JP3023026B2 - Surface lighting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface illuminating device suitable as a backlight device mainly used for backlighting in a liquid crystal display device or the like.

[0002]

2. Description of the Related Art As is well known, since a liquid crystal panel does not have a light emitting function itself, it is necessary to illuminate it with a back light source from the point of viewability.

It is desired that the back light source has a uniform luminance over the entire display panel and that the entire liquid crystal display device incorporating the back light source is thin. Therefore, as this back light source, an edge type backlight device using a light guide as shown in FIG. 8 is widely used.

In the conventional backlight device shown in FIG. 8, a light beam emitted from light sources 1a and 1b is made incident on a side surface of a light guide 4 made of transparent acryl or the like, and the light guide 4 and a reflection plate on the rear surface are provided. The light guide 4 is configured to be guided to a central portion in the light guide 4 by the action of the diffuse reflection pattern portion 8 in which the portions farther from the light sources 1a and 1b are dense.

[0005]

However, in the conventional edge type backlight device, as shown by a broken line C in FIG. 3, the luminance at the central portion between the light sources is low and the luminance near the light sources is high. This is because the light sources 1a and 1b are diffused light, so that the vicinity of the light sources 1a and 1b is bright, and most of the light emitted from the light sources 1a and 1b is reflected by the light sources 1b and 1 on the reflection side.
This is because the light reaches the light source 1a, 1b, and the area around the light sources 1a, 1b is further brightened. As a result, in the conventional backlight device, the effective illumination range (effective light emitting surface) of the entire backlight device is narrowed in order to match the uniform luminance of the entire backlight to the low luminance of the central portion between the light sources, and There is a problem that the light use efficiency of the entire light device is poor.

Also, in order to increase the brightness at the center between the light sources,
As shown in FIGS. 9 (a) and 9 (b), a method of guiding the light flux to the central part by making the central part of the light guide downward or concave is shown in FIG.
It is known in Japanese Patent Application Laid-Open No. 3-8703 and Japanese Patent Application Laid-Open No. 01-91955. According to these methods, as shown by the dotted line B in FIG. 3, it is possible to increase the luminance at the central portion between the light sources of the backlight device. However, such light guides
Since the shape is non-uniform, when manufacturing by molding, the larger the size, the longer the molding cycle to eliminate the influence of warpage and the like, so it is not realistic in terms of mass productivity. Further, even in the case of manufacturing by cutting, considering the problem of warpage and the variation of the polishing process, the cost becomes high, which is not realistic.

Therefore, in the conventional example, in order to increase the brightness of the entire rear light source, a light source having a large total luminous flux must be used. Therefore, the light source itself becomes large and the entire liquid crystal display device becomes thick. In addition, various problems have occurred, such as an increase in power consumption due to an increase in current consumption, an increase in heat generation of the light source itself, and a need to take measures for heat dissipation of the liquid crystal display device. Further, at present, there is a demand for a liquid crystal display panel having a larger size and a color display having a poor transmittance, and the above-mentioned problems have been further emphasized.

In view of the above problems, an object of the present invention is to provide an edge-type surface lighting device which can be made thin even if it is large in size, has excellent brightness uniformity and efficiency, and is inexpensive.

[0009]

In order to solve the above-mentioned problems, a surface illuminating device according to the present invention comprises a light guide made of a transparent body, which receives linear light source light from two opposite sides thereof, and a reflecting plate and a diffusing plate. In the surface illumination device for emitting light to the front side of the light guide after uniformizing the light amount, the light guide is divided in the longitudinal direction of the line light source, the divided surfaces are directly bonded to each other, and the light beam of the line light source is bonded to the light source. Diffuse reflection at the surface.

In a preferred embodiment of the present invention, the light guide is made of glass or plastic material. Further, the light guide is divided at a center between two opposing side surfaces on which light is incident or at an equal position on both sides with the center as a symmetry axis, or both. These divided surfaces are set at an angle of 45 to 90 degrees with respect to the back surface, and are bonded by bonding, welding, ultrasonic welding, or the like.

