Abstract:
Provided is an illumination apparatus which prevents variations in the distance between the light-receiving surface of a light guide plate and a light source. Also provided is a display device which incorporates the illumination apparatus. The light guide plate, which constitutes a backlight unit, receives light through a light-receiving surface with the light-receiving surface oriented toward the light being emitted. In the backlight unit, pillars extend to intersect the direction of emission from an LED and are thus brought into contact with a device-carrying board and the light guide plate, which are superposed one on the other, thereby securing the device-carrying board and the light guide plate.

Description:
RELATED APPLICATIONS 
     The present application is based on International Application No. PCT/JP2011/050413, filed Jan. 13, 2011 and claims priority from, Japanese Application No. 2010-080450, filed Mar. 31, 2010. 
     TECHNICAL FIELD 
     The present invention relates to an illumination apparatus such as a backlight unit and the like, and to a display device (liquid crystal display device and the like) that incorporates the illumination apparatus. 
     BACKGROUND ART 
     Conventionally, a liquid crystal display device, which incorporates a liquid crystal display panel (display panel) of non-light emitting type, incorporates a backlight unit as well that supplies light to the liquid crystal display panel. It is desirable that the backlight unit generates surface light which spreads throughout the entire region of the surface-shaped liquid crystal display panel. To achieve this, the backlight unit sometimes includes a light guide plate that mixes light from an incorporated light source (e.g., a light emitting device such as an LED and the like) with a high degree. 
     For example, as shown in  FIG. 8 , in a backlight unit  149  disclosed in a patent document 1, a light emitting surface  132 L of an LED  132  of an LED module mj opposes a light reception surface  111 Sa of a light guide plate  111  and supplies light to this light reception surface  111 Sa. And, the light guide plate  111  makes the light undergo multiple reflection inside itself and outputs surface light from a top surface  111 U. 
     CITATION LIST 
     Patent Literature 
     
         
         PLT1: JP-A-2009-272096 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the meantime, in the backlight unit  149  in the patent document 1, a shaft pl formed on the light reception surface  111 Sa of the light guide plate  111  fits in an opening  131 H formed through a mount board  131 . Because of this, the LED module mj does nor deviate along a thickness direction of the light guide plate  111  and a longitudinal direction of the light reception surface  111 Sa. 
     However, the shaft pl of the light guide plate  111  is along a light output direction of the LED  132 . Because of this, there is a risk that the LED module mj could move along the shaft direction and the output direction of LED  132 . In other words, there is a risk that a distance between the light emitting surface  132 L of the LED  132  and the light reception surface  111 Sa of the light guide plate  111  could change. 
     And, if the change between the light emitting surface  132 L of the LED  132  and the light reception surface  111 Sa of the light guide plate  111  deviates from a predetermined distance, it is hard for the light output from the light guide plate  111  to become suitable surface light expected in the design, and for example, surface light including light amount unevenness is produced. 
     The present invention has been made in light of the above situation. And, it is an object of the present invention to provide an illumination apparatus that does not allow a change in distance between a light reception surface of a light guide plate and a light source; and a display device that incorporates the illumination apparatus. 
     Solution to Problem 
     The illumination apparatus includes: a light source; a mount board on which the light source is mounted; a light guide plate that faces a light reception surface toward a light emission direction of the light source to receive light via the light reception surface; and a stator that extends in a direction intersecting the light emission direction, touches the mount board and the light guide plate overlying each other, and fix the mount board and the light guide plate. 
     According to this, the stator intersects the emission direction of the light from the light source, accordingly, the mount board and the light guide plate, which are fixed by the stator, do not move along the emission direction. Because of this, a distance between the light emitting surface of the light source mounted on the mount board and the light reception surface of the light guide plate does not change. Accordingly, the light output from the light guide plate easily becomes suitable surface light expected in the design. 
     Here, the stator is, for example, a shaft disposed on the mount board; and the light guide plate is provided with an engagement portion that engages with the shaft. 
