Patent Publication Number: US-2012044224-A1

Title: Liquid crystal display device

Description:
TECHNICAL FIELD 
     The present invention relates to a liquid crystal display device, and specifically to a liquid crystal display device including a plurality of light sources located a rear surface of a liquid crystal display section. The present invention claims the benefit of priority based on the legislation of a member country of the Paris Convention or in a country into which the PCT International Application enters the national phase based upon Japanese Patent Application No. 2009-121255 filed on May 19, 2009. The contents of this patent application is incorporated herein by reference. 
     BACKGROUND ART 
     One type of liquid crystal display (LCD) device includes a backlight device located on the side of a rear surface of a liquid crystal display section including a liquid crystal layer. The liquid crystal display section has a structure in which the liquid crystal layer is held between two substrates. Through a manipulation of a voltage applied between the two substrates, the liquid crystal layer is put into a form of shielding light or a form of transmitting light. The backlight device directs light toward the rear surface of the liquid crystal display section. The liquid crystal display section includes a plurality of pixels. When the liquid crystal layer is manipulated while the light which has passed the liquid crystal layer is allowed to pass a color filter, light of a desired color is displayed by each of the pixels. 
     Regarding such a liquid crystal display device, for example, Japanese Patent Laid-Open Publication No. 2005-121997 (Patent Document 1) discloses a method for adjusting the brightness of the backlight device. According to the disclosure of this publication, a plurality of light sensors are attached at different positions on a peripheral portion on the side of a front surface (on the side of a display plane) of a liquid crystal display device. Illuminance data of external light is captured at every unit time and subjected to a comparative computation. When a numerical value representing the result of the comparative computation exceeds a prescribed value, the illuminance of the peripheral portion of the liquid crystal panel is regarded as being partially changed and therefore the brightness of the backlight device is not adjusted. When the numerical value representing the result of the comparative computation is the prescribed value or less, the illuminance data of the external light is processed by a predetermined operation procedure to calculate the optimum value for controlling the brightness of the backlight device, and thus the brightness of the backlight device is automatically adjusted. According to this method for adjusting the brightness, even when the illuminance of the peripheral portion of the liquid crystal panel is partially changed, the luminance of the backlight device is not changed, and only when the illuminance of the environment in which the liquid crystal panel is installed is uniformly changed, the brightness of the backlight device is automatically adjusted in accordance with the illuminance of the environment. 
     Japanese Patent Laid-Open Publication No. 2008-209508 (Patent Document 2) describes a device using a light emitting diode as a light source of a backlight device. According to the description of this publication, the backlight device includes a plurality of partial lighting sections which can be controlled independently from each other. The light emission amount of each partial lighting section is controlled in accordance with the amount of environmental light around the device and the luminance distribution of the displayed video included in the video signal. Specifically, when the amount of the environmental light is smaller than a prescribed threshold value, the light emission amount of each partial lighting section, which emits light with a prescribed luminance or higher, is controlled to be decreased. When the amount of the environmental light is larger than the prescribed threshold value, the light emission amount of each partial lighting section, which emits light with the prescribed luminance or higher, is controlled to be increased. It is disclosed that in the case where a plurality of light receiving elements (external light sensors) for sensing the environmental light are provided at, for example, different positions with respect to a light source section from each other, a backlight driving section is controlled by finding an average value of light receiving data from the plurality of light receiving elements. 
     CITATION LIST 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent Laid-Open Publication No. 2005-121997 
         Patent Document 2: Japanese Patent Laid-Open Publication No. 2008-209508 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     A large liquid crystal display device having a side longer than 1 meter used for an application of TVs or the like has a large screen. Therefore, a part of the screen is likely to be illuminated differently from other parts thereof. For example, even when the liquid crystal display device is located indoors, the screen is illuminated by external light (e.g., by illumination in the room or light coming through the window) and as a result, a part of the screen may become brighter than the other parts. More specifically, there may be cases where a top part of the screen is brighter than a bottom part thereof due to the influence of the illumination in the room, or a part on one side of the screen is brighter than a part on the other side due to the influence of light coming through a window which is located to the one side of the liquid crystal display device. In such cases, a part of the screen of the liquid crystal display device may become difficult to view. 
     Solution to the Problem 
     In one embodiment of the present invention, a liquid crystal display device includes a liquid crystal display section including a plurality of pixels; and a backlight device for directing light from a plurality of light sources toward a rear surface of the liquid crystal display section. Along an edge portion of a front surface of the liquid crystal display section, light receiving sensors are located at a plurality of sites. The liquid crystal display device also includes a control section for dividing the liquid crystal display section into a plurality of areas, and controlling the liquid crystal display section and/or the backlight device based on light receiving information obtained from the light receiving sensors to perform control of adjusting a contrast of each of the areas independently. 
     According to this liquid crystal display device, for example, the contrast of each of the areas can be appropriately adjusted independently in consideration of the influence of external light. Owing to this, a screen of the liquid crystal display section can be prevented from becoming partially difficult to view by being illuminated by the external light, and the liquid crystal display device can be made easier to view as a whole. 
     In this case, the plurality of areas into which the liquid crystal display section is divided may be preset by the control section in accordance with the plurality of sites at which the light receiving sensors are located. The contrast of borders between the areas may be controlled such that the contrast is gradually changed between the areas. 
     In the case where the liquid crystal display section includes a generally rectangular screen, the light receiving sensors may be respectively located on four sides surrounding the generally rectangular screen. The present invention is not limited to this, and in the case where the liquid crystal display section includes the generally rectangular screen, the light receiving sensors may be respectively located at four corners of a peripheral edge portion of the screen. The control section may include a switching section for switching between a mode of performing control of adjusting the contrast of each of the areas independently and a mode of not performing the control of adjusting the contrast. The control section may perform control of adjusting the contrast of each of the areas independently in the case where certain light receiving information is obtained from the light receiving sensors for a predefined time duration. A structure may be adopted in which the rear surface of the liquid crystal display section is divided into areas, different light guide plates are respectively located for the areas, and the light sources direct light toward the rear surface of the liquid crystal display section via the light guide plates. The control section may adjust the contrast of each of the plurality of areas of the screen of the liquid crystal display section independently based on the light receiving information obtained from the light receiving sensors. The control section may adjust the contrast of each of the plurality of areas independently based on a video signal and the light receiving information obtained from the light receiving sensors. The light sources may be light emitting diodes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a liquid crystal display device according to one embodiment of the present invention. 
         FIG. 2  is a block diagram schematically showing a structure of the liquid crystal display device according to the embodiment of the present invention. 
         FIG. 3  is a cross-sectional view showing a structure of a liquid crystal panel of the liquid crystal display device according to the embodiment of the present invention. 
         FIG. 4A  is a partially enlarged plan view showing locations of light emitting diodes of the liquid crystal display device according to the embodiment of the present invention. 
         FIG. 4B  is a view showing the locations of the light emitting diodes of the liquid crystal display device according to the embodiment of the present invention. 
         FIG. 5  is a schematic view of the liquid crystal display device according to the embodiment of the present invention. 
         FIG. 6  is a view showing a circuit configuration of each of pixels of the liquid crystal display device according to the embodiment of the present invention. 
