WO2005121639A1 - Optical waveguide, and planar illuminating apparatus and liquid crystal display apparatus using the optical waveguide - Google Patents

Abstract

An optical waveguide is provided with a plurality of transparent optical waveguides, and thin edge parts of the adjacent optical waveguide units are connected. The connected optical waveguide units are arranged to constitute a same flat plane by light projecting planes of the optical waveguide units. A shape of the optical waveguide unit satisfies 1.6R≤L and 0.6R≤D, where, R is a diameter of a bar-shaped light source, L is a distance from a plane, which passes a center axis of the bar-shaped light source and is vertical to the light projecting plane, to an edge plane of the thin edge part, which is a connecting part of the adjacent optical waveguide units, and D is the maximum thickness of a thick part of the optical waveguide unit. Thus, the larger size light projecting plane is provided, and projecting efficiency of the light projected from the light source is improved.

Description

 Specification

 Light guide plate, planar lighting device and liquid crystal display device using the same

 Technical field

 The present invention relates to a transparent light guide plate that diffuses light incident from a rod-shaped light source in a plane direction and emits illumination light from a light exit surface, a planar illumination device using the same, and a liquid crystal display device. Background art

 [0002] A knock light unit that illuminates the liquid crystal panel by illuminating the back surface of the liquid crystal panel (LCD) is used in the liquid crystal display device. The knock light unit includes a light source for illumination, a light guide plate that diffuses the emitted light and irradiates the liquid crystal panel, and a prism sheet and a diffusion sheet that equalize the light emitted from the light guide plate. A known backlight unit is known.

 In recent years, there has been a demand for thinner and lower power consumption liquid crystal display devices, and light guide plates of various shapes have been proposed in order to realize such! (Japanese Patent Laid-Open No. 9-304623, See JP-A-8-62426, JP-A-10-133027 and JP-A-5-249320.

 FIG. 29 is a schematic sectional view of a surface light source device having a light guide plate 100 disclosed in Japanese Patent Application Laid-Open No. 9-304623.

 In the surface light source device (backlight unit) shown in the figure, after a fluorescent lamp 102 is embedded in a light guide plate 100, a reflection sheet 104 is disposed on the back of the light guide plate 100, and a transmission light amount correction sheet is provided on an emission surface of the light guide plate 100. It is formed by laminating 106, light diffusion plate 108, and prism sheet 110.

The light guide plate 100 has a substantially rectangular shape, and is formed using a resin into which fine particles that diffuse illumination light are dispersed and mixed. In addition, the upper surface of the light guide plate 100 is flat, and is allocated to the emission surface. Further, a U-shaped cross section groove 100a for embedding the fluorescent lamp 102 is formed on the back surface (the surface opposite to the emission surface) of the light guide plate 100, and the emission surface of the light guide plate 100 is formed just above the fluorescent lamp 102. By avoiding this, a light quantity correction surface 100b that promotes emission of illumination light is formed. As described above, Japanese Patent Application Laid-Open No. 9-304623 discloses that a light guide plate 100 is formed by mixing fine particles, and a light amount correction surface formed on a part or all of an emission surface except a portion right above a fluorescent lamp 102. It is described that by promoting the emission of the illumination light by 100b, the overall thickness can be reduced and unnatural luminance unevenness of the emitted light can be reduced.

 [0004] Also, Japanese Patent Application Laid-Open No. H8-62426 discloses a liquid crystal display device capable of realizing a small and lightweight liquid crystal display device without reducing the irradiation amount of a knock light, a thinner liquid crystal display device, and a reduction in cost and power consumption. In order to obtain the backlight of the display device, a rectangular illuminated surface, a rectangular section with a rectangular section cut out in the center of the short side parallel to the long side and for inserting a light source, and a long There is disclosed a light guide plate having a back surface formed such that the plate thickness is gradually reduced toward both side surfaces of the side.

 Japanese Patent Application Laid-Open No. 10-133027 discloses a liquid crystal display device in which the frame is narrowed and the thickness thereof is reduced, and a light source is disposed in order to obtain a bright backlight unit with good light use efficiency. A light guide (light guide plate) having a parabolic shape whose cross section parallel to the width direction of the concave portion has the principal axis in the depth direction has been disclosed!

 [0005] Further, Japanese Patent Application Laid-Open No. 5-249320 discloses that in order to keep the in-plane brightness of the display panel uniform and to provide high-luminance illumination, the light is sequentially refracted on a high-reflection layer having a C-shape. There is disclosed a light guide plate in which a plurality of plate-shaped optical waveguide layers are stacked so as to increase the efficiency, and the light diffusion layer is brightened by light emitted from each light emitting end face. Here, the concave portion for arranging the light source has a triangular shape.

 The light guide plate disclosed in each of the above-mentioned patent documents is designed to reduce the thickness, size, and weight of the liquid crystal display device, reduce power consumption, and reduce costs. One or a plurality of grooves are provided, and the rod-shaped light source is accommodated in the grooves. Preferably, the groove force is formed so as to gradually decrease the plate thickness toward the end face, thereby achieving a reduction in thickness.

 Patent Document 1: Japanese Patent Application Laid-Open No. 9-304623

 Patent Document 2: JP-A-8-62426

 Patent Document 3: JP-A-10-133027

Patent Document 4: JP-A-5-249320 Disclosure of the invention

 Problems to be solved by the invention

 [0006] In the light guide plate 100 disclosed in Japanese Patent Application Laid-Open No. 9-304623, a light amount correction surface 100b such as a rough surface or a microprism surface is formed on the emission surface of the light source (fluorescent lamp) 102 so as not to be directly above the light source (fluorescent lamp) 102. It is said that this promotes the emission of illumination light that enters the emission surface at an angle greater than the critical angle. However, the relationship between the shape of the light guide plate and the light emission efficiency of the light emitted from the light source from the emission surface is completely taken into consideration.

 Further, in the backlight of the liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 8-62426, components on the electronic circuit board are arranged in gaps created by tilting the back surface of the light guide plate, thereby reducing power consumption. A power that can achieve a reduction in the size and weight of the liquid crystal display device and a reduction in the thickness of the liquid crystal display device.

 [0007] Further, in the backlight unit of the liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 10-133027, the cross-sectional shape of the groove-shaped recess provided in the light guide (light guide plate) is made parabolic, so that the light guide is formed. It is stated that light is incident on the light guide, which makes light diffusion almost uniform in the light body, and that the light utilization efficiency can be improved.However, the shape of the light guide plate and the light source power The relationship between the output efficiency of the light from the output surface and the output efficiency is completely taken into consideration.

 In addition, the light guide plate disclosed in Japanese Patent Application Laid-Open No. 5-249320 has a complicated structure in which a plurality of plate-like optical waveguide plates are stacked, so that the attenuation of the brightness is reduced and uniform brightness is obtained as compared with the related art. However, no consideration is given to the relationship between the shape of the light guide plate and the light output efficiency of the light emitting surface force with respect to the light emitted from the light source.

 Further, the light guide plate disclosed in Japanese Patent Application Laid-Open No. 5-249320 has a problem that the manufacturing cost is increased due to the complicated structure.

 [0008] Further, all of the light guide plates disclosed in the above patent documents have a problem that it is difficult to form a large-sized light exit surface.

Furthermore, the light guide plates disclosed in the above patent documents all have uneven light emitted from the light exit surface, and cannot emit uniform, high-brightness light from the light exit surface. There are also problems.

 A first object of the present invention is to reduce the thickness and weight of the light emitting surface, to provide a light emitting surface of a larger size, and to achieve a light emitting efficiency of a light emitting surface force with respect to emitted light. It is an object of the present invention to provide a light guide plate having a shape that increases the height.

 Another object of the present invention is to provide, in addition to the first object, a light guide plate capable of emitting illumination light with higher uniformity, less unevenness, and higher luminance. You.

 [0010] A second object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a thin and light-weight light emitting surface with high light emission efficiency with respect to light emitted from a light source. An object of the present invention is to provide a planar lighting device which can be manufactured at low cost, can have a large-sized lighting surface, and can be applied to a liquid crystal display device such as a wall-mounted television. Further, a third object of the present invention is to solve the above-mentioned problems of the prior art, and to reduce the cost and the thickness at a low cost because the light emitting efficiency of the light emitting surface force with respect to the light emitted from the light source is high. An object of the present invention is to provide a liquid crystal display device which can be manufactured, can have a large display screen, or can be of a wall-mounted type such as a wall-mounted television. Means for solving the problem

[0011] In order to solve the above first problem, a first mode of the first aspect of the present invention is a first mode of the present invention, which comprises a rectangular light emitting surface, a position parallel to one side thereof and substantially at the center of the light emitting surface. A thick portion to be formed, a thin end portion formed in parallel with the thick portion, and a parallel groove formed substantially in the center of the thick portion and parallel to the one side, for accommodating a rod-shaped light source; The thick groove portion includes the axis of the rod-shaped light source on both sides of the parallel groove and is symmetrical with respect to a plane perpendicular to the light emission surface, and faces the thin end portions on both sides in a direction orthogonal to the one side. And a plurality of transparent light guide plate units each having a thin rear surface and an inclined back surface portion forming an inclined back surface, wherein the thin end portions of adjacent light guide plate units are connected, and the connected light guide plates are connected. The light emitting surfaces of the unit are arranged on the same plane, the diameter of the rod-shaped light source is R, and the center of the rod-shaped light source is When the distance from the surface perpendicular to the light exit surface to the light-emitting plate unit adjacent to the light guide plate unit to the end surface of the thin end portion is L, and the maximum thickness of the thick portion is D, A light guide plate satisfying the following expression is provided. 1.6R≤L

 0.6R≤D

 It is preferable that the maximum thickness D of the thick portion satisfies the following expression.

 0.6R≤D≤3.3R

 [0013] Further, assuming that the brightness of the light emitted from the light source is B (nt), the distance L (mm) and the brightness

 Is

 It is preferable that the relationship with the luminance B (nt) satisfies the following expression.

 Is

 B / L≥133

 Is

 [0014] In order to solve the above-mentioned other problem, a second mode of the first aspect of the present invention is directed to the second aspect of the present invention, wherein: In the first portion corresponding to the parallel groove, the peak value of the illuminance or luminance formed by the emitted light of the rod-like light source housed in the parallel groove is emitted in the second portion corresponding to the inclined back surface portion. According to the ratio of the illuminance or luminance formed by light to the average value, the tip of the parallel groove is directed toward the light emitting surface with respect to the center line of the parallel groove perpendicular to the rectangular light emitting surface. The present invention provides a light guide plate characterized by having a symmetrical shape.

