Abstract:
A discontinuity-containing, light-diffusing substrate is placed within an LED light source. In one embodiment, the substrate is placed between an LED light source and a light guide. The light diffusing substrate may include a plurality of air bubbles, grooves or both, effective to mix the colored light and yield a white light exiting the light guide. Methods of constructing optical devices and light sources having a bubble-containing substrate are also disclosed.

Description:
TECHNICAL FIELD 
     The invention relates to a light source and more particularly to a light-emitting diode light source in association with a discontinuity diffusant to improve light mixing. 
     BACKGROUND OF THE INVENTION 
     Light emitting diodes (LEDs) generally emit light in a specific color or range of wavelengths. To produce a white light, it is usually necessary to combine or mix the light from multiple LEDs which emit different colors, for example, red, green and blue. Initially, light mixing was accomplished by placing LEDs of different colors next to each other such that the light emitted by each LED would mix with the light from the others. A common structure associated with such mixing is a light guide. This approach has several drawbacks including poor color mixing, uneven light intensity, and the presence of dark regions near the edges of the light guide plate. 
     Several techniques exist to improve the light mixing needed to produce white light. One is the insertion of LEDs in a mixing cavity within the light guide. Another is the use of a light diffusant layer to mix the colors. However, known light diffusant layers significantly reduce output of the light sources. While these techniques have resulted in slightly better color mixing, there remains a need for further improvement. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to systems and methods for producing a well-mixed white light from a plurality of colored light sources. A white light source is constructed by combining a plurality of colored light sources with a light discontinuity diffusant layer. In one embodiment, the discontinuity can be an air bubble. The bubble-containing diffusant allows for effective mixing of the light generated by the light sources contained within the light source. In one embodiment, a light source is arranged with light sources, each of which emit light of a different color, and one or more encapsulating layers, including a bubble-containing layer. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  is a cross-sectional view of an embodiment of the present invention; 
         FIG. 2  is an exploded cross-sectional view of an alternate embodiment of the present invention; 
         FIG. 3  shows a flow chart of a manufacturing process; and 
         FIG. 4  is a is a cross-sectional view of a prior art light source. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A brief discussion of a prior art light source may be useful.  FIG. 4  shows an embodiment  40  of a prior art light source having a plurality of differently colored LED dice  41  arranged on light source body  42 . Light source  40  utilizes multiple colored LED dice  41  to create white light. Encapsulant  44  may be used to protect LED dice  40 . LED dice  40  may include LED dice for producing red, green, and blue light. Light guide  46  having walls  47  for controlling light emission is coupled to body  42  and receives light emitted from LED dice  40 . Insufficient light mixing may result in a nonuniform colored light. Colored blotches may appear (shown by broken lines) at the base of light guide  46  as a result of insufficient light mixing. These colored blotches or hot spots typically reduce the quality of light produced by the LED light source. 
       FIG. 1  shows a cross-sectional view of one embodiment  10  of a light source having an array of LED dice  11  arranged on light source body  12 . LED dice  11  may be arranged in a particular pattern and produce various colored light. In the embodiment shown, a generally transparent first encapsulant layer  14  is provided directly upon LED dice  11 . A light diffusing element  15  is embodied as a second encapsulant layer provided over first encapsulant layer  14 . Second encapsulant layer  15  includes a generally transparent substrate  16  containing a plurality of air bubbles  17 . Bubbles  17  are, in effect, discontinuities between one medium and another which serve to diffuse the light, resulting in a better mix of the colors. Light guide  18  is connected to body  12  and receives light emitted from LED dice  11 . Bubbles  17  of second encapsulant layer  15  effectively diffuse light from dice  11  to yield a white light source with improved uniformity. In another embodiment of the invention (not shown), first and second encapsulant layers  14 ,  15  can be combined into a single encapsulant layer having a plurality of air bubbles contained therein. 
       FIG. 2  shows an exploded cross-sectional view of another light source embodiment  20  having grooved substrate  21 . In the embodiment shown, grooves  22  are defined upon a surface of substrate  20 . With substrate  20  overlaid upon first encapsulant layer  14 , grooves  22  create medium discontinuities, here embodied as air gaps, which diffuse and redirect light emitted from LED dice  11 . Grooves  22  may be considered elongated bubble elements and may be closed at ends of substrate  20 . 
     In operation, LED dice  11  ( FIG. 1 ) produces colored lights, typically red, green and/or blue which are used to create a white light for communication into light guide  18 . Discontinuities, such as air bubbles  17  or grooves  22 , effectively diffuse colored light emanating from LED dice  11  prior to introduction into light guide  18 . Consequently, embodiments of the present invention can produce a well-mixed white light, preferably devoid of color blotches. 
       FIG. 3  shows a manufacturing process flow chart  30  in accordance with an embodiment of the invention. In an initial step  31 , LED dice are arranged on a body in a pattern which enhances color mixing and minimizes heat build up. At step  32 , the first encapsulant layer is placed over the LED dice. The first encapsulant layer is of clear resin, epoxy or silicon material. The first encapsulant layer may be a curable liquid resin which flows into intimate contact with individual LEDs and which is subsequently hardened. At step  33 , a second encapsulant layer containing discontinuities (such as bubbles) is placed over the first encapsulant layer. The second encapsulant layer may be a sheet laminate which overlays the first encapsulant layer. The sheet laminate may be a cured resin, such as an epoxy or silicone. At step  34 , the body is connected at a light entry edge of the light guide. 
     In another embodiment, the second encapsulant layer may be manufactured by introducing water into a laminate resin. The resin may then be cured at appropriate temperatures and pressures to create and/or maintain water and/or air bubbles within the cured resin. An alternative method of creating the second encapsulant layer may include vigorously stirring a resin to entrain air bubbles, forming the resin into a sheet form, and quickly curing the sheet, for example, in a heated vacuum chamber. Bubbles within the encapsulant layer may be generally spherical or may assume alternative configurations or shapes. The bubbles need not necessarily be air bubbles, but may be defined by other fluids, for example by introduction of bubble-generating fluids within the second encapsulant layer. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter,