Patent Publication Number: US-2019196094-A1

Title: Lighting device and display device

Description:
TECHNICAL FIELD 
     The present invention relates to a lighting device and a display device. 
     BACKGROUND ART 
     One example of a known surface-emitting device mounted in a liquid crystal display device is described in Patent Document 1. In the production of the surface-emitting device in Patent Document 1, a board unit is inserted when an acrylic light guide plate is formed by injection molding. The board unit includes a board having a circuit on an upper surface thereof and LEDs, which are point light sources connected to the upper surface. The board unit is inserted such that the lower surface is exposed. The board unit is integrated with the light guide plate at portions other than the exposed portion. 
     RELATED ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-143517 
     Problem to be Solved by the Invention 
     In the surface-emitting device in Patent Document 1, a large portion of the board on which the LEDs are mounted is in the light guide plate. This makes the shape of a portion of the light guide plate near the light sources complex. The complex shape may reduce the amount of outgoing light from the light guide plate. Furthermore, the thickness of the light guide plate increases by the thickness of the board in the light guide plate, making the optical path of the light traveling through the light guide plate longer. The longer optical path results in an increase in the amount of light absorbed by the light guide plate, leading to a reduction in the amount of outgoing light from the light guide plate. 
     DISCLOSURE OF THE PRESENT INVENTION 
     The present invention was made in view of the above circumstances. An object is to improve the brightness. 
     Means for Solving the Problem 
     A lighting device according to the present invention includes a light source having a light emitting surface, a light source board having a mount surface on which the light source is mounted with one of outer surfaces of the light source that is adjacent to the light emitting surface being in contact with the mount surface, and a light guide plate in which at least a portion of an outer end surface thereof is a light input surface that receives light from the light source, one of two plate surfaces thereof is a light-exit surface through which the light exits, and the other of the plate surfaces is a light-exit opposite surface. The light source board at least includes a light-source overlapping portion overlapping the light source and an extension portion extending from the light-source overlapping portion in a direction in which the light emitting surface faces. The light guide plate is integrated with the light source and the light source board with the light input surface being in direct contact with the light emitting surface of the light source and the light-exit surface or the light-exit opposite surface being in direct contact with the mount surface of the extension portion. 
     In this configuration, outgoing light from the light emitting surface of the light source enters the light guide plate through the light input surface and the light that has traveled in the light guide plate exits through the light-exit surface. Since the light guide plate is in direct contact with the light emitting surface of the light source at the light input surface, input efficiency of light to the light input surface is high. Furthermore, since the light guide plate is integrated with the light source and the light source board while being in direct contact with the light emitting surface of the light source, the positional relationship between the light input surface and the light emitting surface of the light source is unlikely to change when the light guide plate is thermally expanded or contracted due to a change in temperature. This configuration advantageously allows the light input efficiency to remain high. 
     Furthermore, since the light guide plate is integrated with the light source and the light guide board with the light-exit opposite surface thereof being in direct contact with the mount surface of the extension portion, which is a portion of the light source board extending from the light-source overlapping portion in a direction in which the light emitting surface faces, the light source board is not located in the light guide plate. This does not make the shape of the portion of the light guide plate near the light source complex and allows light to efficiently travel through the light guide plate. Furthermore, the light guide plate is thin compared to the known light guide plate having the light source board therein. This makes the optical length of light traveling through the light guide plate shorter, reducing the amount of light absorbed by the light guide plate. With this configuration, the amount of outgoing light from the light guide plate through the light-exit surface increases and the brightness of the outgoing light improves. 
     The following configurations are preferable embodiments of the invention. 
     (1) The light guide plate may be selectively in direct contact with the light emitting surface. The light emitting surface is one of the outer surfaces of the light source. In this configuration, the light source is in contact with the light guide plate only at the light emitting surface, which is one of outer surfaces of the light source, and thus heat generated by the light source is less likely to be transferred to the light guide plate. 
     (2) One of the light-exit surface and the light-exit opposite surface of the light guide plate that is opposite the surface in contact with the extension portion is flush with an outer surface of the light source opposite the outer surface in contact with the light source board. This configuration allows the input efficiency of light to the light input surface to remain high and allows the thickness of the light source to decrease up to the thickness of the light guide plate. Furthermore, in this configuration, the center of the light source in the height direction matches the center of the light guide plate in the thickness direction. This makes the input efficiency of light to the light input surface very high. 
     (3) The light source board includes a circuit formation portion extending from the light-source overlapping portion toward a side away from the extension portion and having a circuit for applying current to the light source. In this configuration, the circuit formation portion, which extends from the light-source overlapping portion toward a side away from the extension portion, does not overlap the light guide plate. With this configuration, when the circuit is heated due to application of current to the light source, the heat is less likely to be transferred to the light guide plate. 
     Next, to solve the above-described problems, a display device according to the present invention includes the above-described lighting device and a display panel configured to display an image by using light from the lighting device. The display device having such a configuration has improved display quality and lower power consumption, because outgoing light from the lighting device has improved brightness. 
     Advantageous Effect of the Invention 
     According to the present invention, brightness is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view illustrating a schematic configuration of a liquid crystal display device according to a first embodiment of the invention. 
