Patent Publication Number: US-2006002148-A1

Title: Optical member, backlight assembly having the optical member and display apparatus having the backlight assembly

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical member, a backlight assembly having the optical member and a display apparatus having the backlight assembly. More particularly, the present invention relates to an optical member capable of enhancing luminance and having smaller volume, a backlight assembly having the optical member, and a display apparatus having the backlight assembly.  
      2. Description of the Related Art  
      Generally, a backlight assembly provides a display apparatus with light to display images using the light. An example of a display apparatus that requires external light is a liquid crystal display (LCD) apparatus.  
      In order to emit light, a conventional backlight assembly employs a light source such as a light emitting diode (LED), a cold cathode fluorescent lamp (CCFL), a flat fluorescent lamp (FFL), etc.  
      The CCFL and the FFL are employed mainly by large display apparatuses, and LEDs are employed mainly by small display apparatuses.  
      LEDs have many merits such as high luminance, low power consumption, etc. However, LEDs have low luminance uniformity, therefore, large display apparatuses do not employ LEDs.  
      A backlight assembly having LEDs arranged in a matrix has been developed recently. A backlight assembly having the LEDs employs a light guide plate disposed over the LEDs. However, the light guide plate in such a backlight assembly increases the volume of the backlight assembly.  
     SUMMARY OF THE INVENTION  
      Exemplary embodiments of the invention include an optical member capable of enhancing luminance uniformity and reducing volume of a backlight assembly.  
      Exemplary embodiments of the invention further include a backlight assembly having the above-mentioned optical member.  
      Exemplary embodiments of the invention further include a display apparatus having the above-mentioned backlight assembly.  
      In one exemplary embodiment of the optical member, the optical member includes a light incident surface, a light exiting surface and a plurality of luminance uniformity enhancing members. The light exiting surface is opposite the light incident surface. The luminance uniformity enhancing members are formed on at least one of the light incident surface and the light exiting surface. Each of the luminance uniformity enhancing members includes a recessed surface formed between a first closed loop and a second closed loop surrounding the first closed loop.  
      In one exemplary embodiment of the backlight assembly, the backlight assembly includes an optical member, a light source and a receiving container. The optical member includes a first surface, a second surface opposite the first surface, and a plurality luminance uniformity enhancing members. The luminance uniformity enhancing members are formed on the first surface. Each of the luminance uniformity enhancing members includes a recessed surface formed between a first closed loop and a second closed loop surrounding the first closed loop. The light source provides the optical member with light. The receiving container receives the optical member and the light source.  
      In one exemplary embodiment of the display apparatus, the display apparatus includes a backlight assembly and a display panel. The backlight assembly includes an optical member, a light source and a receiving container. The optical member includes a first surface, a second surface opposite the first surface, and a plurality luminance uniformity enhancing members. The luminance uniformity enhancing members are formed on the first surface. Each of the luminance uniformity enhancing members includes a recessed surface formed between a first closed loop and a second closed loop surrounding the first closed loop. The light source provides the optical member with light. The receiving container receives the optical member and the light source. The display panel is disposed over the backlight assembly to convert a light generated from the backlight assembly into an image containing light.  
      In another exemplary embodiment of the backlight assembly, the backlight assembly includes an optical member, a plurality of light emitting diodes directing light toward the optical member, and a plurality of luminance uniformity enhancing members formed on the optical member and aligned with the plurality of light emitting diodes.  
