Abstract:
Provided is a back-light unit. The back-light unit includes: a reflective layer; a light transmitting plate including a plurality of light emitting diodes; and an optical member disposed on the light transmitting plate and separated from the light transmitting plate with an air layer therebetween, in which light generated from the light emitting diode is reflected to the reflective layer and then passes through the light transmitting plate to reach the optical member.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0077801 filed in the Korean Intellectual Property Office on Jul. 17, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     Embodiments of the present invention relate to a back-light unit and a liquid crystal display including the same. 
     (b) Description of the Related Art 
     In general, a liquid crystal display (LCD) is a typical flat panel display in which a transmittance of light is controlled corresponding to an image signal to display an image. However, since the liquid crystal display is not a self-light emitting element being capable of emitting light by itself, a separate light source which supplies the light at the rear side of a liquid crystal screen is required in order to visually display the image. 
     In this case, the liquid crystal display requires a back-light unit which has a complex power supply circuit for driving a light source and the light source itself including a lamp and additional elements which is needed to form uniform planar light, in order to irradiate the light from a rear side of a liquid crystal module to a liquid crystal panel of a front side thereof. 
     The back-light unit is classified into two types, a direct-lit type and an edge-lit type, according to an irradiating method of light. Recently, the direct-lit type and the edge-lit type flat panel backlights which apply planar light sources such as a light emitting diode (LED) have been actively researched. 
     In particular, in the direct-lit type LED backlight using a plurality of LEDs as light sources, a bright spot defect occurs due to a distance between the adjacent light emitting diodes. In order to solve the bright spot defect, the number of LEDs may be increased, but it accompanies an increase in manufacturing cost. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention have been made in an effort to provide a back-light unit having advantages of solving a white spot defect due to a distance between light emitting diodes and a liquid crystal display including the same. 
     An exemplary embodiment of the present invention provides a back-light unit, including: a reflective layer; a light transmitting plate including a plurality of light emitting diodes; and an optical member disposed on the light transmitting plate and spaced apart from the light transmitting plate with an air layer therebetween, in which light generated from the light emitting diode is reflected by the reflective layer and then passes through the light transmitting plate to reach the optical member, and in which the light emitting plate is formed of a plate without an opening. 
     The light transmitting plate may include a wiring electrically connecting the light emitting diodes to an external power supply. 
     The wiring may be formed of a light transmitting material. 
     The light transmitting material may be ITO or IZO. 
     The reflective layer may include a substrate and a support partition protruding up from an edge of the substrate, and the light transmitting plate may be fixed to the support partition. 
     The substrate and the support partition may be integrally formed. 
     The plurality of light emitting diodes may include a first light emitting diode which is disposed to be parallel to a horizontal surface of the reflective layer and a second light emitting diode which is disposed to be tilted to the horizontal surface of the reflective layer. 
     The first light emitting diode and the second light emitting diode may be randomly arranged. 
     Another exemplary embodiment of the present invention provides a back-light unit, including: a reflective layer; a plurality of light emitting diodes which is disposed at a portion which faces the reflective layer; a plurality of supporters supporting the plurality of light emitting diodes on the reflective layer; and an optical member disposed on the plurality of light emitting diodes, in which light generated from the light emitting diode is reflected to the reflective layer and then passes through a surface where the light emitting diode is disposed to reach the optical member. 
     The plurality of supporters may include at least one of glass, ITO and IZO. 
     The back-light unit may further include a support frame covering the reflective layer, in which the support frame may protrude up from the reflective layer, and the optical member may be positioned at a protruding end of the support frame. 
     The plurality of light emitting diodes may include a first light emitting diode which is disposed to be parallel to a horizontal surface and a second light emitting diode which is disposed to be tilted to the horizontal surface. 
