JPH0772477A - Illumination device - Google Patents

Abstract

PURPOSE:To improve a light utilization rate by inclining and forming diffuse reflecting surfaces, thereby setting the direction of the max. intensity of scat tered and reflected luminous fluxes at a direction perpendicular to the exit surface of a transmission plate. CONSTITUTION:This liquid crystal display is composed of a cylindrical light source 1, a reflection sheet 2, a light transmission body 3, a diffusion sheet 4 and a liquid crystal panel 5. The transmission body 3 consists of a transparent body such as polymethyl methacrylate, is formed with diffuse reflecting patterns on the surface opposite to the liquid crystal panel 5 and has a function to transmit the light from a light source 1 and to emit the light to the liquid crystal panel 5 side. The diffuse reflecting patterns consist of microdot patterns. The respective diffuse reflecting surfaces 6 forming the dot patterns are formed to incline with the base surface of the transmission body 3. The dot patterns are so changed in density that the luminance is made uniform on the liquid crystal panel side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to liquid crystal displays such as liquid crystal televisions, word processors and personal computers, and more particularly to a lighting device (backlight) used for these liquid crystal displays.

[0002]

2. Description of the Related Art Cold cathode fluorescent lamps and hot cathode fluorescent lamps are used as backlight sources for liquid crystal displays. Conventionally, a liquid crystal display using this cylindrical light source (hereinafter, simply referred to as a light source) has generally been arranged by arranging one or more light sources under a diffusion plate.
It was necessary to secure a sufficient distance between the diffusion plate and the light source in order to ensure the uniformity of brightness. In order to make the device thinner in such a device, the distance between the light source and the diffusion plate is set to be small. For example, as disclosed in Japanese Patent Application Laid-Open No. 1-107236, a method of arranging a light source in an optical transmission body has been proposed. However, in such a device, uneven brightness is likely to occur on the diffusion plate. In order to prevent this, a method of increasing the diffusivity of the diffuser plate is generally adopted, but on the other hand, there is a problem that the transmittance of light is lowered and the brightness of the liquid crystal display is impaired. Therefore, in order to secure the same brightness, the number of light sources has to be increased, but measures against increase in power consumption and temperature rise must be considered.

Therefore, a backlight using an optical transmission medium has been recently proposed. (JP-A-63-309918
This is an illuminating device called an edge light system, in which a light source is arranged at the end of a light transmission body to guide light to a liquid crystal display. At this time, an optical transmission body (hereinafter simply referred to as a transmission body)
Partially coated with a material that diffuses and reflects light on one surface of
As a result, the light traveling while refracting in the transmission body is reflected by this diffuse reflection surface, and the light is emitted toward the liquid crystal panel. According to this method, since it is not necessary to arrange the light source under the liquid crystal panel, it is possible to reduce the thickness of the backlight device.

[0004]

However, in the above edge light type illuminating device, the diffusing material for emitting the light to the liquid crystal panel side does not completely diffuse the light.
It has directivity in the diffusion direction according to the incident direction of light.
The light incident on the diffusing material is light that propagates in the transmission body by total internal reflection, and therefore enters the surface coated with the diffusing material at an angle in the range of 48 ° from parallel. When this is reflected by the diffusing material, little light is reflected in the direction perpendicular to the surface, and the maximum intensity of light is reflected in the inclined direction.

Since the liquid crystal display is viewed from a direction perpendicular to the panel surface during normal use, the display is viewed from a direction different from the direction of the maximum intensity light. This is a large loss in terms of light utilization efficiency.

FIG. 6 is a conceptual diagram showing how light is reflected by the diffusing agent. The light rays incident on the printed diffusing material 43 are the light rays that have been totally reflected in the transmission body, and are therefore in the range of the light rays 21 to 22 shown in FIG. This value is, for example, in the range of 42 ° to 90 ° with respect to the normal line of the diffusing agent application surface when the transmission body is an acrylic resin. After the incident light having the intensity distribution deviated with respect to the angle is diffused and reflected by the diffusing material 43, the direction of the maximum intensity of the light intensity distribution is the surface normal 3
The direction 23 is a little inclined to the traveling direction side of the incident light beam with respect to the 0 direction. When this light ray is emitted from the upper surface 27 of the transmitter, it is further bent (26), and the direction of the maximum brightness of the emitted light is largely deviated from the direction perpendicular to the surface. FIG. 7 shows the state of light emission characteristics in which the maximum brightness is deviated from the vertical direction. In this way, the maximum intensity of the emitted light deviates from the direction perpendicular to the surface. Normally, when the user views the liquid crystal panel from a direction substantially perpendicular to the plane, the emission characteristic as shown in FIG. 7 shows the brightness only at about half the maximum brightness. This means that the luminous flux utilization factor of the lighting device is substantially reduced.

An object of the present invention is to prevent the above-described loss of light flux utilization and to obtain an edge-light type illumination device having substantially high light utilization efficiency.

