JP2005038747A - Surface light source element and display device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source element capable of providing uniformity of luminance while realizing miniaturization and cost reduction; and to provide a display device using it. <P>SOLUTION: Since a light source 1 is installed at least in one corner part 3 of a plate-like light guide body 2, light of the light source can efficiently be diffused throughout the entire light guide body by diffusing it from the corner part; and, since the light from the light source is diffracted to the peripheral part of the light guide body through reflection type or transmission type diffraction gratings 4 and 4A, uniformity of luminance can be provided. Since the light source is installed in the corner part of the light guide body, this surface light source can be miniaturized without projecting sideward by a light source disposed on an end face of the light guide body like a conventional one. In addition, since the diffraction gratings are installed only in a part in the vicinity of the corner part instead of a whole part of the light guide body, cost can be reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface light source element used for a mobile phone, a personal digital assistant (PDA), and the like, and a direct-view display device using the same.

  A display device used for a cellular phone or the like includes a surface light source element (backlight) that emits light in a planar shape and a display panel that provides information, and the light transmittance is controlled by the information provided by the display panel. Characters and images are displayed. As the backlight, a combination of a light source such as a fluorescent tube and a light guide is used.

  In recent years, a small display device often uses a light emitting diode (LED) as a light source for power saving. The light emitting area of the LED is small and is almost a point light source, and the brightness of the emitted light is also high in the front direction. For this reason, as shown in FIG. 2C, for example, in a surface light source element in which a point light source is placed at the center of the end face of the light guide, the light guide is used with respect to the bright region 31 at the center of the light guide that illuminates the display panel. There is a problem that the peripheral portion becomes a dark region 32 darker than this, and luminance uniformity cannot be obtained. In addition, since the light source is disposed on the end face of the light guide, there is a problem that it cannot be reduced in size by projecting sideways.

In addition, in order to obtain luminance uniformity, a proposal has been made to use a surface light source element by converting a point light source into a line light source. As a conventional example, a surface light source element in which a plurality of point light sources are provided on the end face of a light guide and a diffraction grating is provided on the entire surface of the light guide is known (for example, Patent Document 1).
Japanese Patent No. 2986733

  However, in this conventional example, since different diffraction gratings are provided on the front and back surfaces of the light guide and used in combination, the configuration becomes complicated and the cost cannot be reduced, and a point light source is provided on the end face of the light guide. Therefore, it cannot be downsized.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a surface light source element capable of obtaining luminance uniformity while achieving downsizing and cost reduction and a display device using the same. .

  In order to achieve the above object, a surface light source element according to one configuration of the present invention includes a light source that generates light and a plate-shaped light guide that emits light in a planar shape when light from the light source is incident thereon. The light source is disposed in at least one corner portion of the light guide, and the light guide body receives light from the corner portion and has an exit surface in the vicinity of the corner portion. A reflection type diffraction grating is provided in part.

  A surface light source element according to another configuration of the present invention is a surface light source element that includes a light source that generates light and a plate-shaped light guide that emits light in a planar shape when light from the light source is incident thereon. The light source is disposed at at least one corner portion of the light guide, and the light guide is incident with light from the corner portion, and light is incident on a part of the interior near the corner portion. A transmission type diffraction grating orthogonal to the direction is provided.

  According to this configuration, since the light source is provided at one corner (corner) of the plate-like light guide such as a flat rectangular parallelepiped, the light is diffused from the corner to guide the light. Since the light can be efficiently diffused over the entire body and the light from the light source is diffracted to the periphery of the light guide through the reflective or transmissive diffraction grating, luminance uniformity can be obtained. In addition, since the light source is provided at the corner portion of the light guide, it is possible to reduce the size without projecting to the side by the light source disposed on the end face of the light guide as in the prior art. Further, since the diffraction grating is provided not only on the entire light guide but only on a part near the corner, the cost can be reduced.

  Preferably, the diffraction grating is wider than the light source. Therefore, more light is diffracted to the peripheral part through the wide part of the diffraction grating, so that more uniform brightness can be obtained.

  Preferably, the light source is a point light source, a corner portion of the corner portion of the light guide is cut, and the point light source is disposed in the corner cut portion. Therefore, since the point light source is accommodated in the corner cut portion, the size can be further reduced.

  Preferably, a texture or lens pattern may be formed on the back surface of the light guide. Moreover, you may have the output light control board which a some convex part is formed in the output surface of a light guide, and a convex part top part closely_contact | adheres to the light guide surface. Thereby, the luminance can be improved. Further, it is desirable that the point light source is an LED for miniaturization.

  Preferably, by combining the surface light source element and a transmissive display element such as an LCD, a compact display device capable of emitting light on both sides can be obtained.