         FIG. 2  is a cross-sectional view illustrating a cross-sectional configuration of the liquid crystal display device taken in a short-side direction. 
         FIG. 3  is a plan view of LEDs, an LED board, and a light guide plate. 
         FIG. 4  is a cross-sectional side view illustrating the LEDs and the LED board set in a molding die for molding the light guide plate from resin. 
         FIG. 5  is a cross-sectional view taken along line A-A in  FIG. 4 . 
         FIG. 6  is a cross-sectional view illustrating a liquid crystal display device according to a second embodiment of the present invention taken in a short-side direction. 
         FIG. 7  is a cross-sectional side view illustrating LEDs, an LED board, and a light guide plate according to a third embodiment of the present invention. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     A first embodiment of the invention is described with reference to  FIGS. 1 to 5 . In this embodiment, a liquid crystal display device (display device)  10  is described as an example. The X, Y, and Z axes are indicated in some of the drawings, and each of the axes indicates the same direction in the respective drawings. The upper side in  FIGS. 2 and 4  is a front side and the lower side in those figures is a rear side. 
     As illustrated in  FIG. 1 , the liquid crystal display device  10  according to the embodiment has a horizontally-long (longitudinal) oblong (rectangular) overall shape and includes a liquid crystal panel (display panel)  11  configured to display an image and a backlight device (lighting device)  12  that is an external light source configured to supply light for displaying to the liquid crystal panel  11 . The liquid crystal panel  11  and the backlight device  12  are held together by a frame-shaped bezel, which is not illustrated, for example. The liquid crystal display device  10  according to the embodiment is preferably used in a mobile information terminal such as a tablet notebook computer or an in-vehicle device such as a car navigation system. The liquid crystal panel  11  has a screen size of about a few inches to about a dozen inches, which is categorized as a small size or a small to medium size in general. 
     Next, the liquid crystal panel  11  and the backlight device  12  included in the liquid crystal display device  10  will be described sequentially. As illustrated in  FIG. 1 , the liquid crystal panel (display panel)  11  has a horizontally-long oblong shape in plan view and includes two glass substrates  11   a  and  11   b  bonded together with a predetermined gap therebetween and a liquid crystal layer (not illustrated) sealed between the substrates  11   a  and  11   b.  The liquid crystal layer includes liquid crystal molecules, which are substances whose optical properties are changed by application of an electrical field. On an inner surface of one of the glass substrates (array substrate, active matrix substrate)  11   b,  switching devices (for example, TFTs), which are connected to source lines and gate lines positioned perpendicular to each other, and pixel electrodes, which are disposed in a rectangular area defined by the source lines and the gate lines and connected to the switching devices, are planarly arranged in a matrix, and also an alignment film, for example, is disposed. On an inner surface of the other glass substrate (counter substrate, CF substrate)  11   a,  a color filter including coloring portions, such as R (red), G (green), and B (blue) coloring portions are planarly arranged in a matrix in a predetermined arrangement, and also a grid-shaped light blocking layer (black matrix) positioned between the respective coloring portions, a planar counter electrode facing the pixel electrodes, and an alignment film, for example, are disposed. A polarizing plate, which is not illustrated, is disposed on an outer surface of each glass substrate  11   a  and  11   b.  The long-side direction, the short-side direction, and the thickness direction of the liquid crystal panel  11  respectively match the X-axis direction, the Y-axis direction, and the Z-axis direction. 
     As illustrated in  FIG. 1 , the backlight device  12  at least includes LEDs  13 , which are light sources, an LED board  14  on which the LEDs  13  are disposed, a light guide plate  15  which guides the light from the LEDs  13 , an optical sheet  16  disposed on a front surface of the light guide plate  15  (adjacent to the liquid crystal panel  11 , light exiting side), and a reflection sheet (reflector)  17  disposed on a rear surface of the light guide plate  15 . The LED board  14  is located at one of end portions of the backlight device  12  along a long side, and thus the LEDs  13  on the LED board  14  are only located relative to only one end portion of the liquid crystal panel  11  along the long side. As can be seen from this, the backlight device  12  according to the embodiment is an edge-lit (side-lit) backlight device in which light from the LEDs  13  enters the light guide plate  15  through only one side thereof. Next, components of the backlight device  12  will be descried in detail. 
     As illustrated in  FIGS. 1 and 2 , the LED  13  has a block-like overall shape and one of outer surfaces thereof is a light-emitting surface  13   a  that emits light. An outer surface of the LED  13  that is adjacent to the light-emitting surface  13   a  is a mounted surface  13   b  in contact with the LED board  14 . The LED  13  is a side-lit LED. In other words, in the side-lit LED  13 , a surface (side surface) lateral to the mounted surface  13   b,  which is in contact with the LED board  14 , is the light-emitting surface  13   a.  The light-emitting surface  13   a  of the LED  13  is a substantially flat surface extending in the X-axis and Z-axis directions and faces the right side in  FIG. 2  in the Y-axis direction. The light from the light-emitting surface  13   a  travels in a direction in which the light-emitting surface  13   a  faces. The optical axis of the LED  13  extends in the Y-axis direction, which is a normal direction with respect to the light-emitting surface  13   a.  Here, the “optical axis” is a traveling direction of light having the highest intensity from the LED  13  (light distribution). The LEDs  13  each have an LED chip that emits a single-color light such as blue light and a sealing material containing a phosphor (such as a yellow phosphor, a green phosphor, and a red phosphor) in a dispersed state, and thus the LEDs  13  emit white light as a whole. 
