JP2007087659A - Plane lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize plane lighting without color drift by preventing monochromatic light without white composition from being emitted from a light guide plate. <P>SOLUTION: Point light source arrays 141, 142 are structured by arraying light-emitting diodes 12 of different emission colors on printed wiring boards 131, 132, and the light-emitting diodes 12 are arranged in opposition on light-incident faces 151, 152 of the light guide plate 15. A crossing angle between a light emission face 153 and the light-incident faces 151, 152 of the light guide plate 15 is to be nearly 90°. Slanted parts 155, 156 are formed in a region in the vicinity of the light-incident faces 151, 152 of a rear face 154 opposing the light emission face 153, and a crossing angle between the slanted parts 155, 156 and the light-incident faces 151, 152 is to be 90° or more. Except for the slanted parts 155, 156 formed in a region in the vicinity of the light-incident faces of the rear face 154 of the light guide plate 15, a diffusion reflection part 17 with dots 17S, 17M, 17L distributed is provided, so that emission light without white composition is prevented from being emitted from the light guide plate 15 to realize plane lighting without color drift. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface illumination device that uses a point light source such as a light emitting diode and is mainly used as a backlight for liquid crystal.

  Currently, a backlight using a white light emitting diode as a light source is used in a liquid crystal display device such as a cellular phone. White light-emitting diodes are mainly composed of a combination of a blue light-emitting chip and a phosphor that emits yellow light when excited by the light. Such a type of white light emitting diode has a drawback that red reproducibility is poor when liquid crystal is displayed because the light emission intensity in the red region is relatively small.

  Therefore, the color reproducibility can be improved by using red (R), green (G), and blue (B) light emitting diodes and synthesizing the emitted light into white. It is necessary that the light is emitted from the light guide plate. In order to synthesize RGB light in white within the light guide plate, an illumination device having a light guide plate having a thickness that is minimized at the light incident end surface and maximized at the counter light incident end facing the light incident end surface is shown. Has been.

Even if the RGB light incident on the light guide plate having such a shape is reflected on the front and back surfaces of the light guide plate, it proceeds without reaching the critical emission angle, and is not incident on the way. It can reach the end face. Then, the light reflected by the anti-incident end face part returns to the incident end face part, but each time it is reflected by the front and back surfaces, it approaches the emission critical angle, and finally the light synthesized sufficiently white is It is explained that the light is emitted from the back surface. (For example, Patent Document 1)
JP 2004-38108 A

  Since the technique of Patent Document 1 described above has a structure in which the emission distribution is controlled by the polarizing elements on the front and back surfaces of the light guide plate, the RGB monochromatic light before being synthesized into white is actually emitted by the polarizing element, and on the light emitting surface. Color unevenness occurs.

  An object of the present invention is to provide a surface illumination device having high chromaticity uniformity by preventing monochromatic light having different emission colors not synthesized from being emitted from a light guide plate.

  In order to solve the above-described problems, a surface illumination device according to the present invention includes a point light source array in which point light sources of different emission colors are arranged in a straight line, and a light incident surface of light from the point light source array arranged in an opposing manner. The angle of intersection with the light emitting surface that emits light is approximately 90 °, an inclined portion is formed from the light incident surface on the back surface facing the light emitting surface to a predetermined distance, and the angle of intersection between the inclined portion and the light incident surface And a light guide plate having an angle of 90 ° or more.

  According to the present invention, in addition to the inclined portion formed in the vicinity of the light incident surface on the back surface, the diffused reflecting means distributed in a dot shape is provided on the light guide plate, so that the monochromatic light which is not synthesized in white is guided to the light guide plate. Surface illumination without color unevenness is realized without being emitted from the light source.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 and FIG. 2 are each for explaining a first embodiment of the surface illumination device of the present invention, FIG. 1 is an exploded perspective view, and FIG. 2 is a sectional view of the assembled state of FIG. .

  In FIG. 1, reference numeral 11 denotes a box-shaped case with one open surface. A plurality of light emitting diodes 12 are linearly arranged on the wiring boards 131 and 132 on the inner side surfaces 111 and 112 on the long side facing the case 11. Point light source arrays 141 and 142 arranged in a shape are attached. The point light source arrays 141 and 142 are obtained by periodically arranging light emitting diodes of different light emitting colors such as red, green, and blue on a wiring board, or by combining a plurality of light emitting diodes of different light emitting colors in one package. The wiring boards 131 and 132 are respectively arranged.

  A light guide plate 15 formed of a transparent resin such as methyl methacrylate (acrylic) or polycarbonate is disposed in front of the light emitting diode 12 on the radiation side. The light incident surfaces 151 and 152 of the light guide plate 15 and the radiation side of the light emitting diode 12 are arranged opposite to each other so that the light emitted from the light emitting diode 12 enters the light incident surfaces 151 and 152.

