JP2006127954A - Backlight and liquid crystal display panel using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display panel capable of easily adjusting white points among a plurality of panels at a low cost and with low power consumption. <P>SOLUTION: This backlight is equipped with a reflective sheet and a lighting system disposed on the reflective sheet, and the lighting system is composed of a fluorescent lamp and a rod-shaped illumination tube to linearly emit light. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display panel in which a white point can be matched between a plurality of panels, or a white point that has changed over time with use can be readjusted.

  The liquid crystal display cell requires external irradiation light because the liquid crystal itself does not emit light. As this external irradiation light, those using a fluorescent lamp, a light emitting diode (LED), or electroluminescence (EL) are known. However, fluorescent lamps are widely used as an external light source of a liquid crystal display panel, that is, a backlight from the viewpoint of power consumption, luminance, price, and the like.

  There are mainly a sidelight system and a direct system for the backlight. The sidelight type backlight is a method in which light from a fluorescent lamp is incident from the side surface of a light guide plate such as acrylic, and the light is multiple-reflected by the reflection / diffusion surface of the light guide plate and supplied to the liquid crystal display cell. The direct type backlight is a type in which one or a plurality of fluorescent lamps are arranged directly below the liquid crystal display cell to supply light to the liquid crystal display cell.

  For example, as shown in FIG. 10, the sidelight type backlight includes a light collecting portion having a fluorescent lamp 112 and a lamp reflector 162, a light guide plate 160 for guiding light by providing dots on the bottom surface, and a reflecting sheet 116 on the lower surface thereof. And a diffusion sheet 118 is provided on the top. Since the sidelight type backlight 151 has a lamp 112 attached to the side, it is useful for reducing the thickness of the liquid crystal display panel, and has recently become mainstream.

  On the other hand, in the direct type backlight, as shown in FIG. 9, a fluorescent lamp 112 is disposed between the reflecting sheet 116 and the diffusion sheet 118 facing each other, and the light emitted from the fluorescent lamp 112 is reflected and diffused to obtain a surface light source. To do. High luminance can be obtained because the light emission amount of the fluorescent lamp can be used with high efficiency, but luminance unevenness is likely to occur because the lamp is viewed directly. For this reason, an aluminum-deposited light curtain 120 or the like other than the diffusion sheet 118 is inserted between the fluorescent lamp 112 and the liquid crystal display cell, and the distance between the fluorescent lamp 112 and the liquid crystal display cell is designed to be kept moderate. To achieve uniform brightness.

  For this reason, the direct type backlight is thicker than the side light type, but is preferably used for a liquid crystal display panel that requires high image quality and high luminance such as a medical monochrome panel for displaying X-ray photographs. Such a liquid crystal display panel for medical use is often used by arranging a plurality of liquid crystal display panels side by side in order to compare X-ray photographs taken from different angles or to observe changes over time of an affected area. However, especially when a plurality of liquid crystal display panels are used at the same time, there is a possibility that a doctor may make a diagnosis error due to a slight shift in display color between the arranged liquid crystal display panels.

Various methods for quantifying the color of light have been developed, and the CIE color system, the L ^* a ^* b ^* color system L ^* u ^* v ^* color system, and the like are known. For example, in the CIE color system, all visible light (380 nm to 780 nm) is quantitatively measured at a point within a horseshoe shape on an XY chromaticity diagram (CIE1931 chromaticity diagram) as shown in FIG. Can be expressed in

  The color of light emitted from the liquid crystal display panel or the backlight can also be quantified by measurement and expressed on the XY chromaticity diagram. For example, the standard white point (white) established by organizations such as CIE and NTSC (National Television System Committee) is X = 0.31, Y in the XY chromaticity diagram (CIE1931 chromaticity diagram) of FIG. = White near 0.32. The color shift between the liquid crystal display panels as described above is often caused by variations in the emission color of the backlight light source (fluorescent lamp). For example, the white point displayed on each liquid crystal display panel is shifted from the reference white point.

  However, the white point depends on each person's senses and preferences, and in fact, the standard white point of the liquid crystal display panel is determined by the model, application, and manufacturer. Panel manufacturers have strict tolerances on the white point of each product, and panels that deviate from this range cannot be used, resulting in very poor yields.

