LIGHTING DEVICE, DISPLAY DEVICE, AND TELEVISION DEVICE

A backlight device 12 includes LEDs 17, a light guide plate 16, an optical member 15, and heat dissipation members 30. The light guide member 16 includes light entrance surfaces 16b and a light exit surface 16a. The optical member 15 is arranged on the light exit surface 16a of the light guide plate 16. The heat dissipation members 30 are configured to dissipate heat from the LEDs 17. Each heat dissipation member 30 includes a light source mounting portion 31 to which the LEDs 17 are mounted, an extending portion 32, and protrusions 33. The extending portion 32 continues from the light source mounting portion 31 and extends from the light source mounting portion 31 along an opposite surface 16c of the light guide plate 16 from the light exit surface 16a. The protrusions 33 protrude from a surface 32a of the extending portion 32 on the light guide plate 16 side. The protrusions 33 are arranged in an extending direction of the extending portion 32 so as to be parallel to each other such that an area of the protrusions 33 per unit area decreases as a distance from the light source mounting portion 31 increases.

TECHNICAL FIELD

The present invention relates to a lighting device, a display device, and a television device.

BACKGROUND ART

Display components in image display devices, such as television devices, are now being shifted from conventional cathode-ray tube displays to thin display panels, such as liquid crystal panels and plasma display panels. With the thin display panels, the thicknesses of the image display devices can be reduced. A liquid crystal display device such as a liquid crystal television device requires a backlight device as a separately provided lighting device because a liquid crystal panel, which is a display panel, does not emit light itself. The backlight device in such a liquid crystal display device is generally classified into either a direct type or an edge-light type according to a mechanism thereof. It is considered that an edge-light type backlight device is more preferable for further reduction of the thickness of the liquid crystal display device. An example of such a display device is disclosed in Patent Document 1.

Patent Document 1 discloses a lighting device including a light source, a light guide member (a light guide plate), a heat dissipation member (a chassis), and a heat transfer member (a heat dissipation member). The light guide member includes a light entrance surface and a light exit surface that is perpendicular to the light entrance surface. The heat transfer member includes a light source holding portion (a light source mounting portion) and a plate-like portion (an extended portion) which is adjacent to the light source holding portion. The light source holding portion includes a surface that is opposed to the light entrance surface. The plate-like portion includes a surface that is opposed to the light exit surface and a surface that is opposed to the heat dissipation member.

RELATED ART DOCUMENT

Patent Document

Problem to be Solved by the Invention

An optical sheet may be disposed inside the lighting device. Heat is more likely to be transferred from the heat dissipation member to an overlapping portion of the optical sheet which overlaps the extended portion in comparison to a non-overlapping portion thereof which does not overlap the extended portion. If a temperature gap at a border between the overlapping portion and the non-overlapping portion is large, a thermal expansion rate of the optical member may vary at the border. Namely, the thermal expansion rate of the overlapping portion may be significantly larger than the thermal expansion rate of the non-overlapping portion. Wrinkles or a deformation in the optical member may occur due to thermal expansion of the overlapping portion that overlaps the extending portion.

DISCLOSURE OF THE PRESENT INVENTION

A present invention was made in view of the above circumstances. An object of the present invention is to reduce a temperature gap that occurs in the optical member to suppress wrinkles or a deformation in an optical member.

Means for Solving the Problem

A lighting device according to the present invention includes a light source, a light guide plate, an optical sheet, and a heat dissipation member. The light guide plate is arranged opposite the light source. The light guide plate includes a light entrance surface through which light from the light source enters and a light exit surface through which the light exits. The optical sheet is arranged on the light exit surface of the light guide plate. The heat dissipation member is to dissipate heat from the light source. The heat dissipation member includes a light source mounting portion, an extending portion, and protrusions. The light source is mounted to the light source mounting portion. The extending portion is arranged on an opposite side of the light guide plate from the light exit surface. The extending portion continues from the light source mounting portion and extends from the light source mounting portion along an opposite surface of the light guide plate from the light exit surface. Protrusions protrude from a surface of the extending portion on the light guide plate side. The protrusions are arranged in an extending direction of the extending portion so as to be parallel to each other and such that an area of the protrusions per unit area decreases as a distance from the light source mounting portion increases.

In the lighting device, the area of the protrusions per unit area decreases as the distance from the light source mounting portion increases. Therefore, the amount of heat transferred from the heat dissipation member to the light guide plate via the protrusions decreases as the distance from the light source mounting portion increases. In comparison to the configuration that does not include the protrusions, the temperature gap in the optical sheet between the portion that does not overlap the extending portion and the portion that overlaps the extending portion is small. This configuration suppresses wrinkles or deformation of the optical sheet due to thermal expansion of the portion that overlaps the extending portion.

A lighting device according to the present invention includes a light source, a light guide plate, an optical sheet, and a heat dissipation member. The light guide plate is arranged opposite the light source. The light guide plate includes a light entrance surface through which light from the light source enters and a light exit surface through which the light exits. The optical sheet is arranged on the light exit surface of the light guide plate. The heat dissipation member is to dissipate heat from the light source. The heat dissipation member includes a light source mounting portion, an extending portion, and a low thermally conductive portion. The light source is mounted to the light source mounting portion. The extending portion is arranged on an opposite side of the light guide plate from the light exit surface. The extending portion continues from the light source mounting portion along an opposite surface of the light guide plate from the light exit surface such that a thickness of the extending portion increases as a distance from the light source mounting portion increases. The low thermally conductive portion is on a surface of the extending portion. The low thermally conductive portion has thermal conductivity lower than the extending portion. The low thermally conductive portion has a thickness that decreases as a distance from the light source mounting portion increases.

In the lighting device, the thickness of the extending portion decreases as the distance from the light source mounting portion increases and the thickness of the low thermally conductive portion increases as the distance from the light source mounting portion increases. Therefore, the amount of heat transferred from the heat dissipation member to the light guide plate via the extending portion and the low thermally conductive portion decreases as the distance from the light source mounting portion increases. In comparison to the configuration that does not include such an extending portion or a low thermally conductive portion, the temperature gap in the optical sheet between the portion that does not overlap the extending portion and the portion that overlaps the extending portion is small. This configuration suppresses wrinkles or deformation of the optical sheet due to thermal expansion of the portion that overlaps the extending portion.

Preferable embodiments may include the following configurations.