      Therefore, luminance uniformity is enhanced due to the luminance uniformity enhancing member. Furthermore, a distance between the display panel and the backlight assembly may be reduced in order to reduce the volume of the display apparatus, and luminance of the display apparatus may be enhanced.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent by describing in detail the exemplary embodiments thereof, with reference to the accompanying drawings, in which:  
       FIG. 1  is a plan view illustrating a portion of an exemplary embodiment of an optical member according to the present invention;  
       FIG. 2  is a cross-sectional view taken along a line I-I′ in  FIG. 1 ;  
       FIG. 3  is a cross-sectional view illustrating a light reflecting layer formed on a light incident surface of the optical member in  FIG. 1 ;  
       FIG. 4  is a cross-sectional view illustrating an exemplary embodiment of a backlight assembly according to the present invention;  
       FIG. 5  is a cross-sectional view illustrating another exemplary embodiment of a backlight assembly according to the present invention;  
       FIG. 6  is a cross-sectional view illustrating a further exemplary embodiment of a backlight assembly according to the present invention;  
       FIG. 7  is a cross-sectional view illustrating yet another exemplary embodiment of a backlight assembly according to the present invention;  
       FIG. 8  is a cross-sectional view illustrating another exemplary embodiment of a backlight assembly according to the present invention;  
       FIG. 9  is a graph showing a distribution of luminance of an optical member having no luminance uniformity enhancing member formed thereon;  
       FIG. 10  is a graph showing the distribution of luminance in accordance with a distance between a diffusion plate and the optical member in  FIG. 9 ;  
       FIG. 11  is a graph showing a distribution of luminance of an optical member having luminance uniformity enhancing members formed thereon;  
       FIG. 12  is a graph showing the distribution of luminance in accordance with a distance between a diffusion plate and the optical member in  FIG. 11 ; and  
       FIG. 13  is a schematic cross-sectional view illustrating an exemplary embodiment of a display apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter the embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the thickness of layers, films, and regions are exaggerated for clarity. Like numerals refer to like elements throughout. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present.  
       FIG. 1  is a plan view illustrating a portion of an exemplary embodiment of an optical member according to the present invention, and  FIG. 2  is a cross-sectional view taken along line I-I′ in  FIG. 1 .  
      Referring to  FIGS. 1 and 2 , an optical member  100  includes, for example, PolyMethylMethAcrylate (PMMA). PMMA, a member of the acrylic family, is a clear and rigid plastic having a high degree of transparency and is often used as a shatterproof replacement for glass. The optical member  100  may correspond to a light guide plate.  
      In the illustrated embodiment, the optical member  100  has a rectangular plate shape with four side surfaces, a light incident surface  110 , and a light exiting surface  120 . The four side surfaces connect the light incident surface  110  to the light exiting surface  120 , and the light exiting surface  120  faces the light incident surface  110 . Both the light incident surface  110  and the light exiting surface  120  have a first area. The area of each of the side surfaces is smaller than the first area. While a rectangular plate shape is illustrated, it should be understood that alternate shapes would be within the scope of the optical member  100 .  
      Light that enters the optical member  100  through the light incident surface  110  exits the optical member  100  through the light exiting surface  120 . Light generated from LEDs that are arranged to form a regular pattern will have low luminance uniformity through an optical member having no luminance uniformity enhancing members.  
      In order to enhance luminance uniformity, the optical member  100  includes at least one luminance uniformity enhancing member  130  formed on one of the light incident surface  110  and the light exiting surface  120 . As shown in  FIG. 2 , and by example only, the luminance uniformity enhancing member  130  is formed on the light incident surface  110 . The luminance uniformity enhancing member  130  includes a first closed loop  134 , a second closed loop  133  disposed outside the first closed loop  134 , and a recessed surface  132  corresponding to a region defined between the first and second closed loops  134  and  133 .  
      The first and second closed loops  134  and  133  may have various shapes. For example, as shown, the first and second closed loops  134  and  133  may have a circular shape resulting in the recessed surface  132  of the luminance uniformity enhancing member  130  having the shape of an annulus, a doughnut shape. The luminance uniformity enhancing member  130  enhances luminance uniformity of light that exits the optical member  100  through the light exiting surface  120 .  