  For example, FIG. 12 shows a distribution of X color coordinates / Y color coordinates in an XY chromaticity diagram (CIE1931 chromaticity diagram) of a liquid crystal display panel of a certain model. In this example, if the white point displayed on the liquid crystal display panel is in the range of X = 0.294 ± 0.005 and Y = 0.212 ± 0.005, it is an example in which the product is allowed. In this example, it can be seen that a defect in which the white point is shifted to an allowable range is generated in a liquid crystal display panel having more than 20% of both the X color coordinate and the Y color coordinate.

  Conventionally, in order to match the white point between liquid crystal display panels having different white points, variations at the time of product completion have been dealt with by selecting panels having substantially the same color coordinates. In addition, the liquid crystal display panel has to be replaced only when the white point changes with time due to consumption. However, a liquid crystal display panel with a white point deviating from a specified range is a defective product, and the yield is reduced as described above.

  Alternatively, as a countermeasure against the occurrence of the defect, a method of using a light emitting diode (LED) capable of white point adjustment as a light source of a backlight and matching a white point displayed on a liquid crystal display panel with a reference white point can be considered. However, since many expensive LEDs are used, there are problems that the manufacturing cost increases and the power consumption increases drastically.

  Patent Document 1 discloses a liquid crystal display panel in which a main light source is a fluorescent lamp and a point light source auxiliary light source is converted into a surface light source using a light guide plate. However, since the light guide plate is thick and heavy, the larger the panel size, the thicker and the heavier it becomes.

  In addition, since the light guide plate exists between the main light source and the reflection plate, a part of the light emitted from the main light source goes to the panel via the light guide plate → the reflection plate → the light guide plate. At this time, the reflection efficiency of the main light source is lowered due to the light guide plate itself, or the scattered dot pattern carved on the light guide plate, and the luminance is lowered.

Japanese Patent Laid-Open No. 2000-310776

  Therefore, an object of the present invention is to provide a liquid crystal display panel that can easily adjust the white point between a plurality of panels at low cost and low power consumption.

  Another object of the present invention is to provide a liquid crystal display panel that can readjust the white point that has changed over time with use.

  The backlight according to the present invention includes a reflection sheet and illumination disposed on the reflection sheet, and the illumination includes a fluorescent lamp and a rod-shaped illumination tube that emits light in a linear shape.

  In the backlight of the present invention, a light source is disposed at least at one end of the rod-shaped arc tube.

  In the backlight of the present invention, the light source may be at least one light emitting element of red, green, and blue. The light emitting element is, for example, a light emitting diode, but is not particularly limited.

  The backlight of the present invention may have a diffusion sheet that is disposed on the illumination and scatters light emitted from the illumination.

  In the liquid crystal display panel of the present invention, a liquid crystal display cell is placed immediately above the backlight according to any one of claims 1 to 4.

  The liquid crystal display panel of the present invention can adjust the brightness and white point of the light emitted from the liquid crystal display panel by changing the brightness and color of the light emitted from the rod-shaped arc tube.

  The liquid crystal display panel of the present invention may be a monochrome display.

  In this specification, “display white point” or “display white point” is a white point displayed by each panel. As described above, the display white point generally has an initial variation and a variation with time, and is different among the panels. The “reference white point” or the “reference white point” is a white point that serves as a reference for matching the white points between the panels having variations, for example, color coordinates on the XY chromaticity diagram (CIE1931 chromaticity diagram). It is represented by

  Hereinafter, red, green, and blue colors are also expressed as R, G, and B, respectively.

  The liquid crystal display panel of the present invention can match the brightness and white point between a plurality of panels at the time of panel shipment. The white points that vary during the manufacturing process can be matched, and the yield is significantly improved.

  In addition, the liquid crystal display panel of the present invention can correct a change in luminance and white point over time between a plurality of panels. Even when the white point changes with time, it is possible to match the white point by adjustment.

  Accordingly, it is possible to eliminate a slight difference in white point that is felt when a plurality of panels are viewed side by side.

  Furthermore, since the liquid crystal display panel of the present invention has no light guide plate between the main light source and the reflection plate, the thickness can be reduced and the weight can be reduced. Furthermore, it is possible to prevent the reflection efficiency of the main light source from being lowered.

  As shown in FIGS. 1A and 1B, the backlight of the present invention includes a reflection sheet 16, a fluorescent lamp 12 disposed on the reflection sheet 16, and a rod-shaped illumination tube 2 that radiates light linearly. . In the present embodiment, the rod-like arc tube 2 has red, green, and blue light emitting elements such as light emitting diodes (hereinafter referred to as “LEDs”) 4 as light sources at one end or both ends. In this specification, the illumination 10 is a generic term for the rod-shaped illumination tube 2 including the fluorescent lamp 12 and the LED 4.

