Abstract:
Provided are a backlight assembly and a display device including the same. 
     The backlight assembly comprises: a housing; a plurality of light sources disposed on the housing; a plurality of optical lenses disposed on the light sources, respectively; a main reflective sheet covering an upper surface of the housing and comprising a reflective portion and a main opening which exposes each of the optical lenses; and a sub reflective sheet disposed under each of the optical lenses, wherein the sub reflective sheet comprises a body portion and a fitting portion partially separated from the body portion and is fitted to the main reflective sheet in the reflective portion.

Description:
[0001]    This application claims priority to Korean Patent Application No. 10-2014-0011608 filed on Jan. 29, 2014 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The inventive concept relates to a backlight assembly and a display device including the same. 
         [0004]    2. Description of the Related Art 
         [0005]    A liquid crystal display (LCD) displays an image by altering the arrangement of the liquid crystals disposed between two glass substrates. The altering the arrangement of the liquid crystals is performed by applying different voltages to electrodes in the upper and lower glass substrates. Unlike cathode ray tubes (CRTs) and plasma display panels (PDPs), LCDs are non-self-luminous display devices. Therefore, LCDs cannot be used in places without light. To overcome this drawback and use LCDs in dark places, a backlight assembly which irradiates light uniformly to a liquid crystal display panel is required. 
         [0006]    A backlight assembly includes a light source, a diffusion plate, and optical sheets. A light-emitting diode (LED) light source having high efficiency is widely used as the light source of the backlight assembly. In a direct-illumination type backlight assembly, an optical lens is placed on an LED light source in order to increase the diffusion of light emitted from the LED light source. 
         [0007]    In this case, light emitted upward from the LED light source is diffused by the optical lens. However, light emitted from sides of the LED light source or emitted downward from the LED light source fails to enter the optical lens and leaks toward a lower housing. To recycle the leaked light, a reflective sheet is placed on the lower housing. 
         [0008]    Here, the reflective sheet should not cover the optical lens. Thus, the reflective sheet includes an opening through which the optical lens can pass. Meanwhile, no reflective sheet is placed under the optical lens. Therefore, it is difficult to reflect light properly. To improve reflection efficiency, a sub reflective sheet may be placed under the optical lens. However, if the sub reflective sheet is not properly coupled to a main reflective sheet, a lifting of the main reflective sheet may occur, thereby degrading light quality. 
       SUMMARY 
       [0009]    Aspects of the inventive concept provide a backlight assembly which can improve luminance by having high reflection efficiency and improve light quality by suppressing the lifting of a reflective sheet. 
         [0010]    Aspects of the inventive concept also provide a display device having high luminance and improved display quality. 
         [0011]    However, aspects of the inventive concept are not restricted to the one set forth herein. The above and other aspects of the inventive concept will become more apparent to one of ordinary skill in the art to which the inventive concept pertains by referencing the detailed description of the inventive concept given below. 
         [0012]    According to an aspect of the inventive concept, there is provided a backlight assembly comprising: a housing; a plurality of light sources disposed on the housing; a plurality of optical lenses disposed on the light sources, respectively; a main reflective sheet covering an upper surface of the housing and comprising a reflective portion and a main opening which exposes each of the optical lenses; and a sub reflective sheet disposed under each of the optical lenses, wherein the sub reflective sheet comprises a body portion and a fitting portion partially separated from the body portion and is fitted to the main reflective sheet in the reflective portion. 
         [0013]    A periphery of the body portion of the sub reflective sheet is disposed on one surface of the main reflective sheet and the fitting portion of the sub reflective sheet is disposed on the other surface of the main reflective sheet. 
         [0014]    The fitting portion may be partially separated from the body portion by a cutting portion. 
         [0015]    The fitting portion may include a first end, sides, and a second end, wherein the first end is formed integrally with the body portion. 
         [0016]    The first end may be located inside than an outer circumference of the body portion. 
         [0017]    The second end may be protruded toward the outside than the outer circumference of the body portion. 
         [0018]    The cutting portion may include a concave portion whose width decreases toward the inside of the body portion. 
         [0019]    A diameter of the body portion of the sub reflective sheet may be greater than a diameter of the main opening. 
         [0020]    The backlight assembly further may comprise a lens support which supports each of the optical lenses and separates each of the optical lenses from a surface of the housing, wherein each of the light sources comprises a light-emitting diode (LED) chip, and the sub reflective sheet comprises a sub opening which exposes the LED chip and the lens support. 
         [0021]    According to another aspect of the inventive concept, there is provided a backlight assembly comprising: a housing; a plurality of light sources disposed on the housing; a plurality of optical lenses disposed on the light sources, respectively; a main reflective sheet covering an upper surface of the housing and comprising a reflective portion, a fitting portion and a main opening which exposes each of the optical lenses, wherein the fitting portion is separated from the reflective portion by a cutting portion and is fitted to the sub reflective sheet. 
         [0022]    A periphery of the reflective portion of the main reflective sheet is disposed on one surface of the sub reflective sheet and the fitting portion of the main reflective sheet is disposed on the other surface of the sub reflective sheet. 
         [0023]    A circumference of the sub reflective sheet is larger than a circumference of the main opening. 
         [0024]    The fitting portion may include a first end, sides, and a second end, wherein the first end is formed integrally with the body portion. 
         [0025]    The second end may protrude toward the inside of the main opening. 
         [0026]    According to another aspect of the inventive concept, there is provided a display device comprising: a display panel; and a backlight assembly disposed under the display panel, wherein the backlight assembly comprises: a lower housing; a plurality of light sources disposed on the housing; a plurality of optical lenses disposed on the light sources, respectively; a main reflective sheet covering an upper surface of the housing and comprising a reflective portion and a main opening which exposes each of the optical lenses; and a sub reflective sheet disposed under each of the optical lenses, wherein the sub reflective sheet comprises a body portion and a fitting portion partially separated from the body portion and is fitted to the main reflective sheet in the reflective portion. 
         [0027]    A periphery of the body portion of the sub reflective sheet may be disposed on a surface of the main reflective sheet, and the fitting portion of the sub reflective sheet is disposed on the other surface of the main reflective sheet. 
         [0028]    The fitting portion may be partially separated from the body portion by a cutting portion. 
         [0029]    The fitting portion may include a first end, sides, and a second end, wherein the first end is formed integrally with the body portion. 
         [0030]    The first end may be located inside of an outer circumference of the body portion. 
         [0031]    The second end may be protruded toward the outside than the outer circumference of the body portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The above and other aspects and features of the inventive concept will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
           [0033]      FIG. 1  is an exploded perspective view of a backlight assembly according to an embodiment of the inventive concept; 
           [0034]      FIG. 2  is a partial layout view illustrating a light source module and a reflective sheet coupled to each other in a display device according to an embodiment of the inventive concept; 
           [0035]      FIG. 3  is a cross-sectional view taken along the line III-III′ of  FIG. 2 ; 
           [0036]      FIG. 4  is a cross-sectional view taken along the line IV-IV′ of  FIG. 3 ; 
           [0037]      FIG. 5  is a plan view of a sub reflective sheet according to an embodiment of the inventive concept; 
           [0038]      FIG. 6  is a perspective view of the sub reflective sheet according to an embodiment of the inventive concept; 
           [0039]      FIG. 7  is a plan view of a sub reflective sheet of a backlight assembly according to other embodiment of the inventive concept; 
           [0040]      FIG. 8  is a plan view of a sub reflective sheet of a backlight assembly according to another embodiment of the inventive concept; 
           [0041]      FIG. 9  is a plan view of a sub reflective sheet of a backlight assembly according to still another embodiment of the inventive concept; 
           [0042]      FIG. 10  is a plan view of a sub reflective sheet of a backlight assembly according to still another embodiment of the inventive concept; 
           [0043]      FIG. 11  is a plan view of a sub reflective sheet of a backlight assembly according to still another embodiment of the inventive concept; 
           [0044]      FIG. 12  is a plan view of a sub reflective sheet of a backlight assembly according to still another embodiment of the inventive concept; 
           [0045]      FIG. 13  is a plan view of a main reflective sheet of a backlight assembly according to still another embodiment of the inventive concept; 
           [0046]      FIG. 14  is a partial layout view illustrating the main reflective sheet of  FIG. 13  and a sub reflective sheet coupled to each other; and 
           [0047]      FIG. 15  is a cross-sectional view taken along the line XV-XV′ of  FIG. 14 . 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    Advantages and features of the inventive concept and methods of accomplishing the same may be understood more readily by reference to the following detailed description of preferred embodiments and the accompanying drawings. The inventive concept may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the inventive concept to those skilled in the art, and the inventive concept will only be defined by the appended claims. 
