Lighting device, display device, and television device

A backlight unit 12 includes a light guide plate 16, first LEDs 17A, second LEDs 17B, first support members 28, and second support members 29. The first LEDs 17A are opposed to a first light entrance surface 16nA that is a first edge surface 16E1 of the light guide plate 16. The second LEDs 17B are opposed to a second light entrance surface 16bB that is a second edge surface 16E2 of the light guide plate 16. The second LEDs 17B are arranged to be away from the second light entrance surface 16bB with a distance B relatively greater than a distance A between the first LEDs 17A and the first light entrance surface 16bA. The first support members 28 are in contact with the first edge surface 16E1 of the light guide plate 16 to support the light guide plate 16 from a first LED 17A side. The second support members 29 are arranged on a same side as the second LEDs 17B with respect to the light guide plate 16 to be away from the light guide plate 16. The second support members 29 are to be in contact with the second edge surface 16E2 according to thermal expansion of the light guide plate 16 to support the light guide plate 16 from a second light source side. The second support members 29 are made of an elastic material softer than a material of the first support members 28.

TECHNICAL FIELD

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

BACKGROUND ART

In recent years, displays in image display devices, such as television devices, are being shifted from conventional cathode-ray tube displays to thin displays, such as liquid crystal displays and plasma displays. With the thin displays, thicknesses of the image display devices can be decreased. Liquid crystal panels do not emit light. Therefore, liquid crystal display devices including liquid crystal panels require backlight devices. The backlight devices are classified broadly into a direct type and an edge-light type based on mechanisms. For further reduction in thicknesses of the liquid crystal display devices, the edge-light type backlight devices are more preferable. A backlight device disclosed in Patent Document 1 is known as an example of the kind.

RELATED ART DOCUMENT

Patent Document

Problem to be Solved by the Invention

In the edge-light type backlight device, as a distance between a light source and a light entrance surface of a light guide plate is decreased, the light entrance efficiency is improved, and as the distance is increased, the light entrance efficiency is lowered. The light guide plate expands due to heat from the lighted light source, and therefore, a space is necessarily provided between the light source and the light entrance surface of the light guide plate so that the light guide plate that is increased in size due to thermal expansion does not contact the light source. This requirement limits the improvement of the entrance efficiency of light emitted from the light source and entering the light guide plate through the light entrance surface.

Disclosure of the Present Invention

The technology disclosed herein was made in view of the above circumstances. An object is to improve light use efficiency.

Means for Solving the Problem

A lighting device according to this invention includes a light guide plate having an edge surface as a light entrance surface and one plate surface as a light exit surface, a first light source, a second light source, a first support member, and a second support member. The first light source is opposed to a first light entrance surface that is a first edge surface of the light guide plate. The second light source is opposed to a second light entrance surface that is a second edge surface of the light guide plate and the second edge surface is opposite to the first edge surface. The second light source is arranged to be away from the second light entrance surface with a distance relatively greater than a distance between the first light source and the first light entrance surface. The first support member is arranged on a same side as the first light source with respect to the light guide plate, and the first support member is in contact with the first edge surface of the light guide plate to support the light guide plate from a first light source side. The second support member is arranged on a same side as the second light source with respect to the light guide plate to be away from the light guide plate. The second support member is to be in contact with the second edge surface according to thermal expansion of the light guide plate to support the light guide plate from a second light source side. The second support member is made of an elastic material softer than a material of the first support member.

According to such a configuration, light emitted from the first light source enters the light guide plate through the first light entrance surface and light emitted from the second light source enters the light guide plate through the second light entrance surface and then, the light entering the light guide plate travels within the light guide plate and exits the light guide plate through the light exit surface. The distance between the first light source and the first light entrance surface of the light guide plate is relatively small and the distance between the second light source and the second light entrance surface of the light guide plate is relatively great. Therefore, the light entrance efficiency of the light emitted from the first light source and entering the light guide plate through the first light entrance surface is relatively high and the light entrance efficiency of the light emitted from the second light source and entering the light guide plate through the second light entrance surface is relatively low. According to the inventor's studies, it is found that if the distance between the respective light sources and the respective light entrance surfaces becomes a certain value or more, the light entrance efficiency of light is less likely to be decreased even if the distance is increased and the light entrance efficiency does not change. Therefore, the light entrance efficiency of the light emitted from the second light source and entering the light guide plate through the second light entrance surface becomes lower than the light entrance efficiency of the light emitted from the first light source and entering the light guide plate through the first light entrance surface. However, the light entrance efficiency of the light emitted from the second light source and entering the light guide plate through the second light entrance surface is not further decreased from the certain value because the light entrance efficiency of light is less likely to be decreased even with the increase of the distance. Therefore, the light entrance efficiency is not decreased from a certain value. The light entrance efficiency of light with the distances between the respective light sources and the respective light entrance surfaces being equal to each other is referred to as a reference value. A plus difference value between the reference value and the light entrance efficiency of light emitted from the first light source and entering the light guide plate through the first light entrance surface (the light entrance efficiency is higher than the reference value) is greater than a minus difference value between the reference value and the light entrance efficiency of light emitted from the second light source and entering the light guide plate through the second light entrance surface (the light entrance efficiency is lower than the reference value). Thus, the light use efficiency as a whole is improved compared to the light use efficiency in the configuration in which the distances between the respective light sources and the respective light entrance surfaces are equal to each other.

The first support member arranged on the same side as the first light source is in contact with the first edge surface so as to support the light guide plate from the first light source side. The first support member that is made of a material harder than the material of the second support member stably support the light guide plate and a support position of the light guide plate is less likely to be changed. Accordingly, the positional relation between the first light source and the first light entrance surface is maintained stably and the distance between the first light source and the first light entrance surface is set to be smallest. Therefore, the light entrance efficiency of light emitted from the first light source and entering the light guide plate through the first light entrance surface is greatly improved.

The second support member is arranged on the same side as the second light source and spaced from the light guide plate. However, the second support member comes in contact with the second edge surface if the light guide plate thermally expands, and the light guide plate is supported from the second light source side. The second support member is made of an elastic material that is softer than the material of the first support member. Therefore, compared to a configuration including the second support member made of a material having same hardness as the material of the first support member, the distance between the second support member and the second edge surface of the light guide plate can be decreased. If the second support member is made of a material having same hardness as the material of the first support member, the second support member is necessary to be arranged to have a sufficient distance including an extra space from the second edge surface of the light guide plate with considering the dimension error that may be caused in the light guide plate. The second support member made of the elastic material that is softer than the material of the first support member elastically deforms when the second edge surface of the light guide plate that thermally expands comes in contact with the second support member. Therefore, even if the light guide plate is greater in size than a standard size due to the dimension error, the error amount can be absorbed by the elastic deformation. Accordingly, the second support member is arranged much closer to the light guide plate and the thermally expanded light guide plate is supported further stably.

The following configurations may be preferably employed as embodiments of the present invention.

(1) The first light source, the light guide plate, and the second light source may be arranged in a vertical direction. The first light source and the first support member may be arranged on a lower side in the vertical direction with respect to the light guide plate. The second light source and the second support member may be arranged on an upper side in the vertical direction with respect to the light guide plate. According to such a configuration, the light guide plate is supported from the lower side in the vertical direction by the first support member having hardness greater than the second support member. Therefore, the first edge surface of the light guide plate is kept in closely contact with the first support member due to the weight of the light guide plate. Accordingly, the positional relation between the first light source and the first light entrance surface is maintained more stable. Thus, the light guide plate is positioned precisely in the vertical direction by the first support member. Therefore, the second support member arranged on the upper side in the vertical direction with respect to the light guide plate is arranged much closer to the light guide plate. Accordingly, the thermally expanded light guide plate is stably supported.

(2) The lighting device may further include a horizontal side second support member arranged to be away from the light guide plate in a horizontal direction that is perpendicular to the vertical direction. The horizontal second support member may be in contact with an edge surface of the light guide plate adjacent to the first edge surface and the second edge surface of the light guide plate according to thermal expansion of the light guide plate along the horizontal direction to support the light guide plate from an outer side in the horizontal direction, and the horizontal side second support member may be made of a material softer than the material of the first support member. According to such a configuration, the light guide plate is supported by the horizontal side second support member from the outer side with respect to the horizontal direction when the light guide plate increases its size in the vertical direction and the horizontal direction according to the thermal expansion thereof. The horizontal side second support member is made of the elastic material that is softer than the material of the first support member. Therefore, the distance between the horizontal side second support member and each of the edge surfaces of the light guide plate is set to be smaller compared to the configuration including the horizontal side second support member made of a material having hardness same as that of the first support member. According to such a configuration, the horizontal side second support member is arranged close to the light guide plate and the thermally expanded light guide plate is supported more stably.

(3) The second support member and the horizontal side second support member may be made of a same elastic material. Accordingly, a material cost for the second support member and the horizontal side second support member is reduced. The elastic coefficient of the second support member and that of the horizontal side second support member are same. Therefore, a distance between the second support member and the corresponding edge surface of the light guide plate and a distance between the horizontal side second support member and the corresponding edge surface of the light guide plate are easily set.

(4) The first support member may be made of a material having plasticity. Accordingly, the light guide plate is supported by the first support member made of the material having plasticity more stably compared to the configuration including the first support member made of an elastic material. Therefore, variations in support position of the light guide plate are less likely to be caused.

(5) The first support member may be made of the material having plasticity that is metal or a thermoplastic resin, and the second support member may be made of rubber. According to such a configuration, the first support member made of the metal or the thermoplastic resin support the light guide plate more stably. The second support member that is made of the rubber become in contact with the second edge surface of the light guide plate and elastically deform if the light guide plate thermally expands. Accordingly, even if a size of the light guide plate becomes greater than a normal size thereof due to the dimension errors, the dimension errors are effectively absorbed by the elastic deformation.

(6) The first edge surface that is the first light entrance surface and the second edge surface that is the second light entrance surface may extend linearly over an entire length of the light guide plate. The light guide plate may be processed to have a step between the first light entrance surface and a portion of the first edge surface that is in contact with the first support member or between the second light entrance surface and the second edge surface that is in contact with the second support member. However, in such a configuration, the light guide plate is necessary to be processed to have the above configuration. In the configuration of the present embodiment, the above processing is not necessary for the light guide plate and therefore, the size precision of the first edge surface and the second edge surface of the light guide plate is improved. The first light entrance surface of the light guide plate is positioned with high precision relative to the first light source by the contact between the first support member and the first edge surface of the light guide plate. Further, the second support member is arranged much closer to the second edge surface of the light guide plate and therefore, the thermally expanded light guide plate is supported more stably.

(7) The first support member may include first support members in a pair that are arranged on two end portions of the light guide plate, respectively, and the second support member may include second support members in a pair that are arranged on two end portions of the light guide plate, respectively. Accordingly, the light guide plate is supported more stably at its edge positions by the first support member and the second support member.

(8) The first light source and the second light source may be same type of parts. Accordingly, a manufacturing cost for the first light source and the second light source is reduced and a cost for parts control is also reduced.

(9) The first light source and the second light source may represent a lambertian light intensity distribution. The first light source and the second light source represent a lambertian light intensity distribution. The light intensity distribution of light from the first light source and the second light source represents the lambertian light intensity distribution. In such a light intensity distribution, the rays of light traveling along the optical axis have a peak light intensity and the light emission intensity tends to decrease with a curved line in the graph as the angle with respect to the optical axis increases. In the lambertian light intensity distribution, the light entrance efficiency of light emitted from the respective light source and being incident on the respective light entrance surface is improved as the distance between the respective light sources and the respective light entrance surfaces of the light guide plate is decreased, and the light entrance efficiency is decreased as the distance is increased. However, if the distance is greater than a certain value, the lowering rate of the light entrance efficiency becomes less likely to be decreased and does not change from a certain value. The distance between the first light entrance surface and the first light source representing the lambertian light intensity distribution is relatively decreased to improve the light entrance efficiency, and the distance between the second light entrance surface and the second light source representing the lambertian light intensity distribution is relatively increased to keep the light entrance efficiency to be the lowest certain value with allowing the size increase of the light guide plate. Accordingly, the whole light use efficiency is improved.

(10) Each of the first light source and the second light source may include LEDs that are mounted on a base board. The LEDs generally represent a lambertian light intensity distribution. In such a light intensity distribution, the rays of light traveling along the optical axis have a peak light intensity and the light emission intensity tends to decrease with a curved line in the graph as the angle with respect to the optical axis increases. In the lambertian light intensity distribution, the light entrance efficiency of light emitted from the light sources including the LEDs and being incident on the respective light entrance surfaces is improved as the distance between the light sources including the LEDs and the respective light entrance surfaces is decreased, and the light entrance efficiency is decreased as the distance is increased. However, if the distance is greater than a certain value, the lowering rate of the light entrance efficiency is less likely to be decreased and does not change from a certain value. The distance between the first light entrance surface and the first light source including the LED representing the lambertian light intensity distribution is relatively decreased to improve the light entrance efficiency, and the distance between the second light entrance surface and the second light source including the LED representing the lambertian light intensity distribution is relatively increased to keep the light entrance efficiency to be the lowest certain value with allowing the size increase of the light guide plate. Accordingly, the whole light use efficiency is improved.

(11) The light guide plate may be rectangular and further include a third light source, a fourth light source, a third support member, and a fourth support member. The third light source may be opposed to a third light entrance surface that is a third edge surface adjacent to the first edge surface and the second edge surface of the light guide plate. The fourth light source may be opposed to a fourth light entrance surface that is a fourth edge surface of the light guide plate opposite to the third edge surface, and the fourth light source may be arranged to be away from the fourth light entrance surface with a distance that is relatively greater than a distance between the third light source and the third light entrance surface. The third support member may be arranged on a same side as the third light source with respect to the light guide plate, and the third support member may be in contact with the third edge surface of the light guide plate to support the light guide plate from a third light source side. The fourth support member may be arranged on a same side as the fourth light source with respect to the light guide plate to be away from the light guide plate. The fourth support member may be in contact with the fourth edge surface according to thermal expansion of the light guide plate to support the light guide plate from a fourth light source side, and the fourth support member may be made of an elastic material softer than a material of the third support member. According to such a configuration, the edge surfaces included in the rectangular light guide plate are the first light entrance surface, the second light entrance surface, the third light entrance surface, and the fourth light entrance surface, respectively. Light from the first light source, the second light source, the third light source, and the fourth light source is incident on the first light entrance surface, the second light entrance surface, the third light entrance surface, and the fourth light entrance surface, respectively. Accordingly, the amount of light entering the light guide plate is sufficiently obtained and such a configuration is effective for increase in size of the backlight unit. The distance between the third light source and the third light entrance surface is relatively decreased so that the light entrance efficiency of light from the third light source is increased. The distance between the fourth light source and the fourth light entrance surface is relatively increased and the light entrance efficiency of light from the fourth light source is not decreased from the lowest value. Accordingly, the whole light use efficiency is further improved.

