Patent Publication Number: US-2013242612-A1

Title: Light guide panel and backlight unit having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Application No. 61/610,736, filed on Mar. 14, 2012 in the United States Patent and Trademark Office, and from Korean Patent Application No. 10-2012-0049468, filed on May 10, 2012, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     Panels and units consistent with what is disclosed herein relate to a light guide panel and a backlight unit having the same, and more particularly, to a light guide panel having lenticular patterns and a backlight unit having the same. 
     2. Description of the Related Art 
     The liquid crystal display (LCD) generally includes a display panel which displays an image thereon, and a backlight unit which supplies light from the back of the display panel. The LCD is widely used in display devices such as televisions, computer monitors, or the like. 
     Among various types of backlight units, the edge backlight unit includes a plurality of light sources (e.g., LEDs) which are generally arranged on a side surface, and a light guide panel (LGP) to guide the light supplied from the light sources to the display panel. 
     The LGP generally includes a plurality of light emitting patterns in a dot form to guide the light toward the display panel. Meanwhile, when implemented in a display device to provide three dimensional (3D) images, the LGP may have a plurality of lenticular patterns on one surface to improve 3D scanning efficiency. In such LGP having the lenticular patterns with the light emitting patterns, the light emitting patterns are generally formed on a rear surface of the LGP, and the lenticular patterns are formed on a front surface of the LGP. 
     SUMMARY 
     Accordingly, one or more exemplary embodiments overcome the above disadvantages and other disadvantages not described above. Also, the exemplary embodiments are not required to overcome the disadvantages described above, and exemplary embodiments may not overcome any of the problems described above. 
     According to an aspect of an exemplary embodiment, there is provided a light guide panel (LGP) of improved productivity and reduced manufacturing cost, which provides at least the same level of light efficiency and 3D scanning efficiency as those of a conventional LGP, and a backlight unit having the same. 
     According to aspect of an exemplary embodiment, there is provided a light guide panel (LGP) for use in a display device, which may include a front surface, a rear surface, and four edge surfaces, in which rays of light emitted from light sources are introduced through at least one of the four edge surfaces, a plurality of lenticular patterns formed on one of the front surface and the rear surface, and a plurality of light emitting patterns which induce the rays of light emitted from the light sources toward the front surface, wherein the plurality of light emitting patterns are integrally formed with the plurality of lenticular patterns. 
     Each of the light emitting patterns may have one curved surface. 
     The light emitting patterns may each be formed concavely or convexly on surfaces of the lenticular patterns. 
     The light emitting patterns may each be formed concavely on the lenticular patterns, and have two reflection surfaces inclined with respect to the front or rear surface. 
     The two reflection surfaces may be planar. 
     The two reflection surfaces may be inclined with respect to the rear surface by 35° to 80°. 
     The two reflection surfaces may be at an angle of 70° to 110°. 
     Pitch between two adjacent light emitting patterns may be below 0.5 mm. 
     The LGP may receive the ray of lights through two edge surfaces among the four edge surfaces that are arranged opposite to each other. 
     According to an aspect of another exemplary embodiment, there is provided a backlight unit for use in a display device which may include a light guide panel (LGP) comprising a front surface, a rear surface, and four edge surfaces, at least one light source which provides a ray of light into the LGP through at least one of the four edge surfaces, a rear optical sheet unit which is arranged in back of the LGP, and a front optical sheet unit which is arranged in front of the LGP, in which the LGP may include a plurality of lenticular patterns formed convexly on one of the front surface and the rear surface, and a plurality of light emitting patterns which induce the rays of light emitted from the light sources toward of the front surface. The plurality of light emitting patterns may be formed integrally with the plurality of lenticular patterns. 
     The light emitting patterns may each include one curved surface. 
