Abstract:
A dimming and correlated color temperature (CCT) tuning lighting system comprises a controller and multiple light-emitting diode (LED)-based lighting devices. Each lighting device comprises a control circuit, at least two LED driving circuits, and at least two types of LED-based light sources. When the controller receives low voltage dimming and CCT tuning signals from its inputs, it generates pulse-width modulated (PWM) dimming and CCT tuning signals delivered to the control circuit and at least two LED driving circuits in each of the multiple lighting devices, which then individually power the at least two types of LED-based light sources to emit a light with a lighting level and a CCT. The controller may be integrated in each of the multiple lighting devices to further simplify system design, ultimately achieving the lowest cost.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a lighting control of light-emitting diode (LED)-based lighting devices, and more particularly to a system and a method for LED-based lighting devices that require dimmability and correlated color temperature (CCT) tunability using class  2 , low voltage controllers. 
       BACKGROUND 
       [0002]    Solid-state lighting from semiconductor LED light sources has received much attention in general lighting applications today. Because of its potential for more energy savings, better environmental protection (with no hazardous materials used), higher efficiency, smaller size, and longer lifetime than conventional incandescent bulbs and fluorescent tubes, the LED-based solid-state lighting will be a mainstream for general lighting in the near future. Meanwhile, as LED technologies develop with the drive for energy efficiency and clean technologies worldwide, more families and organizations will adopt LED-based lighting for their illumination applications. In this trend, more energy saving with a dimming control, more efficient CCT tunability, more environmental protection, and more aesthetic perception in lighting quality have become especially important and need to be well addressed. 
         [0003]    The relationship between actual dimming and perceived dimming is not linear but logarithmic by nature because the human eye responds to low light levels by enlarging the pupil, allowing more light to enter the eye. This response results in a difference between measured and perceived light levels. For example, a lamp that is dimmed to 10% of its maximum measured light output is perceived as being dimmed to only 32%. Similarly, a lamp dimmed to 25% is perceived to be at 50%. Taking advantage of such differences, the use of a dimmer on LED-based lamps can save even more energy than actual dimming itself. Besides, reduced electrical consumption can further prolong life expectancy of the LED-based lamps and reduce maintenance or replacement costs. 
         [0004]    A conventional wall-mount dimmer uses a leading-edge phase angle, trailing-edge phase angle, or phase cut to control a power delivering to a lighting device. Whereas such a dimmer seems to provide energy efficiency and is driving consumers to replace standard incandescent lamps with LED-based retrofit lamps, consumers often find that the performance they expect is not being achieved, at least when the solid-state lighting (SSL) products are used with existing TRIAC or phase-cut dimmers. Dimmer compatibility with LED-based lighting devices is a main issue. Basically, the wall-mount TRIAC dimmers are not so designed for LED loads that the existing residential wiring infrastructure can limit their capabilities for modern lighting controls. Furthermore, there are no industry standards that specifically guide LED dimming performance, and as such, a number of undesirable results may occur when one uses a dimmable LED-based lamp with an incandescent dimmer, such as reduced dimming range, flickering or strobing of the lamp, and inconsistent performance based on the number and classification of lamps being controlled by one incandescent dimmer. Moreover, a recent IEEE report raised a health concern due to invisible flicker at frequencies below 165 Hz including seizures, headaches, migraines, impaired ocular motor control, and impaired visual performance, etc. 
         [0005]    Most of the existing residential and commercial electrical dimming infrastructures are single channel wall dimmers, which are crucial to serve the market with high quality solutions and to solve the various challenges to come. Furthermore, power factor of an electrical appliance refers simply to the degree to which the voltage potential and electric current draw required by the electrical appliance are in-phase for each half-cycle of the sinusoidal AC waveform. In fact, the current waveform should be in phase with AC voltage waveform to have a maximum power delivered to the load resulting in a unity power factor as in a purely resistive circuit. Conventional dimmers themselves have a major effect on power factor for all kinds of loads—capacitive, inductive, non-linear, and even linear and resistive, because such dimmers typically cut voltage phase over the current peak as required by the load, causing imbalance and harmonic distortion on the AC line. Poor power factor is rarely noticed by residential end-users because their utility companies usually pay the price by spending money on hardware and additional power to correct for this imbalance throughout their distribution systems. However, commercial users may either pay additional surcharges for low power factor or improve it at their own cost. For example, if their loads are highly inductive, they may have to install capacitor switch banks to compensate for this power loss. 
         [0006]    A conventional driver employed to drive an LED-based lamp basically uses a switch-mode power supply (SMPS) and is considered to be nonlinear with reactive loads, which requires power factor correction (PFC) to reduce non-sinusoidal current distortion and excess energy at harmonics of the line frequency of the voltage. The EU standard EN61000-3-2 regulates harmonic contents and basic PFC criteria for all such switch-mode power supplies. Passive PFC in drivers/power supplies adopted in LED-based lamps usually involve adding capacitors, resistors and steering diodes in a valley-fill circuit. However, the power factor improvement using such a passive PFC circuit is limited. Active PFC involves redistributing the current over the voltage half-cycle waveform. The key is how to improve load regulation without adversely affecting the power factor or to make the load look like a linear resistor. Today, a conventional LED driver employing active PFC typically uses an energy transfer element that includes a flyback transformer to store energy which then directly provides LED current to an LED load. Although simple and low-cost, such a single-stage driver configuration provides so limited functionalities that can barely meet market demands. For example, market needs an external LED driver which can flexibly control one to several LED-based lighting devices in a luminaire. When part of lighting devices are removed from the luminaire for maintenance or replacement, an overall rated current can flow into the remaining LED-based lighting devices, resulting in excessive driving current for LED-based light sources. Market also needs an LED driver which can provide two or three sets of electric current to two or three types of LED-based light sources in order to control CCT of an LED lighting device that comprises such two or three types of LED-based light sources. The conventional LED driver can only provide single channel current control and thus fails to meet these market requirements. 
