Patent Publication Number: US-9433042-B2

Title: High-end trim control of lighting fixtures

Description:
BACKGROUND 
     1. Field 
     This disclosure relates generally to the field of dimming control of light fixtures. More particularly, the disclosure relates to high-end trim adjustment in a dimming controller for light-emitting diode (LED) based light fixtures. 
     2. Related Art 
     Light sources may be controlled by a light switch or a dimmer control. A light switch is used to turn a light source on or off. A dimmer control is used to reduce the light emitted by a light source, thereby setting the ambient light intensity to be somewhere between that experienced when the light source is off and that experienced when the light source produces light at full intensity. 
     Some dimming controls cause drivers to power light emitting diodes (LEDs) at a light intensity that depends on the voltage of a lighting control signal. In some lighting systems, potentiometers are used as a dimmer to set the intensity of the light fixture when it is on. 
       FIG. 1  illustrates a lighting fixture  102  that is powered through a power line  180  by a power source  101 . The lighting fixture  102  includes a light emitting diode (LED) driver  110  that is controlled by a potentiometer  100  and drives an LED array  120 . The LED driver  110  receives a 0-10 volt lighting control signal through a control channel  160 . 
     The LED driver  110  drives a current from an internal 10V reference (not shown) through an internal pull-up resistor (not shown) into one terminal of the control channel  160  to the potentiometer  100 . The potentiometer  100  has a variable resistance. The potentiometer  100  causes the voltage across the control channel  160  to be between 0 and 10 volts depending on the variable resistance of the potentiometer  100  relative to the resistance of the internal pull-up resistor. 
     The LED driver  110  drives onto a controlled power line  170  a current that depends on the voltage of the lighting control signal on the control channel  160 . The controlled power line  170  powers the LED array  120 . The LED array  120  includes one or more LED devices configured to be powered by the controlled power line  170 . The light intensity produced by the LED array  120  depends on the lighting control signal. 
     SUMMARY 
     Embodiments of the disclosure include components, lighting fixtures and lighting systems that control the light intensity produced by one or more light sources, such as light-emitting diode (LED) arrays. In some embodiments, an LED driver drives an LED array using an output current that increases as a voltage of a 0-10 volt lighting control signal increases from 0 to 10 volts. The LED array receives the output current and produces light with an intensity that depends on the voltage of the lighting control signal. 
     In some embodiments, a high-end trim control apparatus has a rotary switch that selects one of several zener diodes to be coupled across two lighting control terminals, or selects none of the zener diodes to produce an open circuit across the lighting control terminals. 
     When the rotary switch is positioned to select none of the zener diodes, a pull-up resistor coupled to a 10 volt reference within the LED driver pulls one of the lighting control terminals to 10 volts. When the voltage across the lighting control terminals is 10 volts, the LED driver drives the LED array at the maximum light intensity. In some embodiments, when the voltage across the lighting control terminals is within the range of 0 to 10 volts, the LED driver drives the LED array to produce a light intensity increasing with increasing voltage as a linear function of the voltage across the control terminals. 
     When the rotary switch is positioned to select one of the zener diodes, the selected zener diode conducts current in a reverse biased state. The high-end trim control apparatus causes the lighting control signal to be approximately the zener voltage of the selected zener diode. Each of the zener diodes has a different zener voltage between 0 and 10 volts. When the lighting control signal is less than 10 volts, the driver drives the LED array at less than full light intensity. When the rotary switch is positioned to select a zener diode with a higher zener voltage, the LED driver drives the LED array to produce a higher light intensity. When the rotary switch is positioned to select a zener diode with a lower zener voltage, the LED driver drives the LED array to produce a lower light intensity. 
     In some embodiments, a light switch controls whether power is supplied to the lighting fixture including a high-end trim control apparatus, driver and LED array. When the light switch is off, the driver does not drive power to the LED array such that light is not generated by the LED array. When the light switch is on, the driver drives the LED array to generate a light intensity based on the voltage across the lighting control terminals. The voltage across the lighting control terminals depends on whether a zener diode is selected, and if a zener diode is selected, the zener voltage of the selected zener diode. 
