JPH07120752A - Backlight for liquid crystal display device - Google Patents

Abstract

PURPOSE:To make a backlight for a liquid crystal display device used for a computer driven by a battery such a portable personal computer thin in structure and low in power consumption. CONSTITUTION:The shape of the bottom surface of a light transmission body 13 is formed to be thinner as it goes away from a light source. The bottom surface of the light transmission body 13 has microstructure 52 where light propagated through the light transmission body is reflected onto the upper surface of the light transmission body, and the pitch 24 of the microstructure is 0.1 to 2mm. Since the light diffusivity of the bottom surface of the light transmission body 13 is changed in accordance with a distance from the light source, the in-panel uniformity and directivity of projected light from the upper surface of the light transmission body 13 are set in a desired direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin liquid crystal display backlight having high light utilization efficiency.

[0002]

2. Description of the Related Art The structure of a conventional backlight for a liquid crystal display device is shown in FIG. The configuration includes a lamp 12 as a light source, a transparent light guide 13 that guides light from the lamp 12 that is a light source, a diffusion sheet 11 arranged on the front surface of the transparent light guide 13, and a bottom surface of the transparent light guide 13. The scattered printed material 14 whose scattered property is changed according to the distance from the lamp, the reflector plate 21 arranged around the lamp 12, and on the bottom surface of the transparent light guide 13.
And 20.

In FIG. 5, in-plane uniformity can be obtained by increasing the diffusivity of the scattering printing body 14 disposed on the bottom surface of the transparent light guide 13 in accordance with the distance from the lamp. Further, there is a configuration in which the thickness of the transparent light guide is changed according to the distance of the lamp to achieve uniformity.
28435 and JP-A-59-1758.

[0004]

However, in the prior art in which the diffusivity is increased on the bottom surface of the light guide according to the distance from the lamp, the light from the lamp is transmitted through the opposite lamp by 5 times.
It is 0% or more, and is reflected by the reflection plate on the back surface of the lamp and is incident on the light guide again, but the absorption loss absorbed by the light emitting portion of the lamp is large. Therefore, when a battery-driven liquid crystal display device such as a notebook personal computer or a laptop computer is used, two-thirds or more of the liquid crystal display device is used as the power consumption of the backlight, which makes it difficult to use for a long time. Further, in the configuration in which the thickness of the light guide body is changed, the in-plane uniformity of the light emitted from the light guide body can be obtained, but the directivity is directed in the normal direction of the upper surface of the light guide body, and the liquid crystal display device has good It was difficult to obtain good display characteristics.

An object of the present invention is to provide a liquid crystal display device for use in a portable personal computer or the like, which maintains in-plane uniformity of light emitted from a light guide, has directivity, and has little light loss. To provide a backlight.

[0006]

In order to solve the above problems, a backlight for a liquid crystal display device according to the present invention is a backlight for a liquid crystal display device in which a light source is arranged on one end surface of a light guide. The shape of the bottom surface of the light body is formed thin as it goes away from the light source, the light guide bottom surface has a fine structure that reflects the light propagating in the light guide to the light guide upper surface, and the pitch of the fine structure is It is 0.1 mm to 2 mm, and the light diffusivity of the bottom surface of the light guide body is changed according to the distance from the light source.

[0007]

In a liquid crystal display device used for a notebook personal computer, a laptop computer or the like, it is necessary to obtain a bright liquid crystal display device with low power consumption. Therefore, in a backlight for a liquid crystal display device in which a light source is arranged on one end surface of the light guide, the bottom shape of the light guide is made thinner as it gets away from the light source, and the bottom surface of the light guide propagates through the light guide. Has a fine structure that reflects light to the upper surface of the light guide, the pitch of the fine structure is 0.1 mm to 2 mm, and the light diffusivity of the bottom surface of the light guide changes depending on the distance from the light source. By using the backlight for a liquid crystal display device characterized by, it is possible to obtain the in-plane uniformity of the light emitted from the upper surface of the light guide and set the directivity in a desired direction. Therefore, it is possible to reduce the thickness and power consumption of the backlight for a liquid crystal display device used in a portable personal computer or the like.

