Abstract:
A light guide bar for improving external characteristics by inducing light projection through side surfaces. The light guide bar comprises: a main body in the shape of a bar having a predetermined length; a light incident surface to which light is incident from one side end portion in the lengthwise direction of the main body; a reflection surface for reflecting the incident light from the light incident surface to the inside of the main body; a projection surface for projecting the incident light from the light incident surface to the outside of the main body; and a light extraction pattern formed on the projection surface. The light guide bar, as configured above, induces the projection of light through the light projection surfaces at both side surfaces such that a dark area between the light guide bars can be removed in a backlight device so as to improve external characteristics.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a light guide bar, and more particularly, to a light guide bar capable of improving appearance characteristics by inducing light emission to side surfaces, and a backlight device including the same. 
       BACKGROUND OF THE INVENTION 
       [0002]    In recent times, a backlight device in which an LED light source is disposed at side sections of a light guide body having a bar shape is disclosed.  FIG. 1  is an exploded perspective view showing a backlight device of the related art, and  FIG. 2  is a perspective view showing a light guide bar serving as a major part of  FIG. 1 . The backlight device using the light guide bar of the related art includes a reflection plate  20  and a plurality of light guide bars  30  disposed in a cover bottom  10  at equal intervals, and LEDs  40  serving as light sources disposed at both side sections of the light guide bar  30 . A diffusion plate  50  and various optical sheets  60  are disposed over the light guide bar  30 . A guide panel  70  is fastened to the cover bottom  10 . 
         [0003]    The light guide bars  30  have one side surface or both side surfaces in a longitudinal direction thereof that constitute a light incident surface through which light of the LED  40  enters, and an upper surface and both side surfaces that constitute a light emission surface through which light is emitted. Lower surfaces of the light guide bars  30  constitute a reflection surface configured to reflect light scattered therein upward. A light reflection pattern  31  configured to efficiently reflect light to improve brightness is formed at the lower surface. 
         [0004]    However, the light guide bar  30  having such a structure concentrates most of the light to the upper surface due to the light reflection pattern  31  formed at the lower surface and emits the concentrated light. In this case, while optical characteristics over the light guide bar  30  have high brightness in a region in which the light guide bar  30  is disposed, a relative dark area is generated in a space between the light guide bars  30 . This difference in light and shade according to a position of the light guide bar  30  may cause a decrease in optical characteristics such as the entire brightness of the backlight device, brightness uniformity, and so on. 
         [0005]    In particular, the decrease in appearance caused by the light guide bar becomes serious as the backlight device is slimmed in recent times. In order to prevent this, while a method of narrowing a gap between the light guide bars  30  is proposed, in this case, a relatively large number of light guide bars  30  are used to increase manufacturing costs and power consumption of the backlight device. In addition, while a method of increasing a gap between the light guide bar  30  and the diffusion plate  50  is also provided, brightness is decreased and slimming of the backlight device is prohibited. 
       SUMMARY OF THE INVENTION 
       [0006]    In order to solve the problems, an object of the present invention is to provide a light guide bar capable of improving appearance characteristics by removing a dark area between light guide bars, and a backlight device including the same. 
         [0007]    Another object of the present invention is to provide a light guide bar capable of reducing manufacturing costs and further reducing a thickness of a backlight device using a relatively small number of light guide bars on the same area, and a backlight device including the same. 
         [0008]    Still another object of the present invention is to provide a backlight device capable of relatively increasing an effective emission region by minimizing a bezel region. 
         [0009]    In order to achieve the aforementioned objects, a light guide bar of the present invention includes a light guide main body having a bar shape with a certain length; a light incident surface into which light enters from at least one end of the light guide main body in a longitudinal direction; a reflection surface configured to reflect light entering from the light incident surface into the light guide main body; a light emission surface configured to emit the light entering from the light incident surface to the outside of the light guide main body; and a light extraction pattern formed at the light emission surface. 