(1) Each of the protrusions may have a dimension that measures in the extending direction of the extending portion. The dimension may decrease as the distance from the light source mounting portion increases. This configuration is preferable for implementing the configuration in which the area of the protrusions per unit area decreases as the distance from the light source mounting portion increases.

(2) The protrusions may be arranged such that an interval between the protrusions increases as the distance from the light source mounting portion increases. This configuration is preferable for implementing the configuration in which the area of the protrusions per unit area decreases as the distance from the light source mounting portion increases.

(3) Each of the protrusions may extend from one end to another in a direction perpendicular to the extending direction of the extending portion. With this configuration, the heat is uniformly transferred from the heat dissipation member to the light guide plate in the direction perpendicular to the extending direction of the extending portion.

(4) The heat dissipation member may be formed such that the light source mounting portion and the extending portion form an L-like cross section. The protrusions are integrally formed with the extending portion. The protrusions extend along a corner defined by the light source mounting portion and the extending portion. According to this configuration, the protrusions are formed at the same time when the light source mounting portion and the extending portion are formed in the extrusion process of the heat dissipation member. Namely, the heat dissipation member can be easily formed.

(5) The protrusions may be made of material having lower thermal conductivity than the extending portion. With this configuration, the amount of heat transferred from the heat dissipation member to the light guide plate via the protrusions further decreases.

(6) The extending portion may include a surface on a light guide plate side configured as a sloped surface that is sloped such that a distance from the opposite surface of the light guide plate from the light exit surface increases as a distance from the light source mounting portion increases. According to this configuration, the amount of heat transferred from the light source mounting portions to the light guide plate via the extending portion gradually decreases as the distances from the light source mounting portions increase.

(7) The extending portion and the low thermally conductive portion may be attached to each other in a flat plate-like form. Because the extending portion and the low thermally conductive portion are in the flat plate-like form, the extending portion and the low thermally conductive portion that are attached to each other can be arranged parallel to the light guide plate. Therefore, the heat dissipation member and the light guide plate are stably fixed together.

(8) The lighting device may further include a chassis arranged on an opposite side from the light exit surface of the light guide plate relative to the light guide plate and the extending portion. The chassis may include a bottom plate portion and a holding portion. An opposite surface of the light guide plate from the light exit surface may be plated on the bottom plate portion. The holding portion may form a step together with the bottom plate. The holding portion may hold the extending portion while being in contact with a surface of the extending portion on a side opposite from the light guide plate. With this configuration, the light guide plate is stably supported by the bottom-plate portion and the heat from the light source is dissipated via the entire area of the chassis by transferring the heat from the extending portion to the holding portion. Namely, this configuration has high heat dissipation capability.

(9) The lighting device may further include a light source board on which light sources each having the same configuration as that of the light source are mounted. The light sources are mounted to the light source mounting portion via the light source board. According to this configuration, the light sources are easily mounted to the heat dissipation member and the heat from the light sources is efficiently transferred to the light source mounting portion.

To solve the problem described earlier, a display device according to the present invention includes the above described lighting device and a display panel configured to display images using light from the light exit surface of the light guide plate included in the lighting device. According to this display device, because the backlight device includes the optical member configured to have less wrinkles and deformation, high display quality of the liquid crystal display device is achieved.

Examples of the display panel include the liquid crystal panel. Such a display device, that is, the liquid crystal display device can be applied to various devices including television devices and displays for personal computers. The liquid crystal display device is especially suitable for large screen applications.

Advantageous Effect of the Invention

According to the present invention, a lighting display device in which wrinkles or a deformation in an optical member is suppressed is provided.

MODE FOR CARRYING OUT THE INVENTION

First Embodiment

A first embodiment will be described with reference to the drawings. A liquid crystal display device10(an example of a display device) will be described. The drawings may include X-axis, Y-axis and Z-axis. The axes in each drawing correspond to the respective axes in other drawings. The Y-axis direction corresponds to a vertical direction and the X-axis direction corresponds to a horizontal direction. An upper side and a lower side are defined based on the vertical direction unless otherwise specified.

As illustrated inFIG. 1, a television device TV includes a liquid crystal display unit LDU, boards PWB, MB, and CTB, a cover CV, and a stand ST. The boards PWB, MB, and CTB are attached to a rear surface (a back surface) of the liquid crystal display unit LDU. The cover CV is attached to the rear surface of the liquid crystal display unit LDU so as to cover the boards PWB, MB, and CTB. The stand ST holds the liquid crystal display unit LDU such that a display surface of the liquid crystal display unit LDU extends in the vertical direction (the Y-axis direction). The liquid crystal display device10according to this embodiment has the same configuration as the above-described television device TV except for at least a component for receiving television signals (e.g. a tuner included in a main board MB). As illustrated inFIG. 2, the liquid crystal display unit LDU has a horizontally-long rectangular overall shape (rectangular and longitudinal). The liquid crystal display unit LDU includes a liquid crystal panel11as a display panel and a backlight device12as a light source. The liquid crystal panel11and the backlight device12are collectively held by a frame13and a chassis14. The frame13and the chassis14are external members that form an external appearance of the liquid crystal display device10. The chassis14in this embodiment is one of the external members and a portion of the backlight device12.

A configuration of the liquid crystal display device10on a rear surface side will be described. As illustrated inFIG. 2, stand fitting members STA are attached to a rear surface of the chassis14that forms the rear external appearance of the liquid crystal display device10. The stand fitting members STA are spaced away from each other in an X-axis direction and extend along the Y-axis direction. Each stand fitting member STA has a channel beam-like cross section that opens to the chassis14. A space is provided between the stand fitting member STA and the chassis14. Support portions STb included in the stand ST are inserted in the respective stand fitting members STA. The space provided in the stand fitting member STA is configured to be a path through which wiring members (e.g. electric wires) which are connected to an LED board18are passed. The LED board18is included in the backlight device12. The stand ST includes abase STa and the support portions STb. The base STa extends parallel to the X-Z plane. The support portions STb stand on the base STa in the Y-axis direction. The cover CV is made of synthetic resin and attached to a part of the rear surface of the chassis14. Specifically, as illustrated inFIG. 2, the cover CV covers a lower half part of the chassis14so as to cross over the stand fitting members STA in the X-axis direction. A component storage space is provided between the cover CV and the chassis14such that the boards PWB, MB, and CTB, which will be described next, are arranged therein.

