Lighting device and display device

A lighting device includes a light source, a light guide plate, a chassis, a reflection sheet, and a supplementary member. The light guide plate is configured to guide light from the light source. The chassis includes a bottom for housing the light guide plate and recesses in the bottom. The reflection sheet is disposed between the light guide plate and the bottom and configured to reflect light toward the light guide plate. The supplementary member includes a body having a plate shape and is disposed between the reflection sheet and the bottom. The body includes a plate surface on a reflection sheet side including a flat surface.

TECHNICAL FIELD

The technology described herein relates to a lighting device and a display device.

BACKGROUND

A liquid crystal display device including an edge-light type (a side-light type) backlight unit in which a light source is disposed behind an edge of a liquid crystal panel such as one disclosed in Japanese Unexamined Patent Application Publication No. 2009-272451 has been known. In the edge-light type backlight unit, light from the light source such as an LED enters a light guide plate, travels through the light guide plate, and exits toward the liquid crystal panel. A reflection sheet is disposed behind the light guide plate (on an opposite side from the liquid crystal panel). The reflection sheet reflects leakage light from the back surface of the light guide plate to return the light to the light guide plate. The light guide plate and the reflection sheet are housed in a chassis made of metal. The chassis has a box shape with an opening on a liquid crystal panel side.

The light guide plate and the reflection sheet made of synthetic resins may expand and contact according to operating temperatures. If variations in operating temperature repeatedly occur, from low to high and from high to low, the light guide plate and the reflection sheet repeatedly expand and contract. If the reflection sheet and the light guide plate are placed on the bottom of the chassis in this sequence and housed in the chassis, surfaces of the bottom of the chassis and the reflection sheet that contact each other or surfaces of the reflection sheet and the light guide plate that contact each other may rub against each other due to the expansion and the contraction.

The bottom of the chassis may include a recess formed in a flat surface by drawing a section of the flat surface to recess toward the rear (an opposite side from the liquid crystal panel). If the reflection sheet and the bottom of the chassis rub against each other due to the expansion and the contraction, the reflection sheet may be drawn into an internal space of the recess due to a weight of the light guide plate and warped or scarred along a border between the flat surface and the recess. The reflection sheet made of the synthetic resin has a thickness in a range from 100 μm to 300 μm, that is, the reflection sheet is thin. The recess may affect the light guide plate on the reflection sheet, that is, the back surface of the light guide plate may be scarred. Scars on the reflection sheet or the light guide plate or warp of the reflection sheet may cause uneven brightness in the backlight unit or the liquid crystal display device includes the backlight unit.

SUMMARY

The technology described herein was made in view of the above circumstances. An object is to reduce uneven brightness.

A lighting device according to the technology described herein includes a light source, a light guide plate, a chassis, and a supplementary member. The light guide plate is configured to guide light from the light source. The chassis includes a bottom for housing the light guide plate and recesses in the bottom. The supplementary member includes a body having a plate shape. The supplementary member is disposed between the reflection sheet and the bottom. The body includes a plate surface on a reflection sheet side includes a flat surface.

A display device according to the technology described herein includes the lighting device and a display panel configured to display as image using light applied by the lighting device.

According to the technology described herein, uneven brightness can be reduced.

DETAILED DESCRIPTION

First Embodiment

A first embodiment of the technology described herein will be described in detail with reference toFIGS. 1 and 2. In this section, a liquid crystal display device10(an example of a display device) including a backlight unit30(an example of a lighting device) will be described. In the drawings, X-axes, Y-axes, and Z-axes may be present. The axes in each drawing correspond to the respective axes in other drawings. A liquid crystal panel20side in the Z-axis direction and an opposite side from the liquid crystal panel20in the Z-axis direction correspond to the front side and the rear side of the liquid crystal display device10.

As illustrated inFIG. 1, the liquid crystal display device10includes a liquid crystal panel20(an example of a display panel) configured to display images and the backlight unit30(an example of the lighting device) configured to apply light to the liquid crystal panel20. The liquid crystal panel20and the backlight unit30are held together by a bezel14having a frame shape. The liquid crystal panel20has a horizontally rectangular overall shape. The liquid crystal panel20includes a pair of glass substrates that are bonded together with a predefined gap therebetween and a liquid crystal layer sealed between the glass substrates. The glass substrates are transparent (having high light transmissivity). Polarizing plates are disposed on outer surfaces of the glass substrates.

