JPH08287710A - Planar lighting apparatus - Google Patents

Abstract

PURPOSE: To provide a background light source with high brightness and without unevenness of the brightness in order to heighten the visual property of a liquid crystal display apparatus and a transparent photograph. CONSTITUTION: A lighting apparatus is a box-like one of which the whole inner face except a light source is opaque and white and has a large open face 7 in one face and rod-like light sources 3 are installed in the side faces of the box-like body. The parts in three directions of the light sources 3 are so covered with white-color diffusion covers as not to be seen from the upper part of the open face and a smoothly and moderately curved face is formed in the bottom face 6 of the box-like body, so that the light-rays from the light source are emitted out of the open face as uniformly diffused light-rays.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source for illuminating a liquid crystal display or an illuminated signboard which requires a planar illumination light source.

[0002]

2. Description of the Related Art Currently, a planar illumination light source mainly used for a liquid crystal display is a liquid crystal display, that is, a light source such as a fluorescent lamp is arranged behind an object to be illuminated, and the light from the light source directly projects an image. A structure with a diffusion sheet such as a milky white transparent plate placed so that it does not affect, or a light source is placed behind the side of the illuminated object, and acrylic resin or polycarbonate resin, etc. is directly behind the illuminated object that is laterally separated from the light source. The transparent plate has a lenticular or Fresnel-shaped groove on the back surface, or a white dot-shaped or striped printed pattern is placed on the transparent plate so that the light incident from the side can be The structure uses a plate of a so-called light guide plate that distributes light from the groove or the printed back surface of the transparent plate as if it were emitted in a plane.

[0003]

Since it is difficult to obtain uniform illumination in a lighting device using such a light guide plate, a diffusing sheet must be used on the upper surface of the lighting 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 use a special material called a prism sheet to distribute the diffused light to the central portion of the upper surface of the lighting device. There are some drawbacks.

As the size of the illuminated object increases, the thickness of the light guide plate increases and the total weight of the display device increases. Or serious problems still exist, such as the price of prism sheets becoming very high. In particular, liquid crystal displays will become larger in the future and will also have higher definition, thinner walls and lighter weight.
There is a strong demand from the industry for a lighting device that is energy-saving, inexpensive, and highly functional.

In view of the above situation, the present invention can obtain sufficiently uniform and high brightness without using a light guide plate and without using a cold cathode tube having a particularly high brightness, even if a normal fluorescent tube is used. Moreover, it is an object of the present invention to provide a lighting device having an extremely simple structure.

[0006]

To achieve the above object, according to the present invention, there is provided a box-shaped container having an opaque white inner surface, the front wall of which is provided with an opening, and at least one side wall of the container is provided. A rod-shaped light source is provided inside so as to illuminate the inner surface of the box, and the inner surface of the rear wall facing the opening surface of the box is a diffuse reflection surface, and the cross section of the diffuse reflection surface is Formed by a smooth and gentle concave curved surface that is slightly away from the opening surface, gradually approaches the opening surface as it goes away from the light source, and has the largest change in the distance from the opening surface at the portion farthest from the light source. A lighting device is provided.

According to a preferred embodiment of the present invention, the inside of the side wall of the box-like container located on the side of the light source is a flat or convex curved diffuse reflection surface, which is in front of the light source on the front wall surrounding the opening. The inner surface of the portion where it is located is a diffuse reflection surface that is inclined so as to distribute light farther than that, including the portion that is closest to the concave diffuse reflection surface on the inner surface of the rear wall of the container. Inside the portion of the rear wall located, a light shield having a triangular cross section is provided 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, the 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 at the rear surface of the container. On the other hand, it is composed of a flat or convex curved diffuse reflection surface inclined at an angle of 90 ° or more.

[0009]

The operation principle of the present invention will be described below. In the case of a lantern or the like, it is apparent that there is a method of covering the periphery of the light source with Japanese paper or the like in order to make the light source apparently large when the light source is located at a single point in a pitch dark space. An incandescent lamp can also be said to apply this principle. In this case, if transparent glass is used instead of Japanese paper, the light source does not look large. This is because glass does not diffuse even if it allows light to pass through.

Similarly, even if a light source located at a point in a closed space is covered with a transparent glass wall, the light only escapes to the outside of the glass and the space does not become bright. Even if the wall is changed to a mirror in the same situation, only the light source is reflected on the wall, the closed space is not brightened, and only the virtual image of the light source is reflected on the surrounding mirrors.

When the wall is covered with a diffusing surface in the same situation, the light from the light source is reflected by the diffusing surface to illuminate the closed space brightly. There are two types of diffusion surface, an incomplete diffusion surface and a perfect diffusion surface, but the perfect diffusion surface has a better spatial brightness. These can be easily understood by considering an example of an integrating sphere type photometer. That is, it is more suitable for illumination to cover the periphery of the light source with a perfect diffusion surface than to cover it with a perfect reflection surface such as a mirror. Magnesium oxide or magnesium carbonate is used as a material that reflects light that is close to perfect diffusion, and it is preferable that the reflection surface itself has fine and random irregularities.