 Further, a tip portion of the parallel groove so that a peak value of relative illuminance or relative luminance of the first portion of the light exit surface is three times or less of an average value of relative illuminance or relative luminance of the second portion. It is more preferable to make symmetrically thin.

[0015] In a third aspect of the first aspect of the present invention, in the cross-sectional shape of the parallel groove of each of the light guide plates in the direction perpendicular to the first direction, the first shape corresponds to the parallel groove of the light exit surface. Illuminance or peak value power of luminance formed by the emitted light of the rod-shaped light source housed in the parallel groove in the portion The illuminance formed by the emitted light in the second portion corresponding to the inclined back surface Alternatively, the tip of the parallel groove is symmetrically thinned toward the light exit surface with respect to a center line of the parallel groove perpendicular to the light exit surface so as to be three times or less the average value of luminance. It is intended to provide a light guide plate characterized by the above.

Further, the peak of the relative illuminance or relative luminance of the first portion of the light exit surface is preferably 3 times or less of the average value of the relative illuminance or relative luminance of the second portion, and more preferably 2 times or less. Is more preferred. [0016] Further, in the cross-sectional shape of the parallel groove in the orthogonal direction, a front end portion of the parallel groove toward the light emitting surface with respect to a center line perpendicular to the rectangular light emitting surface of the parallel groove. Is preferably a symmetrically thin shape.

 Further, in the cross-sectional shape of the parallel groove, it is preferable that the tip portion is a portion in which the angle with respect to the vertical force perpendicular to the central force of the rod-shaped light source on the light emitting surface is within 90 degrees on both sides.

 In addition, it is preferable that at least the cross-sectional shape of the distal end portion of the parallel groove is a part of two straight lines or curves symmetrical with respect to the center line, each having one sharp intersection point intersecting with each other.

 In addition, it is preferable that a cross-sectional shape of at least the distal end portion of the parallel groove or a cross-sectional shape of the parallel groove is a triangle.

 Further, it is preferable that the two curves that are the cross-sectional shapes of at least the distal end portion of the parallel groove are convex or concave toward the center of the parallel groove.

 In addition, it is preferable that the two curves, which are the cross-sectional shapes of at least the distal end portion of the parallel groove, can be approximated by a 10th order function and are convex or concave toward the center of the parallel groove. At least the two curves that are the cross-sectional shape of the tip portion or the cross-sectional shape of the parallel groove are a part of a circle, ellipse, parabola, or hyperbola that is convex or concave toward the center of the parallel groove. Is preferred.

[0017] The cross-sectional shape of the top of the tip portion of the parallel groove is connected to each other by a straight line or a curve symmetrical with respect to the center line before the two symmetrical straight lines or the curves intersect. Preferably in the shape.

 In addition, it is preferable that a cross-sectional shape of the top portion of the tip portion of the parallel groove is a shape having a portion parallel to the rectangular light exit surface where the one sharp intersection point is chamfered.

Also, the cross-sectional shape of at least the tip portion of the parallel groove or the cross-sectional shape of the parallel groove is triangular, and the cross-sectional shape of the top of the tip portion of the parallel groove with respect to the center line. Preferably, it has a symmetric trapezoidal shape. Further, it is preferable that a cross-sectional shape of the top portion of the distal end portion of the parallel groove is a curved shape that is convex or concave with respect to the rectangular light emission surface and symmetric with respect to the center line. Further, the cross-sectional shape of the top portion of the tip portion of the parallel groove is a circle, an ellipse, a parabola, or a hyperbola in which the one point of intersection is rounded symmetrically with respect to the center line. Is preferred,.

 Preferably, at least the cross-sectional shape of the tip portion of the parallel groove is an elliptical shape or a part of a hyperbola.

 In addition, it is preferable that the top portion of the tip portion of the parallel groove is a sand surface. Further, it is preferable that the rectangular light emitting surface has a halftone dot at a portion corresponding to the top of the tip portion of the parallel groove.

[0018] In order to solve the second problem, a second aspect of the present invention provides a light guide plate according to any one of the above, and a rod-shaped light source housed in the parallel groove of the light guide plate; A reflector provided behind the rod-shaped light source so as to close the parallel groove; and a reflection sheet attached to the inclined back surface of the inclined back surface portion on both sides of the thick portion of the light guide plate. A planar lighting device is provided.

 Furthermore, it is preferable that a diffusion sheet is disposed on the light exit surface of the light guide plate. Preferably, the reflector has a curved surface shape that is convex in a direction away from the light emitting surface.

 Further, it is preferable that a prism sheet is provided between the light exit surface of the light guide plate and the diffusion sheet.

[0019] In order to solve the third problem, a third aspect of the present invention is directed to a backlight unit having any of the above-mentioned planar lighting devices, and a light emitting surface of the backlight unit. A liquid crystal display device comprising: a liquid crystal display panel disposed on the side; and a drive unit for driving the backlight unit and the liquid crystal display panel.

 The invention's effect

According to the first aspect of the first aspect of the present invention, the light emission efficiency of the light emitted from the rod-shaped light source can be increased with respect to the light emitted from the rod-shaped light source. ,Light guide plate The size of the light exit surface can be made larger. More specifically, the maximum thickness D of the thick portion of the light guide plate unit with respect to the diameter R of the rod-shaped light source and the surface force passing through the center of the rod-shaped light source and perpendicular to the light emitting surface are the joints between the adjacent light guide plate units. By setting the distance L to the end face of the thin end to 1.6R≤L and 0.6R≤D, the emission efficiency for light emitted from the rod-shaped light source can be increased, and the adjacent light guide plate unit can be By connecting, the size of the light emitting surface of the light guide plate can be further increased.

 Further, according to the second and third embodiments of the first aspect of the present invention, the peak of the illuminance can be further reduced by the shape of the tip groove of the light guide plate, and the illuminance on the light emitting surface can be made more uniform. And the required uniformity of the light exit surface can be achieved.

According to the second aspect of the present invention, by using the light guide plate of the first aspect, the light guide plate is thin and lightweight, can be manufactured at lower cost, and is emitted from the rod-shaped light source. The surface that can increase the light emission efficiency with respect to the emitted light, can increase the size of the illumination surface, or can be applied to a liquid crystal display device such as a wall-mounted television. An illumination device can be provided.

 Further, according to the third aspect of the present invention, by using the spread illuminating apparatus of the second aspect described above, it is thin and lightweight, and the rod-shaped light source emits light having a light emission surface power with respect to the emitted light. A liquid crystal display device that can increase efficiency, can be manufactured at lower cost, can have a large display screen, or can be a wall-mounted type such as a wall-mounted television. Can be provided.

 Brief Description of Drawings

 FIG. 1A and FIG. 1B are a schematic perspective view and a schematic sectional view, respectively, of a liquid crystal display device using a backlight unit having a light guide plate of the present invention.

 FIG. 2 is a schematic sectional view of a light guide plate of the present invention.

 FIG. 3A is a schematic cross-sectional view showing a state in which a prism sheet is disposed between a reflection sheet and an inclined surface of a light guide plate, and FIG. FIG. 3 is a schematic plan view and a schematic cross-sectional view of a prism sheet disposed therebetween as viewed from the light guide plate side.

[FIG. 4] FIGS. 4A to 4C show the shapes of the light guide plate when the maximum thickness of the light guide plate is changed, respectively. FIG. 3 is a schematic cross-sectional view for explaining the method.

 FIG. 5A is a schematic sectional view when the reflector is a plane reflector, and FIG. 5B is a schematic sectional view when the reflector is a curved reflector.

 FIG. 6 is a graph showing the relationship between the maximum thickness of the light guide plate unit and the emission efficiency.

FIG. 7A to FIG. 7C are schematic cross-sectional views for explaining the shape of the light guide plate when the length of the light guide plate unit is changed.

 FIG. 8 is a graph showing the relationship between the length of the light guide plate unit and the emission efficiency.

 FIG. 9 is a graph showing the relationship between the maximum thickness of the light guide plate unit and the emission efficiency according to the number of connected light guide plate units.

 FIG. 10 is a graph showing the relationship between the length of the light guide plate unit and the emission efficiency according to the number of connected light guide plate units.

 FIG. 11 is a graph showing the relationship between the maximum thickness of the light guide plate unit and the emission efficiency when the light guide plate unit has a curved inclined surface.

[12] FIG. 12 is a schematic sectional view showing a shape of a light guide plate unit having a curved inclined surface.

 FIG. 13 is a graph showing the relationship between the maximum thickness of the light guide plate unit and the emission efficiency when the light guide plate unit has a curved inclined surface.

 FIG. 14 is a graph showing the relationship between the length of the light guide plate unit and the emission efficiency when the light guide plate unit has a curved inclined surface.

 FIG. 15 is a schematic cross-sectional view of the light guide plate unit when the cross-sectional shape perpendicular to the length direction of the parallel groove is hyperbolic.

 FIG. 16 is a schematic cross-sectional view of the light guide plate unit when the cross-sectional shape perpendicular to the length direction of the parallel groove is elliptical.

 FIG. 17 is a graph showing the relationship between the maximum thickness of the light guide plate unit and the emission efficiency according to the shape of the parallel groove of the light guide plate unit.

 FIG. 18 is a graph showing the relationship between the length of the light guide plate unit and the emission efficiency according to the shape of the parallel groove of the light guide plate unit.

[Figure 19] Figure 19 shows that the cross-sectional shape perpendicular to the length direction of the parallel groove passes through the center of the parallel groove. FIG. 4 is a schematic cross-sectional view of a light guide plate unit formed by partially forming two arc curves symmetrical with respect to a center line perpendicular to a light exit surface of the plate unit.

 FIG. 20 shows one of two parabolas whose cross-sectional shape perpendicular to the length direction of the parallel groove is symmetric with respect to a center line passing through the center of the parallel groove and perpendicular to the light exit surface of the light guide plate unit. FIG. 4 is a schematic cross-sectional view of a light guide plate unit formed with a partial force.

 [FIG. 21] FIG. 21 is a schematic cross-sectional view of a light guide plate unit in which a cross-sectional shape perpendicular to the length direction of the parallel groove is formed with two convex curving forces directed toward the center of the parallel groove.

