JP2000010094A - Backlight device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To irradiate dispersedly a beam emitted from a fluorescent lamp to a dispersion plate and to improve uniformity in the luminance of the beam emitted from the dispersion plate by making the cross section of the fluorescent lamp an elliptic shape and arranging it so that the direction of the major axis of the ellipse becomes vertical to the surface of the dispersion plate. SOLUTION: A backlight device 1 is constituted so that plural pieces of fluorescent lamps 4 are arranged in parallel at an interval with each other in a boxy reflection plate 3 and the opening of the reflection plate 3 is closed with a cloudy-colored dispersion plate 5 made of a resin of acryl, etc. The fluorescent lamp 4 whose cross section is an elliptic shape is used and is arranged so that the direction of the major axis of the ellipse becomes vertical to the surface of the dispersion plate. In the backlight device 1 using the fluorescent lamp of the elliptic cross section, since the light quantity going obliquely for the surface of the dispersion plate 5 is more than that of backlight device using the fluorescent lamp of a circular cross section and dispersedly radiates the beam in the left/right directions, the uniformity in the luminance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device used as a light source of a liquid crystal display device, and more particularly to a direct backlight device having a lamp disposed below a diffusion plate.

[0002]

2. Description of the Related Art Since a liquid crystal display device itself does not have a light emitting function, it is general to arrange a backlight device as a light source on the back and to display information by transmitting light from the backlight device to the liquid crystal display device. It is. Broadly,
There are two types of backlight devices, a direct type backlight and an edge light type backlight.

First, a conventional direct-type backlight device will be described. FIG. 5 is a sectional view showing a conventional direct type backlight device together with a liquid crystal display device.

In FIG. 5, a backlight device 101 is shown.
The liquid crystal display device comprises a plurality of fluorescent lamps 102 each having a circular cross section of a hot cathode or a cold cathode type arranged in a box-shaped reflecting plate 103, and the upper portion thereof is covered with a diffusion plate 105. 106 is arranged on the back side. Reflector 1
Numeral 03 is a metal or resin light reflecting member. The light emitted from the fluorescent lamp 102 is directly or reflected by the reflection plate 103 and applied to the diffusion plate 105. The light applied to the diffusion plate 105 is scattered in all directions when passing through the diffusion plate 105 and illuminates the liquid crystal display device 106 from the back.

As described above, the direct type backlight device 1
Since the fluorescent lamp 102 is disposed immediately below the display surface of the liquid crystal display device 106, the luminance of the fluorescent lamp 102
, And the brightness uniformity of the entire backlight device becomes low. That is, the luminance unevenness increases.

[0006] This phenomenon will be described with reference to FIG. FIG. 6 is an enlarged sectional view of one fluorescent lamp 102 of the backlight device shown in FIG. In FIG. 6, a two-dot chain line indicates a light beam emitted from a point at which the circumference of the fluorescent lamp 102 is equally divided. The luminous flux is considered to be emitted uniformly from the center O of the fluorescent lamp 102 in all directions, so that the light intensity of each luminous flux is equal.

Here, two ranges A and B having the same size on the surface of the diffusion plate 105 are considered. The range A is a range between a point P on the diffusion plate 105 on a straight line passing through the center O of the fluorescent lamp 102 and perpendicular to the diffusion plate 105 and a point Q separated from the point P by a distance L, and the range B is , Point Q and point Q
And a point R further away from the point R by a distance L.
At this time, as schematically shown in FIG. 6, four light beams reach the range A and three light beams reach the range B. This indicates that the portion of the diffusion plate close to the fluorescent lamp 102 has high luminance, and the portion far from it has low luminance.

If the angle between the straight line OP and the light beam is θ, and the distance from the center O of the fluorescent lamp 102 to the diffusion plate 105 is t, the arrival position y of the light beam on the diffusion plate 105 is y =
t × tan θ. Since this is a non-linear function, the density of the luminous flux applied to the diffusion plate 105 is not constant. As can be seen from the graph of FIG. 7 showing the outline of a general luminance distribution on the diffusion plate 105, the luminance has a peak at the center of the fluorescent lamp 102, and rapidly decreases as the distance from the center of the fluorescent lamp 102 increases. This difference in brightness appears as uneven brightness. Since the diffusion ability of the diffusion plate 105 is limited, it is necessary to make the luminance of the fluorescent lamp 102 uniform to some extent before the light reaches the diffusion plate.

