Abstract:
Methods and apparatuses for image display are disclosed. There is provided an image display apparatus. The apparatus includes a plurality of display modules including display elements manufactured from different bins; a plurality of driving circuits providing different driving conditions for the display modules, at least one driving circuit for each display module; and a control circuit controlling the driving circuits to compensate each display module for variation of characteristics amongst modules of bins. The driving control circuit may include a look up table storing information about one or more characteristics of each display module.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to display arrays and more particularly to controlling the driving of a large panel of display arrays. 
         [0003]    2. Description of Related Art 
         [0004]    Light emitting diodes (LEDs) have been widely used in lighting systems due to their high efficiency, fast response time and long life span. LEDs also give off less heat than conventional incandescent light bulbs. Importantly, LEDs emit incoherent narrow-spectrum light from the electroluminescence effect. By controlling the doping of semiconductor materials at a p-n junction, the energy band gap can be fine-tuned and hence the wavelength or color of the light emitted by the LED can be controlled. 
         [0005]    Characteristics of LEDs include the wavelength of emitted light, luminance, temperature response, current-voltage characteristics (I-V characteristics). Due to process variation, such characteristics of the LEDs usually differ between production bins. Even for the same production bin, variations in LED characteristics still exist and follow a normal distribution. For quality control, only LEDs satisfying the production specification are adopted, while others falling outside the selection window for quality control are discarded. If higher quality is required, the selection window is narrower and the yield becomes lower. This results in higher manufacturing costs. 
         [0006]    For LEDs to be used for large panel display, such as the backlight for LCD panel, performance criteria such as brightness and color of the LEDs within the same panel must be uniform. For the reasons described above, it is difficult to obtain a large amount of LEDs with consistent characteristics. Hence, the size of an LED panel is limited by the size of the production bin. The cost for manufacturing large size LED panels is consequently expensive. 
         [0007]    Currently, some manufacturers try to increase the yield by relaxing the production specifications, in other words, to trade off cost with quality. However, this does not fundamentally solve the technical problem, and the cost remains high for good quality LED panels. 
         [0008]    Another alternative to lower the manufacturing cost is by keeping a stock of disqualified LEDs, and categorizing those LEDs into groups according to their characteristics such as wavelength. These categorized LEDs are reused in future production when a sufficient number are accumulated. However, such a method still does not fundamentally solve the technical problem. Furthermore, the method has disadvantages: i) even if the characteristics remain uniform within a single panel, the characteristics can vary from panel to panel; ii) extra cost in incurred keeping stock of the disqualified LEDs for reuse; iii) the quantity for these reused LEDs produced by the manufacturing process is unpredictable; and, iv) the variation always happens to more than one characteristic, and there are lots of combinations from the wavelength, brightness, biasing voltage, etc. making it difficult to collect disqualified LEDs with the same exact characteristics from different production bins. 
         [0009]    Circumstances arise under which part of the LEDs in an operating display panel may burn out after prolong use and need to be replaced. According to conventional technology, it is difficult to produce LEDs of consistent characteristics with the defective LED. Hence the repair cost tends to be high. 
         [0010]    Accordingly, a need exists for improved methods and apparatuses to enhance the manufacturing yield, assembly yield and repairability of LED panels. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    According to an aspect of the present invention, there is provided an image display apparatus. The apparatus comprises: a plurality of display modules including display elements manufactured from different bins; a plurality of driving circuits providing different driving conditions for the display modules, at least one driving circuit for each display module; a control circuit controlling said driving circuits to compensate each display module for variation of characteristics amongst display modules manufactured from different bins. 
         [0012]    The driving control circuit may comprise a look up table storing information about one or more characteristics of each display module. 
         [0013]    The apparatus may further comprise a circuit for dynamically controlling the display modules dependent on the operating conditions of the display modules. 
         [0014]    The operating conditions are wavelength of emitted light, intensity of emitted light, working temperature, or operation time. The display element may be a light emitting diode. The characteristics of display elements are based on wavelength of emitted light, intensity of emitted light, or biasing current-voltage relationship. A driving condition provided by each driving circuit may be biasing current or biasing voltage. 
         [0015]    The image display apparatus may be used in applications of LCD backlight or LED display panel. The image display apparatus provides uniform, white-balance back lighting or a special pattern composed of different colors. 
         [0016]    In accordance with a further aspect of the invention, there is provided a process for manufacturing an image display apparatus. The process comprises the steps of:
       characterizing and inspecting manufactured display elements from different bins;   assembling display modules, each having display elements from a single bin, to form a large display array, at least two modules comprising display elements from different bins;   determining the driving conditions for each bin based on the characteristics obtained from characterizing and inspecting said display elements to achieve a desired performance; and   providing compensated driving circuit for each display module with said respective determined driving condition determined to produce light of substantially uniform wavelength or intensity from said large display array.       
 
