Patent Publication Number: US-7719208-B2

Title: Color control method for LED lighting systems

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a color control method, and more particularly, to a color control method for LED lighting systems. 
   2. Description of the Prior Art 
   Due to lightweight, small size, low power consumption and high-bright lighting capability, light emitting diodes (LEDs) are now in widespread use, including a variety of indication applications, indoor or outdoor lighting applications, vehicle auxiliary lighting applications, camera flashlights, and so forth. In particular, the designs of backlights for different display panels are switched from traditional cold cathode fluorescent lamps (CCFLs) or external electrode fluorescent lamps (EEFLs) to LED lighting modules gradually. While the LED lighting modules are applied to devise the backlights for different display panels, corresponding control methods for the LED lighting modules are required to control the luminance and chromaticity of light outputs for achieving high-quality visual appearances. 
     FIG. 1  is a functional block diagram schematically showing a prior-art LED lighting system  100 . The LED lighting system  100  comprises an LED module  101 , an LED driving circuit  111 , a color sensor  180 , and a controller  150 . The LED driving circuit  111  is utilized to provide a driving signal to the LED module  101 . The color sensor  180  detects the light emitted from the LED module  101  for generating a feedback signal. The controller  150  generates a control signal based on the feedback signal. Then, the LED driving circuit  111  is capable of regulating the driving signal based on the control signal so that the LED module  101  is able to generate the light having desired luminance and chromaticity. 
   However, when the operating temperature of the LED dice of the LED module  101  is rising, wavelength shifts will occur to the light emitted from the LED module  101  accordingly. The prior-art LED lighting system  100  is not able to compensate the wavelength shifts in response to temperature variations. That is, the control accuracy concerning the luminance and chromaticity of the light generate by the LED module  101  is getting worse as the operating temperature of the LED dice of the LED module  101  rises. 
   SUMMARY OF THE INVENTION 
   In accordance with an embodiment of the present invention, a color control method for an LED lighting system is provided. The LED lighting system comprises a red LED module, a green LED module, and a blue LED module. The color control method comprises: providing a first driving current to the red LED module during a first interval; generating a first feedback voltage corresponding to the red LED module based on a first voltage drop corresponding to the red LED module, and generating a first red light signal, a first green light signal, a first blue light signal, and a first set of CIE tristimulus values corresponding to the red LED module through detecting light emitted from the red LED module at a first time of the first interval; generating a second feedback voltage corresponding to the red LED module based on a second voltage drop corresponding to the red LED module, and generating a second red light signal, a second green light signal, a second blue light signal, and a second set of CIE tristimulus values corresponding to the red LED module through detecting light emitted from the red LED module at a second time of the first interval; providing a second driving current to the green LED module during a second interval; generating a first feedback voltage corresponding to the green LED module based on a first voltage drop corresponding to the green LED module, and generating a first red light signal, a first green light signal, a first blue light signal, and a first set of CIE tristimulus values corresponding to the green LED module through detecting light emitted from the green LED module at a first time of the second interval; generating a second feedback voltage corresponding to the green LED module based on a second voltage drop corresponding to the green LED module, and generating a second red light signal, a second green light signal, a second blue light signal, and a second set of CIE tristimulus values corresponding to the green LED module through detecting light emitted from the green LED module at a second time of the second interval; providing a third driving current to the blue LED module during a third interval; generating a first feedback voltage corresponding to the blue LED module based on a first voltage drop corresponding to the blue LED module, and generating a first red light signal, a first green light signal, a first blue light signal, and a first set of CIE tristimulus values corresponding to the blue LED module through detecting light emitted from the blue LED module at a first time of the third interval; generating a second feedback voltage corresponding to the blue LED module based on a second voltage drop corresponding to the blue LED module, and generating a second red light signal, a second green light signal, a second blue light signal, and a second set of CIE tristimulus values corresponding to the blue LED module through detecting light emitted from the blue LED module at a second time of the third interval; providing the first driving current to the red LED module, providing the second driving current to the green LED module, and providing the third driving current to the blue LED module; generating a third feedback voltage corresponding to the red LED module based on a third voltage drop corresponding to the red LED module; generating a third set of CIE tristimulus values corresponding to the red LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first set of CIE tristimulus values, and the second set of CIE tristimulus values corresponding to the red LED module; generating a third red light signal, a third green light signal, and a third blue light signal corresponding to the red LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first red light signal, the first green light signal, the first blue light signal, the second red light signal, the second green light signal, the second blue light signal corresponding to the red LED module; generating a third feedback voltage corresponding to the green LED module based on a third voltage drop corresponding to the green LED module; generating a third set of CIE tristimulus values corresponding to the green LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first set of CIE tristimulus values, and the second set of CIE tristimulus values corresponding to the green LED module; generating a third red light signal, a third green light signal, and a third blue light signal corresponding to the green LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first red light signal, the first green light signal, the first blue light signal, the second red light signal, the second green light signal, the second blue light signal corresponding to the green LED module; generating a third feedback voltage corresponding to the blue LED module based on a third voltage drop corresponding to the blue LED module; generating a third set of CIE tristimulus values corresponding to the blue LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first set of CIE tristimulus values, and the second set of CIE tristimulus values corresponding to the blue LED module; generating a third red light signal, a third green light signal, and a third blue light signal corresponding to the blue LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first red light signal, the first green light signal, the first blue light signal, the second red light signal, the second green light signal, the second blue light signal corresponding to the blue LED module; calculating a first coefficient matrix based on the third set of CIE tristimulus values, the third red light signal, the third green light signal, and the third blue light signal corresponding to the red LED module, the third set of CIE tristimulus values, the third red light signal, the third green light signal, and the third blue light signal corresponding to the green LED module, and the third set of CIE tristimulus values, the third red light signal, the third green light signal, and the third blue light signal corresponding to the blue LED module; calculating a first control signal, a second control signal, and a third control signal based on the first coefficient matrix and a set of preset CIE tristimulus values; and regulating the first driving current based on the first control signal, regulating the second driving current based on the second control signal, and regulating the third driving current based on the third control signal; wherein the first interval, the second interval, and the third interval are not overlapped between each other. 