     In other embodiments, a dimmer control is also coupled across the lighting control terminals having a variable resistance depending on a user control such as a knob or slider (not shown). When a zener diode is not selected, the dimmer control can control the lighting control signal without restriction by the high-end trim control based on a voltage divider relationship with the internal pull-up resistor of the LED driver. When a zener diode is selected, and the variable resistance of the dimmer control is small enough that the voltage across the selected zener diode is below the zener voltage, the selected zener diode is off and the driver drives the LED array according to the voltage determined by the voltage divider relationship between the internal pull-up resistor and the variable resistance of the dimmer control. When the variable resistance of the dimmer is large enough that the selected zener diode turns on, the selected zener diode sinks sufficient current to keep the voltage across the lighting control terminals at approximately the zener voltage of the selected zener diode even as the variable resistance continues to increase. Thus, the voltage range of the lighting control signal is limited by the selected zener diode. The selected zener diode limits the maximum light intensity of the LED array even when the dimmer control knob is positioned such that it would otherwise cause the driver to drive the LED array at the maximum intensity of the LED array. 
     In some situations, a person may want to equalize the light intensity of two independently controlled light fixtures. Potentiometers can vary resistance to provide for finely tuned adjustments within a particular resistance range, but someone may have to visually estimate the comparative light intensity of two independently controlled light fixtures when trying to set the corresponding potentiometers to the same level. This may lead to variations in intensity that may be perceptible and distracting to others. Alternatively, a technician may need to be called in to measure the light intensity for each fixture using a light meter and adjusting each potentiometer accordingly to equalize the light intensity of multiple potentiometer-controlled light fixtures. In some embodiments, people can reliably and quickly equalize the high end trim of two or more independently controlled light fixtures by selecting a zener diode with the same zener voltage for each light fixture. 
     Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, characteristic, advantage or benefit described in connection with the embodiment is included in at least one embodiment of the disclosure, but may not be exhibited by other embodiments. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Similarly, various requirements are described which may be requirements for some embodiments but not for other embodiments. The specification and drawings are to be regarded in an illustrative sense rather than a restrictive sense. Various modifications may be made thereto without departing from the spirit and scope as set forth in the claims. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of one embodiment of a prior art light fixture using a potentiometer. 
         FIG. 2  is a diagram of one embodiment of a light fixture including a high-end trim control apparatus. 
         FIG. 3A  is a diagram of one embodiment of a zener diode. 
         FIG. 3B  is a plot of the relationship between current and voltage across the zener diode of  FIG. 3A . 
         FIG. 4  is a diagram of one embodiment of a lighting system including a high-end trim control apparatus and a dimmer control. 
         FIG. 5  is a simplified circuit diagram of one embodiment of an LED driver, high-end trim control apparatus, and a dimmer control. 
         FIG. 6A  is a diagram of an LED array. 
         FIG. 6B  is one embodiment of a plot of the relationship between a 0-10V control signal input to a driver of the LED array shown in  FIG. 2A , and the light intensity of the LED array. 
         FIG. 7  is a diagram of one embodiment of a lighting system having multiple light fixtures each including a high-end trim control apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding of the disclosure. However, in certain instances, well known or conventional details are not described in order to avoid obscuring the description. 
       FIG. 2  illustrates one embodiment of a light fixture using a high-end trim control apparatus  200 . 
     The high-end trim control apparatus  200  includes a selector  215  that selectively couples a terminal  210  to one of a terminal  221 , a terminal  222 , a terminal  223 , a terminal  224 , a terminal  225 , a terminal  226 , a terminal  227 , and a terminal  228 . The dotted lines between the terminal  210  and the terminal  222  illustrates that the selector  215  is positioned to electrically couple the terminal  210  to the terminal  222 , but the selector  215  may be positioned to electrically couple any one of the terminals  221 - 228  to the terminal  210 . In some embodiments, the selector  215  is a rotary switch that can select any one the terminals  221 - 228 . In other embodiments, the selector  215  includes one or more toggle switches that select between multiple terminals. Other types of mechanical and electrical devices can be used as the selector  215  to selectively couple the terminal  210  to one of the terminals  221 - 228 . It will be apparent to one skilled in the art that the selector  215  may be configured to selectively connect to one of a different number of zener diodes and that other zener voltages may be used. 
     The high-end trim control apparatus  200  includes seven zener diodes. Each zener diode has an anode and a cathode. When the voltage at the anode is greater than the voltage at the cathode the zener diode is forward biased. When the voltage at the cathode is greater than the voltage at the anode, the zener diode is reverse biased. In a preferred embodiment, the zener diodes are oriented in the high-end trim control apparatus  200  to be reverse biased when selected by the selector  215 . 
