JPH0797445B2 - Lighting device for transmissive image display device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illuminating device which is arranged on the back surface of a transmissive image display device and uniformly illuminates from the back surface of an image display element.

2. Description of the Related Art In a transmissive image display apparatus using an image display element such as liquid crystal, for example, an illumination apparatus as shown in FIG. 5 is used in order to illuminate the image display element brightly and uniformly from the back surface. .

That is, a reflection plate 2 having a parabolic cross section for efficiently collecting the light emitted from the light source 1 is provided below the linear light source 1 such as a straight tube fluorescent lamp, and the light is directly emitted from the light source 1. By irradiating the diffuser plate 3 provided above the light source 1 with the light and the reflected light from the reflector plate 2, the back surface of the image display element 4 placed in parallel on the diffuser plate 3 is illuminated.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In such a conventional lighting device, when the light source 1 is a straight tube fluorescent lamp, the luminance distribution characteristic in the transverse direction (X direction in the figure) of the lamp is as shown in FIG. In addition, there is a problem that the brightness is high right above the light source 1 (the central portion of the diffusion plate 3) and decreases as the distance from the light source 1 (the end portion of the diffusion plate 3) decreases.

As a method of making the brightness distribution characteristic of the diffusion plate 3 uniform, a dot pattern for removing brightness unevenness is provided on a straight tube type fluorescent lamp, as in the case of a thin Shark Sten described in JP-A-55-133008. In order to obtain uniformity by lowering the brightness of the portion directly above the lamp, it is necessary to accurately arrange the dot pattern between the lamp and the diffusion plate. The pattern also has a demerit that it becomes complicated because it matches the uniform luminance distribution characteristic.

As another method, as in the backlight structure of the display device described in Japanese Patent Application Laid-Open No. 57-13478, the thickness of the diffuser plate is increased by increasing the brightness of the high brightness portion and decreasing the low brightness portion of the display device. Although it is considered that the luminance distribution is made uniform by changing the thickness to 1, it is difficult to control the thickness relative to the required luminance distribution.

Furthermore, both of the above two methods have a problem in that the utilization efficiency of the light from the light source is poor because the high luminance portion is reduced to make the luminance distribution uniform.

On the other hand, in the surface light source unit described in Japanese Patent Application Laid-Open No. 62-186405, a fluorescent lamp bent in a U shape is used, and the same effect as that of a plurality of light sources is provided side by side. The brightness distribution of is made uniform.

The size (length) of the fluorescent lamp relative to the size of the diffusion plate
If there is no restriction on the condition, the brightness of the electrode part at the tube end is lower than the brightness of the positive column part at the tube center of the fluorescent lamp. The backlight may be constructed by the above method in which the fluorescent lamps are arranged so as to be outside. However, in a transmissive image display device or the like, it is always required that the size of the backlight is equal to or smaller than the size of the image display portion.

In addition, when a plurality of such image display devices are arranged side by side to obtain a larger screen, the distance between adjacent image display devices is more restricted. The size is also limited, and there is a problem in that the above method cannot be used.

Further, in the conventional method, since a single light source is often used, there is a fatal problem as an image display device in that necessary image information is lost, for example, when the light source becomes defective.

For this reason, it is considered to prevent the loss of image information due to the defect of the light source by arranging a large number of light sources (for example, Tange et al. "Development of backlight for liquid crystal" Showa 63).
Proceedings of the Annual Meeting of the Lighting Society of Japan, P.20), but in this case, since it is necessary to provide a dedicated lighting device for each light source, the configuration of the lighting device is not only complicated, but it also has the disadvantage of increasing the size. .

Therefore, the present invention aims to make the diffuser plate uniform in luminance distribution characteristics without reducing the utilization efficiency of the light from the light source while reducing the size of the device.

Means for Solving the Problems The present invention provides a linear light source, a reflecting member that surrounds a part of the light source and reflects a part of the light from the light source, and a direct light from the light source that is provided above the light source. A light diffusing plate for irradiating light and light reflected from the reflecting member, wherein the light source has two or more straight pipe portions, and the lengths in the pipe axis direction are different from each other, and the respective pipe end portions are provided. Is a configuration including a plurality of fluorescent lamps that are bent in a direction orthogonal to the straight tube portion and in the direction of the reflecting member.

