JP2723481B2 - Flat 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 an illumination light source for a liquid crystal display or an illumination signboard requiring a planar illumination light source.

[0002]

2. Description of the Related Art At present, a planar illumination light source mainly used for a liquid crystal display is provided with a liquid crystal display, that is, a light source such as a fluorescent lamp behind an object to be illuminated, and the light of the light source is directly applied to an image before the light source. A structure in which a diffusion sheet such as a milky white transparent plate is placed so as not to affect, or a light source is placed behind the side of the illuminated object, and acrylic resin, polycarbonate resin, etc. are directly behind the illuminated object that is laterally separated from the light source On the back side of the transparent plate, lenticular or fresnel-shaped grooves are provided, or a white dot-shaped or striped printed pattern is arranged, and light incident on the transparent plate from the side is A light guide plate that distributes light as if emitted in a planar manner from the groove of the transparent plate or the printed back surface is used.

[0003]

In an illumination device using such a light guide plate, it is difficult to obtain uniform illumination. Therefore, a diffusion sheet must always be used on the upper surface of the illumination device. Since the light is absorbed and becomes dark, and the light reflected by the light guide plate and the diffusion sheet is scattered, it is necessary to distribute the diffused light to the center of the upper surface of the lighting device by using a special material called a prism sheet in many cases. There are disadvantages such as there.

[0004] As the size of the illuminated body increases, the thickness of the light guide plate increases, and the total weight of the entire display device increases. Serious problems still exist, such as the very high price of prism sheets. In particular, liquid crystal displays will increase in size in the future, as well as higher definition, thinner, lighter,
There is a strong demand in the art for an energy-saving, inexpensive and sophisticated lighting device.

In view of the above situation, the present invention can provide sufficiently uniform and high luminance even without using a light guide plate and without using a particularly high-brightness cold-cathode tube and using a normal fluorescent tube. Another object of the present invention is to provide a lighting device having a very simple structure.

[0006]

According to the present invention, there is provided a thin, opaque white box-like container having an opening in a front wall, and at least one side wall of the container. Inside, a rod-shaped light source is provided to illuminate the inner surface of the box, and the rear wall facing the opening surface of the box has an inner surface that is a diffuse reflection surface, and the cross section of the diffuse reflection surface is close to the light source. The part gradually moves away from the opening surface as it moves away from the light source, gradually approaches the opening surface as it further moves away from the light source, and is smooth and gradual so that the change in the distance from the opening surface becomes largest at the part farthest from the light source. A planar illumination device characterized by being formed with a concave concave surface is provided.

According to a preferred embodiment of the present invention, the inside of the side wall of the box-shaped container located on the side of the light source is a diffuse reflection surface having a flat or convex curved surface, and is provided in front of the light source on the front wall surrounding the opening. The inner surface of the located part is a diffuse reflection surface inclined to distribute light farther, including the closest part of the concave diffuse reflection surface on the inner surface of the container rear wall, and is located behind the light source. A light shield having a triangular cross section is provided inside the rear wall portion so that the light source does not directly illuminate the diffuse reflection surface of the rear wall.

According to another preferred embodiment of the present invention, a rod-shaped light source is provided only inside one side wall of the box-shaped container, and the inside of the side wall opposite to the side wall having the rod-shaped light source is provided on the rear surface of the container. On the other hand, it is composed of a diffuse reflection surface of a flat or convex curved surface inclined at an angle of 90 ° or more.

[0009]

The principle of operation of the present invention will be described below. Generally, when a light source is located at a single point in a completely dark space, it is clear from the case of a lantern or the like that there is a method of covering the light source with Japanese paper or the like in order to increase the apparent size of the light source. It can be said that a white incandescent lamp applies this principle. In this case, if transparent glass is used instead of Japanese paper, the light source cannot be seen large. This is because glass does not diffuse even if it transmits light.

[0010] Similarly, even if the light source at one point in the closed space is covered with a transparent glass wall, the light only passes through the outside of the glass, and the space does not become bright. In the same situation, turning a wall into a mirror only reflects the light source on the wall, but does not brighten the enclosed space, but merely reflects the virtual image of the light source on the surrounding mirror.