In order to improve the uniformity of the luminance, as shown in FIG.
Pattern 1 made of a substance having an action of absorbing or reflecting light, such that the area is the largest on the center line of the fluorescent lamp 112 and the area decreases as the distance from the center increases.
No. 16 (see Japanese Patent Application Laid-Open No. Sho 62-40151), or a device in which a sufficient distance is provided between the diffuser and the fluorescent lamp to allow the light emitted from the fluorescent lamp to diffuse naturally to some extent before reaching the diffuser. It has been known.

Next, an edge light type backlight device will be described. The edge light type backlight device has a light guide disposed on the back surface of the liquid crystal display device, a reflective cover provided on a side end, and a fluorescent lamp provided in the reflective cover. Generally, an edge-light type backlight device has a drawback that light emitted from a fluorescent lamp is reflected by a reflector, but most of the light hits the fluorescent lamp and the brightness is attenuated, so that it is difficult to obtain high brightness. is there.

In order to overcome this disadvantage, FIG.
As shown in FIG.
A backlight device has been proposed in which the length in the thickness direction is smaller than the length in the direction perpendicular to the thickness direction of the light guide 127 (see JP-A-8-5840). This makes it difficult for the light reflected by the reflector 123 to hit the fluorescent lamp 122.

[0012]

However, the above-mentioned conventional backlight device has the following problems.

First, in a direct-type backlight device, when a pattern made of a substance having a function of absorbing light is printed on the surface of the fluorescent lamp, the amount of light emitted from the fluorescent lamp becomes small. The brightness of the entire device is reduced. Even when a pattern made of a substance having a function of reflecting light is printed instead of a substance having a function of absorbing light, light reflected by the pattern and returned to the fluorescent lamp is applied to the fluorescent lamp. It is absorbed and attenuated by the phosphor or glass that has been emitted, and hardly contributes to the brightness of the backlight device.

Further, if the distance between the diffusion plate and the fluorescent lamp is sufficiently long, the thickness of the entire backlight device is increased. A liquid crystal display device is mainly used for a device that requires thinness, and it is not preferable that a backlight device used as a light source of such a liquid crystal display device be thick. By the way, 10 fluorescent lamps with a diameter of 3 mm and a diffuser with a thickness of 2 mm were used, and the luminance unevenness was ± 20%.
In order to suppress the distance below, the distance between the fluorescent lamp and the diffusion plate needs to be 14.5 mm or more, and the entire backlight device needs to have a thickness of 23 mm or more.

On the other hand, the edge light type backlight device is difficult to produce high luminance as described above.
Even if a fluorescent lamp as shown in FIG. 9 is used, the number of fluorescent lamps is limited in the edge light type, and more light is reflected on the side surface of the reflector, resulting in efficient light. Does not radiate toward the light guide, and the brightness does not improve much.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thin backlight device which improves the uniformity of luminance without lowering the luminance.

[0017]

In order to achieve the above object, a backlight device according to the present invention is used as a light source of a liquid crystal display device, and the backlight device disposed on the back of the liquid crystal display device reflects light. A concave reflector formed of a member and having an opening, at least one fluorescent lamp disposed in the reflector, and an exterior of the reflector that diffuses light emitted from the fluorescent lamp. And a diffusion plate fixed by closing the opening of the reflection plate, and the fluorescent lamp has a cross section that is oblique to the surface of the diffusion plate as compared with a fluorescent lamp having a circular cross section. It is characterized in that it has a shape in which the amount of light going to it increases.

In the backlight device of the present invention configured as described above, the fluorescent lamp is disposed on the back side of the diffuser plate. However, the fluorescent lamp has a lower surface than the circular fluorescent lamp. The light emitted from the fluorescent lamp is further diffused and applied to the diffuser plate because the shape of the light is oblique to the light. As a result, the uniformity of the luminance is improved, and the distance between the diffusion plate and the fluorescent lamp can be reduced, so that the thickness of the entire backlight device can be reduced.

Regarding the shape of the fluorescent lamp that emits such light, the cross-sectional shape is largest in a region where the curvature is closest to the diffusion plate on the side closer to the diffusion plate than the center of the fluorescent lamp,
It may be constituted by a curve that becomes smaller as the distance from the diffusion plate increases. In this case, a fluorescent lamp having an elliptical cross section can be used.

The fluorescent lamp may have a flat surface whose surface is inclined with respect to the surface of the diffusion plate, in addition to the above-described shape. In this case, a fluorescent lamp having a rhombic cross section can be used. When a fluorescent lamp having a rhombic cross section is used, it is preferable that the long diagonal line of the two diagonal lines of the rhombus is arranged to be perpendicular to the surface of the diffusion plate.

[0021]

Next, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment) FIG. 1 is a cross-sectional view of a backlight device according to a first embodiment of the present invention.