As illustrated inFIG. 2, the boards PWB, MB, and CTB are a power source board PWB, a main board MB, and a control board CTB. The power source board PWB is a power supply of the liquid crystal display device10, which is configured to supply drive power to the other boards MB and CTB and LEDs17included in the backlight device12. Namely, the power source board PWB is configured as “an LED drive board that drives the LEDs17”. The main board MB includes at least a tuner and an image processor (both of them are not illustrated). The tuner is configured to receive television signals. The image processor performs image processing on the received television signals. The main board MB is configured to output the processed image signals to the control board CTB. If an external image reproducing device, which is not illustrated, is connected to the liquid crystal display device10, image signals from the image reproducing device are input to the main board MB. The image processor included in the main board MB processes the image signals, and the main board MB outputs the processed image signals to the control board CTB. The control board CTB is configured to convert the image signals, which is sent from the main board, to driving signals for liquid crystals and to supply the driving signals to the liquid crystal panel11.

As illustrated inFIG. 3, components of the liquid crystal display unit LDU included in the liquid crystal display device10are arranged in a space provided between the frame13that forms the front external appearance and the chassis14that form the rear external appearance. The components arranged between the frame13and the chassis14include at least the liquid crystal panel11, an optical member15, a light guide plate16, and LED units LU. The liquid crystal panel11, the optical member15, and the light guide plate16are placed on top of one another and held between the frame13on the front side and the chassis14on the rear side. The backlight device12includes the optical member15, the light guide plate16, the LED units LU, and the chassis14. Namely, the backlight device12corresponds to the liquid crystal display unit LDU without the liquid crystal panel11and the frame13. Two LED units LU included in the backlight device12are arranged so as to sandwich the light guide plate16in the short-side direction of the light guide plate16(in the Y-axis direction). Each LED unit LU includes the LEDs17as light sources, the LED board18, and a heat dissipation member (a heat spreader)19. The LEDs17are mounted on the LED board18. The LED board18is attached to the heat dissipation member19. Each component will be described next.

As illustrated inFIG. 3, the liquid crystal panel11has a horizontally-long rectangular shape (rectangular and longitudinal) in a plan view and includes a pair of glass substrates11aand11band liquid crystals. The substrates11aand11bhaving high light transmissivity are bonded together with a predetermined gap therebetween. The liquid crystals are sealed between the substrates11aand11b. On one of the substrates (an array board11b), switching elements (e.g. TFTs), pixel electrodes, and an alignment film are arranged. The switching elements are connected to gate lines and source lines that are arranged perpendicular to each other. The pixel electrodes are connected to the switching elements. On the other one of the substrates (a CF board11a), color filters, a counter electrode, and an alignment film are arranged. The color filters include red (R), green (G), and blue (B) color portions that are arranged in a predetermined arrangement. The liquid crystal panel11is placed on a front side of the optical member15, which will be described later. A rear-side surface of the liquid crystal panel11(an outer-side surface of a polarizing plate on the rear side) is fitted to the optical member15with minimal gaps therebetween. Therefore, dust is less likely to enter between the liquid crystal panel11and the optical member15. The liquid crustal panel11includes a display surface11c. The display surface11cincludes a display area and a non-display area. The display area is an inner area of a screen in which images are displayed. The non-display area is an outer area of the screen around the display area with a frame-like shape. The liquid crystal panel11is connected to the control board CTB via a driver for driving the liquid crystals and flexible boards26. The liquid crustal panel11displays images in the display area of the display surface11cbased on signals sent from the control board CTB. The polarizing plates (not illustrated) are arranged on outer sides of the substrates11aand11b.

As illustrated inFIG. 3, similar to the liquid crystal panel11, the optical member15has a horizontally-long rectangular shape in a plan view and has a size (i.e., a short-side dimension and a long-side dimension) about equal to the liquid crystal panel11. The optical member15is placed on the front side of the light guide plate16(a light exit side), which will be described later, and sandwiched between the light guide plate16and the liquid crystal panel11. The optical member15includes three sheets that are placed on top of one another. Specifically, a diffuser sheet15a, a lens sheet (a prism sheet)15b, and a reflecting type polarizing sheet15care placed on top of one another in this sequence from the rear side (the light guide plate side). The three sheets15a,15b, and15chave the substantially same size in a plan view.

The light guide plate16is made of substantially transparent (high transmissivity) synthetic resin (e.g. acrylic resin or polycarbonate such as PMMA) which has a refractive index sufficiently higher than that of the air. As illustrated inFIG. 3, the light guide plate16has a horizontally-long rectangular shape in a plan view similar to the liquid crystal panel11and the optical member15. A thickness of the light guide plate16is larger than a thickness of the optical member15. A long-side direction and a short-side direction of a main surface of the light guide plate16correspond to the X-axis direction and the Y-axis direction, respectively. A thickness direction of the light guide plate16that is perpendicular to the main surface of the light guide plate16corresponds to the Z-axis direction. The light guide plate16is arranged on the rear side of the optical member15and sandwiched between the optical member15and the chassis14. As illustrated inFIG. 4, at least a short-side dimension of the light guide plate16is larger than those of the liquid crystal panel11and the optical member15. The light guide plate16is arranged such that ends of the short dimension thereof (i.e., ends along a long-side direction of the light guide plate16) protrude over ends of the liquid crystal panel11and the optical member15(so as not to overlap in a plan view). The LED units LU are arranged on sides of the short dimension of the light guide plate16so as to have the light guide plate16between the LED units LU in the Y-axis direction. Rays of light from the LEDs17enter the light guide plate16through the ends of the short dimension of the light guide plate16. The light guide plate16is configured to transmit the light, which is from the LEDs17and enters the light guide plate16through the ends of the short dimension, therethrough and guide toward the optical member15(to the front side).

One of the main surfaces of the light guide plate16facing the front side (a surface opposite the optical member15) is a light exit surface16a. Light exits the light guide plate16through the light exit surface16atoward the optical member15and the liquid crystal panel11. The light guide plate16includes outer peripheral surfaces that are adjacent to the main surfaces of the light guide plate16, and long edge surfaces (at ends of the short dimension) which have elongated shapes along the X-axis direction are opposite the LEDs17(the LED boards18). A predetermined space is provided between each long-side end and the LEDs17(the LED boards18). The long edge surfaces are light entrance surfaces16bthrough each of which light from LEDs17enters. The light entrance surfaces16bare parallel to each other along the X-Z plane (or the main surfaces of the LED boards18) and substantially perpendicular to the light exit surface16a. An arrangement direction of the LEDs17and the light entrance surface16bcorresponds to the Y-axis direction and parallel to the light exit surface16a.

