JP2010003455A - Backlight unit and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit capable of preventing deterioration of display quality caused by lighting failure of a fluorescent tube in advance. <P>SOLUTION: The backlight 4 arranged on a back surface of a display panel 3 has n sets of fluorescent tubes L1 to Ln, a lighting-up control means 71 for controlling lighting-up of respective fluorescent tubes L1 to Ln, light sensors 8a, 8b for detecting brightness of the fluorescent tubes L1 to Ln, and a determination means 72. The lighting-up control means 71 makes each of the fluorescent tubes L1 to Ln light up, and the determination means 72 determines whether or not respective fluorescent tubes L1 to Ln are required to exchange on the basis of individual brightness of the fluorescent tubes L1 to Ln. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a backlight unit using a plurality of fluorescent tubes and a liquid crystal display device including the backlight unit.

  In an ultra-large liquid crystal display device such as 108 type, a large fluorescent tube such as a hot cathode tube or a cold cathode tube is generally used as a backlight. Examples of the fluorescent tube include a hot cathode tube and a cold cathode tube, but a hot cathode tube having higher luminance is often used. However, the fluorescent tube has a predetermined life, and in particular, the life of the hot cathode tube is often shorter than that of the display panel.

  When a fluorescent tube is not lit due to its life, the fluorescent tube is replaced. For example, in a backlight of a general household LCD television that uses a backlight having a plurality of fluorescent tubes, one fluorescent tube is not lit because it is necessary to faithfully receive and reproduce broadcast signals that change in real time. In such a case, a method of turning off all other fluorescent tubes is also performed. However, the ultra-large liquid crystal display device such as the 108 type is a business display that displays still image data from a personal computer, advertisement still image data, etc. in addition to receiving general broadcast signals at the place of negotiations such as exhibitions. It is often used for information display in public places. In this case, since the liquid crystal display device may be continuously displayed for the purpose of use, even if one of the backlight fluorescent tubes is not lit, the image must be continuously displayed by some backup means. There is a problem. For this reason, it is necessary not only to estimate the lifetime in advance and to quickly replace the non-lighted fluorescent tube, but also to avoid the non-lighting of the fluorescent tube as much as possible.

  Therefore, in an ultra-large liquid crystal display device such as a 108 type using a plurality of fluorescent tubes, the lifetime is preliminarily estimated before the non-lighting due to the lifetime of the fluorescent tube occurs. Techniques that enable exchange have been proposed.

  For example, Patent Document 1 discloses a technique for measuring the usage time of a fluorescent tube and displaying the lifetime of the fluorescent tube as a message when the usage time exceeds the half-life inherent to the fluorescent tube. Thereby, the lifetime of the fluorescent tube can be predicted, and deterioration of the image display can be prevented beforehand by replacing the fluorescent tube before the fluorescent tube becomes unlit due to the lifetime.

Further, it is known that the luminance of the fluorescent tube decreases as the usage time elapses and the lifetime approaches. Therefore, a table for measuring the luminance maintenance ratio with respect to the lighting time of the fluorescent tube is provided in advance, and the backlight brightness is measured by a light detection element provided in the vicinity of the backlight unit, and the brightness value is detected as the backlight brightness. The content which inputs into a circuit and correct | amends the brightness | luminance fallen by the time-dependent change of a backlight with a backlight control circuit is disclosed (for example, patent document 2). Thereby, the light emission luminance of the backlight can be controlled in consideration of the secular change of the light emission luminance of the backlight.
Japanese Patent Laid-Open No. 2001-125064 (published on May 11, 2001) Japanese Patent Application Laid-Open No. 2008-9090 (released on January 17, 2008)

  However, the above-described conventional configuration causes a problem that it is impossible to avoid unlighting of the fluorescent tube while economically using the fluorescent tube.

  In the configuration disclosed in Patent Document 1, the lifetime of the fluorescent tube is estimated based on the half-life of the fluorescent tube. However, the lifetime of the same fluorescent tube varies depending on the variation between products. For this reason, even when the cumulative lighting time reaches the half-life, the usable time until the lighting is turned off differs depending on the fluorescent tube. In order to prevent the non-lighting of the fluorescent tube more reliably, it is necessary to set the half-life of the fluorescent tube short. However, since the replacement cycle of the fluorescent tube is shortened, it is also uneconomical to replace the fluorescent tube having a relatively long remaining usable time although the accumulated lighting time has reached the half-life. On the other hand, if the half-life of the fluorescent tube is set to be long, the replacement cycle of the fluorescent tube becomes long, which increases the risk of causing the fluorescent tube to become unlit.

