Liquid crystal display device

Abstract

To improve the display luminance relating to an image, to improve a reflection rate of light, and to reduce costs.SOLUTION: A liquid crystal display device 10 comprises: a first polarizer 13; a second polarizer 14; a liquid crystal panel 11 held between the first polarizer 13 and the second polarizer 14; an illumination device 12 holding the second polarizer 14 in a gap formed with the liquid crystal panel 11; a first control part 52 for controlling drive of the liquid crystal panel 11; and a second control part 53 for controlling drive of the illumination device 12. In the liquid crystal panel 11, in a state that an electric field is not imparted to a liquid crystal layer 22, a first linearly polarized light LP1 transmitted by the first polarizer 13 or the second polarizer 14 is transmitted with the polarized state maintained. The illumination device 12 includes a red light source 40, a green light source 41, and a blue light source 42. The first control part 52 imparts an electric field to the liquid crystal layer 22, so as to change the polarized state of the first linearly polarized light LP1 transmitted by the first polarizer 13 or the second polarizer 14. The second control part 53 sequentially turns on the red light source 40, the green light source 41, and the blue light source 42.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a liquid crystal display device. [Background technology]

[0002] Conventionally, one example of a liquid crystal display device is known, which is described in Patent Document 1 below. Patent Document 1 describes a mirror display including a liquid crystal display device. The mirror display described in Patent Document 1 is a mirror display including a half mirror plate having a reflective polarizing plate and a liquid crystal display device, and the half mirror plate further has a light diffusing member that diffuses at least a part of the incident light, and the liquid crystal display device, the reflective polarizing plate, and the light diffusing member are arranged in this order from the rear side. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 141350 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the mirror display described in the above-mentioned Patent Document 1, the texture of the surface of the half mirror plate can be made to blend with the texture of the surrounding environment by diffusing external light with a light diffusion member. However, when a diffusion film or a light diffusion layer is used as a light diffusion member, the light from the backlight is diffused by the diffusion film or the light diffusion layer when displaying an image. Therefore, if the haze value of the diffusion film or the light diffusion layer is increased, there is a risk that the display brightness of the image cannot be sufficiently obtained.

[0005] Patent Document 1 also describes that a polymer dispersed liquid crystal display panel is used as a light diffusing member, and that the polymer dispersed liquid crystal display panel is in a transparent state when displaying an image. However, the polymer dispersed liquid crystal display panel has a problem that the light reflectance is not sufficiently high in the opaque state, and also has a problem that the procurement cost is very high.

[0006] The technology described in this specification was developed based on the above circumstances, and aims to improve the display brightness of images, improve the light reflectance, and reduce costs. [Means for solving the problem]

[0007] (1) A liquid crystal display device according to the technology described in this specification includes a first polarizing plate having a first transmission axis that transmits the first linearly polarized light and a first absorption axis that absorbs the second linearly polarized light, the first linearly polarized light and the second linearly polarized light being orthogonal to each other in polarization directions, a second polarizing plate having a second transmission axis that transmits the first linearly polarized light and a second absorption axis that absorbs the second linearly polarized light, a liquid crystal panel sandwiched between the first polarizing plate and the second polarizing plate and having a liquid crystal layer whose alignment state changes with the application of an electric field, an illumination device sandwiching the second polarizing plate between the liquid crystal panel and the illumination device, a first control unit that controls driving of the liquid crystal panel, and a front and a second control unit that controls the driving of the lighting device, wherein when an electric field is not applied to the liquid crystal layer, the liquid crystal panel transmits the first linearly polarized light that has passed through the first polarizer or the second polarizer while maintaining its polarization state, and the lighting device has a red light source that emits red light, a green light source that emits green light, a blue light source that emits blue light, and a reflecting unit that reflects light toward the second polarizer, and the first control unit applies an electric field to the liquid crystal layer to change the polarization state of the first linearly polarized light that has passed through the first polarizer or the second polarizer, and the second control unit sequentially turns on the red light source, the green light source, and the blue light source.

[0008] (2) In addition to the above (1), the liquid crystal display device may further include a first control unit that applies a predetermined electric field to the liquid crystal layer and converts the first linearly polarized light transmitted through the first polarizer or the second polarizer into the second linearly polarized light.

[0009] (3) In addition to the above (1) or (2), the liquid crystal display device may further include a first reflective polarizing plate sandwiched between the second polarizing plate and the lighting device, and the first reflective polarizing plate may have a third transmission axis that transmits the first linearly polarized light and a first reflection axis that reflects the second linearly polarized light.

[0010] (4) In addition to any one of (1) to (3) above, the liquid crystal display device may further include a second reflective polarizing plate arranged between the liquid crystal panel and the first polarizing plate, the second reflective polarizing plate having a fourth transmission axis that transmits the first linearly polarized light and a second reflection axis that reflects the second linearly polarized light.

[0011] (5) In addition to the above (4), the liquid crystal display device may further include a dichroic liquid crystal panel arranged with the second reflective polarizing plate sandwiched between the first polarizing plate, the dichroic liquid crystal panel having a dichroic liquid crystal layer containing a dichroic dye, the orientation state of which changes upon application of an electric field, and when no electric field is applied to the dichroic liquid crystal layer, unpolarized light, the first linearly polarized light, and the second linearly polarized light are all transmitted while maintaining their polarization states, and when an electric field is applied to the dichroic liquid crystal layer by the first control unit, the first linearly polarized light is selectively transmitted, and the second linearly polarized light is absorbed by the dichroic dye.

[0012] (6) In addition to the above (5), the liquid crystal display device may further include a light detection sensor that detects the amount of external light, and the first control unit may apply an electric field to the dichroic liquid crystal layer when the amount of external light detected by the light detection sensor is equal to or greater than a threshold value, and may not apply an electric field to the dichroic liquid crystal layer when the amount of external light detected by the light detection sensor is less than the threshold value. Effect of the Invention

[0013] According to the technology described in this specification, it is possible to improve the display brightness of images, improve the light reflectance, and reduce costs. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is an exploded perspective view of a liquid crystal display device according to a first embodiment. [Diagram 2] FIG. 1 is a circuit diagram showing a pixel arrangement in a display area of ​​an array substrate provided in a liquid crystal panel constituting a liquid crystal display device according to a first embodiment. [Diagram 3] 1 is a cross-sectional view of a display area of ​​a liquid crystal panel according to a first embodiment. [Figure 4] 1 is a cross-sectional view of each LED, an LED substrate, and a reflective sheet provided in a backlight device constituting a liquid crystal display device according to embodiment 1. [Diagram 5] FIG. 1 is a block diagram showing an electrical configuration of a liquid crystal display device according to a first embodiment. [Figure 6] FIG. 1 is a diagram for explaining timing related to control of a liquid crystal panel and a backlight device according to the first embodiment. [Figure 7] Table showing preconditions for calculating the external light utilization rate and the backlight utilization rate according to the first embodiment. [Figure 8] Table showing the external light utilization rate and the backlight utilization rate according to the first embodiment [Figure 9] FIG. 13 is an exploded perspective view of a liquid crystal display device according to a second embodiment. [Figure 10] Table showing preconditions for calculating the external light utilization rate and the backlight utilization rate according to the second embodiment. [Figure 11] Table showing the external light utilization rate and the backlight utilization rate according to the second embodiment [Figure 12] FIG. 13 is an exploded perspective view of a liquid crystal display device according to a third embodiment. [Figure 13] 1 is a cross-sectional view of a dichroic liquid crystal panel constituting a liquid crystal display device according to a third embodiment. [Figure 14] FIG. 11 is a block diagram showing an electrical configuration of a liquid crystal display device according to a third embodiment. [Figure 15]Table showing preconditions for calculating the external light utilization rate and the backlight utilization rate according to the third embodiment. [Figure 16] Table showing the external light utilization rate and the backlight utilization rate according to the third embodiment [Figure 17] FIG. 11 is a block diagram showing an electrical configuration of a liquid crystal display device according to a fourth embodiment. [Figure 18] Table showing the external light utilization rate and the backlight utilization rate according to the fourth embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] <Embodiment 1> A first embodiment will be described with reference to Fig. 1 to Fig. 8. In this embodiment, a liquid crystal display device 10 will be illustrated. Note that an X-axis, a Y-axis, and a Z-axis are shown in a part of each drawing, and each axis direction is drawn to be the direction shown in each drawing. Also, the upper side of Fig. 1, Fig. 3, and Fig. 4 is the front side, and the lower side of the drawings is the back side.

[0016] 1, a liquid crystal display device 10 includes a liquid crystal panel 11, a backlight device (illumination device) 12 arranged on the back side (rear side) of the liquid crystal panel 11, a pair of polarizing plates 13, 14 arranged with the liquid crystal panel 11 sandwiched therebetween, and a first reflective polarizing plate 15 arranged on the front side (front face side) of the backlight device 12. The liquid crystal panel 11 is capable of displaying a video (image) by utilizing light irradiated from the backlight device 12.

[0017] The liquid crystal display device 10 according to the present embodiment performs image display in a field sequential manner. The configurations of the liquid crystal panel 11 and the backlight device 12 for realizing image display in the field sequential manner will be described below. First, as shown in FIG. 2, the liquid crystal panel 11 has at least a pair of substrates 20, 21 and a liquid crystal layer 22 interposed between the pair of substrates 20, 21. The front side of the pair of substrates 20, 21 is the counter substrate 20, and the back side is the array substrate 21. The counter substrate 20 and the array substrate 21 are both formed by laminating various films on the inner side of a glass substrate. The liquid crystal layer 22 contains liquid crystal molecules, which are a substance whose optical properties change with the application of an electric field. A seal portion for sealing the liquid crystal layer 22 is interposed between the outer peripheral ends of the pair of substrates 20, 21.

