Abstract:
The present disclosure provides a lighting system. In one example, the lighting system includes a circuit board including a plurality of light emitting groups, an integrated circuit electrically coupled to the light emitting groups, a rectifier circuit electrically coupled to the integrated circuit and configured to generate a rectified sine waveform of a power source, and a dimmer circuit electrically coupled to the integrated circuit and configured to transmit a dimming signal to the integrated circuit. In one case, the integrated circuit is configured to modify a power current of the light emitting groups to globally control an emission intensity of all of the light emitting groups uniformly in accordance with the dimming signal.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of priority to U.S. Provisional Application No. 61/975,437, filed on Apr. 4, 2014, the entire contents of which are incorporated herein by reference for all purposes. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to a lighting system and a method for driving the lighting system. More particularly, the present disclosure relates to a lighting system including light emitting diodes (LEDs) and a method for driving the LEDs without the need of a power supply. 
         [0003]    Recent developments in lighting technologies include advances in efficiency and power of lighting systems. Some of the advanced lighting systems use, for example, light emitting diodes (LEDs). LEDs are available in various colors. They also have relatively high luminous efficiencies and long life times. 
         [0004]    Nevertheless, existing LED systems have some limitations. For instance, the lighting systems that use LEDs may have an overall lifetime that is shorter than that of its LEDs due to the failure of other parts. Moreover, the light from these lighting systems may have a look and feel that is different from those of natural light or of traditional incandescent lights. The difference may exist for a full light profile or a dimmed light profile. As a result, a user may not be willing to use LED systems, despite their advantages. And even when a user decides to upgrade the lighting system in a building, the user may encounter practical and financial burdens. For example, instead of gradually replacing old incandescent lights that fail with new LED based lights, the user may have to replace all old lights at the same time to avoid inhomogeneous lighting that may result from the differences between the incandescent lights and the LED lights. The cost and burden of such a complete replacement may deter the use of new lighting systems, despite their advantages. 
         [0005]    Moreover, many locations such as museums or libraries would benefit from a lighting system that can vary at different times and location in its color, color temperature, or luminosity. But, existing lighting systems may not provide such flexibilities. 
       SUMMARY 
       [0006]    The present disclosure provides a light system that is operable by directly using a AC power source, without using a power supply or a AC/DC converter. 
         [0007]    In accordance with one aspect, a lighting system of the present disclosure includes a circuit board including a plurality of light emitting groups; an integrated circuit electrically coupled to the light emitting groups; a rectifier circuit electrically coupled to the integrated circuit and configured to generate a rectified waveform of a power source; and a dimmer circuit electrically coupled to the integrated circuit and configured to transmit a dimming signal to the integrated circuit. The integrated circuit can be configured to modify the rectified waveform into a truncated rectified waveform in accordance with the dimming signal; and wherein the integrated circuit is configured to selectively turn on or off a number of the light emitting groups in accordance with the truncated rectified waveform. 
         [0008]    In one embodiment, the dimmer circuit can include a user interface configured to receive a dimming input and generate an interface output; and a transducer configured to receive the interface output and generate the dimming signal. 
         [0009]    In one embodiment, the transducer can be configured to generate the dimming signal in accordance with a dimming style which determines a relationship between the dimming input and the dimming signal, and wherein the relationship is linear. 
         [0010]    In one embodiment, the transducer can be configured to generate the dimming signal in accordance with a dimming style which determines a relationship between the dimming input and the dimming signal, and wherein the relationship is non-linear. 
         [0011]    In one embodiment, the dimming style can be one of a logarithmic profile and an exponential profile. 
         [0012]    In one embodiment, each of the light emitting groups can include at least one light emitting diode. 
         [0013]    In one embodiment, one of the light emitting groups can include an equal number of light emitting diodes as another one of the light emitting groups. 
         [0014]    In one embodiment, the dimming signal can include at least one of a DMX signal, a digital addressable lighting interface (DALI) signal, a power-line communication signal, a global dimming signal having a voltage between 0-10 volts, a Bluetooth signal, a Bluetooth Low Energy signal, a WIFI signal, a Zigbee signal, and a visible light signal. 
         [0015]    In one embodiment, the dimmer circuit can be electrically coupled to the integrated circuit through at least one circuit protector. 
         [0016]    In one embodiment, the at least one circuit protector can include at least one of a capacitor, a Zener diode, an opto-isolator, and a combination thereof. 
         [0017]    In one embodiment, the integrated circuit can be configured to sequentially turn on the light emitting groups in a first quarter wave cycle of the rectified waveform and to sequentially turn off the light emitting groups in a second quarter wave cycle of the rectified waveform following the first quarter wave cycle. 
         [0018]    In one embodiment, each of the light emitting groups can include at least one white color light emitting diode. 
         [0019]    In one embodiment, the light emitting groups can include at least one light emitting diode of a first color and at least one light emitting diode of a second color different from the first color. 
         [0020]    In one embodiment, the first color can be white and the second color can be red. 
         [0021]    In one embodiment, the light emitting groups can include at least one light emitting diode of a first color, at least one light emitting diode of a second color different from the first color, and at least one light emitting diode of a third color different from the first color and the second color. 
         [0022]    In one embodiment, the first color can be white, the second color can be red, and the third color can be blue. 
         [0023]    In accordance with one aspect, a lighting system of the present disclosure includes a circuit board including a plurality of light emitting groups; an integrated circuit electrically coupled to the light emitting groups; a rectifier circuit electrically coupled to the integrated circuit and configured to generate a rectified waveform of a power source; and a dimmer circuit electrically coupled to the integrated circuit and configured to transmit a dimming signal to the integrated circuit; wherein the integrated circuit is configured to modify a power current of the light emitting groups to globally control an emission intensity of all of the light emitting groups uniformly in accordance with the dimming signal. 