As illustrated inFIGS. 1 and 2, the backlight unit30includes a chassis40(a backlight chassis) having a box shape with an opening on the front side (on the light exiting side, the liquid crystal panel20side). Light emitting diodes (LEDs)52(a light source), an LED substrate51, a light guide plate60, an optical sheet33, a reflection sheet70, and a supplementary member80are housed in the chassis40. The LEDs52are mounted on the LED substrate51. The light guide plate60is configured to guide light from the LEDs52. The optical sheet33is configured to exert predefined optical effects on the light exiting from the light guide plate60. The reflection sheet70is configured to reflect leakage light toward the light guide plate60. The supplementary member80is disposed between the reflection sheet70and the bottom41of the chassis40. The backlight unit30includes a frame15having a frame shape to surround the LEDs52, the light guide plate60, and the optical sheet33. As illustrated inFIG. 1, the LEDs52are disposed along a long edge of the backlight unit30, that is, the backlight unit30is a single-side light entering type edge-lit (side-lit) backlight in which light from the LEDs52enters the light guide plate60only from one side. Next, components of the backlight unit30will be described in detail.

As illustrated inFIGS. 1 and 2, the LEDs52are arranged in line and at equal intervals on a surface (a mounting surface) of the LED substrate51. The LED substrate51has an elongated plate shape that extends along one of long edges of the chassis40. The LEDs52are adjacent to a side surface61(a light entering end surface) of the light guide plate60with a predefined gap between the light guide plate60and the LEDs52.

As illustrated inFIGS. 1 and 2, the light guide plate60has a horizontally-long rectangular shape in the plan view similar to the liquid crystal panel20and the bottom41of the chassis40. The light guide plate60has a thickness larger than the thickness of the optical sheet. The light guide plate60is made of a substantially transparent synthetic resin material having a refractive index sufficiently higher than the refractive index of air (e.g., acrylic resin such as PMMA, poly carbonate). The light guide plate60receives the light that is emitted by the LEDs52in the Y-axis direction through the light entering end surface61, transmits the light therethrough, and guides the light toward the optical sheet33such that the light exits through the front surface62(a light exiting plate surface) on the front side.

The optical sheet has flexibility. As illustrated inFIGS. 1 and 2, the optical sheet33has a horizontally-long rectangular shape in the plan view similar to the liquid crystal panel20and the bottom41of the chassis40. The optical sheet33includes at least a diffuser sheet and a light collecting (prism) sheet that are disposed on top of each other. The optical sheet33is disposed between the liquid crystal panel20and the light guide plate60to exert predefined optical effects on the light exiting from the light guide plate60and to guide the light toward the liquid crystal panel20.

As illustrated inFIGS. 1 and 2, the reflection sheet70has a horizontally-long rectangular shape in the plan view similar to the liquid crystal panel20and the bottom41of the chassis40. The reflection sheet70is made of synthetic resin and includes a white surface having high light reflectivity. The reflection sheet70is disposed on a back surface63of the light guide plate60. The reflection sheet70reflects leakage light from the back surface63of the light guide plate60or the LEDs52toward the light guide plate60.

The chassis40is made of metal or resin. As illustrated inFIGS. 1 and 2, the chassis40has shallow box shape with an opening on the front side. The chassis40includes the bottom41and sides42. The bottom41has a horizontally-long rectangular shape similar to the liquid crystal panel20. The sides42project from the outer edges of the bottom41toward the front side. On an outer surface of the bottom41on the rear side, substrates32such as a control circuit for supplying control signals to the liquid crystal panel20and a power supply substrate are mounted.

As illustrated inFIGS. 1 and 2, the bottom41includes recesses43that are formed to protrude from the back of the chassis40. The recesses43are formed by drawing sections of the bottom41toward the rear side. The recesses43are mounting bases for mounting the substrates32. The substrates32are placed on the recesses43and fixed to the bottom41with screws B. The recesses43include insertion holes43A. The screws B are inserted into internal spaces of the recesses43through the insertion holes43A.

The supplementary member80that includes a body81having a plate shape is disposed between the bottom41and the reflection sheet70. The body81includes a single plate that may be made of synthetic resin such as poly carbonate or metal such as aluminum, stainless steel, and iron (including alloy). At least a plate surface81A that is one of plate surfaces of the body81on a reflection sheet70side may include a flat surface without irregularity.

As described above, the backlight unit30according to this embodiment includes the LEDs52, the light guide plate60, the chassis40, the reflection sheet70, and the supplementary member80. The light guide plate60guides the light from the LEDs52. The chassis40includes the bottom41that houses the light guide plate60. The bottom41includes the recesses43. The reflection sheet70is disposed between the light guide plate60and the bottom41to reflect the light toward the light guide plate60. The supplementary member80includes the body81that is disposed between the reflection sheet70and the bottom. The plate surface81A of the body81on the reflection sheet70side includes the flat surface.

