Patent Publication Number: US-2022217825-A1

Title: Color temperature controlled and low thd led lighting devices and systems and methods of driving the same

Description:
PRIORITY CLAIM 
     The present application is a continuation of U.S. patent application Ser. No. 17/001,074, filed Aug. 24, 2020, which is a continuation of U.S. patent application Ser. No. 16/440,884, filed Jun. 13, 2019, which is a continuation of U.S. patent application Ser. No. 15/369,218, filed Dec. 5, 2016, which is a continuation of U.S. patent application Ser. No. 15/005,108, filed Jan. 25, 2016, which is a continuation of U.S. patent application Ser. No. 14/362,173, filed Jun. 2, 2014, which is a national phase of PCT Application No. PCT/US2012/067623, filed Dec. 3, 2012, which claims priority to U.S. Provisional Application No. 61/630,025, filed Dec. 2, 2011, U.S. Provisional Application No. 61/570,200, filed Dec. 13, 2011, and is a continuation-in-part of PCT Application No. PCT/US2012/051531 filed Aug. 20, 2012—the contents of all of which are expressly incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to light emitting diode (“LED”) circuits for use with AC voltage sources. More specifically, the present invention relates to LED devices capable of having color temperature control, low total harmonic distortion, and methods of driving the same. This document discloses technology relating to architecture for high power factor and low harmonic distortion of LED lighting systems. Related examples may be found in previously-filed disclosures that have common inventorship with this disclosure. Various embodiments relate generally to lighting systems that include light emitting diodes (LEDs). 
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
     BACKGROUND OF THE INVENTION 
     LEDs are semiconductor devices that produce light when a current is supplied to them. LEDs are intrinsically DC devices that only pass current in one polarity, and historically have been driven by constant current or constant voltage DC power supplies. When driven by these DC power supplies, LEDs are typically provided in a series string, in parallel strings or in series parallel configurations based on the drive method and LED lighting system design. 
     Recent advancements in the field of lighting have led to the use of LED circuits which are capable of using AC power to drive LEDs configured in particular devices and/or circuit arrangements such that some of the LEDs may operate during the positive phase of the AC power cycle, some LEDs may operate during the negative phase of the AC power cycle, and, in some cases, some or all LEDs may operate during both the positive and negative phases of the AC power cycle. LEDs powered with AC power typically last substantially longer than traditional halogen and incandescent devices or lamps, and typically require much less power to produce a substantially similar amount of light. However, LEDs powered by AC power sources act as a non-linear load. As a result of the non-linearity, LEDs powered using AC power sources may have a lower power factor, and may have a greater total harmonic distortion, than existing halogen or incandescent lighting devices. Having a low power factor and increased distortion may result in higher energy costs, transmission losses, and/or damage to electrical equipment. While the amount of power needed to drive an LED lighting device may be less than to drive a halogen or incandescent lighting device producing a substantially similar amount of light, the overall cost of operating an LED lighting device using AC power may be equal to or more than the amount required to drive the halogen or incandescent lighting device using the same AC power source. 
     Another advantage that traditional halogen and incandescent lighting devices have over present LED lighting devices driven with AC power is that halogen and incandescent lighting devises have the ability to change color temperature when the voltage provided to them is changed. Light in halogen and incandescent lighting devices are typically generated by a hot wire filament. As the power provided to the bulb is decreased, the temperature of the filament typically decreases, causing the color temperature of the emitted light to move down the color spectrum and make the light appear warmer, i.e. closer to yellow or amber or red than white or blue. In order to achieve this effect in LED lighting devices driven with AC power, complicated and expensive drive schemes are currently required which drive up the cost of the lighting device and the cost to operate the same. One example would be color mixing with red, green and blue LEDs referred to as “RGB” which typically uses pulse width modulation to create any color of light desired. However, the power supplies for this are very complex and larger in size. Other complex versions of constant current or constant voltage DC with only two different LED colors can also be used, however these power supplies can also be large and complex. These drive schemes may also be inefficient and waste additional power or electricity, further increasing operating costs. 
     Therefore, it would be advantageous to design a circuit, device, or system utilizing LEDs that maximizes power factor while reducing the total harmonic distortion resulting from driving the circuit, device or system using AC power. 
     It would also be advantageous to design a circuit, device, or system where the color temperature of the LEDs driven with AC power may be dynamically adjusted using simple control methods without having to utilize any complicated or expensive drive mechanisms. 
     Power factor is important to utilities who deliver electrical power to customers. For two loads that require the same level of real power, the load with the better power factor actually demands less current from the utility. A load with a 1.0 power factor requires the minimum amount of current from the utility. Utilities may offer a reduced rate to customers with high power factor loads. 
     A poor power factor may be due to a phase difference between voltage and current. Power factor can also be degraded by distortion and harmonic content of the current. In some cases, distorted current waveforms tend to increase the harmonic energy content, and reduce the energy at the fundamental frequency. For a sinusoidal voltage waveform, only the energy at the fundamental frequency may transfer real power to a load. Distorted current waveforms can result from non-linear loads such as rectifier loads. Rectifier loads may include, for example, diodes such as LEDs, for example. 
     LEDs are widely used device capable of illumination when supplied with current. For example, a single red LED may provide a visible indication of operating state (e.g., on or off) to an equipment operator. As another example, LEDs can be used to display information in some electronics based devices, such as handheld calculators. LEDs have also been used, for example, in lighting systems, data communications and motor controls. 
     Typically, an LED is formed as a semiconductor diode having an anode and a cathode. In theory, an ideal diode will only conduct current in one direction. When sufficient forward bias voltage is applied between the anode and cathode, conventional current flows through the diode. Forward current flow through an LED may cause photons to recombine with holes to release energy in the form of light. 
     The emitted light from some LEDs is in the visible wavelength spectrum. By proper selection of semiconductor materials, individual LEDs can be constructed to emit certain colors (e.g., wavelength), such as red, blue, or green, for example. 
     In general, an LED may be created on a conventional semiconductor die. An individual LED may be integrated with other circuitry on the same die, or packaged as a discrete single component. Typically, the package that contains the LED semiconductor element will include a transparent window to permit the light to escape from the package. 
     The present invention is provided to solve these and other issues. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is provided to increase the performance of LED lighting devices driven by AC power. The LED lighting devices of the present invention seek to provide one or more of a color temperature controllable AC LED lighting device and/or an AC LED lighting device having an increased power factor and reduced total harmonic distortion. 
     According to one aspect of the invention, an LED lighting device having at least two LED circuits connected in parallel, each of the at least two LED circuits having one or more LEDs is provided. Each of the at least two LED circuits that are connected in parallel have a different forward operating voltage than the other LED circuit(s) within the device, and, each of the at least two LED circuits are capable of emitting light having one or more of a different color or wavelength than the other LED circuit(s) within the device. The device further includes at least one active current limiting device connected in series with at least one LED in at least one of the at least two LED circuits. The device and/or circuits are configured such that each LED circuit is capable of emitting light during both a positive and a negative phase of a provided AC voltage when the LED lighting device is connected to an AC voltage source. 
     According to another aspect of the invention, the at least one current limiting device may be, for example, a current limiting diode or a constant current regulator. 
     According to another aspect of the invention, each of the LED circuits and the at least one active current limiting device are integrated onto a single substrate to form the device. 
     According to another aspect of the invention, the device may include additional active current limiting devices, which may also be integrated on the single substrate. Each LED circuit in the device may be connected in series to at least one active current limiting device. Where each LED circuit is connected in series to at least one active current limiting device, each circuit may be connected to its own current limiting device which may each allow a similar or different amount of current to flow through each circuit, or multiple circuits may be connected to at least one common current limiting device which acts to limit the current for each of the circuits. 
