JP2006235436A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device changing brightness by simple constitution. <P>SOLUTION: The liquid crystal display device 100 includes a liquid crystal panel 102 and a light unit 101 irradiating the liquid crystal panel 102 with light. The light unit 101 includes a light guide plate 108 introducing the light incident on a side end face to the overall surface to irradiate the liquid crystal panel 102, a plurality of high luminosity LEDs 110a disposed opposite the side end face of the light guide plate 108, and low luminosity LEDs 110b disposed between the high luminosity LEDs 110a. The high luminosity LEDs 110a is controlled so as to be switched so that the high luminosity LEDs 110a is turned off in the state in which the low luminosity LEDs 110b are turned on. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device including a light unit having a plurality of point light sources.

  Currently, display devices are widely used as an interface for connecting people and machines, and have made remarkable progress. Liquid crystal display devices (LCDs) are widely applied as display devices for PCs and portable terminal devices because they have advantages such as low power consumption, thinness, and light weight.

  Usually, in a transmissive liquid crystal display device, a backlight unit is disposed on the non-viewing side of the liquid crystal panel. This backlight unit typically includes a light source and a plurality of optical members for effectively emitting light from the light source to the liquid crystal panel. Since this backlight unit can be easily reduced in thickness, a linear or dot light source is used as a side end face of a transparent plate-shaped light guide plate made of acrylic resin or the like (hereinafter referred to as a light incident surface). Side light type attached along the mainstream is the mainstream.

  Such a sidelight-type backlight unit is configured such that illumination light is incident from the light incident surface of the light guide plate, is repeatedly reflected inside the light guide plate to propagate the illumination light, and is emitted from the light exit surface. Planar light is generated using illumination light of a light source.

Conventionally, a fluorescent tube has been used as the light source. However, light emitting diodes (hereinafter referred to as LEDs) have come to be used due to consideration of environmental problems, long life, and good light emission (see, for example, Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 2002-258281 JP 2005-26077 A

  By the way, the transmissive liquid crystal display device described above is usually used in a certain brightness environment such as an office. Therefore, conventionally, the brightness of the backlight unit has been set to be constant.

However, in recent years, with the widespread use of mobile phones, car navigation systems, and the like, liquid crystal display devices are required to perform good display in various brightness environments. For example, in-vehicle liquid crystal display devices used in car navigation systems are required to have a high luminance of 500 cd / m ^{2 in} a bright environment such as daytime. On the other hand, in a dark environment such as nighttime, if the same luminance as in the daytime is used, the luminance is too high. Therefore, the luminance needs to be lowered to 1/50 to 1/100 of the daytime luminance.

  In a backlight unit using LEDs, the luminance can be adjusted by changing the light intensity of the LEDs by changing the current supplied to each LED. However, there is a problem that the LED does not light up when the current supplied is lowered so as to reduce the luminance as described above. Even when the lamp is lit, luminance unevenness occurs on the display surface.

  As is well known, the chromaticity of the light emitted from the LED changes depending on the value of the supplied current. For this reason, the problem that the display performance of a liquid crystal display device will deteriorate also arises.

  The present invention has been made in the background as described above, and an object of the present invention is to provide a liquid crystal display device capable of changing luminance with a simple configuration.

  A liquid crystal display device according to a first aspect of the present invention is a liquid crystal display device including a liquid crystal panel and a light unit that irradiates light to the liquid crystal panel, and the light unit is configured to face light incident from a side end surface. A light guide plate that guides the entire surface and irradiates the liquid crystal panel, a plurality of high-luminance point light sources disposed to face side end surfaces of the light guide plate, and a low-luminance point light source disposed between the high-luminance point light sources The high-luminance point light source can be controlled to be turned on / off so that the high-luminance point light source can be turned off while the low-luminance point light source is turned on. By having such a configuration, the luminance of the light unit can be adjusted.

  The liquid crystal display device according to the second aspect of the present invention is the above-described liquid crystal display device, wherein a plurality of the low light intensity point light sources are arranged between the adjacent high light intensity point light sources. By having such a configuration, luminance unevenness can be suppressed.

  A liquid crystal display device according to a third aspect of the present invention is the above-described liquid crystal display device, wherein the low light intensity point light source can be turned off while the high light intensity point light source is turned on. It is possible to control on / off of the light source. Thereby, power consumption can be suppressed.

  The liquid crystal display device according to a fourth aspect of the present invention is the above liquid crystal display device, wherein the high luminous intensity point light source and the low luminous intensity point light source are arranged in a line along the longitudinal direction of the side end surface of the light guide plate. It is what. By having such a configuration, it is possible to use an optical member such as a light guide plate conventionally used as it is.