As shown in FIG. 1, in a backlight device 1 according to the present embodiment, a plurality of fluorescent lamps 4 are arranged in parallel in a box-shaped reflector 3 at an interval from each other. Has a structure in which the opening is closed by a cloudy diffusion plate 5 made of a resin such as acrylic.

The reflection plate 5 is made of a metal or resin member that reflects light.
In addition to the box shape as shown in FIG. 1, any concave shape such as a bowl-shaped or V-shaped cross section for receiving the fluorescent lamp 4 may be used.

The fluorescent lamp 4 has an elliptical cross section, and is arranged so that the major axis of the ellipse is perpendicular to the surface of the diffusion plate. The number and intervals of the fluorescent lamps 4 are appropriately set according to the required luminance of the backlight device 1 and the size of the illuminated surface.

Here, with reference to FIG. 2, the optical path of the light emitted from the fluorescent lamp 4 will be described in comparison with the case of the fluorescent lamp 2 having a circular cross section. In FIG. 2, the fluorescent lamp 4 having an elliptical cross section and the fluorescent lamp 2 having a circular cross section, both having the same circumference, are superimposed so that the centers of the two are at the same position. For example, if the length of the major axis of the fluorescent lamp 4 having an elliptical cross-section is 3 mm and the length of the minor axis is 2 mm, and the diameter of the fluorescent lamp 2 having a circular cross-section is 2.51 mm, the circumferential length of both lamps will be described. Is about 7.9 mm, which is almost equal. That is, the amount of light emitted from the fluorescent lamp 4 having an elliptical cross section is equal to the amount of light emitted from the fluorescent lamp 2 having a circular section.

At this time, the points A ₀ , A ₁ , and A _{0 represent} the entire circumference of the fluorescent lamp 2 having a circular cross section and the entire circumference of the fluorescent lamp 4 having an elliptical cross section.
₂ , A ₃ , to _An , B ₀ , B ₁ , B ₂ , B ₃ , to B _n
When the light 8, 9 emitted from each of these points is indicated by an arrow together with the traveling direction thereof, the amount of light per arrow becomes equal. Also, the light 8,8 emitted from the fluorescent lamps 2,4
9 is radiated in the normal direction of the surfaces of the fluorescent lamps 2 and 4, but the fluorescent lamp 4 having an elliptical cross section is arranged in the above-mentioned direction. The curvature is largest in a region near the diffusion plate 5 and becomes smaller as the distance from the diffusion plate 5 increases. Therefore,
The angle of the light emitted from the point corresponding to the suffix on the circumference of each fluorescent lamp 2 and 4 with the center line on the long axis side of the fluorescent lamp 4 having the elliptical cross section is defined by the fluorescent lamp 2 having the circular cross section.
The light 9 emitted from the fluorescent lamp 4 having an elliptical cross section is larger than the light 8 emitted from the fluorescent lamp 4.

That is, the backlight device 1 according to the present embodiment using the fluorescent lamp 4 having an elliptical cross section has a larger diffusion surface than the backlight device using the fluorescent lamp 2 having a circular cross section. The amount of light traveling obliquely is large, and the light is diffused in the horizontal direction and emitted.

Accordingly, in FIG. 1, the light emitted from the fluorescent lamp 4 is diffused to the right and left to some extent,
, The uniformity of luminance is improved as compared with the conventional case using a fluorescent lamp having a circular cross section. Moreover, it is not necessary to print a predetermined pattern on the surface of the fluorescent lamp in order to reduce the brightness immediately above the fluorescent lamp as disclosed in Japanese Patent Application Laid-Open No. 62-40151, Since the reflected light is not reflected on the side surface of the reflection plate 5, the luminance itself does not decrease.

When emphasis is placed on reducing the thickness of the entire backlight device, the distance between the fluorescent lamp 4 and the diffusion plate 5 is reduced by the improvement in the uniformity of the luminance, thereby reducing the thickness of the entire backlight device. Can be reduced.

As shown in FIG. 3, when the light 9 emitted from the fluorescent lamp 4 having an elliptical cross section is applied to the diffusion plate 5, the fluorescent lamp 2 having a circular cross section is compared with the fluorescent lamp 2 having a circular cross section. ± 2% variation in luminance using lamp 2
Within this range, the distance E from the center O of the fluorescent lamp 2 to the diffusion plate 5 needs to be 14.5 mm.

