JP2762187B2 - LCD lighting system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device used in a backlight portion of a liquid crystal display device, wherein a light source is arranged behind a light emitting surface, and more particularly to a lighting device having uniform brightness on the light emitting surface. .

[0002]

2. Description of the Related Art FIG. 7 shows an example of a direct type illumination device in which a conventional light source is arranged behind a light emitting surface (conventional example 1). In the figure, 1 is a tubular light source, 2 is a reflector for reflecting light backward from the light source 1 forward, 3 is a polycarbonate lighting curtain for uniformizing the light from the light source 1, and 4 is aluminum vapor deposition on the lighting curtain. A shielding pattern 5, which is etched in a mesh shape and shields and absorbs the direct light from the light source 1, is an acrylic diffusion plate 5 mixed with a diffusing agent.

FIG. 8 shows another conventional example (conventional example 2). This example is an example of achieving high luminance of the light emitting surface. In addition to the same tubular light source 1, reflecting plate 2, lighting curtain 3 and diffusing plate 5 as in the conventional example 1, each direction on the surface of the diffusing plate 5 And a prism plate 6 made of polycarbonate for increasing the luminance in the vertical direction on the light emitting surface by condensing the light. Further, since the pitch of the prism of the prism plate 6 and the pixel pitch of the liquid crystal panel interfere with each other, an interference image (moire) is formed.
In order to prevent this, polycarbonate light diffusion sheet 7
Is provided.

[0004]

FIGS. 9 and 1 show the results of measuring the luminance distribution of each of the illumination devices of the prior art examples 1 and 2 when passing through each member.
0 is shown. Here, FIG. 9 corresponds to Conventional Example 1 and FIG. 10 corresponds to Conventional Example 2, in which L1 is the luminance distribution when light passes through the lighting curtain 3, and L2 is the light L3 indicates the luminance distribution when passing through the liquid crystal display panel, L3 indicates the luminance distribution when further passing through the prism plate 6, and L4 indicates the luminance distribution when further passing through the light diffusion sheet 7.

In the lighting curtains 3 of the prior art examples 1 and 2, in order to secure a certain level of brightness, it is necessary to directly pass a large amount of light through the gap between the shielding patterns 4 as shown in FIG. A distribution in which the luminance peak protrudes as described above.

For this reason, in the first prior art, it is necessary to lower the light transmittance of the diffusion plate 5 and increase the diffusion ratio in order to make the luminance distribution on the diffusion plate 5, that is, the light emitting surface to some extent uniform. Then, high luminance cannot be obtained as indicated by L2 in FIG.

Further, in the second conventional example, in order to improve the low luminance of the first conventional example, a prism plate 6 for condensing light in each direction on the diffusing plate 5 is added, so that a light emitting surface is provided. Thus, the brightness as viewed from the vertical direction is improved, but the brightness (angle characteristic) in directions other than the vertical direction is deteriorated, and the visibility of the display surface is narrowed (see FIGS. 5 and 6).

Further, in the conventional example 2, since the light diffusing sheet 7 is added, as shown in FIG. 10, the brightness is reduced as compared with the case where the light diffusing sheet 7 is not used.

Here, in the prior art examples 1 and 2, the lighting curtain 3 shown in FIG.
When the shielding pattern 4 is darkened, the light loss here becomes large, and the luminance of the entire light emitting surface is reduced.

In view of the above problems, an object of the present invention is to provide a lighting device for a liquid crystal capable of obtaining light having substantially uniform brightness on a light emitting surface with high brightness in a wide angle range.

[0011]

As shown in FIGS. 1 and 2, a means for solving the problem according to the first aspect of the present invention comprises a light source 12 for illuminating a liquid crystal display panel 11 from behind, and a rearward irradiation light from the light source 12. A reflection plate 13 that reflects the light to the liquid crystal display panel 11, and a diffusion plate 14 that is disposed in front of the light source 12 and that diffuses the direct light from the light source 12 and the reflection light from the reflection plate 13 to the liquid crystal display panel 11. In the illumination device for a liquid crystal, the light obliquely incident on the back of the diffusion plate
And a light-transmitting light-guiding plate 21 for guiding the light from the light source 12 in a direction parallel to the light-guiding plate 21 on the rear surface of the light- guiding plate 21. Is formed, and a light diffusion sheet 23 is provided in front of the diffusion plate 14 to condense light from the diffusion plate 14 forward to prevent interference.