  The liquid crystal display device according to a fifth aspect of the present invention is the above-described liquid crystal display device, wherein the point light sources having the same luminous intensity among the high light intensity point light source and the low light intensity point light source are each in the longitudinal direction of the side end face of the light guide plate. Are arranged symmetrically with respect to the center line. Thereby, the display characteristics can be further improved.

  The liquid crystal display device according to a sixth aspect of the present invention is the above-described liquid crystal display device, wherein the high luminous intensity point light source and the low luminous intensity point light source are switched on / off according to ambient brightness. By having such a configuration, the luminance of the light unit suitable for the ambient brightness is selected, and the display characteristics can be improved.

  According to the present invention, a liquid crystal display device capable of changing luminance with a simple configuration can be provided.

  Hereinafter, embodiments to which the present invention can be applied will be described. The following description explains the embodiment of the present invention, and the present invention is not limited to the following embodiment. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. Further, those skilled in the art can easily change, add, and convert each element of the following embodiments within the scope of the present invention. In addition, in each drawing, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted as needed for clarification of description.

  A liquid crystal display device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is an exploded perspective view for explaining the overall configuration of an example of the liquid crystal display device of the present invention. FIG. 1 schematically shows a liquid crystal display device 100 having a sidelight type backlight unit. As shown in FIG. 1, the liquid crystal display device 100 includes a backlight unit 101, a liquid crystal panel 102, a source driver 103, a gate driver 104, and a holder 105. Here, an example in which an active matrix liquid crystal panel is used as the liquid crystal panel 102 will be described.

  The backlight unit 101 irradiates the liquid crystal panel 102 with planar light. The liquid crystal panel 102 is driven by the source driver 103 and the gate driver 104 and displays an image by controlling transmission of light from the backlight unit 101. The holder 105 holds and protects the liquid crystal panel 102 and the backlight unit 101 from the outside. The holder 105 is made of resin or metal.

  The liquid crystal panel 102 has a configuration in which liquid crystal is sandwiched between a TFT (Thin Film Transistor) array substrate (not shown) and a counter substrate (not shown) arranged to face each other. On the TFT array substrate, gate lines (scanning lines) are formed in the horizontal direction, and source lines (signal lines) are formed in the vertical direction, and TFTs are provided near the intersections of the gate lines and the source lines. In addition, a plurality of pixel electrodes are formed in a matrix between the gate line and the source line. The gate of the TFT is connected to the gate line, the source is connected to the source line, and the drain is connected to the pixel electrode.

  The TFT array substrate and the counter substrate are maintained at a predetermined interval by bead spacers or columnar spacers. Polarizing plates are attached to the outer surface of the TFT array substrate and the outer surface of the counter substrate, respectively. For example, in a TN type liquid crystal panel which is a typical example of a liquid crystal panel, polarizing plates on the non-viewing side and the viewing side are arranged so that their transmission axes are vertical or parallel.

  On the other hand, a common electrode and R (red), G (green) and B (blue) color filters are formed on the counter substrate. The common electrode is actually a transparent electrode formed on the substantially entire surface of the counter substrate so as to face the pixel electrode.

  The liquid crystal panel 102 has a display area composed of a plurality of pixels and a peripheral area formed around the display area. A source driver 103 and a gate driver 104 are connected to the peripheral region. The source driver 103 and the gate driver 104 are typically connected to the array substrate by TAB (Tape Automated Bonding), but may be provided directly on the array substrate by COG (Chip On Glass).

  A scanning signal is supplied to each gate line, and all TFTs connected to one gate line selected by each scanning signal are turned on simultaneously. Then, a gradation voltage corresponding to the display data signal is supplied to each source line, and charges are accumulated in the pixel electrode.

  The arrangement of the liquid crystal between the pixel electrode and the common electrode changes according to the potential difference between the pixel electrode where the charge is accumulated and the common electrode. The direction of polarization of the linearly polarized light that has passed through the non-viewing-side polarizing plate is controlled by the liquid crystal, and the transmittance of light transmitted through the viewing-side polarizing plate is controlled. Each pixel of the liquid crystal display panel 101 performs display of various shades by color shading according to the amount of transmitted light and RGB color display. In the case of monochrome display, a color filter may not be provided.

  As the liquid crystal panel 102, a simple matrix type having no switching elements is known in addition to the above active matrix type. Other types of liquid crystal panels include TN (Twisted Nematic) type liquid crystal panels, STN (Super Twisted Nematic) type liquid crystal panels, and IPS (In Plane Switching) type in which pixel electrodes and common electrodes are formed on the same substrate. Liquid crystal panels are known. The present invention is applicable to various types of liquid crystal panels as described above.