         FIG. 7  is a block diagram schematically showing a backlight driving circuit of the liquid crystal display device according to the embodiment of the present invention. 
         FIG. 8  is a block diagram schematically showing a structure of a liquid crystal display device according to another embodiment of the present invention. 
         FIG. 9  is a control flowchart of a liquid crystal display device according to one embodiment of the present invention. 
         FIG. 10  is a control flowchart of a liquid crystal display device according to another embodiment of the present invention. 
         FIG. 11  is a block diagram showing control performed on a liquid crystal display device according to still another embodiment of the present invention. 
         FIG. 12  is a view conceptually showing contrast adjustment control. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a liquid crystal display device according to one embodiment of the present invention will be described with reference to the drawings. The figures are provided for easier understanding of the present invention and embodiments thereof. Therefore, the sizes in the figures do not reflect the sizes of actual products embodying the present invention. The figures, even illustrating the same embodiment, do not necessarily match each other. Elements having the same functions bear the same reference characters for the sake of convenience of explanation. 
       FIG. 1  is a vertical cross-sectional view of a liquid crystal display device  100  according to one embodiment of the present invention.  FIG. 2  is a view schematically showing a structure of the liquid crystal display device  100 . As shown in  FIG. 1 , the liquid crystal display device  100  includes a backlight device  20  located on a rear surface of a liquid crystal display section  10 . In  FIG. 2 , the liquid crystal display section  10  and the backlight device  20  are shown separately for the sake of convenience of explanation. 
     As shown in  FIG. 1 , the liquid crystal display device  100  includes a liquid crystal panel  10  as the liquid crystal display section and the backlight device  20 . The backlight device  20  directs light from a plurality of light sources  22  toward the rear surface of the liquid crystal panel  10 . In this embodiment, light emitting diodes  22  (LEDs) are adopted as the light sources  22 . The liquid crystal display device  100  includes light receiving sensors  122   a  through  122   d  at a plurality of sites along an edge portion of a front surface of the liquid crystal panel  10 . As shown in  FIG. 8  and  FIG. 9 , a control section  200  obtains light receiving informational through d 1  from the light receiving sensors  122   a  through  122   d  (S 1 ). Next, based on the obtained light receiving informational a 1  through d 1  and a video signal, the control section  200  creates control signals for the plurality of light sources (S 2 ). Then, based on the created control signals, the control section  200  adjusts the brightness of the backlight device  20  (S 3 ). At this point, a screen  10   a  of the liquid crystal panel  10  is divided into a plurality of areas A 1  through D 1  (see  FIG. 2 ), and the contrast of each of the areas A 1  through D 1  is adjusted independently based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d.    
     In the liquid crystal display device  100 , even in the case where, for example, a part of the screen  10   a  is difficult to view by being illuminated by external light, the contrast of each of the areas A 1  through D 1  is appropriately adjusted independently in consideration of the influence of the external light. Therefore, the screen  10   a  of the liquid crystal display device  100  can be made easier to view as a whole. Hereinafter, the structure of the liquid crystal display device  100  according to this embodiment will be described in the order of the liquid crystal panel  10  and the backlight device  20 . Then, control on the liquid crystal display device  100  will be described. 
     &lt;Liquid Crystal Panel  10 &gt; 
     In this embodiment, the liquid crystal panel  10  of the liquid crystal display device  100  has a generally rectangular overall shape, and includes a pair of light-transmissive substrates  11  and  12  (in this example, glass substrates) holding a liquid crystal layer  13  therebetween. In this embodiment, among the substrates  11  and  12 , the substrate on the rear side (on the side of a rear surface; the backlight device side) is the array substrate  11  (TFT substrate), and the substrate on the front side (on the side of a front surface; the display side) is the color filter substrate  12  (CF substrate). 
     In this embodiment, as shown in  FIG. 1 , the array substrate  11  and the color filter substrate  12  are located to face each other. The array substrate  11  and the color filter substrate  12  include a pixel area (area in which pixels are formed) which forms the screen  10   a  of the liquid crystal display device  100 . Between the array substrate  11  and the color filter substrate  12 , a seal  15  is provided so as to enclose a peripheral portion of the pixel area (external peripheral edge portion) in a circumferential direction. In a space enclosed by the array substrate  11 , the color filter substrate  12  and the seal  15 , the liquid crystal layer  13  is formed. In the liquid crystal layer  13 , a liquid crystal material containing liquid crystal molecules is enclosed. In such a liquid crystal material (liquid crystal molecules), the alignment direction of the liquid crystal molecules is manipulated by an electric field generated between the array substrate  11  and the color filter substrate  12 . Thus, optical characteristics of the liquid crystal layer  13  are changed. 
       FIG. 3  is a cross-sectional view showing, in enlargement, a part of the liquid crystal panel  10 , the part including the pixels formed therein. As shown in  FIG. 3 , spacers  16  are provided between the array substrate  11  and the color filter substrate  12 . The array substrate  11  and the color filter substrate  12  are kept distanced from each other by a prescribed gap by means of the spacers  16 . Now, a structure of the array substrate  11  and a structure of the color filter substrate  12  will be described sequentially. 
     As shown in  FIG. 3 , the array substrate  11  includes pixel electrodes  42 , bus lines  43 , a flattening layer  44 , and an alignment film  46 , and thin film transistors  47  (TFTs; see  FIG. 5  and  FIG. 6 ), which are formed on the side of a front surface of a glass substrate  41  (on the liquid crystal layer  13  side). The pixel electrodes  42  are formed of ITO (indium tin oxide), which is a transparent conductive material. These pixel electrodes  42  are each supplied with a voltage in accordance with an image via corresponding bus lines  43  and a corresponding thin film transistor  47  at a prescribed timing. The flattening layer  44  is formed of an insulating material and covers the pixel electrodes  42  and the bus lines  43 . On the flattening layer  44 , the alignment film  46  formed of polyimide or the like is formed. In  FIG. 3 , the bus lines  43  are data signal lines. As shown in  FIG. 5  and  FIG. 6 , the array substrate  11  includes the data signal lines  43  and also various other signal lines. The wiring structure of the signal lines and control thereon in the array substrate  11  and the liquid crystal panel  10  will be described later. 
     The color filter substrate  12  includes a black matrix  52 , color filters  53 , a flattening layer  54 , a counter electrode  55 , and an alignment film  56  (horizontal alignment film), which are formed on the side of a rear surface of a glass substrate  51  (on the liquid crystal layer  13  side). The black matrix  52  is formed of a non-light-transmissive material (e.g., metal such as Cr (chromium) or the like), and is provided between the pixels so as to demarcate the pixels. The color filters  53  are filters for adjusting the color of the light. In this embodiment, the color filters  53  are available in three colors of red (R), green (G) and blue (B). As shown in  FIG. 3 , one pixel electrode  42  of the array substrate  11  faces the color filter  53  of either one of the colors of R, G and B of the color filter substrate  12 . 