  According to the present invention, it is possible to obtain a surface light source element with uniform luminance and a display device using the same while achieving downsizing and cost reduction.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration diagram of a surface light source element according to a first embodiment of the present invention. This surface light source element is used for a small display device, and includes a light source 1 that generates light, a plate-shaped light guide 2 that emits light in a planar shape when light from the light source 1 is incident thereon, and It has. The light source 1 is a point light source such as a light emitting diode (LED), and the light guide 2 is a flat rectangular parallelepiped, for example.

  The light source 1 is disposed at, for example, one corner portion 3 of the light guide 2. In this light guide 2, light from the light source 1 is incident from the corner portion 3, and a reflection type diffraction grating 4 wider than the light source 1 is provided on a part of the exit surface in the vicinity of the corner portion 3. Yes.

  In the present invention, since the light source 1 is provided at one corner (corner) 3 of the light guide 2 made of a rectangular parallelepiped, the light of the light source 1 is diffused from the corner 3 as shown in FIG. By doing so, the light of the light source 1 can be efficiently diffused over the entire light guide 2. Thus, conventionally, unlike the case where the light source is disposed on the end face of the light guide as shown in FIG. 2C, the light guide entrance portions on both sides of the light source are the dark regions 32. In the present invention, FIG. As shown in a), the entire surface of the light guide 2 is a bright region 31.

  At the same time, in the present invention, since the reflection type diffraction grating 4 wider than the light source 1 is provided on a part of the exit surface in the vicinity of the corner portion 3, a well-known Bragg equation is used as shown in FIG. Accordingly, the light from the light source 1 is diffracted by the diffraction grating 4 not only to the central portion of the light guide but also to the peripheral portion of the light guide according to the order of reflection. Therefore, the presence of the diffracted light makes the luminance of the entire light guide uniform, and the luminance uniformity can be obtained at low cost. Moreover, since the diffraction grating 4 is wider than the light source 1, more light from the light source 1 is diffracted to the periphery of the light guide through the wide part of the diffraction grating 4, so that more uniform brightness can be obtained. . Here, the vicinity of the corner portion 3 refers to a region between the light guide end surface where the light source 1 is installed and the light emitting region.

  For example, as shown in FIG. 2B, when the light source 1 is provided at the corner portion 3 and the diffraction grating 4 is not provided at a part of the exit surface in the vicinity of the corner portion, the corner portion 3 is irradiated and guided. The light incident on the light body 2 has a high luminance in the normal direction of the light emitting surface of the light source 1 and has a low luminance in the oblique direction because there is little light propagating along the end surface direction of the light guide 2. The periphery of the light guide becomes darker than the dark region 32 with respect to the bright region 31 of the portion, and luminance uniformity cannot be obtained.

  Further, since the point light source 1 is provided at the corner portion 3 of the light guide 2, the surface light source element can be downsized without protruding sideways by the point light source disposed on the end face of the light guide as in the prior art. Is possible. In the display device using this surface light source element, the portion of the light exiting surface of the light guide 2 excluding the diffraction grating 4 faces a liquid crystal panel (not shown).

  In the present invention, for a surface light source element used in a small display device, the light source 1 is arranged at the corner portion 3 of the light guide 2 and the diffraction grating 4 is provided on a part of the exit surface in the vicinity of the corner portion 3. With this configuration, luminance uniformity can be obtained with a small size and low cost.

  In this embodiment, since the protruding part of the corner part 3 of the light guide 2 is cut and the point light source 1 is disposed in the corner cut part 3a, the point light source 1 is accommodated in the corner cut part 3a. The surface light source element can be further downsized.

  In this embodiment, as shown in FIG. 3, the reflection type diffraction grating 4 is a surface relief type one-dimensionally arranged with respect to the light incident direction of the light source 1. The top of the pattern of the diffraction grating 4 is in intimate contact with the light guide exit surface via an adhesive layer (not shown). An air layer 25 is formed between the patterns. Further, as shown in FIG. 4, the space between the patterns may be filled with an adhesive 26 having a refractive index different from that of the material forming the pattern. Note that the diffraction grating 4 may be arranged in a dot-like two-dimensional arrangement instead of a one-dimensional arrangement.

  As shown in FIG. 5, the light guide 2 can be caused to emit light by forming a textured portion 15 that has been subjected to a texture processing that generates scattered reflection on the back surface of the light guide 2. Thereby, the brightness | luminance of the light from an output surface can be improved.

  Moreover, as shown in FIG. 6, the lens pattern part 16 can be formed in the back surface of the light guide 2, and it can also be made to light-emit by controlling a propagation direction by refraction | bending and reflection. Thereby, the brightness | luminance of the light from an output surface can be improved.

