Abstract:
A monolithic light guiding and dispersing plate is provided in a backlighted display panel for receiving input light from one or more edge sources and for guiding the received light throughout the plate for substantially uniform reflection upwardly and substantially uniform dispersal toward an image forming plane located above the light guiding and dispersing plate. In one embodiment, the light guiding and dispersing plate has a light receiving surface upon which the light generated by an edge light source is incident, a top major surface which is adjacent to the light receiving surface and on which a plurality of first protrusions are formed and elongated in a first direction, wherein the first protrusions have cross-sections in the shapes of partial ellipses. The plate further has a bottom major surface in which light reflecting recesses are defined to reflect light upwardly towards the top major surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2007-0114992 filed on Nov. 12, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of Invention 
     The present disclosure of invention relates to a light guiding and dispersing plate and a display device having the same, and more particularly, to a light guiding plate which can improve the luminance and the luminance uniformity of a display device (such as a liquid crystal display (LCD) device) equipped with a backlight assembly, and a display device having the light guiding plate. 
     2. Description of the Related Technology 
     Backlight assemblies, which are widely used in liquid crystal display (LCD) devices, are important elements that can affect the brightness and the external appearance of LCD devices. Backlight assemblies are classified into a direct-type backlight driven assembly and an edge-type driven backlight assembly where the latter includes an edge mounted light source, a light guiding plate that receives light from the edge mounted light source and various optical sheets such as a prism sheet, a diffusion sheet and a protection film. However, such backlight assemblies generally include a series of light transmitting mediums (e.g., layers) having different refractive indexes so that the interfaces between these mediums may cause a considerable amount of light loss since light passes through all the mediums and a portion can be refracted at each interface crossing. In addition, since backlight assemblies often include a number of separate optical sheets, it is relatively difficult to manage the assembly of such backlight assemblies, in which the manufacturing cost of the backlight assemblies is generally high due to the large number of separate parts and the overhead for handling each. 
     In particular, backlight assemblies using point type light sources such as light-emitting diodes (LED&#39;s), which has high luminance and high color representation capability, may result in a hot spot phenomenon in which the bright and dark portions (constructive reinforcement and destructive interference) both appear visible. 
     SUMMARY 
     Aspects of the present disclosure of invention include the provision of a light guiding plate which can provide appropriate optical properties for displaying an image and improve luminance uniformity without requiring optical sheets, and a display device having the light guiding plate. However, the aspects of the present disclosure are not to be restricted to the specific embodiments set forth herein. 
     According to an aspect of the present disclosure, there is provided a display device including a display panel; an edge mounted light source; and a monolithic light guiding and dispersing plate which guides light generated by the edge-mounted light source along parallel waveguides and redirects the guided light toward and disperses the redirected light to the display panel, where the light guiding plate comprises a light receiving surface upon which the light generated by the edge-mounted light source is incident, a first surface which is adjacent to the light receiving surface and on which a plurality of first protrusions (waveguides) are defined to extend longitudinally in a first direction parallel to one another, and a second surface which faces the first surface and in which a plurality of light reflecting structures (e.g., recesses) are formed. In one embodiment, the first protrusions have cross-sections in the shape of partial ellipses where the cross-sections are taken along a plane perpendicular to the first direction, and where each ellipse has a minor axis parallel to the first surface and a major axis perpendicular to the first surface. 
     The light guiding plate may also include a plurality of spacing portions which are interposed either regularly or periodically between the first protrusions and extend longitudinally in parallel with the first protrusions. 
     The spacing portions may have at least one of a flat surface, a protruding surface, and a recessed surface. 
     The spacing portions may have a cross-section of the shape of a partial circle along the plane perpendicular to the first direction. 
     The ellipse may have a minor axis radius a and a major axis radius and the circle may have a radius r, wherein the minor axis radius a and the radius r satisfy the following relation: r&lt;a. 
     A height of the first protrusions from an imaginary horizontal surface may be greater than a height of the spacing portions from the imaginary horizontal surface. 
     One or more immediately adjacent first protrusions may be formed between a pair of successive spacing portions and one or more immediately adjacent spacing portions may be formed between a pair of successive first protrusions. 
