Patent Publication Number: US-9907133-B2

Title: Backlight device and backlight control method

Description:
The present application is a Continuation Application of U.S. patent application Ser. No. 14/352,301, filed on Apr. 16, 2014, which is based on International Application No. PCT/JP2011/074312, filed on Oct. 21, 2011, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a backlight device and a backlight control method. 
     BACKGROUND ART 
     Liquid crystal display devices of conventional art include an RGB color filter substrate, a liquid crystal layer, and a backlight device. It is proposed in the backlight device of this type of liquid crystal display device that red (R), green (G), and blue (B) colors are mixed to emit white color light to improve the display color reproduction range in the liquid crystal display device. 
     In the backlight devices of the conventional art, brightness of emitted light is detected by color sensors with color filters that comply with spectral characteristics corresponding to each color of RGB LEDs (light emitting diodes). Then, a calculation means of the backlight device controls output to the backlight of each color so that the brightness and chromaticity of the mixed white color light take predetermined values. After light emission is started, the temperature of a connection unit in the light emitting diode interior rises due to the heat generated by the light emitting diode itself, causing the brightness of each light emitting diode to change. Consequently, there is a device in which the current light emission amount is controlled to be a predefined standard light emission amount (for example, refer to Patent Document 1). 
     Prior Art Document 
     Patent Document 
     [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2008-262032 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     However, in the technique disclosed in Patent Document 1, the color temperature takes time to converge, for some color temperatures that are set to white by the operation unit of the liquid crystal display device. 
     The present invention takes into consideration the above problem, and an exemplary object thereof is to provide a backlight device and a backlight control method capable of reducing the length of time taken to converge to a set color temperature, regardless of the set color temperature of white. 
     Means for Solving the Problem 
     In order to achieve the above object, a backlight device according to the present invention includes: alight emitting unit of a plurality of light sources of different light emission colors; a detection unit that detects light emission states of the plurality of light sources; a temperature sensor that measures a temperature in a proximity of the plurality of light sources; a brightness conversion unit that converts values indicating the light emission states detected by the detection unit into a detection value for each component of the light emission colors; and a calculation unit that performs temperature correction on the detection value converted by the brightness conversion unit for each of the light emission colors by using information when determining drive values for the light sources based on the detection values, the information indicating a relationship between the temperature measured by the temperature sensor and a correction value. 
     In order to achieve the above object, the present invention provides a backlight control method for a backlight device that controls a light emission amount of a light emitting unit of a plurality of light sources of different light emission colors, which includes: a detection step of detecting, by a detection unit, light emission states of the plurality of light sources; a temperature measuring step of measuring, by a temperature sensor, a temperature in a proximity of the plurality of light sources; a brightness conversion step of converting, by a brightness conversion unit, values indicating the light emission states detected in the detection step into a detection value for each component of the light emission colors; and a calculation step of performing temperature correction, by a calculation unit, on the detection value converted in the brightness conversion step for each of the light emission colors by using information when determining drive values for the light sources based on the detection values, the information indicating a relationship between the temperature measured in the temperature measuring step and a correction value. 
     Effect of the Invention 
     The backlight device of the present invention is such that the conversion unit converts the light emission state detected by the detection unit into a detection value for each light source. The calculation unit performs temperature correction on the detection values converted by the conversion unit using a predefined temperature correction coefficient for each light emission color, when determining drive values for the light sources based on the detection values. As a result, the length of time taken to converge to a set color temperature can be reduced regardless of the set color temperature of white. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a schematic configuration of a backlight device according to a first exemplary embodiment. 
         FIG. 2  is a diagram showing an example of a light transmission characteristic of an RGB color filter. 
         FIG. 3  is a diagram for describing temperature drift in a red color sensor according to the first exemplary embodiment. 
         FIG. 4  is a diagram for describing temperature correction made to a red light emission color in the red color sensor according to the first exemplary embodiment. 
         FIG. 5  is a diagram for describing an example of color temperature changes in a case where a temperature correction is made regarding a temperature drift characteristic of a color sensor. 
         FIG. 6  is a diagram for describing an example of color temperature changes in a case where a temperature correction is made for each color of the backlight according to the first exemplary embodiment. 
         FIG. 7  is a block diagram of a schematic configuration of a backlight device according to a second exemplary embodiment. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     First, a brief overview of the present invention is described. 
     In a backlight device used in such as a liquid crystal display device, the light amount of backlight is detected with a color sensor that includes a color filter. Due to the spectral characteristic of the color filter, the color sensor also detects the light amount of backlight other than that of the color that needs to be detected. In the present exemplary embodiment, the conversion unit converts a detection value detected by the color sensor into a light amount for each color emitted by the backlight, using a conversion equation. Then the temperature correction unit performs temperature correction on the detection value for each color that is converted by the conversion unit. 