      With the first and second closed loops  134 ,  133  formed as circular shapes, the luminance uniformity enhancing member  130  formed on the light incident surface  110  corresponds to a circularly depressed portion. Therefore, the luminance uniformity enhancing member  130  includes the first and second closed loops  134  and  133 , and the recessed surface  132 . Each luminance uniformity enhancing member  130  is disposed such that each luminance uniformity enhancing member  130  corresponds to an LED. In one embodiment, a line passing perpendicularly through the light incident surface  110  and light exiting surface  120  and through a center of the luminance uniformity enhancing member  130  will also pass through a center of the LED that corresponds to that particular luminance uniformity enhancing member  130 .  
      In the illustrated embodiment where the first loop and second loop  134 ,  133  are circular shaped, the first loop  134  has a first radius L 1  and the second loop  133  has a second radius L 2  that is greater than the first radius L 1 . The first and second loops  134  and  133  are concentric.  
      The width W between the first and second loops  134  and  133  may be adjusted according to a desired amount of light to pass through the luminance uniformity enhancing member  130 . When the width W increases, a large amount of light is passed through the luminance uniformity enhancing member  130  as compared to when the width W decreases, a small amount of light is passed through the luminance uniformity enhancing member  130 .  
      The recessed surface  132  is inclined with respect to the light incident surface  110 . That is, a depth of the recessed surface  132  at the first loop  134  is deeper than a depth of the recessed surface  132  at the second loop  132 . In an exemplary embodiment of the luminance uniformity enhancing member  130 , the recessed surface  132  is flat. By example only, the recessed surface  132  may form an angle between approximately 0 and approximately 43 degrees with respect to the light incident surface  110 , although other angles outside the above described range may also be used in some embodiments of the optical member  100 .  
      In another exemplary embodiment of the luminance uniformity enhancing member  130 , the recessed surface  132  is rounded or otherwise curved (having a curved cross-section) or generally not flat. A boundary region between the recessed surface  132  and the light incident surface  110  may be rounded. Alternatively, one of the boundary regions formed among the first and second loops  134  and  133 , and the recessed surface  132  may be rounded. That is, any angled corners between the first and second loops  134 ,  133  and the recessed surface  132  may be smoothed.  
       FIG. 3  is a cross-sectional view illustrating a light reflecting layer formed on a light incident surface of the optical member in  FIG. 1 .  
      Referring to  FIG. 3 , the optical member  100  further includes a light reflecting layer  136  formed on a region enclosed by the first loop  134 . The light reflecting layer  136  reflects a portion of light advancing toward the region enclosed by the first loop  134 .  
      The optical member described with respect to  FIGS. 1-3  may be applied within a backlight assembly having a point like light source such as an LED.  
       FIG. 4  is a cross-sectional view illustrating an exemplary embodiment of a backlight assembly according to the present invention.  
      Referring to  FIG. 4 , a backlight assembly  600  includes a receiving container  200 , an optical member  300  having at least one luminance uniformity enhancing member  330 , and a light source  400 .  
      The receiving container  200  includes a bottom plate  210  and sidewalls (not shown) that extend from edges of the bottom plate  210 . The bottom plate  210  may have various shapes depending on the shape of the display panel. The bottom plate  210  and the sidewalls define a receiving space  215 .  
      The optical member  300  includes, for example PMMA. By example only, the optical member  300  has a rectangular plate shape. Therefore, the optical member  300  has four side surfaces, and first and second opposing surfaces  310  and  320 , which may be parallel facing surfaces as shown.  
      The first surface  310  faces the bottom plate  210  of the receiving container  200 . The first and second surfaces  310  and  320  each have a first area that is greater than an area of each of the four side surfaces of the optical member  300 .  
      The luminance uniformity enhancing member  330  is formed on one of the first and second surfaces  310  and  320 . In the illustrated embodiment, the luminance uniformity enhancing member  330  is formed on the first surface  310 . The luminance uniformity enhancing member  330  includes a first closed loop  336 , a second closed loop  334  disposed outside the first closed loop  336 , and a recessed surface  332  corresponding to a region defined by the first and second closed loops  336  and  334 .  