  Patent Document 2 discloses a configuration in which the luminance of a backlight is detected by a light detection element. However, since a configuration for measuring individual detection of the fluorescent tubes provided in the backlight is not disclosed, it is not possible to specify a fluorescent tube that needs to be replaced. For this reason, in order to prevent deterioration of display quality due to non-lighting of the fluorescent tubes, all the fluorescent tubes are periodically replaced. Therefore, the remaining fluorescent tubes having a relatively long usable time at the time of replacement are also replaced, and the fluorescent tubes cannot be used economically.

  The present invention has been made in view of the above-described problems, and its purpose is to prevent a deterioration in display quality due to non-lighting of the fluorescent tube, and to realize a backlight unit that can economically use the fluorescent tube. There is to do.

  In order to solve the above problems, a backlight unit according to the present invention is disposed on the back surface of a display panel, and includes a plurality of fluorescent tubes, lighting control means for controlling lighting of each fluorescent tube, and luminance of the fluorescent tubes. In the backlight unit comprising: a light sensor for detecting the fluorescence sensor, the lighting control means turns on the fluorescent tubes one by one, and each fluorescent tube is based on the individual luminance of each fluorescent tube detected by the optical sensor. It is characterized by comprising a judging means for judging whether or not the pipe needs to be replaced.

  According to said structure, since the fluorescent tube is lighted one by one by the lighting control means, the optical sensor can detect the individual brightness | luminance of each fluorescent tube. Since the luminance of the fluorescent tubes decreases as the lifetime approaches, the determination unit can determine whether or not each fluorescent tube needs to be replaced based on the individual luminance of each fluorescent tube.

  In this way, by detecting the individual brightness of the fluorescent tube provided in the backlight, it is possible to identify the fluorescent tube that needs to be replaced. Therefore, the deterioration of the display quality due to the non-lighting of the fluorescent tube can be prevented in advance. The backlight unit can be used economically.

  In the backlight unit according to the present invention, the lighting control means turns on the fluorescent tubes one by one for each OFF period of the PWM dimming drive of the fluorescent tubes, and the determination means sets the light in the off period. It is preferable to determine whether it is necessary to replace each fluorescent tube based on the individual luminance of each fluorescent tube detected by the sensor.

  In particular, in a public place, even though the liquid crystal display device is often used continuously for a long time, until one of the fluorescent tubes is turned off and a service person is called to the site and the exchange is completed, If the use is to be stopped, there is a risk that it will cause a significant hindrance compared to the use at home.

  Here, according to the above configuration, the lighting control means turns on the fluorescent tubes one by one for every OFF period of the PWM dimming drive in which all the fluorescent tubes are turned off in the normal dimming drive of the fluorescent tubes. ing. Therefore, even when the backlight unit is being driven, the optical sensor can detect the individual luminance of each fluorescent tube, and thus the liquid crystal display device including the backlight unit is used continuously for a long time. Even in public places, it is possible to determine whether or not the fluorescent lamp needs to be replaced without interrupting use.

  In the backlight unit according to the present invention, when the luminance detected by the optical sensor is less than a predetermined ratio with respect to the luminance in the new use state of the fluorescent tube, the luminance is the predetermined ratio. It is preferable to determine that it is necessary to replace a fluorescent tube that is less than.

  Since the luminance of the fluorescent tube decreases as the lifetime approaches, the risk of non-lighting increases as the luminance decreases. According to the above configuration, the luminance corresponding to the predetermined ratio with respect to the luminance in the new use state is set to the minimum luminance with no risk of non-lighting, so that each fluorescent tube can be used economically and displayed. Deterioration of quality can be prevented in advance.

  The backlight unit according to the present invention further includes cumulative lighting time measuring means for measuring the cumulative lighting time of the fluorescent tube, and the determination means is based on the luminance detected by the photosensor and the cumulative lighting time. It is preferable to determine whether the fluorescent tube needs to be replaced.

  According to the above configuration, since it is determined whether or not the fluorescent tube needs to be replaced in consideration of not only the luminance of the fluorescent tube but also the cumulative lighting time of the fluorescent tube, the determination accuracy can be further improved.

  In the backlight unit according to the present invention, it is preferable that the determination unit starts determining whether or not the fluorescent tube needs to be replaced simultaneously with the start of driving of the backlight unit.