   In accordance with another embodiment of the present invention, a color control method for an LED lighting system is provided. The LED lighting system comprises a red LED module, a green LED module, and a blue LED module. The color control method comprises: providing a first driving voltage to the red LED module during a first interval; generating a first feedback voltage corresponding to the red LED module based on a first current flowing through the red LED module, and generating a first set of CIE tristimulus values corresponding to the red LED module through detecting light emitted from the red LED module at a first time of the first interval; generating a second feedback voltage corresponding to the red LED module based on a second current flowing through the red LED module, and generating a second set of CIE tristimulus values corresponding to the red LED module through detecting light emitted from the red LED module at a second time of the first interval; providing a second driving voltage to the green LED module during a second interval; generating a first feedback voltage corresponding to the green LED module based on a first current flowing through the green LED module, and generating a first set of CIE tristimulus values corresponding to the green LED module through detecting light emitted from the green LED module at a first time of the second interval; generating a second feedback voltage corresponding to the green LED module based on a second current flowing through the green LED module, and generating a second set of CIE tristimulus values corresponding to the green LED module through detecting light emitted from the green LED module at a second time of the second interval; providing a third driving voltage to the blue LED module during a third interval; generating a first feedback voltage corresponding to the blue LED module based on a first current flowing through the blue LED module, and generating a first set of CIE tristimulus values corresponding to the blue LED module through detecting light emitted from the blue LED module at a first time of the third interval; generating a second feedback voltage corresponding to the blue LED module based on a second current flowing through the blue LED module, and generating a second set of CIE tristimulus values corresponding to the blue LED module through detecting light emitted from the blue LED module at a second time of the third interval; providing the first driving voltage to the red LED module, providing the second driving voltage to the green LED module, and providing the third driving voltage to the blue LED module; generating a third feedback voltage corresponding to the red LED module based on a third current flowing through the red LED module; generating a third set of CIE tristimulus values corresponding to the red LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first set of CIE tristimulus values, and the second set of CIE tristimulus values corresponding to the red LED module; generating a third feedback voltage corresponding to the green LED module based on a third current flowing through the green LED module; generating a third set of CIE tristimulus values corresponding to the green LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first set of CIE tristimulus values, and the second set of CIE tristimulus values corresponding to the green LED module; generating a third feedback voltage corresponding to the blue LED module based on a third current flowing through the blue LED module; generating a third set of CIE tristimulus values corresponding to the blue LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first set of CIE tristimulus values, and the second set of CIE tristimulus values corresponding to the blue LED module; calculating a first duty cycle control signal, a second duty cycle control signal, and a third duty cycle control signal based on the third set of CIE tristimulus values corresponding to the red LED module, the third set of CIE tristimulus values corresponding to the green LED module, the third set of CIE tristimulus values corresponding to the blue LED module, and a set of preset CIE tristimulus values; and regulating the first driving voltage based on the first duty cycle control signal, regulating the second driving voltage based on the second duty cycle control signal, and regulating the third driving voltage based on the third duty cycle control signal; wherein the first interval, the second interval, and the third interval are not overlapped between each other. 
   In accordance with the other embodiment of the present invention, a color control method for an LED lighting system is provided. The LED lighting system comprises a red LED module, a green LED module, and a blue LED module. The color control method comprises: providing a first driving current to the red LED module during a first interval; generating a first feedback voltage corresponding to the red LED module based on a first voltage drop corresponding to the red LED module, and generating a first set of CIE tristimulus values corresponding to the red LED module through detecting light emitted from the red LED module at a first time of the first interval; generating a second feedback voltage corresponding to the red LED module based on a second voltage drop corresponding to the red LED module, and generating a second set of CIE tristimulus values corresponding to the red LED module through detecting light emitted from the red LED module at a second time of the first interval; providing a second driving current to the green LED module during a second interval; generating a first feedback voltage corresponding to the green LED module based on a first voltage drop corresponding to the green LED module, and generating a first set of CIE tristimulus values corresponding to the green LED module through detecting light emitted from the green LED module at a first time of the second interval; generating a second feedback voltage corresponding to the green LED module based on a second voltage drop corresponding to the green LED module, and generating a second set of CIE tristimulus values corresponding to the green LED module through detecting light emitted from the green LED module at a second time of the second interval; providing a third driving current to the blue LED module during a third interval; generating a first feedback voltage corresponding to the blue LED module based on a first voltage drop corresponding to the blue LED module, and generating a first set of CIE tristimulus values corresponding to the blue LED module through detecting light emitted from the blue LED module at a first time of the third interval; generating a second feedback voltage corresponding to the blue LED module based on a second voltage drop corresponding to the blue LED module, and generating a second set of CIE tristimulus values corresponding to the blue LED module through detecting light emitted from the blue LED module at a second time of the third interval; providing the first driving current to the red LED module, providing the second driving current to the green LED module, and providing the third driving current to the blue LED module; generating a third feedback voltage corresponding to the red LED module based on a third voltage drop corresponding to the red LED module; generating a third set of CIE tristimulus values corresponding to the red LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first set of CIE tristimulus values, and the second set of CIE tristimulus values corresponding to the red LED module; generating a third feedback voltage corresponding to the green LED module based on a third voltage drop corresponding to the green LED module; generating a third set of CIE tristimulus values corresponding to the green LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first set of CIE tristimulus values, and the second set of CIE tristimulus values corresponding to the green LED module; generating a third feedback voltage corresponding to the blue LED module based on a third voltage drop corresponding to the blue LED module; generating a third set of CIE tristimulus values corresponding to the blue LED module based on the third feedback voltage, the first feedback voltage, the second feedback voltage, the first set of CIE tristimulus values, and the second set of CIE tristimulus values corresponding to the blue LED module; calculating a first duty cycle control signal, a second duty cycle control signal, and a third duty cycle control signal based on the third set of CIE tristimulus values corresponding to the red LED module, the third set of CIE tristimulus values corresponding to the green LED module, the third set of CIE tristimulus values corresponding to the blue LED module, and a set of preset CIE tristimulus values; and regulating the first driving current based on the first duty cycle control signal, regulating the second driving current based on the second duty cycle control signal, and regulating the third driving current based on the third duty cycle control signal; wherein the first interval, the second interval, and the third interval are not overlapped between each other. 
   These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a functional block diagram schematically showing a prior-art LED lighting system. 
       FIG. 2  is a functional block diagram schematically showing an LED lighting system having color control mechanism in accordance with a first embodiment of the present invention. 
       FIG. 3  is a functional block diagram schematically showing an LED lighting system having color control mechanism in accordance with a second embodiment of the present invention. 
       FIGS. 4 ,  5 , and  6  present a flowchart depicting a color control method based on the LED lighting system shown in  FIG. 2 . 
       FIGS. 7 and 8  present a flowchart depicting a color control method based on the LED lighting system shown in  FIG. 3 . 
       FIG. 9  is a functional block diagram schematically showing an LED lighting system having color control mechanism in accordance with a third embodiment of the present invention. 
       FIGS. 10 and 11  present a flowchart depicting a color control method based on the LED lighting system shown in  FIG. 9 . 
   

