Abstract:
Disclosed is an LED lighting device which is easily assembled and disassembled and has a stable assemblability without structural shaking. The LED lighting device is able to improve a heat radiating characteristic and optical efficiency. The LED lighting device according to the embodiment includes a lower case; a light source unit disposed on one side of the lower case; a light guide plate disposed in parallel with the light source unit; and an upper case disposed on the light guide plate and coupled to the lower case in an attachable and removable way.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. §119(e) of Korean Patent Applications Nos. 10-2011-0018405 filed on Mar., 02, 2011, 10-2011-0018909 filed on Mar., 03, 2011 and 10-2011-0033606 filed on Apr., 12, 2011, which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Embodiments may relate to a light emitting diode (LED) lighting device. 
         [0004]    2. Background 
         [0005]    An electric bulb or a fluorescent lamp is now widely used as an indoor or outdoor lighting lamp. However, the electric bulb or the fluorescent lamp has a short life span, so that it should be frequently changed. Moreover, as the use time of the electric bulb or the fluorescent lamp lapses, illuminance is deteriorated. 
         [0006]    In order to overcome such problems, a conventional lighting device increasingly uses a light emitting diode (hereafter, referred to as LED). Because the LED has an excellent controllability, a rapid response speed, a high light conversion efficiency, a long life span, low power consumption and a high luminance value and improves an emotional lighting. 
         [0007]    However, the conventional lighting device has its limited structure depending on an installation structure. Therefore, there is a demand for a lighting device which is not limited by the installation structure. 
       SUMMARY 
       [0008]    One embodiment provides an LED lighting device having an improved assemblability. 
         [0009]    The LED lighting device has a stable assemblability without structural shaking. 
         [0010]    The LED lighting device improves a heat radiating characteristic. 
         [0011]    The LED lighting device improves optical efficiency. 
         [0012]    The LED lighting device according to the embodiment may include a lower case; a light source unit disposed on one side of the lower case; a light guide plate disposed in parallel with the light source unit; and an upper case disposed on the light guide plate and coupled to the lower case in an attachable and removable way. 
         [0013]    The LED lighting device may further include a reflective sheet disposed between the light guide plate and the upper case. 
         [0014]    Here, the lower case may include a body including two planes which are formed perpendicular to each other; a bezel formed extending perpendicular to one plane of the body; and a guide formed projecting perpendicular to the other plane of the body. In the lower case, an insertion groove in which a driver of the light source unit is disposed may be formed on one side of the body, and an opening may be formed in such a manner that the insertion groove is connected to the plane on which the light source unit is disposed. 
         [0015]    The LED lighting device may further include a reflective sheet in the bezel of the lower case, to which the light guide plate is connected. 
         [0016]    The lower case may include a plurality of guide recesses formed inside the body under the guide in the longitudinal direction of the body. 
         [0017]    In the LED lighting device, a louver which adjusts a light direction may be inserted and set in the guide recess. The louver may be formed symmetrical or asymmetrical with respect to an opening of a case in accordance with an orientation angle of light which is emitted from the light guide plate. The louver may be made of a plastic material or a metallic material. An inner surface of the louver may be coated with a reflective material. 
         [0018]    In the lower case, an effective area, that is, a light emitting area is determined by selectively setting a width or a size of the bezel, so that a light spot can be prevented. 
         [0019]    The upper case may include a plate shaped base; and an edge formed extending from both sides of the base and having a level difference, which is stepped with respect to and extends from the base. An open access in which a driver of the light source is disposed may be formed on both sides of the base. In the upper case, a locking recess into which the substrate of the light source unit is inserted may be formed in the longitudinal direction of the edge on a junction between the base and the edge. 
         [0020]    The light guide plate may include a pattern formed on one side thereof or a coating film having a roughness. One side of the light guide plate may include locally or entirely a shape of a plurality of lenses. 
         [0021]    The light source unit may include: a rectangular substrate; a plurality of light emitting devices disposed on one side of the substrate in the longitudinal direction of the substrate; and a driving driver driving the light emitting device. 
         [0022]    The LED lighting device may include a photo luminescent film disposed between the light source unit and the light guide plate. The photo luminescent film may include a transparent resin and a fluorescent material. The transparent resin may include at least one of a curing agent, an additive and a diffusing agent. 