     The first light emitting diode and the second light emitting diode may be randomly arranged. 
     The back-light unit may further include a lens portion formed on the light emitting diode. 
     Yet another exemplary embodiment of the present invention provides a liquid crystal display, including: a liquid crystal panel; and a back-light unit supplying light to the liquid crystal panel, in which the back-light unit includes a reflective layer, a light transmitting plate including a plurality of light emitting diodes which is disposed on an surface facing to the reflective layer and a wiring electrically connecting the light emitting diodes to an external power supply, and an optical member disposed on the light transmitting plate and separated from the light transmitting plate with an air layer therebetween, and a light emitting surface of the light emitting diode faces the reflective layer, and light generated from the light emitting diode is reflected to the reflective layer and then reaches the optical member. 
     According to the exemplary embodiments of the present invention, it is possible to solve a white spot defect of a back-light unit without increasing a thickness of a backlight module and the number of light emitting diodes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view illustrating a liquid crystal display according to an exemplary embodiment of the present invention. 
         FIG. 2  is a cross-sectional view illustrating a back-light unit according to an exemplary embodiment of the present invention. 
         FIG. 3  is a cross-sectional view illustrating a back-light unit according to another exemplary embodiment of the present invention. 
         FIG. 4  is a simulation result graph in a direct type back-light unit according to Comparative Example, and  FIGS. 5 and 6  are simulation result graphs according to a position of a light emitting diode according to the exemplary embodiment of  FIG. 2 . 
         FIG. 7  is a cross-sectional view illustrating a back-light unit according to yet another exemplary embodiment of the present invention. 
         FIG. 8  is a cross-sectional view illustrating a back-light unit according to yet another exemplary embodiment of the present invention. 
         FIG. 9  is a cross-sectional view illustrating a back-light unit according to yet another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. On the contrary, exemplary embodiments introduced herein are provided to make disclosed contents thorough and complete and sufficiently transfer the spirit of the present invention to those skilled in the art. 
     In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. It will be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening them may also be present. Like reference numerals designate like elements throughout the specification. 
       FIG. 1  is an exploded view illustrating a liquid crystal display according to an exemplary embodiment of the present invention.  FIG. 2  is a cross-sectional view illustrating a back-light unit according to an exemplary embodiment of the present invention. 
     Referring to  FIGS. 1 and 2 , the liquid crystal display according to the exemplary embodiment includes a bottom cover  100 , a support frame  130 , a reflective layer  110 , a light transmitting plate  140  with a light emitting diode (LED), an optical member  70 , a liquid crystal panel  300 , and a top cover  200 . 
     In the exemplary embodiment, the support frame  130 , the reflective layer  110 , the light transmitting plate  140  with a light emitting diode (LED), and the optical member  70  may be constituent elements of the back-light unit, and the back-light unit is a unit of irradiating light to the liquid crystal display which may not self-emit light. 
     The top cover  200  may cover an edge of the optical member  70  and may be assembled and fastened to the bottom cover  100 . 
     Hereinafter, a back-light unit according to the exemplary embodiment of the present invention will be described in detail with reference to  FIG. 2 . 
     In the back-light unit according to the exemplary embodiment, the light transmitting plate  140  is positioned on the reflective layer  110 . A plurality of light emitting diodes (LEDs) is positioned on the light transmitting plate  140 . In this case, the light emitting diode (LED) is positioned on the light transmitting plate  140  surface which faces the reflective layer  110  so that the light emitted from the light emitting diode (LED) faces the reflective layer  110 . 
     The light transmitting plate  140  may be made of at least one of glass, indium-tin oxide (ITO), and indium-zinc oxide (IZO) so that the light emitted from the light emitting diode (LED) is reflected by the reflective layer  110  and pass through the light transmitting plate  140 . 