     Spacing portions that are formed in the vicinity of the light receiving surface may have at least one of a protruding surface and a recessed surface and other spacing portions may have a flat surface. 
     The width of the spacing portions may be less than one fifth of the width of the first protrusions. 
     The ellipse may have a minor axis radius a and a major axis radius b, wherein the minor axis radius a and the major axis radius b satisfy the following relation: 1&lt;b/a&lt;4. 
     The light guiding plate may also include a plurality of triangular protrusion patterns which are formed on the first surface and elongated in parallel with the first protrusions and have a cross-section of the shape of a triangular prism along a plane perpendicular to the first direction. 
     The first protrusions may be formed on portions of the first surface which are adjacent to either lateral surface of the light guiding plate that is perpendicular to the light receiving surface, the first surface and the second surface, and the triangular patterns may be formed between the first protrusions in parallel with the first protrusions. 
     The sum of the widths of first protrusions on one side of the light guiding plate may be two or more times greater than a thickness of the light guiding plate. 
     The triangular patterns and the first protrusions may be alternately arranged in parallel with each other. 
     The display panel may include a plurality of pixels and a pitch of the first protrusions may be less than or the same as a pitch of the pixels. 
     The display device may also include a prism sheet which is formed between the light guiding plate and the display panel and on which a plurality of prism patterns are formed, wherein a pitch of the first protrusions is less than or the same as a pitch of the prism patterns. 
     The light guiding plate may also include one or more light reflecting recesses which are interposed between second protrusions protruding from a bottom surface of the plate. 
     The second protrusions may extend in the same direction as the first protrusions in parallel with the first protrusions. 
     The light source may include point type light sources such as light emitting diodes. 
     According to another aspect of the present disclosure, there is provided a light guiding plate including a light receiving surface; a first surface which is adjacent to the light receiving surface and on which a plurality of first protrusions that extend in a direction perpendicular to the light receiving surface are formed; a second surface which faces the first surface and on which a plurality of second protrusions are formed, wherein the first protrusions have a cross-section of the shape of a partial ellipse along a plane parallel to the light receiving surface, the ellipse having a minor axis parallel to the first surface and a major axis perpendicular to the first surface. 
     The light guiding plate may also include a plurality of spacing portions which are formed among the first protrusions in parallel with the first protrusions. 
     The width of the spacing portions may be less than one fifth of the width of the first protrusions. 
     The ellipse may have a minor axis radius a and a major axis radius b, wherein the minor axis radius a and the major axis radius b satisfy the following relation: 1&lt;b/a&lt;4. 
     The light guiding plate may also include one or more reflection patterns which are formed among the second protrusions and have at least one reflection surface that faces the light receiving surface. 
     The second protrusions may extend in the same direction as the first protrusions in parallel with the first protrusions. Other aspects of the disclosure will be become clearer from the below detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and features of the present disclosure of invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
         FIG. 1  illustrates an exploded perspective view of a liquid crystal display (LCD) device according to an exemplary embodiment; 
         FIG. 2A  illustrates a perspective view of a light guiding plate according to a first exemplary embodiment; 
         FIG. 2B  illustrates a cross-sectional view taken along line IIb-IIb′ of  FIG. 2A ; 
         FIG. 2C  illustrates a cross-sectional view taken along line IIc-IIc′ of  FIG. 2A ; 
         FIG. 2D  illustrates a detailed cross-sectional view taken along line IIb-IIb′ of  FIG. 2A ; 
         FIG. 3A  illustrates a perspective view of a light guiding plate according to a second exemplary embodiment; 
         FIG. 3B  illustrates a cross-sectional view taken along line IIIb-IIIb′ of  FIG. 3A ; 
         FIG. 4A  illustrates a perspective view of a light guiding plate according to another exemplary embodiment; 
         FIG. 4B  illustrates a cross-sectional view taken along line IVb-IVb′ of  FIG. 4A ; 
         FIG. 4C  illustrates a detailed cross-sectional view taken along line IVb-IVb′ of  FIG. 4A ; 
         FIG. 5A  illustrates a perspective view of a light guiding plate according to another exemplary embodiment; 
         FIG. 5B  illustrates a cross-sectional view taken along line Va-Va′ of  FIG. 5A ; 
         FIG. 6A  illustrates a perspective view of a light guiding plate according to another exemplary embodiment; 
         FIG. 6B  illustrates a cross-sectional view taken along line VIa-VIa′ of  FIG. 6A ; 
         FIG. 7  illustrates a light guiding plate according to another exemplary embodiment; 
         FIG. 8A  illustrates a light guiding plate according to another exemplary embodiment; 
         FIG. 8B  illustrates a cross-sectional view taken along line VIIIa-VIIIa′ of  FIG. 8A ; 
         FIG. 9A  illustrates a light guiding plate according to another exemplary embodiment, 
