Patent Publication Number: US-2011068354-A1

Title: High power LED lighting device using high extraction efficiency photon guiding structure

Description:
The application is related to an expired provisional application with the application number of U.S. 61/131,563 filed on Jun. 10, 2008. 
    
    
     BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The invention relates to high power light emitting diode device using high extraction efficiency photon guiding structure for producing high-efficiency white light output with large viewing angle and large amount of light emitted from the side surfaces so that they can provide different light patterns for different applications such as street lighting, parking lighting, tunnel lighting, and etc., as they are used with a reflector. 
     2. Background Art 
     Light emitting diodes (LEDs) can emit different colors of light. For producing white light, various colors can be combined. The common way for producing white LED (WLED) light is to use phosphor materials that absorb blue LED-emanated light and emit yellow or greenish yellow light. With an increase in the adoption of WLEDs into different lighting applications such as home lighting, industrial lighting, office lighting, tunnel light, and street lighting that require high power, low power WLED is not appropriate since low power LEDs for these applications can increase manufacturing cost associated with equipment investment and assembly cost. Therefore, high power LED packages are required. 
     In conventional phosphor-based high power WLED packages, light is often trapped inside the package, resulting in a low efficiency and lifetime. The conventional WLED package usually uses a hemispherical lens structure to improve light extraction and efficiency. This hemispherical lens or convex lens is appropriate for relatively low power package that has small size but it is not appropriate for high power or large emitting area package, especially extreme high power package. This structure still does not achieve maximum extractable level, increases material cost, and is bulky to use this structure in high power or large emitting area package. Moreover, this hemispherical lens or convex lens for extreme high power LED package results in reliability problem. Therefore, high power or large emitting area package usually has a low-extraction flat surface of encapsulant dispensed in a recess region of a reflection cup as an extraction structure. 
     Another issue with conventional high power WLED packages is angular light distribution. The conventional high power WLED package usually has emitted light concentrating within low viewing angle or a small solid angle. It is thus difficult to control light pattern and to provide wide view angle with uniform intensity distribution for foregoing applications. 
     SUMMARY OF THE INVENTION 
     The present invention is to provide an LED lighting device for providing white light with high efficiency, high uniform color/CCT distribution in space, and large viewing angle so that it can be used with a reflector to control light pattern for different applications such as street lighting, parking lighting, and tunnel lighting. The LED light device includes a substrate, a supporting structure, encapsulation layer, photon-extraction structure, and a plurality of LED chips forming at least one array of linear LED chips. Blue light emanated from LED chips is partially absorbed by phosphor materials followed by emission of orange and/or red light, and/or greenish-yellow light by phosphor materials. The phosphor materials emitting different color types of light can form each individual layer with the layer closer to the LED chips containing phosphor particles that emit light at a longer wavelength of light such as red light and orange light. 
     Emitted light is not only emitted from the top surface of the optical structure but also on the side surfaces of the optical structure, resulting in more light emitted in high viewing angle. 
     The top surface of the optical part of the device can be a curved surface to direct more light to the side surfaces, resulting in emitted light with large viewing angle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an LED of the invention 
         FIG. 2  is a cross-section view of a lead-frame as an example of lead-frame for this invention 
         FIG. 3  is a cross-section view of a LED device as an example of the LED device described in this invention 
         FIG. 4  is a schematic drawing of a cross-section view of the photon-extraction structure with multilayer of phosphors 
         FIG. 5  is a cross-section view of a LED device as an example of the LED device described in an alternative embodiment of the invention 
         FIG. 6 : a schematic drawing of top encapsulation or cover lens as an alternative embodiment of the LED packages shown in  FIGS. 3 and 5   
         FIG. 7 : angular intensity distribution of light output from a conventional extreme power (100 W) LED packages (dash line) and the 100 W LED package of the invention (solid line) 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention discloses a lighting device with a high extraction efficiency photon guiding structure for generating white light with wide viewing angle that can be used with conventional fixture to generate light pattern that can be used in various application such as street lighting, parking lighting, tunnel lighting, and etc. With high amount of light emitted from the side, the light emitted from the LED device of the invention can be easily directed to desired direction by using conventional lighting fixture or reflector. 