         [0049]    It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be formed directly on the other layer or substrate, or be formed with intervening layers. The same reference numbers indicate the same components throughout the specification. 
         [0050]    It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by the terms used. The terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the inventive concept. 
         [0051]    Hereinafter, embodiments of the inventive concept will be described with reference to the attached drawings. 
         [0052]      FIG. 1  is an exploded perspective view of a display device according to an embodiment of the inventive concept. 
         [0053]    Referring to  FIG. 1 , the display device  50  includes a display panel  20  and a backlight assembly  10  disposed under the display panel  20 . 
         [0054]    The display panel  20  may include an upper display substrate  22  and a lower display substrate  21  which face each other. The upper display substrate  22  and the lower display substrate  21  may be coupled to each other by a sealant (not shown). A liquid crystal layer (not shown) may be interposed between the upper display substrate  22  and the lower display substrate  21 . A polarizing sheet (not shown) may be attached to the outside of the upper display substrate  22  and the lower display substrate  21 . 
         [0055]    A plurality of pixel electrodes, wirings for driving the pixel electrodes, and switching elements may be formed in the lower display substrate  21 . In addition, a common electrode may be provided in the upper display substrate  22  or the lower display substrate  21  to apply an electric field to the liquid crystal layer. A color filter and a black matrix may be formed in the upper display substrate  22  or the lower display substrate  21 . 
         [0056]    The backlight assembly  10  may include a lower housing  310 , a light source module, a reflective sheet  15 , an optical plate  350 , and an optical sheet  360 . 
         [0057]    The lower housing  310  accommodates the light source module, the reflective sheet  15 , the optical plate  350 , the optical sheet  360 , etc. The lower housing  310  may be a bottom chassis. The lower housing  310  may include a recessed portion  312  (see  FIG. 3 ) in which the light source module is placed. 
         [0058]    The light source module provides light to the display panel  20 . The light source module may include a plurality of light sources. The light sources may be point light sources. Examples of the point light sources may include light-emitting diode (LED) light sources. Each of the LED light sources may include an LED chip  330  and an optical lens  340 . The LED chip  330  may be mounted on a substrate. The substrate on which the LED chip  330  is mounted may be a bar-type printed circuit board (PCB)  320 . A plurality of LED chips  330  may be mounted on the PCB  320 , and the optical lens  340  may be disposed on each of the LED chips  330 . The optical lens  340  may diffuse light emitted from each of the LED chips  330 . The light source module may include a plurality of bar-type PCBs  320  on which a plurality of LED chips  330  are mounted. The number of the LED chips  330  mounted on each of the PCBs  320  may be equal or different. The PCBs  320  on which the LED chips  330  are mounted may be arranged parallel to each other. Each of the PCBs  320  may be placed in the recessed portion  312  (see  FIG. 3 ) of the lower housing  310 . The light source module will be described in greater detail later. 
         [0059]    The reflective sheet  15  reflects light traveling downward toward an upward direction. The reflective sheet  15  includes a main reflective sheet  200  and a sub reflective sheet  100 . The main reflective sheet  200  may be formed as a single piece. The main reflective sheet  200  may include a reflective portion and a plurality of main openings  210 . The number of openings may be equal to the number of the LED chips  330 . The sub reflective sheet  100  may be formed in a plurality. The number of the sub reflective sheets  100  may be equal to the number of the LED chips  330 . The sub reflective sheets  100  may be disposed on the lower housing  310  while being fitted into the main openings  210  of the reflective sheet  15 , respectively. The sub reflective sheet  100  and the main reflective sheet  200  may be made of the same material and formed to have an equal thickness, but the inventive concept is not limited thereto. 
         [0060]    As a light-modulating structure that modulates light, the optical plate  350  and/or the optical sheet  360  may be disposed on the light source module. In an exemplary embodiment, the optical plate  350  may be a diffusion plate. The optical sheet  360  may be a prism sheet, a diffusion sheet, a microlens sheet, a lenticular sheet, a phase-difference compensation sheet or a reflective polarizing sheet, etc. and any combination thereof. A composite optical sheet in which more than one of the above light modulating characteristics is incorporated into one optical sheet  360  may be used. Various combinations of the light-modulating structures are widely known to those skilled in the art, and thus a detailed description thereof will be omitted. 