         [0007]    Used as an early fluorescent dimming system and still used today, 0-10 V dimming has been employed to become one of reliable LED dimming control protocols although it is one of the earliest and simplest electronic lighting control signaling systems. A 0-10 V dimmer does not cut AC voltage for introducing phases and thus keep the AC voltage waveform intact. However, to control a dimming level of a lighting device using such a 0-10 V dimmer, one needs to have two extra low-voltage wires separately connected to the lighting device to be dimmed in addition to the power lines from the AC mains. This is so called 4-wire low voltage 0-10 VDC dimming. The low voltage control wires are polarity sensitive, and so accuracy is critical in wiring. This increases the wiring difficulty and installation cost, especially for the existing residential and commercial infrastructures that have two or three power wires in a wall-mount electrical box. However, because 0-10 VDC dimming can provide dimming levels seamlessly from 1% to 100% with continuous dimming voltages from 1 to 10 V, more and more consumers adopt it, taking further advantages such as being less expensive, easily integrating with occupancy sensors, daylight harvesting, DMX, DALI, and wireless 2-channel, and no compatibility issue that has ever been reported to use with LED-based luminaires. 
         [0008]    In today&#39;s lighting applications, CCT tuning is important. Although consumers demand a CCT tunable lamp that can tune from warm-white at 2,700 K, via sun-white and natural-white at 4,100 K, to cool-white at 6,200±300 K in general lighting to help improve the atmosphere in their working, exhibiting, or living areas, there have been very few such lighting products in luminaire markets. Manufacturers can generally make an LED-based lighting device using two types of phosphor coated white LEDs, one cool white and the other warm white, to mix the light emissions with different ratios to come up with a CCT. By tuning from cool LEDs to warm LEDs, with the intermediate CCTs created by mixing different levels of cool and warm white light, an extent of colors proximate to the black body locus can be obtained. The number of colors used in a CCT tuning system affects color rendering index (CRI), CCT consistency, CCT tuning range, and an efficacy of the system. However, the approach needs a proper LED driver to provide two or more sets of electric current with a proper ratio to the cool white and the warm white LEDs or other types of LEDs such as to emit a light emission with a CCT, a controlled deviation from the blackbody locus (Duv), and CRI. A conventional driver apparently cannot provide various sets drive current to meet such requirements. Furthermore, even if there exists such a driver, an additional CCT tuning signal needs to add to a dimming signal, and ultimately, the two signals from the dimming channel and the CCT tuning channel need to be mixed to generate a completely different format of control signals to control output current from the driver and to power LED-based light sources in multiple lighting devices. 
         [0009]    Building Automation Control Network (BACnet) is a data communication object-oriented protocol for building automation and control networks. Its applications include HVAC control, lighting control, access control, security, and fire detection systems. Lighting is typically controlled and monitored via BACnet through manipulation of the object property called present value. Reading the present value will return the on/off status of a switched lighting load or the level of a dimmed lighting load. To control the load it is only necessary to write to the present value of the object representing the lighting load, In BACnet, a dimmer output can be modeled using an Analog Output object with units of 0% to 100% to represent intensity. However, CCT tuning output has not yet been modeled. Once the CCT tuning output, like the dimmer output, is modeled as another Analog Output object, then how a luminaire simultaneously responds to two analog output signals may become challenging. It is therefore the purpose of this patent disclosure to present an approach for controlling dimming level and CCT in a luminaire using two low voltage signals. Not only for BACnet, the approach should also apply to any other protocols adopting low voltage signals. In the context hereafter, the “low voltage” implies a nominal voltage less than or equal to 12 VDC. 
       SUMMARY 
       [0010]    The present disclosure relates to a lighting control of LED-based lighting devices that adopt two low voltage controllers to control dimming level and CCT of multiple LED-based lighting devices that require dimmability and CCT tunability. As mentioned in the description of related art, the cost-effective solution to avoiding a proprietary controller is to adopt two widely used two low voltage controllers originally employed in dimming control, one for dimming input and the other for CCT tuning input. By incorporating dimming and CCT control signals, a dimming and CCT tuning control circuit mixes and converts the two signals into two sets of pulse-width modulation (PWM) signals used to control two sets of current driving two types of LED light sources in a lighting device. In this case, AC voltage in the power line remains intact in all time, thus providing an acceptable power factor. 
         [0011]    In one embodiment, a dimming and CCT tuning lighting system may comprise a low voltage dimming input, a low voltage CCT tuning input, a dimming and CCT tuning control circuit, and multiple LED-based lighting devices. The dimming and CCT tuning control circuit receives a dimming signal from the dimming input and a CCT tuning signal from the CCT tuning input to generates at least two sets of PWM control signals. Each LED-based lighting device in the multiple LED-based lighting devices comprises at least two types of LED-based light sources and a dimming and CCT tuning controllable driver configured to receive the at least two PWM control signals and to control LED current to drive the at least two types of LED-based light sources in each LED-based lighting device of the multiple lighting devices to emit a light with a dimming level and CCT. 
