JP2004227856A - Surface light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light-emitting device from which more light quantity can be obtained and which is capable of adjusting the light emission ratio, with a relatively simple configuration. <P>SOLUTION: A surface light-emitting device A comprises a light source 1 and a lightguide plate 2, that is provided with a side surface 2c which the light from the light source 1 enters, and an upper surface 2a and a lower surface 2b, where the light that has entered exits. A semitransparent mirror 4 is provided to the upper surface 2a side or to the lower surface 2b side of the lightguide plate 2, and the semitransparent mirror 4 comprises a semitransparent plate, with a pattern of a reflective material is provide on its surface. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique related to a surface light emitting device used for a liquid crystal display device or the like.
[0002]
[Prior art]
As a device for illuminating a liquid crystal display panel or the like, a surface light emitting device called a front light or a backlight has been proposed. Further, as disclosed in Patent Documents 1 to 3, two-sided display type liquid crystal display devices in which two liquid crystal display plates are bonded to each other have been proposed, and are used as display devices of mobile phones.
[0003]
In such a double-sided display type liquid crystal display device, for example, when liquid crystal cells are arranged on both sides of a surface light emitting device as disclosed in Patent Document 3, it is necessary to adjust the light output ratio for each liquid crystal cell. . For example, there is a demand that one liquid crystal cell emits light brighter than the other liquid crystal cell.
[0004]
In the case of performing such double-sided light emission, for example, a semi-transmissive mirror in which a metal film is coated on the surface of a transparent plate or a semi-transmissive mirror using a dielectric multilayer film is arranged on one light emitting surface of the surface emitting device, and It is conceivable to emit light from the device in both directions.
[0005]
[Patent Document 1] Japanese Patent Application Laid-Open No. Hei 10-198291 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-298519 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-189230
[Problems to be solved by the invention]
However, in a semi-transmissive mirror coated with a metal film, the amount of light absorbed by the metal film is large, and when the transmission amount is increased, the metal film needs to be thin, and a sufficient amount of light cannot be obtained. In addition, in a semi-transmissive mirror using a dielectric multilayer film, many layers must be stacked in order to uniformly attenuate light over the entire visible range, which increases the cost and increases the number of layers. Lamination also causes problems such as peeling and cracking.
[0007]
Therefore, an object of the present invention is to provide a surface emitting device that can obtain a larger amount of light and can adjust the light output ratio with a relatively simple configuration.
[0008]
[Means for Solving the Problems]
According to the present invention, in the surface light emitting device including a light source, a light guide plate including a side surface on which light from the light source enters, and an upper surface and a lower surface from which the incident light exits, the light guide plate includes: A semi-transmissive mirror is provided on the upper surface side or the lower surface side of the light-emitting device, and the semi-transmissive mirror is formed of a light transmitting plate having a pattern of a reflective material provided on a surface thereof.
[0009]
Further, according to the present invention, in a surface light emitting device including a light source, a light guide plate having a side surface on which light from the light source enters, and an upper surface and a lower surface on which the incident light exits, A surface emitting device is provided, wherein a semi-transmissive mirror having polarization selectivity is provided on the upper surface side or the lower surface side of the light guide plate.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0011]
<First embodiment>
FIG. 1 is a schematic diagram showing an example in which a surface light emitting device A according to one embodiment of the present invention is applied to a double-sided display type liquid crystal display device. FIG. 2 is an exploded sectional view showing the configuration of the liquid crystal display device of FIG.
[0012]
In this liquid crystal display device, a liquid crystal cell B is provided on each of the upper surface side and the lower surface side of the surface light emitting device A, so that an observer can enjoy an image displayed on each liquid crystal cell. The device A emits light in both directions up and down, and illuminates each liquid crystal cell B.
[0013]
The surface light emitting device A has a light source 1, a light guide plate 2, an optical function film 3, and a semi-transmissive mirror 4, and the light guide plate 2, the optical function film 3, and the semi-transmissive mirror 4 are all rectangular. And are vertically stacked.
[0014]
The light source 1 is a linear light source, for example, a cold cathode tube, and is arranged so that its longitudinal direction is along the side surface of the light guide plate 2. The reflector 1 a is provided so as to cover the periphery of the light source 1, and has an inner surface formed as a mirror surface so that light from the light source 1 a efficiently enters the light guide plate 2. Although a linear light source is used as the light source 1 in the present embodiment, a point light source such as an LED may be used.
[0015]
The light guide plate 2 is a plate-shaped member made of, for example, optical glass, synthetic resin, or the like, and is preferably made of a transparent substrate. In the case of this embodiment, the light guide plate 2 includes an upper surface 2a serving as a light emitting surface for the upper liquid crystal cell B, a lower surface 2b opposite to the upper surface 2a and serving as a light emitting surface for the lower liquid crystal cell B, and a side surface 2c. , And is configured so that light from the light source 1 is incident on one of the four side surfaces 2c. The light guide plate 2 is optimally a rectangular plate as described above, but the shape is not limited to this, and various shapes can be adopted.