       FIG. 1  shows a perspective view of an LED device using high extraction efficiency photon guiding structure.  FIG. 2  shows cross-section views of lead-frame  10  shown in  FIG. 1 . The LED lead-frame consists of a substrate  11 , and a supportive structure  12  that is used to hold the substrate  11  and lead-frame  13  together and electrically insulates them. The substrate  11  can be made of high thermal conductive materials such as copper, aluminum, ceramics, and etc. The supportive structure  12  can be made of dielectric materials such as PPA, silicone, epoxy, and etc. It is preferred that the exposed surface of the supportive structure  12  and chip-bonding area  17  are coated with high reflectivity materials such as silver, aluminum, and metal alloys. There are two reflective cups  14  and  15  with its exposed surface forming titled angles of equal or larger than 90 degree with horizontal or substrate surface. The titled angles are used to facilitate light extraction from the LED device. 
       FIG. 3  shows a cross-sectional view of the LED device shown in  FIG. 1 . The LED device is made by attaching LED chips  16  onto chip-bonding area  17 . The LED chips  16  forming arrays of linear LED chips and are electrically connected to each other by pad-to-pad connection through gold wires  18 . After LED chips are bonded to the substrate and electrically connected, encapsulation layer  19  is dispensed into the cups following by attaching a photon-guiding structure  20 . 
     The encapsulation layer  19  is made of transparent materials such as silicone and contains one or more wavelength conversion materials such as green, yellow, orange, and red phosphors. The photon-guiding structure  20  is made of transparent materials such as silicone or PMMA or glass and may contain wavelength conversion materials such as green, yellow, orange, and red phosphors. 
     Phosphor materials can be blended together and mixed with materials using for making the encapsulation layer  19  and/or the photon-guiding structure  20 . The phosphors can be YAG, TAG, silicate based phosphor, etc. For the package using more than one wavelength conversion material, the encapsulation layer  19  contains three phosphor materials in which red, orange, and green-yellow phosphors are embedded in the red, orange, and green-yellow phosphor encapsulation regions, respectively, as shown in  FIG. 4 . The red phosphor encapsulant is coated on the surface containing LED chips and partially covers LED chips, while the orange phosphor encapsulant resides on top of the red phosphor encapsulant and the green-yellow phosphor encapsulant resides on top of the orange phosphor encapsulant and fully covers LED chips. By this way, double conversion lass by phosphor can be reduced and backwardly phosphor-emitted green and/or yellow light can excite orange or red phosphors. Thus, absorption loss of backwardly emitted light by phosphor can be reduced and the efficiency of the lighting device can be enhanced. This structure also improves efficiency of the device because orange and red phosphor can be excited by back scattered blue, green and yellow light, or backwardly emitted green and yellow light, and emit orange or red light. It thus reduces the absorption loss of backward phosphor-emitted and scattered blue, green and yellow light. 
     Alternatively, red and orange phosphors are blended together to form red-orange phosphor mixture. 
       FIG. 5  is a schematic drawing of a light device as another example of an alternative of embodiment of the invention. The LED device shown in  FIG. 5  has a supporting structure  22  that is made of transparent materials such as silicone, glass, or PMMA. The supporting structure  22  can be clear or contain phosphor materials and/or fused silica or fused titanium dioxide. The photon-extraction structure  21  is formed by dispensing silicon containing phosphor materials and fuse silica or fused titanium dioxide into the recess of the supporting structure  22 . 
     In order to provide large viewing angle, more light is directed to the side surfaces followed by the emission of light from the side surfaces. To increase emission of light at the side surfaces, a curvature is introduced to the top surface of the encapsulation layer or lens.  FIG. 6  shows the alternative photon-guiding structure  20  shown in  FIG. 1  and  FIG. 2 . The top surface of the photon-guiding structure can be a curved surface in one direction or in two directions as shown in  FIG. 6 . With these structures, there is more light directed to the side surfaces and emitted to the ambient through these side surfaces. 
     The use of photon-guiding structure  20  increases the efficiency of WLED package, especially when it is compared with a conventional extreme high power package. Four 100-watt WLED samples, two samples of the conventional WLED and two samples of the WLED package of the invention, were made. The WLED packages of the invention provide the average neutral white light lumen output of 9412 lm while the conventional WLED packages provide the average neutral white light lumen output of only 8002 lm. 
     The photon-guiding structure  20  not only improves the efficiency but also provides light output with large viewing angle that is suitable for generating different pattern of light distribution for different applications such as street lighting, parking lighting, and tunnel lighting when a simple reflector is incorporated with.  FIG. 7  shows angular light intensity distribution of light emitted from a conventional extreme high power (100 W) LED package (dash line) and the 100 W LED package of the invention. The light output of the conventional package has a cosine distribution while that of the invented LED package has a butterfly distribution which is more uniform on a flat surface and has a larger viewing angle. The invented LED package has more light emitted at large viewing angle than conventional LED package.