  The backlight unit 101 is disposed by laminating a diffusion sheet 106, a prism sheet 107, a light guide plate 108, and a reflection sheet 109 in this order from the viewing side. The backlight unit 101 is a side light type, and a plurality of LEDs (Light Emitting Diodes), which are light sources, are arranged in a line along a side end surface (hereinafter referred to as a light incident surface) of the light guide plate 108. 110. Here, an example is shown in which six high-intensity LEDs 110a and ten low-intensity LEDs are arranged. In the present invention, a point to be noted is the LED light source 110, which will be described in detail later.

  The diffusion sheet 106, the prism sheet 107, the light guide plate 108, the reflection sheet 109, and the LED light source 110 are accommodated in the frame 111. L-shaped convex positioning portions (not shown) are formed at the four corners of the viewing side surface of the light guide plate 108. The diffusion sheet 106, the prism sheet 107, and the liquid crystal panel 102 are fitted with the positioning portions. It is disposed on the light guide plate 108.

  The diffusion sheet 106 diffuses incident light and emits it. As the diffusion sheet 106, for example, the surface of the base sheet coated with a binder in which a light diffusing agent such as beads is dispersed, or the light diffusing layer in which the light diffusing agent is dispersed is laminated on the surface of the base sheet. Alternatively, conventional materials such as those in which a plurality of irregularities are formed on the surface of the base sheet can be used by embossing the surface of the base sheet made of synthetic resin.

  The prism sheet 107 improves the luminance of the display front by condensing light. The prism sheet 107 can be formed by forming an uneven structure with an organic resin on a base film such as polyethylene terephthalate. The prism sheet 107 is typically formed with a plurality of triangular cross-sectional prism structures, anisotropic diffraction gratings, and the like. Although only one sheet is shown here, two prism sheets may be used as a set, and the ridge lines of each prism sheet may be arranged so as to be orthogonal to each other.

  As described above, the LED light sources 110 are arranged such that the LEDs are arranged in a line along the light incident surface of the light guide plate 108. The light guide plate 108 guides and diffuses the light from the LED light source 110 and emits planar light. A dot pattern is provided on the non-viewing side of the light guide plate 108. This dot pattern is formed by dot printing or processing. Or the uneven structure may be provided in the back surface of the light-guide plate.

  The reflection sheet 109 makes the light emitted from the non-viewing side of the light guide plate 108 reenter the light guide plate 108. The reflection sheet 109 is provided on the non-viewing side of the light guide plate 108. As the reflection sheet 109, a conventional sheet such as a coating made of a white pigment or a coating with a fine resin hollow powder can be used.

  Here, the optical action of the backlight unit 101 will be described. An example in which a dot pattern is formed on the back surface of the light guide plate 108 is shown. Light from the LED light source 110 enters the light guide plate 108 and propagates through the light guide plate 108 while repeating total reflection. A part of the light that does not satisfy the total reflection condition due to the dot pattern is emitted from the light exit surface of the light guide plate 108 to the viewing side. Further, a part of the light is emitted from the non-viewing side of the light guide plate 108, reflected by the reflection sheet 109, and reenters the light guide plate 108. Light from the light exit surface of the light guide plate 108 is condensed in a direction perpendicular to the display surface of the liquid crystal panel 102 by the prism sheet 107 and enters the diffusion sheet 106. The diffusion sheet 106 has a function of diffusing incident light and emitting it to the viewing side.

  Here, with reference to FIG. 2, the LED light source 110 concerning this Embodiment is demonstrated. FIG. 2 is a schematic view of the liquid crystal display device 100 of FIG. 1 viewed from the viewing side. In FIG. 2, illustration of components that are not visible after being stacked is omitted. For the sake of explanation, the holder 105 is not shown.

In LED light source 110 concerning this Embodiment, LED used as a light source uses two types of LED from which luminous intensity differs. For example, as shown in FIG. 2, a combination of six high-intensity LEDs 110a and ten low-intensity LEDs 110b is used. As the high-luminance LED 110a, for example, in a 7-inch liquid crystal display device, when six high-luminance LEDs 110a are used and a current of 500 mA is supplied, an LED capable of obtaining a luminance of a liquid crystal display device of 500 cd / m ² can be used. . In addition, as the low-luminance LED 110b, one that can obtain the luminance of a liquid crystal display device of ²⁰ cd / m ² when ten low-luminance LEDs 110b are used and a current of 5 mA is supplied can be used.