[FIG. 22] FIG. 22 shows a light guide plate unit in which a cross-sectional shape perpendicular to the length direction of a parallel groove is formed into a curved force that combines a convex curve and a concave curve toward the center of the parallel groove. It is an outline sectional view of.

 FIG. 23 is an example of a halftone dot pattern formed on the light exit surface side of the light guide plate unit.

FIG. 24 is a graph showing the illuminance distribution of light emitted from the light exit surface of the light guide plate when the cross-sectional shape of the parallel groove of the light guide plate is changed to various shapes.

 FIG. 25 is a graph showing the illuminance distribution of light emitted from the light guide plate when the deepest portion of the parallel groove is flattened and the length of the flat portion is changed to various values. It is a graph shown.

 [FIG. 26] FIGS. 26A to 26D are schematic cross-sectional views of the light guide plate when the flat portions at the deepest portions of the parallel grooves are 1.5 mm, 1. Omm, 0.5 mm, and 0.25 mm, respectively. It is.

 [FIG. 27] FIG. 27 shows that the deepest portion of the parallel groove is formed into a curved surface having a radius of curvature R, and the radius of curvature of the curved surface is changed to various values. It is a graph which shows illuminance distribution.

 [FIG. 28] FIGS. 28A to 28D are schematic diagrams of the light guide plate when the radii of curvature of the apexes of the parallel grooves having a triangular cross section are 1.5 mm, 1.0 mm, 0.5 mm, and 0.25 mm, respectively. It is sectional drawing.

 FIG. 29 is a schematic perspective view of a conventional surface light source device having a light guide plate.

Explanation of symbols

 2 Knock light unit

4 LCD panel 6 Drive unit

 10 Liquid crystal display

 12 light source

 13, 100 light guide plate

 14 Diffusion sheet

 16, 17, 19 Prism sheet

 18, 40, 50, 60, 70, 80 Light guide plate unit

 18a, 52 Light exit surface

 18b Thick part

 18c thin end

 18d, 40d slope

 18e inclined back

 18f parallel groove

 18g thick tip

 18h Thin end face

 20 Reflector

 22, 42 reflective sheet

 24 Reflector

 30 plane reflector

 32 Curved reflector

 54a, 54b Arc curve

 56 intersection

 64a, 64b parabola

 72a, 72b, 82a, 82b, 84a, 84b Curve

 92 Halftone pattern

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a light guide plate of the present invention, a planar lighting device and a liquid crystal display device using the same will be described in detail based on preferred embodiments shown in the accompanying drawings. FIG. 1A and FIG. IB show a liquid crystal of a third embodiment of the present invention using the planar lighting device of the second embodiment of the present invention having the light guide plate of the first embodiment of the present invention as a backlight unit. 1 shows a schematic perspective view and a schematic cross-sectional view of a display device. As shown in FIGS.1A and 1B, the liquid crystal display device 10 basically includes a backlight unit 2, a liquid crystal display panel 4 arranged on the light emitting surface side of the backlight unit 2, and a driving unit for driving the liquid crystal display panel 4. And a drive unit 6.

 The backlight unit 2 is a planar illumination device for irradiating the entire surface of the liquid crystal display panel 4 with uniform light from behind the liquid crystal display panel 4, and is substantially the same as the image display surface of the liquid crystal display panel 4. Light emitting surface (light emitting surface). The knock light unit 2 basically includes a light source 12, a light guide plate 13, a diffusion sheet 14, two prism sheets 16 and 17, and a reflector 20, as shown in FIGS. 1A and 1B. , And a reflection sheet 22. Here, in FIGS.1A and 1B, the light guide plate 13 has a force indicating one light guide plate unit 18.The light guide plate 13 of the present invention connects a plurality of light guide plate units 18 as shown in FIG. It is something. The connection of the plurality of light guide plate units 18 in the light guide plate 13 of the present invention will be described later.

 The light source 12 is a small-diameter rod-shaped cold cathode tube, and is used for illuminating the liquid crystal display panel 4. The light source 12 is arranged in a parallel groove 18f formed in the light guide plate unit 18, and is connected to the drive unit 6. Here, a cold cathode tube is used as the light source 12, but the present invention is not limited to this, and any rod-shaped light source may be used. As the light source 12, for example, a normal fluorescent tube (hot cathode tube), an LED (light emitting diode), or the like can also be used.

In FIG. 1A and FIG. 1B, the diffusion sheet 14 is for diffusing and uniformizing the light emitted from the light exit surface 18a of the light guide plate unit 18, for example, PET (polyethylene terephthalate). , PP (polypropylene), PC (polycarbonate), PMMA (polymethinolemethacrylate), benzyl methacrylate or MS resin, other acrylic resins, or optically transparent materials such as COP (cycloolefin polymer) It is formed by giving light diffusivity to a flat member made of resin. Although the method is not particularly limited, for example, the surface of the plate-shaped member is roughened by fine unevenness processing or polishing (hereinafter, the surface subjected to these treatments is referred to as a “sand rubbing surface”) to impart diffusivity. Or silica, titanium oxide, or A material for scattering light, such as a pigment such as zinc or beads such as resin, glass or zirconia, is coated on a surface together with a binder, or the light scattering material is dispersed in the transparent resin described above. It is formed by kneading pigments or beads. In the present invention, as the diffusion sheet 14, a mat type or coating type diffusion sheet can be used.

 In the present invention, as the diffusion sheet 14, it is also preferable to use a film-like member having a thickness of 500 μm or less, which is made of the above-mentioned material and has light diffusing properties.

 The diffusion sheet 14 is preferably disposed at a predetermined distance from the light exit surface 18a of the light guide plate unit 18, and the distance is preferably equal to the light amount distribution from the light exit surface 18a of the light guide plate unit 18. Can be changed as appropriate. By separating the diffusion sheet 14 from the light exit surface 18a of the light guide plate unit 18 by a predetermined distance in this manner, the light exiting from the light exit surface 18a of the light guide plate unit 18 is transmitted to the light exit surface 18a and the diffusion sheet 14a. Mixing (mixing) between Thereby, the illuminance of the light passing through the diffusion sheet 14 and illuminating the liquid crystal display panel 4 can be further uniformed. As a method of separating the diffusion sheet 14 from the light exit surface 18a of the light guide plate unit 18 by a predetermined distance, for example, a method of providing a spacer between the diffusion sheet 14 and the light guide plate unit 18 can be used.

 In particular, when the thickness of the knock light unit 2 may be slightly increased, the cross-sectional shape of the parallel groove 18f of the light guide plate unit 18 may cause the light exit surface 18a of the light guide plate unit 18 corresponding to the parallel groove 18f to be formed. It is not necessary to sufficiently reduce the peak value of the illuminance. For example, the peak value is reduced to a predetermined value, a gap is provided between the diffusion sheet 14 and the light exit surface 18a of the light guide plate unit 18, and the illuminance distribution of the illumination light emitted from the diffusion sheet 14 is increased. May be made uniform. In addition, there is a limit to the improvement of the cross-sectional shape of the parallel groove 18f of the light guide plate unit 18 (the tapering of the front end portion of the parallel groove), and the illuminance peak at the light exit surface 18a of the light guide plate unit 18 corresponding to the parallel groove 18f is limited. Even when the value cannot be reduced completely or sufficiently, a gap is provided between the diffusion sheet 14 and the light exit surface 18a of the light guide plate unit 18 so that the illumination light emitted from the diffusion sheet 14 can be reduced. The illuminance distribution may be made uniform.

The prism sheets 16 and 17 are transparent sheets formed by arranging a plurality of prisms in parallel, and have a function of condensing light emitted from the light exit surface 18 a of the light guide plate unit 18. It can be raised to improve the brightness. One of the prism sheets 16 and 17 is arranged so that the direction in which the prism row extends is parallel to the parallel groove 18f of the light guide plate unit 18, and the other is arranged so as to be vertical. That is, the prism sheets 16 and 17 are arranged such that the directions in which the prism rows extend are perpendicular to each other. The prism sheet 16 is disposed such that the apex angle of the prism faces the light exit surface 18a of the light guide plate unit 18. Here, the arrangement order of the prism sheets 16 and 17 is such that a prism sheet 16 having a prism extending in a direction parallel to the parallel groove of the light guide plate is arranged immediately above the light guide plate, and the prism sheet 16 is placed on the prism sheet 16. Alternatively, a prism sheet having a prism extending in a direction perpendicular to the parallel groove 18f of the light guide plate unit 18 may be provided, or vice versa.

 In the illustrated example, a prism sheet is used, but a sheet in which optical elements similar to prisms are regularly arranged may be used instead of the prism sheet. In addition, a sheet regularly provided with an element having a lens effect, for example, an optical element such as a lenticular lens, a concave lens, a convex lens, or a pyramid type can be used instead of the prism sheet.

 In the present invention, as shown in FIGS. 3A and 3B, the prism sheet 19 is also provided between the reflection sheet 22 and the inclined surface 18d of the light guide plate unit 18 opposite to the light exit surface 18a. It is preferable to provide them. FIG. 3A is a schematic cross-sectional view showing a state where the prism sheet 19 is disposed between the reflection sheet 22 and the inclined surface 18d of the light guide plate unit 18, and FIG. 3B is a sectional view showing the reflection sheet 22 and the light guide plate unit. 18A and 18B are a schematic plan view and a schematic cross-sectional view of a part of the prism sheet 19 disposed between the inclined surface 18d and the light guide plate side force, respectively. The prism sheet 19 provided between the reflection sheet 22 and the inclined surface 18d of the light guide plate unit 18 is arranged such that the direction in which the prism 19a extends is perpendicular to the parallel groove 18f of the light guide plate unit 18. In particular, it is preferable to arrange the prism 19a such that the apex angle of the prism 19a faces the inclined surface 18d of the light guide plate unit 18.

 Here, an optical element having a lens effect that can be obtained by using an optical element having the same effect as the prism sheet, such as a lenticular lens, a concave lens, a convex lens, or a pyramid type optical element. A sheet in which elements are regularly arranged may be provided.

In the illustrated example, the prism sheets 16 and 17, more preferably, the prism sheets When the illuminance on the light exit surface 18a is made more uniform by the parallel grooves 18f of the light guide plate unit 18, the prism sheet 19 is of course unnecessary, and the prism sheets 16 and 17 are used. Either one or both may not be used. The installation cost can be reduced by reducing the number of expensive prism sheets used or by omitting the use of prism sheets.