   DETAILED DESCRIPTION 
   Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, it is to be noted that the present invention is not limited thereto. Furthermore, the step serial numbers concerning the color control method are not meant thereto limit the operating sequence, and any rearrangement of the operating sequence for achieving same functionality is still within the spirit and scope of the invention. 
     FIG. 2  is a functional block diagram schematically showing an LED lighting system  200  having color control mechanism in accordance with a first embodiment of the present invention. The LED lighting system  200  comprises a red LED module  201 , a green LED module  202 , a blue LED module  203 , a red LED driving circuit  211 , a green LED driving circuit  212 , a blue LED driving circuit  213 , a first signal amplifier  215 , a second signal amplifier  220 , a third signal amplifier  225 , a first differential amplifier  231 , a second differential amplifier  232 , a third differential amplifier  233 , a color controller  250 , and a color sensor  280 . 
   Each of the red LED module  201 , the green LED module  202 , and the blue LED module  203  comprises at least a column of LEDs. Each column of LEDs comprises at least an LED or a plurality of series-connected LEDs. The color controller  250  can be coupled to a CIE tristimulus colorimeter  290 . The CIE tristimulus colorimeter  290  is utilized to detect the light generated by the red LED module  201 , the green LED module  202 , or the blue LED module  203  for generating a set of CIE tristimulus values X, Y, and Z. The set of CIE tristimulus values X, Y, and Z is forwarded to the color controller  250 . 
   The red LED driving circuit  211  functions as a current driving circuit and is coupled to the red LED module  201  for providing a first driving current Ir. The green LED driving circuit  212  functions as a current driving circuit and is coupled to the green LED module  202  for providing a second driving current Ig. The blue LED driving circuit  213  functions as a current driving circuit and is coupled to the blue LED module  203  for providing a third driving current Ib. 
   The first differential amplifier  231  is coupled to the red LED module  201  for generating a first differential voltage by performing a differential amplifying operation on a first reference voltage Vrefr and a first voltage drop corresponding to the red LED module  201 . The first signal amplifier  215  is coupled to the first differential amplifier  231  for generating a first feedback voltage by performing a signal amplifying operation on the first differential voltage. 
   The second differential amplifier  232  is coupled to the green LED module  202  for generating a second differential voltage by performing a differential amplifying operation on a second reference voltage Vrefg and a second voltage drop corresponding to the green LED module  202 . The second signal amplifier  220  is coupled to the second differential amplifier  232  for generating a second feedback voltage by performing a signal amplifying operation on the second differential voltage. 
   The third differential amplifier  233  is coupled to the blue LED module  203  for generating a third differential voltage by performing a differential amplifying operation on a third reference voltage Vrefb and a third voltage drop corresponding to the blue LED module  203 . The third signal amplifier  225  is coupled to the third differential amplifier  233  for generating a third feedback voltage by performing a signal amplifying operation on the third differential voltage. 
   The first signal amplifier  215  can be a non-inverting amplifying circuit comprising an operational amplifier  216 , a resistor Rr 1 , and a resistor Rr 2 . The second signal amplifier  220  can be a non-inverting amplifying circuit comprising an operational amplifier  221 , a resistor Rg 1 , and a resistor Rg 2 . The third signal amplifier  225  can be a non-inverting amplifying circuit comprising an operational amplifier  226 , a resistor Rb 1 , and a resistor Rb 2 . 
   In one embodiment, the first signal amplifier  215 , the second signal amplifier  220 , and the third signal amplifier  225  can be omitted. That is, the first, second, and third differential voltages can be forwarded directly to the color controller  250  and function as the first, second, and third feedback voltages respectively. In another embodiment, the first differential amplifier  231 , the second differential amplifier  232 , and the third differential amplifier  233  can be omitted. That is, the first signal amplifier  215 , the second signal amplifier  220 , and the third signal amplifier  225  can be coupled directly to the red LED module  201 , the green LED module  202 , and the blue LED module  203  respectively, and the first, second, and third feedback voltages can be generated by performing signal amplifying operations directly on the first, second, and third voltage drops respectively. 
   The color sensor  280  is coupled to the color controller  250  for generating at least a red light signal Sr, at least a green light signal Sg, and at least a blue light signal Sb through detecting the light generated by the red LED module  210 , the green LED module  202 , or the blue LED module  203 . The red light signal Sr, the green light signal Sg, and the blue light signal Sb are forwarded to the color controller  250 . The color controller  250  comprises a signal processor  255 , a matrix multiplier  260 , a first comparator  261 , a second comparator  262 , a third comparator  263 , a first pulse-width-modulation (PWM) signal generator  271 , a second pulse-width-modulation signal generator  272 , and a third pulse-width-modulation signal generator  273 . 
   The signal processor  255  is utilized to generate a coefficient matrix based on the first feedback voltage, the second feedback voltage, the third feedback voltage, the red light signal Sr, the green light signal Sg, the blue light signal Sb, and the set of CIE tristimulus values X, Y, and Z. The matrix multiplier  260  is coupled to the signal processor  255  for generating a first control signal Rc, a second control signal Gc, and a third control signal Bc based on the coefficient matrix and a set of preset CIE tristimulus values Xpreset, Ypreset, and Zpreset. In another embodiment, the matrix multiplier  260  can be incorporated in the signal processor  255 . That is, the first control signal Rc, the second control signal Gc, and the third control signal Bc can be generated directly by the signal processor  255 . 
   The first comparator  261  is coupled to the matrix multiplier  260  for generating a first duty cycle control signal Pr by comparing the first control signal Rc with a corresponding red light signal Sr. The second comparator  262  is coupled to the matrix multiplier  260  for generating a second duty cycle control signal Pg by comparing the second control signal Gc with a corresponding green light signal Sg. The third comparator  263  is coupled to the matrix multiplier  260  for generating a third duty cycle control signal Pb by comparing the third control signal Bc with a corresponding blue light signal Sb. 
   The first PWM signal generator  271  is coupled between the first comparator  261  and the red LED driving circuit  211  for regulating the duty cycle of a first PWM signal based on the first duty cycle control signal Pr. The first PWM signal is forwarded to the red LED driving circuit  211  for adjusting the first driving current Ir. The second PWM signal generator  272  is coupled between the second comparator  262  and the green LED driving circuit  212  for regulating the duty cycle of a second PWM signal based on the second duty cycle control signal Pg. The second PWM signal is forwarded to the green LED driving circuit  212  for adjusting the second driving current Ig. The third PWM signal generator  273  is coupled between the third comparator  263  and the blue LED driving circuit  213  for regulating the duty cycle of a third PWM signal based on the third duty cycle control signal Pb. The third PWM signal is forwarded to the blue LED driving circuit  213  for adjusting the third driving current Ib. 
   In the operation of the LED lighting system  200 , as the wavelength shift of the light emitted from the red LED module  201 , the green LED module  202 , or the blue LED module  203  occurs due to temperature variation, the first, second, or third feedback voltage is changed accordingly. For that reason, the light generated by the red LED module  201 , the green LED module  202 , or the blue LED module  203  can be controlled precisely based on the first, second, or third feedback voltage. A corresponding color control method based on the LED lighting system  200  will be detailed below. 
     FIG. 3  is a functional block diagram schematically showing an LED lighting system  300  having color control mechanism in accordance with a second embodiment of the present invention. The LED lighting system  300  comprises a red LED module  301 , a green LED module  302 , a blue LED module  303 , a first resistor Rr, a second resistor Rg, a third resistor Rb, a red LED driving circuit  311 , a green LED driving circuit  312 , a blue LED driving circuit  313 , a first signal amplifier  315 , a second signal amplifier  320 , a third signal amplifier  325 , and a color controller  350 . 
   Each of the red LED module  301 , the green LED module  302 , and the blue LED module  303  comprises at least a column of LEDs. Each column of LEDs comprises at least an LED or a plurality of series-connected LEDs. The color controller  350  can be coupled to a CIE tristimulus colorimeter  390 . The CIE tristimulus colorimeter  390  is utilized to detect the light generated by the red LED module  301 , the green LED module  302 , or the blue LED module  303  for generating a set of CIE tristimulus values X, Y, and Z. The set of CIE tristimulus values X, Y, and Z is forwarded to the color controller  350 . 
   The red LED driving circuit  311  functions as a voltage driving circuit and is coupled to the red LED module  301  for providing a first driving voltage Vr. The green LED driving circuit  312  functions as a voltage driving circuit and is coupled to the green LED module  302  for providing a second driving voltage Vg. The blue LED driving circuit  313  functions as a voltage driving circuit and is coupled to the blue LED module  303  for providing a third driving voltage Vb. The first resistor Rr is coupled to the red LED module  301  for generating a first voltage drop proportional to the current flowing through the red LED module  301 . The second resistor Rg is coupled to the green LED module  302  for generating a second voltage drop proportional to the current flowing through the green LED module  302 . The third resistor Rb is coupled to the blue LED module  303  for generating a third voltage drop proportional to the current flowing through the blue LED module  303 . 
   The first signal amplifier  315  is coupled to the first resistor Rr and the red LED module  301  for generating a first feedback voltage by performing a signal amplifying operation on the first voltage drop. The first signal amplifier  315  can be a non-inverting amplifying circuit comprising an operational amplifier  316 , a resistor Rr 1 , and a resistor Rr 2 . The second signal amplifier  320  is coupled to the second resistor Rg and the green LED module  302  for generating a second feedback voltage by performing a signal amplifying operation on the second voltage drop. The second signal amplifier  320  can be a non-inverting amplifying circuit comprising an operational amplifier  321 , a resistor Rg 1 , and a resistor Rg 2 . The third signal amplifier  325  is coupled to the third resistor Rb and the blue LED module  303  for generating a third feedback voltage by performing a signal amplifying operation on the third voltage drop. The third signal amplifier  325  can be a non-inverting amplifying circuit comprising an operational amplifier  326 , a resistor Rb 1 , and a resistor Rb 2 . 
   The color controller  350  comprises a signal processor  355 , a first PWM signal generator  371 , a second PWM signal generator  372 , and a third PWM signal generator  373 . The signal processor  355  is utilized to generate a first duty cycle control signal Pr, a second duty cycle control signal Pg, and a third duty cycle control signal Pb based on the first feedback voltage, the second feedback voltage, the third feedback voltage, the set of CIE tristimulus values X, Y, and Z, and a set of preset CIE tristimulus values Xpreset, Ypreset, and Zpreset. 