         FIG. 9B  illustrates a cross-sectional view taken along line IXa-IXa′ of  FIG. 9A ; 
         FIGS. 10A through 10C  illustrate color-coded diagrams of computer simulation results of the luminance properties of the light guiding plate of the embodiment of  FIGS. 2A through 2D ; 
         FIG. 11  illustrates a diagram of the relationship between the pitch of first protrusions of the light guiding plate of the exemplary embodiment of  FIGS. 2A through 2D  and the pitch of pixels of a display panel; 
         FIG. 12  illustrates a diagram of the relationship between the pitch of the first protrusions of the light guiding plate of the exemplary embodiment of  FIGS. 2A through 2D  and the pitch of prism patterns on a prism sheet; 
         FIG. 13A  illustrates a diagram of an optical phenomenon that occurs in a first protrusion of the light guiding plate of the exemplary embodiment of  FIGS. 2A through 2D ; 
         FIG. 13B  illustrates a diagram of an optical phenomenon that occurs in a first protrusion of a light guiding plate according to a comparative example; and 
         FIGS. 14A through 14C  illustrate color-coded diagrams of computer simulation results of the optical properties of light guiding plates having different shapes of first protrusions. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure of invention will now be provided more fully with reference to the accompanying drawings, in which exemplary embodiments are shown. 
       FIG. 1  illustrates an exploded perspective view of a liquid crystal display (LCD) device  1  according to an exemplary embodiment. Referring to  FIG. 1 , an LCD device  1  includes a display panel assembly  10  which displays an image with the aid of light, a backlight assembly  20  which provides light to the display panel assembly  10 , and a housing unit  30  which accommodates and fixes the display panel assembly  10  and the backlight assembly  20 . 
     The display panel assembly  10  includes a display panel  110  which displays an image and a driving unit  120  which drives the display panel  110 . The display panel  110  includes a thin film transistor (TFT) substrate  112 , a color filter substrate  112  and a liquid crystal layer (not shown) which is interposed between the TFT substrate  112  and the color filter substrate  112 . The driving unit  120  is disposed on one side of the TFT substrate  112 . The driving unit  120  includes a plurality of flexible printed circuit boards (FPCBs)  121 , a plurality of driving chips  122  which are mounted on the respective FPCBs  121 , and a printed circuit board (PCB)  123  which is connected to the FPCBs  121 . The driving unit  120  may be formed using a chip-on-film method. Alternatively, the driving unit  120  may be formed using a tape carrier package (TCP) method or a chip-on-glass (COG) method. All or some of the driving chips  122  may be formed during the formation of a TFT (not shown) of the TFT Substrate  112 . 
     The backlight assembly  20 , which supplies light to the display panel  110 , is disposed at a rear side of the display panel  110 . The backlight assembly  20  includes a light source  210 , a light guiding plate  220  which is disposed between the light source  210  and the display panel  110  and transmits light generated by the light source  210  to the display panel  110 , a prism sheet  230  which is disposed between the light guiding plate  220  and the display panel  110  and refracts and transmits light emitted from the light guiding plate  220  toward the display panel  110 , a diffusion sheet  240  which diffuses light, and a reflection sheet  250  which is disposed at a rear side of the light guiding plate  220  and reflects leakage light upward. The light source  210  may include edge-mounted point light sources such as light-emitting diodes (LED&#39;s). Alternatively, an elongated linear lamp (not shown) such as a fluorescent lamp may be used as the edge-mounted light source  210 . The light guiding plate  220  has a light emission surface  227  which is configured to enable light incident upon an edge of the light guiding plate  220  to be uniformly transmitted across the entire surface of the display panel  110 . The light guiding plate  220  also has an opposite surface  228  which is on the opposite side of the light emission surface  227 . A plurality of patterns having a predetermined shape may be formed on the light emission surface  227  and/or on the opposite surface  228  of the light guiding plate  220 , which will be described later in detail. The backlight assembly  20  may be disposed at a front side of the display panel  110 , and the positions and structures of the prism sheet  230 , the diffusion sheet  240  and the reflection sheet  250  may be altered if desired. 
     The housing unit  30  includes a bottom chassis  330  which accommodates the backlight assembly  20 , a molded frame  320  which is disposed between the backlight assembly  20  and the display panel  110 , fixes the backlight assembly  20 , and guides the position of the display panel  110 , and a top chassis  310  which covers the front of the display panel  110  to support the backlight assembly  20  and the display panel  110 . 
     A light guiding plate according to an exemplary embodiment of the present disclosure of invention will hereinafter be described in detail with reference to  FIGS. 2A through 2D . 
       FIG. 2A  illustrates a perspective view of a light guiding plate  220   a  made of a transparent material (e.g., plastic) having a predetermined refractive index greater than that of air and shaped according to a first exemplary embodiment,  FIG. 2B  illustrates a first cross-sectional view taken along line IIb-IIb′ of  FIG. 2A ,  FIG. 2C  illustrates a cross-sectional view taken along line IIc-IIc′ of  FIG. 2A , and  FIG. 2D  illustrates another detailed cross-sectional view taken along line IIb-IIb′ of  FIG. 2A . 