In FIG. 1A and FIG. 1B, the reflection sheet 22 reflects light leaking from the back surface (the lower surface in the figure) of the light guide plate unit 18 and makes the light enter the light guide plate unit 18 again. Light emission efficiency can be improved. The reflection sheet 22 is formed so as to cover the lower surface (inclined surface) of the light guide plate unit 18. The reflector 20 is provided behind the light source 12 so as to close the parallel groove 18f of the light guide plate unit 18. The reflector 20 reflects the light from the lower surface of the light source 12 and can also input the light with the side wall surface force of the parallel groove 18f of the light guide plate unit 18. Here, the force forming the reflector 20 as a flat surface is not particularly limited, and may be a curved surface.

 [0035] The reflection sheet 22 may be made of any material as long as it can reflect light leaking from the back surface (the lower surface in the figure) of the light guide plate unit 18, for example, PET, A resin sheet with high reflectivity by forming voids by kneading a filler into PP (polypropylene) etc. and then forming a mirror surface on the surface of a transparent or white resin sheet as described above by aluminum evaporation It can be formed of a sheet, a metal foil of aluminum or the like, a resin sheet carrying the metal foil, or a thin metal plate having a sufficient reflectivity on the surface. In addition, the reflector 20 can be formed of, for example, the same material as the above-mentioned reflective sheet, that is, a resin material, a metal foil or a metal plate having a surface with sufficient reflectivity.

1A and 1B, the light guide plate unit 18 has a rectangular light exit surface 18a, a thick portion 18b parallel to one side thereof, and a thick light portion 18b on both sides of the thick portion 18b parallel to the one side. A thin end portion 18c to be formed, an inclined back surface portion 18e which becomes thinner from the thick portion 18b toward the thin end portions 18c on both sides in a direction perpendicular to the one side, and forms an inclined surface 18d; A parallel groove 18f for accommodating the light source 12 is formed in the meat portion 18b in parallel to the one side. That is, the light guide plate unit 18 is a flat plate having a rectangular outer shape on the surface, and is formed of a transparent resin. The light guide plate unit 18 has one surface flat and the other surface flat. The force is inclined with respect to one side so that the plate thickness becomes thinner toward one side.

 On the opposite side of the light emitting surface 18a of the thick portion 18b of the light guide plate unit 18, a parallel groove 18f for accommodating the light source 12 is formed extending in the longitudinal direction. The depth of the parallel groove 18f is preferably determined so that a part of the light source 12 does not protrude from the lower surface of the light guide plate unit 18, the dimensions of the light source 12, the mechanical strength of the light guide plate unit 18, and the time. It is preferable to determine in consideration of changes. The thickness of the thick portion 18b and the thin end portion 18c of the light guide plate unit 18 can be arbitrarily changed according to the dimensions of the light source 12. Here, the parallel groove 18f of the light guide plate unit 18 may be formed in a direction perpendicular to the longitudinal direction of the light guide plate unit 18, but the emission efficiency from the light source 12 accommodated in the parallel groove 18f is increased. For this purpose, it is preferable to form them in the longitudinal direction.

 In the light guide plate unit 18 having the structure shown in FIGS. 1A and 1B, of the light emitted from the light source 12 disposed in the parallel groove 18f, the light guide plate unit 18 is formed from the side wall forming the parallel groove 18f. The light that has entered the inside of the device is reflected on the inclined surface 18d of the light guide plate unit 18 and then exits from the light exit surface 18a. At this time, part of the light leaks from the lower surface of the light guide plate unit 18, but the leaked light is reflected by the reflection sheet 18 formed on the inclined surface 18d side of the light guide plate unit 18, and is returned again. The light enters the inside of the light source 18 and exits from the light exit surface 18a. Thus, uniform light is emitted from the light exit surface 18a of the light guide plate unit 18.

 Here, in such a light guide plate unit, the light emission efficiency of the light emitted from the rod-shaped light source from the light emission surface is increased for power saving, high luminance, light weight, and the like. Can be considered.

 The inventors of the present invention have conducted intensive studies on the light emission efficiency of the light emitted from the rod-shaped light source from the light emission surface (hereinafter referred to as the light emission efficiency of the light guide plate unit). As a result, the shape of the light guide plate, It has been found that the size of the light guide plate unit with respect to the diameter of the rod-shaped light source and the thickness of the light guide plate unit with respect to the diameter of the rod-shaped light source have a large effect.

Further, as shown in FIG. 1B, the diameter of the light source 12 is R, and a thin end portion 18c to be joined to an adjacent unit is taken from a plane passing through the central axis of the light source 12 and perpendicular to the light emitting surface 18a. The distance to the end face (the thin end face 18h) of the above (hereinafter, referred to as half the length of the light guide plate unit 18) is L, Assuming that the thickness of the portion where the thickness of the thick portion 18b is the maximum (hereinafter, referred to as the maximum thickness of the light guide plate unit 18) is D, the present inventors consider that 1.6R≤L and 0.6R By setting ≤D, it has been found that the emission efficiency of the light guide plate unit 18 can be increased. In the case of the shape shown in FIG.1B, the maximum thickness D of the light guide plate unit 18 is the farthest from the light emitting surface 18a of the thick portion 18b, and the junction between the surface forming the parallel groove 18f and the inclined surface 18d. This corresponds to the distance from (the thick end portion 18g) to the light exit surface 18a.

Hereinafter, the dependence of the emission efficiency of the light guide plate unit on the relationship between the diameter R of the light source 12 and the maximum thickness D of the light guide plate unit 18 will be described, together with measurement results measured by simulation.

 In the simulation, a cold cathode tube with R = 3 mm was used as the light source 12, the length L of the light guide plate unit was half as L = 15mm, the thickness of the thin end face 18h was 0.5mm, and the top of the parallel groove 18f and the light emitting surface 18a were used. Is 0.5 mm. In addition, a reflection sheet 22 was disposed on the inclined surface 18d side of the light guide plate unit 18, and a reflector was disposed behind the light source 12 so as to close the parallel groove 18f of the light guide plate unit 18.

 Next, the thin end face 18h of the light guide plate unit 18 and the top (deepest) position of the parallel groove are fixed, and the thick end 18g of the thick part 18b is moved in a direction perpendicular to the light emitting surface. As a result, the maximum thickness D of the light guide plate unit 18 was changed. The light source 12 was disposed at a position inscribed in the parallel groove 18f according to the maximum thickness D of the light guide plate unit. In other words, when the maximum thickness D of the light guide plate unit 18 having the shape shown in FIG. 4A is reduced, as shown in FIG. 4B, the thick end portion 18g is replaced with the thick end portion 18g ′ to form the light guide plate unit. Decrease the maximum thickness D. At this time, the light source 12 'is arranged at a position inscribed in the parallel groove 18f'. When increasing the maximum thickness D of the light guide plate unit 18 having the shape shown in Fig. 4A, as shown in Fig. 4C, the maximum thickness D of the light guide plate unit is increased by setting the thick tip 18g to the thick tip 18g ". At this time, the light source 12 "is arranged at a position inscribed in the parallel groove 18f".

Here, the measurement by simulation is based on the case where a planar reflector 30 having a plane shape parallel to the light emitting surface 18a is used as a reflector as shown in FIG. 5A, and the case where a light emitting device is used as shown in FIG. 5B. This was performed in the case where a curved reflector 32 having a curved shape convex in a direction away from the surface 18a was used. The shape of the curved reflector 32 was an arc shape. Curved reflector 32 When the maximum thickness D of the light guide plate unit 18 is 5 mm or less, the radius of the arc is changed according to the maximum thickness D because it is necessary to cover the lower surface of the light source accommodated in the parallel groove. In the simulation where the maximum thickness D of the light guide plate unit 18 is Omm <D≤5 mm, the point where a straight line passing through the central axis of the light source 12 and perpendicular to the light exit surface 18a intersects the lower surface of the light source 12 is shown. The distance A between the object and the curved reflector 21 was fixed at A = 0.7 mm. On the other hand, in the simulation where the maximum thickness D of the light guide plate unit 18 is 5 mm and D, the curved reflector has the same arc shape as the curved reflector when the maximum thickness D = 5 mm.

 [0044] In the case of a planar reflector, the maximum thickness D of the light guide plate unit 18 is variously 5 mm or more, and in the case of a curved reflector, the maximum thickness D of the light guide plate unit 18 is 0.5 mm or more. For various sizes, the relationship between the maximum thickness D of the light guide plate unit 18 and the emission efficiency of the light guide plate unit 18 was measured by simulation. FIG. 6 shows the measurement results thus measured.

 It can be seen from the graph of FIG. 6 that the emission efficiency of the light guide plate unit 18 changes according to the maximum thickness D of the light guide plate unit 18. In particular, it is understood that the emission efficiency of the light guide plate unit 18 can be made 80% or more by setting the maximum thickness D of the light guide plate unit 18 to 2≤D.

 Also, as shown in the graph of FIG. 6, it can be seen that the emission efficiency is improved by setting the length of the light guide plate within the above range regardless of the shape of the reflector.

 Here, in the above example, in the light guide plate unit where the maximum thickness D of the light guide plate unit 18 is D <1.6R, the planar reflector cannot be used because the rod-shaped light source does not fit in the parallel groove. However, even such a light guide plate unit can be used by making the reflector a curved surface reflector.

 As described above, even when the maximum thickness D of the light guide plate unit is small, the use of the curved reflector as the reflector makes the lighter and thinner, and the light emitting efficiency of the light emitting surface with respect to the light emitted from the rod-shaped light source. Can be used. Here, the shape of the curved reflector is not limited to the above shape, and the distance A between the reflector and the light source is not limited to 0.7 mm as long as it covers the light source, and may be various values.

Next, a measurement result obtained by performing a simulation on the dependence of the emission efficiency of the light guide plate unit on the relationship between the diameter R of the light source 12 and the half length L of the light guide plate unit 18 It will be explained together.

 In the simulation, a cold cathode tube with R = 3 was used as the light source 12, the maximum thickness D of the light guide plate unit 18 was 5mm, the thickness of the thin end face 18h was 0.5mm, the top of the parallel groove 18f and the light exit surface 18a Is 0.5 mm. In addition, a reflection sheet 22 was arranged on the inclined surface 18d side of the light guide plate unit 18, and a reflector was provided behind the light source 12 so as to close the parallel groove 18f of the light guide plate unit 18. Note that a planar reflector was used as the reflector.

