JPH08146415A - Back light unit - Google Patents

Abstract

PURPOSE: To assure a sufficient light quantity without unequal luminance while reducing the thickness of a back light unit. CONSTITUTION: Cold cathode ray tubes 30 are fitted about half into semicircular recessed parts 21 of transparent or translucent light transmission members 20. The light from the upper half parts of the cold cathode tubes 30 which is direct light is partly reflected by the upper surface pats of light transmission plates 22, 23 and the light from the lower half parts of the cold cathode tubes 30 is introduced by light transmission piece parts 22a, 22b, 23a, 23b of the light transmission plates 22, 23 in a direction parting from the cold cathode tubes 30 and is reflected by the lower surface parts of the light transmission plates 22, 23. The effective use of the direct light from the cold cathode tubes 30 and the reflected light by the rear surface parts of the light transmission piece parts is made possible and the control of the directivity of light is made easy as the rear surface parts are formed as mirror finished surfaces. The more light is introduced from the cold cathode tubes 30 tending to be dark and the middle of the cold cathode tubes 30 and, therefore, the uniform illumination distribution is realized even if the diameter of the cold cathode tubes 30 is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit used for backlight illumination of a liquid crystal panel, and more particularly to a backlight unit which is thin and can secure a sufficient amount of light without uneven brightness.

[0002]

2. Description of the Related Art In order to enlarge a liquid crystal panel and improve its visibility, it is important to uniformly illuminate the backlight.

As a method of illuminating such a liquid crystal panel, a backlight method and an edge light method are known.

The basic structure of the backlight system is to arrange one or a plurality of straight or U-shaped or W-shaped lamps directly under the screen. For example, as shown in FIG. The direct light from the diffuser 3 and the reflected light from the reflector 2
The screen is made to shine by diffusing it.

On the other hand, the basic structure of the edge light system is to arrange one or a plurality of lamps on one side or a plurality of sides of the outer side of the screen. For example, as shown in FIG. The light from the light source 4 installed on the side is diffused by the dot printing unit 8 and guided inside by the light pipe 5, and the light from the light pipe 5 and the reflected light from the reflection plate 6 are diffused by the diffusion plate 7. The screen is designed to glow.

[0006]

However, in the above-mentioned conventional backlight system, since the lamp is arranged directly below the screen, there is a degree of freedom in setting the length of the lamp, and moreover, there is a direct rear surface. Since it is irradiation, sufficient brightness (light amount) can be secured, but there is a problem that uneven brightness occurs when attempting to reduce the thickness.

[0007] That is, in order to reduce the thickness of the backlight system, there are methods such as reducing the distance between the lamp (light source 1) and the diffusion plate 3 or reducing the diameter of the lamp. When the distance between the light source 1) and the diffuser plate 3 is reduced, as shown in FIGS. 3 and 4, when the broad illuminance distribution obtained at an appropriate distance d1 is a distance d2 smaller than the distance d1, it becomes sharp. Since the illuminance distribution becomes large, the amount of light to both sides of the lamp cannot be made sufficient, resulting in large brightness unevenness.

Further, since the reflection plate 2 in the backlight system is mainly made of white resin, not only a high reflectance cannot be expected, but also diffuse reflection occurs on the resin surface, and the directionality of light is controlled. In order to collect light between the lamps, which tends to be difficult to obtain, and the illuminance tends to be low, the distance between the lamps and the diffusing plate 7 must be secured, which is a limitation in reducing the thickness.

On the other hand, in the edge light system, since the lamp is arranged on the outer edge of the screen, it is advantageous in reducing the thickness, but the length of the usable lamp is limited as compared with the backlight system. Receiving and sufficient brightness (light intensity)
Has become difficult to obtain.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a backlight unit capable of ensuring a sufficient amount of light without unevenness in brightness while achieving a reduction in thickness.

[0011]

According to the first aspect of the present invention,
A backlight unit for performing backlight illumination by reflecting light from the cylindrical light source in a predetermined direction by a light guide piece portion of a light guide plate of a light guide member in which a cylindrical light source is fitted into a semicircular concave portion about half, The upper surface of the light guide piece rises away from the semi-circular recess with a predetermined inclination, and the lower surface of the light guide piece has a slope greater than the inclination of the upper surface and a mirror surface. The light from the lower half of the cylindrical light source is guided by the light guide piece in a direction away from the cylindrical light source, and is reflected in a predetermined direction by the lower surface of the light guide piece. Characterize.