[0008]

In order to solve the above-mentioned problems, a dot pattern for diffusively reflecting light is formed on the surface of the transmission body facing the light emission surface, and the surface of the diffuse reflection portion is formed. It is formed so as to be inclined with respect to the surface of the transmission body, and the direction of the inclination is such that the normal line of the diffuse reflection surface is inclined toward the cylindrical light source. Alternatively, if the cylindrical light source is located on two sides of the transmitter, the dot pattern that diffuses and reflects the light is used as a roof-shaped diffuse reflection surface, and the two diffuse reflection surfaces have their normals corresponding to each other. It is formed so as to face the direction of the cylindrical light source.

[0009]

By thus forming the diffuse reflection surface with an inclination, the direction of the maximum intensity of the light beam scattered and reflected can be made perpendicular to the emission surface of the transmission body, and the light utilization efficiency is improved. You can

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a cross-sectional view of a lighting device of this embodiment and a liquid crystal display using the same. FIG. 2 is an enlarged schematic view of a part of the transmission body according to the present invention, that is, a part of the diffuse reflection dot.

This embodiment comprises a cylindrical light source 1, a reflection sheet 2, a light transmission body 3, a diffusion sheet 4 and a liquid crystal panel 5.

Although not shown in detail, the liquid crystal display 5 is, for example, a device for recognizing electro-optical modulation of liquid crystal by an illumination device on the back surface and recognizing it as an image. The columnar light source 1 is a columnar fluorescent lamp. The reflection sheet 2 is
The reflector is formed so as to surround the cylindrical light source, and acts so that the light emitted from the cylindrical light source in the direction opposite to the transmission body is made to enter the transmission body 3 as much as possible. The transmitter 3 is, for example, polymethacrylmethyl (PMM).
The diffuse reflection pattern is formed on the surface opposite to the liquid crystal panel, and has a function of transmitting the light from the light source 1 and emitting the light to the liquid crystal panel side. The diffusion plate 4 has a function of reducing unevenness in the amount of light emitted from the transmission body.

The transmitter according to the present invention will be described in more detail with reference to FIG. A minute dot pattern that diffuses and reflects light as shown in FIG. 2 is formed on the surface of the transmitter opposite to the liquid crystal panel side. In each minute dot, the surface that diffuses and reflects light is shown by hatching. The surface is formed to be tilted with respect to the base surface of the transmission body, and the tilting direction is a direction in which the upward normal line 17 of the diffuse reflection surface is tilted toward the light source side in a plane perpendicular to the cylindrical light source 1.

The dots on such a slanted surface are formed by the transmitter 3.
Is formed by denting the surface, and a minute unevenness of several μm is formed on the diffuse reflection surface shown by hatching. At the same time, the surface 16 of the transmission body 3 on the side opposite to the liquid crystal panel is coated or vapor-deposited with a material (for example, silver or aluminum) that reflects light including the dot portion. As a result, the diffuse reflection surface 6 acts to reflect the light in the direction of the liquid crystal panel while diffusing the light.

The transmission body having such a depression can be manufactured by, for example, an injection molding method or the like.

FIG. 3 is a conceptual diagram showing how the light incident on the diffuse reflection surface 6 is reflected. Since the light incident on the diffuse reflection surface 6 is the light that has propagated through the transmission body 3 by total reflection, the incident angles of all the light are the light rays 10 and 11 shown in FIG.
Lies between the angles. When an incident light flux having a deviated angular distribution is reflected by a diffusive reflection surface having no inclination, the angular distribution of the reflected light flux is such that the direction of maximum light intensity is tilted from the direction perpendicular to the transmission body surface 15 as described above. Become.
Therefore, as shown in FIG. 3, by tilting the reflecting surface by an angle α, the direction of the maximum intensity of the reflected light flux is changed to the transmitter surface 1.
It is possible to match the direction perpendicular to 5.

The magnitude of the tilt angle α is obtained as follows. As shown in FIG. 7, when α = 0, assuming that the direction of the maximum brightness of the light beam reflected by the diffuse reflection surface and emitted from the surface 27 on the liquid crystal panel side is θ, the angle θ of this light beam within the transmitter is θ. ′ Is obtained from Snell's law: sin θ ′ = sin θ / n (1) n: Refractive index of transmitter. If the transmitter is acrylic resin, the refractive index n
Is about 1.5. The value of the maximum brightness direction θ differs depending on the material forming the reflecting surface. Assuming that the material is the essential material of this embodiment, θ is about 60 °. In this case, θ ′ is approximately 35 ° from the equation (1). The value of α is this θ
It suffices to set ′ to zero, and α = θ ′ / 2 (2) Therefore, in the case of this embodiment, it is set to about 17.6 °.

The following equation is obtained by putting together the equations (1) and (2).

[0019] ^{α = 0.5 · sin ~ 1 (} sinθ / n) ......... (3) as described above, the value of θ varies depending on the material constituting the diffuse reflection surface, instead up to about 20 ° to 65 ° obtain. θ =
When 20 °, α = 6.6 °, and when θ = 65 °, α = 18.6.
The value of α is 6.6 ° to 18.6 depending on the material.
It can change up to °.

Needless to say, the density of the diffuse reflection dots is changed so that the brightness becomes uniform on the liquid crystal panel surface.