     Thereby, the brightness of the backlight with respect to temperature change is precisely controlled to suppress influence of temperature drift with respect to a white point setting. 
     First Exemplary Embodiment 
     Hereunder, exemplary embodiments of the present invention are described in detail, with reference to the drawings. 
       FIG. 1  is a block diagram of a schematic configuration of a backlight device  1  according to the present exemplary embodiment. As shown in  FIG. 2 , the backlight device  1  includes a backlight driving unit  10 , a light emitting unit  20 , a detection unit  30 , a backlight target color setting unit  40 , a temperature sensor  55 , and a calculation unit  50 . 
     The backlight driving unit  10  includes a red backlight driving circuit  101 , a green backlight driving circuit  102 , and a blue backlight driving circuit  103 . The red backlight driving circuit  101  drives a red backlight  201  of the light emitting unit  20 , based on driving signals output from a red backlight drive value calculation unit  541  of the calculation unit  50 . The green backlight driving circuit  102  drives a green backlight  202 , based on driving signals output from a green backlight drive value calculation unit  542 . The blue backlight driving circuit  103  drives a blue backlight  203 , based on driving signals output from a blue backlight drive value calculation unit  543 . 
     The light emitting unit  20  includes a red backlight  201 , a green backlight  202 , and a blue backlight  203 . 
     The red backlight  201  is a light source that emits red color light based on driving signals output from the red backlight driving circuit  101 . The center wavelength of red color light is, for example, approximately 660 [nm]. The green backlight  202  is a light source that emits green color light based on driving signals output from the green backlight driving circuit  102 . The center wavelength of green color light is, for example, approximately 540 [nm]. The blue backlight  203  is a light source that emits blue color light based on driving signals output from the blue backlight driving circuit  103 . The center wavelength of blue color light is, for example, approximately 460 [nm]. 
     The red backlight  201 , the green backlight  202 , and the blue backlight  203  are, for example, light emitting diodes (LEDs) or semiconductor lasers. 
     The detection unit  30  includes a red color sensor  301 , a green color sensor  302 , and a blue color sensor  303 . 
     The red color sensor  301  has a color filter of a spectral sensitivity characteristic corresponding to the light emission color of the red backlight  201 . The spectral sensitivity characteristic of the color filter of the red color sensor  301  is such that, for example, as with the curved line g 103  in  FIG. 1 , the band with transmittance 20[%] or higher is approximately 590 [nm] to 720 [nm]. The red color sensor  301  receives light emitted from the light emitting unit  20 , and detects the light emission state of the light emitting unit. The red color sensor  301  then converts the received light amount into an electric signal, and outputs the converted electric signal to the calculation unit  50  as a detection value Rs. The light emission state detected by the detection unit  30  is a detection value such as brightness or chromaticity. A detection value is described as brightness in the following description. 
     The green color sensor  302  has a color filter of a spectral sensitivity characteristic corresponding to the light emission color of the green backlight  202 . The spectral sensitivity characteristic of the color filter of the green color sensor  302  is such that, for example, as with the curved line g 102  in  FIG. 1 , the band with transmittance 20[%] or higher is approximately 480 [nm] to 600 [nm] like the curved line g 102 . The green color sensor  302  receives light emitted from the light emitting unit  20 , then converts the received light amount into an electric signal, and outputs the converted electric signal to the calculation unit  50  as a detection value Gs. 
     The blue color sensor  303  has a color filter of a spectral sensitivity characteristic corresponding to the light emission color of the blue backlight  203 . The spectral sensitivity characteristic of the color filter of the blue color sensor  303  is such that, for example, as with the curved line g 101  in  FIG. 1 , the band with transmittance 20[%] or higher is approximately 400 [nm] to 540 [nm]. The blue color sensor  303  receives light emitted from the light emitting unit  20 , then converts the received light amount into an electric signal, and outputs the converted electric signal to the calculation unit  50  as a detection value Bs. 
     Moreover, the red color sensor  301 , the green color sensor  302 , and the blue color sensor  303  are, for example, photo sensors. 
     The backlight target color setting unit  40  stores setting values for the red backlight  201 , the green backlight  202 , and the blue backlight  203  when emitting white color light, which have been preliminarily set by a user of the backlight device  1  for example. The backlight target color setting unit  40  outputs the set setting values to a red sensor target value calculation unit  531 , a green sensor target value calculation unit  532 , and a blue sensor target value calculation unit  533  of the calculation unit  50 . 
     The setting values are, for example, values that are adjusted by a user while looking at a display of a display unit (not shown in the figure) so that the user feels the brightness of the red backlight  201 , the green backlight  202 , and the blue backlight  203  as white color light emission, and these values are set on an operation unit (not shown in the figure). 
     The temperature sensor  55  is attached in the proximity of the light emitting unit  20 . The temperature sensor  55  detects temperatures, and outputs information indicating detected temperatures to a temperature correction unit  510 . 
     The calculation unit  50  includes a sensor value/BL brightness conversion unit  500  (conversion unit), a temperature correction unit  510 , a BL brightness/sensor value conversion unit  520 , a sensor target value calculation unit  530 , and a drive value calculation unit  540 . 
     The sensor value/BL brightness conversion unit  500  includes a red color detection value temperature correction unit  511 , a green color detection value temperature correction unit  512 , and a blue color detection value temperature correction unit  513 . The sensor value/BL brightness conversion unit  500  stores conversion equations, which have been preliminarily calculated by means of actual measurement and simulation. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     [ 
                     