   The first PWM signal generator  371  is coupled between the signal processor  355  and the red LED driving circuit  311  for regulating the duty cycle of a first PWM signal based on the first duty cycle control signal Pr. The first PWM signal is forwarded to the red LED driving circuit  311  for adjusting the first driving voltage Vr. The second PWM signal generator  372  is coupled between the signal processor  355  and the green LED driving circuit  312  for regulating the duty cycle of a second PWM signal based on the second duty cycle control signal Pg. The second PWM signal is forwarded to the green LED driving circuit  312  for adjusting the second driving voltage Vg. The third PWM signal generator  373  is coupled between the signal processor  355  and the blue LED driving circuit  313  for regulating the duty cycle of a third PWM signal based on the third duty cycle control signal Pb. The third PWM signal is forwarded to the blue LED driving circuit  313  for adjusting the third driving Voltage Vb. 
   In the operation of the LED lighting system  300 , as the wavelength shift of the light emitted from the red LED module  301 , the green LED module  302 , or the blue LED module  303  occurs due to temperature variation, the first, second, or third feedback voltage is changed accordingly. For that reason, the light generated by the red LED module  301 , the green LED module  302 , or the blue LED module  303  can be controlled precisely based on the first, second, or third feedback voltage. A corresponding color control method based on the LED lighting system  300  will be detailed below. 
     FIGS. 4 ,  5 , and  6  present a flowchart depicting a color control method based on the LED lighting system  200  shown in  FIG. 2 . The color control method comprises:
     Step S 401 : provide a first driving current Ir to the red LED module  201  by the red LED driving circuit  211  during a first interval;   Step S 403 : generate a first feedback voltage V 1   a  corresponding to the red LED module  201  through performing differential amplifying and signal amplifying operations on a first voltage drop corresponding to the red LED module  201  by the first differential amplifier  231  and the first signal amplifier  215 , and generate a first red light signal R 1   a , a first green light signal G 1   a , a first blue light signal B 1   a , and a first set of CIE tristimulus values X 1   a , Y 1   a , and Z 1   a  corresponding to the red LED module  201  through detecting the light emitted from the red LED module  201  by the color sensor  280  and the CIE tristimulus colorimeter  290  at a first time of the first interval;   Step S 405 : generate a second feedback voltage V 1   b  corresponding to the red LED module  201  through performing differential amplifying and signal amplifying operations on a second voltage drop corresponding to the red LED module  201  by the first differential amplifier  231  and the first signal amplifier  215 , and generate a second red light signal R 1   b , a second green light signal G 1   b , a second blue light signal B 1   b , and a second set of CIE tristimulus values X 1   b , Y 1   b , and Z 1   b  corresponding to the red LED module  201  through detecting the light emitted from the red LED module  201  by the color sensor  280  and the CIE tristimulus colorimeter  290  at a second time of the first interval;   Step S 407 : provide a second driving current Ig to the green LED module  202  by the green LED driving circuit  212  during a second interval;   Step S 409 : generate a first feedback voltage V 2   a  corresponding to the green LED module  202  through performing differential amplifying and signal amplifying operations on a first voltage drop corresponding to the green LED module  202  by the second differential amplifier  232  and the second signal amplifier  220 , and generate a first red light signal R 2   a , a first green light signal G 2   a , a first blue light signal B 1   a , and a first set of CIE tristimulus values X 2   a , Y 2   a , and Z 2   a  corresponding to the green LED module  202  through detecting the light emitted from the green LED module  202  by the color sensor  280  and the CIE tristimulus colorimeter  290  at a first time of the second interval;   Step S 411 : generate a second feedback voltage V 2   b  corresponding to the green LED module  202  through performing differential amplifying and signal amplifying operations on a second voltage drop corresponding to the green LED module  202  by the second differential amplifier  232  and the second signal amplifier  220 , and generate a second red light signal R 2   b , a second green light signal G 2   b , a second blue light signal B 1   b , and a second set of CIE tristimulus values X 2   b , Y 2   b , and Z 2   b  corresponding to the green LED module  202  through detecting the light emitted from the green LED module  202  by the color sensor  280  and the CIE tristimulus colorimeter  290  at a second time of the second interval;   Step S 413 : provide a third driving current Ib to the blue LED module  203  by the blue LED driving circuit  213  during a third interval;   Step S 415 : generate a first feedback voltage V 3   a  corresponding to the blue LED module  203  through performing differential amplifying and signal amplifying operations on a first voltage drop corresponding to the blue LED module  203  by the third differential amplifier  233  and the third signal amplifier  225 , and generate a first red light signal R 3   a , a first green light signal G 3   a , a first blue light signal B 3   a , and a first set of CIE tristimulus values X 3   a , Y 3   a , and Z 3   a  corresponding to the blue LED module  203  through detecting the light emitted from the blue LED module  203  by the color sensor  280  and the CIE tristimulus colorimeter  290  at a first time of the third interval;   Step S 417 : generate a second feedback voltage V 3   b  corresponding to the blue LED module  203  through performing differential amplifying and signal amplifying operations on a second voltage drop corresponding to the blue LED module  203  by the third differential amplifier  233  and the third signal amplifier  225 , and generate a second red light signal R 3   b , a second green light signal G 3   b , a second blue light signal B 3   b , and a second set of CIE tristimulus values X 3   b , Y 3   b , and Z 3   b  corresponding to the blue LED module  203  through detecting the light emitted from the blue LED module  203  by the color sensor  280  and the CIE tristimulus colorimeter  290  at a second time of the third interval;   Step S 419 : provide the first driving current Ir to the red LED module  201  by the red LED driving circuit  211 , provide the second driving current Ig to the green LED module  202  by the green LED driving circuit  212 , and provide the third driving current Ib to the blue LED module  203  by the blue LED driving circuit  213 ;   Step S 421 : generate a third feedback voltage V 1   t  corresponding to the red LED module  201  through performing differential amplifying and signal amplifying operations on a third voltage drop corresponding to the red LED module  201  by the first differential amplifier  231  and the first signal amplifier  215 ;   Step S 423 : calculate a third set of CIE tristimulus values X 1   t , Y 1   t , and Z 1   t  corresponding to the red LED module  201  based on the third feedback voltage V 1   t , the first feedback voltage V 1   a , the second feedback voltage V 1   b , the first set of CIE tristimulus values X 1   a , Y 1   a , and Z 1   a , and the second set of CIE tristimulus values X 1   b , Y 1   b , and Z 1   b  corresponding to the red LED module  201  by the signal processor  255  according to the formulas (1), (2), and (3) listed below:   
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 425 : calculate a third red light signal R 1   t , a third green light signal G 1   t , and a third blue light signal B 1   t  corresponding to the red LED module  201  based on the third feedback voltage V 1   t , the first feedback voltage V 1   a , the second feedback voltage V 1   b , the first red light signal R 1   a , the first green light signal G 1   a , the first blue light signal B 1   a , the second red light signal R 1   b , the second green light signal G 1   b , the second blue light signal B 1   b  corresponding to the red LED module  201  by the signal processor  255  according to the formulas (4), (5), and (6) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 427 : generate a third feedback voltage V 2   t  corresponding to the green LED module  202  through performing differential amplifying and signal amplifying operations on a third voltage drop corresponding to the green LED module  202  by the second differential amplifier  232  and the second signal amplifier  220 ; 
       Step S 429 : calculate a third set of CIE tristimulus values X 2   t , Y 2   t , and Z 2   t  corresponding to the green LED module  202  based on the third feedback voltage V 2   t , the first feedback voltage V 2   a , the second feedback voltage V 2   b , the first set of CIE tristimulus values X 2   a , Y 2   a , and Z 2   a , and the second set of CIE tristimulus values X 2   b , Y 2   b , and Z 2   b  corresponding to the green LED module  202  by the signal processor  255  according to the formulas (7), (8), and (9) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 431 : calculate a third red light signal R 2   t , a third green light signal G 2   t , and a third blue light signal B 2   t  corresponding to the green LED module  202  based on the third feedback voltage V 2   t , the first feedback voltage V 2   a , the second feedback voltage V 2   b , the first red light signal R 2   a , the first green light signal G 2   a , the first blue light signal B 2   a , the second red light signal R 2   b , the second green light signal G 2   b , the second blue light signal B 2   b  corresponding to the green LED module  202  by the signal processor  255  according to the formulas (10), (11), and (12) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 433 : generate a third feedback voltage V 3   t  corresponding to the blue LED module  203  through performing differential amplifying and signal amplifying operations on a third voltage drop corresponding to the blue LED module  203  by the third differential amplifier  233  and the third signal amplifier  225 ; 
       Step S 435 : calculate a third set of CIE tristimulus values X 3   t , Y 3   t , and Z 3   t  corresponding to the blue LED module  203  based on the third feedback voltage V 3   t , the first feedback voltage V 3   a , the second feedback voltage V 3   b , the first set of CIE tristimulus values X 3   a , Y 3   a , and Z 3   a , and the second set of CIE tristimulus values X 3   b , Y 3   b , and Z 3   b  corresponding to the blue LED module  203  by the signal processor  255  according to the formulas (13), (14), and (15) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 437 : calculate a third red light signal R 3   t , a third green light signal G 3   t , and a third blue light signal B 3   t  corresponding to the blue LED module  203  based on the third feedback voltage V 3   t , the first feedback voltage V 3   a , the second feedback voltage V 3   b , the first red light signal R 3   a , the first green light signal G 3   a , the first blue light signal B 3   a , the second red light signal R 3   b , the second green light signal G 3   b , the second blue light signal B 3   b  corresponding to the blue LED module  203  by the signal processor  255  according to the formulas (16), (17), and (18) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   16 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         G 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   17 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         B 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   18 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 439 : calculate a coefficient matrix [Dij] 3×3  based on the third set of CIE tristimulus values X 1   t , Y 1   t , and Z 1   t , the third red light signal R 1   t , the third green light signal G 1   t , and the third blue light signal Bit corresponding to the red LED module  201 , the third set of CIE tristimulus values X 2   t , Y 2   t , and Z 2   t , the third red light signal R 2   t , the third green light signal G 2   t , and the third blue light signal B 2   t  corresponding to the green LED module  202 , and the third set of CIE tristimulus values X 3   t , Y 3   t , and Z 3   t , the third red light signal R 3   t , the third green light signal G 3   t , and the third blue light signal B 3   t  corresponding to the blue LED module  203  through matrix inverting and matrix multiplying operations performed by the signal processor  255  according to the formula (19) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     
                       
