JP3506021B2 - Surface lighting device and display device using this 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 lighting device for illuminating a liquid crystal display device from the back, and more particularly to a surface lighting device using a point light source such as a light emitting diode (hereinafter referred to as "LED"). The present invention relates to a display device using a surface lighting device.

[0002]

2. Description of the Related Art A surface illumination device used as a backlight of a liquid crystal display device such as a mobile phone or a personal handyphone system uses a point light source using a chip-shaped LED because of its small size and low power consumption. ing. Furthermore, recently, for the display section of portable devices such as various portable information terminals, digital cameras, video cameras, etc., the surface lighting device has been reduced in size, has a longer battery life, and has improved impact resistance.
The use of cold-cathode tubes is shifting to LED light sources.

There are various configurations of conventional surface lighting devices using these LED light sources. For example, Japanese Patent Fairness 3-3
As described in Japanese Patent No. 2075, there is a device in which a top-emission LED light source is arranged on the back side of a liquid crystal display body to directly illuminate the back surface of the liquid crystal display body for illumination. However, as a backlight of a liquid crystal display device such as a mobile phone, an LED light source is arranged directly on the back surface side of the liquid crystal display body because of the thinning of the device and the problem of installing an electronic circuit on the back surface of the liquid crystal display element. Is running low. On the other hand, as a backlight of a liquid crystal display device such as a mobile phone, an L is provided outside the display surface of the liquid crystal display element.
There are many methods of arranging the ED light source, and the method is described in, for example, Japanese Patent Publication No. 5-21233. This is to illuminate by arranging a top-emission LED light source on the outside of the display surface of the unit and using a reflecting surface and a resin plate to guide the light below the liquid crystal display unit.

An example in which the LED light source is arranged outside the display surface of the liquid crystal display element in this way will be described as a conventional surface illumination device with reference to FIGS. 8 and 9.

FIG. 8 is a plan view of a conventional surface illuminating device, and FIG. 9 is a longitudinal sectional view of the same. 1 is an LED light source, 2 is a light guide plate, 3 is a light guide part of the light guide plate 2, and 3a is a light guide part. 3 is an incident surface, 4 is a light emitting portion of the light guide plate 2, 5 is a scattering portion formed on the lower surface of the light emitting portion 4, 5a is scattering dots printed on the scattering portion 5 with milky white to white ink, 6 is a reflection sheet, Reference numeral 7 is a diffusion sheet, 8 is a holder for holding the light guide plate 2, the reflection sheet 6, and the diffusion sheet 7, and 9 is a reflection surface formed on the holder 8.

In such a surface lighting device, the LED light source 1 is used.
The light emitted from is incident on the inside of the light guide plate 2 through the incident surface 3a of the light guide portion 3 after being reflected by the reflecting surface 9. The light entering the inside of the light guide plate 2 is partly diffused by the scattering part 5 and emitted from the light emitting part 4, and part of the light is transmitted through the scattering part 5 and reflected by the reflection sheet 6 to be reflected again on the light guide plate 2. After entering the inside, the light is emitted from the light emitting unit 4. The light emitted from the light emitting section 4 is disturbed in the traveling direction of the light by the diffusion sheet 7, so that the luminance distribution is slightly uniformed.

However, in the above-described conventional surface lighting device, since the LED light source 1 is a point light source, if there is only one LED light source 1 in the center in the height direction in FIG. High brightness. Therefore, the brightness distribution, which is the unevenness of the brightness of the light emitting unit 4, becomes large, and the vicinity of the portion A in FIG. 8 tends to be dark. In particular, this brightness distribution becomes remarkable as the area to be illuminated increases. When such a brightness distribution is generated, when used as a backlight of a liquid crystal display element or the like, it is difficult to see displayed characters and the like, and further, a display portion that is dark and cannot be recognized is generated.
In order to solve this problem, a conventional means has been used to improve the luminance distribution of the surface lighting device by increasing the number of LED light sources 1 used and reducing the arrangement interval of the LED light sources 1.

[0008]

However, if the number of LED light sources 1 used in the surface lighting device is increased in a liquid crystal display device of a mobile device such as a mobile phone, not only the power consumption increases but also the LED light source 1 This leads to complexity of mounting and increase of manufacturing cost.

On the other hand, in order to improve the luminance distribution, the dimension shown by B in FIG. 8, that is, the light guide portion 3 of the light guide plate 2 is made long in the incident direction of the light, and the light is sufficiently diffused before the light is emitted. A structure in which the light is emitted from the light emitting section 4 has already been proposed. However, since the light guide plate 2 becomes long and the entire device becomes large, it becomes impossible to cope with the miniaturization.