                       
                         
                           R 
                         
                       
                       
                         
                           G 
                         
                       
                       
                         
                           B 
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             1.007 
                           
                           
                             0.016 
                           
                           
                             0.005 
                           
                         
                         
                           
                             
                               - 
                               0.155 
                             
                           
                           
                             1.225 
                           
                           
                             
                               - 
                               0.017 
                             
                           
                         
                         
                           
                             
                               - 
                               0.046 
                             
                           
                           
                             0.014 
                           
                           
                             1.093 
                           
                         
                       
                       ] 
                     
                     × 
                     
                       [ 
                       
                         
                           
                             Rs 
                           
                         
                         
                           
                             Gs 
                           
                         
                         
                           
                             Bs 
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     In Equation (1), Rs denotes a detection value of the red color sensor  301 , Gs denotes a detection value of the green color sensor  302 , and Bs denotes a detection value of the blue color sensor  303 . Furthermore, in Equation (1), R denotes a detection value of the component of the red color sensor  301 , G denotes a detection value of the component of the green color sensor  302 , and B denotes a detection value of the component of the blue color sensor  303 . Hereunder, the red color sensor  301 , the green color sensor  302 , and the blue color sensor  303  are collectively referred to as color sensors  300 . 
     A sensor value/BL brightness first conversion unit  501  converts the detection value Rs detected by the red color sensor  301 , the detection value Gs detected by the green color sensor  302 , and the detection value Bs detected by the blue color sensor  303  into a detection value R of the red backlight component, using Equation (1). The sensor value/BL brightness first conversion unit  501  outputs the converted detection value R of the component of the red backlight  201 , to the red color detection value temperature correction unit  511 . 
     Similarly, a sensor value/BL brightness second conversion unit  502  converts the detection value of the detection unit  30  into a detection value G of the green backlight component, using Equation (1). The sensor value/BL brightness second conversion unit  502  outputs the converted detection value G to the green color detection value temperature correction unit  512 . A sensor value/BL brightness third conversion unit  503  converts the detection value of the detection unit  30  into a detection value B of the blue backlight component, using Equation (1). The sensor value/BL brightness third conversion unit  503  outputs the converted detection value B to the blue color detection value temperature correction unit  513 . 
     The temperature correction unit  510  includes the red color detection value temperature correction unit  511 , the green color detection value temperature correction unit  512 , and the blue color detection value temperature correction unit  513 . The temperature correction unit  510  receives input of information that indicates temperatures detected by the temperature sensor  55 . 
     The red color detection value temperature correction unit  511  stores a temperature correction coefficient (correction value) for the detection value of the component of the red backlight  201  and a temperature that are associated with each other. This temperature correction coefficient is calculated preliminarily by means of actual measurement or simulation. The red color detection value temperature correction unit  511  corrects the detection value R output from the sensor value/BL brightness first conversion unit  501 , using the information that indicates the temperature detected by the temperature sensor  55  and a temperature correction equation or a temperature correction coefficient for the component of the red backlight  201 . The red color detection value temperature correction unit  511  outputs the corrected detection value R′ to the BL brightness/sensor value conversion unit  520 . 
     The green color detection value temperature correction unit  512  stores a temperature correction coefficient for the detection value of the component of the green backlight  202  and a temperature that are associated with each other. The green color detection value temperature correction unit  512  corrects the detection value G output from the sensor value/BL brightness second conversion unit  502 , using the information that indicates the temperature detected by the temperature sensor  55  and a temperature correction equation or a temperature correction coefficient for the component of the green backlight  202 . The green color detection value temperature correction unit  512  outputs the corrected detection value G′ to the BL brightness/sensor value conversion unit  520 . 
     The blue color detection value temperature correction unit  513  stores a temperature correction coefficient for the detection value of the component of the blue backlight  203  and a temperature that are associated with each other. The blue color detection value temperature correction unit  513  corrects the detection value B output from the sensor value/BL brightness third conversion unit  503 , using the information that indicates the temperature detected by the temperature sensor  55  and a temperature correction equation or a temperature correction coefficient for the component of the blue backlight  203 . The blue color detection value temperature correction unit  513  outputs the corrected detection value B′ to the BL brightness/sensor value conversion unit  520 . 
     The BL brightness/sensor value conversion unit  520  includes a BL brightness/sensor value first conversion unit  521 , a BL brightness/sensor value second conversion unit  522 , and a BL brightness/sensor value third conversion unit  523 . The BL brightness/sensor value conversion unit  520  stores conversion equations, which have been preliminarily calculated by means of actual measurement or simulation. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     [ 
                     
                       
                         
                           
                             Rs 
                             ′ 
                           
                         
                       
                       
                         
                           
                             Gs 
                             ′ 
                           
                         
                       
                       
                         
                           
                             Bs 
                             ′ 
                           
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       
                         [ 
                         
                           
                             
                               1.007 
                             
                             
                               0.016 
                             
                             
                               0.005 
                             
                           
                           
                             
                               
                                 - 
                                 0.155 
                               
                             
                             
                               1.225 
                             
                             
                               
                                 - 
                                 0.017 
                               
                             
                           
                           
                             
                               
                                 - 
                                 0.046 
                               
                             
                             
                               0.014 
                             
                             
                               1.093 
                             
                           
                         
                         ] 
                       
                       
                         - 
                         1 
                       
                     
                     × 
                     
                       [ 
                       
                         
                           
                             
                               R 
                               ′ 
                             
                           
                         
                         
                           
                             
                               G 
                               ′ 
                             
                           
                         
                         
                           