                         [ 
                         
                             
                         
                         ⁢ 
                         
                           
                             
                               
                                 R 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                                 ⁢ 
                                 t 
                               
                             
                             
                               
                                 R 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                                 ⁢ 
                                 t 
                               
                             
                             
                               
                                 R 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 3 
                                 ⁢ 
                                 t 
                               
                             
                           
                           
                             
                               
                                 G 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                                 ⁢ 
                                 t 
                               
                             
                             
                               
                                 G 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                                 ⁢ 
                                 t 
                               
                             
                             
                               
                                 G 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 3 
                                 ⁢ 
                                 t 
                               
                             
                           
                           
                             
                               
                                 B 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                                 ⁢ 
                                 t 
                               
                             
                             
                               
                                 B 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                                 ⁢ 
                                 t 
                               
                             
                             
                               
                                 B 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 3 
                                 ⁢ 
                                 t 
                               
                             
                           
                         
                         ] 
                       
                       = 
                         
                       ⁢ 
                       
                         
                           [ 
                           
                               
                           
                           ⁢ 
                           
                             
                               
                                 
                                   D 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   11 
                                 
                               
                               
                                 
                                   D 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   12 
                                 
                               
                               
                                 
                                   D 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   13 
                                 
                               
                             
                             
                               
                                 
                                   D 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   21 
                                 
                               
                               
                                 
                                   D 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   22 
                                 
                               
                               
                                 
                                   D 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   23 
                                 
                               
                             
                             
                               
                                 
                                   D 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   31 
                                 
                               
                               
                                 
                                   D 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   32 
                                 
                               
                               
                                 
                                   D 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   33 
                                 
                               
                             
                           
                           ] 
                         
                         × 
                       
                     
                   
                 
                 
                   
                     
                         
                       ⁢ 
                       
                         
                           [ 
                           
                               
                           
                           ⁢ 
                           
                             
                               
                                 
                                   X 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   1 
                                   ⁢ 
                                   t 
                                 
                               
                               
                                 
                                   X 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   2 
                                   ⁢ 
                                   t 
                                 
                               
                               
                                 
                                   X 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   3 
                                   ⁢ 
                                   t 
                                 
                               
                             
                             
                               
                                 
                                   Y 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   1 
                                   ⁢ 
                                   t 
                                 
                               
                               
                                 
                                   Y 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   2 
                                   ⁢ 
                                   t 
                                 
                               
                               
                                 
                                   Y 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   3 
                                   ⁢ 
                                   t 
                                 
                               
                             
                             
                               
                                 
                                   Z 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   1 
                                   ⁢ 
                                   t 
                                 
                               
                               
                                 
                                   Z 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   2 
                                   ⁢ 
                                   t 
                                 
                               
                               
                                 
                                   Z 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   3 
                                   ⁢ 
                                   t 
                                 
                               
                             
                           
                           ⁢ 
                           
                               
                           
                           ] 
                         
                         , 
                       
                     
                   
                 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   19 
                   ) 
                 
               
             
           
         
       
     
       
       
         
           wherein the coefficient matrix [Dij] 3×3  is the matrix comprising coefficients D 11  through D 33  in the formula (19); 
         
       
       Step S 441 : calculate a first control signal Rc, a second control signal Gc, and a third control signal Bc based on the coefficient matrix [Dij] 3×3  and a set of preset CIE tristimulus values Xpreset, Ypreset, and Zpreset through a matrix multiplying operation performed by the matrix multiplier  260  according to the formula (20) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           Rc 
                         
                       
                       
                         
                           Gc 
                         
                       
                       
                         
                           Bc 
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       [ 
                       
                           
                       
                       ⁢ 
                       
                         
                           
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               11 
                             
                           
                           
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               12 
                             
                           
                           
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               13 
                             
                           
                         
                         
                           
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               21 
                             
                           
                           
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               22 
                             
                           
                           
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               23 
                             
                           
                         
                         
                           
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               31 
                             
                           
                           
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               32 
                             
                           
                           
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               33 
                             
                           
                         
                       
                       ] 
                     
                     × 
                     
                       [ 
                       
                         
                           
                             Xpreset 
                           
                         
                         
                           
                             Ypreset 
                           
                         
                         
                           
                             Zpreset 
                           
                         
                       
                       ] 
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   20 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 443 : generate a fourth red light signal, a fourth green light signal, and a fourth blue light signal through detecting the light emitted from the red LED module  201 , the green LED module  202 , and the blue LED module  203  by the color sensor  280 ; 
       Step S 445 : generate a first duty cycle control signal Pr through comparing the first control signal Rc with the fourth red light signal by the first comparator  261 , generate a second duty cycle control signal Pg through comparing the second control signal Gc with the fourth green light signal by the second comparator  262 , and generate a third duty cycle control signal Pb through comparing the third control signal Bc with the fourth blue light signal by the third comparator  263 ; 
       Step S 447 : regulate the duty cycle of a first PWM signal based on the first duty cycle control signal Pr by the first PWM signal generator  271 , regulate the duty cycle of a second PWM signal based on the second duty cycle control signal Pg by the second PWM signal generator  272 , and regulate the duty cycle of a third PWM signal based on the third duty cycle control signal Pb by the third PWM signal generator  273 ; and 
       Step S 449 : adjust the first driving current Ir based on the first PWM signal by the red LED driving circuit  211 , adjust the second driving current Ig based on the second PWM signal by the green LED driving circuit  212 , and adjust the third driving current Ib based on the third PWM signal by the blue LED driving circuit  213 , go back to step S 419 . 
     