[0018] As shown in FIG. 2, at least a TFT (thin film transistor, switching element) 23 and a pixel electrode 24 are provided on the inner surface side of the array substrate 21. The TFTs 23 and the pixel electrodes 24 are arranged in a matrix shape (row and column shape) with a plurality of TFTs 23 and pixel electrodes 24 arranged at intervals along the X-axis direction and the Y-axis direction. Gate wiring (scanning wiring) 25 and source wiring (image wiring, signal wiring) 26 that are orthogonal (intersecting) to each other are arranged around the TFTs 23 and the pixel electrodes 24. The gate wiring 25 extends along the X-axis direction, and a plurality of the gate wirings 25 are arranged at intervals along the Y-axis direction. The source wirings 26 extend along the Y-axis direction, and a plurality of the source wirings 26 are arranged at intervals along the X-axis direction. The TFT 23 has a gate electrode 23A connected to the gate wiring 25, a source electrode 23B connected to the source wiring 26, a drain electrode 23C connected to the pixel electrode 24, and a semiconductor portion 23D connected to the source electrode 23B and the drain electrode 23C and made of a semiconductor material. The TFT 23 is driven based on a scanning signal supplied to the gate electrode 23A by the gate wiring 25. Then, a potential related to an image signal (data signal) supplied to the source electrode 23B by the source wiring 26 is supplied to the drain electrode 23C via the semiconductor portion 23D. As a result, the pixel electrode 24 is charged to the potential related to the image signal. The pixel electrode 24 is disposed in a region surrounded by the gate wiring 25 and the source wiring 26, and has a planar shape of, for example, a substantially rectangular shape.

[0019] As shown in FIG. 3, a pixel circuit section 27, a common electrode 28, a pixel electrode 24, and the like are provided on the inner surface side of the display area AA of the array substrate 21. The pixel circuit section 27 is composed of the above-mentioned TFT 23, the gate wiring 25, the source wiring 26, and the like, and supplies a predetermined potential to the plurality of pixel electrodes 24 at a predetermined timing. The common electrode 28 is formed in a solid shape over almost the entire area of ​​the main surface of the array substrate 21 so as to overlap with all the pixel electrodes 24. A common potential signal that is a common potential (reference potential) is supplied to the common electrode 28 by the pixel circuit section 27. The common electrode 28 and the pixel electrode 24 are both made of a transparent electrode material such as ITO (Indium Tin Oxide). The pixel electrode 24 is disposed on the upper layer side (liquid crystal layer 22 side) of the common electrode 28 via an insulating film 29. A plurality of slits 24S are formed in the pixel electrode 24. When the pixel electrode 24 is charged, a potential difference is generated between the pixel electrode 24 and the common electrode 28. Then, a fringe electric field (oblique electric field) including a component in the normal direction to the main surface of the array substrate 21 is generated between the opening edge of the slit 24S in the pixel electrode 24 and the common electrode 28 in addition to a component along the main surface of the array substrate 21. Therefore, by utilizing this fringe electric field, the orientation state of the liquid crystal molecules contained in the liquid crystal layer 22 can be controlled, and a predetermined display is performed based on the orientation state of the liquid crystal molecules. That is, the liquid crystal panel 11 according to this embodiment operates in a FFS (Fringe Field Switching) mode. An orientation film 30 for orienting the liquid crystal molecules contained in the liquid crystal layer 22 is provided on the innermost surface of the array substrate 21. An orientation film 31 for orienting the liquid crystal molecules contained in the liquid crystal layer 22 is provided on the innermost surface of the counter substrate 20.

[0020] Next, the configuration of the backlight device 12 will be described. As shown in Fig. 4, the backlight device 12 at least includes a plurality of LEDs (light sources) 40, 41, 42, an LED substrate 43 on which the plurality of LEDs 40, 41, 42 are provided, and a reflection sheet (reflection section) 44. This backlight device is a so-called direct type. The backlight device 12 may also include optical members (e.g., a diffusion plate, a prism sheet, a diffusion sheet, etc.) that impart optical effects to the light emitted from the LEDs 40, 41, 42.

[0021] As shown in Fig. 4, the LEDs 40, 41, and 42 include three types of LEDs: a red LED (red light source) 40 that emits red light, a green LED (green light source) 41 that emits green light, and a blue LED (blue light source) 42 that emits blue light. Each of the LEDs 40, 41, and 42 is configured by sealing each LED chip with a sealing material on a substrate portion mounted on an LED substrate 43. Each of the LEDs 40, 41, and 42 is configured such that the sealing material does not contain phosphor. Each of the LEDs 40, 41, and 42 is a so-called top-emitting type in which light-emitting surfaces 40A, 41A, and 42A that emit light of each color face the opposite side to the LED substrate 43 side (front side, first reflective polarizing plate 15 side).

[0022] Specifically, the red LED 40 has a red LED chip that emits monochromatic red light in the red wavelength region (approximately 600 nm to approximately 780 nm). The red LED chip is made of, for example, AlGaAs (aluminum gallium arsenide), GaAsP (gallium arsenide phosphide), or the like. The green LED 41 has a green LED chip that emits monochromatic green light in the green wavelength region (approximately 500 nm to approximately 570 nm). The green LED chip is made of, for example, GaN (gallium nitride), InGaN (indium gallium nitride), AlGaN (aluminum gallium nitride), AlGaInP (aluminum indium gallium phosphide), or the like. The blue LED 42 has a blue LED chip that emits monochromatic blue light in the blue wavelength region (approximately 400 nm to approximately 500 nm). The blue LED chip is made of, for example, GaN, InGaN, AlGaN, or the like.

[0023] As shown in FIG. 4, the LED board 43 is arranged with the mounting surface on which the LEDs 40, 41, and 42 are mounted facing the front side. The LEDs 40, 41, and 42 are arranged on the mounting surface of the LED board 43 at intervals. The reflective sheet 44 is made of a synthetic resin whose surface is white or silver with excellent light reflectivity. The reflective sheet 44 is laminated so as to cover almost the entire mounting surface of the LED board 43 from the front side, and a plurality of LED insertion holes 44A are formed at positions overlapping with the LEDs 40, 41, and 42 to pass the LEDs 40, 41, and 42 individually. The reflective sheet 44 can reflect the light of each color emitted from the LEDs 40, 41, and 42 toward the front side.

[0024] Next, the pair of polarizing plates 13, 14 and the first reflective polarizing plate 15 will be described with reference to FIG. 1. First, as shown in FIG. 1, of the pair of polarizing plates 13, 14 arranged across the liquid crystal panel 11, the one arranged on the front side of the liquid crystal panel 11 is referred to as the first polarizing plate 13, and the one arranged on the back side of the liquid crystal panel 11 is referred to as the second polarizing plate 14. The first polarizing plate 13 and the second polarizing plate 14 each include a polarizer formed by mixing an absorber such as iodine or a dichroic dye into a polymer resin film such as a PVA (polyvinyl alcohol) film and uniaxially stretching the film to orient the absorber. The first polarizing plate 13 and the second polarizing plate 14 selectively transmit light vibrating in a specific direction, and are capable of extracting linearly polarized light from unpolarized light such as natural light.

[0025] Specifically, as shown in FIG. 1, the first polarizing plate 13 has a first transmission axis TX1 and a first absorption axis AX1 that are orthogonal to each other. The first polarizing plate 13 transmits linearly polarized light parallel to the first transmission axis TX1 and absorbs linearly polarized light parallel to the first absorption axis AX1. In the following, the linearly polarized light parallel to the first transmission axis TX1 is referred to as a "first linearly polarized light LP1" and the linearly polarized light parallel to the first absorption axis AX1 is referred to as a "second linearly polarized light LP2". The second polarizing plate 14 has a second transmission axis TX2 and a second absorption axis AX2 that are orthogonal to each other. The second polarizing plate 14 is configured such that the second transmission axis TX2 is parallel to the first transmission axis TX1 and the second absorption axis AX2 is parallel to the first absorption axis AX1. Therefore, the second polarizing plate 14 transmits the first linearly polarized light LP1 that is parallel to the second transmission axis TX2 and absorbs the second linearly polarized light LP2 that is parallel to the second absorption axis AX2. Thus, in the liquid crystal display device 10 according to this embodiment, the pair of polarizing plates 13, 14 can be said to be arranged in a parallel Nicol state such that the transmission axes TX1, TX2 are parallel to each other.

[0026] As shown in FIG. 1, the first reflective polarizing plate 15 is sandwiched between the second polarizing plate 14 and the backlight device 12. The first reflective polarizing plate 15 has a multilayer structure in which layers having different refractive indices are alternately stacked, and selectively transmits linearly polarized light that vibrates in a specific direction and reflects linearly polarized light that vibrates in a direction perpendicular to the transmitted linearly polarized light. Specifically, an APF (Advanced Polarizing Film) is used as the first reflective polarizing plate 15. The first reflective polarizing plate 15 has a third transmission axis TX3 and a first reflection axis RX1 that are perpendicular to each other. The first reflective polarizing plate 15 is configured such that the third transmission axis TX3 is parallel to the first transmission axis TX1 and the second transmission axis TX2, and the first reflection axis RX1 is parallel to the first absorption axis AX1 and the second absorption axis AX2. Therefore, the first reflective polarizer 15 transmits the first linearly polarized light LP1 parallel to the third transmission axis TX3 and reflects the second linearly polarized light LP2 parallel to the first reflection axis RX1.

[0027] Next, a circuit configuration for controlling the driving of the liquid crystal panel 11 and the backlight device 12 will be described with reference to the block diagram of FIG. 5. As shown in FIG. 5, the liquid crystal display device 10 has a control unit 50 for controlling the driving of the liquid crystal panel 11 and the backlight device 12. The control unit 50 includes a video signal processing circuit 51, a panel control circuit (first control circuit) 52, and a backlight control circuit (second control circuit) 53. The video signal processing circuit 51 processes a video signal supplied from an external host system and outputs the processed video signal. The panel control circuit 52 writes an image based on the processed video signal output from the video signal processing circuit 51 to the liquid crystal panel 11. When the liquid crystal display device 10 includes a gate driver and a source driver for writing an image to the liquid crystal panel 11, the panel control circuit 52 controls the driving of the gate driver and the source driver. The backlight control circuit 53 controls the LEDs 40, 41, and 42 to adjust the amount of light emitted by the LEDs 40, 41, and 42. The backlight control circuit 53 can perform, for example, PWM (Pulse Width Modulation) dimming when controlling the LEDs 40, 41, and 42. When the liquid crystal display device 10 includes an LED driver that drives the LEDs 40, 41, and 42, the backlight control circuit 53 controls the driving of the LED driver.

