JP4421583B2 - Light guide plate and surface light emitting device - Google Patents

Description

  The present invention relates to a light guide plate and a surface light emitting device.

  2. Description of the Related Art A surface light emitting device that illuminates a liquid crystal display from the back surface thereof is adopted in a portable phone or the like. A surface light emitting device generally employs a configuration in which a light source is disposed on a side surface of a light guide plate. In such a surface light emitting device, it is desirable that the light from the light source incident on the side surface of the light guide plate is uniformly emitted from the light exit surface of the light guide plate. For this reason, in order to eliminate luminance unevenness and the like, a light guide plate provided with various patterns has been proposed.

  For example, Patent Document 1 proposes a technique for providing unevenness including a smoothly continuous curved surface on the light source side surface, uniforming the light intensity distribution, and reducing luminance unevenness. Patent Document 2 discloses a technique for reducing the generation of bright lines by providing a plurality of prism convex portions extending in a direction orthogonal to the light source side surface so as to meander.

JP 2005-228719 A JP 2005-347122 A

  By the way, along with a request for thinning a device such as a portable telephone on which the surface light emitting device is mounted, the surface light emitting device is also required to be thinned, and the light guide plate is being thinned. However, there is a limit to reducing the thickness of the light source, and light from the light source must be efficiently incident on the light guide plate. Therefore, measures are taken to increase the thickness of a part of the region on the light source side and reduce the thickness of the region of the light output surface without making the light guide plate uniform.

  In such a light guide plate, the upper surface on the light exit surface side has an inclined surface that is inclined so that the plate thickness on the light source side is thick at the boundary portion between the thick and thin portions. As a result, the primary reflected light from the light source reflected on the lower surface serving as the reflecting surface is easily emitted from the inclined surface exceeding the absolute reflection critical angle with respect to the inclined surface. Since the primary reflected light is light having high directivity and high intensity, there is a problem that the inclined surface portion becomes bright and a spot with uneven brightness is generated.

  Accordingly, an object of the present invention is to suppress the primary reflected light from being emitted from the inclined surface of the upper surface of the light guide plate, and to reduce the occurrence of luminance unevenness.

According to the present invention, it has a light source side surface on which light from a light source is incident, an upper surface from which light from the light source is emitted, and a lower surface that is a reflection surface that reflects light from the light source, In the light guide plate having an inclined surface whose upper surface is inclined so that the thickness of the side surface on the light source side is increased, primary reflected light reflected from the lower surface of the light source is emitted through the inclined surface. A light diffusion pattern is formed on the lower surface, and the light diffusion pattern is formed in a range of a distance from the light source side surface to a center portion of the light source side surface and the inclined surface. A featured light guide plate is provided.

Further, according to the present invention, the light source side surface on which light from the light source is incident, an upper surface from which the light from the light source is emitted, and a lower surface serving as a reflective surface that reflects the light from the light source are provided. In the light guide plate, the upper surface has an inclined surface that is inclined so that the thickness of the side surface on the light source side is increased, and the primary reflected light reflected by the lower surface of the light source passes through the inclined surface and is emitted. A light diffusion pattern is formed on the lower surface, and the light diffusion pattern is formed in a range where the primary reflected light is incident on the inclined surface. .

According to the present invention, the surface light emitting device employing the light guide plate includes a light source, a light source side surface on which light from the light source is incident, an upper surface from which light from the light source is emitted, and the light source. A light guide plate having a lower surface that serves as a reflection surface for reflecting the light, and the upper surface has an inclined surface that is inclined so that the plate thickness of the side surface on the light source side is increased, and a reflection plate provided on the lower surface When, in the surface light-emitting device in which a to form a light diffusion pattern to reduce the primary reflected light which the light from the light source is reflected by the lower surface is the light exit through said inclined surface to said bottom surface, said light The diffusion pattern is formed in a range of the distance between the light source side surface and the light source side surface and the central portion of the inclined surface .
According to the present invention, the light source, the light source side surface on which the light from the light source is incident, the upper surface from which the light from the light source is emitted, and the lower surface to be a reflective surface that reflects the light from the light source In the surface light emitting device, comprising: a light guide plate having an inclined surface inclined so that a plate thickness of the side surface on the light source side is increased; and a reflection plate provided on the lower surface. A light diffusion pattern is formed on the lower surface to reduce primary reflected light reflected by the lower surface from the light source passing through the inclined surface, and the primary diffused light is inclined. A surface light emitting device is provided that is formed in a range incident on a surface.