     The terminal  221  is coupled to the anode of a zener diode  231  having a zener voltage of 4.3 volts. The terminal  222  is coupled to the anode of a zener diode  232  having a zener voltage of 4.7 volts. The terminal  223  is coupled to the anode of a zener diode  233  having a zener voltage of 5.1 volts. The terminal  224  is coupled to the anode of a zener diode  234  having a zener voltage of 5.6 volts. The terminal  225  is coupled to the anode of a zener diode  235  having a zener voltage of 6.2 volts. The terminal  226  is coupled to the anode of a zener diode  236  having a zener voltage of 6.8 volts. The terminal  227  is coupled to the anode of a zener diode  237  having a zener voltage of 7.5 volts. The terminal  228  is not coupled to a zener diode. 
     The cathodes of each of the zener diodes  231 - 237  are coupled together and coupled to the terminal  291 . The terminal  210  is coupled to the terminal  292 . A control channel  290  includes the terminal  291  and the terminal  292 . 
     A light-emitting diode (LED) driver  110  includes a ten-volt (10V) source  152 , a resistor  103 , a comparator  154  and a power stage  156 . The LED driver  110  receives power from a power source (not shown) over a power line  180 . The 10V reference  152  and other components in the LED driver  110  may be directly or indirectly powered by the power source. In some embodiments, power can be supplied according to one of many residential and commercial power standards for power lines or for battery-based power sources. 
     The comparator  154  receives the lighting control signal on the control channel  290 . The terminal  291  is generally at a higher voltage than the terminal  292  such that it causes any connected zener diode to be reverse biased. For this reason, the terminal  291  may be referred to as a positive terminal and the terminal  292  may be referred to as a negative terminal. 
     The 10V reference  152  is coupled to the terminal  291  through the resistor  103 . When the selector  215  selects the terminal  228 , an open circuit is created between the terminal  291  and the terminal  292  and the resistor  103  pulls the terminal  291  to 10 volts. 
     When the selector  215  selects one of the zener diodes, it causes a current to flow from the 10V reference  152  through the resistor  103  and the selected zener diode. The zener diode is reverse biased at roughly its zener voltage (V z ) relatively independent of current so that sufficient current flows to cause the voltage drop across the resistor  103  to be about 10-V z  volts. For example, when the terminal  222  is selected, the voltage across the zener diode  232  is about 4.7 volts and the voltage across the resistor  103  is about 5.3 volts. If the resistor  103  has a 1 kilo-ohm resistance, the current that flows when the zener diode  252  is selected is about 5.3 milliamps (mA). Thus, the voltage across the terminal  291  and the terminal  292  is set by the zener voltage of the selected zener diode. Power consumption used for generating the lighting control voltage is about 0-10 milliwatts (mW), depending on the zener voltage of the selected zener diode. 
     The comparator  154  receives the lighting control signal on the control channel  290  and drives a comparator output signal on a control channel  158  based on the lighting control signal. The power stage  156  receives the comparator output signal on the control channel  158 . The power stage  156  drives an output current on a controlled power line  170  based on the comparator output signal. 
     An LED array  120  receives the output current on the controlled power line  170 . The LED array  120  includes an LED  161  and an LED  162  in series, in parallel with an LED  163  and an LED  164  in series. The LEDs are powered by the controlled power line  170  and produce light of an intensity that depends on the output current on the controlled power line  170 . LED arrays having a broad range of characteristics in terms of the number of LEDs, arrangement of LEDs, color and electrical characteristics, including power, voltage and current requirements, may be used. 
     In some embodiments, the high-end trim control apparatus  200  is implemented with LED drivers that are specified to receive a lighting control signal according to a 0-10 volt lighting control standard accepted by LED drivers from several manufacturers. By working with the 0-10 volt lighting control standard, embodiments of the high-end trim control apparatus may be deployed to interface with LED drivers from different manufacturers and be used in conjunction with existing LED lighting fixtures and existing LED lighting systems. 
