Patent Publication Number: US-2011051042-A1

Title: Liquid crystal display device

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a liquid crystal display device, particularly, a liquid crystal display device using a backlight device which converts, using light guide plates, the illumination light outputted from light emitting diodes into surface light and outputs the surface light to a liquid crystal panel. 
     (2) Description of the Related Art 
     There have been edge-light (side-light) type backlight devices in which light is supplied from a side and direct type backlight devices in which light is supplied from behind (from a rear side). In edge-light type backlight devices, light emitted from a primary light source, for example, a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) is converted into surface light using a light guide plate formed of a highly scattering optical transmission (HSOT) polymer or a transparent material. Such edge-light type backlight device is widely used in liquid crystal display device. Furthermore, so-called tandem-type backlight device in which plural light guide plates and light source combinations is two-dimensionally arranged so as to secure a relatively wide emission area have also been proposed. 
     Tandem-type backlight systems including two-dimensionally arranged plural light guide plates are disclosed, for example, in Japanese Patent Publication No. 3373427 and Japanese Patent Application Laid-Open No. 2006-286638. 
     SUMMARY OF THE INVENTION 
     In recent years, liquid crystal display devices, while being made thinner, have been growing larger in screen size. The tandem-type backlight device described above is, compared with other types of backlight device, advantageous in making liquid crystal display device thinner and larger in screen size. 
     In a tandem-type backlight device, light fluxes outputted from primary light sources (hereinafter generically referred to as “LED” as being representative of primary light sources) is inputted to light guide plates formed of transparent material (for example, acrylic resin, polycarbonate resin, or cycloolefin resin). The light fluxes inputted to the light guide plate are reflected at the reflection surface of reflection sheet provided at the rear side of the light guide plate and also at the diffuse reflection patterns provided on the light guide plate, and are then outputted as surface light via a diffusion sheet disposed over the output surface of the light guide plate. The light guide plate are shaped with their thickness gradually decreasing along the direction from the LED side toward their light output side. The diffuse reflection patterns are provided in an arrangement in which they are denser where they are more away from the LEDs. 
     A tandem-type backlight device is configured using such light guide plates and LEDs arranged in plural blocks (light guide plate blocks). In a tandem-type backlight device including plural light guide plate blocks, however, a clearance and a mechanical deformation can be generated between light guide plate blocks because of differences between them as to thermal expansion or contraction dependent on, for example, their materials, dimensions, and shapes. Such the clearance and the deformation cause brightness unevenness (differences in brightness level) in the output light of the backlight device or on the screen of the liquid crystal display device. The brightness unevenness can be eliminated by increasing the distance between the light guide plate and the diffusion sheet, but doing so increases the thickness of the backlight device. 
     The present invention has been made in view of the above problem and it is an object of the invention to provide a liquid crystal display device in which the generation of the clearance and the mechanical deformation between light guide plate blocks resulting from their thermal expansions or contractions caused by temperature changes is reduced. 
     According to a first aspect of the present invention, a liquid crystal display device for displaying an image using a liquid crystal panel is provided which comprises: a plurality of light sources which are arranged in a horizontal direction to be spaced apart by a predetermined distance and which emit light downwardly; a plurality of light guide plate blocks to which the light emitted from the plurality of light sources is downwardly incident and which output the incident light to the liquid crystal panel as surface light; and a chassis which fixes the plurality of light sources and the plurality of light guide plate blocks from behind. In the liquid crystal display device: the plurality of light guide plate blocks are arranged along a vertical direction of the liquid crystal display device, each of the plurality of light guide plate blocks having a rectangular shape longitudinally extending along a horizontal direction of the liquid crystal display device; and each of the plurality of light guide plate blocks is fixed, at a portion thereof corresponding to a center in the horizontal direction of the liquid crystal display device, to the chassis, and a clearance is provided at each end in the horizontal direction of each of the plurality of light guide plate blocks. 
     Preferably, in the liquid crystal display device, a rear side of each of the plurality of horizontal rows including the plurality of light guide plate blocks is entirely covered by a reflection sheet. 