     Besides, in a case where the illumination apparatus includes a housing body that houses the light source, the mount board, the light guide plate and the stator, it is desirable that the stator is a shaft that is disposed on the housing body; and the light guide plate and the mount board are each provided with an engagement portion that engages with the shaft. 
     Here, it is desirable that the illumination apparatus meets the following formula:
 
 RL≦GL/ 4
 
     where 
     RL: a shortest distance from the light reception surface to the engagement portion; 
     GL: a total length of the light guide plate in a direction along the light emission direction of the light source. 
     Usually, the light guide plate receives the light (heat) from the light source to thermally expand. Especially, the thermal expansion is prone to occur with respect to the engagement portion of the light guide plate. However, in the case where the formula (1) is met, the engagement portion is situated near the light reception surface of the light guide plate. Because of this, even if the light guide plate expands thermally to become deformed, the thermal expansion has a slight influence on a central portion and a near place of the surface light. Accordingly, the illumination apparatus is able to supply high-quality surface light. 
     Here, the engagement portion is not especially limited, but it is desirable that the engagement portion is a dimple, a cutout, or an opening. 
     Besides, it is desirable that a sectional shape of the engagement portion in a sectional direction with respect to a surface direction identical to the light output surface of the light guide plate has: a short edge along the light emission direction of the light source; and a long edge perpendicular to the light emission direction of the light source; and a transversal sectional shape of the shaft has a width that tightly fits in a gap between inner walls of the long edge of the engagement portion. 
     According to this, the distance between the light reception surface of the light guide plate and the light source does not easily change, while a clearance is produced between the engagement portion and the shaft in the direction perpendicular to the light emission direction of the light source. Because of this, the stator is easily mountable on the light guide plate. 
     Besides, in a case where the light source supplies the light to opposing two side surfaces of the light guide plate and the two side surfaces each define the light reception surface, to secure the easy mounting of the stator onto the light guide plate, a structure described below may be employed. 
     Specifically, in the sectional direction with respect to the surface direction identical to the light output surface of the light guide plate, it is desirable that the sectional shape of the engagement portion near one light reception surface has: a short edge along the light emission direction of the light source, and a long edge perpendicular to the light emission direction of the light source; and the transversal sectional shape of the shaft, which fits in the engagement portion near the one light reception surface, has a width that tightly fits in the gap between the inner walls of the long edge of the engagement portion. Further, the sectional shape of the engagement portion near the other light reception portion has: a long edge along the light emission direction of the light source, and a short edge perpendicular to the light emission direction of the light source; and the transversal sectional shape of the shaft, which fits in the engagement portion near the other light reception surface, has a width that tightly fits in the gap between the inner walls of the long edge of the engagement portion. 
     Here, it is desirable that the sectional shape of the engagement portion in the sectional direction with respect to the surface direction identical to the light output surface of the light guide plate is an elliptic shape that has a minor axis along the short edge and a major axis along the long edge, or a tongue shape that includes an elliptic shape; and further, it is desirable that the transversal sectional shape of the shaft is a perfect circle that tightly fits in the gap between the inner walls of the long edge of the engagement portion. 
     Besides, in a case where a plurality of the engagement portions are formed, it is desirable that one sectional shape of the engagement portion in the sectional direction with respect to the surface direction identical to the light output surface of the light guide plate is a perfect circle whose length along the light emission direction of the light source and whose length perpendicular to the light emission direction of the light source are equal to each other; and the transversal sectional shape of the shaft, which fits in the perfect circular engagement portion is a perfect circle that tightly fits in the gap between the inner walls of the long edge of the engagement portion. 
     According to this, the engagement portion and the shaft fitting in each other define a reference, accordingly, there may be a clearance between another engagement portion and another shaft fitting in each other. Because of this, the stator becomes easily mountable on the light guide plate. 
     Besides, it is sayable that also a display device, which includes the above apparatus and a display panel that receives the light from the illumination apparatus, is the present invention. 
