The present invention relates to a liquid crystal display device, and in particular to a liquid crystal display device including a light diffuser for diffusing light going out from a liquid crystal display panel.
In recent years, portable electronic devices such as mobile phones and PDAs (Personal Digital Assistants) are in wide use. In a display section of a portable electronic device, a liquid crystal display device is frequently used because of its advantages in terms of thinness, light weight, and low power consumption.
In a liquid crystal display device, the display element itself does not emit light, unlike self-light-emitting type display devices such as CRTs and PDPs (plasma display panels). Therefore, in a transmission-type liquid crystal display device, an illuminator called a backlight is provided at the rear face side of the liquid crystal display element, and an image is displayed as the transmitted amount of the illumination light from this backlight is controlled by the liquid crystal display element in a pixel-by-pixel manner.
Liquid crystal display devices of various methods are known. However, some methods (e.g., methods using a TN type or STN type liquid crystal display element) have a disadvantage of narrow viewing angles, and various techniques are under development for overcoming this disadvantage.
As a representative technique for improving the viewing angle characteristics of a liquid crystal display device, there is a method of adding an optical compensation plate. There is also known a method of enhancing the directivity (degree of parallelism) of light which is emitted from a backlight before the light enters a liquid crystal display element, and allowing the light having traveled through the liquid crystal display element to be diffused by a lenticular lens sheet which is disposed on the front face of the liquid crystal display element (e.g., Patent Document 1).
The backlight 510 includes a light source 501 and a light guide plate 502 for guiding the light having been emitted from the light source 501 to the liquid crystal display panel 520. The light guide plate 502 has an outgoing face 502a through which light goes out toward the liquid crystal display panel 520 and a rear face 502b opposing the outgoing face 502a. A plurality of prisms 503 are provided on the rear face 502b.
While propagating within the light guide plate 502, the light having been emitted from the light source 501 is reflected toward the liquid crystal display panel 520 by the prisms 503 on the rear face, so as to go out through the outgoing face 502a. Each prism 503 has two slopes that are slanted at respectively difference predetermined angles with respect to the outgoing face 502a, so that the light which is emitted from the backlight 510 has a very strong intensity along the display surface normal direction (frontal direction). In other words, a high directivity is imparted to the light emitted from the backlight 510.
Since the liquid crystal display panel 520 is designed so that light entering parallel to the display surface normal direction has the highest contrast ratio, it is possible to obtain an improved contrast ratio by allowing the aforementioned high-directivity light to enter the liquid crystal display panel 520. Moreover, the light having traveled through the liquid crystal display panel 520 is diffused by the lenticular lens sheet 530, whereby the viewing angle is broadened. In this manner, with the liquid crystal display device 500, both a high contrast ratio and wide viewing angle characteristics are realized.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 9-22011
However, blurriness of display occurs in the liquid crystal display device 500 disclosed in Patent Document thus deteriorating the display quality. This blurriness of display occurs when light emitted from one pixel is mixed with light which is emitted from another pixel and diffused by the lenticular lens sheet 530 (which is a light diffuser), which causes an intermixing of colors and deteriorates the displayed image.
The present invention has been made in view of the aforementioned problems, and an objective thereof is to suppress blurriness of display in a liquid crystal display device having a light diffuser.
A liquid crystal display device according to the present invention is a liquid crystal display device comprising: a light source; a liquid crystal display panel for modulating light emitted from the light source; and a light diffuser being disposed at a viewer's side of the liquid crystal display panel and diffusing light traveling through the liquid crystal display panel, wherein, the liquid crystal display panel includes a color filter; and the light diffuser is disposed so that a distance d between the color filter and the light diffuser, a pixel pitch p of the liquid crystal display panel, and a display surface luminance L satisfy the relationship d/p<12.151L−0.3186.
In a preferred embodiment, the light diffuser is disposed so that the distance d, the pixel pitch p, and the display surface luminance L satisfy the relationship d/p<11.267L−0.3156.
In a preferred embodiment, the light diffuser is disposed so that the distance d, the pixel pitch p, and the display surface luminance L satisfy the relationship d/p<10.368L−0.3133.
In a preferred embodiment, the light diffuser is disposed so that the distance d, the pixel pitch p, and the display surface luminance L satisfy the relationship d/p<9.1486L−0.3068.
