JP2009192793A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of efficiently improving color reproducibility and suppressing an extreme reduction in the luminance even when the device is made small or thin. <P>SOLUTION: The liquid crystal display device is equipped with a light source containing a white LED that emits white light and a liquid crystal panel displaying a color image on the basis of the light from the light source and is disposed a wavelength selection filter that attenuates light at wavelengths in a range from 580 nm to 600 nm on an optical path of the white light from the white LED. Thus, color reproducibility in color display is improved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device using a liquid crystal display panel. In particular, the present invention relates to a liquid crystal display device using a liquid crystal panel that displays a color image based on light from a light source.

  Liquid crystal display devices are used in various devices such as mobile phones, PDAs, electronic dictionaries, car navigation systems, and music players. In the above-described liquid crystal display device, a backlight using a cold cathode tube is mainly disposed, and light from the backlight is irradiated toward the liquid crystal display panel. In addition, even when liquid crystal display devices are used in highly portable terminal devices, liquid crystal display panels equipped with color filters and capable of displaying color images have recently become mainstream, and more color reproducibility. It is desired to display an excellent color image.

  Thus, for example, as shown in Patent Document 1, an example is shown in which a wavelength selection filter corresponding to the light spectrum of a cold cathode ray tube as a light source is provided. Specifically, a wavelength selective filter having a transmittance of about 80% in the wavelength ranges of 420 nm to 460 nm, 500 nm to 550 nm, and 620 nm to 710 nm and a transmittance in the other wavelength ranges of about 10% is used. As a result, the liquid crystal display device having a color reproducibility of “71%” is improved to “88%”.

Further, for example, in Patent Document 2, a cold cathode ray tube is used as a light source, and a wavelength selection filter that selectively absorbs wavelengths at wavelengths of 450 nm, 490 nm, 545 nm, 580 nm, and 610 nm is used on the optical path from the light source to the liquid crystal display panel. The liquid crystal display device having a color reproducibility of “75%” is improved to “80%”.
JP 2006-72249 A JP 2007-147688 A

  However, in the above-described liquid crystal display device, adopting a backlight using a cold cathode tube as a light source makes it difficult to reduce the thickness and size and increase power consumption because it requires external parts to drive. It is not easy to reduce the size and thickness. For this reason, in a liquid crystal display device used in a portable terminal device that is carried around, a backlight using a white LED as a light source may be employed to reduce the size and thickness.

  In addition, when the wavelength selection filter having the characteristics in the liquid crystal display device described above is applied to a liquid crystal display device using a white LED, the luminance is remarkably attenuated and the color reproducibility is not significantly increased. There was a risk that the color reproducibility could not be balanced.

  Concretely, it will be described in detail using Table 1 to be described later. In the configuration of Patent Document 1 (known example 1 in the table), although the color reproducibility is increased to “94%”, the luminance is remarkable as “330”. In the configuration of Patent Document 2 (known example 2 in the table), the luminance is not significantly attenuated to “420”, but the color reproducibility is not as high as “72%”.

  The present invention has been made in view of the above-described problems, and can effectively improve color reproducibility and suppress a significant reduction in luminance even in the case of downsizing and thinning. It is an object of the present invention to provide a liquid crystal display device that can be used.

  In order to achieve the above object, the liquid crystal display device of the present invention includes a light source including a white LED that emits white light and a liquid crystal panel that displays a color image based on the light from the light source. The wavelength selection filter that attenuates the wavelength range of 580 nm to 600 nm is arranged on the optical path of white light from the white LED. Further, a reflective polarizer that transmits light of a specific polarization direction and reflects other light is disposed on the optical path of white light.

  According to the present invention, color reproducibility can be improved efficiently and a significant reduction in luminance can be suppressed even when downsizing and thinning are achieved.

  The display device of the present invention is a liquid crystal display device including a lighting device that includes a blue LED and a yellow phosphor and emits pseudo white light, and a liquid crystal panel that performs color display based on light from the lighting device, A wavelength selection filter that attenuates a wavelength component in the range of 580 nm to 600 nm is provided on the optical path of the illumination light. Thereby, the wavelength component in the range of 580 nm to 600 nm contained in the pseudo white light is reduced, and the color reproducibility of the color display is improved.

  Furthermore, a reflective polarizer that transmits light in a specific polarization direction and reflects other light is provided between the wavelength selection filter and the liquid crystal panel. With such a configuration, light incident on the liquid crystal panel is increased, and luminance can be improved.

  According to another aspect of the present invention, a display device is a liquid crystal display device that performs color display including a liquid crystal panel including a color filter, and an illumination device that includes a light source and irradiates light to the liquid crystal panel. A wavelength-selective filter that attenuates light components in the wavelength range that does not transmit light is provided on the optical path of the light from the light source, and a reflective polarizer that transmits light in a specific polarization direction and reflects other light is used. It was decided to be provided between the selection filter and the liquid crystal panel. According to such a configuration, the wavelength selection filter cuts components unnecessary for the color filter among components included in the light source, so that the color reproducibility is improved and the illumination light that the reflective polarizer reaches the liquid crystal panel. Therefore, the luminance is improved. In other words, color reproducibility and luminance can be improved at the same time.

