JP2008041520A - Light guide plate and planar illumination device - Google Patents

Abstract

Even when a point light source is used, occurrence of unevenness in light luminance on an exit surface near a light incident portion is reduced.
A reflection surface provided with a light scattering pattern; an emission surface facing the reflection surface and emitting light; and formed on a side portion connecting the edge of the reflection surface and the edge of the emission surface. An inclined surface 15 that forms an acute angle with the emission surface 11; and an incident surface 14 that is provided closer to the reflective surface 12 than the position where the inclined surface 15 is formed and is incident on the light source from the light source.
[Selection] Figure 1

Description

  The present invention relates to a planar (or thin plate) light guide plate having a reflection surface provided with a light scattering pattern, and a planar illumination device using the light guide plate.

  Conventionally, a surface illumination device has been studied on the assumption that a surface having a desired size is a unit of illumination. However, when light is incident on the light guide plate by using an LED as a light source to realize surface light emission, there is a problem that light brightness is uneven on the exit surface near the light incident portion. That is, since the LED is not a linear light source such as a fluorescent lamp but a point light source, the exit surface of the light guide plate becomes bright only in the vicinity of the portion where the LED is disposed. Moreover, in the part between LED arrange | positioned and LED, the output surface of a light-guide plate becomes dark.

Therefore, as a countermeasure against this, a surface light source device that gives a curvature to the shape of the light incident portion (light incident surface) is disclosed in Patent Document 1.
Japanese Patent Laid-Open No. 10-255530

  As shown in Patent Document 1, when the shape of the light incident portion (light incident surface) is not a flat shape but a curvature, a countermeasure is provided for the shape of the light incident portion (light incident surface) for each LED to be arranged. Was necessary.

  For example, when changing the type of LED, it is necessary to change the optimal arrangement pitch from the viewpoint of thermal design, and changing the arrangement pitch changes the shape of the light incident part (light incident surface), that is, the light guide plate. Changes are required. Since the light guide plate is usually manufactured by injection molding, there is a problem that a new mold needs to be manufactured with a change in the specification of the light guide plate, leading to an increase in cost. In addition, a space for providing a light source such as an LED needs to be provided outside the light guide plate. When a plurality of light guide plates are used side by side, a configuration like a frame that covers the light source is required.

  The present invention has been made in view of the problem of unevenness in light brightness on the exit surface near the light incident portion, particularly when a point light source such as an LED is used, and the object of the present invention is particularly the LED or the like. When a point light source is used, a light guide plate that can reduce the occurrence of unevenness in light intensity on the exit surface in the vicinity of the light incident portion and a planar illumination device using the same are provided.

  The light guide plate according to the present invention is formed on a reflection surface provided with a light scattering pattern; an emission surface facing the reflection surface and emitting light; and a side portion connecting the edge of the reflection surface and the edge of the emission surface. An inclined surface that forms an acute angle with the surface; and an incident surface that is provided closer to the reflective surface than the position where the inclined surface is formed and is incident with light from a light source.

  The light guide plate has a quadrilateral shape, particularly a square shape, on the exit surface side. The acute angle formed by the exit surface and the inclined surface is preferably around 45 degrees, and allows an angle that acts so that light is reflected toward the exit surface side inside the light guide plate where the inclined surface is formed. The light source allows a point light source such as an LED.

  The light guide plate according to the present invention is characterized in that the position of the inclined surface exists inside or outside the incident surface.

  A planar illumination device according to the present invention includes: the light guide plate according to claim 1; and a light source provided in the vicinity of the incident surface.

  The light guide plate according to the present invention is formed on a side portion connecting the edge of the reflection surface and the edge of the emission surface, and has an inclined surface that forms an acute angle with the emission surface, so that light incident from the light source is guided. Inside the optical plate, reflection occurs on the inclined surface, and this portion becomes bright, and luminance spots that have conventionally occurred on the periphery of the light guide plate are reduced.

  In the light guide plate according to the present invention, since the position of the inclined surface exists inside or outside the incident surface, the arrangement space of the light source is inclined particularly when the position of the inclined surface exists outside the incident surface. It occurs below the surface, which is advantageous when connecting a plurality of light guide plates. In addition, when the position of the inclined surface is on the inner side of the incident surface, the light incident from the incident surface does not go directly to the output surface on the upper side, and there is an effect that it is difficult to form luminance spots.