  Further, as shown in FIG. 7, the emission light control plate 18 having a plurality of convex patterns is arranged so that the convex portion faces the light guide output surface, and light emission can be achieved by bringing the top of the convex portion into close contact with the light guide output surface. Can be made. By this convex part, the light from the exit surface of the light guide 2 can be directed in the front direction, and the luminance in the front direction can be improved. Further, when the top of the convex portion of the outgoing light control plate 18 is brought into close contact with the outgoing surface of the light guide 2, there is no gap between the outgoing light control plate 18 and the light guide 2 and the surface light source element can be miniaturized.

  FIG. 8 is a perspective view showing another example of the surface light source element according to the first embodiment. In this surface light source element, the light source 1 is disposed on both diagonals, and the diffraction grating 4 is disposed on a part of the emission surface in the vicinity of both corner portions 3. In this case, it is possible to obtain a surface light source element that is small in size and uniform in brightness and realizes higher brightness.

  FIG. 9 is a perspective view showing a surface light source element according to the second embodiment. In the second embodiment, instead of providing the reflection type diffraction grating 4 on a part of the exit surface in the vicinity of the corner portion 3 of the light guide 2 as in the first embodiment, the inner portion in the vicinity of the corner portion 3 is arranged. A transmission type diffraction grating 4A orthogonal to the incident direction of light is provided in the part. The diffraction grating 4 </ b> A may be provided on the incident surface of the light guide 2, or a slit may be provided near the corner portion 3 of the light guide 2 and disposed therein. Other configurations are the same as those of the first embodiment.

In this case, since the light from the light source 1 is diffracted not only by the central part of the light guide but also by the peripheral part of the light guide by the transmission type diffraction grating 4A, the presence of this diffracted light is the same as in the first embodiment. The brightness of the entire surface of the light guide becomes uniform, and brightness uniformity can be obtained at low cost.
As a result, the light source 1 is arranged at the corner 3 of the light guide 2 and the diffraction grating 4 is provided at a part of the inside in the vicinity of the corner 3 so that the surface is small, low-cost and uniform in luminance. A light source element is obtained.

  A small display device can be configured by using each surface light source element described above and providing a transmissive light modulation device such as a liquid crystal display (LCD) on the light emitting surface.

  In each of the above embodiments, the light guide is a rectangular parallelepiped, but may be a wedge shape, a triangular prism, or a polygonal prism that is a pentagonal prism or more.

(A) is a perspective view which shows the surface light source element concerning one Embodiment of this invention, (b) is a top view which shows the locus | trajectory of the light from the light source in a light guide. (A)-(c) is a top view which shows the area | region of the brightness in a light guide surface. It is a side view which shows one example of the diffraction grating of this invention. It is a side view which shows the other example of the diffraction grating of this invention. It is a perspective view which shows the other examples of the light guide of this invention. It is a perspective view which shows the other examples of the light guide of this invention. It is a perspective view which shows the other examples of the light guide of this invention. It is a perspective view which shows the surface light source element of the other example which concerns on 1st Embodiment of this invention. It is a perspective view which shows the surface light source element which concerns on 2nd Embodiment of this invention.

Explanation of symbols

1: Light source 2: Light guide 3: Corner portion 4, 4A: Diffraction grating 15: Textured portion 16: Lens pattern portion 18: Emission light control plate

Claims (9)

A surface light source element including a light source that generates light and a plate-shaped light guide that emits light in a planar shape when light from the light source is incident thereon,
The light source is disposed at at least one corner portion of the light guide, and the light guide body receives light from the corner portion, and a reflection type diffraction grating on a part of the exit surface in the vicinity of the corner portion. A surface light source element provided with A surface light source element including a light source that generates light and a plate-shaped light guide that emits light in a planar shape when light from the light source is incident thereon,
The light source is disposed at at least one corner portion of the light guide, and the light guide is made to receive light from the corner portion, and is orthogonal to the incident direction of light in a part of the interior near the corner portion. A surface light source element provided with a transmissive diffraction grating. The surface light source element according to claim 1, wherein the diffraction grating is wider than the light source. The surface light source element according to claim 1, wherein the light source is a point light source, a corner portion of a corner portion of the light guide is cut, and the point light source is disposed in the corner cut portion. The surface light source element according to claim 1, wherein the back surface of the light guide is subjected to a textured process. The surface light source element of Claim 1 or 2 with which the lens pattern is formed in the back surface of the said light guide. 3. The surface light source element according to claim 1, further comprising an output light control plate having a plurality of convex portions formed on the light exit surface of the light guide and having a convex portion top portion in close contact with the surface of the light guide. The surface light source element according to claim 1, wherein the light source is a light emitting diode (LED). A display device comprising a liquid crystal display (LCD) on a light emitting surface of the surface light source element according to claim 1.