Here, the circumference of the fluorescent lamp 2 having a circular cross section is divided into 36 equal parts, and the position at which the light 8 radiated from the fluorescent lamp 2 reaches the diffuser plate 5 is defined as P ₀ , P ₁ , P ₂ , P ₃ ,. In the case of the fluorescent lamp 4 having an elliptical cross section, the light 9 emitted from the point obtained by dividing the circumference into 36 equal parts is also the positions P ₀ , P ₁ ,
When the position of the diffusion plate 5 is set so as to reach P ₂ , P ₃ ,..., The diffusion plate 5 moves from the center O of the fluorescent lamp 4 having an elliptical cross section.
The distance D up to this is 9.4 mm. That is, the distance between the fluorescent lamp 4 and the diffusion plate 5 can be reduced by 5.1 mm, and as a result, the thickness of the backlight device is reduced by 5.1 mm while suppressing the variation in luminance to within ± 20%. be able to.

In this embodiment, an example is shown in which the fluorescent lamp 4 having an elliptical cross section is used. However, the side closer to the diffuser plate 5 than the center of the fluorescent lamp is closest to the diffuser plate 5. In the case of a fluorescent lamp having a curvature that is large in the region and becomes smaller as the distance from the diffusion plate 5 increases, the amount of light oblique to the surface of the diffusion plate 5 increases, so that the shape of the fluorescent lamp is elliptical. It is not limited to the fluorescent lamp 4 having a cross section.

(Second Embodiment) FIG. 4 is a sectional view of a backlight device according to a second embodiment of the present invention.

In this embodiment, a plurality of fluorescent lamps 14 are arranged in parallel in the reflector 13. The first embodiment differs from the first embodiment in that the fluorescent lamps 14 have a rhombic cross section. different. Each of the fluorescent lamps 14 has a longer diagonal line between two rhombic diagonal lines, and a diffuser plate 15.
And the surface of the fluorescent lamp 14 is inclined with respect to the surface of the diffusion plate 15. Others
The reflecting plate 13 and the diffusing plate 15 are the same as those of the first embodiment, and the description is omitted.

The fluorescent lamp 14 having such a rhombic cross section is
Unlike a circular or elliptical fluorescent lamp, which is all curved, it is composed of four planes. Accordingly, uniform light is emitted from the respective surfaces of the fluorescent lamp 14 in a direction perpendicular to the surfaces. That is, since the amount of light oblique to the surface of the diffusion plate 15 is larger than that of a fluorescent lamp having an elliptical cross-section in which the peripheral surface of the cross-section of the fluorescent lamp 14 is equal, the uniformity of luminance is low. Further improve. In addition, since uniform light is emitted from each surface of the fluorescent lamp 14,
It is easier to simulate uneven brightness, and the diffusion plate 1
Even when the dot pattern is printed on 5 to finely adjust the brightness unevenness, the dot pattern density design can be easily performed.

In this embodiment, the fluorescent lamp 14
An example in which the longer diagonal of the two diamond-shaped diagonals is arranged perpendicular to the surface of the diffusion plate 15 has been described. The diagonal lines may be arranged so as to be perpendicular to the surface of the diffusion plate 15. However, arranging the fluorescent lamps 14 as shown in FIG. 4 irradiates the light to the diffusion plate 15 at a larger angle, so that it is excellent in terms of uniformity of luminance, Since the distance between the lamps 14 can be increased, the light reflected by the reflection plate 13 is more efficiently guided to the diffusion plate 15, and a decrease in the overall luminance can be suppressed, which is preferable.

[0038]

As described above, the backlight device of the present invention uses a fluorescent lamp having a shape in which the amount of light oblique to the surface of the diffuser plate is larger than that of a fluorescent lamp having a circular cross section. Accordingly, the light emitted from the fluorescent lamp is further diffused and irradiated to the diffusion plate, so that the uniformity of the luminance of the light emitted from the diffusion plate can be improved. Further, by improving the uniformity of luminance, the thickness of the entire backlight device can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of a backlight device according to the present invention.

FIG. 2 is a diagram showing light emitted from an elliptical fluorescent lamp used in the backlight device shown in FIG. 1 in comparison with light emitted from a circular fluorescent lamp.

FIG. 3 is a diagram illustrating a state in which light emitted from an elliptical fluorescent lamp is applied to a diffusion plate, in comparison with a case of a circular fluorescent lamp.

FIG. 4 is a sectional view of a backlight device according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a conventional direct-type backlight device together with a liquid crystal display device.

6 is an enlarged cross-sectional view of one fluorescent lamp for explaining non-uniformity of luminance of the backlight device shown in FIG. 5;

FIG. 7 is a graph schematically showing a general luminance distribution on a diffusion plate of a direct type backlight device.

FIG. 8 is a plan view of a conventional fluorescent lamp having a predetermined pattern printed on its surface.