         [0023]    The LED lighting device may include a cap which is coupled to the side of the lower case and prevents light from being emitted from the side of the light guide plate. 
         [0024]    The LED lighting device may further include a heat radiation sheet or a thermal grease between the upper case and the lower case or between the light source unit and the lower case. 
         [0025]    Another embodiment is an LED lighting device. The LED lighting device may include: a light source unit; a light guide plate disposed in parallel with the light source unit; and a coating film which has a roughness and is disposed on the light guide plate. 
         [0026]    The roughness of the coating film formed in an effective area where light is emitted to the outside through the light guide plate may be different from the roughness of the coating film formed in an ineffective area where the light is not emitted. 
         [0027]    According to the embodiment, the lower case surrounding the light source unit and the light guide plate is attachable to and removable from the upper case. The reflective sheet and the light guide plate become closer to each other. The light source unit is stable fixed. The upper case is prevented from moving right and left. As a result, the LED lighting device has a stable supporting structure and is easily assembled and disassembled. 
         [0028]    The heat radiation sheet is disposed on a contact area of the upper case and the lower case or disposed between the light source unit and the lower case, thereby radiating the heat generated from the light source unit to the outside. As a result, a heat radiating characteristic can be enhanced. 
         [0029]    The cap is coupled to the side of the lower case and prevents light from being emitted from the side of the light guide plate. The photo luminescent film is disposed between the light source unit and the light guide plate. The reflective sheet is disposed in a contact area of the lower case and the light guide plate. The reflective sheet is disposed between the upper case and the light guide plate. The coating film having a roughness is formed on the top surface of the light guide plate. A plurality of the lenses are formed on the top of the light guide plate. As a result, optical efficiency can be improved. 
         [0030]    The LED lighting device has no limited installation structure. A manufacturing cost of the LED lighting device can be reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Arrangements and embodiments may be described in detail with reference to the following drawings in which like reference numerals refer to like elements and wherein: 
           [0032]      FIG. 1  is a perspective view of an LED lighting device according to an embodiment; 
           [0033]      FIG. 2  is an exploded perspective view of the LED lighting device; 
           [0034]      FIG. 3  is a side exploded view of the LED lighting device; 
           [0035]      FIG. 4  is a side view of the LED lighting device; 
           [0036]      FIG. 5  is a cross sectional view showing a first structure of a coating film disposed on a light guide plate; 
           [0037]      FIG. 6  is a cross sectional view showing a second structure of the coating film; 
           [0038]      FIG. 7  is a cross sectional view showing a third structure of the coating film; 
           [0039]      FIG. 8  is a cross sectional view showing a first structure of a lourver coupled to the LED lighting device; 
           [0040]      FIG. 9  is a cross sectional view showing a second structure of the lourver coupled to the LED lighting device; and 
           [0041]      FIG. 10  is a cross sectional view showing a third structure of the lourver coupled to the LED lighting device. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    A thickness or a size of each layer may be magnified, omitted or schematically shown for the purpose of convenience and clearness of description. The size of each component may not necessarily mean its actual size. 
         [0043]    It should be understood that when an element is referred to as being ‘on’ or “under” another element, it may be directly on/under the element, and/or one or more intervening elements may also be present. When an element is referred to as being ‘on’ or ‘under’, ‘under the element’ as well as ‘on the element’ may be included based on the element. 
         [0044]    Hereafter, detailed technical characteristics to be embodied will be described in detail with reference to the accompanying drawings. 
         [0045]      FIG. 1  is a perspective view of an LED lighting device according to an embodiment.  FIG. 2  is an exploded perspective view of the LED lighting device.  FIG. 3  is a side exploded view of the LED lighting device.  FIG. 4  is a side view of the LED lighting device. 
         [0046]    Referring to  FIGS. 1 to 4 , the LED lighting device basically includes an upper case  200 , a lower case  300 , a light guide plate  500  and a light source unit  700 . Further, in the embodiment, light can be prevented from being emitted through the light guide plate  500  by providing a cap  100  on the side of the lower case  300 . Also, a reflective sheet  400  may be disposed between the upper case  200  and the light guide plate  500 . 
         [0047]    The upper case  200  and the lower case  300  function as a case of the LED lighting device and are disposed in an attachable and removable manner. 