  According to the above configuration, since it is determined whether or not the fluorescent tube needs to be replaced immediately after the start of use, even if it is determined that the fluorescent tube needs to be replaced and the start of use is delayed for replacement work, Compared to the case where use is interrupted after a certain amount of time has elapsed since the start of use, there are fewer problems.

  In the backlight unit according to the present invention, it is preferable that the determination unit always determines whether or not the fluorescent tube needs to be replaced while the backlight unit is driven.

  According to the above configuration, it is possible to determine whether or not the fluorescent tube needs to be replaced even during use of the liquid crystal display device including the backlight unit, and it is possible to quickly identify the fluorescent tube that needs to be replaced. It is possible to avoid a situation in which the fluorescent tube is not lit.

  In the backlight unit according to the present invention, it is preferable that the determination unit determines whether or not each fluorescent tube needs to be replaced when the illuminance of the ambient light around the backlight unit is a predetermined value or less.

  The determination of whether or not the fluorescent tube needs to be replaced is performed at the time of dimming driving of the backlight. Therefore, when the illuminance of the ambient light is strong, the display quality is deteriorated. Therefore, according to the above configuration, by setting the predetermined value to an illuminance that does not cause a problem in display quality at the time of backlight dimming drive, even when determining whether or not the fluorescent tube needs to be replaced, the display quality is reduced. Can be prevented.

  In the backlight unit according to the present invention, when the determination unit determines that the fluorescent tube needs to be replaced, the lighting control unit blinks only the fluorescent tube determined to be replaced during the replacement operation. It is preferable to make it.

  According to the above configuration, it is possible to notify the user of the life of the fluorescent tube more clearly and to promote maintenance.

  In the backlight unit according to the present invention, when the determination unit determines that the fluorescent tube needs to be replaced, the lighting control unit determines whether the replacement is necessary according to the luminance of the fluorescent tube. It is preferable to change the blinking interval.

  According to the above configuration, the user can easily estimate the remaining usable time of the fluorescent tube based on the blinking interval.

  In the backlight unit according to the present invention, when the determination unit determines that the fluorescent tube needs to be replaced, the determination unit displays the position of the fluorescent tube determined to require the replacement as the display panel. Is preferably displayed.

  According to said structure, the replacement | exchange operation | work of a fluorescent tube becomes easy.

  In the backlight unit according to the present invention, it is preferable that when the determination unit determines that the fluorescent tube needs to be replaced, the determination unit displays a contact information of a maintenance company on the display panel.

  According to said structure, even if it determines with replacement | exchange of a fluorescent tube being required, it can respond more rapidly.

  The backlight unit according to the present invention may further include a communication unit that notifies the user that the fluorescent tube needs to be replaced when the determination unit determines that the fluorescent tube needs to be replaced. preferable.

  According to said structure, even if the user of a liquid crystal display device is away from the use field, it can be made to recognize that a user needs to replace | exchange fluorescent tubes.

  The liquid crystal display device according to the present invention includes the backlight.

  According to said structure, the non-lighting by the lifetime of a fluorescent tube can be prevented, and the liquid crystal display device which improved the usability and maintainability significantly is realizable.

  In the backlight unit according to the present invention, as described above, the lighting control unit turns on the fluorescent tubes one by one, and each fluorescent tube is based on the individual luminance of each fluorescent tube detected by the photosensor. Since the determination means for determining whether or not the tube needs to be replaced is provided, it is possible to prevent a deterioration in display quality due to non-lighting of the fluorescent tube, and to realize a backlight unit that can use the fluorescent tube economically. .

  An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a block diagram showing a configuration of a liquid crystal display device 1 according to the present embodiment. The liquid crystal display device 1 is, for example, a TFT (thin film transistor) type liquid crystal display device, and includes a controller unit 2, a display panel 3, and a backlight unit 4.

  The controller unit 2 is a module that generates signals for input to the display panel 3 and the backlight unit 4, and includes a signal source 21 and a video signal processing unit 22. From the signal source 21, display data R / G / B, horizontal synchronization signal HD, vertical synchronization signal VD, and clock signal CLK are output to the video signal processing unit 22.

  The video signal processing unit 22 includes a γ correction unit 221 and a timing adjustment unit 222. The display data R / G / B input to the video signal processing unit 22 is converted into a video signal VS by the γ correction unit 221. The timing adjustment unit 222 outputs the horizontal synchronization signal HD, the vertical synchronization signal VD, and the clock signal CLK to the backlight unit 4.

  The display panel 3 includes a source driver and a gate driver (not shown), and displays a video on the display screen based on the video signal VS input from the controller unit 2. Since a well-known display panel 3 can be used, a detailed description of its configuration is omitted.

