JP2009036890A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an STN-LCD which has a high contrast ratio and excellent viewing angle characteristics. <P>SOLUTION: The liquid crystal display device includes: a backlight using a light source having a monochromatic light emission peak; a pair of substrates placed opposite to each other; a nematic liquid crystal layer interposed between the substrates; electrode patterns formed on the nematic liquid crystal layer side of the respective substrates; and polarizing plates disposed on the upper and lower sides with respect to the normal direction of the substrates, and has an STN mode liquid crystal display section of which the twist angle of the liquid crystal is 15-210°, wherein the aligning directions of liquid crystal molecules of the nematic liquid crystal layer at positions on which the liquid crystal molecules are in contact with the respective upper and lower substrates of the pair of substrates and the axis directions of the polarizing plates are not identical to one another, and with respect to a smaller angle out of angles which they form, the sum of the upper substrate side angle and the lower substrate side angle is 90±7°. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a device using liquid crystal, and more particularly to a liquid crystal display device.

  STN (super twisted nematic) -LCD has been used as a high duty liquid crystal display element. A blue mode display will be described as an embodiment of the STN-LCD. Among the polarizing plates arranged above and below the liquid crystal cell, the analyzer is arranged so that the polarization axis of the analyzer is 30 degrees counterclockwise with respect to the liquid crystal molecule long axis direction on the outgoing light side, and the polarization axis of the polarizer is incident By disposing 30 degrees clockwise with respect to the long axis direction of the liquid crystal molecule on the light side, so-called blue mode display is possible in which the color is blue when no voltage is applied and white when voltage is applied.

  Japanese Patent Application Laid-Open No. 2004-62021 proposes that a liquid crystal composition of a blue-mode STN-LCD contains a dichroic dye to improve the light-shielding property in a blocked state. As another means for improving the light shielding property, there is a method using a compensation plate.

  In the blue mode, a white backlight is usually used as a backlight, but a monochromatic light source such as a light emitting diode (LED) may be used. In this case, if the transmittance at the light emission wavelength of the backlight is lowered when no voltage is applied, and the light is transmitted at an appropriate transmittance for displaying the wavelength when the voltage is applied, the display color is normally black. The following mode can be obtained.

JP 2004-62021 A

  The STN-LCD has a transmittance curve having a minimum value at a certain wavelength. In the mode of performing monochrome display with normally black, it is required to increase the contrast ratio between when no voltage is applied and when voltage is applied.

  In particular, in the case of an in-vehicle liquid crystal display device, improvement in viewing angle characteristics is also desired.

  An object of the present invention is to provide an STN type liquid crystal display element with improved contrast ratio and viewing angle characteristics in a normally black mode.

  According to one aspect of the present invention, a backlight using a light source having a single wavelength emission peak, a pair of opposing substrates, a nematic liquid crystal layer sandwiched between the substrates, and the nematic liquid crystal in each of the substrates An STN-type liquid crystal display unit having a liquid crystal twist angle of 155 ° to 210 °, including an electrode pattern formed on the layer side and a polarizing plate disposed vertically with respect to the normal direction of the substrate; The liquid crystal molecule alignment direction of the nematic liquid crystal layer and the axial direction of the polarizing plate are not the same at the position of the pair of substrates in contact with each of the upper substrate and the lower substrate, and a smaller angle formed by these directions. A liquid crystal display device in which the sum of the upper substrate side angle and the lower substrate side angle is 90 ° ± 7 ° is provided.

  In a normally black display STN-LCD, a display with a high contrast ratio and good viewing angle characteristics can be obtained.

  FIG. 1 is a cross-sectional view of a liquid crystal display unit 101 and a backlight 102 in a liquid crystal display device. The liquid crystal display device in the embodiment includes a liquid crystal display unit 101 and a backlight 102 as main components. The liquid crystal display unit 101 displays the pattern of the electrode 2 by transmitting or blocking light from the backlight 102.

  A method for creating the liquid crystal display unit 101 will be described. A transparent ITO film is formed on each of the two glass substrates 1A and 1B by CVD, vapor deposition, sputtering, or the like, and a desired ITO electrode pattern 2 and external extraction wiring 21 are formed by photolithography. An insulating film 4 is formed on the glass substrate with the ITO electrode pattern 2 by flexographic printing. The insulating film 4 is not essential, but is desirably formed to prevent a short circuit between the upper and lower substrates. In addition to flexographic printing, the insulating film may be formed by vapor deposition or sputtering using a metal mask.