 Next, the shape of the parallel groove 18f is not changed, and the surface farthest from the light source 12, that is, the thin end surface 18h is translated in a direction parallel to the light emitting surface 18a and perpendicular to the central axis of the light source. This changes the length L of half of the light guide plate unit 18. In other words, when shortening the half length L of the light guide plate unit 18 from the shape shown in FIG. 7A, as shown in FIG. 7B, the position of the thin end face 18h is moved to the position indicated by 18h ', and When increasing the half length L of the light guide plate unit 18 from the shape shown in 7A, as shown in FIG. 7C, the position of the thin end face 18h is moved to the position indicated by 18h ".

 As described above, for various lengths of the half length L of the light guide plate unit 18 and the force of not less than 40 mm, the output efficiency of the light guide plate unit and the half length L of the light guide plate unit 18 are different. The relationship was measured by simulation. Fig. 8 shows the measurement results. As shown in the graph of FIG. 8, it can be seen that the emission efficiency of the light guide plate changes according to the half length L of the light guide plate unit 18. In particular, it is understood that the emission efficiency of the light guide plate can be made 80% or more by setting the half length L of the light guide plate unit 18 to 5 mm ≦ L.

 Here, in each of the above examples, a cold cathode tube with R = 3 mm is used for the light source 12, and when R = 3, 2 mm ≦ D and 5 mm ≦ L, so that the light guide plate unit 18 The extraction efficiency is more than 80%.

 From the above results, the range of the thickness D of the light guide plate unit and the half length L of the light guide plate unit where the emission efficiency of the light guide plate is 80% or more is expressed using the diameter R of the light source, and 0.6R≤D , And 1. 6R≤L.

 Thus, it can be seen that the emission efficiency of the light guide plate unit can be made 80% or more by setting 0.6R≤D and 1.6R≤L.

Here, the thickness D of the light guide plate unit 18 is more preferably 0.6R ≦ D ≦ 3.3R. By setting the thickness D of the light guide plate to 0.6R or more, the emission efficiency can be increased as described above. Although there is no upper limit for D, it is practically possible to obtain a lightweight lighting device if it is set to 3.3R or less.

 Here, the light guide plate 13 of the present invention is formed by joining the thin end faces 18 h of the adjacent light guide plate units 18 as described above. Thus, the plurality of light guide plate units 18 are formed into a body and connected (see FIG. 2). Further, the light guide plate units 18 are arranged in parallel so that the light emitting surfaces all form the same plane.

 By connecting the plurality of light guide plate units 18 in this manner, a large light guide plate can be configured. Here, when the light guide plate units 18 are arranged in parallel, the inclined surface of one light guide plate unit 18 does not intersect with the inclined surface of the other light guide plate unit 18 connected thereto, that is, The inclination angle of the inclined surface of the light guide plate can also be adjusted so that a smooth flat surface or a curved surface is formed at the connecting portion of the inclined surfaces.

 By using a light guide plate having such a large light emitting surface, a backlight unit having a large light irradiating surface can be obtained. Therefore, the present invention is applied to a liquid crystal display device having a large display screen. In particular, the present invention can be applied to a wall-mounted type liquid crystal display device such as a wall-mounted television.

 In addition, by connecting a plurality of light guide plate units, light emitted from adjacent rod-shaped light sources enters from the thin end. As a result, the emission efficiency can be made higher than in the case where the light guide plate is a single unit. Furthermore, by using a plurality of cold cathode fluorescent lamps (CCFLs), it is possible to increase the luminance on the light emitting surface, increase the surface area of the light guide plate, and improve the heat radiation effect.

 In addition, by integrally forming a plurality of light guide plate units, light scattering at the connection portions (thin end faces) of the light guide plate units can be further reduced, and the emission efficiency can be further improved.

 Here, the relationship between the maximum thickness D of the light guide plate unit 18 and the emission efficiency of the light guide plate unit with respect to the number of connected light guide plate units will be described together with measurement results measured by simulation.

In the simulation, the number of connected light guide plate units was 3, 5, 7, and infinite Regarding the plates, the relationship between the maximum thickness D of the light guide plate unit and the emission efficiency was measured when the reflector was a planar reflector and a curved reflector.

 Here, the configuration of the light guide plate and the measuring method are the same as those of the light source diameter R and the maximum thickness D of the light guide plate unit except that the number of connected light guide plate units is changed. This is the same as the case of simulating the dependence of the light emission efficiency of the light guide plate, and the relationship between the maximum thickness of the light guide plate unit and the light emission efficiency of the light guide plate unit was measured according to such a configuration of the light guide plate and the measuring method.

 FIG. 9 shows the results of a simulation of the relationship between the maximum thickness D of the light guide plate unit and the emission efficiency of the light guide plate unit for light guide plates of various numbers of units. Here, in the graph of FIG. 9, similarly to FIG. 6, the vertical axis represents the emission efficiency%, and the horizontal axis represents the maximum thickness Dmm of the light guide plate unit.

 As shown in FIG. 9, regardless of the number of units connected with the light guide plate units, as in the graph of FIG. 6, when 2 ≦ D, the emission efficiency is 80% or more.

 As described above, regardless of the number of connected light guide plate units, it is possible to increase the emission efficiency by setting the maximum thickness D of the light guide plate unit to 0.6R≤D with respect to the diameter R of the light source.ゎ ゎ

 Next, the dependence of the relationship between the half length L of the light guide plate unit 18 and the emission efficiency of the light guide plate unit on the number of connected light guide plate units will be described together with measurement results measured by simulation.

 In the simulation, as described above, the relationship between the half length L of the light guide plate unit and the emission efficiency was set for light guide plates with the number of connected light guide plate units set to 3, 5, 7, and infinity, respectively. It was measured.

 Here, the configuration of the light guide plate and the measuring method are the same as those of the light source diameter R and the half length L of the light guide plate unit except that the number of connected light guide plate units is changed. This is the same as the case of simulating the dependence of the light output efficiency of the light guide plate, and the relationship between the half length L of the light guide plate unit and the light output efficiency of the light guide plate unit is measured using such a light guide plate configuration and measurement method. did.

Figure 10 shows half the length of the light guide plate unit and the light guide plate of various numbers of units. The result of having measured the relationship with the emission efficiency of a light guide plate unit by simulation is shown. Here, in the graph of FIG. 10, the vertical axis represents the emission efficiency%, and the horizontal axis represents the half length L mm of the light guide plate unit.

 As shown in FIG. 10, regardless of the number of units connected with the light guide plate units, the emission efficiency is 80% or more when 5 ≦ L, as in the graph of FIG.

 As described above, regardless of the number of connected light guide plate units, the emission efficiency can be increased by setting the half length L of the light guide plate unit to the diameter R of the light source to 1.6R≤L.ゎ ゎ

 9 and 10, it can be seen that the light guide plate of the present invention is not particularly limited in the number of light guide plate units connected, and that V and shoes may be connected!

Here, connecting a plurality of light guide plate units of the present invention to form a large light guide plate is limited to integrally forming a shape in which two or more units are connected as described above. Instead, the separately formed light guide plate of the present invention may be arranged such that the thin portions are in contact with each other, or may be formed by bonding. However, in order to improve the uniformity of the emitted light, it is preferable to integrally mold two or more units in a connected shape.

 In addition, from the viewpoint of manufacturing efficiency, it is preferable to integrally form a required number of light guide plate units of the present invention to form a light guide plate corresponding to a required screen size.

The light guide plate 13 is manufactured by, for example, a method of molding a heated raw resin by extrusion molding or injection molding, or a casting polymerization method of polymerizing monomers and oligomers in a mold and molding. Can be. The light guide plate 13 may be made of, for example, PET (polyethylene terephthalate), PP (polypropylene), PC (polycarbonate), PMMA (polymethinolemethacrylate), benzyl methacrylate or MS resin, other acrylic resin, or A transparent resin such as COP (cycloolefin polymer) can be used. The transparent resin may be mixed with fine particles for scattering light. This makes it possible to further increase the efficiency of light emission from the light exit surface 18a.

Further, as shown in FIG. 2, in the light guide plate 13 of the present embodiment, as a preferred embodiment, a reflection plate 24 is provided on the side surface of the light guide plate unit 18 arranged at the outermost side. By arranging such a reflection plate 24 on the side surface, the side of the outermost light guide plate unit 18 can be removed. Such light can be prevented from leaking, and the emission efficiency of the outermost light guide plate unit 18 can be increased. The reflection plate 24 can be formed using the same material as the above-described reflection sheet or reflector.

Here, it is preferable that the light guide plate emits light having a light emission surface force with a luminance equal to or higher than a certain value.

 Hereinafter, the relationship between the luminance at which the light emitting surface force is emitted and the length of the light guide plate will be described together with specific examples.

 In this embodiment, the half length L of the light guide plate unit is 15 mm, and the light source brightness B

Using a light source of Is Force OOOnt (40, OOOcdZm ² ), a reflection sheet, a prism sheet, a diffusion sheet, and the like, a planar illumination device as shown by reference numeral 2 in FIG. 1A was fabricated and measured. The above light source was arranged in the parallel groove of the light guide plate unit, and the luminance on the surface of the planar lighting device was measured. As a result, the luminance was 10, OOOnt. In this example, the average luminance of the emitted light was calculated as the luminance of the light guide plate unit.

 Furthermore, a color LCD panel was installed as a liquid crystal display panel on the upper surface of the planar lighting device, and the luminance of light emitted from the liquid crystal display panel was measured. As a result, the surface luminance of the liquid crystal display panel was about 1, OOOnt. Was. This indicates that the transmittance of the liquid crystal display panel is about 10%.

 Here, half the length of the light guide plate unit L (mm), the brightness of the light source B (nt), and the liquid crystal display panel

 Is

 The relationship with the surface luminance X (nt) of the flannel can be expressed by the following equation 1.

 B X O. l X k / L = X Equation 1

 Is

 Here, k is a constant determined by the shape of the light guide plate, and 0.1 is the transmittance of the liquid crystal display panel.

 Here, the above equation 1 shows the measured values in the present embodiment, half the length of the light guide plate unit L = 15 mm, the brightness of the light source B = 40, OOOnt, and the brightness X on the surface of the liquid crystal display panel. = 1,000

 Is

 By substituting nt, the following equation 2 is obtained, and the constant k can be calculated.

