JPH04329520A - Lighting device - Google Patents

Abstract

PURPOSE:To obtain high brightness by arranging a couple of L-shaped tubular light sources in a diagonal direction of a light guide plate and lighting the light guide plate in all directions. CONSTITUTION:The lighting device lights a liquid crystal display plate from behind by an edge light system and is equipped with the light guide plate 11 arranged in parallel to the liquid crystal display plate and the couple of tubular light sources 12 which irradiate the light incidence end surfaces 11a of the light guide plate 11 with light. The four flanks of the light guide plate 11 are formed as the light incidence end surfaces 11a perpendicularly to the front surface and rear surface. A reflection sheet which reflects the backward light in the light guide plate 11 toward the liquid crystal display plate is fitted on the rear surface of the light guide plate 11 and a diffusion sheet which uniforms the brightness of lighting over the entire surface is brought into contact with the light guide plate 11. Then the tubular light sources 12 are formed in an L shape and arranged in the diagonal direction across the light guide plate 11. Then the length of each of the tubular light source 12 is set long enough to light the respective light incidence end surfaces 11a of the light guide plate 11 thoroughly.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge-light illumination device used as a backlight for a light-receiving liquid crystal display device.

0002

2. Description of the Related Art Conventionally, as shown in FIGS. 3 and 4, an edge-light type illumination device used as a liquid crystal display device uses a lamp such as a cold cathode tube or a hot cathode tube as a light source 1, and uses a translucent The light guide plate 2 is arranged on both sides of the light guide plate 2 made of material.
A diffusion sheet 3 made of a milky white synthetic resin plate having a light scattering effect is provided on the upper surface in order to uniformize the brightness of the illumination surface over the entire surface, and a reflection sheet 4 is provided with a specular reflection plate or a light scattering acrylic plate. Boards etc. are used. This reflective sheet 4 is provided to improve the efficiency of light utilization by reflecting the light emitted from the light source and directed toward the back surface and guiding it toward the front surface.

[0003] Particularly in the field of color LCD unit panels, it is essential to use the optical isomerism of liquid crystals to overlap polarizing plates.
%, and there is a strong demand from the market for backlight systems with higher brightness.

In FIG. 3, 7 is a light source reflector that reflects outward light from the light source toward the light guide plate 2, and X is a liquid crystal display panel.

[0005]

[Problems to be Solved by the Invention] In the conventional edge light type illumination device in which light enters from the light incident end surfaces 5 at both the left and right ends of the light guide plate 2, a very uniform luminance distribution can be achieved, but generally the light Usage efficiency is low. In order to solve this problem and achieve brightness on the diffusion sheet, it is possible to increase the thickness of the light guide plate 2 (thickness in the light incident direction). However, this would not match market needs from the perspective of realizing a thinner LCD unit.
This has always been a problem, especially in the field of color LCD units.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a lighting device that has high brightness and can be made thinner.

[0007]

Means for Solving the Problems The means for solving the problems according to claim 1 of the present invention is to illuminate a liquid crystal display panel from the rear, as shown in FIG. and a tubular light source 12 that irradiates light onto the light incident end surface 11a of the light guide plate 11, wherein the tubular light source 12 is arranged so as to surround the light guide plate 11 on all four sides in a surface direction thereof. It is.

Further, the problem solving means according to claim 2 of the present invention is that the tubular light source 12 according to claim 1 is formed in an L-shape,
They are arranged in a pair diagonally with the light guide plate 11 in between.

[0009]

[Operation] In the problem solving means according to claims 1 and 2, the light from the light source 12 is transmitted to the light incident end face 11a of the light guide plate 11.
The light enters the interior of the light guide plate 11 and is then irradiated from the front surface of the light guide plate 11 to the back surface of the liquid crystal display panel.

At this time, since the L-shaped tubular light sources 12 are arranged on the four light incident end faces 11a of the light guide plate 11 and light is incident from all four directions of the light guide plate 11, the light guide plate 11 Compared to entering light only from a pair of opposing surfaces,
The amount of incident light can be increased while using the same light guide plate 11.

[0011] Therefore, it is possible to realize a backlight compatible with brightness while maintaining the same thickness of the light guide plate as the conventional one and maintaining its thinness.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS A lighting device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing an illumination device for a liquid crystal display according to an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the luminance of a light guide plate and the incident luminous flux per unit area.

As shown in the figure, the liquid crystal lighting device of this embodiment illuminates the liquid crystal display panel from behind using an edge light method, and includes a light guide plate 11 arranged parallel to the liquid crystal display panel.
and a pair of tubular light sources 12 that irradiate light onto the light incident end surface 11a of the light guide plate 11.