     According to a second aspect of the present invention, a liquid crystal display device for displaying an image using a liquid crystal panel is provided which comprises: a plurality of light sources which are arranged in a horizontal direction to be spaced apart by a predetermined distance and which emit light downwardly; a plurality of light guide plate blocks to which the light emitted from the plurality of light sources is downwardly incident and which output the incident light as surface light; a diffusion sheet which diffuses light coming from the plurality of light guide plate blocks and outputs the diffused light to the liquid crystal panel; and a chassis which fixes the plurality of light sources and the plurality of light guide plate blocks from behind. In the liquid crystal display device: the plurality of light guide plate blocks are arranged along a vertical direction of the liquid crystal display device, each of the plurality of light guide plate blocks having a rectangular shape longitudinally extending along a horizontal direction of the liquid crystal display device; and each of the plurality of light guide plate blocks is provided, on a rear side thereof, with a reflection sheet support member for supporting the light guide plate block from behind, the reflection sheet support member having a projection formed integrally therewith for supporting the diffusion sheet from behind. 
     In the liquid crystal display device, each of the reflection sheet support member and the projection may have a white surface. 
     In the liquid crystal display device, the reflection sheet support member may further have a fixing part formed integrally therewith for fixing another light guide plate block provided adjacently below the light guide plate block supported by the reflection sheet support member, the fixing part having, on a front side thereof, the projection formed integrally therewith. 
     According to a third aspect of the present invention, a liquid crystal display device for displaying an image using a liquid crystal panel is provided which comprises: a plurality of light sources which are arranged in a horizontal direction to be spaced apart by a predetermined distance and which emit light downwardly; a plurality of light guide plate blocks to which the light emitted from the plurality of light sources is downwardly incident and which output the incident light as surface light; a diffusion sheet which diffuses light coming from the plurality of light guide plate blocks and outputs the diffused light to the liquid crystal panel; and a chassis which fixes the plurality of light sources and the plurality of light guide plate blocks from behind. In the liquid crystal display device: the plurality of light guide plate blocks are arranged along a vertical direction of the liquid crystal display device, each of the plurality of light guide plate blocks having a rectangular shape longitudinally extending along a horizontal direction of the liquid crystal display device; and each of the plurality of light guide plate blocks is provided, on a rear side thereof, with a reflection sheet support member for supporting the light guide plate block from behind, the reflection sheet support member having a fixing part formed integrally therewith for fixing another light guide plate block provided adjacently below the light guide plate block supported by the reflection sheet support member. 
     In the liquid crystal display device, each of the reflection sheet support member and the projection may be configured to reflect light at a surface thereof. 
     In the liquid crystal display device: the reflection sheet support member may further have a projection formed integrally therewith for supporting the diffusion sheet from behind, the projection being formed integrally with the fixing part. 
     In the liquid crystal display device, the plurality of light guide plate blocks are arranged in two vertical columns arranged side by side in a horizontal direction of the liquid crystal display device. 
     According to the present invention, a surface light source unit and a liquid crystal display device using the same can be provided in which clearances or mechanical deformations generated between divided blocks when such blocks are thermally expanded or contracted as a result of a temperature change are reduced. Therefore, unevenness of the light outputted from the surface light source unit and the brightness unevenness of the liquid crystal display device can be reduced. 
     The present invention can also provide a liquid crystal display device in which no clearance is formed between divided blocks so as not to allow mechanical deformations to be generated between such blocks when such blocks are thermally expanded or contracted. It is therefore possible to reduce the distance between the surface light source and a diffusion sheet and thereby reduce the thickness of the liquid crystal display device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram for describing a light guide plate block used in a backlight device according to an embodiment of the present invention; 
         FIGS. 2A to 2G  are diagrams for describing an example structure of a light guide plate block according to an embodiment of the present invention; 
         FIGS. 3A and 3B  are diagrams for describing the shifting, caused by temperature changes, of a row of light guide plate blocks according to the present invention relative to the corresponding LEDs; 
         FIG. 4  is a partial sectional view of a backlight device included in a liquid crystal display device according to an embodiment of the present invention; 
         FIG. 5  is a partial sectional view of the backlight device and the liquid crystal panel included in the liquid crystal display device; 
         FIGS. 6A to 6D  is a diagram for describing effects of the thermal expansion and contraction of a light guide plate caused by temperature changes in an arrangement where an LED is provided on a side (left or right) of each light guide plate; 
         FIG. 7  is a diagram for outlining an example overall structure of the liquid crystal display device according to an embodiment of the present invention; 
         FIG. 8  is a partial sectional view of a liquid crystal display device according to the present invention in which the fixing part  405 , pin mold  502 , and reflection sheet guide  404  are combined into an integral structure; and 
         FIGS. 9A to 9C  are diagrams, including partial sectional views, of an example fixing part integrated with a reflection sheet guide included in a liquid crystal display device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the accompanying drawings. In the accompanying drawings, identical components having identical functions are denoted by identical reference numerals, and their descriptions are omitted where appropriate to avoid duplication. Also, any enlarged view of a component drawn for use in relevant description may not represent the real dimensional proportions of the component and, moreover, different portions of the component may be drawn differently enlarged even along a same dimensional direction. 