     Referring to  FIGS. 2A through 2C , the light guiding plate  220   a  includes an upper major surface having a plurality of light emission surface portions  227   a  where each light outputting surface portion  227   a  includes a convex first protrusion  221  contiguous with and extending above an adjacent flat portion  222   a . The light guiding plate  220   a  further includes on at least one edge thereof, a light receiving surface  224  which faces an edge-mountable light source (not shown). In one embodiment, the first protrusions  221  extend longitudinally in a direction perpendicular to the plane of the light receiving surface  224  so as to define partial cylinders or elongations of a partial ellipse. In other words, the first protrusions  221  may each have a cross-section of the shape of a partial ellipse or a partial circle when viewed in cross section (e.g.,  FIG. 2B ,  2 D) along a plane parallel to the light receiving surface  224 . As indicated above, plurality of flat spacing portions  222   a  are interposed between the first protrusions  221 . 
     Still referring to  FIGS. 2A through 2C , the light guiding plate  220   a  includes a lower major surface  228  having a plurality of convex second protrusions  223  formed thereon. The second protrusions  223  may be elongated in the same elongation direction as the first protrusions  221 , and as seen in  FIG. 2B  there may be a one-for-one correspondence between the first and second convex protrusions,  221  and  223 . The lower major surface  228  may further include a plurality of light refracting cutouts referred to herein as reflection patterns  225   a  where the latter are interposed between the second protrusions  223  as may be best seen in  FIG. 2A . Referring to  FIG. 2C , each of the reflection patterns  225   a  has a first reflection surface  226   a  which is closer to and faces the light receiving surface  224  at a first angle (θ 1 ). In one embodiment, the reflection patterns  225  are engraved into the bottom surface  228  as hollow regions in the shape of rectangular prisms. Alternatively, the reflection patterns  225  may be formed on the bottom surface  228  as printed patterns of reflective metal angled at appropriate angles for providing desired light reflection functions. 
     Referring to the embodiment of  FIG. 2C , the light guiding plate  220   a  is shaped to includes a plurality of reflection zones  225   1  and  225   2  which are V-shaped and are formed on the lower surface  228  of the light guiding plate  220   a  as recessed patterns. Each of the reflection zones  225   1  and  225   2  has a first reflection surface  226   1  closer to surface  224  and a second reflection surface  226   2  farther from surface  224 , respectively. In order to improve the efficiency of the reflection of light, a base angle θ 1  of the first reflection surface  226   1  and a base angle θ 2  of the second reflection surface  226   2  may be set to satisfy the following relation: θ 1 ≦θ 2 . The more distant the reflection zones  225   1 ,  225   2 , etc. are from the primary light inputting or receiving surface  224 , the lower the luminance of a reflected light pattern tends to be for the respective reflection zone. Thus, in accordance with the disclosure and in order to improve the luminance of a reflected light pattern at a position more distant from the light receiving surface  224 , the corresponding height (e.g., H 2 ) of the more distant reflection zone (e.g.,  225   2 ) is set to be greater than a height (e.g., H 1 ) of the closer reflection pattern (e.g.,  225   1 ). In one embodiment, the light guiding plate  220   a  is formed of a plastic comprising at least one of a polycarbonate (PC)-series resin, a polymethylmethacrylate (PMMA)-series resin or a methacrylate-styrene (MS) copolymer. 
     Referring to  FIG. 2D , in one class of embodiments, the cross-sections of the first protrusions  221  have the shape of part of an imaginary ellipse E. The minor axis (minor axis radius: a) of the imaginary ellipse E is parallel with an imaginary horizontal surface H that extends between the interfaces between the first protrusions  221  and the spacing portions  222 A, and the major axis (major axis radius: b) of the imaginary ellipse E is perpendicular to the imaginary horizontal surface H. Ideally, the cross-sections of the first protrusions  221  have the shape of part of the imaginary ellipse E. However, preferably, the first protrusions  221  may partially have an angular cross-section, rather than a round filet cross-section, near the interfaces with the spacing portions  222   a  due to a process margin. In order to improve luminance uniformity, the minor axis radius a and the major axis radius b of the imaginary ellipse E may satisfy the following relation: 1&lt;b/a&lt;4. In its implementation, the surface of the imaginary ellipse E may be approximated by a fourth-degree polynomial if the imaginary ellipse E satisfies the following relation: a&lt;b/2. On the other hand, the imaginary ellipse E may be approximated by an ellipse function or a fourth-degree or higher polynomial if the imaginary ellipse E satisfies the following relation: a&gt;b/2. A height h of an apex Z of the imaginary ellipse E from the imaginary horizontal surface H may be less than the major axis radius b of the ellipse E. A distance between a pair of adjacent first protrusions  221 , i.e., a width d of the spacing portions  222   a , may be the same as or less than one fifth of a width w of the first protrusions  221 . More specifically, the width d may be the same as or less than one tenth of the width w. That is, a distance between the apexes Z of the pair of adjacent first protrusions  221 , i.e., a pitch p of the first protrusions  221 , may satisfy the following relation: p=w+d where d&lt;2. 