  Further, as shown in FIG. 2, the liquid crystal display panel of the present invention is a liquid crystal display panel 6 in which a liquid crystal display cell 14 is placed immediately above the backlight 1 of the present invention. The liquid crystal display cell 14 is not particularly limited, and may have the same configuration as a conventional known liquid crystal display panel except that the backlight 1 described in detail below is used, and the structure is not particularly limited.

  In the backlight 1 of the present invention, the fluorescent lamp 12 as the main light source may be an inexpensive cold-cathode tube lamp that has been conventionally used. As described above, the liquid crystal display cell 14 has a luminescent color variation among the lamps. You may arrange | position in the position which opposes. A plurality of sheets such as a diffusion sheet 18 may be sandwiched between the fluorescent lamp 12 and the liquid crystal display cell 14 as shown in FIG.

  Moreover, as shown in FIG.1 (b), the rod-shaped luminous tube 2 has LED4 connected to the power supply at least at one end. As the LED 4, a known one may be used. For example, the LED 4 that emits stable red, green, and blue colors is attached to the rod-shaped arc tube 2. It is preferable that a plurality of each color LED 4 is attached to each rod-shaped arc tube 2, but one LED 4 capable of controlling the light emission intensity may be attached to each rod-shaped arc tube 2. Further, the LEDs 4 may be attached to both ends of the rod-shaped arc tube 2, and the rod-shaped arc tube is not particularly limited in color and material as long as the rod portion is transparent.

  As shown in FIG. 1 (a), in this embodiment, the illumination 10 has a fluorescent lamp 12 as a main light source and a rod-shaped arc tube 2 as an auxiliary light source arranged alternately. However, as shown in FIG. Two rod-like arc tubes 2 may be arranged between the two, or three or more rod-shaped arc tubes 2 may be arranged. Further, as shown in FIG. 6, the rod-shaped arc tube 2 may be constituted by an optical fiber in which LEDs are arranged at both ends or one end.

  Others The backlight 1 of the present invention may have the same configuration as the conventional direct type backlight except for the illumination 10, and the structure is not particularly limited.

  Next, the operation of the rod-like arc tube 2 will be described. Since the operation of the liquid crystal display panel 6 other than the backlight 1 is known, the description thereof is omitted.

  Each color light emitted from the LED 4 reciprocates while repeating total reflection on the reflection sheet 16 at the bottom of the rod-like arc tube 2 and the inner surface of the rod-like arc tube 2 as shown in FIG. Light that is smaller than the internal total reflection angle is emitted in the direction of the liquid crystal display cell 14. The radiated light diffused by the diffusion sheet 18 or the like is supplied into the liquid crystal display cell 14 substantially evenly, and the liquid crystal display panel 6 performs display. The operation of the fluorescent lamp 12 is the same.

  The rod-shaped arc tube 2 as an auxiliary power source corrects, for example, the white point displayed on the liquid crystal display panel by the light emission of the fluorescent lamp 12 as the main power source so as to coincide with the reference white point.

  In the liquid crystal display panel 6 according to the present invention having the above-described configuration, the rod-shaped arc tube 2 is arranged in parallel between the fluorescent lamps in the direct type backlight constituting the conventional liquid crystal display panel. It can be easily manufactured simply by forming a driver circuit connected to the LED 4 installed inside.

  Next, a method for white point adjustment will be described. The liquid crystal display panel 6 of the present invention may be a color display, but will be described as a monochrome display for the sake of simplicity.

  FIG. 4A is a schematic diagram showing an XY chromaticity diagram (CIE1931 chromaticity diagram), for example. In FIG. 4A, it is assumed that the inside of the circle is the initial deviation range of the white point displayed on the liquid crystal display panel 6. The center of the circle is the reference white point, and the white points A and B displayed by the panels A and B are positioned on the circle.

  A method for adjusting the white point when each liquid crystal display panel is in the initial displacement will be described with reference to FIG.

(1) The deviation of the color coordinates of the white points A and B displayed on each liquid crystal display panel and the reference white point is measured. That is, the color coordinates of white light displayed on each panel are measured and calculated by a known method, and the deviation (ΔX, ΔY) of the color coordinates from the reference white point is calculated.

