Abstract:
A liquid crystal display apparatus includes a liquid crystal panel; an illumination device that illuminates the liquid crystal panel; a cooler cooling the liquid crystal panel; a first detector detecting a surrounding temperature of the liquid crystal panel; a second detector detecting a surrounding temperature of the cooler; a controller controlling the illumination device and the cooler based on output of the first and the second detector, wherein the controller activates the cooler when the output of the second detector is larger than a second value and the output of the first detector exceeds a first value, and the controller decreases a luminance level of the illumination device without activating the cooler when the output of the second detector is less than the second value and the output of the first detector exceeds a first value.

Description:
[0001]    This application which claims priority under 35 U.S.C. §119 from Japanese patent application number 2009-022918 filed Feb. 3, 2009, is hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to liquid crystal display apparatus, and in particular relates to liquid crystal display apparatus for outdoor installation. 
         [0004]    2. Description of Related Art 
         [0005]    In recent years, displays which can be installed outdoors have been proposed. Liquid crystal displays are especially promising for outdoor installations because they are slim in size and resolutions are high. 
         [0006]    The liquid crystal has a characteristic that varies between a solid and a liquid state. In the liquid crystal displays, images are displayed by controlling the orientation of liquid crystal material by varying a voltage applied to the liquid crystal. However, when the temperature of the liquid crystal rises, the images cannot be displayed correctly since the liquid crystal liquefies and loses its orientation. 
         [0007]    To enable an outdoor installation of the liquid crystal display, it is necessary to have a structure that is adapted for outdoor installation, for example, a waterproofing structure or a dustproof structure. However, when these structures are applied, they introduce problems with heat dissipation since air cannot circulate inside and outside of display apparatus that has a watertight sealed casing. It is thus difficult to dissipate heat generated inside the apparatus, and it may cause a temperature rise inside the housing. Thereby, the temperature of the liquid crystal of the panel may rise undesirably. 
         [0008]    Moreover, in a transmissive liquid crystal display, in order to improve visibility in the outdoors, where under a strong light such as direct sunlight, it is necessary to make a display portion (screen) brighter than usual. To make the display portion brighter, it is necessary to increase the light output from the illuminating device (backlight etc.), and accordingly the amount of heat generated by the illuminating device increases. Thereby, the temperature of the liquid crystal also may rise undesirably. 
         [0009]    Further, when the liquid crystal display is installed outdoors, the display may be exposed to direct sunlight. When strong daylight is irradiated onto its display surface, the temperature of the liquid crystal of the display rises. 
         [0010]    Therefore, problems exist with displaying images on a liquid crystal display that is installed outdoors, because of the temperature rise of the liquid crystal in the display due to the various factors mentioned above. Accordingly there remains a need in the art to reduce the problem of liquid crystal temperature rise in outdoor installations of liquid crystal display apparatus. 
       SUMMARY OF THE INVENTION 
       [0011]    A liquid crystal display apparatus according to a first aspect of the present invention comprises: 
         [0012]    a liquid crystal panel; 
         [0013]    an illumination device lightening the liquid crystal panel; 
         [0014]    a cooler cooling the liquid crystal panel; 
         [0015]    a first detector detecting a surrounding temperature of the liquid crystal panel; 
         [0016]    a second detector detecting a surrounding temperature of the cooler; 
         [0017]    a controller controlling the lightening device and the cooler based on output of the first and the second detector, wherein 
         [0018]    the controller activates the cooler when the output of the second detector is larger than a second value and the output of the first detector exceeds a first value, and 
         [0019]    the controller decreases a luminance level of the lightning device without activating the cooler when the output of the second detector is less than the second value and the output of the first detector exceeds a first value. 
         [0020]    A liquid crystal display apparatus according to a second aspect of the present invention comprises: 
         [0021]    a liquid crystal panel; 
         [0022]    an illumination device lightening the liquid crystal panel; 
         [0023]    a detector arranged near the liquid crystal panel, detecting the outdoor light, and 
         [0024]    a controller which decreases the luminance level of the illuminating device, when it is determined that the outdoor light is irradiated for predetermined time based on the output from the detector. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a longitudinal sectional view of a liquid crystal display apparatus structure according to a first embodiment. 
           [0026]      FIG. 2  is a functional block diagram of a liquid crystal display apparatus according to the first embodiment. 
           [0027]      FIG. 3  is a flow chart showing an operation of the liquid crystal display apparatus of the first embodiment. 
           [0028]      FIG. 4  is a longitudinal sectional view of a liquid crystal display apparatus structure in accordance with a second embodiment. 
           [0029]      FIG. 5  is a functional block diagram of the liquid crystal display apparatus according to the second embodiment. 