     Advantageous Effects of Invention 
     According to the present invention, the mount board and the light guide plate overlying each other come not to move. Especially, the light guide plate does not move with respect to the mount board along the light emission direction of the light source mounted on the mount board. Because of this, the distance between the light emitting surface of the light source mounted on the mount board and the light reception surface of the light guide plate does not change, and the light output from the light guide plate easily becomes the suitable surface light expected in the design. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exploded perspective view of a liquid crystal display device. 
         FIG. 2  is a 2-side view illustrating a sectional view and a plan view of a backlight unit. 
         FIG. 3  is an exploded perspective view of a liquid crystal display device. 
         FIG. 4  is a 2-side view illustrating a sectional view and a plan view of a backlight unit. 
         FIG. 5  is a plan view of a light guide plate and an LED module. 
         FIG. 6  is a plan view of a light guide plate and an LED module. 
         FIG. 7  is a plan view of a light guide plate and an LED module. 
         FIG. 8  is an exploded perspective view of a conventional backlight unit. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     An embodiment is described based on drawings as follows. Here, for the sake of convenience, there is a case where hatching, a member reference number and the like are omitted; in such a case, other drawings are referred to. Besides, a black dot in a drawing means a direction perpendicular to the paper surface. 
       FIG. 1  is an exploded perspective view of a liquid crystal display device  69  (for the sake of convenience, a reflection sheet  41  later described is skipped in  FIG. 1  and shown in a sectional view of  FIG. 2  later described). As shown in  FIG. 1 , the liquid crystal display device  69  includes a liquid crystal display panel  59  and a backlight unit  49  (here, the liquid crystal display panel  59  is protected by a frame-shaped bezel BZ). 
     The liquid crystal display panel  59  attaches an active matrix board  51  that includes switching elements such as a TFT (Thin Film Transistor) and the like to an opposite board  52  opposing the active matrix board  51  by means of a seal material (not shown). And, liquid crystal (not shown) is injected into a gap between both boards  51  and  52 . 
     Here, a light polarization film  53  is disposed on a light receiving side of the active matrix board  51  and an output side of the opposite board  52 . And, the above liquid crystal display panel  59  makes use of a change in light transmittance due to an inclination of liquid crystal molecules, thereby displaying an image. 
     Next, the backlight unit  49 , which is situated right under the liquid crystal display panel  59 , is described. The backlight unit  49  includes: an LED module (light source module) MJ; a light guide plate  11 ; a reflection sheet  41  (see  FIG. 2 ); a backlight chassis  42 ; a diffusion plate  43 ; a prism sheet  44 ; and a lens sheet  45 . 
     The LED module MJ is a module that emits light and includes: a mount board  31 ; and an LED (Light Emitting Diode)  32  mounted on a board surface of the mount board  31 . 
     The mount board  31  is a plate-shaped and rectangular board, and a plurality of electrodes (not shown) are arranged on a mount surface  31 U. And, the LEDs  32  are mounted on these electrodes that are linearly arranged. Here, the backlight unit  49  incorporates one mount board  31 ; an extension direction of the mount board  31  is defined as an X direction, a direction, which intersects (meets at right angles and the like) the X direction and is an emission direction of the LED  32 , is defined as a Y direction, and a direction, which intersects (meets at right angles and the like) the X direction and the Y direction, is defined as a Z direction. 
     The LED  32  receives supply of an electric current via the electrode (not shown) that is formed on the mount surface of the mount board  31 , thereby emitting light (here, a light emitting surface  32 L of the LED  32  intersects a board surface direction of the mount board  31 , whereby the light emission direction of the LED  32  is along the board surface direction). Besides, to secure a light amount, it is desirable a plurality of the LEDs (light emitting device, point light source)  32  are mounted on the mount board  31 . However, in the figure, for the sake of convenience, only part of the LEDs  32  are shown. 