  Next, an alignment film 5 having substantially the same pattern as the insulating film 4 is formed on the insulating film 4 by flexographic printing.

  Next, the alignment film 5 is rubbed. The rubbing is a process in which a cylindrical roll wound with a cloth is rotated at high speed and rubbed on the alignment film 5.

  A seal material 6 having a predetermined pattern is screen-printed. The sealing material 6 may be formed using a dispenser instead of screen printing. Thermosetting ES-7500 (Mitsui Chemicals) is used as the sealing material. As other materials, a photo-curable material or a light / heat combination type sealing material may be used. This sealing material 6 contains several percent of glass fiber having a diameter of 6 μm.

  Next, a material containing several percent of 6.5 μm Au balls in the sealing material ES-7500 is screen printed as the conductive material 7.

  The sealing material pattern 6 and the conductive material pattern 7 are formed only on the substrate 1B, and a gap control material is sprayed on the substrate 1A by a dry spraying method. A plastic ball of 6 μm is used as a gap control material.

  The two substrates 1A and 1B are overlapped at predetermined positions so that the alignment film 5 is on the inside to form cells, and the sealing material 6 is cured by heat treatment in a pressed state.

  Next, the glass substrate is scratched with a scriber device, and is divided into a predetermined size and shape by breaking to create empty cells.

  The liquid crystal 3 is injected into the above empty cell by a vacuum injection method, and then the injection port is sealed with an end seal material. Thereafter, the glass substrate is chamfered and washed to form a liquid crystal cell.

  Further, polarizing plates 8 are attached to the top and bottom of the liquid crystal cell to complete the STN mode liquid crystal display unit 101.

  As a reference example, a blue mode STN-LCD will be described.

  FIG. 2A shows a schematic plan view of a blue mode STN-LCD. FIG. 2A is a diagram regarding a liquid crystal molecule alignment direction and a polarizing plate axis direction on each side of the upper and lower substrates. As shown in the figure, the twist angle of the liquid crystal is 270 °. The smaller angle (angle a) between the liquid crystal molecule alignment direction closest to the upper substrate (front substrate) and the upper polarizing plate axis direction is 30 °, and the closest position to the lower substrate (back substrate). The smaller angle (angle b) formed by the liquid crystal molecule alignment direction and the lower polarizing plate axis direction is also 30 °. In the drawing relating to the polarizing plate axis direction, the angle is expressed as an absolute value.

  The transmittance characteristic of the blue mode STN-LCD having the above configuration will be described.

  FIG. 2B shows a transmittance curve in a substantially visible region of the liquid crystal display unit. In addition, the transmittance curve shown in the specification was calculated by a self-made simulation software. As shown in the figure, the transmittance of the liquid crystal display unit in the reference example has a maximum value and a minimum value when no voltage is applied. The maximum value is the blue wavelength, and the transmittance is about 50% when no voltage is applied. Such a liquid crystal display device has a blue background color. When voltage is applied, the transmittance in the blue region is slightly lower than in other visible regions, but has a transmittance of about 50% over the entire visible region, and the white backlight transmits light to display white. .

  On the other hand, a light emitting device having a single wavelength emission peak may be used as a backlight of an LCD. The inventors studied to perform normally black monochromatic display by matching the wavelength in which the transmittance when no voltage is applied to the backlight in the wavelength region of the backlight.

  First, it was examined whether or not normally black single color display is possible for a liquid crystal display unit having the same configuration as the blue STN-LCD. The wavelength at which the transmittance of the liquid crystal display takes the minimum value is 540 nm. The transmittance of the liquid crystal display when no voltage is applied at a wavelength of 540 nm is about 6%, and the transmittance of the liquid crystal display when a voltage at the same wavelength is applied is about 48%. When a single color display STN-LCD is manufactured using a backlight having a light emission wavelength region near 540 nm for the liquid crystal display unit 101, at least about 6% of light is lost, so normally black cannot be realized, and a single color shading is not achieved. It becomes display. The contrast ratio is only about 8 at the maximum. For this reason, it is desired that the minimum value of the transmittance when no voltage is applied is close to 0% to improve the light shielding property and the contrast ratio.

