JP4509913B2 - Surface light source device and display device - Google Patents

Description

  The present invention relates to a surface light source device and a display device, and more particularly to a surface light source device suitable for a backlight light source such as a liquid crystal display and a display device including the surface light source device.

  In recent years, light emitting diode elements have significantly improved luminous efficiency, and their application to lighting has been advanced. In particular, when a light emitting diode element is used as a backlight of a liquid crystal display, good color reproducibility and high speed response can be realized, and high quality image quality is expected.

  Conventionally, as a backlight of a liquid crystal display, a so-called edge light type backlight in which a cold cathode tube is arranged on an end face of a casing as a light source has been mainly used for thinning and low power consumption (Patent Document 1). 2) In recent years, demand for larger liquid crystal displays has increased, and there is a limit to the improvement and uniformity of luminance in the edge light type. Therefore, the adoption of a direct type light for a large-sized liquid crystal display has been studied (Patent Document 3).

  FIG. 18 is a cross-sectional view showing the structure of a conventional direct type surface light source device used for a liquid crystal display. The surface light source device 11 is disposed immediately below the liquid crystal display panel 21. In the surface light source device 11, LED lamps 1 using light emitting diode elements are two-dimensionally arranged on the bottom surface of the housing 12, and these LED lamps 1 are used as light sources. The bottom surface and side surfaces of the housing 12 are covered with a reflection sheet 13. Above the LED lamp 1, a diffusion plate 14 and a prism sheet 15 are disposed at a distance of usually 2 to 5 cm from the LED lamp 1.

  When the LED lamp 1 is caused to emit light, the emitted light is reflected directly or by the reflecting sheet 13 toward the diffusing plate 14, diffusely reflected in the diffusing plate 14, and then passes through the prism sheet 15 so as to be reflected in the vertical direction. Is inclined and enters the liquid crystal display panel 21. Light emitted from different LED lamps 1 is mixed in the space between the diffuser plates 14 and further diffusely reflected in the diffuser plate 14 to promote mixing, thereby making the luminance and chromaticity uniform. In general, the LED lamp 1 has an anisotropy in the luminance distribution such that the upward direction is the brightest, and the luminance corresponding to the portion directly above the LED lamp 1 is increased. By doing so, it is possible to improve the uniformity of luminance.

  However, in the conventional surface light source device, as described above, a diffusion plate is provided to make the luminance and chromaticity uniform, and the distance between the LED lamp and the diffusion plate is further increased. There was a problem that the brightness was increased.

In particular, when color mixing is performed using a multi-color (RGB) LED lamp instead of a single color LED lamp, there is a problem that the color mixture is not sufficient and color unevenness is visible.
In order to reduce such unevenness in brightness, the diffusion level of the diffuser is increased in the portion corresponding to the portion directly above the LED lamp, or a so-called lighting curtain is provided directly above the LED lamp to decrease the brightness directly above the LED lamp. It has been done.

  However, these means lead to a decrease in light use efficiency. Further, if the distance between the LED lamp and the diffusion plate is increased, the luminance unevenness and the chromaticity unevenness can be reduced. However, this causes an increase in the thickness of the backlight, which is not preferable for a flat panel display.

In such a direct type surface light source device, in order to sufficiently achieve uniform luminance and chromaticity and to prevent the surface light source device from becoming thick, the LED lamp 1 is arranged as shown in FIG. It is effective to disperse light in the light guide plate 4 and to propagate the light guide plate 4 uniformly by disposing the light guide plate 4 facing the LED lamp 1 in front of the substrate 3.

However, even when such a light guide plate is used, the luminance of the light guide plate increases at the front position of the LED lamp, and the luminance unevenness cannot be eliminated.
JP 2003-344852 A Japanese Patent Laying-Open No. 2005-268021 Japanese Patent Laid-Open No. 7-191311

An object of the present invention is to provide a surface light source device in which luminance unevenness due to high luminance at a position immediately above a light source is reduced without increasing the thickness.
Another object of the present invention is to provide a surface light source device in which not only luminance unevenness but also color unevenness is reduced when light sources of a plurality of colors such as RGB are used.

  A further object of the present invention is to provide a display device provided with such a surface light source device.