(2) The intensity of light to be emitted by each color LED in the rod-shaped arc tube 2 is calculated so that the deviation (ΔX, ΔY) is corrected.

(3) The light emission intensity of each color LED is adjusted from the calculation in (2), and the white point of each liquid crystal display panel is adjusted to the reference white point by emitting light.

  By the above operation, the white point displayed on the liquid crystal display panel A and the liquid crystal display panel B can be substantially matched with a desired reference white point.

  Next, with reference to FIG. 4C, a method of white point readjustment when the display white point changes with time due to the use of each liquid crystal display panel 6 will be described.

  The direction of the change with time is determined as shown by the arrow, and the white point of each liquid crystal display panel adjusted to the initial O point (reference white point) as described above is an abbreviation in FIG. It changes to A ′ and B ′ at the same position.

  The method of readjusting the liquid crystal display panels A ′ and B ′ displaying the white points of A ′ and B ′ so as to display the reference white point is the same as the procedures (1) to (3).

  Next, using the XY chromaticity diagram (CIE1931 chromaticity diagram) in FIGS. 11A and 11B, the adjustment range in which the initial display white point of each panel can be matched with the reference white point will be described. (Hereinafter referred to as “adjustment range”).

  In FIG. 11A, a region surrounded by two parallel lines extending in the X direction and two parallel lines extending in the Y direction is a display white point range required for each liquid crystal display panel (hereinafter, “ Required specification range ”). FIG. 11B is an enlarged view of the required specification range. In this example, the required specification ranges are 0.248 ≦ X ≦ 0.2600 and 0.278 ≦ Y ≦ 0.2940. A point near (0.2525, 0.2862) is set as a reference white point for convenience.

  Further, the region within the substantially elliptical shape of the required specification range is to match the display white point of a certain commercially available fluorescent lamp 12 with the above reference white point by using a certain commercially available LED for a plurality of rod-like arc tubes 2. Indicates the area where This adjustment range can vary in size and shape depending on the performance of the LED 4 and the fluorescent lamp 12, such as color, brightness, and output.

FIG. 3 is a diagram in which the histogram of FIG. 12 is displayed on an XY chromaticity diagram (CIE1931 chromaticity diagram), and represents the distribution of display white points of an initial liquid crystal display panel. In this example, the reference white point at the center is X = 0.294 and Y = 0.212, the rectangular area surrounding this is the required spec range, and the elliptical area that intersects the required spec range is the adjustment range.
In FIG. 3, the outer ellipse surrounding the required specification range and the adjustment range indicates a range in which the display white point of the liquid crystal display panel can be adjusted within the required specification range.

  The method (1) to (3) and the example for correcting the initial deviation and change with time of the white point displayed on the liquid crystal display panel have been described above, but the actual procedure is easily executed using a known luminance meter and controller. it can. The color coordinates of the white point displayed on the liquid crystal display panel can be directly displayed using a luminance meter, and the current value flowing through each color LED is changed so that the color coordinate deviation (ΔX, ΔY) approaches (0, 0). The chromaticity can be adjusted.

  In the following embodiments, the respective states of the initial liquid crystal display panel (Panel A and Panel B) immediately after manufacture, the correction of the initial shift state, the state after change with time, and the correction of change with time will be described. In the following examples, the reference white point is (0.300, 0.320).

  In the above embodiment and the examples described below, the liquid crystal display panel is a monochrome display, but the liquid crystal display panel of the present invention may be a color display of three or more colors. The reference color is not limited to the white point, and all other colors that can be expressed by the liquid crystal display panel can be used as the reference color.

In the above embodiment and the examples described below, the colored light is quantified using the CIE color system, but other color systems such as L ^* a ^* b ^* color system and L ^* u ^* v ^* color system are used. It is possible to perform color matching by using.

  Further, in the above-described embodiment and the examples described below, description has been made using a direct type backlight, but the backlight of the present invention may be a sidelight type. For example, as shown in FIG. 7, a plurality of LEDs may be juxtaposed between two fluorescent lamps. Alternatively, as shown in FIG. 8, LEDs may be juxtaposed on the side where no fluorescent lamp is installed. In this case, the light emission of the LED does not necessarily pass through the light guide plate, and the white point can be finely adjusted without making the liquid crystal display panel heavy.