  Since the planar illuminating device according to the present invention includes the light guide plate according to claim 1 or 2, it is possible to provide a planar illuminating device in which luminance spots that have conventionally occurred on the periphery of the light guide plate are reduced.

  Embodiments of a light guide plate according to the present invention and embodiments of a planar lighting device using the same will be described below with reference to the accompanying drawings. In each figure, the same components are denoted by the same reference numerals, and redundant description is omitted.

<Example 1>
1 to 3 show a configuration diagram of a first embodiment of a light guide plate according to the present invention and an embodiment of a planar illumination device using the same. The shape of the light guide plate 10 viewed from the light exit surface 11 side from which light exits is a quadrilateral shape, and here, it is a square shape having a side of about 20 mm. The light guide plate 10 is made of, for example, an acrylic resin, and a light scattering pattern is provided on the reflection surface 12 that is a surface facing the emission surface 11 by forming a large number of fine holes 13 at a constant pitch, for example. The method of creating the light scattering pattern is not limited to this.

  A side surface from the reflecting surface 12 toward the emitting surface 11 side is an incident surface 14 formed so as to be orthogonal to the reflecting surface 12 and the emitting surface 11 (FIG. 2). An inclined surface 15 that forms an acute angle with the emission surface 11 is formed on the side portion that connects the edge of the reflection surface 12 and the edge of the emission surface 11. Although the inclined surface 15 is formed on all four sides of the light guide plate 10, it is formed on at least one side. In this embodiment, an inclined surface 15 is formed from the end portion of the incident surface 14 toward the edge of the exit surface 11, and the position of the inclined surface 15 exists outside the incident surface 14.

  The height H1 of the incident surface 14 is, for example, about 3 mm to 5 mm, and the height H2 of the portion where the inclined surface 15 is formed is, for example, about 3 mm to 4 mm. The portions of the height H1 and the height H2 can be made of an integral acrylic resin and can be cut to form the inclined surface 15. Alternatively, the height H1 and the height H2 may be created as separate plates, and the two plates may be bonded together. In this configuration, cutting may be performed to form the inclined surface 15, or the inclined surface 15 may be created in advance by injection molding.

  On the incident surface 14, a plurality of LEDs 21 are provided at a predetermined pitch for each side. In this example, a plurality of LEDs 21 are arranged on the left and right sides in FIG. In the light guide plate 10 of the present embodiment, the position of the inclined surface 15 exists outside the incident surface 14, and an arrangement space for the LEDs 21 is made. Since the LED 21 is arranged on the lower side of the inclined surface and inside the edge of the emission surface, when a plurality of light guide plates 10 are connected in a planar shape or a linear shape, a gap is generated in the connection portion. It is possible to create an integrated lighting surface.

  The LED 21 may be a single color or a unit type that emits two or more colors and emits a mixed color (for example, a so-called three-in-one type in which three primary colors are united into one). The LED 21 is of a type that does not have a strong light directivity, and the light emitted from the LED 21 travels directly above, brightening the portion corresponding to the position of the LED 21 and darkening the portion without the LED 21. Is generated.

  The light emitted from the LED 21 also travels in the direction of the opposing inclined surface 15, is reflected by the inclined surface 15 that forms an acute angle with the emission surface 11, and is emitted from the emission surface 11 side. It is important that the reflection on the inclined surface 15 is appropriately performed and that the reflected light is appropriately emitted from the emission surface 11 side. Therefore, the angle formed by the exit surface 11 and the inclined surface 15 is preferably about 45 degrees, and when the angle is changed from 45 degrees to a large angle, the reflected light is emitted from a portion near the center of the exit surface 11 and luminance spots are observed. The action to reduce decreases. On the other hand, if the angle is changed from 45 degrees to a large and small angle, the reflected light is emitted from a portion close to the edge of the emission surface 11, and the degree of reduction in luminance spots is reduced. For this reason, it is considered that the allowable range is 45 degrees to plus or minus 10 degrees.

  In the present embodiment, the position of the inclined surface 15 exists outside the incident surface 14, and no light scattering pattern exists below the inclined surface 15. The light reflected from the inclined surface 15 and emitted from the emitting surface 11 side is emitted on the upper side of the inclined surface 15, and the edge of the emitting surface 11 becomes bright as shown in the left diagram of FIG. Due to the influence of this light, the portion corresponding to the position of the LED 21 is brightened and the unevenness of brightness due to the darkening of the portion without the LED 21 is reduced. There is less to feel.