     According to another aspect of the invention, the LED lighting device may include a bridge rectifier having at least one of the at least two LED circuits connected across the output of the bridge rectifier. 
     According to another aspect of the invention, at least one of the at least two circuits may include two or more LEDs connected in an anti-parallel configuration. 
     According to another aspect of the invention, at least one of the at least two circuits may include at least five diodes, at least four of the diodes being LEDs. The at least four LEDs may be connected in a bridge rectifier configuration and the at least fifth diode may be connected across the output of the bridge rectifier. The at least fifth diode connected across the output of the bridge rectifier may be a standard diode, an LED or a constant current diode, or may alternatively a constant current regulator. 
     According to another aspect of the invention, at least one of the at least two circuits may include seven or more diodes, at least six of the diodes being LEDs. The at least six LEDs being connected in an imbalanced bridge rectifier configuration, with the at least seventh diode being connected across the output of the imbalanced bridge rectifier. The at least seventh diode connected across the output of the bridge rectifier may be a standard diode, an LED or a constant current diode, or may alternatively a constant current regulator. 
     According to another aspect of the invention, the light emitted by the one or more LEDs forming at least one of the at least two LED circuits may be one or more of a different color or wavelength than the light emitted by the one or more LEDs of the other connected LED circuit(s) in the device. Using different colored of LEDs in each circuit will allow each circuit to emit different colors of light to contribute to the overall color temperature of light emitted by the device. 
     According to another aspect of the invention, each of the at least two circuits may be coated in phosphor, each of the at least two circuits having a different phosphor coating than the other connected at least two LED circuits. The different phosphor coating on each of the at least two circuits may cause each circuit to emit one or more of a different color or wavelength of light than the other connected LED circuits. 
     According to another aspect of the invention, the LED lighting device may be integrated into a lighting system, the lighting system having a dimmer switch capable of providing AC voltage to the LED lighting device, i.e. the dimmer switch be a connected AC power source or supply. The dimmer switch may be used to control the AC voltage provided to the at least two LED circuits to control the light output of each circuit to control a color temperature of light emitted by the LED lighting device. 
     According to one aspect of the invention, a method of controlling color temperature of light emitted by an LED lighting device is provided. In order to control the color temperature of the light emitted by the device, at least two LED circuits are connected in parallel. Each connected LED circuit has a different forward operating voltage and is capable of emitting light of one or more of a different color or wavelength than the other LED circuits connected in parallel. The current provided to at least one of the at least two LED circuits is limited, and at least one of the provided voltage and current to control the light output of the LED circuits connected in parallel is adjusted. The voltage and current provided to each circuit may be a direct AC voltage and current or a rectified AC voltage or current, with the possibility that some circuits in the device are provided a direct AC voltage and current and some of the circuits in the device are provided with a rectified AC voltage and current. 
     According to one aspect of the invention, an LED lighting device is provided. The LED lighting device may include at least one LED circuit having two or more LEDs connected in series, and at least one active current limiting device, the active current limiting device being connected in parallel with the at least one LED in the at least one LED circuit. 
     According to another aspect of the invention, the LED lighting device may include at least a second active current limiting device, the second active current limiting device being connected in series with the at least one LED circuit. 
     According to another aspect of the invention, the LED lighting device may further include a bridge rectifier, wherein the at least one LED circuit is connected across the output of the bridge rectifier. The bridge rectifier may be constructed using either standard diodes, LEDs or some combination thereof. 
     According to another aspect of the invention, the LED lighting device may include at least one additional LED circuit having two or more LEDs connected in series and at least one active current limiting device connected in parallel with at least one of the two or more LEDs, the at least one additional LED circuit being connected to the at least one LED circuit in parallel. The at least one additional LED circuit may be capable of emitting light having one or more of a different color or wavelength than the at least one LED circuit in the device. 
     According to another aspect of the invention, the at least one LED circuit may include at least three LEDs connected in series. 
     According to another aspect of the invention, the LED lighting device may include a resistor connected in series with the at least one LED circuit. 
     According to another aspect of the invention, each active current limiting device may be a constant current regulator or a current limiting diode. 
     According to one aspect of the invention, an LED lighting device is provided. The LED lighting device includes at least one LED circuit having at least two LEDs connected in series and two sets of connection leads. The first set of connection leads in the device are configured to provide a connection to the at least two—as well as any additional—LEDs in the at least one LED circuit in order to provide a connection to all of the LEDs. The first set of connection leads having a first connection lead and a second connection lead, where the first connection lead is connected to an input of the at least one LED circuit and the second connection lead is connected to an output of the at least one LED circuit. The second set of connection leads in the device include a third connection lead and a fourth connection lead where the third connection lead is connected to the anode of at least one of the at least two LEDs and the fourth connection lead being connected to the cathode of at least one of the at least two LEDs. The second set of connection leads are configured to provide a connection to less than all of the LEDs in the at least one circuit, i.e. only one of two LEDs or only two of four LEDs, etc. 
     According to another aspect of the invention, at least two LEDs may be configured into at least two sets of LEDs connected in series. Each set of LEDs includes at least one LED, and may have multiple LEDs. The first connection leads may be configured to provide a connection to both of the at least a first and a second set of LEDs, while the second connection leads are configured to provide a connection to only one of the first or second set of LEDs. 
     According to another aspect of the invention, the at least one circuit may include at least three LEDs, the at least three LEDs being connected in series between the first and second connection lead. Each the at least three LEDs may be configured into at least three sets of LEDs, each set having at least one, and sometimes multiple, LED(s). When the at least one circuit includes at least three LEDs, the third connection lead may connect the anode of the first LED in one of the first, second or third sets of LEDs, i.e. the anode of the first LED in a particular set. The fourth connection lead may be connected to the cathode of the last LED in the same set of LEDs, i.e. if the third connection lead is connected to the anode of the first LED in the first set, the fourth connection lead may be connected to the cathode of the last LED in the first set. 
     According to another aspect of the invention, the lighting device may be integrated into a lighting system. The lighting system may include a driver having a bridge rectifier, at least two active current limiting devices, and at least three sets of driver connection leads. The first active current limiting device may be connected to the output of the bridge rectifier while the second active current limiting device may be electrically unconnected to the bridge rectifier and the first constant current diode. The first set of driver connection leads may provide a connection for the bridge rectifier to connect to an AC voltage source. The second set of driver connection leads may include a third driver connection lead providing an output from the first active current limiting device connected in series with the output of the bridge rectifier and a fourth driver connection lead providing a return from a load to the bridge rectifier. The third set of driver connections leads may include a fifth driver connection lead providing an input to the second active current limiting device, and a sixth driver connection lead providing an output from the second active current limiting device. When integrating the lighting device, the third driver connection lead may connect to the first connection lead of the lighting device and the fourth driver connection lead may connect to the second connection lead of the lighting device to drive the LED circuit. The fifth driver connection lead may connect to the third connection lead of the lighting device and the sixth driver connection lead may connect to the fourth connection lead of the lighting device to provide a bypass or shunt of the one or more LEDs located between the third and fourth connection leads of the lighting device. 
     According to one aspect of the invention, an LED lighting device is provided. The LED lighting device includes a bridge rectifier and at least one LED circuit having at least two LEDs connected in series across the output of the bridge rectifier. The lighting device includes two sets of connection leads. The first set of connection leads may be configured to provide a connection to the bridge rectifier with a first connection lead and a second connection lead. The first and second connection leads may be connected to provide an electrical input to and output from the bridge rectifier from an AC power source. The second set of connection leads may be configured to provide a connection to at least one of the least two LEDs connected in series across the output of the bridge rectifier. The second set of connection leads include a third connection lead and a fourth connection lead with the third connection lead being connected to the anode of one of the at least two LEDs and the fourth connection lead being connected to the cathode of one of the at least two LEDs. The second set of connection leads may be configured to provide a connection to all or less than all of the LEDs connected in series across the output of the bridge rectifier. The bridge rectifier may be constructed using diodes, LEDs, or some combination thereof. 