     The light guide plate  11  is a plate-shaped member that has: a side surface  11 S; a top surface  11 U and a bottom surface  11 B which are situated oppositely so as to sandwich the side surface  11 S. And, a surface (light reception surface  11 Sa) of the side surface  11 S faces the light emitting surface  32 L of the LED  32 , thereby receiving the light from the LED  32 . The received light undergoes multiple reflection in an inside of the light guide plate  11  and goes out as the surface light from the top surface (output surface)  11 U to outside. 
     The reflection sheet  41  (see  FIG. 2 ) is a sheet covered by the bottom surface  11 B of the light guide plate  11 , and a reflection surface of the sheet faces the bottom surface  11 B of the light guide plate  11 . And, the reflection sheet  41  reflects light leaking from the bottom surface  11 B of the light guide plate  11  back to the light guide plate  11 , thereby preventing light loss. 
     The backlight chassis (housing body)  42 , as shown in  FIG. 1 , is a box-shaped member, for example, and houses the reflection sheet  41 , the light guide plate  11 , the LED modules MJ, the diffusion plate  43 , the prism sheet  44 , and the lens sheet  45 . 
     The diffusion plate  43  is an optical member that overlies the top surface  11 U of the light guide plate  11  and diffuses the light output from the light guide plate  11 . In other words, the diffusion plate  43  diffuses the surface light formed by the light guide plate  11  to spread the light to the entire region of the liquid crystal display panel  59 . 
     The prism sheet  44  is an optical member that overlies the diffusion plate  43 . And, on the prism sheet  44 , triangular prisms each extending in one direction (linear) are arranged on a sheet surface in a direction that intersects the one direction. According to this, the prism sheet  44  deflects a radiation characteristic of the light from the diffusion plate  43 . 
     The lens sheet  45  is an optical member that overlies the prism sheet  44 . And, in an inside of the lens sheet  45 , micro-particles for refracting and scattering the light are dispersed. According to this, the lens sheet  45  does not locally concentrate the light from the prism sheet  44 , thereby curbing brightness difference (light-amount unevenness). 
     And, the above-described backlight unit  49  changes the light from the plurality of LED modules MJ into the surface light by means of the light guide plate  11 , transmits the surface light through the plurality of optical members  43  to  45 , thereby supplying the light to the liquid crystal display panel  59 . According to this, the liquid crystal display panel  59  of non-light emitting type receives the light (backlight) from the backlight unit  49  to increase a display function. 
     Here, the light guide plate  11 , the reflection sheet  41 , the LED module MJ, and the backlight chassis  42  are described in detail by means of  FIG. 1  and  FIG. 2 . Here,  FIG. 2  is a 2-side view illustrating a partial sectional view and a plan view of the backlight unit  49  (incidentally, the sectional view is a sectional view taken in a direction of an arrow A-A′ of  FIG. 1 , and the plan view chiefly illustrates the light guide plate and the LED module MJ for the sake of convenience.). 
     The light guide plate  11 , as shown in  FIG. 1  and  FIG. 2 , is provided with a cutout CT and a dimple DH. In detail, as for the cutout (engagement portion) CT, cutting-away extends from the bottom surface  11 B of the light guide plate  11  toward the top surface  11 U and the cutting-away reaches the side surface  11 S of the light guide plate  11 , whereby the cutout CT is formed (however, the cutting-away does not reach the top surface  11 U.). On the other hand, as for the dimple (engagement portion) DH, cutting-away extends from the bottom surface  11 B of the light guide plate  11  toward the top surface  11 U, whereby the dimple DH is formed (however, like the cutout CT, the cutting-away for forming the dimple DH does not reach the top surface  11 U.). 
     The reflection sheet  41  is covered by the bottom surface of the light guide plate  11 . Because of this, the reflection sheet  41  is provided with a sheet opening  41 H through positions that overlie the cutout CT and the dimple DH of the light guide plate  11  (here, a size of the sheet opening  41 H is larger than outer circumferences of the cutout CT and the dimple DH.). In other words, the cutout CT and the dimple DH of the light guide plate  11  are not blocked by the reflection sheet  41  and exposed. 