In a preferred embodiment, the light diffuser is disposed so that the distance d, the pixel pitch p, and the display surface luminance L satisfy the relationship d/p<7.2083L−0.2848.
In a preferred embodiment, the light diffuser is disposed so that the distance d, the pixel pitch p, and the display surface luminance L satisfy the relationship d/p<3.8036L−0.2003.
In a preferred embodiment, the liquid crystal display device according to the present invention comprises an illuminator which includes the light source.
In a preferred embodiment, the illuminator has an intensity distribution such that a luminance in directions at an angle of 30° or more with respect to a display surface normal direction is 13% or less of a luminance in the display surface normal direction.
In a preferred embodiment, the illuminator has an intensity distribution such that a luminance in directions at an angle of 30° or more with respect to a display surface normal direction is 3% or less of a luminance in the display surface normal direction.
In a preferred embodiment, the illuminator includes a directivity controlling element for controlling directivity of light emitted from the light source.
A light diffuser of a liquid crystal display device according to the present invention is disposed so that a distance d between a color filter and a light diffuser, a pixel pitch p of a liquid crystal display panel, and a display surface luminance L satisfy a predetermined relationship, whereby blurriness of display is suppressed.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiment.
The liquid crystal display panel 20 includes a pair of substrates 21 and 22, and a liquid crystal layer 23 provided therebetween. On surfaces of the substrates 21 and facing the liquid crystal layer 23, electrodes for applying voltages across the liquid crystal layer 23 and alignment films for defining the orientation directions of liquid crystal molecules contained in the liquid crystal layer 23 (neither of them is shown) are formed. Moreover, a color filter 24 is provided on the liquid crystal layer 23 side of the substrate 22 which is disposed at the viewer's side (i.e., between the substrate 22 at the viewer's side and the liquid crystal layer 23).
At the viewer's side of the liquid crystal display panel 20, a phase difference compensation element 40a and a polarizing plate 50a are provided. Also at the rear face side of the liquid crystal display panel 20, a phase difference compensation element 40b and a polarizing plate 50b are provided. Various known phase difference plates may be used as the phase difference compensation elements 40a and 40b. Note that the number and placement of the phase difference compensation elements are not limited to what is exemplified herein. Three or more phase difference compensation elements may be provided, or only one phase difference compensation element may be provided between either one of the polarizing plates 50a and 50b and the liquid crystal display panel 20. The light diffuser 30 is disposed between the phase difference compensation element 40a at the viewer's side and the liquid crystal display panel 20.
The illuminator 10 at least includes a light source. Light which is emitted from the illuminator 10 of the present embodiment has a significantly strong intensity in the display surface normal direction (frontal direction). In other words, a high directivity is imparted to the light emitted from the illuminator 10.
Furthermore, the illuminator 10 includes a prism sheet 3 for controlling the directivity of light going out from the light guide plate 2. The prism sheet 3 functioning as a directivity controlling element is provided between the light guide plate 2 and the liquid crystal display panel 20.
The prism sheet 3 includes a plurality of prisms 4 formed on its principal face closer to the light guide plate 2, and as shown in
When the light emitted from the illuminator 10 has a high directivity, light traveling through the liquid crystal layer 23 can be substantially uniformly modulated (i.e., a substantially uniform retardation can be imparted to the light traveling through the liquid crystal layer 23), whereby the viewing angle dependence of display quality associated with the refractive index anisotropy of the liquid crystal molecules can be reduced. As it is, the light having traveled through the liquid crystal layer 23 has a high directivity and a large imbalance in luminance (that is, a very high luminance exists along the display surface normal direction whereas luminances along oblique directions are low). However, through diffusion by the light diffuser 30, the luminance imbalance is reduced, whereby the viewing angle is broadened.
As the light diffuser 30, various devices having a function of diffusing light can be used. The light diffusers 30 may be a lens sheet 30A having a plurality of lenses 31 as shown in
Alternatively, the light diffuser 30 may be a diffusion film 30C which utilizes internal scatter, as illustrated in
The light diffuser 30 of the present embodiment is disposed so that a distance d between the color filter 24 and the light diffuser 30, a pixel pitch p of the liquid crystal display panel 20, and a display surface luminance L satisfy the relationship of eq. (1) below.
d/p<12.151L−0.3186 (1)
Note that the distance d between the color filter 24 and the light diffuser 30 as mentioned herein is, strictly speaking, the interval between a surface of the color filter 24 closer to the viewer's side and a surface of the light diffuser 30 closer to the rear face side (opposite from the viewer's side), as is also shown in
By disposing the light diffuser 30 so that the distance d, the pixel pitch p, and the display surface luminance L satisfy the relationship of eq. (1) above, a high-quality displaying with suppress blurriness of display can be performed. Hereinafter, the reason behind this will be specifically described.