         [0024]    The above listed embodiments provide at least some of the following advantages. One key advantage allows for the removal of standard AC/DC power supplies that are traditionally found in solid state lighting systems. This allows products to become smaller, while simultaneously becoming more efficient, as the losses associated with traditional AC/DC conversion are nonexistent. Simultaneously, the components used in these systems remove the weakest link, e.g., the AC/DC power supply that includes electrolytic capacitors and inductors. The elimination of the standard AC/DC power supply allows for a lower cost structure to allow for broadening adoption of the technology as well as increasing the overall life of the lighting units. Another advantage, is the dimming capabilities provide smooth, consistent, dimming without the need for complex, costly circuitry. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The foregoing and other objects, features and advantages will be apparent from the following more particular description of the embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the embodiments. 
           [0026]      FIG. 1  depicts an LED lighting system; 
           [0027]      FIG. 2  is a block diagram of a lighting system using an ASIC according to some embodiments; 
           [0028]      FIG. 3  is a block diagram of another lighting system using an ASIC according to some embodiments; 
           [0029]      FIGS. 4A and 4B  illustrate the basic functionality of LEDs powered directly from a high voltage AC source and controlled by a custom ASIC, according to some embodiments; 
           [0030]      FIGS. 5A-5C  include a schematic of a lighting system according to an embodiment; 
           [0031]      FIGS. 6A-6D  include a schematic of a lighting system according to another embodiment; 
           [0032]      FIG. 7  depicts structures of two LEDs according to some embodiments; 
           [0033]      FIG. 8  is a schematic of a dimmer mechanism according to some embodiments; 
           [0034]      FIGS. 9A and 9B  illustrate two types of relationships between dimmer input and output according to various embodiments; 
           [0035]      FIG. 10  shows a schematic of a lighting system and its dimmer input according to an embodiment; 
           [0036]      FIG. 11  shows a schematic of a lighting system and its dimming mechanism according to another embodiment; 
           [0037]      FIG. 12  depicts a CIE 1931 chromaticity diagram; 
           [0038]      FIGS. 13A and 13B  show the measured dimming profile of an incandescent light source in a CIE diagram; 
           [0039]      FIG. 14  shows a white LED board according to an embodiment; 
           [0040]      FIGS. 15A and 15B  show the measured dimming profile of a white LED light source in a CIE diagram; 
           [0041]      FIG. 16  shows a bi-color LED board according to an embodiment; 
           [0042]      FIGS. 17A and 17B  show the measured dimming profile of a bi-color light source in a CIE diagram according to an embodiment; 
           [0043]      FIG. 18A  shows the measured dimming profile of a bi-color light source in a CIE diagram according another embodiment; 
           [0044]      FIG. 18B  shows some measurements for dimming profile of the bi-color light source of  FIG. 18A ; 
           [0045]      FIG. 19  depicts a block diagram of a lighting system with more than one ASIC according to some embodiments; 
           [0046]      FIG. 20  shows a tri-color LED board according to an embodiment; 
           [0047]      FIGS. 21A and 21B  show the measured dimming profile of a tri-color light source in a CIE diagram according to an embodiment; and 
           [0048]      FIG. 21C  shows a black body curve and exemplary dimming points, as implemented by a system similar to that discussed in  FIGS. 21A and 21B . 
       
    
    
     DETAILED DESCRIPTION 
       [0049]    The following detailed description refers to the accompanying drawings. Wherever possible, the same or similar reference numbers are used in the drawings or in the description to refer to the same or similar parts. Also, similarly-named elements may perform similar functions and may be similarly designed, unless specified otherwise. Numerous details are set forth to provide an understanding of the described embodiments. The embodiments may be practiced without these details. In other instances, well-known methods, procedures, and components have not been described in detail to avoid obscuring the described embodiments. 
         [0050]    While several exemplary embodiments and features are described here, modifications, adaptations, and other implementations may be possible, without departing from the spirit and scope of the invention. Accordingly, unless explicitly stated otherwise, the descriptions relate to one or more embodiments and should not be construed to limit the invention as a whole. This is true regardless of whether or not the disclosure states that a feature is related to “one,” “one or more,” “some,” or “various” embodiments. Instead, the proper scope of the invention is defined by the appended claims. Further, stating that a feature may exist indicates that the feature exists in one or more embodiments. 
         [0051]    In this disclosure, the terms “include,” “comprise,” “contain,” and “have,” when used after a set or a system, mean an open inclusion and do not exclude addition of other, non-enumerated, members to the set or to the system. Moreover, as used in this disclosure, a subset of a set can include one or more than one, including all, members of the set. 
         [0052]    Various embodiments address one or more problems of the existing lighting systems. For example, the life time of existing lighting systems may be limited due to the failure of some non-lighting parts.  FIG. 1  depicts an LED lighting system  100 , which includes various lighting and non-lighting parts. System  100  includes an AC power line  110 , a dimmer  120 , and an LED assembly  130 . LED assembly  130  includes a power supply unit  132 , a control unit  134 , and one or more LEDs  136 . Power supply unit  132  may receive an AC voltage from power line  110 , convert the AC voltage into a DC voltage (using, for example, an A/D converter), and deliver that voltage to control unit  134 . Dimmer  120  delivers a dimming signal to control unit  134 . Control unit  134  delivers DC voltage and current to LEDs  136 . Control unit  134  may modify the delivered DC voltage and current based on the dimming signal. In some embodiments, control unit  134  includes a processor. 
         [0053]    The life time of a lighting system may be limited not by its lighting units but by other units. In system  100 , for example, a non-lighting unit such as power supply unit  132  may fail before LEDs  136 . For instance, the LEDs may normally last around 100,000 hours, while the power supply unit  132  may in average fail after about 50,000 hours of usage. Thus, the normal lifetime of system  100  may be determined to be 50,000 hours; that is, the system has to be replaced after the failure of power supply unit  132 , while the more expensive parts, i.e., the LEDs, are still usable. Inclusion of such short lifetime, non-lighting units may therefore result in economic or environmental waste. In some embodiments, these problems can be avoided and a lighting system can achieve a higher lifetime by operating without the short lifetime, non-lighting units. 