     The LED module MJ is provided with a shaft (stator) PL that protrudes from the mount surface  31 U of the mount board  31 . The shafts PL disposed on the mount board  31  correspond to the cutout CT and the dimple DH of the light guide plate  11  (in short, oppose each other). Further, a shaft circumference (outer circumference) of the shaft PL is smaller than inner circumferences of the cutout CT and the dimple DH of the light guide plate  11 . Because of this, the shaft PL fits into (engages with) the cutout CT and the dimple DH, whereby the LED module MJ comes not to move with respect to the light guide plate  11 . 
     The backlight chassis  42  includes a step  42 P on a bottom surface  42 B that is able to house the mount board  31 . In detail, the step  42 P, which has an area slightly larger than an outer circumference of the mount board  31 , is included in the backlight chassis  42 . And, when the mount board  31  fits in a region of the step  42 P (recessed step  42 P) that sinks from the bottom surface  42 B, even if the mount board  31  tries to move in a surface direction of the bottom surface  42 B, the mount board  31  touches a side wall  42 S of the backlight chassis  42  and a wall  42 Ps of the step  42 P, and comes not to move (here, a depth of the step  42 P is slightly longer than a thickness of the mount board  31 .). 
     The backlight unit  49 , which includes the reflection sheet  41 , the LED module MJ and the backlight chassis  42 , is assembled as described hereinafter. 
     Specifically, the mount board  31  of the LED module MJ rests on the step  42 P formed on the bottom surface  42 B of the backlight chassis  42  with a non-mount surface  31 B (rear surface  31 B of the mount board  31 U) facing the step  42 P (here, the backlight chassis  42  and the mount board  31  may be fixed to each other by means of, for example, double-coated tape, or a screw.). According to this, the shaft PL of the mount board  31  extends upward with respect to the bottom surface  42 B of the backlight chassis  42 . 
     And, the reflection sheet  41  covers the bottom surface  42 B of the backlight chassis  42  such that the shaft PL penetrates the sheet opening  41 H. Because of this, the shaft PL is exposed through the sheet opening  41 H of the reflection sheet  41 . 
     Further, the light guide plate  11  is placed such that the cutout CT and the dimple DH fit onto the shaft PL. Here, the light reception surface  11 Sa of the light guide plate  11  is designed to have a suitable distance from and not to touch the light emitting surface  32 L of the LED  32  in the state where the shaft PL engages with the cutout CT and the dimple DH. 
     As described above, in the backlight unit  49  which incorporates the light guide plate  11  that faces the light reception surface  11 Sa toward a light emission direction of the LED  32  to receive the light via the light reception surface  11 Sa, the shaft PL extends in a direction that intersects the emission direction of the LED  32 , touches the mount board  31  and the light guide plate  11  overlying each other, thereby fixing the mount board  31  and the light guide plate  11 . 
     According to this, the shaft PL interests the emission direction of the LED  32 , accordingly, the mount board  31  and the light guide plate  11  fixed by the shaft PL do not move in the emission direction. Because of this, the distance between the light emitting surface  32 L of the LED  32  mounted on the mount board  31  and the light reception surface  11 Sa of the light guide plate  11  does not change. Accordingly, the light output from the light guide plate  11  easily becomes suitable surface light expected in the design. 
     Besides, by only fitting the light guide plate  11  to the shaft PL, it is possible to assemble the LED module MJ and the light guide plate  11  while keeping a predetermined positional relationship between the light reception surface  11 Sa and the light emitting surface  32 L of the LED  32 , accordingly, the assembly of the backlight unit  49  is easy. Especially, if there are a plurality of the shafts PL, the light guide plate  11  fitted to the shafts PL does not rotate. 
     Here, widths of the cutout CT and the dimple DH along the Y direction that is a direction meeting (intersecting) the light reception surface  11 Sa at right angles are lengths substantially equal to a diameter of the shaft PL whose transversal cross section (sectional surface perpendicular to the shaft direction) is a perfect circle. If this is not met, even if the shaft PL fits into the cutout CT and the dimple DH, the light guide plate  11  moves in the Y direction with respect to the mount board  31 , and the distance between the light reception surface  11 Sa and the light emitting surface  32 L of the LED  32  changes. 