         [0012]    Because a low voltage signal attenuates significantly along a long distance from the low voltage dimming and CCT tuning inputs to multiple LED-based lighting devices, a first LED-based lighting device rather closer to the dimming and CCT tuning inputs may emit higher light intensity and higher CCT than the last LED-based lighting device. This difficulty can be overcome by mixing and converting the dimming and CCT tuning signals into at least two modulated PWM signals before sending to multiple LED-based lighting devices in a lighting zone. Thus, a dimming and CCT tuning controller may comprise a low voltage dimming input, a low voltage CCT tuning input, and a dimming and CCT tuning control circuit configured to receive the dimming signal and the CCT tuning signal from the low voltage dimming input and the low voltage CCT tuning input and to generate at least two PWM control signals to send to the dimming and CCT tuning controllable driver in each LED-based lighting device to power the at least two types of LED-based light sources accordingly. Because the dimming and CCT information is embedded in duty cycles of the modulated PWM signals after mixing and conversion, the signal strength/amplitude has no effect on the duty cycles, and thus the dimming and CCT information can be recovered. This guarantees all the lighting devices in a lighting zone can emit a light with the same dimming level and the same CCT. 
         [0013]    In another embodiment, a dimming and CCT tuning lighting system may comprise the foregoing dimming and CCT tuning controller and multiple lighting devices in a lighting zone, taking advantages of a wide range of dimming and CCT tuning control without inconsistent CCTs due to voltage drop. Each lighting device comprises a dimming and CCT tuning controllable driver, a color filter and temperature sensor module, and at least three types of LED-based light sources. The dimming and CCT tuning controllable driver comprising a power supply section, a dimming and CCT tuning control section, and an LED driving section comprising at least three LED driving circuits. The power supply section, connecting to the AC mains, receives and converts a regular AC power into a DC power supplying the color filter and temperature sensor module, dimming and CCT tuning control section, and the at least two LED driving circuits which then drive at least three types of LED-based light sources to emit light. Based on the recovered dimming and CCT tuning signal and the sensing signals from the color filter and temperature sensor module, the dimming and CCT tuning control section generates at least three PWM control signals to send to the at least three LED driving circuits to provide driving current to drive the at least three types of LED-based light sources to emit a resultant light with a dimming level, CCT, and Duv. The lighting control according to the present disclosure may find applications in general lighting, signage, stage lighting, wall-washer, etc. 
         [0014]    The present disclosure provides a method in the dimming and CCT tuning lighting system that comprises the dimming and CCT tuning control circuit configured for mixing and converting dimming and CCT tuning signals in a PWM signal format. The dimming and CCT tuning control circuit first reads the CCT tuning signal from the low voltage CCT tuning input and determines a ratio related to extreme CCTs of LED-based light sources used a first user signal. Then the dimming and CCT tuning control circuit reads a dimming level signal from the low voltage dimming input and determines a dimming level in response to a second user signal. The dimming and CCT tuning control circuit further integrates the ratio related to extreme CCTs of LED-based light sources with the dimming level to determine factors relevant to a target light intensity and CCT. Finally, the dimming and CCT tuning control circuit generates at least two modulated PWM signals based on the factors relevant to a target light intensity and CCT. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The accompanying drawings are included to aid further understanding of the present disclosure, and are incorporated in and constitute a part of the present disclosure. The drawings illustrate a select number of embodiments of the present disclosure and, together with the detailed description below, serve to explain the principles of the present disclosure. It is appreciable that the drawings are not necessarily in scale as some components may be shown to be out of proportion than the size in actual implementation in order to clearly illustrate the concept of the present disclosure. 
           [0016]      FIG. 1  is a functional block diagram of a low voltage dimming and CCT tuning controller connected with multiple lighting devices according to the present disclosure. 
           [0017]      FIG. 2 , which includes  FIG. 2(A) - FIG. 2(F) , is a timing diagram of a series of modulated dimming and CCT tuning signal waveforms when dimming level is set to “No Dim” according to the present disclosure. 
           [0018]      FIG. 3 , which includes  FIG. 3(A) - FIG. 3(F) , is a timing diagram of a series of modulated dimming and CCT tuning signal waveforms when dimming level is set to “Half Dim” (50% Dim) according to the present disclosure. 
           [0019]      FIG. 4  is a chromaticity diagram showing linear tuning and nonlinear blackbody tuning according to the present disclosure. 
           [0020]      FIG. 5  is an enlarged view of the chromaticity diagram in  FIG. 5  showing linear tuning and nonlinear blackbody tuning according to the present disclosure. 