As illustrated inFIGS. 4 and 5, a reflection sheet20is arranged on the rear side of the light guide plate16, i.e., on an opposite surface16cthat is opposite from the light exit surface16a(a surface opposite the chassis14). The reflection sheet20is configured to reflect the light that exits from the opposite surface16cto the rear side toward the front side. The reflection sheet20is arranged to cover an entire area of the opposite surface16c. The reflection sheet20is arranged so as to be sandwiched between the chassis14and the light guide plate16. The reflection sheet20is made of synthetic resin and has a white surface having high light reflectivity. A short-side dimension of the reflection sheet20is larger than that of the light guide plate16. The reflection sheet20is arranged such that ends of the short dimension thereof protrude closer to the LEDs17compared to the light entrance surfaces16bof the light guide plate16. Light that travels at an angle from the LEDs17toward the chassis14is effectively reflected toward the light entrance surfaces16bof the light guide plate16by the protruded portions of the reflection sheet20. At least one of the light exit surface16aand the opposite surface16cof the light guide plate16includes a reflecting portion (not illustrated) or a scattering portion (not illustrated). The reflecting portion reflects light inside the light guide plate16. The scattering portion scatters light inside the light guide plate16. Each of the reflecting portion and the scattering portion is patterned so as to have predetermined in-plane distribution so that the light that exits from the light exit surface16ais controlled to have uniform distribution within the surface.

Next, configurations of each of the LEDs17, the LED board18, and the heat dissipation member30included in each LED unit LU will be described. As illustrated inFIGS. 3 and 4, the LED17included in the LED unit LU has a configuration in which each LED chip fixed on the LED board18is sealed with resin. The LED chip mounted on the board has one main light emission wavelength. Specifically, the LED chip that emits light in a single color of blue is used. The resin that seals the LED chip contains phosphors dispersed therein. The phosphors emit light in a predetermined color when excited by blue light emitted from the LED chip. Thus, overall color of light emitted from the LED17is white. The phosphors may be selected, as appropriate, from yellow phosphors that emit yellow light, green phosphors that emit green light, and red phosphors that emit red light. The phosphors may be used in combination of the above phosphors. The LED17includes a main light-emitting surface that is opposite from a mounting surface mounted to the LED board18(an opposed surface opposite the light entrance surfaces16bof the light guide plate16). Namely, the LED17is a so-called top-surface-emitting type LED.

The heat dissipation member30included in each LED unit LU is made of metal having high thermal conductivity, such as aluminum. The heat dissipation member30is configured to dissipate heat from the LEDs17. As illustrated inFIGS. 6 and 7, the heat dissipation member30includes a light source mounting portion31, an extending portion32, and protrusions33. The LEDs17are mounted on the light source mounting portion31. The extending portion32continues from the light source mounting portion31and extends from the light source mounting portion31along the opposite surface16cof the light guide plate16opposite from the light exit surface16a. The protrusions33protrude from a surface32aof the extending portion32on the light guide plate16side. The protrusions33are arranged in an extending direction in which the extending portion32extends. The heat dissipation member30bends such that the light source mounting portion31and the extending portion32form an L-like shape in a cross section. The heat dissipation member30may be formed by extrusion with the X-axis direction as an extruding direction. Portions of the heat dissipation member30will be described in detail later.

Next, configurations of the frame13and the chassis14that are members to form the exterior appearance and holding members will be described. The frame13and the chassis14are made of metal such as aluminum. In comparison to synthetic resin, the mechanical strength (rigidity) and thermal conductivity are higher. The frame13and the chassis14hold the liquid crystal panel11, the optical member15, and the light guide plate16, which are placed on top of the other, from the front side and the rear side, respectively, while holding the LED units LU corresponding to each other at ends of the short dimension (i.e., on the long edges) therein.

As illustrated inFIG. 3, the frame13has a horizontally-long rectangular frame-like overall shape that surrounds the display area of the display surface11cof the liquid crystal panel11. The frame13includes a panel holding portion13aand the sidewall portion13b. The panel holding portion13ais parallel to the display surface11cof the liquid crystal panel11and holds the liquid crystal panel11from the front side. The sidewall portion13bcontinues from the panel holding portion13aand extends on the light entrance surface12bside of the light guide plate16toward the rear side. The panel holding portion13aand the sidewall portion13bform an L-like shape in a cross section. The panel holding portion13ahas a horizontally-long rectangular frame-like shape that corresponds to an outer edge portion of the liquid crystal panel11(i.e., the non-display area, a frame-like portion). The panel holding portion13aholds a substantially entire area of the outer portion of the liquid crystal panel11from the front side. The long edges of the light guide plate16are located outer in the radial direction than the long edges of the liquid crystal panel11. The panel holding portion13ahas a width that is sufficient to cover not only the outer edge portion of the liquid crystal panel11but also the long edges of the light guide plate16and LED units30from the front side. Similar to the display surface11cof the liquid crystal panel11, a front exterior surface of the panel holding portion13a(an opposed surface from the surface facing the liquid crystal panel11) is viewable from the front side of the liquid crystal display device10. The panel holding portion13aand the display surface11cof the liquid crystal panel11form a front exterior of the liquid crystal display device10. The sidewall portion13bhas a rectangular column-like shape that projects from an outer peripheral portion (specifically, an outer peripheral end portion) of the panel holding portion13ato the rear side. The sidewall portion13bis configured to surround the liquid crystal panel11, the optical member15, the light guide plate16, and the LED units LU held therein for an entire periphery. Furthermore, the sidewall portion13bis configured to surround the chassis14on the rear side for the entire periphery. An outer surface of the sidewall portion13balong the periphery of the liquid crystal display device10is viewable, that is, located at the outer periphery of the liquid crystal display device10. The outer surface forms a top surface, a bottom surface, and side surfaces of the liquid crystal display device10.