  The backlight unit 4 is a unit constituting a so-called direct type backlight, and includes a backlight 5, an inverter unit 6, and a microcomputer unit 7.

  The backlight 5 is provided on the back side of the display panel 3 and includes n fluorescent tubes L1... Ln. For example, when the size of the liquid crystal display device 1 is 108 type, n = 24. Further, the backlight 5 is provided with an optical sensor 8a for detecting the luminance of the fluorescent tubes L1... Ln. Further, an optical sensor 8 b that detects the illuminance of external light incident on the display panel 3 is provided outside the backlight 5.

  2A is a plan view showing the configuration of the backlight 5 when the same number of photosensors 8a as the fluorescent tubes L1 are provided, and FIG. 2B is a plan view of the fluorescent tubes L1 as viewed from the longitudinal direction. It is sectional drawing which shows the structure of the backlight 5 in the case of being. The fluorescent tubes L1 are supported at both ends by a fluorescent tube folder 51 and are arranged in parallel to each other. Further, one photosensor 8a is arranged in the vicinity of each of the fluorescent tubes L1. Further, a reflecting plate 52 is provided below the fluorescent tubes L1... The reflecting plate 52 reflects light emitted from the fluorescent tubes L1. Thereby, the utilization efficiency of light can be improved.

  In the backlight unit 4, a PWM (Pulse Width Modulation) dimming method is used as a dimming method for the backlight 5. The PWM dimming method is a method of dimming the backlight 5 by periodically blinking the fluorescent tubes L1... Ln and changing the time ratio between the lighting period and the extinguishing period.

  The inverter unit 6 and the microcomputer unit 7 are provided in the vicinity of the backlight 5. The microcomputer unit 7 includes a lighting control unit 71, a determination unit 72, and a dimming pulse generation circuit PWM1... PWMn.

  The lighting control unit 71 controls the dimming pulse generation circuit PWM1... PWMn based on the horizontal synchronizing signal HD, the vertical synchronizing signal VD and the clock signal CLK input from the controller unit, and the dimming pulse generating circuit PWM1. The dimming pulses V1... Vn indicating the lighting timing of the fluorescent tubes L1. The dimming pulses V1... Vn are converted into high voltage / high frequency AC power in the inverters INV1... INVn provided in the inverter unit 6 and supplied to the fluorescent tubes L1.

  The determination unit 72 has a function of determining whether or not each of the fluorescent tubes L1... Ln needs to be replaced, and includes a photometric processing unit 721, a photometric timing setting unit 722, a photometric result memory 723, a comparison unit 725, and a reference value memory. 724. The photometric processing unit 721 calculates and digitizes the luminance of each fluorescent tube L1... Ln from the detection results from the optical sensor 8a and the optical sensor 8b, and stores them in the photometric result memory 723 as individual luminance values. The calculation method of the brightness | luminance of each fluorescent tube L1 ... Ln is mentioned later.

  The photometric timing setting unit 722 generates a timing pulse Vt based on the horizontal synchronizing signal HD, the vertical synchronizing signal VD, and the clock signal CLK from the controller unit 2 and outputs the timing pulse Vt to the photometric processing unit 721. When the timing pulse Vt is at a high level, the photometry processing unit 721 is controlled to detect the luminance of the fluorescent tubes L1... Ln every OFF period of the PWM dimming drive of the fluorescent tubes L1.

  The reference value memory 724 stores reference luminance values for determining that the fluorescent tubes L1. The reference luminance value is set based on, for example, a luminance reduction curve of the fluorescent tube, and in this embodiment, 70% of the luminance in the new usage state of the fluorescent tubes L1... Ln is used as the reference luminance value.

  FIG. 3 is a graph showing a relationship between a general fluorescent tube lighting time and luminance. The luminance of the fluorescent tube gradually decreases as the lighting time elapses, and the risk of non-lighting increases as the luminance decreases. According to the JIS standard, a fluorescent tube whose luminance is 70% of the luminance in a new use state is determined to have a lifetime.

  In addition, the setting of the reference luminance value that is a reference for whether or not the fluorescent tube needs to be replaced is not limited to this, and the reference luminance value includes the type of fluorescent tube, the risk of non-lighting, the replacement cost of the fluorescent tube Is set as appropriate. In general, it is desirable to set the minimum luminance with no risk of non-lighting as the reference luminance value.