         [0010]    Here, the light guide main body may have a cross-section in a progress direction of light formed in a quadrangular shape or a hemispherical shape. 
         [0011]    The light extraction pattern may be formed at both side surfaces only of the light guide main body having a quadrangular cross-section, or formed at both side surfaces and an upper surface, the light guide main body may be formed in a separation type in which a central section is separated, and the light guide main body may have a plane formed at an end of the central section in a curved shape or a polygonal shape. In addition, the light guide main body may include: an extension section extending from an upper surface of an end of the central section; a space section provided under the extension section; and a light scattering pattern formed at an upper surface of the extension section. 
         [0012]    The light extraction pattern may be formed in a ring shape through embossing or engraving along a hemispherical shape of the light guide main body having a hemispherical shape cross-section, the light extraction pattern may have a shape having a size increased from a central section of an upper surface toward both side sections of the light emission surface, the light extraction pattern may be controlled with respect to a surface curve of the light guide main body defined as 
         [0000]    
       
         
           
             
               
                 
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         [0013]    (here, a and b are radii of a major axis and a minor axis), 
         [0014]    an embossed light extraction pattern may be controlled according to a surface curve by Mathematical Equation defined as 
         [0000]    
       
         
           
             
               
                 
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         [0000]      (here,  a   1   &gt;a, b   1   &gt;b , and  c   1 &gt;( b   1   −b )&gt;0), and 
         [0015]    an engraved light extraction pattern may be controlled according to a surface curve by Mathematical Equation defined as 
         [0000]    
       
         
           
             
               
                 
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         [0000]      (here,  a   2   &lt;a, b   2   &lt;b , and  c   2 &gt;( b−b   2 )&gt;0). 
         [0016]    Abacklight device of the present invention includes a cover bottom; a plurality of light guide bars disposed in the cover bottom, each comprising a light guide main body having a bar shape with a certain length, a light incident surface into which light enters from at least one end of the light guide main body in a longitudinal direction, a reflection surface configured to reflect light entering from the light incident surface into the light guide main body, a light emission surface configured to emit the light entering from the light incident surface to the outside of the light guide main body, and a light extraction pattern formed at the light emission surface; a light source disposed at the light incident surface of the light guide bar to cause light to enter the light guide bar; a light control member disposed over the light guide bar; and a fixing grip configured to press both side surfaces of the light guide main body to fix the light guide main body to the cover bottom, wherein the light guide main bodies are formed in a separation type in which a central section is separated, and are disposed in a zigzag on the same line in a longitudinal direction, the light incident surface of the light guide bar is fixed to the cover bottom, and a pupillary light surface side is assembled to be thermally expanded. 
         [0017]    According to the light guide bar having the above-mentioned configuration, as light emission is induced to both light emission surfaces, the dark area between the light guide bars can be removed from the backlight device to improve appearance characteristics. 
         [0018]    In addition, even when the backlight device of the present invention uses a relatively small number of light guide bars, brightness and uniformity characteristics can be improved to reduce manufacturing costs and a thickness thereof. 
         [0019]    The backlight device of the present invention can increase an effective emission region by minimizing the bezel region. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is an exploded perspective view showing a backlight device of the related art; 
           [0021]      FIG. 2  is an enlarged perspective view of a light guide bar of  FIG. 1 ; 
           [0022]      FIG. 3  is an exploded perspective view of a backlight device according to the present invention; 
           [0023]      FIG. 4  is an enlarged perspective view showing a first embodiment of a light guide bar of the present invention; 
           [0024]      FIG. 5  is an enlarged perspective view showing a second embodiment of the light guide bar of the present invention; 
           [0025]      FIG. 6  is a side view showing variants in which ends of the light guide bars of  FIG. 5  are various modified; 
           [0026]      FIG. 7  is an enlarged perspective view showing a third embodiment of the light guide bar of the present invention; 
           [0027]      FIG. 8  is an enlarged perspective view showing a fourth embodiment of the light guide bar of the present invention; 
           [0028]      FIG. 9  is a partially enlarged view showing shapes of an embossed pattern and an engraved pattern of a light extraction pattern of the light guide bar of  FIG. 8 ; 
           [0029]      FIG. 10  is a view showing a light emission path of the light guide bar of the present invention; 
           [0030]      FIG. 11  is a photograph in which optical characteristics of the light guide bar of the present invention and the light guide bar of the related art are compared; 
           [0031]      FIG. 12  is a photograph in which optical characteristics of the backlight device of the present invention and the backlight device of the related art are compared; 
           [0032]      FIG. 13  is an enlarged perspective view showing fifth and sixth embodiments of the light guide bar of the present invention; 
           [0033]      FIG. 14  is a cross-sectional view of the backlight device including the light guide bar of  FIG. 13(   a ). 
