Patent Publication Number: US-2019196083-A1

Title: Lighting device and image display apparatus

Description:
This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application 2017-246848 filed in Japan on 22 Dec. 2017, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a lighting device and an image display apparatus used in an image display apparatus with a LCD (Liquid Crystal Display). 
     (2) Description of the Prior Art 
     Generally, liquid crystal display devices used as a display portion of a television set, a personal computer, a monitor and the like include a lighting device because LCDs do not produce light by themselves. 
     Such lighting devices are backlight type illuminators which illuminate the liquid crystal panel from its rear side. The backlighting systems are mainly categorized into two types, i.e., the edge light type (also called the side light system or the light guide system) and the direct type. For LCDs adopted for various kinds of small monitors and laptop personal computers, lighting devices of the edge light type are mainly used. 
     Regarding an edge light type lighting device, Japanese Patent Application Laid-Open No. 2013-89565 (Patent Document 1) discloses a flat lighting device unit. This flat lighting device unit includes, as shown in  FIGS. 5 and 6 , a light guide a 0  and a light source unit c such as an LED (Light Emitting Diode) that emits light O incident on one endface b of the light guide a 0 . Here, the light guide a 0  is constructed such that a light condensing regulator having fine convex portions for refracting light is provided on the surface a 1  while a light reflecting regulator for reflecting light is provided on the reverse face a 2  of the light guide a 0 , whereby the incident light is refracted and reflected so as to exit from the surface a 1 . 
     In the above flat lighting device unit, the light guide a 0  guides light O so as to exit from the surface a 1  toward an unillustrated light converter having fine apertures. A light regulating sheet having arcuate patterns for refracting light arrayed on the surface side is laid over the light converter. 
     In the flat lighting device unit of Patent Document 1, the light condensing regulator with fine convex patterns on the surface a 1 , the light converter with fine apertures and the light regulating sheet with arcuate patterns are adjusted in position so as to create a predetermined relationship, to thereby produce a highly luminous and clear image. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     [Patent Document 1] 
     Japanese Patent Application Laid-Open No. 2013-89565 
     Problems to be Solved by the Invention 
     However, in the flat lighting device unit described in the above Patent Document 1, there is a limit to the high luminance. Because in the lighting device unit the LEDs are arranged in a line, the number of LEDs that can be mounted on the light source unit is limited by the screen size of the image display apparatus. 
     In addition, in order to obtain a highly luminous and clear image in the flat lighting device unit of the above Patent Document 1, the light condensing regulator with fine convex patterns on the surface a 1 , the light converter with fine apertures and the light regulating sheet with arcuate patterns need to be adjusted so as to create a predetermined positional relationship. However, because the light guide a 0 , the light converter and the light regulating sheet are different in thermal expansion coefficient and the like, it is difficult to keep the predetermined positional relationship constant. 
     SUMMARY OF THE INVENTION 
     The present invention has been devised in view of the above circumstances, it is therefore an object of the present invention to provide a lighting device which can achieve high luminance while suppressing cost without complicating the structure, as well as providing an image display apparatus provided with the lighting device. 
     Means for Solving the Problem 
     The gist of the present invention resides in a lighting device, comprising: light sources; and a light guide having an obverse face, a reverse face, and an endface, wherein: the reverse face has a first light incident portion located near the endface; the obverse face has a second light incident portion located near the endface and a light emitting portion for emitting light incident from the first light incident portion and the second light incident portion; the endface has a concave portion formed along the longitudinal direction of the endface; and the light sources are disposed in each of the first light incident portion and the second light incident portion so as to sandwich the concave portion. 
     Effect of the Invention 
     According to the lighting device of the present invention, in the lighting device including light sources and a light guide having an obverse face, a reverse face, and an endface, the reverse face has a first light incident portion located near the endface, and the obverse face has a second light incident portion located near the endface and a light emitting portion for emitting light incident from the first light incident portion and the second light incident portion. The endface has a concave portion formed along the longitudinal direction of the endface, and the light source is disposed in each of the first light incident portion and the second light incident portion so as to sandwich the concave portion. Therefore, since the light source can be arranged in the first light incident portion on the obverse face side of the light guide and the second light incident portion on the reverse face side, at least two light sources can be arranged (if multiple light sources are provided for each of the first and second light incident portions, a further increased number of light sources can be provided). In addition, as compared with the conventional case where only one light source directed to the endface of the light guide can be arranged, the number of light sources can be increased to enhance the intensity of light and easily achieve high luminance. 