     As illustrated in  FIGS. 1 and 3 , the LED board  14  is a flexible film (sheet) formed of an insulating material and has a thin band-like shape extending in the long-side direction of the light guide plate  15 , which will be described later. The plate surfaces of the LED board  14  extend parallel to the plate surfaces of the light guide plate  15 . The LED board  14  is located such that the longitudinal direction (long-side direction), the width direction (short-side direction), and the thickness direction, respectively, match the X axis direction, the Y axis direction, and the Z axis direction. The LED board  14  is in contact with the mounted surfaces  13   b  of the LEDs  13  at the front one of the two plate surfaces, and the front plate surface is referred to as a mount surface  14   a  on which the LEDs  13  are mounted. Multiple LEDs  13  (seven LEDs in  FIGS. 1 and 3 ) are disposed with a space therebetween in the X axis direction on the LED board  14 . 
     As illustrated in  FIGS. 2 and 3 , the LED board  14  includes LED overlapping portions (light-source overlapping portions, light-source mount portions)  18  having the LEDs  13  thereon and overlapping the LEDs  13  in plan view, LED non-overlapping portions  19  adjacent to the LED overlapping portions  18  in the X axis direction and not overlapping the LEDs  13  in plan view, an extension portion (light-guide-plate overlapping portion)  20  extending from the LED overlapping portions  18  and the LED non-overlapping portions  19  in the Y axis direction (normal direction with respect to the light-emitting surface  13   a,  direction along the optical axis) to the right side in  FIG. 2  (in a direction in which the light emitting surfaces  13   a  of the LEDs  13  face), and a circuit formation portion  21  extending from the LED overlapping portions  18  and the LED non-overlapping portion  19  in the Y axis direction to the left side in  FIG. 2  (side away from the extension portion  20 ) and having a circuit (not illustrated) for applying current to the LEDs  13 . The multiple LED overlapping portions  19  and the multiple LED non-overlapping portions  19  are repeatedly alternately arranged in the X axis direction. The number of LED overlapping portions  18  is equal to the number of LEDs  13 . The number of LED non-overlapping portions  19  is one more than the number of LEDs  13 . The extension portion  20  is disposed on the rear surface of the light guide plate  15  (side away from the light exit side). On the mount surface  14   a  of the circuit formation portion  21 , a circuit for applying current to the LEDs  13  is disposed. The circuit at least includes a wiring pattern connected in parallel with the LEDs  13  and circuit components such as a constant-current diode and a resistor (both of the wiring pattern and the circuit element are not illustrated). The circuit components are separately connected in series with the LEDs  13  to equalize the amount of light emitted by the parallel-connected LEDs  13 . The LED non-overlapping portions IS and the circuit formation portion  21  do not overlap the LEDs  13  and the light guide plate  15  in plan view. 
     The light guide plate  15  is formed of a substantially transparent synthetic resin material having a refractive index sufficiently higher than that of air. As illustrated in  FIGS. 1 and 2 , the light guide plate  15  is located directly below the liquid crystal panel  11  and the optical sheet  16  and the plate surfaces thereof are parallel to the plate surfaces of the liquid crystal panel  11  and the optical sheet  16 . The light guide plate  15  is a plate having a thickness larger than that of the optical sheet  16  and has a horizontally-long oblong shape in plan view. The light guide plate  15  include two outer end surfaces along the long sides and two outer end surfaces along the short sides, which are perpendicular to each other. One of the outer end surfaces of the light guide plate  15  that is along the left long side in  FIG. 2  is a light input surface (light-source opposing end surface)  15   a  that faces the LEDs  13  and directly receives light from the LEDs  13 . The remaining three end surfaces (the end surface along the other long side and the two end surfaces along the short sides) are non-light input surfaces (light-source non-opposing surfaces)  15   d  that do not face the LEDs  13  and not directly receive light from the LEDs  13 . The light input surface  15   a  extends parallel to the light-emitting surfaces  13   a  of the LEDs  13  in the X axis direction (direction in which the LEDs  13  are arranged). One of the plate surfaces of the light guide plate  15  that faces the front side (the liquid crystal panel  11 , the optical sheet  16 ) is a light-exit surface  15   b  through which light is output toward the liquid crystal panel  11  and the optical sheet  16 . One of the plate surfaces that faces the rear side is a light-exit opposite surface  15   c  opposite the light-exit surface  15   b.  The light guide plate  15  having such a configuration receives light, which has been emitted from the light-emitting surfaces  13   a  of the LEDs  13  in the Y-axis direction, through the light-input surface  15   a  and allows the light that has traveled therein to travel upward in the Z axis direction such that the light exits through the light-exit surface  15   b  toward the optical sheet  16  (front side, light-exit side). 