According to a second aspect of the present invention, the light guide member has a plurality of the light guide plates, the ends of the light guide pieces of the light guide plate are connected to each other, and It is characterized in that the connecting portion of the end portion is set lower than the top portion of the cylindrical light source.

According to a third aspect of the present invention, the end portion of the light guide piece is set higher than the top of the cylindrical light source.

The invention as set forth in claim 4 is characterized in that the lower surface of the light guide piece is arcuate.

[0015]

In the backlight unit of the present invention, the light from the substantially lower half of the cylindrical light source is guided by the light guide piece of the light guide plate in the direction away from the cylindrical light source, and is reflected in the predetermined direction by the lower surface of the light guide piece. Can be made.

Therefore, more light can be guided between the light sources which tend to be dark, and a uniform illuminance distribution can be realized even when the diameter of the cylindrical light source is reduced. it can.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. 5 and 6 show one embodiment of the backlight unit of the present invention. As shown in these figures, the transparent or semitransparent light guide member 20 of the backlight unit 10 has a semicircular recess 21 formed in a W shape. Here, as the material of the light guide member 20, PC
(Refractive index 1.590) is used.

The semi-circular recess 21 has the semi-circular recess 21.
A cold cathode tube 30 having a shape of is fitted in about half. The cold cathode tube 30 has an outer diameter of Φ4.8 mm, an inner diameter of Φ3.5 mm, and a refractive index of 1.558. Further, the gap between the cold cathode tubes 30 fitted in the semi-circular recess 21 is set to 1.5 mm or less.

The light guide member 20 is composed of a plurality of light guide plates 22 and 23. The light guide pieces 22a and 22b of the light guide plate 22 located on the center side of the diffusion plate 40 are symmetrical. The light guide piece 23a and the light guide piece 23b of the light guide plate 23 located on the outer peripheral side of the diffusion plate 40 are left-right asymmetric. Details of these light guide members 20 will be described later.

FIG. 7 shows the details of the light guide member 20. The upper surface 24 of the light guide pieces 22a and 22b of the light guide plate 22 has a shape that rises from the semicircular recess 21 at a predetermined inclination. Has been done. The lower surface 25 of each of the light guide pieces 22a and 22b is formed in an arc shape having a gradient larger than the inclination of the upper surface 24, and the lower surface 25 is coated with a reflection coat. The upper surface portion 26 and the lower surface portion 27 of the light guide plate 23 on the light guide piece portion 23b side have the same shape as the light guide plate 22, but the upper surface portion 28 on the light guide piece portion 23a side is larger than the inclination of the lower surface portion 27. The lower surface 29 having a slope and having a reflection coating is formed in an arc with a slope greater than the inclination of the upper surface 28.

The end 23A of the light guide piece 23a of the light guide plate 23
Is set higher than the top of the cold cathode tube 30, and the connecting portion 23B between the light guide piece 22b of the light guide plate 22 and the light guide piece 23b of the light guide plate 23 is set lower than the top of the cold cathode tube 30. There is.

As a result, the light from the lower half of the cold cathode fluorescent lamp 30 is guided by the light guide plates 22 and 23 in the direction away from the cold cathode fluorescent lamp 30, and then reflected by the lower surface portions 25, 27 and 29. The diffusion plate 40 side is irradiated.

Next, the operation of the backlight unit having such a configuration will be described. First, looking at the state of progress of light from the upper half side of the cold cathode tube 30 on the light guide plate 22 side, as shown in FIG. 8, the light from the point a of the cold cathode tube 30 is directed upward as direct light. It is irradiated to the above-mentioned diffuser plate 40 side located. However, the light guide plate 22 may be included in a part of the light from the point a.
Some of the light enters the inside of the light guide piece 22b from the upper surface 24, and the light entering the inside has a large angle of incidence with respect to the lower surface 25, so after being reflected by the lower surface 25 which is a mirror surface, The part 24 comes out to the surface.

When looking at the light guide plate 23 side from the point a, which is the upper half side of the cold cathode tube 30, on the light guide plate 23 side, as shown in FIG. Similarly to the above, the above-mentioned diffuser plate 40 located above is directly irradiated with light. However, in the case of this light guide plate 23, the light guide piece 23a
Since the gradient is larger than that of the light guide piece portion 22b, most of the light is reflected by the upper surface portion 28 inside the light guide piece portion 23a. Therefore, leakage to the outside from the end portion 23A is reduced as much as possible. ing.