The problem to be solved in the present invention is the LED
It is possible to provide a surface lighting device having a good brightness distribution with a simple configuration even if the number of point light sources such as LED is small, and to provide a liquid crystal display device even if the number of point light sources such as LEDs is used as the backside illumination. An object of the present invention is to provide a display device capable of clearly recognizing a display.

[0011]

In order to solve the above-mentioned problems, a surface lighting device of the present invention includes a point light source composed of a light emitting diode or the like, and a light guide for spreading incident light from the point light source to spread it in a plane. At least one light diffusion portion having a through hole or a concave hole for diffusing the incident light toward the light emitting portion is provided in the light guiding portion having a light emitting portion and a light emitting portion for planarly emitting light from the light guiding portion. A light guide plate, a reflection sheet, a scattering sheet, and a holder that houses each part and has a reflection part that reflects light from a point light source toward the light guide plate, and stacks the reflection sheet, the light guide plate, and the scattering sheet in order. Each part is stored in a holder, and most of the light emitted from the point light source is reflected by the reflection part of the holder, then enters the light guide plate from the incident surface of the light guide part, and enters the light guide plate. The light is diffused in the light diffusing section.

With this, the spread of the incident light of the LED light source can be increased without lengthening the light guide portion of the light guide plate, whereby a surface illuminating device having a good luminance distribution can be obtained.

Further, the display device of the present invention is characterized in that the above surface illumination device is arranged on the back side of the liquid crystal display element so that the light diffusion hole does not overlap the display surface of the liquid crystal display element. To do.

As a result, since it is not necessary to increase the size of the light guide plate and the like for at least the number of point light sources used, and the luminance distribution is made uniform, a display device in which the display of the liquid crystal display element can be clearly recognized is obtained. be able to.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 is a point light source comprising a light emitting diode or the like, a light guide portion which introduces incident light from the point light source and spreads it in a plane, and the light guide. A light emitting portion that emits light from the surface in a planar manner, the light guide portion,
A surface illuminating device comprising one or more through-hole or concave-shaped light diffusing holes for diffusing incident light toward the light emitting part, which is a point light source incident on a light guiding part of a light guide plate. Part of the light is reflected by the side wall of the light diffusion hole, and the light is diffused in the width direction of the light guide plate, so that the luminance distribution can be made uniform.

The invention according to claim 2 is the surface illuminating device according to claim 1, characterized in that the opening cross-sectional shape of the light diffusing hole is substantially circular, and the light diffusing comprises a through hole or a concave hole. Since the opening cross section of the hole is substantially circular, with the critical angle resulting from the difference in the refractive index between these portions and the light guide plate as a boundary,
A part of the light of the point light source entering the light guide part is reflected and transmitted, whereby the light is diffused in the width direction of the light guide plate and the brightness distribution can be made uniform.

The invention according to claim 3 is the surface illuminating device according to claim 1, wherein the light diffusion hole is a combination of two or more different diameter holes having different radii. By configuring the light diffusion holes by combining the different-diameter holes, the diffusion degree of the incident light can be adjusted in the thickness direction of the light guide plate, so that the brightness distribution can be made more uniform.

The invention according to claim 4 is the surface illuminating device according to claim 1, wherein the opening cross-sectional shape of the light diffusion hole is a combination of two or more substantially circular arcs. By configuring the light diffusing holes by combining the substantially circular arcs, the traveling direction of the light that enters and passes through the light diffusing holes can be widened in the width direction of the light guide plate, and the brightness distribution can be made uniform.

According to a fifth aspect of the present invention, the hole area of the light diffusion hole provided in a region having a high intensity distribution of the incident light introduced from the point light source and spread in a plane by the light guide portion has a dot shape. Incident light that is larger than the hole area of the light diffusion hole that is provided in the region where the intensity distribution of the incident light that is introduced from the light source and spread in a plane by the light guide is low. A large light diffusion hole provides a strong scattering effect in a region with a high intensity distribution, and a small light diffusion hole provides a weak scattering effect in a region with a low intensity distribution of incident light, which reduces the brightness of the point light source. This is combined so that the light is uniformly diffused in the width direction of the light guide plate, which has the effect that the luminance distribution in the light emitting portion can be made uniform.

According to a sixth aspect of the present invention, the surface lighting device according to any one of the first to fifth aspects is provided on the back side of the liquid crystal display element, wherein the light diffusion hole overlaps the display surface of the liquid crystal display element. It is a display device characterized by being arranged as a positional relationship that does not become a problem, in which part of the light of the point light source incident on the light guide part of the light guide plate in the surface lighting device is reflected by the side wall of the light diffusion hole, and the light guide plate. Since the light is diffused in the width direction of the liquid crystal display, the luminance distribution is made uniform, so that the display of the liquid crystal display element can be clearly recognized.