           [0030]      FIG. 6  is a flow chart showing an operation of the liquid crystal display apparatus of the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    The present invention embodied in a display apparatus will be specifically described below with reference to the accompanying drawings. 
       First Embodiment 
       [0032]      FIG. 1  is a longitudinal sectional view of the liquid crystal display apparatus in accordance with a first embodiment. 
         [0033]    The liquid crystal display apparatus has a housing  2 , a front display glass  1  arranged in the housing  2  at the front side of the display apparatus, and a cooler device  3 . 
         [0034]    In an interior space  4  surrounded by the front display glass  1 , the housing  2 , and the cooler device  3 , a liquid crystal panel  5 , a back light  6 , ventilation fans  7  and  8  for circulating the air in the space  4 , and first temperature sensors  9 A- 9 D detecting a surrounding temperature of the panel  5  are arranged. The panel  5  is arranged so that its display screen faces the front side of the display, and thus a user can see the display screen through the front display glass  1 . The back light  6  is arranged behind the panel  5 , and irradiates the panel  5 . The fan  7  is arranged at the upper part of the space  4 , and the fan  8  is arranged at the lower part of the space  4 . Each of the sensors  9 A- 9 D is arranged near the corners of the front inner side of the housing  2 . 
         [0035]    Further, a second temperature sensor  10  for detecting the temperature of the setting position of a liquid crystal display is arranged at the back side of and outside of the housing  2 . 
         [0036]    The cooler device  3  has an evaporator  11 , a compressor  12 , a radiator  13 , and a coolant course. The coolant vaporized by the evaporator  11  is sent to the compressor  12  through the coolant path, then compressed by the compressor  12 , and becomes a hot gas. The coolant which is turned to a hot gas by the compressor  12  is sent to the radiator  13  through the coolant path, and is condensed by heat dissipation of the radiator  13  under a high pressure. During the heat dissipation, the radiator  13  emits heat outside the liquid crystal display apparatus. The high pressure liquid condensed at the radiator  13  is then sent to the evaporator  11  through a coolant path, and then evaporated by lowering its pressure in the vaporizer  11 . During the evaporation, the evaporator  11  absorbs the heat from the interior space  4  as an evaporation heat. 
         [0037]    Next, outlined functional block diagram of the above liquid crystal display apparatus is shown in  FIG. 2 . In  FIG. 2 , the same reference numerals are given to the portions already described in  FIG. 1 , and for such portions, detailed explanations are omitted hereafter. 
         [0038]    The liquid crystal display apparatus has an image signal input unit  14 , an image display part  15 , first temperature sensors  9 A- 9 D, a second temperature sensor  10 , a microcomputer  16 , a luminosity control part  17 , a backlight  6 , and a liquid crystal panel  5 . 
         [0039]    The image signal input unit  14  is connected to a LAN (Local Area Network) for example, and when an image signal is input from the LAN to the unit  14 , it outputs an image signal of a DVI (Digital Visual Interface) format. The image display part  15  converts a signal from the unit  14  into a suitable format for the liquid crystal display panel  5  and outputs the signal to the panel  5 . Then, an image is displayed on the panel  5 . 
         [0040]    The backlight  6  irradiates light from the back side of the liquid crystal display panel  5  in order to illuminate the panel  5  to display an image by the panel  5 . The backlight  6  is formed by a CCFL (Cold Cathode Fluorescent Lamp) for example. The microcomputer  16  outputs a backlight control signal which indicates a luminosity of the backlight  6  to the luminosity control part  17 . The control part  17  outputs a PWM (Pulse Width Modulation) drive signal to the backlight  6  according to the backlight control signal from the microcomputer  16 . The backlight  6  emits a light according to the PWM drive signal from the control part  17 . 
         [0041]    The first temperature sensors  9 A- 9 D and the second temperature sensor  10  are connected to the microcomputer  16 , and the microcomputer  16  converts analog temperature detection signals from the sensors  9 A- 9 D and the sensor  10  to digital signals. Further, the microcomputer  16  executes on/off controls of the ventilation fans  7  and  8 , and the cooler device  3 . 
         [0042]    Generally, a guaranteed operating temperature range is defined in coolers, and the operation of the cooler is not guaranteed when a surrounding temperature (an air temperature on the emitting side of the cooler) is less than the lower limit of, or higher than the upper limit of the guaranteed temperature range. 
         [0043]    For example, in the cooler device  3 , the lower limit of the guaranteed temperature range is defined as the minimum temperature at which the cooler components can continue to operate, considering that the lubricating oil used inside the cooler cannot serve as a lubricator in low temperatures (for example, under 10 degrees Celsius) because the viscosity of the oil becomes too high. 