         [0021]    The process may further comprise the step of manufacturing a plurality of bins of display elements. 
         [0022]    The process may further comprise the step of creating display modules using display elements selected from a single bin for each display module. 
         [0023]    The display element may be a light emitting diode. The characteristics of display element are based on wavelength of emitted light, intensity of emitted light, or biasing current-voltage relationship. A driving condition provided by each driving circuit may be biasing current or biasing voltage. 
         [0024]    In accordance with a further aspect of the invention, there is provided a method of displaying an image. The method comprises the steps of: providing a plurality of display modules consisting of display elements manufactured from different bins; providing different driving conditions for the display modules, at least one driving condition being provided for each display module; and controlling the driving conditions to compensate each display module for variation of characteristics amongst modules of bins. 
         [0025]    The controlling step may comprise storing information about one or more characteristics of each display module in a look up table. 
         [0026]    The display modules may be controlled dynamically dependent on the operating conditions of said display modules. 
         [0027]    The operating conditions are wavelength of emitted light, intensity of emitted light, working temperature, or operation time. The display element may be a light emitting diode. The characteristics of display element are based on wavelength of emitted light, intensity of emitted light, or biasing current-voltage relationship. A driving condition provided by each driving circuit may be biasing current or biasing voltage. 
         [0028]    The method may be used for providing LCD backlighting or displaying an image in a LED display panel. The method provides a uniform, white-balance back lighting or a special pattern composed of different colors. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0029]    One or more embodiments are described hereinafter, by way of examples only, with reference to the accompanying drawings in which: 
           [0030]      FIG. 1   a  is a schematic block diagram representing an LED driving system architecture with static compensated control in accordance with an embodiment of the present invention; 
           [0031]      FIGS. 1   b - 1   e  are plots showing the characteristics of LED bins before and after compensation control according to embodiments of the present invention; 
           [0032]      FIG. 1   f  is a typical implementation of the driving circuits in  FIG. 1   a;    
           [0033]      FIG. 2   a  is a plot showing the relationship of LED wavelength shift against forward biasing current and control mechanism for wavelength shift compensation; 
           [0034]      FIG. 2   b  is a plot showing the relationship of LED intensity against forward biasing current and control mechanism for intensity compensation; 
           [0035]      FIG. 2   c  is a plot showing the relationship of LED forward biasing current against forward biasing voltage; 
           [0036]      FIG. 3  is a flow diagram illustrating a manufacturing process for the LED driving system with compensated control in accordance with an embodiment of the present invention; 
           [0037]      FIG. 4  is a schematic block diagram representing a LED driving system architecture with dynamic compensated control in accordance with an embodiment of the present invention; 
           [0038]      FIG. 5  is a plot showing the relationship of LED wavelength shift against the junction temperature and control mechanism for temperature compensation; 
           [0039]      FIG. 6  is a flow diagram illustrating the process of dynamic compensation in accordance with an embodiment of the present invention; and 
           [0040]      FIG. 7  is a flow diagram illustrating the method of displaying an image in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0041]    Where reference is made in any one or more of the accompanying drawings to steps and/or features, which have the same reference numerals, those steps and/or features have for the purposes of this description the same function(s) or operations(s), unless the contrary intention appears. 
         [0042]    A LED array system comprising LED modules manufactured from at least two different production bins is described hereinafter. LEDs are assembled into LED modules which are driven by separate driving circuits. All LEDs in a single LED module are manufactured from the same production bin, the characteristics within each module such as wavelength, brightness are consistent. While different LED modules may have LEDs from different production bins, the characteristics may vary between different LED modules. To provide a uniform performance across the whole LED array, each module is biased under different driving conditions to compensate the difference. Such driving conditions are determined by the individual characteristics of each bin, which are measured during the manufacturing process. In one embodiment, the compensation control is provided in a static manner and is preset in the manufacturing process. In another embodiment, the compensation control is dynamic and determined also by the operating conditions of the LED array system. 
         [0043]    The methods in accordance with the embodiments described herein have general applicability to LED display array systems. For ease of explanation, the embodiments of the invention are described with reference to LED backlight array systems in white balance for LCD backlight. However, it is not intended that the present invention be limited to the described embodiments. For example, the methods may have application to multicolor LED display panel, wherein each LED device represents a pixel of the image and operates independently. Nevertheless, the whole panel desirably provides a uniform performance, especially when the neighboring pixels are required to display the same color and intensity. To apply the method to such LED panel, the whole panel is similarly partitioned into smaller modules. A default offset biasing is applied to each module to compensate for the variation of characteristics between modules. The compensated control may also vary for different colors of LEDs (e.g., Red, Green, Blue). 
         [0044]    According to the process of manufacturing LED array system in the present invention, the required quantity of LEDs with consistent characteristics can be substantially reduced. Therefore, it is easier to manufacture large LED panels of high quality. In other words, the manufacturing yield and assembly yield is also enhanced and subsequently lead to a reduction in manufacturing cost. 
         [0045]      FIG. 1   a  is a block diagram of a LED array system  100  in accordance with an embodiment of the invention. A large LED array  101  is partitioned spatially into LED modules  111 ,  112 ,  113 ,  114  of smaller size. For example, a large LED array of 240 red LEDs, 240 green LEDs and 120 blue LEDs can be divided into 12 modules. Each module uses LEDs from a different production bin, for example, module  111  has LEDs from bin  1 , module  112  from bin  2 , module  113  from bin  3  and module  114  from bin  4 . 
         [0046]    Despite the different characteristics of different modules  111 - 114 , such as wavelength, luminosity, each module has substantially uniform characteristics among its LEDs because the LEDs come from the same bin. The performance of all modules  111 - 114  can be united by separate LED driving circuits through providing driving conditions to compensate for the variations. Compensated control is provided based on the offset of characteristics, such as the wavelength, and the intensity of the relevant LED module. 
         [0047]    Each LED module  111 - 114  is biased under separate driving conditions, for example, biasing voltage or current. Individual LED driving circuits  121 ,  122 ,  123 ,  124 , each receiving instructions from the driving control circuit  103 , can provide adjustable driving voltages or currents to the LED modules  111 ,  112 ,  113 ,  114 , respectively. 
         [0048]    In an embodiment of the invention, the driving control circuit  103  contains a storage unit  104  to store the driving parameters for each module  111 - 114 . The driving control circuit may further contain a look up table (LUT)  131  to convert the driving parameters into control signals for driving circuits  121 ,  122 ,  123 ,  124 . 
         [0049]    Table 1 shows the contents of LUT  131 . 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Address 
                 Contents 
               