As described above, when the diffuse reflection surface is inclined, the maximum brightness of the luminous flux emitted from the transmission body can be made perpendicular to the surface, and the light utilization efficiency can be improved.

Although the diffuse reflection pattern in the above embodiment is a dot, it does not necessarily have to be a dot. Figure 4
FIG. 7 shows an enlarged sketch of the diffuse reflection surface portion of the second embodiment in which the diffuse reflection pattern is formed in a strip shape. In FIG. 4, the hatched portion is a diffuse reflection surface, which is a reflection surface on which fine irregularities of several μm are formed. The material forming the reflecting surface is the same as that of the first embodiment, and therefore the inclination angle β of the surface is also formed to have the same value. The other parts such as the light source of the second embodiment are the same as those of the first embodiment.

On the other hand, when the cylindrical light sources are arranged on both sides of the transmission body, light propagates from both sides inside the transmission body. In this case, it is effective to form the diffuse reflection surface in a roof shape corresponding to the light from both.
FIG. 5 shows a sectional view of a third embodiment in which the diffuse reflection surface is formed in a roof shape. In this cross-sectional view, the light flux coming from the light source on the right side of the figure is the right side surface of the roof type diffuse reflection surface, and the light flux coming from the light source on the left side of the figure is the left side surface of the roof type diffuse reflection surface, respectively. It is diffusely reflected so as to have the maximum brightness in the direction perpendicular to the plane of the transmitter. The inclination of the left and right surfaces of the roof type diffuse reflection surface is set in the same manner as in the case of the first embodiment.

Such a roof type diffuse reflection surface is also effective in the first embodiment when a reflection sheet is attached to the surface of the transmission body opposite to the light source.

[0025]

As described above, according to the present invention, the emission characteristics of the light emitted from the transmission body can be controlled with a simple structure without adding a new device to the conventional lighting device, and the light utilization efficiency can be improved. Is substantially improved, the power consumption of the light source can be reduced when the brightness is the same, and the screen can be brightened when the power consumption is the same. Further, it is possible to obtain an effect that the thickness of the entire liquid crystal display device can be reduced as compared with the direct type illumination device in which the light source is arranged directly below the light transmission body.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display and a lighting device showing an embodiment of the present invention.

FIG. 2 is an enlarged schematic view of a diffuse reflection pattern portion of an optical transmission body according to an embodiment of the present invention.

FIG. 3 is a conceptual diagram showing incident light and reflected light on a diffuse reflection portion of the present invention.

FIG. 4 is an enlarged schematic view of a diffuse reflection pattern portion showing a second embodiment of the present invention.

FIG. 5 is a cross-sectional view of a liquid crystal display and a lighting device showing a third embodiment of the present invention.

FIG. 6 is a conceptual diagram showing incident light and reflected light on a conventional diffuse reflection portion.

FIG. 7 is a graph showing an example of deviation of the maximum luminance in the light emission characteristic of the conventional transmission body.

FIG. 8 is a cross-sectional view of a conventional lighting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cylindrical light source, 2 ... Reflection sheet, 3 ... Optical transmission body, 4 ... Diffusion sheet, 5 ... Liquid crystal display, 6 ... Inclined diffuse reflection surface, 7 ... Strip-shaped inclined diffusion reflection surface, 8 ... Roof type diffusion reflection surface, 9 ... Curved reflector.

Claims (6)

[Claims] 1. An edge-light type illuminating device for illuminating a liquid crystal panel, comprising: a cylindrical light source; and a light transmitting body for transmitting light from the cylindrical light source and irradiating the light toward the liquid crystal panel. In the optical transmission body, a minute dot pattern that diffuses and reflects light is formed on the surface opposite to the surface facing the liquid crystal panel, and the surface that diffuses and reflects light at each dot is An illuminating device, which is formed so as to be inclined in the direction of a cylindrical light source. 2. The light source according to claim 1, wherein the pattern for diffusively reflecting the light is a fine band-like pattern parallel to the cylindrical light source, and the surface for diffusing and reflecting the light has a surface normal line of the cylindrical light source. An illuminating device, which is formed so as to be inclined toward the side. 3. An edge light type illuminating device for illuminating a liquid crystal panel, comprising: a cylindrical light source; and a light transmitting body for transmitting light from the cylindrical light source and irradiating the light toward the liquid crystal panel. In the light transmission body, an illumination characterized by forming a minute dot pattern formed by a surface that diffuses and reflects light in the shape of a roof recess on the surface opposite to the surface facing the liquid crystal panel. apparatus. 4. The illumination according to claim 3, wherein the pattern for diffusing and reflecting the light is a fine strip-shaped pattern parallel to the cylindrical light source that is recessed in a roof type for diffusing and reflecting the light. apparatus. 5. The tilt angle of the diffuse reflection surface with respect to the surface of the optical transmission body according to claim 1 or 2, wherein the tilt angle is from 6.6 ° to 1 °.
A lighting device characterized by being set in a range of 8.6 °. 6. The tilt angle of the roof type diffuse reflection surface with respect to the surface of the optical transmission body according to claim 3 or 4, wherein the inclination angle is 6.6 °.
The lighting device is set in a range from 18.6 ° to 18.6 °.