According to the present invention, it is possible to suppress the primary reflected light from being emitted from the inclined surface on the upper surface of the light guide plate, and to reduce the occurrence of luminance unevenness. In particular, according to the first and fifth aspects of the present invention, it is possible to prevent the amount of light emitted from the upper surface of the light guide plate from being reduced in the vicinity of the boundary portion between the upper surface of the light guide plate and the inclined surface. Moreover, according to the invention concerning Claim 2 and 6, the primary reflected light which goes to the inclined surface of a light-guide plate upper surface exceeding an absolute reflection critical angle can be reduced more effectively.

<Overall configuration>
FIG. 1 is an exploded perspective view of a surface light emitting device 100 according to an embodiment of the present invention, and FIG. 2A is a side view of the surface light emitting device 100. The surface light emitting device 100 includes a light guide plate 10, a light source 20, a reflection sheet 30, and optical sheets 40a and 40b.

  The light guide plate 10 is formed in a substantially square shape from a transparent plate-like member, and is formed of, for example, polycarbonate. The light guide plate 10 has four side surfaces 11a to 11d, of which the side surface 11a forms a light source side surface on which light from the light source 20 is incident.

  The upper surface 12 of the light guide plate 10 includes a light output surface portion 12a from which light from the light source 20 is emitted, an inclined surface portion 12b, and a light source side upper surface portion 12c parallel to the light output surface portion 12a. Further, the lower surface 13 of the light guide plate 10 constitutes a reflection surface that reflects the light of the light source 20, and the lower surface 13 is parallel to the light output surface portion 12a. A light diffusion pattern is formed on the lower surface 13. Details will be described later.

  The inclined surface portion 12b is formed to be inclined with respect to the light output surface portion 12a and the light source side upper surface portion 12c in order to relatively increase the thickness of the light guide plate 10 on the side surface 11a side, and the light guide plate 10 in the light output surface portion 12a. Is relatively thinner than the thickness of the light source side upper surface portion 12c.

  The light sources 20 are point light sources such as LEDs, and in the case of this embodiment, a plurality of light sources 20 are arranged along the side surface 11a. The reflection sheet 30 is provided under the lower surface 13 of the light guide plate 10. When the light from the light source 20 is transmitted without being reflected by the lower surface 13, the reflection sheet 30 is reflected and reenters the light guide plate 10. It is. The optical sheets 40a and 40b are disposed on the light exit surface portion 12a of the light guide plate 10, and are, for example, a prism sheet or a diffusion sheet, and adjust the brightness of light emitted from the light exit surface portion 12a and adjust brightness unevenness. The sheet includes both a film and a plate.

  In the surface light emitting device 100 having such a configuration, light emitted from the light source 20 propagates while being repeatedly reflected in the light guide plate 10 and is emitted from the light exit surface portion 12a. The liquid crystal display 200 to be illuminated is disposed on the optical sheets 40a and 40b, and the light emitted from the light exit surface portion 12a passes through the liquid crystal display 200 and illuminates the display screen.

<Light diffusion pattern on the bottom>
Next, the light diffusion pattern formed on the lower surface 13 of the light guide plate 10 will be described. FIG. 2B is a view showing the lower surface 13 of the light guide plate 10. In the lower surface 13, light diffusion patterns 13 a are formed in the vicinity of the light sources 20. The light diffusion pattern 13a is composed of a plurality of concave portions or convex portions or a combination thereof, and in the case of the present embodiment, the light diffusion pattern 13a is composed of a plurality of concave portions. The light diffusion pattern 13a reduces the primary reflected light, which is reflected from the lower surface 13 of the light from the light source 20, and exits through the inclined surface portion 12b. The principle will be described.