According to a second aspect of the present invention, the surface of the light diffusing sheet 23 according to the first aspect is formed in a wrinkle shape to enhance scattering.

[0013]

According to the first aspect of the present invention, light from the light source 12 enters the inside of the light guide plate 21. At this time, the light is scattered by the light transmitting scattering film 22 and enters the light guide plate 21 in an oblique direction. The light in the light guide plate 21 undergoes total reflection.
The liquid crystal is repeatedly guided in a wide range in the direction parallel to the liquid crystal display panel 11, and the uneven brightness is reduced. Thereafter, the light is emitted forward from the light guide plate 21, passes through the diffusion plate 14 and the light diffusion sheet 23, and illuminates the liquid crystal display panel 11 from behind.

In this case, the light is diffused over a wide area with respect to the light emitting surface, and the brightness unevenness is reduced without blocking the light as in the conventional examples 1 and 2.

According to the second aspect of the present invention, when the light passes through the light diffusion sheet 23 having a surface wrinkle shape, the light does not converge as regularly as the conventional prism plate and has a certain degree of scattering. Can maintain the luminance angle characteristics of the light scattered over a wide range.

[0016]

FIG. 1 is a sectional view of a liquid crystal lighting device according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view showing a light guide plate and a light-transmitting and scattering film, and FIG. FIG. 4, FIG.
FIG. 5 is a comparison diagram of the luminance distribution on the light emitting surface with Conventional Examples 1 and 2, FIG. 5 is a comparison diagram of the luminance angle characteristics in the vertical direction with Conventional Example 2, and FIG. FIG.

As shown in the figure, the liquid crystal display device of this embodiment is
The light source 1 is used for a laptop type personal computer or the like, and illuminates the liquid crystal display panel 11 from behind.
2 and light emitted backward from the light source 12 to the liquid crystal display panel 1.
1, a diffuser 14 disposed in front of the light source 12 and diffusing the direct light from the light source 12 and the reflected light from the reflector 13 to the liquid crystal display panel 11. Behind 14, a light-transmitting light guide plate 21 for guiding light from the light source 12 in a direction parallel to the liquid crystal display panel 11
Is provided in front of the diffusion plate 14, and a light diffusion sheet 2 for condensing light from the diffusion plate 14 forward to prevent the interference.
3 is provided.

As the light source 12, as shown in FIG. 1, for example, a hot cathode U-shaped tube having a radius of 6.5 mm is used, and the tube luminance is 9,0.
00nt. The light source 12 is connected to the liquid crystal display panel 11.
It is arranged directly below.

As the reflector 13, a metal plate having a high reflectance is used. At the center of the reflector 13, an intermediate reflector 17 for reflecting the light from the light sources 12 to the side inward toward the liquid crystal display panel 11 projects forward in an inverted V-shape having a pair of inclined surfaces. Is formed.

The diffusion plate 14 has, for example, a total light transmittance of 5
A translucent opaque acrylic material having a diffusion rate of 6% and a diffusion rate of 92% is used, is formed in a rectangular flat plate having a thickness of 1.5 mm, and is arranged behind and parallel to the display panel.

The light guide plate 21 has, for example, a total light transmittance of 9.
A transparent acrylic plate having a diffusion rate of 3% and a diffusion rate of 5% is used.
mm-thick rectangular flat plate,
It is bonded to the rear surface.

On the rear surface of the light guide plate 21, there is formed a light-transmissive scattering film 22 that transmits and scatters light from the light source 12. The light-scattering film 22 is formed by adding a light-transmitting white pigment (white ink) to polycarbonate or the like and forming a predetermined pattern by a silk screen method or the like. . Thereby, the light-transmitting scattering film 22 has a strong light scattering property, and absorbs light from the light source 12 to prevent the light from being reduced.