 B X 0. l X k / L = 1000

 Is

 k = 10000 X L / B

 Is

 k = 3.75 Equation 2

From the above equation 2, the light guide plate unit in the present embodiment, that is, the light exit surface and the one A thick portion parallel to the side and located substantially at the center of the light emitting surface; a thin end portion formed parallel to the thick portion; and a light source formed substantially at the center of the thick portion parallel to the one side. And the thin ends on both sides in a direction perpendicular to one side, symmetrical with respect to the plane perpendicular to the light exit surface, including the axis of the light source on both sides of the parallel groove. In the transparent light guide plate unit of the present invention, the thickness of which becomes thinner in response to the force and the inclined back surface portion forming the inclined back surface, the constant k = 3.75.

Here, from Equations 1 and 2, the relationship among the half length L of the light guide plate unit of the light guide plate unit of the present invention, the brightness B of the light source, and the surface brightness X of the liquid crystal display panel is expressed by the following equation. Express as 3

 Is

 Can do.

 B X O. 1 X 3.75 / L = X Equation 3

 Is

 Here, the liquid crystal display device can be visually recognized without any problem under a general environment (illuminance: 100 to 200 [lx]) by setting the surface luminance of the liquid crystal display panel to 50 nt or more.

 The light guide plate of the present invention can make the surface luminance of the liquid crystal display panel 50 nt or more by satisfying the following expression from the above expression 3.

 B X O. 1 X 3.75 / L≥50

 Is

 B / L≥133

 Is

 Thus, the relationship between the half length L of the light guide plate unit and the brightness B of the light source is B / L≥13.

 Is Is

 By satisfying 3, the surface luminance of the liquid crystal display panel becomes 50 nt or more, and the liquid crystal display device can be suitably used in a general environment (illuminance 100 to 200 [lx]).

In the present embodiment, when the maximum thickness D of the maximum light source 12 is 0 mm <D ≦ 5 mm, the shape of the curved reflector is changed to a straight line passing through the central axis of the light source 12 and perpendicular to the light emitting surface. When the distance A (hereinafter simply referred to as distance A) between the point that intersects the lower surface of the curved surface and the curved reflector 32 is 0.7 mm, and the maximum thickness D is 5 mm and D, D = 5 mm In this case, the curved reflector has the same arc shape as the curved reflector. However, the present invention is not limited to this, and the distance A between the surface of the light source 12 and the curved reflector 32 can be various sizes.

Hereinafter, the dependence of the relationship between the maximum thickness D of the light guide plate and the emission efficiency of the light guide plate unit on the distance A between the surface of the light source 12 and the curved reflector was measured by simulation. This will be described together with the measured results.

 In the simulation, in addition to the curved reflector with the distance A = 0.7 mm shown in Fig. 6, measurements were taken with the distance A being 0.5 mm and lmm.

 When the distance A = 0.5 mm, the curved reflector should have an arc shape with the distance A of 0.5 mm when the maximum thickness D of the light guide plate unit is Omm <D ≤ 5 mm. When the thickness D is 5 mm <D, the curved reflector has the same arc shape as the curved reflector when D = 5 mm. Similarly, when the distance A = l, when Omm <D ≤ 5 mm, the arc is such that the distance A is lmm, and when the maximum thickness D of the light guide plate unit is 5 mm <D, when D = 5 mm Of the same arc shape as the curved surface reflector.

 Here, the simulation is similar to the case where the simulation is performed on the dependence of the emission efficiency of the light guide plate unit on the diameter R of the light source and the maximum thickness D of the light guide plate unit, except that the distance A is different. Made by the way. FIG. 10 shows the measurement results obtained by the simulation in this manner. For comparison, Fig. 11 also shows the measurement results when the reflector shown in Fig. 6 is a plane reflector and when the reflector is a curved reflector with a distance A = 0.7.

 From the graph of FIG. 11, the emission efficiency is 80% or more when 2 ≦ D, as in the graph of FIG. 6, regardless of the distance A between the surface of the light source and the curved reflector.

 From the above, it can be seen that the emission efficiency can be increased by setting the maximum thickness D of the light guide plate unit to 0.6R≤D regardless of the distance A between the surface of the light source and the curved reflector. As described above, the shape of the curved surface reflector is not limited to the above-described embodiment, and various shapes of the curved surface reflector can be used.

Further, in the present embodiment, the inclined surface of the light guide plate unit has a planar shape, but the present invention is not limited to this, and may have a curved shape.

FIG. 12 shows an example of a light guide plate unit having a curved inclined surface. Here, the light guide plate unit 40 shown in the figure has the same shape and configuration as the light guide plate unit 18 shown in FIGS. 1A to 3 except for the shape of the inclined surface 40d of the light guide plate unit 40 and the shape of the reflection film 42. is there. Therefore, the same components are denoted by the same reference numerals and the detailed description thereof is omitted, and the following description focuses on the features unique to the light guide plate unit 40. The inclined surface 40d of the light guide plate unit 40 shown in the figure has a curved surface shape that is convex on the emission surface side (upper side in the figure). The inclined surface 40d also gradually decreases in thickness toward the thin end, and the thin end has the smallest thickness, and the junction with the inclined surface of the adjacent light guide plate unit is smooth. It has a curved surface shape whose inclination becomes parallel to the light emitting surface as it goes to the thin end side so as to be joined.

 Further, the reflection film 42 has a curved surface shape that is convex on the emission surface side along the shape of the inclined surface 40d. Here, the reflective film 42 and the inclined surface 40d are arranged substantially parallel to each other with a predetermined space therebetween.

 In the light guide plate of the present invention, even if the inclined surface 40d of the light guide plate unit 40 has a curved shape, the maximum thickness D and half length L of the light guide plate unit with respect to the size R of the light source are 0.6R≤D. , And 1.6R≤L can increase the output efficiency of the light guide plate unit

Here, the measurement results of the dependence of the emission efficiency of the light guide plate unit on the maximum thickness D of the light guide plate of the light guide plate unit 40 when the inclined surface of the light guide plate unit is formed into a curved shape are measured by simulation. It will be explained together.

 In the simulation, the light output efficiency of the light guide plate unit with respect to the diameter R of the light source and the maximum thickness D of the light guide plate unit is different except that the shape of the inclined surface 40d of the light guide plate unit 40 and the shape of the reflection film 42 are different. The same method was used as in the case of simulation for the dependence of. The measurement by simulation was performed for the case where the reflector was a plane reflector and the case where the reflector was a curved surface reflector. Fig. 13 shows the measurement results obtained by simulation in this way. For comparison, FIG. 13 also shows the measurement results obtained by using the light guide plate unit having a flat inclined surface shown in FIG.

 As shown in the graph of FIG. 13, even when the inclined surface of the light guide plate unit has a curved surface shape, as in the graph of FIG. 6, the emission efficiency is 80% or more when 2 ≦ D.

 As described above, even when the inclined surface of the light guide plate unit has a curved shape, the emission efficiency can be increased by setting the maximum thickness D of the light guide plate unit to 0.6R≤D with respect to the diameter R of the light source. .

Next, the light guide plate unit 40 in the case where the inclined surface of the light guide plate unit has a curved surface The dependence of the emission efficiency of the light guide plate unit on the half length L of the plate will be described together with the measurement results measured by simulation.

 In the simulation, except for the shape of the inclined surface 40d of the light guide plate unit 40 and the shape of the reflection film 42, the emission of the light guide plate unit with respect to the diameter R of the light source and the half length L of the light guide plate unit described above. We performed the same method as in the case of simulation for efficiency dependence. FIG. 14 shows the measurement results obtained by the simulation in this manner. For comparison, FIG. 14 also shows the measurement results obtained by using the light guide plate unit having the flat inclined surface shown in FIG.

 As shown in the graph of FIG. 14, even when the inclined surface of the light guide plate unit has a curved surface shape, as in the graph of FIG. 8, the emission efficiency is 80% or more when 5 ≦ L.

 Even when the inclined surface of the light guide plate unit has a curved shape, the emission efficiency can be increased by setting the maximum thickness L of the light guide plate unit to the diameter R of the light source to 1.6R≤L.

 According to the graphs of FIGS. 13 and 14, even when the inclined surface has a curved shape, the maximum thickness D and half the length L of the light guide plate unit with respect to the diameter of the light source are 0.6R≤D and 1 It is understood that the output efficiency can be increased by setting 6 R≤L.

 1A and 1B, the parallel groove 18f of the light guide plate unit 18 has a triangular cross-sectional shape (hereinafter, simply referred to as a cross-sectional shape of the parallel groove) perpendicular to the length direction of the parallel groove 18f. It is formed as follows. Here, the cross-sectional shape of the parallel groove 18f is triangular.The cross-sectional shape of the parallel groove 18f passes through the deepest part or the center of the parallel groove 18f to the center line of the light guide plate unit 18 perpendicular to the light exit surface. Any shape that is symmetrical with respect to the light emitting surface 18a and narrows toward the light exit surface 18a may be used. For example, as shown in FIGS. 15 and 16, a hyperbolic shape or an elliptical shape can be used. Alternatively, the cross-sectional shape of the parallel groove 18f of the light guide plate unit 18 may be a catenary line.

 Here, the dependence of the emission efficiency of the light guide plate unit on the maximum thickness D of the light guide plate unit when the cross-sectional shape of the parallel groove of the light guide plate was changed to various shapes was measured by simulation. This will be described with the measurement results.

In the simulation, as examples of the light guide plate unit according to the present embodiment, the case where the cross-sectional shape of the parallel groove 18f is triangular and hyperbolic as shown in FIGS. As examples of the light guide plate used from, measurements were made for a case where the cross-sectional shape was parabolic and semicircular (kamaboko shape).

 Here, the measurement method was performed in the same manner as in the case of simulating the dependence of the emission efficiency of the light guide plate unit on the diameter R of the light source and the maximum thickness D of the light guide plate unit. FIG. 17 shows the measurement results thus measured.

 As shown in the graph of FIG. 17, as with the graph of FIG. 6, when 2 ≦ D, the emission efficiency becomes 80% or more, regardless of the shape of the parallel groove.

 From the above, it can be seen that, with any of the parallel groove shapes, the emission efficiency can be increased by setting the maximum thickness D of the light guide plate unit to the diameter of the light source to satisfy 0.6R≤D. .