[0016]
The optical function film 3 is, for example, a diffusion plate or a prism sheet, and serves to improve the amount of light emitted in the vertical direction and to suppress unevenness in the amount of light. It is not necessary to provide the optical function film 3, but it goes without saying that it is desirable to provide the optical function film 3 in order to improve the amount of emitted light and suppress unevenness in the amount of light. In the present embodiment, the optical function film 3 is provided on both the upper surface 2a side and the lower surface 2b side of the light guide plate 2, but may be provided on either one side. Further, instead of the optical function film 3, a diffusion pattern or a prism groove may be directly provided on the surface of the light guide plate 2.
[0017]
The semi-transmissive mirror 4 is for adjusting the light output ratio between the upper surface side and the lower surface side of the surface light emitting device A, and has a pattern of a reflective material provided on the surface of the light transmitting plate. In the present embodiment, the light guide plate 2 is provided on the lower surface 2b side, but may be provided on the upper surface 2a side, or provided on only one side.
[0018]
Examples of the light transmitting plate include transparent or translucent optical glass, synthetic resin, and the like. As the reflective material, silver having low light absorption is optimal. However, in the case of the present embodiment, since the surface of the light transmitting plate is not entirely covered with the reflecting material, even if another metal or the like having light reflectivity is adopted, the light transmitting plate as in the related art is used. It goes without saying that the amount of emitted light is superior to that obtained by covering the entire surface with a metal film.
[0019]
In the present embodiment, by providing the pattern of the reflecting material on the surface of the light transmitting plate, the portion of the light transmitting plate on which the reflecting material is applied and the portion on which the reflecting material is not applied (the surface of the light transmitting plate) Are exposed) and are mixed. Then, a part of the light emitted from the light guide plate 2 is reflected by the reflection material, and the remaining light passes through the light transmission plate. Therefore, the light output ratio between the upper surface 2a side and the lower surface 2b side of the light guide plate 2 is determined by the area of the portion where the pattern of the reflective material is applied and the area of the portion where the surface of the light transmission plate is exposed, and The area of the portion where the pattern of the reflecting material is applied can be determined according to the light output ratio.
[0020]
As this pattern, any pattern can be adopted, but it is desirable to adopt a pattern that does not cause unevenness in brightness, and it is desirable that the size or width is, for example, 2 to 300 μm. Further, it is desirable that the light transmitting plate is provided uniformly in each region on the surface.
[0021]
FIGS. 3A and 3B are diagrams showing examples of the pattern of the reflecting material, in which the reflecting material 4a (black portion) is applied to the surface of the light transmitting plate 4b. The white portion indicates a portion where the surface of the light transmitting plate 4b is exposed. In the example shown in FIG. 3A, a plurality of dot-shaped reflecting members 4a are arranged side by side vertically and horizontally. The dot shape of the reflector 4a may be square as shown in the figure, or may be circular. Further, the shape of each dot does not necessarily have to be the same, but may be different in size and shape. In the example of FIG. 3B, a plurality of line-shaped reflecting members 4a are vertically arranged substantially in parallel. Such a pattern can also be adopted.
[0022]
As a method of providing such a pattern of the reflective material, for example, a processing method such as printing of the reflective material on the light transmitting plate, film formation of a mask, and etching can be used.
[0023]
In the surface emitting device A having such a configuration, of the light emitted from the upper surface 2a and the lower surface 2b of the light guide plate 2, the light emitted from the lower surface 2b is reflected by the semi-transmissive mirror 4 (x in FIG. 2). When the light is not reflected (y in FIG. 2), the light directly emitted from the upper surface 2a to the upper surface 2a and the light emitted from the lower surface 2b and reflected by the semi-transmissive mirror 4 are combined to form the upper surface 2a. The liquid crystal cell B on the side becomes brighter.
[0024]
That is, although the structure is relatively simple, the upper and lower light emission ratios can be adjusted by the pattern of the reflective material applied to the semi-transmissive mirror 4. At this time, since the surface of the semi-transmissive mirror 4 is not entirely covered with a metal film as in the related art, the amount of light absorption is reduced, and a larger amount of light can be obtained. This effect is remarkable when silver is used as the reflector. Further, the light emission ratio can be freely adjusted depending on the area of the pattern of the reflector.
[0025]
<Second embodiment>
In the first embodiment, as the semi-transmissive mirror 4, a mirror provided with a pattern of a reflective material on the surface of a light transmitting plate is used. Instead, a mirror having polarization selectivity, for example, a polarizing film is used. May be. Even when the semi-transmissive mirror 4 having polarization selectivity is used, it may be provided on the lower surface 2b side of the light guide plate 2 as shown in FIG. 2 or may be provided on the upper surface 2a side. Provided only on the side.
[0026]
As such a polarization selectivity, one having selectivity to linearly polarized light may be employed. In this case, of the light incident on the semi-transmissive mirror 4, of the wave components of the light, one of a longitudinal wave and a transverse wave is transmitted therethrough, and the other is reflected. Therefore, as in the case of the first embodiment, one of the two liquid crystal cells B can be brightened, and the light output ratio can be adjusted. In addition, since the semi-transmissive mirror 4 does not absorb light, a larger output light amount can be obtained.