     As illustrated in  FIGS. 1 and 2 , the optical sheet  16  has a horizontally-long oblong shape in plan view as the liquid crystal panel  11 . The optical sheet  16  is disposed on the light-exit surface  15   b  of the light guide plate  15  and is located between the liquid crystal panel  11  and the light guide plate  15 . In other words, the optical sheet  16  is located adjacent to the exit of the light pathway extending from the LEDs  13 . The optical sheet  16  is a component (optical component) that exerts predetermined optical effects on the light emitted by the LEDs  13  and allows the light to travel toward the liquid crystal panel  11 . Specifically described, the optical sheet  16  according to the embodiment includes three sheets: a microlens sheet  16   a  that exerts isotropic light collecting effect on the light, a prism sheet  16   b  that exerts anisotropic light collecting effect on the light, and reflective polarizing sheet  16   c  that polarizes and reflects the light. The optical sheet  16  includes the microlens sheet  16   a,  the prism sheet  16   b,  end the reflective polarizing sheet  16   c,  in this order from the rear side. 
     As illustrated in  FIGS. 1 and 2 , the reflection sheet  17  has plate surfaces parallel to the plate surfaces of the LED board  14  and the light guide plate  15  and covers the light-exit opposite surface  15   c  of the light guide plate  15  from the rear side. The reflection sheet  17  has high reflectance and efficiently reflects the light that has leaked out through the light-exit opposite surface  15   c  of the light guide plate  15  toward the front side (light-exit surface  15   b ). 
     As illustrated in  FIG. 2 , the light guide plate  15  according to the embodiment is integrated with the LEDs  13  and the LED board  14  with the light input surface  15   a  being in direct contact with the light-emitting surfaces  13   a  of the LEDs  13  and with the light-exit opposite surface  15   c  being in direct contact with the mount surface  14   a  of the extension portion  20  of the LED board  14 . Specifically described, the light input surface  15   a  of the light guide plate  15  is in direct contact with the light-emitting surfaces  13   a  of the LEDs  13  and fixed thereto without any other components therebetween and the light-exit opposite surface  15   c  is in direct contact with the mount surface  14   a  of the extension portion  20  and fixed thereto without any other components therebetween. Of the outer surfaces of the LED  13 , the light guide plate  15  is selectively in direct contact with the light emitting surface  13   a  and is not in contact with the outer surfaces other than the light emitting surface  13   a  (including a mounted-surface opposite surface  13   c,  which will be described later). Similarly, of the outer surfaces of the extension portion  20  of the LED board  14 , the light guide plate  15  is selectively in direct contact with the mount surface  14   a  and is not in contact with the outer surfaces other than the mount surface  14   a.  In this configuration, the LEDs  13  are not located in the light guide plate  15  and the LED board  14  is not located in the light guide plate  5 , and thus the shape of the portion of the light guide plate  15  near the LEDs  13  is not made complex. As described above, the LEDs  13 , the LED board  14 , and the light guide plate  15  according to the embodiment are integrated (assembled, unitized) to become one non-separable component and treated as one unit. This reduces the number of components that constitute the backlight device  12 , resulting in an easy parts control and reducing the number of assembling steps. Steps of integrating the LEDs  13 , the LED board  14 , and the light guide plate  15  include producing the LED board  14  having the LEDs  13  thereon, setting the LED board  14  in a molding die  30  for molding the light guide plate  15  from resin, and pouring a resin material into the molding die  30  to form the light guide plate  15 . The specific method of producing the light guide plate  15  will be described later. 
     As illustrated in  FIG. 2 , the light guide plate  15  has a thickness substantially equal to a protrusion height (height) of the LEDs  13  protruding from the mount surface  14   a  of the LED board  14 . Thus, the light-exit surface  15   b  of the light guide plate  15 , which is a plate surface opposite the light-exit opposite surface  15   c  in contact with the extension portion  20 , is flush with the mounted-surface opposite surface  13   c  of the LED  13 , which is an outer surface opposite the mounted surface  13   b  in contact with the LED board  14 . In other words, the light-exit opposite surface  15   c  of the light guide plate  15  is flush with the mounted surface  13   b  of the LED  13  and the light-exit surface  15   b  thereof is flush with the mounted-surface opposite surface  13   c  of the LED  13 . With this configuration, the light input surface  15   a  of the light guide plate  15  faces the entire area of the light-emitting surfaces  13   a  of the LEDs  13 , allowing the light input efficiency to remain high and reducing the thickness of the LED  13  up to the thickness of the light guide plate  15 . In this configuration, the center of the LED  13  in the height direction (Z axis direction) matches the center of the light guide plate  15  in the thickness direction. The extension portion  20  of the LED board  14  is disposed on the rear surface (the same side as the reflection sheet  17 ) of the light guide plate  15  over an end portion adjacent to the LEDs  13  (light source side end portion), which includes the light input surface  15   a,  and is in contact with the reflection sheet  17  at the leading end portion. When the reflection sheet  17  is attached to the light guide plate  15 , the reflection sheet  17  is brought into contact with the extension portion  20 , which is integrated with the light guide plate  15 , to positionally fix the reflection sheet  17  in the Y axis direction. There is no space between the extension portion  20  and the reflection sheet  17 , which are in contact with each other, reducing the possibility that the light in the light guide plate  15  will leak out through the light-exit opposite surface  15   c  toward the rear side. 
