Lighting control method having a light output ramping function

“LIGHTING CONTROL METHOD WITH A GRADUAL LIGHT OUTPUT CHANGE FUNCTION”

Related Requests

This order is a Continued-in-Part (CIP) of US Order N^O5th 11 / 875,083, filed October 19, 2007 and is hereby incorporated in its entirety for reference purposes.

Field of Invention

The present invention relates generally to lighting control, and more particularly, to a lighting control method with a dual light output shift function to provide a substantially uniform light output over a period of time. heating.

Background of the Invention

In existing lighting control systems, many disadvantages have been identified that may result in underperforming a lighting device. These disadvantages include, but are not limited to, voltage variations between LED lighting modules that result in uneven light output. These voltage variations may result from the lack of uniformity in the manufacture of LEDs used in a lighting device.

Another disadvantage of existing lighting control systems is the inability of the lighting circuit system to compensate for the effects of temperature changes on direct LED voltages, such as the required changes in drive voltage caused by an increase in temperature. In this regard, existing lighting control systems do not compensate for inherent direct voltage changes, as found by an output driver over the entire operating temperature range of the lighting device.

Moreover, as is well known to those skilled in the art, the light output of an LED is inversely proportional to the LED junction temperature. Therefore, when the LED is first activated (ie cold start), the junction temperature is low and the light output is high. As the junction temperature increases over a warm-up period (which lasts approximately 30 minutes), the LED light output will decrease until the LED reaches a steady state condition. Once the steady state condition is reached, the operating temperature of the LED junction will generally remain constant and, as a result, the light output will generally remain constant during the period of continuous use.

The decay in LED light output during the warm-up period can reach 20%. Therefore, the LED light output during the warm-up period is generally not uniform, and the steady state LED light output may be considerably smaller.

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2/14 than the expected steady state light output. It is also possible that the cold light LED light output may exceed an upper light output limit.

The disadvantages reported are particularly aggravating in the event that the illumination device is a surgical luminaire requiring substantially constant light output or lux readings.

The present invention addresses these and other disadvantages to provide an improved lighting control method for a lighting device.

Summary of the Invention

In accordance with the present invention, a lighting control method for controlling an LED light source during an LED heating mode is proposed. The method comprises: (a) recovering a pre-stored setpoint activity cycle corresponding to a light intensity level; (b) operating the LED light source for a first time in an operating duty cycle equal to the setpoint duty cycle minus a pre-stored duty cycle compensation value;

(c) setting a duty cycle gradual change value equal to a pre-stored duty cycle increment value; (d) operate the LED light source for a time interval in an operating duty cycle equal to the setpoint duty cycle minus the duty cycle compensation value plus the duty cycle tap change value; and determining whether (1) a fade-in time has elapsed, (2) if the operating activity cycle is equal to the setpoint activity cycle, or (3) if a new light intensity level has been selected. The LED warm-up mode is terminated if any of (1), (2), or (3) has occurred. If (1), (2) and (3) have not occurred, then the duty cycle incremental change value is increased by the duty cycle increment value, and the method returns to step (d).

According to another aspect of the present invention, a lighting control method for controlling an LED light source during an LED heating mode is proposed, the method comprising: (a) establishing a light intensity level; (b) recovering a pre-stored setpoint activity cycle corresponding to the light intensity level; (c) retrieving a stored pre-30 duty cycle offset value; (d) operating the LED light source for a first time interval in an operating duty cycle equal to the setpoint duty cycle minus the duty cycle compensation value; (e) recovering a pre-stored taper time; (f) retrieving a pre-stored duty cycle increment value; (g) set a duty cycle gradual change value equal to the pre-stored duty cycle increment value; (h) operate the LED light source for a time interval in an operating duty cycle equal to the setpoint duty cycle minus the duty cycle compensation value plus the tapering value.

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3/14 activity cycle; (i) determine if a predetermined condition has been met; (j) if the predetermined condition has been met, then increase the duty cycle tap change value by the duty cycle increment value and return to step (h); and (k) if the predetermined condition has not been met, then terminate the heating mode.

An advantage of the present invention is the attainment of a lighting control method that offers improved uniformity in the light output of an LED light source over a period of LED heating.

Another advantage of the present invention is to obtain a lighting control method that prevents the light output of an LED light source from exceeding an upper light output limit value.

These and other advantages will become apparent from the following description, taken in conjunction with the accompanying drawings and the appended claims.