     The directions such as front-rear (front-back), upper-lower (vertical), and left-right (horizontal) directions denoted by arrows in the accompanying drawings are as seen by a viewer facing the screen of a liquid crystal display device placed on a flat surface (desktop installation). This also applies to the descriptions associated with the accompanying drawings. In this specification, items, for example, power supply cords, wirings between circuit boards, and other miscellaneous parts irrelevant to the present invention are omitted in the description and drawings. 
     An embodiment of a backlight device according to the present invention will be described below with reference to  FIG. 1 .  FIG. 1  is a diagram for describing a light guide plate block used in the backlight device of the present embodiment. The front-rear direction of the liquid crystal display device incorporating the backlight device corresponds to the depth direction of  FIG. 1  with the deeper side of  FIG. 1  corresponding to the rear side and the  FIG. 1  surface side corresponding to the front side, respectively, of the liquid crystal display device installed for viewing. Components such as a liquid crystal panel, to be disposed on the front side of the light guide plate blocks are not illustrated in  FIG. 1 . In  FIG. 1 , reference numeral  101  denotes an upper frame;  102  a lower frame;  103  a left frame;  104  a right frame;  105  a center line indicating the center of the upper frame  101 ;  107  to  122  light guide plate blocks; and  151  and  152  fixing parts. The fixing parts  151  are small circular parts provided at upper and lower sides of each of the light guide plate blocks  107  to  120 . In  FIG. 1 , to avoid complication, only some of them are denoted by their reference number. The fixing parts  152  will be described later. 
     The upper frame  101 , lower frame  102 , left frame  103 , and right frame  104  are made of, for example, aluminum or iron. The light guide plate block is made of, for example, acrylic resin, polycarbonate resin, or cycloolefin resin. 
     As shown in  FIG. 1 , the light guide plate blocks  107  to  122  each have a rectangular shape with a horizontally extending longer side (extending along the horizontal direction of the liquid crystal display device). They are arranged in two columns with each column including eight vertically arranged light guide plate blocks (two columns and eight rows). Two light guide plate blocks, for example,  107  and  108  horizontally (laterally) arranged side by side in a same row are fixed, using the center line  105  as a positioning reference, to a chassis (not illustrated in  FIG. 1 ) provided behind the light guide plate blocks  107  to  120  by fixing parts  151  and  152 . The light guide plate blocks  107  and  120  are each fixed at their upper side to be in a state of being hung. A left-end portion of the light guide plate block  107  and a right-end portion of the light guide plate block  108  are not fixed by fixing parts  151  and  152 , and there is a clearance between the left end (left side) of the light guide plate block  107  and the left frame  103  and also between the right end (right side) of the light guide plate block  108  and the right frame  104  so as to absorb thermal expansion of the light guide plate blocks  107  and  108 , respectively. There is a clearance, which is smaller than that provided between each of the light guide plate blocks  107  and  108  and the corresponding side frame, between the light guide plates  107  and  108 , or alternatively, the two light guide plate blocks are in close contact without any clearance between them. 
     Namely, in the present embodiment, the light guide plate blocks have greater latitude at their left or right end portions to accommodate thermal expansion or contraction (that is, they are arranged to be thermally expanded or contracted more at their portions corresponding to lateral outer portions of the liquid crystal display device than at their portions corresponding to lateral center portions of the liquid crystal display device). 
     Temperature changes, therefore, cause the light guide plate block  107  to expand or contract mainly in its portion toward its left end and the light guide plate block  108  to expand or contract mainly in its portion toward its right end. 
     A preferable arrangement of light guide plate blocks may include eight light guide plate blocks arranged in one column (one column and eight rows) with each of the eight light guide plate blocks being horizontally longitudinal and fixed at the center line  105 . The light guide plate blocks can then thermally expand laterally outwardly and contract laterally inwardly on both sides of the center line  105 . 