     The embodiment has the above-described configuration, and effects obtained by the configuration will be described. When the liquid crystal display device  10  having the above-described configuration is turned on, driving of the liquid crystal panel  11  is controlled by a control circuit, which is not illustrated, and driving of the LEDs  13  on the LED board  14  is controlled by driving power supplied from an LED driving circuit, which is not illustrated, to the LEDs  13 . As illustrated in  FIG. 2 , light from the LEDs  13  is guided by the light guide plate  15  to the liquid crystal panel  11  through the optical sheet  16 , and thus a predetermined image is displayed on the liquid crystal panel  11 . 
     Specifically described, as illustrated in  FIG. 2 , when the LEDs  13  are turned on, light from the light emitting surfaces  13   a  of the LEDs  13  enters the light guide plate  15  through the light input surface  15   a  and then travels through the light guide plate  15  by being totally reflected at an interface between the light guide plate  15  and an outside air layer or being reflected by the reflection sheet  17 . Then, the light exits the light guide plate  15  through the light-exit surface  15   b  toward the optical sheet  16 . Here, the input efficiency of light to the light input surface  15   a  is high, because the light input surface  15   a  of the light guide plate  15  is in direct contact with the light-emitting surfaces  13   a  of the LEDs  13  without any other components therebetween. Furthermore, the light-exit surface  15   b  of the light guide plate  15 , which is a surface opposite the light-exit opposite surface  15   c  in contact with the extension portion  20  of the LED board  14 , is flush with the mounted-surface opposite surface  13   c  of the LED  13 , which is a surface opposite the mounted surface  13   b  in contact with the LED board  14 . This configuration not only allows the input efficiency of the light to the light input surface  15   a  to remain high and the thickness of the LED  13  to decrease up to the thickness of the light guide plate  15 , but also allows the center of the LEDs  13  in the height direction to match the center of the light guide plate  15  in the thickness direction. This makes the input efficiency of light to the light input surface  15   a  very high. 
     In addition, as illustrated in  FIG. 2 , the light guide plate  15  is integrated with the LEDs  13  and the LED board  14  with the light-exit opposite surface  15   c  being in direct contact with the mount surface  14   a  of the extension portion  20 , which extends from the LED overlapping portion  18  of the LED board  14  in the direction in which the light emitting surface  13   a  faces. In this configuration, the LEDs  13  and the LED board  11  are not located in the light guide plate  15 , and thus the shape of the portion of the light guide plate  15  near the LEDs  13  is not made complex. This allows light to more efficiently travel in the light guide plate  15 . Furthermore, since the light guide plate  15  has a thickness smaller than that of the known light guide plate having the LED board therein, the optical path length of the light traveling in the light guide plate  15  is shorter and the amount of light absorbed by the light guide plate  15  is smaller. This increases the amount of outgoing light from the light guide plate  15  through the light-exit surface  15   b,  improving brightness of the outgoing light. 
     When the LEDs  13  are turned on, the temperature inside the backlight device  12  increases because the circuits of the LEDs  13  and the LED board  14  are heated. Contrary to this, when the LEDs  13  are turned off, the temperature inside the backlight device  12  decreases because the circuits of the LEDs  13  and the LED board  14  are not heated. Such changes in temperature in the backlight device  12  may cause the light guide plate  15 , which is a large-size component, to undergo thermal expansion or thermal contraction. However, the positional relationship between the light input surface  15   a  and the light emitting surfaces  13   a  of the LEDs  13  is unlikely to change, because the light guide plate  15  is integrated with the LEDs  13  and the LED board  14  while being in direct contact with the light emitting surfaces  13   a  of the LEDs  13 . This configuration allows the light input efficiency to remain high. Furthermore, the light guide plate  15 , which is in direct contact with the light emitting surfaces  13   a  of the LEDs  13 , is not in contact with the surfaces of the LEDs  13  other than the light emitting surfaces  13   e.  In other words, the LEDs  13  are each in contact with the light guide plate  15  only at the light emitting surface  13   a,  which is one of the outer surfaces of the LEDs  13 , and thus heat generated by the LEDs  13  is less likely to be transferred to the light guide plate  15 . Furthermore, the circuit formation portion  21  of the LED board  14 , which has a circuit, i.e., a heat source, extends from the LED overlapping portion  18  toward the side away from the extension portion  20  and does not overlap the light guide plate  15 . With this configuration, when the circuit is heated due to application of current to the LEDs  13 , the heat is less likely to be transferred to the light guide plate  15 . This reduction in heat transfer to the light guide plate  15  results in a reduction in the amount of elongation and contraction of the light guide plate  15 , reducing the possibility that the light guide plate  15  and another component will rub each other and make noise. 
