Patent Publication Number: US-9426866-B2

Title: Lighting system with lighting dimmer output mapping

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e) and 37 C.F.R. §1.78 of U.S. Provisional Application No. 60/894,295, filed Mar. 12, 2007 and entitled “Lighting Fixture”. U.S. Provisional Application No. 60/894,295 includes exemplary systems and methods and is incorporated by reference in its entirety. 
     U.S. Provisional Application No. 60/909,458 entitled “Ballast for Light Emitting Diode Light Sources”, inventor John L. Melanson, and filed on Apr. 1, 2007 describes exemplary methods and systems and is incorporated by reference in its entirety. 
     U.S. patent application Ser. No. 11/695,023 entitled “Color Variations in a Dimmable Lighting Device with Stable Color Temperature Light Sources”, inventor John L. Melanson, and filed on Apr. 1, 2007 describes exemplary methods and systems and is incorporated by reference in its entirety. 
     U.S. Provisional Application No. 60/909,457 entitled “Multi-Function Duty Cycle Modifier”, inventors John L. Melanson and John Paulos, and filed on Apr. 1, 2007 describes exemplary methods and systems and is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to the field of electronics, and more specifically to a system and method for mapping an output of a lighting dimmer in a lighting system to predetermined lighting output functions. 
     2. Description of the Related Art 
     Commercially practical incandescent light bulbs have been available for over 100 years. However, other light sources show promise as commercially viable alternatives to the incandescent light bulb. Gas discharge light sources, such as fluorescent, mercury vapor, low pressure sodium, and high pressure sodium lights and electroluminescent light sources, such as a light emitting diode (LED), represent two categories of light source alternatives to incandescent lights. LEDs are becoming particularly attractive as main stream light sources in part because of energy savings through high efficiency light output and environmental incentives such as the reduction of mercury. 
     Incandescent lights generate light by passing current through a filament located within a vacuum chamber. The current causes the filament to heat and produce light. The filament produces more heat as more current passes through the filament. For a clear vacuum chamber, the temperature of the filament determines the color of the light. A lower temperature results in yellowish tinted light and a high temperature results in a bluer, whiter light. 
     Gas discharge lamps include a housing that encloses gas. The housing is terminated by two electrodes. The electrodes are charged to create a voltage difference between the electrodes. The charged electrodes heat and cause the enclosed gas to ionize. The ionized gas produces light. Fluorescent lights contain mercury vapor that produces ultraviolet light. The housing interior of the fluorescent lights include a phosphor coating to convert the ultraviolet light into visible light. 
     LEDs are semiconductor devices and are driven by direct current. The lumen output intensity (i.e. brightness) of the LED varies approximately in direct proportion to the current flowing through the LED. Thus, increasing current supplied to an LED increases the intensity of the LED, and decreasing current supplied to the LED dims the LED. Current can be modified by either directly reducing the direct current level to the white LEDs or by reducing the average current through pulse width modulation. 
     Dimming a light source saves energy when operating a light source and also allows a user to adjust the intensity of the light source to a desired level. Many facilities, such as homes and buildings, include light source dimming circuits (referred to herein as a “dimmer”). 
       FIG. 1A  depicts a lighting circuit  100  with a conventional dimmer  102  for dimming incandescent light source  104  in response to inputs to variable resistor  106 . The dimmer  102 , light source  104 , and voltage source  108  are connected in series. Voltage source  108  supplies alternating current at line voltage V line . The line voltage V line  can vary depending upon geographic location. The line voltage V line  is typically 110-120 Vac or 220-240 Vac with a typical frequency of 60 Hz or 70 Hz. Instead of diverting energy from the light source  104  into a resistor, dimmer  102  switches the light source  104  off and on many times every second to reduce the total amount of energy provided to light source  104 . A user can select the resistance of variable resistor  106  and, thus, adjust the charge time of capacitor  110 . A second, fixed resistor  112  provides a minimum resistance when the variable resistor  106  is set to 0 ohms. When capacitor  110  charges to a voltage greater than a trigger voltage of diac  114 , the diac  114  conducts and the gate of triac  116  charges. The resulting voltage at the gate of triac  116  and across bias resistor  118  causes the triac  116  to conduct. When the current I passes through zero, the triac  116  becomes nonconductive, (i.e. turns ‘off’). When the triac  116  is nonconductive, dimmer output voltage V DIM  is 0 V. When triac  116  conducts, the dimmer output voltage V DIM  equals the line voltage V line . The charge time of capacitor  110  required to charge capacitor  110  to a voltage sufficient to trigger diac  114  depends upon the value of current I. The value of current I depends upon the resistance of variable resistor  106  and resistor  112 . 