     As shown in  FIG. 3 , the flattening layer  54  of the color filter substrate  12  is formed so as to cover the black matrix  52  and the color filters  53 . The counter electrode  55  is formed so as to cover the flattening layer  54 . The counter electrode  55  is formed of ITO (indium tin oxide). The alignment film  56  is formed so as to cover the counter electrode  55 . The alignment film  56  faces the alignment film  46  of the array substrate  11 . A front surface of the alignment film  56  of the color filter substrate  12  has a structure of aligning the liquid crystal molecules. The alignment film  46  of the array substrate  11  and the alignment film  56  of the color filter substrate  12  are formed in order to determine the alignment direction of the liquid crystal molecules in the state where no voltage is applied. The alignment direction provided by the alignment film  56  of the color filter substrate  12  and the alignment direction provided by the alignment film  46  of the array substrate  11  are different by 90° from each other. 
     As shown in  FIG. 1  and  FIG. 3 , the liquid crystal panel  10  includes polarizing plates  17  and  18  respectively bonded on the side of a front surface of the color filter substrate  12  (glass substrate  51 ) and on the side of a rear surface of the array substrate  11  (glass substrate  41 ). In a so-called normally white type liquid crystal display device, the two polarizing plate  17  and  18  are located such that polarization axes thereof are perpendicular to each other. In a so-called normally black type liquid crystal display device, the two polarizing plate  17  and  18  are located such that polarization axes thereof are parallel to each other. In this embodiment, the liquid crystal panel  10  is controlled by the control section  200 . The control on the liquid crystal panel  10  will be described later. 
     As shown in  FIG. 1 , the liquid crystal panel  10  is supported while being held between a bezel  30  attached on the front side (on the side of the front surface) of the liquid crystal panel  10  and a frame  32  attached on the rear side (on the side of the rear surface) thereof. As shown in  FIG. 2 , the bezel  30  has an opening at a position corresponding to the screen  10   a  (pixel area) of the liquid crystal panel  10 , and forms an edge portion of the front surface of the liquid crystal panel  10  while being attached to the liquid crystal panel  10 . The frame  32  has an opening at a position corresponding to the screen  10   a  (pixel area) of the liquid crystal panel  10 . On the rear side of the liquid crystal panel  10 , the backlight device  20  supported by a backlight chassis  24  is attached. 
     The backlight chassis  24  has a shape of box opened toward the front side (toward the liquid crystal panel  10  side). In the opening of the backlight chassis  24 , a plurality of optical sheets  26  are located while being stacked. The backlight chassis  24  is attached on the rear side of the frame  32  for supporting the liquid crystal panel  10  in the state where the light emitting diodes  22  are directed toward the liquid crystal panel  10  mentioned above. The optical sheets  26  are held between a rear surface of the frame  32  and a front surface of the backlight chassis  24 . The optical sheets  26  include a plurality of sheets each having a required function (e.g., a diffuser, a diffusion sheet, a lens sheet and a luminance increasing sheet). Light from the backlight device  20  is directed toward the rear surface of the liquid crystal panel  10  via the optical sheets  26 . 
     &lt;Backlight Device  20 &gt; 
     As shown in  FIG. 1 , the backlight device  20  directs the light from the light sources  22  toward the rear surface of the liquid crystal panel  10 . In this embodiment, the backlight device  20  is located on the rear side of the liquid crystal panel  10  (right side in  FIG. 1 ) and illuminates the rear surface of the liquid crystal panel  10 . As the light sources of the backlight device  20 , a plurality of light emitting diodes  22  (LEDs) are used. On the inner side of the backlight chassis  24 , a reflector plate  25  is attached so as to face the rear surface of the liquid crystal panel  10 . The light emitting diodes  22  as the light sources are attached to the reflector plate  25  in the state where light emitting sections thereof are directed toward the rear surface of the liquid crystal panel  10 . The reflector plate  25  has a minor surface for reflecting light on a surface  25   a  (reflecting surface) facing the liquid crystal panel  10 . The light from the light emitting diodes  22  leaking toward the reflector plate  25  is reflected by the surface  25   a  toward the rear surface of the liquid crystal panel  10 . 
       FIGS. 4(   a ) and  4 ( b ) are each a plan view schematically showing the surface  25   a  of the reflector plate  25  facing the liquid crystal panel  10 .  FIG. 4(   a ) is a plan view showing, in enlargement, a portion represented by arrow  5   a  in  FIG. 4(   b ). In this embodiment, as shown in  FIG. 1  and  FIGS. 4(   a ) and  4 ( b ), the light emitting diodes  22  are located on the surface  25   a  facing the liquid crystal panel  10  in a generally dispersed state. In this embodiment, as shown in  FIGS. 4(   a ) and  4 ( b ), the light emitting diodes  22  are located as being arranged in a lattice. The light emitting diodes  22  are not limited to being arranged in a lattice as shown in  FIGS. 4(   a ) and  4 ( b ), and may be arranged such that, for example, the light emitting diodes  22  of every other column are positionally shifted (houndstooth check or zigzag arrangement). 
     As the light from the backlight device  20  of the liquid crystal display device  100 , white light may be desirable. In this case, the backlight device  20  in which the light emitting diodes  22  (LEDs) are used may have a structure in which white LEDs for emitting white light are arranged to emit white illumination light or a structure in which a plurality of LEDs of R (red), G (green), blue (B) and the like are arranged and light of these LEDs are mixed to emit white light. The white LEDs may be of a system of obtaining white color by combining a short-wavelength LED chip with RGB fluorescent substances, a system of obtaining white color by combining a blue LED chip with a yellow fluorescent substance, a system of obtaining white color as a mixture of light of LED chips of RGB three colors, a system of obtaining white color as a mixture of light of LED chips of two complementary colors, or the like. 
     By adjusting the power put to each light emitting diode  22 , the brightness is changed. In this case, for example, when the power put to each light emitting diode  22  is increased, the backlight device  20  is made brighter (the luminance is increased); whereas when the power put to each light emitting diode  22  is decreased, the backlight device  20  is made darker (the luminance is decreased). The brightness of the backlight device  20  may be adjusted using, for example, a pulse width modulation method or a PWM (pulse width modulation) system, by controlling the power put to each light emitting diode  22 . The backlight device  20  is controlled by the control section  200 . 
     &lt;Control Section  200 &gt; 
     The liquid crystal display device  100  includes the control section  200 . The control section  200  is an electronic processing device, and includes computation means including an MPU, a CPU or the like and having a computation function and storage means including a nonvolatile memory or the like. The control section  200  controls the liquid crystal display device  100  by use of a pre-stored program or a mounted electric or electronic circuit, such that the liquid crystal display device  100  exhibits required functions. (Hereinafter, regarding the control section  200 , the pre-stored program or the mounted electric or electronic circuit will be referred to as the “program, etc.” when appropriate.) The control on the liquid crystal display device  100  by means of the control section  200  is appropriately set and modified by the above-mentioned program, etc. 
     Specifically, in the liquid crystal display device  100 , a required control signal is sent to the backlight device  20  and the liquid crystal panel  10  in accordance with a video signal by the action of the control section  200 . In the liquid crystal panel  10 , a controlled voltage is applied to the color filter substrate  12  and the array substrate  11  to manipulate the liquid crystal molecules in the liquid crystal layer  13 . The liquid crystal molecules in the liquid crystal layer  13  are manipulated for each pixel independently (in more detail, for each of sub pixels defined by RGB independently), and thus the light from the backlight device  20  is shielded or passed and also the light transmittance is changed. Owing to this, the screen  10   a  can display, as a whole, a desired image in accordance with the video signal. 