The third support member that supports the light guide plate from the third light source side is made of a material harder than that of the fourth support member. Therefore, the first support member and the third support member stably support the light guide plate and variations in the support position of the light guide plate are less likely to occur. Accordingly, the position of the third light entrance surface relative to the third light source is stably maintained and therefore, the distance between the third light source and the third light entrance surface is set to be shortest as possible. Therefore, the light entrance efficiency of light emitted from the third light source and being incident on the third light entrance surface is highly improved. Further, the fourth support member that supports the thermally expanded light guide plate from the fourth light source side is made of the elastic material softer than the material of the third support member. Therefore, the distance between the fourth support member and the fourth edge surface of the light guide plate is decreased compared to the configuration in which the fourth support member is made of a material having same hardness as the material of the third support member. Accordingly, the fourth support member is arranged much closer to the light guide plate and the thermally expanded light guide plate is supported more stably.

To resolve the problem described earlier, a display device according to the technology includes the lighting device described above and a display panel configured to provide a display using light from the lighting device.

According to such a display device, the lighting device configured to provide light to the display panel has improved light use efficiency. Therefore, the display device can perform high quality image display with high brightness.

Examples of the display panel include a liquid crystal display panel. The display device may be adapted to various purposes such as television devices and display devices of personal computers. Preferable purposes include large screen display devices.

Advantageous Effect of the Invention

According to the technology, light use efficiency is improved.

MODE FOR CARRYING OUT THE INVENTION

First Embodiment

The first embodiment of this technology will be described with reference toFIGS. 1 to 13. In the following description, a liquid crystal display device10will be described. An X-axis, a Y-axis, and a Z-axis are present in some drawings. The axes in each drawing correspond to the respective axes in other drawings. Without any special notes, the description of upper and lower is made regarding a vertical direction (FIGS. 8 and 10) as a reference. In the following description, the upper side and the lower side inFIG. 4correspond to the front and the rear of the liquid crystal display device, respectively, and the left side and the right side inFIG. 4correspond to the lower side and the upper side in the vertical direction, respectively.

As illustrated inFIG. 1, a television device TV according to this embodiment includes a liquid crystal display unit (a display unit) LDU, boards PWB, MB, and CTB, a cover CV, and a stand ST. The boards PWB, MB, and CTB are attached on a rear surface (a back surface) of the liquid crystal display unit LDU. The cover CV is attached on a rear surface side of the liquid crystal display device10so as to cover the boards PWB, MB, and CTB. The stand ST supports 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 television device TV except for at least a component for receiving television signals (e.g. a tuner included in the main board MB). As illustrated inFIG. 3, the liquid crystal display unit LDU has a landscape rectangular shape (a rectangular shape, a longitudinal shape) as a whole. The liquid crystal display unit LDU includes a liquid crystal panel11as a display panel and a backlight unit (a lighting device)12as an external light source. The liquid crystal display device10includes a frame (a holding portion arranged on the display11cside, one holding portion)13and a chassis (a holding portion on the side opposite to the display11cside, another holding portion)14as exterior members that provide an appearance of the liquid crystal display device10. The frame13and the chassis14hold the liquid crystal panel11and the backlight unit12. In other words, the frame13and the chassis14constitute a holding member. The chassis14according to this embodiment is not only a part of the exterior member or the holding member but also a part of the backlight unit12.

Configuration of the liquid crystal display device10on the rear surface side will be described. As illustrated inFIG. 2, two stand attachments STA are attached to a rear surface of the chassis14. The rear surface of the chassis14provides a rear appearance of the liquid crystal display device10. The stand attachments STA are away from each other in the X-axis direction and extend along the Y-axis direction on the chassis14. Each stand attachment STA has a substantially channel-shaped cross section and is open to the chassis14so as to form a space with the chassis14. Support portions STb of the stand ST are each inserted in the space between the respective stand attachments STA and the chassis14. The stand ST includes a base 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 attachments 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 stored therein.

As illustrated inFIG. 2, the boards PWB, MB, and CTB include a power source board PWB, a main board MB, and a control board CTB. The power source board PWB is a power supply source of the liquid crystal display device10and thus supplies drive power to the other boards MB and CTB and to LEDs17of the backlight unit12. In other words, the power source board PWB also serves as “an LED drive board (a light source driving board, a power source) that drives the LEDs17”. The main board MB includes at least a tuner and an image processor, which 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, which will be described later. 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 are sent from the main board MB, 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 between the frame (a front frame)13, which provides a front appearance, and the chassis (a rear chassis)14, which provides a rear appearance. The main components housed in the space between the frame13and the chassis14at least include the liquid crystal panel11, an optical member15, a light guide plate16, and LED units (light source 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 unit12includes the optical member15, the light guide plate16, the LED units LU, and the chassis14. In other words, the liquid crystal display unit LDU without the liquid crystal panel11and the frame13is the backlight unit12. The LED units LU of the backlight unit12are arranged in the space between the frame13and the chassis14so as to hold the light guide plate16from two edges in the short-side direction (the Y-axis direction, the vertical direction). Two sets of the LED units LU are arranged in the long-side direction (the X-axis direction, the horizontal direction) and a total of four LED units LU are arranged. The LED units LU and the light guide plate16are arranged in the vertical direction (the Y-axis direction). The LED unit LU includes LEDs17as light sources, the LED board (a light source board)18on which the LEDs17are mounted, and a heat dissipation member (heat spreader, alight source mounting member)19to which the LED board18is mounted. Each component will be described next.

As illustrated inFIG. 3, the liquid crystal panel11has a landscape rectangular shape (a rectangular shape, a longitudinal shape) in a plan view, and the liquid crystal panel11includes a pair of glass substrates11aand11band liquid crystals. The substrates11aand11beach having high light transmission properties are bonded together with a predetermined gap therebetween. The liquid crystals are sealed between the substrates11aand11b. One of the substrates11aand11bthat is on the front side is a CF substrate11aand the other one of the substrates11aand11bthat is on the rear side (on the backside) is an array substrate11b. On the array substrate11b, 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 CF substrate11a, 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. Polarizing plates, which are not illustrated, are arranged on outer sides of the substrates11aand11b.

As illustrated inFIGS. 4 and 5, the array substrate11b, which is one of the substrates11aand11bof the liquid crystal panel11, has a larger size in a plan view than the CF substrate11aand is arranged such that ends of the array substrate11bare farther out than respective peripheral portions of the CF substrate11a. Specifically, the array substrate11bis slightly larger than the CF substrates11asuch that the entire peripheral portions of the array board11bare farther out than the peripheral portions of the CF substrate11a. The outer peripheral edge of the array substrate11bincludes a pair of long-side edge portions. In one of long-side edge portions of the array substrate11bthat is close to the control board CTB with respect to the Y-axis direction (in a left-side edge portion inFIG. 4), terminals extended from the gate lines and the source lines are arranged. As illustrated inFIGS. 2 and 4, flexible boards (FPC boards)26where drivers DR for liquid crystal driving are connected to the respective terminals. The flexible boards26are arranged apart from each other in the X-axis direction, i.e., a direction along the long-side end of the array substrate11b. A part of each source flexible board26protrudes outwardly from the long-side end of the array substrate11bin the Y-axis direction. Each of the flexible boards26includes a film-like base made of synthetic resin (for example polyimide resin) that has an insulation property and flexibility. Each flexible board26includes traces (not illustrated) arranged on the base and a driver DR on about a middle of the base. The traces are connected to the driver DR. One end of each flexible board26is pressed and connected to each terminal of the array substrate11bvia an anisotropic conductive film (ACF). Another end of each flexible board26is pressed and connected to each terminal of a printed circuit board27, which will be described later, via another anisotropic conductive film. The printed circuit board27is connected to the control board CTB via a wiring member, which is not illustrated, and thus signals from the control board CTB are transmitted to the source flexible boards26. The liquid crystal panel11thus displays images on the display surface11caccording to the signals from the control board CTB.

As illustrated inFIG. 4andFIG. 5, the liquid crystal panel11is placed on a front side (a light exit side) of the optical member15, which will be described later. A rear surface of the liquid crystal panel11(a rear surface of the polarizing plate) 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 display surface11cof the liquid crystal panel11includes 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 terminals and the flexible board26are arranged in the non-display area.

As illustrated inFIG. 3, the optical member15has a landscape rectangular shape in a plan view like the liquid crystal panel11and has about the same size (a short dimension and a long dimension) as the liquid crystal panel11. The optical member15is placed on the front side (the light exit side) of the light guide plate16, 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. Each sheet of the optical member15may be any one selected from a diffuser sheet, a lens sheet, and a reflecting type polarizing sheet.

The light guide plate16is made of a substantially transparent (high light transmissivity) synthetic resin (e.g. acrylic resin or polycarbonate such as PMMA) which has a refractive index considerably higher than that of the air. As illustrated inFIG. 3, the light guide plate16has a landscape 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 plate 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 plate surface corresponds to the Z-axis direction (an overlapping direction of the liquid crystal panel11and the light guide plate16). The light guide plate16is arranged on the rear side of the optical member15and sandwiched between the optical member15and the chassis14. As illustrated inFIGS. 4 and 5, a short dimension and a long dimension of the light guide plate16are larger than those of the liquid crystal panel11and the optical member15. The light guide plate16is arranged such that four sides of the light guide plate16are farther out than four sides of the liquid crystal panel11and four sides of the optical member15(so as not to overlap each other in a plan view). With this configuration, the light from the LED17can travel proper distance inside the light guide plate16. The ends of the light guide plate16from which the light may unevenly exit compared to the middle section thereof can be located outside the display area of the liquid crystal panel11. The LED units LU are arranged on each side in the short-side direction so as to have the light guide plate16therebetween in the Y-axis direction. The light rays from the LEDs17enter the light guide plate16through the ends of the short dimension of the light guide plate16. The light guide plate16is configured such that light rays, which are from the LEDs17and enter through the ends of the short dimension of the light guide plate16, travel through the light guide plate16and exit toward the optical member15(the front side).

As illustrated inFIG. 4, one of the plate surfaces of the light guide plate16facing the front is a light exit surface16a(a surface facing the optical member15). Light exits the light guide plate16through the light exit surface16atoward the optical member15and the liquid crystal panel11. Peripheral edge surfaces16E1to16E4of the light guide plate16that are adjacent to the plate surfaces of the light guide plate16include elongated long-side edge surfaces (first peripheral edge surface and a second peripheral edge surface)16E1,16E2that extend in the X-axis direction. The long-side edge surfaces16E1,16E2are opposite the LEDs17(the LED boards18) with a predetermined distance therebetween and serves as a pair of light entrance surfaces16bthrough which light from LEDs17enters. The light entrance surface16bis parallel to the X-Z plane (plate surfaces of the LED boards18) and substantially perpendicular to the light exit surface16a. The long-side edge surfaces16E1,16E2that are light entrance surfaces16bhave a linear shape along an entire long side length of the light guide plate16. The light entrance surface16bis a portion included in each of the long-side edge surfaces16E1,16E2of the light guide plate16where light from the LEDs17reaches (an illumination area). Therefore, a portion of each of the long-side edge surfaces16E1,16E2of the light guide plate16where light from the LEDs17does not reach (a non-illumination area) is not included in the light entrance surface16b. According to this embodiment, most of a middle part of each long-side edge surface16E1,16E2of the light guide plate16in the longitudinal direction (the X-axis direction) thereof is the illumination area (the light entrance surface16b) and two end portions of each long-side edge surface in the longitudinal direction are the non-illumination areas. Among the outer peripheral edge surfaces16E1to16E4of the light guide plate16, short-side edge surfaces16E3,16E4that extend along the Y-axis direction and are adjacent to the light entrance surfaces16b(edge surfaces adjacent to the first edge surface and the second edge surface) are LED non-opposed edge surfaces (light source non-opposed edge surfaces) that are not opposed to the LEDs17. The LEDs17and the light entrance surfaces16bare arranged in the Y-axis direction and parallel to the light exit surface16a.

As illustrated inFIGS. 4 and 5, a light guide reflection sheet (a reflection member)20is arranged on a rear side of the light guide plate16, that is, a plate surface16copposite to the light exit surface16a(a surface opposed to the chassis14). Light that travels through the plate surface16ctoward the rear is reflected by the light guide reflection sheet20toward the front. The light guide reflection sheet20is arranged to cover an entire area of the plate surface16c. In other words, the light guide reflection sheet20is arranged between the chassis14and the light guide plate16. The light guide reflection sheet20is made of synthetic resin and has a white surface having high light reflectivity. As illustrated inFIGS. 4 and 5, the light guide reflection sheet20has a short-side dimension and a long-side dimension larger than those of the light guide plate16. The light guide reflection sheet20is arranged such that four sides of the light guide reflection sheet20are farther out than the respective four sides of the light guide plate16. Particularly, as illustrated inFIG. 4, long-side edge portions of the light guide reflection sheet20are farther out than the light entrance surfaces16bof the light guide plate16. Namely, the long-side portions of the light guide reflection sheet20protrude toward the LEDs17, and the protruded portions (the long-side edge portions) of the light guide reflection sheet20effectively reflect light traveling from the LEDs17obliquely toward the chassis14so that the refection light is directed toward the light exit surface16bof the light guide plate16. The plate surface16copposite from the light exit surface16aof the light guide plate16has a light reflection portion22. The light reflection portion22is configured to reflect the light inside the light guide plate16toward the light exit surface16ato accelerate exiting of light through the light exit surface16a(FIG. 10). The light reflection portion22is arranged between the plate surface16copposite to the light exit surface16aof the light guide plate16and the light guide reflection sheet20.