  
   The color control method based on the LED lighting system  200  comprises a preliminary detection phase and a feedback control phase. The preliminary detection phase including the steps from S 401  to S 417  is utilized to detect the voltage drop of each LED module and the corresponding color signals and CIE tristimulus values. The first interval, the second interval, and the third interval are not overlapped between each other. The feedback control phase including the steps from S 419  to S 449  is utilized to precisely control the light emitted form each LED module through regulating the driving current for each LED module by performing compensation operations based on the voltage drop variations in conjunction with the color signals and the CIE tristimulus values generated in the preliminary detection phase. 
   In the steps S 403 , S 405 , and S 421 , the processes of performing differential amplifying and signal amplifying operations on the first, second, and third voltage drops corresponding to the red LED module  201  by the first differential amplifier  231  and the first signal amplifier  215  can be simplified to be the processes of performing differential amplifying operations on the first, second, and third voltage drops corresponding to the red LED module  201  in conjunction with the first reference voltage Vrefr by the first differential amplifier  231 , or alternatively, the processes of performing signal amplifying operations on the first, second, and third voltage drops corresponding to the red LED module  201  by the first signal amplifier  215 . 
   Similarly, in the steps S 409 , S 411 , and S 427 , the processes of performing differential amplifying and signal amplifying operations on the first, second, and third voltage drops corresponding to the green LED module  202  by the second differential amplifier  232  and the second signal amplifier  220  can be simplified to be the processes of performing differential amplifying operations on the first, second, and third voltage drops corresponding to the green LED module  202  in conjunction with the second reference voltage Vrefg by the second differential amplifier  232 , or alternatively, the processes of performing signal amplifying operations on the first, second, and third voltage drops corresponding to the green LED module  202  by the second signal amplifier  220 . 
   Likewise, in the steps S 415 , S 417 , and S 433 , the processes of performing differential amplifying and signal amplifying operations on the first, second, and third voltage drops corresponding to the blue LED module  203  by the third differential amplifier  233  and the third signal amplifier  225  can be simplified to be the processes of performing differential amplifying operations on the first, second, and third voltage drops corresponding to the blue LED module  203  in conjunction with the third reference voltage Vrefb by the third differential amplifier  233 , or alternatively, the processes of performing signal amplifying operations on the first, second, and third voltage drops corresponding to the blue LED module  203  by the third signal amplifier  225 . 
   Since the CIE tristimulus calorimeter  290  is used only in the preliminary detection phase, the CIE tristimulus calorimeter  290  can be detached from the LED lighting system  200  at the completion of the step S 417 . 
     FIGS. 7 and 8  present a flowchart depicting a color control method based on the LED lighting system  300  shown in  FIG. 3 . The color control method comprises:
     Step S 501 : provide a first driving voltage Vr to the red LED module  301  by the red LED driving circuit  311  during a first interval;   Step S 503 : generate a first feedback voltage V 1   a  corresponding to the red LED module  301  through performing a signal amplifying operation on a first voltage drop of the first resistor Rr having a first current flowing through the red LED module  301  by the first signal amplifier  315 , and generate a first set of CIE tristimulus values X 1   a , Y 1   a , and Z 1   a  corresponding to the red LED module  301  through detecting the light emitted from the red LED module  301  by the CIE tristimulus colorimeter  390  at a first time of the first interval;   Step S 505 : generate a second feedback voltage V 1   b  corresponding to the red LED module  301  through performing a signal amplifying operation on a second voltage drop of the first resistor Rr having a second current flowing through the red LED module  301  by the first signal amplifier  315 , and generate a second set of CIE tristimulus values X 1   b , Y 1   b , and Z 1   b  corresponding to the red LED module  301  through detecting the light emitted from the red LED module  301  by the CIE tristimulus colorimeter  390  at a second time of the first interval;   Step S 507 : provide a second driving voltage Vg to the green LED module  302  by the green LED driving circuit  312  during a second interval;   Step S 509 : generate a first feedback voltage V 2   a  corresponding to the green LED module  302  through performing a signal amplifying operation on a first voltage drop of the second resistor Rg having a first current flowing through the green LED module  302  by the second signal amplifier  320 , and generate a first set of CIE tristimulus values X 2   a , Y 2   a , and Z 2   a  corresponding to the green LED module  302  through detecting the light emitted from the green LED module  302  by the CIE tristimulus colorimeter  390  at a first time of the second interval;   Step S 511 : generate a second feedback voltage V 2   b  corresponding to the green LED module  302  through performing a signal amplifying operation on a second voltage drop of the second resistor Rg having a second current flowing through the green LED module  302  by the second signal amplifier  320 , and generate a second set of CIE tristimulus values X 2   b , Y 2   b , and Z 2   b  corresponding to the green LED module  302  through detecting the light emitted from the green LED module  302  by the CIE tristimulus colorimeter  390  at a second time of the second interval;   Step S 513 : provide a third driving voltage Vb to the blue LED module  303  by the blue LED driving circuit  313  during a third interval;   Step S 515 : generate a first feedback voltage V 3   a  corresponding to the blue LED module  303  through performing a signal amplifying operation on a first voltage drop of the third resistor Rb having a first current flowing through the blue LED module  303  by the third signal amplifier  325 , and generate a first set of CIE tristimulus values X 3   a , Y 3   a , and Z 3   a  corresponding to the blue LED module  303  through detecting the light emitted from the blue LED module  303  by the CIE tristimulus colorimeter  390  at a first time of the third interval;   Step S 517 : generate a second feedback voltage V 3   b  corresponding to the blue LED module  303  through performing a signal amplifying operation on a second voltage drop of the third resistor Rb having a second current flowing through the blue LED module  303  by the third signal amplifier  325 , and generate a second set of CIE tristimulus values X 3   b , Y 3   b , and Z 3   b  corresponding to the blue LED module  303  through detecting the light emitted from the blue LED module  303  by the CIE tristimulus colorimeter  390  at a second time of the third interval;   Step S 519 : provide the first driving voltage Vr to the red LED module  301  by the red LED driving circuit  311 , provide the second driving voltage Vg to the green LED module  302  by the green LED driving circuit  312 , and provide the third driving voltage Vb to the blue LED module  303  by the blue LED driving circuit  313 ;   Step S 521 : generate a third feedback voltage V 1   t  corresponding to the red LED module  301  through performing a signal amplifying operation on a third voltage drop of the first resistor Rr having a third current flowing through the red LED module  301  by the first signal amplifier  315 ;   Step S 523 : calculate a third set of CIE tristimulus values X 1   t , Y 1   t , and Z 1   t  corresponding to the red LED module  301  based on the third feedback voltage V 1   t , the first feedback voltage V 1   a , the second feedback voltage V 1   b , the first set of CIE tristimulus values X 1   a , Y 1   a , and Z 1   a , and the second set of CIE tristimulus values X 1   b , Y 1   b , and Z 1   b  corresponding to the red LED module  301  by the signal processor  355  according to the formulas (21), (22), and (23) listed below:   
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   21 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   22 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   23 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 525 : generate a third feedback voltage V 2   t  corresponding to the green LED module  302  through performing a signal amplifying operation on a third voltage drop of the second resistor Rg having a third current flowing through the green LED module  302  by the second signal amplifier  320 ; 
       Step S 527 : calculate a third set of CIE tristimulus values X 2   t , Y 2   t , and Z 2   t  corresponding to the green LED module  302  based on the third feedback voltage V 2   t , the first feedback voltage V 2   a , the second feedback voltage V 2   b , the first set of CIE tristimulus values X 2   a , Y 2   a , and Z 2   a , and the second set of CIE tristimulus values X 2   b , Y 2   b , and Z 2   b  corresponding to the green LED module  302  by the signal processor  355  according to the formulas (24), (25), and (26) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
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                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   24 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
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                         a 
                       
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                         Y 
                         ⁢ 
                         
                             
                         
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                       - 
                       
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                         ⁢ 
                         
                             
                         
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                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   25 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
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                   = 
                   
                     
                       
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                         ⁢ 
                         
                             
                         
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                         a 
                       
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                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
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                         a 
                       
                       - 
                       
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                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   26 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 529 : generate a third feedback voltage V 3   t  corresponding to the blue LED module  303  through performing a signal amplifying operation on a third voltage drop of the third resistor Rb having a third current flowing through the blue LED module  303  by the third signal amplifier  325 ; 
       Step S 531 : calculate a third set of CIE tristimulus values X 3   t , Y 3   t , and Z 3   t  corresponding to the blue LED module  303  based on the third feedback voltage V 3   t , the first feedback voltage V 3   a , the second feedback voltage V 3   b , the first set of CIE tristimulus values X 3   a , Y 3   a , and Z 3   a , and the second set of CIE tristimulus values X 3   b , Y 3   b , and Z 3   b  corresponding to the blue LED module  303  by the signal processor  355  according to the formulas (27), (28), and (29) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
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                         ⁢ 
                         
                             
                         
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                         3 
                         ⁢ 
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                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
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                         X 
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                         ⁢ 
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                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
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                         ⁢ 
                         
                             
                         
                         ⁢ 
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                         t 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
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                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   27 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
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                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   28 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
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                         ⁢ 
                         
                             
                         
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                         ⁢ 
                         a 
                       
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                         ⁢ 
                         
                             
                         
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                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
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                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   29 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 533 : calculate a first duty cycle control signal Pr, a second duty cycle control signal Pg, and a third duty cycle control signal Pb based on the third set of CIE tristimulus values X 1   t , Y 1   t , and Z 1   t  corresponding to the red LED module  301 , the third set of CIE tristimulus values X 2   t , Y 2   t , and Z 2   t  corresponding to the green LED module  302 , the third set of CIE tristimulus values X 3   t , Y 3   t , and Z 3   t  corresponding to the blue LED module  303 , and a set of preset CIE tristimulus values Xpreset, Ypreset, and Zpreset by the signal processor  355  according to the formulas (30), (31), and (32) listed below:
 
 PrX 1 t+PgX 2 t+PbX 3 t=X preset  Formula (30),
 
 PrY 1 t+PgY 2 t+PbY 3 t=Y preset  Formula (31), and
 
 PrZ 1 t+PgZ 2 t+PbZ 3 t=Z preset  Formula (32);
 
       Step S 535 : regulate the duty cycle of a first PWM signal based on the first duty cycle control signal Pr by the first PWM signal generator  371 , regulate the duty cycle of a second PWM signal based on the second duty cycle control signal Pg by the second PWM signal generator  372 , and regulate the duty cycle of a third PWM signal based on the third duty cycle control signal Pb by the third PWM signal generator  373 ; and 
       Step S 537 : adjust the first driving voltage Vr based on the first PWM signal by the red LED driving circuit  311 , adjust the second driving voltage Vg based on the second PWM signal by the green LED driving circuit  312 , and adjust the third driving voltage Vb based on the third PWM signal by the blue LED driving circuit  313 , go back to step S 519 . 
     