Because the body81of the supplementary member80is disposed between the reflection sheet70and the bottom41of the chassis40, the reflection sheet70and the bottom41of the chassis40are less likely to contact each other and thus less likely to rub against each other. The reflection sheet70may rub against the body81when the reflection sheet70expands and contracts. Because the body81includes the flat surface on the reflection sheet70side, the reflection sheet70is less likely to have local scars or a warp. Therefore, uneven brightness resulting from the recesses43in the bottom41of the chassis40is less likely to occur.

The body81in this embodiment includes the single plate. In a configuration in which the body31includes multiple plates, a step may be created between the adjacent plates. The step may cause scars on the reflection sheet70and the light guide plate60or a warp of the reflection sheet70. This may result in uneven brightness. Because the body81includes the single plate, such a problem is less likely to occur.

The material of the body81in this embodiment may be resin or metal. Because the body81is made of such a material, the body81has a predefined level of hardness. According to the configuration, the recesses43in the chassis40are less likely to affect the reflection sheet70and the light guide plate60on the body81.

Second Embodiment

A liquid crystal display device110according to a second embodiment of the technology described herein will be described with reference toFIG. 3. In the second embodiment, the supplementary member80is fixed to the chassis40with double-sided adhesive tapes90. Components, functions, and effects similar to those of the first embodiment previously described will not be described.

In this embodiment, the back surface81B of the body81of the supplementary member80and the front surface44of the bottom41of the chassis40are fixed to each other with the double-sided adhesive tapes90(an example of a fixing member) according to the configuration, the supplementary member80is stably disposed. Size and locations of the double-sided adhesive tapes90are not limited as long as the double-sided adhesive tapes90fix the supplementary member80to the chassis40so that the supplementary member80is integrally provided with the chassis40. The fixing member is not limited to the double-sided adhesive tapes90. The fixing member may be an adhesive.

Third Embodiment

A third embodiment of the technology described herein will be described with reference toFIG. 4. In the third embodiment, the supplementary member80and the reflection sheet70are fixed to each other with the double-sided adhesive tape90. Components, functions, and effects similar to those of the first embodiment and the second embodiment previously described not be described.

In this embodiment, the front surface81A (the plate surface on the reflection sheet70side) of the body81of the supplementary member80and the back surface71of the reflection sheet70are fixed to each other with the double-sided adhesive tape90. According to the configuration, the supplementary member80is stably disposed. The reflection sheet70may expand and contract according to the operating temperatures. If double-sided adhesive tapes90are attached to multiple sections, the reflection sheet70may be curved or warped. Therefore, it is preferable to attach the double-sided adhesive tape90to a section of an outer edge of the reflection sheet70. More preferably, the reflection sheet70may be attached to an edge away from the LEDs52as illustrated inFIG. 4so that the double-sided adhesive tape90is less likely to be under an influence of variations in temperature due to heat radiated by the LEDs52.

Fourth Embodiment

A liquid crystal display device310according to a fourth embodiment of the technology described herein will be described with reference toFIG. 5. In the fourth embodiment, the supplementary member80includes projecting portions82that project from outer edges of the body81of the supplementary member80. Components, functions, and effects similar to those the first embodiment to the third embodiment previously described will not be described.

In this embodiment, the supplementary member80includes the projecting portions82that project from the outer edges of the body81toward the front side. The projecting portions82are located the outer edges of the body81, respectively. Therefore, the supplementary member80has a box shape. The shapes and the sizes of outer surfaces (back surfaces) of the body81and the projecting portions82correspond with inner surfaces (front surfaces) of the bottom41and the sides42of the chassis40having the box shape. The outer surfaces of the supplementary member80are fitted with the inner surfaces of the chassis40. Therefore, the supplementary member80is stably disposed. It is not necessary to provide the projecting portions82at all the outer edges of the body81. At least two projecting portions may be provided at opposed edges (opposed long edges or opposed short edges) of the body81.

Other Embodiments

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

(1) In the first embodiment, the recesses in the bottom of the chassis are provided for the mounting bases for mounting of the substrates. However, the recesses may be replaced with ribs with grooves to improve the rigidity of the bottom.

(2) In the first embodiment, the LEDs are disposed on the side surface of the light guide plate. However, the LEDs may be disposed on both of the opposed side surfaces and the backlight unit may be configured as a double-side light entering type edge-lit backlight.

(3) In each of the above embodiments, a method of holding the reflection sheet is not limited. For example, the chassis may include protrusions (e.g., holding pins) provided at the edges of the chassis and inserted in holes formed in edges of the reflection sheet to hang the reflection sheet.

(4) In each of the above embodiments, the LEDs are used for the light source. However, other types of light sources such as organic ELs may be used.

(5) In each of the above embodiments, the liquid crystal display device has the horizontally-long rectangular shape. However, liquid crystal display devices having vertically-long rectangular shapes other shaped may be included in the technical scope.