  As shown in FIGS. 3 and 4, the light guide plate 15 is a both-side light incident type, and the intersection angle θ <b> 1 between the light emitting surface 153 and the light incident surfaces 151 and 152 is approximately 90 °, respectively. In addition, inclined portions 155 and 156 are formed in the vicinity of the light incident surface portion of the back surface 154 facing the light emitting surface 153, and the intersection angles θ2 between the inclined portions 155 and 154 and the light incident surfaces 151 and 152 are set to 90 respectively. More than °.

  As shown in FIG. 3, the back surface 154 excluding the inclined portions 155 and 156 is provided with dots 17S, 17M, and 17L having diffuse reflection functions having different areas by white ink printing or the like in order to equalize the light emission balance. A diffuse reflection portion 17 is formed. The diffuse reflection portion 17 is arranged so that the area gradually increases as the distance from the light incident surfaces 151 and 152 increases.

  That is, the diffuse reflection regions S1 and S2 of the small dot 17S are formed at positions close to the input surfaces 151 and 152, respectively, and the dot 17S is formed in the region far from the diffuse reflection regions S1 and S2 from the input surfaces 151 and 152. The diffuse reflection areas M1 and M2 of the dots 17M having a larger area are respectively formed. Further, a diffuse reflection region L having the size of the dot 17L having the largest area is formed between the diffuse reflection regions M1 and M2.

  A reflective sheet 18 is disposed between the back surface 154 of the light guide plate 15 and the case. The reflection sheet 18 is bent and disposed up to the positions of the inclined portions 155 and 156 of the light guide plate 15. The reflection sheet 18 is for returning the light leaked from the back surface of the light guide plate 15 to the light emitting surface 153 side. Even if it has a diffusive property such as white PET, it is specularly reflected such as silver vapor deposition or dielectric multilayer film. It may have a property.

  Diffusion sheets 20 and 21 made of, for example, white PET (Polyethylene Terephthalate) or the like having a function of condensing and leveling in the horizontal and vertical directions are provided at positions facing the light emitting surface 153 of the light guide plate 15. Deploy. A frame 22 having a display window 221 is disposed on the diffusion sheet 21.

  Here, the vicinity of the light incident from the light emitting diode to the light incident surface of the light guide plate is enlarged and the operation of the light guide plate is described with reference to the cross-sectional view of FIG. 5 showing an example of the optical path of the light emitted from the light emitting diode. Will be described.

  The light emitted from the light emitting diode 12 is incident on the light incident surfaces 151 and 152 of the light guide plate 15. The light immediately after being incident on the light guide plate 15 is not formed with the diffuse reflection portion 17 in the inclined portions 155 and 156 near the light incident surface 151. The light is not emitted from the light emitting surface 151 and travels through the light guide plate 15.

  As described above, the monochromatic light that is not white-combined immediately after entering the light guide plate 15 is not emitted immediately from the light emitting surface 153, but is emitted by emitting light synthesized in white in the light guide plate 15. Generation of unevenness can be prevented. Part of the light that passes through the regions of the inclined portions 155 and 156 and is reflected by the diffuse reflection portion 17 returns to the light incident surfaces 151 and 152 side. When the return light is reflected by the inclined portions 155 and 156, it can enter the light emitting surface 153 at an angle smaller than the total reflection critical angle, so that it is also emitted from the light emitting surfaces in the inclined portions 155 and 156 regions. Can do.

  The light guide plate 15 is made of acrylic, the crossing angle θ2 between the light incident surfaces 151 and 152 and the inclined portions 155 and 156 is 120 °, and the return light b from the diffuse reflector 17 is substantially parallel to the light emitting surface 153 (in the drawing) Is approximately 10 °), the light enters the light emitting surface 153 at an incident angle θ3 of about 30 °. At this time, the total reflection critical angle of the acrylic material is 42 °, and the incident angle is smaller than the critical angle, so that the light c can be emitted from the light emitting surface 153. Since such outgoing light has already undergone white color synthesis in the light guide plate 15, color unevenness does not occur on the light emitting surface 153 near the light incident surfaces 151 and 152.

  In this embodiment, light from the light emitting diodes that emit different colors is emitted from the light emitting surface of the light guide plate in a state where white light is combined in the light guide plate, so that uneven color can be prevented and uniformity can be improved. be able to.

  FIG. 6 is a cross-sectional view of a light guide plate for explaining a second embodiment of the present invention. In this embodiment, the inclined portions 155 and 156 near the light incident surfaces 151 and 152 are provided with inclined portions 61 and 62 that once increase in thickness of the light guide plate 15 and become thinner again toward the center of the bottom surface 154 of the light guide plate 15. It is a thing.