     The front optical sheet unit may include a plurality of optical sheets. 
     The front optical sheet unit may include a diffusion sheet, a prism sheet and a protection sheet. 
     The front optical sheet unit may include a diffusion sheet, a prism sheet and a reflection polarization sheet. 
     The light emitting patterns may each be formed concavely on the lenticular patterns, and may each include two reflection surfaces inclined with respect to the front surface or the rear surface. 
     The front optical sheet unit may have only one optical sheet. 
     The front optical sheet unit may have a diffusion sheet only. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
       The above and/or other aspects will be more apparent by describing certain exemplary embodiments with reference to the accompanying drawings, in which: 
         FIG. 1  is a plan view of a light guide panel (LGP) according to an embodiment; 
         FIG. 2  is a schematic rear perspective view of the LGP of  FIG. 1 ; 
         FIG. 3  is a partially enlarged cross-section view taken on line III-III of  FIG. 2 ; 
         FIG. 4  is a schematic, partial cross-section view of a backlight unit having the LGP of  FIGS. 1 to 3  according to an embodiment; 
         FIG. 5  is a plane view of the LGP according to a second embodiment; 
         FIG. 6A  is a schematic rear perspective view of the LGP of  FIG. 5 ; 
         FIG. 6B  is a rear perspective view of the LGP according to an alternative embodiment; 
         FIG. 7  is a side view of the LGP of  FIG. 5 ; 
         FIG. 8  is a partial cross-section view taken on line VIII-VIII of  FIG. 7 ; 
         FIG. 9  is a schematic, partial cross-section view of a backlight unit having the LGP of  FIGS. 5 to 8  according to an embodiment; 
         FIGS. 10A and 10B  are the brightness distribution image obtained from test #1 and a corresponding graph; 
         FIGS. 11A and 11B  are the brightness distribution image obtained from test #2 and a corresponding graph; 
         FIGS. 12A and 12B  are the brightness distribution image obtained from test #3 and a corresponding graph; 
         FIGS. 13A and 13B  are the brightness distribution image obtained from test #4 and a corresponding graph; 
         FIGS. 14A and 14B  are the brightness distribution image obtained from test #5 and a corresponding graph; 
         FIGS. 15A and 15B  are the brightness distribution image obtained from test #6 and a corresponding graph; 
         FIGS. 16A and 16B  are images of a conventional LGP and a LGP according to an embodiment, each photographed at the 3D scanning efficiency test; and 
         FIG. 17  presents two graphs representing brightness distribution data on the central portion of the LGP among the data of Table 3 and Table 4. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Certain exemplary embodiments will now be described in greater detail with reference to the accompanying drawings. 
     In the following description, same drawing reference numerals are used for the same elements even in different drawings so as to be easily realized by a person having ordinary knowledge in the art. The exemplary embodiments may be embodied in various forms without being limited to the exemplary embodiments set forth herein. Descriptions of well-known parts are omitted for clarity, and like reference numerals refer to like elements throughout. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the exemplary embodiments. Accordingly, it is apparent that the exemplary embodiments can be carried out without those specifically defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the aspects of the exemplary embodiments with unnecessary detail. 
       FIG. 1  is a plan view of a light guide panel (LGP) according to an embodiment, 
       FIG. 2  is a schematic rear perspective view of the LGP of  FIG. 1 , and  FIG. 3  is a partially enlarged cross-section view taken on line III-III of  FIG. 2 . 
     Referring to  FIGS. 1 to 3 , a light guide panel (LGP,  110 ) according to an embodiment may be formed in approximately a rectangular shape, having a front surface  111 , a rear surface  112 , and four edge surfaces  113 ,  114 ,  115 ,  116 . 
     The front surface  111  may face a display panel (not illustrated) and opposed to the rear surface  112 . For convenience of explanation, the four edge surfaces may be referred to as a first edge surface  113 , a second edge surface  114 , a third edge surface  115 , and a fourth edge surface  116 , in which the first and second edge surfaces  113 ,  114  may be arranged opposite to each other, and the third and fourth edge surfaces  115 ,  116  may be arranged opposite to each other. 
