JPH07301795A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a display device where reflected light is little and whose contrast is high even under high illuminance environment such as outdoors in the daytime by providing a circular polarization filter so that it may be arranged on the front surface side of the liquid crystal display panel. CONSTITUTION:Light emitted from a light source 1 is partially transmitted or intercepted by the liquid crystal display panel 2. The light transmitted through the panel 2 (that is, light projected from the panel 2) becomes picture display light for displaying a picture. The picture display light projected from the panel 2 is transmitted through the circular polarization filter 3 arranged on the front surface side of the panel 2. Light transmissivity in such a case is ordinarily about 50%. The filter 3 is a plate member constituted by combining an ordinary linear polarizing plate and a 1/4 wavelength plate with a glass plate, where antireflection processing is performed, being a base material so that the incident light may be changed to the circularly polarized light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device capable of obtaining high contrast even in a relatively bright environment such as outdoors, and more particularly to a display device using a liquid crystal panel.

[0002]

2. Description of the Related Art Conventionally, the following techniques are known as a high-contrast display device used in a bright outdoor environment. (J01) Using a high brightness CRT and a neutral density filter This conventional technique is capable of displaying with high contrast even in direct sunlight. The reason will be described below. Figure 6
FIG. 7 is a diagram for explaining a condition for performing a high-contrast display when only a high-luminance CRT is used. FIG. 7 is a diagram for performing a high-contrast display when a high-luminance CRT and a neutral density filter are used. It is a figure for demonstrating a condition. In FIG. 6, since the phosphor screen of the CRT is coated with a substantially white and fine phosphor powder, external light diffuses and reflects (diffuse reflection) without directivity of reflected light on this surface. In direct sunlight, the surface brightness of the white diffuse reflector is approximately 1.
It is known to be 10,000 Ft-L.

The contrast of the CRT alone shown in FIG. 6 under direct sunlight is as follows. Assuming that the contrast is 10 or more as a high-contrast display condition, contrast value = (target brightness / background brightness) = (white display brightness / black display brightness) = {CRT-specific white display brightness (= X) + Reflected light brightness (10,000 Ft-L)} / {CR
T-specific black display brightness (= about 0) + reflected light brightness (10,
000Ft-L)} ≧ 10, the white luminance X peculiar to the CRT is 90,000.
Ft-L or higher is required. It is difficult for the existing CRT to realize the brightness value of 90,000 Ft-L or more. In addition, white display 100,000 Ft-L (= 90,000 + 1
10,000) is too dazzling to human eyes and is not practical.

Therefore, when the external light is strong, a neutral density filter having a function of attenuating the transmitted light as shown in FIG. 7 is generally used as a method for realizing a high contrast in a CRT. The conditions for displaying a high contrast in this case will be described with reference to FIG. In FIG. 7, for example, assuming that the transmittance of the neutral density filter is 10%,
The display brightness is 1/10 of the brightness of the CRT, but the ambient light passes through the filter twice at the time of incidence and at the time of emission, and as a result, the brightness of reflected light is 1/100 {(1/10)
X (1/10), 100 Ft-L).

Based on the above assumptions, when a condition of contrast 10 or more is calculated, contrast (high brightness CRT + dark filter) = {CR
White display brightness of T (= X) / 10 + reflected light brightness (100
Ft-L)} / {CRT black display brightness (= about 0) / 10 +
Since the reflected light luminance (100 Ft-L)} ≧ 10, the luminance X required for the CRT is 9,000.
Ft-L or more.

The following techniques have been known as a high-contrast display device used outdoors in a bright environment. (J02) Using a high-brightness backlight and a low-reflectance LCD This conventional technique can display with high contrast even in direct sunlight. The reason will be described below. FIG. 8 is a diagram for explaining conditions for performing high-contrast display in a liquid crystal display device using the light source 1 and the liquid crystal display panel 2. In FIG. 8, an LCD (Liquid Crystal Display Panel) 2 has a structure in which a large number of smooth or highly parallel films or flat plates are laminated, and there is no portion where the reflected light is diffusely reflected, so that a diffuse reflection such as a CRT does not occur. almost none.
Instead, the specular reflection at the film interface is relatively large due to the difference in the refractive index of the film that constitutes the LCD, and even with reduced reflection, the reflectance is about 2% in the color LCD. Therefore, when the maximum value of the external brightness is 10,000 Ft-L, the reflected light brightness is 10,000 Ft-L × 2% = 200 Ft-L. Here, this external brightness value is under direct sunlight,
It is a typical value of the brightness of an object that is 100% diffusely reflected in white. (White clouds, white boards, people dressed in white, etc.)

Since the brightness of the sun itself is extremely large (about 500,000,000 Ft-L), the direct reflection of sunlight is not considered. In fact, the image of the sun is small (about 1/2 degree in diameter), so the angle of the display and the viewing angle (slightly changing the position of the head eliminates the effect of sunlight reflection (makes it invisible). Based on the above assumptions, if you calculate a condition with a contrast of 10 or more, the contrast (high brightness backlight + low reflectance LCD)
= {LCD-specific white display brightness (= X) + reflected light brightness (200Ft-L)} / {LCD-specific black display brightness (= approximately 0) + reflected light brightness (200Ft-L)} ≧ 10 Therefore, the display brightness X required for the LCD is 1,8
00Ft-L or more.

