Abstract:
A planar LED lighting apparatus includes a housing and multiple LEDs. The housing includes a reflective body and a light output surface opposing the reflective body. The multiple LEDs are mounted on sidewalls of the housing, and light from the multiple LEDs is reflected by the reflective body to travel toward the light output surface.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a planar lighting apparatus, especially to a planar LED lighting apparatus. 
         [0003]    2. Description of the Related Art 
         [0004]    Lighting is important to our daily life, and after Edison invented the light bulb, we need lighting day and night. Current lighting assemblies mainly include incandescent light bulbs, fluorescent tubes, and compact fluorescent lamps. Compact fluorescent lamps are used to replace incandescent light bulbs to provide compatible luminance in same operation manner. Fluorescent tubes are popularly used in offices or public places of large area. 
         [0005]    As illustrated in  FIG. 1 , a housing  10  has four fluorescent tubes  20  inside. The fluorescent tube  20  emits light uniformly in all directions. To increase light traveling to a light output face at the bottom side of the housing  10 , three reflective bodies  12  are installed in the housing  10  with each of them placed between two adjacent ones of the four fluorescent tubes  20 . The light output face is equipped with an anti-dazzle grille  16  or a lampshade. 
         [0006]    For the present, environmental protection issues of power saving, low carbon consumption, and products without mercury are highly concerned, and LEDs (light emitting diodes) happen to meet the mentioned requirements. Besides, as LEDs are solid state devices, unlike traditional fluorescent tubes made of fragile glass, therefore they are far more convenient for transportation than traditional fluorescent tubes. In addition, LEDs have the advantages of small size and directional lighting, so they are suitable to be applied in lighting applications requiring small size or directional lighting, and are therefore becoming the main choice of next generation lighting in replacing traditional fluorescent tubes. 
         [0007]    Please refer to  FIG. 2 , which illustrates a cross sectional view of a prior art planar lighting apparatus using LEDs. The apparatus has a housing  10 , which includes a plurality of LEDs  22 , and an anti-dazzle grille  16  or a lampshade on a light output face. 
         [0008]    Although the small size of LEDs have the advantage of being capable of reducing the thickness of a lighting apparatus, however, the small size can also make the light intensity in a unit area so high as to result in a dazzling effect. To reduce the dazzling effect, one solution is to utilize a frosted lampshade to diffuse the light rays emitted from each LED. However, the intensity of output light will be attenuated accordingly. Besides, the light emitting efficiency of LEDs has been increasing per year as the manufacturing process keeps improving, and the increased light intensity has added challenges to the diffusion effect of the frosted lampshade. Under this circumstance, the frosted lampshade has to increase scattering effect to make the output light uniform, but this will further sacrifice the intensity of the output light. 
         [0009]    In view of the mentioned problems, the present invention proposes a planar LED lighting apparatus, which is not only capable of reducing the thickness of the lighting apparatus, but capable of using a less frosted lampshade, or even using no lampshade, to provide a uniform planar lighting. 
       SUMMARY OF THE INVENTION 
       [0010]    To attain the goals mentioned above, the present invention proposes a planar LED lighting apparatus, which includes a housing and multiple LEDs. 
         [0011]    The housing has a light output face, a reflective body, a first side wall, and a second side wall, wherein the reflective body is opposing the light output face, the first side wall and the second side wall are opposing each other and located between the light output face and the reflective body. 
         [0012]    The multiple LEDs are located on the first side wall and the second side wall, and light from the multiple LEDs is reflected by the reflective body to travel toward the light output face. 
         [0013]    In one embodiment, the reflective body has a first inclined surface for reflecting LED light from the first side wall, and a second inclined surface for reflecting LED light from the second side wall. 
         [0014]    In another embodiment, the reflective body has a first curved surface for reflecting LED light from the first side wall, and a second curved surface for reflecting LED light from the second side wall. 
         [0015]    The reflective body has a sufficient height for preventing LED light from traveling between the first side wall and the second side wall. 