     A light guiding plate according to an exemplary second embodiment of the present invention will hereinafter be described in detail with reference to  FIGS. 3A and 3B . 
       FIG. 3A  illustrates a perspective view of a light guiding plate  220 B according to the second exemplary embodiment, and  FIG. 3B  illustrates a cross-sectional view taken along line IIIb-IIIb′ of  FIG. 3A . In  FIGS. 2A through 2D ,  3 A and  3 B, like reference numerals represent like elements, and thus, detailed descriptions thereof will be skipped. 
     Referring to  FIGS. 3A and 3B , the light guiding plate  220   b  includes a plurality of rounded spacing portions  222   b  which are formed among a plurality of first protrusions  221  as recesses, and a plurality of reflection patterns  225   b  which are formed as hemispherical recessed patterns. 
     The rounded spacing portions  222   b  are recessed into the light emission surface  227   b  as shown. The spacing portions  222   b  are elongated in the same direction as the first protrusions  221  and are parallel to the first protrusions  221 . The spacing portions  222   b  may have a cross-section of the shape of a partial circle or a partial ellipse along a plane parallel to a light receiving surface  224  and is perpendicular to the direction in which the first protrusions  221  extend. 
     One or more second protrusions  223  are formed on an opposite (bottom) surface  228  which is on the opposite side of the plate from the light emission surface  227   b . A plurality of reflection patterns  225   b  are formed among the second protrusions  223 . Each of the reflection patterns  225   b  includes a forward reflection surface  226   b  which faces and is closer to the light receiving surface  224 . The reflection patterns  225   b  are recessed into the opposite surface  228  as shown. The diameter of a reflection pattern  225   b  that is more distant from the light receiving surface  224  may be greater than the corresponding diameter of a reflection pattern  225   b  that is less distant from the light receiving surface  224  so as to compensate for diminution of incident luminance with increase of distance from the light sourcing surface  224 . However, the shape of the reflection patterns  225   b  is not restricted to that of the hemispherical concavities illustrated in  FIGS. 3A and 3B . That is, the reflection patterns  225   b  may be formed as otherwise shaped concavities or as reflective protrusions formed of reflective metal for example. 
     A light guiding plate according to exemplary third embodiment will hereinafter be described in detail with reference to  FIGS. 4A through 4C . 
       FIG. 4A  illustrates a perspective view of a light guiding plate  220   c  according to the third exemplary embodiment,  FIG. 4B  illustrates a cross-sectional view taken along line IVb-IVb′ of  FIG. 4A , and  FIG. 4C  illustrates a detailed cross-sectional view taken along line IVb-IVb′ of  FIG. 4A . In  FIGS. 2A through 2D  and  4 A through  4 C, like reference numerals represent like elements, and thus, detailed descriptions thereof will be skipped. 
     Referring to  FIGS. 4A through 4C , the light guiding plate  220   c  includes a plurality of first protrusions  221 , a plurality of convex spacing portions  222   c  which are formed to be interposed among the first protrusions  221  and to protrude from a light emission surface  227   c , and a plurality of reflection patterns  225   c  which are formed on an opposite surface  228  as pyramid-shaped hollows for example. The opposite surface  228  is on the opposite side of the light emission surface  227   c.    
     The spacing portions  222   c  are formed on the light emission surface  227   c  as protrusions. The spacing portions  222   c  may extend in the same direction as the first protrusions  221  and may thus be parallel to the first protrusions  221 . The spacing portions  222   c  may have a cross-section of the shape of a partial circle or a partial ellipse along a plane parallel to a light receiving surface  224  and is perpendicular to the direction in which the first protrusions  221  extend. 
     One or more second protrusions  223  are formed on the opposite surface  228 , and the reflection patterns  225   c  are formed among the second protrusions  223  as pyramids. Each of the reflection patterns  225   c  has a reflection surface  226   c  which is triangular. The area of the reflection surface  226   c  of a reflection pattern  225   c  that is more distant from the light receiving surface  224  may be greater than the corresponding area of the reflection surface  226   c  of a reflection pattern  225   c  that is less distant from the light receiving surface  224 . 
     Referring to  FIG. 4C , the cross-sections of the first protrusions  221  have the shape of part of an imaginary ellipse E. The minor axis (minor axis radius: a) of the imaginary ellipse E is parallel with an imaginary horizontal surface H′ that extends between the interfaces between the first protrusions  221  and the spacing portions  222   c , and the major axis (major axis radius: b) of the imaginary ellipse E is perpendicular to the imaginary horizontal surface H′. 
     The cross-sections of the spacing portions  222   c  have the shape of part of an imaginary circle C having a radius r. A height h 1  of the first protrusions  221  from the imaginary horizontal surface H′ may be greater than a height h 2  of the spacing portions  222   c  from the imaginary horizontal surface H′. The height h 2  may be less than the radius r of the imaginary circle C. 