           [0021]      FIG. 6  is a functional block diagram of a dimmable and CCT tunable lighting device according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]      FIG. 1  is a functional block diagram of a low voltage dimming and CCT tuning controller  100  connected with multiple lighting devices  200  according to the present disclosure. In  FIG. 1 , the low voltage dimming and CCT tuning controller  100  comprises a dimming input  110 , a CCT tuning input  111 , a dimming and CCT tuning control circuit  114 , and a set of dimming and CCT tuning signal bus  104  electrically connected to the multiple LED-based lighting devices  200  comprising LED-based lighting devices  201 ,  202 , and  203 , each comprising at least two types of LED-based light sources. The power, connected to AC mains via a power input terminal  102  and a power switch  103 , is supplied to the multiple LED-based lighting devices  200  via a separate power path  105 , going directly to a power supply section in each of the LED-based lighting devices  201 ,  202 , and  203 . The dimming and CCT tuning control circuit  114  comprises a microcontroller  1141 , receiving dimming and CCT tuning signals from the dimming input  110  and the CCT tuning input  111  and generating at least two sets of modulated PWM signals associated with the dimming and CCT tuning signals. The dimming and CCT tuning control circuit  114  may receive ecosystem signals from photo sensors in daylight harvesting and occupancy sensors via an ecosystem port  112 . The at least two sets of modulated PWM signals go through a line driver  1142  to be conditioned so that the at least two sets of modulated PWM signals can be transmitted to the multiple LED-based lighting devices  200 . Although the dimming and CCT tuning control circuit  114  can be integrated in the dimming and CCT tuning inputs  110  and  111  to deal with voltage drop of low-voltage dimming and CCT tuning signals due to long range transmission, it can be integrated in each of the LED-based lighting devices  201 ,  202 , and  203  to add more functionality. Voltage drop of the low-voltage dimming and CCT tuning signals is a serious problem for CCT tuning lighting systems because CCT or light color may be very different and noticeable between an LED-based lighting device significantly closer to the dimming and CCT tuning inputs and another LED-based lighting device far away from the dimming and CCT tuning inputs. This problem can be solved by mixing and converting the dimming and CCT tuning signals into at least two modulated PWM signals before sending to multiple lighting devices. Because the dimming and CCT information is embedded in duty cycles of the at least two modulated PWM signals after mixing and conversion, the signal strength/amplitude reduction has no effect on the duty cycles, and thus the dimming and CCT information can be recovered. This guarantees each LED-based lighting device in a specific control zone can emit a light with a dimming level and CCT. Essentially, a PWM signal controls a time-average current through an LED-based light source, and therefore, the luminance of the LED-based light source. Use of PWM signals to control the LED-based light sources is preferred over other analog luminance control methods because it prevents color-shifting that occurs with changes in drive current. 
         [0023]    Comprising a microcontroller, the dimming and CCT tuning control circuit  114  may have built-in specific lighting settings for different times of the day and may use daylight to offset the amount of electric lighting needed to properly light a space, in order to reduce energy consumption. The energy saving can also be accomplished by using lighting ecosystems adopting photo sensors in daylight harvesting or occupancy sensors to reduce luminance of lighting devices in response to changing daylight availability. When a specific time arrives, the dimming and CCT tuning control circuit  114  automatically generates at least two sets of modulated dimming and CCT tuning PWM signals to achieve automatic luminance and CCT tuning adjustments, such as lighting with higher luminance and lower CCT at night or lighting with lower luminance and higher CCT in the daytime. In the present disclosure, the dimming and CCT tuning control circuit  114  generates the modulated dimming and CCT tuning control signals according to the dimming and the CCT tuning inputs  110  and  111 . The dimming and the CCT tuning inputs  110  and  111  may be locally or remotely controlled by users. For example, the dimming and the CCT tuning inputs  110  and  111  may be replaced by a receiver to receive external dimming and CCT tuning signals from a remote transmitter. In this case, the dimming and the CCT tuning inputs  110  and  111  may be in forms other than the potentiometer/variable resistor as shown in  FIG. 1 , which include wireless receivers such as an infrared, a radio, an occupancy sensor, and an audio receiver. The protocols used may be Daintree, Enlighted, Bluetooth low energy, Zigbee, WiFi or EnOcean. The dimming and the CCT tuning inputs  110  and  111  may be a direct-wired receiver using protocols of 0-10V, RS232, RS485, DMX512, DALI (digital ddressable lighting interface), USB (universal serial bus) or BACnet. According to the specific type of the dimming and the CCT tuning inputs  110  and  111 , users can remotely send dimming and CCT signals to the dimming and the CCT tuning inputs  110  and  111  via a corresponding user interface transmitter. Providing a second independent control signal path to light sources in a CCT tuning lighting system creates complete features enabled by digital color tuning. One alternative to low voltage dimming and CCT tuning is a direct wireless path. The approach can save time and efforts to reconfigure a lighting control zone that have many LED-based lighting devices. For example, a smart phone based commissioning tool can achieve a full CCT tuning of the LED-based light sources and even access operating status and working hours of the light sources. This two-path lighting control offers the compatibility and flexibility required to maximize the value of CCT tuning lighting system because it ensures that the LED-based lighting devices will be compatible with future developments of internet using cloud technologies, where enhanced connectivity is desired. 
         [0024]    The present disclosure provides a method for a dimming and CCT tuning lighting system that comprises the dimming and CCT tuning controller  100  to mix and convert the dimming and CCT tuning signals into a modulated PWM signal format. The dimming and CCT tuning control circuit  114  first reads the CCT tuning signal from the low voltage CCT tuning input  111  and determines a luminance ratio between extreme CCTs of the LED-based light sources based on a first user signal. Then the dimming and CCT tuning control circuit  114  reads a dimming level signal from the low voltage dimming input  110  and determines a dimming level based on a second user signal. The dimming and CCT tuning control circuit  114  further integrates the luminance ratio between the extreme CCTs of the LED-based light sources with the dimming level to determine factors relevant to a target dimming level and CCT. Finally, the dimming and CCT tuning control circuit  114  generates at least two sets of modulated PWM signals with various duty cycles based on the factors relevant to the target dimming level and CCT. 