         [0048]    The upper case  200  includes, as shown in  FIGS. 2 to 4 , a plate-shaped base  210  and a right-left edge  230  which is stepped with respect to the base  210  and extends from the base  210 . Here, the base  210  is formed thicker than the edge  230 . When the upper case  200  is coupled to the lower case  300 , the base  210  hereby presses the top of the reflective sheet  400 , so that the reflective sheet  400  and the light guide plate  500  become closer to each other. Therefore, the reflective sheet  400  and the light guide plate  500  can be prevented from moving. 
         [0049]    The edge  230  has a rectangular shape as a whole. An open recess (see reference numeral  230   a  of  FIG. 2 ) in which a driver is disposed is formed in the right and/or left side of the edge  230 . As shown in  FIG. 3 , a position of the edge  230 , which is connected to the base  210 , includes a locking recess  230   b  formed in the longitudinal direction of the edge  230 . A substrate  710  of the light source unit  700  is inserted into the locking recess  230   b.  Consequently, the locking recess  230   b  functions to stably fix the light source unit  700 . 
         [0050]    The lower case  300  includes, as shown in  FIGS. 2 to 4 , a body  310  including two vertical planes  301  and  303 , a bezel  330  extending perpendicular to the one vertical plane  301  of the body  310 , and a guide  350  projecting perpendicular to the other vertical plane  303  of the body  310 . 
         [0051]    Here, the body  310  includes one side  301  on which the light source unit  700  is disposed and the other side  303  on which the edge  230  of the upper case  200  is disposed. The two planes  301  and  303  are perpendicular to each other. An insertion groove (see reference numeral  300   a  of  FIG. 2 ) and an opening (see reference numeral  300   b  of  FIG. 2 ) are formed in the side of the body  310 . Here, the driver (see reference numeral  900  of  FIG. 2 ) driving the light source unit  700  is disposed in the insertion groove  300   a.  The opening  300   b  is formed in such a manner that the insertion groove  300   a  is connected to the one plane  301  of the body  310 , on which the light source unit  700  is disposed. 
         [0052]    Meanwhile, the corner of the body  310  is rounded and relives external impact. 
         [0053]    Subsequently, the body  310  includes a guide recess  310   a  formed inside the body  310  under the guide  350  in the longitudinal direction of the body  310 . A plurality of the guide recesses  310   a  may be provided and disposed in parallel with the longitudinal direction of the body  310 . 
         [0054]    The guide recess  310   a  of the body  310  increases the surface area for heat radiation. Therefore, the guide recess  310   a  functions to effectively radiate heat generated from the light source unit  700 . 
         [0055]    A louver (see reference numeral  50  of  FIGS. 8 to 10 ) which adjusts the light direction may be inserted and set in the guide recess  310   a  of lower case  300 . The louver  50  functions to adjust the light direction when the light of the light source unit  700  is outwardly emitted through the light guide plate  500 . 
         [0056]    Subsequently, the bezel  330  of the lower case  300 , as shown in  FIGS. 3 and 4 , supports both sides of the bottom surface of the light guide plate  500 . When the light emitted from the light source unit  700  is outwardly emitted, the bezel  330  functions to prevent light spot generated due to a short optical path. 
         [0057]    The bezel  330  determines an effective area, i.e., a light emitting area, depending on the width or size thereof. Therefore, in terms of optical efficiency, it is recommended that the bezel  330  should be reduced as much as possible in such a manner that the effective area is not reduced within a range in which no light spot is generated. 
         [0058]    As shown in  FIGS. 2 to 4 , the guide  350  of the lower case  300  is molded in a projection shape, perpendicular to the other vertical plane  303  of the body  310 . When the upper case  200  is coupled to the lower case  300 , the guide  350  prevents the upper case  200  from moving right and left. Here, the height of the projecting guide  350  may be the same as the thickness of the edge  230  of the upper case  200 . 
         [0059]    After the upper case  200  is coupled to the lower case  300 , the edge  230  of the upper case  200  is, as shown in  FIG. 4 , seated on the vertical plane  303  of the body  310  of the lower case  300 . The upper case  200  is coupled to the lower case  300  by a screw  10 . The upper case  200  and the lower case  300  have a quadrangular cross section having an open lower portion. 
         [0060]    In the LED lighting device, when the structures disposed inside the case, such as the light source unit  700 , the light guide plate  500  and the reflective sheet  400  need repairing, the upper case  200  can be separated from the lower case  300 . 
