JPH06273751A - Backlight for liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce the thickness and the power consumption of the backlight for liquid crystal display device used in a battery-driven computer such as a portable personal computer. CONSTITUTION:The shape of the bottom face of a light guiding body 13 is made thinner as going away from a light source, and such minute structure is provided that total reflected light from the upper face of the light guiding body 13 is reflected in the approximately perpendicular direction to the upper face of the body 13, and the minute structure is inclined at the angle, which is indicated by (sin<-1>(1/n))/2<=theta22<=pi/4 and 0<=theta23<=pi/2-sin<-1>(1/n) where (n) is the refractive index of the transparent light guiding body, to the horizontal surface to not only uniformize the light emitted from the upper face of the light guiding body 13 in a surface but also set the directivity to 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 backlight for a liquid crystal display device 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 structure is such that a lamp 12 as a light source, a transparent light guide 13 for guiding light from the lamp 12 as a light source, a diffusion film 11 arranged on the front surface of the transparent light guide 13 and a bottom surface of the transparent light guide 13 are arranged. The scattering printed material 14 whose scattered property is changed depending on the distance from the lamp, the reflectors 21, 2 arranged around the lamp 12 and on the bottom surface of the transparent light guide 13.
It consists of 0 and.

In the structure shown in FIG. 7, in-plane uniformity can be obtained by increasing the diffusivity of the scattering printing body 14 arranged on the bottom surface of the transparent light guide 13 in accordance with the distance from the lamp. . Further, Japanese Patent Laid-Open No. 62-28435 and Japanese Patent Laid-Open No. 59-1758 disclose a structure for achieving uniformity by changing the thickness of the transparent light guide according to the distance of the lamp.

[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 to the normal line direction of the upper surface of the light guide body, and the liquid crystal display device has good It was difficult to obtain 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 bottom shape of the light body is formed thinner as it goes away from the light source, and has a fine structure that reflects the totally reflected light from the upper surface of the light guide in a direction substantially perpendicular to the upper surface of the light guide. And a backlight for a liquid crystal display device. Furthermore, in the liquid crystal display backlight of the present invention, the fine structure of the bottom surface of the light guide has an angle with respect to a horizontal plane represented by Formulas 1 and 2, and the upper surface of the light guide has a lens effect. And a light source side end surface of the light guide has a shape for enlarging light 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 a light guide, the bottom shape of the light guide is formed to be thinner as it goes away from the light source, and the total reflection light from the upper surface of the light guide is The light emitted from the upper surface of the light guide has a fine structure that reflects light in a direction substantially perpendicular to the upper surface of the light guide, and the fine structure has an angle represented by Equations 1 and 2 with respect to the horizontal plane. The in-plane uniformity can be obtained and the directivity can be set in a desired direction. Further, the directivity can be further improved by providing the lens effect on the upper surface of the light guide. 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] An explanatory view of an embodiment of the present invention is shown in FIGS. 1 and 2 are cross-sectional views showing the structure of a liquid crystal display backlight of the present invention. In FIG. 1, 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 linearly thins as it goes away from the lamp 12, and the bottom of the transparent light guide 13 is shown in FIG. It has the microstructure 52 shown. On the other hand, in FIG. 2, 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 thin with a curved surface convex downward as the distance from the lamp 12 increases. Has a microstructure 52 shown in FIG. In addition, on the side surface of the lamp, the reflector 21,
A reflection plate 20 is arranged on the bottom surface of the transparent light guide 13, a diffusion plate 11 is arranged on the top, and an optical path conversion element array such as a prism sheet is arranged on the diffusion plate 11. In this embodiment, the angles 22 and 23 of the fine structure 52 in FIG. 5 are 21 degrees and 48 degrees, respectively, the pitch 24 of the fine structure is 2 mm, and the size of the transparent light guide is 150 mm × 200 mm × 4 mm.
Although the pitch 24 of the microstructures 52 is constant, the pitch 24 need not 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. In FIG. 2, the shape of the bottom surface of the light guide is a curved surface of a quadratic function.

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.

The fine structure 5 on the bottom surface of the transparent light guide 13 is also provided.
2, the angles 22 and 23 with 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, if 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 is incident on the fine structure 52 again and is repeatedly reflected in the same manner to become outgoing light having many vertical method components uniformly in the surface.