     Here, the control on the liquid crystal panel  10  will be described first.  FIG. 5  schematically shows a structure of the liquid crystal panel  10  of an active matrix type.  FIG. 6  shows a circuit configuration provided for each of pixels  40  of the liquid crystal panel  10 . 
     The liquid crystal panel  10  has a structure in which the liquid crystal layer  13  is held between the pair of substrates (the array substrate  11  and the color filter substrate  12 ) facing each other as described above. In the liquid crystal panel  10 , the pixels  40  are arranged in a lattice. Each pixel  40  includes the thin film transistor  47  as a switching device. The thin film transistor  47  is provided in the array substrate  11  as an active matrix substrate. The array substrate  11  includes signal lines provided in a lattice (in a matrix). 
     In this embodiment, as shown in  FIG. 5 , a plurality of scanning signal lines  48 ( 1 ) through (m) and a plurality of data signal lines  43 ( 1 ) through (n) are provided. The numerical figure in each ( ) is provided in order to distinguish each scanning signal line  48  and each data signal line  43 . The scanning signal lines  48  and the data signal lines  43  will be described with the numerical figures in ( ) when necessary. The scanning signal lines  48 ( l ) through ( m ) are each connected to the thin film transistor  47  of a corresponding pixel  40 , and the plurality of data signal lines  43 ( l ) through ( n ) are each connected to the thin film transistor  47  of a corresponding pixel  40 . The numerical figures in ( ) have the same meaning for storage capacitance lines  62  described later. As shown in  FIG. 6 , the scanning signal lines  48  are each connected to a gate electrode  47   a  of the corresponding thin film transistor  47 . The data signal lines  43  are each connected to a source electrode  47   b  of the corresponding thin film transistor  47 . A drain electrode  47   c  of the thin film transistor  47  is connected to one of the electrodes which form a storage capacitance Ccs described later, i.e., an electrode  42   a , and is further connected to the pixel electrode  42  via the electrode  42   a.    
     As shown in  FIG. 6 , in each pixel  40 , the pixel electrode  42  of the array substrate  11  and the counter electrode  55  of the color filter substrate  12  face each other with the liquid crystal layer  13  being held therebetween. The pixel electrode  42  and the counter electrode  55  form a capacitor Clc for manipulating the liquid crystal layer  13 . 
     The above-mentioned storage capacitance Ccs is formed of one of a pair of electrodes  42   a  and  61  facing each other with the insulating layer held therebetween. One of the pair of electrodes forming the storage capacitance Ccs, i.e., the electrode  42   a  is connected to the drain electrode  47   c  as described above. By contrast, the other electrode  61  forming the storage capacitance Ccs is provided in a corresponding storage capacitance line  62 . The storage capacitance Ccs exhibits a function of keeping the voltage applied to the pixel  40  (capacitance Clc for manipulating the liquid crystal layer  13 ) upon receiving a control signal from the storage capacitance line  62 . 
     As shown in  FIG. 5 , the scanning signal lines  48 ( l ) through ( m ) are connected to a gate driver  81 . The data signal lines  43 ( l ) through ( n ) are connected to a source driver  82 . The gate driver  81  and the source driver  82  are each connected to the control section  200 . The control section  200  is formed by a combination of an IC, an LSI, a CPU, a nonvolatile memory and the like. The control section  200  performs various types of electronic processing in accordance with a preset program and thus exhibits required functions. The driving of the liquid crystal panel  10  is controlled by the control section  200 . The control section  200  includes a signal input section  201 , a timing controller  202 , and a power source  203 . 
     To the signal input section  201 , a control signal  300   a  is input from an external system  300 . The control signal  300   a  includes a signal regarding video to be displayed on the liquid crystal panel  10 . In this embodiment, based on the control signal  300   a , control signals  81   a  and  82   a  are sent from the signal input section  201  to the gate driver  81  and the source driver  82  respectively, via the timing controller  202 . The timing controller  202  is a control section for performing control of adjusting the timing of a control signal. In this example, the timing controller  202  adjusts the timing of a control signal for driving the gate driver  81  and the source driver  82  based on the control signal  300   a  input from the external system  300 . The power source  203  supplies an operating power source to each element of the liquid crystal display device  100 , and also generates a common electrode voltage (Vcom) for the liquid crystal panel  10  and supplies the common electrode voltage to the counter electrode  55  (see  FIG. 5 ). 
     In the liquid crystal display device  100 , as shown in  FIG. 5 , the scanning signal lines  48 ( l ) through ( m ) are located parallel to each other at a prescribed interval. Namely, the scanning signal lines  48 ( l ) through ( m ) are located in one direction of the lattice. In addition, the scanning signal lines  48 ( l ) through ( m ) are located parallel to each other in the other direction of the lattice at a prescribed interval so that the scanning signal lines  48  are connected to the corresponding pixels  40  provided in the liquid crystal panel  10  in a lattice. As shown in  FIG. 5 , the storage capacitance lines  62 ( l ) through ( m ) are also provided in one direction of the lattice. In addition, the storage capacitance lines  62 ( l ) through ( m ) are located parallel to each other in the other direction of the lattice at a prescribed interval so that the electrodes  61  of the storage capacitances Ccs of the pixels  40  provided in the liquid crystal panel  10  in the lattice are connected to the corresponding storage capacitance lines  62 . 
     In the liquid crystal display device  100 , as shown in  FIG. 5  and  FIG. 6 , scanning signals are sequentially sent to the scanning signal lines  48 ( l ) through ( m ). In accordance with the scanning signal input to each scanning signal line  48 , the thin film transistors  47  of the pixels  40  connected to this scanning signal line  48  are turned ON. Namely, in the liquid crystal panel  10 , the thin film transistors  47  of the pixels  40  arranged in each line in one direction of the lattice are turned ON at a time. At the timing at which the thin film transistors  47  are turned ON, data signals (video signals) input to these pixels  40  are sent to the data signal lines  43 ( l ) through ( n ). Thus, the video signals are written in the pixels  40  arranged in each line in one direction of the lattice are turned ON at a time. At the same timing, control signals are sent to the storage capacitance lines  62 . Thus, the voltage applied to the pixels  40  by the action of the storage capacitances Ccs are kept even after the thin film transistors  47  are turned OFF. 
     Now, control on the backlight device  20  will be described. 
     In this embodiment, the brightness of the backlight device  20  is also controlled by the control section  200 . As shown in  FIG. 1  and  FIG. 2 , in the backlight device  20 , the light emitting diodes  22  are each located so as to direct light toward a prescribed area of the rear surface of the liquid crystal panel  10 . Therefore, the control section  200  can divide the liquid crystal panel  10  into areas and adjust the brightness of the backlight device  20  for each of the areas independently by controlling each of the light emitting diodes  22 . The brightness of the backlight device  20  can be adjusted by controlling the power which is put to each light emitting diode  22 . As shown in  FIG. 5 , the control section  200  includes a backlight driving circuit  204  for controlling the driving of the backlight device  20 . The backlight driving circuit  204  sends a control signal to each light emitting diode  22  via the timing controller  202  in accordance with the video signal input to the signal input section  201 . In this embodiment, each light emitting diode  22  is controlled along with the control on the liquid crystal panel  10 . Owing to this, the brightness of the backlight device  20  can be adjusted in accordance with the video signal. At this point, the control section  200  can divide the liquid crystal panel  10  into areas and adjust the brightness of the backlight device  20  for each of the areas independently. The control on each light emitting diode  22  may be, for example, control on the power put to each light emitting diode  22  performed by a pulse width modulation method or a PWM method. 