         [0061]    The display panel  20  may be seated in a middle housing  30 . The middle housing  30  may be a mold frame or a middle mold. The middle housing  30  may be coupled to the lower housing  310 . The optical plate  350  and/or the optical sheet  360  may be seated in the lower housing  310  or the middle housing  30 . In the drawing, the middle housing  30  is shaped like a quadrilateral frame. However, the middle housing  30  may also be provided as two bars, and the two bars may be placed on long or short sides of the display device  50 . 
         [0062]    An upper housing  40  may be disposed on the display panel  20 . The upper housing  40  may be a top chassis or a bezel. The upper housing  40  may include an open window and covers edges of the display panel  20  to protect them. The upper housing  40  may be coupled to the lower housing  310 . 
         [0063]    The light source module and the reflective sheet  15  will now be described in greater detail. 
         [0064]      FIG. 2  is a partial layout view illustrating a light source module and a reflective sheet coupled to each other in a display device according to an embodiment of the inventive concept.  FIG. 3  is a cross-sectional view taken along the line III-III′ of  FIG. 2 .  FIG. 4  is a cross-sectional view taken along the line IV-IV′ of  FIG. 3 . 
         [0065]    Referring to  FIGS. 2 through 4 , the lower housing  310  includes a bottom portion  311  and the recessed portion  312  which is recessed downward from a surface of the bottom portion  311 . The recessed portion  312  may be a line shape, and a PCB  320  is disposed in the recessed portion  312 . A depth of the recessed portion  312  may be substantially equal to a thickness of the PCB  320 . In this case, the surface of the bottom portion  311  and a surface of the PCB  320  may be located at substantially the same level. 
         [0066]    An LED chip  330  is mounted on the PCB  320 . The LED chip  330  may emit white light. In an example, the LED chip  330  may emit white light by including a blue LED chip, a red LED chip, and a green LED chip. In another example, the LED chip  330  may emit white light by including a blue light-emitting element and a fluorescent layer that contains fluorescent materials having red and green emission peaks in response to blue light or a fluorescent material having a yellow emission peak in response to the blue light. In another example, the LED chip  330  may emit white light by including an ultraviolet (UV) light-emitting element and a fluorescent layer that contains fluorescent materials having red, green and blue emission peaks in response to UV light. The configuration of the LED chip  330  emitting white light is not limited to the above examples. 
         [0067]    An optical lens  340  is disposed on the LED chip  330 . The optical lens  340  may diffuse light emitted from the LED chip  330 . The optical lens  340  may be circular when viewed from above. An upper surface of the optical lens  340  includes a convex surface. An upper groove  341  may be formed in the upper surface of the optical lens  340 . A lower groove  342  may be formed in a lower surface of the optical lens  340 . The upper groove  341  and the lower groove  342  may be located in the middle of the optical lens  340  and may overlap each other. In addition, the LED chip  330  may be located at a position corresponding to the middle of the optical lens  340  and thus overlaps the upper groove  341  and the lower groove  342 . 
         [0068]    Lens supports  343  may be formed on the lower surface of the optical lens  340 . The lens supports  343  may be shaped like pillars. In the drawings, three lens supports  343  are illustrated as an example. However, the number of the lens supports  343  may also be four or more or may be less than three. Bottom surfaces of the lens supports  343  may be coupled to the lower housing  310 . For example, the bottom surface of the lens supports  343  may be coupled to the surface of the bottom portion  311  of the lower housing  310  by an adhesive layer (not shown). The lens supports  343  may separate the optical lens  340  from the LED chip  330  by a predetermined distance. 
         [0069]    The LED chip  330  and the optical lens  340  are inserted into a main opening  210  of the main reflective sheet  200 . A sub reflective sheet  100  is disposed under the optical lens  340 . The sub reflective sheet  100  will now be described in detail with reference to  FIGS. 5 and 6 . 
         [0070]      FIG. 5  is a plan view of a sub reflective sheet according to an embodiment of the inventive concept.  FIG. 6  is a perspective view of the sub reflective sheet according to an embodiment of the inventive concept. Referring to  FIGS. 5 and 6 , the sub reflective sheet  100  includes a body portion  110  and a fitting portion  120 . 