[0028] The operation of the liquid crystal panel 11 and the backlight device 12, the driving of which is controlled by the control unit 50, will be described with reference to Fig. 6. Based on the processed video signal output from the video signal processing circuit 51, the panel control circuit 52 drives pixel rows, each of which is made up of a plurality of pixel electrodes 24 arranged in the row direction in the liquid crystal panel 11, by sequentially scanning the pixel rows along the column direction perpendicular to the row direction. Specifically, as shown in Fig. 6, the panel control circuit 52 controls the liquid crystal panel 11 so that one frame period includes a red data writing period in which an image signal relating to a red display gradation is supplied to each pixel electrode 24, a red display period in which the red display gradation (red data) of each pixel electrode 24 is maintained without supplying an image signal, a green data writing period in which an image signal relating to a green display gradation is supplied to each pixel electrode 24, a green display period in which the green display gradation (green data) of each pixel electrode 24 is maintained without supplying an image signal, a blue data writing period in which an image signal relating to a blue display gradation is supplied to each pixel electrode 24, and a blue display period in which the blue display gradation (blue data) of each pixel electrode 24 is maintained without supplying an image signal. Fig. 6 is a diagram for explaining the timing of control of the liquid crystal panel 11 and the backlight device 12. Note that in the column of "Image signal written to liquid crystal panel" shown in Fig. 6, the color of the display gradation related to the image signal supplied to each pixel electrode 24 is described.

[0029] In the red data writing period, an image signal related to a red display gradation is supplied to each pixel electrode 24, and the image signal related to the red display gradation is held in each pixel electrode 24 during the red display period, thereby displaying a red image on the liquid crystal panel 11. In the green data writing period, an image signal related to a green display gradation is supplied to each pixel electrode 24, and the image signal related to the green display gradation is held in each pixel electrode 24 during the green display period, thereby displaying a green image on the liquid crystal panel 11. In the blue data writing period, an image signal related to a blue display gradation is supplied to each pixel electrode 24, and the image signal related to the blue display gradation is held in each pixel electrode 24 during the blue display period, thereby displaying a blue image on the liquid crystal panel 11. In this way, when each pixel electrode 24 is charged to a potential based on the image signal related to the display gradation of each color, an electric field corresponding to the electric potential of each pixel electrode 24 is applied to the liquid crystal layer 22, and the orientation state of the liquid crystal molecules contained in the liquid crystal layer 22 is controlled by the electric field (see FIG. 3). The polarization state of light passing through the liquid crystal layer 22 is changed according to the orientation state of the liquid crystal molecules. When there is a portion in the liquid crystal layer 22 to which no electric field is applied, the polarization state of the light passing through that portion is not changed.

[0030] On the other hand, the backlight control circuit 53 is controlled by the control unit 50, and is synchronized with the operation of the panel control circuit 52 to drive the red LED 40, the green LED 41, and the blue LED 42. Specifically, as shown in Fig. 6, the backlight control circuit 53 turns off the red LED 40, the green LED 41, and the blue LED 42 during a red data writing period in which the panel control circuit 52 supplies an image signal related to a red display gradation to each pixel electrode 24, and turns on the red LED 40 and turns off the green LED 41 and the blue LED 42 during a red display period. The backlight control circuit 53 turns off the red LED 40, the green LED 41, and the blue LED 42 during a green data writing period in which the panel control circuit 52 supplies an image signal related to a green display gradation to each pixel electrode 24, and turns on the green LED 41 and turns off the red LED 40 and the blue LED 42 during a green display period. The backlight control circuit 53 turns off the red LED 40, the green LED 41, and the blue LED 42 during a blue data writing period in which the panel control circuit 52 supplies an image signal related to a blue display gradation to each pixel electrode 24, and turns on the blue LED 42 and turns off the red LED 40 and the green LED 41 during a blue display period.

[0031] In this way, in the red display period, the red light emitted from the red LED 40 passes through each pixel electrode 24 to which an image signal related to a red display gradation is supplied in the liquid crystal panel 11, thereby displaying a red image. In the green display period, the green light emitted from the green LED 41 passes through each pixel electrode 24 to which an image signal related to a green display gradation is supplied in the liquid crystal panel 11, thereby displaying a green image. In the blue display period, the blue light emitted from the blue LED 42 passes through each pixel electrode 24 to which an image signal related to a blue display gradation is supplied in the liquid crystal panel 11, thereby displaying a blue image. In the display period of each color, all light sources of colors different from the display color of the image are turned off, so that the color purity of each color image is high. As described above, the backlight control circuit 53 sequentially turns on the red LED 40, the green LED 41, and the blue LED 42, and the panel control circuit 52 applies an electric field to the liquid crystal layer 22 in synchronization with this, thereby enabling color display in a field sequential manner. Furthermore, the light emitted from the LEDs 40, 41, and 42 can be reflected by the reflective sheet 44 provided in the backlight device 12, thereby improving the light utilization efficiency.

[0032] In this embodiment, when the liquid crystal display device 10 is turned off in an environment where there is external light such as indoor lighting or sunlight, it is possible to display white color using the external light. That is, the liquid crystal display device 10 according to this embodiment is used as a so-called "decorative display". In order to realize white display using external light, the liquid crystal panel 11 provided in the liquid crystal display device 10 is in a normally white mode. The external light is "unpolarized NP".

[0033] In detail, when external light is incident on the first polarizer 13 from the front side, the first linearly polarized light LP1 is transmitted through the first polarizer 13, but the second linearly polarized light LP2 is absorbed by the first polarizer 13. Here, when the power supply of the liquid crystal display device 10 is turned off, no electric field is applied across the entire liquid crystal layer 22. Therefore, the first linearly polarized light LP1 that has transmitted through the first polarizer 13 is transmitted through the liquid crystal layer 22 while maintaining its polarization state. When the first linearly polarized light LP1 that has transmitted through the liquid crystal panel 11 is incident on the second polarizer 14 from the front side, it is transmitted through the second polarizer 14 as it is. When the first linearly polarized light LP1 that has transmitted through the second polarizer 14 is incident on the first reflective polarizer 15 from the front side, it is transmitted through the first reflective polarizer 15 as it is. The first linearly polarized light LP1 that has been transmitted through the first reflective polarizer 15 reaches the backlight device 12, where it is reflected by the reflective sheet 44, converted into unpolarized light NP, scattered, and directed toward the front side. When the light reflected by the reflective sheet 44 is incident on the first reflective polarizer 15 from the back side, the first linearly polarized light LP1 is transmitted through the first reflective polarizer 15, but the second linearly polarized light LP2 is reflected by the first reflective polarizer 15 and directed toward the reflective sheet 44. The first linearly polarized light LP1 that has been transmitted through the first reflective polarizer 15 is transmitted in sequence through the second polarizer 14, liquid crystal layer 22, and first polarizer 13 on the front side, and is emitted to the outside.

[0034] On the other hand, the second linearly polarized light LP2 reflected by the first reflective polarizer 15 toward the reflective sheet 44 is converted into unpolarized light NP by being reflected again by the reflective sheet 44, and then travels toward the first reflective polarizer 15 again, and the first linearly polarized light LP1 passes through the first reflective polarizer 15. By repeating this process, the amount of the first linearly polarized light LP1 passing through the first reflective polarizer 15 increases, so that the efficiency of use of external light can be improved. In this way, when the power supply of the liquid crystal display device 10 is turned off, the external light is scattered and reflected by the reflective sheet 44 provided in the backlight device 12, so that an efficient white display can be performed on the liquid crystal panel 11. Moreover, since the efficiency of use of external light is improved by the first reflective polarizer 15, a more efficient white display can be performed on the liquid crystal panel 11.

[0035] According to this embodiment, when the liquid crystal display device 10 is turned on to display an image, the degree of diffusion of the light emitted from the red LEDs 40, green LEDs 41, and blue LEDs 42 is lower than in the conventional case where light is diffused by a diffusion film, light diffusion layer, etc., so that sufficient display brightness for the image can be obtained. Furthermore, according to this embodiment, the light reflectance of the reflective sheet 44 can be sufficiently increased and procurement costs can be reduced, compared to the conventional case where a polymer dispersed liquid crystal display panel is used.

[0036] Moreover, in a state where the liquid crystal display device 10 according to this embodiment is powered on, the panel control circuit 52 applies a predetermined electric field to the liquid crystal layer 22, and is capable of converting the first linearly polarized light LP1 transmitted through the first polarizer 13 or the second polarizer 14 into the second linearly polarized light LP2. For example, in a state where the backlight control circuit 53 turns off all of the red LED 40, the green LED 41, and the blue LED 42, when a predetermined electric field is applied to the liquid crystal layer 22 by the panel control circuit 52, the first linearly polarized light LP1 of the external light transmitted through the first polarizer 13 is converted into the second linearly polarized light LP2 as it transmits through the liquid crystal layer 22. The second linearly polarized light LP2 incident on the second polarizer 14 is absorbed by the second polarizer 14. As a result, when the liquid crystal display device 10 is powered on but no image is displayed, the liquid crystal panel 11 can display black.