Brief Description of the Drawings

The invention may take physical form in certain parts and arrangements of parts, of which an embodiment will be described in detail in the specification and illustrated in the accompanying drawings which constitute a part of the invention, and in which:

FIG. 1 is a general block diagram of a lighting control system 20 for a lighting device in accordance with an embodiment of the present invention;

FIG. 2 is a schematic view of a drive output circuit in accordance with an embodiment of the present invention;

FIG. 3 is a schematic view of a first LED module including a temperature compensation circuit in accordance with one embodiment of the present invention;

FIG. 4 is a schematic view of a second LED module including a compensation circuit in accordance with an embodiment of the present invention; and

FIGS. 5A and 6B show a flowchart illustrating a lighting control method for a warm-up period according to one embodiment of the present invention.

Detailed Description of the Invention

Referring now to the drawings, which illustrations serve only to illustrate and not to limit an embodiment of the invention, FIG. 1 shows a block diagram of the lighting control system 10 for a lighting device, such as a surgical luminaire, in accordance with one embodiment of the present invention. The lighting control system 10 is generally comprised of a primary controller 20, a drive circuit system 30 composed of at least one drive controller 32 and at least one drive output 34, one or more first LED modules 50

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4/14 (module A), and one or more second LED modules 80 (module B). In the illustrated embodiment, primary controller 20 and drive circuit system 30 are located on a first printed circuit board PCB1. Each of the first and second LED modules 50 and 80 are respectively located on the second and third printed circuit boards PCB2 and PCB3. PCB1, PCB2 and PCB3 PCBs may be located together within a housing (not shown) for the lighting device. It should be appreciated that, in the alternative embodiment, the components of LED modules 50 and 80 residing separately on PCB2 and PCB3 printed circuit boards may be located together on a single substrate (ie, printed circuit board).

In the illustrated embodiment, primary controller 20 is a microcontroller. For example, the primary controller 20 may take the form of an ARM-based processor with a variety of on-chip peripherals, including, but not limited to, internal program storage FLASH memory, data storage RAM memory , UARTs, timer / counters, a bus interface, a serial interface, a SPI interface, a programmable watchdog timer, programmable I / O lines, an A / D converter, and PWM outputs. Primary controller 20 sends commands to drive controllers 32 and reads condition information from each drive controller 32.

It should be understood that the primary controller 20 may also communicate with other electronic devices not shown in FIG. 1, including, but not limited to, a user interface (e.g., numeric keypad front panel display, control keys or buttons), a communications interface, a video input connector, and a camera module. The user interface allows the user to turn the lighting device on / off and select an intensity level for the lighting device. It may also allow the user to turn on / off other accessories configured with the lighting system.

Primary controller 20 communicates with drive controllers 32 via a bus 22. In the illustrated embodiment, bus 22 is a serial bus (e.g., IC). Primary controller 20 also provides a constant clock signal 30 to drive controllers 32 via a synchronization line 24, as will be explained in more detail below.

In the illustrated embodiment, drive controller 32 is a microcontroller. For example, each drive controller 32 may take the form of an ARM microcontroller with a variety of on-chip peripherals, including, but not limited to, an internal FLASH memory for program storage, a RAM for data storage, UARTs, timer / counters, a serial interface, an A / D converter, a programmable watchdog timer and

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5/14

Programmable I / O. In the illustrated embodiment, each drive controller 32 has a unique identification number that allows primary controller 20 to individually address each drive controller 32.

Referring now to FIG. 2, each drive output 34 is a circuitry generally comprising a comparator 42 (e.g., National Semiconductor LMV7235), a voltage regulator, a diode 45, a setpoint potentiometer (POT) 46, an effect transistor. (FET) 48, and a feedback resistor (Rs) 47. Trigger outputs 34 are triggered (i.e. activated at a fixed frequency (i.e., the fixed frequency activation signal provided by line 43 ). In the illustrated embodiment, the drive outputs 34 are driven with an activation signal with a fixed frequency of 300 Hz.

Voltage regulator 44 provides an accurate fixed output voltage (eg 5V) when activated. The output voltage (Vout) of voltage regulator 44 is electrically connected to power FET 48. FET 48 is used to manage the current required by LED modules 50, 80. Sensing resistor (Rs) 47 provides sensing of chain. Setpoint POT 46 is used to adjust the voltage output of voltage regulator 44 until the detected current associated with Rs 47 is within a target current range.

Comparator 42 monitors the output voltage of a drive output 34.

In this regard, comparator 42 receives a reference voltage (VREF) as a first input and receives a detected voltage (Vs) as a second input via line 49. Comparator 42 compares Vref with Vs to determine if the detected current (Is) associated with Vs exceeds a threshold current (e.g. approximately 1.26 A). If the threshold current has been exceeded, then comparator 42 generates a signal to deactivate voltage regulator 44, thereby deactivating VOUT of voltage regulator 44. Drive controller 32 may also deactivate voltage regulator 44 under certain conditions (eg detection of a short circuit or open circuit failure).