     In order to have a space h of an additional light path, the light transmitting plate  140  may be disposed in the middle of the backlight module. In this case, an edge of the light transmitting plate  140  may be fixed to the reflective layer  110 . In detail, the reflective layer  110  includes a substrate  110   a  and a support partition  110   b  which is protruded from an edge of the substrate  110   a , and the edge of the light transmitting plate  140  may be fastened to the support partition  110   b  or may be attached to the support partition  110   b  by using a tape and the like. 
     The light transmitting plate  140  may be formed of one plate without an opening. A plurality of the light transmitting plate  140  formed of one plate may be formed in the LED back-light unit. Each of the plurality of light transmitting plates  140  may be fastened to the support partition  110   b  or may be attached to the support partition  110   b  by using a tape and the like. 
     The substrate  110   a  of the reflective layer  110  and the support partition  110   b  may be integrally formed by an injection molding method. 
     The light emitting diode (LED) may be connected with a wiring (not shown) in order to be electrically connected to an external power supply, and the wiring may be formed in the light transmitting plate  140 . In this case, the wiring may be formed of a light transmitting material. For example, the wiring made of a light transmitting material such as indium-tin oxide (ITO) or indium-zinc oxide (IZO) may be formed in the light transmitting plate  140  made of glass or the like. 
     An optical member  70  including a prism sheet  50  and a diffuser sheet  60  is positioned on the light transmitting plate  140 . The diffuser sheet  60  is disposed on the reflective layer  110  to uniformly distribute light which is reflected by the reflective layer  110 . In addition, the prism sheet  50  is disposed on the top of the diffuser sheet  60 , and guides the light from the diffuser sheet  60  to a display area of a liquid crystal panel (not shown) in which an image is displayed. 
     The support frame  130  is formed to cover the substrate  110   a  and the support partition  110   b  of the reflective layer  110 . The support frame  130  includes a protruding portion protruding up from the support partition  110   b , and the optical member  70  is positioned at an end of the protruding portion. An air layer AL is formed between the optical member  70  positioned at the end of the protruding portion of the support frame  130  and the light transmitting plate  140 . 
     In the exemplary embodiment, a distance D between the reflective layer  110  and the optical member  70  is substantially equal to a thickness of the backlight module. The light emitting diode (LED) is fixed on the light transmitting plate  140 . In addition, the light emitting diode (LED) emits light toward the reflective layer  110 . As a result, a length of the light path may be a sum of a second distance h and a first distance D. 
     As described above, in the exemplary embodiment, it is possible to reduce a white spot defect due to interval distance between the light emitting diodes (LED) by increasing the length of light paths without increasing the number of the light emitting diodes (LED). The second distance h is larger than 0 and smaller than the first distance D. Furthermore, in a case where the number of the plurality of light emitting diodes (LED) is designed to become smaller by considering cost and the like, it is possible to reduce a white spot defect by increasing the second distance h. 
       FIG. 3  is a cross-sectional view illustrating a back-light unit according to another exemplary embodiment of the present invention. 
     The exemplary embodiment of  FIG. 3  is almost the same as the exemplary embodiment described in  FIG. 2 , and hereinafter, differences will be described. 
     Referring to  FIG. 3 , unlike the exemplary embodiment of  FIG. 2 , a light transmitting plate is not formed. Instead, a supporter  120  is formed between the plurality of light emitting diodes (LED) and the reflective layer  110 . The supporter  120  is made of at least one of glass, indium-tin oxide (ITO), and indium-zinc oxide (IZO). In the exemplary embodiment, the supporter  120  is fastened to the substrate  110   a  of the reflective layer  110  or attached to the substrate  110   a  by using a tape and the like to fix the light emitting diode (LED). The supporter  120  serves to fix the light emitting diode (LED) to the reflective layer  110  while maintaining a light emitting direction of the light emitting diode (LED) toward the reflective layer  110 . In  FIG. 3 , the reflective layer  110  may include the support partition  110   b , but the support partition  110   b  may be omitted. 
     All the contents described in  FIG. 2  may be applied to the exemplary embodiment of  FIG. 3 , except for the differences described above. 
     Hereinafter, a travel of light in the case of forming the back-light unit according to the exemplary embodiment of the present invention will be described. 
       FIG. 4  is a simulation result graph in a direct-lit type back-light unit according to Comparative Example, and  FIGS. 5 and 6  are simulation result graphs according to the exemplary embodiment of  FIG. 2 . 