     Further, in order to increase the luminance of a general image display apparatus, the configuration in Patent Document 1 needs to perform positional adjustment as to the fine light condensing regulator of the light guide, the fine apertures of the light converter and the patterns on the light regulating sheet. However, it is very difficult to always keep the positions of these components because these components have different coefficients of thermal expansion. Further, it is necessary to prepare these components with high dimensional accuracy, which causes a cost increase. 
     In contrast to this, according to the present invention, it is not necessary to consider such positional adjustment, and it is possible to use a general structure as it is for the sheets and the like, so it is possible to reliably achieve high luminance and achieve excellent effects without cost increase. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustrative diagram showing a vertical section of an image display apparatus according to a first embodiment of the present invention; 
         FIG. 2  is an illustrative diagram showing optical paths in a light guide of a lighting device in  FIG. 1 ; 
         FIG. 3  is an illustrative diagram showing optical paths in a light guide in a lighting device according to a second embodiment of the present invention; 
         FIG. 4  is an illustrative diagram showing optical paths in a light guide in a lighting device according to a third embodiment of the present invention; 
         FIG. 5  is a perspective illustrative view of a light guide in a conventional lighting device; and 
         FIG. 6  is an illustrative diagram showing optical paths in a light guide in  FIG. 5 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described hereinbelow with reference to the accompanying drawings. 
       FIG. 1  is an illustrative diagram showing a vertical section of an image display apparatus according to a first embodiment of the present invention.  FIG. 2  is an illustrative diagram showing optical paths OP in a light guide of a lighting device in  FIG. 1 . 
     First Embodiment 
     As shown in  FIG. 1 , the image display apparatus according to the first embodiment includes a lighting device  16  including arrays of light sources  10  such as light emitting diodes (LEDs) and a light guide  14  for guiding the light emitted from the light sources  10  toward a display panel  12  as indicated by optical paths OP. More specifically, the lighting device  16  is formed of the light guide  14  whose obverse side opposes the display panel  12  and having a V-shaped groove (corresponding to a concave portion)  18  formed along the longitudinal direction (perpendicular to the surface of the drawing document in  FIG. 1 ) of the endface, designated at  14   a , and the arrays of light sources  10  (light sources  10 ,  10  at positions sandwiching the bottom facets  18   a  from the obverse side and the reverse side) arranged so as to sandwich the bottom facets  18   a  of the groove  18  on the obverse face  14   u  and the reverse face  14   d  of the light guide  14 . 
     As shown in  FIG. 2 , the reverse face  14   d  has a first light incident portion  14   d   1  near the endface  14   a  so as to allow the light emitted from the lower array of light sources  10  (located on the reverse face  14   d  side of the light guide  14 ) to be incident thereon. Further, the obverse face  14   u  has a second light incident portion  14   u   1  near the endface  14   a  so as to allow the light emitted from the upper array of light sources  10  (located on the obverse face  14   u  side of the light guide  14 ) to be incident thereon and a light emitting portion  14   u   2  allowing the incident light from the first light incident portion  14   d   1  and the second light incident portion  14   u   1  to exit. In  FIG. 2 , the areas of the first light incident portion  14   d   1 , the second light incident portion  14   u   1  and the light emitting portion  14   u   2  are indicated by two-dot chain lines. 
     In this arrangement, the light guide  14  forms light paths OP such that the light beams from the obverse and reverse arrays of light sources  10  and  10  enter the interior of the light guide  14  from the second light incident portion  14   u   1  of the obverse face  14   u  and the first light incident portion  14   d   1  of the reverse face  14   d  and are reflected on the bottom facets  18   a  and  18   a  of the groove  18  and led in the direction perpendicular to the endface  14   a  so that the thus led light can illuminate the display panel  12  through the light emitting portion  14   u   2  on the obverse face  14   u  side. 