  As a result of intensive studies, the present inventors have arranged the light source so that the optical axis is inclined with respect to the light guide plate when a light source such as an LED lamp having an optical axis with the highest luminance is used. Thus, the distance in the optical axis direction between the light source and the light guide plate can be increased without increasing the thickness of the surface light source device, and the light emitted from the light source toward the optical axis direction and the back surface of the light guide plate Reflection and refraction are promoted, and as a result, it has been found that luminance unevenness and color unevenness are reduced, and the present invention has been completed.

Furthermore, the present inventors have found that luminance unevenness and color unevenness can be further reduced by providing a concave portion at a specific position on the back surface of the light guide plate, thereby completing the present invention.
The present invention is as described in the following [1] to [10].

[1] A light guide plate in which a plurality of light sources having an anisotropy in luminance distribution and having an optical axis with the highest luminance are two-dimensionally arranged on a substrate and face the plurality of light sources in front of the substrate Is a surface light source device arranged,
The surface light source device, wherein the plurality of light sources are arranged such that an optical axis is inclined with respect to the light guide plate.

  [2] The surface light source device according to [1], wherein an angle of an optical axis with respect to the light guide plate is 10 degrees to 80 degrees.

  [3] The surface light source device according to [1] or [2], wherein a concave portion is provided at a position on the back surface of the light guide plate where an intersection of the back surface and the optical axis of the light source is included.

  [4] The surface light source device according to [3], wherein the shape of the recess is a cone, a pyramid, a cylinder, a prism, or a hemisphere.

  [5] The surface light source device according to [3] or [4], wherein a concave portion is provided on the front surface of the light guide plate.

  [6] The surface light source device according to [3] or [4], wherein dots for light scattering are provided on the front surface of the light guide plate.

  [7] The surface light source device according to any one of [1] to [6], wherein the plurality of light sources are LED lamps.

  [8] The surface light source device according to [7], wherein the LED lamp includes a red LED lamp, a green LED lamp, and a blue LED lamp.

  [9] A display device comprising the surface light source device according to any one of [1] to [8].

  [10] The display device according to [9], wherein the display unit is a liquid crystal panel.

Although the surface light source device of the present invention is thin, the luminance uniformity is good, and when a light source of a plurality of colors is used, the chromaticity uniformity is also good.
In the display device of the present invention, since a display device such as a liquid crystal display is configured using the above-described surface light source device as a backlight, a high-quality image can be obtained.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The surface light source device of the present invention includes a substrate, light sources arranged two-dimensionally on the substrate, and a light guide plate arranged to face these light sources.

  It is preferable that the board | substrate with which a light source is arrange | positioned has the heat dissipation for releasing the heat | fever generated from a light source fully. Examples of the substrate material having heat dissipation include metals such as aluminum, copper and stainless steel, and high thermal conductive ceramics such as aluminum nitride.

  The circuit board to which the terminal of the light source is electrically connected, for example, an insulating resin substrate such as a glass epoxy substrate, is bonded to the above substrate, and a circuit substrate in which the copper foil is etched into a circuit shape is bonded. May be.

  The light source used in the present invention has an anisotropy in the luminance distribution and has an optical axis with the highest luminance. Such light sources are usually brightest in the direction immediately above, and the brightness gradually decreases as the angle with respect to the direction directly above increases. In this case, the optical axis is the direction immediately above where the luminance is highest.

  As the light source, an LED lamp is preferable. The LED lamp is usually composed of a package part in which a light emitting diode element is mounted in a package and a lens part made of a transparent material and having a lens action for directing light emitted from the light emitting diode element. The package portion is provided with a terminal for supplying a direct current while being electrically connected to the outside.

  As a mode of arranging a plurality of LED lamps on a substrate, a red LED lamp mounted with a red (R) light emitting diode element, a green LED lamp mounted with a green (G) light emitting diode element, and blue (B) light emission A mode in which a blue LED lamp mounted with a diode element is disposed on a substrate and white light is emitted by mixing these three primary colors is preferable.

The R, G, B LED lamps are, for example, one each of R, G, B, one unit, one unit of R1, G2, one unit of B1, R2, G2, Arranged in a manner of regular arrangement on the substrate, with B1 as one unit as a unit arrangement. For example, when the unit arrangement is a linear arrangement of R2, G2, and B1, each color LED lamp is arranged in the order of R, G, B, G, R.

  In addition, when the surface light source device is for white illumination, in addition to the combination of R, G, and B, a so-called intermediate color LED lamp such as yellow or orange is used, and white color is obtained by mixing with light emitted from other LED lamps. You may make it light-emit.