As illustrated inFIG. 10, the light reflection portion22is formed by printing a light reflective material on the plate surface16cof the light guide plate16away from the light exit surface16a. Namely, the light reflection portion22may be referred to as light reflective prints. The light reflective material used for the light reflection portion22is a white ink (or a paste) containing metal oxide such as titanium oxide. The light reflection portion22is configured to diffusely reflect the rays of light entering the light guide plate16and reaching the plate surface16caway from the light exit surface16atoward the light exit surface16a. The light reflection portion22is further configured to vary an angle of incidence at the light exit surface16acompared with an angle of incidence of light that is fully reflected at the plate surface16c. Accordingly, more rays of light have the angles of incidence which do not exceed the critical angle and thus the amount of light that exits through the light exit surface16aincreases. The light reflection portion22may be formed on the light guide plate16by printing methods including silk printing (screen printing) and inkjet printing. With the silk printing, production cost is reduced when the light guide plates are mass-produced. With the inkjet printing, the light reflection portion22can be formed with high accuracy even if the light reflection portion22is formed in a complex pattern. A dot pattern of the light reflection portion22will be described in detail below.

Next, a configuration of each of the LEDs17, the LED board18, and the heat dissipation member19, which are included in the LED unit LU, will be described. As illustrated inFIGS. 3 and 4, each LED17, which is included in the LED unit LU, include an LED chip that is sealed with resin on a board fixed on the LED board18. 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. On the other hand, 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. 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 alone or in combination of the above phosphors. The LED17includes a main light-emitting-surface17athat is opposite to a surface on which the LED board18is mounted (a surface facing the light entrance surface16bof the light guide plate16). Namely, the LED17is a top-surface-emitting type LED. The LED17has a shape that the main light-emitting surface17ahas a substantially landscape square shape with a front view (elongated in the X-axis direction).

As illustrated inFIGS. 3 and 4, each LED board18included in the LED unit LU has an elongated plate-like shape and extends in the long-side direction of the light guide plate16(the X-axis direction, the long-side direction of the light entrance surface16b). The LED board18is placed in the space between the frame13and the chassis14such that a board surface of each LED board18is parallel to the X-Z plane, namely, parallel to the light entrance surface16bof the light guide plate16. The LED board18has a long-side dimension that is smaller than a half of the long-side dimension of the light guide plate16. Therefore, when the two LED boards18are arranged adjacent to each other so as to be opposed to the light entrance surface16b, two end portions of each of the long-side edge surfaces16E1,16E2of the light guide plate16are not opposed to the LED boards18(refer toFIG. 8). The LED board18is made of metal such as aluminum. Traces (not illustrated) are formed on the surface of the LED board via an insulating layer. The LED board18may be made of an insulating material such as ceramic.

As illustrated inFIGS. 4 and 6, the LED board18includes amount surface18aon which the LEDs17are mounted. The mount surface18ais a main board surface that faces inward, namely, a surface that faces the light guide plate16(the surface opposed to the light guide plate16). As illustrated inFIG. 8, the LEDs17are arranged in a line (i.e., linearly) at intervals on the mount surface18aof the LED board18along the long-side direction of the LED board18(the X-axis direction). In other words, multiple LEDs17are arranged apart from each other along the long-side direction in the two long-side edge portions of the backlight unit12. Distances between the adjacent LEDs17in the X-axis direction are substantially equal, that is, the LEDs17are arranged at substantially equal intervals. Traces (not illustrated) that are metal films (such as copper foil) are formed on the mount surface18aof the LED board18. Each trace extends in the X-axis direction and connects in series the adjacent LEDs17each of which is included in different LED17groups. Terminals formed at ends of the respective traces are connected to an external LED drive circuit to supply driving power to the LEDs17. The LEDs17are arranged in the longitudinal direction of the LED board18(the X-axis direction). The LED boards18in a pair sandwiching the light guide plate16therebetween are arranged in the frame13and the chassis14such that the mount surfaces18ahaving the LEDs17thereon are opposed to each other. With such a configuration, the main light emission surfaces17aof the respective LEDs17mounted on each of the LED boards18are opposed to each other. Optical axes of the respective LEDs17substantially match the Y-axis direction, that is an arrangement direction in which the light guide plate16and the LED boards18(the LEDs17) are arranged.

As illustrated inFIGS. 3 and 4, the heat dissipation member19of each LED unit LU is made of metal having high thermal conductivity, such as aluminum. The heat dissipation member19includes an LED mounting portion (a light source mounting portion)19aand a heat dissipation portion19b. The LED board18is mounted on the LED mounting portion19a. The heat dissipation portion19bis in surface-contact with a plate surface of the chassis14. The LED mounting portion19aand the heat dissipation portion19bform an angle therebetween so as to have an L-like shape in a cross-section. The heat dissipation member19has a long-side dimension substantially equal to the long-side dimension of the LED board18. The LED mounting portion19aof the heat dissipation member19has a plate-like shape and is parallel to the plate surface of the LED board18and the light entrance surface16bof the light guide plate16. A long-side direction, a short-side direction, and a thickness direction of the LED mounting portion19acorrespond to the X-axis direction, the Z-axis direction, and the Y-axis direction, respectively. The LED board18is mounted on an inner surface of the LED mounting portion19a, that is, a plate surface that faces the light guide plate16. The LED mounting portion19ahas a long-side dimension that is substantially equal to that of the LED board18, whereas a short-side dimension of the LED mounting portion19ais larger than that of the LED board18. Namely, ends of the LED mounting portion19ain the short-side dimension are farther out than the ends of the LED board18in the Z-axis direction. An outer plate surface of the LED attachment portion19a, that is, a plate surface opposite to the plate surface on which the LED board18is attached, faces a screw attachment portion21(a fixing member attachment portion) included in the frame13, which will be described later. The LED attachment portion19ais located between the screw attachment portion21of the frame13and the light guide plate16. The LED attachment portion19aextends from an inner end of the heat dissipation portion19b, i.e., an end of the heat dissipation portion19bon the LEDs17(the light guide plate16) side, toward the front side in the Z-axis direction (a direction in which the liquid crystal panel11, the optical member15, and the light guide plate16overlap each other), i.e., toward the frame13.

As illustrated inFIGS. 3 and 4, the heat dissipation portion19bhas a plate-like shape and is parallel to the plate surface of the chassis14. A long-side direction, a short-side direction, and a thickness direction of the heat dissipation portion19bmatch the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. The heat dissipation portion19bextends from a rear-side end of the LED attachment portion19atoward the outer side in the Y-axis direction. In other words, the heat dissipation portion19bextends from an end of the LED attachment portion19acloser to the chassis14toward a counter direction from the light guide plate16. The heat dissipation portion19bhas a long-side dimension substantially equal to the long-side dimension of the LED attachment portion19a. An entire rear plate surface of the heat dissipation portion19b, i.e., a plate surface of the heat dissipation portion19bfacing the chassis14, is in contact with the plate surface of the chassis14. A front plate surface of the heat dissipation portion19b, i.e., a plate surface opposite from the surface in contact with the chassis14, faces the screw attachment portion21of the frame13, which will be described later. Specifically, the front plate surface of the heat dissipation portion19bis in contact with a projected end surface of the screw attachment portion21. The heat dissipation portion19bis sandwiched (disposed) between the screw attachment portion21of the frame13and the chassis14. With this configuration, heat generated by the lightened LEDs17is transferred to the chassis14and the frame13including the screw attachment portion21via the LED board18, the LED attachment portion19a, and the heat dissipation portion19b. Therefore, heat is effectively released to the outside of the liquid crystal display device10and thus the heat is less likely to stay therein. The heat dissipation portion19bincludes through holes19b1through which screw members (fixing members) SM are passed. The heat dissipation portion19bis fixed to the screw attachment portion21with the screw members SM.

Next, configurations of the frame13and the chassis14that constitute the external members and the holding member will be described. The frame13and the chassis14are made of metal such as aluminum so as to have mechanical strength (rigidity) and thermal conductivity compared to a frame13and a chassis14made of synthetic resin. As illustrated inFIG. 3, while the frame13and the chassis14have the LED units LU in each edge portion of the frame13and the chassis14with respect to the short-side direction (the long-side edge portions), 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.

As illustrated inFIG. 3, the frame13has a landscape rectangular shape so as to surround the display area in the display surface11cof the liquid crystal panel11. The frame13includes a panel holding portion13aand a sidewall13b. The panel holding portion13ais parallel to the display surface11cof the liquid crystal panel11and presses the liquid crystal panel11from the front side. The sidewall13bprotrudes from an outer peripheral portion of the panel holding portion13atoward the rear side. The panel holding portion13aand the sidewall13bform an L-like shape in a cross-section. The panel holding portion13ahas a landscape-rectangular and frame-like shape as a whole that corresponds to an outer peripheral portion (the non-display area, a frame-like portion) of the liquid crystal panel11. The panel holding portion13apresses a substantially entire area of the outer peripheral portion of the liquid crystal panel11from the front side. The panel holding portion13ahas a width that is large enough to cover not only the outer peripheral portion of the liquid crystal panel11but also the outer peripheral portions of the light guide plate16and the LED units LU from the front side. The outer peripheral portions of the optical members15and the light guide plate16and the LED units LU are located out from the outer peripheral portion of the liquid crystal panel11in a radiation direction. Similar to the display surface11cof the liquid crystal panel11, a front exterior surface (a surface opposite to the surface facing the liquid crystal panel11) of the panel holding portion13ais seen from the front side of the liquid crystal display device10. The panel holding portion13aconstitutes a front exterior of the liquid crystal display device10together with the display surface11cof the liquid crystal panel11. The sidewall13bhas a substantially rectangular hollow shape and protrudes from the outer peripheral portion (specifically, an outer peripheral edge) of the panel holding portion13atoward the rear side. The sidewall13bentirely surrounds the liquid crystal panel11, the optical member15, the light guide plate16, and the LED units LU, which are arranged in the space between the frame13and the chassis14, in a peripheral direction thereof. The sidewall13balso entirely surrounds the chassis14, which is on the rear side, in a peripheral direction thereof. Outer surfaces of the sidewall13bthat extend in the peripheral direction of the liquid crystal display device10face outside of the liquid crystal display device10. Therefore, the outer surfaces of the sidewall13bconstitute a top surface, a bottom surface, and side surfaces of the liquid crystal display device10.

As illustrated inFIGS. 3 and 8, the frame13formed in a frame-like shape having the above configuration includes four frame pieces13S that are assembled together. The frame pieces13S (long-side portions and short-side portions) each correspond to each side of the frame13. Specifically, the frame pieces13S include long-side frame pieces13SL and short-side frame pieces13SS that constitute the long-side portions and the short-side portions of the frame13(the panel holding portions13aand the side walls13b), respectively. Each long-side frame piece13SL is a block member that extends in the X-axis direction and has an L-like cross section. Each short-side frame piece13SS is a block member that extends in the Y-axis direction and has an L-like cross section. With this configuration, in the production process, the frame pieces13S can be formed by extruding metal material, for example. Thus, the production cost can be reduced compared to the frame13formed by cutting metal material. The long-side frame pieces13SL and the short-side frame pieces13SS that are adjacent to each other form the frame13by joining the respective edges thereof in the respective extending directions. The edges of the long-side frame pieces13SL and the edges of the short-side frame pieces13SS, which are the joint portions of the frame pieces13SL and13SS (joints in the frame13), are angled against the X-axis and Y-axis directions in a plan view. Specifically, each edge extends along a line connecting an inner edge and an outer edge of each corner of the panel holding portion13a. The long-side frame pieces13SL (refer toFIG. 4) cover not only the liquid crystal panel11, the optical member15, and the light guide plate16but also the LED units LU. The short-side frame pieces13SS (refer toFIG. 5) do not cover the LED units LU. Therefore, the long-side frame piece13SL has a relatively larger width than the short-side frame piece13SS.

As illustrated inFIGS. 4 and 5, the panel holding portion13aincludes the screw attachment portions (fixing member attachment portions)21at a further interior position than the sidewall13bof the panel holding portion13a(a position away from the sidewall13btoward the light guide plate16). The screw member (the fixing member) SM is attached to the screw attachment portion21. The screw attachment portions21each protrude from an inner surface of the panel holding portion13atoward the rear side in the Z-axis direction and each have an elongated block-like shape that extends along a side of the panel holding portion13a(in the X-axis direction and the Y-axis direction). The screw attachment portions21each extend on each side of the panel holding portion13awith a length equal to the length of each side of the panel holding portion13a. As illustrated inFIG. 8, the screw attachment portions21are each arranged on each frame piece13S included in the frame13. If the frame pieces13S are connected with each other, the screw attachment portions21form a frame-like shape that continues to inner surfaces of the sidewall13bhaving a rectangular hollow shape over its entire length. As illustrated inFIG. 4andFIG. 5, each screw attachment portion21includes a groove21athat opens to the rear side and to which the screw member SM can be fastened. The groove21aextends in the longitudinal direction of the screw attachment portion21over substantially the entire length thereof. The groove21ahas a width that is slightly smaller than that of a shaft portion of the screw member SM. The screw attachment portion21is positioned between the panel holding portion13aof the frame13and the chassis14in the Z-axis direction.

As illustrated inFIG. 4, the screw attachment portions21that extend along the long sides are each positioned between the sidewall13bof the frame13and the LED attachment portion19aof the heat dissipation member19, which is included in the LED unit LU, in the Y-axis direction. The screw attachment portion21is away from the LED attachment portion19aby a predetermined distance. As illustrated inFIGS. 6 and 7, a board space BS in which the printed circuit board27is arranged is provided between one of the heat dissipation members19that overlaps the source flexible board26in a plan view and the screw attachment portion21, to which the heat dissipation member19is attached. In other words, the printed circuit board27is arranged between the screw attachment portion21and the LED attachment portion19a. The printed circuit board27is made of synthetic resin and has an elongated plate-like shape that extends in the longitudinal direction of the screw attachment portion21and the LED attachment portion19a(in the X-axis direction). The printed circuit board27is arranged in the board space BS such that a plate surface of the printed circuit board27extends parallel to an outer plate surface of the LED attachment portion19a(a surface opposite to the LED board18side). On the printed circuit board27, multiple source flexible boards26are arranged away from each other in the long-side direction of the printed circuit board27and connected to the printed circuit board27at the other end thereof. The source flexible boards26that are connected to the printed circuit board27and the array board11bof the liquid crystal panel11extend over the LED attachment portion19a, the LED board18, and the LEDs17in the Y-axis direction. The printed circuit board27includes a connecter (not illustrated) to which an end of an FPC (not illustrated) is connected. The other end of the FPC extends to the rear side of the chassis14through an FPC hole (not illustrated) in the chassis14and is connected to the control board CTB.