  
   The color control method based on the LED lighting system  300  comprises a preliminary detection phase and a feedback control phase. The preliminary detection phase including the steps from S 501  to S 517  is utilized to detect the current-related voltage drop of each LED module and the corresponding CIE tristimulus values. The first interval, the second interval, and the third interval are not overlapped between each other. The feedback control phase including the steps from S 519  to S 537  is utilized to precisely control the light emitted form each LED module through regulating the driving voltage for each LED module by performing compensation operations based on the current-related voltage drop variations in conjunction with the CIE tristimulus values generated in the preliminary detection phase. 
   Similarly, since the CIE tristimulus calorimeter  390  is used only in the preliminary detection phase, the CIE tristimulus calorimeter  390  can be detached from the LED lighting system  300  at the completion of the step S 517 . 
     FIG. 9  is a functional block diagram schematically showing an LED lighting system  900  having color control mechanism in accordance with a third embodiment of the present invention. The LED lighting system  900  comprises a red LED module  901 , a green LED module  902 , a blue LED module  903 , a red LED driving circuit  911 , a green LED driving circuit  912 , a blue LED driving circuit  913 , a first signal amplifier  915 , a second signal amplifier  920 , a third signal amplifier  925 , a first differential amplifier  931 , a second differential amplifier  932 , a third differential amplifier  933 , and a color controller  950 . 
   The red LED driving circuit  911  functions as a current driving circuit and is coupled to the red LED module  901  for providing a first driving current Ir. The green LED driving circuit  912  functions as a current driving circuit and is coupled to the green LED module  902  for providing a second driving current Ig. The blue LED driving circuit  913  functions as a current driving circuit and is coupled to the blue LED module  903  for providing a third driving current Ib. 
   The first differential amplifier  931  is coupled to the red LED module  901  for generating a first differential voltage by performing a differential amplifying operation on a first reference voltage Vrefr and a first voltage drop corresponding to the red LED module  901 . The first signal amplifier  915  is coupled to the first differential amplifier  931  for generating a first feedback voltage by performing a signal amplifying operation on the first differential voltage. 
   The second differential amplifier  932  is coupled to the green LED module  902  for generating a second differential voltage by performing a differential amplifying operation on a second reference voltage Vrefg and a second voltage drop corresponding to the green LED module  902 . The second signal amplifier  920  is coupled to the second differential amplifier  932  for generating a second feedback voltage by performing a signal amplifying operation on the second differential voltage. 
   The third differential amplifier  933  is coupled to the blue LED module  903  for generating a third differential voltage by performing a differential amplifying operation on a third reference voltage Vrefb and a third voltage drop corresponding to the blue LED module  903 . The third signal amplifier  925  is coupled to the third differential amplifier  933  for generating a third feedback voltage by performing a signal amplifying operation on the third differential voltage. 
   The first signal amplifier  915  can be a non-inverting amplifying circuit comprising an operational amplifier  916 , a resistor Rr 1 , and a resistor Rr 2 . The second signal amplifier  920  can be a non-inverting amplifying circuit comprising an operational amplifier  921 , a resistor Rg 1 , and a resistor Rg 2 . The third signal amplifier  925  can be a non-inverting amplifying circuit comprising an operational amplifier  926 , a resistor Rb 1 , and a resistor Rb 2 . 
   In one embodiment, the first signal amplifier  915 , the second signal amplifier  920 , and the third signal amplifier  925  can be omitted. That is, the first, second, and third differential voltages can be forwarded directly to the color controller  950  and function as the first, second, and third feedback voltages respectively. In another embodiment, the first differential amplifier  931 , the second differential amplifier  932 , and the third differential amplifier  933  can be omitted. That is, the first signal amplifier  915 , the second signal amplifier  920 , and the third signal amplifier  925  can be coupled directly to the red LED module  901 , the green LED module  902 , and the blue LED module  903  respectively, and the first, second, and third feedback voltages can be generated by performing signal amplifying operations directly on the first, second, and third voltage drops respectively. 
   The color controller  950  comprises a signal processor  955 , a first PWM signal generator  971 , a second PWM signal generator  972 , and a third PWM signal generator  973 . The signal processor  955  is utilized to generate a first duty cycle control signal Pr, a second duty cycle control signal Pg, and a third duty cycle control signal Pb based on the first feedback voltage, the second feedback voltage, the third feedback voltage, the set of CIE tristimulus values X, Y, and Z, and a set of preset CIE tristimulus values Xpreset, Ypreset, and Zpreset. 
   The first PWM signal generator  971  is coupled between the signal processor  955  and the red LED driving circuit  911  for regulating the duty cycle of a first PWM signal based on the first duty cycle control signal Pr. The first PWM signal is forwarded to the red LED driving circuit  911  for adjusting the first driving current Ir. The second PWM signal generator  972  is coupled between the signal processor  955  and the green LED driving circuit  912  for regulating the duty cycle of a second PWM signal based on the second duty cycle control signal Pg. The second PWM signal is forwarded to the green LED driving circuit  912  for adjusting the second driving current Ig. The third PWM signal generator  973  is coupled between the signal processor  955  and the blue LED driving circuit  913  for regulating the duty cycle of a third PWM signal based on the third duty cycle control signal Pb. The third PWM signal is forwarded to the blue LED driving circuit  913  for adjusting the third driving current Ib. 
   In the operation of the LED lighting system  900 , as the wavelength shift of the light emitted from the red LED module  901 , the green LED module  902 , or the blue LED module  903  occurs due to temperature variation, the first, second, or third feedback voltage is changed accordingly. For that reason, the light generated by the red LED module  901 , the green LED module  902 , or the blue LED module  903  can be controlled precisely based on the first, second, or third feedback voltage. A corresponding color control method based on the LED lighting system  900  will be detailed below. 
     FIGS. 10 and 11  present a flowchart depicting a color control method based on the LED lighting system  900  shown in  FIG. 9 . The color control method comprises:
     Step S 901 : provide a first driving current Ir to the red LED module  901  by the red LED driving circuit  911  during a first interval;   Step S 903 : generate a first feedback voltage V 1   a  corresponding to the red LED module  901  through performing differential amplifying and signal amplifying operations on a first voltage drop corresponding to the red LED module  901  by the first differential amplifier  931  and the first signal amplifier  915 , and generate a first set of CIE tristimulus values X 1   a , Y 1   a , and Z 1   a  corresponding to the red LED module  901  through detecting the light emitted from the red LED module  901  by the CIE tristimulus colorimeter  990  at a first time of the first interval;   Step S 905 : generate a second feedback voltage V 1   b  corresponding to the red LED module  901  through performing differential amplifying and signal amplifying operations on a second voltage drop corresponding to the red LED module  901  by the first differential amplifier  931  and the first signal amplifier  915 , and generate a second set of CIE tristimulus values X 1   b , Y 1   b , and Z 1   b  corresponding to the red LED module  901  through detecting the light emitted from the red LED module  901  by the CIE tristimulus colorimeter  990  at a second time of the first interval;   Step S 907 : provide a second driving current Ig to the green LED module  902  by the green LED driving circuit  912  during a second interval;   Step S 909 : generate a first feedback voltage V 2   a  corresponding to the green LED module  902  through performing differential amplifying and signal amplifying operations on a first voltage drop corresponding to the green LED module  902  by the second differential amplifier  932  and the second signal amplifier  920 , and generate a first set of CIE tristimulus values X 2   a , Y 2   a , and Z 2   a  corresponding to the green LED module  902  through detecting the light emitted from the green LED module  902  by the CIE tristimulus colorimeter  990  at a first time of the second interval;   Step S 911 : generate a second feedback voltage V 2   b  corresponding to the green LED module  902  through performing differential amplifying and signal amplifying operations on a second voltage drop corresponding to the green LED module  902  by the second differential amplifier  932  and the second signal amplifier  920 , and generate a second set of CIE tristimulus values X 2   b , Y 2   b , and Z 2   b  corresponding to the green LED module  902  through detecting the light emitted from the green LED module  902  by the CIE tristimulus colorimeter  990  at a second time of the second interval;   Step S 913 : provide a third driving current Ib to the blue LED module  903  by the blue LED driving circuit  913  during a third interval;   Step S 915 : generate a first feedback voltage V 3   a  corresponding to the blue LED module  903  through performing differential amplifying and signal amplifying operations on a first voltage drop corresponding to the blue LED module  903  by the third differential amplifier  933  and the third signal amplifier  925 , and generate a first set of CIE tristimulus values X 3   a , Y 3   a , and Z 3   a  corresponding to the blue LED module  903  through detecting the light emitted from the blue LED module  903  by the CIE tristimulus calorimeter  990  at a first time of the third interval;   Step S 917 : generate a second feedback voltage V 3   b  corresponding to the blue LED module  903  through performing differential amplifying and signal amplifying operations on a second voltage drop corresponding to the blue LED module  903  by the third differential amplifier  933  and the third signal amplifier  925 , and generate a second set of CIE tristimulus values X 3   b , Y 3   b , and Z 3   b  corresponding to the blue LED module  903  through detecting the light emitted from the blue LED module  903  by the CIE tristimulus colorimeter  990  at a second time of the third interval;   Step S 919 : provide the first driving current Ir to the red LED module  901  by the red LED driving circuit  911 , provide the second driving current Ig to the green LED module  902  by the green LED driving circuit  912 , and provide the third driving current Ib to the blue LED module  903  by the blue LED driving circuit  913 ;   Step S 921 : generate a third feedback voltage V 1   t  corresponding to the red LED module  901  through performing differential amplifying and signal amplifying operations on a third voltage drop corresponding to the red LED module  901  by the first differential amplifier  931  and the first signal amplifier  915 ;   Step S 923 : calculate a third set of CIE tristimulus values X 1   t , Y 1   t , and Z 1   t  corresponding to the red LED module  901  based on the third feedback voltage V 1   t , the first feedback voltage V 1   a , the second feedback voltage V 1   b , the first set of CIE tristimulus values X 1   a , Y 1   a , and Z 1   a , and the second set of CIE tristimulus values X 1   b , Y 1   b , and Z 1   b  corresponding to the red LED module  901  by the signal processor  955  according to the formulas (33), (34), and (35) listed below:   
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
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                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
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                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
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                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   33 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
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                   = 
                   
