Abstract:
The invention relates to a direct backing type LED backlight apparatus which supplies a white light source by mixing monochromatic LEDs to a display device. The backlight apparatus includes a first LED row composed of red LEDs disposed adjacent to opposed peripheries of a substrate with green, blue and red LEDs alternately disposed between the red LEDs at the peripheries. The backlight apparatus also includes a second LED row having a similar arrangement of LEDs with blue LEDs disposed adjacent to the opposed peripheries. The backlight apparatus regulates the amount of radiation from the red and blue LEDs to be smaller than the amount of radiation from the rest of the LEDs. This allows elimination of color deflection at the peripheries of a light guide panel.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims the benefit of Korean Patent Application No. 2005-129039 filed on Dec. 23, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a light emitting diode (LED) backlight apparatus for supplying a white light source by mixing monochromatic LEDs to a display device. More particularly, the invention relates to an LED backlight apparatus which includes a first LED row and a second LED row alternating on a substrate. The first LED row includes red LEDs disposed adjacent to opposed peripheries of a substrate, with green, blue and red LEDs alternately disposed between the red LEDs adjacent to the peripheries. The second LED row includes a similar arrangement of LEDs with blue LEDs disposed adjacent to the opposed peripheries of the substrate. The backlight apparatus regulates the amount of radiation directly incident upward from a position of the red and blue LEDs adjacent to the opposed peripheries to be smaller than the amount of radiation from the rest of the LEDs, thereby eliminating color deflection occurring at the opposed peripheries of a light guide plate. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, a Lucid Crystal Display (LCD) does not have a light source of its own, thus requiring an external illumination which typically is a backlight apparatus. The backlight apparatus illuminates the LCD from the back using Cold Cathode Fluorescent Lamp (CCFL) and LED as a light source. 
         [0006]    An LED backlight apparatus using LED as a light source can be classified into an edge type and a direct illumination type. In the edge type, a light guide panel made of transparent material is disposed on a substrate, and light from LEDs disposed at one side or both sides of the light guide panel is incident into the light guide panel to be propagated upward by an optical pattern formed on a bottom of the light guide panel, thereby backlighting the LCD. On the other hand, in the direct illumination type, a plurality of LEDs are installed underneath the LCD to backlight the LCD. These two types have merits and demerits, respectively, but the direct illumination type is especially advantageous for backlighting a large area with high output. 
         [0007]      FIG. 1  is a schematic exploded perspective view illustrating a conventional LED backlight apparatus, and  FIG. 2  is a sectional view illustrating the LED backlight apparatus shown in  FIG. 1 . 
         [0008]    The conventional LED backlight apparatus  10  includes a substrate  12 , a plurality of LEDs  14 R,  14 G and  14 B disposed on the substrate, a side reflector  20  disposed in opposed peripheries of the substrate  14  and a planar optical element  30  disposed above the substrate  14 . An LCD  40  is disposed above the planar optical element  30 , and the light beams generated from the LEDs  14 R,  14 G and  14 B are mixed to form white light, which passes through the planar optical element  30  to provide backlight for the LCD  40 . In this specification, the planar optical element  30  designates any optical element including a diffusion plate (e.g. a microprism sheet) and an optical filter which processes the light beams emitted from the LEDs  14 R,  14 G and  14 B before they are incident onto the LCD  40  disposed above. 
         [0009]    The conventional LED backlight apparatus  10  has following disadvantages. As shown in  FIG. 3 , color deflection occurs at the opposed peripheries of the LCD  40 . That is, the opposed peripheries of the LCD  40  exhibit a specific color, which is due to the fact that the light beams from the red LEDs  14 R or the blue LEDs  14 B disposed at the peripheries are predominant over and do not mix well with other colors of light beams. 
         [0010]    Therefore, in order to overcome such a problem, the planar optical element  30  should be disposed apart in a sufficient interval from the underlying LED  14 . Alternatively, the planar optical element  30  should be formed sufficiently thick or in more layers. 
         [0011]    However, increasing the interval between the planar optical element  30  and the LEDs  14  increases the thickness of the LED backlight apparatus  10 . In addition, forming the planar optical element  30  sufficiently thick or in more layers results in increase in the weight or costs of the LED backlight apparatus  10 . 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention has been made to solve the foregoing problems of the prior art and therefore an object of certain embodiments of the present invention is to provide an LED backlight apparatus which includes red and blue LEDs alternately disposed adjacent to opposed peripheries of a substrate and regulates the amount of light directly incident upward from the red and blue LEDs, thereby eliminating color deflection occurring at the opposed peripheries of a light guide panel. 