     In some embodiments, the terminal  291  is color coded in purple and the terminal  292  is color coded in gray according dimmer control wiring standards to provide a visual cue so that installers may reliably connect the high-end trim control apparatus  200  and the LED driver  110  with the correct polarity across the control channel  290 . However, other LED drivers, lighting control signal specifications, and color coding schemes may be used. 
       FIG. 3A  is a diagram of a zener diode having a zener voltage of V z  volts, a voltage across the anode  301  and the cathode  302  of the zener diode, and a current through the zener diode. 
       FIG. 3B  is a plot of current through the zener diode of  FIG. 3A  in relation to the voltage across the zener diode. When the voltage is positive, the zener diode is forward biased and turns on when the voltage exceeds a turn-on voltage of the zener diode. When the voltage of the cathode exceeds the voltage of the anode, the zener diode is reverse biased and turns on when the reverse biased voltage reaches about V z  volts. As the reverse-biased current increases, the reverse biased voltage remains at approximately V z  volts. 
       FIG. 4  illustrates an embodiment of a lighting system having a dimmer control  240  including a variable resistor  142  and the high-end trim control apparatus  200 . The dimmer control  240  is coupled to the control channel  290 . In some embodiments, the dimmer control  240  is mounted on a wall. 
     In some embodiments, the dimmer control  240  has a variable resistor  142  that depends on a user control such as a user-adjustable position of a rotatable knob or linearly sliding handle (not shown). 
     In some embodiments, the variable resistor  142  may be controlled using other mechanical or electrical devices. In some embodiments, the selector  215  and the user control are both easily accessible on the external part of the dimmer control  240 . In other embodiments, the selector  215  is less accessible on the internal part of the dimmer control  240  to provide a high-end limit on the light intensity range produced by the user control. 
     The power source  101 , the LED driver  110 , the LED driver  112 , the LED array  120  and the LED array  122  are similar to the power source, the LED driver and the LED array described with reference to  FIG. 2 . 
     A light fixture  702  includes the LED driver  110  coupled to receive power from the power source  101  on the power line  180  and the lighting control signal on the control channel  290 . Similarly, a light fixture  704  includes the LED driver  112  coupled to receive power from the power source  101  on the power line  180  and coupled to receive the lighting control signal on the control channel  290 . 
     The LED driver  110  drives a current on the controlled power line  170  based on the lighting control signal to power the LED array  120 . The LED driver  112  drives a current on the controlled power line  172  based on the lighting control signal to power the LED array  122 . 
     When the selector  215  selects the terminal  228  to create an open circuit on the control channel  290 , the dimmer control  240  controls the lighting control signal on the control channel  290  without restriction by the high-end trim control apparatus  200 . The lighting control signal is generated as a fraction of the 10V reference voltage based on a voltage divider relationship between the variable resistor  142  of the dimmer control  240  and the parallel pull-up resistors to each 10V reference in the LED driver  110  and the LED driver  112 . The LED driver  110  drives an output current on a controlled power line  170  based on the lighting control signal on the control channel  290 . The LED driver  112  drives an output current on a controlled power line  172  based on the same lighting control signal on the control channel  290 . Thus, the LED array  120  and the LED array  122  generate light intensity corresponding to the lighting control signal controlled by the variable resistor  142  of the dimmer control  240 . 
     When the selector  215  selects one of the zener diodes, the selected zener diode is coupled across the control channel  290 . When the variable resistor  142  has a resistance that causes the voltage across the selected zener diode to be less than the zener voltage according to the voltage divider relationship, the selected zener diode is off and the lighting control signal is determined by the voltage divider relationship described above with reference to the scenario where none of the zener diodes are selected. 
     When the variable resistor  142  has a resistance that causes the lighting control signal to reach the zener voltage of the selected zener diode, the zener diode reaches reverse breakdown and sinks current to maintain the voltage across the control channel  290  at approximately the zener voltage of the selected zener diode as the variable resistance continues to increase up to the point where the lighting control signal would be at full-intensity had none of the zener diodes been selected. Thus, the lighting control signal is limited by the zener voltage of the selected zener diode. The light intensity of the LED array  120  and the LED array  122  are limited due to the limited range of the lighting control signal. 
     In some embodiments, the high-end trim control apparatus  200  is coupled to LED drivers that use 0-10V references without pull-up resistors. 