  In this embodiment, not only monochromatic light that is not synthesized in the vicinity of the light incident surfaces 151 and 152 is not emitted from the light emitting surface of the light guide plate 15, but also the light incident from the light incident surface 151 reflects the inclined portion 61 to emit light. Since the light incident from the light incident surface 152 is reflected on the inclined portion 62 and is reliably emitted from the light emitting surface 153, surface illumination with the luminance of the entire light emitting surface 153 increased can be obtained.

  FIG. 7 is a cross-sectional view of a light guide plate for explaining a third embodiment of the present invention. In this embodiment, the light guide plate 15 of the first embodiment is replaced with a one-side light incident type.

  In this embodiment, even when the light incident surface is only on one side, it is possible to realize surface illumination in which monochromatic light that is not synthesized near the light incident surface 151 is not emitted from the light emitting surface 153 of the light guide plate 15.

  FIG. 8 is a cross-sectional view of a light guide plate for explaining a fourth embodiment of the present invention. This embodiment is an inclined back surface 1541 in which the back surface of the light guide plate 15 of the third embodiment is inclined.

  In this embodiment, monochromatic light that is not synthesized in the vicinity of the light incident surface 151 is not emitted from the light emitting surface 153 of the light guide plate 15, and in addition to the effect of the surface illumination of the embodiment of FIG. Since the light incident from the light surface 152 reflects the inclined back surface 1541 and is reliably emitted from the light emitting surface 153, the luminance of the entire light emitting surface 153 can be improved as compared with FIG.

  The present invention is not limited to the above-described embodiment. For example, instead of changing the size of the diffuse reflection unit 17 for each region, the density of the diffuse reflection unit having the same area may be changed for each region. In this case, the density is higher in the region farther from the light incident surface. Further, it may be arranged such that the area and density gradually increase as the distance from the light incident surface increases. In this case, it is possible to expect a further improvement in uniformity.

  Furthermore, although the shape of the inclined portion of the light guide plate in each of the above embodiments is a plane, the surface shape of the inclined portion may be a curved surface or a step shape.

Next, in addition to the technical idea described in the claims, the technical idea grasped by the above-described embodiment will be described below together with its effects.
(1) The angle of intersection between a point light source array in which point light sources of different emission colors are linearly arranged and a light incident surface from the point light source array arranged opposite to the light emitting surface for emitting light is approximately 90 °. A first inclined portion is formed from the light incident surface on the back surface facing the light emitting surface to a predetermined distance, and an intersection angle between the first inclined portion and the light incident surface is 90 ° or more, and And a light guide plate having a second inclined portion that becomes thinner again from the one inclined portion toward the back surface.

  In this technical idea, it is possible to prevent the point light source color from being emitted in the vicinity of the light incident surface, and it is possible to reflect more light on the light emitting surface side of the light guide plate at the second inclined portion. The luminance can be improved.

1 is an exploded perspective view for explaining a first embodiment of the present invention. Sectional drawing of the state by which FIG. 1 was assembled. The rear view of the principal part of FIG. The side view of FIG. FIG. 3 is a partially cutaway enlarged cross-sectional view for explaining the operation of FIG. 1. The side view for demonstrating 2nd Embodiment of this invention. A side view for explaining a 3rd embodiment of this invention. The side view for demonstrating 4th Embodiment of this invention.

Explanation of symbols

11 Case 12 Light emitting diode 131, 132 Wiring board 141, 142 Point light source array 15 Light guide plate 151, 152 Light incident surface 153 Light emitting surface 154 Back surface 155, 156, 61, 62 Inclined portion 17 Diffuse reflecting portion 17S, 17M, 17L Dot 18 Reflective sheet 19 Diffusion plate 20, 21 Diffusion sheet 22 Frame 221 Display window S1, S2, M1, M2, L Diffuse reflection area 1541 Inclined back surface

Claims (3)

A point light source array in which point light sources of different emission colors are linearly arranged;
The crossing angle between the light incident surface from the point light source array disposed opposite to the light emitting surface for emitting light is set to approximately 90 °, and the inclined portion extends from the light incident surface on the back surface facing the light emitting surface to a predetermined distance. And a light guide plate having an intersection angle between the inclined portion and the light incident surface of 90 ° or more.   2. The surface illumination device according to claim 1, wherein the light guide plate is provided with a diffuse reflection portion distributed in a dot shape in addition to the inclined portion formed in a region near the light incident surface on the back surface.   3. The surface illumination device according to claim 2, wherein the diffuse reflection portion has a larger area or a larger number of distributions as the position is farther from the light incident surface.

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