When the wall is covered with the diffusion surface in the same situation, the light of the light source is reflected by the diffusion surface, and illuminates the closed space brightly. The diffusion surface includes an incomplete diffusion surface and a perfect diffusion surface, and the brightness of the space is better with the perfect diffusion surface. These can be easily understood by taking an example of an integrating sphere photometer or the like. In other words, it is more suitable for illumination to cover the periphery of the light source with a completely diffusing surface than with a completely reflecting surface such as a mirror. Magnesium oxide and magnesium carbonate are examples of those that reflect almost completely diffused, and it is better that the reflection surface itself has fine and random irregularities.

The present invention utilizes the above principle to provide a box-shaped container having an opaque inner surface, an opening in the front wall, and a fluorescent lamp, a cold-cathode tube, or a heat source inside at least one side wall of the container. A rod-shaped light source such as a cathode ray tube is provided so as to illuminate the inner surface of the box, and a rear surface facing the opening surface of the box is a diffuse reflection surface, and a cross section of the diffuse reflection surface is slightly closer to the light source. It is formed of a smooth and gentle concave curved surface so as to be farther from the opening surface, gradually approach the opening surface as the distance from the light source increases, and change the distance from the opening surface at the portion farthest from the light source to the maximum. By forming a box-shaped container and covering the opening surface with an illuminated plate such as a liquid crystal display device or a transparent photograph, a very uniform and high-luminance display device can be obtained. That is, even if the light source is turned on and the aperture surface is viewed from the front without placing the plate to be illuminated, the diffuse reflection surface on the rear surface is hardly bright, and is only 300 cd / m ² in the measurement example of luminance. The reason is that the light of the light source is diffused and reflected only inside the container.

A liquid crystal display device having a smooth back surface in contact with the opening surface of a box-shaped container, or a bright illumination device only when a plate to be illuminated such as a transparent photograph is placed, to clearly observe a liquid crystal image or a slide photograph. Can be done. In addition, the brightness does not change as a whole even when the observer approaches a position very close to the aperture plane, so that a very wide viewing angle is obtained.
As an example, when the thickness of the device of the present invention is 6 mm in diameter and a cold cathode tube is used, the maximum height in the lighting device is about 12 mm.

[0014]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a cross section of an embodiment of the present invention, in which one rod-shaped light source 3, 3 is provided inside the side walls 2, 2 of a thin box-shaped container 1 having an opaque white inner surface. The front wall (upper wall) 4 of the container 1 is opened except for the periphery, and the inner surface (upper surface in the figure) 6 of the rear wall 5 has a target-shaped chevron-shaped cross-sectional shape formed of a diffuse reflection surface and having a raised center. ing. More specifically, the section near the light source 3 is gradually separated from the opening surface 7 as the distance from the light source increases, and gradually approaches the opening surface 7 as the distance from the light source 3 further increases toward the top 8 of the mountain. It is a smooth and gentle concave curve so that the change in distance from the opening surface is the largest.

The half of the cross-sectional curve (half of the peak) constituting the diffuse reflection surface is expressed by the following equation when the light source is a point light source.

[0016]

## EQU1 ## X ² + Y ² = AfZ

This equation represents a quadratic curve such as an ellipse, a parabola, or a hyperbola, where A is a coefficient determined by the distance from the light source 3 to the top 8 of the mountain, and f is the coefficient of the inner surface 6 of the rear wall 5. A constant determined by the position farthest from the opening surface 7 and the position of the light source 3, Z is the height itself of the diffuse reflection surface (the inner surface of the rear wall) 6, and X and Y are box-shaped containers shown in FIG. In the embodiment having the rod-shaped light sources on all four sides, each of the four diffuse reflection surfaces is a parabolic surface.

The reflecting surface represented by this equation is described in, for example, the paper “An Aspherical Lens” of the present inventor.
Design by Spheric Geomet
ry "(1985 International Le
ns Design Conference SPI
If the optimum approximate curvature is calculated with reference to E), it can be easily processed by the NC machine. When the illuminated plate 9 such as a liquid crystal display panel or a slide photographic film is placed on the box-shaped container 1 configured as described above so as to cover the opening surface 7, the illuminated plate becomes extremely bright and uniform due to diffuse reflection light. The image illuminated and depicted on the illuminated plate is displayed very clearly.