  Inventors examined various polarizing plate arrangement | positioning in order to make the minimum value of the transmittance | permeability at the time of no voltage application close to 0%. As a result, the upper substrate side angle (angle a and the angle between the liquid crystal alignment direction closest to the upper and lower substrates forming the liquid crystal display element and the polarizing plate axis direction on each of the upper and lower substrates side is smaller. And the lower substrate side angle (assumed to be angle b) have been found to exhibit excellent characteristics in an arrangement in which the sum (assumed to be angle a + b) is 90 °. If the condition is satisfied, there is a wavelength at which the transmittance is almost 0% in the transmittance-wavelength characteristics when no voltage is applied.

  It is assumed that the center value of the emission wavelength is combined with a red backlight having a wavelength of 630 nm. The key to creating a liquid crystal cell is to control the retardation of the cell so that the wavelength at which the transmittance is 0% or close to it (low enough to realize normally black) matches the emission wavelength region of the backlight. It is. Cell retardation can be changed by changing the cell thickness or birefringence (specifically, changing the liquid crystal material. In the range normally used for liquid crystal display devices, retardation can be achieved by mixing liquid crystal materials having different characteristics. Can be controlled).

  FIG. 3A shows a schematic plan view of the STN-LCD. FIG. 3A is a diagram regarding a liquid crystal molecule alignment direction and a polarizing plate axis direction on each of the upper and lower substrates. As shown in the figure, the twist angle of the liquid crystal is 270 °. The smaller angle (angle a) between the liquid crystal molecule alignment direction closest to the upper substrate and the upper polarizing plate axis direction is 45 °, and the liquid crystal molecule alignment direction closest to the lower substrate is The smaller angle (angle b) to the polarizing plate axis direction is 45 °.

  FIG. 3B shows a transmittance curve in a substantially visible region of the liquid crystal display unit. As shown in the figure, the transmittance when no voltage is applied has a minimum value of 0% at a wavelength of 630 nm. By using the LED of this wavelength as a backlight, the light of the backlight can be shielded when no voltage is applied, so that normally black can be realized. When a voltage is applied, the transmittance at a wavelength of 630 nm is about 42%, so that a high contrast ratio can be realized.

  The retardation of the liquid crystal cell is 0.847 μm.

  Note that the angle a + b is not necessarily 90 °. The inventors examined a preferred angle a + b.

  FIG. 4 shows a graph of the transmittance when no voltage is applied to the liquid crystal display unit at a wavelength of 630 nm with respect to the angle a + b. When various samples having different polarizing plate angles were prepared and the display was observed, it was found that a sample having a transmittance of 0.3% or less when no voltage was applied is preferable as a liquid crystal display element. In order to satisfy this condition, the angle a + b should be 90 ° ± 7 ° from the graph shown in the figure.

  The STN-LCD manufactured under the above conditions can obtain a high contrast ratio during frontal observation. Furthermore, the inventors investigated the conditions under which a good display can be obtained even when the viewing angle is swung vertically and horizontally. This is because the viewing angle characteristics, particularly the viewing angle characteristics in the left-right direction, are important for in-vehicle applications.

  FIG. 5A shows the transmissivity-viewing angle characteristic in the left-right direction at a wavelength of 630 nm of the 270 ° STN-LCD shown in FIG. 3A. The horizontal axis is an angle in which the right direction with respect to the front is positive. As shown in the figure, the larger the left and right angles, the smaller the difference in transmittance between when a voltage is applied and when no voltage is applied, resulting in a smaller contrast ratio. Further, the transmittance is reversed when the angle exceeds about 60 ° on both the left and right sides.

  FIG. 5B shows the transmittance-viewing angle characteristic in the vertical direction at a wavelength of 630 nm of the 270 ° STN-LCD shown in FIG. 3A. The horizontal axis is an angle with the upward direction with respect to the front as positive. As shown in the figure, the transmittance when a voltage is applied is asymmetrical in the viewing angle in the vertical direction. On the other hand, the transmittance when no voltage is applied is almost symmetrical up and down up to a viewing angle of about 30 ° and has a sufficient light shielding property.