                             
                               B 
                               ′ 
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     The BL brightness/sensor value first conversion unit  521  converts the temperature-corrected detection values (R′, G′, and B′), which are output from the temperature correction unit  510 , into a detection value Rs′ of the red color sensor, using Equation (2). The BL brightness/sensor value first conversion unit  521  outputs the converted detection value Rs′ to the red backlight drive value calculation unit  541 . 
     Similarly, the BL brightness/sensor value second conversion unit  522  converts the temperature-corrected detection values (R′, G′, and B′), which are output from the temperature correction unit  510 , into a detection value Gs′ of the green color sensor, using Equation (2). The BL brightness/sensor value second conversion unit  522  outputs the converted detection value Gs′ to the green backlight drive value calculation unit  542 . The BL brightness/sensor value third conversion unit  523  converts the temperature-corrected detection values (R′, G′, and B′), which are output from the temperature correction unit  510 , into a detection value Bs′ of the blue color sensor, using Equation (2). The BL brightness/sensor value third conversion unit  523  outputs the converted detection value Bs′ to the blue backlight drive value calculation unit  543 . 
     The sensor target value calculation unit  530  (target value calculation unit) includes a red sensor target value calculation unit  531 , a green sensor target value calculation unit  532 , and a blue sensor target value calculation unit  533 . The red sensor target value calculation unit  531  calculates a target value for the detection value of the red color sensor  301 , based on a setting value for the red backlight  201  at the time of white color light emission, which is output from the backlight target color setting unit  40 . The red sensor target value calculation unit  531  outputs the calculated target value for the detection value of the red color sensor  301  to the red backlight drive value calculation unit  541 . The green sensor target value calculation unit  532  calculates a target value for the detection value of the green color sensor  302 , based on a setting value for the green backlight  202  at the time of white color light emission, which is output from the backlight target color setting unit  40 . The green sensor target value calculation unit  532  outputs the calculated target value for the detection value of the green color sensor  302  to the green backlight drive value calculation unit  542 . The blue sensor target value calculation unit  533  calculates a target value for the detection value of the blue color sensor  303 , based on a setting value for the blue backlight  203  at the time of white color light emission, which is output from the backlight target color setting unit  40 . The blue sensor target value calculation unit  533  outputs the calculated target value for the detection value of the blue color sensor  303  to the blue backlight drive value calculation unit  543 . 
     The drive value calculation unit  540  includes a red backlight drive value calculation unit  541 , a green backlight drive value calculation unit  542 , and a blue backlight drive value calculation unit  543 . 
     The red backlight drive value calculation unit  541  compares the target value for the detection value of the red color sensor  301 , which is output from the red sensor target value calculation unit  531 , with the detection value Rs′, which is output from the BL brightness/sensor value first conversion unit  521 . The red backlight drive value calculation unit  541  generates a driving signal of the red backlight  201  based on the result of the comparison. The red backlight drive value calculation unit  541 , for example, generates a driving signal of the red backlight  201  that makes the difference between the detection value of the red color sensor  301  and the detection value Rs′ zero. Specifically, if the detection value Rs′ is higher than the detection value of the red color sensor  301 , the red backlight drive value calculation unit  541  calculates a driving signal that is smaller than the value of the signal currently driving the red backlight  201 , in order to lower the brightness value. If the detection value Rs′ is lower than the detection value of the red color sensor  301 , the red backlight drive value calculation unit  541  calculates a driving signal that is greater than the value of the signal currently driving the red backlight  201 , in order to raise the brightness value. The red backlight drive value calculation unit  541  outputs the generated driving signal to the red backlight driving circuit  101  of the backlight driving unit  10 . 
     The green backlight drive value calculation unit  542  compares the target value for the detection value of the green color sensor  302 , which is output from the green sensor target value calculation unit  532 , with the detection value Gs′, which is output from the BL brightness/sensor value second conversion unit  522 . The green backlight drive value calculation unit  542  generates a driving signal of the green backlight  202  based on the result of the comparison, and outputs the generated driving signal to the green backlight driving circuit  102 . 
     The blue backlight drive value calculation unit  543  compares the target value for the detection value of the blue color sensor  303 , which is output from the blue sensor target value calculation unit  533 , with the detection value Bs′, which is output from the BL brightness/sensor value third conversion unit  523 . The blue backlight drive value calculation unit  543  generates a driving signal of the blue backlight  203  based on the result of the comparison, and outputs the generated driving signal to the blue backlight driving circuit  103 . 
     Next, the spectral characteristic of the color filter provided in the color sensor  300  is described, with reference to  FIG. 2 .  FIG. 2  is a diagram showing an example of a light transmission characteristic of an RGB color filter. 
     In  FIG. 2 , the horizontal axis represents wavelength, the vertical axis represents light transmittance, the curved line g 101  represents light transmittance with respect to the wavelength of the blue filter, the curved line g 102  represents light transmittance with respect to the wavelength of the green filter, and the curved line g 103  represents light transmittance with respect to the wavelength of the red filter. As shown in  FIG. 2 , the band where the blue filter transmittance is 20[%] or higher is approximately 400 [nm] to 540 [nm] as seen from the curved line g 101 . The band where the green filter transmittance is 20[%] or higher is approximately 480 [nm] to 600 [nm] as seen from the curved line g 102 . The band where the red filter transmittance is 20[%] or higher is approximately 590 [nm] to 720 [nm] as seen from the curved line g 103 . The respective filters have the spectral characteristic shown in  FIG. 2 , and therefore, the green color sensor also detects the light amount with approximate wavelength 450 [nm] to 540 [nm] for example. Moreover, the red color sensor also detects few [%] of the light amount with approximate wavelength 380 [nm] to 540 [nm] of the blue band. Furthermore, the red color sensor also detects few [%] to 20[%] of the light amount with approximate wavelength 570 [nm] to 600 [nm] of the green band. 
     Therefore, in the present exemplary embodiment, the sensor value/BL brightness conversion unit  500  separates the detection value detected by the detection unit  30  into the respective color components of the backlight, using Equation (1). 
     Next, temperature drift of a detection value in the color sensor  300  is described, with reference to  FIG. 3 .  FIG. 3  is a diagram for describing temperature drift in a red color sensor according to the present exemplary embodiment. 
     In  FIG. 3 , the horizontal axis represents temperature within the backlight device  1 , and the vertical axis represents the magnitude of a detection value of the red color sensor. Moreover, in  FIG. 3 , the dashed line g 201  represents a reference value, which is a detection value at the time of supplying a constant drive value to the backlight at a predetermined environmental temperature. The curved line g 211  represents a temperature drift characteristic of the detection value detected by the red color sensor  301  at the time of driving only the red backlight  201 . The curved line g 212  represents a temperature drift characteristic of the detection value detected by the red color sensor  301  at the time of driving only the green backlight  202 . The curved line g 213  represents a temperature drift characteristic of the detection value detected by the red color sensor  301  at the time of driving only the blue backlight  203 . 
     As shown in  FIG. 3 , the temperature drift characteristic of the detection value differs with each color of light received by the red color sensor  301 . Similarly, the temperature drift characteristic of the detection value differs with each color of light received by the green color sensor  302 , and the temperature drift characteristic of the detection value differs with each color of light received by the blue color sensor  303 . 
     Next, an example of the calculation method of Equation (1) is described. When the detection values Rs 1 , Gs 1 , and Bs 1  of the respective color sensors are measured while only the red backlight  201  is made to emit light, the brightness component R 1  of the red backlight  201  is expressed as Equation (3) below. The brightness value of the red backlight  201  is a value found by multiplying the drive value by a predefined constant (for example, amplification multiplier of the driving circuit). Accordingly, the brightness component R 1  of the red backlight  201  is calculated by multiplying the drive value by the constant. The drive value is, for example, a known value such as driving current value or driving voltage value.
 
 R   1   =a   11   ×Rs   1   +a   12   ×Gs   1   +a   13   ×Bs   1   (3)
 
     In Equation (3), a 11 , a 12 , and a 13  are constants. 
     Next, when the detection values Rs 2 , Gs 2 , and Bs 2  of the respective color sensors are measured while only the green backlight  202  is made to emit light, the brightness component G 1  of the green backlight  202  is expressed as Equation (4) below. Similarly, the brightness component G 1  of the green backlight  202  is calculated by multiplying the drive value by the constant.
 