[0027]
When the birefringence characteristics of the light guide plate and the optical film used when employing the transflective mirror 4 having the polarization selectivity are small and the polarization characteristics are maintained, the polarization of the liquid crystal cell B is maintained. It is necessary to make the polarization direction of the film coincide with the polarization direction of the light emitted from the surface emitting device A. For example, in the configuration of FIG. 2, assuming that the upper liquid crystal cell B transmits longitudinal waves and the lower liquid crystal cell B transmits transverse waves, the semi-transmissive mirror 4 reflects longitudinal waves and transmits transverse waves. It must have a polarization selectivity for transmission.
[0028]
Next, as the semi-transmissive mirror 4 having polarization selectivity, a mirror having selectivity to circularly polarized light may be employed. In this case, the light incident on the semi-transmissive mirror 4 is transmitted or reflected depending on whether the component of the light is right circularly polarized light or left circularly polarized light. Therefore, also in this case, one of the two liquid crystal cells B can be brightened, and the light emission ratio can be adjusted. Also in this example, since the semi-transmissive mirror 4 does not absorb light, a larger output light amount can be obtained.
[0029]
When the birefringence characteristics of the light guide plate and the optical film used when adopting the semi-transmissive mirror 4 having selectivity for circularly polarized light are small and the polarization characteristics are maintained, as shown in FIG. By providing the / 4 phase plate 5, light can be efficiently introduced into the liquid crystal cell. As shown in the figure, the λ / 4 retardation plate 5 is provided on both the upper surface 2a side and the lower surface 2b side of the light guide plate 2 in order to convert both transmitted light and reflected light into linearly polarized light.
[0030]
In addition, even when the semi-transmissive mirror 4 having selectivity for circularly polarized light is adopted, the polarization direction of the polarizing film constituting the liquid crystal cell B and the polarization direction of the light emitted from the surface light emitting device A must be matched. Needless to say, it is necessary.
[0031]
Now, in the example of FIG. 4, assuming that the semi-transmissive mirror 4 has a selectivity of reflecting right circularly polarized light, of the light emitted from the lower surface 2b of the light emitted from the upper surface 2a and the lower surface 2b of the light guide plate 2, The right-handed circularly polarized light is reflected by the semi-transmissive mirror 4 (m in FIG. 4), and the left-handed circularly polarized light is not reflected (n in FIG. 4). Therefore, light directly emitted from the upper surface 2a to the upper surface 2a and light emitted from the lower surface 2b. Then, the light is combined with the right circularly polarized light reflected by the semi-transmissive mirror 4, and the liquid crystal cell B on the upper surface 2a becomes brighter.
[0032]
As described above, even when a semi-transmissive mirror 4 having a polarization selectivity is employed, a larger amount of light can be obtained than in the related art, and the light output ratio can be adjusted with a relatively simple configuration.
[0033]
【The invention's effect】
As described above, according to the surface emitting device of the present invention, a larger amount of light can be obtained, and the light emission ratio can be adjusted with a relatively simple configuration.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example in which a surface emitting device A according to a first embodiment of the present invention is applied to a double-sided display type liquid crystal display device.
FIG. 2 is an exploded sectional view showing a configuration of the liquid crystal display device of FIG.
FIGS. 3A and 3B are diagrams showing examples of a pattern of a reflecting material; FIGS.
FIG. 4 is an exploded cross-sectional view illustrating a configuration of a liquid crystal display device when a second embodiment of the present invention is employed.
[Explanation of symbols]
A Surface emitting device B Liquid crystal cell 1 Light source 2 Light guide plate 3 Optical function sheet 4 Semi-transmissive mirror 5 λ / 4 retardation plate

Claims (7)

A light source,
In a surface light emitting device including a light guide plate having a side surface on which light from the light source enters, and an upper surface and a lower surface on which the incident light exits,
A semi-transmissive mirror is provided on the upper surface side or the lower surface side of the light guide plate,
A surface light emitting device, wherein the semi-transmissive mirror comprises a light transmitting plate having a surface provided with a pattern of a reflective material. The surface light emitting device according to claim 1, wherein the pattern of the reflecting material is formed according to a light output ratio between an upper surface and a lower surface of the light guide plate. The surface emitting device according to claim 1, wherein the reflecting material is silver. A light source,
In a surface light emitting device including a light guide plate having a side surface on which light from the light source enters, and an upper surface and a lower surface on which the incident light exits,
A surface light emitting device, wherein a semi-transmissive mirror having polarization selectivity is provided on an upper surface side or a lower surface side of the light guide plate. The surface emitting device according to claim 4, wherein the semi-transmissive mirror has selectivity for linearly polarized light. The transflective mirror has selectivity for circularly polarized light,
The surface light emitting device according to claim 4, wherein a phase difference plate is provided on each of an upper surface side and a lower surface side of the light guide plate. The surface light emitting device according to claim 1, wherein an optical function film is further provided on an upper surface side or a lower surface side of the light guide plate.

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