     According to one aspect of the invention a method of reducing total harmonic distortion in LED lighting circuits and devices is provided. The method requires that at least two LEDs be connected in series and that a bypass around or shunt at least one of the at least two LEDs connected in series is provided. A substantially constant current may be maintained flowing through at least one LED having while at least one LED is bypassed or shunted. 
     According to another aspect of the invention, an active current limiting device may be used as the bypass or shunt and connected in parallel with at least one of the at least two LEDs to provide the bypass or shunt. The active current limiting device may be a constant current regulator or a current limiting diode. 
     Apparatus and associated methods involve operation of an LED light engine in which relative intensities of selected wavelengths shift as a function of electrical excitation. In an illustrative example, current may be selectively and automatically diverted substantially away from at least one of a number of LEDs arranged in a series circuit until the current or its associated periodic excitation voltage reaches a predetermined threshold level. The diversion current may be smoothly reduced in transition as the excitation current or voltage rises substantially above the predetermined threshold level. A color temperature of the light output may be substantially changed as a predetermined function of the excitation voltage. For example, some embodiments may substantially increase or decrease a color temperature output by a solid state light engine in response to dimming the AC voltage excitation (e.g., by phase-cutting or amplitude modulation). 
     In various examples, selective current diversion within the LED string may extend the input current conduction angle and thereby substantially improve power factor and/or reduce harmonic distortion for AC LED lighting systems. 
     Various embodiments may achieve one or more advantages. For example, some embodiments may substantially reduce harmonic distortion on the AC input current waveform using, for example, very simple, low cost, and low power circuitry. In some embodiments, the additional circuitry to achieve substantially reduced harmonic distortion may include a single transistor, or may further include a second transistor and a current sense element. In some examples, a current sensor may be a resistive element through which a portion of an LED current flows. In some embodiments, significant size and manufacturing cost reductions may be achieved by integrating the harmonic improvement circuitry on a die with one or more LEDs controlled by harmonic improvement circuitry. In certain examples, harmonic improvement circuitry may be integrated with corresponding controlled LEDs on a common die without increasing the number of process steps required to manufacture the LEDs alone. In various embodiments, harmonic distortion of AC input current may be substantially improved for AC driven LED loads, for example, using either half-wave or full-wave rectification. Some implementations may require as few as two transistors and three resistors to provide a controlled bypass path to condition the input content for improved power quality in an AC LED light engine. Some implementations may provide a predetermined increase, decrease, or substantially constant color temperature over a selected range of input excitation. 
     The details of various embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
     Accordingly, embodiments of an LED light engine with selective diversion circuitry may advantageously operate with a power factor substantially above 90%, 92.5%, 95%, 97.5%, or at least above about 98%, for example, and simultaneously achieve a THD substantially below 25%, for example, at the rated excitation voltage. Some embodiments of the AC LED light engine may further be substantially smoothly and continuously dimmable over a full range (e.g., 0-100%) of the applied excitation voltage under amplitude modulation and/or phase controlled modulation. 
     Some embodiments may provide a desired intensity and one or more corresponding color shift characteristics. Some embodiments may substantially reduce cost, size, component count, weight, reliability, and efficiency of a dimmable LED light source. In some embodiments, the selective current diversion circuitry may operate with reduced harmonic distortion and/or power factor on the AC input current waveform using, for example, very simple, low cost, and low power circuitry. Accordingly, some embodiments may reduce energy requirements for illumination, provide desired illumination intensity and color over a biological cycle using a simple dimmer control, and avoid illumination with undesired wavelengths. Some embodiments may advantageously be enclosed in a water-resistant housing to permit cleaning using pressurized cold water sprays. In several embodiments, the housing may be ruggedized, require low cost for materials and assembly, and provide substantial heat sinking to the LED light engine during operation. Various examples may include a lens to supply a substantially uniform and/or directed illumination pattern. Some embodiments may provide simple and low cost installation configurations that may include simple connection to a drop cord. 
     In some embodiments, the additional circuitry to achieve substantially reduced harmonic distortion may include a single transistor, or may further include a second transistor and a current sense element. In some examples, a current sensor may include a resistive element through which a portion of an LED current flows. In some embodiments, significant size and manufacturing cost reductions may be achieved by integrating the harmonic improvement circuitry on a die with one or more LEDs controlled by harmonic improvement circuitry. In certain examples, harmonic improvement circuitry may be integrated with corresponding controlled LEDs on a common die without increasing the number of process steps required to manufacture the LEDs. 
     Parameters to supply a desired AC excitation to an LED based light engine. In some implementations, AC excitation to the light engine may be provided using well-known solid state and/or electro-mechanical methods that may combine AC-DC rectification, DC-DC conversion (e.g., buck-boost, boost, buck, flyback), DC-AC inversion (e.g., half- or fullbridge, transformer coupled), and/or direct AC-AC conversion. Solid state switching techniques may use, for example, resonant (e.g., quasi-resonant, resonant), zero-cross (e.g., zero-current, zero-voltage) switching techniques, alone or in combination with appropriate modulation strategies (e.g., pulse density, pulse width, pulse-skipping, demand, or the like). 
     In an illustrative embodiment, a rectifier may receive an AC (e.g., sinusoidal) voltage and deliver substantially unidirectional current to LED modules arranged in series. An effective turn-on voltage of the LED load may be reduced by diverting current around at least one of the diodes in the string while the AC input voltage is below a predetermined level. In various examples, selective current diversion within the LED string may extend the input current conduction angle and thereby substantially reduce harmonic distortion for AC LED lighting systems. 
     In various embodiments, apparatus and methods may advantageously improve a power factor without introducing substantial resistive dissipation in series with the LED string. For example, by controlled modulation of one or more current paths through selected LEDs at predetermined threshold values of AC excitation, an LED load may provide increased effective turn on forward voltage levels for increased levels of AC excitation. For a given conduction angle, an effective current limiting resistance value to maintain a desired peak input excitation current may be accordingly reduced. 
     Various embodiments may provide substantially reduced light intensity modulation that may contribute to flicker, to the extent it may be potentially perceptible to humans or animals, by operating the LEDs to carry unidirectional current at twice the AC input excitation frequency. For example, a full-wave rectifier may supply 100 or 120 Hz load current (rectified sine wave), respectively, in response to 50 or 60 Hz sinusoidal input voltage excitation. The increased load frequency produces a corresponding increase in the flicker frequency of the illumination, which tends to push the flicker energy toward or beyond the level at which it can be perceived by humans or some animals. Moreover, some embodiments of a light engine with selective current diversion as described herein may substantially increase a conduction angle, which may correspondingly reduce a “dead time” during which no light is output by the LEDs. Such operation may further advantageously mitigate detectable light amplitude modulation effects, if any, in various embodiments. 
     Exemplary apparatus and associated methods may involve a bypass module for modulating conductivity of one or more current paths to provide a first set of LEDs that are conducting near minimum output illumination and having a larger conduction angle than that of a second set of LEDs that conduct at a maximum output illumination. In an illustrative example, the conductivity of a bypass path in parallel with a portion of the second set of LEDs may be reduced while the AC input excitation is above a predetermined threshold voltage or current. 