     In at least one embodiment, the duty cycles, and, correspondingly, the phase angle, of dimmer output voltage V DIM  represent dimming levels of dimmer  102 . The limitations upon conventional dimmer  102  prevent duty cycles of 100% to 0% and generally can range from 95% to 10%. Thus, adjusting the resistance of variable resistor  106  adjusts the phase angle and, thus, the dimming level represented by the dimmer output voltage V DIM . Adjusting the phase angle of dimmer output voltage V DIM  modifies the average power to light source  104 , which adjusts the intensity of light source  104 . 
       FIG. 1B  depicts a lighting circuit  140  with a 3-wire conventional dimmer  150  for dimming incandescent light source  104 . The conventional dimmer  150  can be microcontroller based. A pair of the wires carries the AC line voltage V line  to light source controller/driver  152 . In another embodiment, the line voltage V line  is applied directly to the light source controller/driver  152 . A third wire carries a dimmer output signal value D V  to light source controller/driver  152 . In at least one embodiment, the dimmer  150  is a digital dimmer that receives a dimmer level user input from a user via, for example, push buttons, other switch types, or a remote control, and converts the dimmer level user input into the dimmer output signal value D V . In at least one embodiment, the dimmer output signal value D V  is digital data representing the selected dimming level or other dimmer function. The dimmer output signal value D V  serves as a control signal for light source controller/driver  152 . The light source controller/driver  152  receives the dimmer output signal value D V  and provides a drive current to light source  104  that dims light source  104  to a dimming level indicated by dimmer output signal value D V . 
       FIG. 2  depicts the duty cycles and corresponding phase angles of the modified dimmer output voltage V DIM  waveform of dimmer  102 . The dimmer output voltage oscillates during each period from a positive voltage to a negative voltage. (The positive and negative voltages are characterized with respect to a reference direct current (dc) voltage level, such as a neutral or common voltage reference.) The period of each full cycle  202 . 0  through  202 .N is the same frequency as V line , where N is an integer. The dimmer  102  chops the voltage half cycles  204 . 0  through  204 .N and  206 . 0  through  206 .N to alter the duty cycle and phase angle of each half cycle. The phase angles are measurements of the points in the cycles of dimmer output voltage V DIM  at which chopping occurs. The dimmer  102  chops the positive half cycle  204 . 0  at time t 1  so that half cycle  204 . 0  is 0 V from time t 0  through time t 1  and has a positive voltage from time t 1  to time t 2 . The light source  104  is, thus, turned ‘off’ from times t 0  through t 1  and turned ‘on’ from times t 1  through t 2 . Dimmer  102  chops the positive half cycle  206 . 0  with the same timing as the negative half cycle  204 . 0 . So, the phase angles of each half cycle of cycle  202 . 0  are the same. Thus, the full phase angle of dimmer  102  is directly related to the duty cycle for cycle  202 . 0 . Equation [1] sets forth the duty cycle for cycle  202 . 0  is: 
     
       
         
           
             
               
                 
                   
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     When the resistance of variable resistance  106  is increased, the duty cycles and phase angles of dimmer  102  also decreases. Between time t 2  and time t 3 , the resistance of variable resistance  106  is increased, and, thus, dimmer  102  chops the full cycle  202 .N at later times in the positive half cycle  204 .N and the negative half cycle  206 .N of full cycle  202 .N with respect to cycle  202 . 0 . Dimmer  102  continues to chop the positive half cycle  204 .N with the same timing as the negative half cycle  206 .N. So, the duty cycles and phase angles of each half cycle of cycle  202 .N are the same. 
     Since times (t 5 −t 4 )&lt;(t 2 −t 1 ), less average power is delivered to light source  104  by the sine wave  202 .N of dimmer voltage V DIM , and the intensity of light source  104  decreases at time t 3  relative to the intensity at time t 2 . 
       FIG. 3  depicts a measured light versus perceived light graph  300  representing typical percentages of measured light versus perceived light during dimming. The multiple dimming levels of dimmer  102  vary the measured light output of incandescent light source  104  in relation to the resistance of variable resistor  106 . Thus, the measured light generated by the light source  104  is a function of the dimmer output voltage V DIM . One hundred percent measured light represents the maximum, rated lumen output of the light source  104 , and zero percent measured light represents no light output. 