 G   1   =a   21   ×Rs   2   +a   22   ×Gs   2   +a   23   ×Bs   2   (4)
 
     In Equation (4), a 21 , a 22 , and a 23  are constants. 
     Next, when the detection values Rs 3 , Gs 3 , and Bs 3  of the respective color sensors are measured while only the blue backlight  203  is made to emit light, the brightness component B 1  of the blue backlight  203  is expressed as Equation (5) below. Similarly, the brightness component B 3  of the blue backlight  203  is calculated by multiplying the drive value by the constant.
 
 B   3   =a   31   ×Rs   3   +a   32   ×Gs   3   +a   33   ×Bs   3   (5)
 
     In Equation (5), a 31 , a 32 , and a 33  are constants. 
     Each constant in the simultaneous equations of Equation (3) through Equation (5) is calculated, using the detection value of each color sensor obtained while only each backlight is made to emit light at each of the three types of brightness, and using the brightness component of the red backlight  201 , the green backlight  202 , or the blue backlight  203 . The result of performing calculation in this manner is a 11 =1.007, a 12 =0.016, a 13 =0.005, a 21 =−0.155, a 22 =1.225, a 23 =−0.017, a 31 =−0.046, a 32 =0.014, and a 33 =1.093 as shown in Equation (1). The value of each element of Equation (1) is an example, and it may differ, depending on the characteristic, the light receiving sensitivity, and the light receiving band of each color filter of the red color sensor  301 , the green color sensor  302 , and the blue color sensor  303 . 
     Next, temperature correction performed by the temperature correction unit  510  is described, with reference to  FIG. 4 . 
       FIG. 4  is a diagram for describing temperature correction made to a red light emission color in the red color sensor according to the present exemplary embodiment. In  FIG. 4 , the horizontal axis represents temperature within the backlight device  1 , and the vertical axis represents the magnitude of a detection value and the magnitude of a correction value in a case where the red light emission color is red in the red color sensor. Moreover, in  FIG. 4 , the dashed line g 201  represents a reference value as with  FIG. 3 , and the curved line g 211  represents the temperature drift characteristic of the detection value of the red color light emission color of the red color sensor  301  as with  FIG. 3 . The curved line  221  represents the relationship between temperature and temperature correction coefficient stored in the red color detection value temperature correction unit  511 . 
     As shown in  FIG. 4 , the temperature correction coefficient stored in the red color detection value temperature correction unit  511  is a value for correcting the detection value of the red color light emission color (detection value of the component of the red backlight  201 ) to a reference value a, for each temperature measured by the temperature sensor  55 . For example, when the temperature within the device measured by the temperature sensor  55  is c1, the detection value of the red color light emission color takes a detection value b due to the influence of temperature drift. The value of the temperature correction coefficient in this case is c. The red color detection value temperature correction unit  511  can perform temperature correction on the detection value b by multiplying the detection value b by the correction coefficient c. Moreover, when the temperature within the device is c2, the temperature correction coefficient value is 1 since the detection value a matches the reference value a. 
     The temperature correction coefficient stored in the red color detection value temperature correction unit  511  may be a temperature correction equation that expresses the relationship between temperature and a correction coefficient to be multiplied. In this case, the red color detection value temperature correction unit  511  uses the stored temperature correction equation to calculate the temperature correction coefficient based on the temperature measured by the temperature sensor  55 . The red color detection value temperature correction unit  511  then multiplies the detection value by the calculated temperature correction coefficient to thereby perform temperature correction of the detection value. 
     Alternatively, the red color detection value temperature correction unit  511  may add the stored temperature correction coefficient to the detection value to perform temperature correction. In this case, when the temperature within the device is c1, the temperature correction coefficient to be added is c′ (not shown in the figure). The red color detection value temperature correction unit  511  then adds the temperature correction coefficient c′ to the detection value b to thereby perform temperature correction. Moreover, when the temperature within the device is c2, the temperature correction coefficient value to be added is 0 since the detection value a matches the reference value a. The red color detection value temperature correction unit  511  may store temperature and the temperature correction coefficient for correcting temperature by being added to the detection value in this manner, while associating them with each other. Also in this case, the temperature correction coefficient stored in the red color detection value temperature correction unit  511  may be a temperature correction equation that expresses the relationship between the temperature and the correction coefficient to be added. 
     Similarly, in the case of the green detection value temperature correction unit  512 , the temperature drift characteristic for the detection value of the red backlight  201 , the temperature drift characteristic for the detection value of the green back light  202 , and the temperature drift characteristic for the detection value of the blue backlight  203 , of the green color sensor  302  are also different. The green color detection value temperature correction unit  512  performs temperature correction on the detection value Gs of the component of the green backlight  202 , using the temperature correction equation or temperature correction coefficient for the component of the green backlight  202 . 
     Similarly, in the case of the blue detection value temperature correction unit  513 , the temperature drift characteristic for the detection value of the red backlight  201 , the temperature drift characteristic for the detection value of the green back light  202 , and the temperature drift characteristic for the detection value of the blue backlight  203 , of the green color sensor  302  are different. The blue color detection value temperature correction unit  513  performs temperature correction on the detection value Gs of the component of the blue backlight  203 , using the temperature correction equation or temperature correction coefficient for the component of the blue backlight  203 . 
     Next, a temperature correction method for the backlight device  1  of the present exemplary embodiment is described. First, steps of temperature correction for the brightness of the red backlight  201  are described. 
     The detection unit  30  receives light emitted from the light emitting unit  20 , and then outputs a detection value that has been converted from the received light amount into an electric signal, to the calculation unit  50 . 
     Subsequently, a sensor value/BL brightness first conversion unit  501  of the calculation unit  50  converts the detection value output from the detection unit  30  into a detection value Rs of the component of the red backlight  201 , using Equation (1). The sensor value/BL brightness first conversion unit  501  then outputs the converted detection value Rs of the component of the red backlight  201  to the red color detection value temperature correction unit  511 . 
