JP5056292B2 - Surface light source device and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-emitting light source device and a liquid crystal display device excellent in heat dissipation efficiency. <P>SOLUTION: The surface-emitting light source device is provided with a planar light-emitting surface widening toward direction X and direction Y which are orthogonal. Furthermore, the surface-emitting light source device is provided with: a back surface housing portion 26 provided on a side opposite to the light-emitting surface; a box type housing 18 with a first side part housing portion 28 extending in the direction X and two second side part housing portions 30 extending in the direction Y; a light guiding part 14 arranged between the light-emitting surface and the back surface housing portion 26; and a light source 66 arranged inside the first and second side part housing portions 28 and 30 and making light incident to the light guiding part 14. A housing portion for dissipating heat 34 is formed by extending the housing portions of the back surface housing portion 26 and the first and second side part housing portions 28 and 30 and the housing portion for dissipating heat 34 is made to face at least one housing portion with space between the housing portions. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a surface light source device having a planar light emitting surface, for example, a surface light source device used as a backlight device of a liquid crystal display device. The present invention also relates to a liquid crystal display device provided with such a surface light source device.

  Conventionally, light emitting diodes have been used as light sources for backlights for small liquid crystal display devices, but due to the advantages of power saving and improved color reproducibility, use in larger size backlights has been demanded. . However, since a large backlight device naturally has a large light exit surface, it tends to cause a difference between the luminance near the light source and the luminance away from the light source. Therefore, it is necessary to increase the drive current of the light source with an increase in size in order to ensure a luminance of a predetermined amount or more in all portions of the light emitting surface. However, when the drive current of the light source is increased, the amount of heat generated by the light source increases and exceeds the light source usage limit temperature. Therefore, it is necessary to devise a device that reduces the thermal resistance from the light source to the ambient atmosphere and suppresses the temperature rise of the light source.

Therefore, Patent Document 1 discloses a technique in which a light emitting diode as a light source is mounted on a circuit board made of a high thermal conductivity material having an insulating property or having an insulating layer formed on the surface thereof.
JP 2002-216525 A

Patent Document 2 discloses a technique for releasing heat of a light source to the outside through a heat transfer wall in contact with an LED that is a light source and a heat dissipation plate that covers the heat transfer wall.
JP 2006-208723 A

  However, the technique of Patent Document 1 is limited in improving the heat dissipation performance because there is a limit to the size of the case that accommodates the circuit board. Moreover, since the heat transfer wall is not in contact with the outside air, the technique of Patent Document 2 cannot be expected to sufficiently improve the heat dissipation performance.

Therefore, in the surface light source device of the present invention and the liquid crystal display device including the surface light source device, the surface light source device (10A) extends in a first direction (X direction) and a second direction (Y direction) that are orthogonal to each other. A planar light emitting surface (12) having The surface light source device (10A) also includes a rear housing part (26) on the opposite side of the light emitting surface (12), a first side housing part (28) extending in the first direction, and the first A box-shaped housing (18) having two second side housing parts (30) extending in the direction of 2, and a guide disposed between the light exit surface (12) and the rear housing part (26). A light source (66) disposed inside at least one of the light portion (14) and the first and second side housing portions (28, 30), and for making light incident on the light guide portion (14) the a, is bent while extending at least one housing part of the first and second side housing portion (28, 30), positioned outside of the at least one housing part (28 or 30) The first gap (36) Then, the first heat radiating plate portion (38) facing the at least one housing portion and the rear housing portion (26) via the second gap (40) located outside the rear housing portion (26). ) And a heat radiating housing part (26) provided with a second heat radiating plate part (42) facing each other, and the heat radiating housing part (26) is formed integrally with the housing (18). Characterized by

  According to the surface light source device and the liquid crystal display device according to the present invention, the heat generated by the light source can be efficiently released to the outside atmosphere. Therefore, the junction temperature of the light source can be effectively lowered. As a result, it is possible to supply a large amount of current to the light source and increase the luminance and the amount of light emitted from the light emitting surface.

  Hereinafter, a surface light source device according to the present invention and a liquid crystal display device having the surface light source device will be described with reference to the accompanying drawings.

  FIG. 1 shows a surface light source device 10A according to the present invention. 10 A of surface light source devices are arrange | positioned at the back side of a liquid crystal panel (not shown), and comprise a liquid crystal display device with a liquid crystal panel.