     A human eye responds to decreases in the measured light percentage by automatically enlarging the pupil to allow more light to enter the eye. Allowing more light to enter the eye results in the perception that the light is actually brighter. Thus, the light perceived by the human is always greater than the measured light. For example, the curve  302  indicates that at 1% measured light, the perceived light is 10%. In one embodiment, measured light and perceived light percentages do not completely converge until measured light is approximately 100%. 
     Many lighting applications, such as architectural dimming, higher performance dimming, and energy management dimming, involve measured light varying from 1% to 10%. Because of the non-linear relationship between measured light and perceived light, dimmer  102  has very little dimming level range and can be very sensitive at low measured output light levels. Thus, the ability of dimmers to provide precision control at low measured light levels is very limited. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the present invention, a method for mapping dimming output signal values of a lighting dimmer using a predetermined lighting output function and driving a light source in response to mapped digital data includes receiving a dimmer output signal and receiving a clock signal having a clock signal frequency. The method also includes detecting duty cycles of the dimmer output signal based on the clock signal frequency and converting the duty cycles of the dimmer output signal into digital data representing the detected duty cycles, wherein the digital data correlates to dimming levels. The method further includes mapping the digital data to light source control signals using the predetermined lighting output function and operating a light source in accordance with the light source control signals. 
     In another embodiment of the present invention a method for mapping dimming output signal values of a lighting dimmer using a predetermined lighting output function and operating a light source in response to mapped dimming output signal values includes receiving a dimmer output signal, wherein values of the dimmer output signal represent duty cycles having a range of approximately 95% to 10%. The method also includes mapping the dimmer output signal values to light source control signals using the predetermined lighting output function, wherein the predetermined lighting output function maps the dimmer output signal values to the light source control signals to provide an intensity range of the light source of greater than 95% to less than 5%. The method further includes operating a light source in accordance with the light source control signals. 
     In another embodiment of the present invention, a method for mapping dimming output signal values of a lighting dimmer using a predetermined lighting output function and driving a light source in response to mapped dimmer output signal values includes receiving a dimmer output signal, wherein values of the dimmer output signal represents one of multiple dimming levels. The method also includes applying a signal processing function to alter transition timing from a first light source intensity level to a second light source intensity level and mapping the dimmer output signal values to light source control signals using the predetermined lighting output function. The method further includes operating a light source in accordance with the light source control signals. 
     In another embodiment of the present invention, a lighting system includes one or more input terminals to receive a dimmer output signal and a duty cycle detector to detect duty cycles of the dimmer output signal generated by a lighting dimmer. The lighting system also includes a duty cycle to time converter to convert the duty cycles of the dimmer output signal into digital data representing the detected duty cycles, wherein the digital data correlates to dimming levels. The lighting system further includes circuitry to map the digital data to light source control signals using a predetermined lighting output function and a light source driver to operate a light source in accordance with the light source control signals. 
     In a further embodiment of the present invention, a lighting system includes one or more input terminals to receive a dimmer output signal, wherein values of the dimmer output signal represents one of multiple dimming levels. The lighting system also includes a filter to apply a signal processing function to alter transition timing from a first light source intensity level to a second light source intensity level and circuitry to map the dimmer output signal values to light source control signals using the predetermined lighting output function. The lighting system also includes a light source driver to operate a light source in accordance with signals derived from the light source control signals. 
     In another embodiment of the present invention, a lighting system for mapping dimming output signal values of a lighting dimmer using a predetermined lighting output function and operating a light source in response to mapped dimming output signal values includes one or more input terminals to receive a dimmer output signal, wherein values of the dimmer output signal represent duty cycles having a range of approximately 95% to 10%. The lighting system also includes circuitry to map the dimmer output signal values to light source control signals using the predetermined lighting output function, wherein the predetermined lighting output function maps the dimmer output signal values to the light source control signals to provide an intensity range of the light source of greater than 95% to less than 5%. The lighting system also includes a light source driver to operate a light source in accordance with the light source control signals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the several figures designates a like or similar element. 
         FIG. 1A  (labeled prior art) depicts a lighting circuit with a conventional dimmer for dimming incandescent lamp. 
         FIG. 1B  (labeled prior art) depicts a lighting circuit with a conventional dimmer for dimming incandescent lamp. 
         FIG. 2  (labeled prior art) depicts a phase angle modified dimmer output voltage waveform of a dimmer. 
         FIG. 3  (labeled prior art) depicts a measured light versus perceived light graph during dimming. 