         [0054]      FIG. 2  is a block diagram of such a lighting system  200  using an application-specific integrated circuit (ASIC) according to some embodiments. System  200  includes an AC power line  210 , a dimmer  220 , and an LED assembly  230 . LED assembly  230  includes one or more LEDs  236  and a waveform manipulator module  238 . Further, waveform manipulator module  238  includes a rectifier  2382  and an ASIC module  2384 . 
         [0055]    In some embodiments, dimmer  220  delivers dimming signals to LED assembly  230 . In various embodiments, the dimming signals may be in one or more different forms or based on one or more different standards, such as an analog signal, a 0-10 volt signal, a DMX signal, a Digital Addressable Lighting Interface (DALI) signal, or a powerline signal. In alternative embodiments, the dimming signals may be in one or more different forms or based on one or more different standards, such as a global dimming signal having a voltage varied between 0-10 volts, a Bluetooth signal, a Bluetooth Low Energy signal, a WIFI signal, a Zigbee signal, and a visible light signal (having a wavelength of about 400-700 nm), or any other signal for dimming a light. 
         [0056]    The Bluetooth signal may be a data signal exchangeable over a short distance with a wavelength of about 2.4-2.5 GHz. The Bluetooth Low Energy signal may be a data signal exchangeable over a short distance with a wavelength of about 2.4-2.5 GHz and with reduced power consumption. The WIFI signal may be wireless signal in computer networking using 2.4 GHz UHF and/or 5 GHz SHF ISM radio bands, following IEEE 802.11 standards. The Zigbee signal may be a low-cost and low-power wireless signal operable in the industrial, scientific and medical (ISM) radio bands, e.g., 2.4 GHz, 784 MHz, 868 MHz, and 915 MHz, with data rates varying from 20 kbit/s (868 MHz band) to 250 kbit/s (2.4 GHz band). 
         [0057]    In some embodiments, LEDs  236  are located on an LED board. In some embodiments, LEDs  236  are divided into two or more subsets, such as two or more LED banks, respectively disposed on a different LED board. 
         [0058]    In system  200 , waveform manipulator module  238  receives the AC input and the dimming signal. Module  238  delivers voltage and current to LEDs  236 , in a manner as further detailed below. System  200  having the waveform manipulator  238  operates without a traditional power supply. In various embodiments, rectifier  2382  generates a rectified voltage and delivers that rectified voltage to ASIC  2384  and/or LEDs  236 . Further, based on the value of the voltage at each time, the ASIC may turn on a number of the LEDs that can be turned on by that rectified voltage. In some embodiments the waveform manipulator  238  sends a pulsating voltage at any time to a subset of the LEDs. In some embodiments, waveform manipulator module  238  has a normal lifetime that exceeds those of LEDs  236 . Thus, system  200  can achieve a lifetime that is at least around or equivalent to the lifetime of LEDs  236 . In some embodiments in which LEDs  236  last around 100,000 hours, for example, the lifetime of system  200  is also around or greater than 100,000 hours. 
         [0059]      FIG. 3  is a block diagram of a lighting system  300  using an AC step-drive circuit with an ASIC according to some embodiments. System  300  includes an AC power source  310 , a dimmer  320 , an ASIC  330 , and eight LED lights  340 , labeled LED  1  to LED  8 . AC power source  310  provides an AC power to ASIC  330 . In different embodiments, this AC power input can have any suitable effective AC voltages, such as 100, 120, 240, or 277 AC volts, and may have any suitable wave forms, such as a sine wave or a rectified sine wave. ASIC  330  may receive the AC input from power source  310  and a dimming signal from dimmer  320 . ASIC  330  then delivers voltages and currents to LEDs  340 . In some embodiments, based on the amplitude of the input voltage at any moment, ASIC  330  connects different LEDs in series or in parallel, and determines the currents delivered to different LEDs. In some embodiments, for example, different LEDs are grouped in different LED banks, and the ASIC can send different inputs to different banks. 
         [0060]      FIGS. 4A and 4B  illustrate the basic functionality of LEDs powered directly from a high voltage AC source and controlled by an AC step-drive ASIC, according to some embodiments. In general, depending on the amplitude of the input voltage, for example, the AC step-drive ASIC connects different LEDs in series or in parallel and determines the currents delivered to different LEDs. The basic operation is shown in  FIGS. 4A and 4B  for one half of a typical AC sine wave. In various embodiments, the AC voltage of the AC source may be 100, 120, 208, 240, or 277 volts. In some embodiments, the ASIC reads the AC input voltage at different times and accordingly turns on one or more LEDs. 
         [0061]    In particular,  FIG. 4A  shows an input waveform  400 , which is a rectified sine wave, and  FIG. 4B  shows an operation table  450 . The input waveform  400  may be generated by power source  310  of system  300  in  FIG. 3 , or by rectifier  2382  of system  200  in  FIG. 2 . 
         [0062]    For example, the LEDs  340  in  FIG. 3  may be grouped in four banks, each including two LEDs. That is, the four LED banks may include, respectively, LEDs  1  and  5  (LED bank  1 );  2  and  6  (LED bank  2 );  3  and  7  (LED bank  3 ); and  4  and  8  (LED bank  4 ). ASIC  330  be configured to direct the input voltage to one or more LED banks based on the input voltage of power source  310  transmitted to ASIC  330 . In other embodiments, an LED bank may include one, two, or more LEDs. 
         [0063]    Waveform  400  shows a full cycle of the rectified voltage output of power source  330  of  FIG. 3  or rectifier  2382  of  FIG. 2 , and depicts the voltage and current output from ASIC  330  to the LEDs  1 - 8 . Table  450  shows the sequence in which the ASIC  330  turns each LED on or off during the first half cycle shown in waveform  400 . In particular,  FIGS. 4A and 4B  show that the ASIC  330  divides each half cycle into seven regions A to G, based on the input voltages. The input voltages sequentially increase in consecutive regions A, B, C, and D, and sequentially decrease in consecutive regions D, E, F, and G. Regions A and G have the lowest voltage, while region D has the highest voltage. 