     In various examples, the current modulation may extend an effective conduction angle of an input excitation current drawn from an electrical source. For example, selective current diversion within the LED string may extend the input current conduction angle and thereby substantially reduce harmonic distortion for AC LED lighting systems. 
     Other advantages and aspects of the present invention will become apparent upon reading the following description of the drawings and detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a block diagram of a constant current regulator which may be used with the invention; 
         FIG. 2A  shows a color temperature controllable LED lighting device as contemplated by the invention; 
         FIG. 2B  shows a color temperature controllable LED lighting device as contemplated by the invention; 
         FIG. 3A  shows a color temperature controllable LED lighting device as contemplated by the invention; 
         FIG. 3B  shows a color temperature controllable LED lighting device as contemplated by the invention; 
         FIG. 4  shows a color temperature controllable LED lighting device as contemplated by the invention; 
         FIG. 5  shows a color temperature controllable LED lighting device as contemplated by the invention; 
         FIG. 6  shows a graphical representation of the forward voltage versus forward current for various colors of LEDs; 
         FIG. 7  shows a graphical representation of the forward current versus the relative luminous flux for various colors of LEDs; 
         FIG. 8  shows a diagram of a lighting system in which the color temperature controllable LED lighting devices of  FIGS. 1-4  may be used; 
         FIG. 9  shows a lighting device having an increased power factor and reduced total harmonic distortion as contemplated by the invention; 
         FIG. 10  shows a lighting device having an increased power factor and reduced total harmonic distortion as contemplated by the invention; 
         FIG. 11  shows a lighting device having an increased power factor and reduced total harmonic distortion as contemplated by the invention; 
         FIG. 12  shows a lighting device having an increased power factor and reduced total harmonic distortion as contemplated by the invention; 
         FIG. 13  shows a lighting device having an increased power factor and reduced total harmonic distortion as contemplated by the invention; 
         FIG. 14  shows a lighting device having multiple power connection leads for increasing power factor and reducing total harmonic distortion as contemplated by the invention; 
         FIG. 15  shows a driver for driving to the device of  FIG. 13 ; 
         FIG. 16  shows a lighting device having multiple power connection leads for increasing power factor and reducing total harmonic distortion as contemplated by the invention; 
         FIG. 17  shows a lighting device having multiple power connection leads for increasing power factor and reducing total harmonic distortion as contemplated by the invention; 
         FIG. 18  shows a graphical representation of an applied voltage and forward current in a known LED lighting device; and, 
         FIG. 19  shows a graphical representation of an applied voltage and forward current in an LED lighting device having an increased power factor and reduced total harmonic distortion as contemplated by the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     While this invention is susceptible to embodiments in many different forms, there is described in detail herein, various embodiments of the invention with the understanding that the present disclosures are to be considered as exemplifications of the principles of the invention and are not intended to limit the broad aspects of the invention to the embodiments illustrated. 
     The present invention is directed to multiple lighting devices or systems, the light emitting circuits contained therein, and methods of driving and operating the same. As discussed herein, a lighting device may include any device capable of emitting light no matter the intention. Examples of lighting devices which are contemplated by this invention include, but are not limited to, LED chips, LED packages, LED chip on board assemblies, LED assemblies or LED modules. The devices may also include any required power connections or leads or contacts, or drivers, required to provide power to the circuits and allow the circuits within the device to emit light. A lighting system may include multiple such devices, and some or all of the required parts to drive such a device or multiple devices, including but not limited to, power supplies, transformers, inverters, rectifiers, sensors or light emitting circuitry discussed herein. While a lighting device may be incorporated into a lighting system or into a lamp or light bulb, it is contemplated that any required light emitting elements may be included within the system directly, whether in the form of a device as a chip or package, or as circuits within the system. 
     The purposes of the devices described herein are twofold, and may be accomplished independent of each other. One intention of the devices described herein is to provide an LED lighting device capable of efficiently and economically emitting light having a selectable color temperature or a warm-on-dim feature when driven with AC power. The second intention of the devices described herein is to provide LED lighting devices which have an improved power factor and a reduced total harmonic distortion when powered with AC power. 
     In order to achieve either of the goals of the devices described herein, it may be necessary to include one or more active current limiting devices within each LED lighting device, regardless of whether the device is designed to allow color temperature control, increase power factor while reducing THD, or both. While any known current limiting device which sets a substantially upper limit on the current which is allowed to flow through a circuit may be used with any of the circuits or devices described herein, the devices in the present application will primarily discuss using a constant current regulator (CCR), like for example those sold by ON Semiconductor or operating having the internal structures as shown in the block diagram of  FIG. 1 , and a current limiting or current controlled diode (CLD). Both CCRs and CLDs actively limit the current flowing through a particular circuit or device by substantially limiting the current to, and maintaining the current at, a threshold level once the current in a connected circuit or device has reached or exceeded a particular value. Using such devices is advantageous over using current limiting resistors insofar as CCRs and CLDs both cap the total current which is allowed to flow through a connected circuit or device, while the resistor only acts to reduce any every climbing current. With a current limiting resistor, as the input voltage to the circuit continues to increase, the current will likewise continue to increase without limit, albeit it at a lower value than without the resistor. With a CCR or a CLD, once the current reaches a threshold maximum, the current will remain substantially constant until the input voltage is reduced, even if the input voltage continues to climb. As will be described herein, in some cases the combination of a CCR or CLD and a current limiting resistor may be beneficial or required. 
     While both CCRs and CLDs may be used interchangeably to accomplish the goals of the devices described herein, there are differences between the devices. The primary difference between the devices is that CCRs, like those sold by ON Semiconductor, typically have internal transistor based control circuits and have little or no turn on voltage. CLDs are a form of a diode which are based in part on a JFET having a gate shorted to the power source and have a measurable turn on voltage. While the CLDs may be utilized with any of the devices described herein, it may be advantageous to use a CCR when possible in order to avoid the additional turn on voltage requirements of the CLD. However, CCRs and CLDs may be used interchangeably to accomplish the goals of the invention. 
       FIGS. 2-5  show exemplary LED lighting devices capable of emitting color temperature controlled light. As seen in  FIG. 2A , lighting device  10  includes at least two LED circuits  12 ,  14  which are connected in parallel. Each LED circuit  12 ,  14  includes one or more LEDs  16 ,  18  respectively. Each LED circuit  12 ,  14  has a different forward operating voltage and is capable of emitting light having one or more of a different color or a different wavelength than the other circuit. For example, LED circuit  12  may emit amber or yellow light, while LED circuit  14  emits white or blue light. In order to limit the current within either LED circuit  12 ,  14 , an active current limiting device such as a CCR or CLD, shown as CCR  20  connected in series with at least one LED  16  in first circuit  12 , may be provided. As seen in  FIG. 2B , additional active current limiting devices, like for example CCR  22 , may be added to the device so that each LED circuit is connected in series with an active current limiting device. LED device  10  may further include connection leads  24 ,  26  for connecting the device to an AC power source, like for example mains power or a switch or dimmer connected to mains power. In order to fully utilize AC power and produce a substantially constant light output, device  10  and/or circuits  12 ,  14  should be configured such that each circuit  12 ,  14  is capable of emitting light during both a positive and negative phase of the provided AC voltage. 