Next, this embodiment of the present invention will be described with reference to FIGS. 1, 2, 3, 4, 5, 6 and 7.

(Embodiment 1) FIG. 1 is a plan view of a surface lighting device according to Embodiment 1 of the present invention, and FIG. 2 is a longitudinal sectional view of the same. It should be noted that the same components as those of the conventional technique shown in FIGS. 8 and 9 are designated by common reference numerals.

In FIGS. 1 and 2, 1 is an LED light source formed of a chip-shaped light emitting diode, 2 is a light guide plate made of a highly transparent material such as polycarbonate resin or acrylic resin, 3 is a light guide portion of the light guide plate 2, 3a Is the incident surface of the light guide unit 3,
Reference numeral 4 is a light emitting portion of the light guide plate 2, 5 is a scattering portion formed on the lower surface of the light emitting portion 4, 5a is a scattering dot printed on the scattering portion 5 with milky white to white ink, 6 is a reflective sheet having high reflectance, 7 Is a diffusion sheet, 8 is a light guide plate 2, a reflection sheet 6 and a diffusion sheet 7.
Is a holder for holding, and 9 is a reflecting surface formed on the holder 8.

These constituent members and their respective positional relationships are the same as those of the prior art except for the number of LED light sources 1, but in the present invention, a light diffusion hole formed as a through hole in the light guide section 3. 3b is different. Further, the scattering part 5 is made to have a scattering action by a large number of printed scattering dots 5a, and in order to further reduce the uneven brightness of the surface lighting device, the printing area ratio of the scattering dots 5a is increased as the distance from the LED light source 1 increases. There is. Instead of the scattering dots 5a, a large number of minute protrusions or depressions may be formed to give a scattering effect.

In the above structure, most of the light emitted from the LED light source 1 is reflected by the reflecting surface 9 and enters the inside of the light guide plate 2 through the incident surface 3a of the rear light guide portion 3, and one of the incident light is reflected. The portion corresponds to the peripheral wall of the light diffusion hole 3b formed of a through hole. Among the lights that have hit the peripheral wall of the light diffusion hole 3b, the light whose incident angle with respect to the peripheral wall of the light diffusion hole 3b is less than or equal to the critical angle due to the difference in refractive index passes through the peripheral wall of the light diffusion hole 3b. The light enters the light diffusing hole 3b, passes through the peripheral wall of the light diffusing hole 3b again, and enters the light guide plate 2. Further, among the lights hitting the peripheral wall of the light diffusing hole 3b, the light whose incident angle with respect to the peripheral wall of the light diffusing hole 3b is equal to or greater than the critical angle is totally reflected by the peripheral wall of the light diffusing hole 3b, and A of FIG. Proceed to the section. Further, three kinds of light, that is, the light that has not hit the peripheral wall of the light diffusion hole 3b, the light that has transmitted through the peripheral wall of the light diffusion hole 3b, and the light that has hit and reflected on the peripheral wall of the light diffusion hole 3b, are reflected by the scattering section 5 after that. Part of the light is diffusely reflected and emitted from the light emitting unit 4, and part of the light is transmitted through the scattering unit 5 and reflected by the reflection sheet 6 and emitted from the light emitting unit 4. Of these three kinds of light, the light reflected by hitting the peripheral wall of the light diffusing hole 3b illuminates the portion A in FIG. 1 which becomes dark if the light diffusing hole 3b is solid. The light emitted from the light emitting unit 4 is disturbed by the diffusion sheet 7 in the traveling direction of the light, so that the luminance distribution is further uniformized.

Here, in the first embodiment, the light diffusion hole 3b.
The plane shape of No. 2 is circular, but this is one reason that the light diffusion holes can be easily manufactured when the mold of the light guide plate 2 is manufactured. Then, the light diffusion hole 3b formed of a through hole or a concave hole
Since the planar shape of the light guide portion 3 is circular, the light guide portion 3 is separated by the critical angle resulting from the difference in the refractive index between these portions and the light guide plate 2 as a boundary.
A part of the light of the point light source incident on the can be easily reflected and transmitted. However, in light guide design of light, the same effect may be obtained even if the planar shape of the light diffusion hole 3b is a polygon such as a triangular pyramid or a rectangular parallelepiped.