  The comparison unit 725 compares the individual luminance value of each fluorescent tube L1... Ln stored in the photometric result memory 723 with the reference luminance value. In the comparison unit 725, if any individual luminance value of the fluorescent tubes L1... Ln is equal to or higher than the reference luminance value, it is determined that all the fluorescent tubes L1.

  On the other hand, in the comparison unit 725, when any one or more individual luminance values of the fluorescent tubes L1... Ln are less than the reference luminance value, it is determined that the fluorescent tube that does not satisfy the reference luminance value needs to be replaced. In this case, the comparison unit 725 instructs the lighting control unit 71 to blink all the fluorescent tubes L1... Ln or change the blinking interval only for the fluorescent tubes that do not satisfy the reference luminance value. For example, the blinking interval is shortened as the fluorescent tube has a lower luminance. Thus, the user can easily know on the display screen that the replacement is necessary and the location of the fluorescent tube that needs to be replaced among the plurality of fluorescent tubes.

  In addition, the comparison unit 725 outputs a predetermined signal to the signal source 21 so that the position of the fluorescent tube to be replaced and the contact information of the maintenance company are displayed on the display panel using the OSD or the like. 3 may be displayed. Moreover, you may notify the user of the liquid crystal display device 1 that the replacement | exchange of a fluorescent tube is required by the communication means which is not shown in figure. Thereby, even if the user is away from the site of use, the user can know that the fluorescent tube needs to be replaced.

  As described above, the backlight unit 4 has a function of notifying the user that the fluorescent tube needs to be replaced. Further, when replacing the fluorescent tube, the comparison unit 725 may cause the lighting control unit 71 to light only the fluorescent tube that needs to be replaced. This facilitates the work of the service person performing the exchange.

  Next, a specific method for detecting the luminance of the fluorescent tubes L1... Ln by the optical sensor 8a will be described.

  FIG. 4 is a timing chart showing waveforms of the video signal VS, the dimming pulses V1... Vn, and the timing pulse Vt when the backlight 5 is dimming driven. In the blanking period of the video signal Vt, an off period of PWM dimming driving of the fluorescent tubes L1... Ln is provided. When the backlight 5 is normally driven, all the fluorescent tubes L1... Ln are turned off during the PWM dimming drive off period.

  On the other hand, when it is determined whether or not the fluorescent tube needs to be replaced, only one of the fluorescent tubes L1... Ln is turned on every PWM dimming drive off period, and the timing pulse Vt becomes high level at that timing. At this time, the optical sensor 8a detects the luminance of the incident light and outputs the luminance to the photometric processing unit 721 shown in FIG. Even when ambient light is incident on the display panel 3 from the outside, since the optical sensor 8b is provided outside, the photometric processing unit 721 detects the light sensor 8b from the luminance detected by the optical sensor 8a. By calculating the luminance difference, it is possible to detect the luminance of only the fluorescent tube that is lit during the OFF period of the PWM dimming drive. Thus, the individual luminance of each fluorescent tube L1... Ln can be detected by sequentially lighting each fluorescent tube L1.

  In this way, it is possible to determine whether or not each fluorescent tube L1... Ln needs to be replaced while using the liquid crystal display device 1. Therefore, even in an environment where the liquid crystal display device 1 needs to be used continuously all the time, such as in public places, it is not necessary to interrupt the use of the liquid crystal display device 1 in order to determine whether or not the fluorescent tube needs to be replaced. Even if it is determined that the fluorescent tube needs to be replaced, the fluorescent tube will not be turned off immediately unless the reference luminance value is set too low. It is possible to take measures such as exchanging the fluorescent tube in a relatively short time.

  Further, it is desirable to determine whether or not the fluorescent tube needs to be replaced at the beginning of lighting of the backlight unit 4, particularly at the same time as the driving of the backlight unit 4 is started. Particularly in public places, since it is used continuously for a long time (in some cases, 24 hours), even if it is determined that the fluorescent tube needs to be replaced, the use cannot be immediately stopped in many cases. On the other hand, if it is immediately after the start of use, it is determined that the fluorescent tube needs to be replaced, and even if the start of use is delayed for replacement work, the use is suspended after a certain amount of time has passed since the start of use. There are few obstacles compared to the case.

  It can also be confirmed by entering the life judgment mode with a dedicated button or the like. Accordingly, it is possible to determine whether or not the backlight unit needs to be replaced in accordance with the convenience of the user, and the user convenience can be further improved.