  The surface light source device 10A includes a rectangular light emitting surface 12 having a spread along a plane parallel to the XY plane including the X direction (first direction) and the Y direction (second direction) of the orthogonal coordinate system shown in the drawing. And is configured to project light emitted from a light guide unit 14 (described later) disposed behind the light emitting surface 12 (below the drawing) onto the light emitting surface 12. Therefore, in a state where the surface light source device 10A is combined with the liquid crystal panel, the liquid crystal panel is disposed on the light emitting surface 12 of the surface light source device 10A.

  The surface light source device 10 </ b> A includes a housing 16 or a frame surrounding the periphery excluding the light emitting surface 12. The housing 16 is preferably formed of a material having high thermal conductivity, such as aluminum. As shown in FIGS. 2 to 5, the housing 16 includes a lower housing (lower frame) 18 that houses a light guide unit 14 described later. Preferably, as illustrated, the housing 16 includes an upper housing (upper frame) 20 that holds the light guide portion accommodated in the lower housing 18 in the lower housing 18. The lower housing 18 includes a pair of parallel lateral edges 22 (22a, 22b) (particularly see FIGS. 3 and 4) extending in the X direction and a pair of parallel longitudinal edges 24 (particularly FIG. 4), and a rectangular bottom plate (back housing portion) 26. Both lateral edge portions 22 (22a, 22b) of the bottom plate 26 are extended in the Z direction or substantially perpendicular direction to the XY plane to form a pair of lateral side plates (two first housing portions) 28 (28a, 28b). ) Is formed. Similarly, both vertical edge portions 24 of the bottom plate 26 are also extended in the Z direction or substantially perpendicular direction to the XY plane to form a pair of vertical side plates (two second housing portions) 30.

  In the embodiment, one lateral side plate 28a is higher in height (dimension in the Z direction) than the other lateral side plate 28b. In accordance with this, the height of the pair of vertical side plates 30 is gradually decreased from one horizontal side plate 28a toward the other horizontal side plate 28b. As a result, the light guide portion accommodating space 32 having a substantially rectangular shape and a substantially trapezoidal cross section in the Y direction is enclosed inside the bottom plate 26, the pair of lateral side plates 28, and the pair of longitudinal side plates 30. Is formed.

  As a feature of the present invention, the lower housing 18 further includes a heat radiating housing portion formed of a heat radiating plate 34. As shown in FIGS. 4 and 5, the heat radiating plate 34 extends from the upper end of the lateral side plate 28a to the back of the bottom plate 26 via the back of the lateral side plate 28a, and is roughly the outer surface of the lateral side plate 28a. And the first heat radiating plate portion (heat radiating housing portion) 38 facing each other with a predetermined gap (gap 36) and the outer surface of the bottom plate 26 extending in parallel or substantially in parallel with a predetermined gap (gap 40). A second heat radiating plate portion (heat radiating housing portion) 42 is provided. In the embodiment, the first heat radiating plate portion 38 is formed with a plurality of openings 44 at predetermined intervals. As shown in FIG. 5, a plurality of openings 46 are also formed in the second heat radiating plate portion 42 at a predetermined interval. In the embodiment, the second heat radiating plate portion 42 has substantially the same size as the bottom plate 26 (dimensions in the X and Y directions) and faces almost the entire bottom plate 26. Further, a gap holding portion 48 extending toward the bottom plate 26 is formed by cutting and raising a part of both end portions of the second heat radiating plate portion 42 in the vicinity of the lateral side plate 28b. The heat radiation space 50 having a certain size is stably formed in the gap 40 between the two heat radiation plate portions 42.

  Returning to FIG. 2, the light guide unit 14 includes a plurality of optical members. In the embodiment, the plurality of optical members constituting the light guide unit 14 include a reflection plate (reflection sheet) 52, a light guide plate 54, a diffusion plate (diffusion sheet) 56, and a prism sheet 58 in order from the lower housing 18 side. . Here, the light guide plate 54 has a size and shape that substantially match the size and shape of the light guide housing space 32, and gradually increases in thickness from one end side (left side in the figure) to the other end side (right side in the figure). Is thin. As the reflecting plate 52, the diffusing plate 56, and the prism sheet 58, a conventionally provided reflecting plate, diffusing plate, and prism sheet are used. Thus, the light guide part 14 comprised from a member is laminated | stacked as shown in figure, and is accommodated in the light guide part accommodation space 32 in the state which made the one end side end surface of the light guide plate 54 oppose the horizontal direction side board 28a.