[0037] Next, the "external light utilization rate" which is the utilization rate of external light and the "backlight light utilization rate" which is the utilization rate of light emitted from the backlight device 12 were calculated for the cases where the liquid crystal display device 10 was turned on to display an image, where the above-mentioned black display was performed, and where the liquid crystal display device 10 was turned off to display a white image. The preconditions for calculating the external light utilization rate and the backlight light utilization rate are as shown in the table of FIG. 7. Specifically, as shown in FIG. 7, as a precondition, the transmittance of the first linearly polarized light LP1 in the first polarizer 13 and the second polarizer 14 (LP1 transmittance in FIG. 7) is 95%. The transmittance of the second linearly polarized light LP2 in the first polarizer 13 and the second polarizer 14 (LP2 transmittance in FIG. 7) is 0%. The transmittance of the first linearly polarized light LP1 in the case where a maximum grayscale potential is supplied to all pixel electrodes 24 provided in the liquid crystal panel 11 (LP1 transmittance in FIG. 7) is 90%. The transmittance of the second linearly polarized light LP2 (LP2 transmittance in FIG. 7) when a potential of the maximum gradation is supplied to all pixel electrodes 24 of the liquid crystal panel 11 is set to 90%. The transmittance of the first linearly polarized light LP1 in the first reflective polarizer 15 (LP1 transmittance in FIG. 7) is set to 100%. The transmittance of the second linearly polarized light LP2 in the first reflective polarizer 15 (LP2 transmittance in FIG. 7) is set to 0%. The transmittance of the unpolarized NP in the first reflective polarizer 15 (NP transmittance in FIG. 7) is set to 50%, and all light that is transmitted is the first linearly polarized light LP1. The reflectance of the unpolarized NP in the first reflective polarizer 15 (NP reflectance in FIG. 7) is set to 50%, and all light that is reflected is the second linearly polarized light LP2.

[0038] The calculation results of the external light utilization rate and the backlight utilization rate are as shown in the table of FIG. 8. In addition to the external light utilization rate and the backlight utilization rate, the table of FIG. 8 also lists the electric field of the liquid crystal panel 11, the polarization state of the light (external light) incident on the liquid crystal display device 10, the polarization state of the light emitted from the liquid crystal display device 10, etc. When displaying an image, the electric field of the liquid crystal panel 11 ranges from minimum to maximum depending on the display gradation of each pixel electrode 24. When displaying black, the electric field of the liquid crystal panel 11 is maximum. When displaying white, the electric field of the liquid crystal panel 11 is minimum.

[0039] The polarization state of the incident light when an image is displayed will be described. When an image is displayed, the incident light is unpolarized NP externally, and when it is incident on the first polarizing plate 13, the second linearly polarized light LP2 is absorbed and only the first linearly polarized light LP1 is transmitted. When the incident light is transmitted through the liquid crystal panel 11 when an image is displayed, the polarization state is determined according to the display gradation of each pixel electrode 24. When the incident light is incident on the second polarizing plate 14 when an image is displayed, the second linearly polarized light LP2 is absorbed and only the first linearly polarized light LP1 is transmitted. When the incident light is incident on the first reflective polarizing plate 15 when an image is displayed, the first linearly polarized light LP1 is transmitted as it is. When the incident light is reflected by the reflective sheet 44 when an image is displayed, the incident light becomes unpolarized NP.

[0040] The polarization state of the emitted light during image display will be described. The light of each color emitted from each LED 40, 41, 42 is unpolarized NP. When the emitted light is reflected by the reflection sheet 44 during image display, it becomes unpolarized NP. When the emitted light is incident on the first reflective polarizing plate 15 during image display, the second linearly polarized light LP2 is reflected toward the reflection sheet 44 side, and only the first linearly polarized light LP1 is transmitted. When the emitted light is incident on the second polarizing plate 14 during image display, the first linearly polarized light LP1 is transmitted as it is. When the emitted light is transmitted through the liquid crystal panel 11 during image display, it becomes a polarization state according to the display gradation of each pixel electrode 24. When the emitted light is incident on the first polarizing plate 13 during image display, the second linearly polarized light LP2 is absorbed, and only the first linearly polarized light LP1 is transmitted. Therefore, the emitted light during image display becomes the first linearly polarized light LP1.

[0041] Next, the polarization state of the incident light during black display will be described. During black display, the incident light is unpolarized NP externally, and when it is incident on the first polarizing plate 13, the second linearly polarized light LP2 is absorbed and only the first linearly polarized light LP1 is transmitted. During black display, when the incident light passes through the liquid crystal panel 11, the first linearly polarized light LP1 is converted into the second linearly polarized light LP2. During black display, when the incident light is incident on the second polarizing plate 14, the second linearly polarized light LP2 is absorbed and does not pass through the second polarizing plate 14. Thus, during black display, external light does not reach the reflective sheet 44 of the backlight device 12, so there is almost no outgoing light.

[0042] Next, the polarization state of the incident light during white display will be described. During white display, the incident light is unpolarized NP externally, and when it is incident on the first polarizer 13, the second linearly polarized light LP2 is absorbed and only the first linearly polarized light LP1 is transmitted. During white display, when the incident light is incident on the liquid crystal panel 11, the first linearly polarized light LP1 is transmitted through the liquid crystal panel 11 while maintaining its polarization state. During white display, when the incident light is incident on the second polarizer 14, the first linearly polarized light LP1 is transmitted as it is. During white display, when the incident light is incident on the first reflective polarizer 15, the first linearly polarized light LP1 is transmitted as it is. During white display, when the incident light is reflected by the reflective sheet 44, it becomes unpolarized NP.

[0043] The polarization state of the outgoing light during white display will be described. During white display, when the outgoing light reflected by the reflective sheet 44 and turned into unpolarized light NP is incident on the first reflective polarizing plate 15, the second linearly polarized light LP2 is reflected toward the reflective sheet 44 side, and only the first linearly polarized light LP1 is transmitted. During white display, when the outgoing light is incident on the second polarizing plate 14, the first linearly polarized light LP1 is transmitted as it is. During white display, when the outgoing light is incident on the liquid crystal panel 11, the first linearly polarized light LP1 is transmitted through the liquid crystal panel 11 while maintaining its polarization state. During white display, when the outgoing light is incident on the first polarizing plate 13, the first linearly polarized light LP1 is transmitted as it is. Therefore, the outgoing light during white display becomes the first linearly polarized light LP1.

[0044] Next, the calculation results of the external light utilization rate and the backlight utilization rate will be described. The external light utilization rate is the percentage of the amount of external light emitted from the liquid crystal display device 10, with the amount of external light incident on the liquid crystal display device 10 taken as the reference (100%). The backlight utilization rate is the percentage of the amount of emitted light from the liquid crystal display device 10, with the amount of light emitted from each of the LEDs 40, 41, and 42 taken as the reference (100%). According to FIG. 8, the external light utilization rate during video display was 34.7% at its maximum (value during full-screen white display), and the backlight utilization rate was 81.2% at its maximum. Thus, since the backlight utilization rate tends to be sufficiently higher than the external light utilization rate during video display, even in an environment where there is a lot of external light, degradation of display quality due to reflection is suppressed, and high display quality can be obtained.

[0045] The external light utilization rate during black display was 0%. In this way, the reflection of external light can be sufficiently suppressed, so that a stable black display can be performed. In both black display and white display, the LEDs 40, 41, and 42 are all off, so that the backlight utilization rate is naturally 0%. And the external light utilization rate during white display was 34.7%. In this embodiment, the light reflected by the reflective sheet 44 is repeatedly reflected by the first reflective polarizing plate 15 to increase the utilization efficiency, so that the external light utilization rate can be increased compared to when the first reflective polarizing plate 15 is not used. Thus, according to this embodiment, a white display can be performed with sufficient brightness.

[0046] As described above, the liquid crystal display device 10 of this embodiment includes the first polarizing plate 13 having a first transmission axis TX1 that transmits the first linearly polarized light LP1 and a first absorption axis AX1 that absorbs the second linearly polarized light LP2 of the first linearly polarized light LP1 and the second linearly polarized light LP2, the second polarizing plate 14 having a second transmission axis TX2 that transmits the first linearly polarized light LP1 and a second absorption axis AX2 that absorbs the second linearly polarized light LP2, a liquid crystal panel 11 that is sandwiched between the first polarizing plate 13 and the second polarizing plate 14 and has a liquid crystal layer 22 whose alignment state changes with the application of an electric field, a backlight device (illumination device) 12 that is sandwiched between the liquid crystal panel 11 and the second polarizing plate 14, a panel control circuit (first control unit) 52 that controls the driving of the liquid crystal panel 11, and the backlight device 1 and a backlight control circuit (second control unit) 53 that controls the driving of the first linearly polarized light LP1 that has passed through the first polarizer 13 or the second polarizer 14. When no electric field is applied to the liquid crystal layer 22, the liquid crystal panel 11 transmits the first linearly polarized light LP1 while maintaining its polarization state. The backlight device 12 has a red LED (red light source) 40 that emits red light, a green LED (green light source) 41 that emits green light, a blue LED (blue light source) 42 that emits blue light, and a reflective sheet (reflective unit) 44 that reflects light toward the second polarizer 14. The panel control circuit 52 applies an electric field to the liquid crystal layer 22 to change the polarization state of the first linearly polarized light LP1 that has passed through the first polarizer 13 or the second polarizer 14. The backlight control circuit 53 sequentially lights up the red LED 40, the green LED 41, and the blue LED 42.

[0047] Color display by the field sequential method is possible by applying an electric field to the liquid crystal layer 22 by the panel control circuit 52 in synchronization with the backlight control circuit 53 sequentially lighting the red LED 40, the green LED 41, and the blue LED 42. Also, the light utilization efficiency can be improved by reflecting the light emitted from the LEDs 40, 41, and 42 by the reflective sheet 44 provided in the backlight device 12.