     &lt;Light Receiving Sensors  122   a  Through  122   d&gt;   
     In this embodiment, as shown in  FIG. 2 , the light receiving sensors  122   a  through  122   d  are located at a plurality of sites along the edge portion of the front surface of the liquid crystal panel  10 . As shown in  FIG. 2  and  FIG. 5 , the control section  200  can divide the liquid crystal panel  10  into a plurality of areas A 1  through D 1  and control the plurality of light emitting diodes  22  based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d . In this embodiment, the liquid crystal panel  10  is divided into the plurality of areas A 1  through D 1  based on the locations of the light receiving sensors  122   a  through  122   d . Based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d , the contrast of each of the areas A 1  through D 1  is adjusted independently. 
     Specifically, in this embodiment, as shown in  FIG. 1  and  FIG. 2 , the light receiving sensors  122   a  through  122   d  are attached to a front surface of the bezel  30  forming the edge portion of the liquid crystal panel  10 . As shown in  FIG. 2 , the liquid crystal panel  10  includes the generally rectangular screen  10   a . The light receiving sensors  122   a  through  122   d  are respectively located on four sides surrounding the generally rectangular screen  10   a  of the liquid crystal panel  10 . In more detail, in the embodiment shown in  FIG. 2 , the light receiving sensors  122   a  through  122   d  are respectively attached to a central part of the four sides of the bezel  30  surrounding the generally rectangular screen  10   a  of the liquid crystal panel  10 . By locating the light receiving sensors  122   a  through  122   d  along the edge portion of the front surface of the liquid crystal panel  10  (for example, as shown in  FIG. 2 , on the front surface of the bezel  30 ), the external light illuminating the front surface of the liquid crystal panel  10  can be received appropriately. By locating the light receiving sensors  122   a  through  122   d  along the edge portion of the front surface of the liquid crystal panel  10 , the screen  10   a  of the liquid crystal panel  10  can be prevented from being narrowed and the light of the pixels forming the screen  10   a  can be prevented from being shielded. 
     As shown in  FIG. 2 , the light receiving sensors  122   a  through  122   d  are connected to the control section  200  by the signal lines. The light receiving sensors  122   a  through  122   d  each receive light (mainly, external light other than the light generated from the liquid crystal panel  10 ). The light receiving informational a 1  through d 1  based on the light received by the light receiving sensors  122   a  through  122   d  is sent to the control section  200  via the signal lines. As the light receiving sensors  122   a  through  122   d , any of various types of light sensors can be used. As the light receiving sensors  122   a  through  122   d , for example, photodiodes, phototransistors, photoresistors, the electric resistance of which is changed in accordance with the intensity of the light incident thereon, or the like may be used. Herein, the “light receiving information” is information sent from each light receiving sensor to the control section  200  based on the received light. Specifically what type of information is the “light receiving information” is varied in accordance with the type of sensor, circuit configuration or the like. Each of the light receiving sensors  122   a  through  122   d  sends information in accordance with the intensity of the light, for example, information on the brightness or luminance of the light, to the control section  200  as the light receiving information. Although not shown, the light receiving informational through d 1  may be obtained by converting light receiving signals sensed by the sensors by means of I/V (current/voltage) conversion, A/D (analog/digital) conversion or the like when necessary. 
     &lt;Control on the Liquid Crystal Display Device  100 &gt; 
     As shown in  FIG. 2 , the control section  200  divides the liquid crystal panel  10  into the plurality of areas A 1  through D 1  and adjusts the contrast of each of the plurality of areas A 1  through D 1  independently based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d . The control of adjusting the contrast may be, for example, control of adjusting the brightness of the backlight device  20 . Alternatively, the control of adjusting the contrast may be control of adjusting the brightness of the liquid crystal panel  10 . The contrast may be adjusted by controlling both of the backlight device  20  and the liquid crystal panel  10 . It is preferable that the plurality of areas A 1  through D 1  are preset in accordance with, for example, the plurality of sites at which the light receiving sensors  122   a  through  122   d  are located as shown in  FIG. 2 . 
     In this embodiment, the control of adjusting the contrast is control of adjusting the brightness of the backlight device  20 . The backlight device  20  includes the plurality of light emitting diodes  22  as the light sources. For adjusting the brightness of the backlight device  20 , it is preferable that the brightness of the light emitting diodes  22  is adjusted for each of the areas A 1  through D 1  independently. The brightness of each light emitting diode  22  can be adjusted by controlling the power put to the light emitting diode  22 . Specifically, in this embodiment, as shown in  FIGS. 4(   a ) and  4 ( b ), the light emitting diodes  22  are arranged in a lattice on the surface  25   a  facing the liquid crystal panel  10 . As shown in  FIG. 2 , the control section  200  divides the liquid crystal panel  10  into the plurality of areas A 1  through D 1  by the setting provided by the program, etc. The light emitting diodes  22  are controlled based on the light receiving information obtained from the light receiving sensors  122   a  through  122   d , and the brightness of the backlight device  20  is adjusted for each of the areas A 1  through D 1  independently. 
     The light receiving sensors  122   a  through  122   d  receive external light illuminating the screen  10   a  of the liquid crystal panel  10 . In the case where the liquid crystal display device  100  is illuminated by the external light (light other than the light generated from the liquid crystal display device  100 ) and thus a part of the screen  10   a  is made brighter than the other parts, the light receiving sensors  122   a  through  122   d  sense different levels of brightness from each other. The light emitting diodes  22  are controlled based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d , and the brightness of the backlight device  20  is adjusted for each of the areas A 1  through D 1  independently. Therefore, the problem that the screen  10   a  is made difficult to view when the screen  10   a  is illuminated by the external light and thus a part thereof is made brighter than the other parts can be alleviated. 
     In this case, it is preferable that, for example, the control section  200  appropriately adjusts the brightness of the backlight device  20  for each of the areas independently in accordance with a difference in the light receiving information sensed by the light receiving sensors  122   a  through  122   d , so as to prevent the liquid crystal panel  10  from becoming partially difficult to view. It is also preferable that, for example, as shown in  FIG. 2 , the liquid crystal panel  10  is divided into a plurality of areas A 1  through D 1  in correspondence with the sites at which the light receiving sensors  122   a  through  122   d  are located. It is preferable that the light emitting diodes  22  for illuminating each of the areas A 1  through D 1  are controlled independently based on the light receiving informational a 1  through d 1  obtained by the light receiving sensors  122   a  through  122   d . Such control is preferably realized by the program, etc. set in the control section  200 . 
       FIG. 7  schematically shows the backlight driving circuit  204 . In this case, as shown in  FIG. 7 , the backlight driving circuit  204  can, for example, send a control signal to each light emitting diode  22  based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d  in addition to a control signal  202   a  sent from the timing controller  202 . To the backlight driving circuit  204 , the control signal  202   a  sent from the timing controller  202  and the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d  are input. The backlight driving circuit  204  creates control signals a 2  through d 2  for controlling the areas A 1  through D 1  predefined in the backlight device  20  based on the input control signal  202   a  and light receiving informational a 1  through d 1 . Based on the control signals a 2  through d 2 , the light emitting diodes  22  in the areas A 1  through D 1  of the backlight device  20  are controlled. 