FIG. 9 is a cross-sectional view of an example of a conventional edge light type backlight device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Backlight device 3,13 Reflector 4,14 Fluorescent lamp 5,15 Diffuser 9 Light

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[Procedure amendment]

[Submission date] October 1, 1999 (1999.10.
1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

[0017]

In order to achieve the above object, a backlight device according to the present invention is used as a light source of a liquid crystal display device, and the light is reflected in a backlight device disposed on the back of the liquid crystal display device. Box composed of components
Shaped reflector and a cross-sectional shape disposed in the reflector
There a fluorescent lamp elliptical, said to fluorescent lamps to diffuse the light emitted from the irradiation to the outside of the reflecting plate has a fixed diffusion plate closes the opening of the reflector, before
The bottom surface of the reflection plate is a plane parallel to the surface of the diffusion plate,
In the fluorescent lamp, the direction of the major axis of the ellipse is the diffusion plate.
Characterized by being disposed so as to be perpendicular to the surface . It is also used as a light source for liquid crystal display devices.
The backlight unit is located on the back of the LCD.
A concave member having an opening
Shaped reflector and a diamond-shaped cross section disposed in the reflector.
Shaped fluorescent lamp and light emitted from the fluorescent lamp
In order to diffuse and irradiate the outside of the reflector, the reflection
A diffusion plate fixed by closing an opening of the plate;
The lamp is the longest of the two diagonal lines of the diamond.
Arranged so that the square line is perpendicular to the surface of the diffusion plate
It is characterized by having been done. In this case, the reflection plate
Has a box shape whose bottom surface is a plane parallel to the surface of the diffusion plate.
Preferably.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

In the backlight device of the present invention configured as described above, the fluorescent lamp is disposed on the back side of the diffusion plate, but the fluorescent lamp has an elliptical or rhombic cross section.
Since respectively are arranged as described above, cross-section as compared to the circular fluorescent lamp, a diffusion plate surface Ri of a number the amount of light directed obliquely with respect to the light emitted from the fluorescent lamp ,
The light is further diffused and irradiated to the diffusion plate. As a result, the uniformity of the luminance is improved, and the distance between the diffusion plate and the fluorescent lamp can be reduced, so that the thickness of the entire backlight device can be reduced.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Deleted

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0020

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[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction contents]

[0038]

As described above, according to the backlight device of the present invention, a fluorescent lamp having an elliptical cross section is moved in the direction of the major axis of the ellipse.
Direction is perpendicular to the surface of the diffuser,
Is a fluorescent lamp with a diamond-shaped cross-section.
Arrange so that the longer side is perpendicular to the surface of the diffuser
It is, cross Ri is much amount of light directed obliquely to the plane of the circular fluorescent lamp compared to the diffusion plate, the light emitted from the fluorescent lamp is irradiated to a more diffuse and diffuser, It is possible to improve the uniformity of the luminance of the light emitted from the diffusion plate. Further, by improving the uniformity of luminance, the thickness of the entire backlight device can be reduced.

Claims (7)

[Claims] 1. A backlight device used as a light source of a liquid crystal display device and disposed on a back surface of the liquid crystal display device, comprising: a concave reflector having an opening, comprising a member for reflecting light; And at least one fluorescent lamp, which is disposed inside the diffuser fixed to cover the opening of the reflector in order to diffuse the light emitted from the fluorescent lamp and irradiate the light to the outside of the reflector. A backlight device, wherein the fluorescent lamp has a shape in which the amount of light obliquely directed toward the surface of the diffuser plate is larger than that of a fluorescent lamp having a circular cross section. . 2. A sectional shape of the fluorescent lamp has a curvature on a side closer to the diffusion plate than a center of the fluorescent lamp.
2. The backlight device according to claim 1, wherein the backlight device is configured by a curve that is largest in a region closest to the diffusion plate and becomes smaller as the distance from the diffusion plate increases. 3. 3. The fluorescent lamp has an elliptical cross section,
The backlight device according to claim 2, wherein the direction of the major axis of the ellipse is arranged to be perpendicular to the surface of the diffusion plate. 4. The backlight device according to claim 1, wherein a surface of the fluorescent lamp has a plane inclined with respect to a surface of the diffusion plate. 5. The backlight device according to claim 4, wherein a cross-sectional shape of the fluorescent lamp is rhombic. 6. The backlight according to claim 5, wherein the fluorescent lamp is arranged such that a longer one of the two diagonal lines of the rhombus is perpendicular to a surface of the diffusion plate. apparatus. 7. The backlight device according to claim 1, wherein a plurality of the fluorescent lamps are arranged in the reflector in parallel with each other.