FIG. 2 is a plan view of an embodiment in which the rod-shaped light sources 3 are provided on four sides of the box-shaped container 1, and FIG. 3 is a sectional view taken along the line III-III of FIG. In this embodiment, four diffuse reflection surfaces 6 are arranged in a pyramid shape, and each surface can be processed into a parabolic surface by the NC machine as described above. It is effective to make the ridge line in contact with each reflection surface as acute as possible to uniformly illuminate the image of the illuminated object covering the opening surface.

In the present illuminating device, it is important how the light emitted from the light source 3 is reflected into the box-shaped container. The surface behind the light source 3, that is, the inner surface of the container side wall 2 is a flat or convex curved diffuse reflection surface, and the inner surface of the front wall portion of the container located above the light source 3 is a diffuse reflection surface 6 in which diffuse reflection light is curved. Is a diffuse reflection surface inclined so that light is distributed from the lowest part to the top part 8. In this lighting device, the lowest part of the rear wall diffuse reflection surface 6 should not be lower than the lower surface of the light source by 3 mm or more and the highest part of the rear wall diffuse reflection surface 6 should be several mm lower than the top surface of the light source. Is good. The wall surface surrounding the light source, especially the diffuse reflection surface on the upper part of the light source, that is, the inner surface of the front wall 4 is higher than the upper surface of the light source so that the reflected light reaches the farthest from the lowest part of the rear wall diffuse reflection surface 6. It is better to keep the height around 3mm. A light shield 10 having, for example, a triangular cross section is provided on the inner surface of the rear wall facing the light source 3 so that the light source does not directly illuminate the rear wall diffuse reflection surface 6. By arranging the inner surface of the upper container 1 as described above, the diffusion of light from the rear wall diffuse reflection surface 6 becomes more uniform, and the illumination object 9 is placed on the opening surface 7 to be uniform and bright. An image is obtained.

The light source 3 provided on the two opposite sides of the box-shaped container 1 and the light source 3 provided on the four sides of the box-shaped container 1 have been described above. It is also possible to use a structure that ends at the apex of the chevron-shaped curved surface, that is, only one-half of the chevron-shaped curved surface. A structure in which two light sources are provided in an L-shape on two adjacent sides or a structure in which three light sources are provided in a U-shape on three sides is also possible.

[0022]

Test Example 1 As shown in FIG. 4, the inside of a box-shaped container 1 having a width of 88 mm, a width of 78 mm and a depth of 4 mm is white and opaque as shown in FIG. A U-shaped space 11 was provided, and a cold cathode tube 3 'having a diameter of 3.6 mm was arranged in the space. U-shaped space 1 of the container in contact with the opening surface
The ceiling of No. 1 was increased in width by 1 mm so that the cold cathode fluorescent lamp 3 ′ could not be seen directly from the upper surface of the opening. 1mm from the bottom of the light source on the bottom of the container by 10mm in the lateral direction from the light source
The diffuse reflection curved surface 6 'is formed in a concave shape.
4 mm in height from a distance of mm to the end 88 mm
As a smooth concave diffuse reflection curved surface 6 that changes by millimeters,
In addition, it is considered that the height change becomes larger as approaching the side 12 opposite to the light source. Therefore, the side 1 on the opposite side of the light source
The wall height of No. 2 is zero. On the diffusion curved surface on the lower surface of the cold cathode tube 3 ', a white light shield 10 having a height of 0.5 mm and a lower portion having a width of 1 mm and having a triangular cross section was provided. The opening of the lighting device was covered with a transparent diffusion plate (not shown), and the brightness was measured at nine locations. Brightness of cold cathode fluorescent lamp 3 '15,000
respect cd / m ^2, the average luminance of the diffusion plate upper surface 5,200Cd /
m ² was obtained, and the luminance unevenness was 15%.