  As shown in FIG. 3, a light source device 60 is provided on the inner surface of the lateral side plate 28 a adjacent to the light guide member accommodation space 32. The light source device 60 includes a strip-shaped flexible wiring board (FPC) 62 disposed along the inner surface of the lateral side plate 28a. The flexible wiring board 62 is bonded to the lateral side plate 28a using, for example, a double-sided adhesive tape 64. The flexible wiring board 62 is arranged on the flexible wiring board 62 at equal intervals, and is a light emitting diode (LED) that is a plurality of light sources electrically connected to power supply wirings (not shown) provided on the flexible wiring board 62. LED) 66 is supported. The flexible wiring board 62 also includes a lead portion 68 having a wiring electrically connected to the above-described power supply wiring. In the present embodiment, the lead portion 68 is an opening formed at a corner of the bottom plate 26 or It is led out through the slot 70.

  Returning to FIG. 2, the upper housing 20 has a square-shaped top plate 72 having a plane size slightly larger than the plane size (X and Y direction sizes) of the lower housing 18, and light is emitted inside the top plate 72. Opening 74 is formed. The four edges (two lateral edges 76 and two longitudinal edges 78) of the top plate 72 are respectively extended downward (Z direction) in the figure to form four side plates (two lateral side plates 80 and 80). Two longitudinal side plates 82) are formed. Therefore, as shown in FIG. 1, when the upper housing 20 is mounted on the lower housing 18 containing the light guide portion 14 as described above, the light emitting surface 12 is formed inside the square-shaped top plate 72. To do. In order to stably hold the upper housing 20 with respect to the lower housing 18, a plurality of inward convex portions 84 or concave portions are formed on the side plates 80 and 82 of the upper housing 20 with an appropriate interval therebetween. The side plates 28 and 30 of the housing 18 are formed with corresponding engaging portions (for example, convex portions or concave portions 86), and the upper housing 20 and the convex portions of the lower housing 18 are mounted with the upper housing 20 mounted on the lower housing 18. You may make it engage a recessed part or a convex part, and a convex part.

  According to the surface light source device 10 </ b> A configured as described above, the light emitted from the light emitting diode 66 enters the light guide plate 54 from the end surface 88 (see FIG. 2) on one end side of the light guide plate 54. The light incident on the light guide plate 54 travels toward the other end while being repeatedly reflected on the upper and lower surfaces of the light guide plate and is emitted from the upper surface of the light guide plate 54. The light emitted from the lower surface of the light guide plate 54 is reflected by the reflecting plate 52 and incident on the light guide plate 54 again, and finally exits from the upper surface of the light guide plate 54. The light emitted from the upper surface of the light guide plate 54 passes through the diffusion plate 56 and the prism sheet 58, is emitted to the outside through the upper light emitting opening 74, and is disposed on the surface light source device 10A. (Not shown).

  Most of the heat generated in the light emitting diode 66 is transmitted to the lower housing lateral side plate 28 a located behind the light emitting diode 66. In the present invention, the lateral side plate 28a is integrally formed with not only the bottom plate 26 of the lower housing 18 but also the heat radiating plate 34 extending from the lateral side plate 28a, so that the heat transmitted to the lateral side plate 28a. Part of the heat is transmitted to the bottom plate 26, and the remaining part of the heat is transmitted from the first heat radiating plate portion 38 of the heat radiating plate 34 to the second heat radiating plate portion 42. Further, the heat transferred to the bottom plate 26 and the heat radiating plate 34 is released to the heat radiating space 50 and the surrounding atmosphere (heat radiating space) 90 behind the heat radiating plate 34 in direct contact with them. The heat of the heat dissipation space 50 between the bottom plate 26 and the heat dissipation plate 34 is released to the surrounding atmosphere 90 through the outer peripheral portion of the heat dissipation space 50 or the plurality of openings 46 formed in the heat dissipation plate 34. Therefore, the heat of the light emitting diode 66 can be efficiently released to the surrounding atmosphere 90 as compared with the case where heat is simply radiated through the bottom plate 26. Thereby, the temperature rise of the light emitting diode 66 can be suppressed. As a result, it is possible to supply a large amount of drive current to the light emitting diodes 66, increase the amount of light emitted from each light emitting diode 66, and obtain a high-luminance surface emitting source.

