JPH02208631A - Surface light emission body device for lighting liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the surface light emission body device which has high brightness and a uniform surface brightness distribution by combining linear light sources and a light guide plate which are arranged right below a light diffusion plate. CONSTITUTION:A reflecting frame 2 is molded out of white plastic with excellent light reflection characteristics and has a light-reflective bottom surface, a flank, and an opening opposite the bottom surface. An opening is formed lengthwise in the bottom surface of the reflecting frame 2 so as to incorporate a couple of parallel fluorescent tubes 3. Then the light guide plate 6 is stored in the reflecting frame 2 and formed of an optical material which has excellent light transmissivity in an inverted flatly- sectioned trapezoid shape matching the reflecting frame 2. Grooves 6a which are sectioned in a U shape are cut in the bottom part of the light guide plate 6 where the couple of fluorescent tubes 3 are stored, and a layer 6b which provides the light guide plate 6 with light scattering characteristics and light reflection characteristics is provided on the bottom surface and flank. Consequently, the surface light emission body device which has the uniform brightness distribution and high brightness level is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a flat surface light emitter device used for illuminating a liquid crystal display panel or the like from the back thereof.

More specifically, the present invention relates to a surface light emitting device having a built-in small tube-shaped linear light source and a light diffusing plate for optically converting the light source into a surface light source.

[Conventional technology]

2. Description of the Related Art Surface light emitting device devices incorporating various linear light sources have been known. For example, what is shown in FIG. 6A is a so-called blackout curtain type direct light source type surface light emitter device. A light diffusing plate 1 is placed so as to cover an opening of a reflective frame 2 having an inverted trapezoidal cross section. A pair of linear light sources, such as fluorescent tubes 3, are arranged on the bottom surface of the reflective frame 2, directly below the diffuser plate 1. A light-shielding curtain member 4 is interposed between the diffuser plate 1 and the fluorescent tube 3. A light-shielding aluminum vapor-deposited dot pattern 4a is applied to a portion of the light-shielding curtain member 4 corresponding to the fluorescent tube 3 to partially shield light emitted from the top of the fluorescent tube 3. This is intended to make the luminance distribution uniform over the entire surface of the diffuser plate 1.

What is shown in FIG. 6B is a so-called direct light source type surface light emitter device with a slit. A pair of fluorescent tubes 3 are arranged on the bottom surface of the reflective frame 3 covered with the diffuser plate 1 directly below the diffuser plate. A barcode-shaped slit 3a is provided at the top of the fluorescent tube 3 along its axis. The slits 3a are formed by silk screen printing and suppress the amount of light emitted directly upward from the fluorescent tube 3, thereby making the surface brightness distribution of the diffuser plate 1 uniform.

What is shown in FIG. 6C is a so-called light guide plate type side light source type surface light emitter device. A pair of fluorescent tubes 3 are disposed at both inner end portions of a reflective frame 2 having a rectangular cross section and covered with a diffuser plate 1. A light guide plate 6 is arranged between a pair of separated fluorescent tubes 3. The light guide plate 6 is composed of a light guide member having a side face that faces the fluorescent tube 3 and receives the emitted light, a back face that scatters and reflects the light, and a front face that emits the light. The light is guided in a plane-parallel direction and is emitted from the surface portion toward the diffuser plate.

Figure 6 shows an improved light guide plate type side light source type surface light emitter device. Although the structure is similar to that shown in FIG. 6C, the thickness of the light guide plate 6 is tapered to become smaller toward the center, thereby making the brightness surface distribution of the diffuser plate 1 uniform.

[Problem that the invention seeks to solve]

However, the conventional surface light emitter device described above has the following problems. For example, in the light-shielding curtain type direct light source type surface light emitter device shown in FIG. 6A and the direct light source type surface light emitter device with slits shown in FIG. Since the planar luminance distribution is made uniform by a passive means of partially limiting using the method, there is a problem that the optical conversion efficiency from a line light source to a planar light emitter is low. Furthermore, since the light-shielding pattern on the light-shielding curtain or the barcode-like slit pattern on the surface of the fluorescent tube is formed with certain dimensional conditions using printing technology, it is possible to prevent variations in brightness between or within the lofts of the fluorescent tube. However, there is a problem in that surface illuminant products have large unevenness in surface brightness. In addition, there is also the problem that product assembly is complicated because it is necessary to position and fix each used component relative to another.