         FIG. 4A  depicts a lighting system that maps dimming levels of a lighting dimmer to light source control signals in accordance with a predetermined lighting output function. 
         FIG. 4B  depicts a duty cycle time converter that converts the dimmer input signal into digital data. 
         FIG. 4C  depicts a duty cycle time converter. 
         FIG. 4D  depicts a duty cycle detector. 
         FIG. 5  depicts a graphical depiction of an exemplary lighting output function. 
         FIGS. 6 and 7  depict exemplary dimmer output signal values and filtered dimmer output signal values correlated in the time domain. 
     
    
    
     DETAILED DESCRIPTION 
     A system and method map dimming levels of a lighting dimmer to light source control signals using a predetermined lighting output function. In at least one embodiment, the dimmer generates a dimmer output signal value. At any particular period of time, the dimmer output signal value represents one of multiple dimming levels. In at least one embodiment, the lighting output function maps the dimmer output signal values to any lighting output function such as a light level function, a timing function, or any other light source control function. In at least one embodiment, the lighting output function maps the dimmer output signal value to one or more different dimming values that is/are different than the dimming level represented by the dimmer output signal value. In at least one embodiment, the lighting output function converts a dimmer output signal values corresponding to measured light levels to perception based light levels. A light source driver operates a light source in accordance with the predetermined lighting output function. In at least one embodiment, the system and method includes a filter to apply a signal processing function to alter transition timing from a first light source intensity level to a second light source intensity level. 
       FIG. 4A  depicts a lighting system  400  that maps dimming levels of a lighting dimmer  402  to light source control signals in accordance with a predetermined lighting output function  401 . In at least one embodiment, dimmer  402  is a conventional dimmer, such as dimmer  102  or dimmer  150 . Dimmer  402  provides a dimmer output signal V DIM . During a period of time, the dimmer output signal V DIM  has a particular value D V . For example, the dimmer output signal value D V  is the phase angle of dimmer output signal V DIM . The dimmer output signal value D V  represents a dimming level. Without the map, the light source controller/driver  406  would map the dimmer output signal value D V  to a dimming level corresponding to a measured light percentage. U.S. Provisional Application entitled “Ballast for Light Emitting Diode Light Sources” describes an exemplary light source controller/driver  406 . 
     In at least one embodiment, a user selects a dimmer output signal value D V  using a control (not shown), such as a slider, push button, or remote control, to select the dimming level. In at least one embodiment, the dimmer output signal V DIM  is a periodic AC voltage. In at least one embodiment, in response to a dimming level selection, dimmer  402  chops the line voltage V line  ( FIG. 1 ) to modify a phase angle of the dimmer output signal V DIM . The phase angle of the dimmer output signal V DIM  corresponds to the selected dimming level. The dimmer output signal phase detector  410  detects the phase angle of dimmer output signal V DIM . The dimmer output signal detector  410  generates a dimmer output signal value D V  that corresponds to the dimming level represented by the phase angle of dimmer output signal V DIM . In at least one embodiment, the dimmer output signal phase detector  410  includes a timer circuit that uses a clock signal f clk  having a known frequency, and a comparator to compare the dimmer output signal V DIM  to a neutral reference. Increasing the clock frequency increases the accuracy of phase detector  410 . The dimmer output signal V DIM  has a known frequency. The dimmer output signal phase detector  410  determines the phase angle of dimmer output signal V DIM  by counting the number of cycles of clock signal f clk  that occur until the chopping point (i.e. an edge of dimmer output signal V DIM ) of dimmer output signal V DIM  is detected by the comparator. 
       FIG. 4B  depicts a duty cycle time converter  418  that converts the dimmer input signal V DIM  into a digital dimmer output signal value D V . The duty cycle time converter  418  is a substitution for dimmer output signal phase detector  410  in lighting system  400 . The digital data of dimmer output signal value D V  represents the duty cycles of dimmer output voltage V DIM . The duty cycle time converter  418  determines the duty cycle of dimmer output signal V DIM  by counting the number of cycles of clock signal f clk  that occur until the chopping point of dimmer output signal V DIM  is detected by the duty cycle time converter  418 . 