The panel holding portion13aincludes screw mounting portions21. Each of the screw mounting portions21is located closer to an interior side than the peripheral wall13bof the panel holding portion13a(a position close to the light guide plate16). Screw members SM are attached to the screw mounting portions21. The screw mounting portion21protrudes from an inner surface of the panel holding portion13ain the Z-axis direction toward the rear side and has an elongated block-like shape that extends along each side of the panel holding portion13a(in the X-axis direction or the Y-axis direction). As illustrated inFIGS. 4 and 5, the screw mounting portion21includes a groove21athat opens to the rear side and for fastening the screw member SM. The chassis14includes insertion holes25that are aligned with the groove31aand through which the screws SM are passed.

As illustrated inFIGS. 4 and 5, a panel holding projection24is integrally formed with the panel holding portion13aat the inner edge portions of the panel holding portion13a. The panel holding projection24projects toward the rear side, that is, toward the liquid crystal panel11. A cushioning member24ais attached to distal end surfaces of the panel holding projections24. The panel holding projection24holds the liquid crystal panel11from the front side via the cushioning member24a. Each of the panel holding projection24and the cushioning member24ahas a frame-like overall shape. The panel holding projection24and the cushioning member24aare arranged along the inner peripheral edge of the panel holding portion13afor the entire periphery. As illustrated inFIGS. 4 and 5, light guide plate holding projections23are integrally formed with the panel holding portion13abetween the panel holding projection24and the screw mounting portion21. The light guide plate holding projections23project on the rear side, that is, toward the light guide plate16. The light guide plate holding projections23press long edge portions of the light guide plate16(peripheral edge portions) from the front side toward the chassis14. The light guide plate holding projection23of one of long-side portions of the frame13includes cutout23aformed in a portion so as to run through the frame13in the short-side direction of the frame13(the Y-axis direction). A source-side flexible circuit board261connected to an end of the liquid crystal panel11is passed through the cutout23a.

As illustrated inFIG. 3, the chassis14has a horizontally-long shallow tray-like overall shape and covers substantially entire areas of the light guide plate16and the LED units LU from the rear side. A rear outer surface of the chassis14(a surface of the chassis14opposite from a surface that faces the light guide plate16and the LED units LU) is viewed from the rear side and forms a back exterior of the liquid crystal display device10. The chassis14includes a bottom-plate portion14aand a pair of holding portions14b. The bottom-plate portion14ahas a horizontally-long rectangular shape similar to the light guide plate16. The holding portions14bprotrude from long edges of the bottom-plate portion14atoward the rear side in a step-like form. The holding portions14bhold the extending portions32of the respective heat dissipation members30. As illustrated inFIG. 4, the bottom-plate portion14ahas a flat plate-like shape to hold the most of the middle portion of the short-edge portions of the light guide plate16(portions of the short-edge portions except for end portions) from the rear side. Namely, the bottom-plate portion14ais a receiving portion for the light guide plate16.

As illustrated inFIG. 4, the holding portions14bare arranged so as to sandwich the bottom-plate portion14afrom sides with respect to the short-edge direction. Each of the holding portions14bis formed recessed toward the rear than the bottom plate14afor holding the extending portion32of the corresponding heat dissipation member30therein. Each holding portion14bincludes a raised portion that projects from the bottom-plate portion toward the rear and a holding bottom-plate portion that is parallel to the bottom-plate portion14a. The extending portion32of the heat dissipation member30included in the LED unit LU is disposed on a plate surface of the holding bottom plate portion of the holding portion14bsuch that the extending portion32and the plate surface are in surface contact.

Next, each of the heat dissipation members30, which is one of main components of this embodiment, will be described. As illustrated inFIG. 6, the light source mounting portion31of the heat dissipation member30has a plate-like shape parallel to a plate surface of the LED board18and the light entrance surface16bof the light guide plate16with a long-side direction, a short-side direction, and a thickness direction aligned with the X-axis direction, the Z-axis direction, and the Y-axis direction, respectively. The LEDs17are mounted to an inner plate surface of the light source mounting portion31, that is, a plate surface opposite the light guide plate16via the LED board18. The light source mounting portion31has a long dimension about equal to the long dimension of the LED board18and the short dimension larger than the short dimension of the LED board18. Ends of the short dimension of the light source mounting portion31project outward over the respective ends of the LED board18in the Z-axis direction. An outer surface of the light source mounting portion31, that is, a surface opposite from the surface on which the LED board18is mounted is opposite the screw mounting portion21of the frame18. Namely, the light source mounting portion31is arranged between the screw mounting portion21of the frame13and the light guide plate16.

As illustrated inFIG. 7, the extending portion32has a rectangular shape in a plan view. The extending portion32has a plate-like shape parallel to the plate surfaces of the light guide plate16and the chassis14with a long-side direction, a short-side direction, and a thickness direction thereof aligned with the X-axis direction, the Z-axis direction, and the Y-axis direction, respectively. As illustrated inFIG. 6, the extending portion32extends inward from an end of the light source mounting portion31on the rear side, that is, an end closer to the chassis14, that is, extends on the light guide plate16side along the Y-axis direction. A distal end of the extending portion32is located behind the light guide plate16and the reflection sheet20. Namely, the extending portion32is sandwiched between the reflection sheet20and the chassis14. A length of the extending portion32that measures in a direction in which the extending portion32extends is defined based on heat dissipation capability of the heat dissipation member30. The extending portion32extends in an area that overlaps the optical member14in a plan view. A rear plate surface of the extending portion32, that is, a surface32bopposite the chassis14is in surface contact with the plate surface of the chassis14(a holding bottom surface) for an entire area thereof. Protrusions33are formed on a front plate surface of the extending portion32, that is, a surface32aopposite the light guide plate (or the reflection sheet20).

As illustrated inFIG. 6, the protrusions33protrude from the surface32aof the extending portion32on the rear side in a form of ribs. The protrusions33are integrally formed with the extending portion32. The protrusions33extend along a corner30adefined by the light source mounting portion31and the extending portion32that form an L-like cross section. As illustrated inFIG. 7, each of the protrusions33has a rectangular column-like shape that extends from one edge to the other in a direction perpendicular to the extending direction of the extending portion32(the X-axis direction). As illustrated inFIG. 6, the surface32aof the protrusion33on the light guide plate16side is in surface contact with the reflection sheet20. Heat is transferred from the surface33aon the light guide plate16side to the light guide plate16via the reflection sheet20. Groove-like recesses34are formed between the adjacent protrusions33,33, respectively. Each of the recesses34is defined by opposed side surfaces of the adjacent protrusions33,33and the surfaces32aof the extending portion32on the light guide plate16side. An inside of each recess34is an air space. The thermal conductivity of the heat dissipation member30is lower in the recess34than at the protrusion33.

