JPH0934371A - LED surface light source - Google Patents

Abstract

(57) [Abstract] [Purpose] A surface that uses a light guide plate with an LED as a light source to make the in-plane brightness of the surface light source uniform, widen the effective light emitting area, and obtain a uniform light emitting surface with a small number of LEDs. Provide a light source. [Structure] The LED lamp 1 is arranged on the end surface of the light guide plate 2,
On the back surface of the light guide plate 2, a first light diffusion surface 11 that diffuses the light in the vicinity of the LED lamp 1 and a second light diffusion surface 12 that diffuses the light of the LED lamp to the entire light guide plate are provided. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source using an LED (light emitting diode) used as a backlight of a liquid crystal display device or the like.

[0002]

2. Description of the Related Art Generally, a surface light source using a light guide plate is used as a backlight of a display device such as a liquid crystal display device which does not emit light by itself. A small fluorescent lamp called a cold cathode tube is often used as the light source of the surface light source.The cold cathode tube is arranged on the end surface of the light guide plate, and white light introduced from the end surface is provided on the back surface of the light guide plate. The linear light source is converted into a surface light source by uniformly diffusing the light on the surface.

The light diffusing surface is provided by using various methods. For example, a white material such as titanium oxide or barium titanate is directly printed on the back surface of the light guide plate, or a sheet on which the white material is printed is attached to the back surface of the light guide plate. There is a means for applying light and reflecting the light toward the light emission observation surface side with unevenness. That is, the light diffusing surface has a function of uniformly spreading the linear light source inside the light guide plate to form a surface light source. The light diffusing surface is usually gradation. Typical gradations include, for example, JP-A-57-128383 and JP-A-63-6210.
As shown in Japanese Patent Publication No. 4, a pattern is selected in which the coverage rate per unit area is small at a position close to the light source, and the coverage rate increases as the distance from the light source increases. As described above, the conventional surface light source using the light guide plate mainly uses a cold cathode tube of a linear light source as a light source.

On the other hand, a high-intensity blue LE is used as a new light source.
D was recently announced. Since blue light can be converted into white light when combined with a wavelength conversion substance, it is very promising as a light source to replace the cold cathode tube. For example, JP-A-6-281
No. 929 and JP-A-6-289231 disclose surface light sources using LEDs. Each of these publications discloses a technique for improving the light diffusion surface provided on the back surface of the light guide plate in order to uniformly spread the LED light source arranged on the end surface of the light guide plate in the plane.

[0005]

SUMMARY OF THE INVENTION However, LEDs
Unlike a cold cathode tube, is a point light source, and therefore, in order to approach a line light source as in the conventional case, it is necessary to increase the number of light sources installed on the end surface of the light guide plate. If the number is large, the power consumption becomes large, and the advantage of the LED cannot be utilized. Also on the light diffusing surface of the light guide plate, in the gradation where the coverage increases with distance from the light source as in the past, a uniform light emitting surface can be obtained on the surface away from the light source, but there is a difference in brightness around the light source. However, there is a problem that a uniform light emitting surface cannot be obtained. FIG. 7 is a schematic plan view of a conventional surface light source using an LED light source as seen from the light emitting surface side.
Is an LED, and 72 is a light guide plate. As described above, in the conventional light diffusing surface, since a bright and dark portion of brightness is generated in the light guide plate around the LED, there is a drawback that the effective light emitting area of the light guide plate plane where uniform brightness is obtained becomes narrow.

Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide an LED.
It is an object of the present invention to provide a surface light source that uses a light guide plate having a light source as a light source to uniformize the in-plane brightness of the surface light source to widen the effective light emitting area and obtain a uniform light emitting surface with a small number of LEDs.

[0007]

The LED surface light source of the present invention comprises two kinds of modes. In the first mode, the LED lamp is arranged on the end surface of the light guide plate, and the LED is provided on the back surface of the light guide plate.
It is characterized in that a first light diffusing surface for diffusing light near the lamp and a second light diffusing surface for diffusing light of the LED lamp over the entire light guide plate are provided.