               
                   
               
             
             
               
                 0x0000 
                 driving current duty cycle when biasing voltage = V0 (For bin 1) 
               
               
                 0x0001 
                 driving current duty cycle when biasing voltage = V1 
               
               
                 0x0002 
                 driving current duty cycle when biasing voltage = V2 
               
               
                 0x0003 
                 driving current duty cycle when biasing voltage = V3 
               
               
                 . . . 
                 . . . 
               
               
                 0x0010 
                 driving current duty cycle when brightness = LUX0 (For bin 1) 
               
               
                 0x0011 
                 driving current duty cycle when brightness = LUX1 
               
               
                 0x0012 
                 driving current duty cycle when brightness = LUX2 
               
               
                 0x0013 
                 driving current duty cycle when brightness = LUX3 
               
               
                 . . . 
                 . . . 
               
               
                 0x0020 
                 driving current duty cycle when wavelength = Lamda0 
               
               
                   
                 (For bin 1) 
               
               
                 0x0021 
                 driving current duty cycle when wavelength = Lamda1 
               
               
                 0x0022 
                 driving current duty cycle when wavelength = Lamda2 
               
               
                 0x0023 
                 driving current duty cycle when wavelength = Lamda3 
               
               
                 . . . 
                 . . . 
               
               
                 0x0100 
                 driving current duty cycle when biasing voltage = V0 (For bin 2) 
               
               
                 . . . 
                 . . . 
               
               
                 0x0110 
                 driving current duty cycle when brightness = LUX0 (For bin 2) 
               
               
                 . . . 
                 . . . 
               
               
                 0x0120 
                 driving current duty cycle when wavelength = Lamda0 
               
               
                   
                 (For bin 2) 
               
               
                 . . . 
                 . . . 
               
               
                 0x0200 
                 driving current duty cycle when biasing voltage = V0 (For bin 3) 
               
               
                 . . . 
                 . . . 
               
               
                 0x0210 
                 driving current duty cycle when brightness = LUX0 (For bin 3) 
               
               
                 . . . 
                 . . . 
               
               
                 0x0220 
                 driving current duty cycle when wavelength = Lamda0 
               
               
                   
                 (For bin 3) 
               
               
                 . . . 
                 . . . 
               
               
                   
               
             
          
         
       
     