     Referring to  FIG. 1 , lights L emitted from the light sources are introduced into the LGP  110  through the first and second edge surfaces  113 ,  114 . Although the lights are entered through two edge surfaces  113 ,  114  in one embodiment, this is only for illustrative purpose. Accordingly, in other embodiments, the lights may be introduced through only one  113  of the four edge surfaces or through more than three of the edge surfaces. 
     Referring to  FIGS. 2 and 3 , a plurality of lenticular patterns  117  may be convexly formed on the rear surface  112  to enhance 3D scanning efficiency. The lenticular patterns  117  may be uniformly formed between the first and second edge surfaces  113 ,  114  where the lights are entered, and arranged parallel to each other. Each of the lenticular patterns  117  may have approximately semi-circular cross-section, but this may be varied depending on the embodiments. 
     The lenticular patterns  117  minimize the spreading of the lights which enter through the first and second edge surfaces  113 ,  114  in a widthwise direction (i.e., in Y direction) of the LGP  110 . That is, due to the lenticular patterns  117 , the lights which enter through the first and second edge surfaces  113 ,  114  extend along the lengthwise direction (i.e., in X direction) of the LGP  110 . That is, higher 3D scanning efficiency is obtained, as the incident light extends along the lengthwise direction (i.e., in X direction) of the LGP due to the lenticular patterns  117 . 
     In one embodiment, the lenticular patterns  117  may be formed on the rear surface  112  of the LGP  110 . Alternatively, the lenticular patterns  117  may be formed on the front surface  111  of the LGP  110 . 
     Referring to  FIGS. 2 and 3 , a plurality of light emitting patterns  118  may be integrally formed with the lenticular patterns  117 . The light emitting patterns  118  scatter the lights in several directions, thereby inducing the lights toward the direction of the display panel. 
     The light emitting patterns  118  may have one curved shaped corresponding to a portion of the spherical surface. In alternative embodiments, the light emitting patterns  118  may have curved shapes other than a spherical surface. The light emitting patterns  118  may be concavely formed on the surfaces  117   a  of the lenticular patterns  117 . In alternative embodiments, the light emitting patterns  118  may be convexly formed on the surfaces  117   a  of the lenticular patterns  117 . 
     The shape of the light emitting patterns  118  may generally be referred to as ‘dots’. To be more specific, the light emitting patterns  118  are called ‘dots’ when the light emitting patterns  118  have substantially circular cross-section along an X-Y plane. In alternative embodiments, the light emitting patterns  118  may be bars rather than dots. That is, instead of having circular cross-section with respect to X-Y plane, the light emitting patterns  118  may have a more extended cross-section in lengthwise (i.e., X) or widthwise (i.e., Y) direction of the LGP  110 . 
     Since the light emitting patterns  118  are integrated with the lenticular patterns  117 , the lenticular patterns  117  and the light emitting patterns  118  may be concurrently formed. That is, the lenticular patterns  117  along with the light emitting patterns  118  may be imprinted, extruded, or injected for concurrent shaping. 
     In one example, the LGP  110  may be fabricated by imprinting as follows. First, shapes of the lenticular patterns  117  integrated with the light emitting patterns  118  are formed on a LGP material (e.g., polymethymethacrylate, PMMA) by pressing a mold corresponding to the lenticular patterns  117  integrated with the light emitting patterns  118  on the PMMA in a paste state containing therein hardening initiator. After that, by allowing the PMMA to harden under ultraviolet rays, the final form of the LGP  110  is prepared. 
     As explained above, the lenticular patterns  117  and the light emitting patterns  118  may be shaped by, for example, one processing (i.e., concurrently) during the preparation of the LGP  110 . As a result, fabrication of the LGP  110  becomes simpler and the manufacturing cost decreases. 
     Meanwhile, the conventional LGP generally requires that the lenticular patterns and the light emitting patterns be formed on two different surfaces separately, instead of being integrated with each other. By way of example, the lenticular patterns are formed on the front surface, while the light emitting patterns are formed on the rear surface of the LGP. In such a conventional LGP, the lenticular patterns are formed first on the circular LGP disk and then the light emitting patterns are formed thereon in the post processing by laser processing or printing. 