      The first and second closed loops  336  and  334  may have various shapes. In one embodiment, the first loop  336  has a circular shape having a first radius L 1 . The second loop  334  also has a circular shape having a second radius L 2  that is greater than the first radius L 1 . The first and second loops  336  and  334  are concentric.  
      A width W between the first and second loops  336  and  334  may be adjusted according to a desired amount of light to be passed through the luminance uniformity enhancing member  330 . When the width W increases, a large amount of light is passed through the luminance uniformity enhancing member  330 . On the contrary, when the width W decreases, a comparatively smaller amount of light is passed through the luminance uniformity enhancing member  330 .  
      The recessed surface  332  is inclined with respect to the first surface  310 . That is, the depth of the recessed surface  332  at the first loop  336  is deeper than a depth of the recessed surface  332  at the second loop  334 . In one exemplary embodiment, the recessed surface  332  is flat. By example only, the recessed surface  332  may form an angle between approximately 0 and approximately 43 degrees with respect to the first surface  310 , although other angles outside of this range would be within the scope of some embodiments of the luminance uniformity enhancing member  330 .  
      The optical member  300  further includes a light reflecting layer  338  formed on a region enclosed by the first closed loop  336 . The light reflecting layer  338  reflects light advancing toward the region enclosed by the first loop  336 .  
      A light source  400  is disposed within the receiving container  200  and is positioned between the bottom plate  210  and the optical member  300 . The light source  400  is disposed on the bottom plate  210  and faces the first surface  310 . An LED may be employed as the light source  400 .  
      The light source  400  is disposed at a region corresponding to a center 0 of the first loop  336 . That is, a line passing perpendicularly through the first surface  310  and second surface  320  and through the center 0 of the luminance uniformity enhancing member  330  will also pass through a center of the light source  400  that corresponds to that particular luminance uniformity enhancing member  330 . Light generated from the light source  400  advances toward the second surface  320 .  
      A large portion of the light generated from the light source  400  advances toward the luminance uniformity enhancing member  330 , and a first portion of the light is reflected from the light reflecting layer  338 .  
      A second portion of the light, which advances toward the luminance uniformity enhancing member  330 , is reflected on the recessed surface  332 . The remaining third portion of the light enters the optical member  300  through the recessed surface  332 , and spreads. Therefore, luminance may be uniformized.  
       FIG. 5  is a cross-sectional view illustrating another exemplary embodiment of a backlight assembly according to the present invention. The backlight assembly of  FIG. 5  is the same as the backlight assembly of  FIG. 4  except for the light source. Therefore, the same reference numerals will be used to refer to the same or like parts as those described with respect to the backlight assembly of  FIG. 4 , and any further explanation will be omitted.  
      In the illustrated embodiment shown in  FIG. 5 , the light source  400  of a backlight assembly  600  is arranged on the bottom plate  210  of the receiving container  200 . By example only, the light source device  400  includes a red light emitting diode RLED, a green light emitting diode GLED and a blue light emitting diode BLED.  
      Although only one LED for each color red, green, and blue is illustrated in  FIG. 5 , a plurality of each color LED are utilized in the backlight assembly  600  and the red, green and blue light emitting diodes RLED, GLED and BLED are arranged in a matrix such that the red, green and blue light emitting diodes RLED, GLED and BLED are alternately disposed on the bottom plate  210  of the receiving container  200 .  
      Alternatively, an LED that generates a white light may be used in place of the red, green, and blue light emitting diodes RLED, GLED, and BLED. In either embodiment, there may be one to one correspondence between the LEDs and the luminance uniformity enhancing members.  
       FIG. 6  is a cross-sectional view illustrating another exemplary embodiment of a backlight assembly according to the present invention. The backlight assembly shown in  FIG. 6  is the same as the backlight assembly of  FIG. 4  except for the light source. Therefore, the same reference numerals will be used to refer to the same or like parts as those described with respect to the embodiment shown in  FIG. 4 , and any further explanation will be omitted.  