  The right diagram of FIG. 4 is a histogram of illuminance created by associating the illuminance on the exit surface 11 with the color, and is distributed to a portion with high illuminance according to the edge of the exit surface 11 becoming brighter. It can be seen that is concentrated to some extent. The portion with the high frequency portion corresponds to the central portion of the emission surface 11.

<Example 2>
5 to 7 show a configuration diagram of a light guide plate according to a second embodiment and a planar illumination device using the same. In the light guide plate 10A according to the second embodiment, the incident surface 14 protrudes outward as compared with the light guide plate 10 according to the first embodiment. That is, the position of the inclined surface 15 exists inside the incident surface 14.

  In the present embodiment, the inclined surface 15 is formed on two opposing sides of the light guide plate 10 (two sides on the left and right in FIG. 5), but is formed on at least one side. On the incident surface 14, a plurality of LEDs 21 are provided at a predetermined pitch for each side. In this example, a plurality of LEDs 21 are arranged on the left and right sides in FIG.

  Other configurations are the same as those of the first embodiment. In the present embodiment, since the position of the inclined surface 15 exists on the inner side of the incident surface 14, the light emitted from the LED 21 and proceeding to the upper side is between the inclined surface 15 and the ceiling portion of the incident surface 14. It is obstructed by the notch 31 formed between them, and does not proceed to the emission surface 11, but has a feature that it is difficult to generate brightness spots that brighten the part corresponding to the position of the LED 21 and darken the part without the LED 21.

  In addition to the above configuration, the light is incident from the incident surface 14, reflected by the inclined surface 15 on the opposite side, and light is emitted from the exit surface 11, so that the light is emitted on the upper side of the inclined surface 15, as shown in FIG. As shown on the right side, the edge of the emission surface 11 becomes brighter. As described above, the brightness spots that brighten the portions corresponding to the positions of the LEDs 21 and darken the portions that do not have the LEDs 21 are hardly seen, and when used as a lighting device, the spots are hardly bothered.

  The right figure in FIG. 8 is a histogram of illuminance created by matching the illuminance on the exit surface 11 with the color, and with respect to a portion with high illuminance according to the edge of the exit surface 11 becoming brighter. It can be seen that the distribution is concentrated to some extent. It is clear from the comparison with the right figure of FIG. 4 that the brightness corresponding to the brightness spot that brightens the part corresponding to the position of the LED 21 and darkens the part without the LED 21 does not appear.

The top view of the light-guide plate which concerns on 1st Example of this invention, and a planar illuminating device using the same. The front view of the light-guide plate which concerns on 1st Example of this invention, and a planar illuminating device using the same. The left view of the light-guide plate which concerns on 1st Example of this invention, and a planar illuminating device using the same. The figure which shows the illumination intensity histogram which produced the luminance distribution and illumination intensity of the output surface by the planar illuminating device which concerns on 1st Example of this invention corresponding to the color. The top view of the light-guide plate which concerns on the 2nd Example of this invention, and a planar illuminating device using the same. The front view of the light-guide plate which concerns on the 2nd Example of this invention, and a planar illuminating device using the same. The left view of the light-guide plate which concerns on 2nd Example of this invention, and a planar illuminating device using the same. The figure which shows the illumination intensity histogram produced by matching the luminance distribution and illumination intensity of the output surface by the planar illuminating device based on 2nd Example of this invention corresponding to a color.

Explanation of symbols

10, 10A Light guide plate
11 Output surface
12 Reflective surface
13 micropores
14 Incident surface
15 Inclined surface
21 LED
31 Notch

Claims (3)

A reflective surface with a light scattering pattern;
An exit surface facing the reflecting surface and emitting light;
An inclined surface formed on a side portion connecting the edge of the reflecting surface and the edge of the exit surface and forming an acute angle with the exit surface;
An incident surface that is provided on the reflective surface side with respect to the position where the inclined surface is formed and receives light from the light source;
A light guide plate characterized by comprising: The light guide plate according to claim 1, wherein the position of the inclined surface exists inside or outside the incident surface. A light guide plate according to claim 1 or 2;
A light source provided near the entrance surface;
The planar illumination device according to claim 1, comprising:

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