As illustrated inFIGS. 4 and 5, the panel holding portion13aintegrally includes a light guide plate support portion23at a portion inner than the screw attachment portion21. The light guide plate support portion23supports the light guide plate16from the front side (a display surface11cside). The light guide plate support portion23projects from an inner surface of the panel holding portion13atoward the rear side (the light guide plate16) along the Z-axis direction (a direction in which the screw attachment portion21projects). The light guide plate support portion23has a substantially thin elongated block shape extending along a side of each of the panel holding portion13a. The light guide plate support portion23is provided at a side of each panel holding portion13aand has a length dimension extending over an entire length of each side. The light guide plate support portion23is provided separately on each of the frame pieces13S included in the frame13similar to the screw attachment portion21. The frame pieces13S are mounted together to form a frame-shaped light guide plate support portion23that extends along an entire periphery of the panel holding portion13a(the light guide plate16) as a whole. The light guide plate support portion23has a projected distal end surface that is in contact with a front-side surface of an edge portion of the light guide plate16, i.e., the light exit surface16a. The edge portion of the light guide plate16projects to an outer side than the liquid crystal panel11. Therefore, the light guide plate support portion23and the chassis14hold the light guide plate16therebetween such that the light guide plate support portion23supports the light guide plate16from the front side (the display surface11cside) and has a light guide plate supporting function.

A pair of long-side light guide plate support portions23is provided on the long-side frame pieces13SL and extends along the long sides of the panel holding portions13a. As illustrated inFIG. 4, the long-side light guide plate support portions23support the long-side edge portions of the light guide plate16having the light entrance surfaces16bso that a positional relation between the LEDs17and the light entrance surface16bwith respect to the Z-axis direction is maintained stably. Further, the long-side light guide plate support portions23are arranged between the liquid crystal panel11and the LEDs17. Specifically, each of the long-side light guide plate support portions23is located in and divides a space between the LEDs17and the LED17side end surfaces of the liquid crystal panel11and the optical member15and close a divided space. Accordingly, light from the LEDs17is less likely to enter the liquid crystal panel11and the optical member15through the edge surfaces thereof without passing through the light guide plate16. Namely, the long-side light guide plate support portions23have a light blocking property and function as a light blocking member. As illustrated inFIGS. 6 and 7, one of the long-side light guide plate support potions23overlaps the flexible boards26with a plan view and the one of the long-side light guide plate support potions23has flexible board insertion recesses23athat are arranged at intervals along the X-axis direction. The flexible boards26are inserted through the respective flexible board insertion recesses23a. The arrangement of the flexible board insertion recesses23ais same as that of the flexible boards26.

As illustrated inFIGS. 4 and 5, the panel holding portion13aintegrally includes a holding protrusion24that protrudes from an inner edge of the panel holding portion13atoward the rear-surface side, i.e., toward the liquid crystal panel11. The holding protrusion24includes a shock absorber24aat its protruded end. The holding protrusion24can press the liquid crystal panel11from the front side via the shock absorber24ain between. Similar to the screw mounting portion21, the holding protrusion24and the shock absorber24aextend along a side of each of the frame pieces13S, which form the frame13, and each holding protrusion24and each shock absorber24aare provided on each of the sides of the frame pieces13S, separately. The frame pieces13S are mounted together to form a frame-like shape as a whole at an entire inner peripheral edge of the panel holding portion13a.

As illustrated inFIG. 3, the chassis14has a substantially longitudinal shallow tray shape as a whole and covers overall 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 seen from the rear side and constitutes a back surface of the liquid crystal display device10. The chassis14includes a light guide plate receiving portion14aand housings14b. The light guide plate receiving portion14ahas a landscape rectangular shape similar to the light guide plate16. Each of the housings14bprotrudes from an outer peripheral end of the light guide plate receiving portion14atoward the rear side to form a step and holds the LED unit LU.

As illustrated inFIGS. 3 to 5, the light guide plate receiving portion14ahas a flat plate shape to receive a most of a middle portion of the light guide plate16from the rear side. The holding portion14bis recessed from the long-side portion of the light guide plate receiving portion14atoward the rear side to provide a space for holding the LED units LU therein. As illustrated inFIG. 4, the holding portion14bincludes a bottom plate14b1, which extends parallel to the light guide plate receiving portion14a, and sidewalls14b2and14b3, which extend upward from respective ends of the bottom plate14b1toward the front side. An inner sidewall14b2of the sidewalls14b2,14b3continues to the light guide plate receiving portion14a. On the bottom plate14b1, the heat dissipation portion19bof the heat dissipation member19, which is included in the LED unit LU, is disposed such that a surface of the heat dissipation portion19bis in contact with the inner surface of the bottom plate14b1. The screw members (fixing members) SM are mounted to the bottom plate14b1from the outside to fix the frame13and the chassis14together.

As illustrated inFIGS. 3, 6, and 7, the light guide plate receiving portion14aand the bottom plate14b1of the holding portion14binclude multiple screw holes25in which the screw members SM are inserted. The screw holes25of light guide plate receiving portion14aand the screw holes25of the bottom plate14b1of the holding portion14bare arranged corresponding to the screw mounting portions21of the frame13in a plan view. Each screw hole25is communicated with the groove21aof the corresponding screw mounting portion21. Accordingly, the screw member SM is passed through the screw hole25in the Z-axis direction (the overlapping direction of the liquid crystal panel11, the optical member15, and the light guide plate16) from the rear side of the chassis14(the side opposite to the display surface11cside). The screw member SM is inserted in the groove21aand fastened to the screw mounting portion21with the bottom plate14b1disposed therebetween. When the screw member SM is fastened, thread grooves are formed in the groove21aby the threads formed on the shaft of the screw member SM. The screw holes25in the bottom plate14b1of the holding portion14binclude a joint screw hole25A and a heat dissipation member screw hole25B. As illustrated inFIG. 6, the joint screw hole25A has a size through which only the shaft of the screw member SM passes. As illustrated inFIG. 7, the heat dissipation member screw hole25B has a size through which both of a head and the shaft of the screw member SM pass. The screw member SM is passed through the joint screw hole25A to fasten the heat dissipation portion19band the bottom plate14b1together to the screw mounting portion21. The screw member SM is passed through the heat dissipation member screw hole25B to fasten only the heat dissipation portion19bto the screw mounting portion21.

Next, a light intensity distribution of the LEDs17that are the light source will be described with reference toFIG. 11. InFIG. 11, a lateral axis represents an angle (degrees) with respect to an optical axis (a front direction) of light from the LED17and a vertical axis represents light emission intensity (appropriate unit). Herein, a specific unit of the light intensity includes a radiant intensity (W/sr·m2), a radiant flux (W), and irradiance (W/m2). Any other physical quantities relating to quantity of radiation may be used as the specific unit of the light intensity. In the light intensity distribution of light from the LED17, the rays of light traveling toward a front direction of the main light emission surface17a, i.e., along the optical axis have a peak light intensity and the light emission intensity tends to decrease with a curved line in the graph as the angle with respect to the optical axis increases. Namely, the light intensity distribution is represented by the curved graph having an angle range with certain light emission intensity or more or having a width continuously increasing and decreasing. Thus, the LED17represents a lambertian light intensity distribution. Such a light intensity distribution represents a graph having a shape similar to a normal distribution and a substantially symmetrical shape with respect to an optical axis. In the lambertian light intensity distribution, the light entrance efficiency is improved as the distance between the LED17and the light entrance surface16bof the light guide plate16is decreased, and the light entrance efficiency is decreased as the distance is increased. On the other hand, the light guide plate16thermally expands due to heat generated by light emission from the LED17and increases its size. Therefore, a clearance is required to be provided between the LEDs17and the light entrance surface16bto allow the size increase of the light guide plate16due to the thermal expansion. This limits improvement of the light entrance efficiency of light entering the light guide plate16.

As a result of enthusiastic studies, the inventor found that if the distance between the LED17having the lambertian light intensity distribution and the light entrance surface16bof the light guide plate16is a certain value or more, the light entrance efficiency is unlikely to be decreased according to the increase of the distance and the light entrance efficiency becomes constant. Hereinafter, relation between the distance between the LED17and the light entrance surface16bof the light guide plate16and the light entrance efficiency will be described with reference toFIG. 12. InFIG. 12, a lateral axis represents a distance between the LED17and the light entrance surface16bof the light guide plate16, and a vertical axis represents relative brightness of light exiting the light guide plate16through the light exit surface16a. Herein, the relative brightness represents a relative brightness value with a total flux of rays of emission light from the LED17as a reference value. According to the graph inFIG. 12, when the distance between the LED17and the light entrance surface16bof the light guide plate16is substantially zero, the maximum relative brightness is approximately 0.5, and the relative brightness decreases gradually as the distance increases. When the distance is between 1.0 mm and 1.5 mm, the relative brightness decreases more moderately, and when the distance is between 1.5 mm and 2 mm, the relative brightness decreases much more moderately. Thus, the relative brightness, i.e., the decreasing rate of light entrance efficiency of the light emitted from the LED17and entering the light guide plate16through the light entrance surface16b(a rate of the decreasing amount in the relative brightness with respect to the increase amount of the distance (entrance efficiency)) is unlikely to be decreased when the distance between the LED17and the light entrance surface16bof the light guide plate16exceeds 1.0 mm. When the distance reaches 2 mm, the relative brightness substantially remains a certain value and becomes constant.

According to the result of the studies, the inventor arranges the light guide plate16and the LEDs17as follows. The LEDs17are mounted on the LED boards18that sandwich the light guide plate16therebetween. One of the light entrance surfaces16bof the light guide plate16is a first light entrance surface16bA and the LEDs17opposed to the first light entrance surface16bA are first LEDs17A. The other light entrance surface16bthat is on an opposite side from the first light entrance surface16bA is a second light entrance surface16bB and the LEDs17opposed to the second light entrance surface16bA are second LEDs17B. As illustrated inFIG. 10, the first LEDs17A are arranged to have a relatively small distance A from the first light entrance surface16bA, and the second LEDs17B are arranged to have a relatively great distance B from the second light entrance surface16bB. A total dimension of the distance A and the distance B substantially equal to a maximum size increase amount of the light guide plate16that increases its size in the vertical direction (the Y-axis direction, the direction in which the LEDs17A,17B and the light guide plate16are arranged) due to its thermal expansion. The first LEDs17A are arranged on a lower side of the light guide plate16with respect to the vertical direction and the first light entrance surface16bA is a lower long-side edge surface16E1in the vertical direction. The second LEDs17B are arranged on an upper side of the light guide plate16with respect to the vertical direction and the second light entrance surface16bB is an upper long-side edge surface16E2of the light guide plate in the vertical direction. Hereinafter, the LEDs17arranged on the lower side ofFIG. 10are referred to as the first LEDs and the light entrance surface16barranged on the lower side inFIG. 10is referred to as the first light entrance surface, and “A” is added to the respective reference numerals and symbols. The LEDs17arranged on the upper side inFIG. 10are referred to as the second LEDs and the light entrance surface16barranged on the upper side inFIG. 10is referred to as the second light entrance surface, and “B” is added to the respective reference numerals and symbols. No additional character is added to the reference numerals and symbols when the LEDs17or the light entrance surface16bis generally referred to.FIG. 10generally illustrates a plan-view arrangement configuration of the LEDs17, the light guide plate16, and the positioning portions34and a dot pattern of the light reflection portion22.

With the above positional relation between the LEDs17A,17B and the light entrance surfaces15bA,16bB, the light entrance efficiency of light emitted from the first LED17A and entering the light guide plate16through the first light entrance surface16bA becomes relatively high and the light entrance efficiency of light emitted from the second LED17B and entering the light guide plate16through the second light entrance surface16bB becomes relatively low. However, the light entrance efficiency is unlikely to be decreased according to the increase of the distance and therefore, the light entrance efficiency stops decreasing from a certain value. Hereinafter, the relation between the respective distances A, B and the respective light entrance surfaces16bA,16bB and the brightness of light exiting the light guide plate16will be described with reference toFIG. 13. InFIG. 13, a lateral axis represents the distance A between the first LEDs17A and the first light entrance surface16bA of the light guide plate16(the distance B between the second LEDs17B and the second light entrance surface16bB of the light guide plate16) and a vertical axis represents relative brightness of light exiting the light guide plate16through the light exit surface16a. Herein, the relative brightness represents a relative brightness value regarding a total flux of rays of emission light from the first LED17A and the second LED17B as a reference value. InFIG. 13, a total value of the distance A and the distance B is 3.2 mm. Therefore, the distance A is equal to a value obtained by subtracting the distance B from 3.2 mm and the distance B is equal to a value obtained by subtracting the distance A from 3.2 mm. According to the graph inFIG. 13, when both of the distance A and the distance B are same and approximately 1.6 mm, the relative brightness is lowest and the relative brightness tends to increase as difference between the distance A and the distance B increases. If the distance A is equal to the distance B, the light entrance efficiency of light emitted from each LED17and entering the light guide plate16through each light entrance surface16bis low and the light use efficiency is low as a whole. The light entrance efficiency of light with the distance A being equal to the distance B is referred to as a reference value and with the above-described positional relation between the respective LEDs17A,17B and the respective light entrance surfaces16bA,16bB, a plus difference value between the reference value and the light entrance efficiency of light emitted from the first LED17A and entering the light guide plate16through the first light entrance surface16bA (the light entrance efficiency is higher than the reference value) is greater than a minus difference value between the reference value and the light entrance efficiency of light emitted from the second LED17B and entering the light guide plate16through the second light entrance surface16bB (the light entrance efficiency is lower than the reference value). Thus, with the arrangement configuration in which the distance A differs from the distance B, the light use efficiency as a whole is improved compared to the configuration in which the distance A is equal to the distance B.

According to the present invention, the LEDs17A,17B and the light guide plate16are arranged such that the distance A between the first LEDs17A and the first light entrance surface16bA is ⅓ of or less than the total of the distance A and the distance B (the maximum size increase amount of the light guide plate16in the vertical direction), for example, 1.067 mm or less. According to this configuration, as illustrated inFIG. 13, the distance A between the first LEDs17A and the first light entrance surface16bA of the light guide plate16is sufficiently small, and the light entrance efficiency of light emitted from the first LEDs17A and entering the light guide plate16through the first light entrance surface16bA is further improved. On the other hand, the light entrance efficiency of light emitted from the second LEDs17B and entering the light guide plate16through the second light entrance surface16bB already has a lowest value, and therefore the light entrance efficiency is less likely to be further decreased even if the distance B increases. Accordingly, the light use efficiency becomes high as a whole.