As shown in FIG. 1, the light guide plate 11 is made of, for example, acrylic resin with a total light transmittance of 93% and a refractive index n=1.49, and has a length dimension A=20.5 cm and a width dimension B=1.
It is formed into a flat plate shape with a thickness of 5.5 cm and a thickness of t=0.6 cm. The four side surfaces of the light guide plate 11 are light incident end surfaces 11a.
It is formed perpendicular to the front and rear surfaces. A reflective sheet is attached to the rear surface of the light guide plate 11 to reflect the backward light inside the light guide plate 11 toward the liquid crystal display panel, and a reflective sheet is attached to the front surface of the light guide plate 11 to make the illumination brightness uniform across the front panel. A diffusion sheet is placed in close contact with the

[0016] Each of the tubular light sources 12 uses a straight hot cathode tube or the like, which is composed of a light emitting body such as a filament and an exterior tube that covers it, and has a diameter of, for example, 4.1 m.
m, tube brightness is set to 20400 cd. The tubular light sources 12 are formed in an L-shape and are arranged diagonally to each other with the light guide plate 11 in between. The length dimension of each of the tubular light sources 12 is formed to be long enough so that each light incident end surface 11a of the light guide plate 11 can be completely illuminated.

The lighting device having the above structure is manufactured as follows. First, when manufacturing the tubular light source 12, after going through the steps of weighing raw materials, mixing, continuous melting, and stirring, it is formed into an L-shaped tube, then slowly cooled, inspected, cut, press-sealed, and annealed. After the process is complete, inspect again. Also,
The light guide plate 11 is also formed by curing a transparent resin into a flat plate shape.

After that, a reflective sheet is closely attached to the rear surface of the light guide plate 11, and a diffusion sheet is closely attached to the front surface of the light guide plate 11, and then a pair of tubular light sources 1 are attached.
2 are arranged diagonally across the light guide plate 11, and the illumination device is completed.

Next, to explain the operation of the illumination device in use, light from the tubular light source 12 is transmitted through the light incident end surface 1 of the light guide plate 11.
Enter the interior from 1a. Thereafter, the incident light is applied to the back surface of the liquid crystal display panel from the front surface through the diffusion sheet so that the light is almost uniformly distributed.

At this time, since the L-shaped tubular light sources 12 are disposed on the four light incident end faces 11a of the light guide plate 11, it is possible to enter the light from only one pair of ends of the light guide plate 11 as in the conventional case. In comparison, the amount of incident light can be increased while using the same light guide plate 11. Therefore, it is possible to realize a backlight compatible with brightness while maintaining the same thickness of the light guide plate as in the past.

The degree of increase in the amount of light will be explained below. Here, if we use the brightness evaluation method for projection television screens, the lighting device can be organized as a group of straight lines with an inclination of 45° on a log-logarithmic graph, as shown in Figure 2, and is generally expressed by the following equation (1). It will be possible.

logL=log(I/S)+C (constant)
...(1) In the formula (1), I is the incident luminous flux (lm) per unit length at the light incidence end surface 11a, S is the area of the illumination surface (cm2), and L is the brightness on the diffusion sheet (nt), respectively. It shows. Figure 2 shows this on a graph for each liquid crystal display board.
It is. In the figure, C1 indicates a directional edge light using a prismatic diffusion sheet, C2 indicates a non-directional edge light, and C3 indicates a direct type edge light. In both cases, it can be confirmed that good approximation is achieved as a group of straight lines with an inclination of 45° on the logarithmic graph.

Here, when the conventional example is expressed mathematically based on equation (1), logL=log(I/S)+C=log(I/S)
/A・B)+C...(2). Here, A indicates the length dimension of the light guide plate 11, and B indicates the width dimension of the light guide plate 11. On the other hand, in this embodiment, logL=log[
{2(A+B)/2A}I/S]+C =log[{(A+B)/A}I/(A・B)}]+C
...(3) becomes. Therefore, the difference is the difference between equations (2) and (3), and can be expressed by the following equation (4).

[0024]log[{(A+B)/A}I/(A・B
)}]+C - {log(I/A・B)+C} =log[[{(A+B)/A}I/(A・B)]/(
I/A・B)]=log{(A+B)/A}...(4) In this example, the brightness on the illumination surface is 1800 nt,
We have achieved a backlight system that supports higher brightness than conventional examples.

It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

For example, in the above embodiment, two L-shaped tubular light sources are used, but four normal linear light sources may be used, or an annular light source such as a circle light may be used. may be used.

[0027]

As is clear from the above description, according to claims 1 and 2 of the present invention, the tubular light sources are arranged in the plane direction of the light guide plate so as to surround it on all four sides. The amount of incident light can be increased compared to the conventional method. Therefore, there is an excellent effect that a backlight corresponding to brightness can be realized while maintaining the same thickness of the light guide plate as the conventional one.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a liquid crystal lighting device according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the luminance of a light guide plate and the incident light flux per unit area.

FIG. 3 is a plan view showing a conventional lighting device.

FIG. 4 is also a side view thereof.

[Explanation of symbols]

11 Light guide plate 11a Light incident end face 12 Light source

Claims (2)

[Claims] 1. An illumination device that illuminates a liquid crystal display board from behind, and includes a light guide plate arranged parallel to the liquid crystal display board, and a tubular light source that irradiates light to a light incident end surface of the light guide plate. An illumination device characterized in that the tubular light source is arranged so as to surround the light guide plate on all sides in a surface direction thereof. 2. An illumination device according to claim 1, wherein the tubular light sources are L-shaped and arranged in a pair diagonally across a light guide plate.