  When the luminance of the backlight 5 is maximum, as shown in FIG. 5, there is no PWM dimming drive off period, so that the luminance of the fluorescent tube cannot be detected. That is, when detecting the luminance of the fluorescent tube, it is necessary to provide an off period of the PWM dimming drive, and thus it is necessary to reduce the luminance of the backlight 5. For this reason, when the liquid crystal display device 1 is used outdoors, if the luminance of the fluorescent tube is detected in the daytime when the ambient light around the backlight 5 is strong, the display quality is deteriorated. Therefore, it is desirable to detect the luminance of the fluorescent tube in the evening or at night when the ambient light around the backlight 5 is relatively weak and the screen luminance can be lowered.

  When the liquid crystal display device 1 is used indoors, the luminance of the backlight 5 is not normally maximized, so that the luminance of the fluorescent tube can always be detected.

  In addition, if only one fluorescent tube is turned on during the PWM dimming drive off period, the screen brightness is lowered. Therefore, by increasing the brightness during the PWM dimming drive on period to prevent a decrease in total brightness, The brightness of the fluorescent tube can be measured while displaying the screen.

  Moreover, it is good also as a structure which switches whether the determination of the necessity of replacement | exchange of a fluorescent tube is performed according to the illumination intensity of environmental light. For example, when the illuminance of the ambient light incident on the optical sensor 8b provided outside is not more than a predetermined value, it may be automatically determined whether or not the fluorescent tube needs to be replaced.

  In the above description, the optical sensor 8a is provided in the vicinity of each fluorescent tube L1 ... Ln, but the number of the optical sensors 8a can be arbitrarily set.

  FIG. 6 shows the configuration of the backlight 15 according to a modification of the present embodiment, (a) is a plan view showing the configuration of the backlight 15, and (b) is the length of the fluorescent tubes L 1. It is sectional drawing which shows the structure of the backlight 15 at the time of seeing from a direction. The number of photosensors 8a provided in the backlight 15 is less than the number of fluorescent tubes L1... Ln. In FIG. 6, the photosensor 8a is provided only in the vicinity of the fluorescent tube L3.

  Since the fluorescent tube L1 and the fluorescent tube L2 are further away from the optical sensor 8a than the fluorescent tube L3, the emitted light from the fluorescent tube L1 is significantly attenuated before reaching the optical sensor 8a. Therefore, as shown in FIG. 6B, in the backlight 15, a light guide plate 53 is provided so as to cover the reflection plate 52 and the optical sensor 8a. Thereby, attenuation | damping of the emitted light from the fluorescent tube L1 and the fluorescent tube L2 can be relieved to some extent.

  In this case, for example, even if the luminances of the fluorescent tube L1 and the fluorescent tube L3 are the same, the incident light from the fluorescent tube L1 to the optical sensor 8a is weaker than the incident light from the fluorescent tube L3 to the optical sensor 8a. . Therefore, the photometry processing unit 721 considers the difference in distance between each fluorescent tube L1... L3 and the optical sensor 8a, and each fluorescent tube L1... When the fluorescent tube L1. The individual luminance of L3 is calculated.

  With this configuration, even if there is only one optical sensor provided in the backlight, the individual luminance of each fluorescent tube can be detected, so that the configuration can be further simplified.

  In the above description, the necessity of replacement of the fluorescent tube is determined based on the luminance of the fluorescent tube. However, the necessity of replacement of the fluorescent tube may be determined in consideration of the cumulative lighting time of the fluorescent tube.

  FIG. 7 is a block diagram showing a configuration of a liquid crystal display device 11 according to a modification of the present embodiment. The liquid crystal display device 11 has a configuration in which a cumulative lighting time measuring unit 726 is further provided in the liquid crystal display device 1 shown in FIG.

  The cumulative lighting time measuring unit 726 measures the cumulative lighting time of each of the fluorescent tubes L1... Ln based on the driving of the fluorescent tubes L1. The comparison unit 725 needs to replace the fluorescent tube even if the fluorescent tube has a luminance higher than the reference luminance stored in the reference value memory 724 if the accumulated lighting time of the fluorescent tube is longer than a predetermined time. It is determined that

  The determination as to whether the fluorescent tube needs to be replaced based on the luminance and the cumulative lighting time is not limited to the above. For example, a value obtained by subtracting the cumulative lighting time from a value obtained by multiplying the luminance by a predetermined constant is a predetermined value or more. It may be determined depending on whether or not. Thereby, the determination accuracy can be improved as compared with the necessity determination for replacement based only on the luminance.

  Subsequently, a modification of the luminance detection of the fluorescent tube will be described.