     The radius r of the imaginary circle C may be less than the minor axis radius a of the imaginary ellipse E. 
     A light guiding plate according to another exemplary embodiment will hereinafter be described in detail with reference to  FIGS. 5A and 5B . 
       FIG. 5A  illustrates a perspective view of a light guiding plate  220   d  according to another exemplary embodiment, and  FIG. 5B  illustrates a cross-sectional view taken along line Vb-Vb′ of  FIG. 5A . In  FIGS. 4A through 4C ,  5 A and  5 B, like reference numerals represent like elements, and thus, detailed descriptions thereof will be skipped. 
     Referring to  FIGS. 5A and 5B , the light guiding plate  220   d  includes a plurality of first protrusions  221  and a plurality of spacing portions  222   d . More specifically, one or more spacing portions  222   d  may be formed between a pair of successive first protrusions  221  as raised patterns. The spacing portions  222   d  may extend in the same direction as the first protrusions  221 . The spacing portions  222   d  may have an almost hemi-circle or hemi-elliptical cross-section when taken along a plane parallel to a light receiving surface  224  and is perpendicular to the direction in which the first protrusions  221  extend. 
     More specifically, one or more spacing portions  222   d  may be formed between a pair of adjacent first protrusions  221  as protrusions, and the cross-sections of the spacing portions  222   d  may have the shape of a partial circle or a partial ellipse. The shape of the spacing portions  222   d  and the number of spacing portions  222   d  formed between the pair of adjacent first protrusions  221  may be altered if necessary. For example, the shapes of the first protrusions  221  and the spacing portions  222   d  may be altered according to the position and the type of a light source. 
     The width of the spacing portions  222   d  may be varied to provide different optical effects as may be deemed appropriate. For example, one or more spacing portions  222   d  may be formed between a pair of adjacent first protrusions  221  as raised patterns, and the number of spacing portions  222   d  formed between the pair of adjacent first protrusions  221  may vary from one portion to another portion of the light guiding plate  220   d  according to the type and the position of a light source. 
     A light guiding plate according to another exemplary embodiment will hereinafter be described in detail with reference to  FIGS. 6A and 6B . 
       FIG. 6A  illustrates a perspective view of a light guiding plate  220   e  according to another exemplary embodiment, and  FIG. 6B  illustrates a cross-sectional view taken along line VIb-VIb′ of  FIG. 6A . In  FIGS. 4A through 4C ,  6 A and  6 B, like reference numerals represent like elements, and thus, detailed descriptions thereof will be skipped. 
     Referring to  FIGS. 6A and 6B , the light guiding plate  220 E includes a plurality of first protrusions  221 ′ which are formed as raised patterns. The first protrusions  221 ′ extend in a direction perpendicular to a light receiving surface  224 . The cross-sections of the first protrusions  221 ′ may have the shape of a partial circle or a partial ellipse. Two or three first protrusions  221 ′ and two or three spacing portions  222   e  may be alternately arranged as shown. 
     A light guiding plate according to another exemplary embodiment will hereinafter be described in detail with reference to  FIG. 7 . 
       FIG. 7  illustrates a perspective view of a light guiding plate  220   f  according to another exemplary embodiment. In  FIGS. 4A through 4C  and  7 , like reference numerals represent like elements, and thus, detailed descriptions thereof will be skipped. 
     Referring to  FIG. 7 , the light guiding plate  220   f  includes a plurality of spacing portions  222   f . Each of the spacing portions  222   f  includes a raised portion and a flat portion. The light guiding plate  220   f  also includes a light receiving surface  224  which faces a light source (not shown); a light emission surface  227   f , and a plurality of first protrusions  221  which are formed on the light emission surface  227   f . The light emission surface  227   f  is adjacent the light receiving surface  224 . The first protrusions  221  may extend in a direction perpendicular to the light receiving surface  224 . The spacing portions  222   f  may be disposed among the first protrusions  221 . Portions of the spacing portions  222   f  close to the light receiving surface  224  may be formed as raised patterns, and portions of the spacing portions  222   f  distant from the light receiving surface  224  may be formed as non-raised flat patterns. However, the present disclosure of invention is not restricted to that illustrated in  FIG. 7 . That is, the portions of the spacing portions  222   f  close to the light receiving surface  224  may be formed as recessed patterns, and the portions of the spacing portions  222 F distant from the light receiving surface  224  may be formed as raised patterns. The shape of the spacing portions  222   f  may be altered according to the type, position and shape of the corresponding light source so as to provide the desired uniform distribution of refracted light. 
     A light guiding plate according to another exemplary embodiment will hereinafter be described in detail with reference to  FIGS. 8A and 8B . 
       FIG. 8A  illustrates a perspective view of a light guiding plate  220   g  according to another exemplary embodiment, and  FIG. 8B  illustrates a cross-sectional view taken along line VIIIb-VIIIb′ of  FIG. 8A . In  FIGS. 4A through 4C ,  8 A and  8 B, like reference numerals represent like elements, and thus, detailed descriptions thereof will be skipped. 