[0008]

The above-mentioned conventional techniques have the following problems. Problem of (J01) In the technology of (J01), the brightness of a CRT is 9.00
0Ft-L or more is required. For this reason, it is possible to realize with a monochrome CRT, but it is difficult to achieve the required display brightness with a color CRT.

Problem of (J02) In the technology of (J02), the display brightness of the LCD is 1,
800Ft-L or more is required. LC for monochrome LCD
Since the transmittance of D itself is about 30%, 6,000 Ft-L
Some backlight brightness is required, but this is feasible. On the other hand, a color LCD has a transmissivity of only about 4%, so a backlight of 45,000 Ft-L and such an ultra-high brightness can be realized with a fluorescent tube with high luminous efficiency which is generally used as a backlight for LCDs. Is difficult and requires a special type of backlight. Therefore, in the case of performing color display, the device becomes large and power consumption becomes large.

As described above, in the prior art, monochrome display is possible, but in color display, it is not easy to raise the display brightness to a required level. For this reason, it has been necessary to reduce the required contrast in the color display device, provide a blind to prevent sunlight from directly entering the display surface, and orient the display device in a direction in which the reflected light is small.

In view of the above circumstances (and examination results), the present invention has the following contents. (O01) To provide a high-contrast display device with little reflected light even in a high-illuminance environment such as outdoors in the daytime.

[0012]

The present invention devised to solve the above problems will now be described. The elements of the present invention are to facilitate correspondence with the elements of the embodiments described later. Note that the reference numerals of the elements of the embodiments are enclosed in parentheses. The reason why the present invention is described in association with the reference numerals of the embodiments described later is to facilitate the understanding of the present invention and not to limit the scope of the present invention to the embodiments.

In order to solve the above problems, the first aspect of the present application
The liquid crystal display device of the invention comprises a light source (1) and the light source (1).
A liquid crystal display device (U) including a liquid crystal display panel (2) for displaying an image by partially transmitting or blocking light emitted from the liquid crystal display device (U), characterized by having the following requirements (Y01 ) A circular polarization filter (3) arranged on the front surface side of the liquid crystal display panel (2).

(Detailed Description of Means for Solving the Problem) The circularly polarized light filter (3) comprises a glass plate on which an antireflection treatment is applied as a base material, and an ordinary linear polarization plate (3a) and 1 / It is a plate-shaped member that can convert incident light into circularly polarized light by combining a four-wave plate (3b).

[0015]

Next, the operation of the present invention having the above features will be described. The liquid crystal display device (U) of the present invention having the above-mentioned characteristics
The light emitted from the light source (1) is partially transmitted or blocked by the liquid crystal display panel (2). Therefore, the light transmitted through the liquid crystal display panel (2) (that is,
The light emitted from the liquid crystal display panel (2) becomes image display light for displaying an image. The image display light emitted from the liquid crystal display panel (2) passes through the circular polarization filter (3) arranged on the front surface side of the liquid crystal display panel (2). The light transmittance at that time is usually about 50%.

FIG. 5 is a view for explaining the action of the circular polarization filter arranged on the front surface of the liquid crystal display panel (2). Figure 5
At, the external light J is converted into linearly polarized light by the linearly polarizing plate (3a). This linearly polarized light is then converted into circularly polarized light by the quarter-wave plate (3b). The external light J converted into circularly polarized light is specularly reflected on the LCD surface. The circularly polarized light that is specularly reflected is converted into linearly polarized light by the quarter-wave plate (3b). The plane of polarization of this linearly polarized light is rotated by 90 ° compared to when it is incident. The linearly polarized light whose plane of polarization is rotated by 90 ° cannot pass through the linearly polarizing plate (3a).

As described above, in principle, by combining the LCD and the circular polarization filter (3), reflection of external light can be completely eliminated. However, in reality, due to various factors, the reflected light cannot be completely reduced to 0, and about 0.3% of the reflection actually remains (30 Ft-L
= 10,000 Ft-L × 0.3%). The conditions for displaying high contrast in this case will be described with reference to FIG. FIG. 4 is a diagram for explaining the conditions for performing high-contrast display in the liquid crystal display device (U) using the light source 1, the liquid crystal display panel 2, and the circular polarization filter 3. In FIG. 4, the transmittance which attenuates the transmitted light, that is, the display light of the LCD by the circularly polarized light filter is 5 as an actual measurement value.
It is about 0% (1/2). Under the above conditions, if a contrast of 10 or more is calculated, contrast (high brightness backlight + LCD + circular polarization filter) = {white display brightness peculiar to LCD (= X / 2) +
Reflected light brightness (30Ft-L)} / {LCD display brightness (= about 0/2) peculiar to LCD + reflected light brightness (30Ft-L)} ≧ 10, so the display brightness X required for the LCD is 540
Ft-L or more. Thus, compared with the case of using the low reflectance LCD of the prior art (J02), it is 0.3 (= 540 /
With the brightness of 1800), the same contrast can be realized.