     When three or more light guide plate blocks are arranged in each row, it becomes necessary to provide, in addition to the two clearances to be provided at the left and right ends of the horizontal rows, two or more horizontally spaced-apart clearances for absorbing thermal expansion and contraction of the light guide plate blocks. This complicates the configuration of the light guide plate blocks. The light guide plate block configuration of the present embodiment shown in  FIG. 1 , on the other hand, is very simple with a clearance provided only at each side of each row. 
     Generally, the clearance between light guide plate blocks shows as a dark line on the screen, so that more clearances cause greater brightness unevenness possibly resulting in failure to meet optical specification requirements of the liquid crystal display device. In the case of the present embodiment shown in  FIG. 1  including only two clearances (the smallest numerical clearances) at both ends of each row of light guide plate block, however, it will be easier to meet the optical specifications required of the liquid crystal display device. 
     In the case of the present embodiment shown in  FIG. 1 , the liquid crystal display device is assumed to have, for example, a 42-inch (diagonal) screen. It will be necessary to change the number of light guide plate blocks to be used according to the screen size involved. 
     With reference to  FIGS. 2A to 2G , the light guide plate block  109  among the light guide plate blocks  107  to  122  will be described in detail below.  FIGS. 2A to 2G  are diagrams for describing an example structure of a light guide plate block according to the present embodiment. In  FIGS. 2A to 2G , reference numerals  201  to  208  denote light guide plates; each reference numeral  222  denotes a groove between adjacent ones of the light guide plates  201  to  208 ; reference numeral  216  denotes a concave portion of the light guide plate block  109  provided to receive the lower end of the light guide plate block  107  directly above the light guide plate block  109 ; reference numerals  215  denote concave portions for fixing use provided at both ends of the concave portion  216 ; each reference numeral  217  denotes a concave portion for fixing use provided inside the concave portion  216 ; each reference numeral  218  denotes a cutout portion for fixing use provided in the lower end portion of the light guide plate block  109 ; reference numerals  221  denote cutout portions for fixing use provided in lower end portions on both sides of the light guide plate block  109 ; and each reference numeral  219  denotes a positioning pin used to position the light guide plate block  109 . The concave portions  215  and  217  and the cutout portions  218  and  221  for positioning use are provided in position ranges predetermined using the grooves  222  between the light guide plates  201  to  208  as positioning references. The positioning pins  219  are also provided in positions predetermined relative to both ends of the light guide plate block  109 . 
       FIGS. 2A ,  2 B, and  2 C are a front view, a side view, and a perspective view of the light guide plate block  109 , respectively.  FIGS. 2D ,  2 E,  2 F, and  2 G are enlarged views of circled portions  250 ,  260 ,  270 , and  280  shown in  FIG. 2C , respectively. 
     With reference to  FIGS. 3A and 3B , the shifting of light guide plate blocks relative to corresponding LEDs caused by thermal expansion or contraction of the light guide plate blocks will be described.  FIGS. 3A and 3B  are diagrams for describing the shifting, caused by temperature changes, of a row of light guide plate blocks according to the present invention relative to the corresponding LEDs.  FIG. 3A  shows two light guide plate blocks arranged in one of the rows of light guide plate blocks described above with reference to  FIG. 1  (for example, the light guide plate blocks  207  and  208  shown in  FIG. 2A to 2G ).  FIG. 3B  is for describing the shifting of a light guide plate block replacing, for example, the two light guide plate blocks arranged side by side in a row as shown in  FIG. 3A . In  FIGS. 3A and 3B , reference numeral  301  denotes an LED which corresponds to the light guide plate block  207  (or  307 ) and is disposed, in the lateral direction, closest to the center of the row (closest to the center line  105 ); reference numeral  303  denotes an LED which corresponds to the light guide plate block  207  (or  307 ) and is disposed, in the lateral direction, most leftwardly (farthest from the center line  105 ); reference numeral  302  denotes an LED which corresponds to the light guide plate block  208  (or  307 ) and is disposed, in the lateral direction, closest to the center of the row (closest to the center line  105 ); reference numeral  304  denotes an LED which corresponds to the light guide plate block  208  (or  307 ) and is disposed, in the lateral direction, most rightwardly (farthest from the center line  105 ); each symbol ml denotes an arrow representing the direction of shifting, caused by thermal expansion or contraction, of a light guide plate block relative to the LED  301  or LED  302 ; and reference numeral  307  denotes a light guide plate block. 