         [0050]    The address bits of LUT  131  represent conditions for a certain driving current duty cycle. In the example, bit  0 - 3  represent the variation in a certain characteristics (V 0 , V 1 , V 2  . . . ); bit  4 - 7  represent the type of characteristics (biasing voltage, brightness, wavelength); bit  8 - 12  represent the bin number. Accordingly, the content in address  0 x 0110  is the driving current for bin  1  to provide a brightness of LUX 0 . If the manufacturer wishes to bias module  112  comprising bin  1  LEDs to emit light of brightness LUX 0 , the binary value of  0 x 0110  should be fed into LUT  131  address bus either from storage unit  104  or control circuits like microcontroller. LUT  131  then outputs the desired driving current duty cycle in binary format to the control bus of driving circuit  121 . 
         [0051]    FIG. if shows a typical implementation of driving circuits  121 - 124 , comprising a series of pulse width modulation (PWM) controllers  132  and constant current drivers  133 , while each constant current driver  133  provides biasing current for a single LED  134  in the module. The output of LUT  131  is coupled to PWM controllers  132  through control bus  131 . PWM controllers  132  control constant current drivers  133  to provide biasing current with desired duty cycle. A higher duty cycle ratio is equivalent to a larger driving current. Therefore, by varying the duty cycle of a constant biasing current, the brightness of the LED  134  can be adjusted to LUX 0 . 
         [0052]      FIGS. 1   b - 1   e  illustrate the compensation for LED characteristics, for example, the compensated wavelength λ 0 emitted light of modules  111 - 114 .  FIG. 1   b  shows the original distribution of module  111  with λ 1  as the average or center wavelength. Assuming that the target wavelength of the whole LED array  101 , λ 0 , is slightly smaller than λ 1 , the driving control circuit  103  causes the driving circuit  121  to adjust the driving condition, for example, by increasing the driving current for module  111 , such that the average value of the distribution is reduced to λ 0 . 
         [0053]      FIG. 1   c  shows the original distribution of module  112  with λ 2  as medium wavelength. Assuming that the target wavelength of the whole LED array  101 , λ 0 , is slightly larger than λ 2 , the driving control circuit  103  causes the driving circuit  122  to adjust the driving condition, for example, by reducing the driving current for module  112 , such that the medium of the distribution is increased to λ 0 . 
         [0054]      FIG. 1   d  shows the original distribution of module  113  with λ 3  as medium wavelength. Assuming that the target wavelength of the whole LED array  101 , λ 0 , is slightly larger than λ 3 , the driving control circuit  103  causes the driving circuit  123  to adjust the driving condition, for example, by reducing the driving current for module  113 , such that the medium of the distribution is increased to λ 0 . 
         [0055]      FIG. 1   e  shows the original distribution of module  114  with λ 4  as medium wavelength. Assuming that the target wavelength of the whole LED array  101 , λ 0 , is slightly smaller than λ 4 , the driving control circuit  103  causes the driving circuit  124  to adjust the driving condition, for example, by increasing the driving current for module  114 , such that the medium of the distribution is reduced to λ 0 . As a result, all the modules  111 - 114  in LED array  101  emit light of substantial uniform wavelength of λ 0  under compensated driving conditions. 
         [0056]      FIG. 2  further illustrates how the performance of each LED module  111 - 114  can be tuned by varying the driving conditions.  FIG. 2   a  shows the relationship of LED wavelength shift against forward biasing current, which is a control mechanism for wavelength shift compensation. λ A  is the wavelength shift of the emitted light under default driving current I A . Assuming that λ A  is the desired shift to provide the target wavelength of the whole LED array, the driving circuit increases the driving current by ΔI to I B . 
         [0057]      FIG. 2   b  shows the relationship of LED intensity against forward biasing current which is a control mechanism for intensity compensation. lx A  is the intensity of the emitted light under default driving current I A . Assuming that lx B  is the desired intensity to provide a uniform intensity of the whole LED array, the driving circuit increases the driving current by ΔI to I B  to produce an intensity shift of Δlx. 
         [0058]    The above measures to compensate any LED&#39;s performance may at the same time affect some other performances. For example, when trying to minimize the wavelength shift, the driving current may have to be reduced. Such current reduction also results in a decrease of luminosity for the LED module  111 - 114  and hence non-uniform intensity across the LED array  101 . Therefore, the priority of the performances must be decided when applying compensation according to the embodiments of the present invention. Generally speaking, uniform wavelength is of higher priority for home theater TV, but the intensity is more important for outdoor display. 