     In devices where one or both of LED circuits  12 ,  14  include only a single LED, or, as shown in  FIGS. 2A and 2B  a series string of LEDs  16 ,  18  respectively, in order to insure each circuit emits light during both the positive and negative phase of the provided AC power device  10  may include bridge rectifier  28 . The electrical inputs of bridge rectifier  28  may connect directly to leads  24 ,  26 , while the output and return of the bridge rectifier connects to parallel circuits  12 ,  14 , providing rectified AC power to each circuit. Providing the rectified power insures that each circuit is capable of emitting light during both the positive and negative when device  10  is electrically connected to an AC power source. When utilized herein, unless otherwise noted, connecting an LED circuit across the output of a bridge rectifier refers to connecting the LED circuit to both the output and return of the bridge rectifier, such that the circuit receives power from the output of the bridge rectifier at one end and has a return path to the return of the bridge rectifier, effectively creating a closed loop between the LED circuit and the bridge rectifier. 
     While single LEDs or series strings like LED circuits  12 ,  14  may require device  10  to include a bridge rectifier to utilize both phases of connected AC power, one or more of circuits  12 ,  14  may be modified to use direct AC power without the requirement of rectification. For example, as seen in  FIGS. 3A and 3B , device  10 ′ may include LED circuits  12 ′,  14 ′ where each circuit includes at least one LED  16 ′,  18 ′ respectively, connected in an antiparallel configuration. With LEDs  16 ′,  18 ′ connected in an anti-parallel configuration, LED circuits  12 ′,  14 ′ are capable of emitting light during both phases of AC power without the need for rectification as each circuit has one or more LEDs configured to use both the positive and negative phase of a connected AC power source. As a result, circuits  12 ′,  14 ′ may be directly connected to leads  24 ′,  26 ′ as shown in  FIGS. 3A and 3B  without an intervening rectifier. When utilizing an anti-parallel configuration, however, in order to protect the LEDs during both phases of AC power in at least one of circuit  12 ′,  14 ′, more than one active current limiting device may be required. For example, as seen in  FIG. 3A , each anti-parallel branch in circuit  12 ′ (or  14 ′) may include an active current limiting device, which may be either a CCR or CLDs  30 ′. Rather than connect one current limiting device in series with each branch of anti-parallel circuit  12 ′, back-to-back CLDs or CCRs may be attached at one end of the circuit, between circuit  12 ′ and either lead  24 ′ or  26 ′ as seen in  FIG. 3B . Inasmuch as both CLDs and CCRs have very low reverse breakdown characteristics, it is possible to connect CLDs or CCRs in a back-to-back fashion and realize the current protecting features of the forward-biased CLD or CCR. 
     Other circuit configurations which may directly use AC power may be utilized in the LED lighting device as well. For example, rather than use a separate bridge rectifier connected to circuits having a single LED or series string of LEDs, one or more of the LED circuits may be configured in a bridge rectifier configuration with an additional diode, LED, CLD or CCR connected across the output of the rectifier. As seen in  FIG. 4  LED lighting device  10 ″ may include circuits  12 ″,  14 ″ which each include at least five diodes, at least four of the diodes being LEDs  16 ″,  18 ″ respectively. LEDs  16 ″,  18 ″ may be configured in a bridge rectifier configuration with a fifth diode, which may be a standard diode, LED  32 ″ as shown in circuit  12 ″, or CLD  30 ″ as shown in circuit  14 ″. Configuring circuit  10 ″ in a bridge configuration with a diode, LED, or active current limiting device across the output of the rectifier allows for AC power to be used during both the positive and negative phase when provided to device  10 ″. As a result, like the device shown in  10 ′, circuits  12 ″,  14 ″ may be directly connected to connection leads  24 ″,  26 ″ without an intervening bridge rectifier. As seen in each circuit, unlike the circuits shown in  FIG. 2 , a single active current limiting device may be used to protect each of circuit  12 ″,  14 ″ if it is located across the output of each rectifier circuit. Inasmuch as current will flow through the at least fifth diode during both the positive and negative phases, placing the active current limiting device in series with the at least fifth diode (or making the at least fifth diode the active current limiting device) will insure that current during both phases of provided AC power flows through the current limiting device, effectively limiting the current for each LED within the circuit. 
     In order to further protect the LEDs in a circuit directly using AC power, each circuit in the LED lighting device may be configured in an imbalanced bridge configuration. As seen in  FIG. 5 , device  10 ′″ may include circuits  12 ′″,  14 ′″ which each include at least diodes, at least six of which are LEDs connected in an imbalanced bridge configuration. The imbalanced bridge configuration-will act substantially similar to, and have substantially the same characteristics as the circuits described in  FIG. 4  with the added benefit of reverse breakdown protection for the LEDs forming the bridge. In order to imbalance the bridge, at least one additional LED is placed in series with one input LED (shown as the left branch of circuits  12 ′″,  14 ′″) than the other input LED, and at least one additional LED is placed in series with the opposing output LED (output LED during the opposite phase) than the aligned output LED. Configuring the LEDs forming the bridge in this manner helps reduce reverse breakdown of any of the LEDs in the circuit. Like a standard bridge, the cross-connecting branch across the output of the imbalanced bridge may be a standard diode, LED  32 ′″, CLD  30 ′″, or some combination thereof. 
     While  FIGS. 2-5  show each of the aforementioned circuits in pairs, it is contemplated that the circuits disclosed in each FIG. may be mixed and matched within a single device as desired. For example, an LED lighting device may be made using circuits  12 ,  14 ″ or  12 ′,  14 ′″. Additional circuits may further be connected in parallel within a single device, the additional circuits having a different forward operating voltage than the other connected circuits, and each additional circuit being capable of emitting light of a different color than the other connected LED circuits within the device. The additional circuits may be configured in any manner shown in  FIGS. 2-5  and connected to or include any rectifiers or connection leads as needed to receive power and emit light during both phases of any provided AC power. 
     Regardless of how many circuits are connected in parallel and the configuration of each circuit, any circuits forming an LED lighting device, along with the at least one active current limiting device, the connection leads and any required rectifiers or additional current limiting devices may be integrated on a single substrate  33  ( FIGS. 2A, 2B ),  33 ′ ( FIGS. 3A, 3B ),  33 ″ ( FIG. 4 ), or  33 ′″ ( FIG. 5 ). The single substrate may then be directly incorporated into a lighting system or fixture, or a lamp or light bulb as desired. 
     While any known method for creating LED circuits capable of emitting light of a different color within a single device is contemplated by the invention, two examples will be discussed herein. 
     The first method by which the light emitted by each circuit may be made different is by using a different phosphor coating on each circuit. When using a phosphor coating, the color of the LEDs used in each circuit, for example LEDs  16 ,  18  in  FIG. 2A , may emit a substantially similar color, like for example blue, or different colors, as the phosphor coating substantially creating the different colors of emission light for each circuit. Though the device and circuits of  FIG. 2A  will be used for examples herein, it should be appreciated that the devices and circuits of  FIG. 2B-5 , or any combination of circuits as discussed above, may be used in substantially the same manner to achieve substantially the same effect. 
     In order to create different forward operating voltages when using a phosphor coating, different colored LEDs having a different turn on voltage may be used, or the circuits may utilize a different number of similar colored LEDs. For example, a first circuit, like circuit  12  in  FIG. 2A , may include five blue LEDs and be coated in yellow or amber phosphor, while circuit  14  may include 10 blue LEDs and be coated in white phosphor. Since the first circuit includes fewer LEDs, it will begin operating first as it will have a lower turn on voltage, causing the emission of light by device  10  substantially equal to the color of the phosphor coating on circuit  12 , or yellow or amber. As the voltage provided to device  10  increases, the current flowing through circuit  12  will increase, causing the yellow or amber light to more brightly emit. The current flowing through circuit  12  will continue to increase until the current threshold of the at least one active current limiting device (CCR  20 ) connected in series therewith is reached. It should be noted that when only a single active current limiting device is used, it is important that the current limiting device be connected to the circuit having the lower turn on voltage in order to protect and prevent the LEDs of the circuit from overdriving as the voltage is increased to turn on and intensify the LEDs of the LED circuit having the higher turn on voltage. 