         [0025]      FIG. 2 , which includes  FIG. 2(A) - FIG. 2(F) , is a timing diagram of a series of modulated dimming and CCT tuning modulated PWM signal waveforms when dimming level is set to “No Dim” according to the present disclosure. Referring to  FIGS. 1-2 , when a user controls the low voltage dimming input to the brightest and the CCT tuning input to 20%180%, the dimming and CCT tuning control circuit  114  first reads the CCT tuning signal voltage from the low voltage CCT tuning input  111  and determines the luminance ratio 20%/80% related to the extreme CCTs of the LED-based light sources based on the first user signal. Then the dimming and CCT tuning control circuit  114  reads the dimming level signal voltage from the low voltage dimming input  110  and determines a dimming level of 0 (No Dim). Finally the dimming and CCT tuning control circuit  114  mixes the dimming and CCT tuning signals and generates two sets of modulated PWM signal waveforms shown in  FIG. 2(A)  and  FIG. 2(B) .  FIG. 2(A)  and  FIG. 2(B)  respectively correspond to the two sets of modulated PWM signals with duty cycles of 20% and 80%, which will send to the two LED-based light sources in the LED-based lighting devices  201 ,  202 , or  203  to emit a light with a particular CCT based on the luminance ratio for a mixture of the two LED-based light sources.  FIG. 2(C)  and  FIG. 2(D)  respectively correspond to two sets of modulated PWM signals with duty cycles of 30% and 70%.  FIG. 2(E)  and  FIG. 2(F)  respectively correspond to two sets of modulated PWM signals with duty cycles of 40% and 60%. Essentially, for each pair of the two sets of modulated PWM signals, their duty cycles should be complementary to each other with a sum of unity and the ratio of the duty cycles kept constant to guarantee that a CCT can be achieved regardless of the dimming level. The dimming and CCT tuning control circuit  114  then reads the dimming signal from the low voltage dimming input  110 . If a dimming level, D, where 0≦D≦1 is determined, then the initial duty cycles are further reduced by the dimming level D. For example, if initial duty cycles of two sets of modulated PWM signals are set to be 60% and 40%, a dimming level of 30% gives final duty cycles of 18% and 12% for the two sets of modulated PWM signals. Thus not only the ratio of supplied current to the two types of the LED light sources is preserved, the dimming level also applies to the two types of the LED-based light sources, which in turn can emit a light with an intensity and a CCT. 
         [0026]      FIG. 3 , which includes  FIG. 3(A) - FIG. 3(F) , is a timing diagram of a series of modulated dimming and CCT tuning signal waveforms when dimming level is set to “Half Dim” (50% Dim) following the cases in  FIG. 2  according to the present disclosure.  FIG. 3(A)  and  FIG. 3(B)  respectively correspond to two sets of modulated PWM signals with duty cycles of 10% and 40%, which will send to the two types of the LED-based light sources in each of the LED-based lighting devices  201 ,  202 , and  203  to emit a light with the 50% dimming level and the CCT same as the case in  FIG. 2 , based on a light mixture of the two types of LED-based light sources. Note that because ratio of the two duty cycles of this modulated PWM signal pair is the same as that in  FIG. 2(A)  and  FIG. 2(B) , the CCT of the light mixture does not change, but the intensity of light reduces to 50%. Similarly,  FIG. 3(C)  and  FIG. 3(D)  respectively correspond to two sets of modulated PWM signals with duty cycles of 15% and 35% from original 30% and 70% in  FIG. 2(C)  and  FIG. 2(D) .  FIG. 3(E)  and  FIG. 3(F)  respectively correspond to two sets of modulated PWM signals with duty cycles of 20% and 30% from original 40% and 60% in  FIG. 2(E)  and  FIG. 2(F) . 
         [0027]    In dimming and CCT tuning, users may adjust a dimming level and a CCT up or down. For example, an original light level is at 100% maximum luminance, and adjusting a dimming level up means making the light level less than 100% of its maximum luminance. The minimum luminance is 0%. An original light is at a CCT of 2,700K (warm white), and adjusting a CCT up means increasing the CCT of the light to be greater than 2,700K. In general lighting applications, CCT may vary from 2,700K (warm white) to 5,700K (cool white). Users can adjust CCT of a lighting device within this range to change a room atmosphere for their working or living requirements. Furthermore, since the dimming and CCT tuning controller  100  may have built-in dimming and CCT tuning commands configured for different schedules and scenes, the present disclosure may automatically generate dimming and CCT tuning control signals upon configured schedules without having to receive users&#39; adjustment signals through the dimming and the CCT tuning inputs. 