Further, according to the present embodiment, the liquid crystal display device10includes support members28-30that support the light guide plate16to maintain a positional relation between the light entrance surface16bA of the light guide plate16and the LEDs17A and a positional relation between the light entrance surface16bB of the light guide plate16and the LEDs17B. As illustrated inFIG. 8, the support members28-30include first support members28, second support members29and horizontal side second support members30. The first support members28are arranged on the same side as the first LEDs17A are arranged with respect to the light guide plate16in a vertical direction. The second support members29are arranged on the same side as the second LEDs17B are arranged with respect to the light guide plate16in the vertical direction to be spaced from the light guide plate16. The horizontal side second support members30are arranged to be spaced from the light guide plate16with respect to a horizontal direction. The support members28-30are attached to the frame13that holds the light guide plate16and the liquid crystal panel11with the chassis14that is arranged on the rear side. Configurations of the respective support members28-30will be described in detail.

As illustrated inFIGS. 8 and 9, the first support members28are arranged on the same side as the first LEDs17A are arranged with respect to the light guide plate16, namely, on a lower side in the vertical direction. The first support members28are attached to the ling-side screw mounting portion21that is located on a lower side with respect to the vertical direction. The screw mounting portion21is included in the frame13. The first support members28are arranged between the screw mounting portion21and the light guide plate16with respect to the vertical direction. The first support members28are mounted on a side surface of the screw mounting portion21that faces upwardly (faces the light guide plate16) with respect to the vertical direction with a fixing member31such as a double-sided adhesive tape or an adhesive. The first support member28is mounted on each of two end portions of the screw mounting portion21, which are end portions with respect to the longitudinal direction (the horizontal direction). Namely, two first support members28are arranged to sandwich a group of the first LEDs17A, which is arranged in a middle portion with respect to the horizontal direction. Each first support member28has a substantially horizontally long (elongated in the horizontal direction) block shape in a plan view. The first support members28are in contact with the long-side edge surface16E1of the light guide plate16that is opposed to the screw mounting portion21. The long-side edge surface16E1is located on the lower side with respect to the vertical direction. Specifically, the two first support members28are in contact with two end portions of the long-side edge surface16E1of the light guide plate16, respectively. The long-side edge surface16E1includes the two end portions with respect to the longitudinal direction (the horizontal direction) thereof. The long-side edge surface16E1of the light guide plate16has portions where the first support members28are in contact with. Such portions are non-illumination areas where light from the first LEDs17A is less likely to reach and are located besides the first light entrance surface16bA that is an illumination area. An area where the first support member28is provided substantially matches the non-illumination area with respect to the X-axis direction.

As illustrated inFIGS. 8 and 10, the first support members28are made of a material that has plasticity (a non-elastic material) and is harder than a material of the second support members29, which will be described later. The first support members28are made of a material having plasticity such as metal or thermoplastic resins (hard resins). The metal includes iron (Fe) and aluminum (Al), for example. The thermoplastic resins include polyethylene terephthalate (PET) and polycarbonate (PC), for example. The light guide plate16is placed on the first support members28from the upper side with respect to the vertical direction. The lower long-side edge surface16E1of the light guide plate16with respect to the vertical direction is kept in close contact with the first support members28due to its own weight. Since the first support members28are made of the hard resin as described before, the first support members28are less likely to be deformed even if receiving the weight of the light guide plate16. Accordingly, the positional relation with respect to the vertical direction between the lower long-side edge surface16E1of the light guide plate16, that is the first light entrance surface16bA, and the first LEDs17A is kept stable and the positional relation is less likely to change. In other words, a distance between the first light entrance surface16bA and the first LEDs17A is always kept constant. Therefore, a quite small value that is close to zero can be set for the distance (an interval) between the first light entrance surface16bA and the first LEDs17A. Accordingly, light entrance efficiency of light emitted from the first LEDs17A and being incident on the first light entrance surface16bA becomes extremely high and such high light entrance efficiency is stably maintained without being varied according to each product.

As illustrated inFIGS. 8 and 9, the second support members29are arranged on the same side as the second LEDs17B are arranged with respect to the light guide plate16, namely, on an upper side in the vertical direction. The second support members29are attached to the long-side screw mounting portion21that is located on an upper side with respect to the vertical direction. The screw mounting portion21is included in the frame13. The second support members29are arranged between the screw mounting portion21and the light guide plate16with respect to the vertical direction. The second support members29are mounted on a side surface of the screw mounting portion21that faces downwardly (faces the light guide plate16) with respect to the vertical direction. The second support members29are integrally mounted on the side surface with the fixing member31such as a double-sided adhesive tape or an adhesive. The second support member29is mounted on each of two end portions of the screw mounting portion21, which are end portions with respect to the longitudinal direction (the horizontal direction). Namely, two second support members29are arranged to sandwich a group of the second LEDs17B, which is arranged in a middle portion with respect to the horizontal direction. Each second support member29has a substantially horizontally long (elongated in the horizontal direction) block shape in a plan view. The second support members29are arranged to have a predetermined distance from the long-side edge surface16E2of the light guide plate16that is opposed to the screw mounting portion21. The long-side edge surface16E2is located on the upper side with respect to the vertical direction. Specifically, the two second support members29are arranged to be opposed to and spaced from two end portions of the long-side edge surface16E2of the light guide plate16. The long-side edge surface16E2includes the two end portions with respect to the longitudinal direction thereof (the horizontal direction). The long-side edge surface16E2of the light guide plate16has portions where the respective second support members29are opposed to. Such portions are non-illumination areas where light from the second LEDs17B is less likely to reach and are located besides the second light entrance surface16bB that is an illumination area. An area where the second support member29is provided substantially matches the non-illumination area with respect to the X-axis direction.

As illustrated inFIGS. 8 and 10, the second support members29are made of an elastic material that is softer than the material of the first support members28. The second support members29are made of rubber that is an elastic material, for example, natural rubber or synthetic rubber (such as butyl rubber, urethane rubber, silicon rubber). At normal temperature (for example, from 5° C. to 35° C.), the second support members29and the upper long-side edge surface16E2of the light guide plate16in the vertical direction have a certain distance therebetween to be maintained in a non-contact state. If the temperature increases from the normal temperature to 35° C. or higher, for example, the light guide plate16increases its size in a direction along its plate surface (in the X-axis direction and the Y-axis direction) according to the thermal expansion and moves relative to the frame13, since the light guide plate16made of a synthetic resin has a rate of thermal expansion higher than the metal frame13. The distance between the second support members29and the edge surface16E2of the light guide plate16is set to be substantially equal to a maximum expansion amount of the light guide plate16in the vertical direction. The maximum expansion amount is predicted according to the environment where the liquid crystal display device10is used and calculated based on the design dimension of the short side of the light guide plate16. A positive dimension error may be caused in the mass-produced light guide plates16within a tolerance range, that is, the short-side dimension of the light guide plate16may become greater than the predetermined dimension. If the light guide plate16having such a dimension error expands to a maximum extent in the vertical direction according to the thermal expansion, the upper long-side edge surface16E2in the vertical direction moves to be closer to the second LEDs17B from the state being in contact with the second support members29. Even if the light guide plate16expands as is in the above, the second support members29that are made of the elastic material elastically deform and support the light guide plate16stably from the upper side in the vertical direction. Namely, even if a positive dimension error is caused in the light guide plate16, the second support members29that are in contact with the edge surface16E2of the light guide plate16elastically deform to absorb an amount of the error. If the second support members are made of the same material as the first support members28, the second support members are necessary to be arranged to have a sufficient great distance from the light guide plate16with considering the dimension error that may be caused in the light guide plate16. Compared to such a configuration of the second support members, the second support members29are arranged much closer to the light guide plate16. Accordingly, the thermally expanded light guide plate16is supported further stably.

As illustrated inFIGS. 5 and 8, the horizontal side second support members30are arranged to be spaced from the light guide plate16in the horizontal direction. The horizontal side second support members30are mounted on the two short-side screw mounting portions21that are located on a left side and a right side, respectively, with respect to the horizontal direction. The screw mounting portions21are included in the frame13. The horizontal side second support members30are arranged between the respective screw mounting portions21and the light guide plate16with respect to the horizontal direction. The horizontal side second support members30are mounted on side surfaces of the respective screw mounting portions21facing inwardly (facing the light guide plate16) with respect to the horizontal direction. The horizontal side second support members30are integrally mounted on the side surfaces with the fixing member31such as a double-sided adhesive tape or an adhesive. Two horizontal side second support members30are mounted on the respective two end portions of each screw mounting portion21and a total of four horizontal side second support members30are mounted in the device. Each screw mounting portion21includes the end portions with respect to the longitudinal direction (the vertical direction) thereof. Each horizontal side second support member30has a substantially vertically long (elongated in the vertical direction) block shape in a plan view. The horizontal side second support members30are arranged to be opposed to each of the short-side edge surfaces16E3,16E4and to have a predetermined distance therebetween. The short-side edge surfaces16E3,16E4are on a left side and a right side, respectively, in the horizontal direction. Specifically, the two horizontal side second support members30are arranged to be opposed to and spaced from the respective two end portions of each short-side edge surface16E3,163E4of the light guide plate16. Each short-side edge surface16E3,16E4includes the end portions with respect to the longitudinal direction (the vertical direction) thereof.

As illustrated inFIGS. 8 and 10, the horizontal second support members30are made of an elastic material that is softer than the material of the first support members28. The horizontal second support members30are made of the same material as that of the second support members29. The common material is used for the horizontal side second support members30and the second support members29, and this reduces a cost for the components. At a normal temperature, the horizontal side second support members30and the respective short-side edge surfaces16E3,16E4of the light guide plate16have a certain distance therebetween so as to be maintained in a non-contact state. The distance between the horizontal side second support members30and the respective edge surfaces16E3,16E4of the light guide plate16is set to be approximately a half of the maximum expansion amount of the light guide plate16in the horizontal direction. The maximum expansion amount is predicted according to the environment where the liquid crystal display device10is used. If a distance between the second support members29and the upper edge surface16E2of the light guide plate16in the vertical direction is set to “9 (a ratio of the short side dimension of the light guide plate16)”, a distance between the horizontal side second support members30and each of the edge surfaces16E3,16E4is set to “8 (a half of a ratio of the long side dimension of the light guide plate16)”. The maximum expansion amount of the light guide plate16in the horizontal direction is calculated based on the design dimension of the long side of the light guide plate16. A positive dimension error may be caused in the mass-produced light guide plates16within a tolerance range, that is, the long-side dimension of the light guide plate16may be greater than the predetermined dimension. If the light guide plate16having such a dimension error expands to a maximum extent in the horizontal direction according to the thermal expansion, the short-side edge surfaces16E3,16E4further move outwardly in the horizontal direction from the state being in contact with the horizontal side second support members30. Even if the light guide plate16expands as is in the above, the horizontal side second support members30that are made of the elastic material elastically deform and support the light guide plate16stably from the two sides in the horizontal direction. Namely, even if a positive dimension error is caused in the light guide plate16, the horizontal side second support members30that are in contact with the edge surfaces16E3,16E4of the light guide plate16elastically deform to absorb an amount of the error. If the horizontal side second support members are made of the same material as the first support members28, the horizontal side second support members are necessary to be arranged to have a sufficient great distance from the light guide plate16with considering the dimension error that may be caused in the light guide plate16. Compared to such a configuration of the horizontal side second support members, the horizontal side second support members30are arranged much closer to the light guide plate16. Accordingly, the thermally expanded light guide plate16is supported further stably. Further, the horizontal side second support members30are made of the same material as the material of the second support members29and the elastic coefficient of the horizontal side second support members30and that of the second support members29are same. Therefore, it is easy to set a distance between the horizontal side second support members30and the light guide plate16and a distance between the second support members29and the light guide plate16.

As is described before, according to the present embodiment, a distance A between the first LEDs17A and the first light entrance surface16bA differs from a distance B between the second LEDs17B and the second light entrance surface16bB. With this configuration, the amount of rays of light emitted from the first LEDs17A and entering the light guide plate16through the first light entrance surface16bA is relatively great and the amount of rays of light emitted from the second LEDs17B and entering the light guide plate16through the second light entrance surface16bB is relatively small. According to the present embodiment, as illustrated inFIG. 10, a light reflection portion22that accelerates exit of the light from the light guide plate16has an area distribution within a surface plane of a plate surface of the light guide plate16as follows. The area distribution of the light reflection portion22increases as is farther away from the respective first LEDs17A and the second LEDs17B and becomes maximum in a second LED17B-side portion of the plate surface of the light guide plate16. With such a distribution, within the plane of the plate surface of the light guide plate16, the light entering through the first light entrance surface16bA having a relatively great amount of incident light is less likely to be reflected by the light reflection portion22and the light entering through the second light entrance surface16bB having a relatively small amount of incident light is likely to be reflected by the light reflection portion22. Accordingly, the amount of light exiting the light guide plate16through the light exit surface16ais averaged within the plane surface and unevenness of the brightness is less likely to occur. Specifically, the light reflection portion22includes dots22aformed with ink and the dots22aare dispersed in a plate surface16con an opposite side from the light exit surface16aof the light guide plate16with a predetermined distribution. An area of each of the dots22ais increased as is farther away from the first LEDs17A and the second LEDs17B and becomes maximum in a portion closer to the second LEDs17B than the first LEDs17A.

As is described before, according to the present embodiment, the backlight device (the lighting device)12includes the light guide plate16, the first LEDs (a first light source)17A, the second LEDs (a second light source)17B, a first support member28, and a second support member29. The light guide plate16includes the light entrance surface16bthat is at least one of side surfaces thereof and the light exit surface16athat is one of plate surfaces thereof. The first LEDs17A are opposed to the first light entrance surface16bA that is a first edge surface16E1of the light guide plate16. The second LEDs17B are opposed to the second light entrance surface16bB that is a second edge surface16E2. The second edge surface16E2is an opposite surface from the first edge surface16E1of the light guide plate16. The second LEDs17B are arranged such that the distance B between the second entrance surface16bB and the second LEDs17B is relatively greater than the distance A between the first LEDs17A and the first light entrance surface16bA. The first support member28is arranged on a side where the first LEDs17A are arranged with respect to the light guide plate16and is in contact with the first edge surface16E1of the light guide plate16to support the light guide plate16from the first LED17A side. The second support member29is arranged on a side where the second LEDs17B are arranged with respect to the light guide plate16to be spaced from the light guide plate16and comes in contact with the second edge surface16E2if the light guide plate16thermally expands. According to the contact with the second edge surface16E2, the second support member29supports the light guide plate16from a second LED17B side. The second support member29is made of an elastic material that is softer than the material of the first support member28.