In the light guide plate type side light source type surface light emitter device shown in Fig. 6C and D, since the fluorescent tubes are arranged at both ends of the surface light emitter, the brightness at the center of the surface light emitter is lower than that at the ends. The problem was that it was smaller and darker. Furthermore, compared to the linear light source arrangement type shown in FIGS. 6A and B, the light radiation from the side light sources is guided to the center of the surface light source by the light guide plate, so the optical conversion efficiency from the linear light source to the surface light source is improved. There is a problem that the luminance level of the surface emitter is low.

The present invention aims to solve the problems of the prior art described above, and provides a surface light emitter device with good optical conversion efficiency, that is, high brightness and uniform surface brightness distribution.

[Means for solving problems]

In order to achieve the above object, the present invention has a structure in which a linear light source and a light guide plate are arranged directly below a light diffusing plate. The surface light emitter device according to the present invention uses, as a frame, a reflective frame having a light-reflective bottom surface, light-reflective side surfaces surrounding the bottom surface, and an opening surrounded by the ends of the side surfaces. A linear light source is arranged on the bottom surface of the reflective frame, spaced apart from the side surface. Furthermore, it has a back surface part disposed opposite to the bottom surface in which a groove for accommodating the linear light source is formed, and a surface part facing the back surface part, which guides the light emitted from the linear light source in a plane parallel direction and A light guide plate is provided for emitting guided light from the surface portion. In addition, a diffusion plate is provided which covers the opening of the reflection frame and is disposed opposite to the surface of the light guide plate, and forms a surface light emitting part by diffusing and emitting the light received from the light guide plate.

[For production]

According to the present invention, the light emitted from the linear light source enters the light guide plate through the side wall of the groove provided in the light guide plate. Within the light guide plate, light propagates in a plane-parallel direction and is repeatedly reflected diffusely on the back and side surfaces of the light guide plate surrounded by the reflective frame. Of the reflected light rays, light rays that are incident on the light guide plate surface at a critical angle or more are emitted from the surface and proceed to the diffuser plate. The diffuser plate forms a surface emitting section having a uniform and high level brightness surface distribution by emitting light received from the surface of the light guide plate.

〔Example〕

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a partially cutaway sectional perspective view of a surface light emitter device according to the present invention. In this embodiment, a reflective frame 2 having a flat inverted trapezoidal cross section is used.

The reflective frame 2 is a molded product made of white plastic with good light reflecting properties, and has a light reflective bottom surface, side surfaces, and an opening facing the bottom surface. The reflective frame 2 may have a rectangular cross section (or may be a metal molded product).

A pair of parallel fluorescent tubes 3 are arranged on the bottom surface of the reflective frame 2. In the case of this embodiment, a notch is provided in the bottom surface of the reflection frame 2 along the longitudinal direction in order to incorporate the fluorescent tube 3, but a method in which the fluorescent tube 3 is simply placed may also be used.

2A and 3B and 3A and 3B show specific examples of the fluorescent tube 3 used in the present invention. In the example shown in FIGS. 2A and 2B, a portion of the fluorescent layer 3c coated on the inner wall of the fluorescent glass tube 3b has a radial opening angle θ (for example, 60”).
) along the axial aperture 3
d is formed. When the fluorescent tube 3 is installed, the aperture 3d is oriented in the thickness direction of the light guide plate, which will be described later, so that the light flux introduced into the light guide plate can be concentrated.

In the example shown in FIGS. 3A and 3B, a pair of apertures 3d facing each other in the radial direction of the fluorescent tube 3 have an opening angle θ (for example, 30°).
along the axis within the range of In this example, the concentrated light beam can be emitted in both directions, and the light beam can be more effectively introduced into the light guide plate.

Of course, it is also possible to use an ordinary fluorescent tube whose entire inner wall of the fluorescent glass tube is covered with fluorescent paint.