[0048] On the other hand, when external light (unpolarized light NP) is incident on the first polarizer 13, the first linearly polarized light LP1 passes through the first polarizer 13, and the second linearly polarized light LP2 is absorbed by the first polarizer 13. Here, for example, when the power supply of the liquid crystal display device 10 is turned off, no electric field is applied to the liquid crystal layer 22 of the liquid crystal panel 11, so the first linearly polarized light LP1 that has passed through the first polarizer 13 passes through the liquid crystal panel 11 while maintaining its polarization state, and then passes through the second polarizer 14. The first linearly polarized light LP1 that has reached the backlight device 12 is reflected by the reflective sheet 44, converted into unpolarized light NP, scattered, and directed toward the second polarizer 14. The first linearly polarized light LP1 of the external light reflected by the reflective sheet 44 passes through the second polarizer 14, the liquid crystal layer 22, and the first polarizer 13 in sequence, and is emitted to the outside. In this manner, when the liquid crystal display device 10 is in a power-off state, external light is scattered and reflected by the reflective sheet 44 provided in the backlight device 12, thereby enabling efficient white display on the liquid crystal panel 11.

[0049] Compared to the conventional case where light is diffused by a diffusion film or light diffusion layer, the degree of diffusion of light emitted from the red LED 40, green LED 41, and blue LED 42 when displaying an image is reduced, so that sufficient display brightness for the image can be obtained. Also, compared to the conventional case where a polymer dispersed liquid crystal display panel is used, the light reflectance by the reflective sheet 44 can be sufficiently increased and procurement costs can be reduced.

[0050] Moreover, the panel control circuit 52 applies a predetermined electric field to the liquid crystal layer 22, and converts the first linearly polarized light LP1 transmitted through the first polarizer 13 or the second polarizer 14 into the second linearly polarized light LP2. For example, when the backlight control circuit 53 turns off the red LED 40, the green LED 41, and the blue LED 42, and the panel control circuit 52 applies a predetermined electric field to the liquid crystal layer 22, the first linearly polarized light LP1 of the external light transmitted through the first polarizer 13 is converted into the second linearly polarized light LP2 as it transmits through the liquid crystal layer 22. The second linearly polarized light LP2 incident on the second polarizer 14 is absorbed by the second polarizer 14. This allows the liquid crystal panel 11 to display black when the liquid crystal display device 10 is turned on but no image is displayed.

[0051] The liquid crystal display device 10 also includes a first reflective polarizing plate 15 sandwiched between the second polarizing plate 14 and the backlight device 12, and the first reflective polarizing plate 15 has a third transmission axis TX3 that transmits the first linearly polarized light LP1 and a first reflection axis RX1 that reflects the second linearly polarized light LP2. For example, when the liquid crystal display device 10 is turned off, the first linearly polarized light LP1 of external light passes through the first polarizing plate 13, the liquid crystal panel 11, and the second polarizing plate 14, and then passes through the first reflective polarizing plate 15 and is reflected by the reflective sheet 44. The first linearly polarized light LP1 of external light, which has become unpolarized NP due to reflection, passes through the first reflective polarizing plate 15, but the second linearly polarized light LP2 of external light is reflected by the first reflective polarizing plate 15 and heads toward the reflective sheet 44. The second linearly polarized light LP2 heading toward the reflective sheet 44 is reflected again by the reflective sheet 44 and converted into unpolarized light NP, and then heads toward the first reflective polarizer 15 again, where the first linearly polarized light LP1 passes through the first reflective polarizer 15. By repeating this process, the amount of first linearly polarized light LP1 passing through the first reflective polarizer 15 increases, thereby improving the efficiency of use of external light. This allows the liquid crystal panel 11 to display white color more efficiently.

[0052] <Embodiment 2> 9 to 11. In this embodiment, a second reflective polarizing plate 16 is added. Note that a duplicated description of the structure, operation, and effects similar to those of the above-mentioned embodiment 1 will be omitted.

[0053] As shown in FIG. 9, the liquid crystal display device 110 according to this embodiment includes a second reflective polarizing plate 16 arranged with a first polarizing plate 113 sandwiched between the liquid crystal panel 111 and the second reflective polarizing plate 16. That is, the second reflective polarizing plate 16 is arranged on the outermost side of the components of the liquid crystal display device 110. The second reflective polarizing plate 16, like the first reflective polarizing plate 115, has a multilayer structure in which layers having different refractive indices are alternately stacked, and selectively transmits linearly polarized light vibrating in a specific direction and reflects linearly polarized light vibrating in a direction perpendicular to the transmitted linearly polarized light. Specifically, like the first reflective polarizing plate 115, for example, an APF is used as the second reflective polarizing plate 16. The second reflective polarizing plate 16 has a fourth transmission axis TX4 and a second reflection axis RX2 that are perpendicular to each other. The second reflective polarizing plate 16 is configured such that the fourth transmission axis TX4 is parallel to the first transmission axis TX1, the second transmission axis TX2, and the third transmission axis TX3, and the second reflection axis RX2 is parallel to the first absorption axis AX1, the second absorption axis AX2, and the first reflection axis RX1. Therefore, the second reflective polarizing plate 16 transmits the first linearly polarized light LP1 parallel to the fourth transmission axis TX4, and reflects the second linearly polarized light LP2 parallel to the second reflection axis RX2.

[0054] As described above, according to the present embodiment, when the liquid crystal display device 110 is powered off and external light that is unpolarized NP is incident on the second reflective polarizer 16 located on the opposite side of the first polarizer 113 from the liquid crystal panel 111, the first linearly polarized light LP1 of the external light is transmitted through the second reflective polarizer 16, and the second linearly polarized light LP2 is reflected by the second reflective polarizer 16. That is, by using the second linearly polarized light LP2 reflected by the second reflective polarizer 16 in addition to the light reflected by the reflection sheet 44 (see FIG. 4) provided in the backlight device 112, the luminance during white display can be improved. This improves the utilization efficiency of the external light, and therefore, when the liquid crystal display device 110 is powered off, the liquid crystal panel 111 can display white more efficiently.

[0055] Next, the "external light utilization rate" which is the utilization rate of external light and the "backlight light utilization rate" which is the utilization rate of light emitted from the backlight device 112 were calculated for the cases where the liquid crystal display device 110 was turned on to display an image, the above-mentioned black display was performed, and the white display was performed with the liquid crystal display device 110 turned off. The prerequisites for calculating the external light utilization rate and the backlight light utilization rate are as shown in the table of FIG. 10. The prerequisites for the first polarizer 113, the second polarizer 114, the liquid crystal panel 111, and the first reflective polarizer 115 are the same as those of the first embodiment. The prerequisites for the second reflective polarizer 16 are the same as those of the first reflective polarizer 115. Specifically, as shown in FIG. 10, the prerequisite is that the transmittance of the first linearly polarized light LP1 in the second reflective polarizer 16 (LP1 transmittance in FIG. 10) is 100%. The transmittance of the second linearly polarized light LP2 in the second reflective polarizer 16 (LP2 transmittance in FIG. 10) is 0%. The transmittance of unpolarized NP in the second reflective polarizer 16 (NP transmittance in FIG. 10) is 50%, and all light transmitted is the first linearly polarized light LP1. The reflectance of unpolarized NP in the second reflective polarizer 16 (NP reflectance in FIG. 10) is 50%, and all light reflected is the second linearly polarized light LP2.

[0056] The calculation results of the external light utilization rate and the backlight utilization rate are shown in the table of Fig. 11. The items listed in the table of Fig. 11 (the electric field of the liquid crystal panel 111, the polarization state of the light (external light) incident on the liquid crystal display device 110, the polarization state of the light emitted from the liquid crystal display device 110, etc.) are the same as the items listed in the table of Fig. 8 shown in the above-mentioned embodiment 1.

[0057] The polarization state of the incident light will be described. In any of the video display, black display, and white display, the incident light is unpolarized NP externally, and when it enters the second reflective polarizing plate 16, the second linearly polarized light LP2 is reflected and only the first linearly polarized light LP1 is transmitted. Since the incident light transmitted through the second reflective polarizing plate 16 does not contain the second linearly polarized light LP2, when it enters the first polarizing plate 113, the first linearly polarized light LP1 is transmitted as it is. Note that, in any of the video display, black display, and white display, the polarization state of the incident light at the liquid crystal panel 111, the second polarizing plate 114, the first reflective polarizing plate 115, the reflective sheet 44, and each of the LEDs 40, 41, and 42 (see FIG. 4) is as described in the first embodiment.

[0058] The polarization state of the emitted light will be described. In both the image display and the white display, the polarization state of the emitted light at the first polarizer 113, the liquid crystal panel 111, the second polarizer 114, the first reflective polarizer 115, the reflective sheet 44, and the LEDs 40, 41, 42 (see FIG. 4) is as described in the first embodiment. In both the image display and the white display, the emitted light transmitted through the first polarizer 113 does not contain the second linearly polarized light LP2, and therefore when it enters the second reflective polarizer 16, the first linearly polarized light LP1 is transmitted as it is.

[0059] Next, the calculation results of the external light utilization rate and the backlight utilization rate will be described. According to FIG. 11, the external light utilization rate during video display was 83% at its maximum (value during full-screen white display), and the backlight utilization rate was 81.2% at its maximum. Thus, since the external light utilization rate during video display tends to be slightly higher than the backlight utilization rate, in an environment with little external light, a sufficiently high display quality can be obtained, but in an environment with a lot of external light, there is a concern that the display quality may be reduced due to reflection. In addition, the external light utilization rate during black display was 50%. Therefore, during black display, reflection due to external light tends to be more easily visible than in embodiment 1 (see FIG. 8). The reason why the external light utilization rate is about 50% higher than in embodiment 1 (see FIG. 8) both during video display and black display is that the second linearly polarized light LP2 contained in the non-polarized external light NP is reflected by the second reflective polarizing plate 16.

[0060] On the other hand, the external light utilization rate during white display was 83%. In this embodiment, the light reflected by the reflective sheet 44 is repeatedly reflected by the first reflective polarizer 115 to increase utilization efficiency, and the second reflective polarizer 16 reflects the second linearly polarized light LP2 contained in the external light, which is unpolarized NP, to further increase utilization efficiency, so that the external light utilization rate can be increased by just under 50% compared to the above-described first embodiment (see FIG. 8). Thus, according to this embodiment, white display can be performed with improved brightness.