[0008]

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

(Embodiment 1) A schematic view of an embodiment of the present invention is shown in FIG. FIG. 1 is a sectional view showing the structure of a liquid crystal display backlight of the present invention. In FIG. 1 of the present invention, a lamp 12 is arranged on one end surface of a transparent light guide 13 that guides light, and the shape of the light guide 13 becomes thinner as it goes away from the lamp 12, and the bottom surface of the transparent light guide 13 is shown in FIG. The microstructure 52 shown in FIG. Further, a reflector 21 is arranged on the side surface of the lamp, and a reflector 20 is arranged on the bottom surface of the transparent light guide 13. In this embodiment, the angles 22 and 23 of the fine structure 52 in FIG. 2 are 20 degrees and 45 degrees, respectively, and the pitch 24 of the fine structure is 0.5 mm.
The size of the transparent light guide was 150 mm × 200 mm × 4 mm. In this embodiment, the pitch of the fine structure is set to 0.5 mm, but if it is about 0.1 mm to 2 mm, both directivity and uniformity can be achieved. Although the pitch 24 of the microstructures 52 is constant, the pitch 24 does not have to be constant from the left end 50 to the right end 51. Further, since the acrylic plate is used for the transparent light guide, the total reflection angle 25 is about 42 degrees. Moreover, the bottom shape of the transparent light guide 13 is not limited.

Light from the lamp 12 arranged on one end face of the transparent light guide 13 is incident from the end face of the transparent light guide 13, reflected by the reflection plate on the bottom surface, and totally reflected at the upper boundary repeatedly. It is emitted uniformly. At this time, if the scattering property of the back surface of the light guide body 13 is constant, it is difficult to obtain the uniformity. Therefore, the scattering property of the fine structure 52 is increased from 50 to 52.

The fine structure 5 on the bottom surface of the transparent light guide 13 is also provided.
2, the angles 22 and 23 with respect to the horizontal plane are set as shown in FIG. Therefore, totally reflected light having an angle of total reflection of 25 or more is reflected by the surface of the fine structure 52 perpendicularly to the upper surface of the transparent light guide. At this time, since the surface of the fine structure 52 has a scattering property, it is reflected with a symmetrical distribution centered on the specular reflection light.
Therefore, the light is emitted from the upper surface of the light guide in a symmetrical distribution centered on the vertical direction. Further, the light reflected on the upper surface again enters the fine structure 52, and repeats similar reflection, and becomes emitted light having a large number of vertical method components uniformly in the surface.

In the present embodiment, the in-plane uniformity of the current backlight is about 10%, and it is possible to obtain the characteristics having no practical problem.

In FIG. 1, by making the bottom shape thinner as it goes away from the lamp, the transmission of light to the opposite surface is reduced and the light utilization efficiency is high. Further, in the conventional two lamp type shown in FIG. 7, the absorption loss due to the facing lamp was large, but in the present embodiment, the absorption loss due to the lamp is small. Figure 7
Then, the light utilization efficiency was improved from 50% or less to 70% or more.

(Embodiment 2) FIG. 3 shows an embodiment of the present invention. FIG. 3 is a sectional view showing the structure of the liquid crystal display backlight of the present invention. In FIG. 3, the lamp 12 is arranged on one end surface of the transparent light guide 13 that guides light, and the shape of the light guide 13 becomes thinner as it goes away from the lamp 12, and the bottom surface of the transparent light guide 13 has a fine structure 52. , Fine structure pitch 2
4 becomes finer as it moves away from the lamp. Further, a reflector 21 is arranged on the side surface of the lamp, and a reflector 20 is arranged on the bottom surface of the transparent light guide 13. Further, as shown in FIG. 4, the diffusion plate 11 is provided on the upper side and the prism sheet 1 is provided on the diffusion plate 11.
When an optical path conversion element array such as 0 is arranged, in-plane uniformity can be further obtained. In this embodiment, the angles 22 and 23 of the fine structure 52 in FIG.
The pitch 24 of the fine structure was changed from 8 mm to 2 mm to 0.2 mm, and the size of the transparent light guide was set to 150 mm × 200 mm × 4 mm. Further, since the acrylic plate is used for the transparent light guide, the total reflection angle 25 is about 42 degrees.

The configurations of FIGS. 3 and 4 have the same effects as those of the first embodiment. Current backlight in-plane uniformity is 10%
It was a level, and it was possible to obtain the characteristics with no practical problems.

In both FIGS. 3 and 4, the bottom face is made thinner as it gets farther from the lamp, so that the light transmission to the opposite face is reduced and the light utilization efficiency is high. Further, in the conventional two-lamp type shown in FIG. 7, the absorption loss due to the facing lamp was large, but in the present embodiment, the absorption loss due to the lamp is small. In FIG. 7, the light utilization efficiency was 50% or less, but was improved to 70% or more in this embodiment.