     Then, the red color detection value temperature correction unit  511  performs temperature correction on the detection value Rs of the component of the red backlight  201 , using the information that indicates the temperature detected by the temperature sensor  55  and a preliminarily stored temperature correction equation or temperature correction coefficient, and outputs the corrected detection value Rs′ to the BL brightness/sensor value first conversion unit  521 . 
     Next, the BL brightness/sensor value first conversion unit  521  converts the temperature-corrected detection value Rs′ output from the temperature correction unit  510  into a detection value Rs′, which is a detection value of the red color sensor  301 , using Equation (2). The BL brightness/sensor value first conversion unit  521  outputs the converted detection value Rs′ to the red backlight drive value calculation unit  541 . 
     Then, the red backlight drive value calculation unit  541  compares the target value for the detection value of the red color sensor  301 , which is output from the red sensor target value calculation unit  531 , with the detection value Rs′, which is output from the BL brightness/sensor value first conversion unit  521 , and generates a driving signal of the red backlight  201  based on the result of the comparison. 
     With the above process, the backlight device  1  can perform temperature correction for the temperature drift of the red color sensor  301 . 
     Similarly, the sensor value/BL brightness second conversion unit  502  converts the detection value output from the detection unit  30  into a detection value G of the component of the green backlight  202 . The sensor value/BL brightness third conversion unit  503  converts the detection value output from the detection unit  30  into a detection value B of the component of the blue backlight  203 . Next, the green color detection value temperature correction unit  512  and the blue color detection value temperature correction unit  513  performs temperature correction on each detection value of each backlight component, which has been converted in the above manner, using the information indicating the temperature detected by the temperature sensor  55 , and the preliminarily stored temperature correction equation or temperature correction coefficient. In this manner, the backlight device  1  uses the corrected detection values Gs′ and Bs′ to perform temperature correction for the brightness of the green and blue backlights as with the brightness of the red back light  201 . 
     Next, an example of color temperature changes in the backlight device  1  due to temperature drift is described, with reference to  FIG. 5  and  FIG. 6 . 
       FIG. 5  is a diagram for describing an example of color temperature changes in a case where a temperature correction is made to a temperature drift characteristic of a color sensor.  FIG. 6  is a diagram for describing an example of color temperature changes in a case where a temperature correction is made to each color of the backlight according to the present exemplary embodiment. 
     In  FIG. 5  and  FIG. 6 , the horizontal axis represents warm-up time, and the vertical axis represents color temperature level. The warm-up time refers to a length of time elapsed after the power supply of the backlight device  1  is switched on. 
     In  FIG. 5 , the dashed line g 301  represents a setting value where the color temperature is set to 3,000 [K (Kelvin)], and the dashed line g 302  represents a setting value where the color temperature is set to 6,500 [K]. Moreover, the curved line g 311  represents changes in the color temperature characteristic in the display unit (not shown in the figure) where the color temperature is set to 3,000 [K]. The curved line g 312  represents changes in the color temperature characteristic in the display unit where the color temperature is set to 6,500 [K]. 
     In  FIG. 6 , the dashed line g 401  represents a setting value where the color temperature is set to 3,000 [K (Kelvin)], and the dashed line g 402  represents a setting value where the color temperature is set to 6,500 [K]. Moreover, the curved line g 411  represents changes in the color temperature characteristic in the display unit where the color temperature is set to 3,000 [K]. The curved line g 412  represents changes in the color temperature characteristic in the display unit where the color temperature is set to 6,500 [K]. 
       FIG. 5  shows changes in the color temperature in the display unit with respect to the warm-up time in the supposed case where the temperature correction unit provided in the backlight device performs temperature correction for the temperature drift characteristic of the detection value of each color sensor. In this case, for example, temperature correction is performed on the detection value of the red color sensor based on the temperature drift characteristic of the detection value at the time of the red color sensor receiving white color light. Similarly, temperature correction is performed on the detection value of the green color sensor based on the temperature drift characteristic of the detection value at the time of the green color sensor receiving white color light. Furthermore, temperature correction is performed on the detection value of the blue color sensor based on the temperature drift characteristic of the detection value at the time of the blue color sensor receiving white color light. 
     When a user sets white point chromaticity in an image display device having a backlight device that performs temperature correction in this manner, if the color temperature is set to 6,500 [K], the color temperature of the display unit converges to the setting value at time t 1  as illustrated with the curved line g 312 . However, if the color temperature is set to 3,000 [K], the color temperature of the display unit still does not take the setting value even at time t 2  as illustrated with the curved line g 311 . In this way, the color temperature convergence time for the warm-up time differs for each set white point setting. 
     On the other hand, as shown in  FIG. 6 , in the case where the detection value of each color sensor is converted into a detection value of the component of the backlight and it is temperature-corrected to the converted detection value of the backlight component as practiced in the present exemplary embodiment, if the color temperature is set to 6,500 [K], the color temperature of the display unit takes the setting value at time t 1  as illustrated with the curved line g 413 . Next, if the color temperature is set to 3,000 [K], the color temperature of the display unit takes the setting value at time t 3 , at which a shorter length of time has elapsed than time t 2 , as illustrated with the curved line g 403 . In this manner, according to the present exemplary embodiment, it is possible to reduce the length of time taken by the color temperature of the display unit to converge, and match the convergence time for each white point setting. 
     As described above, the backlight device  1  of the present exemplary embodiment converts the detection value detected by the color sensor into a detection value of the component of each backlight. The backlight device  1  of the present exemplary embodiment perform temperature correction on the converted detection value of the backlight component, using a temperature correction equation or temperature correction coefficient that is preliminarily set for each color component. The drive value calculation unit  540  compares each target value output from the sensor target value calculation unit  530  with each corrected detection value output from the BL brightness/sensor value conversion unit  520 . The drive value calculation unit  540  generates each driving signal for the light emitting unit  20  based on the comparison result, and drives each backlight of the light emitting unit  20  with each generated driving signal. 