     Owing to this, in the case where, for example, the top part of the screen  10   a  is brighter than the bottom part due to the influence of the illumination in the room, it is sensed that the top part of the liquid crystal panel  10  is brighter than the bottom part by the light receiving sensors  122   a  through  122   d  shown in  FIG. 2 . In this case, it is preferable that the brightness of the backlight device  20  is adjusted for the top and bottom parts set in the liquid crystal panel  10  based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d . Thus, the contrast of each of the areas can be adjusted independently in accordance with the brightness difference between the top and bottom parts of the liquid crystal panel  10 . 
     There may be a case where, for example, a left part of the liquid crystal display device  100  is brighter than a right part thereof due to the influence of light coming through a window (not shown) located to the left of the liquid crystal display device  100  as seen from the observer. In this case, it is sensed that the left part of the liquid crystal panel  10  is brighter than the right part by the light receiving sensors  122   a  through  122   d  shown in  FIG. 2 . In this case, it is preferable that the brightness of the backlight device  20  is adjusted for the left and right parts set in the liquid crystal panel  10  based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d . Thus, the contrast of each of the areas can be adjusted independently in accordance with the brightness difference between the left and right parts of the liquid crystal panel  10 . 
     In this case, the control section  200  may be structured to adjust the contrast of each of the areas A 1  through D 1  independently in accordance with the brightness of the sites at which the light receiving sensors  122   a  through  122   d  are located based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d . For example, it is preferable that the contrast is appropriately adjusted in accordance with the degree (e.g., the degree of brightness) of the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d . Regarding how the contrast is to be adjusted based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d , it is preferable that, for example, the ease of viewing the screen  10   a  is evaluated by a test performed in advance. It is preferable that based on the test results, the control on the contrast based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d  is appropriately set by the program, etc. 
     &lt;Control of Adjusting the Contrast&gt; 
     The control section  200  may be structured to be capable of adjusting the contrast of the screen  10   a  of the liquid crystal panel  10  for each of the plurality of areas A 1  through D 1  independently based on the video signal and the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d . In this case, it is preferable that the control section  200  adjusts the contrast such that the contrast is strengthened at a bright site of the liquid crystal panel  10  and is weakened at a dark site of the liquid crystal panel  10  based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d . In this case, it is preferable that the brightness of the liquid crystal panel  10  is determined based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d  as a result of a comparison with a certain threshold value provided for the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d.    
     For example, in the case where a top part of the screen  10   a  is brighter than a bottom part thereof due to the influence of the illumination in the room, it is sensed that the top part of the liquid crystal panel  10  is brighter than the bottom part by the light receiving sensors  122   a  and  122   c  shown in  FIG. 2 . In this case, the control may be set such that the contrast of the backlight device  20  is adjusted in the top and bottom areas A 1  and C 1  set in the liquid crystal panel  10  in accordance with the brightness difference between the top and bottom parts of the liquid crystal panel  10 . In this manner, the contrast of each of the areas A 1  through D 1  set in the liquid crystal panel  10  can be adjusted independently based on the light receiving information a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d . Therefore, the liquid crystal panel  10  can be prevented from becoming partially difficult to view as a result of being illuminated by the external light, and thus the screen  10   a  can be made easier to view as a whole. For example, it is preferable that the contrast of a prescribed area of the screen  10   a  is strengthened or weakened based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d.    
     Regarding how the contrast of the screen  10   a  is to be adjusted based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d , it is preferable that, for example, the ease of viewing the screen  10   a  is evaluated by a test performed in advance. It is preferable that based on the test results, the control on the brightness of the backlight device  20  based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d  is appropriately set by the program, etc. Regarding the adjustment of the contrast, instead of only the backlight device  20  being controlled, the control on the liquid crystal panel  10  may be associated with the control on the backlight device  20  for each of the areas A 1  through D 1 , so that the contrast of the screen  10   a  is adjusted for each of the areas A 1  through D 1  independently. Owing to this, the contrast of the screen  10   a  can be appropriately adjusted for each of the areas A 1  through D 1  independently in consideration of the influence of the external light. Thus, the screen  10   a  of the liquid crystal panel  10  can be prevented from becoming partially difficult to view as a result of being illuminated by the external light, and the screen  10   a  can be controlled as a whole to display video more appropriately in a manner desired by a user. 
     Some liquid crystal display devices include a contrast adjustment controller (e.g., a contrast enhancer) for strengthening or weakening the contrast based on the setting by a user or the video signal. The contrast enhancer performs processing of adjusting the contrast of the output video in accordance with the luminance distribution of the input video information. 
       FIG. 12  conceptually shows contrast adjustment control. In this example, when an image including a bright part and a dark part (e.g., an image of a landscape having a bright part and a dark part such as, for example, a glow of dawn and a sunset glow) is displayed on a part of the screen, the contrast is strengthened. 
     In this case, video information (input image  401 ) is input to the control section  200 . In this embodiment, the control section  200  adjusts the contrast of the screen  10   a  for each of the areas independently based on the video information (input image  401 ) (area active processing  220 ; see  FIG. 5 ). At this point, the control section  200  generates control information for controlling the backlight device  20  for each of the areas of the screen  10   a  independently (LED control data  402 ) and control information for controlling each of the pixels in the liquid crystal panel  10  (LCD control data  403 ). For strengthening the contrast, it is preferable that the LED control data  402  and the LCD control data  403  are generated such that, for example, a bright part of the input image  401  becomes still brighter and a dark part of the input image  401  becomes still darker. In an example, it is preferable that a certain threshold value is provided for luminance information of the input image  401 , and for a pixel having a luminance higher than the threshold value, such a high luminance is multiplied by a predefined coefficient to increase the luminance; whereas for a pixel having a luminance lower than the threshold value, such a low luminance is multiplied by the predefined coefficient to decrease the luminance. Owing to this, the generated LED control data  402  and LCD control data  403  each have the contrast strengthened. 
     In  FIG. 12 , the LED control data  402  represents an image of the backlight device  20  controlled by the LED control data  402  processed as described above. In this case, the backlight device  20  is bright in a part where the input image  401  is bright and is dark in a part where the input image  401  is dark. In  FIG. 12 , the LCD control data  403  represents an image of the liquid crystal panel  10  controlled by the LCD control data  403  processed as described above. In this case, the pixels of the liquid crystal panel  10  are controlled such that the liquid crystal panel  10  is bright in a part where the input image  401  is bright and is dark in a part where the input image  401  is dark. Owing to this, an output image  404  from the liquid crystal display device  100  has the contrast strengthened as compared with the input image  401  as shown in  FIG. 12 . 
     The liquid crystal display device  100  in this embodiment may perform, in addition to the above processing, the processing of adjusting the contrast of each of the areas A 1  through D 1  of the screen  10   a  independently based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d  described above (see  FIG. 2 ). Owing to this, in addition to the contrast adjustment control being performed as described above, the contrast of the screen  10   a  can be appropriately controlled for each of the areas independently in consideration of the case where a part of the screen  10   a  is brighter than the other parts due to the influence of the illumination in the room. As described above, as the control of adjusting the contrast, control of adjusting the contrast by adjusting the brightness of each pixel of the liquid crystal panel  10  may be performed. 