[0023]

EXPERIMENTAL EXAMPLE 2 As shown in FIG. 5, the inside of the box-shaped container 1 having a width of 265 mm, a width of 190 mm, and a depth of 60 mm is white, and the inside surface is white. The U-shaped spaces 11, 11 are provided, and the hot cathode tube 3 ″ of 8 W, φ15 mm is arranged in the spaces. The ceiling of the U-shaped space 11 on the side in contact with the opening surface 7 is located on the lower surface of the container. The diffuse reflection surface 13 inclined at 30 ° was provided so that the hot cathode tube 3 ″ was not directly visible from the upper surface of the opening. The bottom of the container is a diffusely reflecting surface 6 'having a concave curved surface 6' that is 30 mm in length from the lower surface of the light source (hot cathode tube 3 ") and 1 mm below the lower surface of the light source, and is 95 mm from a position 30 mm in the horizontal direction. Up to a millimeter, a concave diffuse reflection curved surface approaching the opening surface direction by 10 mm was considered, and the height change of the 10 mm was considered so as to become larger toward the end of the 95 mm curved surface. The cross section in the direction has a gentle mountain shape.A member 14 having an L-shaped cross section is provided from the lower surface to the side surface of the hot cathode tube 3 ", the inner surface of which is a diffuse reflection surface, and particularly the inner side surface of the member is slightly convex. It was curved. The opening of the lighting device was covered with a transparent diffusion plate (not shown), and the brightness at the top of the diffusion plate was measured at nine locations. The average luminance of the diffusion plate was 5,900 cd / m ² , and the luminance unevenness was only 8%, with respect to the luminance of the hot cathode tube 3 ″ of 7,000 cd / m ² .

[0024]

The so-called backlight of the light guide plate type which is currently mainly used has an average luminance of about 3,000 cd / m ² and a luminance unevenness of 20% or more. Therefore, a scattering sheet is used on the lower surface of the light guide plate, and a plurality of diffusion sheets and prism sheets are used on the upper surface. In the lighting device of the present invention, since a high luminance is obtained and luminance unevenness is low, a diffusion sheet or a prism sheet is not required. It is also more suitable for large size lighting devices. Since there is no difficulty in terms of design and manufacturing technology, a low-cost lighting device can be provided, and significant industrial contribution is expected.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an embodiment of the illumination device of the present invention having two rod-shaped light sources.

FIG. 2 is a plan view of another embodiment of the illuminating device of the present invention when the light source is of a four-rod type.

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a perspective view showing an outline of a lighting device of Test Example 1 of the present invention.

FIG. 5 is a cross-sectional view illustrating an outline of a lighting device of Test Example 2 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Box-shaped container 2 Side wall 3 Light source 4 Front wall 5 Back wall 6 Diffuse reflection surface 7 Opening 8 Top 9 Illuminated plate 10 Light shield 11 U-shaped space 12 L-shaped sectional member

Claims (4)

(57) [Claims] 1. A thin box-shaped container having an opaque white inner surface, having an opening in a front wall thereof, and a rod-shaped light source provided inside at least one side wall of the container so as to illuminate the inner surface of the box. There, the rear wall facing the open surface of the box has an inner surface becomes a diffuse reflection surface, the cross section of the diffuse reflection surface portion near the light source away from progressively opening surface as the distance from the light source Resona
It is characterized by being formed with a smooth and gently concave curved surface so as to gradually approach the opening surface further away from the light source and to have the largest change in the distance from the opening surface at the portion farthest from the light source. Flat lighting device. 2. The inside of the side wall of the box-shaped container located on the side of the light source is a flat or convexly curved diffuse reflection surface, and the inner surface of the front wall surrounding the opening and located in front of the light source. Is a diffuse reflection surface which is inclined so as to distribute light farther, including the lowest part of the concave diffuse reflection surface on the inner surface of the container rear wall, and which is located behind the light source. 2. The light shield according to claim 1, wherein a light shield having a triangular cross section is provided inside the wall so that the light source does not directly illuminate the diffuse reflection surface of the rear wall. Planar lighting device. 3. A bar-shaped light source is provided inside each of two opposing side walls of the container, and the diffuse reflection surface facing the opening surface is formed by a concave-shaped curved surface having a middle height. planar lighting device according to claim 1,. 4. A plane having a rod-shaped light source only inside one side of the container, and the inside of the side wall facing the side wall with the rod-shaped light source inclined at an angle of 90 ° or more with respect to the rear wall of the container. The planar illumination device according to claim 1, wherein the planar illumination device is configured by a diffuse reflection surface having a convex or curved shape.