         [0059]    Alternatively, the driving conditions can be adjusted through the driving voltage instead of the driving current.  FIG. 2   c  shows the relationship of LED forward biasing current against forward biasing voltage. If a LED module must be biased at a current of I B  instead of an original current of I A  to provide compensation, the driving circuit  102  can alternatively drive in voltage mode and adjust the driving voltage from V A  to V B . 
         [0060]      FIG. 3  shows a process  300  of manufacturing a LED driving system with compensated control in accordance with an embodiment of the invention. In step  301 , LEDs are manufactured in any convention manners. 
         [0061]    In step  302 , the LEDs are characterized and inspected from a bin. Relevant parameters for each production bin may be recorded in a database. The parameters include wavelength, intensity, and I-V characteristics for biasing current and voltage. The LEDs are inspected and those that fail to satisfy the production specification under compensated driving are discarded. 
         [0062]    In step  303 , the LEDs from each production bin are assembled to create LED modules from the respective bin, such that all LEDs in a module are produced from the same bin. 
         [0063]    In step  304 , the LED modules are assembled to form a panel. Such modules composing the large panel are not required to have the same characteristics. The characteristics may vary between different modules, a lower manufacturing cost is therefore resulted because a smaller quantity of LEDs having substantially uniform characteristics are required by this method. 
         [0064]    Steps  305  and  306  on the one hand and steps  307  and  308  on the other, while shown as parallel branches in  FIG. 3  are alternate embodiments of the invention, as described hereinafter. 
         [0065]    According to one embodiment of the invention (steps  305  and  306 ), in step  305  the data in LUT  131  of the driving control circuit  103  is generated for compensated control. This may be done using the LED characteristics measured in step  302 . In step  306 , the parameters are written into memory and the LUT  131  is programmed with the data. The storage unit  104  is written into with parameters, such as the medium wavelength of the relevant bin. The driving control circuit  103  translates and converts such parameters to control signals for the driving circuit  102  to provide adequate driving conditions such that the LEDs achieve a target performance. Each address space of the storage unit  104  stores the parameters for one LED module. 
         [0066]    In another embodiment of the invention (steps  307  and  308 ), in step  307 , the driving conditions for each production bin are computed for compensated control. This is done based on the bin parameters obtained in characterization step  302 . In step  308 , the circuit parameters are adjusted to provide compensated driving conditions as determined in step  307 . The parameters may be, for example, resistor values in a feedback network. 
         [0067]    Processing continues from either step  306  or  308 . In step  309 , compensated driving is applied to each LED module to obtain uniform performance. The LED module is coupled to individual driving circuit and receives optimum driving conditions to provide a uniform performance throughout the whole array  101 . 
         [0068]    The yield can be further enhanced if the disqualified LEDs in each bin can be categorized according to their characteristics and form some other modules. These modules are again driven by compensated control by appropriate driving conditions to provide substantially the same performance as other modules in the LED array  101 . 
         [0069]    Compensation provided by above methods is static and is usually predetermined during the manufacturing process. In contrast, another embodiment of the invention provides dynamic compensation to adapt changes in LED characteristics during operation. 
         [0070]    In the embodiment shown in  FIG. 4 , dynamic compensation can be performed using a timer  411  in the LED panel system  400 , which keeps record of the operation time of the LED panel  101 . The timer  411  is coupled to the driving control circuit  403  which receives timer information and commands the driving circuits  102  to adjust the driving conditions accordingly. As such, the aging effect of the LED system  400 , for example, reduction in intensity, can be compensated (such as, by increasing biasing current) based on the timer value. 
         [0071]    In particular, LUT  431  in control circuit  403  contains additional address bits (bit  16 - 19 ) compared to LUT  131  of  FIG. 1 . These additional address bits represent the time that a LED module has operated and are driven by time signal provided by timer  411 . The contents in LUT  431  are shown in Table 2 below. Based on different values of the time signal, LUT  431  looks up the corresponding address and outputs data representing the desired driving condition stored therein, which is the value of driving current duty cycle in this example. The LUT output is in binary format and directly controls the LED driving circuits  121 - 124  to provide desired driving condition. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Address 
                 Contents 
               