As illustrated inFIG. 6, the protrusions33are arranged parallel to each other in the extending direction of the extending portion32(the Y-axis direction). Namely, in a plan view of the extending portion32, the protrusions33and the surfaces32aof the extending portion32on the light guide plate side (in the recesses34) are arranged in a strip pattern. The protrusions33are configured such that an area of the protrusions per unit area decreases as a distance from the light source mounting portion31increases. The area of the protrusions33per unit area is a sum of the areas of the protrusions33that are formed within a predetermined region when the heat dissipation member30and the extending portion32are viewed in plan. Namely, a percentage of a dimension of the protrusions relative to a dimension of the recesses34per unit length in the extending direction of the extending portion32decreases as a distance from the light source mounting portion31increases. The protrusions33are configured such that the dimensions in the extending direction of the extending portion33(the Y-axis direction) decrease as the distance from the light source mounting portion31increases. The protrusions33are further configured such that an interval therebetween in the extending direction increases as the distance from the light source mounting portion31increases. Dimensions of the protrusions33in a direction in which they protrude (dimensions that measure in the Z-axis direction) are equal. The surfaces33aon the light guide plate16side are on the same plane. According to such a configuration, the light guide plate16is stably supported by the protrusions33.

Next, functions of this embodiment will be described. When the liquid crystal display device10is turned on, power is supplied from the power source board PWB to the control board CTB and signal are transmitted to the liquid crystal panel11via the printed circuit board27and the flexible circuit boards26. As a result, driving of the liquid crystal panel11is controlled and the LEDs17in the backlight device12are turned on. Rays of light from the LEDs17are guided by the light guide plate16and passed through the optical member15. As a result, the light from the LEDs17is converted to even planar light. The liquid crystal panel11is illuminated with the planar light and predetermined images are displayed on the liquid crystal panel11. Functions of the backlight device12will be described in detail. After the LEDs17are turned on, rays of light emitted by the LEDs17enter the light entrance surface16bof the light guide plate16as illustrated inFIG. 4. In a transmission process of the rays of light that enter the light entrance surface16band may be totally reflected off an interface between the light guide plate16and an air space outside the light guide plate16or reflected by the reflection sheet20, the rays of light may be reflected by a reflection portion or scattered by a scattering portion. Then, the rays of light exit through the light exit surface16and the optical member15is irradiates with the rays of light. The reflection portion and the scattering portion are not illustrated.

After the liquid crystal display device10is turned on and the LEDs17are turned on, heat is produced by the LEDs17. The heat produced by the LEDs17is transferred to the light source mounting portions31of the heat dissipation member30via the LED boards18. The heat is transferred from the light source mounting portion31to the extending portions32and then from the rear surfaces32bof the extending portions32to the chassis14(the holding portions14b). The heat is dissipated to an air space behind the back surface of the chassis14. Part of heat transferred to the extending portions32is transferred to the protrusions33and from the surfaces33aon the light guide plate16side to the light guide plate16via the reflection sheet20. The optical member15is disposed on the light exit surface16aof the light guide plate16and thus the heat transferred to the light guide plate16is further transferred to the optical member15.

A solid line curve inFIG. 8illustrates temperatures of the optical member15measured at points specific distances from the light source mounting portion31. The X axis indicates a distance from the light source mounting portion31and the Y axis indicates a temperature of the optical member15. As illustrated inFIG. 3and as described earlier, heat is transferred to a portion of the optical member15which overlaps the extending portion32indicated below the X axis and a lower amount of heat is transferred from the heat dissipation member30to a portion of the optical member15which does not overlap the extending portion32than the portion that overlaps the extending portion32. Therefore, a temperature gap occurs at the boundary between the portion that overlaps the extending portion32and the portion that does not overlap the extending portion32.

A dotted line curve inFIG. 8illustrates temperatures of an optical member (or an optical sheet) in a configuration in which a heat dissipation member that does not include protrusions measured at points specific distances from a light source mounting portion. In the configuration that does not include the protrusions, surfaces of plate-like shaped extending portions on the light guide plate side is in surface contact with a reflection sheet. Therefore, temperatures in a portion that overlaps the extending portion are substantially constant. In this embodiment, the area of the surfaces32aof the projections33in contact with the reflection sheet20decrease as the distance from the light source mounting portion31increases. The temperature in the portion that overlaps the extending portion32decreases as the distance from the light source mounting portion31increases. In a condition that the amount of heat transferred from the heat dissipation member to the optical member in this embodiment (illustrated with the solid line curve) is equal to that in the configuration that does not include the protrusions (illustrated with the dashed line curve), the curves are compared. In this embodiment, the temperature of the optical member15is high in the area closer to the light source mounting portion31in comparison to the configuration that does not include the protrusions. The temperature is low at the boundary between the portion that overlaps the light source mounting portion31and the portion that does not overlap the light source mounting portion31in comparison to the configuration that does not include the protrusions. In comparison to the configuration in which the heat dissipation member does not include the protrusions, a temperature gap between the portion that overlaps the extending portion and the portion that does not overlap the extending portion is small.

The backlight device according to this embodiment includes the LEDs17, the light guide plate16, the optical member15, and the heat dissipation members30. The light guide plate16includes the light entrance surfaces16bthat are opposite the LEDs17and through which light from the LEDs17enters. The light guide plate16includes the light exit surface16athrough which the light exits. The optical member15is arranged on the light exit surface16aside of the light guide plate16. The heat dissipation members30are configured to dissipate the heat from the LEDs17. Each heat dissipation member30includes the light source mounting portion31, the extending portion32, and the protrusions33. The LEDs17are mounted to the light source mounting portion31. The extending portion32is arranged on the opposite side of the light guide plate16from the light exit surface16a. The extending portion32continues from the light source mounting portion31and extends from the light source mounting portion31along the opposite surface16cof the light guide plate16from the light exit surface16a. The protrusions33protrude from the surface32aof the extending portions32on the light guide plate16side. The protrusions33are arranged parallel to each other in the extending direction of the extending portions32. The area of the protrusions33per unit area decreases as the distance from the corresponding light source mounting portion31increases.