In the first aspect, the first light diffusing surface and the second light diffusing surface can be separated from each other. Specifically, the light guide plate provided with the first light diffusing surface and the light guide plate provided with the second light diffusing surface can be separated, or a sheet having the first light diffusing surface formed, It means that the sheet provided with the second light diffusing surface can be separated on the back surface of the light guide plate.

According to a second aspect of the present invention, the LED lamp is arranged on the end face of the light guide plate via a transparent support for fixing the LED lamp, and the light near the LED lamp is provided on the back face of the support. And a second light diffusing surface for diffusing the light of the LED lamps over the entire light guiding plate, are provided on the back surface of the light guiding plate.

In the second aspect of the present invention, the support for fixing the LED means that the LED can be mounted and fixed on a support such as an acrylic plate or a polycarbonate plate, and the light emission of the LED is introduced to the end surface of the light guide plate. It refers to a support that is wholly or internally transparent. The back surface of this support matches the back surface of the light guide plate, and the first light diffusion surface formed on the back surface of this support diffuses the light in the vicinity of the LED lamp and introduces it as a uniform light source on the end surface of the light guide plate. To do.

In the first and second aspects of the present invention, the light diffusing surface refers to a surface having a function of reflecting the emitted light of the LED and diffusing it to the surroundings, and to form the light diffusing surface. Conventional methods can be used. For example, a method of printing and applying a white material that reflects the light of the LED on the back surface of the light guide plate, a method of making fine irregularities on the back surface of the light guide plate, or a method of installing a sheet on which the white material is applied on the back surface of the light guide plate, etc. Is a typical method of forming a light diffusing surface.

Next, the light guide plate is not particularly a substitute for the conventional light guide plate, and a resin plate such as a transparent acrylic plate or a polycarbonate plate can be used, and the resin serves as a wavelength conversion substance. It is also possible to use those colored by mixing dyes and pigments. In addition to this, a box-shaped light guide plate having a hollow inside can also be used.

The end surface of the light guide plate on which the LEDs are arranged is not necessarily one side, and may be arranged on the end surfaces of the opposite sides.

[0014]

The LED light source arranged on the end surface of the light guide plate as described above is a point light source. In the first aspect, the first light diffusing surface installed on the light guide plate diffuses the light of the point light source,
It has a function of diffusing light near the end face where D is installed to make it uniform. Next, the second light diffusing surface has a function of uniformly diffusing the light diffused by the first diffusing surface over the entire light guide plate. That is, the first diffusion surface uniformly diffuses the light emission of the LED, and the second diffusion surface uniformly diffuses the LED light over the entire light guide plate. Therefore, the area of the light guide plate that uniformly emits light increases due to the action of both the diffusion surfaces, and the light emitting area that can be effectively used as a whole expands.

Next, when the first light diffusing surface and the second light diffusing surface can be separated, for example, when the light diffusing surface formed on the sheet surface is closely attached to the back surface of the light guide plate, the same sheet is used. It is not necessary to continuously form the first diffusion surface and the second diffusion surface, and only the first light diffusion surface corresponding to the light distribution characteristics of the LED can be freely exchanged, which is very advantageous in the manufacturing process. Becomes Similarly, when the first light diffusion surface is printed on the back surface of the light guide plate, only the light guide plate having the first diffusion surface needs to be replaced, which is very advantageous.

The functions of the first light diffusing surface and the second light diffusing surface of the second aspect of the present invention are basically the same as those of the first aspect. In other words, the first diffusion surface is installed on the back surface of the support body that fixes the LED lamp, so that the support body functions as a light guide plate and the surface brightness is made uniform on the first diffusion surface.
Further, the second diffusion surface has a function of making the surface brightness of the light guide plate having a larger area uniform. Further, since the support body of the LED lamp and the light guide plate are separated, L having different directivity is provided.
There is no need to change the pattern of the entire light diffusing surface by ED, and it is only necessary to change the pattern of only the first light diffusing surface provided on the support, which is very advantageous in the manufacturing process.