           [0034]      FIG. 15  is a view showing another embodiment of a backlight device on which a light guide bar of the present invention is mounted; 
           [0035]      FIG. 16  is a view showing a fixing structure of the light guide bar of the present invention; 
           [0036]      FIG. 17  is an enlarged perspective view showing a seventh embodiment of the light guide bar of the present invention; 
           [0037]      FIG. 18  is a longitudinal cross-sectional view schematically showing the backlight device including the light guide bar of  FIG. 17 ; 
           [0038]      FIG. 19  is a partially enlarged view showing a fixing structure of the light guide bar of the backlight device of  FIG. 18 ; and 
           [0039]      FIG. 20  is a partially enlarged view showing another embodiment of the fixing structure of the light guide bar of  FIG. 18 . 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
         [0041]      FIG. 3  is an exploded perspective view of a backlight device according to the present invention. As shown, the backlight device includes a reflection surface  200  and a plurality of light guide bars  300  disposed in a cover bottom  100 . LED light sources  400  are installed at both sides of the light guide bar  300 , and a diffusion plate  500  and an optical sheet  600  are disposed on the light guide bar  300 . A guide panel  700  is fastened to the cover bottom  100 . 
         [0042]    The light guide bar  300  has abar shape havingapredetermined length, and side surfaces of both ends form a light incident surface through which light enters. The light incident surface can be formed on both side surfaces or only one side surface thereof according to disposition of the LED light source  400 . The light incident surface is configured to receive light from the LED light source  400  to totally reflect the light in the light guide bar  300 . 
         [0043]    A lower surface of the light guide bar  300  forms a reflection surface configured to reflect light leaking downward into the light guide bar  300 . The reflection surface increases brightness by reflecting and scattering the light leaking from the lower surface thereinto. 
         [0044]    An upper surface and both side surfaces of the light guide bar  300  form a light emission surface through which light is emitted. The light emission surface emits the light dispersed into the entire region of the light guide bar  300  to an upper section or side sections. The light emitted through the light emission surface is emitted toward a linear light source according to a shape of the light guide bar  300 . That is, the light guide bar  300  of the present invention functions as an optical transducer configured to switch light of a point light source emitted from the LED light source  400  to a linear light source. 
         [0045]      FIGS. 4 to 6  are views showing first and second embodiments of the light guide bar of the present invention. The light guide bar  300  of  FIG. 4  includes a light guide main body  310  having a quadrangular cross-section, a light reflection pattern  320  formed at a lower surface of the light guide main body  310 , and light extraction patterns  330  formed at left and right side surfaces of the light guide main body  310 . The light guide main body  310  may be formed of a transparent resin such as PMMA. The light of the point light source entering a light incident surface  310   a  by the light guide main body  310  having a bar shape is totally reflected along the inside of the light guide main body  310  to be switched to the linear light source to be emitted to a light emission surface  310   c.    
         [0046]    The light reflection pattern  320  reflects the light leaking downward into the light guide main body  310 , and efficiently scatters the reflected light in the light guide main body  310 . The light reflection pattern  320  may be an optical pattern such as a prism pattern or a dot pattern, or may be a reflection layer on which paste of a reflective material is printed. 