     LEDs  301  to  304  are mounted on printed circuit boards (not illustrated) provided behind (on the rear side of) the light guide plate blocks. For the light guide plate block  207 , two printed circuit boards are horizontally arranged side by side. Like the light guide plate blocks, the printed circuit boards are discrete from those arranged above and below them (those arranged in other rows). They are manufactured using, for example, glass epoxy resin substrate as a base material and by applying known technology. 
     As shown in  FIGS. 3A and 3B , the light guide plate blocks are fixed using the center line  105  as a positioning reference to be laterally expandable and contractible. For the present example, each light guide plate block is assumed to thermally expand, in its longitudinal direction (laterally or horizontally), 2.5 mm in an outermost portion and 0.5 mm in an innermost portion, and is also assumed to thermally expand, in the vertical direction, 0.6 mm. 
     The light guide plates are manufactured such that their optical performance can tolerate their thermal expansion and contraction assumed as described above. 
     With reference to  FIG. 4 , the arrangement for absorbing the vertical shifting of each light guide plate block will be described below.  FIG. 4  is a partial sectional view of a backlight device included in a liquid crystal display device according to an embodiment of the present invention. In  FIG. 4 , reference numeral  401  denotes a chassis;  402  a printed circuit board;  403  an LED;  404  a reflection sheet guide (reflection sheet support member) for supporting a reflection sheet;  405  a fixing part;  406  a reflection sheet; each  407  a light guide plate block; and  408  a clearance. 
     Referring to  FIG. 4 , first the printed circuit board  402  on which the LED  403  is mounted is fixed to the chassis  401 ; then the reflection sheet guide  404  is placed over (on the front side of) the printed circuit board  402  and is fixed with the fixing part  405  using a screw. The light guide plate block  407  is attached over (on the front side of) the reflection sheet  406 . Whereas the light guide plate block  407  has an approximately right-triangular section with a front side being horizontally flat (parallel with the horizontal direction) and a rear side being inclined, the reflection sheet guide  404  has an approximately right-triangular section with a rear side being horizontally flat (parallel with the horizontal direction) and a front side which comes in contact with the reflection sheet  406  and the light guide plate block  407  being inclined. In this arrangement, the front sides of the chassis  401 , printed circuit board  402  and light guide plate block  407  are kept in parallel with the horizontal direction. 
     The clearance CL is, for example, 0.6 mm. 
     With reference to  FIG. 5 , an example part fixing structure of the liquid crystal display device according to the present embodiment will be described below.  FIG. 5  is a partial sectional view of the backlight device and the liquid crystal panel included in the liquid crystal display device. Whereas  FIG. 4  is a sectional view showing a section of an LED,  FIG. 5  is a sectional view showing no section of any LED but showing sections of a light guide plate and a printed circuit board on which an LED is mounted. Namely,  FIG. 5  showing a section of the backlight device different from the section shown in  FIG. 4  does not show the LED  403 , but it shows a liquid crystal panel  504  which is not shown in  FIG. 4 . In  FIG. 5 , reference numeral  501  denotes a fixing screw;  502  a pin mold placed over the fixing screw  501 ;  503  a diffusion sheet; and  504  a liquid crystal panel. 
     As done with reference to  FIG. 4 , a procedure for assembling (fitting) a light guide plate block according to the present embodiment will be described below with reference to  FIG. 5 , too. 
     First, the printed circuit board  402  on which an LED (see  FIG. 4 ) is mounted is fixed to the front of the chassis  401  using, for example, screws. Next, the reflection sheet guide  404  is placed on the front of the printed circuit board  402 , then the reflection sheet guide  404  is positioned and fixed with the fixing screw  501  while pressing, from the front side, the fixing part  405  attached with the pin mold  502 . Subsequently, the reflection sheet  406  is placed over the front of the assembly thus prepared including the reflection sheet guide  404 . The fixing part  405  is the same as the fixing part  152  described with reference to  FIG. 1 . The pin mold  502  is the same as the fixing part  151  described with reference to  FIG. 1 . The center of the fixing part  151  (fixing part  405 ) in the portion shown in  FIG. 5  is located where it crosses the width center line  105  shown in  FIG. 1  of the liquid crystal display device. The pin mold  502  is projecting on the front side to support the diffusion sheet  503  from behind. 