         [0028]      FIG. 4  is a CIE 1976 UCS chromaticity diagram showing linear white tuning and blackbody white tuning according to the present disclosure.  FIG. 5  is an enlarged view of the chromaticity diagram in  FIG. 5 . In  FIGS. 4-5 , six saturated colors  10 ,  20 ,  30 ,  40 ,  50 , and  60  at dominant wavelengths of 380, 520, 560, 570, 580, and 780 nm are respectively designated on the color gamut. The eight quadrangles  70  that specify available white color region of solid-state lighting are along the Planckian locus  80  in a CIE 1976 UCS chromaticity diagram expressed by (u′, v′) coordinates. Each of the eight quadrangles is defined by a range of CCT and a distance from Planckian locus on the diagram. The eight quadrangles represent eight CCT categories at nominal CCTs of 2,700, 3,000, 3,500, 4,000, 4,500, 5,000, 5,700, and 6,500 K, from top to bottom along the Planckian locus  80  in  FIGS. 4 and 5 . When a warm white LED at a CCT of 2,700K corresponding to a first point  901  at a coordinate (0.2613, 0.5268) mixes with a cool white LED at a CCT of 5,700K corresponding to a second point  902  at a coordinate (0.205, 0.4745), the light mixture may be at a CCT corresponding to a third point with a coordinate along the straight line  903  connecting between the first and the second points  901  and  902 , depending on a luminance ratio between the two. If the luminance ratio is 1:1, the light mixture will emit a CCT with a coordinate at the midpoint  904  along the straight line  903  connecting between the first and the second points  901  and  902  shown in  FIG. 6 . The distance from the midpoint  904  to the closest point  905  on the Planckian locus  80  is the largest, where the Duv of the midpoint  904  may exceed 2-step MacAdam ellipse  906  which defines variance of a color whose chromaticity coordinate can be acceptably associated with a target correlated color temperature. Without additional light sources to compensate for this deviation from the Planckian locus  80  for the linear white tuning, the light mixture will never be close to Planckian locus  80  within the 2-step MacAdam ellipse  906 . In other words, the average human eye may see this distinguishably different light color. However, if a third LED-based light source emits a light with a color coordinate on a line  907  that passes the midpoint  904  and perpendicular to the line  903  connecting between the first and the second color points  901  and  902 , then the resultant mixture light with a proper luminance ratio of the third light and the mixture of the first and the second light can have an emission with a color coordinate within the 2-step MacAdam ellipse  906  of the closest point  905  on the Planckian locus  80 . This blackbody white tuning ensures that standard deviation of color matching is within the 2-step MacAdam ellipse  906  for different lighting devices. The example of the third LED-based light source is a type of LEDs with a saturated color at a wavelength between 560 and 567 nm at a coordinate 801 or a phosphor-coated LED having yellow-green color hue and a color coordinate in a region  908  encircled by four coordinates (0.23, 0.524), (0.19, 0.5671), (0.1701, 0.5486), (0.2101, 0.5055) on CIE 1976 UCS chromaticity diagram. Furthermore, this methodology enables the use of off-Planckian phosphor-coated LEDs to improve the efficacy and performance of color tuning light sources. Use of off-Planckian such phosphor-coated LEDs can increase efficacy of tunable light sources by as much as 20% to 30%. 
         [0029]      FIG. 5  also depicts utilizing a linear tuning of either two types of white LEDs—one warm white at 2,700K and one cool white at 5,700K or one cool white 5,700K and one LED with a saturated color  909  to form a white light in the CCT 4,000K quadrangle but out of Planckian locus. Also shown is a nonlinear blackbody tuning of such a light emission in the CCT 4,000K quadrangle and the LEDs whose emissions have a peak wavelength  801  between 560 and 565 nm, forming a white light with a CCT of 4,100K on the Planckian locus. In the same fashion, a nonlinear blackbody tuning of the light emission in the 4,000K quadrangle but out of 2-step-MacAdam ellipse and the phosphor-coated LEDs whose coordinate of the emissions located in the region  908  (perceived as yellow-green) can form a white light exactly on the Planckian locus in the CIE chromaticity diagram. Both nonlinear blackbody tuning result in a better CRI, Duv, and color consistency. 
         [0030]      FIG. 6  is a functional block diagram of a dimmable and CCT tunable lighting device  201  according to the present disclosure. In  FIG. 6 , the lighting device  201  comprises an LED module  700  and a dimming and CCT tuning controllable driver  205  comprising a power supply section  300 , an LED driving circuit section  400 , and a dimming and CCT tuning control section  115 . The LED driving circuit section  400  comprises at least two LED driving circuits  401  and  402  respectively connected to at least two types of LED-based light sources  701  and  702  in the LED module  700 . The at least two types of LED-based light sources  701  and  702  emit two different white light at the two extreme CCTs; different wavelengths with different saturated colors such as red, green, and blue; or combinations such as one white light at a specific CCT and the other one with a saturated colors of red, green, or blue. In one embodiment, a first type of the at least two types of LED-based light sources may be a white LED having a CCT at 6,200±300 K whereas a second type may have a saturated color at a peak wavelength from 583 to 586 nm to ensure that a resultant light can be in the Planckian locus of the CIE chromaticity diagram. In another embodiment, the first type of the at least two types of LED-based light sources is a white LED having a CCT at 5,700±300 K whereas the second type is a white LED having a CCT at 2,700±300 K. In color mixing applications, LED chips of the at least two types of LED-based light sources  701  and  702  should be mounted in a way that they interlace or encircle each other on an LED printed circuit board (not shown) to ensure color uniformity in the resultant light. On the LED module  700  mounted a module  704  comprising color filters and temperature sensors to monitor the spectrum and lumen depreciation of the light mixture and junction temperature on the LED printed circuit board. The monitored signals are then fed back into the dimming and CCT tuning control section  115  to calculate an optimal operating driving current for a third type of LED-based light source to compensate possible CCT deviations for every color point in the tuning range. 
         [0031]    In  FIG. 6 , the power input terminals  301  in the power supply section  300 , connected to the AC power to convert to a DC power supplying the at least two LED driving circuits  401  and  402  which also receive at least two sets of modulated PWM signals from dimming and CCT tuning control section  115  to provide two sets of driving current respectively powering the two types of LED-based light sources  701  and  702 . The power supply section  300  can be any switch mode power supplies with multiple regulated voltages comprising a low voltage source. The low voltage source in each LED-based lighting device can also provide the power needed for additional sensors such as occupancy sensors, photo sensors in daylight harvesting, and indoor positioning. The LED driving circuit  401  is configured with an internal MOSFET switch  405  to drive the LED-based light source  701 . In the LED driving circuit  401 , a PWM port (PWM 1 ) is connected to one of PWM output terminal ports  605  of the dimming and CCT tuning control section  115  to receive a PWM control signal from the one of PWM output terminal ports  605  with a specific duty cycle to control supplied current to the LED-based light source  701  to emit a light brighter or dimmer according to the duty cycle of the modulated PWM signal. The LED driving circuits  402  and  403  serve the same functions as the LED driving circuits  401 , except that their modulated PWM signals have another specific duty cycles to control the LED-based light sources  702  and  703 . 
         [0032]    For color consistency, the in-line spectral capture enables a color point match of less than 2-step MacAdam ellipse across CCT tuning range. The use of color filters and temperature sensors ensures in-line spectral monitoring based on combined LED, driver, and diffusing element over a range of CCT, electric current settings, and thermal status. For example, when the dimming and CCT tuning control section  115  determines that Duv is out of Mac Adam ellipse associated with a specific CCT along Planckian locus of the CIE chromaticity diagram, it may generate a third set of modulated PWM signal to drive the third type of LED-based light source  703  in the LED module  700 . For another example, when the dimming and CCT tuning control section  115  determines that intensity of one of the at least two types of LED-based light sources  701  and  702  is lower than the original preset value due to lumen depreciation, it may modify the two sets of modulated PWM signals to drive the first type or the second type of the LED-based light sources  701  and  702  in the LED module  700  so as to maintain high color quality such as CRI, R9 and Duv over the full CCT tuning range. Although it is desirable to control a CCT of the dimming and CCT tuning lighting system within 2-step MacAdam ellipse along the Planckian locus in the CIE chromaticity diagram, a tolerance of 7-step MacAdam ellipse may be acceptable in some cases. Also note that the color filters and the temperature sensors in the module  704  do not have to be placed together to monitor the designated parameters. 
         [0033]    In  FIG. 6 , the dimming and CCT tuning control section  115  comprises an input terminal  503  connected to the dimming and CCT tuning controller  100  in  FIG. 1 , a feedback input  504  connected to the additional module  704  on the LED module  700  to monitor the spectrum and lumen depreciation of the light mixture and junction temperature in the LED PCB, and the output terminal ports  605  connected to the LED driving circuit section  400 . The dimming and CCT tuning control section  115  comprises an analog-to-digital converter (ADC)  601  to convert analog data into digital ones, a flash memory  602  to store the dimming and CCT tuning signal portion digitized by ADC  601 , a processor  603  to generate at least two sets of PWM control signals according to the dimming and CCT tuning signal and to send to the at least two LED driving circuits  401  and  402  so that the LED driving circuit section  400  can drive the at least two types of the LED-based light sources  701  and  702  to emit a light with a luminance and a CCT. Although the dimming and CCT tuning control section  115  is configured to receive the modulated PWM signals related to dimming and CCT tuning signals from the dimming and CCT tuning controller  100 , dimming and CCT tuning signals in their original low voltage signal formats are acceptable, taking advantage of use of the processor  603 . This feature increases flexibility and compatibility for connectivity. Furthermore, the flash memory  602  in the dimming and CCT tuning control circuit  600  may also store a lighting status of the at least two types of the LED-based light sources  701  and  702  and even an address of the lighting device  201 . Once receiving dimming and CCT tuning signals, the dimming and CCT tuning control section  115  increases or decreases the duty cycles of the modulated PWM signals coupled to the PWM inputs of the at least two LED driving circuits  401  and  402  such that the two sets of driving current provided to the two types of LED-based light sources  701  and  702  can change accordingly. Based on the duty cycles of the currents and their ratio, a resultant light emitting from the two types of the LED-based light sources  701  and  702  can mix to exhibit a luminance or a CCT. 
         [0034]    In  FIG. 6 , the LED-based lighting device  201  can be down lights, par lights, A19 lights, linear tubes, troffer luminaires, panel lights, and the combination. The lighting device can have its compatible socket adapter such as E27, E26, MR16, GU10, GU24, G13, etc. or just wire connections. 
         [0035]    In view of the above, highlight of a number of example implementations and select features thereof is provided below. 
         [0036]    A dimming and CCT tuning controller may include a low voltage dimming input, a low voltage CCT tuning input, and a dimming and CCT tuning control circuit configured to receive and to mix a dimming signal and a CCT tuning signal from the low voltage dimming input and the low voltage CCT tuning input and to generate at least two PWM control signals. In response to either the dimming signal or the CCT tuning signal from either the low voltage dimming input or the low voltage CCT tuning input, the dimming and CCT tuning control circuit may send the at least two PWM control signals to at least two LED drivers in one or more lighting devices to power at least two types of LED-based light sources therein accordingly in an event that the dimming and CCT tuning control circuit is coupled to the at least two LED drivers in the one or more lighting devices. 
         [0037]    In some implementations, the low voltage dimming input may include a 0-10 V controller. 
         [0038]    In some implementations, the low voltage CCT tuning input may include a 0-10 V controller. 
         [0039]    In some implementations, at least one of the low voltage dimming input and the low voltage CCT tuning input may include a type of potentiometer or a variable resistor. 
         [0040]    In some implementations, at least one of the low voltage dimming input and the low voltage CCT tuning input may include a wireless receiver. In some implementations, the wireless receiver may include a radio receiver, an infrared receiver, an occupancy sensor, an audio receiver, a photo sensor of daylight harvesting, or an internet-based receiver controllable by a smart phone. 