      Referring to  FIG. 6 , the light source device  400  may include a red light emitting diode RLED, a green light emitting diode GLED and a blue light emitting diode BLED. Furthermore, the backlight assembly  600  includes a lens  410  positioned with respect to the light source device  400 . A center of the lens  410  may be aligned with a center of the light source device  400 . The lens  410  may include an outer periphery that is thicker than an inner portion of the lens  410 , although other lens shapes for the dispersion of light are within the scope of this embodiment. By employing the lens  410 , more portions of light may advance toward the luminance uniformity enhancing member  330  by modulating a path of the light from the light source device  400 .  
      More specifically, light that passes through the lens  410  advances such that the path of the light forms an acute angle with respect to a normal line of a light incident surface of the optical member  300 . While the lens  410  is shown with respect to the embodiment of  FIG. 6 , it should be understood that any of the embodiments disclosed herein may also employ a lens with respect to a light source.  
       FIG. 7  is a cross-sectional view illustrating another exemplary embodiment of a backlight assembly according to the present invention. The backlight assembly of  FIG. 7  is the same as the embodiment of  FIG. 4  except for an optical member. Therefore, the same reference numerals will be used to refer to the same or like parts as those described in the embodiment of  FIG. 4 , and any further explanation will be omitted.  
      Referring to  FIG. 7 , the optical member  300  includes a luminance uniformity enhancing member  335  formed on the second surface  320  through which light generated from a light source  400  exits the optical member  300 .  
      The luminance uniformity enhancing member  335  includes a first closed loop  336   a,  a second closed loop  334   a  disposed outside the first closed loop  336   a,  and a recessed surface  335   a  corresponding to a region defined between the first and second closed loops  336   a  and  334   a.    
      The first and second loops  336   a  and  334   a  may have various shapes. In one exemplary embodiment, the first loop  336   a  has a circular shape having a first radius L 1  and the second loop  334   a  also has a circular shape having a second radius L 2  that is greater than the first radius L 1 . The first and second loops  336   a  and  334   a  are concentric.  
      A width W between the first and second loops  336   a  and  334   a  may be adjusted according to a desired amount of light to be passed through the luminance uniformity enhancing member  335 . When the width W increases, a large amount of light is passed through the luminance uniformity enhancing member  335 . On the contrary, when the width W decreases, a comparatively smaller amount of light is passed through the luminance uniformity enhancing member  335 .  
      The recessed surface  335   a  is inclined with respect to the second surface  320 . More specifically, a depth of the recessed surface  335   a  at the first loop  336   a  is deeper than a depth of the recessed surface  335   a  at the second loop  334   a.  In one embodiment, the recessed surface  335   a  is flat. By example only, the recessed surface  335   a  may form an angle between approximately 0 and approximately 43 degrees with respect to the second surface  320 .  
      The optical member  300  may further include a light reflecting layer  338  formed on the first surface  310  corresponding to a region enclosed by the first loop  336   a.  That is, a line extending perpendicularly through the second surface  320  will pass through a center point of the first closed loop and a center of the light reflecting layer  338 . The light reflecting layer  338  reflects the light that advances towards the region enclosed by the first loop  336   a.  Alternatively, the light reflecting layer  338  may be formed on a portion of the second surface  320 , which is enclosed by the first loop  336   a.    
      It should be noted that placing the luminance uniformity enhancing members upon the light exiting surface as shown in the embodiment to  FIG. 7  may also be applied to any of the other embodiments disclosed herein.  
       FIG. 8  is a cross-sectional view illustrating another exemplary embodiment of a backlight assembly according to the present invention. The backlight assembly of  FIG. 8  is the same as the backlight assembly of  FIG. 4  except for a light diffusing plate. Therefore, the same reference numerals will be used to refer to the same or like parts as those described in the embodiment of  FIG. 4 , and any further explanation will be omitted.  