  The light shielding property plays a major role in the contrast ratio of the LCD. In the embodiment, it is better that the transmittance in a state where no voltage is applied is closer to 0%. The inventors paid attention to the transmittance in a state in which no voltage was applied. Then, the transmittance-wavelength characteristics in a substantially visible range when no voltage is applied are summarized with the viewing angle as a parameter.

  FIG. 6 shows the transmittance-wavelength characteristics in a substantially visible range when no voltage is applied to the 270 ° STN-LCD shown in FIG. 3A. The figure shows the transmittance-wavelength characteristics when the viewing angle is swung to the right (down) or down (down) with respect to the front, up to 60 ° for each 20 °, using the viewing angle as a parameter. “Normal” means a viewing angle of 0 °.

  As shown in the figure, when the viewing angle is about 20 °, there is no big difference in the transmittance curve compared to the case where the viewing angle is 0 ° in both the right direction and the downward direction, but the viewing angle is greatly swung to 40 ° and 60 °. The transmittance curve gradually shifts. Further, the minimum value of the transmittance is about 2% when the viewing angle is 40 °, and about 8 to 9% when the viewing angle is 60 °. If the liquid crystal display device is viewed from this angle, the light is lost.

  The transmittance-wavelength characteristics when the viewing angle is swung leftward and upward, not shown in FIG. 6, will be described. From the result shown in FIG. 5A, the transmittance-wavelength characteristic when the viewing angle is moved in the left direction can be regarded as almost the same as that when the viewing angle is moved in the right direction. On the other hand, the transmittance-wavelength characteristic when the viewing angle is swung upward can be regarded as substantially the same as the case where the viewing angle is swung downward at least up to a viewing angle of about 30 ° from the result shown in FIG. 5B. The transmittance-wavelength characteristic at a viewing angle of 30 ° or later may be different from the case where the viewing angle is shifted downward or may be substantially symmetric (depending on the twist angle of the liquid crystal layer).

  The inventors investigated how the transmittance-viewing angle characteristic when no voltage is applied is changed by changing the twist angle of the liquid crystal layer. In the process, not only the STN-LCD but also the transmittance-viewing angle characteristics of the 90 ° twisted TN-LCD were examined.

  FIG. 7A shows a schematic plan view of a 90 ° TN-LCD. FIG. 7A is a diagram relating to a liquid crystal molecule alignment direction and a polarizing plate axis direction on each side of the upper and lower substrates. In the illustrated 90 ° TN-LCD, the liquid crystal molecules are twisted by 90 ° and the axial directions of the polarizing plates are parallel.

  FIG. 7B shows transmittance-wavelength characteristics in a substantially visible range when no voltage is applied to the 90 ° TN-LCD. The view of FIG. 7B is the same as that of FIG. In the example shown in FIGS. 7A and 7B, a polarizing plate is disposed in a TN cell with a 90 ° twist and a cell retardation Δnd of about 0.555 μm with an axial orientation as shown in FIG. 7A, and the center value of the emission wavelength is 630 nm. By combining a red backlight, a red display is realized on a black background during frontal observation (viewing angle 0 °).

  However, as shown in FIG. 7B, it can be seen that the transmittance curve is greatly shifted by swinging the viewing angle to 40 ° and 60 °. The transmittance when no voltage is applied at a wavelength of 630 nm is about 2% (when the viewing angle is 40 °) or about 8% (when the viewing angle is 60 °). Therefore, it is difficult to realize good viewing angle characteristics.

  FIG. 8 shows transmittance-wavelength characteristics in a substantially visible range when no voltage is applied to the 180 ° STN-LCD. The retardation of the liquid crystal cell is 0.847 μm. As shown in the figure, when the viewing angle is viewed as a parameter, in the case of 180 ° twist, there is little deviation of the transmittance curve up to a viewing angle of 40 °, and the minimum value is maintained at almost 0%.

  Based on the above results, the inventors considered that there is an optimum range for the transmittance-viewing angle characteristics when no voltage is applied and the twist angle of the liquid crystal layer, and studied a preferred twist angle in the STN-LCD.

  FIG. 9 shows the transmittance-twist angle characteristics of the STN-LCD using the viewing angle as a parameter at a wavelength of 630 nm.