  FIG. 8 is a block diagram showing a configuration of a liquid crystal display device 12 according to another modification of the present embodiment. The liquid crystal display device 12 has a function of detecting ambient light in addition to the function of determining whether or not the fluorescent tube needs to be replaced. In the liquid crystal display device 1 shown in FIG. 1, instead of the optical sensors 8a and 8b. In this configuration, an optical sensor 8c is provided. That is, the liquid crystal display device 12 has a configuration in which an optical sensor is provided only inside the backlight without providing an optical sensor that detects ambient light outside the backlight.

  When determining whether or not the fluorescent tube needs to be replaced, in the liquid crystal display device 12, as in the timing chart shown in FIG. 4, only one of the fluorescent tubes L1. Turn on the light, and measure the brightness of the lighted fluorescent tube at that time.

  FIG. 9 is a cross-sectional view showing the structure of the display panel 3 and the backlight 5, and the display panel 3 has a color filter 31, a liquid crystal element 32, and an optical sheet 33 laminated from the surface side.

  FIG. 9A shows a case where the liquid crystal element 32 is turned on, and not only light from the fluorescent tube L1 but also ambient light from the outside transmitted through the display panel 3 is incident on the optical sensor 8c. Since the liquid crystal display device 12 is not provided with an illuminance light sensor for detecting the illuminance of the ambient light, in the state shown in FIG. 9A, the luminance of only the fluorescent tube L1 cannot be detected. Therefore, it is not possible to accurately determine whether the fluorescent tube L1 needs to be replaced.

  Therefore, in the liquid crystal display device 12, the liquid crystal element 32 is turned off as shown in FIG. 9B during the PWM dimming drive off period. Thereby, since ambient light from the outside does not enter the optical sensor 8c, the optical sensor 8c can detect the luminance of only the fluorescent tube L1.

  FIG. 10 is a timing chart showing waveforms of the video signal VS, dimming pulses V1... Vn, and timing pulse Vt in the liquid crystal display device 12 when detecting ambient light. In the next PWM dimming drive off period (the rightmost off period in the figure) in which the luminance of the fluorescent tube Ln is detected, all the fluorescent tubes L1 to Ln are turned off.

  As a result, as shown in FIG. 11A, only the external environmental light transmitted through the display panel 3 is incident on the optical sensor 8c during the off period. Therefore, the optical sensor 8c can also detect only ambient light, like the optical sensor 8b of the liquid crystal display device 1 shown in FIG. For example, when the illuminance of the ambient light becomes weak, the brightness of the backlight 5 may be controlled by automatically extending the off period of the PWM dimming drive.

  FIGS. 11B to 11D are cross-sectional views showing a state in which ambient light is transmitted through only the R filter, only the G filter, and only the B filter of the color filter 31 in the off period of the PWM dimming drive. . In this way, the ambient light transmitted through the R filter, the G filter, and the B filter is separately detected, thereby measuring not only the illuminance of the ambient light but also the chromaticity, and the white balance according to the external environment is determined as the video signal VS. Can provide feedback.

  Further, as in the configuration according to Patent Document 2, even with a backlight that uses an LED or a hybrid of an LED and a fluorescent tube as a light source, the white balance of the light source can be controlled by controlling the light source.

[Summary of Embodiment]
In the above embodiment, when any one of the fluorescent tubes is turned on in the off period of the PWM dimming drive, as shown in FIGS. 4 and 10, the timing pulse Vt of the timing pulse Vt is once turned off. Although it is made to light according to the input, it is not limited to this. For example, as shown in FIG. 12, by shifting the timing of the PWM dimming drive, only the fluorescent tube corresponding to the dimming pulse V2 can be turned on during the OFF period of the PWM dimming drive.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  Further, not only the fluorescent tube but also a backlight unit configured by combining a plurality of light source units with an LED or a unit including a plurality of LEDs can be similarly applied.

  The present invention can be applied to, for example, an edge light type backlight as long as the backlight uses a plurality of fluorescent tubes.