               
                   
                   
               
             
             
               
                   
                 . . . 
                 . . . 
               
               
                   
                 0x00010 
                 driving current duty cycle when brightness = LUX0 
               
               
                   
                   
                 (For bin 0, 0–5000 operating hrs) 
               
               
                   
                 0x00011 
                 driving current duty cycle when brightness = LUX1 
               
               
                   
                 0x00012 
                 driving current duty cycle when brightness = LUX2 
               
               
                   
                 0x00013 
                 driving current duty cycle when brightness = LUX3 
               
               
                   
                 . . . 
                 . . . 
               
               
                   
                 0x10010 
                 driving current duty cycle when brightness = LUX0 
               
               
                   
                   
                 (For bin 0, 5000–10000 operating hrs) 
               
               
                   
                 0x10011 
                 driving current duty cycle when brightness = LUX1 
               
               
                   
                 0x10012 
                 driving current duty cycle when brightness = LUX2 
               
               
                   
                 0x10013 
                 driving current duty cycle when brightness = LUX3 
               
               
                   
                 . . . 
                 . . . 
               
               
                   
                 0x20010 
                 driving current duty cycle when brightness = LUX0 
               
               
                   
                   
                 (For bin 0, 10000–15000 operating hrs) 
               
               
                   
                 0x20011 
                 driving current duty cycle when brightness = LUX1 
               
               
                   
                 0x20012 
                 driving current duty cycle when brightness = LUX2 
               
               
                   
                 0x20013 
                 driving current duty cycle when brightness = LUX3 
               
               
                   
                 . . . 
                 . . . 
               