         [0047]    The light extraction pattern  330  induces the light to be emitted to the side surfaces of the light guide main body  310 . That is, the light extraction pattern  330  induces the light entering fromboth ends in the longitudinal direction to be emitted toward both side surfaces. Accordingly, a sufficient amount of light can be distributed in an empty space between the plurality of light guide bars  300  arranged by the pattern. The light extraction pattern  330  may be formed in a prism pattern like (a) or a dot pattern like (b). The light extraction pattern  330  may be formed to have a gap reduced as being spaced apart from the light source. The light extraction pattern  330  may be embossed or engraved from the surface of the light guide main body  310 , and may be formed only on both side surfaces or further on an upper surface. 
         [0048]    The light guide bar  300  of  FIG. 5  is constituted by the pair of light guide main bodies  310 , a central section of which is separated. Each of the light guide main bodies  310  has an outer end at which the LED light source  400  is disposed to form the light incident surface  310   a , and an inner end at which a pupillary light surface  310   a ′ is formed. Here, a plane of an inner end B may have a quadrangular shape, a curved shape, or a polygonal shape. Such a curved or polygonal shape can prevent a hot spot phenomenon due to concentration of light from being generated at a vertical angle section perpendicular to a corner in the quadrangular shape. 
         [0049]    The light guide main body  310  may have the inner end B having various shapes. As shown in  FIG. 6(   a ), the upper side surface may have a spherical surface or a non-spherical surface, or as shown in  FIG. 6(   b ), may have an inclined surface. In addition, as shown in  FIG. 6(   c ), the lower side surface may have a spherical surface or a non-spherical surface, or as shown in  FIG. 6(   d ), may have an inclined surface. These shapes prevent a decrease in optical characteristics due to a hot spot or the like at a side end of the pupillary light surface of the light guide main body  310 . The light guide main body  310  may have a wedge shape having a thickness reduced as being spaced apart from the light source such that uniform light can be emitted throughout the entire length. 
         [0050]      FIGS. 7 to 9  are views showing third and fourth embodiments of the light guide bar of the present invention. The light guide bar  300  of  FIGS. 7 and 8  is constituted by the light guide main body  310  having a hemispherical cross-section, and the light extraction pattern  330  formed at the light emission surface  310   c  of the light guide main body  310 . The light guide main body  310  has an upper section and side sections that form a circular or oval hemi-spherical surface, and the hemi-spherical surface forms the light emission surface  310   c  through which light is emitted. The light emission surface  310   c  having such a shape is configured to uniformly emit light radially with respect to an xz plane. 
         [0051]    The light extraction pattern  330  is formed on a surface of the light guide main body  310  in a ring shape through embossing or engraving. The light extraction patterns  330  are formed in a longitudinal direction of the light guide main body  310  at predetermined intervals and formed along a surface of a cross-section of the light emission surface  310   c  (i.e., an xz direction). The light extraction pattern  330  having such a shape is configured to uniformly emit light with respect to an yz plane of the light emission surface  310   c . The light extraction pattern  330  of  FIG. 7  is formed in the same shape at a central section of an upper surface and both side sections of a lower surface of the light guide main body  310 . The plurality of light extraction patterns  330  may be formed at equal intervals or may be formed at intervals reduced as being spaced apart from the light source. In addition, the light extraction pattern  330  may have various cross-sectional shapes such as a round shape, a prism shape, or a prism shape with a round apex angle. 
         [0052]    The light extraction pattern  330  of  FIG. 8  may be formed in a shape varied from the central section of the upper surface of the light guide main body  310  toward the both side sections of the lower surface. The light extraction patterns  330  having a variable shape are formed to have a small width and height (or depth) at the central section and formed to have a width and height (or depth) gradually increased toward the both side sections. The light extraction patterns  330  having a variable shape are configured to induce a large amount of light to be emitted with respect to lower sections of both sides of the light emission surface  310   c  through which a relatively small amount of light is emitted, and uniformly emit the light with respect to the light emission surface  310   c  having a hemi-spherical surface. 
