JP3994447B2 - Illumination device and liquid crystal display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lighting device for irradiating a liquid crystal display surface from the back and a liquid type display device in a liquid crystal display device.
[0002]
[Prior art]
An example of the configuration of a lighting device (hereinafter referred to as a backlight) in a conventional liquid crystal display device will be described with reference to FIG. FIG. 3 is a side sectional view showing a conventional backlight, and the upper side of the figure is the liquid crystal display surface side. In FIG. 3, 1 is a light source composed of a fluorescent tube, 2 is a light guide plate that guides light from the light source 1, 3 is a reflector that reflects light emitted from the light guide plate 2, and 4 is emitted from the light guide plate 2. A diffusing plate for diffusing light, 5 is a prism plate for condensing the light emitted from the diffusing plate 4, and 6 is a reflecting plate for reflecting the light from the light source 1 and condensing it on the light guide plate 2 side. In this case, the lower surface of the light guide plate 2 is processed to have an uneven surface 2a.
[0003]
The light incident on the light guide plate 2 from the light source 1 repeats total reflection on the upper and lower surfaces of the light guide plate 2 while being scattered on the uneven surface 2a, and increases the incident angle to exceed the critical angle from the light guide plate 2. Exit. The light emitted from the lower surface of the light guide plate 2 is reflected by the reflecting plate 3 and returns to the light guide plate 2, and the light emitted from the upper surface is transmitted through the diffusion plate 4 and the prism plate 5 to be uniformed and is not shown in the figure. Is irradiated.
[0004]
FIG. 4 is a side sectional view showing another conventional backlight, and this type of structure is described in Japanese Patent Laid-Open No. 4-29291. In FIG. 4, 1a is a bundle of optical fibers, and light from an external light source enters the light guide plate 2a through the optical fiber 1a. The light guide plate 2a has bubbles 2b, 2b,. The light incident from the optical fiber 1a strikes the bubbles 2b, 2b,... And diffuses and is emitted from the light guide plate 2 in the same manner as in FIG. And the back surface of the liquid crystal display surface which is not shown in figure is irradiated.
[0005]
[Problems to be solved by the invention]
By the way, in the conventional backlight described above, on the other hand, in the method using the interface reflection as shown in FIG. 3, the interface is not mirror-like, so that the reflection loss increases, and on the other hand, the bubbles as shown in FIG. Since the second and third order reflections can be considered in the method used, the reflection loss is still large, and both methods have a problem that the luminance is reduced due to the reflection loss. Moreover, in order to compensate for this and increase the luminance, it is necessary to increase the intensity of the light source, resulting in a problem that the power consumption increases.
[0006]
The present invention has been made under such a background, and it is an object of the present invention to provide a lighting device that has a light guide plate with higher brightness and higher efficiency than before, and is bright with low power.
[0007]
[Means for Solving the Problems]
The illuminating device of the present invention has a light source and a light guide plate that receives light from the light source and guides it from the side surface, and illuminates the liquid crystal display surface from the back surface with light emitted from the upper surface of the light guide plate. The light guide plate is formed by laminating a plurality of wedge-shaped light guide plate pieces in the thickness direction, and each light guide plate piece includes a first surface on the upper surface side of the light guide plate and a first surface on the lower surface side of the light guide plate. The angle of inclination between the two surfaces is gradually reduced from the lower surface side of the light guide plate toward the upper surface side, and the refractive index from the lower surface side of the light guide plate toward the upper surface side thereof. Of the light guide plate pieces, the one light guide plate piece provided on the lower surface side of the light guide plate is a side surface of the light guide plate that receives light from the light source, and the light guide plate. The inclination angle is formed on the opposite side of the side surface of the light guide plate. The remaining light guide plate pieces among the light guide plate pieces are provided on the one light guide plate piece, and the inclined angle is formed on the side surface side of the light guide plate that receives light from the light source. The light emitted from the light source and passing through the light guide plate piece on the lower surface side of the light guide plate of the two adjacent light guide plate pieces to the light guide plate piece on the upper surface side of the light guide plate is between these light guide plate pieces. The refractive index of the light guide plate increases stepwise from the lower surface side to the upper surface side, because a part thereof is refracted toward the upper surface side of the light guide plate. And it is characterized by increasing in steps as the distance from the light source increases.
According to this illuminating device, each light guide plate piece constituting the light guide plate has a uniform inclined plane with respect to the back side surface of the liquid crystal display surface in the light guide plate by being formed in a wedge shape, In addition, since the refractive index is arranged so as to gradually increase from the surface side opposite to the back surface side to the surface side facing the back surface side, the light incident on the side surface of the light guide plate from the light source The light is repeatedly refracted at the boundary surface between the light plate pieces, and is emitted from the upper surface of the light guide plate (the surface side facing the back side) while uniformly adjusting the light distribution state. Therefore, after the emitted light is diffused by, for example, a diffusion plate, the rear surface of the liquid crystal display surface is irradiated as diffused light with high uniformity.