         [0013]    Another object of certain embodiments of the invention is to provide an LED backlight apparatus which includes red and blue LEDs alternately disposed adjacent to opposed peripheries of a substrate and regulates the amount of light directly incident upward from the red and blue LEDs through a reflector structure, thereby eliminating color deflection occurring at the opposed peripheries of a light guide panel. 
         [0014]    Further another object of certain embodiments of the invention is to provide an LED backlight apparatus which includes red and blue LEDs alternately disposed adjacent to opposed peripheries of a substrate and regulates the amount of light directly incident upward from the red and blue LEDs through an electronic driving circuit, thereby eliminating color deflection occurring at the opposed peripheries of a light guide panel. 
         [0015]    According to an aspect of the invention for realizing the object, there is provided a light emitting diode (LED) backlight apparatus comprising: a substrate with a reflecting surface formed thereon; a first LED row placed on or above the reflecting surface, the first LED row including a pair of first blue LEDs positioned adjacent to opposed peripheries of the substrate and second green, red and blue LEDs alternately positioned between the first blue LEDs; a second LED row placed on or above the reflecting surface adjacent to the first LED row, the second LED row including a pair of first red LEDs each positioned adjacent the opposed peripheries of the substrate and second green, blue and red LEDs alternately positioned between the first red LEDs; and means for regulating the amount of upward radiation from a position of each of the first blue and red LEDs to be smaller than the amount of upward radiation from a position of each of the second LED. 
         [0016]    In the LED backlight apparatus, the means for regulating may comprise a cover which blocks the first blue and red LEDs at least partially from above. In addition, the LED backlight apparatus may further comprise reflecting means which is disposed in the opposed peripheries of the substrate and includes a cavity for at least partially housing the first blue and red LEDs underneath the cover. Moreover, the cavity may have an opening in a portion opposite to the first blue and red LEDs or the LED backlight apparatus may further comprise a light absorbing material disposed in a portion of the cavity opposite to the first blue and red LEDs. 
         [0017]    In the LED backlight apparatus, the means for regulating may comprise a driving circuit having a resistance for controlling the amount of radiation from the first blue and red LEDs to be smaller than the amount of radiation from the second LEDs. 
         [0018]    According to another aspect of the invention for realizing the object, there is provided a light emitting diode (LED) backlight apparatus comprising: a substrate with a reflecting surface formed thereon; a first LED row placed on or above the reflecting surface, the first LED row including a pair of first type blue LEDs positioned adjacent to opposed peripheries of the substrate and second type green, red and blue LEDs alternately positioned between the first blue LEDs; a second LED row placed on or above the reflecting surface adjacent to the first LED row, the second LED row including a pair of first type red LEDs positioned adjacent to the opposed peripheries of the substrate and second green, blue and red LEDs alternately positioned between the first type red LEDs; and a driving circuit for regulating the first and second type LEDs such that the amount of radiation from each of the first type blue and red LEDs is smaller than the amount of radiation from each of the second type LEDs. 
         [0019]    In the LED backlight apparatus, the driving circuit may regulate both of the first and second type LEDs. Alternatively, the driving circuit may regulate the first and second type LEDs separately. 
         [0020]    In the LED backlight apparatus, the driving circuit may regulate the first and second LED rows separately. 
         [0021]    In the LED backlight apparatus, it is preferable that each of the first type LEDs has smaller output than each of the second type LEDs. In addition, the LED backlight apparatus may further comprise a resistance disposed at an input side of each first type LED. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0023]      FIG. 1  is a schematic exploded perspective view illustrating a conventional LED backlight apparatus; 
           [0024]      FIG. 2  is a sectional view illustrating the LED backlight apparatus shown in  FIG. 1 ; 
           [0025]      FIG. 3  is a plan view illustrating the surface of an LCD backlighted by the LED backlight apparatus shown in  FIG. 1 ; 
           [0026]      FIG. 4  is a plan view illustrating the arrangement of LEDs in an LED backlight apparatus according to the present invention; 
           [0027]      FIG. 5  is a sectional view illustrating an LED backlight apparatus according to a first embodiment of the present invention; 
           [0028]      FIG. 6  is a perspective view illustrating an interior of the LED backlight apparatus shown in  FIG. 5 ; 
           [0029]      FIG. 7  is a plan view illustrating the surface of an LCD backlighted by the backlight apparatus according to the present invention; 
           [0030]      FIGS. 8   a  and  8   b  are sectional views illustrating variations from the LED backlight apparatus according to the first embodiment of the present invention; 
           [0031]      FIG. 9  is a plan view illustrating an LED backlight apparatus according to a second embodiment of the present invention; 
           [0032]      FIG. 10  is a plan view illustrating a variation to the LED backlight apparatus according to the second embodiment of the present invention; and 
           [0033]      FIG. 11  is a plan view illustrating another variation to the LED backlight apparatus according to the second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0034]    Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0035]      FIG. 4  is a plan view illustrating an arrangement of LEDs in an LED backlight apparatus according to the present invention. 