      Referring to  FIG. 8 , a light diffusing plate  500  is spaced apart from an optical member  300  by a distance ‘D’. The light diffusing plate  500  diffuses light that exits the optical member  300  in order to increase luminance uniformity. It should be noted that the other embodiments of the backlight assembly described herein may also utilize a light diffusing plate  500  placed relative to the optical member.  
      The distance ‘D’ is adjusted in consideration of luminance uniformity and the volume of the backlight assembly. In particular, the distance ‘D’ is optimized to maximize luminance uniformity while minimizing the volume of the backlight assembly.  
      When the distance ‘D’ increases, luminance uniformity is enhanced, but the volume of the backlight assembly also increases. On the contrary, when the distance ‘D’ decreases, the backlight assembly volume also decreases but the uniformity of luminance deteriorates. Conventionally, the distance ‘D’ is equal to or more than about 50 mm.  
      However, the distance ‘D’ between the light diffusing plate  500  and the optical member  300  may be reduced by utilizing a luminance uniformity enhancing member  330 . Therefore, the volume of the backlight assembly may be reduced, while maintaining the luminance uniformity.  
      In an embodiment employing the luminance uniformity enhancing members  330 , or other uniformity enhancing members described herein, the distance ‘D’ is in a range from about 20 mm to about 30 mm.  
      Hereinafter, a simulation result of a backlight assembly having no luminance uniformity enhancing member and a backlight assembly having a luminance uniformity enhancing member will be demonstrated and compared.  
       FIG. 9  is a graph showing a distribution of luminance of a comparative optical member having no luminance uniformity enhancing member formed thereon, and  FIG. 10  is a graph showing the distribution of luminance in accordance with a distance between a diffusion plate, such as light diffusing plate  500 , and the comparative optical member in  FIG. 9 .  
      Referring to FIGS.  8  to  10 , a light source  400  is disposed under the optical member  300 . In an experiment, an LED was employed as the light source  400 , and luminance and luminance distribution (uniformity) was measured at points 7 mm, 10 mm, 20 mm, 30 mm and 50 mm along the vertical axis (distances measured with a starting point at the light exiting surface  320  and measured outwardly from the optical member  300 ) and 0 mm, 40 mm, 80 mm, 120 mm, etc. along the horizontal axis over the optical member  300  (distances measured with a starting point at the center point 0), respectively.  
      A graph ‘A’ was obtained by measuring the luminance at a point spaced apart from the optical member  300  by 7 mm along the vertical direction. A graph ‘B’ was obtained by measuring the luminance at a point spaced apart from the optical member  300  by 10 mm along the vertical direction. A graph ‘C’ was obtained by measuring the luminance at a point spaced apart from the optical member  300  by 20 mm along the vertical direction. A graph ‘D’ was obtained by measuring the luminance at a point spaced apart from the optical member  300  by 30 mm along the vertical direction. A graph ‘E’ was obtained by measuring the luminance at a point spaced apart from the optical member  300  by 50 mm along the vertical direction.  
      Luminance in graph ‘A’ is the highest, but uniformity is the lowest. As a distance ‘D’ increases the luminance decreases, but the uniformity increases. Referring to graphs ‘A’ to ‘E’, luminance may become uniform when the distance from the optical member  300  is at least approximately 50 mm, such as shown by graph ‘E’.  
       FIG. 11  is a graph showing a distribution of luminance of an optical member having luminance uniformity enhancing members formed thereon, and  FIG. 12  is a graph showing the distribution of luminance in accordance with a distance between a diffusion plate, such as light diffusing plate  500 , and the optical member in  FIG. 11 .  