According to such a configuration, the light emitted from the first LEDs17A enters the light guide plate16through the first light entrance surface16bA and the light emitted from the second LEDs17B enters the light guide plate16through the second light entrance surface16bB and then, the light entering the light guide plate16travels within the light guide plate16and exits the light guide plate16through the light exit surface16a. The distance A between the first LEDs17A and the first light entrance surface16bA of the light guide plate16is relatively small and the distance B between the second LEDs17B and the second light entrance surface16bB of the light guide plate16is relatively great. Therefore, the light entrance efficiency of the light emitted from the first LEDs17A and entering the light guide plate16through the first light entrance surface16bA is relatively high and the light entrance efficiency of the light emitted from the second LEDs17B and entering the light guide plate16through the second light entrance surface16bB is relatively low. According to the inventor's studies, it is found that if the distance A, B between the respective LEDs17A and17B and the respective light entrance surfaces16bA,16bB becomes a certain value or more, the light entrance efficiency of light is less likely to be decreased even if the distance is increased and the light entrance efficiency does not change. Therefore, the light entrance efficiency of the light emitted from the second LEDs17B and entering the light guide plate16through the second light entrance surface16bB becomes lower than the light entrance efficiency of the light emitted from the first LEDs17A and entering the light guide plate through the first light entrance surface16bA. However, the light entrance efficiency of the light emitted from the second LEDs17B and entering the light guide plate16through the second light entrance surface16bB is not further decreased from the certain value because the light entrance efficiency of light is less likely to be decreased even with the increase of the distance. Therefore, the light entrance efficiency is not decreased from a certain value. The light entrance efficiency of light with the distance between the LEDs17A and the light entrance surface16bA being equal to the distance between the LEDs17B and the light entrance surface16bB is referred to as a reference value. A plus difference value between the reference value and the light entrance efficiency of light emitted from the first LED17A and entering the light guide plate16through the first light entrance surface16bA (the light entrance efficiency is higher than the reference value) is greater than a minus difference value between the reference value and the light entrance efficiency of light emitted from the second LED17B and entering the light guide plate16through the second light entrance surface16bB (the light entrance efficiency is lower than the reference value). Thus, the light use efficiency as a whole is improved compared to the light use efficiency in the configuration in which the distances between the respective LEDs17A,17B and the respective light entrance surfaces16bA,16bB are equal to each other.

The first support members28arranged on the same side as the first LEDs17A are in contact with the first edge surface16E1so as to support the light guide plate16from the first LED17A side. The first support members28that are made of a material harder than the material of the second support members29stably support the light guide plate16and a support position of the light guide plate16is less likely to be changed. Accordingly, the positional relation between the first LEDs17A and the first light entrance surface16bA is maintained stably and the distance A between the first LEDs17A and the first light entrance surface16bA is set to be smallest. Therefore, the light entrance efficiency of light emitted from the first LED17A and entering the light guide plate16through the first light entrance surface16bA is greatly improved.

The second support members29are arranged on the same side as the second LEDs17B and spaced from the light guide plate16. However, the second support members29come in contact with the second edge surface16E2if the light guide plate16thermally expands, and the light guide plate16is supported from the second LEDs17B side. The second support members29are made of an elastic material that is softer than the material of the first support members28. Therefore, compared to a configuration including the second support members made of a material having same hardness as the material of the first support members28, the distance between the second support members and the second edge surface16E2of the light guide plate16can be decreased. If the second support members are made of a material having same hardness as the material of the first support members28, the second support members are necessary to be arranged to have a sufficient distance including an extra space from the second edge surface16E2of the light guide plate16with considering the dimension error that may be caused in the light guide plate16. The second support members29made of the elastic material that is softer than the material of the first support members28elastically deform when the second edge surface16E2of the light guide plate16that thermally expands comes in contact with the second support members29. Therefore, even if the light guide plate16is greater in size than a standard size due to the dimension error, the error amount can be absorbed by the elastic deformation. Accordingly, the second support members29are arranged much closer to the light guide plate16and the thermally expanded light guide plate16is supported further stably.

The first LEDs17A, the light guide plate16, and the second LEDs17B are arranged in the vertical direction. The first LEDs17A and the first support members28are arranged on the lower side in the vertical direction with respect to the light guide plate16. The second LEDs17B and the second support members29are arranged on the upper side in the vertical direction with respect to the light guide plate16. According to such a configuration, the light guide plate16is supported from the lower side in the vertical direction by the first support members28having hardness greater than the second support members29. Therefore, the first edge surface16E1of the light guide plate16is kept in closely contact with the first support members28due to the weight of the light guide plate16. Accordingly, the positional relation between the first LEDs17A and the first light entrance surface16bA is maintained more stable. Thus, the light guide plate16is positioned precisely in the vertical direction by the first support members28. Therefore, the second support members29arranged on the upper side in the vertical direction with respect to the light guide plate16are arranged much closer to the light guide plate16. Accordingly, the thermally expanded light guide plate16is stably supported.

The horizontal side second support members30are arranged to be spaced from the light guide plate16in the horizontal direction that is perpendicular to the vertical direction. The horizontal side second support members30become in contact with the edge surfaces16E3,16E4that are adjacent to the first edge surface16E1and the second edge surface16E2of the light guide plate16when the light guide plate16thermally expands in the horizontal direction. Accordingly, the horizontal side second support members30support the light guide plate16from an outer side with respect to the horizontal direction. The horizontal side second support members30are made of an elastic material that is softer than the material of the first support members28. According to such a configuration, the light guide plate16is supported by the horizontal side second support members30from the outer side with respect to the horizontal direction when the light guide plate16increases its size in the vertical direction and the horizontal direction according to the thermal expansion thereof. The horizontal side second support members30are made of the elastic material that is softer than the material of the first support members28. Therefore, the distance between the horizontal side second support members30and each of the edge surfaces16E3,16E4of the light guide plate16is set to be smaller compared to the configuration including the horizontal side second support members made of a material having hardness same as that of the first support members28. According to such a configuration, the horizontal side second support members30are arranged close to the light guide plate16and the thermally expanded light guide plate16is supported more stably.

The second support members29and the horizontal side second support members30are made of the same elastic material. Accordingly, a material cost for the second support members29and the horizontal side second support members30is reduced. The elastic coefficient of the second support members29and that of the horizontal side second support members30are same. Therefore, a distance between the second support members29and the corresponding edge surface of the light guide plate16and a distance between the horizontal side second support members30and the corresponding edge surface of the light guide plate16are easily set.

The first support members28are made of a material having plasticity. Accordingly, the light guide plate16is supported by the first support members28made of the material having plasticity more stably compared to the configuration including the first support members made of an elastic material. Therefore, variations in support position of the light guide plate16are less likely to be caused.

The first support members28are made of the material having plasticity such as metal or thermoplastic resin and the second support members29are made of rubber. According to such a configuration, the first support members29made of the metal or the thermoplastic resin support the light guide plate16more stably. The second support members29that are made of the rubber become in contact with the second edge surface16E2of the light guide plate16and elastically deform if the light guide plate16thermally expands. Accordingly, even if a size of the light guide plate16becomes greater than a normal size thereof due to the dimension errors, the dimension errors are effectively absorbed by the elastic deformation.

The light guide plate16includes the first edge surface16E1that is the first light entrance surface16bA and the second light edge surface16E2that is the second light entrance surface16bB, and each of the first edge surface16E1and the second edge surface16E2extends linearly along an entire length of the light guide plate16. The light guide plate may be processed to have a step between the first light entrance surface16bA and a portion of the first edge surface that is in contact with the first support members28or between the second light entrance surface16bB and the second edge surface that is in contact with the second support members29. However, in such a configuration, the light guide plate is necessary to be processed to have the above configuration. In the configuration of the present embodiment, the above processing is not necessary for the light guide plate and therefore, the size precision of the first edge surface16E1and the second edge surface16E2of the light guide plate16is improved. The first light entrance surface16bA of the light guide plate16is positioned with high precision relative to the first LEDs17A by the contact between the first support members28and the first edge surface16E1of the light guide plate16. Further, the second support members29are arranged much closer to the second edge surface16E2of the light guide plate16and therefore, the thermally expanded light guide plate16is supported more stably.

The first support member28and the second support member29are arranged at edge positions of the light guide plate16, respectively, to form a pair. Accordingly, the light guide plate16is supported more stably at its edge positions by the first support members28and the second support members29.

The first LEDs17A and the second LEDs17B are same type of LEDs. Accordingly, a manufacturing cost for the first LEDs17A and the second LEDs17B is reduced and a cost for parts control is also reduced.

The first LEDs17A and the second LEDs17B represent a lambertian light intensity distribution. The light intensity distribution of light from the first LEDs17A and the second LEDs17B represents the lambertian light intensity distribution. In such a light intensity distribution, the rays of light traveling along the optical axis have a peak light intensity and the light emission intensity tends to decrease with a curved line in the graph as the angle with respect to the optical axis increases. In the lambertian light intensity distribution, the light entrance efficiency of light emitted from the respective LEDs17A,17B and being incident on the respective light entrance surface16bA,16bB is improved as the distance between the respective LEDs17A,17B and the respective light entrance surface16bA,16bB of the light guide plate16is decreased, and the light entrance efficiency is decreased as the distance is increased. However, if the distance is greater than a certain value, the lowering rate of the light entrance efficiency becomes less likely to be decreased and does not change from a certain value. The distance A between the first light entrance surface16bA and the first LEDs17A representing the lambertian light intensity distribution is relatively decreased to improve the light entrance efficiency, and the distance B between the second light entrance surface16bB and the second LEDs17B representing the lambertian light intensity distribution is relatively increased to keep the light entrance efficiency to be the lowest certain value with allowing the size increase of the light guide plate16. Accordingly, the whole light use efficiency is improved.

The first light source corresponds to the LEDs17A mounted on the LED board (board)18and the second light source corresponds to the LEDs17B mounted on the LED board (board)18. The LEDs17generally represent a lambertian light intensity distribution. In such a light intensity distribution, the rays of light traveling along the optical axis have a peak light intensity and the light emission intensity tends to decrease with a curved line in the graph as the angle with respect to the optical axis increases. In the lambertian light intensity distribution, the light entrance efficiency of light emitted from the LEDs including the LEDs17A,17B and being incident on the respective light entrance surface16bA,16bB is improved as the distance between the LEDs including the LEDs17A,17B and the respective light entrance surface16bA,16bB is decreased, and the light entrance efficiency is decreased as the distance is increased. However, if the distance is greater than a certain value, the lowering rate of the light entrance efficiency is less likely to be decreased and does not change from a certain value. The distance A between the first light entrance surface16bA and the LEDs including the first LEDs17A representing the lambertian light intensity distribution is relatively decreased to improve the light entrance efficiency, and the distance B between the second light entrance surface16bB and the LEDs including the second LEDs17B representing the lambertian light intensity distribution is relatively increased to keep the light entrance efficiency to be the lowest certain value with allowing the size increase of the light guide plate16. Accordingly, the whole light use efficiency is improved.

Second Embodiment

A second embodiment of this invention will be described with reference toFIG. 14orFIG. 15. In the second embodiment, a reflection sheet32is further included. Configurations, functions, and effects similar to those in the first embodiment will not be described.

As illustrated inFIG. 14, a reflection sheet32is arranged between an edge portion of a light guide plate116having a second light entrance surface116bB and a light guide plate support portion123of a frame113. The reflection sheet32covers the edge portion of the light guide plate116having the second light entrance surface116bB and extends further from the second light entrance surface116bB toward second LEDs117B to form an extended portion. The extended portion of the reflection sheet32defines and covers a space between the second light entrance surface116bB and the second LEDs117B from a front-side area. Alight guide reflection sheet120is arranged along a rear-side plate surface116cof the light guide plate116and extends further from the second light entrance surface116bB toward the second LEDs117and an extended portion are opposed to the reflection sheet32. Namely, the reflection sheet32and the light guide reflection sheet120sandwich a space provided between the second light entrance surface116bB and the second LEDs117B. Accordingly, light from the second LEDs117B reflects off the reflection sheets32,120repeatedly and travels within the space between the second LEDs117B and the second light entrance surface116bB and enters the light guide plate116through the second light entrance surface116bB. Therefore, the light is less likely to leak outside the space. Accordingly, the light entrance efficiency of light from the second LEDs117B and being incident on the second light entrance surface116bB is improved. No such a reflection sheet32is arranged between an edge portion of the light guide plate116having a first light entrance surface116bA and the light guide plate support member123of the frame113.

Relation between brightness of light exiting the light guide plate116and each of the distance A and the distance B will be described with reference toFIG. 15. The distance A is between the LEDs117A and the light entrance surface116bA and the distance B is between the LEDs117B and the light entrance surface116bB. InFIG. 15, a lateral axis represents the distance A between the first LEDs117A and the first light entrance surface116bA of the light guide plate116(the distance B between the second LEDs117B and the second light entrance surface116bB of the light guide plate116), and a vertical axis represents relative brightness of light exiting the light guide plate116through the light exit surface116a. The relative brightness refers to a relative brightness value regarding total flux of light emitted from each of the first LED117A and the second LED117B as a reference value. InFIG. 15, a graph of a solid line represents relation in the configuration according to the present embodiment (including the reflection sheet32), and a graph of a two-dot chain line represents relation in the configuration according to the first embodiment (without including the reflection sheet32). Provided with the second reflection sheet32as is in the present embodiment, the whole light use efficiency is improved as the distance A between the first LEDs117A and the first light entrance surface116bA is decreased and the distance B between the second LEDs117B and the second light entrance surface116bB is increased. The whole light use efficiency is thus improved because improvement effects in the light entrance efficiency obtained by using the reflection sheet32becomes remarkable as the distance B between the second LEDs117B and the second light entrance surface116bB is increased. In such a configuration, the distances A, B are set to have the relation described in the first embodiment and the whole light use efficiency is highly improved.

Third Embodiment

A third embodiment of this invention will be described with reference toFIG. 16. In the third embodiment, LEDs217are arranged to be opposed to four sides of a light guide plate216. Configurations, functions, and effects similar to those in the first embodiment will not be described.