         [0016]    Preferably, the mentioned planar LED lighting apparatus further includes a lampshade on the light output surface, and the lampshade can be a transparent lampshade, a frosted lampshade, or a lampshade having a specific optical structure. 
         [0017]    In still another embodiment, the housing further has a third side wall and a fourth side wall, opposing each other and located between the light output face and a second reflective body. 
         [0018]    The mentioned planar LED lighting apparatus further has a third set of LEDs installed on the third side wall and a fourth set of LEDs installed on the fourth side wall. 
         [0019]    In one embodiment, the shape of the reflective body is a reversed pyramid. 
         [0020]    In another embodiment, the shape of the reflective body is a reversed pyramid having four curved surfaces for reflecting light. 
         [0021]    To make it easier for our examiner to understand the objective of the invention, its structure, innovative features, and performance, we use preferred embodiments together with the accompanying drawings for the detailed description of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  illustrates a cross sectional view of a prior art planar lighting apparatus using fluorescent tubes. 
           [0023]      FIG. 2  illustrates a cross sectional view of a prior art planar lighting apparatus using LEDs. 
           [0024]      FIG. 3  illustrates a cross sectional view of a planar lighting apparatus using LEDs according to a preferred embodiment of the present invention. 
           [0025]      FIG. 4  illustrates a cross sectional view of a planar lighting apparatus using LEDs according to another preferred embodiment of the present invention, wherein each of the side walls of a housing has an inclined surface. 
           [0026]      FIG. 5  illustrates a cross sectional view of a planar lighting apparatus using LEDs according to another preferred embodiment of the present invention, wherein a reflective body has a curved surface. 
           [0027]      FIG. 6  illustrates a cross sectional view of a planar lighting apparatus using LEDs according to another preferred embodiment of the present invention, wherein a reflective body has two different slopes on both sides. 
           [0028]      FIG. 7  illustrates a cross sectional view of a planar lighting apparatus using LEDs according to still another preferred embodiment of the present invention, wherein the planar lighting apparatus has two reflective bodies. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    The present invention mainly puts LEDs on the sides or side walls of a housing, and designs a reflective body for reflecting the axial light from the LEDs to a light output face, and thereby provides a planar light source. The reflective body can also prevent LED light from traveling between two opposite sides of the housing. 
         [0030]    The reflective body basically is an extruding object, having a sufficient height for preventing LED light from traveling between two opposite sides, and providing an excellent reflection effect. The reflecting surface of the reflective body can be a plain surface, a multi-slope surface, or a curved surface, to reflect light from the LEDs to the light output surface. The present invention will be described in more detail hereinafter with reference to the accompanying drawings that show the preferred embodiments of the invention. 
         [0031]    Please refer to  FIG. 3 . A housing  110  has a side wall  114  and a reflective body  118 , and a lampshade  116  can be installed on a light output face of the housing  110 . Multiple LEDs  130  are mounted on the side wall  114 , and light from the LEDs  130  is reflected by the reflective body  118  and traveling to the light output face. 
         [0032]    The material of the housing  110  can be a metal to provide a supporting structure for the whole planar lighting source. 
         [0033]    The reflective body  118 , fixed on an inner surface of the housing  110 , is an extruding structure. In  FIG. 3 , the reflective body  118  has a first reflecting surface  1181  and a second reflecting surface  1182  for reflecting light from the LEDs  130 , wherein the first reflecting surface  1181  and the second reflecting surface  1182  are both of a plain shape, capable of providing a metallic reflecting surface or a scattering surface. The peak of the reflective body  118  is lower than the LEDs  130 , so that light of the LEDs  130  one side (left side, for example) can be prevented from reaching the other side (right side, for example). As can be seen in  FIG. 3 , a dash line is used to indicate the lowest level of the reflective body  118 , and all the LEDs  130  are located higher than the dash line. This arrangement can offer a superior lighting effect. The LEDs  130  can be of a multi-line structure, with the lowest line of the multi-line structure higher than the dash line. 