     Specifically, the image display apparatus shown in  FIG. 1  is a liquid crystal display device in which the display panel  12  is a liquid crystal panel. 
     This liquid crystal display device includes the lighting device  16  having the light sources  10 , the light guide  14  and the like, a liquid crystal panel, i.e., the display panel  12  and an unillustrated circuit board for driving these components. 
     The lighting device  16  includes a light source unit  10   a  provided with the light sources  10 , the light guide  14  for guiding light from the light sources  10  so as to illuminate the display panel  12 , an optical sheet  20  disposed on the obverse face  14   u  side of the light guide  14  and a reflection sheet  22  disposed on the reverse face  14   d  side of the light guide  14 , as well as including a P-chassis  24  made of resin and a rear metal sheet  26  which sandwich the above components from the obverse side and the reverse side. The display panel  12  is configured to be held and sandwiched between the lighting device  16  and a metallic bezel  28  from the obverse side and the reverse side. 
       FIG. 2  is a diagram schematically showing the light source unit  10   a  (on one side) and part of the light guide  14  in  FIG. 1 . A plurality light sources  10  are mounted on a long plate-like substrate. The substrates are arranged so as to oppose each other and fixed to the light source holder  10   b  having a U-shaped section with, for example, high heat radiation double-sided tape. Thus, the light sources  10  and the light source holder  10   b  constitute the light source unit  10   a . The light source unit  10   a  is fixed by the rear metal sheet  26 . 
     As the material of the plate-like substrate on which multiple LEDs as the light sources  10  are mounted, for example an FR4 substrate (an aluminum substrate is preferable if high power is expected) can be used. As the light source holder  10   b , materials having a high thermal conductivity such as aluminum are preferably used. Here, the light source unit  10   a  may be removably mounted to the light guide  14 . The array of light source  10  is arranged not on the endface  14   a  of the light guide  14  but on each of the obverse and reverse faces  14   u  and  14   d  of the light guide  14  so as to extend along the endface  14   a  of the light guide  14 . Specifically, the arrays of light sources are arranged parallel to the longitudinal direction of the endface  14   a  of the light guide  14  (for example, arranged in the direction perpendicular to the document surface of  FIGS. 1 and 2 ). 
     In the present embodiment, the groove (concave portion)  18  has a shape in which two facets adjoin each other so as to form a valley-like or V-shaped cross-section, and the valley line, designated at  18   b , of the groove formed by the intersection of the two adjacent facets extend parallel to the longitudinal direction of the endface  14   a.    
     Specifically, the groove  18  having a valley-like or V-shaped cross-section is formed on the endface  14   a  (each of left and right endfaces perpendicular to the obverse and reverse faces  14   u  and  14   d  in  FIG. 1 ) of the light guide  14  along the longitudinal direction of endface  14   a . The two bottom facets  18   a ,  18   a  forming the V-shaped section of the groove  18  intersect each other to form the valley line  18   b  of the groove. The groove  18  is parallel to the valley line (the direction perpendicular to the surface of the drawing document in  FIG. 1  or  FIG. 2 ) formed by the obverse face  14   u  of the light guide  14  and the endface  14   a  while the two bottom facets  18   a ,  18   a  extending from the valley line  18   b  of the groove toward the endface  14   a  are angled 45 degrees with respect to the obverse and reverse faces  14   u  and  14   d  of the light guide  14 , respectively. 
     As shown in  FIG. 1 , the endface  14   a  of the light guide  14  may be formed with the groove  18  from the edge to the edge (from the obverse face  14   u  to the reverse face  14   d ). Alternatively, as shown in  FIG. 2  the groove  18  may be incised in part of the endface  14   a . The bottom facets  18   a  and  18   a  of the grooves  18  intersect at 90 degrees but 90 degrees is not always necessary, and the angle between the two bottom facets  18   a  and  18   a  can freely be set at an angle form 60 to 120 degrees. 