         [0071]    An outer circumference of the body portion  110  may be substantially circular when viewed from above. A sub opening  130  is formed in the body portion  110 . The sub opening  130  provides a space into which an LED chip  300  and lens supports  343  are inserted. The sub opening  130  may be formed along the periphery of the space in which the LED chip  330  and the lens supports  343  are disposed. 
         [0072]    The fitting portion  120  is partially separated from the body portion  110 . The fitting portion  120  may have a shape like a boss that protrudes outward from a first end  120   a . The first end  120   a  of the fitting portion  120  is connected to the body portion  110 . The fitting portion  120  may be integrally connected to the body portion  110  at the first end  120   a . A connecting portion of the fitting portion  120  and the body portion  110  may be located inside the outer circumference of the body portion  110  having circular shape. 
         [0073]    Both sides  120   b  of the fitting portion  120  which face each other may be separated from the body portion  110  by cutting portions  140 , respectively. Each of the cutting portions  140  may be defined as a gap having a fine width between the fitting portion  120  and the body portion  110 . The sides  120   b  of the fitting portion  120  may be formed as lines parallel to each other or straight lines heading toward a center of the body portion  110 , but the inventive concept is not limited thereto. A second end  120   c  of the fitting portion  120  may be curved. The second end  120   c  of the fitting portion  120  may protrude outward than the outer circumference of the body portion  110 . 
         [0074]    Since an area including the sides  120   b  of the fitting portion  120  and the second end  120   c  is separated from the body portion  110 , the fitting portion  120  can move independently in a vertical direction with respect to the body portion  110 . That is, the fitting portion  120  can be bent or folded upward or downward from the body portion  110 . If the fitting portion  120  is placed in the same plane with the body portion  110  (that is, the state that the sub reflective sheet  100  is not fitted to the main reflective sheet  200 ), the sides  120   b  of the fitting portion  120  may be adjacent to the body portion  110 . 
         [0075]    The sub reflective sheet  100  may include a plurality of fitting portions  120 . In the drawings, two fitting portions  120  are arranged to have a line of symmetry. 
         [0076]    Referring back to  FIGS. 2 through 4 , the sub reflective sheet  100  under the optical lens  340  is disposed on the lower housing  310 . A diameter or width of the body portion  110  of the sub reflective sheet  100  may be greater than that of the optical lens  340  and that of the main opening  210  of the main reflective sheet  200 . In addition, the diameter or width of the main opening  210  of the main reflective sheet  200  may be greater than that of the optical lens  340 . The main reflective sheet  200  may overlap a periphery of the body portion  110 . 
         [0077]    The periphery of the body portion  110  may be disposed on one surface (e.g., a lower surface) of the main reflective sheet  200 . On the other hand, the fitting portions  120  may be disposed on the other surface (e.g., an upper surface) of the main reflective sheet  200 . As each of the fitting portions  120  is bent upward, a space of the cutting portion  140  is widened. Accordingly, the sub reflective sheet  100  may be fitted into the main opening  210  of the main reflective sheet  200  through the space. After the sub reflective sheet  100  is fitted to the main reflective sheet  200  by the fitting portions  120 , the movement of the sub reflective sheet  100  relative to the main reflective sheet  200  may be limited. This can prevent or reduce the lifting of the sub reflective sheet  100  or the main reflective sheet  200 , thereby improving the light quality of the backlight assembly  10  and the display quality of the display device  50 . 
         [0078]    In addition, since the sub reflective sheet  100  is disposed under the optical lens  340 , even if light emitted from the LED chip  300  travels downward, opposite to the optical lens  340 , the sub reflective sheet  100  can effectively reflect the light toward the optical lens  340 . Therefore, the luminance of the backlight assembly  10  can be improved. 
         [0079]    According to an example method of assembling the reflective sheet  15 , the PCB  320  having the LED chip  330  mounted thereon is placed in the recessed portion  312  of the lower housing  310 . 
         [0080]    Then, the sub reflective sheet  100  is placed on the LED chip  330 . Here, the sub reflective sheet  100  is placed such that the LED chip  330  can be exposed through the sub opening  130  of the sub reflective sheet  100 . 