Furthermore, if an ultra-high-intensity cold cathode fluorescent lamp with a tube diameter of 6.51 mm or less is used as the fluorescent tube, the surface light emitter can be made thinner. Incidentally, in a hot cathode fluorescent lamp, it is difficult to reduce the tube diameter to 8H or less due to its electrode structure.

Returning to FIG. 1 again, the light guide plate 6 is housed in the reflective frame 2, and has a flattened inverted trapezoidal cross section to match the reflective frame 2, and is made of an optical material with good light transmittance, such as transparent polymethacrylic resin. made of plastic. A groove 6a having a U-shaped cross section is provided in the bottom surface of the light guide plate 6 at a corresponding position for accommodating the pair of fluorescent tubes 3. Further, on the bottom and side surfaces of the light guide plate 6, a layer 6b (for example, a Fresnel lens surface layer, a roughened layer such as hairline or satin finish, a full white painted layer, (partial white paint layer, aluminum evaporated layer, etc.). On the other hand, the light guide plate surface portion 6c, which faces the back surface and constitutes a light emitting surface, has a smooth plastic transparent surface.

The transparent surface may be a geometrical plane, but as shown in FIG. The distribution may be made uniform. Further, a fluorescent tube 3 is provided on the light guide plate surface portion 6c.
In addition to this matte finish layer 6d, a matte finish layer 6d may be provided in a portion corresponding to the top of the fluorescent tube 3. Alternatively, or instead of this, a similar effect can be obtained by providing another satin layer on the ceiling of the U-shaped groove 6a. In this example, the light guide plate 6 is composed of a single component, but instead of this, it may have a structure in which a plurality of divided parts are combined.

Finally, the diffuser plate 1 is placed so as to face the light guide plate 6 and cover the opening of the reflective frame l. The diffuser plate 1 has light scattering performance and is made of, for example, frosted glass.

A surface light emitter with uniform brightness is formed by receiving light from the light guide plate and emitting scattered light to the outside. The wall thickness of the portion 1a of the diffuser plate 1 corresponding to the fluorescent tube 3 is thicker than other portions, and this difference in wall thickness limits the amount of luminous flux that directly enters from the top of the fluorescent tube 3. This makes it possible to obtain a more uniform surface brightness distribution.

The surface light emitter device described above operates as follows. That is, the luminous flux emitted from the fluorescent tube 3 is introduced into the interior of the light guide plate 6 via the side wall of the U-shaped groove 6a. In this case, if a fluorescent tube having a pair of apertures shown in FIGS. 3A and 3B is used, the luminous flux emitted by the fluorescent tube can be efficiently and concentratedly introduced into the light guide plate. The light that has entered the light guide plate 6 propagates inside the light guide plate, undergoes repeated diffuse reflections at its bottom and side surfaces, and is eventually emitted from its surface. At this time, additional means are provided to limit the intensity of the luminous flux emitted upward from the top of the fluorescent tube 3. The light emitted from the light guide plate 6 is incident on the diffuser plate 1 from the surface to the surface, and is emitted to the outside as scattered light. At this time, by increasing the thickness of the portion 1a of the diffuser plate 1 corresponding to the fluorescent tube 6, the intensity of the scattered light is made more uniform.

〔Effect of the invention〕

FIG. 4 is a diagram showing a relative comparison of the luminance distributions of the conventional example and the surface light emitter device according to the present invention. Curve A shows the luminance distribution along the side end F from the fluorescent tube 3 in the conventional light-blocking curtain type direct light source type surface light emitter device shown in FIG. 5A. curve B
5B shows the luminance distribution along the side end F from the fluorescent tube 3 in the conventional direct light source type surface light emitter device with slit shown in FIG. 5B.

A curve C shows the luminance distribution along the central portion F from the fluorescent tube 3 in the conventional light guide plate type side light source type surface light emitter device shown in FIG. 5C. As shown in Figure 5, the curve shows the luminance distribution along the side end F from the fluorescent tube 3 in a surface light emitter device having a structure according to the present invention in which only the light guide plate is removed. song[
E shows the luminance distribution along the side edge F from the fluorescent tube 3 in the surface light emitter device of the present invention using a fluorescent tube having a pair of apertures, as shown in FIG. 5E.