     To prepare the conventional LGP wherein the lenticular patterns and the light emitting patterns are not integrally formed with each other, separate processing is required to shape the lenticular patterns and the light emitting patterns respectively. Accordingly, compared to the exemplary embodiment, fabrication of the conventional LGP is rather complicated and is of a higher cost. 
       FIG. 4  is a schematic, partial cross-section view of a backlight unit having the LGP of  FIGS. 1 to 3  according to an embodiment. 
     Referring to  FIG. 4 , the backlight unit  110  may include the LGP  110 , a light source unit  120 , a rear optical sheet unit  130 , and a front optical sheet unit  140 . 
     As explained above, the LGP  110  may have a plurality of lenticular patterns  117  formed on the rear surface  112  thereof, and the light emitting patterns  118  may be integrally formed with the lenticular patterns  117 . 
     The light source unit  120  may be arranged opposite to the first edge surface  113  of the LGP  110 . The light source unit  120  may include a circuit board  121  and a plurality of light sources  122  mounted on the circuit board  121 . By way of example, the light source  122  may include LED. The rays of light emitted from the plurality of light sources  122  may be introduced into the LGP  110  through the first edge surface  113 . Although not illustrated, another light source unit with the same structure as the light source unit  120  of  FIG. 4  may be arranged opposite to the second edge surface  114  of the LGP  110 . 
     The rear optical sheet unit  130  may be arranged in back of the LGP  110  and may include a reflection sheet  131 . The reflection sheet  131  reflects the light leaking out from the rear surface  112  of the LGP  110  back to the LGP  110 . 
     The front optical sheet  140  may be arranged in front of the LGP  110  and may include a diffusion sheet  141 , a prism sheet  142  and a protection sheet  143 . The diffusion sheet  141  diffuses the light emitted from the LGP  110 , the prism sheet  142  focuses the light diffused at the diffusion sheet  141 , and the protection sheet  143  protects the prism sheet  142  and also increases light uniformity. In an alternative embodiment, the protection sheet  143  may be substituted with a reflection polarization sheet for the purpose of enhancing light efficiency. The reflection polarization sheet may be a multi-layer reflective polarization prism sheet which collects, polarizes, and emits light, such as DBEF™ (Dual Brightness Enhancement Film) by 3M. 
     Referring to  FIG. 4 , the lights L generated at the light sources  122  are emitted in the front direction of the LGP  110  due to the LGP  110  and the reflection sheet  131 , the brightness uniformity and viewing angle of the emitted lights are improved as the lights pass through three front optical sheets  141   142 ,  143 , and then the lights L enter onto the display panel (not illustrated). 
       FIG. 5  is a plane view of the LGP according to a second embodiment,  FIG. 6A  is a schematic rear perspective view of the LGP of  FIG. 5 ,  FIG. 6B  is a rear perspective view of the LGP according to an alternative embodiment,  FIG. 7  is a side view of the LGP of  FIG. 5 , and  FIG. 8  is a partial cross-section view taken on line VIII-VIII of  FIG. 7 . 
     Referring to  FIGS. 5 to 8 , the LGP  210  according to a second embodiment may be formed in approximately rectangular shape, and may include a front surface  211 , a rear surface  212 , and four edge surfaces  213 ,  214 ,  215 ,  216 . For convenience of explanation, the four edge surfaces may be referred to as a first edge surface  213 , a second edge surface  214 , a third edge surface  215 , and a fourth edge surface  216 . 
     The lights L emitted from the light sources are introduced into the LGP  210  through the first and second edge surfaces  213 ,  214 . Although the lights enter through the two edge surfaces  213 ,  214  in one embodiment, this is only for illustrative purposes. Accordingly, in another embodiment, the lights may be introduced into the LGP  210  through only one of the four edge surfaces or through more than two edge surfaces. 
     The LGP  210  according to the second embodiment may have a similar structure as that of the LGP  110  explained above. Accordingly, like the LGP  110  explained above, the LGP  210  according to the second embodiment may have a plurality of lenticular patterns  217  formed on the rear surface  212  thereof, and the light emitting patterns  218  may be integrally formed with the lenticular patterns  217 . Referring to  FIG. 6A , the light emitting patterns  218  formed on the LGP  210  may have a regular arrangement. Alternatively, referring to  FIG. 6B , the light emitting patterns  218  may have irregular patterns in another embodiment. 