         [0034]    The lampshade  116  can be a transparent lampshade, a frosted lampshade, a lampshade with a striped pattern or a decorative pattern, or a lampshade with a specific optical structure. In one embodiment, the first reflecting surface  1181  and the second reflecting surface  1182  are metallic reflecting surfaces, and the lampshade  116  can be a frosted lampshade or a lampshade having a specific diffusion structure to diffuse LED light and produce a uniform light source. In another embodiment, the first reflecting surface  1181  and the second reflecting surface  1182  are scattering surfaces, and the lampshade  116  is preferably transparent. 
         [0035]    General LEDs have a light emitting angle or a light pattern determined by their packaging structures, and the light pattern has a central axis. To be applied to the present invention, the packaging structure of LEDs can be designed to provide a special light emitting angle. However, a more practical design, as illustrated in  FIG. 4 , is to install a supporter having an inclined surface  112  on the side wall  114  of the housing  110 , and mount the LEDs  130  on the inclined surface  112 . By this, LEDs of general packaging structures can be used in the present invention—no special request is made on the LEDs, making the supply of the LEDs much easier. The supporter can be constructed by a printed circuit board, an aluminum substrate, a ceramic substrate, or by bending the side wall  114  inward. 
         [0036]    In the present invention, the LEDs can be cool white light LEDs, or warm white light LEDs, or LEDs of a specific light wavelength, or a combination of LEDs of different light wavelengths. 
         [0037]    In another embodiment, the reflecting surface of the reflective body is a curved surface (instead of a plain surface). Please refer to  FIG. 5 , a reflective body  119  has a curved surface  1191  and a curved surface  1192 . Although, as illustrated in  FIG. 5 , both the curved surface  1191  and the curved surface  1192  are of concave shape, they can also be of convex shape. 
         [0038]    In the embodiments of  FIG. 3  and  FIG. 5 , two sets of LEDs are located on two opposite side walls. However, as the housing  110  is in fact of a rectangular shape having four side walls, all the four side walls can be used to mount LEDs to increase light intensity. When all the four side walls are mounted with LEDs, the structure of the reflective body can be of the shape of a reversed pyramid, and each face of the reversed pyramid can be a plain surface or a curved surface. 
         [0039]    In another embodiment, the reflecting surface of the reflective body can have different slopes. As illustrated in  FIG. 6 , a reflective body  120  has two inclined surfaces  1201  and  1202  of two different slopes. In this embodiment, the inclined surface  1201 , nearer to the LEDs  130  than the inclined surface  1202 , has a smaller slope than that of the inclined surface  1202 . However, it can also be designed in another way that the inclined surface  1201 , nearer to the LEDs  130  than the inclined surface  1202 , has a larger slope than that of the inclined surface  1202 . By using different slopes combinations, the lighting apparatus of the present invention can have different light patterns to meet different market requirements. 
         [0040]    In still another embodiment, more than one reflective body is used. Please refer to  FIG. 7 , which illustrates two reflective bodies  118 , and each of them is located between two sets of LEDs  130 . This kind of multiple reflective bodies design can provide a brighter light source. Each of the multiple reflective bodies can be designed to have a single inclined surface, multiple inclined surfaces, or a curved surface, etc. 
         [0041]    The present invention, using light reflection to provide a planar LED light source, can have more uniform light output than traditional designs do, and can be free of a frosted lampshade, which is for light diffusion, to reduce light attenuation. To reduce light attenuation caused by reflection, the present invention is preferably designed to have one time reflection. 
         [0042]    While the invention has been described by way of example and in terms of preferred embodiments, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures. 
         [0043]    In summation of the above description, the present invention herein enhances the performance than the conventional structure and further complies with the patent application requirements and is submitted to the Patent and Trademark Office for review and granting of the commensurate patent rights.