JPH0277726A - liquid crystal display device - Google Patents

Abstract

PURPOSE:To realize the liquid crystal display device capable of being obtained an uniform reproduced image with even luminance on the screen by disposing a condenser lens with an aspherical surface which has a larger curvature at the circumferential part of the lens than that at the center part thereof, between a point light source and a transmission type liquid crystal panel. CONSTITUTION:A part of light uniformly radiated from the point light source 1 at all directions is made incident to the condenser lens 2. The lens 2 is a convex lens with the aspherical surface which has a smaller radius of curvature at the circumferential part of the lens than that on the center axis thereof. Accordingly, as the lens 2 has a larger converging ratio at the circumferential part thereof than that at the center part thereof, the deterioration of light quantity of the lens 2 at the circumferential part thereof is compensated. The light passed through the lens 2 reaches to a fresnel lens 4 provided immediately after the liquid crystal panel 3. As the lens 4 is constituted so as to be put the image of a light source in the position of the focal point of the lens 4 with the lens 2, the light passed through the lens 2 is almost parallel beam thereby being reproduced an uniform display picture which is reduced the unevenness of luminance of the panel 3.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a liquid crystal display device with no unevenness in brightness, and in particular to a display device that enables a large screen display by combining a plurality of small screen liquid crystal display panels. The present invention relates to an optical system suitable for the device.

[Conventional technology]

Liquid crystal display devices require external light because they are not self-luminous.

Therefore, sufficient brightness may not be obtained in a dark environment. To this end, a backlight such as a fluorescent lamp is provided behind the liquid crystal, and the light is irradiated onto the liquid crystal to ensure brightness.

Further, although there has been remarkable progress in liquid crystal display devices, if a large display screen is to be realized, there are problems such as poor manufacturing yields and the need for large equipment, and the cost is also extremely high.

Therefore, by piecing together multiple small-screen LCD panels,
Various attempts have been made to realize large screen display. A representative example thereof is JP-A-61-138288. This configuration is shown in Figure 2.

It is shown in Figure 3. FIG. 2 is a longitudinal sectional view, and FIG. 3 is a plan view. 9 small screen LCD panels 311°312.313
... 319, point light sources 12 are provided. A transmission/diffusion surface 13 is provided on the front surface of the liquid crystal panel. Light from a point light source illuminates the liquid crystal, and the image on the liquid crystal is projected onto a diffusing surface. The image of each liquid crystal is reflected on this diffusion surface. By optimizing the distance between the light source and the liquid crystal, or between the liquid crystal and the diffusion surface, the adjacent blank portions 14 of each liquid crystal can be seen on the diffusion surface. There is no longer a screen on top, and you get one continuous large screen.

[Problem to be solved by the invention]

The above conventional technology has the following problems.

For example, in a liquid crystal display device equipped with a backlight, a fluorescent lamp is generally used as the backlight.

As this fluorescent lamp, one or two direct type, or a U-tube type is used. In order to reduce the thickness of the device, this fluorescent lamp is placed just in front of the liquid crystal.

Therefore, the amount of light irradiated onto the liquid crystal varies greatly depending on the position on the liquid crystal, which appears as uneven brightness and significantly deteriorates the image quality. In extreme cases, the exact shape of the fluorescent light may be displayed on the LCD screen.

Luminance unevenness, which is bright at the center of the screen and monotonically darkens toward the periphery, is not very noticeable, but when there are many repeated bright and dark areas, it seriously impairs image quality. An object of the present invention is to provide an optical system that eliminates brightness unevenness caused by this backlight.

Furthermore, the conventional example shown in FIG. 2, in which a large screen is obtained by piecing together small liquid crystals, has the following problems.

In Figure 2, the positions A and A' of the diffusion surface.

At A'', the light from the light source is irradiated vertically, but
The second position of the diffusion surface is B, l'3', +(" and C9
At positions C' and c'', the distance from the light source increases, so the amount of light per unit area decreases compared to positions A, A', and A''. Furthermore, the diffused light distribution after irradiating the diffused surface also has directionality. For example, A, A'.

At "A", as shown in Figure 2, the amount of light diffused in the vertical direction is the largest, and the more the direction is diagonal, the less the sight becomes. ′, c″, the distribution of diffused light is the brightest in the direction irradiated from the light source, as shown in Figure 2, but the amount of light gradually decreases in many directions. When looking at the image on the diffusing surface in the vertical direction, even if the diffusing surface is uniformly irradiated with light, Δ, A',
A'' is bright, B, B', B'' and (':, C',
C", it becomes dark. Also, when viewed from the right direction, [
It appears dark at points 3°B' and B'', and bright at points c, c', and c''.

For the above two reasons, in the conventional example shown in Fig. 2,
This causes uneven brightness and deteriorates the image quality.

An object of the present invention is to provide a liquid crystal display device in which the above-mentioned luminance unevenness is improved.