[0017]

【Example】

[Embodiment 1] A specific example of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a gradation of a light diffusion surface of a surface light source according to an embodiment of the present invention, and FIG. 2 is a structure of the surface light source according to the first aspect of the present invention having the light diffusion surface of FIG. FIG.

In the surface light source shown in FIG. 2, a plurality of LEDs 1
Has a structure embedded in the end surface of the light guide plate 2, and an end portion of a sheet 20 made of a resin on which a white material is printed is attached to the back surface of the light guide plate 2. A first light diffusing surface 11 and a second light diffusing surface 12 are integrally gradation printed on the sheet 20, and the light diffusing surface and the back surface of the light guide plate 2 face each other.

The first light diffusing surface 11 is gradation so that the coverage of the white substance per unit area is low in the area where the brightness of the LED 1 is high, and the coverage is high in the area where the brightness of the LED 1 is low. That is, multiple LEDs
Since the LEDs are dark between the LEDs when they are arranged on a straight line, the luminance of the light emitting surface near the LEDs is made uniform by the light diffusing surface having a high coverage.

Next, a gradation is printed on the second light diffusing surface 12 so that the coverage of the white substance increases in the direction away from the LED 1. The second light diffusing surface 12 guides the LED light to the LED light. Can be spread evenly throughout.

The light guide plate 1 of this embodiment uses a boat-shaped light guide plate whose thickness decreases with distance from the light source. However, the light guide plate 1 is not limited to such a shape, and a simple plate-like light guide plate may be used. Well, the LED is also shown molded with resin, but it is not limited to this LED but a chip type LED.
Needless to say, may be used. Further, the light diffusion surface is formed by printing a white material on a resin sheet, but it may be printed directly on the back surface of the light guide plate, or unevenness may be formed on the back surface of the light guide plate to reflect light to the light emitting surface side. Is also good.

[Embodiment 2] FIG. 3 is an exploded perspective view showing the structure of another surface light source according to the first embodiment of the present invention. The difference between this surface light source and the surface light source of FIG. 2 is that the LED 1 is not directly embedded in the end surface of the light guide plate 2 but L
The point is that the ED is fixed and the LED light is introduced from the end surface of the light guide plate 2.

The support 30 is made of a white resin such as white polycarbonate, acrylic, or vinyl chloride that can be easily processed. A through hole is formed in the support 30 and an LED is inserted into the through hole to form an LED. It is fixed. LED light can be introduced by bringing the support 30 into close contact with the end surface of the light guide plate 2 in the direction shown by the arrow. The support 30 does not have to be transparent because it does not form a light diffusing surface.

The surface light source shown in FIG. 3 also has a first light diffusing surface 11 formed on the surface of the sheet 20, similarly to the surface light source of FIG.
And a second light diffusing surface 12. The gradation of these light diffusing surfaces is shown in FIG. FIG. 4 shows a part of the surface light source of FIG. 3, and thus the first light diffusing surface 1 is
In No. 1, the area where the brightness of the LED 1 is high has a small coverage, and the area where the brightness is low has a large coverage to form a gradation so that the surface brightness near the LED is uniform.

Further, in the sheet 20 of the surface light source shown in FIGS. 2 and 3, the first light diffusing surface 11 and the second diffusing surface 12 are formed on different sheets, or the sheet 20 is broken line a. If separated at the position shown in (1), only the sheet having the first diffusion surface 11 needs to be replaced according to the brightness and type of the LED 1, which is very convenient in terms of production technology.

[Embodiment 3] FIGS. 5 and 6 are views showing a structure of a surface light source according to a second embodiment of the present invention, and FIG. 5 is a view showing gradation of a light diffusion surface of the surface light source. Figure 6
FIG. 6 is an exploded perspective view showing the structure of a surface light source having the light diffusing surface of FIG. 5.