  An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a cross-sectional view schematically showing the liquid crystal display device of this embodiment. As illustrated, the liquid crystal display device 10 includes a light guide plate 2, a wavelength selection filter 1, a reflective polarizer 4, a lower absorption polarizer 6, a liquid crystal display panel 5, and an upper absorption polarizer 7, in that order. Arranged in a stacked state. A white LED 3 is disposed in the vicinity of the side surface of the light guide plate 2 to constitute a backlight. The wavelength selection filter 1, the reflective polarizer 4, the lower absorption polarizer 6, the liquid crystal display panel 5, and the upper absorption polarizer 7 are disposed on the same optical path of the light emitted from the irradiation surface of the light guide plate 2. The light guide plate 2 guides white light from the white LED 3 toward the wavelength selection filter 1 and the liquid crystal display panel 5. FIG. 2 is a diagram illustrating wavelength characteristics regarding the liquid crystal display device of the present embodiment. In FIG. 2, the wavelength (nm) is on the horizontal axis, and the luminance or transmittance is on the vertical axis.

  The white LED 3 of the present embodiment emits white light by exciting a yellow phosphor using a blue light emitting diode. Such a white LED 3 emits white light having a wavelength characteristic as shown in FIG.

  The wavelength selection filter 1 splits the light emitted from the light guide plate 2 and transmits the light toward the reflective polarizer 4. That is, the wavelength selection filter 1 has a characteristic that does not transmit light in a specific wavelength range. The wavelength selection filter 1 of the present embodiment is a filter having wavelength characteristics as shown in FIG. 2B, and has a function of attenuating light having a wavelength of 580 nm to 600 nm.

  The reflective polarizer 4 transmits light in a specific polarization direction and reflects other light. The reflective polarizer 4 transmits part of the light transmitted through the wavelength selection filter 1 and reflects other light. The transmitted light travels toward the absorption polarizer 6 and the liquid crystal display panel 5. On the other hand, the light reflected by the reflective polarizer 4 is repeatedly reflected between the backlight and the reflective polarizer 4. While the reflection is repeated, the light changed in the polarization direction that is transmitted through the reflective polarizer becomes light incident on the liquid crystal display panel 5. In other words, light that has not reached the liquid crystal display panel in the conventional configuration can be used, thereby suppressing luminance attenuation.

  The absorptive polarizer transmits light in a specific polarization direction and absorbs other light. The lower absorption polarizer 6 and the upper absorption polarizer 7 are arranged so as to sandwich the liquid crystal display panel 5. Each absorption polarizer 6 and 7 performs polarization suitable for the liquid crystal display panel 5. In the present embodiment, the retardation film or the like is not provided. However, the configuration is not limited thereto, and for example, a configuration including a retardation film may be used.

  The liquid crystal display panel 5 includes a liquid crystal layer whose molecular arrangement changes when an external voltage or the like is applied, and three color filters of red (R), green (G), and blue (B) corresponding to each pixel. . In the liquid crystal display device of the present embodiment, the wavelength selection filter 1 for attenuating the wavelength range of 580 nm to 600 nm is disposed between the liquid crystal display panel 5 and the illumination device that emits white light. A color image is displayed based on the generated white light. That is, of the white light from the white LED, the wavelength of 580 nm to 600 nm is attenuated, and the light having the wavelength characteristic as shown in FIG. 2D becomes the illumination light of the liquid crystal display panel. This light has wavelength characteristics with peaks in blue, green, and red, and approaches the wavelength characteristics of blue light, green light, and red light as shown in FIG. Become.

Table 1 shows the results of calculating the luminance and color reproducibility of the liquid crystal display device 10 having the configuration according to the present invention and the liquid crystal display device having the conventional configuration. The comparative example in the table is a configuration in which a white LED similar to the present embodiment is used but the wavelength selective filter 1 is not provided, that is, the present invention is not adopted. Known example 1 is the configuration of Patent Document 1 described above, and known example is the configuration of Patent Document 2, and a white fluorescent tube is used as the light source. As the configuration according to the present invention, the configuration having only the wavelength selective filter 1 and the configuration having both the wavelength selective filter and the reflective polarizer are exemplified. Luminance and color reproducibility were calculated for each of these configurations, and the luminance attenuation rate, color reproducibility change rate, and efficiency were calculated based on the results. Here, the luminance attenuation rate and the color reproducibility change rate indicate the ratios based on the luminance and color reproducibility of the comparative example, and the efficiency is the product of the luminance attenuation rate and the color reproducibility change rate. .