         [0064]    Based on the input voltage in each region, ASIC  330  may turn on or off different LED banks. Table  450  of  FIG. 4B  shows which LED banks ASIC  330  turns on or off in each region of the half cycle. More specifically, at the start of the first half cycle, when the input voltage is zero, ASIC  330  turns off all LEDs. In this first half cycle, as the voltage increases from region A to D, ASIC  330  consecutively turns on the LED banks  1  to  4 . In particular, ASIC  330  turns on LEDs  1  and  5  in region A, turns on LEDs  2  and  6  in region B, turns on LEDs  3  and  7  in C, and turns on LEDs  4  and  8  in region D. In one embodiment, after an LED bank is turned on, it will remain as turned-on until it is turned off again in another region of the waveform  400 . 
         [0065]    As the voltage decreases beyond region D, ASIC  330  turns off the LED banks in the reverse order, starting from fourth bank. That is, ASIC  330  turns off LEDs  4  and  8  in region E, turns off LEDs  3  and  7  in region F, turns off LEDs  2  and  6  in region G, and turns off LEDs  1  and  5  after region G. ASIC  330  acts similarly in the second half cycle of each full cycle of the rectified voltage. 
         [0066]    Thus, as seen in table  450 , the first LED bank (LEDs  1  and  5 ) is on in all regions A to G, the second bank (LEDs  2  and  6 ) is on in regions B to F, the third LED bank (LEDs  3  and  7 ) is on in regions C to E, and the fourth LED bank (LEDs  4  and  8 ) is on only in region D. In other words, in regions A and G only LEDs  1  and  5  are on, and all other LED banks are off. Conversely, in region D all eight LEDs  1 - 8  are on. In each region, turning on and off of the LED banks, and their currents are controlled by ASIC  330  based on AC line voltage. 
         [0067]    Based on this exemplary sequence of turning the LED banks on and off, ASIC  330  can control the output characteristics of the light system, such as its luminosity, color, color temperature, or dimming profile, as further detailed below. ASIC  330  may do so, for example, if different LED banks have different input voltages or different light characteristics, such as color or color temperature. The ASIC may also determine the percentage by which each LED bank contributes to the overall light output by determining at what percentage of the time that bank is on. This contribution may also depend on the total number of LEDs or the forward voltage (V f ) for each bank. In one embodiment, for example, LEDs  1  and  5  may have a V f  of 36 volts, which corresponds to the voltage in regions A and G. LEDs  2  and  6 , on the other hand, may have a V f  of 18 volts, such that the step voltages for regions B and F are around 54 ( 36  plus 18). Further, LEDs  3  and  7  may have a V f  of 3 volts and the step voltages of regions C and E may be around 57 volts (54+3). And LEDs  4  and  8  may have a V f  of 18 volts and the step voltage of region D may be around 85 volts (57+18). 
         [0068]      FIGS. 5A-5C  include a schematic of a lighting system  500  according to some embodiments. System  500  includes a power input module  510 , a rectifier  515 , a dimmer module  520 , an ASIC module  530 , and a light section  540 . 
         [0069]    Power input module  510  includes input terminals J142, a resistor R 5  and a variable resistor (or varistor) MOV 1 . Terminals J1-J2 are the input terminals through which an AC input voltage (from, for example, a wall power outlet) is applied to the system. In various embodiments, the AC voltage of the AC input may be 100, 120, 208, 240, or 277 AC volts or any other know voltage. Resistor R 5  and varistor MOV 1  protect the circuit from over current and lighting surges. Rectifier D 13  rectifies the AC voltage into pulsating DC voltage. 
         [0070]    Dimmer module  520  includes input terminals J3-J4, capacitor C 1 , diodes D 14  and D 15 , and resistors R 2 , R 11 , and R 12 . Terminals J3-J4 are the input terminals for receiving dimming input (or dimming signals). Resisters R 12 , R 2 , and R 11  serve as a voltage divider, and terminal J3 is connected to a terminal (e.g., LS) of ASIC  532  through the voltage divider. Terminal J4 is grounded. In some embodiments, a dimmer input is a DC voltage. A dimmer input of 10 Vdc, for example, may indicate a full on and a dimmer input of 0 Vdc may indicate an off. In some embodiments, the dimmer input is a digital signal. This digital signal may include signals based on common industry protocols, such as DALI, DMX, RDM, digital power line communication, or any other diming protocol. 
         [0071]    ASIC module  530  includes resistors R 1 , R 3 , R 4 , and R 7 -R 10 ; capacitor C 3 , and ASIC  532 . ASIC module  530  may additional include resister R 6 , capacitor C 4 , and diodes  23  and  24 . Elements C 3 , R 1 , and R 9  filter the rectified voltage and provide power to a terminal (e.g., VDD) of ASIC  532 . Elements R 7 , R 8 , and R 10  provide a reference voltage to a terminal (e.g., NTCFB) of ASIC  532  that is relative to the rectified AC input. In some embodiments, element R 3  sets the LEDs operating current via a switch, through a terminal (e.g., IVSET) of ASIC  532 . 
         [0072]    In this embodiment, light section  540  includes twelve LEDs D 1 -D 12 . These LEDs are grouped into five banks. The first bank includes four LEDs D 1 , D 3 , D 7 , and D 8 . The second to fifth banks each include two LEDs. The second bank, for example, includes LEDs D 3  and D 9 , the third bank includes LEDs D 4  and D 10 , the fourth bank includes LEDs D 5  and D 11 , and the fifth bank includes LEDs D 6  and D 12 . Based on the forward voltage, ASIC module  530  may connect one or more of these banks to terminals I 0 , I 1 , I 2 , I 3 , I 4 , and I 5  of ASIC  532 . 