[0011]

According to the present invention having the above structure, the light guide is divided in the longitudinal direction of the line light source, the divided surfaces are directly bonded to each other, and the luminous flux of the line light source is diffusely reflected at the bonding surface. This makes it possible to increase the luminance of a portion having a low luminance in the conventional example of the central portion between the light sources, thereby increasing the luminance efficiency of the entire backlight device, and at the same time, being thin, uniform in luminance and inexpensive, especially a liquid crystal display device and the like. An edge-type surface lighting device suitable as the backlight device described above can be obtained.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are block diagrams of a liquid crystal backlight device according to an embodiment of the present invention. FIGS. 3 and 4 show examples of luminance characteristics on the backlight device surface for describing the operation of the backlight device of the present invention.

According to a first embodiment of the present invention, as shown in FIGS. 1 and 2, light sources 1a and 1b
Are divided at the central portion of the substrate and bonded together with the translucent adhesive 7, thereby obtaining a luminance characteristic as shown by a solid line A in FIG. In FIG. 3, a dotted line B shows the luminance characteristics of the conventional device (V-shaped light guide) shown in FIG. 9, and a broken line C shows the luminance characteristics of the conventional device (flat light guide) shown in FIG.

Next, the principle of the present invention will be described in comparison with a conventional example. First, in the conventional edge type backlight, as shown in FIG. 8, light beams emitted from the light sources 1a and 1b are incident on a light guide 4 such as a transparent acryl, and the light guide 4 and the back surface of the light guide 4 are formed. Reflector 2 and light source 1
a, diffuse reflection pattern portion 8 having a portion farther than 1b
As a result, the light beam is guided to the center. However, the characteristics are such that the luminance near the light source is high and the luminance at the central portion between the light sources is low as shown by the characteristic C in FIG. 3 for the reason described above. This is because only the diffuse reflection pattern portion on the back surface of the light guide 4 cannot sufficiently increase the luminance at the central portion between the light sources, and reaches the light sources 1a and 1b on the reflection side, and the light sources 1b and 1a on the reflection side. The light sources 1b and 1a are also brightly reflected by the light source 1b, thereby brightening the vicinity of the light sources 1b and 1a. For example, the diffuse reflection pattern portion 8 on the back surface of the light guide 4
When only one of the light sources 1a and 1b is turned on, the light source 1a (lights) as shown in the characteristic B of FIG.
Most of the light beam on the side is the light source 1b on the opposite side (not lit)
You can see that we have arrived at FIG. 4 shows the conventional apparatus shown in FIG. 8 and the embodiment apparatus shown in FIG.
The luminance characteristic when only a is turned on is shown.

According to the first embodiment of the present invention, as shown in FIGS. 1 and 2, light sources 1a and 1b
Are divided in the longitudinal direction of the line light source at the center of the line, and the divided surfaces are directly bonded to each other, and the luminous flux of the line light source is diffusely reflected at the bonding surface. When the light guide 4 is divided in this way, as shown by the characteristic A in FIG. 4, the light flux on the light source 1a (lighted) side is reflected near the central divided surface, so that the light source 1a
The brightness of the intermediate portion between the light source 1a on the side and the split surface is improved, and the transmitted light of the split surface improves the brightness of the intermediate portion between the light source 1b on the opposite side and the split surface using the split surface as a secondary light source. Can be done. Therefore, a diffuse reflection pattern portion 8 is provided on the back surface of the light guide 4, and the diffuse reflection pattern portion 8 is provided.
Is further increased with respect to the distance from the light sources 1a and 1b and with respect to the distance from the division surface, thereby further increasing the intermediate portion between the light source and the division surface, as shown by the characteristic A in FIG. Can be improved. The density of the diffuse reflection pattern depends on the brightness and reflection, transmission, diffusion,
The optimization can be performed by the luminance on the division surface side determined by the optical characteristics of the division surface such as refraction. As shown by the characteristic A in FIG. 3, the brightness at the central portion between the light sources was increased, so that the overall brightness was improved as compared with the conventional example.