     Referring to  FIGS. 8A and 8B , the light guiding plate  220 G includes a plurality of first protrusions  221   g  and a plurality of triangular patterns  322  which are all formed on a light emission surface  227   g . More specifically, the light guiding plate  220   g  also includes a light receiving surface  224  which faces a light source (not shown) and the first protrusions  221   g  and the triangular patterns  322  which are formed on the light emission surface  227   g . The light emission surface  227   g  is adjacent to the light receiving surface  224 . The first protrusions  227   g  may extend in a direction perpendicular to the light receiving surface  224 . The first protrusions  227   g  may be formed on portions of the light guiding plate  220   g  that are adjacent to either a lateral surface  229   a  or a lateral surface  229   b  of the light guiding plate  220   g . The lateral surfaces  229   a  and  229   b  are perpendicular to the light receiving surface  224 , the light emission surface  227   g , and an opposite surface  228  that faces the light emission surface  227   g . The cross-sections of the first protrusions  221   g  may be partially elliptical when taken along a plane parallel to the light receiving surface  224 . More specifically, the cross-sections of upper portions of the first protrusions  221   g  may have the shape of a partial ellipse, and the cross-sections of lower portions of the first protrusions  221   g  may have an angular shape. That is, the cross-sections of the first protrusions  221   g  may have the shape of a triangle with a rounded top. The triangular patterns  322  may be formed between the first protrusions  221   g . That is, the first protrusions  221   g  may be formed on both sides of the light guiding plate  220   g , and the triangular patterns  322  may be formed between the first protrusions  221   g.    
     The first protrusions  221   g  function to remove dark portions that may be generated in the output light due to frames on the lateral surfaces  229   a  and  229   b  being reflected by the light emission surface  227   g . For this, the sum of the widths of first protrusions  221   g  on one side of the light guiding plate  220   g  may be two or more times greater than the width of the light guiding plate  220   g.    
     A light guiding plate according to another exemplary embodiment will hereinafter be described in detail with reference to  FIGS. 9A and 9B . 
       FIG. 9A  illustrates a perspective view of a light guiding plate  220   h  according to another exemplary embodiment, and  FIG. 9B  illustrates a cross-sectional view taken along line IXb-IXb′ of  FIG. 9A . In  FIGS. 4A through 4C ,  9 A and  9 B, like reference numerals represent like elements, and thus, detailed descriptions thereof will be skipped. 
     Referring to  FIGS. 9A and 9B , the light guiding plate  220 H includes a plurality of first protrusions  221   g  and a plurality of triangular patterns  322  which are alternately formed on a light emission surface  227   h . The first protrusions  221   g  may be partially elliptical when taken along a plane parallel to a light receiving surface  224 . More specifically, the cross-sections of upper portions of the first protrusions  221   g  may have the shape of a partial ellipse, and the cross-sections of lower portions of the first protrusions  221   g  may have an angular shape. That is, the cross-sections of the first protrusions  221   g  may have the shape of a triangle with a rounded top. The triangular patterns  322  may be formed among the first protrusions  221   g . The first protrusions  221   g  and the triangular patterns  322  may extend in parallel with one another and may be alternately arranged on the light emission surface  227   h.    
       FIGS. 10A through 10C  illustrate color-coded diagrams of computer simulation results of the luminance properties of the light guiding plate  220   a  of the embodiment of  FIGS. 2A through 2D ,  FIG. 11  illustrates a diagram of the relationship between the pitch p of the first protrusions  221  of the light guiding plate  220   a  and a pitch p′ of pixels  113  of a display panel  110 , and  FIG. 12  illustrates a diagram of the relationship between the pitch p and a pitch p″ between a pair of adjacent prism patterns  231  on a prism sheet  230 . 
       FIGS. 10A through 10C  illustrate spatial luminance charts of computer simulation results obtained by simulating, with the aid of a light tool, luminance deviations resulting from varying the ratio (w:d) of the width w of the first protrusions  221  and the width d of the spacing portions  222   a  from 10:1 to 10:2 and from 10:2 to 10:5. More specifically,  FIGS. 10A through 10C  illustrate diagrams of luminance distributions in an area near the light receiving surface  224  of the light guiding plate  220   a  for different ratios of the width w of the first protrusions  221  and the width d of the spacing portions  222   a . The luminance distribution of  FIG. 10A  is more uniform than the luminance distribution of  FIG. 10B  or  10 C. That is, referring to the luminance distribution of  FIG. 10A , dark portions and bright portions are uniformly distributed, rather than being concentrated in certain areas. Referring to Table 1 below, as the ratio of the width w of the first protrusions  221  and the width d of the spacing portions  222   a  increases, a luminance deviation R (per unit distance) decreases, i.e., luminance uniformity increases. 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 w:d 
               