     The reflection sheet  406  is sized preferably such that it can be used also for two light guide plate blocks arranged longitudinally side by side in a row, for example, the light guide plate blocks  107  and  108  described with reference to  FIG. 1 . In the present embodiment, the single reflection sheet  406  is used for two light guide plate blocks horizontally arranged in each row, for example, the light guide plate blocks  107  and  108 . The reflection sheet  406  used in such an arrangement can minimize the backlight brightness unevenness caused by light leakage resulting from the use of plural discrete light guide plates, for example, light leakage through boundaries, along the center line  105  (see  FIG. 1 ), between light guide plate blocks or through the grooves  222  (see  FIG. 2A ) included in each light guide plate block. 
     The upper portion of each light guide plate block  407  is positioned in a clearance  505  formed below the reflection sheet guide  404 . The lower portion of each light guide plate block  407  is inserted in a concave portion (bent portion) of the fixing part  405  to be fixed there. The clearance  408  formed at this time in the concave portion (bent portion) of the fixing part  405  serves to absorb downward thermal expansion of the light guide plate block  407 . In this arrangement, an upper portion of the light guide plate block  407  is, together with the reflection sheet  406  and the printed circuit board  402 , held between a pressing part formed by the concave portion (bent portion) of the fixing part  405  and the chassis  401 . The lower portion of the light guide plate block  407 , on the other hand, is inserted in the concave portion (bent portion) of the fixing part  405  without being pressed. Namely, the lower portion of the light guide plate block  407  is inserted in the concave portion (bent portion) of the fixing part  405  in a movable state. Thus, the lower portion of the light guide plate block  407  can move to absorb thermal expansion and contraction of the light guide plate block  407 . The light guide plate block  407  is fixed in position by the positioning pins  219 , not illustrated in  FIGS. 4 and 5 , as described with reference to  FIGS. 2A to 2G . 
     The above procedure for installing the light guide plate block  407  is repeated for each row, beginning with the top row, then proceeding downwardly. 
     Subsequently, the diffusion sheet  503  is placed over the light guide plate blocks  407  such that the projection of each pin mold  502  comes in contact with the back (rear side) of the diffusion sheet  503  thereby determining the distance between the light guide plate blocks  407  and the diffusion sheet  503 . The pin mold  502  is equivalent to the fixing part  151  shown in  FIG. 1 . 
     The fixing part  405  is made of metal, for example, iron to secure high reflectance. According to an embodiment of the present invention, the projection on the front side (on the liquid crystal panel side) of the fixing part  405  has a white surface so as to reflect light with high reflectance. Furthermore, a reflective coating may be applied to the projection as required. Allowing the pin mold  502  to reflect light efficiently makes it possible to efficiently guide the light outputted frontwardly from the light guide plate blocks  407  toward the liquid crystal panel. 
     The optical operation of the light guide device configured as described above will be described below. LEDs are provided above the light guide plate blocks  407 . The LEDs emit light downward causing the light to be inputted to the light guide plate blocks  407 . The light inputted to the light guide plate blocks  407  is, after undergoing reflection, refraction, and diffusion at the light guide plate blocks  407  as well as reflection by the reflection sheets  406 , outputted as surface light toward the front side (the liquid crystal panel side). The surface light outputted from the light guide plate blocks  407  is inputted to the liquid crystal panel  504  after passing through the diffusion sheet  503  and a prism sheet, not illustrated. In the liquid crystal panel  504 , light transmittance is controlled pixel by pixel thereby allowing the light inputted to the liquid crystal panel  504  to be spacially modulated to display an image. 
     A liquid crystal display device according to an embodiment of the present invention will be described below with reference to  FIGS. 6A to 6D .  FIGS. 6A to 6D  is a diagram for describing effects of the thermal expansion and contraction of a light guide plate caused by temperature changes in an arrangement where an LED is provided on a side (left or right) of each light guide plate. In  FIGS. 6A to 6D , reference numeral  601  denotes an LED;  602  a light guide plate fixed at a position on a center line  605 ;  602 ′ the light guide plate  602  in a thermally expanded state;  603  a light guide plate fixed at a position near the LED  601  (on a center line  606 ; and  603 ′ the light guide plate  603  in a thermally expanded state. 
     As shown in  FIG. 6A , when the light guide plate  603  is fixed at a center thereof (on the center line  605 ), the distance between the LED  601  and where the light guide plate  602  is fixed (on the center line  605 ) is large. When the light guide plate  602  fixed in this manner is thermally expanded, it laterally expands equally to both sides as shown in  FIG. 6B . This causes the distance between the light guide plate  602 ′ and the LED  601  to be reduced from d 0  (see  FIG. 6A ) to d 1  (see  FIG. 6B ). When the light guide plate  602 ′ is thermally contracted, the distance increases. Large changes in the distance between the light guide plate  602  or  602 ′ and the LED  601  largely changes the amount of light incident to the light guide plate to cause great brightness unevenness of the backlight device or liquid crystal display device. 