     Using the example of a five “blue LED circuit coated in yellow or amber phosphor and a ten blue LED circuit coated in white phosphor for circuits  12 ,  14  given above, as is known in the art, each blue LED has a turn on voltage of approximately 2.2V and will reach a nominal operating current at approximately 3.2V. The total turn on voltage for circuit  12  having five blue LEDs would therefore be approximately 11V (2.2V time five LEDs) while the nominal current would reached at approximately 16V. The turn on voltage for circuit  14  would be approximately 22V with the nominal current being reached at approximately 32V. Using this example, as voltage is applied to device  10  in  FIG. 2A , once the applied voltage reaches 11V (assuming a CCR is connected as the active current limiting device, otherwise slightly higher than 11V if a CLD is used), LEDs  16  of circuit  12  will begin to emit light, which will be yellow or amber as a result of the phosphor coating applied to the circuit. The brightness of the light emitted by device  10  and circuit  12  will increase until the current flowing through circuit  12  reaches the maximum threshold of CCR  20 . If the maximum threshold current of CCR  20  is matched to nominal current of LEDs  16 , this means that the current will be capped once 16V input is reached, which is well below the turn on or voltage for nominal current in circuit  14 . Having the CCR connected in series with circuit  12  will prevent the overdrive of LEDs  16 , protecting them from early burnout resulting from overdrive or overheating as the voltage increases to turn on circuit  14 . 
     Once the input voltage is increased to 22V, LEDs  18  of circuit  14  will begin emitting white light as a result of the white phosphor coating. As circuit  14  begins emitting white light, the combination of yellow or amber and white light will be emitted by device  10 , causing the color temperature to begin moving towards the cooler end of the color spectrum. As the voltage continues to increase to device  10 , the amount of white light mixed in with the already fully emitted yellow or amber light will continue to increase as the current in circuit  14  increases, causing the color temperature to become cooler and cooler. As is shown in  FIG. 2B , an additional or second active current limiting device may be included in device  10 , CCR  22 , which may limit the current within circuit  14  to the nominal current which will be reached at approximately 32V. Using this example, if CCR  22  is used in device IO, the maximum light output of device  10  will be reached at 32V along with the coolest possible temperature color. If the provided voltage increases over 32V, substantially no additional current will flow through either circuit, setting the uppermost light output of each circuit. When the voltage begins to be reduced and device  10  is dimmed, once the voltage begins falling below 32V, circuit  14  will begin emitting less white colored light as the current will drop below nominal level. As the current in circuit  14  decreases and circuit  14  dims, the light emitted by device  10  will both dim and become warmer as the yellow or amber component will become a larger percentage of the light emitted. Eventually at approximately 22V, circuit  14  will turn off and the only light emitted by device  10  will come from circuit  12 , providing less light and creating a warmer yellow or amber light than when both circuit  12  and  14  were emitting light. 
     By using a set amount of LEDs in each LED circuit and setting the current at a level for one or more of the circuits, the amount of each color of light emitted by the device may be controlled by controlling the input voltage, and the color temperature change and light intensity characteristics can be known and tailored to a desired output. 
     The second method by which the color of the light emitted by the circuits may be made different is by using different colored LEDs in each circuit. The different colored LEDs will emit light of different colors, thereby causing each circuit to emit light of different colors. However, rather than using different numbers of LEDs to different forward operating voltages, the turn on voltage characteristics of the different colored LEDs may utilized to create the difference depending on the colors of the LEDs in the circuits. As is known in the art, there are two common turn on voltages for LEDs emitting colored light. The first turn on voltage is approximately 1.5V for InP diodes which are typically red, amber and yellow LEDs which each reach their nominal operating current at about 2.2V. The second turn on voltage is approximately 2.2V for GaN diodes which are typically green or blue which reach their nominal operating current at about 3.2V. 
     When using different colored LEDs, in order to create the amber-white device like that described above, circuit  12  may include five LEDs  16  which emit amber light while circuit  14  may include five LEDs  18  which emit blue light and are coated in white phosphor. Using this example, circuit  12  will begin emitting light at approximately 7.5V (again, if a CCR is connected in series, and at a higher voltage if a CLD is used) and reach nominal current at approximately 11V. Circuit  14  will begin emitting light at 11V but will not reach nominal current until approximately 16V. As circuit  12  begins to emit, a low level of amber light will be emitted by device  10  until the current value of the series active current limiting device is reached. The active current limiting device connected in series with the LEDs of circuit  12  may be set to prevent the current from rising higher than the nominal current value for the circuit, effectively fixing the intensity of light emitted by circuit  12  while protecting the one or more LEDs therein from overdrive as the voltage increases. As the voltage increases to 11V, circuit  14  will begin emitting white light, cooling the color temperature of the light emitted by device  10 . The cooling will continue until either the voltage stops rising, or an active current limiting device connected in series with circuit  14  prevents the current flowing through circuit  14  from rising higher. As the voltage is decreased, the current and intensity of light emitted by circuit  14  will fall, causing the light to both dim and become warmer as the amount of light emitted from the amber LEDs will provide a greater percentage of the light emitted, creating a wanner color temperature colored light. At approximately 11V circuit  14  will turn off, and only circuit  12  and the amber LEDs will continue to emit light, creating a warmer and dimmer light as only the amber colored LEDs will be emitting light at this voltage. As the voltage continues to drop towards 7.5V, the amber LEDs will become dimmer and eventually turn off. 
       FIGS. 6 and 7  show the forward operating voltage and current characteristics for red (lines indicated by  34 ), blue (lines indicated by  36 ), and green (lines indicated by  38 ) LEDs. These graphical representations of the forward voltage for each LED vs. the forward operating current for each LED and the forward operating current for each LED vs. the luminous flux of each LED show the operating characteristics of different colored LEDs and the importance of connecting an active current limiting device in series with at least the lowest turn on voltage in the, device. As seen in  FIG. 7 , each LED color reaches approximately 100% relative luminous flux, i.e. nominal flux, at around 350 mA. Less current than this will cause the LEDs to emit less than 100% flux while more current will overdrive the LEDs, causing more than 100% flux and unwanted heat and eventual breakdown or premature failure.  FIG. 5  shows that red LEDs typically reach 350 mA around 2.2V (which is substantially similar for yellow or amber LEDs), blue LEDs around 3.1V, and green LEDs around 3.3V. Using the example above with circuit  12  having five amber LEDs and circuit  14  having five blue LEDs and being coated in white phosphor, by the time the blue LEDs reach nominal current and luminosity, approximately 15.5V-16V will be applied to each of circuit  12 ,  14  as they are connected in parallel. Assuming each amber LED will have an approximately equal amount of voltage across it, this means that each amber LED will have approximately 3.1V-3.2V like the blue LEDs. As seen in  FIG. 6 , this will cause a current of greater than 1000 mA to flow through each amber LED, and as seen in  FIG. 7  cause of luminous flux of greater than 200%. This places the amber LEDs at significant risk for overheating and overdriving, causing potential premature failure of the LEDs. By placing the active current limiting device in series with circuit  12 , the current is effectively limited at the selected value, i.e. the nominal value, and as the voltage applied to circuit  12  increases, the circuits are current limited and the one or more LEDs therein are protected. However, as seen in  FIG. 6 , slight variations in voltage across each LED can cause significant increases in the current through each LED. Therefore, it may be advantageous to place an active current limiting device in series with each LED circuit in the device, in order to protect each circuit against increases or spikes in voltage. 