               
                   
                   
               
             
          
         
       
     
         [0072]    In another embodiment, dynamic compensation can be implemented using performance sensors  412 , such as color sensor or light intensity sensor, in each LED module  111 - 114 . Performance of the LED modules  111 - 114  is monitored continuously or at time intervals in respect of conditions such as wavelength or intensity of the emitted light. In case any variation of performance is detected, the sensors  412  will feedback such information to the driving control circuit  403  (through a comparator or ADC). The driving control circuit  403  refers to the LUT  431  and commands the driving circuit  102  to adjust the driving conditions and compensate the offset in performance. 
         [0073]    Similar to Table 2 in time compensation case, LUT  431  can be extended to include driving conditions under various measured performance. The additional address bits may represent the performance deviation. For example, when the intensity of a certain module, say  111 , drops by 10 Lux, sensor  412  such as a phototransistor detects the change and feedbacks a signal to LUT  431 . If it is analog signal, an Analog to Digital Converter (ADC) is required to convert it to digital signal. This digital sensor signal is fed to the address input of LUT  431  to fetch the driving condition which can provide an additional 10 Lux. LUT  431  outputs the corresponding content in binary format and commands the LED driver, say  111 , to provide driving for compensating the 10 Lux drop. 
         [0074]    In another embodiment, dynamic compensation can be implemented by incorporating temperature sensors  413  to the LED array system  400 . A common disadvantage of LEDs is that the wavelength may shift substantially due to the change in the working temperature of the operating environment. According to this embodiment of the invention, the driving control circuit  403  uses the feedback signal from the temperature sensor  413  and estimates the temperature effect on each LED module  111 - 114 . The estimation is based on the relevant parameters measured during the manufacturing process and stored in the LUT  431  to provide driving conditions on each LED module to achieve uniform and desirable performance throughout the whole LED array  101  even under temperature change. The contents of LUT  431  in this embodiment are similar to Table 2, except the additional address bits now represent variation of temperature. 
         [0075]      FIG. 5  shows the relationship of LED wavelength shift against the junction temperature and control mechanism for temperature compensation. λ A  is the wavelength shift of the emitted light under junction temperature T A . Assuming that the junction temperature rises to T B , the wavelength shift therefore becomes λ B . To recover the wavelength shift to λ A  and provide the target wavelength of the whole LED array, the driving conditions should be adjusted according to the mechanism depicted in  FIGS. 2   a - 2   c.    
         [0076]      FIG. 6  shows the flow diagram to summarize the dynamic compensation. In step  601 , either the timer is incremented or a change in operating conditions of a LED module is detected by sensors, such as color sensor, intensity sensor and temperature sensor. In step  602 , the address bits relevant to the time or change in conditions are updated. In step  603 , an updated binary output is read out from the LUT based on the change of address bits, such binary output represents the desired driving condition to compensate the change in operating conditions. In step  604 , the LUT output is fed to the control bus of the LED driving circuits which is instructed to update driving conditions for the relevant LED module. After compensated driving is provided, the system flow goes back to step  601  and waits for another timer increment or change in operating conditions. 
         [0077]      FIG. 7  shows the flow diagram of displaying an image according to an embodiment of the present invention. In step  701 , display modules are provided by assembling LEDs manufactured from different bins. 
         [0078]    In step  702 , independent driving condition is provided for each display module. 
         [0079]    In step  703 , information about one or more characteristics of each display module is stored in a look up table. The module characteristics can be wavelength of emitted light, intensity of emitted light, and biasing current-voltage relationship. 
         [0080]    In step  704 , the driving conditions are controlled to compensate each display module for variation of characteristics amongst modules of bins. The driving conditions may be biasing current or biasing voltage. Each display module are controlled dynamically dependent on the operating conditions of the display modules, such as wavelength of emitted light, intensity of emitted light, working temperature, and operation time. 
         [0081]    In step  705 , uniform, white-balance backlighting is provided in a LCD display or a special pattern composed of different colors is provided in a LED display panel. 
       INDUSTRIAL APPLICABILITY 
       [0082]    The embodiments and arrangements described hereinafter are applicable to electronics, lighting and display industries, amongst others. 
         [0083]    The foregoing describes only a few embodiments of the present invention, and modifications and/or substitutions can be made thereto without departing from the scope and spirit of the invention, the embodiments being illustrative and not restrictive.