         [0073]    In some embodiments, the LEDs in system  500  have a forward voltage (Vf) of about 21V and have the same color output. In some other embodiments, different LEDs have different forward voltages. Such a variation in forward voltages may allow the LED string to turn on at a lower AC input voltage. 
         [0074]    Moreover, in some embodiments, different LEDs may also have different colors or color temperatures. In one embodiment, for example, the LEDs include a combination of amber LEDs and white LEDs. Some such embodiments may be configured such that when the system is dimmed, the color shifts to warmer or cooler color temperatures, or dim to other color points. Such a shift may be tuned to mimic the behavior of a traditional incandescent bulb. 
         [0075]    In some embodiments, the lighting system can operate with different input voltages, such as commercial and industrial voltages.  FIGS. 6A-6D  include a schematic of a lighting system  600  according to one such embodiment. System  600  includes a power input module  610 , a rectifier  615 , a dimmer module  620 , an ASIC module  630 , and a light section  640 . 
         [0076]    In system  600 , dimmer module  620  is electrically isolated from possible surges in the remainder of the system by one or more of capacitors C 2 , C 13 , and C 14 . In some embodiments such protections is provided via Zener diodes or some opto-isolators such as PC817 or any other protection device. 
         [0077]    Light section  640 , includes fourteen LEDs D 1 -D 14  grouped into five banks. Section  640 , however, also includes fifteen switch resistors R 13 -R 27 . These switches open or close to form different serial configurations based on the input voltage to system  600 . Based on the input voltage, a user may change the serial configuration by operating the switches, separately or all together. Alternatively, the system may automatically change the states of the switches based on the input voltage. In some embodiments, ASIC module  630  reads in the input voltage and accordingly operates the switches. 
         [0078]    For example, when operating with a low voltage (such as a commercial or residential 120 volts/AC), switches R 14 , R 17 , R 20 , R 23 , and R 26  may open while the other switches may close. In such a configuration, LED banks one to five are connected in series. Further, in the first LED bank, for example, the series combination of D 1 -D 3  is connected in parallel with the series combination of D 4 -D 6 . Similarly, in the second to fifth banks, respectively, D 7  is connected in parallel to D 8 ; D 9  is connected in parallel to D 10 ; D 11  is connected in parallel to D 12 ; and D 13  is connected in parallel to D 14 . 
         [0079]    When operating at a higher input voltage (such as an industrial 270 volts/AC), switches R 14 , R 17 , R 20 , R 23 , and R 26  may close, while the other switches open. In such a configuration, therefore, banks one to five are still connected in series. But, unlike in the lower voltage example, the LEDs in each bank are also all connected in series. That is, the first bank includes a series connection of six LEDs D 1 -D 6 . Similarly, the second to fifth banks respectively include series connections of pairs of LEDs D 7  and D 8 , D 9  and D 10 , D 11  and D 12 , and D 13  and D 14 . 
         [0080]    Some embodiments may use LEDs of different input voltages. In some embodiments, the input voltage of an LED may change based on the internal combination of dyes.  FIG. 7  depicts structures of two such LEDs  710  and  750  according to some embodiments. LED  710  includes six dyes that are connected in series. LED  750 , on the other hand, includes a parallel connection of three pairs of dyes, each pair of dyes connected in series. In some embodiments, each dye has a three volt input. The operating voltage of LED  710 , therefore, can be around 18 volts, while that of LED  750  can be around 6 volts. A system may use in some locations the 18 volt LED  710  or connect in series three of the 6 volt LEDs  750 . 
         [0081]    In various embodiments, a user can utilize the dimmer to modify the visual characteristics of the light output. The user may, for example, set the dimmer to a low, medium, or high level. The dimmer, in turn, may cause the lighting system to set a characteristic of the output light at a corresponding level. The characteristic of the light may, for example, be its intensity, color, temperature, or a combination of these characteristics. 
         [0082]      FIG. 8  is a schematic of a dimmer mechanism  800  according to some embodiments. 
         [0083]    Dimmer  800  includes a dimming dial  810  and a transducer  820 . In some embodiments, dimming dial  810  is a dimmer user interface and transducer  820  is a dimmer communication device. Transducer  820  may be an analog or a digital transducer. 
         [0084]    Dimming dial  810  is configured to receive an input  802  and generate, based on the input, a dial output  812 . Dimming dial  810  may be a mechanical dial, such as a linear multi-level dial or a circular turning dial. Input  802  may be a mechanical input from a user who sets the dial at a desired level, e.g., low, medium, or high. Dimming dial  810  may alternatively be another type of dial, such as a digital or visual dial. A user may, for example, set the dial via a display screen or a touch screen. 
         [0085]    Based on the dial&#39;s setting, dial  810  generates dial output  812 . In some embodiments, dial output  812  is a DC voltage. In a 0-10 volt DC dial, for example, dial output  812  is a DC voltage between 0 and 10 volts, which is proportional to the input. For example, when the input is at very low dim, dial output  812  may be very close or equal to 0 volts. Similarly, at mid and high dim levels, dial output  812  may be around 5 and 10 volts, respectively. Dial output  812  may also be a digital signal. 
         [0086]    Transducer  820  receives dial output  812  and transforms it into dimming signal  822 . Dimming signal  822  may, for example, determine a quantitative characteristic of the light output, such as its intensity or temperature. Dimming signal  822  may alternatively determine a qualitative characteristic of the output light, such as its color or color combination. Dimming signal  822  may also determine a combination of two or more characteristics, which may be quantitative, qualitative, or both. In various embodiments, dial output  812  or dimming signal  822  may be in one or more different forms or based on one or more different standards, such as an analog signal, a 0-10 volt signal, a DMX signal, a DALI signal, a powerline signal, or any other known signal. 