  First, a problem when the light diffusion pattern 13a is not provided (conventional configuration) will be described. FIG. 3A is an explanatory diagram of primary reflected light when the light diffusion pattern 13a is not provided. As shown in the figure, the light incident from the light source 20 into the light guide plate 10 is reflected by the lower surface 13 and travels toward the upper surface 12 (primary reflected light). At this time, if the thickness of the light guide plate 10 is uniform, the incident angle of the primary reflected light on the upper surface 12 is an angle θ1 formed by the virtual line L1 and the primary reflected light.

  However, when the thickness of the light guide plate 10 is not uniform as in the present embodiment, the incident angle of the primary reflected light to the inclined surface portion 12b is an angle θ2 formed by the inclined surface portion 12b and the primary reflected light, and is larger than the angle θ1. . For this reason, the primary reflected light which goes to the inclined surface part 12b exceeding the absolute reflection critical angle with respect to the inclined surface part 12b increases, and the primary reflected light emitted from the inclined surface part 12b increases. Since the primary reflected light has strong directivity and high intensity, when light is emitted from the inclined surface portion 12, the incident light enters the optical sheets 40 a and 40 b and out of the light emitted from the surface light emitting device 100, the inclined surface portion 12 b side. The luminance of a part of the region increases, resulting in uneven luminance.

  On the other hand, when the light diffusion pattern 13a is provided on the lower surface 13 as in the present embodiment, the reflection angle of the primary reflected light can be controlled by diffusing the light from the light source 20, as shown in FIG. The angle of reflection of the primary reflected light at the lower surface 13 can be reduced. As a result, it is possible to reduce the primary reflected light toward the inclined surface portion 12b beyond the absolute reflection critical angle with respect to the inclined surface portion 12b. Thus, in the present embodiment, it is possible to suppress the primary reflected light from being emitted from the inclined surface portion 12b, and to reduce the occurrence of luminance unevenness.

  In addition, although the light emitted from the lower surface 13 may increase by forming the light diffusion pattern 13a, the light guide plate is reflected by the reflection sheet 30 as reflected light indicated by reference numeral 1 in FIG. Therefore, the amount of light emitted from the surface light emitting device 100 is not reduced.

  The shape of the concave portion and the convex portion constituting the light diffusion pattern 13a can be determined according to the angle of the inclined surface portion 12b and the refractive index of the light guide plate 10, and is primary toward the inclined surface portion 12b at an absolute reflection angle with respect to the inclined surface portion 12b. It can be determined that the reflected light increases.

  When the light source 20 is a point light source as in the present embodiment, the light emitted from the light source 20 spreads radially, so the light diffusion pattern 13a is desirably formed so as to surround the light source 20. For example, as shown in FIG. 2 (b), the light source 20 is formed in a semicircular region indicated by a virtual line 13b, or the light source 20 is formed in a semielliptical region. Can be formed.

  On the other hand, when a linear light source such as a cold cathode ray tube is employed as the light source 20, as shown in FIG. 5A, the light diffusion pattern 13a is formed in the band-shaped range along the linear light source 20 ′. It is desirable.

  Next, the formation range of the light diffusion pattern 13a is desirably as narrow as possible. This is because the light diffusion pattern 13a reduces the light reflection angle on the lower surface 13, and if formed over a wide range, the light output rate of the light from the light output surface portion 12a may decrease. FIG. 4 is an explanatory diagram showing an example of the formation range of the light diffusion pattern 13a.

  First, the light diffusion pattern 13a can be formed in a range where primary reflected light is incident on the inclined surface portion 12b. For example, it is area | region R1 shown in FIG. 4, and area | region R1 is an area | region from the side surface 11a by the side of the light source 20 to the light emission surface part 12a.

  When the light diffusion pattern 13a is formed in the region R1, the amount of light emitted from the light exit surface 12a may be reduced in the vicinity of the boundary between the light exit surface 12a and the inclined surface 12b. Therefore, the light diffusion pattern 13a can also be formed in the region R2. Region R2 is the range of the distance between the side surface 11a and the side surface 11a and the central portion (indicated by the imaginary line CL) of the inclined surface portion 12b. In the case of this example, in the region of the inclined surface portion 12b on the light output surface portion 12a side, there is a possibility that the primary reflected light is emitted from the inclined surface portion 12b to some extent. It can prevent that the emitted light quantity from 12a falls.