Action The present invention determines the length of each of the straight tube portions of the fluorescent lamp by
It can be set so that the brightness distribution in the transverse direction of the fluorescent lamp and the tube axis direction is uniform, and the diffuser plate provides a more uniform brightness balance between the direct light from the fluorescent lamp and the reflected light from the reflecting member. In addition, since the tube end of the fluorescent lamp is bent in the direction perpendicular to the straight tube and toward the reflecting member, the influence of the decrease in brightness at the tube end of the fluorescent lamp is reduced. The above is not taken into account, which makes the luminance distribution more uniform.

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

FIG. 1 is a diagram showing a cross section of an illuminating device according to an embodiment of the present invention, and 5 is a linear light source in which two U-shaped fluorescent lamps are arranged in parallel.

A diffuser plate 6 is provided above the light source 5, and an image display element 7 is placed on the diffuser plate 6 with a distance of several mm.
It is located close to and parallel to.

On the other hand, a reflection plate 8 having a polygonal cross section is arranged below the light source 5 to efficiently reflect the irradiation light from the light source 5 to the diffusion plate 6.

FIG. 2 shows the appearance of the light source 5, and FIG. 3 shows the arrangement of the light source 5. As can be seen from FIG. 2 and FIG. 3, the light source 5 is a fluorescent lamp that has a straight tube portion A and a straight tube portion B having different lengths in the tube axis direction and is bent into a U-shape.
Two light sources are facing each other.

The length relationship between the straight pipe portion A and the straight pipe portion B of the light source 5 is A
> B, and the ratio may be set while confirming the balance of the luminance distribution in the transverse direction of the light source 5 and the tube axis direction.

In FIG. 4, the solid line shows the luminance distribution characteristic in the transverse direction (X direction) when both the light sources 5 in the lighting device of the present invention are turned on, and the luminance when one side of the light sources 5 has a spot. The distribution characteristics are indicated by broken lines.

In the present invention, the tube end portion of the light source 5 is orthogonal to the straight tube portion A and the straight tube portion B, and is bent in the direction of the reflection plate. Since the brightness is lower than the brightness of the central positive column part, the influence of this part is made as small as possible.

EFFECTS OF THE INVENTION The present invention provides a fluorescent lamp having two or more straight tube portions having different lengths in the tube axis direction and having a tube end portion bent in a direction orthogonal to the straight tube portion and toward a reflector. Since a plurality of light sources are arranged side by side, the same effect as that of a plurality of straight tube light sources arranged side by side can be obtained, so that the luminance distribution in the transverse direction of the light source and the diffusion plate can be made uniform. Not only that, even if any one of the plurality of light sources becomes defective, the uniformity of brightness is slightly reduced, and the image information is not completely lost.

Further, since the tube end is bent in the direction of the reflection plate, there is no portion where the brightness is reduced, and the brightness of the entire surface of the image display element can be increased and made uniform. Further, since it is not necessary to provide a dot pattern for improving the luminance distribution characteristic between the light source and the diffusion plate or change the thickness of the diffusion plate, not only can the structure of the lighting device be simplified, but Uses light efficiently.

Furthermore, since the number of light sources used is minimized, not only the number of lighting devices associated with the light sources can be reduced, but also the lighting device can be downsized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a lighting device according to an embodiment of the present invention,
FIG. 4 is an external view of a light source used in the lighting device of the present invention, FIG. 3 is a layout diagram of the light source used in the lighting device of the present invention, and FIG. 4 is a luminance distribution characteristic diagram showing effects of the lighting device of the present invention. FIG. 5 is a configuration diagram of a conventional lighting device, and FIG. 6 is a luminance distribution characteristic diagram of the conventional lighting device. 5 ... Light source, 6 ... Diffusion plate, 7 ... Image display element, 8 ...
…a reflector.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Haruo Yamazaki Inventor Haruo 1006 Kadoma, Osaka Prefecture Matsuda Denshi Kogyo Co., Ltd. (72) Inventor Kazumasa Nomi 1006 Kadoma, Kadoma City Osaka Pref. 56) References JP-A-64-35477 (JP, A)

Claims (1)

[Claims] 1. A linear light source and a part of the light source are surrounded,
The reflecting member that reflects a part of the light from the light source, the diffuser plate that is provided above the light source, and that radiates the direct light from the light source and the reflected light from the reflecting member, and the light source includes 2
It has three or more straight pipe portions, and the lengths in the pipe axial direction are different from each other, and each pipe end portion is in a direction orthogonal to the straight pipe portion,
An illumination device for a transmissive image display device including a plurality of fluorescent lamps bent in the direction of a reflecting member.