The present invention is a box-shaped container having an opaque inner surface, which has an opening on the front wall thereof and has at least one side wall of the container inside a fluorescent lamp, a cold-cathode tube, or a heat source. A rod-shaped light source such as a cathode tube is provided so as to illuminate the inner surface of the box, the rear surface facing the opening surface of the box is a diffuse reflection surface, and the cross section of the diffuse reflection surface is a little near the light source. It is formed from a smooth and gentle concave curved surface that is far from the opening surface, gradually approaches the opening surface as it goes away from the light source, and has the largest change in the distance from the opening surface at the portion farthest from the light source. By forming a box-shaped container and covering the opening surface with a liquid crystal display device or an illuminated plate such as a transparent photograph, a display device with extremely uniform and high brightness can be obtained. That is, even if the opening surface is viewed from the front without turning on the light source and placing the illumination target plate, the diffuse reflection surface on the rear surface does not become bright and the measured brightness is only 300 cd / m ² . The reason is that the light from the light source is diffused and reflected only inside the container.

When a liquid crystal display device having a smooth back surface in contact with the opening surface of the box-like container or an illuminated plate such as a transparent photo is placed, it becomes a bright illuminating device to clearly observe liquid crystal images and slide photos. Can be done. In addition, its brightness does not change as a whole when the observer approaches a position very close to the aperture surface, and as a result, an extremely wide viewing angle is obtained.
As an example, the thickness of the device of the present invention is about 12 mm when the cold cathode tube having a diameter of 6 mm is used.

[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. Inside the side walls 2 and 2 of a thin box-shaped container 1 whose inner surface is opaque white, one bar-shaped light source 3 is provided. 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 is formed of a diffuse reflection surface, and has a symmetrical mountain-shaped cross-sectional shape with a raised central portion. ing. This cross-sectional shape will be described in more detail. The part closer to the light source 3 is gradually separated from the opening surface 7 as it is farther from the light source, and as the distance from the light source 3 is further increased toward the top 8 of the mountain, it gradually approaches the opening surface 7 and near the top of the mountain. The concave curve is smooth and gentle so that the change in the distance from the opening surface is the largest.

Half of the cross-sectional curve (half of the peak) that constitutes this diffuse reflection surface is expressed by the following mathematical formula when the light source is a point light source.

[0016]

[Formula 1] X ² + Y ² = AfZ

This equation represents a quadratic curve such as an ellipse, a parabola, and 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 inner surface 6 of the rear wall 5. It is a constant determined by the position farthest from the opening surface 7 and the position of the light source 3, Z is the height of the diffuse reflection surface (inner surface of the rear wall) 6 itself, and X and Y are the box-like containers shown in FIG. In the embodiment having the bar-shaped light source on all four sides, each of the four diffuse reflection surfaces is a parabolic surface.

The reflecting surface represented by this mathematical formula can be obtained, for example, by the inventor's paper "An Asperial Lens".
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 an illuminated plate 9 such as a liquid crystal display plate 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 diffused reflected light. The image illuminated and drawn on the illuminated plate is displayed extremely clearly.

FIG. 2 is a plan view of an embodiment in which the rod-shaped light source 3 is provided on the four sides of the box-shaped container 1, and FIG. 3 is a sectional view taken along 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 an NC machine as described above. It is effective to make the ridgeline where each reflecting surface is in contact as sharp as possible in order to uniformly illuminate the image of the illuminated object covering the opening surface.

In the present lighting device, it is important how to reflect the light emitted from the light source 3 into the box-shaped container. The rear surface of 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 the diffuse reflected light is curved. Is a diffuse reflection surface that is inclined so that the light is distributed from the lowest portion to the top portion 8. In this illuminating 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 lower than the top surface of the light source by several mm. Is good. The diffuser reflection surface of the wall surface surrounding the light source, especially the upper portion 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 far from the lowest portion of the rear wall diffuse reflection surface 6. Although it is easy to win, it is better to keep the height within 3 mm. A light shield 10 having, for example, a triangular cross section is provided on the inner surface of the rear wall facing below the light source 3 so that the light source does not directly illuminate the rear wall diffuse reflection surface 6. By configuring the inner surface of the box-shaped container 1 as described above, the diffusion of light from the rear wall diffuse reflection surface 6 becomes more uniform, and by placing the illuminated body 9 on the opening surface 7, it is uniform and bright. An image is obtained.

The light sources 3 provided on the two opposite sides and the four sides of the box-shaped container 1 have been described above, but the light source 3 is provided on one side of the box-shaped container 1 and the diffuse reflection surface 6 on the rear wall is the light source. It is also possible to form the end of the more angled curved surface, that is, to form only half of the angled curved surface. Further, a structure in which two light sources are provided in L-shape on two adjacent sides and a structure in which three light sources are provided in U-shape on three sides are also possible.