Thermal characteristics analysis

  The heat radiation characteristics of the surface light source device (Example 1) having the lower housing 18 provided with the heat sink 34 and the surface light source device (Comparative Example 1) obtained by removing the heat sink from the surface light source device were analyzed.

FIG. 6 is a diagram modeling heat dissipation characteristics of the surface light source device according to Comparative Example 1. Specifically, in modeling, the surface light source device was examined for the width (10 mm) of one LED in the lateral direction (X direction), and heat balance was assumed between adjacent LEDs. The surface light source device was divided into 10 parts every 10 mm in the horizontal direction (Y direction), and thermal resistance was considered individually for each divided part. Specifically, FIG. 6 (a) shows the thermal resistance of each thermal resistance part from the LED to the end of the bottom plate, and FIG. 6 (b) is a simplified version of the model diagram of FIG. 6 (a). In the figure, the meaning of each symbol is shown in Table 1 below, and the material, size, thermal resistance, and thermal conductivity of each thermal resistance portion are shown in FIG. 7 (FIGS. 7A and 7B). In FIG. 6, the numerical value given below the symbol of each thermal resistance portion is the thermal resistance (K / W).

  As is clear from FIG. 6 (particularly FIG. 6A), the heat dissipation from the bottom plate to the ambient atmosphere is largely related to the heat dissipation from the LED to the ambient atmosphere. In order to improve the heat dissipation of the bottom plate, for example, there are methods such as increasing the heat transfer coefficient and expanding the surface area. However, in the case of adopting the former method (improvement of heat transfer coefficient), it is conceivable to forcibly convection the ambient atmosphere using a fan, but this is not practical in terms of cost. Further, since the surface area of the bottom plate is determined by the size of the surface light source device, it is very difficult to enlarge the bottom plate.

モデル化の手法は上述した比較例１と同一で、放熱板についても、面光源装置を横方向（Ｘ方向）に関してＬＥＤ１個分の幅（１０ｍｍ）を検討の対象とし、隣接するＬＥＤの間では熱バランスがとれているものとした。具体的に、図８（ａ）はＬＥＤから底板と放熱板の末端までの各熱抵抗部の熱抵抗を示し、図８（ｂ）は図８（ａ）のモデル図をより簡略化したもので、図６に追加した部分（図の下のモデル図部分）が放熱板の熱抵抗を示している。また、放熱特性の計算を簡略化するため、放熱板における第１の放熱板部の放熱は無視した。さらに、底板と放熱板との間の空気の温度は周辺雰囲気の温度と同じとした。さらにまた、放熱板部の両面と底板の熱伝達率は同一とした。 FIG. 8 is a diagram modeling the heat dissipation characteristics of the surface light source device according to Example 1 described above. In FIG. 8, the meanings of the respective symbols relating to the heat sink are shown in the following Table 2 (however, the portions overlapping those in FIG. 6 are omitted).

The modeling method is the same as in Comparative Example 1 described above, and for the heat radiating plate, the width of the surface light source device in the horizontal direction (X direction) (10 mm) is considered, and between adjacent LEDs It was assumed that heat balance was achieved. Specifically, FIG. 8 (a) shows the thermal resistance of each thermal resistance part from the LED to the bottom plate and the end of the heat sink, and FIG. 8 (b) is a simplified version of the model of FIG. 8 (a). Thus, the part added to FIG. 6 (model part below the figure) shows the thermal resistance of the heat sink. Further, in order to simplify the calculation of the heat dissipation characteristics, the heat dissipation of the first heat dissipation plate portion in the heat dissipation plate was ignored. Furthermore, the temperature of the air between the bottom plate and the heat radiating plate was the same as the temperature of the surrounding atmosphere. Furthermore, the heat transfer coefficient of both surfaces of the heat radiating plate portion and the bottom plate is the same.

  As apparent from the comparison of the combined thermal resistance in FIG. 8 (FIG. 8A) and FIG. 6 (FIG. 6A) showing the thermal resistance calculated for the surface light source devices of Example 1 and Comparative Example 1. In Comparative Example 1, the thermal resistance from the bottom plate to the surrounding atmosphere is 144 (K / W), whereas in Example 1, the thermal resistance from the bottom plate and the heat sink to the surrounding atmosphere is 53 (K / W). It decreased to about one third. As a result, the thermal resistance Rja from the LED to the surrounding atmosphere is 208 (K / W) in the case of the comparative example 1, whereas it is reduced to about 1/2 by 117 in the example 1 (K / W). did.