The arrangement interval of the LED lamps is not particularly limited, but is preferably 5 mm or more when a high power element is used.
A reflective layer is provided between the substrate and the light guide plate. Examples of such a reflective layer include a white reflective sheet bonded to the front surface of the substrate, a white paint film printed on the front surface of the substrate, and the like.

  The light guide plate is a plate-like member typically made of a transparent resin, and the thickness thereof is preferably 0.3 mm to 30 mm, more preferably 0.5 mm to 20 mm, and still more preferably 0.8 mm to 15 mm. It is. If the thickness is less than 0.3 mm, the function of the light guide plate may be insufficient. On the other hand, if the thickness exceeds 30 mm, there is a risk that the attenuation of the amount of light will increase and the required luminance cannot be ensured. In a so-called direct type backlight, it is effective to use a light guide plate in order to sufficiently achieve uniform brightness and chromaticity and to prevent the surface light source device from becoming thick. That is, in the direct type backlight, since a light source such as an LED lamp is installed forward, it is desirable that light is diffused and uniformly propagated in the light guide plate, and then extracted forward.

  It is preferable to dispose a diffuser plate in the front of the light guide plate of the LED lamp disposed on the substrate, preferably at a distance of 1 cm to 5 cm, similarly to the surface light source device shown in FIG. For example, LED lamps are arranged on the bottom surface of a housing whose bottom surface and side surfaces are covered with a reflection sheet, and a diffusion plate is disposed on the top surface side of the housing.

  In the surface light source device of the present invention having the above-described configuration, the light source is disposed such that the optical axis is inclined with respect to the light guide plate. 1-3 is sectional drawing which showed embodiment of the surface light source device of this invention, and has shown the board | substrate with which the LED lamp is arrange | positioned, and a part of light-guide plate.

  As shown in FIG. 1, the LED lamp 1 is installed on an inclined surface in a recess 3 a provided in the substrate 3, and its optical axis 2 is arranged in front of the substrate 3 so as to face the LED lamp 1. The light guide plate 4 is inclined by an angle θ.

Thus, by arranging the LED lamp 1 so that the optical axis 2 is inclined with respect to the light guide plate 4, the LED lamp 1 and the LED lamp 1 can be formed without increasing the thickness t from the back surface of the substrate 3 to the front surface of the light guide plate 4. The distance l ₂ in the optical axis direction with respect to the light guide plate 4 is compared with the distance l ₁ when the LED lamp 1 is arranged so that the optical axis 2 is not inclined with respect to the light guide plate 4 as shown in FIG. And can be enlarged. Further, reflection / refraction of the light emitted from the LED lamp 1 toward the optical axis direction and the back surface of the light guide plate 4 is promoted. By doing so, the luminance unevenness is reduced, and when an LED lamp of a plurality of colors such as RGB is used, the color unevenness is simultaneously reduced.

  The angle θ of the optical axis 2 with respect to the light guide plate 4 is preferably 10 to 80 degrees, more preferably 15 to 75 degrees, and further preferably 30 to 60 degrees. If the angle θ is too small, the area per LED lamp increases, and the brightness as a whole may decrease. If the angle θ is too large, the above-described effect due to tilting the optical axis with respect to the light guide plate may not be obtained sufficiently.

In addition to the structure shown in FIG. 1, the substrate may have a structure in which the recesses 3 a of the substrate 3 to which the LED lamp 1 is attached are provided at intervals via the flat part 3 b as shown in FIG. 2.
Further, as shown in FIG. 3, the package portion 1b of the LED lamp 1 may be embedded in the substrate 3, and only the lens portion 1a may be exposed on the front surface of the substrate 3. In this case, the terminal of the LED lamp 1 can be positioned on the back side of the substrate 3.

  The method of installing a plurality of LED lamps on the substrate may be such that the inclination direction of the optical axis is directed to the arrangement direction of the LED lamps, and the inclination direction of the optical axis is directed to a direction perpendicular to the arrangement direction of the LED lamps. May be. Or you may make it the inclination direction of the optical axis in each LED lamp face a mutually different direction.

The aspect which installs a some LED lamp in a board | substrate is shown in FIGS. Of the LED lamps arranged two-dimensionally, only one row is partially shown, and only two rows are partially shown in FIG.
In FIG. 4, the LED lamp 1 is arranged in the concave portion 3 a of the substrate 3 so that the inclination direction of the optical axis 2 of the LED lamp 1 is oriented in a direction perpendicular to the arrangement direction of the LED lamps 1.