     As described above, the liquid crystal display device  100  includes the plurality of light emitting diodes  22  in the backlight device  20  and also includes the light receiving sensors  122   a  through  122   d  at a plurality of sites along the edge portion of the front surface of the liquid crystal panel  10 . The control section  200  divides the liquid crystal panel  10  into the plurality of areas A 1  through D 1 , and controls the contrast of each of the areas A 1  through D 1  independently based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d.    
     As shown in  FIG. 8  and  FIG. 9 , the backlight driving circuit  204  obtains the light receiving informational a 1  through d 1  from the light receiving sensors  122   a  through  122   d  located at a plurality of sites along the edge portion of the front surface of the liquid crystal panel  10  (first step (S 1 )). Next, based on the light receiving informational a 1  through d 1  obtained in the first step (S 1 ), the contrast of each of the areas A 1  through D 1  is adjusted independently (second step (S 2 , S 3 )). For example, in the liquid crystal display device  100 , the contrast is controlled based on the light receiving informational a 1  through d 1  obtained from the light receiving sensors  122   a  through  122   d  in addition to based on the control signal  202   a  sent from the timing controller  202 . Therefore, for example, the brightness of the backlight device  20  can be appropriately adjusted for each of the areas A 1  through D 1  independently in consideration of the influence of the external light. Thus, the screen  10   a  of the liquid crystal panel  10  can be prevented from becoming partially difficult to view by being illuminated by the external light, and the screen  10   a  can be made easier to view as a whole. 
     In this case, it is preferable that the plurality of divided areas A 1  through D 1  into which the liquid crystal panel  10  is divided is preset in accordance with the plurality of sites at which the light receiving sensors  122   a  through  122   d  are located, by means of the control section  200  by use of the program, etc. Owing to this, the liquid crystal panel  10  can be appropriately divided into the plurality of areas A 1  through D 1  in accordance with the locations of the light receiving sensors  122   a  through  122   d , and thus the backlight device  20  can be appropriately controlled. For example, in the above-described embodiment, in the liquid crystal panel  10  including the generally rectangular screen  10   a , the light receiving sensors  122   a  through  122   d  are respectively located on four sides surrounding the generally rectangular screen  10   a  along the edge portion of the front surface of the liquid crystal panel  10 . In this case, it is preferable that as shown in  FIG. 2 , the areas A 1  through D 1  into which the liquid crystal panel  10  is divided are respectively set in the bottom, left, top and right parts of the liquid crystal panel  10  in accordance with the locations of the light receiving sensors  122   a  through  122   d  on the four sides, i.e., the bottom, left, top and right sides. 
     Regarding the above-described control method, in the second step (S 2 ), the contrast of borders between the areas A 1  through D 1  may be controlled such that the contrast is gradually changed between the areas A 1  through D 1 . Owing to this, an event that the contrast is conspicuously changed at the borders between the areas A 1  through D 1  set in the liquid crystal panel  10  can be prevented. For example, it is preferable that the brightness of the backlight device  20  is gradually changed between the areas A 1  through D 1 . 
     In this case, it is preferable, for example, that the centers of the areas A 1  through D 1  are set in the vicinity of the light receiving sensors  122   a  through  122   d , respectively. It is preferable that the light emitting diodes  22  are controlled such that the brightness of the backlight device  20  is gradually changed between the areas A 1  through D 1 , for example, such that the brightness of the backlight device  20  is gradually changed in accordance with the distance from each of the areas A 1  through D 1 . 
     So far, one embodiment of the present invention has been described. The present invention is not limited to the above-described embodiment. 
     For example, the locations of the light receiving sensors  122   a  through  122   d  on the liquid crystal panel  10  are not limited to those described above. In the above-described embodiment, as shown in  FIG. 2 , on the liquid crystal panel  10  including the generally rectangular screen  10   a , the light receiving sensors  122   a  through  122   d  are respectively located on four sides surrounding the generally rectangular screen  10   a  along the edge portion of the front surface of the liquid crystal panel  10 . By contrast,  FIG. 8  shows a liquid crystal display device  100 A according to another embodiment of the present invention. As shown in  FIG. 8 , the light receiving sensors  122   a  through  122   d  may be located at four corners of the peripheral edge portion of the generally rectangular screen  10   a . The four corners of the peripheral edge portion of the generally rectangular screen  10   a  each have a diagonal length greater than the width of the four sides surrounding the generally rectangular screen  10   a . Therefore, it is easier to securely keep an area size sufficiently large to locate the light receiving sensors  122   a  through  122   d.    
     In this case, for example, as shown in  FIG. 8 , it is preferable that a plurality of areas A 2  through D 2  into which the liquid crystal panel  10  is divided are set so as to center around the four corners of the screen  10   a , in correspondence with the locations of the light emitting sensors  122   a  through  122   d . It is also preferable that the brightness of the backlight device  20  is controlled each of the areas A 2  through D 2  independently based on the light receiving informational a 1  through d 1  obtained by the light receiving sensors  122   a  through  122   d . As understood from this, the locations of the light receiving sensors  122   a  through  122   d  may be variously altered. Although not shown, the number of the light receiving sensors  122   a  through  122   d  located along the edge portion of the front surface of the liquid crystal panel  10  may be increased or decreased, or may be appropriately increased in accordance with the size of the liquid crystal panel  10 . 
     For example, a plurality of light receiving sensors may be located at an appropriate interval around the generally rectangular screen  10   a  (on the four sides surrounding the screen  10   a  (see  FIG. 2 ), at the four corners of the peripheral edge portion of the screen  10   a  (see  FIG. 8 ), etc.). In this case, as the number of the light receiving sensors is increased, the screen  10   a  can be divided into areas in a finer manner. Therefore, finer control on the brightness adjustment and on the contrast is made possible. However, when the number of the light receiving sensors is increased, the production cost of the liquid crystal display device  100  is raised. Hence, it is preferable that the number and the locations of the light receiving sensors are determined such that the backlight device  20  is appropriately controlled to prevent the liquid crystal panel  10  from becoming partially difficult to view, and also in consideration of the production cost or the like. 
     In the above-described embodiment, the control section  200  controls the contrast and also performs other controls on the liquid crystal display device  100 . The present invention is not limited to such an embodiment, and the other controls on the liquid crystal display device  100  and the control on the contrast may be performed by different control circuits from each other. The above-described control of adjusting the brightness or the contrast of each of the areas independently may be set to be performed when necessary. For example, as shown in  FIG. 2 , the control section  200  may include a switching section  200   a  for switching between a mode of performing the above-described control of adjusting the contrast and a mode of not performing the above-described control of adjusting the contrast. 
     For example, when a person walks in front of the liquid crystal display device, a part of the light receiving sensors temporarily senses darkness caused by the shadow of the person. If the above-described control of adjusting the brightness is performed in such a case, an unpleasant event that, for example, the image flickers may occur. Therefore, the control section  200  may be set to perform the above-described brightness adjustment control when certain light receiving information is obtained for a predefined time duration. 