According to the present embodiment, as illustrated inFIG. 16, the LEDs217are arranged to be opposed to each of four edge surfaces216E1to216E4included in the light guide plate216having a plan view rectangular shape. Specifically, long-side edge surfaces216E1,216E2of the light guide plate216are a first light entrance surface216bA and a second light entrance surface216bB, respectively. First LEDs217A and second LEDs217B are arranged to be opposed to the first light entrance surface216bA and the second light entrance surface216bB, respectively. Short-side edge surfaces216E3,216E4of the light guide plate216are a third light entrance surface216bC and a fourth light entrance surface216bD, respectively. Third LEDs217C and fourth LEDs217D are arranged to be opposed to the third light entrance surface216bC and the fourth light entrance surface216bD, respectively. The third LEDs217C are arranged on a left side with respect to the light guide plate216in the horizontal direction inFIG. 16. The third light entrance surface216bC is a left short-side edge surface (a third edge surface)216E3of the light guide plate216in the horizontal direction inFIG. 16. The fourth LEDs217D are arranged on a right side with respect to the light guide plate216in the horizontal direction inFIG. 16. The fourth light entrance surface216bD is a right short-side edge surface (a fourth edge surface)216E4of the light guide plate216in the horizontal direction inFIG. 16. Hereinafter, the left-side LEDs217inFIG. 16are referred to as the third LEDs and the left-side light entrance surface216bof the light guide plate216inFIG. 16is referred to as the third light entrance surface, and a character C is added to each of the reference numerals. The right-side LEDs217inFIG. 16are referred to as the fourth LEDs and the right-side light entrance surface216bof the light guide plate216inFIG. 16is referred to as the fourth light entrance surface, and a character D is added to each of the reference numerals. The LEDs217and the light entrance surfaces216bare generally referred to without any additional character.

According to this embodiment, the third LEDs217C are arranged to have a relatively small distance C from the third light entrance surface216bC and the fourth LEDs217D are arranged to have a relatively great distance D from the fourth light entrance surface216bD. A total of the distance C and the distance D is substantially equal to a maximum size increase amount of the light guide plate216that increases its size in the horizontal direction (in a direction in which the third LEDs217C, the fourth LEDs217D and the light guide plate216are arranged) according to the thermal expansion of the light guide plate216. Accordingly, light entrance efficiency of light emitted from the third LEDs217C and entering the light guide plate216through the third light entrance surface216bC is relatively increased and light entrance efficiency of light emitted from the fourth LEDs217D and entering the light guide plate216through the fourth light entrance surface216bD is relatively decreased. However, the light entrance efficiency is less likely to be decreased according to the increase of the distance, and therefore, the light entrance efficiency does not decrease from a certain value. If the light entrance efficiency in case of that the distance C is equal to the distance D is regarded as a reference value, the light entrance efficiency of light from the third LEDs217C and being incident on the third light entrance surface216bC is higher than the reference value and the light entrance efficiency of light from the fourth LEDs217D and being incident on the fourth light entrance surface216bD is lower than the reference value. A difference value between the reference value and the light efficiency of light from the third LEDs217C and being incident on the third light entrance surface216bC is greater than a difference value between the reference value and the light efficiency of light from the fourth LEDs217D and being incident on the fourth light entrance surface216D. Accordingly, in the configuration having the distance C different from the distance D, the whole light use efficiency is improved compared to the configuration having the distance C equal to the distance D.

According to the present embodiment, third support members33are arranged on the same side as the third LEDs217C in the horizontal direction with respect to the light guide plate216and fourth support members34are arranged on the same side as the fourth LEDs217D in the horizontal direction with respect to the light guide plate216so as to have a distance from the light guide plate216. According to such a configuration, the light guide plate216is supported in the horizontal direction. As illustrated inFIG. 16, the third support members22are arranged on the same side as the third LEDs217C with respect to the light guide plate216, that is, on the left side in the horizontal direction inFIG. 16. The third support members33are mounted on a short-side screw mount portion included in a frame, which is not illustrated. The short-side screw mount portion is arranged on a left side in the horizontal direction inFIG. 16. The third support members33are arranged between the screw mount portion and the light guide plate216in the horizontal direction. The third support members33are integrally mounted on a right side surface (facing the light guide plate216) of the screw mount portion in the horizontal direction inFIG. 16by a fixing member such as a double-sided tape and adhesive. The two third support members33are mounted on two end portions of the screw mount portion in its longitudinal direction (the vertical direction), respectively. Namely, the two third support members33sandwich a group of the third LEDs217C arranged in a middle portion in the vertical direction therebetween. Each of the third support members33has a substantially elongated block shape (elongated in the vertical direction) in a plan view. The third support members33are in contact with the left short-side edge surface216E3of the light guide plate216in the horizontal direction. Specifically, the two third support members33are in contact with two end portions of the short-side edge surface216E3of the light guide plate in the longitudinal direction (the vertical direction), respectively. Portions of the short-side edge surface216E3of the light guide plate216in contact with the respective third support members33are non-illumination areas that are less likely to be illuminated with light from the third LEDs217C and differ from the third light entrance surface216bC that is an illumination area. A dimension of the third support member33in the X-axis direction substantially matches a range of the non-illumination area.

The third support members33are made of a material having plasticity (non-elastic material) that is harder than a material of the fourth support members34, which will be described next. The third support members33are made of a material same as that of first support members228. The third support members33are in contact with the edge surface216E3of the light guide plate216on their right side in the horizontal direction inFIG. 16. The third support members33are made of the hard material having plasticity as described before. Therefore, the third support members33are less likely to be deformed even if receiving stress from the light guide plate216side. Accordingly, the position of the third light entrance surface216bC relative to the third LEDs217C in the horizontal direction is kept stable and the positional relation is less likely to be changed. The third light entrance surface236bC is the left short-side edge surface216E3of the light guide plate216in the horizontal direction inFIG. 16. Namely, the distance between the third light entrance surface216bC and the third LEDs217C is always kept constant. Therefore, the distance between the third light entrance surface216bC and the third LEDs217C is set to a quite small value close to zero. Accordingly, the light entrance efficiency of light emitted from the third LEDs217C and being incident on the third light entrance surface216bC is highly improved and the high light entrance efficiency is maintained stable without depending on each product.

The fourth support members34are arranged on the same side as the fourth LEDs217D in the horizontal direction with respect to the light guide plate216, that is, on the right side in the horizontal direction inFIG. 16. The fourth support members34are integrally mounted on a left side surface (facing the light guide plate216) of the screw mount portion in the horizontal direction inFIG. 16by a fixing member such as a double-sided tape and adhesive. Two fourth support members34are mounted on two end portions of the screw mount portion in its longitudinal direction (the vertical direction), respectively. Namely, the two fourth support members34sandwich a group of the fourth LEDs217D arranged in a middle portion in the vertical direction therebetween. Each of the fourth support members34has a substantially elongated block shape (elongated in the vertical direction) in a plan view. The third support members34are arranged to have a certain distance from the right short-side edge surface216E4of the light guide plate216in the horizontal direction inFIG. 16. Specifically, the two fourth support members34are opposed to the two end portions of the short-side edge surface216E4of the light guide plate216in the longitudinal direction (the vertical direction), respectively, to have the certain distance therebetween. Portions of the short-side edge surface216E4of the light guide plate216opposed to the respective fourth support members34are non-illumination areas that are less likely to be illuminated with light from the fourth LEDs217D and differ from the fourth light entrance surface216bD that is an illumination area. A dimension of the fourth support member34in the X-axis direction substantially matches a range of the non-illumination area.

The fourth support members34are made of an elastic material that is softer than the material of the third support members33. The fourth support members34are made of a material same as that of the second support members229. At normal temperature (for example, from 5° C. to 35° C.), the fourth support members34and the right short-side edge surface216E4of the light guide plate216in the vertical direction inFIG. 16have a certain distance therebetween so as to be maintained in a non-contact state. If the temperature increases from the normal temperature to a high temperature (such as 35° C. or higher), for example, the light guide plate216increases its size in a direction along its plate surface (along the X-Y axis plane) according to the thermal expansion and moves relative to the frame, since the light guide plate216made of a synthetic resin has a thermal expansion rate higher than the metal frame. The distance between the fourth support members34and the edge surface216E4of the light guide plate216is set to be substantially equal to a maximum expansion amount of the light guide plate216in the horizontal direction. The maximum expansion amount in the horizontal direction is calculated based on the design dimension of the long side of the light guide plate216. A dimension error may be caused in the mass-produced light guide plates216within a tolerance range, that is, the long-side dimension of the light guide plate216may become greater than the predetermined dimension. If the light guide plate216having such a dimension error expands to a maximum extent in the horizontal direction according to the thermal expansion, the right short-side edge surface216E4in the horizontal direction moves to be closer to the fourth LEDs217D from the state being in contact with the fourth support members34. Even if the light guide plate216further expands as is in the above, the fourth support members34that are made of the elastic material elastically deform and support the light guide plate216stably from the right side in the horizontal direction inFIG. 16. Namely, even if a positive dimension error is caused in the light guide plate216, the fourth support members34that are in contact with the edge surface216E4of the light guide plate216elastically deform to absorb an amount of the error. If the fourth support members are made of the same material as the third support members33, the fourth support members are necessary to be arranged to have a sufficient great distance from the light guide plate216with considering the dimension error that may be caused in the light guide plate216. Compared to such a configuration of the fourth support members, the fourth support members34are arranged much closer to the light guide plate216. Accordingly, the thermally expanded light guide plate216is supported further stably. The fourth support members34according to the present embodiment have substantially similar functions as those of the horizontal side second support members30according to the first embodiment.

As described before, according to the present embodiment, the light guide plate216has a rectangular shape and has the first edge surface216E1, the second edge surface216E2, and the third edge surface216E3that is adjacent to the first edge surface216E1and the second edge surface216E2. The third edge surface216E3is the third light entrance surface216bC and the third LEDs (third light source)217C are arranged to be opposed to the third light entrance surface216bC. The light guide plate216has the fourth edge surface216E4that is opposite to the third edge surface216E3and the fourth edge surface216E4is the fourth light entrance surface216bD. The fourth LEDs (fourth light source)217D are arranged to be opposed to the fourth light entrance surface216bD and a distance D between the fourth LEDs217D and the fourth light entrance surface216bD is relatively greater than a distance C between the third LEDs217C and the third light entrance surface216bC. The third support members33are arranged on a same side as the third LEDs217C with respect to the light guide plate216. The third support members33are in contact with the third edge surface216E3of the light guide plate216so as to support the light guide plate216from the third LEDs217C side. The fourth support members34are arranged on a same side as the fourth LEDs217D with respect to the light guide plate216to have a distance from the light guide plate216. The fourth support members34are in contact with the fourth edge surface216E4to support the light guide plate216from the fourth LEDs217D side when the light guide plate216thermally expands. The fourth support members34are made of an elastic material that is softer than the material of the third support members33. According to such a configuration, the edge surfaces216E1to216E4included in the rectangular light guide plate216are the first light entrance surface216bA, the second light entrance surface216bB, the third light entrance surface216bC, and the fourth light entrance surface216bD, respectively. Light from the first LEDs217A, the second LEDs217B, the third LEDs217C, and the fourth LEDs217D is incident on the first light entrance surface216bA, the second light entrance surface216bB, the third light entrance surface216bC, and the fourth light entrance surface216bD, respectively. Accordingly, the amount of light entering the light guide plate216is sufficiently obtained and such a configuration is effective for increase in size of the backlight unit212. The distance C between the third LEDs217C and the third light entrance surface216bC is relatively decreased so that the light entrance efficiency of light from the third LEDs217C is increased. The distance D between the fourth LEDs217D and the fourth light entrance surface216bD is relatively increased and the light entrance efficiency of light from the fourth LEDs217D is not decreased from the lowest value. Accordingly, the whole light use efficiency is further improved.

The third support members33that support the light guide plate216from the third LED217C side are made of a material harder than that of the fourth support members34. Therefore, the first support members228and the third support members33stably support the light guide plate216and variations in the support position of the light guide plate216are less likely to occur. Accordingly, the position of the third light entrance surface216bC relative to the third LEDs217C is stably maintained and therefore, the distance C between the third LEDs217C and the third light entrance surface216bC is set to be shortest as possible. Therefore, the light entrance efficiency of light emitted from the third LEDs217C and being incident on the third light entrance surface216bC is highly improved. Further, the fourth support members34that support the thermally expanded light guide plate216from the fourth LEDs217D side are made of the elastic material softer than the material of the third support members33. Therefore, the distance between the fourth support members34and the fourth edge surface216E4of the light guide plate216is decreased compared to the configuration in which the fourth support members are made of a material having same hardness as the material of the third support members33. Accordingly, the fourth support members34are arranged much closer to the light guide plate216and the thermally expanded light guide plate216is supported more stably.

Fourth Embodiment

A fourth embodiment of this invention will be described with reference toFIG. 17. In the fourth embodiment, a posture of a light guide plate316differs from that in the third embodiment. Configurations, functions, and effects similar to the third embodiment will not be described.

According to the present embodiment, as illustrated inFIG. 17, the light guide plate316is postured such that the long side matches the vertical direction and the short side matches the horizontal direction. Specifically, the light guide plate316is postured such that the light guide plate316of the third embodiment (seeFIG. 16) is rotated about 90 degrees in the counterclockwise direction. Third LEDs317C and third support members333arranged along the short side of the light guide plate316are arranged on a lower side in the vertical direction with respect to the light guide plate316, and fourth LEDs317D and fourth support members334are arranged on an upper side in the vertical direction with respect to the light guide plate316. First LEDs317A and first support members328arranged along the short side of the light guide plate316are arranged on the right side with respect to the light guide plate316in the horizontal direction inFIG. 17. Second LEDs317B and second support members329are arranged on the left side with respect to the light guide plate316in the horizontal direction inFIG. 17. In such a configuration, operations and effects similar to those in the third embodiment are obtained. The configuration of the light guide plate316in the vertical position is effective for using the liquid crystal display device as an electronic device such as digital signage.

Fifth Embodiment

A fifth embodiment of this invention will be described with reference toFIGS. 18 to 21. In the fifth embodiment, cabinets Ca, Cb that hold a liquid crystal display device410from front and rear sides are further included. Configurations, functions, and effects similar to the first embodiment will not be described.

As illustrated inFIG. 18, a television device TV according to this embodiment includes a liquid crystal display device410, front and rear cabinets Ca and Cb that hold the liquid crystal display device410therebetween, a power source P, a tuner T, and a stand S. The liquid crystal display device410is held in a vertical position. As illustrated inFIG. 19, the liquid crystal display device410includes a liquid crystal panel411and a backlight unit412as an external light source. The liquid crystal panel411and the backlight unit412are held with a bezel35having a frame-like shape and surrounding a display area in the liquid crystal panel411. The liquid crystal panel411has a configuration similar to that in the first embodiment.