     The difference of the second embodiment lies in the shape of the light emitting patterns  218  of the LGP  210  which is different from the light emitting patterns  118  of the LGP  110  of the embodiment explained above. This will be explained in detail below. 
     Referring to  FIGS. 6A and 8 , the light emitting patterns  218  may be concavely formed from the surfaces of the lenticular patterns  217 . The respective light emitting patterns  218  may have two reflection surfaces  218   a ,  218   b  and thus have similar shape as the prism. The reflection surfaces  218   a ,  218   b  of the light emitting patterns  218  may be planar, which is different from the spherically-curved surfaces of the light emitting patterns  118  explained above (see  FIG. 3 ). 
     Referring to  FIG. 8 , the pair of reflection surfaces  218   a ,  218   b  are at an angle α and may be arranged symmetrically to each other. The angle between the two reflection surfaces  218   a ,  218   b  may range between 70° and 110°. Further, the respective reflection surfaces  218   a ,  218   b  are inclined with respect to the front surface  211  or the rear surface  212  (i.e., to X axis) of the LGP  210 , and the angle β of inclination may preferably range between 35° and 80°. 
     Meanwhile, the pitch between two adjacent light emitting patterns  218  may preferably be 0.5 mm or below. For convenience of illustration, only three light emitting patterns  218  are depicted as being formed with one lenticular pattern  217 , but it will be appreciated that the actual number of light emitting patterns  218  may advantageously be more than those illustrated in the figures. 
     As in the LGP  110  of the previous embodiment explained above, the LGP  210  according to the second embodiment may be fabricated by using imprinting, extruding or injection, and by applying these processes, the lenticular patterns  217  and the light emitting patterns  218  may be formed or shaped only by one process (i.e., concurrently). Accordingly, compared to the conventional LGP in which the light emitting patterns are formed by post-processing such as laser processing or printing, the fabrication of the LGP according to the second embodiment becomes simpler and requires less cost. 
       FIG. 9  is a schematic, partial cross-section view of a backlight unit having the LGP of  FIGS. 5 to 8  according to an embodiment. 
     Referring to  FIG. 9 , the backlight unit  200  may include the LGP  210 , a light source unit  220 , a rear optical sheet unit  230  and a front optical sheet unit  240 . 
     As explained above, the LGP  210  may have a plurality of lenticular patterns  217  formed on the rear surface  212  thereof, and the light emitting patterns  218  may be integrally formed with the lenticular patterns  217 . The respective light emitting patterns  218  may have two reflection surfaces  218   a ,  218   b  and thus have similar cross-section as the prism. 
     The light source unit  220  and the rear optical sheet unit  230  are identical to the light source unit  120  and the rear optical sheet  130  explained above with reference to  FIG. 4 . 
     The front optical sheet unit  240  may have only one diffusion sheet  241 , which is distinct from the front optical sheet unit  140  explained above. 
     Although the backlight unit  200  has only one diffusion sheet  241  in front of the LGP  210 , the backlight unit  200  can at least maintain the same level of optical performance (such as light efficiency, viewing angle, 3D scanning efficiency, etc.) as the backlight units (such as the backlight unit  100 ) having a plurality of front optical sheets, by implementing light emitting patterns  218  having two planar reflection surfaces  218   a ,  218   b.    
     The inventors have conducted tests to confirm the optical performance of the LGP  210  according to the second embodiment. Accordingly, the inventors used the LGP  210  explained above according to one embodiment, and compared this with a conventional LGP in which the lenticular patterns are formed on the front surface and the light emitting patterns, in a dot form, are formed on the rear surface. 
     Referring to Table 1 below, the test has been conducted four times with respect to the conventional LGP alone, the conventional LGP added with the diffusion sheet thereon, the conventional LGP added with the diffusion sheet and the prism sheet thereon, and the conventional LGP added with the diffusion sheet, the prism sheet thereon, and the protection sheet thereon, and two times with respect to the LGP  210  according to an embodiment, and the LGP  210  according to an embodiment added with the diffusion sheet. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Resultant 
               