     However, the widths of the cutout CT and the dimple DH along the X direction that is a long-edge direction of the light reception surface  11 Sa may be longer than the diameter of the shaft PL. This is because when the shaft PL fits into the cutout CT and the dimple DH, the light guide plate  11  does not move in the Y direction with respect to the mount board  31  and the distance between the light reception surface  11 Sa and the light emitting surface  32 L of the LED  32  does not change. Besides, if there is not a little clearance (space) between the shaft PL and the cutout CT and between the shaft PL and the dimple DH, the assembly of the LED module MJ and the light guide plate  11  becomes onerous. 
     In other words, it is desirable that sectional shapes (in detail, shapes in a sectional direction along a surface direction identical to the top surface  11 U of the light guide plate  11 ) of the cutout CT and the dimple DH have a short edge along the light emission direction of the LED  32  and a long edge perpendicular to the light emission direction of the LED  32  (e.g., an elliptic sectional shape that has a minor axis along the short edge and a major axis along the long edge, or a tongue-shaped sectional shape that includes an elliptic shape); and a transversal sectional shape of the shaft PL has a width (e.g., a perfect circular sectional shape) that tightly fits into a gap between inner walls of the long edge of the cutout CT and the dimple DH. According to this, the distance between the light reception surface  11 Sa and the light emitting surface  32 L of the LED  32  does not change, and the assembly of the LED module MJ and the light guide plate  11  becomes easy. 
     However, in a case where all the shafts PL have the perfect circular transversal sectional shape, the widths of the dimple DH in the X direction and the Y direction may be substantially equal to the diameter of the shaft. This is because according to this, the light guide plate  11  does not move in a surface direction (XY plane direction) of the mount board  31 . 
     Here, in a case where the shaft PL does not have the perfect circular transversal sectional shape but has a polygon-shaped transversal sectional shape and the shaft PL fits into the dimple DH with no gap, the number of the shafts PL may be one. This is because even one shaft PL is able to prevent the movement of the light guide plate  11  in the XY plane direction with respect to the mount board  31 . In short, the number of combinations of the engagement portion such as the cutout CT or the dimple DH and the shaft PL fitting in the engagement portion is not especially limited. 
     Besides, the position of the shaft PL is not limited to the mount surface  31 U of the mount board  31 . For example, as shown in an exploded perspective view of  FIG. 3  and a 2-side view (the same way of illustrating as  FIG. 2 ) of  FIG. 4 , the shaft PL may be formed not only on the mount board  31  but also on the step  42 P of the bottom surface  42 B of the backlight chassis  42  (however, a board opening (engagement portion)  31 H, through which the shaft PL disposed on the step  42 P of the backlight chassis  42  extends, must be formed through the mount board  31 .). 
     In other words, the backlight chassis  42  houses not only the LED module MJ and the light guide plate  11  but also the shaft PL disposed on the step  42 P of the bottom surface  42 B. And, the shaft PL engages with the cutout CT and the dimple DH of the light guide plate  11  and the board opening  31 H of the mount board  31 , thereby fixing the mount board  31  and the light guide plate  11  that overlie each other. 
     Besides, as shown in  FIG. 2  and  FIG. 4 , it is desirable that the backlight unit  49  meets the following formula (1):
 
 RL≦GL/ 4  the formula (1)
 
     where 
     RL: a shortest distance from the light reception surface  11 Sa of the light guide plate  11  to the cutout CT, or a shortest distance from the light reception surface  11 Sa of the light guide plate  11  to the dimple DH; 
     GL: a total length of the light guide plate  11  in a direction along the light emission direction (e.g., the Y direction) of the LED  32 . 