         [0041]    In some implementations, at least one of the low voltage dimming input and the low voltage CCT tuning input may include a hardwired receiver. In some implementations, the hardwired receiver may operate based on a protocol of RS232, RS485, DMX512, USB, or DALI. 
         [0042]    A dimming and CCT tuning lighting system may include a low voltage dimming input, a low voltage CCT tuning input, and at least one LED-based lighting device. The at least one LED-based lighting device may include at least two types of LED-based light sources and a dimming and CCT tuning controllable driver. The dimming and CCT tuning controllable driver may include a power supply section, a dimming and CCT tuning control section, and an LED driving section. The power supply section may be configured to receive an alternating current (AC) power to generate a direct current (DC) power. The dimming and CCT tuning control section may be configured to receive and to mix a dimming signal and a CCT tuning signal from the low voltage dimming input and the low voltage CCT tuning input and to generate at least two PWM control signals. The LED driving section may be connected to the power supply section and configured to receive the DC power and the at least two PWM control signals to drive the at least two types of LED-based light sources to emit a light with a dimming level and a CCT. 
         [0043]    In some implementations, each of the at least two types of the LED-based light sources may include an LED, an organic LED (OLED), or a polymer LED (PLED). 
         [0044]    In some implementations, the dimming and CCT tuning control section may include a flash memory configured to store lighting status and an address of each LED-based lighting device of the at least one LED-based lighting device. 
         [0045]    In some implementations, the at least two types of the LED-based light sources may include a first type of a white LED having a CCT at 5,700±300 K and a second type of an LED having a saturated color at a peak wavelength from 575 to 583 nm. 
         [0046]    In some implementations, the at least two types of LED-based light sources may include a first type of a white LED having a CCT at 5,700±300 K and a second type of a white LED having a CCT at 2,700±300 K. 
         [0047]    In some implementations, the at least two types of LED-based light sources may include a red LED, a green LED, and a blue LED. 
         [0048]    In some implementations, the at least one LED-based lighting device may further include a color filter and temperature sensor module configured to monitor light spectrum and junction temperatures of the LED-based light sources. 
         [0049]    In some implementations, the at least one LED-based lighting device may further include a third type of LED-based light source configured to control a CCT of the dimming and CCT tuning lighting system within 7-step MacAdam ellipse along the Planckian locus in CIE chromaticity diagram. 
         [0050]    In some implementations, the third type of LED-based light source may have a saturated color at a peak wavelength from 560 to 567 nm. 
         [0051]    In some implementations, the third type of LED-based light source may include a phosphor-coated LED having yellow-green color hue and a color coordinate in a region encircled by four coordinates (0.23, 0.524), (0.19, 0.5671), (0.1701, 0.5486), (0.2101, 0.5055) on CIE 1976 UCS chromaticity diagram. 
         [0052]    A dimming and CCT tuning lighting system may include a low voltage dimming input, a low voltage CCT tuning input, a dimming and CCT tuning control circuit, and at least one LED-based lighting device. The dimming and CCT tuning control circuit may be configured to receive and to mix a dimming signal and a CCT tuning input signal from the low voltage dimming input and the low voltage CCT tuning input and to generate at least two PWM control signals. The at least one LED-based lighting device may include at least two types of LED-based light sources and a dimming and CCT tuning controllable driver. The dimming and CCT tuning controllable driver may include a power supply section and an LED driving section. The power supply section may be configured to receive an AC power to generate a DC power. The LED driving section may be connected to the power supply section and configured to receive the DC power and the at least two PWM control signals from the dimming and CCT tuning control circuit to drive the at least two types of LED-based light sources to emit a light with a dimming level and a CCT. 
         [0053]    In some implementations, each of the at least two types of LED-based light sources may include an LED, an OLED, or a PLED. 
         [0054]    In some implementations, the dimming and CCT tuning control circuit may include a flash memory configured to store lighting status and an address of each lighting device of the at least one lighting device. 
         [0055]    In some implementations, the at least two types of LED-based light sources may include a first type of a white LED having a CCT at 5,700±300 K and a second type of an LED having a saturated color at a peak wavelength from 575 to 583 nm. 
         [0056]    In some implementations, the at least two types of LED-based light sources may include a first type of a white LED having a CCT at 5,700±300 K and a second type of a white LED having a CCT at 2,700±300 K. 
         [0057]    In some implementations, the at least two types of LED-based light sources may include a red LED, a green LED, and a blue LED. 
         [0058]    A method implemented in a dimming and CCT tuning lighting system for controlling driving currents to light-emitting diode (LED)-based light sources in multiple lighting devices may involve a number of operations. The method may involve determining a ratio related to extreme CCTs of the LED-based light sources from a CCT tuning input based on a first user signal. The method may also involve determining a dimming level from a dimming input based on a second user signal. The method may still involve integrating the ratio related to the extreme CCTs of the LED-based light sources with the dimming level to obtain factors relevant to a target dimming level and CCT. The method may further involve generating PWM signals based on the factors relevant to the target dimming level and CCT. The method may additionally involve controlling driving currents to the LED-based light sources in the multiple lighting devices using the PWM signals. 
         [0059]    Whereas preferred embodiments of the present disclosure have been shown and described, it will be realized that alterations, modifications, and improvements may be made thereto without departing from the scope of the following claims. Accordingly, the foregoing description and attached drawings are by way of example only, and are not intended to be limiting.