As illustrated inFIGS. 19 and 20, the backlight unit412includes a chassis414and an optical member415. The chassis414having a substantially tray-like shape includes a light exit portion414cthat opens to the front side. The optical member15covers the light exit portion414cof the chassis414. A pair of LED boards418on which LEDs417are mounted, a light guide plate419, and a frame36are arranged in the chassis414. The frame36holds down the light guide plate416and the optical member415from the front side of the light guide plate416and receives the liquid crystal panel411from the rear side of the light guide plate416.

As illustrated inFIGS. 19 and 20, the chassis414includes a light guide plate receiving portion414aand side plates37. The light guide plate receiving portion414ahas a landscape rectangular shape similar to the liquid crystal panel411. The side plates37extend from respective long-side outer edges and respective short-side outer edges of the light guide plate receiving portion414a. The light guide plate receiving portion414aextends along the light guide plate416and a light guide reflection sheet420arranged in the chassis414and supports them from the rear side. A LED board418is mounted on an inner surface of each of the long-side side plates37. The frame36and the bezel35are fixed to outer surfaces of the side plates37with screws.

The frame36is made of synthetic resin, and as illustrated inFIGS. 19 and 20, the frame36has a frame portion36aand a wall frame portion36b. The frame portion36aextends parallel to the optical member415and the light guide plate416and has a frame-like plan view shape. The wall frame portion36bprojects from an outer peripheral edge of the frame portion36atoward the rear side and has a substantially short wall frame shape. The frame portion36ais opposite the outer edge portions of the optical member415and the light guide plate416so as to hold down substantially entire edges of the optical member415and the light guide plate416from the front side. The wall frame portion36bis mounted to fit to outer surfaces of the side plates37of the chassis414. The frame portion36areceives outer edge portions of the liquid crystal panel411from the rear side.

As illustrated inFIGS. 20 and 21, LED boards418in a pair are attached to the respective long-side side plates37of the chassis414. The LEDs417mounted on each LED board418are arranged to be opposed to the corresponding light entrance surface416bof the light guide plate416. The LEDs417arranged on a lower side with respect to the light guide plate416inFIG. 21(on the left side inFIG. 20) are first LEDs417A, and the LEDs417arranged on an upper side with respect to the light guide plate415inFIG. 21(on the right side inFIG. 20) are second LEDs417B. A distance A between the first LEDs417A and an opposed first light entrance surface416bA is relatively small and a distance B between the second LEDs417B and an opposed second light entrance surface416bB is relatively great.

As illustrated inFIG. 21, first support members428, second support members429, and horizontal side second support members430hold the light guide plate416with the frame36and are mounted on the chassis414that holds the light guide plate416and the liquid crystal panel411with the bezel35. Specifically, the first support members428are mounted on an inner surface of a lower side one of the four side plates37included in the chassis414with a fixing member. The side plate37including the first support members428is located on a lower side in the vertical direction. The two first support members428are mounted on two end portions of the lower side plate37, respectively, with respect to the longitudinal direction of the side plate37(the horizontal direction). The two first support members428sandwich the LED board418arranged in a middle portion from two sides with respect to the horizontal direction. The second support members429are mounted on an inner surface of an upper side plate37, which is located on an upper side in the vertical direction, with a fixing member. The two second support members429are mounted on two end portions of the upper side plate37, respectively, with respect to the longitudinal direction of the side plate37(the horizontal direction). The two second support members429sandwich the LED board418arranged in a middle portion from two sides with respect to the horizontal direction. The horizontal side second support members430are mounted on inner surfaces of two side plates37, which are on horizontal ends, with a fixing member. Two horizontal side second support members430are mounted on respective two ends of each side plate37, respectively. The two side plates37are on two sides in horizontal direction. The two ends of each side plate37are two ends in the longitudinal direction of the side plate37(the vertical direction). The first support members428are in contact with a lower edge surface416E1of the light guide plate416in the vertical direction. The second support members429and the horizontal side second support members430are opposed to and away from a vertically upper edge surface416E2and horizontal-side edge surfaces416E3,416E4, correspondingly, with a certain distance. In such a configuration, operations and effects similar to those in the first embodiment are obtained.

Sixth Embodiment

A sixth embodiment of this invention will be described with reference toFIG. 22. In the sixth embodiment, a light guide plate516has a different shape. Configurations, functions, and effects similar to the first embodiment will not be described.

The light guide plate516according to the present embodiment, as illustrated inFIG. 22, includes cutouts38at four corners. Specifically, the light guide plate516has two cutouts38on each of upper and lower edge surfaces516E1,516E2in the vertical direction. The two cutouts38are recessed at two end portions of each edge surface516E1,516E2, respectively, and the two end portions are on ends in the longitudinal direction of the edge surface. The cutouts38are recessed from a first light entrance surface516bA and a second light entrance surface516bB to form steps. Each of the edge surfaces516E1,516E2has portions including the cutouts38and such portions are non-illumination areas where light from the first LEDs517A and the second LEDs517B is less likely to reach. Each of the first support members528is in contact with a recessed edge surface of each of the cutouts38included on the vertically lower edge surface516E1. The recessed edge surface is parallel to the first light entrance surface516bA. Each of the second support members529is arranged to be opposed to and away from a recessed edge surface of each of the cutouts38on the vertically upper edge surface516E2with a certain distance. The recessed edge surface is parallel to the second light entrance surface516bB. Provided with such cutouts38, surfaces of the light guide plate516opposed to the respective support members528,529are recessed inwardly from the respective light entrance surfaces516bA,516bB. Therefore, the first support members528and the second support members529are arranged close to an inner side (close to a middle portion of the light guide plate516) with respect to the vertical direction by a recessed amount. Accordingly, a frame portion is effectively decreased in size in the liquid crystal display device.

Other Embodiments

The present invention is not limited to the embodiments described in the above description and the drawings. The scope of the present invention includes the following embodiments.

(1) Other than the above embodiments, a specific ratio (a relative value) and a specific value (an absolute value) of the distance A between the first LEDs and the first light entrance surface and the distance B between the second LEDs and the second light entrance surface may be altered, as appropriate.

(2) An example of the above (1) is as follows. The first support members are in contact with the first light entrance surface to support the light guide plate and the light guide plate thermally expands and shrinks regarding the contact portion (a first edge surface) as an original point. Therefore, a value of the distance A between the first LEDs and the first light entrance surface is substantially zero. The distance B between the second LEDs and the second light entrance surface is substantially equal to a maximum expansion amount of the light guide plate in the vertical direction. According to such a configuration, the light entrance efficiency of light from the first LEDs and being incident on the first light entrance surface is increased to a maximum value and the light entrance efficiency of light from the second LEDs and being incident on the second light entrance surface is decreased to a lowest value and does not change further (see the graph inFIG. 12). The light entrance efficiency of light with the distance A being equal to the distance B is referred to as a reference value and a plus difference value between the reference value and the light entrance efficiency of light emitted from the first LEDs and entering the light guide plate through the first light entrance surface (the light entrance efficiency is higher than the reference value) is greater than a minus difference value between the reference value and the light entrance efficiency of light emitted from the second LEDs and entering the light guide plate through the second light entrance surface (the light entrance efficiency is lower than the reference value), and the plus difference value is maximum (see the graph inFIG. 13). Accordingly, the light use efficiency becomes highest.

(3) Other than the configuration (2), for example, the distance A between the first LEDs and the first light entrance surface may be one third of the total of the distance A and the distance B (the maximum expansion amount of the light guide plate in the vertical direction) or may be one third of the total of the distance A and the distance B or greater and equal to a half of the total or smaller.

(4) The technical matters described in the above (1) to (3) may be applied to a relation between the distance C between the third LEDs and the third light entrance surface and the distance D between the fourth LEDs and the fourth light entrance surface according to the third and fourth embodiments.

(5) According to a modification of the above embodiments, the first support members may be integrally formed with the frame or the chassis. Specifically, the screw mount portion of the frame described in the first embodiment may have projections as the first support members. Each of the projections projects from a part of the screw mount portion. The chassis in the fifth embodiment may have projections on the side plate or the bottom plate of the chassis as the first support members. The projections may be formed by hammering a part of the side plate or the bottom plate.

(6) In the above embodiments, the examples of the material having plasticity for the first support members include Fe, Al, PET, and PC. Other metals or other thermoplastic resins may be used for the first support members.

(7) In the above embodiments, the material having plasticity (metal or thermoplastic resins) is used for the first support members. However, an elastic material may be used for the first support members. In such a configuration, materials harder than the elastic material used for the second support members (for example, elastic materials having relatively high Durometer hardness or relatively high elastic modulus) may be effective for the first support members.

(8) In the above embodiments, natural rubber of synthetic rubber (butyl rubber, urethane rubber, silicone rubber) are included in the examples of the elastic material for the second support members. For example, elastic materials such as urethane foam or gel may be used for the second support members.

(9) In the above embodiments, the elastic material is used for the second support members. However, materials having elasticity (metal or thermoplastic resins) may be used for the second support members. In such a configuration, the material having elasticity that is softer than the material having elasticity used for the first support members (for example, material having plasticity having relatively low Rockwell hardness) may be effective for the second support members.

(10) In the above embodiments, the first support members and the second support members are mounted on the frame or the chassis. However, the first support members and the second support members may be mounted on the LED board. In such a configuration, the LED board extends further to be opposed to respective two edge surfaces of the light guide plate in the vertical direction or the horizontal direction, and the first support members or the second support members may be mounted on the extended end portions of the LED board (opposed to two end portions of each of the edge surfaces).

(11) In the configuration of (10), the LED board may include connectors that supply power to the LEDs and the connectors may be used as the first support members. In such a configuration, the second support member may be mounted on a surface of each connector facing the edge surface of the light guide plate.

(12) In the above embodiments, portions of the edge surfaces of the light guide plate being contact with the respective support members (the first support members, the second support members, the third support members, the fourth support members, the horizontal side second support members) are parallel to the vertical direction or the horizontal direction. However, the edge surfaces that are in contact with the respective support members may be inclined with respect to the vertical direction and the horizontal direction.

(13) Other than the above embodiments, specific mounting methods of mounting the respective support members (the first support members, the second support members, the third support members, the fourth support members, the horizontal side second support members) on the frame or the chassis may be altered, if necessary. Examples of the mounting methods of mounting the support members may include fixing with screws, rivets, and clips.

(14) In the first, second, fifth, and sixth embodiments, the light guide plate is in the horizontal position. However, as is described in the fourth embodiment, the light guide plate may be in the vertical position. In such a configuration, it may be effective that the first support members and the second support members are arranged to be contact with short-side edge surfaces of the light guide plate.

(15) In the second embodiment, the reflection sheet is arranged to define the space between the second LEDs and the second light entrance surface. However, in addition to the reflection sheet on the second LEDs side, a reflection sheet may be arranged to define a space between the first LEDs and the first light entrance surface.

(16) In the above embodiments, the liquid crystal display device is used such that the display surface of the liquid crystal panel is substantially parallel to the vertical direction. However, the present invention may be applied to a liquid crystal display device that is used with the display surface of the liquid crystal panel substantially parallel to the horizontal direction.

(17) Other than the above embodiments, a planar shape, a cross-sectional shape, the arrangement number, and a planar arrangement of the respective support members (the first support members, the second support members, the third support members, the fourth support members, the horizontal side second support members) may be altered, if necessary.

(18) In the first and fifth embodiments, the LEDs are arranged to be opposed to the two long-side edge surfaces of the light guide plate. However, the LEDs may be arranged to be opposed to two short-side edge surfaces of the light guide plate. In such a configuration, the two short-side edge surfaces of the light guide plate may be the first light entrance surface and the second light entrance surface, respectively, and the first support members and the second members may be arranged to be opposed to the short-side edge surfaces, respectively.

(19) In the above embodiments, the LEDs are arranged to be opposed to a pair of edge surfaces or four edge surfaces of the light guide plate. However, the LEDs may be arranged to be opposed to any three edge surfaces of the light guide plate.

(20) In the above embodiments, the LED board including the first LEDs and the LED board including the second LEDs are same type of components. However, the LED board including the first LEDs and the LED board including the second LEDs may be different types of components.

(21) Other than the above embodiments, the number of LED boards, the specific number of LEDs mounted on the LED board, and the interval between the LEDs on the LED board may be altered as appropriate.

(22) Other than the above embodiments, the light reflection portion formed on the surface opposite to the light exit surface of the light guide plate may have a different arrangement configuration of the dot pattern as appropriate.

(23) In the above embodiments, the LED is used as alight source. However, a light source other than the LED, such as an organic EL, a cold cathode tube, or a hot cathode tube may be used.

(24) In the above embodiments, the color filter of the liquid crystal panel includes color portions in three colors, red, green, and blue. However, the color filter may include color portions in four or more colors.

(25) In the above embodiments, TFTs are used as switching components of the liquid crystal display device. However, the technology described above can be applied to liquid crystal display devices including switching components other than TFTs (e.g. thin film diode (TFD)). The technology can be applied to not only color liquid crystal display devices but also black-and-white liquid crystal display devices.

(26) In the above embodiments, the liquid crystal display device including the liquid crystal panel as a display panel is used. However, the technology can be applied to display devices including other types of display panels.

(27) In the above embodiments, the television device including the tuner is used. However, the technology can be applied to a display device without a tuner. Specifically, the technology can be applied to a liquid crystal display device used as an electronic blackboard.

EXPLANATION OF SYMBOLS

10,410: liquid crystal display device (display device),11,411: liquid crystal panel (display panel),12,212,412: backlight unit (lighting device),16,116,216,316,416,516: light guide plate,16a,116a: light exit surface,16b,216b,416b: light entrance surface,16bA,116bA,216bA,416bA,516bA: first light entrance surface,16bB,116bB,216bB,416bB,516bB: second light entrance surface,16E1,416E1,516E1: edge surface (first edge surface),16E2,416E2,516E2: edge surface (second edge surface),16E3,16E4,416E3,416E4: edge surface (adjacent edge surface),17A,117A,217A,317A,417A,517A: first LED (first light source),17B,117B,217B,317B,417B,517B: second LED (second light source),28,228,328,428,528: first support member,29,229,329,429,529: second support member,30,430: horizontal side second support member,33,333: third support member,34,334: fourth support member,216bC: third light entrance surface,216bD: fourth light entrance surface,216E3: edge surface (third edge surface),216E4: edge surface (fourth edge surface),217C,317C: third LED (third light source9,217D,317D: fourth LED (fourth light source), A-D: distance, TV: television device