The light diffusing sheet 23 is, for example, a light-transmitting acrylic sheet having a thickness of 0.2 mm. The surface of the light diffusing sheet 23 is formed into a wrinkle shape by a press, a roller, or the like so as to enhance scattering. The light collection rate in the direction perpendicular to the plane) is 116%.

In the liquid crystal lighting device having the above-described structure, when the light source 12 emits light during use, the light forward from the light source 12 toward the inside and the light from the light source 12 toward the inside and the rear are once reflected by the reflector 13. After being reflected, the light is irradiated to the light guide plate 21 side.

At this time, the light passes through the light transmitting and scattering film 22 before entering the light guide plate 21, is scattered, and then obliquely enters the light guide plate 21.

Since the incident light is obliquely incident, total reflection is further repeated inside the light guide plate 21 due to the difference in refractive index from the outside, and the light is guided over a wide range in the direction parallel to the liquid crystal display panel 11. I will Then, when the light is emitted forward from the light guide plate 21, the light amount is considerably leveled with respect to the light emitting surface.

The light emitted from the light guide plate 21 is diffused by the diffusion plate 14, then emitted forward, and enters the light diffusion sheet 23. Then, the light is collected forward, and the liquid crystal display panel 1
1 is irradiated from behind.

As described above, since the light is scattered by the members 21, 22, and 23, a large amount of light that has conventionally passed directly passes in the scattering direction, and there is also a refraction effect when the light guide plate 21 enters and exits. And a gentle distribution with a reduced peak luminance value. For this reason, even if a high transmittance material is used for the diffusion plate 14, the luminance on the diffusion plate 14 can be made uniform.

Here, in FIG. 3, La1 is a luminance distribution when light passes through the light transmitting and scattering film 22 and the light guide plate 21;
Denotes a luminance distribution when the light passes through the diffusion plate 14, and La3 denotes a luminance distribution when the light further passes through the light diffusion sheet 23. In this way, the luminance distribution La3 at the forefront is more uniform than the luminance distribution La1 when passing through the light-transmitting and scattering film 22 and the light guide plate 21, and the high transmittance material is used for the diffusion plate 14, It can be seen that the overall luminance is also good.

In addition, unlike the prior art examples 1 and 2, in order to suppress the difference in luminance when transmitted through the lighting curtain, the luminance can be reduced without using a diffusion plate having a low transmittance or using a shielding pattern of the lighting curtain. Can be made uniform. That is, the brightness can be made uniform by guiding or scattering the light to a dark place, instead of blocking and reducing the strong light. Therefore, light can be used effectively, and the entire light emitting surface can be made brighter than conventional examples 1 and 2. At the same time, lamp streaks due to uneven brightness can be eliminated, and the display quality of the liquid crystal display surface is improved. I can make it.

In FIG. 4, Lb1 is the luminance distribution of this embodiment,
b2 is the luminance distribution of Conventional Example 1, and Lb3 is the luminance distribution of Conventional Example 2. As is clear from this, it can be seen that the overall luminance of the present embodiment is higher than that of the first and second embodiments.

Further, since the light diffusing sheet 23 having a surface wrinkle shape having a light condensing effect has a scattering property itself, the light diffusing sheet 23 cannot exert the light condensing power as regularly as the prism plate of the conventional example 2, and
Therefore, its light collection rate is not as large as in the past. Therefore, it is possible to irradiate the liquid crystal display panel 11 at a wide angle without obstructing the luminance angle characteristics of the light scattered by the light guide plate 21 and the diffusion plate 14.