         [0036]    Referring to  FIG. 4 , the LED backlight apparatus of the present invention includes a substrate  102  and first LEDS  104  and second LEDs  106  disposed on an upper surface of the substrate  102 . 
         [0037]    The first LEDs  104  include first blue LEDs  104 B and first red LEDs  104 R, and the second LEDs  106  include second green, red and blue LEDs  106 G,  106 R and  106 B. 
         [0038]    The first blue LEDs  104 B are disposed adjacent to opposed peripheries of the substrate  102  and the second green, red and blue LEDs  106 G,  106 R and  106 B are alternately disposed between the opposed first blue LEDs  104   b  to form first LED rows. 
         [0039]    In addition, the first red LEDs  104 R are disposed adjacent to opposed peripheries of the substrate  102  and the first blue LEDs  104 B, and the second green, blue and red LEDs  106 G,  106 B and  106 R are alternately disposed between the opposed first red LEDs to form second LED rows. 
         [0040]    The first and second LED rows are alternately disposed on an upper surface of the substrate  102 , forming an LED arrangement according to the present invention. 
         [0041]      FIG. 5  is a sectional view illustrating an LED backlight apparatus according to a first embodiment using the LED arrangement of  FIG. 4 , and  FIG. 6  is a perspective view illustrating the LED backlight apparatus shown in  FIG. 5 . 
         [0042]    Referring to  FIGS. 5 and 6  together with  FIG. 4 , the backlight apparatus  100  according to this embodiment includes a substrate  102 , first and second LEDs  104  and  106  disposed according to the LED arrangement shown in  FIG. 4  on an upper surface of the substrate  102 , a reflector  110  disposed at opposed peripheries of the substrate  102 , a planar optical element  130  such as a diffusion plate (e.g. a micro prism sheet) and an optical filter disposed above the LEDs  104  and  106 . 
         [0043]    The reflector  110  comprises an upper cover  112  and a sidewall  120 . The upper cover  112  includes a sloped surface  114  and a lower surface  116  formed at a lower end of the sloped surface  114 . The sidewall  120  has a cavity  122  and an inner wall  118  formed inside the cavity  122 . The inner wall  118  and the lower surface  116  are reflecting surfaces outwardly reflecting the light beams L 1  introduced into the cavity  122 . 
         [0044]    In this way, a decreased amount of light beams emitted from the first red LED  104  directly propagates to the overlying LCD region  130 . Thus, the light beams are uniformly mixed underneath the planar optical element  130  as they enter the LCD  140 , providing white light illumination without color spots or color deflection. This effect is seen in  FIG. 7 , and is contrasted with the conventional technology resulting in color deflection as shown in  FIG. 3 . Therefore, the present invention eliminates the color deflection without increasing the thickness or the weight of the backlight apparatus, thereby achieving miniaturization. 
         [0045]    In  FIGS. 5 and 6 , the embodiment is exemplified by the first red LEDs  104 R, but the same applies to the case using the first blue LEDs  104 B. Because of low luminosity factor of green, however, the green LEDs do not need to be disposed adjacent to the peripheries like the first red and blue LEDs  104 R and  104 B. 
         [0046]    The cover  112  is for appropriately decreasing the amount of light beams emitted upward from the first red and blue LEDs  104 R and  104 B, and the amount of the decrease may vary according to the shape of the lens of the LED or the package. For example, in a case of an LED having a lens or a package for emitting light laterally, it is preferable that the amount of upward light beam is decreased by about ½. In addition, in a case of an LED having a dome or hemisphere-shaped lens or package, it is preferable that the amount of upward light beam is decreased by about ⅓. 
         [0047]    The upper cover  112  can be configured such that it completely blocks the directly upward light beams from the first red and blue LEDs  104 R and  104 B depending on the purpose or the design of the backlight apparatus  100 . In this case, the cavity  122  completely houses the first red and blue LEDs  104 R and  104 B. 
         [0048]    In the meantime, instead of forming the cavity  120  in the sidewall  120 , the entire portion of sidewall  120  can be shifted back to the position of the inner wall  118  to allow the substantially same effect. 