     In order to control the power provided to device  10 , and therefore the voltage and current provided to each circuit and the overall color temperature of the light emitted by device  10  (or  10 ′,  10 ″,  10 ′″), the power provided to device  10  may be adjusted and controlled using any means known in the art. For example, device  10  may be integrated into a lighting system or fixture  40  having a dimmer switch providing the AC power to device  10 . As seen in  FIG. 8 , dimmer switch  42  may be connected to AC power source  44 , which may be, for example, mains power or a dimmer switch connected to mains power, and may be used to control the voltage provided to device  10 . The dimmer switch may be any known in the art, like for example, a phase dimmer switch. The dimmer switch may be used to control the voltage to the circuit, causing more or less voltage to be applied to device  10 . As the dimmer switch is turned to provide more voltage to the circuit, circuit  12  which may have amber colored LEDs or be coated in amber phosphor may be turned on and increased in intensity. As the switch continues to be turned and provide more power and voltage to the device, circuit  14 , which may have blue LEDs or be coated in white phosphor, will turn on and add to the intensity of light emitted by device  10 . As the dimmer switch is continually turned up and the light emitted by circuit  14  increases, the intensity of the light emitted by device  10  will increase while the color temperature decreases. When dimmer switch  42  is finally turned down and less voltage is provided to device  10 , eventually circuit  14  will begin decreasing in intensity, causing the circuit  12  to produce a greater percentage of the light emitted by device  10 , causing the light to have a warmer color temperature. 
     While the circuits, devices and systems described above will provide an AC LED lighting device option having the ability warm on dim, AC LED devices may be further or alternatively enhanced by increasing the power factor and reducing the total harmonic distortion (THD) of the devices and light emitting circuits therein. 
       FIGS. 9-13  show LED lighting devices which have both an increased power factor and a reduced THD regardless of the color of the LEDs contained therein. As seen in  FIG. 9 , device  100  includes at least one LED circuit, LED circuit I  02 , having at least two or more LEDs, LEDs  104 ,  106 ,  108 , connected in series. Connected in parallel with at least one of the LEDs, shown as LEDs  106 , is an active current limiting device, shown as CCR  110 . As discussed throughout, though a CCR may be advantageous due to its low or non-existent turn on voltage, using a CLD may replace CCR and accomplish similar results. When using a CLD, however, the turn on voltage of the CLD will at least somewhat lower the power factor gains and reduction of THD realized by using a CCR. When connected in parallel with LEDs  106  (and any additional LEDs), the active current limiting device will provide a current bypass around the LEDs until the turn on voltage for the bypassed or shunted LEDs is reached. This will allow LEDs  104 ,  108  in circuit  102  to turn on earlier than if all LEDs had to be turned on before any LEDs emit light when a voltage is applied to connection leads  112 ,  114 , increasing the power factor of the circuit. For as long as the active current limiting device is utilized to bypass or shunt LEDs  106 , the current flowing through LEDs  104 ,  108  will be effectively limited and controlled. The controlled current will protect LEDs  104 ,  108  as the voltage is increased to turn on LEDs  106  and substantially reduce the effect of any harmonic currents created by the non-linear reacting LEDs. The harmonic currents and current gains and non-linearity can be effectively reduced by controlling a threshold amount current flowing through the circuit until the additional LEDs are ready to turn on. As with color temperature controlled LED lighting devices, all elements of any low THD LED lighting devices may be integrated on a single substrate  115 , not matter the configuration and elements included within the device. 
     While CCR  110  will help keep the current limited to a threshold value while LEDs  106  are bypassed, once the input voltage to device  100  reaches a level where LEDs  106  will turn on with LEDs  104 ,  108 , the current will be allowed to increase unimpeded through circuit  102  as current will substantially flow through LEDs  104 ,  106 ,  108  without a limiter in place to maintain the current. In order to protect all the LEDs in circuit  102  once LEDs  106  reach their turn on voltage, a second active current limiting device, shown in  FIG. 9  as CLD  116  though it may advantageously be a CCR substantially eliminating any turn on voltage, and/or a current limiting resistor  118  (as shown in  FIG. 10  for example) may be connected in series with LEDs  104 ,  106 ,  108  and formed as part of circuit  102 . The additional current limiting device or current limiting resistor will help keep the current in the circuit down once LEDs  106  turn on, with the active current limiting device having the added benefit of creating an upper threshold of current flowing through the circuit. 
     While circuit  102  in  FIGS. 9 and 10  are capable of being driven off of DC power, in order to connect and drive device  100  with AC power where THD and power factor present a greater problem, like for example mains power, device  100  may be integrated into a system or connected to a driver having a bridge rectifier, wherein rectified power is provided to circuit  102  through connection leads  112 ,  114 . Alternatively, an additional circuit substantially identical to circuit  102  may be connected to circuit  102  in an anti-parallel configuration (like for example circuits  12 ″ in  FIG. 3A ) to utilize both the positive and negative phases of a supplied AC power. Each circuit may then have a connection to leads  112 ,  114  to receive a provided AC power and operate during its respective phase. 
     Alternatively, as seen in  FIGS. 12 and 13 , device  100 ′ may include a bridge rectifier  120  or  122  with circuit  102  connected across the output, either internally or externally. When a bridge rectifier is incorporated into the device, leads  112 ,  114  may connect to the inputs of the rectifier, allowing the rectifier to receive AC power from an AC power source. Circuit  102  may then connect across the output of the rectifier, receiving and utilizing the rectified AC power. The bridge rectifier may be made using standard diodes, LEDs or some combination thereof. 
     As seen in  FIG. 11 , a THD lowering active current device may be utilized in devices having color changing LEDs as well. As seen in  FIG. 11 , circuits  124 ,  126  may be substantially identical and placed in parallel with each other. Like circuits  12 ,  14  in  FIG. 2A , for example, circuit  124 ,  126  may each have a different forward operating voltage and be capable of emitting light of a different color. Circuits  124 ,  126  may be incorporated into a system or driven by a driver having a bridge rectifier, or may be used to replace any of circuits  12 ,  14  or  12 ′,  14 ′ in  FIGS. 2-3 . The parallel current limiting device in each circuit will have substantially the same effect as described above, allowing some of the LEDs in the lower voltage circuit to turn on at a lower voltage than all of the LEDs, and reduce the harmonic distortion current resulting from the non-linearity of the LEDs. A portion of the LEDs in the higher voltage circuit may likewise turn on earlier, creating further temperature control as more intermediate levels of color may be realized as only some LEDs in the higher voltage circuit may turn on at first before all LEDs in the higher voltage circuit turn on. This configuration may allow for some or all LEDS in the lower voltage circuit to turn on, followed by some LEDs in the higher voltage circuit to turn on, beginning a cooling or warming of the light emitted by the device before all the LEDs are turned on. Eventually, shunted LEDs will turn on, further cooling or warming the light emitted by the device as it provided power and voltage increase. 
     An example of a driver and alternative lighting device which may be used to create a lower THD LED lighting device when driven with AC power may be seen in  FIGS. 14 and 15 . As seen in  FIG. 14 , LED lighting device  200  may include LED circuit  202  having at least two LEDs, shown as LEDs  204  connected in series. Device  200  may include a first set of connection leads  206 ,  208  which are connected to the input and output of circuit  202 , effectively providing a connection to all of the LEDs within the circuit. A second set of connection leads  210 ,  212  may be provided as well. Connection leads  210 ,  212  may provide a connection to the anode of one LED and a connection to the cathode of one LED respectively. Connection leads  210 ,  212  may be configured, as seen in  FIG. 14 , to provide a connection to less than all of the LEDs in circuit  202 . The first set of connection leads may be used to receive and return power for circuit  202 , while the second set of connection leads may be used to connect a bypass or shunt, like for example an active current limiting device, to a subset or a portion of the LEDs forming circuit  202 . Though shown as extending outside device  200 , it should be understood that where power connections are used herein, whether with device  200 , driver  220 , or alternative devices  200 ′, that any power connections may extend outside the device or include contacts formed as a portion of the device on or inside the substrate. 