It is a block diagram which shows the structure of the liquid crystal display device which concerns on embodiment of this invention. (A) is a top view which shows the structure of a backlight when an optical sensor is provided with the same number as each fluorescent tube, (b) is a cross section which shows the structure of a backlight when it sees from the longitudinal direction of a fluorescent tube FIG. It is a graph which shows the relationship between the lighting time of a general fluorescent tube, and a brightness | luminance. It is a timing chart which shows the waveform of a video signal, a light control pulse, and a timing pulse at the time of light control drive of a backlight. It is a timing chart which shows the waveform of a video signal, a light control pulse, and a timing pulse when the luminance of a backlight is maximum. (A) is a top view which shows the structure of the backlight which concerns on the modification of embodiment of this invention, (b) shows the structure of the said backlight at the time of seeing from the longitudinal direction of fluorescent tube L1 .... It is sectional drawing. It is a block diagram which shows the structure of the liquid crystal display device which concerns on the modification of embodiment of this invention. It is a block diagram which shows the structure of the liquid crystal display device which concerns on the other modification of embodiment of this invention. 2A and 2B are cross-sectional views illustrating the structure of a display panel and a backlight, in which FIG. 3A illustrates a case where a liquid crystal element of the display panel is turned on, and FIG. Show. FIG. 9 is a timing chart showing waveforms of a video signal, a light control pulse, and a timing pulse in the liquid crystal display device shown in FIG. It is sectional drawing which shows the structure of a display panel and a backlight, (a) has shown the case where the liquid crystal element of the said display panel is ON, (b)-(d) each shows environmental light of a color filter. Of these, only the R filter, only the G filter, and only the B filter are transmitted. It is a timing chart which shows the modification of a light control pulse.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11, 12 Liquid crystal display device 3 Display panel 4 Backlight unit 5 Backlight 8a, 8b, 8c Photosensor 71 Lighting control part (lighting control means)
72 determination unit (determination means)
726 Cumulative lighting time measuring unit (cumulative lighting time measuring means)
L1, L2, L3 ... Ln fluorescent tube

Claims (13)

Placed on the back of the display panel,
In a backlight unit comprising a plurality of fluorescent tubes, lighting control means for controlling the lighting of each fluorescent tube, and an optical sensor for detecting the luminance of the fluorescent tube,
The lighting control means lights the fluorescent tubes one by one,
A backlight unit comprising determination means for determining whether or not each fluorescent tube needs to be replaced based on the individual luminance of each fluorescent tube detected by the optical sensor. The lighting control means turns on the fluorescent tubes one by one for each off period of the PWM dimming drive of the fluorescent tubes,
2. The back according to claim 1, wherein the determination unit determines whether or not each fluorescent tube needs to be replaced based on individual luminance of each fluorescent tube detected by the optical sensor during the off period. Light unit.   When the luminance detected by the optical sensor is less than a predetermined ratio with respect to the luminance in the new use state of the fluorescent tube, it is necessary to replace the fluorescent tube whose luminance does not satisfy the predetermined ratio. The backlight unit according to claim 1, wherein the backlight unit is determined to be. It further comprises cumulative lighting time measuring means for measuring the cumulative lighting time of the fluorescent tube,
The said determination means determines the necessity of replacement | exchange of the said fluorescent tube based on the brightness | luminance detected by the said optical sensor, and the said cumulative lighting time, The any one of Claims 1-3 characterized by the above-mentioned. The backlight unit described.   The backlight unit according to any one of claims 2 to 4, wherein the determination unit starts determining whether or not the fluorescent tube needs to be replaced simultaneously with the start of driving of the backlight unit.   The backlight unit according to any one of claims 2 to 5, wherein the determination unit always determines whether or not the fluorescent tube needs to be replaced while the backlight unit is being driven.   The said determination means determines the necessity of replacement | exchange of each fluorescent tube, when the illumination intensity of the ambient light around the said backlight unit is below predetermined value, The replacement | exchange necessity of each fluorescent tube is characterized by the above-mentioned. The backlight unit described. If the determination means determines that the fluorescent tube needs to be replaced,
The backlight unit according to any one of claims 1 to 7, wherein the lighting control unit blinks only the fluorescent tube determined to be replaced at the time of replacement work. If the determination means determines that the fluorescent tube needs to be replaced,
9. The backlight unit according to claim 1, wherein the lighting control unit changes a blinking interval according to a luminance of a fluorescent tube that is determined to require the replacement. . If the determination means determines that the fluorescent tube needs to be replaced,
10. The backlight unit according to claim 1, wherein the determination unit causes the display panel to display a position of a fluorescent tube determined to require the replacement. If the determination means determines that the fluorescent tube needs to be replaced,
The backlight unit according to claim 1, wherein the determination unit displays a contact information of a maintenance company on the display panel. If the determination means determines that the fluorescent tube needs to be replaced,
The backlight unit according to claim 1, further comprising communication means for notifying a user that the fluorescent tube needs to be replaced.   A liquid crystal display device comprising the backlight unit according to claim 1.

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