             
          
           
               
                   
                 10:1 
                 10:2 
                 10:5 
               
               
                   
                   
               
             
          
           
               
                 Luminance Deviation R 
                 7.828548 
                 8.740752 
                 11.63732 
               
               
                   
               
             
          
         
       
     
     Referring to  FIG. 11 , the display panel  110  includes a plurality of pixels  113 . Each of the pixels  113  has red (R), green (G), and blue (B) cells. In order to reduce noise caused by optical interference, the pitch p of protrusions  221  may be less than rather than the same as the pitch p′ of the pixel areas, i.e., the width of the adjacent pixels  113 . Since each of the pixels  113  has R, G and B cells, the pitch p′ may be the same as the width of R, G and B cells combined. 
     Referring to  FIG. 12 , in order to reduce noise caused by optical interference, the pitch p may be less than or the same as the pitch p″ of the prism patterns on a corresponding prism sheet  230 . 
       FIG. 13A  illustrates a diagram of an optical phenomenon that occurs in a first protrusion  221  of the light guiding plate  220   a  of the exemplary embodiment of  FIGS. 2A through 2D , and  FIG. 13B  illustrates a diagram of an optical phenomenon that occurs in a first protrusion  221   d  of a light guiding plate according to a comparative example.  FIGS. 14A through 14C  illustrate color-coded computer simulation results of the optical properties of light guiding plates  200  having different shapes of first protrusions  221  as shown in the respective figures. 
     Referring to  FIG. 2A , part of light incident upon the light guiding plate  220   a  through the light receiving surface  224  collides with the reflection surfaces  226  of the reflection patterns  225  and thus travels toward the light emission surface  227  of the light guiding plate  220   a . Then, the light is refracted by passing through the first protrusions  221 . Thereafter, the refracted light is emitted. In this manner, it is possible to emit a considerable amount of light toward the front of the light emissions surface  227  of the light guiding plate  220   a.    
     Referring to  FIGS. 13A and 13B , a first protrusion  221  whose cross-section has the shape of a partial circle or a partial ellipse can disperse light more widely than a first protrusion  221   d  whose cross-section has the shape of a triangle. Thus, the first protrusion  221  is more suitable than the first protrusion  221   d  for use in an optical mixing operation and can provide more excellent luminance uniformity properties than the first protrusion  221   d.    
       FIGS. 14A through 14C  illustrate color-coded spatial luminance charts of computer simulation results obtained by simulating the luminance uniformity properties, along an XY plane, of a light guiding plate  200  having triangular first protrusions (A), a light guiding plate  200  having semicircular first protrusions (B), and a light guiding plate  200  having semi-elliptical first protrusion (C) using a light tool. Upon comparing the spatial luminance charts of  FIGS. 14A through 14C , it is recognized that bright portions and dark portions are more uniformly distributed in the light guiding plate  200  of  FIG. 14A  than in the light guiding plate  200  of  FIG. 14B  or  14 C. This becomes more apparent by referencing Table 2 below. 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Cross-Sectional Shape 
               
             
          
           
               
                   
                 Triangle 
                   
                   
               
               
                   
                 (A) 
                 Semicircle (B) 
                 Semi-ellipse (C) 
               
               
                   
                   
               
             
          
           
               
                 Luminance Deviation R′ 
                 9.648759 
                 8.363411 
                 7.70808 
               
               
                   
               
             
          
         
       
     
     Referring to Table 2, a luminance deviation R′ (per unit length) is about 9.65 for the triangular first protrusions (A), about 8.36 for the semicircular first protrusions (B), and about 7.71 for the semi-elliptical first protrusions (C). That is, referring to Table 2, the luminance deviation R′ is lower when the first protrusions  221  have a round cross-section, like the semicircular first protrusions (B) or the semi-elliptical first protrusions (C), than when the first protrusions  221  have an angular cross-section, like the triangular first protrusions (A). In addition, the luminance deviation R′ is lower when the first protrusions  221  have a cross-section of the shape of a partial ellipse, like the semi-elliptical first protrusions (C), than when the first protrusions  221  have a cross-section of the shape of a partial circle, like the semicircular first protrusions (B). That is, when the first protrusions  221  have a cross-section of the shape of a partial ellipse, the first protrusions  221  can provide high luminance uniformity. Therefore, it is possible for the light guiding plate  220  of the LCD device  1  to provide high luminance uniformity without requiring optical sheets such as a diffusion sheet or a prism sheet and to decrease a hot spot phenomenon even when using an LED as a light source. 
     According to the present disclosure of invention, a plurality of protruding patterns having a cross-section of the shape of a partial ellipse are formed on a light emission surface of a light guiding plate. Thus, it is possible to achieve excellent optical properties without requiring additional optical processing sheets. In addition, since the here disclosed concepts are is suitable for application to optical mixing operations other than just those used in LCD backlighting, it is possible to use the disclosed light guiding plates to decrease the hot spot phenomenon in other applications. 
     While the here-disclosed inventive concepts have been particularly shown and described with reference to exemplary embodiments, it will be understood by those of ordinary skill in the art from the above that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure.