Abstract:
A method of controlling a correlated color temperature for light output by a lighting device including a dim-to-warm circuit having a first light channel and a second light channel. The method including receiving a current input; measuring current of the current input to obtain a measured current value; and determining a light control value based on the measured current value. The method further including using the light control value, determining a first current value for applying a first current to the first light channel and determining a second current value for applying a second current to the second light channel; and providing the first current to the first light channel and providing the second current to the second light channel to obtain different desired correlated color temperatures for the light output at different ones of the light control values.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Application No. 62/147,914, filed Apr. 15, 2015, the entire contents of which are hereby incorporated. 
     
    
     BACKGROUND 
       [0002]    The present application relates generally to light-emitting diodes (LEDs). 
       SUMMARY 
       [0003]    LEDs are typically used as indicator lights or signs. Recently, LEDs have been deployed in other lighting applications, such as but not limited general lighting or illumination. The relatively-low power consumption for LEDs as compared to incandescent lights in combination with LEDs&#39; color quality and warm correlated color temperature (CCT) at high color rendering index (CRI) levels, make LEDs a popular choice both for new construction and for replacement/retrofit of older less efficient systems. CCT is a measure of light source color appearance defined by the proximity of the light source&#39;s chromaticity coordinates to the blackbody locus. CRI describes how the light source makes the color of an object appear to a human eye and how well subtle variations in color shades are revealed. The CRI of a given light source is provided as a scale from 0 to 100 percent, which indicates how accurate the light source is at rendering color when compared to a “reference” light source, such as a halogen light source which has a CRI of 100. 
         [0004]    Replacing or retrofitting older light sources, such as those using incandescent, fluorescent, and/or halogen lamps, with more efficient LED-based sources, however, is not always as easy as simply replacing the bulb. For example, because LEDs are solid-state lighting (SSL) devices they have different electrical requirements than more traditional light sources or lamps. Thus, LED lighting systems often require additional design considerations and circuitry to render them a favorable replacement for older lamps. One area where different circuitry is needed is in the driver, which receives the input power, such as mains power (e.g., approximately 120 volts alternating current (VAC) at approximately 60 Hz, or approximately 220 VAC at approximately 60 Hz, in the U.S.), and delivers a proper voltage and current to the LEDs being used. Because many lighting applications also require the ability to dim the lights, dimmer circuits is another area where different circuitry is needed to render LEDs a good replacement or retrofit for older lamps. 
         [0005]    Properly designed driver circuits can dim SSL products smoothly and linearly while also delivering linear energy savings. Problems arise, however, when legacy phase-cut or triac dimmers are used to dim LEDs. Such legacy dimmers were not intended to work with a switching power supplies, such as those typically found in an LED driver. 
         [0006]    Another related issue results from the manner by which an LED itself dims. As the light level decreases, LEDs generally maintain the same color temperature (CCT) that they exhibit at full power. Incandescent and halogen lamps, on the other hand, dim to a warm CCT at lower levels, an often desirable effect, for example, in the hospitality industry. 
         [0007]    Several drivers for luminaires, both with and without integral LED lamps, that are functionally capable of dimming are known. Dimming to a warm color temperature, i.e., “dim-to-warm,” however, is rapidly becoming a feature desired by many lighting customers. The dim-to-warm functionality is generally achieved by adding red or amber LEDs into a fixture or lamp and mixing the amber/red light with white light to achieve a warmer color temperature. Typically, adding different color LEDs requires one or more additional driver channels to control the separate LED strings. As the overall drive current is reduced, e.g., by operation of a standard phase-cut dimmer, the percentage of energy supplied to the amber/red channel is raised relative to the power supplied to the white channel. 
         [0008]    The result of dim-to-warm technology is lighting products that deliver 2700K-3000K CCT light at full power yet smoothly reduce the CCT to the 1800K range at the lowest light levels. However, such existing dim-to-warm technology is relatively expensive because of the dual-channel driver and additional LEDs. Efficient compact fluorescent lamps (CFLs) or ceramic metal-halide sources have never been capable of such a functionality. 