Also, since the incident angle of light is gradually increased by utilizing the change in refractive index, the loss due to reflection can be kept low, the luminance can be improved, and the light distribution from the light guide plate is also distributed. Can be easily improved. Therefore, for example, a conventionally used prism plate can be omitted.
In addition, a liquid crystal display device of the present invention includes the above-described illumination device.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view showing the structure of a backlight according to an embodiment of the present invention. In this figure, portions corresponding to the respective portions in FIG. In FIG. 1, 2b is a light guide plate, and is composed of four light guide plate pieces 2b-1, 2b-2, 2-b3, and 2b-4 having different refractive indexes. The four light guide plate pieces 2b-1, 2b-2, 2-b3, and 2b-4 are formed of an acrylic plate or the like, and extend from the lower side of the light guide plate 2b (the reflection plate 3 side) to the diffusion plate 4. It arrange | positions so that a refractive index may become large gradually toward the upper side which faces. Each of these light guide plate pieces is integrally formed in a wedge shape so that the upper and lower planes gradually decrease the inclination angle from the bottom to the top with respect to the upper and lower surfaces of the light guide plate 2b. .
[0009]
With the above configuration, the light emitted from the light source 1 is reflected and collected by the reflecting plate 6 and is incident on the light guide plate piece 2b-1 of the light guide plate 2b. At this time, the light incident on the light guide plate piece 2b-1 travels in various directions toward the center direction and the vertical direction of the light guide plate 2b. A part of the incident light that has reached the lower plane of the light guide plate 2b is emitted to the outside of the light guide plate piece 2b-1, reaches the reflection plate 3, is reflected there, and is again reflected by the light guide plate piece 2b-. 1 is incident. Most of the remaining light is reflected by the lower plane and travels upward. On the other hand, light that does not reach the lower plane and reaches the boundary surface between the light guide plate piece 2b-1 and the light guide plate 2b-2 has an incident angle larger than the critical angle of the boundary surface. 2, the remaining part is reflected and proceeds to the lower surface of the light guide plate 2 b.
[0010]
The light incident on the light guide plate piece 2b-2 is refracted at such an angle that the traveling direction approaches the perpendicular direction of the boundary surface between the light guide plate pieces 2b-1 and 2b-2. And it progresses in the light-guide plate piece 2b-2 further upwards. And the light which reached the boundary surface of the light-guide plate pieces 2b-2 and 2b-3 is refracted so that it may approach the perpendicular direction of a boundary surface again, when injecting into the light-guide plate piece 2b-3. Then, the light travels through the light guide plate piece 2b-3 and reaches the boundary surface between the light guide plate pieces 2b-3 and 2b-4. Therefore, the light is refracted again at the boundary surface between the light guide plate pieces 2b-3 and 2b-4 and enters the light guide plate piece 2b-4. The light reaching the upper plane of the light guide plate piece 2b-4 has an incident angle exceeding the critical angle of the upper surface of the light guide plate piece 2b-4. The light is emitted from the upper plane of 2b. The emitted light is diffused by the diffusion plate 4 and irradiates the back surface of the liquid crystal display surface installed on the upper surface (not shown).
[0011]
On the other hand, the light that has not reached the critical angle on the upper plane of the light guide plate piece 2b-4 is reflected and travels down the light guide plate 2b-4. Then, while passing through each light guide plate piece or being reflected by each light guide plate piece, it again reaches the upper plane of the light guide plate piece 2b-4 through the same path as described above. And the light which has an incident angle exceeding a critical angle radiate | emits from the upper plane of the light-guide plate piece 2b-4. In this way, the light incident on the light guide plate piece 2b-1 from the light source 1 is emitted from the upper surface of the light guide plate piece 2b-4 to irradiate the liquid crystal display surface.
[0012]
As described above, according to the embodiment shown in FIG. 1, the light incident on the light guide plate 2b has a uniform inclined plane with respect to the upper plane, and the refractive index gradually decreases from the bottom to the top. The light is repeatedly refracted at the boundary surface between the plurality of light guide plate pieces, and is emitted from the upper surface of the light guide plate 2b while uniformly adjusting the light distribution state. Therefore, the emitted light is diffused by the diffusion plate 4 and then irradiates the back surface of the liquid crystal display surface as highly uniform diffused light.