Here, in FIG. 5, Lc1 indicates the vertical luminance angle characteristic of this embodiment, Lc2 indicates the vertical luminance angle characteristic of Conventional Example 2, and Ld1 indicates the left and right luminance characteristics of this embodiment. The luminance angle characteristics in the direction, Ld2, represent the luminance angle characteristics in the left-right direction of Conventional Example 2, respectively. In general, the contrast reversal viewing angle of the liquid crystal (angle range in which an image can be normally recognized) is 30 ° vertically and 45 ° horizontally. As shown in FIGS. 5 and 6, the luminance at this angle is significantly superior to the conventional example, ie, 90% in the vertical direction and 80% in the horizontal direction in the present embodiment, compared to the peak value in the conventional example 2 of 50% in the vertical direction and 55% in the horizontal direction. You can see that it is. Therefore, it can be seen that the viewing angle of the display surface is wider than in Conventional Example 2.

The intermediate reflector 1 is provided at the center of the reflector 13.
Since the projections 7 are formed, the light emitted from each light source 12 toward the light source on the opposite side (side inward) can be effectively guided forward.

As described above, it is possible to increase the luminance of the illumination device for liquid crystal, to make the luminance uniform, and to improve the display quality.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made to the above-described embodiment within the scope of the present invention.

[0037]

As is clear from the above description, according to the first aspect of the present invention, since the light guide plate is provided behind the diffusion plate and the light scattering film is formed on the rear surface of the light guide plate, the light scattering is achieved. The light scattered by the film enters the light guide plate obliquely, and can be guided to a wide range with respect to the light emitting surface by the light guide plate, and diffused from the light guide plate.
When emitting light to the plate, the light amount can be leveled to the light emitting surface.
You . Then, a smooth distribution with a reduced peak luminance value can be obtained without blocking light, and uniform luminance can be obtained on the diffusion plate even if a high transmittance material is used for the diffusion plate. Therefore, it is possible to improve the overall luminance at the same time as making the luminance uniform.

According to the second aspect, since the surface of the light diffusing sheet has a wrinkled shape, the light diffusing sheet can have scattering properties as compared with the case where a conventional prism plate is used, and can maintain the luminance angle characteristics in a wide range. Accordingly, there is an excellent effect when the viewing angle of the display surface is widened as compared with the related art.

[Brief description of the drawings]

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

FIG. 2 is an enlarged sectional view showing a light guide plate and a light-scattering film.

FIG. 3 is a diagram showing a luminance distribution when passing through each member.

FIG. 4 is a comparison diagram of the luminance distribution on the light emitting surface with Conventional Examples 1 and 2;

FIG. 5 is a diagram illustrating a comparison between a luminance angle characteristic in the vertical direction and Conventional Example 2;

FIG. 6 is a comparison diagram of the luminance angle characteristics in the left-right direction with Conventional Example 2;

FIG. 7 is a sectional view of Conventional Example 1.

FIG. 8 is a cross-sectional view of Conventional Example 2.

FIG. 9 is a diagram showing a luminance distribution when passing through each member of the conventional example 1.

FIG. 10 is a diagram showing a luminance distribution when passing through each member according to Conventional Example 2.

FIG. 11 is an enlarged sectional view showing a light guide plate and a light-transmitting and scattering film of Conventional Examples 1 and 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Liquid crystal display panel 12 Light source 13 Reflecting plate 14 Diffusion plate 21 Light guide plate 22 Light transmission scattering film 23 Light diffusion sheet

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-213824 (JP, A) JP-A-3-48281 (JP, A) JP-A-1-234822 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G02F 1/1335 F21V 13/00

Claims (2)

(57) [Claims] 1. A light source for illuminating a liquid crystal display panel from behind,
A reflector for reflecting the rearward irradiation light from the light source to the liquid crystal display panel, and a diffusion plate arranged in front of the light source to diffuse the direct light from the light source and the reflected light from the reflector to the liquid crystal display panel. A light-transmitting light-guiding plate that guides obliquely incident light in a direction parallel to the liquid crystal display panel is provided behind the diffusion plate, and a light source is provided on a rear surface of the light-guiding plate. The light from the light guide
A light-scattering film to be incident on the plate is formed, and a light-diffusing sheet is provided in front of the diffusion plate to condense light from the diffusion plate forward and prevent interference thereof. Lighting equipment. 2. The surface of the light diffusion sheet according to claim 1,
A lighting device for a liquid crystal, wherein the lighting device has a wrinkle shape so as to enhance scattering.