     The maximum power rating of the zener diodes should be sufficient to accommodate the maximum current that the zener diodes will sink given the electrical characteristics of the dimmer control  240 , and the electrical characteristics and number of LED drivers on the control channel  290 . In some embodiments, four or more LED drivers are coupled to receive the lighting control signal on the control channel  290 . 
       FIG. 5  shows one embodiment of a simplified circuit model of the control channel  290  with an LED driver  110 , a high-end trim control apparatus  200  and a dimmer control  240 . The model shows how the lighting control signal across the control channel  290  is generated but does not show the comparator circuitry that responds to the voltage across the control channel  260 . 
     The LED driver  110  has a 10V reference  152  and a resistor  103  in series. The dimmer control  240  changes a variable resistance across the control channel  290  depending on the position of a dimmer control knob or handle (not shown). 
     When the high-end trim control apparatus  200  does not select a zener diode (modeled by removing the zener diode  253  from the circuit model shown in  FIG. 5 ), the lighting control signal is generated as a fraction of the voltage of the 10V reference  152  based on a voltage divider relationship between the resistance of the variable resistor  142  of the dimmer control  240  and the resistor  103  within the LED driver  110 . 
     When the selector selects one of the zener diodes as described with reference to  FIG. 2 , the selected zener diode is coupled across the control channel  290 .  FIG. 5  shows that the high-end trim apparatus  240  has the zener diode  253  coupled across the control channel  290 , but other zener diodes may be selected and similarly modeled. The zener diode  253  has a zener voltage of 5.1 volts. 
     When the variable resistor  142  has a resistance that is low enough, the zener diode  253  is off (in some embodiments with some leakage current) and the voltage across the control channel  290  is determined by the voltage divider relationship between the variable resistor  142  and the resistor  103  as described above in the scenario where none of the zener diodes are selected. 
     When the resistance of the variable resistor  142  is increased to the point that the voltage across the zener diode  253  reaches the zener voltage of 5.1 volts, the zener diode turns on in reverse breakdown and begins to sink current. As the resistance of the variable resistor  142  increases from that point, the zener diode  253  maintains the voltage across the control channel  260  at about the zener voltage of 5.1 volts. 
     In one embodiment, the resistance of the resistor  103  is 1000 ohms. When the resistance of the variable resistor  142  is increased to about 1040 ohms, the voltage divider relationship causes the voltage at the terminal  291  to be about 5.1 volts, causing the zener diode  253  to turn on. As the voltage of the variable resistor  142  continues to increase, the zener diode  253  sinks more current so that the current pulled through the resistor  103  by the variable resistor  142  and the zener diode  253  operating in parallel causes the voltage drop across the resistor  103  to maintain the terminal  291  at the zener voltage of the zener diode  253 . 
     The LED driver  110  drives an output current on a controlled power line (not shown) having a magnitude that is dependent on the lighting control signal on the control channel  290 . Thus, the LED array (not shown) generates light intensity corresponding to the lighting control signal. 
       FIG. 6A  shows an embodiment of an LED array receiving a driver output voltage and a driver output current.  FIG. 6B  is a plot showing one embodiment of light intensity of the LED array of  FIG. 6A  as a function of voltage of the 0-10 volt lighting control signal—a line  410 . As the voltage of the lighting control signal increases, the driver output current through the LED array increases, and the intensity of the light generated increases. 
     When the LED array is driven by the light fixture of  FIG. 2 , the selected zener diode sets the 0-10 volt lighting control signal to a voltage less than 10 volts—approximately the zener voltage of the selected zener diode—thereby causing the light intensity to be less than the maximum intensity at a point  408  on the line  410 . In one embodiment, the light intensity with a lighting control signal at 5 volts is about half the light intensity with a lighting control signal at 10 volts. However, in other embodiments, the line  410  may have a less linear relationship to the voltage of the lighting control signal. By selecting zener diodes with different zener voltages between 0 and 10 volts, the light intensity of the LED array can vary between off at a point  400  and full intensity at the point  408 . 
     In a lighting system without a dimmer control, the lighting fixture operates at a point  401  on the line  410  when the zener diode  281  is selected. In a lighting system including the dimmer control  240 , the lighting fixture operates between the point  400  and the point  401  on the line  410  depending on the variable resistance of the dimmer control  240 . As the variable resistance increases, the light intensity increases up to the limit set by the zener diode  281 . 