     Usually, the light guide plate  11  is made of resin, accordingly, thermally expands when receiving the light (heat) from the LED  32 . Especially, the thermal expansion is prone to occur with respect to the cutout CT and the dimple DH of the light guide plate  11 . Because of this, to secure the quality of the surface light from the light guide plate  11 , for example, it is desirable to prevent the thermal expansion from occurring near a center of the light guide plate  11  that corresponds to a center of the surface light. To achieve this, it is desirable that the above formula (1) is met. According to this, the cutout CT and the dimple DH are disposed near an end of the light guide plate  11  that has a slight influence on the quality of the surface light, the quality of the surface light hardly deteriorates despite the cutout CT and the dimple DH. 
     Other Embodiments 
     Here, the present invention is not limited to the above embodiments, and various modifications are possible without departing the spirit of the present invention. 
     For example, the cutout CT and the dimple DH shown in  FIG. 1  and  FIG. 2  may have a shape that penetrates from the bottom surface  11 B to the top surface  11 U of the light guide plate  11  (e.g., the dimple DH may be an opening.). Besides, of the three openings  31 H shown in  FIG. 3  and  FIG. 4 , the outer two openings  31 H may be a cutout disposed on the short edge of the mount board  31 . 
     In short, in the case where the mount board  31  and the light guide plate  11  overlying each other are made not to move, the mount board  31 , which is one member near the shaft PL, is sufficiently provided with the opening  31 H or a cutout that penetrates from the non-mount surface  31 B to the mount surface  31 U such that the shaft PL reaches the light guide plate  11  which is the other member. Besides, the light guide plate  11  is sufficiently provided with the cutout CT, the dimple DH, or an opening to engage with the shaft PL. 
     Besides, the shaft PL is not limited to a bar shape that has a perfect circular transversal sectional shape or a polygonal transversal sectional shape, and may have a conic solid-shaped (cone-shaped, pyramid-shaped and the like) projection or a conic solid stool-shaped (conical stool-shaped, pyramid stool-shaped and the like) projection. 
     Besides, in the case where the plurality of engagement portions (the dimple DH and the cutout CT) are formed, as shown in  FIG. 5 , the sectional shape of one dimple DH (e.g., a central engagement portion of the three engagement portions arranged in parallel with one another) may be a perfect circle whose length along the light emission direction of the LED  32  and whose length perpendicular to the light emission direction of the LED  32  are equal to each other; and the transversal sectional shape of the shaft PL, which fits in the perfect circular dimple DH may be a perfect circle that tightly fits between the opposing inner walls of the dimple DH. 
     According to this, the dimple DH having the perfect circular sectional surface and the shaft PL having the perfect circular sectional surface tightly touch each other, accordingly, define a reference position. On the other hand, the remaining two cutouts CT do not tightly touch the shaft PL in the X direction (in short, there is a clearance between the cutout CT and the shaft PL.). Because of this, even if the dimple DH and the shaft PL, which define the reference position, fit in each other, the two cutouts CT and the shaft PL easily fit in each other. Accordingly, the assembly of the LED module MJ and the light guide plate  11  does not become onerous, and the light guide plate  11  does not move in the surface direction (the XY plane direction) of the mount board  31 . 
     Besides, in the above description, the LED module MJ is disposed on one side surface  11 S of the light guide plate  11 , which is however not limiting. For example, as shown in  FIG. 6 , the LED module MJ may be disposed on the opposing two side surfaces  11 S. In other words, the opposing two side surfaces  11 S of the light guide plate  11  may function as the light reception surface  11 Sa. 
     And, it is desirable that the backlight unit  49  shown in  FIG. 6  is structured as described hereinafter. Specifically, it is desirable that the sectional shape of the engagement portion (the dimple DH and the cutout CT) near one light reception surface  11 Sa of the two light reception surfaces  11 Sa has a short edge along the light emission direction of the LED  32  and a long edge perpendicular to the light emission direction of the LED  32  (e.g., an elliptic sectional shape that has a minor axis along the short edge and a major axis along the long edge, or a tongue-shaped sectional shape that includes an elliptic shape); and the transversal sectional shape of the shaft PL has a width (e.g., a perfect circular sectional shape) that tightly fits into the gap between the inner walls of the long edge of the cutout CT and the dimple DH. 