In the backlight device12, the area of the protrusions33per unit area decreases as the distance from the corresponding light source mounting portion31increases. Therefore, the amount of heat transferred from the heat dissipation member30to the light guide plate16via the protrusions33decreases as the distance from the light source mounting portion31increases. In comparison to the configuration that does not include the protrusions, the temperature gap at the boundary between the portion that does not overlap the extending portion32and the portion that overlaps the extending portion32can be reduced. This configuration suppresses wrinkles or deformation of the optical member15due to thermal expansion of the portion that overlaps the extending portion32.

In this embodiment, the dimensions of the protrusions33that measure in the extending portion (the Y-axis direction) decrease as the distance from the light source mounting portion31increases. This configuration is preferable for implementing the configuration in which the area of the protrusions33per unit area decreases as the distance from the light source mounting portion31increases.

In this embodiment, the interval between the protrusions33in the extending direction (the Y-axis direction) increases as the distance from the light source mounting portion31increases. This configuration is preferable for implementing the configuration in which the area of the protrusions33per unit area decreases as the distance from the light source mounting portion31increases.

In this embodiment, each protrusion33extends in the direction perpendicular to the extending direction of the extending portion (the X-axis direction) from one edge to the other. With this configuration, the heat is uniformly transferred from the heat dissipation members30to the light guide plate16in the direction perpendicular to the extending direction of the extending portions32.

In this embodiment, each heat dissipation member30has the L-like cross section formed by the light source mounting portion31and the extending portion32. The protrusions33are integrally formed with the extending portion32. The protrusions33extend along the corner30adefined by the light source mounting portion31and the extending portion32. According to this configuration, the protrusions33are formed at the same time when the light source mounting portion31and the extending portion32are formed in the extrusion process of the heat dissipation member30. Namely, the heat dissipation member30can be easily formed.

This embodiment further includes the chassis14arranged on the opposite side of the light guide plate16from the light exit surface16arelative to the light guide plate16and the extending portions32. The chassis14includes the bottom-plate portion14aand the holding portions14b. The surface16cof the light guide plate16opposite from the light exit surface16ais placed on the bottom-plate portion14a. The holding portions14bform steps together with the bottom-plate portion14aand hold the respective extending portions32while being in surface contact with the surfaces32baway from the light guide plate16. With this configuration, the light guide plate16is stably supported by the bottom-plate portion14aand the heat from the LEDs17is dissipated via the entire area of the chassis14by transferring the heat from the extending portions32to the holding portions14b. Namely, this configuration has high heat dissipation capability.

This embodiment further includes the LED boards18on which the LEDs17are mounted. The LEDs17are mounted to the light source mounting portions via the LED boards18. According to this configuration, the LEDs17are easily mounted to the heat dissipation members30and the heat from the LEDs17is efficiently transferred to the light source mounting portions31.

The liquid crystal display device10according to this embodiment includes the backlight device12and the liquid crystal panel11configured to display images using the light from the light exit surface16aof the light guide plate16included in the backlight device12. According to the liquid crystal display device10, because the backlight device12includes the optical member15configured to have less wrinkles and deformation, high display quality of the liquid crystal display device10is achieved.

This embodiment includes the liquid crystal panel11as a display panel. Such a display device, that is, the liquid crystal display device10can be applied to various devices including television devices and displays for personal computers. The liquid crystal display device10is especially suitable for large screen applications.

First Modification of the First Embodiment

A first modification of the first embodiment will be described with reference toFIG. 9. This modification includes protrusions33-1arranged at different intervals from those of the protrusions33.

A dimension of the protrusion33-1which measures in an extending direction of extending portions32-1(the Y-axis direction) decreases as a distance from the light source mounting portions31increases. The protrusions33-1are arranged at an equal interval. Therefore, a heat dissipation configuration of heat dissipation members30-1is easily designed through alteration of the dimensions of the protrusion33-1in the extending direction.

Second Modification of the First Embodiment

A second modification of the first embodiment will be described with reference toFIG. 10. This modification includes protrusions33-2having a different dimension that measures in the extending direction of the extending portions32from that of the protrusions33.

The dimensions of the protrusions33-2in an extending direction of extending portions32-2(the Y-axis direction) are equal. The interval between the protrusions33-2in the extending direction increases as a distance from the light source mounting portions31increases. Therefore, a heat dissipation configuration of heat dissipation members30-2is easily designed through alteration of the interval between the protrusions33-2in the extending direction.

Second Embodiment

A second embodiment will be described with reference toFIG. 11. The second embodiment includes heat dissipation members130that include protrusions133having thermal conductivity lower than the extending portions32. This configuration is different from the first embodiment. Other configurations are the same as the first embodiment. Similar configurations, operations, and effects to the first embodiment will not be described.

The protrusions133are made of synthetic resin such as expandable polycarbonate and PET, that is, the protrusions133have lower thermal conductivity than the extending portions that are made of metal. Each of the protrusions133is a rectangular column-like member. Each protrusion133is mounted to the extending portion32such that one of side surfaces thereof is in contact with the surface32aof the extending portions32on the light guide plate16side. Examples of method of mounting the protrusions133to the extending portions32include mounting of the protrusions133to the extending portions32via adhesive layers and fitting of a projection formed on a surface of each protrusion133in a recess formed in the surface32aof the corresponding extending portion32on the light guide plate16side.

The protrusions133of a backlight device112according to this embodiment are members having lower thermal conductivity than the extending portions32. With this configuration, the amount of heat transferred from each heat dissipation member130to the light guide plate16via the protrusions133further decreases.

Third Embodiment

A third embodiment will be described with reference toFIG. 12. The third embodiment includes extending portions232having a different configuration from the first embodiment and heat dissipation members230include low thermally conductive portions236, which is different from the first embodiment. Similar configurations, operations, and effects to the first embodiment will not be described.

Each heat dissipation member230in an LED unit LU includes a metal component having high thermal conductivity such as aluminum and a component having lower thermal conductivity than the metal component. The heat dissipation member230is configured to dissipate heat from the LEDs17to the backside. The heat dissipation member230includes a light source mounting portion31, an extending portion232, and a low thermally conductive portion236. The LEDs17are mounted to the light source mounting portion31. The extending portion232extends from the light source mounting portion31along an opposite surface of the light guide plate16from the light exit surface16a. The low thermally conductive portion236having the thermal conductivity lower than the extending portion is disposed on the surface32aof the extending portion232on the light guide plate16side.