               
                   
                   
                 viewing 
               
               
                   
                 Condition (Front optical sheets) 
                 angle 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Conventional 
                 Test #1 
                 None 
                 80°  
               
               
                   
                 Test #2 
                 Diffusion sheet 
                 50°  
               
               
                   
                 Test #3 
                 Diffusion sheet + prism sheet 
                 0° 
               
               
                   
                 Test #4 
                 Diffusion sheet + prism sheet + 
                 0° 
               
               
                   
                   
                 protection sheet 
               
               
                 Embodiment of 
                 Test #5 
                 None 
                 −10°~+10° 
               
               
                 the invention 
                 Test #6 
                 Diffusion sheet 
                 0° 
               
               
                   
               
            
           
         
       
     
     As a result of conducting test on six cases based on the conventional technology and the embodiment, brightness distribution image photographed from the front surface of the LGP and corresponding graph thereof are obtained as shown in  FIGS. 10A to 15B . 
     That is,  FIGS. 10A and 10B  are the brightness distribution image obtained from test #1 and a corresponding graph,  FIGS. 11A and 11B  are the brightness distribution image obtained from test #2 and a corresponding graph,  FIGS. 12A and 12B  are the brightness distribution image obtained from test #3 and a corresponding graph,  FIGS. 13A and 13B  are the brightness distribution image obtained from test #4 and a corresponding graph,  FIGS. 14A and 14B  are the brightness distribution image obtained from test #5 and a corresponding graph, and  FIGS. 15A and 15B  are the brightness distribution image obtained from test #6 and a corresponding graph. 
     Referring to  FIGS. 10A to 13B  related with the conventional technology, the conventional technology exhibited good brightness distribution and viewing angle 0° only in test #4 where there were three optical sheets (i.e., diffusion sheet, prism sheet, protection sheet) were arranged in front of the LGP. 
     On the contrary, referring to  FIGS. 14A to 15B  related with the embodiment, the embodiment exhibited good brightness distribution and viewing angle 0° in test #6 where there was only one optical sheet arranged in front of the LGP. 
     The central brightness, median brightness and brightness uniformity calculated from tests #4 and #6 are as follows: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Test #6 (Embodiment 
               
               
                   
                 Test #4 (Conventional) 
                 of invention) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Front optical sheets 
                 3 sheets 
                 1 sheet 
               
               
                 used 
                 (Diffusion sheet + prism 
                 (Diffusion sheet) 
               
               
                   
                 sheet + protection sheet) 
               
               
                 Central brightness 
                 6100 nits (100%) 
                 6710 nits (110%) 
               
               
                 Median brightness 
                 5861 nits (100%) 
                 6447 nits (110%) 
               
               
                 Brightness uniformity 
                 82% 
                 82% 
               
               
                   
               
            
           
         
       
     
     Referring to Table 2, the LGP  210  according to an embodiment can provide the same level of brightness uniformity as the conventional technology, without requiring more than one diffusion sheet. Further, the LGP  210  according to an embodiment can provide central brightness and median brightness which are enhanced by approximately 10%. 
     Further, test to compare 3D scanning performance between the LGP  210  according to an embodiment and the conventional LGP was conducted, in which LGPs of tests #1 to #4 were used as the conventional LGPs, and the LGPs of tests #5 and #6 were used as the LGP according to the embodiment. 
     The test was conducted by measuring the brightness of the light entering portion and the central portion of the LGP corresponding to the light sources, while keeping only one light source among the plurality of light sources (LEDs) arranged on one side of the LGP in on state, and keeping the others off. 
       FIGS. 16A and 16B  present the images captured in the above-explained tests. Additionally, numerical data calculated from the tests are tabulated into Table 3 and Table 4, and the graphs corresponding to the data of the tables is provided in  FIG. 17 . 
       FIGS. 16A and 16B  are images of a conventional LGP and a LGP according to an embodiment, each photographed at the 3D scanning efficiency test. Table 3 and Table 4 list the data calculated from the 3D scanning efficiency test on the conventional LGP and the LGP according to the embodiment.  FIG. 17  presents two graphs representing brightness distribution data on the central portion of the LGP among the data of Table 3 and Table 4. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Measurement 
                   