     Each group of LEDs located either inside or outside the second set of connection leads may get categorized as a group, and may include additional connection leads as needed. For example, group  214  may comprise a first set of LEDs, group  216  may comprise a second group of LEDs and group  218  may comprise a third group of LEDs. Though shown in  FIG. 14  as providing a connection to group  216 , it should be appreciated that connection leads  210 ,  212  may be moved to provide a connection to group  214  or group  218 . A third set of connection leads may also be provided to provide a connection to a second group, to create a further bypass or shunt if needed. 
     Providing device  200  with second connection leads  210 ,  212  instead of a fixed active current limiting device allows for an end user to better control the current that will flow through circuit  202  when the LEDs between connection leads  210 ,  212  are bypassed or shunted. The connection leads will allow an end user to select a driver or active current limiting bypass which will allow a particular amount of current to flow through the non bypassed LEDs to create a desired level of luminance from device  200 . Creating devices  200  with connection leads instead of bypasses also allows for different LED circuits to be connected to the same bypass or driver if the light needs of device  200  change. For example, device  200  may initially include a circuit which includes 20 LEDs, 10 of which are bypassed, but now requires a circuit of 40 LEDs, 10 of which are bypassed, to provide more light. Rather than have to buy a new LED lighting device having the active current limiting device already incorporated into the device, which may be more costly, the end user would be able to purchase a new LED lighting device having connection leads capable of connecting some of the LEDs to an active current limiting device the end user already has. Such is particularly advantageous if the LEDs in the lighting device fail before the active current limiting device, as a cheaper LED lighting device may be purchased to replace the failed device and the still operational current limiting device may be utilized with the new LED lighting device. Likewise, if the driver or bypass or shunt active current limiting device fails, the LED lighting device may be disconnected from the failed driver or bypass and be re-used with a new driver or bypass. 
     In order to drive device  200  in  FIG. 14 , device  200  should be integrated into a lighting system or fixture having a driver having a bridge rectifier and one or more active current limiting devices. An exemplary driver can be seen in  FIG. 15 . As seen in  FIG. 15 , driver  220  may include bridge rectifier  222  and at least two active current limiting devices, shown as CCRs  224 ,  226 . CCR  224  may be connected to an output of the bridge rectifier to control any current flowing from the bridge rectifier, while CCR  226  may be electrically unconnected to both the bridge rectifier and CCR  224  to effectively be able to provide a bypass or shunt for LEDs in circuit  202 . In order to receive and provide power, and provide an effective bypass, driver  220  may include three sets of driver connection leads. A first set of driver connection leads  228 ,  230  may be utilized to provide a connection between the bridge rectifier and an AC power source. A second set of driver connection leads  232 ,  234  may be used to connect the rectifier and associated CCR to the circuit. Connection lead  232  may, for example, extend from the output of CCR  224  and connect to connection lead  206  of device  200  to provide rectified AC power from rectifier  222  to circuit  202 . Connection lead  234  may, for example, extend from the return of rectifier  222 , and connect to connection lead  208  of circuit  202  to receive a return form circuit  202  to complete the circuit. Connecting leads  232 ,  234  and  206 ,  208  in this manner will provide power to each LED and active current limiting device in circuit  202  and enable the circuit to be driven. 
     In order to provide a bypass or shunt for one or more of the LEDs in circuit  202 , the third set of connection leads  236 ,  238  in driver  220  should connect to the input and output of CCR  226  respectively. Connection lead  236  may then connect to connection lead  210  while connection lead  238  connects to connection  212  to effectively provide a bypass around the LEDs connected between leads  210 ,  212  in circuit  202 . Since CCR  226  is electrically unconnected to rectifier  222  and CCR  224 , it will effectively act as a bypass when connected across one or more of the LEDs in circuit  202  in a substantially identical manner as bypass CCR  110  does in  FIG. 9 . 
     As seen in  FIGS. 16 and 17 , the bypass connections may likewise be utilized in circuit  100 ′ with a first set of connection leads  210 ′,  212 ′ being connected to the inputs of the bridge rectifier and one or more of the LEDs  250 ′ connected across the output of the bridge rectifier being connected to a second set of connection leads  214 ′,  216 ′ in device  200 ′. Such a configuration would allow an end user to select a bypass of choice, with particular current limiting characteristics for driving any LEDs formed as part of the bridge rectifier  248 ′, and/or any LEDs  250 ′ connected across the output of the rectifier which are not bypassed by the parallel current limiting device. As described above, connection leads may also help keep the costs of the device down as end users will be able to purchase a separate active current limiting device and use it with multiple rectifier devices. 
     Regardless of whether an active current limiting bypass is incorporated into a device, like in  FIGS. 9-13 , or is externally connected to connection leads like in  FIGS. 14, 16, and 17 , it has been found by the inventors that the ratio of circuit efficiency is inversely proportional to the THD realized by the circuit as more or less LEDs are bypassed. For example, in a circuit having 20 LEDs, if five are bypassed the circuit may be highly efficient but realize a smaller reduction in THD. If 15 LEDs are bypassed, the circuit may be less efficient, but have a greater reduction in THD. It is therefore contemplated that the number of the two or more LEDs which are bypassed in any given circuit may be adjusted to match the desired characteristics of the end user of the lighting device. If a more efficient light is desired, then a device having fewer bypassed LEDs may be provided, while if lower THD is required a device having more LEDs bypassed may be provided. This inverse reaction to more or less LEDs being bypassed provides a further advantage to using devices having connection leads which attach to external active current limiting device bypasses, as it allows an end user to use a single active current limiting device to bypass different LED devices which may operate with greater efficiency or lower THD as is currently needed by the end user. 
     The improvement of any circuit using an active current limiting device bypass, again regardless of whether it is integrated within the device or externally connected, can be seen in  FIGS. 18 and 19 .  FIG. 18  shows curve  240  which represents an AC input voltage to a known LED lighting device not using an active current limiting bypass and instead using a current limiting resistor, for example, and the current response curve  242  of the same device.  FIG. 19  shows the same two curves, curve  244  showing an AC input voltage and curve  246  showing current, when a device having an identical number of LEDs to the circuit producing the curve in  FIG. 18  is used with an active current limiting bypass as described herein. As seen in  FIGS. 18 and 19 , utilizing the bypass in the present invention increases power factor, as current begins flowing through the device much closer to the voltage turn on point when a bypass is used than when it is not. This better power factor is the result of the device having the bypass circuit beginning to emit light much earlier as only enough voltage to turn on the non-bypassed (and CLD if used instead of a CCR) is required for the device to begin emitting light. If each circuit includes 20 LEDs which each turn on at 2.2V, for example, and 10 LEDs are bypassed in a circuit and device as described herein, it will turn on once the provided AC voltage reaches 22V whereas the device not having the bypass will not turn on until provided AC voltage reaches 44V. The bypass allows the device to turn on much earlier, allowing light to be emitted much earlier in the provided voltage waveform, i.e. increasing the power factor. As a result of the bypass, the current response using a bypass also has a substantially reduced THD, as the current waveform better approximates the provided AC voltage. 
     While the foregoing there has set forth embodiments of the invention, it is to be understood that the present invention may be embodied in other forms without departing from the spirit or central characteristics thereof. The present embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. While specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the characteristics of the invention and the scope of protection is only limited by the scope of the accompanying claims.