[0061] As described above, according to this embodiment, the second reflective polarizer 16 is provided with the first polarizer 113 sandwiched between the liquid crystal panel 111 and the second reflective polarizer 16, and the second reflective polarizer 16 has a fourth transmission axis TX4 that transmits the first linearly polarized light LP1 and a second reflection axis RX2 that reflects the second linearly polarized light LP2. For example, when the liquid crystal display device 110 is turned off, when external light of unpolarized light NP is incident on the second reflective polarizer 16 located on the opposite side of the liquid crystal panel 111 with respect to the first polarizer 113, the first linearly polarized light LP1 is transmitted through the second reflective polarizer 16, and the second linearly polarized light LP2 is reflected by the second reflective polarizer 16. This can improve the utilization efficiency of the external light, and therefore, when the liquid crystal display device 110 is turned off, the liquid crystal panel 111 can display white more efficiently.

[0062] <Embodiment 3> A third embodiment will be described with reference to Fig. 12 to Fig. 16. In this third embodiment, a dichroic liquid crystal panel 17 is added to the second embodiment. Note that a duplicated description of the structure, operation, and effects similar to those of the second embodiment will be omitted.

[0063] As shown in FIG. 12, the liquid crystal display device 210 according to this embodiment includes a dichroic liquid crystal panel 17 arranged with a second reflective polarizing plate 216 sandwiched between the first polarizing plate 213 and the dichroic liquid crystal panel 17. That is, the dichroic liquid crystal panel 17 is arranged on the outermost side of the components of the liquid crystal display device 210. As shown in FIG. 13, the dichroic liquid crystal panel 17 at least includes a pair of substrates 32, 33 and a dichroic liquid crystal layer 34 interposed between the pair of substrates 32, 33. The pair of substrates 32, 33 are made of a glass material or a synthetic resin material. A pair of electrodes 35, 36 and a pair of alignment films 37, 38 are provided on the inner surface side of the pair of substrates 32, 33. An electric field can be applied to the dichroic liquid crystal layer 34 by the pair of electrodes 35, 36. The pair of alignment films 37, 38 can align the liquid crystal molecules 34A included in the dichroic liquid crystal layer 34. One electrode 35 of the pair of electrodes 35, 36 is provided on the inner surface of one of the substrates 32. One alignment film 37 of the pair of alignment films 37, 38 is provided on the inner surface of one electrode 35. The other electrode 36 of the pair of electrodes 35, 36 is provided on the inner surface of the other substrate 33. The other alignment film 38 of the pair of alignment films 37, 38 is provided on the inner surface of the other electrode 36.

[0064] As shown in FIG. 13, the dichroic liquid crystal layer 34 includes liquid crystal molecules 34A and dichroic dye 34B, which are substances whose optical properties change with the application of an electric field. In FIG. 13, the liquid crystal molecules 34A and the dichroic dye 34B are illustrated in a simplified form. The dichroic dye 34B is a rod-shaped compound like the liquid crystal molecules 34A, and has a property that the degree of light absorption varies depending on the axial direction. Specifically, for example, the dichroic dye 34B transmits almost no light without absorbing it in a position in which its axial direction is almost aligned with the normal direction of the substrates 32 and 33 (hereinafter referred to as a first position), but absorbs most of the light in a position in which its axial direction is almost perpendicular (intersecting) with the normal direction of the substrates 32 and 33 (hereinafter referred to as a second position). Note that FIG. 13 illustrates a representative case in which the axial direction of the dichroic dye 34B is aligned with the normal direction of the substrates 32 and 33. The dichroic dye 34B is aligned along the liquid crystal molecules 34A and follows the movement of the liquid crystal molecules 34A. The alignment state of the liquid crystal molecules 34A changes according to the electric field applied to the dichroic liquid crystal layer 34 by the pair of electrodes 35, 36. Therefore, by controlling the electric field applied to the dichroic liquid crystal layer 34 by the pair of electrodes 35, 36, the attitude of the dichroic dye 34B is controlled, and thus it is possible to control whether or not light is absorbed and transmitted. Specifically, for example, when no electric field is applied to the dichroic liquid crystal layer 34 by the pair of electrodes 35, 36, the dichroic dye 34B is in the first attitude. At this time, the light (unpolarized light NP, first linearly polarized light LP1, and second linearly polarized light LP2) transmits through the dichroic liquid crystal layer 34 while maintaining its polarization state. On the other hand, when an electric field is applied to the dichroic liquid crystal layer 34 by the pair of electrodes 35, 36, the dichroic dye 34B is in the second attitude. At this time, most of the light (most of the first linearly polarized light LP1 and almost all of the second linearly polarized light LP2) is absorbed by the dichroic dye 34B, but only a certain amount of the first linearly polarized light LP1 is selectively allowed to pass through the dichroic liquid crystal layer 34.

[0065] As shown in FIG. 14, the dichroic liquid crystal panel 17 having such a configuration is driven and controlled by the panel control circuit 252. According to this embodiment, when an image is displayed on the liquid crystal panel 211, the panel control circuit 252 applies an electric field to the dichroic liquid crystal layer 34 of the dichroic liquid crystal panel 17, so that the second linearly polarized light LP2 of the external light can be absorbed by the dichroic dye 34B contained in the dichroic liquid crystal layer 34. This suppresses "glare" caused by reflection of external light, so that the display quality (contrast performance) of the image can be improved. Also, for example, when the liquid crystal display device 210 is turned off, no electric field is applied to the dichroic liquid crystal layer 34, so that the unpolarized light NP, the first linearly polarized light LP1, and the second linearly polarized light LP2 all pass through the dichroic liquid crystal panel 17 while maintaining their polarization states. This allows the utilization efficiency of the external light to be kept sufficiently high.

[0066] Next, the "external light utilization rate" which is the utilization rate of external light, and the "backlight light utilization rate" which is the utilization rate of light emitted from the backlight device 212 were calculated for the cases where the liquid crystal display device 210 was powered on to display an image, the above-mentioned black display was performed, and the liquid crystal display device 210 was powered off to display a white color. The prerequisites for calculating the external light utilization rate and the backlight light utilization rate are as shown in the table of FIG. 15. The prerequisites for the first polarizer 213, the second polarizer 214, the liquid crystal panel 211, the first reflective polarizer 215, and the second reflective polarizer 216 are the same as those of the second embodiment (see FIG. 10). The prerequisites for the dichroic liquid crystal panel 17 will be described. When an electric field is applied to the dichroic liquid crystal layer 34 of the dichroic liquid crystal panel 17 (indicated as "ON" in FIG. 15), the transmittance of the first linearly polarized light LP1 in the dichroic liquid crystal panel 17 is set to 10%, and the transmittance of the second linearly polarized light LP2 is set to 0%, as shown in FIG. 15. At this time, almost all of the second linearly polarized light LP2 is absorbed by the dichroic dye 34B. On the other hand, when no electric field is applied to the dichroic liquid crystal layer 34 of the dichroic liquid crystal panel 17 (indicated as "OFF" in FIG. 15), the transmittance of unpolarized light NP is set to 95%. At this time, 5% of the unpolarized light NP is absorbed by the dichroic dye 34B.

[0067] The calculation results of the external light utilization rate and the backlight utilization rate are as shown in the table of Fig. 16. The items described in the table of Fig. 16 (the electric field of the liquid crystal panel 211, the polarization state of the light (external light) incident on the liquid crystal display device 210, the polarization state of the light emitted from the liquid crystal display device 210, etc.) are the same as the items described in the table of Fig. 8 shown in the above-mentioned embodiment 1. In this embodiment, an electric field is applied to the dichroic liquid crystal layer 34 of the dichroic liquid crystal panel 17 by the panel control circuit 252 both during video display and during black display. On the other hand, during white display, the power supply of the liquid crystal display device 210 is turned off, so that no electric field is applied to the dichroic liquid crystal layer 34 of the dichroic liquid crystal panel 17.

[0068] The polarization state of the incident light will be described. In both the image display and black display, the incident light is unpolarized NP outside, and when it enters the dichroic liquid crystal panel 17, most of the first linearly polarized light LP1 (about 90%) and almost all of the second linearly polarized light LP2 are absorbed by the dichroic dye 34B, and only a part of the first linearly polarized light LP1 (about 10%) is transmitted through the dichroic liquid crystal layer 34. Since the incident light transmitted through the dichroic liquid crystal panel 17 does not contain the second linearly polarized light LP2, when it enters the second reflective polarizer 216, the first linearly polarized light LP1 is transmitted as it is. On the other hand, when white is displayed, the incident light is unpolarized NP outside, and when it enters the dichroic liquid crystal panel 17, most of it is transmitted through the dichroic liquid crystal layer 34 while maintaining its polarization state. Since the incident light transmitted through the dichroic liquid crystal panel 17 is unpolarized light NP, when it is incident on the second reflective polarizing plate 216, the second linearly polarized light LP2 is reflected and only the first linearly polarized light LP1 is transmitted. Note that, during any of video display, black display, and white display, the polarization state of the incident light at the first polarizing plate 213, the liquid crystal panel 211, the second polarizing plate 214, the first reflective polarizing plate 215, the reflective sheet 44, and the LEDs 240, 241, and 242 is as described in the second embodiment.

[0069] The polarization state of the emitted light will be described. In both the image display and the white display, the polarization state of the emitted light in the first polarizer 213, the liquid crystal panel 211, the second polarizer 214, the first reflective polarizer 215, the reflection sheet 44, and each of the LEDs 240, 241, and 242 (see FIG. 4) is as described in the first embodiment. In both the image display and the white display, the emitted light transmitted through the second reflective polarizer 216 does not include the second linearly polarized light LP2, so that the first linearly polarized light LP1 is transmitted when it enters the dichroic liquid crystal panel 17. In detail, in the image display, most of the first linearly polarized light LP1 (about 90%) is absorbed by the dichroic dye 34B, and a part of the first linearly polarized light LP1 (about 10%) is transmitted. In contrast, in the white display, most of the first linearly polarized light LP1 (about 95%) is transmitted without being absorbed by the dichroic dye 34B.