     Referring to  FIG. 4 , a difference in a light amount between a first region A corresponding to a directly upper portion of the light emitting diode and a second region B corresponding to a region between the adjacent light emitting diodes is large. The first region A and the second region B may represent boundaries between the air layer AL and the optical member  70  described in  FIG. 2 , and the difference in the light amount between the first region A and the second region B may be represented as a screen defect such as a hot spot when viewed from the outside. 
     However, referring to  FIGS. 5 and 6 , in the exemplary embodiment of  FIG. 2 , when the first distance D is designed as 20 mm and the second distance h is designed as 7 mm and 10 mm, respectively, it may be verified that the difference in the light amount between the first region A and the second region B is significantly decreased as compared with Comparative Example. 
       FIG. 7  is a cross-sectional view illustrating a back-light unit according to yet another exemplary embodiment of the present invention. 
     Referring to  FIG. 7 , a plurality of light emitting diodes (LED) may include a first light emitting diode LED 1  which is disposed to be parallel to a horizontal surface of the reflective layer  110  and a second light emitting diode LED 2  which is disposed to be tilted to the horizontal surface of the reflective layer  110  at a first angle θ. The first light emitting diode LED 1  and the second light emitting diode LED 2  may be randomly arranged. 
       FIG. 7  is a cross-sectional view when viewed in a first direction D 1  with reference to the exemplary embodiment of  FIG. 2 . Although not illustrated in  FIG. 7 , a plurality of light transmitting plates  140  is formed, and an edge of the light transmitting plate  140  may be fastened to the support partition  110   b  of the reflective layer  110  or may be attached to the support partition  110   b  by using a tape and the like, as shown in  FIG. 1 . 
     In the exemplary embodiment, since the second light emitting diode LED 2  which is tilted to the horizontal surface the reflective layer  110  at a predetermined angle, alight path may be increased. 
       FIG. 8  is a cross-sectional view illustrating a back-light unit according to yet another exemplary embodiment of the present invention. 
     The exemplary embodiment of  FIG. 8  is almost the same as the exemplary embodiment described in  FIG. 7 , and hereinafter, differences will be described. 
     Referring to  FIG. 8 , unlike the exemplary embodiment of  FIG. 7 , a light transmitting plate is not formed. Instead, the supporters  120  are formed between the light emitting diodes and the reflective layer  110 . The supporter  120  is made of at least one of glass, indium-tin oxide (ITO), and indium-zinc oxide (IZO). In the exemplary embodiment, the supporter  120  may be fastened to the substrate  110   a  of the reflective layer  110  or attached to the substrate  110   a  by using a tape and the like to fix the first light emitting diode LED 1  and the second light emitting diode LED 2 . The supporter  120  serves to fix the first and the second light emitting diodes, LED 1  and LED 2 , to the reflective layer  110  while maintaining a light emitting direction of the first and the second light emitting diodes, LED 1  and LED 2 , toward the reflective layer  110 . In  FIG. 8 , the reflective layer  110  includes the support partition  110   b , but the support partition  110   b  may be omitted. All the contents described in  FIG. 7  may be applied to the exemplary embodiment of  FIG. 8 , except for the differences described above. 
       FIG. 9  is a cross-sectional view illustrating a back-light unit according to yet another exemplary embodiment of the present invention. 
     Referring to  FIG. 9 , the exemplary embodiment of  FIG. 9  is almost the same as the exemplary embodiment of  FIG. 2 , but has a difference in that a lens portion LP is formed on a portion where the light emitting diode (LED) emits light. 
     The lens portion LP may serve to increase a directional angle of the light emitted from the light emitting diode (LED) to improve uniformity of light. 
     Although not shown, the configuration of the lens portion LP may also be applied to the exemplary embodiments of  FIGS. 3 ,  7 , and  8 . 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 &lt;Description of symbols&gt; 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  50:  
                 Diffuser sheet 
                  60:  
                 Prism sheet 
               
               
                   
                  70:  
                 Optical member 
                 110:  
                 Reflective layer 
               
               
                   
                 120:  
                 Supporter 
                 130:  
                 Support frame 
               
               
                   
                 140:  
                 Light transmitting plate 
                 AL:  
                 Air layer 
               
               
                   
                 LED:  
                 Light emitting diode