         [0009]    The present application solves these issues, by in one embodiment, providing a method of controlling a correlated color temperature for light output by a lighting device including a dim-to-warm circuit having a first light channel and a second light channel. The method including receiving a current input; measuring current of the current input to obtain a measured current value; and determining a light control value based on the measured current value. The method further including using the light control value, determining a first current value for applying a first current to the first light channel and determining a second current value for applying a second current to the second light channel; and providing the first current to the first light channel and providing the second current to the second light channel to obtain different desired correlated color temperatures for the light output at different ones of the light control values 
         [0010]    In another embodiment the invention provides a dim-to-warm lighting system including a current drive, a current measuring device, a first light channel, a first current control, a second light channel, a second current control, and a controller. The current drive provides a current output. The current measuring device receives and measures the current output from the current drive, and further outputs a measured current value of the current output. The first light channel has a first correlated color temperature and is in electrical communication with the current drive. The first current control controls a first current through the first light channel based on a first current value. The second light channel has a second correlated color temperature different than the first correlated color temperature and is in electrical communication with the current drive. The second current control controls a second current through the second light channel based on a second current value. The controller receives the measured current value from the current measuring device. The controller is configured to determine a light control value from the measured current value, using the light control value, determine a first current value for the first current control, using the light control value, determine a second current value for the second current control, communicate the first current value to the first current control, communicate the second current value to the second current control, and provide the light output having a correlated color temperature by providing the first current value to the first current control and the second current value to the second current control. 
         [0011]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a block diagram of a dim-to-warm system according to some embodiments of the application. 
           [0013]      FIG. 2  is a flow chart illustrating an operation, or process, of the dim-to-warm system of  FIG. 1  according to some embodiments of the application 
           [0014]      FIG. 3  illustrates a dimming curve graph of the dim-to-warm system of  FIG. 1  according to some embodiments of the application 
           [0015]      FIG. 4  is a graph illustrating a first current control signal and a second current control signal used in conjunction with the dim-to-warm system of  FIG. 1 , according to one embodiment of the application. 
           [0016]      FIG. 5  is a graph illustrating a first current control signal and a second current control signal used in conjunction with the dim-to-warm system of  FIG. 1 , according to another embodiment of the application. 
           [0017]      FIG. 6  is a graph illustrating correlated color temperatures (CCTs) versus percentage light control values according to some embodiments of the application 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0019]    The phrase “series-type configuration” as used herein refers to a circuit arrangement where the described elements are arranged, in general, in a sequential fashion such that the output of one element is coupled to the input of another, but the same current may not pass through each element. For example, in a “series-type configuration,” it is possible for additional circuit elements to be connected in parallel with one or more of the elements in the “series-type configuration.” Furthermore, additional circuit elements can be connected at nodes in the series-type configuration such that branches in the circuit are present. Therefore, elements in a series-type configuration do not necessarily form a true “series circuit.” 
         [0020]      FIG. 1  illustrates a block diagram of a dim-to-warm system  10 . The dim-to-warm system  10  may include a variable constant current drive, or driver,  12 , a voltage regulator  16 , a current measure device  18 , a ratio controller  20 , a first light channel  22 , a second light channel  24 , a first current control  26 , and a second current control  28 . 
         [0021]    The variable constant current drive  12  receives a mains voltage (e.g., approximately 120 VAC at approximately 60 Hz, approximately 240 VAC at approximately 60 Hz, etc.) and outputs a direct current (DC). In some embodiments, the dim-to-warm system  10  further includes a dimmer, or dimming adjustment device,  29 . The dimmer  29  is a user-controlled device configured to adjust the magnitude of the DC current output from the constant current drive  12 . In some embodiments, the DC current may be adjusted from approximately 10% to approximately 100% of the maximum current output. In other embodiments, rather than a dimmer  29 , the dim-to-warm system  10  may include an on/off switch configured to selectively connect/disconnect the mains voltage from the variable constant current drive  12 . 
         [0022]    The voltage regulator  16  receives the DC current output from the variable constant current drive  12  and outputs a regulated voltage (e.g., 5 VDC) to provide power to the ratio controller  20 . The current measure device  18  receives and measures the DC current output from the variable constant current drive  12 . The current measure device  18  further outputs a measured current value signal to the ratio controller  20  and passes through the DC current output to the first light channel  22  and the second light channel  24 . 
         [0023]    The ratio controller  20  may be a controller including, for example, an electronic processor (e.g., a microprocessor, a microcontroller, or another suitable programmable device) and a memory. In some embodiments, the ratio controller  20  is implemented partially or entirely on a semiconductor (e.g., a field-programmable gate array [“FPGA”] semiconductor) chip, such as a chip developed through a register transfer level (“RTL”) design process. The electronic processor may be connected to the memory, and executes software instructions stored on the memory. The software includes, for example, firmware, one or more applications, program data, filters, rules, one or more program modules, and other executable instructions. The ratio controller  20  is configured to retrieve from the memory and execute, among other things, instructions related to the control processes and methods described herein. For example, and as discussed in more detail below, the ratio controller  20  is configured to process the measured current value signal received from the current measure device  18  and output a first control signal and a second control signal, based on the measured current value signal, to the first current control  26  and the second current control  28 , respectively. 
         [0024]    As discussed above, the first light channel  22  and the second light channel  24  receive the DC current (through the current measure device  18 ) from the variable constant current drive  12 . In some embodiments, the first light channel  22  and the second light channel  24  include one or more LEDs or a plurality of LEDs. In such an embodiment, the LEDs may be electrically connected in series. In some embodiments, the first light channel  22  includes one or more white LEDs having a first correlated color temperature (CCT) while the second light channel  24  includes one or more amber LEDs. In other embodiments, the second channel  24  may include one or more LEDs having other colors, for example but not limited to, red, green, variations of white, or any color different than white. 
         [0025]    The DC current passes through the first light channel  22  and the second light channel  24  to the first current control  26  and the second current control  28 , respectively. In some embodiments, the first current control  26  and the second current control  28  are transistors (e.g., a semiconductor device, such as but not limited to, a bipolar junction transistor (BJT), a field-effect transistor (FET), a metal-oxide-semiconductor field-effect transistor (MOSFET), a junction gate field-effect transistor (JFET), and an insulated-gate bipolar transistor (IGBT)). In such an embodiment, the ratio controller  20  provides the first control signal and the second control signal to a first gate of the first current control  26  and a second gate of the second current control  28 , respectively, in order to control the flow of DC current through the first light channel  22  and the second light channel  24 . 
         [0026]    In some embodiments, such as the one illustrated, the dim-to-warm system  10  further includes a dimming curve adjustment interface  30 . The dimming curve adjustment interface  30  communicates with the ratio controller  20  to adjust a dimming curve for the combination of light channels that are stored in the ratio controller  20 . In one embodiment, the dimming curve adjustment interface  30  is a wireless device configured to provide wireless communication to the ratio controller  20 . In such an embodiment, the dimming curve adjustment interface  30  may be a BlueTooth module, a WiFi module, or any known wireless communication module. In other embodiments, the dimming curve adjustment interface  30  is a resistor (e.g., a variable resistor). 
         [0027]      FIG. 2  is a flow chart illustrating an operation, or process,  50  of the dim-to-warm system  10  according to some embodiments of the application. It should be understood that the order of the steps disclosed in process  50  could vary. Furthermore, additional steps may be added to the sequence and not all of the steps may be required. The variable constant current drive  12  outputs the DC current (through the current measure device  18 ) to the first light channel  22  and the second light channel  24  (step  52 ). As discussed above, in some embodiments the DC current output by the variable constant current drive  12  is set by the dimmer  29 . The ratio controller  20  receives the measured current value signal from the current measure device  18  (step  54 ). 
         [0028]    The ratio controller  20  compares the measured current value signal to a maximum current value to calculate, or otherwise determine, a light control value (step  58 ). In some embodiments, the light control value is approximately 0% to approximately 100%. In other embodiments, the light control value is approximately 10% to approximately 100%. In yet another embodiment, the light control value is approximately 5% to approximately 100%. 
         [0029]    The ratio controller  20  determines a ratio of current provided to the first light channel  22  versus current provided to the second light channel  24  (step  60 ). Specifically, in some embodiments, the ratio controller  20  determines how much of the current output by the variable constant current drive  12  is provided to each of the light channels  22 ,  24 . In some embodiments, the memory of the ratio controller  20  stores proportional current values for each of the light channels  22 ,  24  that correspond to a given percentage light control value. 
         [0030]      FIG. 3  illustrates a dimming curve graph  100  according to some embodiments of the application. In some embodiments, dimming curve graph  100 , and/or values corresponding to the dimming curve graph  100 , are stored in the memory of the ratio controller  20 . The dimming curve graph  100  illustrates a first output  105  versus a second output  110 . In some embodiments, the first output  105  corresponds to the output of the first light channel  22 , while the second output  110  corresponds to the output of the second light channel  24 . Additionally, in some embodiments, the first output  105  may correspond to a white light output, while the second output  110  may correspond to an amber light output. 
         [0031]    In the illustrated embodiment of  FIG. 3 , when the percentage light control value is approximately 75% or greater, the DC current output by the variable constant current drive  12  is provided entirely to the first light channel  22 . Additionally, in the illustrated embodiment of  FIG. 3 , when the percentage light control value is approximately 37%, the DC current output by the variable constant current drive  12  is provided to the first light channel  22  and the second light channel  24  equally. Thus, in the illustrated embodiment of  FIG. 3 , as the amount of DC current output by the variable constant current drive  12  decreases, the light output by second light channel  24  increases as the light output by the first light channel  22  decreases. In other embodiments, the light output by the respective first light channel  22  and the second light channel  24  may differ for a given percentage light control value. In some embodiments, the dimming curve adjustment interface  30  may be used to change the properties of the dimming curve used by the ratio controller  20 . 