     As shown in  FIG. 2 , as to the optical paths OP, the light from the light sources  10  is made incident along the directions parallel to the endface  14   a  of the light guide  14  (made incident in the thickness direction of the light guide  14 ). Then, the incident light is reflected in the direction perpendicular to the endface  14   a  by the bottom facets  18   a ,  18   a  of the groove  18  formed on the endface  14   a  of the light guide  14 . When the position of the light guide  14  with respect to the light sources  10  varies due to a difference in thermal expansion coefficient (a difference in coefficient of thermal expansion between the light guide  14  and the rear metal sheet  26  to which the light source unit  10   a  is fixed), the layout is designed so that the above reflection can be retained throughout the range of variation. Alternatively, the layout may be designed so that the position of the light guide  14  with respect to the light sources  10  can be kept constant. The optical paths OP after being reflected in the direction perpendicular to the endface  14   a  are the same as those of a general image display apparatus so that it is possible to use the structure of the general image display apparatus as it is, for other than the structure of the groove  18 . 
     As the material of the light guide  14 , a resin with high transparency such as PMMA (Polymethyl Methacrylate) resin or PC (Polycarbonate) resin can be used. 
     Arranged on the light guide  14  side opposing the display panel  12  is the aforementioned optical sheet  20  such as a lens sheet or a diffusion sheet. The reflection sheet  22  is arranged on the opposite side of the light guide  14  from the aforementioned optical sheet  20 . For these sheets, the general structure can be used as it is. It is also possible to provide a lighting device that does not have optical sheets, such as a see-through module. Further, well-known configurations can be used for the liquid crystal panel and the drive circuit board of the display panel  12 , so the details will be omitted. 
     Operation and effects of the lighting device according to the present embodiment will be described. 
     In the conventional lighting device (see  FIGS. 5 and 6 ), light from the light source c is incident on the endface b of the light guide a. When an upward lighting LED whose mounted surface is parallel to the surface of light emission is used for the light source c, since the upward lighting LED has a greater width compared to the thickness of the light guide a, it is difficult to arrange multiple rows of LEDs, side by side, in view of the thickness of the light guide a (the thickness of the image display apparatus). Hence, one light source unit with only a single array of LEDs has been used conventionally. Therefore, in the prior art, the number of LEDs that can be mounted on the flat lighting device unit has an upper limit depending on the screen size of the image display apparatus, hence there is a limit in increasing the luminance. 
     In contrast to this, according to the present embodiment, when the light source units  10   a  are arranged on the obverse and reverse side in the vicinity of the endface  14   a  of the light guide  14 , light sources  10  are disposed on each of the obverse face  14   u  and the reverse face  14   d  of the light guide  14 , along the longitudinal direction of the endface  14   a . That is, multiple arrays of light sources can be arranged. Even with the same size of the image display apparatus, the number of the light sources can be doubled as compared to the case where the light sources are provided on one of the endfaces of the light guide as disclosed in Patent Document 1. When the light sources  10  are arranged on both the left and right endfaces of the light guide  14  as shown in  FIG. 1 , a further increase is expected so that the number of the light sources  10  can be increased about four-fold. In this way, adoption of the present embodiment can facilitate increase of the number of light sources. 
     Further, in this case, the thicknesses of the light sources  10  and the light source holder  10   b  are added in the thickness direction of the image display apparatus, but the image display apparatus is not thickened by the same amount. In a general image display apparatus, the thicknesses of the light source and the light source holder are smaller than that of the light guide, and the width of the light source holder (the dimension of the light source holder in the thickness direction of the image display apparatus) is some several times that of the thickness of the light guide (as an example, the thickness of the light source is 1 to 2 mm, the thickness of the light guide is 3 to 5 mm, the width of the light source holder is 10 to 15 mm, the thickness of the light source holder is 1 mm). That is, the factor contributing to the thickness of the image display apparatus is the width of the light source holder. Accordingly, if, in the present embodiment, the light sources  10  are arranged by securing a certain amount of clearance between the light guide  14  and the light source holder  10   b  having a U-shaped cross-section, it is not necessary to increase the thickness of the image display apparatus so much. In some cases, it is possible to suppress the thickness to equivalent to the prior art. 
     Further, since the light source previously arranged facing the endface of the light guide does not exist in the present embodiment, the frame width (the distance from the border of the displayable area to the outward form of the image display apparatus) on the side where the light source is accommodated can be made smaller by the thickness of the light source. That is, even with the same screen size, the outward form can be reduced. 