  As shown in Table 1, in the comparative example not using the wavelength selection filter 1, the luminance is “560” and the color reproducibility is 71% of NTSC ratio.

  The configuration example 1 of the present invention is different from the comparative example in that the wavelength selection filter 1 is provided. In the configuration example 1, the luminance is “400” and the color reproducibility is “83%”, which is compared with the comparative example. The luminance attenuation rate was “71%”, but the color reproducibility change rate at that time was improved to “117%”, and the efficiency was “83%”. Thus, when the wavelength selection filter 1 is provided, color reproducibility is improved as compared with the comparative example. Although the luminance is lowered, it is not significantly attenuated, and a significant reduction in luminance can be suppressed.

  In the configuration example 2 of the present invention in which the wavelength selection filter 1 and the reflective polarizer 4 are provided, the luminance is “520”, the color reproducibility is “85%”, and the luminance attenuation rate is “5” compared to the comparative example. 93% ", the color reproducibility change rate was" 119% ", and the efficiency was" 110% ".

  As described above, in the configuration example 2 in which the wavelength selection filter 1 and the reflective polarizer 4 are provided, the luminance, color reproducibility, and efficiency are all increased compared to the configuration example 1 in which the reflective polarizer 4 is not provided. Further, since there are many filters in the configuration example 2, although the luminance is reduced as compared with the comparative example, both color reproducibility and efficiency are improved. However, the decrease in luminance is slight, and a significant decrease in luminance can be suppressed, and it is not necessary to significantly increase the emission luminance of the light source itself.

  In the known examples 1 and 2 using a cold cathode tube as the light source, the luminance is “330” and “420”, the color reproducibility is “94” and “72”, and the luminance attenuation rate is “ 60% "," 74% ", the color reproducibility change rate was" 131% "," 101% ", and the efficiency was" 77% "," 75% ". In the configuration example 2 in which the white LED 3 is used as the light source and the wavelength selection filter 1 and the reflective polarizer 4 are provided, either the color reproducibility or the luminance is higher than the known examples 1 and 2, and the other is Lower. In particular, in the known example 1 and the known example 2, one of them is remarkably lowered, and the balance between luminance and color reproducibility is deteriorated. In addition, when a cold cathode tube is used as a light source, the liquid crystal display device is reduced in thickness and size and reduced in power consumption due to various reasons such as requiring external parts to drive, and by using the white LED 3 as the light source. Can be realized.

  Thus, a white LED that emits white light as a light source and a wavelength selection filter that is disposed on the optical path of white light from the white LED and attenuates the wavelength range of 580 nm to 600 nm are incorporated in the liquid crystal display device. Thus, color reproducibility can be improved efficiently, and a significant reduction in luminance can be suppressed. Moreover, since white LED is used, thickness reduction and size reduction are realizable, and it can employ | adopt for a highly portable terminal device. Further, by arranging the reflective polarizer on the optical path, further improvement in color reproducibility and luminance can be measured.

  The liquid crystal display panel 5 has an optical switching function such as a TN type, an IPS type, a VA type, and an OCB type.

  In this embodiment, the wavelength selection filter that attenuates the wavelength range of 580 to 600 nm is used. However, the present invention is not limited to this. For example, a wavelength selection filter that attenuates another wavelength range may be used. In this embodiment, a white LED that emits white light as shown in FIG. 2A is used. However, the present invention is not limited to this. For example, a white LED that emits white light having another wavelength characteristic is used. It may be adopted.

It is sectional drawing which shows the liquid crystal display device by this invention. It is explanatory drawing which shows the wavelength characteristic regarding the liquid crystal display device by this invention.

Explanation of symbols

1 Wavelength selection filter 2 Backlight light guide plate 3 White LED
4 reflective polarizer 5 liquid crystal display panel 6 absorptive polarizer 10 liquid crystal display device

Claims (3)

A liquid crystal display device comprising: an illumination device having a light source; and a liquid crystal panel that performs color display based on light from the illumination device,
The illumination device includes a blue LED and a yellow phosphor and emits white light,
A liquid crystal display device comprising a wavelength selection filter for attenuating a wavelength component in a range of 580 nm to 600 nm on an optical path of light from the light source.   2. The liquid crystal display according to claim 1, wherein a reflective polarizer that transmits light of a specific polarization direction and reflects other light is provided between the wavelength selection filter and the liquid crystal panel. apparatus. A liquid crystal display device having a color filter, and a liquid crystal display device having a light source and an illumination device for irradiating the liquid crystal panel with light, and performing color display,
While providing a wavelength selection filter on the optical path of the light from the light source to attenuate the light component in the wavelength region that does not pass through the color filter,
A liquid crystal display device, wherein a reflective polarizer that transmits light of a specific polarization direction and reflects other light is provided between the wavelength selection filter and the liquid crystal panel.

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