In the first embodiment, the structure in which the light guide plate 2 is floated from the substrate (not shown) has been described. However, as shown in FIG. 3, the light guide plate 2 is preferably used in a mobile phone, for example. Alternatively, the side surface light emitting type LED light source 1 may be used. With such a configuration, the light of the LED light source 1 can be directly incident on the incident surface 3a of the light guide plate 2 without passing through the reflecting surface 9, and the same effect as the example of FIGS. 1 and 2 can be obtained.

Further, in the first embodiment, the light diffusion hole 3
Although b is a through hole, it does not necessarily have to be penetrated,
It may be a concave hole. In the case of the concave hole, it is possible to brighten the portion B in FIG. 1 in which the luminance tends to be slightly lower in the case of the through hole, and it is possible to adjust the luminance distribution by setting the depth of the concave hole.

(Second Embodiment) FIG. 4 is a perspective view of a light guide plate 2 of a surface lighting device according to a second embodiment of the present invention.

In this example, the light diffusion hole 3 provided in the light guide plate 2 is used.
The cross section of b is not a circle with a uniform inner diameter, but different diameter holes in which holes with different inner diameters are arranged vertically. By thus forming the light diffusion holes 3b with different diameters, the degree of diffusion of incident light can be adjusted in the thickness direction of the light guide plate 2 such that the upper portion is weaker and the lower portion is stronger, so that the brightness distribution is further enhanced. Uniformity is achieved.

(Third Embodiment) FIG. 5 is a plan view of a surface lighting device according to a third embodiment of the present invention.
The same components as those shown in are designated by common reference numerals.

In the third embodiment, the shape of the opening cross section of the light diffusing hole 3b is such that two arcs are combined and the width is expanded in the transmission path of the light from the LED light source 1. By adopting such a shape of the opening cross section, it is possible to widen the traveling direction of the light that is incident on and transmitted through the light diffusing hole 3b in the width direction of the light guide plate 2, thereby making the luminance distribution uniform.

(Fourth Embodiment) FIG. 6 is a plan view of a surface lighting device according to a fourth embodiment of the present invention, in which a light diffusion hole 3b is provided.
The configuration is the same as that of the previous example except for the above.

In this example, three large-diameter light diffusion holes 3b are arranged at the center of the optical path from the LED light source 1 and small-diameter light diffusion holes 3b are arranged on the left and right sides thereof. That is, the hole area of the large-diameter light diffusing hole 3b provided in the region where the intensity distribution of the incident light introduced from the LED light source 1 and spread in a plane by the light guide portion 3 is high is LE.
D small-diameter light diffusion hole 3 provided in a region with a low intensity distribution of incident light introduced from the D light source 1 and spread in a plane by the light guide portion 3.
It is larger than the hole area of b. Therefore, the light incident on the light guide plate 2 is strongly scattered by the large light diffusion hole 3b on the center side of the light guide portion 3 where the brightness of the LED light source 1 becomes strong,
Light is scattered weakly by the small light diffusion holes 3b on the side near the end of the light guide portion 3 where the brightness of the LED light source 1 becomes weak. And
The strongly scattered light and the weakly scattered light are combined, the light is uniformly diffused in the width direction of the light guide plate 2, and the luminance distribution in the light emitting section 4 is made uniform.

(Fifth Embodiment) FIG. 7 is a vertical sectional view of a display device according to a fifth embodiment of the present invention.

In the figure, members indicated by reference numerals 1 to 9 are constituent members of the surface lighting device shown in the first embodiment, and the details thereof are as already described. Further, the display device of the present invention is one in which the liquid crystal display element 10 is mounted on the surface lighting device described in Embodiment 1, and liquid crystal display is possible from the display surface portion 11 on the surface thereof.

The light guide portion 3 of the light guide plate 2 of the surface illuminator is provided with the light diffusion hole 3b made of a through hole, and as described above, a part of the light of the point light source is in the width direction of the light guide plate. By diffusing the light, the brightness distribution of the illumination light can be made uniform. Therefore, since the luminance distribution of the illumination light, that is, the light from the backlight is uniform on the display surface portion 11 of the liquid crystal element 10, the display of characters and numbers on the liquid crystal display element is easy to see and can be clearly recognized.

Although the embodiment of the invention has been described above, the LED light source 1 is described as a single LED chip mounted in (Embodiment 1) to (Embodiment 5), but it is different. A light source in which a plurality of LED chips having an emission wavelength are mounted can also be used. By using this light source, it is possible to realize a surface lighting device capable of changing the emission color according to a control signal from the device. Further, in the above embodiment, LE
Although the D light source 1 has been described as one, when the area to be illuminated becomes large, it is naturally conceivable to use a plurality of LED light sources 1.

