output from the second light emitting surface in a second direction different from the first direction; and   a plurality of second conductors configured to provide power to the second non-packaged LED dies, where the second non-packaged LED dies are connected to the second conductors without wires, and the second conductors are formed on the second indented surface of the second base substrate and on the second cover surface of the second substrate.   
     
     
         20 . The bidirectional lighting device of  claim 19 , wherein the first sheet surface and the second sheet surface are reflective. 
     
     
         21 . The bidirectional lighting device of  claim 19 , further comprising a plurality of tiles formed on the first and second substrates at locations corresponding to the first and second non-packaged LED dies, the tiles comprising a wavelength conversion material to convert light emitted by the first and second non-packaged LED dies. 
     
     
         22 . The bidirectional lighting device of  claim 19 , further comprising
 a plurality of tiles formed on the first substrate at locations corresponding to the first non-packaged LED dies, the tiles comprising a wavelength conversion material,   wherein the bidirectional lighting device outputs white light in the first direction through the plurality of tiles, and unconverted light emitted by the second non-packaged LED dies in the second direction through the second light emitting surface.   
     
     
         23 . The bidirectional lighting device of  claim 22 , where the unconverted light emitted by the second non-packaged LED dies is blue. 
     
     
         24 . The bidirectional lighting device of  claim 22 , where the unconverted light emitted by the second non-packaged LED dies is UV. 
     
     
         25 . The bidirectional lighting device of  claim 19 , where a light level output by the bidirectional lighting device from the first light emitting surface is modulated differently from another light level output by the bidirectional lighting device from the second light emitting surface. 
     
     
         26 . The bidirectional lighting device of  claim 19 , wherein the bidirectional lighting device is suspended from a ceiling so that the second light emitting surface faces the ceiling and the first light emitting surface faces away from the ceiling. 
     
     
         27 . The bidirectional lighting device of  claim 19 , wherein the first non-packaged LED dies are connected in series by the plurality of first conductors and the second non-packaged LED dies are connected in series by the plurality of second conductors.