  In FIG. 5, the inclination direction of the optical axis 2 of the LED lamp 1 is directed in a direction perpendicular to the arrangement direction of the LED lamps 1, and the inclination directions of the optical axes 2 of the adjacent LED lamps 1 are opposite to each other. The LED lamp 1 is disposed in the recess 3 a of the substrate 3.

In FIG. 6, the LED lamp 1 is arranged in the concave portion 3 a of the substrate 3 so that the inclination direction of the optical axis 2 of the LED lamp 1 faces the arrangement direction of the LED lamp 1.
In FIG. 7, the inclination direction of the optical axis 2 of the LED lamp 1 is oriented in a direction perpendicular to the arrangement direction of the LED lamps 1, and the inclination directions of the optical axis 2 of the LED lamps 1 in two adjacent rows are opposite to each other. The LED lamp 1 is disposed in the concave portion 3a of the substrate 3 so as to face.

  Moreover, the method of installing a plurality of LED lamps on the substrate may be as shown in FIGS. 8A to 8D, in addition to installing the LED lamps in the recesses provided on the substrate. 8 (a) and 8 (b), the LED lamp 1 is installed on the inclined plate 5 supported by the support member 6 so as to be inclined with respect to the substrate 3, whereby the optical axis is inclined with respect to the light guide plate. As shown, the LED lamp 1 is installed.

  In FIG. 8C, the inclined plate 5 on which the LED lamp 1 is installed is supported by the support member 6 so as to be inclined with respect to the substrate 3, and a resin adhesive or the like is interposed between the inclined plate 5 and the substrate 3. Thus, the sealing material 7 having fluidity and curability is filled and cured to fix them, and thus the LED lamp 1 is installed so that the optical axis is inclined with respect to the light guide plate.

  In FIG. 8 (d), a pair of inclined plates 5 on which the LED lamps 1 are installed are supported on the support member 6 installed on the substrate 3 so as to be inclined in opposite directions. The LED lamps 1 are installed so that the optical axes of the LED lamps 1 are inclined in different directions.

In the preferable aspect in this invention, the recessed part is provided in the position where the intersection of the said back surface and the optical axis of a light source is included in the back surface of a light-guide plate. 9 to 16 are sectional views showing such an example. As shown in the drawing, a recess 4 a is provided on the back surface of the light guide plate 4 at a position including the intersection of the back surface and the optical axis 2 of the LED lamp 1.
By providing such a recess 4a, the light emitted from the LED lamp 1 in the optical axis direction is scattered by the recess 4a and further reflected from the front and / or back of the light guide plate and then from the front surface of the light guide plate 4. Emitted. Therefore, it is possible to further improve the uniformity of the luminance distribution on the light exit surface of the light guide plate. In addition, when a multi-color LED lamp is used, color unevenness is reduced at the same time.

  The shape of the recess 4a may be various shapes such as a conical shape as shown in FIG. 9, a cylindrical shape as shown in FIG. 10, and a hemispherical shape as shown in FIG. Further, the shape may be asymmetric as shown in FIGS.

Preferably, the shape of the recess 4a is a cone, a pyramid, a cylinder, a prism, or a hemisphere. When the shape of the recess 4a is a cone or a pyramid, the apex angle is, for example, 90 degrees to 120 degrees.
The recess 4a does not necessarily have to be provided only at a position where the intersection of the back surface of the light guide plate 4 and the optical axis 2 of the LED lamp 1 is included. As shown in FIG. May be provided.

  Further, in order to further reduce luminance unevenness and color unevenness, a recess 4b may also be provided on the front surface of the light guide plate 4 as shown in FIGS. As the arrangement location of the recess 4b, a position just above the recess 4a on the back surface of the light guide plate 4 as shown in FIG. 15, a position between adjacent recesses 4a on the back surface of the light guide plate 4 as shown in FIG. It is done.

  Further, in order to further improve the luminance uniformity without causing light loss, light scattering dots may be provided on the front surface of the light guide plate. The light scattering dots can be formed by dot printing of scattering ink or by forming the light scattering dots integrally with the light guide plate. For example, a pattern that is a circular pattern near the intersection of the front surface of the light guide plate and the optical axis of light emitted from the light source, and the transmittance of the light guide plate is the lowest at the center of the dot pattern and increases toward the periphery Is provided.