     When the light guide plate  603  is fixed at a position near the LED  601  (on the center line  606  as shown in  FIG. 6C , the amount of lateral thermal expansion on the LED  601  side of the light guide plate  603  is small as shown in  FIG. 6D . Therefore, the distance between the light guide plate  603  and the LED  601  does not change much. Namely, the difference between distance d 0  (see  FIG. 6C ) and distance d 2  (see  FIG. 6D ) is small. Similarly, when the light guide plate  603 ′ is thermally contracted, the amount of lateral thermal contraction on the LED  601  side of the light guide plate  603 ′ is small, i.e. the distance between the light guide plate  603 ′ and the LED  601  does not change much. Hence, the amount of light incident to the light guide plate does not change much. 
     As described above with reference to  FIGS. 6A to 6D , the smaller the distance between the LED and the position where the light guide plate is fixed, the smaller the brightness unevenness caused by temperature changes. According to the embodiments described with reference to  FIG. 2A  to  FIG. 5  of the present invention, the light guide plate blocks are each fixed at their upper portions (for example, using the positioning pins  219  and concave portions  215  and  217  for fixing use, and the fixing parts  405  shown in  FIGS. 4 and 5 ). Namely, each light guide plate block is fixed on a horizontal line along the concave portion  216  for fixing use shown in  FIGS. 2A to 2G . For each light guide plate block, plural LEDs are laterally arranged above the light guide plate block. The light emitted from the LEDs is downwardly inputted to the light guide plate block and is, after having its direction changed by a reflection sheet and the light guide plate block, outputted frontwardly from the light guide plate block. 
     Thus, according to the above embodiments, the effects of thermal expansion and contraction in the vertical direction of each light guide plate block caused by temperature changes on the distance between the light guide plate block and the corresponding LEDs is small, so that the brightness unevenness of the backlight device and the liquid crystal display device is small. 
       FIG. 7  is a diagram for outlining an example overall structure of the liquid crystal display device according to an embodiment of the present invention. 
     As described above, the LEDs and light guide plate blocks are arranged on the front side of the chassis  401  (see  FIGS. 4 and 5 ). On the rear side of the chassis  401 , circuit boards, not illustrated, including driver circuits for operating the LEDs for backlighting, a signal processing circuit for processing video signals to be supplied to the liquid crystal panel, and a power supply circuit for supplying power to the driver circuits and the signal processing circuit are provided. 
     As shown in  FIG. 7 , the sides of the chassis  401  are provided with metallic frames (see  FIG. 1 ) for holding the liquid crystal panel and the backlight device. The mechanical strength of the liquid crystal panel and the backlight device increases by being fixedly held by the metallic frames. The liquid crystal panel and the backlight device held by the metallic frames are entirely covered with a resin or metallic cover to make up a tandem type backlight device and liquid crystal display device. 
       FIG. 7  is an exploded view of the liquid crystal display device. In  FIG. 7 , reference numeral  700  denotes a liquid crystal module which includes a liquid crystal panel and a backlight device. The backlight device included in the liquid crystal module is attached to an open side of a frame which is formed of a thin metal plate of, for example, aluminum or iron plate and is shaped like a shallow box with a large bottom area. The reference numeral  401  in  FIGS. 4 and 5  denotes a bottom portion of the box-like frame of the chassis. 
     The liquid crystal module  700  is attached, on its rear side, with a driver board  701  mounted with driver circuits for driving the backlight LEDs, a power supply board  702  mounted with a power supply unit for the liquid crystal display device, a signal processing board  703  mounted with signal processing circuits, and support members  705  for supporting the liquid crystal display device.  FIG. 7  also shows a bezel  751 , a rear cover  752 , and a base  753  to be attached to the support members 
     According to the above embodiments, longitudinally arranging two light guide plate blocks or one light guide plate block in a horizontal direction makes it possible to reduce the effects of thermal expansion and contraction of the light guide plate block caused by temperature changes on the brightness distribution on the backlight device and the liquid crystal display device, so that the brightness unevenness on them can be reduced. 