       FIG. 4C  depicts a duty cycle time converter  420  that represents one embodiment of duty cycle time converter  418 . Comparator  422  compares dimmer output voltage V DIM  against a known reference. The reference is generally the cycle cross-over point voltage of dimmer output voltage V DIM , such as a neutral potential of a household AC voltage. The counter 424 counts the number of cycles of clock signal f clk  that occur until the comparator  422  indicates that the chopping point of dimmer output signal V DIM  has been reached. Since the frequency of dimmer output signal V DIM  and the frequency of clock signal f clk  is known, the duty cycle can be determined from the count of cycles of clock signal f clk  that occur until the comparator  422  indicates that the chopping point of dimmer output signal V DIM . Likewise, the phase angle can also be determined by knowing the elapsed time from the beginning of a cycle of dimmer output signal V DIM  until a chopping point of dimmer output signal V DIM  is detected. 
       FIG. 4D  depicts a duty cycle detector  460 . The duty cycle detector  460  includes an analog integrator  462  that integrates dimmer output signal V DIM  during each cycle (full or half cycle) of dimmer output signal V DIM . The analog integrator  462  generates a current I corresponding to the duty cycle of dimmer output signal V DIM  for each cycle of dimmer output signal V DIM . The current provided by the analog integrator  462  charges a capacitor  468 , and the voltage V C  of the capacitor  468  can be determined by analog-to-digital converter (ADC)  464 . The voltage V C  directly corresponds to the duty cycle of dimmer output signal V DIM . The analog integrator  462  can be reset after each cycle of dimmer output signal V DIM  by discharging capacitors  462  and  468 . The output of analog-to-digital converter  424  is digital data representing the duty cycle of dimmer output signal V DIM . 
     In another embodiment, dimmer output signal V DIM  can be chopped to generated both leading and trailing edges of dimmer voltage V DIM . U.S. Pat. No. 6,713,974, entitled “Lamp Transformer For Use With An Electronic Dimmer And Method For Use Thereof For Reducing Acoustic Noise”, inventors Patchornik and Barak, describes an exemplary system and method for leading and trailing edge dimmer voltage V DIM  chopping and edge detection. U.S. Pat. No. 6,713,974 is incorporated herein by reference in its entirety. 
     In at least one embodiment, the mapping circuitry  404  receives the dimmer output signal value D V . The mapping circuitry  404  includes lighting output function  401 . The lighting output function  401  maps the dimmer output signal value D V  to a control signal C V . The light source controller/driver  406  generates a drive signal D R  in response to the control signal C V . In at least one embodiment, the control signal C V  maps the dimmer output signal value to a different dimming level than the dimming level represented by the dimmer output signal value D V . For example, in at least one embodiment, the control signal C V  maps the dimmer output signal value D V  to a human perceived lighting output levels in, for example, with an approximately linear relationship. The lighting output function  401  can also map the dimmer output signal value D V  to other lighting functions. For example, the lighting output function  401  can map a particular dimmer output signal value D V  to a timing signal that turns the lighting source  408  “off” after a predetermined amount of time if the dimmer output signal value D V  does not change during the predetermined amount of time. 
     The lighting output function  401  can map dimming levels represented by values of a dimmer output signal to a virtually unlimited number of functions. For example, lighting output function  401  can map a low percentage dimming level, e.g. 90% dimming) to a light source flickering function that causes the light source  408  to randomly vary in intensity for a predetermined dimming range input. In at least one embodiment, the intensity of the light source results in a color temperature of no more than 2500 K. The light source controller/driver  406  can cause the lighting source  408  to flicker by providing random power oscillations to lighting source  408 . 
     In one embodiment, values of the dimmer output signal dimmer output signal V DIM  represent duty cycles having a range of approximately 95% to 10%. The lighting output function  402  maps dimmer output signal values to light source control signals using the lighting output function  401 . The lighting output function maps the dimmer output signal values to the light source control signals to provide an intensity range of the light source  408  of greater than 95% to less than 5%. 
     The implementation of mapping circuitry  404  and the lighting output function  401  are a matter of design choice. For example, the lighting output function  401  can be predetermined and embodied in a memory. The memory can store the lighting output function  401  in a lookup table. For each dimmer output signal value D V , the lookup table can include one or more corresponding control signal values C V . Multiple control signal values C V  can be used to generate multiple light source control signals D R . When multiple mapping values are present, control signal C V  is a vector of multiple mapping values. In at least one embodiment, the lighting output function  401  is implemented as an analog function generator that correlates dimmer output signal values with mapping values. 