 Next, the dependence of the emission efficiency of the light guide plate unit on the half length L of the light guide plate unit when the cross-sectional shape of the parallel groove of the light guide plate was changed to various shapes was measured by simulation. This will be described together with the measured results.

 Similar to the above, in the simulation, as an example of the light guide plate unit according to the present embodiment, a case where the cross-sectional shape of the parallel groove 18f is triangular and hyperbolic as shown in FIGS. As an example of the light plate, the measurement was performed when the cross-sectional shape was parabolic or semicircular (kamaboko shape).

 The measurement was performed in the same manner as in the case of simulating the dependence of the emission efficiency of the light guide plate unit on the diameter R of the light source and half the length L of the light guide plate unit. FIG. 18 shows the measurement results thus measured.

 As shown in the graph of FIG. 18, in any of the shapes of the parallel grooves, the emission efficiency is 80% or more when 5 ≤ L, as in the graph of FIG.

 As described above, regardless of the light guide plate unit having any parallel groove shape, the emission efficiency can be increased by setting the half length L of the light guide plate unit to the diameter of the light source to 1.6R≤L. I can help you.

 As described above, in the light guide plate of the present invention, the shape of the parallel groove is not particularly limited, and may be parallel grooves having various shapes.

Further, the sectional shape of the parallel groove 18f is guided through the deepest portion or the center of the parallel groove 18f. The light plate unit 18 has a shape that is symmetrical with respect to a center line perpendicular to the light exit surface, and has a shape that becomes thinner toward the light exit surface 18a. Uniform light can be emitted from the surface.

Further, the cross-sectional shape of the parallel groove may be such that the deepest portion of the parallel groove (the connection portion of the side wall forming the parallel groove) has a cusp. In other words, two curved lines or symmetrical with respect to a center line perpendicular to the light exit surface of the light guide plate passing through the center of the parallel groove and having one sharp point of intersection where the cross-sectional shape of the leading end of the parallel groove crosses each other. It can be formed from a part of a straight line. In the present invention, even when the cross-sectional shape of the parallel groove of the light guide plate unit is any of the above shapes, light with a uniform light exit surface force of the light guide plate unit can be emitted.

 In FIG. 19, the cross-sectional shape of the front end portion of the parallel groove is opposite to the center line perpendicular to the light exit surface of the light guide plate unit passing through the center of the parallel groove 18f and having one sharp point of intersection. An example of the case where the partial force of two symmetric curves is also shown. The light guide plate unit 50 shown in FIG. 19 is a case where two curves 54a and 54b symmetrical with respect to a center line X passing through the center of the parallel groove and perpendicular to the light exit surface 52 of the light guide plate unit 50 are arcs. is there. In this case, as shown in FIG. 19, the center position of the arc 54a corresponding to one side wall forming the parallel groove 18f is different from the center position of the arc 54b corresponding to the other side wall. You. As a result, the portion 56 where the arc-shaped both side walls intersect has a pointed shape as shown in FIG.

 Further, FIG. 20 shows that the cross-sectional shape force of the front end portion of the parallel groove has a sharp point of intersection with one another, and passes through the center of the parallel groove to the center line perpendicular to the light exit surface of the light guide plate unit. Yet another example is shown, in which the partial force of two symmetric curves is also obtained. In the light guide plate 60 shown in FIG. 20, two curves 64a and 64b symmetric with respect to a center line X passing through the center of the parallel groove 18f and perpendicular to the light exit surface of the light guide plate unit are parabolic. In FIG. 20, the side wall of the parallel groove 18f is formed such that the focus of the parabola 64a corresponding to one side wall of the parallel groove 18f is different from the focus of the parabola 64b corresponding to the other side wall. .

As shown in FIG. 20, when the cross-sectional shape of the tip portion of the parallel groove is formed by two curves 64a and 64b intersecting at the intersection 66, a curve 64a corresponding to one side wall of the parallel groove 18f Intersection of the tangent at the intersection (cusp) 66 and the curve 64b corresponding to the other side wall The angle 66 between the tangents at 66 is preferably 90 degrees or less, more preferably 60 degrees or less.

 In FIGS. 1A to 20, in the cross-sectional shape of the parallel groove, the curve forming the side wall of the parallel groove shows the example of the light guide plate unit concave toward the center of the parallel groove. Another embodiment of the light guide plate unit of the present invention is shown in FIGS. FIG. 21 shows an example of the light guide plate unit 70 in which the cross-sectional shape of the parallel groove 18f is also formed with two curves 72a and 72b that are convex toward the center of the parallel groove 18f. FIG. 22 is a cross-sectional view of the parallel groove 18f. The shape is an example of a light guide plate unit 80 in which a curved force formed by combining convex curves 82a and 82b and concave curves 84a and 84b toward the center of the parallel groove 18f is also formed. The light guide plate units 70 and 80 having parallel grooves having cross-sectional shapes as shown in FIGS. 21 and 22 can also emit light with sufficient light emission surface power while suppressing the generation of bright lines.

 As described above, in the present invention, in the cross-sectional shape of the parallel groove of the light guide plate unit, the portion corresponding to the parallel groove is convex or concave toward the center of the parallel groove. , Or a combination thereof. These curves are not limited to the arcs in the illustrated example, and may be any part of a curve such as an ellipse, a parabola, or a hyperbola that is convex or concave toward the center of the parallel groove. Further, in the present invention, if the cross-sectional shape of the front end of the parallel groove is tapered as described later, the curve constituting the parallel groove has a convex or concave circle toward the center of the parallel groove. If it is a part of a curved line such as an ellipse, a parabola, or a hyperbola, the curve is preferably a curve that can be approximated by a 10th order function.

 Next, when the cross-sectional shape of the parallel groove of the light guide plate was changed to various shapes, the light exit surface force of the light guide plate unit was examined for the illuminance distribution of the emitted light. First, as an example of the light guide plate unit according to the present invention, the parallel groove 18f has a triangular or hyperbolic cross-sectional shape as shown in FIGS. 1 and 15, respectively, and a conventional light guide plate has a parabolic or semi-circular cross-sectional shape. The shape (kamaboko shape) was examined. FIG. 24 shows the relative illuminance distribution on the light exit side surface of the light guide plate units. In FIG. 24, the vertical axis indicates the relative illuminance, and the horizontal axis indicates the distance from the center of the light guide plate (the center of the parallel groove). Here, the relative illuminance was measured as follows.

A light source is incorporated into the light guide plate of the present invention, and light enters the light guide plate and light is emitted from the light exit surface. In the state where the light is emitted, fix the illuminometer to the XY stage, and fix the illuminometer so that it is perpendicular to the emission surface of the light guide plate unit. Then, the illuminance is measured at the position of the light exit surface by the illuminometer to obtain information of the illuminance regarding the specific position of the light exit surface of the light guide plate.

 Then, by moving the XY stage, the relationship between the position on the light emitting surface and the illuminance is determined, and the average value of the entire surface is calculated. The ratio of the illuminance at each position divided by the average value of the illuminance, respectively, is the relative illuminance at that position.

 In addition, by measuring one axis perpendicular to the axial direction of the parallel groove and representing the value, it is possible to easily compare the cross-sectional shapes.

 When measuring the relative luminance, a luminance meter may be used instead of the illuminometer, whereby the relative luminance distribution on the light emission side surface of the light guide plate can be obtained.

 As can be seen from FIG. 24, when the cross-sectional shape of the parallel groove of the light guide plate is made hyperbolic, the peak value of relative illuminance at a portion corresponding to the parallel groove depends on the output light of the inclined back surface force. Therefore, the illuminance of the light emitting surface is almost uniform. On the other hand, in a conventional light guide plate having a semicircular or parabolic cross-sectional shape, the relative illuminance is high at the center of the parallel groove, that is, at a position immediately above the light source, as shown in FIG. It can be seen that a bright line is generated. That is, in a conventional light guide plate having a parallel groove having a semicircular or parabolic cross section, the illuminance on the light irradiation surface is not uniform.

 [0081] In a light guide plate in which the cross-sectional shape of the parallel groove is triangular, the relative illuminance at the center is low. When the cross-sectional shape of such a parallel groove is triangular, as shown below, the force for flattening the apex with a predetermined width and the illuminance on the light exit surface are obtained by forming the curved surface with a relatively small radius of curvature. Can be made uniform.

FIG. 25 shows that, when the cross-sectional shape of the parallel groove of the light guide plate unit is triangular, the deepest portion of the parallel groove (apex portion of the triangular parallel groove) is flattened, and the length of the flat portion is varied. This shows the illuminance distribution of the emitted light when the light exit surface force of the light guide plate unit is changed. In FIG. 25, the vertical axis indicates relative illuminance, and the horizontal axis indicates the distance of the central force of the parallel groove formed in the light guide plate unit. Here, in order to simplify the calculation, the diameter of the cold-cathode tube is 3 mm, and the length of the flat part is 1.5 mm, 1. Omm, 0.5 mm, 0.25 mm. It was. Figures 26A to 26D show that when the cross-sectional shape of the parallel groove is triangular, the depth of the flat part at the deepest part of the parallel groove is 1.5 mm, 1.0 mm, 0.5 mm, and 0.25 mm. Schematic sectional views are shown.

 [0083] As shown in the graph of Fig. 25, it can be seen that the relative illuminance at a portion corresponding to the parallel groove of the light guide plate unit changes according to the length of the flat portion. Here, in the present invention, the illuminance can be increased by lengthening the flat end portion at the deepest portion of the parallel groove.However, if the length is too long, the flat end portion may become a bright line. The diameter is preferably 20% or less of the diameter of the tube, more preferably 10% or less.

 FIG. 27 shows that, in a light guide plate unit in which the cross-sectional shape of the parallel groove of the light guide plate unit is triangular, the shape of the deepest portion of the parallel groove is a curved surface with a radius of curvature R, and the radius of curvature of the curved surface is The illuminance distribution of light emitted from the light guide surface unit of the light guide plate unit when various values were changed is shown. Here, the radius of the cold-cathode tube was 3 mm, and the curvature radius at the apex was 0.25 mm, 0.5 mm, 1.0 mm, and 1.5 mm. FIGS.28A to 28D show schematic cross-sectional views of light guide plate units having vertices of curvature radii of 1.5 mm, 1.0 mm, 0.5 mm, and 0.25 mm when the cross-sectional shape of the parallel groove is triangular. Indicated. From the graph in Fig. 27, the relative illuminance at the portion corresponding to the parallel groove of the light guide plate unit changes according to the radius of curvature of the vertex of the parallel groove, and the light guide plate has a radius of curvature R of 0.25 mm at the vertex. It can be seen that the relative illuminance on the light exit surface of the unit is substantially uniform.