         [0087]    Different dimmers may depict different dimming styles. The dimming style may determine one or both of two relationships, which are the relationship between dimming signal  822  and input  802 , and the relationship between dimming signal  822  and dial output  812 . The dimming style may also relate to a relationship between the dimming signal and the output of the ASIC to the LEDs.  FIGS. 9A and 9B  illustrate two different forms of such relationships according to various embodiments.  FIG. 9A  shows a schematic of a linear relationship via linear graph  910 .  FIG. 9B , on the other hand, shows a schematic of a non-linear relationship via a non-linear graph  920 . In graphs  910  and  920 , abscissas stand for a quantitative measurement of the input or the dial output in some arbitrary units, and ordinates stand for a value of a quantitative characteristic, such as color temperature or intensity, also in arbitrary units. 
         [0088]    In graph  910 , the relationship between the input and the output is linear. In other words, the output changes proportional to the input. In non-linear graph  920 , on the other hand, the relationship is logarithmic, that is, the output changes proportional to a logarithm of the input. 
         [0089]    Various embodiments may use a dimmer with a style that is linear (such as that shown in  FIG. 9A ) or non-linear, e.g., logarithmic (such as that shown in  FIG. 9B ). In general, the human eye may perceive the sensory changes logarithmically. That is, when the dimmer reduces a quantitative characteristic by 25%, the human eye may perceive around 50% reduction in the output. Some embodiments may compensate for this perception phenomenon by using a style that is non-linear, e.g., logarithmic or exponential. 
         [0090]    The dimming style may be set through transducer  820  of  FIG. 8 . In some embodiments, transducer  820  is designed to use a linear or a non-linear style. In some embodiments, the transducer&#39;s hardware design enables it to use one or more types of styles. In some embodiments, transducer  820  can be programmed, via software such as firmware, to use one or more types of styles. In some embodiments, dimmer  800  of  FIG. 8  includes a memory that stores information related to different dimming style, and transducer  820  uses that information to set the dimming style. In some embodiments, transducer  820  implements one or another dimming style by using a lookup table, for converting dial output  812  of  FIG. 8  to dimming signal  822  of  FIG. 8 . In some embodiments, different dimming styles are stored in the light fixture or in the ASIC. A light controller may then select one of the dimming styles for the operation of the lighting system at a specific time. 
         [0091]    In various embodiments, an ASIC receives an input waveform that is modified by dimmer  800  of  FIG. 8  and accordingly changes the input current or voltage to the LEDs.  FIG. 10  shows a schematic of a lighting system  1000  and its dimming mechanism according to one such embodiment. System  1000  includes a power input module  1010 , a dimmer module  1020 , an ASIC module  1030 , and a light section  1040 . 
         [0092]    Dimmer  1020  may affect the waveform of the AC input to ASIC  1030 . System  1000 , for example, uses a TRIAC dimming mechanism.  FIG. 10  also shows a waveform section  1050  depicting three different dimming levels, and the corresponding AC waveforms and rectified waveforms according to an embodiment. In particular, when dimmer  1020  is at the highest level  1052 , indicating no dimming, the waveform has a full form. When dimmer  1020  is at the mid-level, indicating half dimming, half of the waveform is truncated. Finally, when dimmer  1020  is at the low level, indicating a “low dim”, most of the waveform is truncated. At each dimming level, ASIC  1030  receives the corresponding waveform and based on that waveform adjusts the voltage or the current sent to different LED banks. 
         [0093]      FIG. 11  shows a schematic of a lighting system  1100  and its dimming mechanism according to another embodiment. In  FIG. 11 , the dimmer is a 0-10 volt type dimmer. 
         [0094]    In some embodiments, the lighting system can control the color rendering index (CRI) of the light output. In various embodiments, the CRI of a light source compares the ability of the light source with an ideal or a natural light source in reproducing the colors of illuminated objects. The CRI of a light source may be measured in a scale of 0 to 100, where the most accurate rendition index of 100 corresponds to a black body radiation light source. In some applications of light sources, such as in museums, exhibitions, or libraries, the accuracy of color rendition may be important. Such applications may thus require a lighting system with a high CRI, e.g., above 85 or 90. Some other applications, such as outdoor lights, may not need a high color rendering accuracy. These applications may be able to use less expensive, such as fluorescent, light systems, which have a lower CRI, e.g., between 60 and 80. In some embodiments, such as those discussed below, a lighting system can provide light outputs with different CRIs. The output can thus be adjusted to the desirable CRI. In some embodiments, for example, the CRI may increase by an increase in a red component of the light. The light output per power input, on the other hand, may increase by an increase in a blue component; such increase in the blue component, however, may lower the CRI. 
         [0095]    In some embodiments, the lighting system can control the color output and its temperature at different dimming levels. These outputs can be traced in various multi-dimensional diagrams of color output.  FIG. 12  depicts a CIE 1931 chromaticity diagram  1200 . The diagram uses a two dimensional x-y space, where x and y may be functions of one or more of the color stimuli (such as red, green, or blue stimuli) or their brightness. In the diagram, the area  1210  may represent the space of all visible colors. The boundary of area  1210  may continuously span the mono-chromatic spectrum from one end to the other. For example, areas  1211 - 1217  may respectively correspond to purple, blue, green, yellowish green, yellow, orange, and red. Diagram  1200  further depicts diming trace  1220  of a black body light source. At its brightest, this light source has a color around point  1222 , which is almost white. As the light source dims, its color spectrum moves towards the red end at point  1224 . 
         [0096]    In some embodiments, an LED based lighting system can provide a color and dimming profile that is similar to those of an incandescent light. Such systems can thus be added to a location which also uses incandescent lights, without generating an inhomogeneous color perception. A dimming profile relates to the change in one or more characteristics of the light output as the dimming input changes.  FIGS. 13A and 13B  show the measured dimming profile  1310  of an incandescent light source in a CIE diagram  1300 . Diagram  1300  also shows dimming trace  1320  of a black body light source for comparison.  FIG. 13B  shows the measure data section of  FIG. 13A , magnified for clarity of its details. Points  1310  show the measured values of the color generated by an incandescent light as it dims. In particular, as the incandescent light dims, the measured color moves from left to right, towards the red spectrum. 