The representative invention of the present invention has been described in the first and second embodiments. Although the transparent light guide of the backlight for liquid crystal display device of this embodiment is manufactured by machining, it can be manufactured by embossing, injection molding or the like, and the manufacturing method is not limited.
There are various methods for the reflector, such as sputtering, vapor deposition, and liquid coating, but the manufacturing method is not limited.

In Examples 1 and 2, the angle of the microstructure 52 is within the range, when the angles 22 and 23 are reduced at the end 50 and the angles 22 and 23 are increased at the end 51, the angle from the lamp 12 is reduced. More light can be guided to the thin part,
This is effective when the transparent light guide 13 is thin and the change in thickness cannot achieve uniformity.

When the diffusion plate 11 and the optical path conversion element array 10 are arranged on the upper surface of the transparent light guide 13 as in the embodiment of FIG. 4, the diffusion plate 11 has an uneven distribution of directivity in the plane.
As a result, the directivity is destroyed, and the directivity is again provided by the optical path conversion element array 10 such as the prism sheet, so that the in-plane uniform directivity can be obtained.

Although the shape of the end surface on the lamp side in FIGS. 1 and 4 is not limited, in order to match the refractive index of the lamp tube with the refractive index of the light guide, if oil having a high heat resistance is inserted, the light guide from the lamp is inserted. The efficiency of coupling light to is increased.

When the thickness of the light guide is large, it is not necessary to change the scattering property of the back surface.
It is especially effective when it is less than or equal to mm. At present, the smaller the tube diameter of the lamp, the higher the luminous efficiency, but in view of manufacturability and the like, it is desirable that the tube diameter is 3 mm or less.

[0022]

EFFECTS OF THE INVENTION The bottom shape of the light guide is made thinner as the distance from the light source increases, and the bottom of the light guide has a fine structure for reflecting the light propagating in the light guide to the upper surface of the light guide. Has a pitch of 0.1 mm to 2 mm and the light diffusivity of the bottom surface of the light guide changes depending on the distance from the light source. A backlight for liquid crystal display device with strong directivity in the direction can be configured, absorption loss due to the lamp itself is small, and in-plane uniformity can be achieved with a thin structure and a fine structure of the light guide, so that the light utilization efficiency is high and thin. A backlight for a liquid crystal display device can be obtained.

Further, in-plane uniformity and directivity can be improved by combining with a diffusion plate or an optical path conversion element array. In particular, it is advantageous for a thin backlight structure.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a backlight for a liquid crystal display device of the present invention.

FIG. 2 is an explanatory diagram showing a part of a backlight for a liquid crystal display device of the present invention.

FIG. 3 is an explanatory diagram showing a part of a backlight for a liquid crystal display device of the present invention.

FIG. 4 is an explanatory view showing a second embodiment of the backlight for a liquid crystal display device of the present invention.

FIG. 5 is an explanatory diagram showing a comparative example of the present invention.

[Explanation of symbols]

13 ... Transparent light guide, 22, 23 ... Angle of fine structure, 24
... fine structure pitch, 25 ... total reflection angle, 52 ... fine structure.

Claims (4)

[Claims] 1. A backlight for a liquid crystal display device, in which a light source is arranged on one end surface of a light guide, wherein the bottom shape of the light guide is formed thinner as the distance from the light source increases, and the bottom surface of the light guide is It has a fine structure that reflects the light propagating in the light guide body to the upper surface of the light guide body,
A backlight for a liquid crystal display device, wherein the pitch of the fine structure is 0.1 mm to 2 mm, and the light diffusivity of the bottom surface of the light guide body changes according to the distance from the light source. 2. A backlight for a liquid crystal display device, in which a light source is arranged on one end surface of a light guide, the bottom shape of the light guide is formed to be thinner as the distance from the light source increases, and the bottom surface of the light guide is formed. Having a fine structure that reflects the light propagating in the light guide to the upper surface of the light guide,
A backlight for a liquid crystal display device, wherein a pitch of the fine structure is changed according to a distance from the light source. 3. The backlight for a liquid crystal display device according to claim 1, further comprising a diffusion sheet and / or a prism sheet on an upper surface of the light guide body. 4. The backlight for a liquid crystal display device according to claim 1, wherein the light guide has a thickness of 4 mm or less, and the light source has a lamp diameter of 3 mm or less.