  In order to realize a display having a wide viewing angle characteristic, it is preferable to realize a low transmittance when no voltage is applied at a viewing angle of 40 ° or less in the right direction. When the produced display of various conditions was observed, when the transmittance | permeability 1% or less was implement | achieved within 40 degree viewing angle range, it turned out that a display is favorable. According to FIG. 9, the twist angle at which the transmittance at a viewing angle of 40 ° in the lower and right direction is 1% or less is 155 ° to 210 °.

  The inventors further limit the preferred twist angle. In an in-vehicle display, since the viewing angle characteristic in the left-right direction is more important, it is desirable that the transmittance when no voltage is applied is as low as possible within the viewing angle range of 40 ° in the left-right direction. When a display with various conditions manufactured from this viewpoint was observed, it was found that if the transmittance of 0.3% or less was realized within the 40 ° viewing angle range, the viewing angle characteristics of the in-vehicle display were further improved. In FIG. 9, the twist angle at which the transmittance at a viewing angle of 40 ° is 0.3% or less is 170 in the left-right direction (right direction in the figure. As described above, the viewing angle characteristics in the left-right direction will substantially correspond). ° to 200 °.

  Examples that satisfy the above conditions will be described below.

Example 1
An embodiment in which a red backlight having a wavelength of 630 nm and a liquid crystal cell are combined will be described.

  FIG. 10A shows a schematic plan view of an STN-LCD. FIG. 10A is a diagram relating to a liquid crystal molecule alignment direction and a polarizing plate axis direction on each side of the upper and lower substrates. As shown in the figure, the twist angle of the liquid crystal is 180 °. The smaller angle (angle a) between the liquid crystal molecule alignment direction closest to the upper substrate and the upper polarizing plate axis direction is 45 °, and the liquid crystal molecule alignment direction closest to the lower substrate is The smaller angle (angle b) to the polarizing plate axis direction is 45 °.

  FIG. 10B shows the transmittance-viewing angle characteristics of the liquid crystal display unit at a wavelength of 630 nm. As shown in the figure, the transmissivity is 1% or less in the 40 ° viewing angle range in both the vertical and horizontal directions. Further, in the left-right direction, the transmittance is kept at 1% or less within the 60 ° viewing angle range, and it can be seen that the viewing angle characteristics are better.

(Example 2)
Another embodiment in which a red backlight having a wavelength of 630 nm and a liquid crystal cell are combined will be described.

  FIG. 11A shows a schematic plan view of an STN-LCD. FIG. 11A is a diagram relating to the liquid crystal molecule alignment direction and the polarizing plate axis direction on each side of the upper and lower substrates. As shown in the figure, the twist angle of the liquid crystal is 190 °. The smaller angle (angle a) between the liquid crystal molecule alignment direction closest to the upper substrate and the upper polarizing plate axis direction is 50 °, and the liquid crystal molecule alignment direction closest to the lower substrate is The smaller angle (angle b) formed with the polarizing plate axis direction is 40 °.

  FIG. 11B shows transmittance-viewing angle characteristics of the liquid crystal display unit at a wavelength of 630 nm. As shown in the figure, good transmittance is maintained in the 40 ° viewing angle range in both the vertical and horizontal directions. Further, in the left-right direction, the transmittance is kept at 1% or less even in the 80 ° viewing angle range, and it can be seen that the viewing angle characteristics are better.

(Example 3)
An embodiment in which a green backlight having a wavelength of 550 nm and a liquid crystal cell are combined will be described. The combination of the alignment direction of the liquid crystal molecules and the polarizing plate axis direction of the STN-LCD and the twist angle of the liquid crystal are the same as in the second embodiment. By adjusting the cell retardation to 0.614 μm, the minimum value of the transmittance when no voltage was applied was adjusted to appear at a wavelength of 550 nm.

  FIG. 12 shows the transmittance-viewing angle characteristics of the liquid crystal display unit at a wavelength of 550 nm. As shown in the figure, good transmittance is maintained in the 40 ° viewing angle range in both the vertical and horizontal directions. Further, in the left-right direction, the transmittance is kept at 1% or less within the range of about 75 ° viewing angle, and it can be seen that the viewing angle characteristic is better.