     Further, in consideration of increasing the luminance of a general image display apparatus, it is necessary to prepare fine patterns on the light guide with high dimensional accuracy in Patent Document 1, which causes a cost increase. On the other hand, in the present embodiment, the optical path OP of light after being reflected on the bottom facet  18   a  is the same as that of a general image display apparatus, so that the light guide  14  having the same structure except the groove  18  can be used as it is. Therefore, it is possible to suppress the manufacturing cost. 
     Furthermore, in Patent Document 1, in order to achieve high luminance, it is necessary to align the fine light condensing regulator of the light guide, the light converter with fine apertures and the light regulating sheet with arcuate patterns, but it is very difficult to always keep the alignment of these components having different coefficients of thermal expansion. In addition, it is necessary to produce the light converter and the light regulating sheet with high dimensional accuracy, which is costly. 
     In contrast to this, in the present embodiment, it is not necessary to take such alignment into consideration and it is possible to use a general structure as it is for the sheets and the like, so it is possible to reliably achieve high luminance and achieve excellent effects without cost increase. 
     That is, the present embodiment facilitates provision of an image display apparatus with high luminance and a narrow frame. In addition, the present embodiment is not only applicable to ordinary image display apparatus, but can be applied further preferably to a see-through type display apparatus which is hard to increase luminance because of a lack of an optical sheet and to a 8K UHDTV ((8K Ultra High Definition Television), 8K is a video format with 7680 pixels in lateral direction and 4320 lines in vertical direction) having lower numerical apertures due to increased number of pixels. 
     Second Embodiment 
       FIG. 3  is a diagram for explaining optical paths OP in a light guide  14  in a lighting device  16  according to the second embodiment of the present invention, schematically showing light source units  10   a  and part of the light guide  14 . The same reference numerals are allotted to the same components as those in  FIGS. 1 and 2 . 
     As shown in  FIG. 3 , in the lighting device  16  according to the second embodiment, the depth of the groove (concave portion)  18  formed on the endface  14   a  of the light guide  14  is made deeper than that in the first embodiment while two arrays of light sources  10  and  10  are arranged along the direction parallel to the longitudinal direction of the endface  14   a  on each of the obverse face  14   u  and the reverse face  14   d  of the light guide  14 . The light sources  10 ,  10 , . . . are arranged parallel in the longitudinal direction of the endface  14   a  so as to sandwich the bottom facets  18   a  and  18   a  of the groove  18  from the obverse face side and the reverse face side of the light guide  14 . Thus, the two arrays of light sources  10 ,  10  can be arranged parallel to the longitudinal direction of the endface  14   a . In the light guide  14 , as in the case described above with  FIG. 2 , light beams from the light sources  10  are made incident at a right angle on the obverse face  14   u  or the reverse face  14   d  of the light guide  14 , then reflected on the bottom facets  18   a ,  18   a  of the groove  18  in the direction perpendicular to the endface  14   a.    
     According to the optical paths OP in the light guide  14  of the lighting device  16  according to the second embodiment, the light sources  10 ,  10  . . . are disposed on both the obverse face  14   u  side and the reverse face  14   d  side of the light guide  14  so as to sandwich the bottom facets  18   a  of the groove  18 . Since the multiple arrays of light sources  10  (the light sources  10 ,  10  . . . ) are arranged along the longitudinal direction of the endface  14   a , it is possible to achieve further higher luminance by increasing the number of the light sources  10 ,  10  . . . (two or more arrays of light sources). 
     Third Embodiment 
       FIG. 4  is an illustrative diagram of optical paths OP in a light guide  14  of a lighting device  16  according to the third embodiment of the present invention, schematically showing light source units  10   a  and part of the light guide  14 . The same reference numerals are allotted to the same components as those in  FIGS. 1 and 2 . 