 From the above, it can be seen that the shape of the tip of the parallel groove of the light guide plate unit largely depends on the illuminance of the light exit surface force. In other words, it can be understood that the illuminance on the light exit surface of the light guide plate unit can be optimally adjusted and made uniform only by designing the shape of the parallel grooves of the light guide plate unit to have the shape shown in the present invention. .

On the surface of the light guide plate unit, the illuminance and the luminance can be handled in substantially the same manner. Therefore, from the graphs of relative illuminance in FIGS. 25 and 27, it is inferred that the present invention has the same tendency in luminance. Therefore, by designing the shape of the parallel groove of the light guide plate unit to be the shape shown in the present invention, it is considered that the brightness on the light exit surface of the light guide plate unit can be made uniform. The cross-sectional shape of the top part (deepest part) of the tip of the parallel groove is only flat or chamfered at one intersection that is sharply symmetrical with respect to the center line of the parallel groove. Of course, the shape may be elliptical, parabolic, or hyperbolic. In addition, as described above, the peak (the deepest portion) of the tip of the parallel groove may be a sand rubbing surface to reduce the illuminance or luminance peak value.

 [0086] As described above, in the first embodiment of the light guide plate unit of the present invention, other than the parallel groove 18f in the light exit surface 18a of the light guide plate unit 18 shown in Fig. 1, that is, a portion corresponding to the inclined back surface 18d. The peak value of the bright line formed in the portion (first portion) corresponding to the parallel groove 18f in the light exit surface 18a of the light guide plate unit 18 with respect to the average value of the illuminance formed in the (second portion) (peak of illuminance) Of the parallel groove 18f of the light guide plate unit 18 according to the ratio of the light guide plate unit 18, i.e., the taper of the tip shape of the parallel groove 18f of the light guide plate unit 18 according to the value of this ratio. Is preferably controlled. In this case, as in the case of a second embodiment described later, this ratio is preferably 3 or less, more preferably 2 or less.

 Note that this ratio depends on the thickness of the knock light unit 2 (the distance between the light exit surface 18a of the light guide plate unit 18 and the diffusion sheet 14) and the diffusion sheet 14 used in the knock light unit 2. It is preferable to set according to the diffusion efficiency and the number of sheets, the diffusion efficiency of the prism sheets 16, 17 and 19, the number of sheets to be used, and the like. That is, when the thickness of the knock light unit 2 (the distance between the light exit surface 18a of the light guide plate 18 and the diffusion sheet 14) can be increased (or increased) to some extent, or when the knock light unit 2 is used. If the diffusion efficiency of the diffusion sheet 14 is high and the number of used sheets can be increased, or if the diffusion efficiency of the prism sheets 16, 17 and 19 can be increased, the light exit surface 18a of the light guide plate unit 18 can be increased. Although it is possible to sufficiently diffuse (mixing, etc.) the illumination light emitted from the light guide plate, the cost is high, but the light guide plate with respect to the average value of the illuminance of the second portion of the light exit surface 18a of the light guide plate unit 18 The ratio of the peak value of the illuminance of the first portion of the light exit surface 18a of the unit 18 can be set to be somewhat large. However, if this is not the case, it is necessary to set the value of this ratio to a low value to reduce the cost.

On the other hand, in the second embodiment of the light guide plate of the present invention, the light exit surface 18 of the light guide plate unit 18 The light guide plate such that the peak value of the illuminance of the first portion of the light guide plate unit is three times or less, more preferably twice or less, the average value of the illuminance of the second portion of the light exit surface 18a of the light guide plate unit 18. It is preferable to taper the tip shape of the parallel groove 18f of the unit 18. Here, the peak value of the illuminance of the first portion of the light exit surface 18a of the light guide plate unit 18 is set to be not more than three times the average value of the illuminance of the second portion of the light exit surface 18a of the light guide plate unit 18. This is because the illuminance distribution of the illumination light emitted from the light exit surface 18a of the light guide plate unit 18 is made more uniform than before, and as a result, the illumination light emitted from the light exit surface 18a of the light guide plate unit 18 It is possible to use a low-cost diffusion sheet 14 that does not need to perform diffusion (mixing, etc.) so much, and that does not have high diffusion efficiency. The ability to stop using 16, 17, and 19 themselves, or to enable the use of low-cost prism sheets 16, 17, and 19 with low diffusion efficiency, and to reduce the number of sheets used is there.

 In the light guide plate according to the first embodiment of the present invention, in the cross-sectional shape of the parallel groove 18f of the light guide plate unit 18, the tip portion of the tapered parallel groove 18f has the central force of the rod-shaped light source 12 that emits light. Direction force on surface 18a Angular force with respect to perpendicular (X) Both sides are preferably within 90 degrees, more preferably within 60 degrees. That is, in the present invention, in order to reduce the peak value of the illuminance of the first portion corresponding to the parallel groove 18f of the light exit surface 18a of the light guide plate unit 18, the portion where the parallel groove 18f is tapered is the parallel groove. The entire 18f may be used, but if the peak value can be reduced, it is good at a predetermined leading end.

 [0090] The parallel grooves of the light guide plate unit of the light guide plate of the present invention are not limited to the above shapes, and may be various shapes such as a square shape, a U shape, and the like. As described above, the parallel groove of the light guide plate of the present invention should have the above-described shape in order to reduce the generation of bright lines and to make the luminance of the emission surface uniform, as described above. Preferred,.

In the light guide plate unit of the light guide plate of the present invention, as shown in FIG. 23, the density of halftone dots is high at a certain center line X and both sides (perpendicular to the center line) from the center line X. A halftone dot pattern 92 in which the density of halftone dots gradually decreases according to the direction of force may be formed on the light exit surface 18a of the light guide plate unit 18 by, for example, printing. The halftone dot pattern 92 is positioned at a position where the centerline X of the halftone dot pattern corresponds to the centerline of the parallel groove of the light guide plate unit 18. By forming them on the light exit surface 18a of the light guide plate unit 18 so as to coincide with the above, the generation and unevenness of bright lines on the light exit surface 18a of the light guide plate unit 18 can be suppressed. Instead of printing the halftone dot pattern 92 on the light guide plate unit 18, a thin sheet having the halftone dot pattern formed thereon may be laminated on the light exit surface. The shape of the halftone dot can be any shape such as a rectangle, a circle, and an ellipse, and the density of the halftone dot can be appropriately selected according to the intensity and spread of the bright line. Instead of forming such a dot pattern by printing, a portion corresponding to the dot pattern may be roughened as a sand rubbing surface. Such a sand rubbing surface may be formed on the deepest part or the side wall of the parallel groove of the light guide plate unit.

[0092] The light guide plate, the knock light unit including the light guide plate, and the liquid crystal display device according to the present invention have been described above in detail. However, the present invention is not limited to the above embodiments, and does not depart from the gist of the present invention. Of course, various improvements and changes may be made to the scope. Industrial applicability

[0093] The light guide plate of the present invention is thin and lightweight, and can enhance the light emission efficiency with respect to light emitted from a rod-shaped light source. The light guide plate of the present invention can be used for a light guide plate for a backlight used in a large-sized liquid crystal display device.

 Further, the spread illuminating apparatus of the present invention is thin and lightweight, can be manufactured at lower cost, and can emit the emitted light with a rod-like light source with high emission efficiency. Therefore, the planar lighting device of the present invention can be applied to a liquid crystal display device such as a large-screen liquid crystal monitor or a wall-mounted television.

 Further, the liquid crystal display device of the present invention is thin and lightweight, and can have a large-sized display screen. The liquid crystal display device of the present invention can be used for a large-screen liquid crystal monitor, a large-screen wall-mounted television, and the like.

Claims

Claims [1] A rectangular light exit surface, a thick portion parallel to one side thereof and located at a substantially central portion of the light exit surface, a thin end portion formed parallel to the thick portion, A parallel groove formed substantially in the center of the thick portion in parallel with the one side, for accommodating a rod-shaped light source; and a surface perpendicular to the light emitting surface, the axis including the rod-shaped light source on both sides of the parallel groove. The thickness of the transparent portion is reduced by a force directed to the thin end portions on both sides in a direction orthogonal to the one side, and the inclined rear portion forms an inclined rear surface. A plurality of light guide plate units, the thin end portions of adjacent light guide plate units are connected, the light emitting surfaces of the connected light guide plate units are arranged on the same plane, the diameter of the rod-shaped light source is R, Surface force passing through the center of the rod-shaped light source and perpendicular to the light exit surface Adjacent light guide plate A light guide plate characterized by satisfying the following expression, where L is the distance to the end face of the thin end portion, which is the joint portion with the socket, and D is the maximum thickness of the thick portion.

 1.6R≤L

 0.6R≤D

 2. The light guide plate according to claim 1, wherein the maximum thickness D of the thick portion satisfies the following expression.

 0.6R≤D≤3.3R

 [3] Further, assuming that the brightness of the light emitted from the light source is B (nt), the distance L (mm) and the brightness

 Is

 3. The light guide plate according to claim 1, wherein the relationship with the brightness B (nt) satisfies the following expression.

 Is

 B / L≥133

 Is

 [4] The light guide plate according to any one of claims 1 to 3,

 A rod-shaped light source housed in the parallel groove of the light guide plate;

A reflector provided behind the rod-shaped light source so as to close the parallel groove, and a reflection sheet attached to the inclined rear surface of the inclined rear portion on both sides of the thick portion of the light guide plate. Surface illumination device.

5. The spread illuminating apparatus according to claim 4, wherein a diffusion sheet is arranged on the light exit surface of the light guide plate.

6. The planar illumination device according to claim 4, wherein the reflector has a curved surface shape that is convex in a direction away from the light exit surface.

7. The spread illuminating apparatus according to claim 4, further comprising a prism sheet disposed between the light exit surface of the light guide plate and the diffusion sheet.

[8] The backlight unit according to any one of claims 4 to 7, which also has the power of the planar lighting device, a liquid crystal display panel arranged on a light emission surface side of the backlight unit, the backlight unit and the liquid crystal. A liquid crystal display device comprising: a driving unit for driving a display panel.