  The display device of the present invention includes the surface light source device described above. Typically, the display unit of the display device is a liquid crystal panel, and the surface light source device is disposed as a backlight on the back surface of the liquid crystal panel as shown in FIG.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to these embodiment, In the range which does not deviate from the summary, various deformation | transformation and change are possible.

FIG. 1 is a partial cross-sectional view showing a surface light source device according to an embodiment of the present invention. FIG. 2 is a partial cross-sectional view showing a surface light source device according to another embodiment of the present invention. FIG. 3 is a partial cross-sectional view showing a surface light source device according to another embodiment of the present invention. FIG. 4 is a partial perspective view showing a light source arrangement of a surface light source device according to another embodiment of the present invention. FIG. 5 is a partial perspective view showing a light source arrangement of a surface light source device according to another embodiment of the present invention. FIG. 6 is a partial perspective view showing a light source arrangement of a surface light source device according to another embodiment of the present invention. FIG. 7 is a partial perspective view showing a light source arrangement of a surface light source device according to another embodiment of the present invention. FIG. 8 is a cross-sectional view showing a specific example for installing the light source so that the optical axis is inclined with respect to the light guide plate. FIG. 9 is a partial cross-sectional view showing the arrangement of light sources and light guide plates of a surface light source device according to another embodiment of the present invention. FIG. 10 is a partial cross-sectional view showing the arrangement of light sources and light guide plates of a surface light source device according to another embodiment of the present invention. FIG. 11 is a partial cross-sectional view showing the arrangement of light sources and light guide plates of a surface light source device according to another embodiment of the present invention. FIG. 12 is a partial cross-sectional view showing the arrangement of light sources and light guide plates of a surface light source device according to another embodiment of the present invention. FIG. 13 is a partial cross-sectional view showing the arrangement of light sources and light guide plates of a surface light source device according to another embodiment of the present invention. FIG. 14 is a partial cross-sectional view showing the arrangement of light sources and light guide plates of a surface light source device according to another embodiment of the present invention. FIG. 15 is a partial cross-sectional view showing the arrangement of light sources and light guide plates of a surface light source device according to another embodiment of the present invention. FIG. 16 is a partial cross-sectional view showing the arrangement of light sources and light guide plates of a surface light source device according to another embodiment of the present invention. FIG. 17 is a partial cross-sectional view showing the arrangement of the light source and the light guide plate of the surface light source device, and shows the case where the light source is arranged so that the optical axis is perpendicular to the light guide plate. FIG. 18 is a cross-sectional view of a conventional direct type surface light source device arranged directly under a liquid crystal display panel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 LED lamp 1a Lens part 1b Package part 2 Optical axis 3 Board | substrate 3a Recessed part 3b Flat part 4 Light guide plate 4a Recessed part 4b Recessed part 5 Inclined board 6 Support member 7 Sealing material 11 Surface light source device 12 Case 13 Reflective sheet 14 Diffuser 15 Lens sheet (prism sheet)
21 angle l ₁ LED lamp and the back and the interval t light guide plate front from the substrate rear in the optical axis direction between the back of the interval l ₂ LED lamp and a light guide plate in the optical axis direction of the light guide plate of the optical axis with respect to the liquid crystal panel θ substrate surface Thickness up to

Claims (10)

A plurality of light sources having an anisotropy in luminance distribution and an optical axis with the highest luminance are two-dimensionally arranged on the substrate, and a light guide plate is disposed in front of the substrate so as to face the plurality of light sources. A surface light source device,
The surface light source device, wherein the plurality of light sources are arranged such that an optical axis is inclined with respect to the light guide plate.   The surface light source device according to claim 1, wherein an angle of an optical axis with respect to the light guide plate is 10 degrees to 80 degrees.   3. The surface light source device according to claim 1, wherein a concave portion is provided at a position on the back surface of the light guide plate at an intersection of the back surface and the optical axis of the light source.   The surface light source device according to claim 3, wherein the shape of the recess is a cone, a pyramid, a cylinder, a prism, or a hemisphere.   5. The surface light source device according to claim 3, wherein a concave portion is provided on the front surface of the light guide plate.   The surface light source device according to claim 3, wherein light scattering dots are provided on a front surface of the light guide plate.   The surface light source device according to claim 1, wherein the plurality of light sources are LED lamps.   The surface light source device according to claim 7, wherein the LED lamp includes a red LED lamp, a green LED lamp, and a blue LED lamp.   A display device comprising the surface light source device according to claim 1.   The display device according to claim 9, wherein the display unit is a liquid crystal panel.

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