[0018]

EXAMPLES Examples of the present invention will now be described with reference to the drawings, but the present invention is not limited to the following examples.

(Embodiment 1) FIG. 1 is an explanatory view of the overall configuration of Embodiment 1 of a liquid crystal display device U of the present invention. FIG. 2 is a sectional view of the liquid crystal display panel used in the first embodiment. FIG. 3 is a plan view of the filter shown in FIG. In FIG. 1, the liquid crystal display device U includes a transmissive liquid crystal display panel 2 and a circular polarization filter 3 which are sequentially arranged in front of the light source 1. The light source 1 is composed of a fluorescent tube of high brightness.

In FIG. 3, the liquid crystal display panel 2 is
It has a lower glass substrate 5 to which a polarizing plate 4 is attached on the lower surface. An individual electrode 6 and an alignment film 7 are formed on the upper surface of the lower glass substrate 5. The lower substrate 8 is composed of the elements indicated by the reference numerals 4 to 7. Further, the liquid crystal display panel 2 has an upper glass substrate 12 having a polarizing plate 11 adhered on the upper surface thereof. A color filter 13, a transparent electrode 14, and an alignment film 15 are formed on the lower surface of the upper glass plate 12.
Are formed. The upper substrate 16 is composed of the elements indicated by the reference numerals 11 to 15. As shown in FIG. 3, the color filter 13 includes light-shielding portions 13a and R.
It is composed of color portions of (red), G (green), and B (blue). The upper substrate 16 and the lower substrate 8 are held at regular intervals by spacers (not shown), and a liquid crystal layer 17 is sealed between the upper and lower substrate lower parts 16 and 8. The liquid crystal display panel 2 is composed of the elements indicated by the reference numerals 4 to 17.

In FIG. 1, the liquid crystal display panel 2 is driven by a liquid crystal drive circuit 21.
The brightness of the light source 1 is adjusted by the brightness adjusting circuit 22. The brightness adjustment circuit 22 is configured to automatically adjust the brightness of the light source 1 according to the illuminance detected by the external illuminance sensor 23. In addition, the brightness adjustment circuit 22
The brightness can be adjusted also by a brightness adjusting knob 24 that is manually operated. Such a brightness adjusting circuit is conventionally known.

(Operation of Embodiment) Next, the operation of the embodiment having the above-described structure will be described. As shown in FIG. 4, the required display brightness of the liquid crystal display panel (LCD) 2 in a place where the external illuminance is high is 540 Ft-L or more. The liquid crystal display panel 2 has a light transmittance of 30 in the case of a monochrome liquid crystal display panel.
%, And for a color liquid crystal display panel 4%, the brightness required for the light source light is 1,800 Ft-L for monochrome and 1 for color.
It is 3,500 Ft-L or more. Since the maximum brightness of the fluorescent tube having high luminous efficiency is about 30,000 Ft-L, sufficient contrast can be obtained even if the fluorescent tube is used as the light source 1.

(Modifications) The embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-mentioned embodiments, and is within the scope of the gist of the present invention described in the claims. Thus, various changes can be made. A modified embodiment of the present invention is illustrated below.

(H01) The present invention can be applied not only to a color liquid crystal display panel but also to a monochrome liquid crystal display panel.

[0025]

The liquid crystal display device of the present invention described above can achieve the following effects. (O01) It is possible to provide a high-contrast display device with little reflected light even in a high-illuminance environment such as outdoors in the daytime.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an overall configuration of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a liquid crystal display panel used in the first embodiment.

FIG. 3 is a plan view of the filter shown in FIG.

FIG. 4 is a diagram for explaining conditions for performing high-contrast display in a liquid crystal display device (U) using a light source 1, a liquid crystal display panel 2, and a circular polarization filter 3.

FIG. 5 is a diagram for explaining the operation of a circular polarization filter arranged on the front surface of a liquid crystal display panel.

FIG. 6 is a diagram for explaining conditions for performing high-contrast display in the case of only a high-luminance CRT.

FIG. 7 is a diagram for explaining conditions for performing high-contrast display when a high-luminance CRT and a neutral density filter are used.

FIG. 8 is a diagram for explaining conditions for performing high-contrast display in a liquid crystal display device using the light source 1 and the liquid crystal display panel 2.

[Explanation of symbols]

U ... Liquid crystal display device 1 ... Light source, 2 ... Liquid crystal display panel, 3 ... Circular polarization filter,
3a ... Linear polarizing plate, 3b ... 1/4 wavelength plate,

Claims (1)

[Claims] 1. A liquid crystal display device comprising a light source and a liquid crystal display panel for displaying an image by partially transmitting or blocking light emitted from the light source, wherein the following requirements are satisfied: Liquid crystal display device, (Y01) A circular polarization filter arranged on the front surface side of the liquid crystal display panel.