In the surface light source shown in FIG. 5, an LED 1'is fixed via a support body 50, and the back surface of the support body 50 in the same direction as the light guide plate 2'is arranged to diffuse light near the LED. One light diffusing surface 11 'is gradation-formed by printing. On the other hand, on the back surface of the light guide plate 2 ', a second light diffusion surface 12' for diffusing the LED light over the entire light guide plate is gradation-formed by printing. The gradation is not particularly different from that of the first aspect of the present invention, and the first light diffusing surface 11 ′ has a gradation in which the coverage is different according to the brightness of the LED in order to diffuse the light in the vicinity of the LED and make it uniform. Similarly, the second diffusing surface 12 ′ is also provided with a gradation with a varying coverage ratio so that the light introduced from the end face can be diffused uniformly over the entire light guide plate.

The LE thus embedded in the support 50
When D1 ′ is used as a light source, the support 50 is made of a transparent material, and the first light diffusion surface 11 ′ for diffusing light near the LED is provided on the back side of the support 50. On the other hand, in order to prevent the LED light from leaking to the light emitting surface side on the flat surface of the support 50 facing the back surface, as shown in FIG. 6, for example, a metal thin film such as aluminum, or a white film that reflects the LED light. It is desirable to apply such a reflector.

A transparent support 50 on which the LED 1'is mounted
The surface light source is completed by closely adhering the end surface of the light guide plate 2'to the end surface of the light guide plate 2'or adhering the end surface of the light guide plate 2'through an adhesive. The second aspect of the present invention is also very advantageous in terms of production technology as in the first aspect, since only the support needs to be replaced according to the brightness of the LED, the directivity angle, and the like. In the second aspect of the present invention, the light diffusing surface printed on the light guide plate is shown. However, the light diffusing surface is formed in the same sheet shape as in the first aspect, or is formed by making the back surface of the light guide plate uneven. It goes without saying that it is okay. Although the light guide plate is described on the premise of a transparent resin such as acrylic resin, the same effect can be obtained by using a box-shaped light guide plate having a hollow inside.

[0030]

As described above, in the LED surface light source of the present invention, the brightness of the light emitting surface of the light guide plate near the LED is made uniform by the first light diffusing surface, and the entire light guide plate is made by the second diffusing surface. The brightness can be made uniform. Therefore, it is not necessary to arrange a large number of LEDs to form a linear light source as if it were a cold cathode tube, and it is possible to obtain a uniform light emitting surface with a small amount of LEDs and reduce the power consumption of the surface light source. Further, since the light guide plate near the LED also uniformly emits light, the effective light emitting area is substantially expanded. As described above, the present invention has great industrial utility value in spreading the surface light source using the LED in the future.

[Brief description of drawings]

FIG. 1 is a diagram showing gradation of a light diffusion surface of a surface light source according to a first aspect of the present invention.

FIG. 2 is a perspective view showing a structure of a surface light source according to the first aspect of the present invention.

FIG. 3 is an exploded perspective view showing the structure of another surface light source according to the first aspect of the present invention.

FIG. 4 is a diagram showing gradation of a light diffusion surface of the surface light source of FIG.

FIG. 5 is a diagram showing gradation of the light diffusion surface of the surface light source according to the second aspect of the present invention.

6 is an exploded perspective view showing the structure of a surface light source having the light diffusion surface of FIG.

FIG. 7 is a schematic plan view of a conventional LED surface light source viewed from the light emitting surface side.

[Explanation of symbols]

 1, 1 '... LED 2, 2' ... Light guide plate 11, 11 '... First light diffusing surface 12, 12' ... Second light diffusing surface 20 ... .... Sheet 30, 50 ... Support

Claims (3)

[Claims] 1. An LED lamp is disposed on an end surface of a light guide plate,
The back surface of the light guide plate is provided with a first light diffusing surface for diffusing light near the LED lamp and a second light diffusing surface for diffusing light of the LED lamp over the entire light guide plate. LED surface light source. 2. The L according to claim 1, wherein the first light diffusing surface and the second light diffusing surface can be separated from each other.
ED surface light source. 3. The LED lamp is arranged on an end face of the light guide plate via a transparent support for fixing the LED lamp, and a first light for diffusing light near the LED lamp is provided on the back surface of the support. An LED surface light source, wherein a diffusion surface and a second light diffusion surface for diffusing light of an LED lamp over the entire light guide plate are provided on the back surface of the light guide plate.