         [0081]    Next, the optical lens  340  is installed. The lens supports  343  of the optical lens  340  are placed on the lower housing  310  exposed through the sub opening  130  of the sub reflective sheet  100  and then coupled onto the bottom portion  311  of the lower housing  310  by an adhesive or a double-sided tape. 
         [0082]    The main reflective sheet  200  is mounted. The optical lens  340  pass through the main opening  210  of the main reflective sheet  200  such that the main reflective sheet  200  is placed over the surface of the lower housing  310  and an upper surface of the sub reflective sheet  100 . 
         [0083]    Then, the fitting portions  120  of the sub reflective sheet  100  are bent upward through the main opening  210  and then bent again toward the upper surface of the main reflective sheet  200 , such that the sub reflective sheet  100  is fitted to the main reflective sheet  200  through the main opening  210 . 
         [0084]    Hereinafter, other embodiments of the inventive concept will be described. 
         [0085]      FIG. 7  is a plan view of a sub reflective sheet  101  of a backlight assembly according to other embodiment of the inventive concept. Referring to  FIG. 7 , the sub reflective sheet  101  according to the current embodiment is different from the sub reflective sheet  100  according to the embodiment of  FIG. 5  in that a sub opening  131  is formed to surround the outside of a space in which lens supports are disposed. Since the sub opening  131  is formed wider, a reflective area is relatively reduced. However, since a pattern of the sub opening  131  is formed regardless of the positions of the lens supports, the sub reflective sheet  100  can be assembled easily. 
         [0086]      FIG. 8  is a plan view of a sub reflective sheet of a backlight assembly according to another embodiment of the inventive concept. Referring to  FIG. 8 , in the sub reflective sheet  102  according to the current embodiment, sub openings  132  are formed only in spaces in which an LED chip and lens supports of an optical lens are disposed, and a space other than these spaces serves as a reflective surface of the sub reflective sheet  102 . Accordingly, in the current embodiment, a reflective area is relatively increased, thereby improving luminance. 
         [0087]      FIG. 9  is a plan view of a sub reflective sheet of a backlight assembly according to still another embodiment of the inventive concept. Referring to  FIG. 9 , the sub reflective sheet  103  according to the current embodiment is different from the sub reflective sheet  100  according to the embodiment of  FIG. 5  in that it includes four fitting portions  123 . That is, two fitting portions  123  form a pair, and two pairs of the fitting portions  123  are arranged to have a line of symmetry. The increased number of the fitting portions  123  enables the sub reflective sheet  103  to be coupled more securely to a main reflective sheet  200 . 
         [0088]    Although not illustrated in the drawing, a plurality of fitting portions may also be arranged at regular intervals along an outer circumference of a body portion. 
         [0089]      FIG. 10  is a plan view of a sub reflective sheet of a backlight assembly according to still another embodiment of the inventive concept. Referring to  FIG. 10 , the sub reflective sheet  104  according to the current embodiment is different from the sub reflective sheet  100  according to the embodiment of  FIG. 5  in that a second end  124   c  of each fitting portion  124  of the sub reflective sheet  104  is not protruded from an outer circumference of a body portion  110  but are formed along the outer circumference of the body portion  110  (that is, a part of a circle). Even if the fitting portions  124  is not protruded from the outer circumference of the body portion  110 , the sub reflective sheet  104  can be fitted to a main reflective sheet  200  by placing the body portion  110  of the sub reflective sheet  104  on a lower surface of the main reflective sheet  200  and placing the fitting portions  124  on an upper surface of the main reflective sheet  200 . For stable coupling, an overlap area between the periphery of the body portion  110  of the sub reflective sheet  104  and the main reflective sheet  200  may be increased relatively. 
         [0090]      FIG. 11  is a plan view of a sub reflective sheet of a backlight assembly according to still another embodiment of the inventive concept. Referring to  FIG. 11 , the sub reflective sheet  105  according to the current embodiment is different from the sub reflective sheet  100  according to the embodiment of  FIG. 5  in that a cutting portion  145  separating each fitting portion  125  from a body portion  110  includes a concave portion whose width increases toward a second end  125   c  (toward an outer circumference of the body portion  110 ) and decreases toward a first end  125   a  (toward a center of the body portion  110 ). The second end  125   c  of each fitting portion  125  may be located outside the outer circumference of the body portion  110 . Since both sides  125   b  of each fitting portion  125  are separated from the body portion  110  by the cutting portions  145  having the concave portions, the fitting portions  125  can move independently in a vertical direction with respect to the body portion  110 . In addition, since the sides  125   b  of each fitting portion  125  are separated relatively far away from the body portion  110 , the fitting portions  125  can move more freely. Accordingly, the sub reflective sheet  105  can be fitted to a main reflective sheet more easily in an assembling process. 
