JPH0545652U - Planar light source device - Google Patents

Abstract

(57) [Summary] (Modified) [Object] The present invention is intended to provide a planar light source device having a light emitting surface with high light utilization rate and high brightness. According to the planar light source device of the present invention, the linear light source is installed in the planar light source device including a linear light source surrounded by a reflector on at least one side surface of a light diffusing plate and a transparent light guide plate in a viewing direction. It is characterized in that the maximum width of the light-receiving side surface portion is larger than the maximum thickness of the light guide plate.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention is an area light source device, particularly an edge light type device that receives light from a linear light source and uniformly illuminates a relatively wide area. The present invention relates to a planar light source device that is useful for backside illumination.

[0002]

[Prior Art]

 It is known that a planar light source device is one in which a light diffusing plate, a transparent light guide plate and a reflecting plate are sequentially stacked in the direction of view, and a linear light source surrounded by a reflector is provided on at least one side surface of the transparent light guide plate. However, when the incident light from the linear light source travels on both sides of the light guide plate in a normal manner, although almost uniform brightness is obtained over the entire surface of the light guide plate, the actual incident light spreads radially or is not guided. Due to the attenuation in the light plate, there is a problem that the amount of incident light is large near the linear light source and small at a position distant from the light source, and uniform surface illumination cannot be obtained.

For this reason, it has been attempted to provide a light scattering means on the light guide line to obtain uniform surface illumination. As the light scattering means of this light guide plate, a light scattering substance is mainly used on the surface of the light guide plate. Application method (Japanese Patent Application Laid-Open No. 63-62104, Japanese Patent Application Laid-Open No. 1-107406, Japanese Patent Application Laid-Open No. 1-245220, Japanese Patent Application Laid-Open No. 2-160215) and method for roughening the back surface of the light guide plate ( (See Japanese Patent Publication No. 58-17957), a method of roughening the back surface of the light guide plate into a hairline shape (see Japanese Utility Model Publication No. 58-25405), and a method of forming one surface of the light guide plate into a special curved shape (Special Publication No. 63-209001), and a method of forming a Fresnel-shaped surface on the back surface of a light guide plate having a wedge-shaped cross section (Japanese Patent Laid-Open No. 64-11203). It is necessary to change its shape, size, density, and roughness appropriately according to the distance from the linear light source. To be done.

[0004]

[Problems to be Solved by the Invention] In addition to the increasing demand for higher quality LCDs such as higher brightness and higher definition, the planar light source device, ie, the backlight, which is a component of the liquid crystal display, has been required to be higher than before. Increasing brightness has been demanded, and the amount of light emitted by the linear light source itself (mainly used in the broad sense of light energy, not as an optical terminology in this specification) is related to this increase in brightness. However, when the planar light source device is evaluated as the ratio of the amount of light extracted from the light emitting surface to the amount of light emitted from the linear light source, the linear light source itself can be used regardless of the amount of light. However, it is difficult to say that the amount of light from the light source is always used effectively at around 30% in the current system, and in particular in the coupling system in which the light source enters the light guide plate, The scan is large at present.

[0005]

[Means for Solving the Problems]

 The present invention relates to a surface light source device that solves the above-mentioned conventional problems. This is a device in which a light diffusion plate, a transparent light guide plate, and a reflection plate are sequentially stacked in the direction of the visual field, and a line is formed on at least one side surface of the transparent light guide plate. In the planar light source device including the linear light source, the maximum width of the light-receiving side surface portion on which the linear light source is installed is larger than the maximum thickness of the light guide plate.

That is, the inventors of the present invention have conducted various studies to develop a planar light source device having a light emitting surface brightness higher than that of the conventional one by guiding the amount of light emitted from the linear light source to the light guide plate as efficiently as possible. If the maximum width of the light-receiving side surface where the linear light source is installed is larger than the maximum thickness of the light guide plate that is the light emitting surface of the planar light source device, the light from the linear light source can be reduced while making the light emitting surface thinner. Since more light can be taken in, it is possible to obtain a planar light source device having a light emitting surface with higher brightness even if a linear light source with a high light utilization rate of the entire device and an equal amount of light is used. We found this and completed this proposal. This will be described in more detail below.