“Blurriness of display” is a phenomenon where irrelevant light is mixed into light (an image) that is meant to be visually perceived, thus causing an intermixing of colors and rendering the image unclear. Therefore, the level of blurriness of display can be expressed by, with respect a given pixel, using a color difference when the luminance of the surrounding pixels is changed, and can be expressed as a color difference ΔE*ab in the L*ab (CIE1976) color system, for example. The color difference ΔE*ab can be measured according to JIS 28729. Table 1 below shows a specific correspondence between values of ΔE*ab and emotive expressions of vision. As can also be seen from Table 1, by ensuring that the color difference ΔE*ab is less than 3.0, a displaying is realized in which blurriness of display is suppressed and which is free of awkwardness.
0-0.5
According to detailed studies of the inventors, it has been found that a blurriness of display which is expressed as a color difference ΔE*ab can be evaluated by using a ratio d/p between the distance d and the pixel pitch p as a parameter. In the case where an object is viewed through a light diffuser, the viewer will be viewing light from a range which is larger than the subject of viewing, as shown in
Since the above discussion straightforwardly applies to any pixel that is distant from the light diffuser by the distance d, the blurriness of display can be evaluated by using the ratio d/p between the distance d and the pixel pitch p (which is an inverse of p/d) as a parameter.
Moreover, a blurriness of display which is expressed as a color difference ΔE*ab can also be evaluated by using the display surface luminance L as a parameter.
As can be seen from
d/p=12.151L−0.3186 (2)
in the graph of
Note that, when measuring the color difference ΔE*ab shown in
Moreover, when measuring the color difference ΔE*ab shown in
As described above, when measuring the color difference ΔE*ab shown in
Note that, in order to further suppress blurriness of display, it is preferable to dispose the light diffuser 30 so that the color difference ΔE*ab becomes even smaller.
d/p=11.267L−0.3156 (3)
d/p=10.368L−0.3133 (4)
d/p=9.1486L−0.3068 (5)
d/p=7.2083L−0.2848 (6)
d/p=3.8036L−0.2003 (7)
Therefore, by disposing the light diffuser 30 so that each point which is defined by d/p and L is located below the curve C2, C3, C4, C5, or C6, i.e., by disposing the light diffuser 30 so that d/p and L satisfy the relationship of eq. (8), (9), (10), (11), or (12) below, it can be ensured that the color difference ΔE*ab is less than 2.5, less than 2.0, less than 1.5, less than 1.0, or less than 0.5, whereby blurriness of display can be further suppressed.
d/p<11.267L−0.3156 (8)
d/p<10.368L−0.3133 (9)
d/p<9.1486L−0.3068 (10)
d/p<7.2083L−0.2848 (11)
d/p<3.8036L−0.2003 (12)
Note that, as is also shown in
Moreover, without limitation to what is exemplified in
In the intensity distribution shown in
Moreover, in the intensity distributions shown in
The level of directivity shown in
According to the present invention, the blurriness of display in a liquid crystal display device including a light diffuser can be suppressed, whereby a high quality displaying can be realized. The present invention is suitably used for liquid crystal display devices in general, and in particular, suitably used for liquid crystal display devices of display modes of poor viewing angle characteristics (e.g., STN mode, TN mode, ECB mode).
In display modes utilizing birefringence, e.g., the STN mode, there is a large unfavorable influence on displaying due to light which obliquely enters the liquid crystal layer, thus making it preferable to employ a viewing angle enlarging technique where highly directive light is allowed to enter a liquid crystal layer and light having been modulated by the liquid crystal layer is diffused by a light diffuser, thus leading to a large significance in applying the present invention.
Number | Date | Country | Kind |
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2006-332809 | Dec 2006 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2007/073789 | 12/10/2007 | WO | 00 | 6/10/2009 |