FIG. 9 shows the calculation result of the junction temperature Tj when current is passed through the LEDs of Example 1 and Comparative Example 1. Figure 10 shows the conditions used for the calculation (current value, ambient temperature, thermal resistance, forward voltage)
Indicates. As shown in the figure, when the maximum value of the junction temperature Tj of the LED is set to 120 ° C., the maximum current is 50 mA in the surface light source device of Comparative Example 1, which is only one third of the rated current 150 mA of the LED. It is very inefficient because no current can flow. On the other hand, in the surface light source device of Example 1, the forward current of the LED can be increased to about 85 mA. As a result, since the current and the luminous intensity of the LED (the luminance of the surface light source device) are in a substantially proportional relationship, the luminance can be improved by about 1.7 times compared to the surface light source device of Comparative Example 1.

  In addition, when the same current is supplied to both, the lifetime of the surface light source device of Example 1 is significantly longer than the lifetime of the surface light source device of Comparative Example 1. Specifically, when the forward current of the LED is 50 mA, the junction temperature can be lowered by about 15 ° C. in the surface light source device of Example 1 compared to the surface light source device of Comparative Example 1. In particular, this is a great advantage in a liquid crystal device for on-vehicle use (for example, a navigation system) having a severe ambient temperature environment.

  Furthermore, in the case of the same junction temperature and the same luminance, the surface light source device of the first embodiment needs a smaller number of LEDs than the surface light source device of the first comparative example in order to ensure the necessary brightness. As described above, since the surface light source device according to the first embodiment can secure 1.7 times the amount of light, for example, 20 expensive LEDs made of ceramic can be reduced from 20 to 12.

  A surface light source device according to Embodiment 2 of the present invention will be described. 11 and 12, in the surface light source device 10B of the second embodiment, a part of the bottom plate 26 of the lower housing 18B is bent twice to form a heat radiating plate 98. Specifically, in the second embodiment, when viewed from the upper side of the figure on the bottom plate portion that is separated from the inner surface of the other lateral side plate 28b away from the vertical side plate 30 and the light emitting diode 66 by a predetermined distance inward. A slit 94 extending in a U-shape as a whole is formed, and a bottom plate portion 96 remaining inside the U-shaped slit 94 is bent twice in the vicinity of one lateral side plate 28a so as to be parallel, almost parallel or non-parallel to the bottom plate 26. A heat radiating plate 98 is formed to extend. Specifically, in the second embodiment, the heat radiating plate 98 includes a first heat radiating plate portion 100 extending at a right angle or substantially orthogonal to the bottom plate 26 in the vicinity of one lateral side plate 28a, and the first heat radiating plate portion 100. The second heat dissipating plate portion 102 extends in parallel or substantially in parallel with the bottom plate 26 at a distance 104 from the bottom edge of the bottom plate 26.

  A heat dissipation characteristic model of the surface light source device 10B according to Example 2 is shown in FIG. 13 (FIGS. 13A and 13B). In particular, as shown in FIG. 13B, in the surface light source device of Example 2, the heat radiation resistance (R-3 = 95 kW) of the bottom plate and the heat sink, and the total heat resistance (R−ja =) from the LED to the bottom plate and the heat sink. 159 KW) is considerably smaller than the heat radiation resistance of Comparative Example 1 (R-3 = 144 KW, R-ja = 208 KW), and it can be seen that the same effect as in Example 1 can be obtained.

  Moreover, since the heat sink of Example 2 can be formed simply by processing the bottom plate in one direction with a press, the manufacturing process of the heat sink is simpler than that of Example 1.