[0017]

[Other embodiments] In the embodiment of the invention, FIG.
As shown in (b), a line light with the central part of the light guide as the axis of symmetry
Divided into three, four or more in the longitudinal direction of the source
The split surfaces are directly bonded to each other,
Are diffusely reflected on the bonding surface. In this way, the number of divisions
By increasing, not only the central part, but also the periphery around the central part
It is possible to increase the brightness of the entire side more uniformly.

As shown in FIGS. 6A and 6B, the bonding surfaces are appropriately set within a range of 45 ° to 90 ° with respect to the horizontal plane (front or back) of the light guide 4. I do. By inclining the bonding surface, there is an effect of increasing diffuse reflection on the bonding surface necessary for securing the emission amount.

As shown in FIGS. 7A and 7B, the present invention can be applied to the conventional example shown in FIGS. 9A and 9B. That is, the central part of the light guide is made concave or concave in the combination of the present invention and the conventional example.
Can be further diffusely reflected in the vicinity of the central portion by bonding the central portions of the light beams.

Alternatively, in addition to these modes, the number of divisions,
The split location or split surface shape, and the reflectance of the split surface,
By changing various characteristics such as a refractive index or a transmittance, an optical design can be made in accordance with the size and application of the backlight device.

[0021]

As described above, according to the present invention, the light guide is divided in the longitudinal direction of the line light source with respect to the light beam of the line light source, and the divided surfaces are directly bonded to each other, so that light enters from both ends. Since the light beam is diffusely reflected in the vicinity of the division surface, it is possible to obtain a large-sized, thin, uniform brightness and efficiency, and low-cost surface illumination device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part of a backlight device for a liquid crystal display according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration of a light guide of the apparatus of FIG.

FIG. 3 is a graph showing luminance characteristics of the device of FIG. 1 in comparison with a conventional example.

FIG. 4 is a luminance characteristic diagram for explaining the principle of the present invention.

FIGS. 5 to 7 are cross-sectional views of main parts of a backlight device for a liquid crystal display according to another embodiment of the present invention.

8 and 9 are cross-sectional views of main parts of a conventional backlight device for a liquid crystal display.

[Explanation of symbols]

1a, 1b: light source, 2: reflection plate, 3: diffusion plate, 4: light guide, 5: liquid crystal display panel, 6: exterior case, 7: transparent adhesive, 8: diffuse reflection pattern portion.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-247686 (JP, A) JP-A-3-6525 (JP, A) JP-A-3-12202 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) G02F 1/1335

Claims (6)

(57) [Claims] 1. A surface illuminating device in which a linear light source is incident on two opposing side surfaces of a light guide made of a transparent body, the amount of light is made uniform by a reflection plate and a diffusion plate, and emitted to the front side of the light guide. , The light guide is divided in the longitudinal direction of the line light source,
The two are directly bonded to each other, and the luminous flux of the linear light source is
A surface lighting device characterized by being diffusely reflected on a surface. 2. The surface lighting device according to claim 1, wherein the light guide is made of glass or plastic material. 3. The surface lighting device according to claim 1, wherein the light guide is divided into at least one of a center between the two opposing side surfaces and an equal position on both sides with the center as a symmetric axis. . 4. A diffuse reflection pattern is provided on a back surface of the light guide, the closer the distance from the light incident surface or the distance from the division surface, the denser the diffuse reflection pattern. A surface lighting device according to claim 1. 5. The surface illumination device according to claim 1, wherein the divided surfaces of the light guide are bonded by bonding, welding, ultrasonic welding, or the like. 6. The surface illumination device according to claim 1, wherein an angle of a division surface of the light guide is 45 to 90 degrees with respect to a back surface.