         [0032]    Referring back to  FIG. 2 , in some embodiments, in step  60 , the ratio controller  20  uses the dimming curve graph  100  to determine the ratio of current. The ratio controller  20  next outputs the first current control signal and the second current control signal, based on the determined ratio of current, to the first current control  26  and the second current control  28 , respectively (step  62 ). In some embodiments, changing the first current control signal and the second current control signal results in different desired correlated color temperatures (CCTs) for the light output. The process  50  then cycles back to step  52 . 
         [0033]      FIG. 4  is a graph  150  illustrating a first current control signal  155  being supplied to the first current control  26  and a second current control signal  160  being supplied to the second current control  28 , according to one embodiment of the application. In some embodiments, the first current control signal  155  and the second current control signal  160  are pulse-width modulated (PWM) signals. As discussed above, the first current control signal  155  may correspond to the light output by the first light channel  22  while the second current control signal  160  may correspond to the light output by the second light channel  24 . In the illustrated embodiment of  FIG. 4 , the first light channel  22  receives one-third of the DC current output by the variable constant current drive  12  per time period (e.g.,  0 -t 1 , t 1 -t 2 , etc.), while the second light channel  24  receives two-thirds of the DC current output by the variable constant current drive  12  per time period. In some embodiments, the time periods (e.g.,  0 -t 1 , t 1 -t 2 , etc.) is within a range of approximately 2.0 milliseconds (msec) to 3.0 msec (e.g., approximately 2.5 msec). 
         [0034]    In some embodiments, the switching of DC current provided to the first light channel  22  and the second light channel  24  occurs at a frequency greater than approximately 120 Hz. In other embodiments, the switching of DC current provided to the first light channel  22  and the second light channel  24  occurs at a frequency greater than approximately 240 Hz. In such embodiments, the switching of DC current occurs at a frequency that avoids the perception of flickering to a user. Additionally, as discussed above, as the percentage light control value changes, the first current control signal  155  and the second current control signal  160  change according to the corresponding ratio of current determined by the ratio controller  20 . 
         [0035]      FIG. 5  is a graph  175  illustrating a first current control signal  180  being supplied to the first current control  26  and a second current control signal  185  being supplied to the second current control  28 , according to another embodiment of the application. As discussed above, the first current control signal  180  may correspond to the light output by the first light channel  22  while the second current control signal  185  may correspond to the light output by the second light channel  24 . In the illustrated embodiment of  FIG. 5 , the first current control signal  180  controls the first current control  26  to provide one-third of the DC current output by the variable constant current drive  12  to the first light channel  22 , while the second current control signal  185  controls the second current control  28  to provide two-thirds of the DC current output by the variable constant current drive  12  to the second light channel  24 . In the illustrated embodiments, as the percentage light control value changes, the first current control signal  180  and the second current control signal  185  change according to the corresponding ratio of current determined by the ratio controller  20 . 
         [0036]      FIG. 6  is a graph  200  illustrating correlated color temperatures (CCTs) versus percentage light control values according to some embodiments of the application. The graph  200  includes a first line  205  and a second line  210 . In the illustrated embodiment, the first line  205  corresponds to an incandescent light bulb while the second line corresponds to the dim-to-warm system  10  according to some embodiments of the present application. As illustrated, in some embodiments, the ratio controller  20  controls the portion of current output to the first light channel  22  and the second light channel  24  such that the average CCT of the dim-to-warm system  10  substantially corresponds to the average CCT of an incandescent light bulb. 
         [0037]    In some embodiments, the dimming curve adjustment interface  30  may be used to change the correlated color temperature (CCT) of the dim-to-warm system  10 . In such an embodiment, the CCT may be changes to accommodate a different desired lighting effect. Additionally, in some embodiments, the dimming curve adjustment interface  30  may be configured to provide information to the ratio controller  20  concerning current output parameters of a replacement current drive having different properties. In such an embodiment, the ratio controller  20  would not replacing when a replacement current drive is used with the dim-to-warm system  10 . 
         [0038]    Thus, the invention provides, among other things, a system and method of controlling a correlated color temperature for light output by a light system having one or more light-emitting diodes (LEDs). Various features and advantages of the invention are set forth in the following claims.