Note that a light source having another emission peak may be used as the backlight if the following conditions are satisfied.
An STN liquid crystal display unit having a liquid crystal twist angle of 155 ° to 210 ° is used.
The liquid crystal molecule alignment direction of the liquid crystal layer and the axial direction of the polarizing plate are not the same, and the smaller angle formed by these directions is the upper substrate side angle (angle a) and the lower substrate side angle (angle b). The sum is 90 ° ± 7 °.
The retardation of the cell can be adjusted because the wavelength at which the transmittance when no voltage is applied is a minimum value exists in the emission wavelength region of the backlight.

  The above-described embodiment may be applied to a multiplex drive type liquid crystal display unit in which a selection voltage application unit, a non-selection voltage application unit, and a no-voltage application unit exist in the liquid crystal cell. In that case, it is preferable to make the liquid crystal alignment state of the non-selection voltage application part and the liquid crystal alignment state of the voltage non-application part as close as possible for high contrast or low crosstalk.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, a laser may be used as the single wavelength light source in addition to the LED.

  It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like can be made.

FIG. 1 is a cross-sectional view of a liquid crystal display unit 101 in a liquid crystal display device. FIG. 2A is a schematic plan view of a blue mode STN-LCD, and FIG. 2B is a transmittance curve in a substantially visible region of the liquid crystal display unit. FIG. 3A is a schematic plan view of an STN-LCD, and FIG. 3B is a transmittance curve in a substantially visible region of the liquid crystal display unit. FIG. 4 shows transmittance-angle characteristics when no voltage is applied to the liquid crystal display unit at a wavelength of 630 nm. 5A shows left-right transmittance-viewing angle characteristics at a wavelength of 630 nm of the 270 ° STN-LCD shown in FIG. 3A, and FIG. 5B shows upper and lower transmittances at a wavelength of 630 nm of the 270 ° STN-LCD shown in FIG. 3A. -Visual angle characteristics. FIG. 6 shows a transmittance-wavelength characteristic in a substantially visible range when no voltage is applied to the 270 ° STN-LCD shown in FIG. 3A. FIG. 7A is a schematic plan view of a 90 ° TN-LCD, and FIG. 7B shows transmittance-wavelength characteristics in a substantially visible region when no voltage is applied to the 90 ° TN-LCD. FIG. 8 shows transmittance-wavelength characteristics in a substantially visible range when no voltage is applied to the 180 ° STN-LCD. FIG. 9 shows transmittance-twist angle characteristics with the viewing angle as a parameter at an STN-LCD wavelength of 630 nm. FIG. 10A is a schematic plan view of an STN-LCD, and FIG. 10B is a transmittance-viewing angle characteristic of a liquid crystal display unit at a wavelength of 630 nm. FIG. 11A is a schematic plan view of an STN-LCD, and FIG. 11B is a transmittance-viewing angle characteristic of a liquid crystal display unit at a wavelength of 630 nm. It is the transmittance | permeability-viewing angle characteristic of the liquid crystal display part in wavelength 550nm.

Explanation of symbols

1A, 1B Substrate 2 Electrode 2l Wiring 3 Liquid crystal 4 Insulating film 5 Alignment film 6 Sealing material 7 Conductive material 8 Polarizing plate 101 Liquid crystal display unit 102 Backlight

Claims (3)

A backlight using a light source having a single wavelength emission peak;
A pair of opposing substrates, a nematic liquid crystal layer sandwiched between the substrates, an electrode pattern formed on the nematic liquid crystal layer side of each of the substrates, and polarized light disposed vertically with respect to the normal direction of the substrate And a STN type liquid crystal display unit having a liquid crystal twist angle of 155 ° to 210 °,
The liquid crystal molecule alignment direction of the nematic liquid crystal layer and the axial direction of the polarizing plate are not the same at the position of the pair of substrates in contact with each of the upper substrate and the lower substrate, and a smaller angle formed by these directions. A liquid crystal display device in which the sum of the upper substrate side angle and the lower substrate side angle is 90 ° ± 7 °.   The liquid crystal display device according to claim 1, wherein a twist angle of the liquid crystal is 170 ° to 200 °.   3. The liquid crystal display device according to claim 1, wherein the liquid crystal display device has a normally black display in which a wavelength at which the transmittance of the liquid crystal display unit is not applied is a minimum value in the emission wavelength region of the backlight.

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