[Means to solve the problem]

The above purpose is to use a point light source as the backlight of a liquid crystal display device, an aspherical lens to focus the light from the point light source, an aspherical Fresnel lens in front of or after the liquid crystal, and an image at the forefront. This is achieved by arranging a transmission-diffusion surface for imaging.

[Effect]

A portion of the light emitted uniformly in all directions from the point light source is incident on the condenser lens. This lens has an aspherical convex lens shape, and the radius of curvature on the central axis is
The radius of curvature at the periphery is small.

Therefore, the light collection rate is higher in the peripheral part than in the central part, and as a result, it works to compensate for the deterioration in the amount of light in the peripheral part.

The light passing through this lens reaches a Fresnel lens provided just before or after the liquid crystal.

The Fresnel lens is configured such that the image of the light source formed by the above-mentioned condensing lens is located at the focal point of the Fresnel lens.

Therefore, the light that passes through the Fresnel lens becomes almost parallel light, and the light intensity in the direction of the central axis of the lens is strongest both at the center and at the periphery. This also applies to the light that has passed through the diffusion surface provided at the forefront, and the light intensity in the central axis direction is the strongest. As a result, uneven brightness of the liquid crystal panel can be reduced and a uniform display screen can be reproduced. Further, when the condensing lens is made of an aspherical surface, the position of the image of the light source differs between paraxially passing light and non-paraxially passing light. In this case, by making the focal position of the Fresnel lens have a different shape on the central axis and at the periphery, depending on the position of the image of the light source, the light after passing through the Fresnel lens becomes approximately parallel light. Become.

Therefore, uneven brightness of the liquid crystal panel can be improved, and a uniform display screen can be obtained when viewed from any direction.

An embodiment of the present invention will be described below with reference to FIG. This figure is a longitudinal sectional view of a liquid crystal display panel according to the present invention. 1
2 is a point light source, 2 is a nonce for condensing light from the light source, 3 is a liquid crystal panel, 4 is a Fresnel lens, and 5 is a diffusion plate, on the surface of which a diffusion layer 6 is provided. light source 1
The light from the lens is condensed by a condensing lens 2. The condenser lens 2 has an aspherical shape, and the curvature of the peripheral part is stronger than that of the central part. Therefore, after the light uniformly emitted from the light source in the same direction passes through the condenser lens, the light amount density is higher in the peripheral part than in the central part. Furthermore, the light 7 that has passed near the center travels as if it were emitted from point A, and the light 8 that has passed through the periphery travels as if it was emitted from point A'. These lights pass through the liquid crystal panel 3. The LCD panel is 7
1 By changing the voltage applied to the electrodes arranged in a helix, the transmittance of each picture element can be changed.
Two-dimensional display images can be played back. The light modulated by the liquid crystal panel reaches the Fresnel lens 4. The focal length of the Fresnel lens is ○Δ at the center and OA' at the periphery. Therefore, all the light that passes through the Fresnel lens becomes parallel to the central axis. This light reaches the diffusing surface 6,
It will be spread. Generally, in the peripheral area, the distance from the light source 1 is long, and the light rays arrive from an oblique direction, so the amount of light is less than in the central area. The same amount of light can be secured for both parts. Additionally, the effect of the two Fresnel lenses makes it possible to eliminate uneven brightness on the screen depending on the viewing direction. Fourth
The figure shows another embodiment, which differs from the embodiment shown in FIG. 1 in that the condenser lens 2 has a spherical surface and the Fresnel lens 4' has a single focal length.

Generally, the amount of light that reaches point B on the display surface 6 is inversely proportional to the square of the distance r between the light source and B. By providing the condenser lens 2', a virtual image of the light source can be created at point A. The apparent distance AB between the light sources A and B becomes large, and the amount of light at the center and the periphery can be reduced.

FIG. 6 shows another embodiment, and in comparison with FIG. 1, the Fresnel lens is omitted. This embodiment also has the same effect as the embodiment shown in FIG. 1, so that the light intensity density at the periphery can be made the same as that at the center. However, the angular distribution of the light beam after passing through the diffusion layer in the peripheral area is not necessarily the strongest in the central axis direction. Therefore, although some brightness unevenness occurs on the screen, it is acceptable depending on the application.

Another embodiment will be explained using FIG. 6. In this embodiment, the positions of the Fresnel lens 4 and the liquid crystal panel 3 are reversed compared to the embodiment shown in FIG.

However, it operates in the same way, following the same principles as described in the embodiment of FIG.

Another embodiment will be described with reference to FIG. The embodiment shown in FIG. 1 is different from the embodiment in that an optical path turning mirror 9 is provided between the condenser lens 2 and the liquid crystal panel 3. This is effective in reducing the thickness of the set. For example, when a 10-inch liquid crystal panel is used and a Fresnel lens with a focal length of 280 mm is used, the thickness of the cell 1 can be approximately 8 cm.