[0070] Next, the calculation results of the external light utilization rate and the backlight utilization rate will be described. According to FIG. 16, the external light utilization rate during video display was 0.7% at its maximum (value during full-screen white display), and the backlight utilization rate was 8.1% at its maximum. Thus, since the backlight utilization rate during video display tends to be 10 times higher than the external light utilization rate, even in an environment where there is a lot of external light, reflections due to external light are sufficiently suppressed, and sufficiently high display quality can be obtained. However, compared with the above-mentioned embodiment 2 (see FIG. 11), since the backlight utilization rate is about 1 / 10, it is necessary to increase the amount of light emitted by each of the LEDs 240, 241, and 242 to obtain sufficient display brightness. The reason why the backlight utilization rate is lower than that of embodiment 2 is that most of the light emitted from each of the LEDs 240, 241, and 242 is absorbed by the dichroic dye 34B of the dichroic liquid crystal panel 17. Moreover, the external light utilization rate during black display was 0%. That is, the utilization rate of external light during black display is equivalent to that of the above-described embodiment 1 (see FIG. 8), and glare due to external light is suppressed well compared to embodiment 2 (see FIG. 11). This is because most of the external light is absorbed by the dichroic dye 34B of the dichroic liquid crystal panel 17, and the remaining first linearly polarized light LP1 is converted to the second linearly polarized light LP2 when passing through the liquid crystal panel 211 and absorbed by the second polarizing plate 214.

[0071] On the other hand, the external light utilization rate during white display is 74.9%. In this embodiment, most of the external light passes through the dichroic liquid crystal panel 17 as unpolarized NP, so the utilization rate can be improved by efficiently reflecting the second linearly polarized light LP2 contained in the unpolarized light NP that has passed through the dichroic liquid crystal panel 17 by the second reflective polarizer 216. The reason why the external light utilization rate during white display is lower than that of the second embodiment (see FIG. 11) is that a part (about 5%) of the reflected light (second linearly polarized light LP2) by the second reflective polarizer 216 is absorbed when passing through the dichroic liquid crystal panel 17, and a part (about 5%) of the reflected light by the reflective sheet 44 (see FIG. 4) is absorbed when passing through the dichroic liquid crystal panel 17. However, the external light utilization rate during white display can be increased by about 40% compared to the above-mentioned first embodiment (see FIG. 8). Thus, according to this embodiment, white display can be performed with sufficient brightness.

[0072] As described above, according to this embodiment, the dichroic liquid crystal panel 17 is provided with the second reflective polarizing plate 216 sandwiched between the first polarizing plate 213 and the dichroic liquid crystal panel 17. The dichroic liquid crystal panel 17 has a dichroic liquid crystal layer 34 containing a dichroic dye 34B, and the orientation state of the dichroic liquid crystal layer 34 changes with application of an electric field. When no electric field is applied to the dichroic liquid crystal layer 34, the unpolarized light NP, the first linearly polarized light LP1, and the second linearly polarized light LP2 are all transmitted while maintaining their polarization state. When an electric field is applied to the dichroic liquid crystal layer 34 by the panel control circuit 252, the first linearly polarized light LP1 is selectively transmitted, and the second linearly polarized light LP2 is absorbed by the dichroic dye 34B. When an image is displayed on the liquid crystal panel 211, the second linearly polarized light LP2 of external light can be absorbed by the dichroic dye 34B contained in the dichroic liquid crystal layer 34 by applying an electric field to the dichroic liquid crystal layer 34 of the dichroic liquid crystal panel 17 by the panel control circuit 252. This suppresses "glares" caused by reflection of external light, improving the display quality (contrast performance) of the image. Furthermore, for example, when the liquid crystal display device 210 is turned off, no electric field is applied to the dichroic liquid crystal layer 34, so that the unpolarized light NP, the first linearly polarized light LP1, and the second linearly polarized light LP2 all pass through the dichroic liquid crystal panel 17 while maintaining their polarization states. This makes it possible to maintain a sufficiently high utilization efficiency of external light.

[0073] <Embodiment 4> A fourth embodiment will be described with reference to Fig. 17 or 18. In this fourth embodiment, a light detection sensor 54 is added to the third embodiment. Note that a duplicated description of the structure, operation, and effects similar to those of the third embodiment will be omitted.

[0074] As shown in Fig. 17, the liquid crystal display device 310 according to this embodiment includes a light detection sensor (light detector) 54 that detects the amount of external light. The light detection sensor 54 is made of a photoelectric sensor or the like, and can output a signal corresponding to the detected amount of light to the control unit 350. A panel control circuit 352 included in the control unit 350 controls the driving of the dichroic liquid crystal panel 317 according to the amount of external light detected by the light detection sensor 54. In detail, the panel control circuit 352 compares the amount of external light detected by the light detection sensor 54 with a preset threshold value, and if the amount of detected external light is equal to or greater than the threshold value, drives the dichroic liquid crystal panel 317 to apply an electric field to the dichroic liquid crystal layer 34 (see Fig. 13), and if the amount of detected external light is less than the threshold value, does not drive the dichroic liquid crystal panel 317 and does not apply an electric field to the dichroic liquid crystal layer 34. As described above, in this embodiment, the panel control circuit 352 can display images in either a first display mode in which the dichroic liquid crystal panel 317 is driven, or a second display mode in which the dichroic liquid crystal panel 317 is not driven.

[0075] According to this embodiment, when an image is displayed on the liquid crystal panel 311, if the amount of external light detected by the light detection sensor 54 is equal to or greater than a threshold value, the panel control circuit 352 applies an electric field to the dichroic liquid crystal layer 34, so that the second linearly polarized light LP2 of the external light can be absorbed by the dichroic dye 34B contained in the dichroic liquid crystal layer 34. This makes it possible to effectively suppress "reflection" caused by reflection of external light that is equal to or greater than the threshold value. On the other hand, when an image is displayed on the liquid crystal panel 311, if the amount of external light detected by the light detection sensor 54 is less than the threshold value, the panel control circuit 352 does not apply an electric field to the dichroic liquid crystal layer 34, so that the light emitted from each of the LEDs 340, 341, and 342 is prevented from being absorbed by the dichroic dye 34B. This makes it possible to improve the display brightness of the image. In this case, since the amount of external light is less than the threshold value, "reflection" caused by reflection of external light is sufficiently suppressed.

[0076] Next, for the case where an image is displayed in the first display mode and the case where an image is displayed in the second display mode, the "external light utilization rate" which is the utilization rate of external light and the "backlight light utilization rate" which is the utilization rate of light emitted from the backlight device 312 were calculated. The prerequisites for calculating the external light utilization rate and the backlight light utilization rate are as described in the second and third embodiments (see Figs. 10 and 15).

[0077] The calculation results of the external light utilization rate and the backlight utilization rate are as shown in the table of FIG. 18. The items described in the table of FIG. 18 (the electric field of the liquid crystal panel 311, the polarization state of the light (external light) incident on the liquid crystal display device 310, the polarization state of the light emitted from the liquid crystal display device 310, etc.) are the same as the items described in the table of FIG. 8 shown in the above-mentioned embodiment 1. In this embodiment, when an image is displayed in the first display mode (when the amount of external light detected by the light detection sensor 54 is equal to or greater than the threshold), an electric field is applied to the dichroic liquid crystal layer 34 of the dichroic liquid crystal panel 317 by the panel control circuit 352. On the other hand, when an image is displayed in the second display mode (when the amount of external light detected by the light detection sensor 54 is less than the threshold), the panel control circuit 352 does not apply an electric field to the dichroic liquid crystal layer 34 of the dichroic liquid crystal panel 317.

[0078] The polarization state of the incident light will be described. When an image is displayed in the first display mode, the incident light is unpolarized NP outside, and when it is incident on the dichroic liquid crystal panel 317, most of the first linearly polarized light LP1 (about 90%) and almost all of the second linearly polarized light LP2 are absorbed by the dichroic dye 34B, and only a part of the first linearly polarized light LP1 (about 10%) is transmitted through the dichroic liquid crystal layer 34. Since the incident light that has transmitted through the dichroic liquid crystal panel 317 does not contain the second linearly polarized light LP2, when it is incident on the second reflective polarizer 16, the first linearly polarized light LP1 is transmitted as it is. On the other hand, when an image is displayed in the second display mode, the incident light is unpolarized NP outside, and when it is incident on the dichroic liquid crystal panel 317, most of it is transmitted through the dichroic liquid crystal layer 34 while maintaining its polarization state. Since the incident light transmitted through the dichroic liquid crystal panel 317 is unpolarized light NP, when it is incident on the second reflective polarizing plate 16, the second linearly polarized light LP2 is reflected and only the first linearly polarized light LP1 is transmitted. Note that, in both cases when an image is displayed in the first display mode and when an image is displayed in the second display mode, the polarization state of the incident light at the first polarizing plate 13, the liquid crystal panel 311, the second polarizing plate 14, the first reflective polarizing plate 15, the reflective sheet 44, and the LEDs 340, 341, and 342 is as described in the second embodiment.

[0079] The polarization state of the emitted light and the like will be described. In both the first display mode and the second display mode, the polarization state of the emitted light at the first polarizer 13, the liquid crystal panel 311, the second polarizer 14, the first reflective polarizer 15, the reflection sheet 44, and the LEDs 340, 341, and 342 is as described in the first embodiment. In both the first display mode and the second display mode, the emitted light transmitted through the second reflective polarizer 16 does not include the second linearly polarized light LP2, and therefore, when the emitted light is incident on the dichroic liquid crystal panel 317, the first linearly polarized light LP1 is transmitted. In more detail, when the image is displayed in the first display mode, most of the first linearly polarized light LP1 (about 90%) is absorbed by the dichroic dye 34B, and a part of the first linearly polarized light LP1 (about 10%) is transmitted. In contrast, when an image is displayed in the second display mode, most (approximately 95%) of the first linearly polarized light LP1 is transmitted without being absorbed by the dichroic dye 34B.