[0022]

Test Example 1 As shown in FIG. 4, the inside of the 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. One side in the vertical direction of the container 1 is white and opaque. 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 of the container that contacts the opening 1
The ceiling of No. 1 has a width increased by 1 mm so that the cold cathode tube 3'cannot be directly seen from the upper surface of the opening. 1mm from the bottom of the light source on the bottom of the container for a length of 10mm laterally from the light source position
Diffuse reflection curved surface 6'having a concave shape, 10 in the lateral direction
4 in the height direction from the position separated by 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 this height change becomes larger as it approaches the side 12 on the opposite side of the light source. Therefore, side 1 on the opposite side of the light source
The wall height of 2 is zero. On the diffusion curved surface of the lower surface of the cold-cathode tube 3 ', a white light shield 10 having a height of 0.5 mm and a width of 1 mm at the lower portion and having a triangular shape was provided. The opening of this illuminating device was covered with a transparent diffusion plate (not shown), and its brightness was measured at 9 points. Brightness of cold cathode tube 3'15,000
For cd / m ² , the average brightness on the top surface of the diffuser is 5,200 cd /
m ² was obtained, and the uneven brightness was 15%.

[0023]

[Experimental Example 2] As shown in FIG. 5, the inside of the box-shaped container 1 having a lateral width of 265 mm, a longitudinal width of 190 mm, and a depth of 60 mm is white. A U-shaped space 11, 11 was provided, and a hot-cathode tube 3 ″ having a diameter of 8 W and a diameter of 15 mm was arranged in the space. The diffuse reflection surface 13 inclined by 30 ° was provided so that the hot cathode tube 3 ″ could not be directly seen from the upper surface of the opening. The bottom of the container is a concave reflective surface 6 ', which is 30 mm laterally from the bottom surface of the light source (hot cathode tube 3 ") and 1 mm below the bottom surface of the light source. A concave diffuse reflection curved surface approaching only 10 mm in the direction of the opening surface up to a millimeter was taken into consideration, and the height change of the 10 mm was taken into consideration so that it became larger toward the end side of the curved surface for 95 mm. The cross section in the direction was a gentle mountain shape. A member 14 having an L-shaped cross section was provided from the lower surface to the side surface of the hot cathode tube 3 ", the inner surface of which was a diffuse reflection surface, and in particular, the inner side surface of the member was slightly convex. It was a curved surface. The opening of this lighting device was covered with a transparent diffuser plate (not shown), and the brightness of the upper part of the diffuser plate was measured at nine points. The average luminance of the diffuser plate was 5,900 cd / m ^2, while the luminance of the hot cathode tube 3 ″ was 7,000 cd / m ² , and the luminance unevenness was only 8%.

[0024]

The so-called backlight of the light guide plate system which is mainly used at present has an average brightness of about 3,000 cd / m ² and uneven brightness of 20% or more. Therefore, the lower surface of the light guide plate has a scattering sheet, and the upper surface has a plurality of diffusion sheets and prism sheets. In the lighting device of the present invention, since high brightness is obtained and brightness unevenness is low, a diffusion sheet or a prism sheet is unnecessary. It is also more suitable for large-sized lighting devices. Since there is no difficulty in terms of design and manufacturing technology, it is possible to provide a low-cost lighting device, which is expected to make a great contribution to the industry.

[Brief description of drawings]

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

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

FIG. 3 is a sectional view taken along line III-III in FIG.

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 showing 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 Rear wall 6 Diffuse reflection surface 7 Opening 8 Top 9 Illuminated plate 10 Light shield 11 U-shaped space 12 L-shaped cross-section member

Claims (4)

[Claims] 1. A box-shaped container having an opaque white inner surface,
There is an opening in the front wall, a rod-shaped light source is provided inside at least one side wall of the container so as to illuminate the inner surface of the box, and the inner surface of the rear wall facing the opening surface of the box is a diffuse reflection surface. The cross section of the diffuse reflection surface is slightly away from the aperture surface in the portion close to the light source, gradually approaches the aperture surface as the distance from the light source increases, and the distance from the aperture surface at the portion farthest from the light source. A planar illumination device, characterized in that it is formed by a concave curved surface that is smooth and gentle so as to maximize the change. 2. The inside of the side wall of the box-shaped container located on the side of the light source is a flat or convex curved diffuse reflection surface, and the inner surface of the portion of the front wall that surrounds the opening is located in front of the light source. Is a diffuse reflection surface inclined so as to distribute light farther than the concave diffuse reflection surface on the inner surface of the rear wall of the container, and is located behind the light source. The light blocking member having a triangular cross section is provided inside the wall portion so that the light source does not directly illuminate the diffuse reflection surface of the rear wall. Planar lighting device. 3. Two bar-shaped light sources are provided inside the opposite side walls of the container, one for each, and the diffuse reflection surface facing the opening surface is formed by a mountain-shaped concave curved surface having a middle height. The flatness proof device according to claim 1. 4. A rod-shaped light source is provided only on the inside of one side of the container, and the inside of the side wall opposite to the side wall where the rod-shaped light source is located is a plane 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 curved surface or a convex curved surface.