     As a result, the backlight device  1  of the present exemplary embodiment can suppress temperature drift of the brightness of each backlight with respect to the temperature, and therefore, can reduce the convergence time to achieve the set white point. 
     Second Exemplary Embodiment 
       FIG. 7  is a block diagram of a schematic configuration of a backlight device  1   a  according to the present exemplary embodiment. As shown in  FIG. 7 , the backlight device  1   a  includes a backlight driving unit  10 , a light emitting unit  20 , a detection unit  30 , a backlight target color setting unit  40 , and a calculation unit  50   a . Moreover, the calculation unit  50   a  includes a sensor value/BL brightness conversion unit  500  (conversion unit), a temperature correction unit  510   a , a drive value calculation unit  540   a , and a backlight target value calculation unit  550 . 
     The same reference symbols are given to the functional units with the same function in the backlight device  1  described in the first exemplary embodiment, and descriptions thereof are omitted. 
     The temperature correction unit  510   a  includes a red color detection value temperature correction unit  511   a , a green color detection value temperature correction unit  512   a , and a blue color detection value temperature correction unit  513   a.    
     As with the first exemplary embodiment, the red color detection value temperature correction unit  511   a  corrects the detection value Rs output from the sensor value/BL brightness first conversion unit  501 , using a temperature correction equation or temperature correction coefficient for the red backlight component, and outputs the corrected detection value R′ to a red backlight drive value calculation unit  541   a . As with the first exemplary embodiment, the green color detection value temperature correction unit  512   a  corrects the detection value Gs output from the sensor value/BL brightness second conversion unit  502 , using a temperature correction equation or temperature correction coefficient for the green backlight component, and outputs the corrected detection value G′ to a green backlight drive value calculation unit  542   a . As with the first exemplary embodiment, the blue color detection value temperature correction unit  513   a  corrects the detection value B output from the sensor value/BL brightness third conversion unit  503 , using a temperature correction equation or temperature correction coefficient for the blue backlight component, and outputs the corrected detection value B′ to a blue backlight drive value calculation unit  543   a.    
     That is to say, in the present exemplary embodiment, the calculation unit  50   a  outputs the detection values (R′, G′, and B′) corrected by the temperature correction unit  510   a  to the drive value calculation unit  540   a  without converting them to the detection values of the sensors using Equation (2) as described in the first exemplary embodiment. 
     The backlight target value calculation unit  550  (target value calculation unit) includes a red backlight target value calculation unit  551 , a green backlight target value calculation unit  552 , and a blue backlight target value calculation unit  553 . 
     The red backlight target value calculation unit  551  calculates a target value for the brightness of the red backlight  201 , based on a setting value for the red backlight  201  at the time of white color light emission, which is output from the backlight target color setting unit  40 . The red sensor target value calculation unit  531  outputs the calculated target value for the brightness of the red backlight  201  to the red backlight drive value calculation unit  541   a . The green backlight target value calculation unit  552  calculates a target value for the brightness of the green backlight  202 , based on a setting value for the green backlight  202  at the time of white color light emission, which is output from the backlight target color setting unit  40 . The green sensor target value calculation unit  532  outputs the calculated target value for the brightness of the green backlight  202  to the green backlight drive value calculation unit  542   a . The blue backlight target value calculation unit  553  calculates a target value for the brightness of the blue backlight  203 , based on a setting value for the blue backlight  203  at the time of white color light emission, which is output from the backlight target color setting unit  40 . The blue sensor target value calculation unit  533  outputs the calculated target value for the brightness of the blue backlight  203  to the blue backlight drive value calculation unit  543   a.    
     The drive value calculation unit  540   a  includes a red backlight drive value calculation unit  541   a , a green backlight drive value calculation unit  542   a , and a blue backlight drive value calculation unit  543   a.    
     The red backlight drive value calculation unit  541   a  compares the target value for the brightness of the red backlight  201 , which is output from the red backlight target value calculation unit  551 , with the detection value R′, which is output from the red color detection value temperature correction unit  511   a . The red backlight drive value calculation unit  541   a  generates a driving signal of the red backlight  201  based on the result of the comparison, and outputs the generated driving signal to the red backlight driving circuit  101 . The green backlight drive value calculation unit  542   a  compares the target value for the brightness of the green backlight  202 , which is output from the green backlight target value calculation unit  552 , with the detection value G′, which is output from the green color detection value temperature correction unit  512   a . The green backlight drive value calculation unit  542   a  generates a driving signal of the green backlight  202  based on the result of the comparison, and outputs the generated driving signal to the green backlight driving circuit  102 . The blue backlight drive value calculation unit  543   a  compares the target value for the brightness of the blue backlight  203 , which is output from the blue backlight target value calculation unit  553 , with the detection value B′, which is output from the blue color detection value temperature correction unit  513   a . The blue backlight drive value calculation unit  543   a  generates a driving signal of the blue backlight  203  based on the result of the comparison, and outputs the generated driving signal to the blue backlight driving circuit  103 . 
     That is to say, the drive value calculation unit  540   a  of the present exemplary embodiment compares the detection values (R′, G′, and B′) of each temperature-corrected color component of the backlight, with the target value output from the backlight target value calculation unit  550 , to control the driving signal of each backlight. 
     Next, a temperature correction method for the backlight device  1   a  of the present exemplary embodiment is described. First, steps of temperature correction for the brightness of the red backlight  201  are described. 
     The detection unit  30  receives light emitted from the light emitting unit  20 , and outputs a detection value that has been converted from the received light amount into an electric signal, to the calculation unit  50 . 
     Subsequently, a sensor value/BL brightness first conversion unit  501  of the calculation unit  50  converts the detection value output from the detection unit  30  into a detection value R of the component of the red backlight  201 , using Equation (1). The sensor value/BL brightness first conversion unit  501  outputs the converted brightness value R of the red backlight  201 , to the red color detection value temperature correction unit  511   a.    
