JPH06265885A - Back light device - Google Patents

Abstract

PURPOSE:To provide the back light device which controls exit light by changing the reflectivity and transmittance of a half mirror according to places and decreases the uneven brightness of the light from a light source. CONSTITUTION:A fluorescent tube or light emitting diode or the like is used for the light source 1 and a reflection plate 2 is so provided as to prevent the leakage of the light from the light source 1. The light transmitted through the half mirror 3 is emitted to the surface through a diffusion sheet 4. The diffusion sheet 4 is used to make the patterns of the half mirror 3 invisible and to remove the uneven brightness. A top right type or side light type is obtd. by disposing the light source 1 in the central part of the reflection plate 2 or in the side part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device, and more particularly, to controlling the unevenness of brightness of a surface emitting device by making the reflectance and transmittance of the half mirror appropriate for the location. The present invention relates to a sidelight type and a direct type backlight device.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of an edge light type surface light emitting device using a conventional light guide plate, in which 11 is a light source,
Reference numeral 12 is a reflection plate, 13 is a light guide plate, and 14 is a diffusion sheet. As the light source 11, a fluorescent tube, a light emitting diode or the like is usually used, and a reflecting plate 12 is provided to prevent the light from the light source 11 from leaking to the outside. Light source 11
Light is refracted and enters the inside of the light guide plate 13. Since the light inside the light guide plate 13 has a critical reflection angle or more, the light guide plate 1
Reflected within 3 and does not appear on the surface. Therefore, a diffusing material or an uneven pattern is provided on the back surface of the light guide plate 13 to change the light reflection angle. Light with an angle within the critical reflection angle 1
It is emitted from the surface of 3 and becomes a surface light source.

Further, the unevenness of the brightness of the surface light source is adjusted by the density of the back surface pattern. The light emitted from the light guide plate 13 passes through the diffusion sheet 14 and is emitted to the surface. The diffusion sheet 1
The purpose of 4 is to make the pattern on the back surface of the light guide plate 13 invisible and to eliminate uneven brightness. Recently, instead of the diffusion sheet, a sheet having a light collecting property is being used.

FIG. 5 is a block diagram of a conventional direct type surface emitting device. In the figure, 15 is an ND filter, and other parts having the same functions as those in FIG. In the direct type, the diffusion plate 14 is thickened to diffuse the light from the light source 11 or absorb the light in the vicinity of the light source with an ND (Neutral Density) filter 15 or the like to remove uneven brightness. Further, in the hollow state without the light guide plate, as shown in FIG. 6, the light is emitted directly from the light source 11 or after being reflected once by the reflection plate 12. For this reason, only the vicinity of the light source glows, resulting in uneven brightness as shown in FIG. 7, which is not practical.

[0005]

As described above, in the conventional edge light type backlight device, when the diffusing material or the unevenness on the back surface of the light guide plate is uniform as a whole, the brightness on the light guide plate increases as the distance from the light source increases. Since it becomes dark, the density is changed depending on the place to prevent it, but the light guide plate still needs a certain thickness. 4 if about 4 inches
Mm thickness is enough, but 8 inches requires about 8 mm,
The light guide plate is made thin at the sacrifice of brightness and brightness unevenness except for a special place because it is not only bulky but also heavy. In the direct type backlight device, the thickness of the diffusion plate must be increased to remove the uneven brightness, and the uneven brightness tends to be larger than that of the edge light type. A diffuser plate with a thickness of about 3 mm is required to obtain good brightness unevenness, and light absorption by the diffuser plate also becomes large. Therefore, the brightness unevenness is sacrificed to some extent to obtain brightness and thinness. Also, N
By using the D filter, it is possible to absorb light near the light source and eliminate uneven brightness, but the brightness is sacrificed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a backlight device in which the unevenness of brightness is adjusted by a half mirror.

[0007]

In order to achieve the above object, the present invention provides (1) a sidelight type backlight device used together with a liquid crystal display device, which comprises a light source and light emitted from the light source. A reflecting plate for reflecting in a direction substantially orthogonal to the optical axis, and transmitting a part of the light flux from the reflecting plate,
And a half mirror configured to reflect the other to the reflector side, and configured to suppress uneven brightness by the half mirror, or (2) a direct type backlight used together with a liquid crystal display device. A light device, a light source, a reflector disposed behind the light source, for reflecting a light flux from the light source, a part of the light flux from the reflector, and the other of the reflectors. And a half mirror configured to reflect the light to the side, and the half mirror suppresses uneven brightness.

[0008]

The light source is provided on the side of the reflector, and the reflector is provided so as to reflect the light emitted from the light source in a direction substantially orthogonal to the optical axis. By providing a half mirror so that a part of the light beam from the reflector is transmitted and the other light beam is reflected to the reflector side, the emitted light is controlled by changing the reflectance / transmittance of the half mirror depending on the location. However, uneven brightness can be suppressed. Further, the same effect can be obtained by providing the light source in the center of the reflector.