     Even in cases where two light guide plate blocks are longitudinally arranged in a horizontal direction, using a reflection sheet which can cover the rear sides of the two light guide plate blocks makes it possible to reduce the effects of dark lines showing at the boundaries between the two light guide plate blocks on the backlight brightness distribution, so that the brightness unevenness on the backlight device and the liquid crystal display device can be reduced. 
     Another embodiment of the present invention will be described below with reference to  FIG. 8 .  FIG. 8  is a partial sectional view of a liquid crystal display device according to the present invention in which the fixing part  405 , pin mold  502 , and reflection sheet guide  404  shown in  FIG. 4  or  5  are combined into an integral structure. In  FIG. 8 , reference numerals  801  and  802  denote electronic parts mounted on the rear side of the chassis  401 ; and reference numeral  803  denotes a fixing part integrated with a reflection sheet guide and is formed, for example, by molding a resin. The functions of these parts are the same as described for the foregoing embodiments. The fixing part  803  integrated with the reflection sheet guide is entirely white so as to improve its reflection efficiency. 
     In the present embodiment, for each light guide plate block, a reflection sheet guide to support the light guide plate block from behind, a fixing part (fixing member) for fixing the light guide plate block provided adjacently below the first mentioned light guide plate block, and a pin mold for supporting a diffusion sheet from behind are integrally formed, for example, by molding a resin. Using the fixing part  803  integrated with a reflection sheet guide makes it possible to reduce the man-hour for fabrication. 
     Another embodiment of a fixing part integrated with a reflection sheet guide included in the liquid crystal display device according to the present invention will be described with reference to  FIGS. 9A to 9C .  FIG. 9A  is a partial perspective view of an array of light guide plate blocks in a state detached from a liquid crystal panel. In  FIG. 9A , fixing parts  901  which are each integrated with a reflection sheet guide and which each have a projection  903  used to keep a predetermined distance between the liquid crystal panel and the light guide plate blocks are shown. The projections  903 , like the pin molds  502  used in the foregoing embodiments, support the diffusion sheet  503  from behind (see  FIG. 5 ). The projections  903  have a white surface like in the foregoing embodiment or are coated with a reflection coating to secure high reflectance. 
     The projection  903  of the fixing part  901  is shaped like, for example, a slim four-sided pyramid as shown in  FIG. 9B . As shown in  FIG. 9C , the projection denoted by reference numeral  903  is, in the lateral direction, not in contact with any of the light guide plate blocks  904  and the reflection sheet guides  905  each integrated with a fixing part  901 . In the vertical direction, a lower portion of the projection  903  is in contact with the light guide plate block  904  therebelow, but it is not in contact with the light guide plate block  904  thereabove, so that a clearance is formed between it and the light guide plate block  904  thereabove. Also, in the vertical direction, the reflection sheet guide  905  integrated with the fixing part  901  is in contact with the projection  903 . 
     As described above, the projection  903  has a shape which can be easily formed. Even when there is a clearance between two light guide plate blocks laterally arranged side by side, the clearance is covered by the projection  903 , so that no dark lines are outputted. This reduces the brightness unevenness on the screen. 
     In the embodiments shown in  FIGS. 8 and 9A  to  9 C, the fixing part ( 803  or  901 ) may have a thin vertical projection or tab which fits a cutout portion provided in the corresponding light guide plate block so as to correctly position the light guide plate block for fixing at a center portion thereof. 
     Also, in the embodiments shown in  FIG. 8  and  FIGS. 9A to 9C , the fixing part ( 803  or  901 ) may have a reference surface for positioning against the upper end face of the corresponding light guide plate block. 
     Furthermore, in the embodiments shown in  FIG. 8  and  FIGS. 9A to 9C , the fixing part ( 803  or  901 ) may have a reference surface which allows an upper front surface portion of each light guide plate block and a lower rear surface portion of the corresponding projection to come in mutual contact for positioning of the light guide plate block and the corresponding projection in the front-to-rear direction and the vertical direction, and also for reinforcing the projection. 
     Even though, in the present embodiment, a reflection sheet guide, a fixing part, and a pin mold are integrally structured, they may be integrated in different manners. For example, a reflection sheet guide and a fixing part may be integrally formed, and a pin mold (projection) may be attached to the integral structure as a discrete part. Or, alternatively, a reflection sheet guide and a pin mold (projection) may be integrally formed, and a fixing part may be attached to the integral structure as a discrete part.