      Referring to  FIGS. 11 and 12 , a light source  400  is disposed under the optical member  300 . In an experiment, an LED was employed as the light source  400 , and luminance and luminance distribution (uniformity) was measured at points 7 mm, 10 mm, 20 mm, 30 mm and 50 mm along the vertical axis (distances measured with a starting point at the light exiting surface  320  and measured outwardly from the optical member  300 ) and 0 mm, 40 mm, 80 mm, 120 mm, etc. along the horizontal axis over the optical member  300  (distances measured with a starting point at the center point 0 ), respectively.  
      A graph ‘A’ was obtained by measuring the luminance at a point spaced apart from the optical member  300  by 7 mm along the vertical direction. A graph ‘B’ was obtained by measuring the luminance at a point spaced apart from the optical member  300  by 10 mm along the vertical direction. A graph ‘C’ was obtained by measuring the luminance at a point spaced apart from the optical member  300  by 20 mm along the vertical direction. A graph ‘D’ was obtained by measuring the luminance at a point spaced apart from the optical member  300  by 30 mm along the vertical direction. A graph ‘E’ was obtained by measuring the luminance at a point spaced apart from the optical member  300  by 50 mm along the vertical direction.  
      Luminance in graph ‘A’ was the highest, but uniformity is the lowest. As the distance ‘D’ increases the luminance decreases, but the uniformity increases.  
      Referring to graphs ‘A’ to ‘E’, luminance may become uniform when the distance from the optical member  300  is approximately 20 mm, such as shown by graph ‘C’.  
      Therefore, when the optical member  300  includes a luminance uniformity enhancing member, the distance between the light diffusing member, such as light diffusing plate  500 , may be reduced while enhancing luminance.  
       FIG. 13  is a schematic cross-sectional view illustrating an exemplary embodiment of a display apparatus according to the present invention.  
      Referring to  FIG. 13 , a display apparatus  800  includes a backlight assembly  600  and a display panel  700 . The backlight assembly may be one of the above-described backlight assembly embodiments. Therefore, the same reference numerals will be used to refer to the same or like parts as those described in the embodiment shown in  FIG. 4  and any further explanation will be omitted.  
      The display panel  700  includes a first substrate  710 , a second substrate  730  and a liquid crystal layer  720 . The first substrate  700  includes a pixel electrode, a thin film transistor (TFT) for applying driving signals to the pixel electrode, and a signal line through which the driving signal is transmitted. The pixel electrode includes an optically transparent and electrically conductive material, for example, such as, but not limited to, indium tin oxide (ITO), indium zinc oxide (IZO), amorphous indium tin oxide (a—ITO), etc.  
      The second substrate  730  faces the first substrate  710 . The second substrate includes common electrode and color filters facing the pixel electrode of the first substrate  710 . The common electrode includes an optically transparent and electrically conductive material, such as, but not limited to, indium tin oxide (ITO), indium zinc oxide (IZO), amorphous indium tin oxide (a—ITO), etc.  
      The liquid crystal layer  720  is interposed between the first and second substrates  710  and  730 . Molecules of the liquid crystal layer  720  are rearranged when electric fields are formed between the pixel electrode of the first substrate  710  and the common electrode of the second substrate  730 , so that light transmittance of the liquid crystal layer  720  is modulated to display black and white images. Furthermore, when a light that has passed through the liquid crystal layer  720  passes through the color filters, the black and white images are converted into color images.  
      It should be understood that because the light diffusing plate  500  may be placed closer to the optical member  300  because of the luminance uniformity enhancing members, the display panel  700  may likewise be placed closer to the optical member  300 , thus reducing the overall volume of the display apparatus  800 .  
      According to the embodiments described herein, the luminance uniformity enhancing member includes an annular (donut) shaped groove formed on a surface of the optical member. Therefore, luminance uniformity is enhanced. Furthermore, a distance between a display panel and the backlight assembly may be reduced to decrease volume of a display apparatus, and a luminance of the display apparatus may be enhanced.  
      Having described the exemplary embodiments of the present invention and its advantages, it is noted that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by appended claims. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the instant specification. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.