  In addition, the present invention can be carried out in a mode in which various improvements, modifications, and changes are added based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

  Table 1 shows each state of the liquid crystal display panels A and B in the initial deviation state immediately after the manufacture, and only the fluorescent lamp emits light. Therefore, the RGB LEDs are not used in the liquid crystal display panels A and B, and the power consumption of the fluorescent lamp and the RGB LEDs is 50 W and 0 W. The fluorescent lamp has a power consumption of 50 W and a luminance of 500 nits.

  Table 2 shows the states of the liquid crystal display panels A and B after the initial deviation state of the liquid crystal display panel A is corrected by the above method. The chromaticity of the liquid crystal display panel A is corrected to the reference white point (0.300, 0.320). The white point of the liquid crystal display panel A is made to coincide with the reference white point by adjusting by turning on six, eight, and two RGB LEDs. However, at this time, the power consumption of the fluorescent lamp and the RGB LED is adjusted to 49 W and 6 W in order to keep the luminance of the panel at 500 nit.

  The liquid crystal display panel B was also adjusted in the same manner as the liquid crystal display panel A, and the chromaticity of the liquid crystal display panel B was corrected to the reference white point (0.300, 0.320).

  Table 3 shows the state after change over time when the liquid crystal display panels A and B are used for 10,000 hours from the initial state of the second embodiment. When the luminance was adjusted to 500 nits after 10,000 hours, the states shown in Table 3 were obtained. As described above, the chromaticity of the liquid crystal display panels A and B tended to shift in substantially the same direction on the XY chromaticity diagram (CIE1931 chromaticity diagram).

  Finally, Table 4 shows a result of correcting the display white point of the liquid crystal display panels A and B to the reference white point after the change with time. It can be seen that when the white point is corrected and 500 nit is maintained after the change with time, the required number of LEDs and the power consumption are significantly increased as compared with the case of correcting the initial deviation.

  The backlight and the liquid crystal display panel using the backlight according to the present invention can be used for all liquid crystal display cells. In particular, it can be suitably used for a panel for comparing a plurality of screens juxtaposed, such as a medical liquid crystal display panel for displaying X-ray images.

(A) It is plane sectional drawing of the backlight of this invention. (B) It is a side view of the rod-shaped arc tube used for the backlight of this invention. It is a schematic diagram of the decomposition | disassembly cross section of the backlight of this invention, and a liquid crystal display cell. It is a part of XY chromaticity diagram (CIE1931 chromaticity diagram) showing the distribution of the initial deviation of the white point. (A) (b) (c) It is a schematic diagram of XY chromaticity diagram which shows the method of making the display white point of the liquid crystal display cell of this invention correspond with a reference | standard white point. It is a plane sectional view showing another embodiment of the backlight of the present invention. It is a plane sectional view showing another embodiment of the back light of the present invention. It is a plane sectional view showing another embodiment of the back light of the present invention. It is a plane sectional view showing another embodiment of the back light of the present invention. It is a disassembled perspective view of the conventional direct type backlight. It is an exploded perspective view of a conventional sidelight type backlight. (A) XY chromaticity diagram (CIE1931 chromaticity diagram). (B) A part of the XY chromaticity diagram of (a). It is a histogram showing the distribution of the initial deviation of the white point expressed in XY color coordinates.

Explanation of symbols

1: Backlight (direct method)
2: Rod-shaped arc tube 4: LED
6, 106: Liquid crystal display panel 10: Illumination 12: Fluorescent lamp 14: Liquid crystal display cell 16: Reflection sheet 18: Diffusion sheet 20: Lighting curtain 51, 151: Backlight (side light system)
60, 160: Light guide plate 162: Lamp reflector

Claims (7)

A reflective sheet;
Illumination disposed on the reflective sheet;
With
The illumination is a backlight composed of a fluorescent lamp and a rod-shaped illumination tube that emits light linearly. The backlight according to claim 1, wherein a light source is disposed on at least one end of the rod-shaped arc tube. The backlight according to claim 2, wherein the light source is a red / green / blue light emitting element. The backlight according to any one of claims 1 to 3, further comprising a diffusion sheet that is disposed on the illumination and diffuses light emitted from the illumination. A liquid crystal display panel in which a liquid crystal display cell is placed immediately above the backlight according to claim 1. The liquid crystal display panel according to claim 5, wherein the brightness and white point of the light emitted from the liquid crystal display panel can be adjusted by changing the brightness and color of the light emitted from the rod-shaped arc tube. The liquid crystal display panel according to claim 5, wherein the liquid crystal display panel is a monochrome display.

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