     Further, it is desirable that the shape of the engagement portion (the dimple DH) near the other light reception surface  11 Sa of the two light reception surfaces  11 Sa has a long edge along the light emission direction of the LED  32  and a short edge perpendicular to the light emission direction of the LED  32  (e.g., an elliptic sectional shape that has a minor axis along the short edge and a major axis along the long edge); and the transversal sectional shape of the shaft PL has a width (e.g., a perfect circular sectional shape) that tightly fits into the gap between the inner walls of the long edge of the dimple DH. 
     According to this, at the side of the one light reception surface  11 Sa, the shaft PL fits into the cutout CT and the dimple DH, whereby the light guide plate  11  comes not to move with respect to the mount board  31  (i.e., the distance between the light reception surface  11 Sa and the light emitting surface  32 L of the LED  32  becomes constant). On the other hand, at the side of the other light reception surface  11 Sa, even if the light guide plate  11  thermally expands thanks to the light form the LED  32  to extend in the X direction, the extension is not excessively limited (e.g., the shaft PL is not be broken despite the thermal expansion of the light guide plate  11 .). In addition, there is a little clearance between the shaft PL and the dimple DH, accordingly, the assembly of the LED module MJ and the light guide plate  11  is also easy. 
     Besides, the number of LED modules MJ may be four as shown in  FIG. 7 . Specifically, as shown in  FIG. 7 , the LED module MJ may be disposed not only on the opposing two side surfaces  11 S shown in  FIG. 6  but also on the other pair of opposing two side surfaces  11 S. In other words, all the side surfaces  11 S of the light guide plate  11  may function as the light reception surface  11 Sa. 
     Her, as shown in  FIG. 7 , the sectional shape of the engagement portion (the dimple DH) near one light reception surface  11 Sa of the other pair of two light reception surfaces  11 Sa has a short edge along the light emission direction of the LED  32  and a long edge perpendicular to the light emission direction of the LED  32  (e.g., an elliptic sectional shape that has a minor axis along the short edge and a major axis along the long edge); and the transversal sectional shape of the shaft PL, which fits into the engagement portion near the one light reception surface  11   a , has a width (e.g., a perfect circular sectional shape) that tightly fits into the gap between the inner walls of the long edge of the dimple DH. 
     Further, the sectional shape of the engagement portion (the dimple DH) near the other light reception surface  11 Sa of the other pair of two light reception surfaces  11 Sa has a long edge along the light emission direction of the LED  32  and a short edge perpendicular to the light emission direction of the LED  32  (e.g., an elliptic sectional shape that has a minor axis along the short edge and a major axis along the long edge); and the transversal sectional shape of the shaft PL, which engages with the engagement portion near the one light reception surface  11 Sa, has a width (e.g., a perfect circular sectional shape) that tightly fits into the gap between the inner walls of the long edge of the dimple DH. 
     REFERENCE SIGNS LIST 
     
         
         
           
             PL shaft (stator) 
             CT cutout (engagement portion) 
             DH dimple (engagement portion) 
             HL opening (engagement portion) 
               11  light guide plate 
               11 U top surface of light guide plate 
               11 B bottom surface of light guide plate 
               11 S side surface of light guide plate 
               11 Sa light reception surface of light guide plate 
             MJ LED module 
               31  mount board 
               31 U mount surface 
               31 B non-mount surface 
               31 H opening (engagement portion) of mount board 
               32  LED (light source) 
               32 L light emitting surface of LED 
               41  reflection sheet 
               42  backlight chassis (housing body) 
               42 B bottom surface of backlight chassis 
               42 P step of bottom surface of backlight chassis 
               42 Ps step wall 
               42 S side wall of backlight chassis 
               43  diffusion plate 
               44  prism sheet 
               45  lens sheet 
               49  backlight unit (illumination apparatus) 
               59  liquid crystal display panel (display panel) 
               69  liquid crystal display device (display device)