     In a lighting system without a dimmer control, the lighting fixture operates at a point  402  on the line  410  when the zener diode  282  is selected. In a lighting system including the dimmer control  240 , the lighting fixture operates between a point  400  and the point  402  on the line  410  depending on the variable resistance of the dimmer control  240 . As the variable resistance increases, the light intensity increases up to the limit set by the zener diode  282 . 
     In a lighting system without a dimmer control, the lighting fixture operates at a point  403  on the line  410  when the zener diode  283  is selected. In a lighting system including the dimmer control  240 , the lighting fixture operates between a point  400  and the point  403  on the line  410  depending on the variable resistance of the dimmer control  240 . As the variable resistance increases, the light intensity increases up to the limit set by the zener diode  283 . 
     In a lighting system without a dimmer control, the lighting fixture operates at a point  404  on the line  410  when the zener diode  284  is selected. In a lighting system including the dimmer control  240 , the lighting fixture operates between a point  400  and the point  404  on the line  410  depending on the variable resistance of the dimmer control  240 . As the variable resistance increases, the light intensity increases up to the limit set by the zener diode  284 . 
     In a lighting system without a dimmer control, the lighting fixture operates at a point  405  on the line  410  when the zener diode  285  is selected. In a lighting system including the dimmer control  240 , the lighting fixture operates between a point  400  and the point  405  on the line  410  depending on the variable resistance of the dimmer control  240 . As the variable resistance increases, the light intensity increases up to the limit set by the zener diode  285 . 
     In a lighting system without a dimmer control, the lighting fixture operates at a point  406  on the line  410  when the zener diode  286  is selected. In a lighting system including the dimmer control  240 , the lighting fixture operates between a point  400  and the point  406  on the line  410  depending on the variable resistance of the dimmer control  240 . As the variable resistance increases, the light intensity increases up to the limit set by the zener diode  286 . 
     In a lighting system without a dimmer control, the lighting fixture operates at a point  407  on the line  410  when the zener diode  287  is selected. In a lighting system including the dimmer control  240 , the lighting fixture operates between a point  400  and the point  407  on the line  410  depending on the variable resistance of the dimmer control  240 . As the variable resistance increases, the light intensity increases up to the limit set by the zener diode  287 . 
     In a lighting system without a dimmer control, the lighting fixture operates at a point  408  on the line  410  when none of the zener diodes are selected. In a lighting system including the dimmer control  240 , the lighting fixture operates between a point  400  and the point  408  on the line  410  depending on the variable resistance of the dimmer control  240 . As the variable resistance increases, the light intensity increases up to the maximum light intensity at the point  408  without restriction by any of the zener diodes. 
     The selected zener diode limits the high-end of the range of the lighting control signal, but has no effect on the operating points of the dimmer control  240  below that limit. On the other hand, if a potentiometer is used in place of the zener diode, the operating points of the dimmer control  240  would shift throughout the range of the lighting control signal. This is important in embodiments where a set point of the variable resistor  142  is at a minimum required light level. If a zener diode is then applied in combination with the variable resistor, it scales back the maximum light intensity while leaving the minimum light intensity unmodified. However, if a potentiometer is used in place of the zener diode, the minimum light level is also scaled back when the potentiometer is applied in combination with the variable resistor. That may lead to inadequate light intensity. 
     Although the high-end trim control apparatus  200  is described with reference to a standard 0-10 volt controlled LED driver, other embodiments may use other voltage-controlled driver input specifications within different voltage ranges and different light intensity responses over the specified voltage range. 
       FIG. 7  illustrates a lighting system having multiple light fixtures each controlled by a high-end trim control apparatus coupled to a light fixture having two LED drivers driving LED arrays. 
     The high-end trim control apparatus  200  shown here is described with reference to  FIG. 2 . Only the first and last of the terminals  221 - 227  and the first and last of the zener diodes  231 - 237  are shown in this figure. The selector  215  selects between the terminals  221 - 228  to connect one of the zener diodes  231 - 237  or create an open circuit across the control channel  290 . The high-end trim control apparatus  200  is coupled through the control channel  290  to the LED driver  110  and an LED driver  112 . 