         [0061]    With regard to the LED lighting device, heat transfer characteristics of the upper and lower cases  200  and  300  are improved by disposing a heat radiation sheet (not shown). Therefore, a heat radiating characteristic can be enhanced. 
         [0062]    The upper and lower cases  200  and  300  may be formed of a PC material which reduces the weights thereof and may be also formed of a material having a high thermal conductivity in order to excellently radiate heat generated from the light source unit  700  to the outside of the case. For example, the upper and lower cases  200  and  300  may be formed of at least one metallic material selected from the group consisting of Cu, Ag, Au, Ni, Al, Cr, Ru, Re, Pb, Cr, Sn, In, Zn, Pt, Mo, Ti, Ta and W, or may be formed of an alloy including the metallic materials. 
         [0063]    Further, to add elasticity to the upper and lower cases  200  and  300 , the upper and lower cases  200  and  300  may be formed of an elastic material. 
         [0064]    Subsequently, the reflective sheet  400  has a plate shape corresponding to one side of the light guide plate  500  and is disposed between the upper case  200  and the light guide plate  500 . Unlike the case, the reflective sheet  400  is made of a ductile material or a plastic material. If the base  210  of the upper case  200  is coated with a reflective material, the reflective sheet  400  may be removed. 
         [0065]    When the light emitted from the light source unit  700  is emitted to the outside through the light guide plate  500 , the reflective sheet  400  reflects the light emitted to the rear of the light guide plate  500 , and then the light is emitted to the outside. 
         [0066]    The light guide plate  500  is optically coupled to the light source unit  700 . That is, the light guide plate  500  is disposed in parallel with the light source unit  700  and guides the path of the light emitted from the light source unit  700 . 
         [0067]    As shown in  FIGS. 2 to 4 , the light guide plate  500  has a rectangular plate shape and a level difference surface in the lower portion thereof. Here, the bezel  330  of the lower case  300  is disposed on the level difference surface and supports the light guide plate  500 . 
         [0068]    The light guide plate  500  functions to convert a point light source generated by the light source unit  700  into a surface light source. Here, one side of the light guide plate  500  may include a particular pattern formed thereon or a coating film (see reference numeral  510  of  FIG. 5 ) having a roughness. The coating film  510  having the particular pattern or a roughness functions to diffuse or scatter the light, and then emits the light to the outside. The light guide plate  500  may be made of a transparent resin and may be printed by a silk-screen printing method. 
         [0069]    As shown in  FIG. 5 , the embodiment includes a reflective sheet  30  disposed in a contact area of the bezel  330  of the lower case  300  and the lower portion of the light guide plate  500 . The reflective sheet  30  may be formed on the bezel  330  of the lower case  300  or may be disposed between the lower case  300  and the light guide plate  500 . 
         [0070]    When the light emitted from the light source unit  700  is irradiated to the bezel  330  of the lower case  300 , the reflective sheet  30  enhances the back reflectance of the light, thereby substantially improving the optical efficiency of the light which is outwardly emitted. 
         [0071]    The light source unit  700  includes, as shown in  FIGS. 2 to 4 , a substrate  710 , a light emitting device  730  and a driving driver  750 . 
         [0072]    Here, the substrate  710  is a rectangular printed circuit board. The light emitting device  730  includes a plurality of LEDs and is disposed on one side of the substrate  710  in the longitudinal direction of the substrate  710 . The light emitting device  730  includes the LEDs emitting the same colored light or includes the LEDs emitting differently colored lights. Therefore, light having various colors can be emitted by a combination of the two different colors, so that an emotional lighting device can be implemented. The LED includes a light emitting diode emitting at least one of blue, red and green colors. 
         [0073]    Though not shown in the drawings, the LED is able to emit light having its own color due to a sealed transparent resin in the upper portion thereof. Here, the LED emitting blue light is also able to emit white light as well by using a resin including a yellow fluorescent material. 
         [0074]    While the LED is taken as an example of a light source in the embodiment, any device capable of emitting light can be included in the light source, without being limited to this. 
         [0075]    The driving driver  750  may be provided on the other side or end of the substrate  710 , on which the light emitting device  730  is not disposed. 