                     
                       
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                         ⁢ 
                         
                             
                         
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                         t 
                       
                     
                     
                       
                         Y 
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                         a 
                       
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                         Y 
                         ⁢ 
                         
                             
                         
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                         1 
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                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   34 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
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                         a 
                       
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                         ⁢ 
                         a 
                       
                       - 
                       
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                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
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                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         a 
                       
                       - 
                       
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                         ⁢ 
                         1 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Z 
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                         1 
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                         a 
                       
                       - 
                       
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                         ⁢ 
                         
                             
                         
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                         1 
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                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   35 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 925 : generate a third feedback voltage V 2   t  corresponding to the green LED module  902  through performing differential amplifying and signal amplifying operations on a third voltage drop corresponding to the green LED module  902  by the second differential amplifier  932  and the second signal amplifier  920 ; 
       Step S 927 : calculate a third set of CIE tristimulus values X 2   t , Y 2   t , and Z 2   t  corresponding to the green LED module  902  based on the third feedback voltage V 2   t , the first feedback voltage V 2   a , the second feedback voltage V 2   b , the first set of CIE tristimulus values X 2   a , Y 2   a , and Z 2   a , and the second set of CIE tristimulus values X 2   b , Y 2   b , and Z 2   b  corresponding to the green LED module  902  by the signal processor  955  according to the formulas (36), (37), and (38) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
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                         ⁢ 
                         
                             
                         
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                         2 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
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                         t 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
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                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   36 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
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                         a 
                       
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                   = 
                   
                     
                       
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                         a 
                       
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                         ⁢ 
                         
                             
                         
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                         t 
                       
                     
                     
                       
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                         2 
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                         a 
                       
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                         ⁢ 
                         
                             
                         
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                         2 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   37 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
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                         ⁢ 
                         
                             
                         
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                   = 
                   
                     
                       
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                         a 
                       
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                         2 
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                         t 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
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                         2 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   38 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 929 : generate a third feedback voltage V 3   t  corresponding to the blue LED module  903  through performing differential amplifying and signal amplifying operations on a third voltage drop corresponding to the blue LED module  903  by the third differential amplifier  933  and the third signal amplifier  925 ; 
       Step S 931 : calculate a third set of CIE tristimulus values X 3   t , Y 3   t , and Z 3   t  corresponding to the blue LED module  903  based on the third feedback voltage V 3   t , the first feedback voltage V 3   a , the second feedback voltage V 3   b , the first set of CIE tristimulus values X 3   a , Y 3   a , and Z 3   a , and the second set of CIE tristimulus values X 3   b , Y 3   b , and Z 3   b  corresponding to the blue LED module  903  by the signal processor  955  according to the formulas (39), (40), and (41) listed below: 
     
  
   
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         X 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   39 
                   ) 
                 
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Y 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 , 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   40 
                   ) 
                 
               
             
           
           
             
               and 
             
             
               
                   
               
             
           
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         b 
                       
                     
                   
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                     
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         a 
                       
                       - 
                       
                         Z 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                         ⁢ 
                         t 
                       
                     
                   
                 
                 ; 
               
             
             
               
                 Formula 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   ( 
                   41 
                   ) 
                 
               
             
           
         
       
     
       
       Step S 933 : calculate a first duty cycle control signal Pr, a second duty cycle control signal Pg, and a third duty cycle control signal Pb based on the third set of CIE tristimulus values X 1   t , Y 1   t , and Z 1   t  corresponding to the red LED module  901 , the third set of CIE tristimulus values X 2   t , Y 2   t , and Z 2   t  corresponding to the green LED module  902 , the third set of CIE tristimulus values X 3   t , Y 3   t , and Z 3   t  corresponding to the blue LED module  903 , and a set of preset CIE tristimulus values Xpreset, Ypreset, and Zpreset by the signal processor  955  according to the formulas (42), (43), and (44) listed below:
 
 PrX 1 t+PgX 2 t+PbX 3 t=X preset  Formula (42),
 
 PrY 1 t+PgY 2 t+PbY 3 t=Y preset  Formula (43), and
 
 PrZ 1 t+PgZ 2 t+PbZ 3 t=Z preset  Formula (44);
 
       Step S 935 : regulate the duty cycle of a first PWM signal based on the first duty cycle control signal Pr by the first PWM signal generator  971 , regulate the duty cycle of a second PWM signal based on the second duty cycle control signal Pg by the second PWM signal generator  972 , and regulate the duty cycle of a third PWM signal based on the third duty cycle control signal Pb by the third PWM signal generator  973 ; and 
       Step S 937 : adjust the first driving current Ir based on the first PWM signal by the red LED driving circuit  911 , adjust the second driving current Ig based on the second PWM signal by the green LED driving circuit  912 , and adjust the third driving current Ib based on the third PWM signal by the blue LED driving circuit  913 , go back to step S 919 . 
     
  
   The color control method based on the LED lighting system  900  comprises a preliminary detection phase and a feedback control phase. The preliminary detection phase including the steps from S 901  to S 917  is utilized to detect the voltage drop of each LED module and the corresponding CIE tristimulus values. The first interval, the second interval, and the third interval are not overlapped between each other. The feedback control phase including the steps from S 919  to S 937  is utilized to precisely control the light emitted form each LED module through regulating the driving current for each LED module by performing compensation operations based on the voltage drop variations in conjunction with the CIE tristimulus values generated in the preliminary detection phase. 
   In the steps S 903 , S 905 , and S 921 , the processes of performing differential amplifying and signal amplifying operations on the first, second, and third voltage drops corresponding to the red LED module  901  by the first differential amplifier  931  and the first signal amplifier  915  can be simplified to be the processes of performing differential amplifying operations on the first, second, and third voltage drops corresponding to the red LED module  901  in conjunction with the first reference voltage Vrefr by the first differential amplifier  931 , or alternatively, the processes of performing signal amplifying operations on the first, second, and third voltage drops corresponding to the red LED module  901  by the first signal amplifier  915 . 
   Similarly, in the steps S 909 , S 911 , and S 925 , the processes of performing differential amplifying and signal amplifying operations on the first, second, and third voltage drops corresponding to the green LED module  902  by the second differential amplifier  932  and the second signal amplifier  920  can be simplified to be the processes of performing differential amplifying operations on the first, second, and third voltage drops corresponding to the green LED module  902  in conjunction with the second reference voltage Vrefg by the second differential amplifier  932 , or alternatively, the processes of performing signal amplifying operations on the first, second, and third voltage drops corresponding to the green LED module  902  by the second signal amplifier  920 . 
   Likewise, in the steps S 915 , S 917 , and S 929 , the processes of performing differential amplifying and signal amplifying operations on the first, second, and third voltage drops corresponding to the blue LED module  903  by the third differential amplifier  933  and the third signal amplifier  925  can be simplified to be the processes of performing differential amplifying operations on the first, second, and third voltage drops corresponding to the blue LED module  903  in conjunction with the third reference voltage Vrefb by the third differential amplifier  933 , or alternatively, the processes of performing signal amplifying operations on the first, second, and third voltage drops corresponding to the blue LED module  903  by the third signal amplifier  925 . 
   Since the CIE tristimulus calorimeter  990  is used only in the preliminary detection phase, the CIE tristimulus calorimeter  990  can be detached from the LED lighting system  900  at the completion of the step S 917 . 
   In summary, the color control methods of the present invention are capable of providing accurate lighting controls on a variety of different LED lighting systems. Especially when temperature variation occurs to the LED dice of an LED lighting system, the temperature-related wavelength shift can be compensated by a feedback control mechanism based on voltage drop variation or current variation of the LED dice so that the LED lighting system is able to generate the light having desired chrominance precisely. 
   The present invention is by no means limited to the embodiments as described above by referring to the accompanying drawings, which may be modified and altered in a variety of different ways without departing from the scope of the present invention. Thus, it should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alternations might occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.