         [0044]    Therefore, it is desirable to stop operating the cooler device  3  when the surrounding temperature of the display apparatus (surrounding temperature of the cooler device  3 ) detected by the second temperature sensor  10  is under the guaranteed operating temperature range. 
         [0045]    When a surrounding temperature of the liquid crystal display is under the guaranteed temperature range, the temperature of the interior space  4  does not rise such that the liquid crystal of the liquid crystal panel  5  liquefies even if the cooler device  3  is not operated, because the temperature of the space  4  does not rise significantly from the relatively cool temperature of the surrounding environment. 
         [0046]    However, the outdoor-installed liquid crystal display apparatus may be exposed to direct sunlight and when the sunlight irradiates the display surface of the liquid crystal panel  5 , the temperature of the liquid crystal of the panel  5  rises. Especially, if the display apparatus has a waterproofing structure or a dust proofing structure, since the air-tightness of the interior space  4  is high, the temperature of the interior space  4  may become high even if the surrounding temperature of the apparatus is low, because of a greenhouse effect. As a result, the temperature of the liquid crystal may rise to a liquefying temperature (approximately 70 degrees Celsius). 
         [0047]    Especially at a high latitude area or in a winter season, the display surface of the liquid crystal panel  5  may receive direct sunlight entering perpendicularly for a long time when the display apparatus is installed facing its display screen southward because an outside temperature is low and the solar altitude is low. In this case, there is a possibility that the temperature of the liquid crystal of the panel  5  rises to a liquefaction temperature, even if the surrounding temperature of the apparatus is low. 
         [0048]    Therefore, the liquid crystal display apparatus of this embodiment executes a procedure shown in a flow chart of  FIG. 3 . 
         [0049]    First, the microcomputer  16  acquires temperature information from four points inside the interior space  4  based on temperature detection signals from each of the first temperature sensors  9 A- 9 D (step S 10 ), and then determines whether at least one of four acquired temperatures is equal to or more than a first threshold value (step S 20 ). 
         [0050]    If all the temperatures acquired are less than the first threshold value (“no” in step S 20 ), the microcomputer  16  sets the cooler to off. In detail, under an assumption that the liquid crystal of the panel  5  does not liquefy even if the output of the backlight  6  is set to a normal setting, the microcomputer  16  keeps the cooler device  3  off when the cooler device  3  is currently off. When the cooler is currently on, the microcomputer  16  turns the cooler device  3  off to extend its operating life and to conserve energy. Further, when the output of the backlight  6  is currently in the normal setting, the microcomputer  16  maintains the normal setting. When the output is not in the normal setting, the microcomputer  16  turns it to the normal setting so that the visibility of the image screen improves (step S 30 ). Then, it returns to step S 10 . 
         [0051]    If one of the temperatures of the interior space  4  is equal to or more than the first threshold value (“yes” in step S 20 ), presuming that daylight is being irradiated on a display surface of the panel  5  for a predetermined period, the microcomputer  16  acquires a surrounding temperature of the display apparatus based on the detecting signal from the second temperature sensor  10  (step S 40 ), and determines whether the acquired temperature is less than a second threshold value or not (step S 50 ). 
         [0052]    Here, the second threshold value is set to a minimum guaranteed operating temperature of the cooler device  3  or a predetermined temperature which is somewhat higher than the guaranteed temperature. 
         [0053]    If the surrounding temperature of the display apparatus is not less than the second threshold value (“no” in step S 50 ), the microcomputer sets the cooler device  3  to on. In detail, if the cooler device  3  is currently on, the microcomputer keeps the cooler device  3  on. If the cooler is currently off, the microcomputer turns the cooler on in order to avoid liquefying the liquid crystal. Further, if the output of the backlight  6  is set to a normal setting, the microcomputer  16  keeps the setting normal. If the output level of the backlight  6  is set lower than the normal setting, the microcomputer turns the setting to normal in order to assure a visibility under strong sunlight (step S 60 ). Then the procedure shown in the flow chart ends. 
         [0054]    If the surrounding temperature of the display apparatus is less than the second threshold value (“yes” in step S 50 ), the microcomputer sets the cooler device  3  to off. In detail, if the cooler device  3  is currently off, the microcomputer  16  keeps the cooler device  3  off, and if the cooler device  3  is currently on, the microcomputer  16  turns the cooler device  3  off. Further, if the output level of the backlight  6  is currently in the normal setting, the microcomputer  16  sets the output level lower than the normal setting because the liquid crystal of the panel  5  might liquefy if the cooler device  3  is kept off while the output level of the backlight  6  is kept normal setting. If the level of the backlight  6  is currently in a level lower than the normal setting, the microcomputer  16  maintains the setting of backlight  6  (step S 70 ). Then the procedure shown in the flow chart ends. 