Each extending portion has a plate-like shape parallel to the plate surfaces of the light guide plate16and the chassis14. A long-side direction, a short-side direction, and a thickness direction of the extending portion232correspond to the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. The extending portion232is configured such that the thickness decreases as a distance from the light source mounting portion31increases. A surface32aof the extending portion232on the front side, that is, opposite the light guide plate16(or the reflection sheet20) is a sloped surface238that is sloped such that a distance from the opposite surface16cof the light guide plate16from the light exit surface16aincreases as a distance from the light source mounting portion31increases.

Each low thermally conductive portion236is configured such that the thickness increases as a distance from the light source mounting portion31increases. The thickness of the low thermally conductive portion236increases as the thickness of the extending portion232decreases so as to complement the thickness of the extending portion232. The extending portion232and the low thermally conductive portion232are attached to each other in a flat plate-like form. Examples of method of attaching the low thermally conductive portion232to the extending portion232include attaching of the low thermally conductive portion232to the extending portion232via adhesive layers and fitting of a projection formed on a surface of the low thermally conductive portion232on the extending portion232side in a recess formed in the surface32aof the extending portion232on the light guide plate16side.

The backlight device212according to this embodiment includes the LEDs17, the light guide plate16, the optical member15, and the heat dissipation members230. The light guide plate16includes the light entrance surfaces16band the light exit surface16a. The light entrance surfaces16bare opposite the LEDs17. Rays of light from the LEDs17enter through the light entrance surfaces16band exit through the light exit surface16a. The optical member15is arranged on the light exit surface16aof the light guide plate16. The heat dissipation members230are configured to dissipate heat from the LEDs17. Each heat dissipation member230includes the light source mounting portion31, the extending portion232, and the low thermally conductive portion236. The LEDs17are mounted to the light source mounting portion31. The extending portion232is arranged on the opposite side of the light guide plate16from the light exit surface16a. The extending portion232continues from the light source mounting portion31and extends from the light source mounting portion31along the opposite surface16cof the light guide plate16from the light exit surface16a. The thickness of the extending portion232decreases as the distance from the light source mounting portion31increases. The low thermally conductive portion236is arranged on the surface32aof the extending portion232. The low thermally conductive portion236has lower thermal conductivity than the extending portion232. The thickness of the low thermally conductive portion236increases as the distance from the light source mounting portion31increases.

In the backlight device212, each extending portion232is configured such that the thickness thereof decreases as the distance from the light source mounting portion31increases. Furthermore, each low thermally conductive portion236is configured such that the thickness thereof increases as the distance from the light source mounting portion31increases. Therefore, the amount of heat transferred from the heat dissipation members230to the light guide plate16via the extending portions232and the low thermally conductive portions236decreases as the distances from the light source mounting portions31increase. In comparison to a configuration that does not include such portions as the extending portions232and the low thermally conductive portions236, the temperature gap is small. This configuration suppresses wrinkles or deformation of the optical member15due to thermal expansion of the portion that overlaps the extending portion232.

In this embodiment, the surface32aof each extending portion232on the light guide plate16side is the sloped surface238hat is sloped such that a distance from the opposite surface16cof the light guide plate16from the light exit surface16aincreases as a distance from the light source mounting portion31increases. According to this configuration, the amount of heat transferred from the light source mounting portions31to the light guide plate16via the extending portions232gradually decreases as the distance from the light source mounting portion31increases.

In this embodiment, each extending portion232and the corresponding low thermally conductive portion232are attached to each other in a flat plate-like form. Because the extending portion232and the low thermally conductive portion232are in the flat plate-like form, the extending portion232and the low thermally conductive portion236that are attached to each other can be arranged parallel to the light guide plate16. Therefore, the heat dissipation members230and the light guide plate16are stably fixed together.

Other Embodiments

The present invention is not limited to the embodiments described above and illustrated by the drawings. For examples, the following embodiments will be included in the technical scope of the present invention.

(1) In the first and the second embodiments, each protrusion has a rectangular column-like shape. However, the shape and the configuration of the protrusion may be modified as appropriate. For example, protrusions having a block-like shape may be arranged in a line along a direction perpendicular to the extending direction of the extending portion and lines of protrusions may be arranged in the extending direction of the extending portion so as to be parallel to each other. In this case, an area of the protrusions per unit area may be adjusted by altering the number of the protrusions in each line.

(2) The number, the shape, and the arrangement of the protrusions may be altered from those of the first embodiment, the second embodiment, or other embodiment (1) as appropriate.

(3) In the third embodiment, each extending portion includes the surface on the light guide plate side configured as a sloped surface. However, the configuration of the surface on the light guide plate can be altered as appropriate as long as the thickness of the extending portion decreases as the distance from the light source mounting portion increases.

(4) In the above embodiments, the heat dissipation members are arranged on the surface of the chassis on the light guide plate side. However, the heat dissipation members may be arranged on the surface of the chassis opposite from the light guide plate.

(5) The number, the kind, and the arrangement of the optical sheets may be altered from those of the above embodiments as appropriate.

(6) In the above embodiments, the liquid crystal display device including the liquid crystal panel as the display panel is used. However, the aspect of this invention can be applied to display devices including other types of display panels.

(7) In each of the above embodiments, two LED units (or two LED boards) are arranged opposite the respective long edges of the light guide plate. However, a configuration in which two LED units are arranged opposite the respective short edges of the light guide plate is included in the aspect of the present invention.

(8) Other than the above embodiment (7), a configuration in which four LED units (or four LED units) are arranged opposite the respective long edges and the respective short edges of the light guide plate is included in the aspect of the present invention. A configuration in which only one LED unit is arranged opposite the long edge or the short edge of the light guide plate is included in the scope of the present invention. Furthermore, a configuration in which three LED units are arranged opposite any of three edges of the light guide plate, respectively, is included in the aspect of the present invention.

(9) In the above embodiments, one LED unit (or one LED board) is arranged for one edge of the light guide plate. However, two or more LED units may be arranged for one edge of the light guide plate.

(10) In each of the above embodiments, the LEDs are used as light sources. However, other types of light sources including organic ELs may be used.

The embodiments have been described in detail. However, the above embodiments are only some examples and do not limit the scope of the claimed invention. The technical scope of the claimed invention includes various modifications of the above embodiments.

EXPLANATION OF SYMBOLS