     Next, a method of producing the light guide plate  15  will be described. To produce the light guide plate  15 , the LED board  14  having the LEDs  13  thereon is prepared in advance, and the molding die  30  for molding the light guide plate  15  from resin is also prepared. As illustrated in  FIGS. 4 and 5 , the molding die  30  includes an upper die  31  and a lower die  32  that are closed and opened in the thickness direction (Z axis direction) of the light guide plate  15 . The upper die  31  and the lower die  32  in a closed state define a molding space  33  for molding the light guide plate  15  therebetween. The LEDs  13  and the LED board  14  are inserted into the molding die  30  before formation of the light guide plate  15 . The light emitting surfaces  13   a  and the mount surface  14   a  of the extension portion  20  face the molding space  33 . Specifically described, as illustrated in  FIG. 5 , the upper die  31  of the molding die  30  has comb teeth  31   a  each shaped like a comb tooth in plan view. The comb teeth  31   a  overlap the LED non-overlapping portions  19  of the LED board  14  in plan view and are in contact with two side surfaces of the LED  13 , which are adjacent to the light emitting surface  13   a,  the mounted surface  13   b,  and the mounted-surface opposite surface  13   c.  The comb teeth  31   a  are flush with the light emitting surfaces  13   a  of the LEDs  13   a.  This configuration allows, of the outer surfaces of the LEDs  13   a,  only the light emitting surfaces  13   a  to selectively face the molding space  33 . As illustrated in  FIG. 4 , the lower die  32  of the molding die  30  has a groove  32   a  that houses the LED board  14 . The depth of the groove  32   a  is substantially equal to the thickness of the LED board  14 . This configuration allows, of the outer surfaces of the extension portion  20  of the LED board  14 , only the mount surface  14   a  to selectively face the molding space  33 . 
     To produce the light guide plate  15 , first, the LEDs  13  and the LED board  14  are set in the lower die  32  of the molding die  30 , and the upper die  31  is closed relative to the lower die  32 . A resin material of the light guide plate  15  in a melted state is poured into the molding space  33  in the closed molding die  30 , which is illustrated in  FIGS. 4 and 5 . At this time, the light emitting surfaces  13   a  of the LEDs  13  and the mount surface  14   a  of the extension portion  20  of the LED board  14 , which face the molding space  33 , come in direct contact with the resin material of the light guide plate  15 . After the resin material of the light guide plate  15 , which fills the molding space  33 , is cooled and solidified, the molding die  30  is opened. The light guide plate  15  is produced in this way. The produced light guide plate  15  is fixed to the light emitting surfaces  13   a  with the light input surface  15  being in direct contact with the light emitting surfaces  13   a  of the LEDs  13  and is fixed to the mount surface  14   a  with a portion of the light-exit opposite surface  15   c  (end portion near the light input surface  15   a ) being in direct contact with the mount surface  14   a  of the extension portion  20  of the LED board  14 . The above-described steps produce one-unit component integrally including the LEDs  13 , the LED board  14 , and the light guide plate  15 . 
     As described above, the backlight device (lighting device)  12  of the embodiment includes the LED (light source)  13  having the light emitting surface  13   a,  the LED board (light source board)  14  having the mount surface  14   a  on which the LED  13  is mounted with the mounted surface  13   b,  which is one of outer surfaces of the LED  13  that is adjacent to the light emitting surface  13   a,  being in contact with the mount surface  14   a,  and the light guide plate  15  in which at least a portion of an outer end surface thereof is the light input surface  15   a  that receives light from the LED  13 , one of two plate surfaces thereof is the light-exit surface  15   b  through which the light exits, and the other of the plate surfaces is the light-exit opposite surface  15   c.  The LED board  14  at least includes the LED overlapping portion (light-source overlapping portion)  18  overlapping the LED  13  and the extension portion  20  extending from the LED overlapping portion  18  in the direction in which the light emitting surface  13   a  faces. The light guide plate  15  is integrated with the LED  13  and the LED board  14  with the light input surface  15   a  being in direct contact with the light emitting surface  13   a  of the LED  13  and the light-exit opposite surface  15   c  being in direct contact with the mount surface  14   a  of the extension portion  20 . 
     In this configuration, the outgoing light from the light emitting surface  13   a  of the LED  13  enters the light guide plate  15  through the light input surface  15   a  and the light that has traveled in the light guide plate  15  exits through the light-exit surface  15   b.  Since the light guide plate  15  is in direct contact with the light emitting surface  13   a  of the LED  13  at the light input surface  15   a,  input efficiency of light to the light input surface  15   a  is high. Furthermore, since the light guide plate  15  is integrated with the LEDs  13  and the LED board  14  while being in direct contact with the light emitting surfaces  13   a  of the LEDs  13 , the positional relationship between the light input surface  15   a  and the light emitting surface  13   a  is unlikely to change when the light guide plate  15  is thermally expanded or contracted due to a change in temperature. This configuration advantageously allows the light input efficiency to remain high. 