     In the third embodiment, as shown in the sectional view in  FIG. 4 , a groove (depressed portion)  18  formed in the longitudinal direction of the endface of the light guide  14  is formed of a pair of bottom facets  18   a   1  and  18   a   1  inclined at a predetermined angle with the obverse face  14   u  and a pair of facets  30  between the paired bottom facets parallel to the obverse face  14   u  and a pair of bottom facets  18   a   1  and  18   a   1  inclined at a predetermined angle with the reverse face  14   d  and a facet  30  between the paired bottom facets parallel to the reverse face  14   d . That is, the groove  18  on the endface of the light guide  14  has across-section in which the inclined bottom facets  18   a   1 ,  18   a   1  and the parallel facets  30  to the obverse and reverse faces  14   u  and  14   d  are combined stepwise. Specifically, the groove  18  formed in the endface includes an edged portion formed by the obverse face  14   u  and the bottom facet  18   a   1 , the bottom facet  18   a   1 , the parallel facet  30 , the bottom facet  18   a   1 , the groove&#39;s valley line  18   b , the bottom facet  18   a   1 , the parallel facet  30 , the bottom facet  18   a   1  and an edge portion formed by the bottom facet  18   a   1  and the reverse face  14   d.    
     More specifically, as shown in  FIG. 4 , two arrays of light sources  10 ,  10  are provided on each of the obverse face  14   u  side and the reverse face  14   d  side of the light guide  14  so as to extend in the longitudinal direction of the endface  14   a  of the light guide  14 . Multiple bottom facets  18   a   1 ,  18   a   1  are formed separately along the direction perpendicular to the endface  14   a  in positions held between the obverse face  14   u  and the reverse face  14   d  corresponding to each of the arrays of light sources  10 ,  10  . . . while the bottom facets  18   a   1  and  18   a   1  are connected by the parallel facet  30  parallel to the obverse face  14   u.    
     That is, the groove  18  has a shape in which the bottom facets  18   a   1 ,  18   a   1  are connected by the parallel facet  30 . With this configuration, similarly to the case shown in  FIG. 2 , light beams from the two arrays of light sources  10 ,  10  are made incident in the direction along the endface  14   a  to the light guide  14 , and then reflected by the bottom facets  18   a   1 ,  18   a   1  in the endface  14   a , in the direction perpendicular to the endface  14   a . In this case, it is desirable to design such that the position of the light guide  14  can be kept constant to the arrays of light sources  10 ,  10 . 
     According to the third embodiment, since the bottom facets  18   a   1  and  18   a   1  are connected by the parallel facet  30 , the groove  18  can be formed with a stepped structure of inclined facets and a flat facet. When multiple arrays of light sources  10  are provided in parallel in the longitudinal direction of the endface  14   a  of the light guide  14  in the configuration of the second embodiment shown in  FIG. 3  in which a single inclined facet  18   a  is formed on either side, it is necessary to enlarge the inclined facet in consideration of the interference between the arrays of light sources  10 ,  10  arranged on the same side, which means increase in thickness of the light guide  14 . In contrast to this, in the third embodiment, even if the arrays of light sources  10  and  10  interfere with each other, the positions of the bottom facets  18   a   1  and  18   a   1  can be shifted with respect to the direction perpendicular to the endface  14   a  without the need of increasing the thickness of the light guide  14 . Accordingly, achievement of further higher luminance as in the above second embodiment can be realized by using a thinner light guide  14  than that of the second embodiment or with a thinner image display apparatus. 
     In the first to third embodiments, multiple arrays of light sources  10  may be appropriately arranged on the obverse face  14   u  and the reverse face  14   d , along the longitudinal direction of the endface  14   a : in the first embodiment, one array of light sources  10  is arranged on each side so as to be parallel to the longitudinal direction of the endface  14   a ; and in the second to third embodiments, two arrays of light sources  10  are arranged on each side in the direction perpendicular to the endface to configure a multiple light source arrangement. However, the present invention is not limited to these. That is, three or more arrays of light sources may be arranged in the direction perpendicular to the endface. 
     INDUSTRIAL APPLICABILITY 
     The lighting device of the present invention can be used as a backlight of a liquid crystal display device. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               10  light source 
               10   a  light source unit 
               10   b  light source holder 
               12  display panel 
               14  light guide 
               14   a  endface 
               14   d  reverse face 
               14   u  obverse face 
               16  lighting device 
               18  groove 
               18   a  bottom facet 
               18   a   1  bottom facet 
               18   b  groove&#39;s valley line 
               20  optical sheet 
               22  reflection sheet 
               30  parallel face 
             OP optical path