The in-plane uniformity between the left end 50 and the right end 51 in FIGS. 1 and 2 was 5% or less. The current in-plane uniformity of the backlight is about 10%, and it is possible to obtain the characteristics having no practical problem. Moreover, in FIG. 1 in which the shape of the bottom surface of the light guide body is linear and in FIG. 2 in which the shape of the bottom surface is a curve, higher luminance can be obtained in FIG.

As a comparative example, the bottom surface of FIG.
The in-plane uniformity of the fine structure shown in FIG. 6 is shown by the curve 120 in FIG. The uniformity is poorer than the conventional configuration using the diffusion printed body 14 (dot pattern), and it is effective only if it is combined with the configuration in which the light guide body is thin according to the distance from the lamp.

In both FIGS. 1 and 2, the bottom shape is made thinner as the distance from the lamp increases, so that 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 the absorption loss due to the lamp is small in this embodiment. In FIG. 7 of the related art, the light utilization efficiency was 50% or less, but improved to 70% or more.

Further, as shown in FIG. 6, by making the upper part of the light guide member convex so as to have a lens effect, the emitted light can be narrowed down in the normal direction of the upper surface. At this time, the lens pitch 26 is preferably aligned in the same size as the pixels of the liquid crystal display device, but if the pitch is 30 times or less of the pixel pitch, no problem will occur.

[Embodiment 2] An explanatory view of an embodiment of the present invention is shown in FIGS. 3 and 4 are cross-sectional views showing the structure of the liquid crystal display backlight of the present invention. FIG. 3 of the present invention
The lamp 12 is disposed on one end surface of the transparent light guide 13 that guides light, and the shape of the light guide 13 becomes linearly thin as the distance from the lamp 12 increases.
The microstructure 52 shown in FIG. On the other hand, FIG. 4 of the present invention
The lamp 12 is disposed on one end surface of the transparent light guide 13 that guides light, and the shape of the light guide 13 becomes thin with a curved surface that is convex downward as the distance from the lamp 12 increases. It has the microstructure 52 shown. The reflector 21 is provided on the side surface of the lamp, and the reflector 2 is provided on the bottom surface of the transparent light guide 13.
0 is arranged, a diffusion plate 11 is arranged on the upper part, and an optical path changing element array such as a prism sheet is arranged on the diffusion plate 11.
Further, although the shape of the end surface on the lamp side of the transparent light guide in FIGS. 3 and 4 is a hemispherical shape in this embodiment, the shape is not limited as long as it is a concave surface with respect to the lamp.

In this embodiment, the fine structure 52 shown in FIG.
The angles 22 and 23 are 21 degrees and 48 degrees respectively, the fine structure pitch 24 is 2 mm, and the size of the transparent light guide is 150 mm ×
It was set to 200 mm x 4 mm. Although the pitch 24 of the microstructures 52 is constant, the pitch 24 need not 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. In FIG. 2, the shape of the bottom surface of the light guide is a curved surface of a quadratic function.

The constructions of FIGS. 3 and 4 have the same effects as those of the first embodiment. Furthermore, since the end surface of the light guide on the lamp side has a hemispherical shape, the light is guided from the lamp to the light guide. The result that the coupling efficiency was higher than that of Example 1 was obtained. Further, the hemispherical shape has a lens effect, and the light incident on the light guide from the lamp is spread uniformly and the in-plane uniformity of the emitted light is improved.

The results of measuring the in-plane uniformity between the left end 50 and the right end 51 in FIGS.
22 and 123. The current in-plane uniformity of the backlight is about 10%, and the in-plane uniformity in this embodiment is 5%.
% Or less, and it was possible to obtain characteristics that are practically unproblematic. Further, comparing FIG. 3 in which the shape of the bottom surface of the light guide is linear and FIG. 4 in which the shape is curved, higher luminance can be obtained in FIG.

In both FIGS. 3 and 4, the bottom shape is made thinner as the distance from the lamp increases, so that the light transmission 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 the absorption loss due to the lamp is small in this embodiment. In FIG. 7 of the related art, the light utilization efficiency was 50% or less, but in this embodiment, it was improved to 80%.