         [0049]    The aforedescribed LED backlight apparatus  100  of the first embodiment can be modified as shown in  FIGS. 8   a  and  8   b . Referring to  FIG. 8   a , in the modified LED backlight apparatus  10 A, the inner wall  118  is removed so that the light beams from the first red LED  104 R incident into the cavity  122  (see  FIG. 6 ) can be directed outward. Alternatively, as in the LED backlight apparatus  100 B shown in  FIG. 8   b,  a light absorbing material  118   b  can be formed in the position of the inner wall  118  to yield substantially the same effect. 
         [0050]      FIG. 9  is a plan view illustrating an LED backlight apparatus according to a second embodiment of the present invention. As shown in  FIG. 9 , the LED backlight apparatus  200  regulates the amount of light of the first green and blue LEDs  204   r  and  204   b  disposed adjacent to opposed peripheries of the substrate through a driver  250 , thereby allowing the substantially same effect as the first embodiment. 
         [0051]    More specifically, each driver  250  includes a main driver  252  and a supplementary driver  256   r,    256   b.  The main driver  252  is connected to a terminal  262  of a main circuit board  260  by wires  254 , and the terminal  262  is connected to second type LEDs  206  by wires  264 ,  266  and  268 . Specifically, the first wires  264  connect a plurality of green LEDs  206 G in series and the second wires  266  connect a plurality of blue LEDs  206 B in series. And the third wires  268  connect a plurality of red LEDs  206 R in series. The configuration and operation of the main circuit board  260  and the main driver  252  is well known in the art, thus not described further. 
         [0052]    In the meantime, the supplementary driver  256   r  is connected to a first type red LED  204   r  via the terminal  272  and the wires  258 , and the first type red LED  204   r  is connected to another first type red LED  204   r  at the opposite side via wires  274   r.    
         [0053]    The first type red LED  204   r  has smaller output than the second type red LED  206 R, and thus they require different drivers, respectively. The first type red LED  204   r  has smaller output than the second type red LED  206 R, and the degree of difference may vary according to the purpose or the design of the backlight apparatus  200 . Preferably, as described above, in a case of the first type red LED  204   r  having a lens or package for emitting light laterally, the first type red LED  204   r  may have an output that is about ½ the output of the second type red LED  204 R. And in a case of the first type red LED  204   r  having a lens or package for emitting light upward, the first type red LED  204   r  may have an output that is about ⅓ the output of the second type red LED  204 R. 
         [0054]    In the meantime, the same applies to the first type blue LED  204   b  and its driver  256   b,  as in the case of the first type red LED  204 r, and thus no further explanation is provided. 
         [0055]    Using such a driver and circuit, first type red and blue LEDs  204   r  and  204   b  having smaller output are disposed adjacent to opposed peripheries of the substrate, thereby eliminating color spots or color deflection as explained in the first embodiment. 
         [0056]      FIG. 10  is a plan view illustrating a variation to the LED backlight apparatus according to the second embodiment of the present invention. Referring to  FIG. 10 , the modified LED backlight apparatus  200 - 1  is identical to the aforedescribed backlight apparatus  200  except for the first type red LEDs  204   r  being installed in the same circuit board  260 - 1  as the second type LEDs  206 G,  206 B,  206 R. Unlike the backlight apparatus  200  which can adjust the distance between the first type LED  204  and the second type LED  206 , the backlight apparatus  200 - 1  cannot adjust the distance therebetween. 
         [0057]      FIG. 11  is a plan view illustrating another variation to the LED backlight apparatus according to the second embodiment of the present invention. Referring to  FIG. 11 , the modified LED backlight apparatus  200 - 2  uses a single driver  250 - 2  and disposes the first and second type LEDs  204  and  206  on the same circuit board  260 - 2  to use the same terminal  262 - 2 . Here, it is noticeable in this embodiment that the first type red LED  204   r  and the second type red LED  204 R are connected in series. In the meantime, each of the first type red LEDs  204   r  has smaller output than each of the second type red LEDs  204 R, and thus in order to decrease the applied voltage, resistances R 1  and R 2  are installed at the input side of the first type red LEDs  204   r.    
         [0058]    This configuration also allows the substantially same effect as in the aforedescribed first and second embodiments. 
         [0059]    As described above, the LED backlight apparatus includes red and blue LEDs alternately disposed and regulates the amount of light beams directly incident upward from the red and blue LEDs, thereby eliminating the color deflection occurring at opposed edges of the light guide panel. In addition, through the reflector structure formed at the peripheries of the substrate, the amount of light beams directly incident upward from the red and blue LEDs can be regulated. Further, using the electric driving circuit, the amount of light beams directly incident from the red and blue LEDs can be regulated to thereby eliminate the color deflection occurring at opposed peripheries of the light guide panel. 
         [0060]    While the present invention has been shown and described in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.