[0080] Next, the calculation results of the external light utilization rate and the backlight utilization rate will be described. According to Fig. 18, the external light utilization rate and the backlight utilization rate when displaying an image in the first display mode are the same as when displaying an image in the above-mentioned embodiment 2 (see Fig. 16), and the external light utilization rate is 0.7% at the maximum (value when the entire screen is displayed in white), and the backlight utilization rate is 8.1% at the maximum. Since the image display in this first display mode is performed when the amount of external light detected by the light detection sensor 54 is equal to or greater than a threshold value, the backlight utilization rate is 10 times higher than the external light utilization rate, so that reflections caused by external light present in an amount greater than the threshold value are sufficiently suppressed, and a sufficiently high display quality is obtained.

[0081] The external light utilization rate during image display in the second display mode is the same as that during white display in the above-described second embodiment (see FIG. 16), and is 74.9% at the maximum. On the other hand, the backlight light utilization rate during image display in the second display mode is 77.2% at the maximum, which is slightly less than 10 times higher than the backlight light utilization rate during image display in the first display mode. This is because the light emitted from each of the LEDs 340, 341, and 342 is hardly absorbed by the dichroic dye 34B of the dichroic liquid crystal panel 317. Thus, both the external light utilization rate and the backlight light utilization rate during image display in the second display mode are high, with a maximum value of 70% or more, and there is a concern that the user may see reflections due to external light. In this regard, images are displayed in the second display mode when the amount of external light detected by the light detection sensor 54 is below a threshold value, so that reflections due to external light are inherently less likely to occur, while the backlight light utilization rate is sufficiently high to obtain sufficiently high display quality.

[0082] As described above, according to this embodiment, the light detection sensor 54 for detecting the amount of external light is provided, and the panel control circuit 352 applies an electric field to the dichroic liquid crystal layer 34 when the amount of external light detected by the light detection sensor 54 is equal to or greater than a threshold value, and does not apply an electric field to the dichroic liquid crystal layer 34 when the amount of external light detected by the light detection sensor 54 is less than the threshold value. When an image is displayed on the liquid crystal panel 311, when the amount of external light detected by the light detection sensor 54 is equal to or greater than a threshold value, the panel control circuit 352 applies an electric field to the dichroic liquid crystal layer 34, so that the second linearly polarized light LP2 of the external light can be absorbed by the dichroic dye 34B contained in the dichroic liquid crystal layer 34. This makes it possible to effectively suppress "glare" caused by reflection of external light present at or above the threshold value. On the other hand, when an image is displayed on the liquid crystal panel 311, if the amount of external light detected by the light detection sensor 54 is less than the threshold value, the panel control circuit 352 does not apply an electric field to the dichroic liquid crystal layer 34, and therefore the light emitted from each of the LEDs 340, 341, and 342 is prevented from being absorbed by the dichroic dye 34B. This makes it possible to improve the display brightness of the image. In this case, since the amount of external light is less than the threshold value, "glares" caused by reflection of external light are sufficiently suppressed.

[0083] <Other embodiments> The technology disclosed in this specification is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included in the technical scope.

[0084] (1) As a modification of each embodiment, the first reflective polarizing plate 15, 115, 215 may be omitted.

[0085] (2) As a modification of the third and fourth embodiments, the second reflective polarizing plate 16, 216 may be omitted.

[0086] (3) Instead of the reflective sheet 44, a reflective portion may be provided integrally with the front main surface of the LED board 43 by printing or the like.

[0087] (4) In the configurations described in the third and fourth embodiments, the dichroic liquid crystal panels 17 and 317 may be controlled by a control circuit different from the panel control circuits 252 and 352. In other words, the liquid crystal panels 11, 111, 211, and 311 and the dichroic liquid crystal panels 17 and 317 may be controlled by different control circuits.

[0088] (5) The panel control circuit 52, 252, 352 may control the liquid crystal panel 11, 111, 211, 311 so that one frame period includes a white data writing period in which an image signal related to a white display gradation in which the gradations of red, green, and blue are the same is supplied to each pixel electrode 24, and a white display period in which no image signal is supplied and the white display gradation (white data) of each pixel electrode 24 is maintained.

[0089] (6) The specific manner in which images are displayed in the field sequential format (such as the order of the display periods for each color) can be changed as appropriate.

[0090] (7) The backlight devices 12, 112, 212, 312 may be of an edge light type other than a direct type. The edge light type backlight device (illumination device) has red LEDs 40, 240, 340, green LEDs 41, 241, 341, and blue LEDs 42, 242, 342, a light guide plate that guides the light emitted from the red LEDs 40, 240, 340, green LEDs 41, 241, 341, and blue LEDs 42, 242, 342, and a reflective sheet (reflection section) that reflects the light from the light guide plate. The light guide plate has a light-entering end surface facing the light-emitting surfaces 40A, 41A, 42A of the red LEDs 40, 240, 340, the green LEDs 41, 241, 341, and the blue LEDs 42, 242, 342, a light-emitting main surface facing the front side for emitting light, and an opposite main surface facing the back side. The reflective sheet is disposed opposite the opposite main surface of the light guide plate.

[0091] (8) It is also possible to use light sources other than LEDs (laser light sources, organic EL (Electro Luminescence), etc.) as the red light source, green light source, and blue light source.

[0092] (9) The display mode of the liquid crystal panels 11, 111, 211, and 311 may be VA (vertical alignment) mode, IPS (in plane switching) mode, or the like. [Explanation of symbols]

[0093] 10,110,210,310...Liquid crystal display device, 11,111,211,311...Liquid crystal panel (display panel), 12,112,212,312...Backlight device (illumination device), 13,113,213...First polarizing plate, 14,114,214...Second polarizing plate, 15,115,215...First reflective polarizing plate, 16,216...Second reflective polarizing plate, 17,317...Dichroic liquid crystal panel, 22...Liquid crystal layer, 34...Dichroic liquid crystal layer, 34B...Dichroic dye, 40,240,340...Red LED (red light source), 41,2 41,341...Green LED (green light source), 42,242,342...Blue LED (blue light source), 44...Reflective sheet (reflecting section), 52,252,352...Panel control circuit (first control section), 53...Backlight control circuit (second control section), 54...Light detection sensor, AX1...First absorption axis, AX2...Second absorption axis, LP1...First linearly polarized light, LP2...Second linearly polarized light, NP...Non-polarized light, RX1...First reflection axis, RX2...Second reflection axis, TX1...First transmission axis, TX2...Second transmission axis, TX3...Third transmission axis, TX4...Fourth transmission axis

Claims

1. a first polarizing plate having a first transmission axis that transmits the first linearly polarized light and a first absorption axis that absorbs the second linearly polarized light, the first linearly polarized light and the second linearly polarized light having mutually orthogonal polarization directions; a second polarizing plate having a second transmission axis that transmits the first linearly polarized light and a second absorption axis that absorbs the second linearly polarized light; a liquid crystal panel having a liquid crystal layer sandwiched between the first polarizing plate and the second polarizing plate, the liquid crystal layer changing its alignment state in response to application of an electric field; an illumination device disposed between the liquid crystal panel and the second polarizing plate; A first control unit that controls driving of the liquid crystal panel; A second control unit that controls the driving of the lighting device, When no electric field is applied to the liquid crystal layer, the liquid crystal panel transmits the first linearly polarized light having passed through the first polarizing plate or the second polarizing plate while maintaining its polarization state; the illumination device includes a red light source that emits red light, a green light source that emits green light, a blue light source that emits blue light, and a reflector that reflects the light toward the second polarizing plate; the first control unit applies an electric field to the liquid crystal layer to change a polarization state of the first linearly polarized light transmitted through the first polarizing plate or the second polarizing plate; The second control unit sequentially turns on the red light source, the green light source, and the blue light source.

2. The liquid crystal display device according to claim 1 , wherein the first control unit applies a predetermined electric field to the liquid crystal layer and converts the first linearly polarized light transmitted through the first polarizer or the second polarizer into the second linearly polarized light.

3. a first reflective polarizing plate disposed between the second polarizing plate and the illumination device; 3. The liquid crystal display device according to claim 1, wherein the first reflective polarizing plate has a third transmission axis that transmits the first linearly polarized light and a first reflection axis that reflects the second linearly polarized light.

4. a second reflective polarizing plate disposed between the liquid crystal panel and the first polarizing plate, 3. The liquid crystal display device according to claim 1, wherein the second reflective polarizing plate has a fourth transmission axis that transmits the first linearly polarized light and a second reflection axis that reflects the second linearly polarized light.

5. a dichroic liquid crystal panel disposed between the first polarizing plate and the second reflective polarizing plate, The liquid crystal display device of claim 4, wherein the dichroic liquid crystal panel has a dichroic liquid crystal layer containing a dichroic dye, the alignment state of which changes when an electric field is applied, and when no electric field is applied to the dichroic liquid crystal layer, unpolarized light, the first linearly polarized light, and the second linearly polarized light are all transmitted while maintaining their polarization states, and when an electric field is applied to the dichroic liquid crystal layer by the first control unit, the first linearly polarized light is selectively transmitted, and the second linearly polarized light is absorbed by the dichroic dye.

6. A light detection sensor is provided to detect the amount of external light, The liquid crystal display device of claim 5, wherein the first control unit applies an electric field to the dichroic liquid crystal layer when the amount of external light detected by the light detection sensor is equal to or greater than a threshold value, and does not apply an electric field to the dichroic liquid crystal layer when the amount of external light detected by the light detection sensor is less than the threshold value.

Images