         [0055]    When the procedure shown in flow chart of  FIG. 3  finishes, the procedure is executed from the beginning again. However, if the cooler device  3  is turned from on to off or vice versa in the procedure, it is desirable to execute the procedure again after a predetermined period has elapsed in order to protect the cooler device  3 . 
         [0056]    According to the above procedure, except in a case when one of the temperatures among four points of the interior space  4  is equal to or more than the first threshold value and the surrounding temperature of the display apparatus is less than the second threshold value, visibility under strong daylight is assured. Further, it can inhibit the liquefaction of the liquid crystal of the panel  5 . 
         [0057]    In step S 10 , the temperature information of four points of the interior space  4  may be acquired in a form of either instantaneous temperature or the average temperature over a predetermined period. If the average temperature is adapted, it can reduce effects from momentary noise or environmental change etc. In order to acquire the average temperature, the microcomputer  16  may sample the temperature detection signal from the first temperature sensors  9 A- 9 D every second, then compute the average value acquired in the last 100 seconds. 
         [0058]    Similarly in step S 40 , the surrounding temperature information of the display apparatus may be acquired in a form of either instantaneous temperature or the average temperature over a predetermined period. If the average temperature is adapted, it can reduce effects from momentary noise or environmental change as well. In order to acquire the average temperature, the microcomputer  16  may sample the temperature detection signal from the second temperature sensor  10  every seconds, then compute the average value acquired in the last 100 seconds. 
       Second Embodiment 
       [0059]    One of the factors causing the temperature of the liquid crystal of the liquid crystal panel  5  to rise is heat emitted from the display apparatus itself (especially heat from the backlight  6 ) or heat caused by the irradiation of strong outdoor light (such as direct sunlight) onto the display surface of the panel  5 . As mentioned above, if the surrounding temperature of the display apparatus is under the guaranteed operating temperature of the cooler device  3 , usually, the temperature of the interior space  4  does not increase and the temperature does not tend to increase to a level which the liquid crystal of the panel  5  liquefies. 
         [0060]    However, even if the surrounding temperature of the display apparatus is low, the liquid crystal will liquefy if the outdoor light irradiates the panel for a long time period. 
         [0061]    Therefore, according to a liquid crystal display apparatus of the present embodiment, it is determined that the liquid crystal of the liquid crystal panel  5  might liquefy if the outdoor light irradiates the display surface of the panel for a predetermined period unless the backlight level is not lowered from the normal setting. 
         [0062]      FIG. 4  is a longitudinal sectional view of the liquid crystal display of this embodiment.  FIG. 5  is a block diagram of the liquid crystal display of this embodiment. In  FIG. 4 , the same reference numerals are given to the portions already described in  FIG. 1 . Similarly, in  FIG. 5 , the same reference numerals are given to the portions already described in  FIG. 2  or  FIG. 4 . For such portions, detailed explanations are omitted hereafter. 
         [0063]    According to the liquid crystal display apparatus of the second embodiment illumination sensors  18 A- 18 D are arranged in the four corners of the front side perimeter side of the housing  2  instead of the first temperature sensors  9 A- 9 D of the first embodiment. 
         [0064]      FIG. 6  is a flow chart showing a procedure which the display apparatus of the present embodiment executes. In  FIG. 6 , the same reference numerals are given to the steps already described in  FIG. 3 , and for such steps, detailed explanations are omitted hereafter. 
         [0065]    According to the flow chart of  FIG. 6 , steps S 10  and S 20  are omitted from the flow chart of  FIG. 3  and steps S 15  and S 25  are added instead. 
         [0066]    In Step S 15 , the microcomputer  16  acquires the illumination information on the four corners of housing  2 , based on the illumination detection signals from the sensors  18 A- 18 D. In Step S 25 , the microcomputer  16  determines whether one of the illumination levels detected at each corners is more than a third threshold value for a predetermined period or not. 
         [0067]    When it is determined “no” in step S 25 , assuming that the liquid crystal of the panel  5  does not liquefy even if the output level of the backlight is kept in normal setting, the microcomputer  16  turns the cooler device  3  off, and then goes to step S 30 . When it is determined “yes” in step S 25 , assuming that the outdoor light is irradiating the display surface of the panel  5  for more than a predetermined time, it goes to step S 40 . 
         [0068]    According to the above procedures, the visibility of the display screen under strong daylight can be assured, or liquefaction of the liquid crystal can be suppressed. 
         [0069]    As well as the first embodiment, the illumination information of four corners acquired in step S 15  may be either instantaneous illumination or average illumination over a predetermined period. 
         [0070]    The present invention is not limited to the foregoing embodiments but can be modified variously by one skilled in the art without departing from the spirit of the invention as set forth in the appended claims.