In each of the embodiments shown in FIGS. 4 to 6, the thickness of the set can be reduced by similarly arranging mirrors for turning the optical path.

Another embodiment will be described using FIGS. 8 and 9.

FIG. 8 is a side view showing the arrangement of the liquid crystal panel, and FIG. 9 is a vertical sectional view. In this embodiment, two liquid crystal panels 3' and 3
The liquid crystal panel consists of a display part 10 and a non-display part 11. Even if you try to make the non-display part as short as possible, it usually remains about 4 mm. Point light sources 1' and 1'' are arranged, respectively. Further, above the liquid crystal panel, Fresnel lenses 4' and 4'' are arranged in correspondence with each other. Above the Fresnel lenses, a diffusion plate 5 having a diffusion layer 6 on its surface is arranged. The light from the point light source 1' is emitted radially and illuminates the liquid crystal.The light then reaches the Fresnel lens 4'.The distance between the Fresnel lens and the light source]-' is approximately equal to the focal length f. It is set.

The light that reaches this Fresnel lens turns into parallel light and heads in the -L direction, reaching the diffusion layer 6 of the second diffusion plate, where the light is diffused and an image is projected on the liquid crystal. In the same way, the images of the liquid crystal panel 3'' are projected onto the diffusion layer 6.The images on these diffusion layers are slightly larger than the images on the liquid crystal panel, and there are no non-display areas on the diffusion layer, and the whole is connected. An image is obtained. In this configuration, the Fresnel lens has the effect of collimating the light from the light source side. As a result, at any position on the diffusing surface, the brightness is highest in the direction parallel to the central axis. , it is possible to reproduce images with very little uneven brightness.

The biggest problem in this case is image blur, but as will be described in detail below, this problem can be practically solved by using a sufficiently small light source.

This winter's liquid crystal display panel will be 10 inches in size with 640 x 480 dots. 1 of this panel, that is, the blur caused by this optical system must be 0.32 mm or less. The amount of blur d is calculated using the thickness Q of the light source, the distance P between the liquid crystal panel and the light source, and the distance between the liquid crystal panel and the diffusion layer.
It can be expressed by the following formula.

When d = Q X'<0.3mm P = 120mm, % = 5mm,! ! (
It becomes 7mm. A light source of this size requires a lamp power of 5
Even 0 to 100 W can be sufficiently realized using xenon, halogen, metal halide lamps, etc.

In particular, the light source of a xenon lamp is very small, and out-of-focus is hardly a problem.

With the above configuration, the number of dots is 640X even though the screen is approximately twice the size of a 10-inch screen.
480, that is, 1280×480, making it possible to construct an extremely high-definition image.

In the embodiment shown in FIG. 10, the liquid crystal is 31.32°33.
34 and 4 pieces are arranged. In this case, the area can be increased four times. For example, 1 with 640 x 480 dots]
When using a 0 inch size liquid crystal, 1.280
It has a high resolution of 960 x 960 dots and can achieve a size of 20 inches.

For example, if red, blue, and green color filters are arranged in a triangle shape on this liquid crystal panel and a color TV image is played back, the horizontal resolution will be 640 TV lines, and it will be able to receive not only normal NTSC reception but also 5-VH8, video Even images from discs etc. can be faithfully reproduced with almost no deterioration.

In addition, in the embodiment shown in FIG. 9, as in FIG. 1, an aspherical condensing lens is provided between the light source and the liquid crystal, and the focal lengths of the Fresnel lens are changed between the center and the periphery. For the same reason as stated in Figure 1,
Luminance unevenness can be greatly improved.

Furthermore, by providing an optical path folding mirror between the light source and the liquid crystal panel, the thickness of the set can be reduced.

〔Effect of the invention〕

According to the present invention, the amount of light to the display surface is constant regardless of the position on the screen, and the angular distribution of the light after diffusion is also constant, so that a uniform reproduced image with no uneven brightness is produced on the screen. can be obtained.

[Brief explanation of the drawing]

FIG. 1, FIG. 4, FIG. 5, FIG. 6, FIG. 7, and FIG. 9 are longitudinal cross-sectional views and FIG. 8 according to embodiments of the present invention. FIG. 10 is a plan view of an embodiment of the present invention, and FIGS. 2 and 3 are a vertical sectional view and a plan view of a conventional structure. 1... Point light source, 2... Aspheric condensing lens, 3...
liquid crystal. 4... Aspherical Fresnel lens, 5... Diffusion plate, 9...
...Optical path folding mirror. 9th page name Figure 10

Claims (1)

[Claims] 1. In a liquid crystal display device configured to emit light from a point light source from behind a transmissive liquid crystal panel, a condensing lens is provided between the point light source and the liquid crystal panel, and the shape of this condensing lens is such that the light from the center A liquid crystal display device characterized by having an aspherical surface with a strong curvature at the periphery.