         [0053]    As shown in  FIG. 9 , the light extraction patterns  330  having a variable shape can control a surface curve. Since the light guide main body  310  has an oval cross-section, an equation of the surface curve of the light guide main body  310  is defined as Mathematical Equation 1. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
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         [0000]    (Here, a and b represent radii of a major axis and a minor axis .) 
         [0054]    In the light guide main body  310  having the embossed light extraction pattern  330  as shown in  FIG. 9(   a ), the surface of the light extraction pattern  330  has radii in x- and y-axes directions of a 1  and b 1  increased to be larger than the surface of the light guide main body  310  as shown in  FIG. 9(   a - 1 ). Here, a vertical reference surface of the light guide main body  310  is increased by c 1 . When the surface curve of the embossed light extraction pattern  330  is represented as an oval equation, the equation is defined as Mathematical Equation 2. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
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         [0000]      (Here,  a   1   &gt;a, b   1   &gt;b , and  c   1 &gt;( b   1   −b )&gt;0.) 
         [0055]    The light guide main body  310  having the embossed light extraction pattern  330  has a height increased to a value c 1  larger than a vertical height (bi-b) of at least the light extraction pattern  330 . 
         [0056]    In the light guide main body  310  having the engraved light extraction pattern  330  as shown in  FIG. 99   b ), the surface of the light extraction pattern  330  has radii in x- and y-axes directions of a 1  and b 2  reduced to be smaller than the surface of the light guide main body  310  as shown in  FIG. 9  (b- 1 ). Here, a vertical reference surface of the light guide main body  310  is reduced by c 2 . When the surface curve of the engraved light extraction pattern  330  is represented as an oval equation, the equation is defined as Mathematical Equation 3. 
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         [0000]      (Here,  a   2   &lt;a, b   2   &lt;b , and  c   2 &gt;( b−b   2 )&gt;0.) 
         [0057]    The light guide main body  310  having the engraved light extraction pattern  330  is reduced to a height c 2  larger than a vertical height (b-bz) of at least the light extraction pattern  330 . 
         [0058]    Eventually, as shown in  FIG. 9 , the height of the light guide main body  310  having an oval light emission surface is increased when the light extraction pattern  330  is formed through embossing, and decreased when formed through engraving. 
         [0059]    Accordingly, in the light guide main body  310  having the oval light emission surface, a and b values are defined as a basic shape, and values of parameters a 1 , b 1 , c 1 , a 2 , b 2  and c 2  are adjusted to control a shape of the light extraction pattern  330 . 
         [0060]      FIGS. 10 to 12  are views showing optical characteristics of the light guide bar and the backlight device of the present invention and the related art. As shown in  FIG. 10(   a ), the light guide bar  300  having the light guidemainbody  310  in aquadrangular shape induces emission of the light toward both side sections by the light extraction patterns  330  formed at both side surfaces of the light emission surface  310   c . As shown in  FIG. 10(   b ), the light guide bar  300  having the light guide main body  310  in a hemispherical shape uniformly emits light by the light emission surface  310   c  and the light extraction pattern  330  having a hemispherical shape. Accordingly, a sufficient amount of light is distributed even in a space between the light guide bars  300  and thus prevents generation of a dark area between the neighboring light guide main bodies  310 . 
         [0061]    It can be confirmed that, as shown in  FIG. 11(   a ), the light guide bar of the related art has low brightness at a central section far from the light source, and weak light is emitted through the side surface. However, it can be confirmed that, as shown in  FIG. 11(   b ), the quadrangular light guide bar having a light emission pattern formed on the side surface has high brightness at the central section, and strong light is emitted through the side surface. This is because the light extraction pattern formed along the side surface of the light emission surface induces emission of the light to the both side sections of the light guide main body and simultaneously to the central section. In addition, it can be confirmed that, as shown in  FIG. 11(   c ), the hemispherical light guide bar having the light extraction pattern having a ring shape with a variable size represents high brightness at the central section, and light of the linear light source having a largest width is emitted with respect to the entire light guide bar. This is because emission of a larger amount of light is induced to the both side sections and the central section by the light guide main body having the hemispherical light emission surface and the light extraction pattern having a size increased from an upper central section to both lower sections of the light emission surface. 