Next, looking at the state of light traveling from the lower half side of the cold cathode fluorescent lamp 30 on the light guide plate 22 side, as shown in FIG. Light that has entered the inside of the light guide piece 22b from the circular recess 21 and has a deep incident angle with respect to the lower surface portion 25 is reflected by the lower surface portion 25, then escapes from the upper surface portion 24 to the surface, and diffuses above the connecting portion 23B. The plate 40 side is irradiated.

Looking at the light traveling state of the light from the lower half side of the cold cathode tube 30 on the light guide plate 23 side, as shown in FIG.
The light from the point b of the cold cathode fluorescent lamp 30 enters the inside of the light guide piece portion 23a from the semicircular concave portion 21, and the light having a large incident angle with respect to the lower surface portion 29 is reflected by the lower surface portion 29, and then from the upper surface portion 28. Light that is emitted to the surface but has a shallow incident angle with respect to the lower surface portion 29 travels inside the light guide piece portion 23a while repeating reflection between the lower surface portion 29 and the upper surface portion 28, and ends at the end portion of the light guide piece portion 23a. It is irradiated to the above-mentioned diffusion plate 40 side inside 23A.

Further, as seen from the light guide plate 22 side, the traveling state of light from a position deeper than the point b of the cold cathode fluorescent lamp 30 is shown in FIG.
As shown in FIG. 2, the light from the point c of the cold cathode fluorescent lamp 30 enters the inside of the light guide piece portion 22b from the semicircular concave portion 21, and the lower surface portion 25
And the semicircular recess 21 are repeatedly reflected, and then proceed inside the light guide piece 22b while repeating reflection between the lower surface portion 25 and the upper surface portion 24, and the upper surface portion 2 near the connecting portion 23B.
4 and is irradiated to the above-mentioned diffusion plate 40 side above the connecting portion 23B.

When the light guide plate 23 is viewed from the deeper side of the cold cathode tube 30 than the point b, the light from the point c of the cold cathode tube 30 is half as shown in FIG. Circular recess 2
After entering the inside of the light guide piece portion 23a from 1 and repeating reflection between the lower surface portion 29 and the semicircular recess 21, the light guide piece portion 23 is repeatedly reflected between the lower surface portion 29 and the upper surface portion 28.
a inside of the light guide piece 23a
After passing through, the diffuser 40 side is irradiated with the light.

Next, the illuminance distribution of the backlight unit in this embodiment will be described in comparison with the conventional one.

That is, FIG. 14A shows a cold cathode tube 30.
It shows the case where the illuminance distribution of the light from the substantially lower half side is viewed from the light guide plate 22 side. As can be seen from comparison with the conventional one in FIG. Even when the reflection portion of the lower surface portion 25 and the reflection portion of the conventional reflection plate 2 are set to be substantially the same, in the case of the present embodiment, when light exits the upper surface portion 26, the illuminance distribution is changed due to the difference in refractive index. It can be seen that the position is closer to the connecting portion 23B side.

Further, as shown in FIG. 15 (a), in the case of light having a small incident angle with respect to the lower surface 25 of the light guide piece 22b, the light is compared with the conventional one shown in FIG. 15 (b). As you can see,
Due to reflection inside the light guide piece portion 22b, the connecting portion 23B is further connected.
You can see that you are close to the side.

Further, when the entire illuminance distribution is compared with that of the conventional one, in the case of the present embodiment shown in FIG. 16 (a), the illuminance is lower than that of the conventional one shown in FIG. 16 (b). It can be seen that the illuminance distribution between the cold cathode tubes 30 (between the light sources 1 in the conventional case) is increased.

As described above, in this embodiment, the cold cathode tube 30 is fitted into the semicircular concave portion 21 of the transparent or semitransparent light guide member 20 by about half, and the upper half of the cold cathode tube 30 which is used as the direct light. A part of the light from the upper surface 24, 2 of the light guide plate 22, 23
The light from the lower half of the cold cathode fluorescent lamp 30 is reflected by the light guide plates 22 and 23 of the light guide plates 22 and 23.
b, 23a, 23b, while guiding in a direction away from the cold cathode tube 30, the lower surface portion 2 of the light guide plate 22, 23.
It can be reflected by 5, 27 and 29.