  In addition, wirings for supplying power to the high-intensity LED 110a and the low-intensity LED 110b are separately formed, and the high-intensity LED 110a and the low-intensity LED 110b can be independently turned on / off.

  The high-intensity LEDs 110a and the low-intensity LEDs 110b are arranged in a line along the light incident surface of the light guide plate. As described above, since the LED light source 110 is arranged on one side as in the case of the conventional sidelight type light source, a complicated optical design is not required. As other optical members such as the light guide plate 108 and the prism sheet 107, conventional members can be used.

  The light emitting surfaces of the high-intensity LED 110a and the low-intensity LED 110b are arranged on the light guide plate 108 side. That is, the light emitting surface of each LED is arranged to face the light incident surface. The light incident surface of the light guide plate 108 is parallel to the light emitting surface of each LED. Therefore, the loss of light emitted from each LED can be minimized.

  In general, the high intensity LED 110a is larger in size than the low intensity LED 110b. Therefore, as shown in FIG. 3, a light guide plate 108 provided with a rectangular cutout 112 on the light incident surface may be used. In this case, one high-intensity LED 110 a can be arranged in the notch 112, and the low-intensity LED 110 b can be arranged in a place other than the notch 112. By doing so, it is possible to narrow the frame of the liquid crystal display device. Further, since the light emitting surface of each LED is disposed so as to face the light incident surface of the light guide plate 108, loss of light emitted from the LED can be reduced.

  Two low-intensity LEDs 110b are arranged between two adjacent high-intensity LEDs 110a. The high-intensity LEDs 110a and the two low-intensity LEDs 110b are alternately arranged. In addition, high-intensity LEDs 110 a are disposed at both ends of the LED light source 110. That is, among the high-intensity LED 110a and the low-intensity LED 110b, LEDs having the same intensity are arranged symmetrically with respect to the center line AA in the longitudinal direction of the light incident surface of the light guide plate. Thereby, luminance unevenness of the backlight unit 101 can be suppressed.

Moreover, on / off of the high-intensity LED 110a and the low-intensity LED 110b can be controlled. Therefore, when the surroundings are bright as in the daytime, the high-intensity LED 110a is turned on and the low-intensity LED 110b is turned off. As a result, the luminance of the liquid crystal display device 100 can be set to 500 cd / m ² and can be easily viewed.

On the other hand, when the surroundings are dark, such as at night, the high-intensity LED 110a is turned off and the low-intensity LED 110b is turned on. As a result, the luminance of the liquid crystal display device 100 can be set to 20 cd / m ^2, which makes it easy to see. Thus, the luminous intensity of the light emitted from the LED light source 110 can be changed according to the surrounding brightness, and a good display suitable for each brightness can be provided.

  Further, when a liquid crystal display device is used as a display device for a conventional car navigation system or the like, the visible luminance is lowered by reversing the display on the liquid crystal panel at night. For example, when displaying a map, a black image is displayed on a white background during the day, and a white image is displayed on the black background at night. In this case, the luminance of the backlight unit was the same during the daytime and at night.

  However, in the present invention, the current required for driving the low-intensity LED 110b used at night is smaller than the current required for driving the high-intensity LED 110a used in the daytime, so that power consumption can be suppressed.

  In the daytime, both the high-intensity LED 110a and the low-intensity LED 110b may be turned on. By doing in this way, the screen of the liquid crystal display device 100 can be made brighter. Further, since the low-intensity LED 110b is always on, the configuration of the power control circuit for the LED can be simplified.

  As is well known, the higher the luminous intensity of an LED, the larger the light irradiation angle. For this reason, the irradiation angle of the low luminous intensity LED 110b is smaller than the irradiation angle of the high luminous intensity LED 110a. In general, light emitted from an LED has high directivity, bright immediately before the light emitting surface, and darkens as the radiation angle increases and the distance increases. In the present invention, the number of low-luminance LEDs 110b is larger than that of the high-luminance LEDs 110a. Therefore, even when only the low-intensity LED 110b is turned on at night, the liquid crystal display panel 102 can be irradiated with planar light having a uniform luminance distribution, and a good display can be provided.

  As described above, one high-intensity LED 110a and two low-intensity LEDs 110b are alternately arranged, and the LEDs having the same intensity are respectively directed to the longitudinal center line AA of the light incident surface of the light guide plate 108. They are arranged symmetrically. Thereby, luminance unevenness can be further suppressed, and display characteristics can be improved.