         [0097]    Some embodiments utilize white color LEDs that mimic the black body radiation in some ranges.  FIG. 14  shows a white LED board  1400  according to one such embodiment. LED board  1400  includes one or more LEDs  1410 . In one embodiment, each LED  1410  is a 3000K white LED. 
         [0098]      FIGS. 15A and 15B  show the measured dimming profile  1510  of a white LED light source in a CIE diagram  1500 . The white LED light source may utilize a white LED board such as LED board  1400  of  FIG. 14 . Diagram  1500  also shows dimming trace  1520  of a black body light source for comparison.  FIG. 15B  shows the measured data section of  FIG. 15A , magnified for clarity of its details.  FIG. 15B  also includes a data table  1550 , summarizing the measured data. 
         [0099]    Data points  1510  show the measured values of the colors generated by the white LED light source as it dims. These data points include multiple points that almost overlap in the CIE diagram  1500 . Further, data points  1510  are located near black body dimming trace  1520 . Data points  1510  thus indicate that the color output of the white LED light source is similar to that of the black body light source at one specific dimming value. Moreover, as the white light source dims, its color point does not change. Data table  1550  indicates same results. It shows that the CCT, i.e., color temperate, of the white light source changes between 2998 and 2968 as the light dims, indicating only about 1% change in the color temperature. The data also show that the CRI of the white light source remains around 84. 
         [0100]    Some embodiments utilize a combination of two or more different color LEDs.  FIG. 16  shows a bi-color LED board  1600  according to one such embodiment. LED board  1600  includes multiple LEDs, some of which are blue LEDs  1610  and some are red LEDs  1620 . In some embodiments, red LED  1620  generates a light that is mainly in the red region of the spectrum, while blue LED  1610  generates light that is essentially in the blue region. In some embodiments, blue LED  1610  generates a greenish yellow light. In some embodiments, different subsets of the LEDs in the LED board are included in different LED banks. For example, in board  1600 , the multiple LEDs may be divided into one or more red LED banks that include red LEDs  1620 , and one or more blue banks that include blue LEDs  1610 . 
         [0101]    In some embodiments that use board  1600 , as the dimmer changes the dimming signal, the ASIC can change the luminance of the red or blue LEDs such that the color temperature or other characteristics of the light changes in a desired manner. In some embodiments, the ASIC can implement more than one dimming profile. The ASIC may implement more than one dimming profile for the same system by using different dimming profile programs. In some embodiments, a dimming profile program determines, based on the dimming signal input to the ASIC, the output from the ASIC to different LEDs in the system. 
         [0102]    In some embodiments, the ASIC may implement a dimming profile in which dimming the light changes one or more of the color temperature and color point in a pre-determined manner. The ASIC may implement the dimming profile by, for example, determining the sequence and percentage of time each LED bank is on or off. 
         [0103]      FIGS. 17A and 17B  show the measured dimming profile  1710  of a bi-color light source in a CIE diagram  1700  according to one embodiment. The bi-color light source may utilize a bi-color board such as LED board  1600  of  FIG. 16 .  FIG. 17B  shows the measured data section of  FIG. 17A , magnified for clarity of its details. 
         [0104]    Data points in dimming profile  1710  show the measured values of the colors generated by the bi-color light source as it dims. The data points indicate that as the light source dims, the ASIC changes the color output such that it moves from the greenish yellow end  1712  towards the red end  1714 . Such a change towards red may mimic for a user the similar dimming change towards red in the incandescent or black body lights. 
         [0105]    The ASIC may implement a different dimming profile in which, for example, dimming the light does not change the color temperature. This setup may be used where, for example, the lighting on an object needs to remain the same as the intensity of the ambient light changes. Such a dimming profile may not be feasible for traditional lighting systems, such as those using incandescent lights, because incandescent lights change temperature as they dim. But some embodiments using ASIC and LEDs can achieve this behavior. Moreover, various embodiments can be configured to change their dimming profile in real time. 
         [0106]      FIG. 18A  shows the measured dimming profile  1810  of another bi-color light source in a CIE diagram  1800  according to such an embodiment. The bi-color light source of  FIG. 18A , similar to that of  FIGS. 17A and 17B , may utilize a bi-color LED board such as LED board  1600  of  FIG. 16 . 
         [0107]    In the embodiment corresponding to  FIG. 18A , however, the ASIC uses a dimming profile different from that corresponding to  FIGS. 17A and 17B . In particular, data points in profile  1810  almost overlap in the CIE diagram  1800 . This indicates that as the light source dims, the ASIC changes the output to the LEDS such that, as the light intensity dims, the color output does not change and remain on the black body radiation trace  1820 . 
         [0108]      FIG. 18B  shows some measurements for dimming profile  1810  of the bi-color light source of  FIG. 18A . In particular,  FIG. 18B  includes color temperature data points  1830  and CRI data points  1840  for the dimming profile data points  1810 .  FIG. 18B  also includes data table  1850  summarizing these two sets of data points in  FIG. 18B . For both sets of data points in FIG.  18 B, the abscissa axis shows the exposure value (EV), which is a decreasing function of dimming. That is, the data points move from right to left as the light dims. The values of color temperature data points  1830  are shown on the left ordinate axis and the values of the CRI data points  1840  are shown on the right ordinate axis. These data indicate that as the light dims, both the color temperature and the CRI of the light source remains essentially unchanged. These results are also summarized in data table  1850 . Data table  1850  shows that as the light dims, the CCT of the bi-color light source changes between 2882 and 2764. The data also show that the CRI of the light source remains around 90. 