         [0091]      FIG. 12  is a plan view of a sub reflective sheet of a backlight assembly according to still another embodiment of the inventive concept. Referring to  FIG. 12 , the sub reflective sheet  106  according to the current embodiment is different from the sub reflective sheet  105  according to the embodiment of  FIG. 11  in that a second end  126   c  of each fitting portion  126  of the sub reflective sheet  106  is not protruded from an outer circumference of a body portion  110 . The second end  126   c  of each fitting portion  126  may be formed along the outer circumference of the body portion  110 . Even if the fitting portions  126  is not protruded from the outer circumference of the body portion  110 , the sub reflective sheet  106  can be fitted to a main reflective sheet as described above in the embodiment of  FIG. 10 . 
         [0092]      FIG. 13  is a plan view of a main reflective sheet of a backlight assembly according to still another embodiment of the inventive concept.  FIG. 14  is a partial layout view illustrating the main reflective sheet of  FIG. 13  and a sub reflective sheet coupled to each other.  FIG. 15  is a cross-sectional view taken along the line XV-XV′ of  FIG. 14 . 
         [0093]    In the current embodiment, fitting portions  212  are formed not in the sub reflective sheet  107 , but in the main reflective sheet  201 . Referring to  FIGS. 13 through 15 , the main reflective sheet  201  may include reflective portion, main openings  211  and the fitting portions  212  which protrude from circumferences of the main openings  211  toward the centers of the main opening  211 . The fitting portions  212  are separated from a body portion of the main reflective sheet  201  by cutting portions  213 . Each fitting portion  212  has a first end connected to the body portion of the main reflective sheet  201 , both sides separated from the body portion of the main reflective sheet  201 , and a second end protruding toward a center of a corresponding main opening  211 . Unlike the illustration in the drawings, the second end of each fitting portion  212  may not protrude from an inner circumferential surface of a corresponding main opening  211  but may be formed along the inner circumference of the corresponding main opening  211 . 
         [0094]    The sub reflective sheet  107  may include a body portion and a sub opening  130 . The sub reflective sheet  107  may not have fitting portions. An outer circumference of the body portion of the sub reflective sheet  107  may be circular. 
         [0095]    The main reflective sheet  201  is basically placed on a surface (e.g., an upper surface) of the sub reflective sheet  107 , but the fitting portions  212  of the main reflective sheet  201  are placed on the other surface (e.g., a lower surface) of the sub reflective sheet  107 . That is, the sub reflective sheet  107  may be fitted to the main reflective sheet  201  by the fitting portions  212  of the main reflective sheet  201 . Therefore, in the current embodiment, the movement of the sub reflective sheet  107  relative to the main reflective sheet  201  is also limited, and the lifting of the main reflective sheet  201  or the sub reflective sheet  107  can be prevented or reduced. 
         [0096]    Although not illustrated in the drawings, both a main reflective sheet and a sub reflective sheet may each include a body portion and fitting portions physically separated from the body portion. 
         [0097]    Embodiments of the inventive concept provide at least one of the following advantages. 
         [0098]    That is, even when an optical lens is disposed on an LED chip, since a sub reflective sheet is placed under the optical lens, luminance can be improved. In addition, since the sub reflective sheet and a main reflective sheet are fitted to each other, their relative movements are limited, which, in turn, prevents the lifting of the reflective sheets. Therefore, the light quality of a backlight assembly and the display quality of a display device can be improved. 
         [0099]    However, the effects of the inventive concept are not restricted to the one set forth herein. The above and other effects of the inventive concept will become more apparent to one of daily skill in the art to which the inventive concept pertains by referencing the claims. 
         [0100]    In concluding the detailed description, those skilled in the art will appreciate that many variations and modifications can be made to the preferred embodiments without substantially departing from the principles of the inventive concept. Therefore, the disclosed preferred embodiments of the inventive concept are used in a generic and descriptive sense only and not for purposes of limitation.