     Then, the red color detection value temperature correction unit  511   a  performs temperature correction on the detection value R of the component of the red backlight  201 , using the information that indicates the temperature detected by the temperature sensor  55  and a preliminarily stored temperature correction equation or temperature correction coefficient, and outputs the corrected detection value R′ to the red backlight drive value calculation unit  541   a.    
     Then, the red backlight drive value calculation unit  541   a  compares the target value for the detection value of the red color sensor  301 , which is output from the red backlight target value calculation unit  551 , with the temperature-corrected detection value R′, which is output from the red color detection value temperature correction unit  511   a , and generates a driving signal of the red backlight  201  based on the result of the comparison. 
     With the above process, the backlight device  1   a  can perform temperature correction for the temperature drift of the red color sensor  301 . 
     Similarly, the sensor value/BL brightness second conversion unit  502  converts the detection value output from the detection unit  30  into a brightness value G of the green backlight  202 . The sensor value/BL brightness third conversion unit  503  converts the detection value output from the detection unit  30  into a brightness value B of the blue backlight  203 . Next, the green color detection value temperature correction unit  512   a  and the blue color detection value temperature correction unit  513   a  performs temperature correction on the brightness value of each backlight component, which has been converted in the above manner so that the brightness value of each backlight takes the reference value, using the information indicating the temperature detected by the temperature sensor  55 , and the preliminarily stored correction equation or correction coefficient. In this manner, the backlight device  1  uses the corrected brightness values G′ and B′ to perform temperature correction for the brightness of the green and blue backlights as with the brightness of the red back light  201 . 
     As described above, the backlight device  1   a  of the present exemplary embodiment compares the temperature-corrected detection values (R′, G′, and B′) of each color component of the backlight, with the target value output from the backlight target value calculation unit  550 , to control the driving signal of each backlight. 
     As a result, in addition to the effect of the first exemplary embodiment, the backlight device  1   a  of the present exemplary embodiment can eliminate the BL brightness/sensor value conversion unit  520  for converting the temperature-corrected detection value to a detection value of each color sensor. 
     When using the backlight device  1  or backlight device  1   a  of the first or second exemplary embodiment in an image display device, it is possible to improve color reproducibility, and therefore, there is an effect of realizing, for example, a high-image-quality image confirmation display for graphic design and broadcasting purposes, and a display for medical purposes. 
     Moreover, the sensor value/BL brightness conversion unit  500  functions as a signal filter as illustrated with Equation (1). Accordingly, this sensor value/BL brightness conversion unit  500  may be configured with an analog circuit, a digital circuit, or a DSP (digital signal processor) or an ASIC (application specific integrated circuit). 
     In the present exemplary embodiments, there has been described an example in which the light emitting unit  20  includes a red backlight  201 , a green backlight  202 , and a blue backlight  203 . However, the light emitting unit  20  may include backlights of colors other than RGB colors such as CMYG (cyan, magenta, yellow, and green) colors. In this case, the detection unit  30  may include a color sensor that matches the wavelength band of the backlights provided in the light emitting unit  20 , and the calculation unit  50  (or  50   a ) may include a sensor value/BL brightness conversion unit  500 , a temperature correction unit  510  (or  510   a ), a sensor target value calculation unit  530 , a backlight target value calculation unit  550 , and a drive value calculation unit  540  (or  540   a ) that match the wavelength band of the backlights provided in the light emitting unit  20 . 
     In the present exemplary embodiments, the sensor detection value is temperature-corrected, and then it is compared with the target value. However, conversely, the target value may be temperature-corrected, and it may then be compared with the sensor detection value. 
     In the present exemplary embodiment, there has been described an example of providing a single sensor value/BL brightness conversion unit  500  and a single temperature correction unit  510 . However, for example, a sensor value/BL brightness conversion unit  500  and a temperature correction unit  510  may be provided for each color of color sensors. 
     The backlight device  1  (or  1   a ) of the present exemplary embodiments may be applied to a liquid crystal display device, a mobile information terminal, a navigation system, an advertisement display lamp, an electronic sign board (digital signage), or the like. 
     When using the backlight device  1  of the present exemplary embodiment in a liquid crystal display device, the red backlight  201 , the green backlight  202 , and the blue backlight  203  may be divided into a plurality of blocks, and lighting control may be performed individually for each of the plurality of divided blocks. 
     A program for realizing the function of the calculation unit  50  of  FIG. 1  or the calculation unit  50   a  of  FIG. 7  of the exemplary embodiments may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read on a computer system and executed, to thereby perform the process of each unit. The “computer system” includes an OS and hardware such as peripheral devices. 
     Moreover, the “computer system” includes a homepage provision environment (or display environment) in the case of using a WWW system. 
     Furthermore, the “computer-readable recording medium” refers to a movable medium such as a flexible disc, magneto-optical disc, ROM (read-only memory), and CD-ROM, a USB memory connected through USB (universal serial bus) I/F (interface), and a memory device such as a hard disk drive built in a computer system. Moreover, the “computer-readable recording medium” includes one that retains a program for a certain length of time such as volatile memory within a computer system serving as a server or a client. The above program may realize part of the functions described above, and further, the program may realize the functions described above in combination with a program that is already recorded on the computer system. 
     REFERENCE SYMBOLS 
     
         
           1 ,  1   a  Backlight device 
           10  Backlight driving unit 
           20  Light emitting unit 
           30  Detection unit 
           301  Red color sensor 
           302  Green color sensor 
           303  Blue color sensor 
           40  Backlight target color setting unit 
           50 ,  50   a  Calculation unit 
           55  Temperature sensor 
           101  Red backlight driving circuit 
           102  Green backlight driving circuit 
           103  Blue backlight driving circuit 
           201  Blue backlight 
           202  Green backlight 
           203  Red backlight 
           301  Red color sensor 
           302  Green color sensor 
           303  Blue color sensor 
           501  Sensor value/BL brightness first conversion unit 
           500  Sensor value/BL brightness conversion unit 
           510  Temperature correction unit 
           520  BL brightness/sensor value conversion unit 
           530  Sensor target value calculation unit 
           540 ,  540   a  Drive value calculation unit 
           550  Backlight target value calculation unit