         [0109]    Some embodiments are thus capable of changing the light output and its dimming characteristics based on the combination of LEDs and the selected dimming profile. Some embodiments can change the color characteristics or diming characteristics for the same lighting system based on different variables, such as time of day, ambient light, or type of use. For example, the luminosity or color temperature may increase as evening approaches or as the ambient light dims. These changes may occur automatically based on, e.g., the time on a clock or the ambient light detected by a light sensor. Alternatively, these changes may occur in response to an input by a user. For example, in a museum, a user may chose the dimming profile of  FIGS. 18A and 18B  for some exhibits. As the ambient light changes during the day or on different days, the intensity of the light source may be adjusted while maintaining some other characteristics such as CCT or CRI. In the same location, however, the user may desire to switch to the dimming behavior of  FIGS. 17A and 17B . This switch may enable the user to change the color of the light as it dims. Such a change may create an ambience that is desirable for a function or get together. Alternatively, a user may decide to change the color output or the dimming behavior based on the type and the colors in the illuminated object or location. 
         [0110]    Various embodiments can achieve the above variations by using one ASIC in the lighting system. In some embodiments, one ASIC can change the relation between the inputs of different LEDs. In the bi-color embodiment of  FIGS. 16 and 17 , for example, the ASIC changes the relative inputs to the blue and red LEDs in accordance with the dimming input. In this embodiment, the light output in the CIE diagram of  FIGS. 17A and 17B  follows a relatively linear trace between the greenish yellow end  1712  and the red end  1714 . Such a linear change may be different from the behavior of the incandescent or black body lights (as shown, e.g., in  FIG. 13A  or  13 B). The difference, however, may not be perceptible to a user. 
         [0111]    Some other embodiments, on the other hand, use more than one ASIC to generate light with more complex color or dimming characteristics.  FIG. 19  depicts a block diagram of such a lighting system  1900  according to some embodiments. System  1900  includes an AC power line  1910 , a dimmer  1920 , and an LED assembly  1930 . LED assembly  1930  includes n pairs of ASICs and LED sets, respectively labeled ASIC- 1  to ASIC-n, and LEDs- 1  to LEDs-n. In various embodiments, n is an integer greater than one. Each LED set LEDs-i can include one or more LEDs. Moreover, each ASIC, such as ASIC-i, controls the inputs to the corresponding LED set LED-i, where i can be one of the numbers 1 to n. In such a system, based on the dimming signal, different ASICs can independently change the characteristics of different LED sets. In some embodiments, each dimming signal is addressed to one of the ASICs and thus affects the input to the corresponding set of LEDs. These embodiments may thus provide n degrees of freedom for changing the light output, each degree of freedom corresponding to the output of one LED set. In some embodiments, each LED set corresponds to an LED bank. 
         [0112]      FIG. 20  shows a multi-color LED board  2000 , which provides three different LED sets according to an embodiment. More specifically, LED board  2000  includes three sets of LEDs. A first LED set includes blue LEDs  2010 ; a second LED set includes red LEDs  2020 ; and a third LED set includes white LEDs  2030 . Some embodiments can utilize board  2000  for generating light output with three degrees of freedom. In particular, some embodiments control the light output of each of the three LED sets with one of three ASICs. 
         [0113]    Using three ASICs and three sets of LEDs with different color outputs enables the system to explore a two dimensional gamut in the color space. Some embodiments use more than three sets of LEDs and ASICs and thus achieve more than three degrees of freedom for exploring the gamut. Using three degrees of freedom, for example, the system may cover different points inside a triangle in the CIE diagram, while using four degrees of freedom may enable the system to cover different points inside a quadrangle area of the CIE diagram. 
         [0114]      FIGS. 21A and 21B  show the measured dimming profile  2110  of a tri-color light source in a CIE diagram  2100  according to an embodiment. The tri-color light source may utilize a tri-color LED board such as LED board  2000  of  FIG. 20 . In this embodiment, the system uses an ASIC for each of the three sets of LEDs.  FIG. 21B  shows the measured data section of  FIG. 21A , magnified for clarity of its details. 
         [0115]    Data points of profile  2110  show the measured values of the colors generated by the tri-color light source as it dims in different manners by the three ASICs. The three ASICs enable the system to provide all colors on or inside the triangle formed by data points  2112 ,  2113 , and  2114 . These three points respectively correspond to the colors of the blue, white, and red LEDs. The system can achieve these colors and all combination of the colors within the triangle by appropriately adjusting the input to the three LED sets. 
         [0116]    Using three or more degrees of freedom, the system can also mimic more complex dimming behaviors.  FIG. 21C  shows a black body curve  2120  and exemplary dimming points  2121 - 2123 , as implemented by a system similar to that discussed in  FIGS. 21A and 21B . In this case, the ASICs change the inputs such that, as the system dims, the light output moves from point  2121  to point  2122  and point  2123 . Point  2121  is located on the black body curve  2120  at or near the 3500 k white point  2113  in  FIGS. 21A and 21B . Points  2122  and  2123 , on the other hand, move further towards the red end of the black body curve and have temperatures  3150  and  2850 , respectively. 
         [0117]    For the purposes of describing and defining the present teachings, it is noted that terms of degree (e.g., “substantially,” “slightly,” “about,” “comparable,” etc.) may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. Such terms of degree may also be utilized herein to represent the degree by which a quantitative representation may vary from a stated reference (e.g., about 10% or less) without resulting in a change in the basic function of the subject matter at issue. 
         [0118]    The foregoing description of the invention, along with its associated embodiments, has been presented for purposes of illustration only. It is not exhaustive and does not limit the invention to the precise form disclosed. Those skilled in the art will appreciate from the foregoing description that modifications and variations are possible in light of the above teachings or may be acquired from practicing the invention. For example, the steps described need not be performed in the same sequence discussed or with the same degree of separation. Likewise various steps may be omitted, repeated, or combined, as necessary, to achieve the same or similar objectives. Similarly, the systems described need not necessarily include all parts described in the embodiments, and may also include other parts not described in the embodiments. Accordingly, the invention is not limited to the above-described embodiments, but instead is defined by the appended claims in light of their full scope of equivalents.