[0007]

The present invention relates to a planar light source device, and in a known planar light source device, the maximum width of the light-receiving side surface portion on which the linear light source is installed is larger than the maximum thickness of the light guide plate. However, according to this, since more light from the linear light source can be taken in while achieving a thinner light emitting surface, the light utilization rate of the entire device is high and the linear light amount is equal. Even if a light source is used, it is possible to obtain a planar light source device having a light emitting surface with higher brightness.

In the planar light source device of the present invention, the width of the light-receiving side surface portion on which the linear light source is installed is larger than the maximum thickness of the light guide plate, as shown in FIG. 1, for example. In the planar light source device including the linear light source 5 surrounded by the reflector 4 on at least one side surface of the transparent light guide plate 2, the light diffusing plate 1, the transparent light guide plate 2 and the reflecting plate 3 are sequentially laminated. The maximum width of the light-receiving side surface portion 6 on which the linear light source 5 is installed is made larger than the maximum thickness of the light guide plate 2.

That is, the light-receiving side surface portion 6 in FIG. 1 has a wide trapezoidal shape, and the linear portion (end surface on the light source side) on the upper surface thereof forms the maximum width, which is the thickness of the light guide plate 2. It is said to be even bigger. In FIG. 1, the light diffusing plate 1 except for the linear light source 5 side is covered with a uniform thickness in the light guide plate, but the thickness is gradually increased and gradually reduced. In the present invention, the maximum width of the light-receiving side surface portion 6 is larger than the maximum thickness of the light guide plate 2.

If the maximum width of the light-receiving side surface portion on which the linear light source is installed is made larger than the thickness of the light guide plate as described above, a larger amount of light emitted from the linear light source can be incorporated into the transparent light guide plate. As a result, it is possible to obtain a planar light source device having higher brightness than conventional ones. The shape and dimensions of the light receiving part where the linear light source is installed are trapezoidal as shown in Fig. 2 (a), or pentagonal with parallel parts as shown in Fig. 2 (b). In addition, as shown in (c) and (d) of FIG. 2, the slope portion from the light receiving portion to the light emitting surface has a curved shape, and further, as shown in (a) of FIG. As shown in the figure, the maximum width of the light emitting surface may be located at the center of the thickness of the light emitting surface, or at a position unevenly distributed on the diffuser or reflector side from the center. May be there. Regarding this, the angle θ formed with the light emitting surface is such that the loss of the light taken in from the light receiving portion at this slope is as small as possible. The total reflection angle α and α <(90-θ ) Relationship is desirable. In addition, if it is difficult to satisfy this due to the design, measures may be taken to prevent light loss, such as by using a reflective sheet in the relevant part, if necessary.

Further, the width of the light-receiving surface of this planar light source device is not limited at all, but if the width is almost equal to the tube diameter of the linear light source used, the volume of the conventional light guide plate is reduced. The light quantity of the light source can be efficiently guided into the light guide plate without increasing it so much. However, the shape of this light receiving surface is not only a vertical straight line, but also a slanted line as shown in Fig. 3 (b). It may be curved as shown in FIG. 3 (c).

The planar light source device of the present invention comprises a light diffusing plate, a transparent light guide plate, a reflecting plate, and a linear light source. The manufacturing method of this transparent light guide plate is shown in FIG. 3, for example. As described above, the light-receiving part and the light-emitting part can be manufactured as separate parts and connected by a method such as adhesion or welding. The material can be acrylic resin, any material, or a combination thereof. However, the cross-sectional shape of the light emitting region of the light guide plate is not limited to the rectangular shape (flat plate) but may be a wedge shape or the like.