     The high-end trim control apparatus  250  shown here is similar to the high-end trim control apparatus  250  described with reference to  FIG. 2 . Only the first and last of the terminals  271 - 277  and the first and last of the zener diodes  281 - 287  are shown in this figure. The selector  215  selects between the terminals  271 - 278  to connect one of the zener diodes  281 - 287  or create an open circuit across a control channel  295 . The high-end trim control apparatus  200  is coupled through the control channel  295  to the LED driver  114  and an LED driver  116 . 
     A power source  101  provides power on the power line  180 . A light switch  105  is coupled to the power line  180  and selectively connects the power line  180  to a power line  185  depending on whether the light switch  105  is switched on or switched off. The LED driver  110 , the LED driver  112 , the LED driver  114  and the LED driver  116  are coupled to the power line  185  and thereby receive power when the light switch  105  is switched on. 
     When the light switch  105  is switched on, the LED driver  110  driver drives a current on the controlled power line  170  and the LED driver  112  drives a current on the controlled power line  172  according to the lighting control signal on the control channel  290 . When the light switch  105  is switched on, the LED driver  114  driver drives a current on the controlled power line  174  and the LED driver  116  drives a current on the controlled power line  176  according to the lighting control signal on the control channel  295 . 
     The LED array  120  is coupled to the controlled power line  170  and the LED array  122  is coupled to the controlled power line  172 . The light intensity of the LED array  120  and the LED array  122  is controlled by the lighting control signal on the control channel  290 . 
     The LED array  124  is coupled to the controlled power line  174  and the LED array  126  is coupled to the controlled power line  176 . The light intensity of the LED array  124  and the LED array  126  is controlled by the lighting control signal on the control channel  295 . 
     The lighting control signal on the control channel  290  and the lighting control signal on the control channel  295  are independently controlled. When the selector  215 , selects the zener diode  231 , the lighting control signal on the control channel  290  is about 4.3 volts—the zener voltage of the zener diode  231 . When the selector  265  selects the zener diode  287 , the lighting control signal on the control channel  295  is about 7.5 volts—the zener voltage of the zener diode  287 . Thus, the light fixture  706  and the light fixture  708  will produce different light intensities based on the different lighting control voltages. 
     One can independently adjust the selector  215  and the selector  265  to independently control the light intensity of the light fixture  706  and the light fixture  708 . On the other hand, if one wanted to match the light intensity of the light fixture  706  and the light fixture  708 , one might use the selector  215  and the selector  265  to select zener diodes with the same zener voltage. For example, when the selector  215  selects the zener diode  237  and the selector  265  selects the zener diode  288 , the lighting control signal on the control channel  290  and the lighting control signal on the control channel  295  will both be 7.5 volts. Thus, both the light fixture  706  and the light fixture  708  will produce a light intensity corresponding to the same lighting control voltage. 
     In some embodiments, the high-end trim control apparatus  200  is mounted on the light fixture  706  and the selector  215  is adjusted by an installer or technician. In other embodiments, the high-end trim control apparatus  200  is installed remotely from the light fixture  706 , such as on a nearby wall, making the selector  215  more easily accessible. The wall-mounted high-end trim control apparatus  200  controls the light fixture  706  using a control channel  290  with a longer wired connection. 
     In some embodiments, the high-end trim control apparatus  250  is mounted on the light fixture  708  and the selector  265  is adjusted by an installer or technician. In other embodiments, the high-end trim control apparatus  250  is installed remotely from the light fixture  708 , such as on a nearby wall, making the selector  265  more easily accessible. The wall-mounted high-end trim control apparatus  250  controls the light fixture  708  using a control channel  295  with a longer wired connection. 
     When the light switch  105  is switched off, the LED driver  110 , the LED driver  112 , the LED driver  114  and the LED driver  116  does not receive power on the power line  185 . The LED array  120 , the LED array  122 , the LED array  124  and the LED array  126  does not receive power on the controlled power line  170 , the controlled power line  172 , the controlled power line  174  and the controlled power line  176 , respectively. Thus the light fixture  706  and the light fixture  708  do not produce light when the light switch  105  is switched off. 
     The maximum power rating of the zener diodes should accommodate the maximum current that the zener diodes will sink given the electrical characteristics and number of LED drivers on the control channel  290  and the control channel  295 . 
     The foregoing specification provides a description with reference to specific exemplary embodiments. The specification and drawings are to be regarded in an illustrative sense rather than a restrictive sense. Various modifications may be made thereto without departing from the spirit and scope as set forth in the following claims.