         [0062]    In the backlight device of the related art and the present invention of  FIG. 12 , five light guide bars are disposed at intervals of 70 mm, one diffusion plate is stacked on the light guide bars, and optical characteristics of light emitted upward from the diffusion plate are shown. As shown in  FIG. 12(   a ), in the backlight device of the related art, a relatively dark area is generated between the light guide bars to exhibit shapes of the linear light sources to degrade appearance of the backlight device. However, as shown in  FIG. 12(   b ), in the backlight device of the present invention, high brightness is exhibited even between the light guide bars, the dark area is removed, and a shape of the linear light source is not exhibited to the outside. 
         [0063]      FIG. 13  is an enlarged perspective view showing fifth and sixth embodiments of the light guide bar of the present invention, and  FIG. 14  is a cross-sectional view of the backlight device including the light guide bar of  FIG. 13(   a ). The light guide bar  300  of  FIG. 13  is constituted by the pair of the light guide main bodies  310 , a central section of which is separated. In particular, the light guide main body  310  has a light source unit  340  at which the LED light source  400  is disposed, and an extension section  311  from which an upper surface of the light source unit  340  extends. The extension section  311  covers the LED light source  400  disposed at the light source unit  340  to prevent the light emitted from the LED light source  400  from being directly emitted upward. The light guide main body  310  has a light scattering pattern  312  formed at an upper surface of the extension section  311 . The light scattering pattern  312  scatters a part of the light emitted to the surface of the light guide main body adjacent to the light source unit  340 , and reflects a part of the light again into the light guide main body  310  to prevent generation of a hot spot in the light source unit  340 . The light scattering pattern  312  may have various shapes such as a dot shape and so on, and may be formed at an upper light emission surface of the extension section  311  to have a larger width than a width of at least the light source unit  340  in the longitudinal direction. 
         [0064]    The light guide main body  310  has the LED light source  400  disposed to be positioned at a center as shown in  FIG. 13(   a ) orpositionedoutside as shown in  FIG. 13(   b ). The LED light source  400  is covered by the extension section  311  of the light guide main body  310 , and a hot spot due to the light source is prevented by the extension section  311  and the light scattering pattern  312  formed at the upper surface of the extension section  311 . Accordingly, since the backlight device to which the light guide bar  300  is applied does not require a separate structure or a bezel region configured to cover the light source unit, it is advantageous to implement a large-area backlight device. 
         [0065]    The backlight device of  FIG. 14  has a light scattering pattern  512  formed at a lower surface of the diffusion plate  500 . The light scattering pattern  512  of the diffusion plate  500  may have various shapes such as a dot shape and so on. The light scattering pattern  512  is formed to have a larger width than a width of the light source units  340  of at least both sides of the central section at which the LED light source  400  is disposed. The light scattering pattern  512  may be formed while varying a shape and density as the LED light source  400  of a center is moved from a central position toward the outside. 
         [0066]      FIG. 15  is aview showing another embodiment of the backlight device on which the light guide bar of the present invention is mounted, and  FIG. 16  is a cross-sectional view taken along line E-E, showing a fixing structure of the light guide bar of the present invention. A separation type light guide bar is applied to the backlight device of  FIG. 15 . Here, the pair of light guide main bodies  310  are disposed in a zigzag structure to become alternate on the same line in the longitudinal direction . Such a disposition structure is configured to more uniformly emit the light by supplementing an empty space between the neighboring light guide main bodies  310  of the other side at an end of the light guide main body  310  of one side. 