  Further, when the liquid crystal display device 100 according to the present invention is used as a display device used in a car navigation system of a car, the high light intensity LED 110a and the low light intensity LED 110b are turned on / off according to the on / off state of the car light. It may be.

  It is also possible to provide a sensor for measuring the ambient brightness so that the high-intensity LED 110a and the low-intensity LED 110b are automatically switched on / off. FIG. 4 shows the LED power supply control circuit 113. The LED power supply control circuit 113 includes a sensor 114, a determination unit 115, a power supply 116a for the high light intensity LED 110a, and a power supply 116b for the low light intensity LED 110b. The sensor 114 is an optical sensor that detects light, and is provided outside the liquid crystal display device 100. Then, the ambient light of the liquid crystal display device 100 is detected and the brightness is measured.

  When the on / off of each LED is automatically controlled using the LED power supply control circuit 113, first, the sensor 114 measures the ambient brightness and transfers the measurement signal to the determination unit 115. The determination unit 115 determines which of the high-intensity LED 110a and the low-altitude LED 110b is turned on based on the measurement signal, and supplies the determination signal to the high-intensity LED power source 116a and the low-intensity LED power source 110b. The high-intensity LED power supply 116a and the low-intensity LED power supply 116b supply a predetermined current to the high-intensity LED 110a and / or the low-intensity LED 110b based on the determination signal.

  When applied to a large liquid crystal display device, in order to obtain a desired luminance, the LED light source 110 may be arranged in an L shape on the adjacent two side end faces of the light guide plate. Even in such a case, as shown in FIG. 5, along the light incident surface of the light guide plate 108 so as to be symmetric with respect to the center lines AA and BB of the respective sides where the LEDs are arranged. Thus, the high-intensity LEDs 110a and the low-intensity LEDs 110b having a larger number may be alternately arranged. Further, the present invention can be similarly applied to the case where LED light sources are arranged on two opposite sides of the light guide plate.

  Although the liquid crystal display device 100 including the backlight unit that emits light from the non-viewing side of the liquid crystal panel 102 has been described above, the present invention is not limited to this. The present invention is also applicable to a liquid crystal display device including a front light unit in which a light unit is arranged on the viewing side of a liquid crystal panel.

It is a disassembled perspective view which shows the structure of the liquid crystal display device concerning embodiment. It is a schematic diagram explaining arrangement | positioning of the LED light source of the liquid crystal display device concerning embodiment. It is a schematic diagram explaining other arrangement | positioning of the LED light source of the liquid crystal display device concerning embodiment. It is a figure which shows the power supply control circuit of the LED light source concerning embodiment. It is a schematic diagram explaining other arrangement | positioning of the LED light source of the liquid crystal display device concerning embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Liquid crystal display device 101 Backlight unit 102 Liquid crystal panel 103 Gate driver 104 Source driver 105 Holder 106 Diffusion sheet 107 Prism sheet 108 Light guide plate 109 Reflection sheet 110 LED light source 110a High luminous intensity LED
110b Low intensity LED
111 Frame 112 Notch 113 LED Power Control Circuit 114 Sensor 115 Judgment 116a High Luminance LED Power Supply 116b Low Altitude LED Power Supply

Claims (6)

A liquid crystal display device comprising a liquid crystal panel and a light unit for irradiating the liquid crystal panel with light,
The light unit is
A light guide plate that guides light incident from the side end surface to the entire surface and irradiates the liquid crystal panel;
A plurality of high-intensity point light sources arranged to face side end surfaces of the light guide plate;
A low luminous intensity point light source disposed between the high luminous intensity point light sources,
A liquid crystal display device capable of controlling on / off of the high light intensity point light source so that the high light intensity point light source can be turned off while the low light intensity point light source is turned on.   The liquid crystal display device according to claim 1, wherein a plurality of the low luminous intensity point light sources are arranged between the adjacent high luminous intensity point light sources.   3. The liquid crystal display according to claim 1, wherein on / off of the low-luminance point light source can be controlled so that the low-luminance point light source can be turned off while the high-luminance point light source is on. apparatus.   4. The liquid crystal display device according to claim 1, wherein the high luminous intensity point light source and the low luminous intensity point light source are arranged in a line along a longitudinal direction of a side end surface of the light guide plate.   5. The point light source having the same light intensity among the high light intensity point light source and the low light intensity point light source is disposed symmetrically with respect to the longitudinal center line of the side end surface of the light guide plate. A liquid crystal display device according to 1.   The liquid crystal display device according to claim 1, wherein the high light intensity point light source and the low light intensity point light source are switched on / off according to ambient brightness.

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