  A surface light source device according to Embodiment 3 of the present invention will be described. 14 and 15, the lower housing 18C of the surface light source device 10C according to the third embodiment extends both ends in the longitudinal direction of the lateral side plate 28a that supports the light emitting diode 66 toward the outside in the X direction. The heat radiating plate 106 that is parallel or non-parallel to the lateral side plate 28a is formed by folding the installation portion. Specifically, in Example 3, the lateral side plate 28a extends outward in the longitudinal direction, and the extended portion is first bent inward by 90 degrees to form the first heat radiating plate portion 108 and further extended. The second heat radiating plate portion 110 is formed by bending the installed portion 90 degrees inward again, and the second heat radiating plate portion 110 is disposed in parallel or substantially parallel to the lateral side plate 28a through the gap 112. . According to the surface light source device of the third embodiment configured as described above, heat can be released to the housing or the like through the heat radiating plate 106 in the immediate vicinity of the light emitting diode 66 that is a heat generation source.

1 is a perspective view of a surface light source device according to Embodiment 1. FIG. The disassembled perspective view of the surface light source device shown in FIG. The perspective view of the lower housing and light source device of the surface light source device shown in FIG. The perspective view which looked at the lower housing of the surface light source device shown in FIG. 1 from the surface. The perspective view which looked at the lower housing of the surface light source device shown in FIG. 1 from back. The thermal resistance model figure of the lower housing in the surface light source device which concerns on the comparative example 1. FIG. The table | surface which shows the characteristic (thermal resistance etc.) of each part which comprises the surface light source device of Example 1 and Comparative Example 1. FIG. FIG. 3 is a thermal resistance model diagram of a lower housing in the surface light source device according to the first embodiment. The graph which shows the relationship of the electric current-junction temperature in Example 1 and Comparative Example 1. FIG. The table | surface which shows the conditions which calculated | required the characteristic of FIG. The perspective view which looked at the lower housing in the surface light source device which concerns on Example 2 from the front. The perspective view which looked at the lower housing in the surface light source device concerning Example 2 from the back. FIG. 9 is a thermal resistance model diagram of the lower housing according to the second embodiment. The perspective view which looked at the lower housing in the surface light source device concerning Example 3 from the surface. The front which looked at the lower housing in the surface light source device which concerns on Example 3 from the back surface.

Explanation of symbols

10A, 10B, 10C: Surface light source device 12: Light exit surface 14: Light guide 16: Housing 18: Lower housing 20: Upper housing 22 (22a, 22b): Horizontal edge 24: Vertical edge 26: Bottom plate 28 ( 28a, 28b): lateral side plate 30: vertical side plate 32: light guide member accommodating space 34: heat sink 36: gap 38: first heat sink 40: gap 42: second heat sink 44, 46: Opening 48: Gap holding part 50: Radiation space 52: Reflecting plate 54: Light guide plate 56: Diffusion plate 58: Prism sheet 60: Light source device 62: Flexible wiring board 64: Double-sided tape 66: Light emitting diode 68: Lead part 70: Slot 72: Top plate 74: Light emitting opening 76: Horizontal edge 78: Vertical edge 80: Horizontal side plate 82: Vertical side plate 84: Convex portion 86: Concave portion 88: End surface 90: Ambient atmosphere 92: Hot plate

Claims (5)

A surface light source device (10A) having a planar light emitting surface (12) extending in a first direction (X direction) and a second direction (Y direction) perpendicular to each other,
A rear housing part (26) opposite the light exit surface (12), a first side housing part (28) extending in the first direction, and two second extending in the second direction. A box-shaped housing (18) having side housing portions (30) of
A light guide (14) disposed between the light exit surface (12) and a rear housing portion (26);
A light source (66) disposed inside at least one of the first and second side housing portions (28, 30) for entering light into the light guide (14);
At least one housing portion of the first and second side housing portions (28, 30) is extended and bent to be positioned outside the at least one housing portion (28 or 30). The first heat dissipating plate (38) facing the at least one housing part via the gap (36) and the outer side of the rear housing part (26) and the second gap (40) A heat radiating housing portion (26) having a second heat radiating plate portion (42) facing the rear housing portion (26) is formed, and the heat radiating housing portion (26) is integrated with the housing (18). A surface light source device that is formed . 2. A surface light source device according to claim 1, wherein said housing (18) and said heat radiation housing part (26) are made of aluminum plates .   3. The surface light source device according to claim 1, wherein the heat radiating housing part (34) includes at least one opening (46) for convection of air in the gap (40).   4. The surface light source device according to claim 1, wherein at least one housing part (28a) in which the heat radiating housing part (34) is extended supports the light source (66).   A liquid crystal display device in which a liquid crystal panel is disposed on the light emitting surface of the surface light source device according to claim 1.

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