As is clear from FIG. 4, the luminance distribution of the surface light emitter of the present invention shown by curve E is similar to curve A which shows the conventional example.

The slope is smaller than that of B and C, and the brightness level is particularly high at the end F. Therefore, the surface light emitter device according to the present invention has the effect that the luminance distribution is more uniform and the luminance level is higher than that of the conventional example. Such a surface light emitter device is particularly suitable for back illumination of a liquid crystal display panel.

As is clear from the comparison of the curve and E, by placing the fluorescent tube directly below the diffuser plate and interposing the light guide plate according to the present invention between the two, the brightness at the end F can be increased by about 1.6 times. I was able to increase it. This is because the light guide plate efficiently propagates light in the plane-parallel direction regardless of the inverse square law regarding light propagation.

As described above, according to the present invention, by using a light guide plate and arranging a line light source directly below the surface emitting part, it is possible to reduce the attenuation of brightness and obtain uniform brightness compared to the conventional method, thereby improving the lighting effect. It is excellent and its product value is high.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway sectional perspective view showing an embodiment of a surface light emitter device according to the present invention, FIG. 2A is a perspective view showing an example of a fluorescent tube used in the present invention, and FIG. 2B is a perspective view showing an example of a fluorescent tube used in the present invention. is a sectional view taken along the line A-A shown in FIG. 2A, FIG. 3A is a perspective view showing another example of the fluorescent tube used in the present invention, and FIG. 3B is a cross-sectional view taken along the line shown in FIG. 3A. FIG. 4 is a cross-sectional view taken along line B-H, FIG.
Figures A to E are partial cross-sectional views of surface light emitter devices that provide the brightness distribution curves A to E shown in Figure 4, and Figures A to D are partially cutaway cross-sectional perspective views showing several examples of conventional surface light emitter devices. It is a diagram. 1 is a diffuser plate, 1a is a thick part, 2 is a reflective frame, 3 is a fluorescent tube,
3b is a fluorescent glass tube, 3C is a fluorescent paint layer, 3d
6 is an aperture, 6 is a light guide plate, 6a is a U-shaped groove, 6b is a light scattering reflection layer, 6C is a surface portion of the light guide plate, and 6d is a diffusion layer.

Claims (1)

[Scope of Claims] 1. A reflective frame having a light-reflective bottom part, a light-reflective side part surrounding the bottom part, and an opening surrounded by an end of the side part; A light emitted from the linear light source has a linear light source arranged therein, a back face part facing the bottom face part and having a groove formed therein for accommodating the linear light source, and a front face part facing the back face part. a light guide plate that guides the light in a plane parallel direction and emits the guided light from the surface portion; and a light guide plate that covers the opening of the reflection frame and is disposed opposite to the surface portion of the light guide plate that directs the light received from the light guide plate. A surface light emitting device comprising a diffuser plate that forms a surface light emitting section by diffusing and emitting light. 2. The surface light emitter device according to claim 1, wherein the diffuser plate has a wall thickness thicker in a portion corresponding to the linear light source than in other portions. 3. The surface light emitter device according to claim 1, wherein the light guide plate has a light diffusing surface in a portion corresponding to the linear light source on its surface portion. 4. The surface light emitter device according to claim 1, wherein a light diffusing surface is provided on the ceiling of the groove provided on the back surface of the light guide plate. 5. The surface light emitter device according to claim 1, wherein the surface portion of the light guide plate has a curved shape having a concave portion in a portion corresponding to the linear light source. 6. The light guide plate has a flat inverted trapezoidal column shape with an axis along the linear light source, and the lower side surface of the inverted trapezoidal column has a pair of parallel grooves and a V-shaped cross-sectional sidewall between the grooves. The surface light emitter device according to claim 1. 7. The surface light emitter device according to claim 1, wherein the linear light source is a fluorescent tube. 8. The surface light emitter device according to claim 7, wherein the fluorescent tube is an ultra-high brightness cold cathode type fluorescent tube. 9. Claim 9, wherein the fluorescent tube has an inner tube portion from which the fluorescent substance is removed in the axial direction of the fluorescent tube along the inner end surface of the groove provided on the back surface of the light guide plate. 7. The surface light emitter device according to 7.