[0013]

【Example】

 Next, examples and comparative examples of the present invention will be given. Example 1 A light diffusing plate made of a polyethylene terephthalate sheet D204 [trade name of Kimoto Co., Ltd.] with a thickness of 90 μm, an outer diameter dimension of 130 × 220 mm, a flat plate portion of 130 × 217 × 3 mm, and a light receiving side surface portion. A transparent light guide plate made of acrylic resin / Acrypet [trade name of Mitsubishi Rayon Co., Ltd.] with a trapezoid of top bottom x bottom bottom x height = 3 x 6 x 3 mm and a maximum width of 6 mm, and a thickness of 125 µm. A light emitting section was made by sequentially laminating a white sheet made of polyethylene phthalate and a mirror made of Lumirror E60 [trade name of Toray Industries, Inc.].

Further, this light source unit is made of the above-mentioned Lumirror E60 which is a three-wavelength type cold cathode fluorescent lamp (manufactured by Harrison Electric Co., Ltd.) having a tube diameter of 5.8 mmφ, an effective emission length of 130 mm and a tube luminance of 7,000 nit. It was stored in the reflector.

Next, a direct current voltage of 12 V is applied to this cold cathode tube via an inverter to turn on the light source, and this effective light emitting area (130 × 200 mm) is divided into 5 × 4 = 20 in a grid pattern, The average luminance thereof was calculated from these 20 points and found to be 220 nit.

Example 2 It is assumed that the transparent light guide plate has an outer diameter of 130 × 220 mm and the flat plate portion is 130 × 212 × 3 mm, and the light receiving plate is a surface on which the diffusion plate shown in FIG. Is a plane, and is a pentagonal injection-molded product having a parallel portion having a thickness of 6 mm and a width of 5 mm and a slope portion connected to a portion having a thickness of 3 mm toward the side on which the reflector is installed, When a planar light source device having the same structure was produced and a DC voltage was applied to the same as in Example 1, the average luminance of the device was 225 nit.

Comparative Example A planar light source device was prepared in the same manner as in Example 1 except that an injection molded product having an outer diameter of 130 × 220 mm and a thickness of 3 mm was used as a transparent light guide plate. When a DC voltage was applied in the same manner as in Example 1, the average luminance of this was 175 nit, which was 80% lower than that in Example 1.

[0018]

[Effect of the device]

 The present invention relates to a planar light source device, as described above, in which a light diffusion plate, a transparent light guide plate, and a reflection plate are sequentially stacked according to the direction of view, and is surrounded by a reflector on at least one side surface of the transparent light guide plate. A planar light source device equipped with a linear light source is characterized in that the maximum width of the light-receiving side surface portion on which the linear light source is installed is larger than the maximum thickness of the light guide plate. Although it is an edge light type that receives light from a light source and uniformly illuminates it over a relatively wide range, it is thin and can take in more light from a linear light source, so the device has a high light utilization rate. In addition, there is an advantage that a planar light source device having a light emitting surface with higher brightness can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a planar light source device of the present invention.

2 (a) and 2 (b) are enlarged vertical cross-sectional views of the light receiving side of the transparent light guide plate in Examples 1 and 2, respectively, and (c) and (d) are from the enlarged thickness portion of the light receiving side to the light emitting surface. FIG. 4 is an enlarged vertical cross-sectional view of a light-receiving side surface of a light guide plate having a curved surface in a sloped portion.

FIG. 3 (a) is a shape in which the light receiving surface is gradually thinned from the thickness-increased portion to the light emitting surface, and FIG.
(c) is an enlarged vertical cross-sectional view of a light-receiving side surface of a transparent light guide plate having a curved shape.

[Explanation of symbols]

 1 ... Light diffusion plate, 2 ... Transparent light guide plate, 3 ... Reflector plate, 4 ... Reflector, 5 ... Linear light source, 6 ... Light receiving side surface.

Claims (1)

[Scope of utility model registration request] 1. A planar light source device comprising a linear light source in which a light diffusing plate, a transparent light guide plate and a reflecting plate are sequentially laminated in the viewing direction, and a linear light source surrounded by a reflector is provided on at least one side surface of the transparent light guide plate. A planar light source device, wherein a maximum width of a light-receiving side surface portion on which a light source is installed is larger than a maximum thickness of a light guide plate.