         [0067]    The backlight device includes a fixing grip  110  configured to fix the light guide bar  300  into the cover bottom  100 . As shown in  FIG. 16 , the fixing grip  110  presses both side sections of the light guide bar  300  to prevent horizontal and vertical movement of the light guide bar  300 . The fixing grip  110  may be constituted by a pair of hooks, and may be integrally formed with the cover bottom  100  or separately formed to be fastened to the cover bottom  100 . 
         [0068]      FIG. 17  is an enlarged perspective view showing a seventh embodiment of the light guide bar of the present invention,  FIG. 18  is a longitudinal cross-sectional view schematically showing the backlight device including the light guide bar of  FIG. 17 , and  FIG. 19  is a partially enlarged view showing a fixing structure of the light guide bar of the backlight device of  FIG. 18 . The light guide bar  300  of  FIG. 17  has a hooking wing  350  formed at an end of a light incident surface side to be fixed to the cover bottom  100 . The hooking wing  350  has ends of the light incident surface  310   a  side protruding from both sides of the light guide main body  310 . As shown in  FIG. 18 , an end of the light guide bar  300  adjacent to the light incident surface  310   a  is fixed to the cover bottom  100  by the hooking wing  350 , and an end adjacent to the pupillary light surface  310   a ′ is assembled not to be restricted by the cover bottom while securing a predetermined gap W from a sidewall of the cover bottom  100 . The light guide bar  300  is thermally expanded by the light totally reflected therein, a variation in light incident properties due to thermal expansion in the light incident surface  310   a  is prevented by the assembly structure, and the pupillary light surface  310   a ′ becomes free from thermal expansion and deformation of the light guide bar  300  is prevented. 
         [0069]    Here, as shown in  FIG. 19 , the light guide bar  300  adjacent to the light incident surface is fixed by the mold frame  800 . The mold frame  800  may be constituted by a horizontal section  800   a  fastened to the cover bottom, a vertical section  800   b  configured to press the light guide bar  300 , and a connecting section  800   c  configured to connect the horizontal section  800   a  and the vertical section  800   b . Here, a groove section  810  into which an end of the light guide bar  300  is inserted is formed in the vertical section  800   b . Apressing protrusion  820  is formed in the vertical section  800   b  of the upper surface of the groove section  810  to prevent vertical movement of the light guide bar  300 . In addition, a hooking piece  830  is formed in the vertical sections  800   b  of both side surfaces of the groove section  810  to be engaged with the hooking wing  350  of the light guide bar  300  to prevent horizontal movement of the light guide bar  300 . In particular, the hooking piece  830  can prevent movement due to thermal expansion of the light guide bar  300 , and thus, an end of the light guide bar  300  adjacent to the light incident surface  310   a  can be stably fixed to the cover bottom  100 . 
         [0070]      FIG. 20  is a partially enlarged view showing another embodiment of a fixing structure of the light guide bar. In the fixing structure of the light guide bar of  FIG. 20 , the light guide bar  300  is fixed to the cover bottom  100  by a hooking protrusion  120 . The hooking protrusion  120  is formed on the cover bottom  100  at a position corresponding to the hooking wing  350  of the light guide bar  300 . The hooking protrusion  120  may protrude in a columnar shape as shown in  FIG. 20(   a ), or a part of a bottom surface of the cover bottom  100  may be cut to be bent upward as shown in  FIG. 20(   b ). The hooking protrusion  120  may be engaged with the hooking wing  350  to fix the end of the light guide bar  300  adjacent to the light incident surface  310   a  to the cover bottom  100 . 
         [0071]    While the embodiments of the present invention having specific shapes and structures have been described with reference to the accompanying drawings, it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the scope of the present invention. 
       REFERENCE SIGNS LIST 
       [0072]      100 : cover bottom  110 : fixing grip  120 : hooking protrusion  200 : reflection surface  300 : light guide bar  310 : light guide main body  320 : light reflection pattern  330 : light extraction pattern  340 : light source unit  350 : hooking wing  311 : extension section  312 ,  512 : light scattering pattern  400 : LED light source  500 : diffusion plate  600 : optical sheet  700 : guide panel  800 : mold frame