Therefore, the direct light from the cold cathode fluorescent lamp 30 and the lower surface 2 of the light guide pieces 22a, 22b, 23a, 23b are provided.
The reflected light from 5, 27, 29 can be effectively used, and since the lower surface portions 25, 27, 29 are mirror surfaces, it is easy to control the direction of light,
Since more light can be guided to the middle of the cold cathode fluorescent lamp 30 and the cold cathode fluorescent lamp 30, which tend to be dark, a uniform illuminance distribution is realized even when the diameter of the cold cathode fluorescent lamp 30 is reduced. Therefore, it is possible to secure a sufficient amount of light without unevenness in brightness while reducing the thickness of the backlight unit.

In the present embodiment, the case where the cold cathode fluorescent lamp 30 having the same shape is fitted in the semicircular recess 21 formed in the W shape has been described, but the present invention is not limited to this example, and the semicircular recess 21 and The cathode tube 30 may have another shape such as a U shape.

[0036]

As described above, according to the backlight unit of the present invention, the light from the substantially lower half of the cylindrical light source is guided by the light guide piece of the light guide plate in the direction away from the cylindrical light source, and the light is guided. It can be reflected in a predetermined direction by the lower surface part of the one part.

Therefore, more light can be guided between the light sources which tend to be dark, and a uniform illuminance distribution can be realized even when the diameter of the cylindrical light source is reduced. As a result, it is possible to secure a sufficient amount of light without unevenness in brightness while achieving thinning.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional backlight unit of a backlight system.

FIG. 2 is a diagram showing a conventional edge light type backlight unit.

FIG. 3 is a diagram showing an illuminance distribution of a single lamp in the backlight unit of FIG.

4 is a diagram showing an illuminance distribution of a single lamp in the backlight unit of FIG.

FIG. 5 is a plan view showing an embodiment of the backlight unit of the present invention.

6 is a cross-sectional view of the backlight unit of FIG. 5 taken along the line AA.

7 is a cross-sectional view showing a light guide plate of the backlight unit of FIG.

FIG. 8 is a view for explaining the action of the light guide plate of the backlight unit of FIG.

FIG. 9 is a view for explaining the action of the light guide plate of the backlight unit of FIG.

10 is a diagram for explaining the operation of the light guide plate of the backlight unit of FIG.

11 is a diagram for explaining the operation of the light guide plate of the backlight unit of FIG.

FIG. 12 is a view for explaining the operation of the light guide plate of the backlight unit of FIG.

13 is a diagram for explaining the operation of the light guide plate of the backlight unit of FIG.

FIG. 14 is a diagram for explaining the illuminance distribution of the backlight unit of FIG. 5 in comparison with a conventional one.

FIG. 15 is a diagram for explaining an illuminance distribution of the backlight unit of FIG. 5 in comparison with a conventional one.

FIG. 16 is a diagram for explaining the illuminance distribution of the backlight unit of FIG. 5 in comparison with a conventional one.

[Explanation of symbols]

 10 Backlight Unit 20 Light Guide Member 21 Semi-Circular Recess 22a, 22b, 23a, 23b Light Guide Piece 22, 23 Light Guide Plate 24, 26, 28 Upper Surface 25, 27, 29 Lower Surface 30 Cold Cathode Tube 40 Diffuser

Claims (4)

[Claims] 1. A backlight for illuminating a backlight by reflecting light from the cylindrical light source in a predetermined direction by a light guide piece of a light guide plate of a light guide member in which a cylindrical light source is fitted into a semi-circular concave portion about half. In the unit, the upper surface of the light guide piece rises with a predetermined inclination facing away from the semicircular recess, and the lower surface of the light guide piece has a slope greater than the inclination of the upper surface. And has a mirror surface, and guides the light from the lower half of the cylindrical light source in a direction away from the cylindrical light source by the light guide piece, and reflects the light in a predetermined direction by the lower surface of the light guide piece. A backlight unit that is characterized by the following features. 2. The light guide member has a plurality of the light guide plates, the ends of the light guide pieces of the light guide plate are connected to each other, and the connecting portions of the ends of the light guide pieces are formed. The backlight unit according to claim 1, wherein the backlight unit is set lower than the top of the cylindrical light source. 3. The end of the light guide piece is set higher than the top of the cylindrical light source.
Backlight unit described. 4. The backlight unit according to claim 1, wherein the lower surface of the light guide piece has an arc shape.