     In this case, as shown in  FIG. 10 , the control section  200  obtains light receiving information from the light receiving sensors  122   a  through  122   d  (step S 1 ), and determines “whether or not the light receiving information obtained in step S 1  has been changed from the light receiving information obtained at an immediately previous timing” (step S 11 ). When it is determined in such determination processing S 11  that the light receiving information obtained in step S 1  has not been changed from the light receiving information obtained at the immediately previous timing (NO), the processing of step S 1  is repeated. When it is determined in the determination processing S 11  that the light receiving information obtained in step S 1  has been changed from the light receiving information obtained at the immediately previous timing (YES), determination processing S 12  is performed. In the determination processing S 12 , it is determined “whether or not the light receiving information obtained in step S 1  was obtained continuously for a predefined time duration”. The “predefined time duration” is used for the purpose of preventing the above-described brightness adjustment control from being performed in an event that a part of the light receiving sensors temporarily senses darkness. It is preferable to set, as the “predefined time duration”, an appropriate time duration suitable for this purpose. 
     When it is determined in the determination processing S 12  that the light receiving information obtained in step S 1  was not obtained continuously for the predefined time duration (NO), the processing of step S 1  is repeated. When it is determined in the determination processing S 12  that the light receiving information obtained in step S 1  was obtained continuously for the predefined time duration (YES), the processing of step S 2  and the processing of step S 3  are performed sequentially. In the processing of step S 2 , control signals for a plurality of light sources are created based on the light receiving information obtained in step S 1  and a video signal. In the processing of step S 3 , the brightness of the backlight device  20  is adjusted based on the control signals created in step S 2 . 
     According to such control, even when a person walks in front of the liquid crystal display device and a part of the light receiving sensors temporarily senses darkness caused by the shadow of the person, an event that the above-described brightness adjustment control is performed and thus the image flickers can be suppressed. 
     So far, various types of liquid crystal display device  100  according to various embodiments of the present invention have been described. The present invention is not limited to these embodiments either, and may be variously altered. 
     For example, the above-described structure of the liquid crystal panel is merely an example. Various proposals have been made by the prior art regarding the structure of the liquid crystal panel, and there is no specific limitation on the structure of the liquid crystal panel according to the present invention. The type of, and the manner of locating, the light emitting diodes as the light sources are not limited to those in the above-described embodiments. In the above-described embodiments, as an example of backlight device, a so-called full-array type LED backlight device in which the light emitting diodes face the rear surface of the liquid crystal panel is shown. The backlight device is not limited to such a type and may be of any type which directs the light from a plurality of light emitting diodes toward the rear surface of the liquid crystal display section. Therefore, for example, the backlight device may direct the light from the light emitting diodes toward the rear surface of the liquid crystal display section via a light guide plate. In this case, for example, the structure may be such that the rear surface of the liquid crystal panel is divided into areas, different light guide plates are located respectively for the areas, and the light guide plates are each controlled independently so as to adjust the brightness of the backlight device for each of the areas independently. 
       FIG. 11  is a block diagram illustrating a liquid crystal display device  100 B in such a modification. 
     In this embodiment, a backlight device  20 B is divided into M rows×N columns of divided illumination areas (11, 12, 13, . . . MN) arranged in a lattice (in a matrix; in the example of the figure, M×N). In this embodiment, the backlight device  20 B is lit up, lit out, adjusted in luminance or the like for each of the divided illumination areas (11, 12, 13, . . . MN) independently. Namely, different light guide plates are respectively located for the areas, and the light guide plates are each controlled independently so as to adjust the brightness of the backlight device for each of the areas independently. 
     The screen  10   a  of a liquid crystal panel  10 B is divided into areas in correspondence with the divided illumination areas (11, 12, 13, . . . MN) of the backlight device  20 B. The areas of the screen  10   a  are also represented with 11, 12, 13, . . . MN in correspondence with the divided illumination areas (11, 12, 13, . . . MN) of the backlight device  20 B for the sake of convenience. 
     As shown in  FIG. 11 , the liquid crystal display device  100 B is controlled by the control section  200 . In this case, as shown in  FIG. 11 , the control section  200  includes a maximum gray scale level detection circuit  91  and a gray scale conversion circuit  92 . The maximum gray scale level detection circuit  91  detects the maximum gray scale level of each of the above-described divided areas (11, 12, 13, . . . MN) independently. The gray scale conversion circuit  92  converts a display image signal  90  in accordance with the maximum gray scale level in one frame of each of the divided areas (11, 12, 13, . . . MN). Then, the gray scale conversion circuit  92  creates an input image signal to be input to the liquid crystal panel  10 B for each of the divided display areas. 
     In this case, it is preferable that as shown in  FIG. 2  or  FIG. 8 , the control section  200  divides the screen  10   a  into areas A 1  through D 1  based on the light receiving informational through d 1  obtained by the light receiving sensors  122   a  through  122   d  and optimizes the control on the backlight device  20  for each of the areas A  1  through D 1  independently. 
     As shown in  FIG. 5 , for example, the control section  200  of the above-described liquid crystal display device  100  may be structured to include a receiving section  201   a  for receiving TV broadcast in the signal input section  201  so that an image based on the TV broadcast received by the receiving section  201   a  is displayed. The control section  200  may control the liquid crystal display section  10  and the backlight device  20  such that an image based on the TV broadcast received by the receiving section  201   a  is displayed by the liquid crystal display device  100 . As understood from this, the liquid crystal display device  100  can be a part of a TV receiver. The video information to be input to the signal input section  201  is not limited to an image based on the TV broadcast, and may be an image sent from any of various video devices. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
         
           
               10 ,  10 B Liquid crystal panel (liquid crystal display section) 
               10   a  Screen 
               11  Array substrate 
               12  Color filter substrate 
               13  Liquid crystal layer 
               15  Seal 
               17 ,  18  Polarizing plate 
               20 ,  20 B Backlight device 
               22  Light emitting diode (light source) 
               24  Backlight chassis 
               25  Reflector plate 
               26  Optical sheet 
               30  Bezel 
               32  Frame 
               41  Glass substrate 
               42  Pixel electrode 
           
         
           42   a  One of electrodes forming a storage capacitance
         43  Bus line     44  Flattening layer     46  Alignment film     47  Thin film transistor     47   a  Gate electrode     47   b  Source electrode     47   c  Drain electrode     48  Scanning signal line     51  Glass substrate     52  Black matrix     53  Color filter     54  Flattening layer     55  Counter electrode     56  Alignment film     61  The other of the electrodes forming a storage capacitance     62  Storage capacitance line     81  Gate driver     81   a ,  82   a  Control signal     82  Source driver     90  Display image signal     91  Maximum gray scale level detection circuit     92  Gray scale conversion circuit     100 ,  100 A,  100 B Liquid crystal display device     122   a - 122   d  Light receiving sensor     200  Control section     201  Signal input section     202  Timing controller     202   a  Control signal sent from the timing controller     203  Power source     204  Backlight driving circuit     220  Area active processing     300  External system     300   a  Control signal     401  Input image     402  LED control data     403  LCD control data     404  Output image   A 1 -D 1 , A 2 -D 2  Area   a 1 -d 1  Light receiving information   a 2 -d 2  Control signal   Ccs Storage capacitance   Clc Capacitor for manipulating the liquid crystal layer