     Furthermore, since the light guide plate  15  is integrated with the LEDs  13  and the LED board  14  with the light-exit opposite surface  15   c  thereof being in direct contact with the mount surface  14   a  of the extension portion  20 , which is a portion of the LED board  14  extending from the LED overlapping portion  18  in a direction in which the light emitting surface  13   a  faces, the LED board  14  is not located in the light guide plate  15 . This does not make the shape of the portion of the light guide plate  15  near the LEDs  13  complex and allows light to efficiently travel through the light guide plate  15 . Furthermore, the light guide plate  15  is thin compared to the known light guide plate having the LED board therein. This makes the optical length of light traveling through the light guide plate  15  shorter, reducing the amount of light absorbed by the light guide plate  15 . With this configuration, the amount of outgoing light from the light guide plate  15  through the light-exit surface  15   b  increases and the brightness of the outgoing light improves. 
     Furthermore, of the outer surfaces of the LED  13 , the light guide plate  15  is selectively in direct contact with the light emitting surface  13   a.  In this configuration, the LEDs  13  are each in contact with the light guide plate  15  only at the light emitting surface  13   a,  which is one of outer surfaces of the LED  13 , and thus heat generated by the LEDs  13  is less likely to be transferred to the light guide plate  15 . 
     Furthermore, one of the light-exit surface  15   b  and the light-exit opposite surface  15   c  of the light guide plate  15  that is opposite the surface in contact with the extension portion  20  is flush with the mounted-surface opposite surface  13   c  of the LED  13 , which is one of the outer surfaces opposite the mounted surface  13   b  in contact with the LED board  14 . This configuration allows the input efficiency of light to the light input surface  15   a  to remain high and allows the thickness of the LED  13  to decrease up to the thickness of the light guide plate  15 . Furthermore, in this configuration, the center of the LED  13  in the height direction matches the center of the light guide plate  15  in the thickness direction. This makes the input efficiency of light to the light input surface  15   a  very high. 
     Furthermore, the LED board  14  includes the circuit formation portion  21  extending from the LED overlapping portion  18  toward the side away from the extension portion  20  and having a circuit for applying current to the LEDs  13 . In this configuration, the circuit formation portion  21 , which extends from the LED overlapping portion  18  toward the side away from the extension portion  20 , does not overlap the light guide plate  15 . With this configuration, when the circuit is heated due to application of current to the LEDs  13 , the heat is less likely to be transferred to the light guide plate  15 . 
     Furthermore, the liquid crystal display device (display device)  10  according to the embodiment includes the above-described backlight device  12  and the liquid crystal panel (display panel)  11  configured to display an image by using light from the backlight device  12 . The liquid crystal display device  10  having such a configuration has improved display quality and lower power consumption, because outgoing light from the backlight device  12  has improved brightness. 
     Second Embodiment 
     A second embodiment of the invention is described with reference to  FIG. 6 . In the second embodiment, the position of an LED board  114  relative to a light guide plate  115  is different. The structures, effects, and advantages substantially identical to those in the first embodiment are not described. 
     As illustrated in  FIG. 6 , an extension portion  120  of the LED board  114  according to the second embodiment is disposed on the front surface of the light guide plate  115 . Specifically described, a rear plate surface of the LED board  114  is a mount surface  114   a  on which LEDs  113  are mounted. Thus, front surfaces of the LEDs  113  are mounted surfaces  113   b  that are in contact with the mount surface  114   a  of the LED board  114 . The light guide plate  115  is fixed to the LED board  114  with the light-exit surface  115   b,  which is the front surface, being in direct contact with the mount surface  114   a  of the extension portion  120  of the LED board  114  without any other components therebetween. The effects and advantages substantially identical to those in the first embodiment are obtained by this configuration, furthermore, the LED board  114  in this embodiment is located between the light guide plate  115  and the optical sheet  116 , and thus a space corresponding to the thickness of the LED board  114  is provided between the light guide plate  115  and the optical sheet  116 . A reflection sheet  117  is disposed over the entire area of a light-exit opposite surface  115   c  of the light guide plate  115 . 
     Third Embodiment 
     A third embodiment of the invention is described with reference to  FIG. 7 . In the third embodiment, a light guide plate  215  has a thickness different from that in the first embodiment. The configurations, effects, and advantages substantially identical to those in the first embodiment are not described. 
     As illustrated in  FIG. 7 , the light guide plate  215  according to the third embodiment has a thickness larger than the height of LEDs  213 . A light-exit surface  215   b  of the light guide plate  215 , which is a surface opposite a light-exit opposite surface  215   c  in contact with an extension portion  220  of an LED board  214 , is located above a mounted-surface opposite surface  213   c  of the LED  213 , which is an outer surface opposite a mounted surface  213   b  in contact with the LED board  214 . In this configuration, a light input surface  215   a  of the light guide plate  215  faces the entire light emitting surface  213   a  of each LED  213 , and thus the light input efficiency remains high. 
     Other Embodiments 
     The present invention is not limited to the embodiments described above and illustrated by the drawings. For example, the following embodiments will be included in the technical scope of the present invention. 
     (1) According to the above embodiments, the LED board includes the circuit formation portion extending from the LED overlapping portion toward a side away from the extension portion. However, a circuit may be formed on the extension portion and the portion extending from the LED overlapping portion toward the side away from the extension portion may be eliminated. 