Further, as shown in FIG. 6, by making the upper part of the light guide convex so as to have a lens effect, the emitted light can be narrowed down in the direction normal to the upper surface. At this time, the lens pitch 26 is preferably aligned in the same size as the pixels of the liquid crystal display device, but if the pitch is 30 times or less of the pixel pitch, no problem will occur.

The representative inventions of the present invention have been described above in the first and second embodiments. The transparent light guide of the backlight for liquid crystal display device of the present embodiment was manufactured by machining,
It can be manufactured by embossing or injection molding, 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.

Although the fine structure 52 shown in FIGS. 5 and 6 is used as the diffuse reflection surface, if the pitch 24 of the fine structure 52 can be made small, there will be no problem even if the fine structure has a mirror surface. Further, the angle of the fine structure 52 is within the range of the formulas 1 and 2, when the angles 22 and 23 are reduced at the end portion 50 and the angles 22 and 23 are increased at the end portion 51, the lamp 1
It is effective in the case where more light from 2 can be guided to the thin portion, and the transparent light guide 13 is thin and the uniformity cannot be achieved only by changing the thickness.

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 shown in FIGS. 1 to 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. 3 and 4 is not limited, in order to match the refractive index of the lamp tube with the refractive index of the light guide body, if a highly heat-resistant oil is inserted, the light guide body is removed from the lamp. The efficiency of coupling light to is increased.

[0026]

EFFECTS OF THE INVENTION By making the transparent light guide thin as it goes away from the light source, and having a fine structure for reflecting the totally reflected light on the upper surface of the light guide in a direction substantially perpendicular to the upper surface of the light guide, It is possible to configure a backlight for a liquid crystal display device, which maintains the uniformity of emitted light distribution and has a strong directivity in the direction perpendicular to the upper surface of the light guide. With this configuration, the absorption loss due to the lamp itself is small, and the in-plane uniformity can be achieved by the thin structure and the fine structure of the light guide body, so that a thin backlight for liquid crystal display device having high light utilization efficiency 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.

[Brief description of drawings]

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

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

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

FIG. 4 is an explanatory diagram of a fourth embodiment of the backlight for a liquid crystal display device of the present invention.

FIG. 5 is an explanatory diagram showing one embodiment of a backlight for a liquid crystal display device of the present invention.

FIG. 6 is an explanatory diagram showing an embodiment of a backlight for a liquid crystal display device of the present invention.

FIG. 7 is an explanatory diagram showing a comparative example of the present invention.

FIG. 8 is a characteristic diagram of a comparative example of the present invention.

FIG. 9 is a characteristic diagram of an example of the backlight for a liquid crystal display device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Optical path conversion element array, 11 ... Diffusion plate, 12 ... Lamp, 13 ... Transparent light guide, 20, 21 ... Reflector, 30 ... Backlight, 50 ... Lamp side fine structure end part, 51 ... Microstructure right end part , 52 ... Fine structure.

Claims (4)

[Claims] 1. A backlight for a liquid crystal display in which a light source is arranged on one end surface of a light guide, wherein a bottom shape of the light guide is formed to be thinner as the distance from the light source is increased, and an upper surface of the light guide is formed. A backlight for a liquid crystal display device, which has a fine structure for reflecting the totally reflected light from the optical waveguide in a direction substantially perpendicular to the upper surface of the light guide. 2. A backlight for a liquid crystal display device in which a light source is arranged on one end surface of a light guide, wherein a bottom shape of the light guide is formed to be thinner as the distance from the light source is increased, and an upper surface of the light guide is formed. Has a fine structure that reflects the total reflected light from the light guide in a direction substantially perpendicular to the upper surface of the light guide, and the fine structure has the following expression with respect to a horizontal plane: (sin ^-1 (1 / n)) / 2 ≤ θ ₂₂ ≤ π / 4 [Formula 2] 0 ≤ θ ₂₃ ≤ π / 2-sin ^-1 (1 / n) where n has angles θ ₂₂ and θ ₂₃ represented by the refractive index of the transparent light guide. A backlight for a liquid crystal display device, which is characterized in that 3. The backlight for a liquid crystal display device according to claim 2, wherein the upper surface of the light guide has a lens effect. 4. The backlight for a liquid crystal display device according to claim 3, wherein the end surface of the light guide on the light source side has a shape for expanding light from the light source.