       FIG. 5  depicts a graphical depiction  500  of an exemplary lighting output function  401 . Referring back to the perceived light graph  300  ( FIG. 3 ), conventionally as measured light percentage changed from 10% to 0%, the perceived light changed from about 32% to 0%. The exemplary lighting output function  401  maps the intensity percentage as indicated by the dimmer output signal value D V  to a value that provides a linear, one-to-one relationship between perceived light percentages and dimming level percentages. Thus, when the dimming level is set to 50%, the perceived light percentage is also 50%, and so on. By providing a one-to-one linear relationship, the exemplary lighting output function  401  provides the dimmer  402  with greater sensitivity at high dimming level percentages. 
     In another embodiment, the lighting output function  401  includes a flickering function that maps a dimmer output signal value D V  corresponding to a low light intensity, such as a 10% duty cycle, to control signals that cause lighting source  408  to flicker at a color temperature of no more than 2500 K. In at least one embodiment, flickering can be obtained by providing random power oscillations to lighting source  408 . 
     The light source controller/driver  406  receives each control signal C V  and converts the control signal C V  into a control signal for each individual light source or each group of individual light sources in lighting source  408 . The light source controller/driver  406  provides the raw DC voltage to lighting source  408  and controls the drive current(s) in lighting source  408 . The control signals D R  can, for example, provide pulse width modulation control signals to switches within lighting source  408 . Filter components within lighting source  408  can filter the pulse width modulated control signals D R  to provide a regulated drive current to each light source in lighting source  408 . The value of the drive currents is controlled by the control signals D R , and the control signals D R  are determined by the mapping values from mapping circuitry  404 . 
     A signal processing function can be applied in lighting system  400  to alter transition timing from a first light source intensity level to a second light source intensity level. The function can be applied before or after mapping with the lighting output function  401 . In at least one embodiment, the signal processing function is embodied in a filter. In at least one embodiment, lighting system  400  includes a filter  412 . When using filter  412 , filter  412  processes the dimmer output signal value D V  prior to passing the filtered dimmer output signal value D V  to mapping circuitry  404 . The dimmer output voltage V DIM  can change abruptly, for example, when a switch on dimmer  402  is quickly transitioned from 90% dimming level to 0% dimming level. Additionally, the dimmer output voltage can contain unwanted perturbations caused by, for example, fluctuations in line voltage that supplies power to lighting system  400  through dimmer  402 . Filter  412  can represent any function that changes the dimming levels indicated by the dimmer output signal value D V . Filter  412  can be implemented with analog or digital components. In another embodiment, the filter filters the control signals D R  to obtain the same results. 
       FIG. 6  depicts exemplary dimmer output signal values  602  and filtered dimmer output signal values  604  correlated in the time domain. The dimmer output signal values  602  abruptly change at time t 0 . The filter  412  filters the dimmer output signal values  604  with a low pass averaging function to obtain a smooth dimming transition as indicated by the filtered dimmer output signal values  604 . In at least one embodiment, abrupt changes from high dimming levels to low dimming levels are desirable. The filter  412  can also be configured to smoothly transition low to high dimming levels while allowing an abrupt or much faster transition from high to low dimming levels. 
       FIG. 7  depicts exemplary dimmer output signal values  702  and filtered dimmer output signal values  704  correlated in the time domain. The dimmer output signal values  702  contain perturbations (ripples) over time. The perturbations can be caused, for example, by fluctuations in line voltage. The filter  412  can use a low pass filter transfer function to smooth perturbations in the dimmer output signal values  702 . 
     Lighting source  408  can include a single light source or a set of light sources. For example, lighting source  408  can include one more light emitting diodes or one or more gas discharge lamps. Each lighting source  408  can be controlled individually, collectively, or in groups in accordance with the control signal C V  generated by mapping circuitry  404 . The mapping circuitry  404 , light source controller/driver  406 , lighting source  408 , dimmer output signal phase detector  410 , and optional filter  412  can be collectively referred to as a lighting device. The lighting device  414  can include a housing to enclose mapping circuitry  404 , light source controller/driver  406 , lighting source  408 , dimmer output signal phase detector  410 , and optional filter  412 . The housing can include terminals to connect to dimmer  402  and receive power from an alternating current (AC) voltage source. The components of lighting device  414  can also be packaged individually or in groups. In at least one embodiment, the mapping circuitry  404 , light source controller/driver  406 , dimmer output signal phase detector  410 , and optional filter  412  are integrated in a single integrated circuit device. In another embodiment, integrated circuits and/or discrete components are used to build the mapping circuitry  404 , light source controller/driver  406 , dimmer output signal phase detector  410 , and optional filter  412 . 
     Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.