[0039]

According to the first aspect of the present invention, by providing the light guide portion with the light diffusion hole, there is an effect that the luminance distribution in the light emitting portion of light can be made uniform.

According to the second aspect of the invention, since the planar shape of the light diffusing hole is substantially circular, there is an effect that the luminance distribution in the light emitting portion can be made more uniform.

According to the third aspect of the present invention, the light diffusion hole is a combination of different-diameter holes having different diameters, so that the brightness distribution can be made more uniform.

According to the fourth aspect of the invention, since the planar shape of the light diffusion hole is a combination of two or more substantially circular arcs, there is an effect that the luminance distribution in the light emitting portion becomes uniform.

In the fifth aspect of the invention, the hole area of the light diffusion hole provided in the region where the intensity distribution of the incident light, which is introduced from the point light source and spread in a plane by the light guide portion, is higher than that of the point light source. Since it is larger than the hole area of the light diffusion hole provided in the region where the intensity distribution of the incident light that has been introduced and spread out in a plane shape in the light guide section is large, the effect that the brightness distribution in the light emitting section becomes uniform Have.

According to the sixth aspect of the invention, by providing the surface illuminating device having the light diffusing hole in the light guide portion, the number of point light sources used can be reduced and the display of the liquid crystal display element can be clearly recognized. Have.

[Brief description of drawings]

FIG. 1 is a plan view of a surface lighting device according to a first embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of the surface lighting device according to Embodiment 1 of the present invention.

FIG. 3 is a vertical cross-sectional view of a surface lighting device according to another configuration example of the first embodiment of the present invention.

FIG. 4 is a perspective view of a light guide plate of the surface lighting device according to the second embodiment of the present invention.

FIG. 5 is a plan view of a surface lighting device according to a third embodiment of the present invention.

FIG. 6 is a plan view of a surface lighting device according to a fourth embodiment of the present invention.

FIG. 7 is a vertical sectional view of a display device according to a fifth embodiment of the present invention.

FIG. 8 is a plan view of a conventional surface lighting device.

FIG. 9 is a vertical cross-sectional view of a conventional surface lighting device.

[Explanation of symbols]

1 LED light source 2 Light guide plate 3 Light guide 3a entrance surface 3b Light diffusion hole 4 Light emitting part 5 Scatterer 5a scattering dots 6 Reflective sheet 7 diffusion sheet 8 holder 9 Reflective surface 10 Liquid crystal display element 11 Display surface

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keita Ihara 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-8-201809 (JP, A) JP-A-10- 199318 (JP, A) JP 10-293213 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F21V 8/00 601 G02B 6/00 331 G02F 1/13357 G09F 9 / 00 332

Claims (6)

(57) [Claims] 1. A point light source including a light emitting diode, a light guide section that introduces incident light from the point light source and spreads it in a plane, and a light emitting section that emits light from the light guide in a plane. And a light guide plate having one or more through-hole or concave-shaped light diffusing portions for diffusing incident light toward the light emitting portions in the light guiding portion, a reflection sheet, a scattering sheet, and housing each portion. A holder having a reflecting portion that reflects the light from the point light source toward the light guide plate, and the reflection sheet, the light guide plate, and the scattering sheet are laminated in this order, and each portion is housed in the holder. At the same time, most of the light emitted from the point light source is reflected by the reflection part of the holder, and then the light is guided.
Is incident on the light guide plate from the light incident surface portion, light incident on the light guide plate surface lighting device is the fact that said diffused by the light diffusing portion. 2. The surface illumination device according to claim 1, wherein the opening cross-sectional shape of the light diffusion hole is substantially circular. 3. The surface lighting device according to claim 1, wherein the light diffusing hole is a combination of two or more different diameter holes having different radii. 4. The surface illuminating device according to claim 1, wherein the opening cross-sectional shape of the light diffusion hole is a combination of two or more substantially circular arcs. 5. The hole area of the light diffusion hole provided in a region having a high intensity distribution of incident light which is introduced from the point light source and spread in a plane by the light guide section is introduced from the point light source. 2. The surface lighting device according to claim 1, wherein the area of the light diffusion hole is larger than the area of the light diffusion hole provided in a region where the intensity distribution of the incident light spread in a planar shape by the light guide portion is low. 6. The liquid crystal display device according to any one of claims 1 to 5, which is provided on the back side.
A display device, wherein the surface lighting device according to any one of items 1 to 3 is arranged in a positional relationship in which the light diffusion hole does not overlap the display surface of the liquid crystal display element.