[0013]
By the way, in the conventional example shown in FIG. 3, since the critical angle is obtained using scattering, the loss due to reflection is large, and the light distribution from the light guide plate is not in a proper state. Therefore, in the example of FIG. 3, the light is collected using the prism plate 5, the light distribution state is adjusted, and the luminance is improved. However, when light is collected using the prism plate 5, there arises a problem that moire occurs. On the other hand, in this embodiment, since the incident angle of light is gradually increased by utilizing the change in the refractive index, the loss due to reflection can be kept low, the luminance can be improved, and the light guide plate The uniformity of the light distribution of the light emitted from 2b can be easily increased. Therefore, a prism plate as shown in FIG. 3 can be omitted.
[0014]
Next, another embodiment will be described with reference to FIG. 2 is a side sectional view showing an embodiment in which the present invention is applied to a backlight using two light sources 1 and 1, and the same components as those shown in FIG. . In FIG. 2, reference numeral 2 c denotes a light guide plate, and two light guide plates having inclined planes that are plane-symmetric with respect to a central cross section parallel to the axial direction of the light sources 1, 1 of the light guide plate 2 c (front-back direction in the figure). It consists of an optical plate piece 2c-1 and light guide plate pieces 2c-2, 2c-3, and 2c-4.
[0015]
Each light guide plate piece has a different refractive index, the light guide plate 2c-1 has the smallest refractive index, and then gradually increases in the order of the light guide plate pieces 2c-2, 2c-3, 2c-4. The refractive index is as follows. The inclined plane formed by the boundary surface between the light guide plate pieces is set so that the inclination angle gradually decreases from the bottom to the top.
[0016]
With such a configuration, in the backlight shown in this figure, the light incident on the light guide plate pieces 2c-1 and 2c-1 from the two light sources 1 and 1 is refracted and reflected as in the embodiment shown in FIG. The light reaches the upper plane of the light guide plate 2c and gradually exits while gradually adjusting the light distribution. In the embodiment shown in this figure, since the light sources 1 are provided on both sides of the light guide plate 2c, the inclination angle of the inclined plane formed by the light guide plate 2c-1 closest to the light source 1 is compared with that shown in FIG. Can be bigger. Therefore, the ratio of the light reflected by the light guide plate 2c-1 in the incident light can be reduced, and the light distribution can be controlled more efficiently.
[0017]
In the above-described embodiment, the light guide plate is formed using a plurality of light guide plate pieces having different refractive indexes. However, the refractive index is gradually increased inside as in FIG. 1a or FIG. A single light guide plate formed so as to be changed can be used instead.
[0018]
【The invention's effect】
As described above, according to the present invention, since the refractive index of the light guide plate increases from the lower surface side to the upper surface side and changes according to the distance from the light source, the light is emitted from the light guide plate. The light distribution can be made uniform, and the light guide plate can be made brighter and more efficient than in the past. Therefore, it is possible to provide a bright illumination device with low power.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing a configuration of a backlight according to an embodiment of the present invention.
FIG. 2 is a side sectional view showing a configuration of a backlight according to another embodiment of the present invention.
FIG. 3 is a side sectional view showing a configuration of a conventional backlight.
FIG. 4 is a side sectional view showing a configuration of another conventional backlight.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light source 2b, 2c Light guide plate 3 Reflection plate 4 Diffusion plate 6 Reflection plate

Claims (2)

In a lighting device that has a light source and a light guide plate that receives light from the light source and guides the light from the side surface, and irradiates the liquid crystal display surface from the back surface with light emitted from the upper surface of the light guide plate.
The light guide plate is formed by laminating a plurality of wedge-shaped light guide plate pieces in the thickness direction,
Each of the light guide plate pieces has an inclination angle between the first surface on the upper surface side of the light guide plate and the second surface on the lower surface side of the light guide plate gradually from the lower surface side of the light guide plate toward the upper surface side thereof. And the refractive index is gradually increased from the lower surface side to the upper surface side of the light guide plate,
One light guide plate piece provided on the lower surface side of the light guide plate among the light guide plate pieces constitutes a side surface of the light guide plate that receives light from the light source and a lower surface of the light guide plate, and The inclination angle is formed on the opposite side of the side surface of the optical plate,
The remaining light guide plate pieces among the light guide plate pieces are provided on the one light guide plate piece, and the inclination angle is formed on the side surface side of the light guide plate that receives light from the light source,
Light that is emitted from the light source and passes through the light guide plate piece on the lower surface side of the light guide plate of the two adjacent light guide plate pieces and reaches the light guide plate piece on the upper surface side of the light guide plate is between these light guide plate pieces. By being configured to be refracted toward the upper surface side of the light guide plate at the boundary surface,
The illuminating device, wherein the refractive index of the light guide plate increases stepwise from the lower surface side toward the upper surface side, and increases stepwise as the distance from the light source increases.   A liquid crystal display device comprising the illumination device according to claim 1.

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