         [0076]    A plurality of the light source units  700  are provided and disposed on the body  310  of the lower case in such a manner that the light emitting devices  730  disposed on the substrate  710  face each other. Here, the substrates  710  of the light source unit  700  are, as shown in  FIGS. 3 and 4 , inserted into the locking recesses  230   b  of the upper case  200  respectively. 
         [0077]    Though not shown in the drawings, a heat radiation sheet may be disposed on a contact area of the light sources unit  700  and the body  310  of the lower case  300 . The heat radiation sheet can improve a heat radiating characteristic by transferring the heat generated from the light source unit  700  to the lower case  300  and radiating the heat to the outside. 
         [0078]    In the LED lighting device of the embodiment, a photo luminescent film (not shown) including a fluorescent material may be disposed between the light source unit  700  and the light guide plate  500 . The photo luminescent film functions to change the color of the light by converting a portion of the wavelength of the light emitted from the light source unit  700 . Here, the photo luminescent film may include a transparent resin and a fluorescent material contained in the transparent resin. Here, a curing agent or an additive may be included in the transparent resin. The curing agent functions to cure the transparent resin. The additive functions to disperse uniformly the fluorescent material within the transparent resin. Also, a diffusing agent may be included in the transparent resin. Here, the diffusing agent functions to increasing the excitation ratio of the fluorescent material by improving the refractive index of the light source. 
         [0079]    Subsequently, the driver  900  is, as shown in  FIGS. 1 and 2 , disposed to be inserted into the open recess  230   a  of the edge  230  of the upper case  200  and insertion groove  300   a  of the body  310  of the lower case  300 . Then, the driver  900  is electrically connected to the driving driver (see reference numeral  750  of  FIG. 2 ) of the light source unit  700  disposed on one side of the lower case  300 . 
         [0080]    Next, the cap  100  is disposed on the front and rear sides of the light guide plate  500  disposed within the case and prevents the light generated from the light source unit  700  from being emitted to the front and rear sides of the light guide plate  500 . The cap  100  includes a coupling hole  100   a  which is coupled to a side of the guide recess  310   a  of the lower case  300  by means of a screw (see reference numeral  20  of  FIG. 2 ). The cap  100  may be made of a metallic material or a lightweight plastic material. 
         [0081]      FIG. 5  is a cross sectional view showing a first structure of a coating film disposed on a light guide plate. 
         [0082]    Referring to  FIG. 5 , when the light emitted from the light source unit  700  is emitted to the outside through the light guide plate  500 , a light emitting effective area “AD” is determined by an opening formed through the coupling of the upper case  200  and the lower case  300 . Here, the light emitting effective area “AD” corresponds to an area through which the light emitted from the light source unit  700  is emitted to the outside the light guide plate  500 . A light emitting ineffective area “NAD” corresponds to an area where the light which is emitted from the light source unit and passes through the light guide plate is not emitted by being blocked by the bezel  330  of the lower case  300 . 
         [0083]    The coating film  510  is formed on the light guide plate  500 . The roughness may be formed on a portion of the surface of the coating film  510  or may be formed on the entire surface of the coating film  510  in order to improve the light uniformity. As a result, the light guide plate  500  causes the light emitted through the top surface of the light guide plate  500  to be diffused or scattered in direction of the bottom surface of the light guide plate  500 , thereby improving not only the optical efficiency but the uniformity of the light which is emitted to the outside. 
         [0084]    Though the roughness of the coating film  510  may be uniform on the entire surface thereof, the roughness may be different depending on the position of the surface of the coating film  510 . In other words, the roughness of the coating film  510  formed in the central portion of the light guide plate  500 , which corresponds to the light emitting effective area “AD” is larger than the roughness of the coating film  510  formed in the peripheral portion of the light guide plate  500 , which corresponds to the light emitting ineffective area “NAD”. This intends to substantially improve the light diffusivity effect and the light scattering effect by increasing the roughness of the portion of the coating film  510 , which corresponds to the light emitting effective area “AD”. 
         [0085]    Though not shown in the drawings, the coating film  510  may be formed on the top and the bottom surfaces of the light guide plate  500 . Here, the surface roughness of the coating film  510  of the bottom surface may be the same as or different from that of the top surface of the coating film  510 . As a result, it is possible to improve the light uniformity and the optical efficiency. 
         [0086]    Another embodiment will be provided. The same effect as the effect mentioned above can be obtained by forming the roughness on the bottom surface itself of the light guide plate  500  in place of the coating film  510  formed on the bottom surface of the light guide plate  500 . 