     (2) According to the above embodiments, the LEDs are connected in parallel through the circuit on the LED board. However, the LEDs may be connected in series through the circuit on the LED board, for example. 
     (3) According to the above embodiments, the molding die of the light guide plate is closed and opened in the Z axis direction. However, the molding die of the light guide plate may be closed and opened in the X axis direction or the Y axis direction. Furthermore, the specific configuration of the molding die (a parting line position, for example) may be suitably changed from that in the drawings. 
     (4) According to the above embodiments, of the outer surfaces of the LED, the light guide plate is selectively in direct contact with the light emitting surface. However, the light guide plate may be in direct contact with another outer surface (mounted-surface opposite surface, for example) of the LED in addition to the light emitting surface. 
     (5) According to the above embodiments, the light emitting surface of the LED is substantially flat. However, the light emitting surface of the LED may be curved. 
     (6) The specific number of LEDs on the LED board may be suitably changed from that in the above embodiments. Furthermore, the specific arrangement of the LEDs on the LED board may be suitably changed. In such a case, an irregular pitch arrangement in which some of the LEDs are arranged at a different interval may be employed. 
     (7) According to the above embodiments, the LED board (LEDs) is positioned such that an end surface of the light guide plate along one of the long sides becomes the light input surface. However, the LED board (LEDs) may be positioned such that an end surface of the light guide plate along one of the short sides becomes the light input surface. 
     (8) According to the above embodiments, the backlight device is a one-side edge-lit backlight device in which the LED board (LEDs) is positioned such that only one of four end surfaces of the light guide plate becomes a light input surface. However, the backlight device may be a two-side edge-lit backlight device in which two LED boards (LEDs) sandwich the light guide plate in the short side direction such that two of the four end surfaces of the light guide plate along the long sides become light input surfaces. Alternatively, the backlight device may be a two-side edge-lit backlight device in which two LED boards (LEDs) sandwich the light guide plate in the long-side direction such that two of the four end surfaces of the light guide plate along the short sides become light input surfaces. 
     (9) Other than the above (8), the LED board(s) (LEDs) may be positioned such that three end surfaces of the light guide plate become light input surfaces, or the LED board(s) (LEDs) may be positioned such that all four end surfaces of the light guide plate become light input surfaces. 
     (10) According to the above embodiments, one LED board is disposed relative to one side of the light guide plate. However, multiple LED boards may be disposed relative to one side of the light guide plate. 
     (11) According to the above embodiments, the light sources are LEDs. However, light sources other than LEDs (such as an organic EL) may be used. 
     (12) According to the above embodiments, the outer shape of the liquid crystal panel, the light guide plate, and the optical sheet, for example, is oblong. However, the outer shape of the liquid crystal panel, the light guide plate, and the optical sheet, for example, may be square, circle, ellipse, or other shapes. 
     (13) According to the above embodiments, the optical sheet includes three sheets. However, the optical sheet may include one, two, or four or more sheets. Furthermore, the order of laminations of the optical sheets and the kind of optical sheet, for example, may also be suitably changed. 
     (14) According to the above embodiments, the TFTs are used as the switching elements of the liquid crystal display device, but the present invention is also applicable to a liquid crystal display device that uses switching elements other than the TFTs (such as a thin film diode (TFD)). The present invention is also applicable to a black-and-white liquid crystal display device other than a color liquid crystal display device. 
     (15) According to the above embodiments, the liquid crystal display is a transmissive liquid crystal display device, but the present invention is also applicable to other liquid crystal display devices such as a semi-transmissive liquid crystal display device. 
     (16) According to the above embodiments, the liquid crystal display device includes a liquid crystal panel as a display panel. However, the present invention is also applicable to display devices including different kinds of display panel such as a microelectromechanical systems (MEMS) display panel. 
     (17) According to the above embodiments, the liquid crystal panel has a small size or a small to medium size. However, the present invention is also applicable to liquid crystal panels having a screen size of 20 inches to 100 inches, for example, which are categorized as a medium or large (very large) size. In such a case, the liquid crystal panel may be used in electronic devices such as a television receiver, an electronic signage (digital signage), and an electronic blackboard. 
     EXPLANATION OF SYMBOLS 
       10  . . . liquid crystal display device (display device),  11  . . . liquid crystal panel (display panel),  12  . . . backlight device (lighting device),  13 ,  113 ,  213  . . . LED (light source),  13   a,    213   a  . . . light emitting surface,  13   b,    113   b,    213   b  . . . mounted surface (surface in contact with light source board),  13   c,    213   c  . . . mounted-surface opposite surface (opposite surface),  14 ,  114 ,  214  . . . LED board (light source board),  14   a,    114   a  . . . mount surface,  15 ,  115 ,  215  . . . light guide plate,  15   a,    215   a  . . . light input surface,  15   b,    115   b,    215   b  . . . light-exit surface,  15   c,    115   c,    215   c  . . . light-exit opposite surface,  18  . . . LED overlapping portion (light-source overlapping portion),  20 ,  120 ,  220  . . . extension portion,  21  . . . circuit formation portion