  Further, the region R3 is a region between the intersections of the imaginary lines L2 and L3 in the absolute reflection critical angle θ3 direction of the inclined surface portion 12b and the lower surface 13 that respectively pass through the end portions of the inclined surface portion 12b. When the light diffusion pattern 13a is formed in this region R3, the primary reflected light that exceeds the absolute reflection critical angle θ3 and goes to the inclined surface portion 12b can be more effectively reduced.

  In the present embodiment, the configuration in which the upper surface 12 of the light guide plate 10 has the light source side upper surface portion 12c is illustrated, but the upper surface 12 does not have the light source side upper surface portion 12c as shown in FIG. The present invention can also be applied to a light guide plate having only the surface portion 12a and the inclined surface portion 12b.

1 is an exploded perspective view of a surface light emitting device 100 according to an embodiment of the present invention. (A) is a side view of the surface light emitting device 100, and (b) is a view showing the lower surface 13 of the light guide plate 10. (A) is explanatory drawing of the primary reflected light when not providing the light-diffusion pattern 13a, (b) is explanatory drawing of the primary reflected light when the light-diffusion pattern 13a is provided. It is explanatory drawing which shows the example of the formation range of the light-diffusion pattern 13a. The figure which shows the example of formation of the light-diffusion pattern 13a at the time of using the linear light source 20 ', (b) is a figure which shows the example of the light-guide plate 10 which does not have the light source side upper surface part 12c.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light guide plate 12 Upper surface 12b Inclined surface part 13 Lower surface 13a Light diffusion pattern 20 Light source 100 Surface light-emitting device

Claims (6)

A light source side surface on which light from the light source is incident;
An upper surface from which light from the light source is emitted;
A lower surface serving as a reflective surface for reflecting light from the light source,
In the light guide plate having an inclined surface that is inclined so that the plate thickness of the side surface on the light source side is thicker,
Forming a light diffusion pattern on the lower surface to reduce primary reflected light reflected by the lower surface from the light source through the inclined surface and exiting the light ;
The light diffusion plate is formed in a range of a distance between the light source side surface and the light source side surface and a central portion of the inclined surface from the light source side surface . A light source side surface on which light from the light source is incident;
An upper surface from which light from the light source is emitted;
A lower surface serving as a reflective surface for reflecting light from the light source,
In the light guide plate having an inclined surface that is inclined so that the plate thickness of the side surface on the light source side is thicker,
Forming a light diffusion pattern on the lower surface to reduce primary reflected light reflected by the lower surface from the light source through the inclined surface and exiting the light ;
The light guide plate , wherein the light diffusion pattern is formed in a range in which the primary reflected light is incident on the inclined surface . The light diffusion patterns, the light guide plate according to claim 1 or 2, characterized in that a plurality of recesses or protrusions formed on the lower surface. The light source is a point light source;
The light diffusion patterns, the light guide plate according to claim 1 or 2, characterized in that it is formed in the region of the semicircular shape around the point light source. A light source;
A light source side surface on which light from the light source is incident, an upper surface from which the light from the light source is emitted, and a lower surface serving as a reflective surface that reflects the light from the light source, wherein the upper surface is the light source. A light guide plate having an inclined surface inclined so that the plate thickness of the side surface is thick;
A reflector provided on the lower surface;
In a surface light emitting device comprising:
Forming a light diffusion pattern on the lower surface to reduce primary reflected light reflected by the lower surface from the light source through the inclined surface and exiting the light ;
The surface light emitting device , wherein the light diffusion pattern is formed in a range of a distance between the light source side surface and the light source side surface and a central portion of the inclined surface . A light source;
A light source side surface on which light from the light source is incident, an upper surface from which the light from the light source is emitted, and a lower surface serving as a reflective surface that reflects the light from the light source, wherein the upper surface is the light source. A light guide plate having an inclined surface inclined so that the plate thickness of the side surface is thick;
A reflector provided on the lower surface;
In a surface light emitting device comprising:
Forming a light diffusion pattern on the lower surface to reduce primary reflected light reflected by the lower surface from the light source through the inclined surface and exiting the light ;
The surface light emitting device , wherein the light diffusion pattern is formed in a range in which the primary reflected light is incident on the inclined surface .

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