                 Percent (%) 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Light 
                   
                 Light 
                   
               
               
                   
                 Light source 
                 entering 
                 Central 
                 entering 
                 Central 
               
               
                 No 
                 (LED) 
                 portion 
                 portion 
                 portion 
                 portion 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 OFF 
                   
                   
                   
                   
               
               
                 2 
                 ON 
                 49 
                 36 
                 18%  
                 50%  
               
               
                 3 
                 OFF 
                 278 
                 72 
                 100%  
                 100%  
               
               
                 4 
                 OFF 
                 35 
                 36 
                 13%  
                 50%  
               
               
                 5 
                 OFF 
                 8 
                 8 
                 3% 
                 11%  
               
               
                 6 
                 OFF 
                 2 
                 2 
                 1% 
                 3% 
               
               
                 7 
                 OFF 
                 1 
                 1 
                 0% 
                 1% 
               
               
                 8 
                 OFF 
                 1 
                 0.5 
                 0% 
                 1% 
               
               
                 9 
                 OFF 
                 0.5 
                 0.5 
                 0% 
                 1% 
               
            
           
           
               
               
               
               
               
               
            
               
                 Maximum (Max) 
                   
                 278 
                 72 
                 100%  
                 100%  
               
            
           
           
               
               
               
               
            
               
                 Contrast (N + 3/N) 
                   
                 0.7%   
                 3.0%   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                 Measurement 
                   
                 Percent (%) 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Light 
                   
                 Light 
                   
               
               
                   
                 Light source 
                 entering 
                 Central 
                 entering 
                 Central 
               
               
                 No 
                 (LED) 
                 portion 
                 portion 
                 portion 
                 portion 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 OFF 
                   
                   
                   
                   
               
               
                 2 
                 ON 
                 34 
                 35 
                 14%  
                 41%  
               
               
                 3 
                 OFF 
                 278 
                 86 
                 100%  
                 100%  
               
               
                 4 
                 OFF 
                 37 
                 37 
                 16%  
                 43%  
               
               
                 5 
                 OFF 
                 7 
                 9 
                 3% 
                 10%  
               
               
                 6 
                 OFF 
                 3 
                 3 
                 1% 
                 3% 
               
               
                 7 
                 OFF 
                 2 
                 2 
                 1% 
                 2% 
               
               
                 8 
                 OFF 
                 1 
                 1 
                 0% 
                 1% 
               
               
                 9 
                 OFF 
                 1 
                 1 
                 0% 
                 1% 
               
            
           
           
               
               
               
               
               
               
            
               
                 Maximum (Max) 
                   
                 238 
                 86 
                 100%  
                 100%  
               
            
           
           
               
               
               
               
            
               
                 Contrast (N + 3/N) 
                   
                 1.3%   
                 3.0%   
               
               
                   
               
            
           
         
       
     
     Referring to Table 3 and Table 4, the ratio between the brightness at the central portion with respect to the second light source and the brightness at the central portion with respect to the fifth light source is identically 3%. From this, it is revealed that the 3D scanning efficient does not deteriorate from that of the conventional LGP when the LGP  210  according to the embodiment is used. The graph of  FIG. 17  also confirms the above. That is, the horizontal axis of the graph of  FIG. 17  represents LED numbers, and the longitudinal axis represents the brightness at the central portion of the LGP. The plot with links ‘▪’ represents the conventional LGP and the plot with links ‘x’ represents the LGP according to the embodiment. 
     The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the inventive concept. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments of the present inventive concept is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.