[0009]

Embodiments will be described below with reference to the drawings. FIG. 1 is a configuration diagram for explaining an embodiment of a sidelight type backlight device according to the present invention.
Is a light source, 2 is a reflector, 3 is a half mirror, and 4 is a diffusion sheet. As the light source 1, a fluorescent tube, a light emitting diode or the like is usually used, and a reflection plate 2 is provided so that the light from the light source 1 does not leak to the outside. The light transmitted through the half mirror 3 passes through the diffusion sheet 4 and is emitted to the surface. The diffusion sheet 4 is used for making the pattern of the half mirror 3 invisible and removing uneven brightness.

First, with reference to FIG. 3, a description will be given of reducing the uneven brightness by using a half mirror. Around the light source, which is a region a with a large amount of light, a half mirror with a transmittance of 33% is attached to limit the emitted light. 100% of light source
Then, 67% of the light is reflected by the mirror, and 67% of the light enters the region b. The transmittance of this area b is set to 50%,
By setting the transmittance of the region c to 100%, the transmitted light becomes 33%. By thus changing the transmittance / reflectance depending on the location, it is possible to obtain a surface-emitting device having good brightness unevenness.

The half mirror 3 is made by vapor-depositing a non-metal type such as ZnS, CeO ₂ , TiO ₂ or a metal type such as Al, Ag, Cr, Au on a glass or plastic film. Reflectance / transmittance is based on material, deposition amount,
It can be controlled by changing the film thickness. Metallic ones have a large absorption loss, and nonmetallic ones have drawbacks such as coloration. Therefore, ZnS-Cr may be used in combination. Around the light source, which is a region a with a large amount of light, a half mirror with a transmittance of 20% is attached to limit the emitted light. Assuming that the light amount of the light source is 100%, 80% of the light is reflected by the mirror, and 80% of the light enters the area b. By setting the transmittance of this region b to 25%, the transmitted light is 80 ×
0.25 = 20%, and reflected light is 80 × 0.75 = 60%. In the region c, the transmittance is 33% so that the transmitted light is 20%, and the reflected light is 40%. By setting the transmittance of the region d to 50% and the transmittance of the region e to 100%, the transmitted light becomes 20%.

By thus changing the transmittance / reflectance depending on the location, it is possible to obtain a surface emitting device having good brightness unevenness.
On the contrary, it is possible to increase or decrease the brightness of a specific area by intentionally making the brightness unevenness worse. In this example, the description has been made by dividing the region into five, but the finer the region is, the finer the uneven brightness can be controlled. For example, by controlling not only the vertical direction but also the horizontal direction, it is possible to shorten the fluorescent tube, which is a light source having a correlation with the uneven brightness in the horizontal direction, or to make a surface light source with a point light source or a plurality of light sources. The position of the light source also has no influence on the brightness unevenness, which increases the degree of freedom in design. It has been confirmed that a diffusion plate of about 0.5 mm, which used to require about 3 mm, is sufficient. Further, if the transmittance and the reflectance are continuously variable, the regions will not be connected, and the change in brightness between the regions will not be recognized, and the diffuser plate will be unnecessary.

FIG. 2 is a block diagram for explaining an embodiment of a direct type backlight device according to the present invention, and the reference numerals in the figure are the same as those in FIG. In FIG. 1, the light source 1 is provided at the end of the reflection plate 2, but in FIG. 2, it is provided at the center of the reflection plate, that is, directly below the half mirror. Further, in a display device such as a liquid crystal display, the external light that has passed through the liquid crystal panel is reflected by the half mirror 3 and the reflection plate 2 and passes through the liquid crystal panel again, so that it has the character of a reflective liquid crystal that utilizes the external light in bright places. You can

[0014]

As is apparent from the above description, the present invention has the following effects. In other words, by using a half mirror that absorbs light slightly, it reflects light in bright areas without absorbing it, and guides it to dark areas to adjust the brightness unevenness, thus achieving high brightness, thinning, and weight reduction. This has the effect of increasing the degree of freedom in design.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a backlight device according to the present invention.

FIG. 2 is a diagram showing another embodiment of the backlight device according to the present invention.

FIG. 3 is a diagram for explaining a method of reducing uneven brightness in a backlight device according to the present invention.

FIG. 4 is a configuration diagram of an edge light type surface light emitting device using a conventional light guide plate.

FIG. 5 is a configuration diagram of a conventional direct-type surface emitting device.

FIG. 6 is a diagram for explaining a brightness state in a conventional surface emitting device without a light guide plate.

FIG. 7 is a diagram showing luminance characteristics in FIG.

[Explanation of symbols]

1 ... Light source, 2 ... Reflector, 3 ... Half mirror, 4 ... Diffusion sheet.

Claims (2)

[Claims] 1. A sidelight type backlight device used together with a liquid crystal display device, comprising a light source, a reflection plate for reflecting light emitted from the light source in a direction substantially orthogonal to an optical axis, and the reflection plate. A half mirror configured to transmit a part of the luminous flux from the other side and reflect the other side to the reflection plate side, and the half mirror suppresses uneven brightness. Light device. 2. A direct type backlight device used together with a liquid crystal display device, comprising a light source, a reflector arranged in the back direction of the light source, for reflecting a light flux from the light source, and the reflector. And a half mirror configured to transmit a part of the light flux of the other and reflect the other to the reflecting plate side, and the half mirror suppresses luminance unevenness. apparatus.