         [0087]      FIG. 6  is a cross sectional view showing a second structure of a coating film disposed on a light guide plate. 
         [0088]    Referring to  FIG. 6 , as in  FIG. 5 , the light guide plate  500  corresponds to the light emitting effective area “AD” and the light emitting ineffective area “NAD”. The roughness is locally or entirely formed on one side of the light guide plate  500 . 
         [0089]    Though the roughness may be uniformly formed on the entire surface of the light guide plate  500 , the roughness may be different depending on the position of the surface of the light guide plate  500 . In other words, the roughness formed in the central portion of the light guide plate  500 , which corresponds to the light emitting effective area “AD” is larger than the roughness formed in the peripheral portion of the light guide plate  500 , which corresponds to the light emitting ineffective area “NAD”. This intends to substantially improve the light diffusivity effect and the light scattering effect by increasing the roughness of the surface of the light guide plate  500 , which corresponds to the light emitting effective area “AD”. 
         [0090]    Though not shown in the drawings, the coating film  510  may be formed on the top and the bottom surfaces of the light guide plate  500 . Here, the surface roughness of the coating film  510  of the bottom surface may be the same as or different from that of the top surface of the coating film  510 . As a result, it is possible to improve the light uniformity and the optical efficiency. 
         [0091]    Another embodiment will be provided. The same effect as the effect mentioned above can be obtained by forming the roughness on the bottom surface itself of the light guide plate  500  in place of the coating film  510  formed on the bottom surface of the light guide plate  500 . 
         [0092]      FIG. 7  is a cross sectional view showing a third structure of a coating film disposed on a light guide plate. 
         [0093]    Referring to  FIG. 7 , as in  FIG. 5 , the light guide plate  500  corresponds to the light emitting effective area “AD” and the light emitting ineffective area “NAD”, and has a shape of a plurality of lenses. Here, the lens has a size of a micro unit. The shape of the lens may be locally or entirely formed on the top surface of the light guide plate  500 . Since a subsequent effect to this has been described above, a description of the effect will be omitted. 
         [0094]    Distances between the lenses of the light guide plate  500  may be the same as each other on the entire surface of the light guide plate  500 , or may be different from each other depending on a position of the light guide plate  500 . That is to say, a distance “D 1 ” between the lenses formed in the central portion of the light guide plate  500 , which corresponds to the light emitting effective area “AD” is less than a distance “D 2 ” between the lenses formed in the peripheral portion of the light guide plate  500 , which corresponds to the light emitting ineffective area “NAD”. 
         [0095]    Though not shown in the drawings, the bottom surface itself of the light guide plate  500  may include a plurality of the lenses and a predetermined pattern formed therein. 
         [0096]      FIGS. 8 to 10  are cross sectional views showing a first to a third structures a lourver  50  coupled to the LED lighting device. 
         [0097]    Referring to  FIGS. 8 to 10 , the louver  50  is coupled in a sliding way to the both guide recesses  310   a  formed in the longitudinal direction of the body  310  of the lower case  300 . 
         [0098]    The louver  50  may be made of a plastic material or a metallic material. The inner surface of the louver  50  may be coated with a reflective material. 
         [0099]    The shape of the louver  50  may be, as shown in  FIGS. 8 and 9 , symmetrical with respect to the opening of the case in accordance with the orientation angle of the light emitted from the light guide plate  500 , or may be, as shown in  FIG. 10 , asymmetrical with respect to the opening of the case. 
         [0100]    Depending on the size of a light irradiation area,  FIG. 8  shows that some of the light irradiation direction of the louver  50  may be formed in the form of a symmetrical curve.  FIG. 9  shows that some of the light irradiation direction of the louver  50  may be formed in the form of a symmetrical flat plane.  FIG. 10  shows that some of the light irradiation direction of the louver  50  may be formed in the form of an asymmetric structure including the curve and the flat plane. 
         [0101]    Although embodiments of the present invention were described above, these are just examples and do not limit the present invention. Further, the present invention may be changed and modified in various ways, without departing from the essential features of the present invention, by those skilled in the art. For example, the components described in detail in the embodiments of the present invention may be modified. Further, differences due to the modification and application should be construed as being included in the scope and spirit of the present invention, which is described in the accompanying claims.