FIGS. 3 and 4 illustrate, respectively, schematic views of LED module 50 (module A) and LED module 80 (module B). LED modules 50, 80 are LED light sources.

In the illustrated embodiment, LED modules 50 and 80 are electrically connected in series by a harness assembly connected between LED module connector J2 50 and LED module connector J4 80. Thus, each pair of LED modules connected in series 50, 80 collectively provides a set of six (6) LEDs connected in series. A first pair of 50, 80 LED modules connected in series can be connected in parallel with a pair of 50, 80 LED modules connected in series. The first and second pairs of 50, 80 LED modules connected in series are driven from a single drive output 34 (ie drive output channel). Each 50 LED module is electricallyPetition 870190021964 of 7/03/2019, p. 17/33

6/14 is connected to a drive output 34 via a harness assembly (not shown) connected to connector J1. In the illustrated embodiment, two pairs of LED modules 50, 80 are electrically connected to drive output A and the two pairs of LED modules 50, 80 are electrically connected to drive output B.

Referring now to FIG. 3, LED module 50 includes a plurality of LEDs 52, a temperature compensation circuit 60 and an optional remote temperature sensor circuit 70. In the illustrated embodiment, LED module 50 includes three (3) LEDs connected in series 52 (e.g., high brightness LEDs). Temperature compensation circuit 60 compensates for changes in direct voltage required to drive the LEDs due to increased temperatures. As LED temperatures increase, the direct voltage must be reduced to keep the drive current constant for the LEDs. Temperature compensation circuit 60 includes a field effect transistor (FET) Q2, a thermistor 62, and a resistor network 64 composed of resistors R1 and R2. Power is supplied to a temperature compensation circuit 60 via connector J1. Thermistor 62 is a resistive temperature sensing device. The FET Q2 balances (ie equalizes) the resistor network 63 by activating more (or less) to regulate the current.

Remote temperature sensor circuit 70 includes a temperature sensor 72 (e.g. Analog Devices low voltage temperature sensor TMP35) to provide the primary controller with 20 temperature data to monitor the temperature around the printed circuit board PCB2. Temperature sensor 72 provides an output voltage that is linearly proportional to the detected temperature. Temperature sensor circuit 70 is electrically connected to primary controller 20 via connector J3 and line 26. Primary controller 20 receives output from temperature sensor circuit 70. Primary controller 20 can read a limited number of temperature inputs. temperature sensor from PCB2 printed circuit boards. In the illustrated embodiment, only two temperature sensing circuits 70 in LED modules 50 are selected or connected to primary controller 20.

Referring now to FIG. 4, LED module 80 includes a plurality of LEDs 82 and a compensation circuit 90. In the illustrated embodiment, LED module 80 includes three (3) LEDs connected in series 82 (e.g., high brightness LEDs).

Compensating circuit 90 compensates for differences in direct voltage values ​​between LEDs due to non-uniformity in LED manufacturing. In this regard, the compensation circuit 90 balances the voltage drop differences between the series connected LEDs 52, 82 to ensure that the appropriate voltage is applied across the series connected LEDs 52, 82 to set the current value. desired light and make all LED modules 50, 80 look identical (ie even lighting). The circuit

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7/14 compensation includes an adjustable Q1 FET controlled by a 96 (comparator) amplifier (for example, Analog Devices AD9220 JFET input instrumentation amplifier) ​​which provides a means by which paired LED modules 50, 80 can be calibrated (ie “reduced”) for a fixed voltage drop across the module pair as described below A digital potentiometer (POT) 92 (e.g. MAX 5417, digital potentiometer from Maxim Integrated Products) is used to fix the gate voltage for FET Q1. A micropotency voltage regulator 94 (for example, Maxim Integrated Products voltage reference LM4040) is used to power amplifier 96 and digital POT 92. Voltage regulator 94 provides 5V for digital POT, for amplifier 96 and for polarization circuits (not shown). The input to voltage regulator 94 uses a D1 locking diode and two capacitors (not shown). The combination of diode D1 and two capacitors provides small capacitive storage between the pulses to keep voltage constant under the minimum duty cycle at normal operating frequency (eg 25% at 300 Hz). Voltage regulator 94 is always powered as voltage is applied to LEDs 52, 82.

The operation of the lighting control system 10 will now be described in detail. Primary controller 20 is programmed to provide general control of the lighting control system 10. In this regard, primary controller 20 communicates with drive controllers 32, as well as other system components, such as a user interface and a camcorder.

In the illustrated embodiment, the primary controller 20 generates a clock signal of 30

KHz composed of fixed duration clock pulses. The clock signal is provided to each drive controller 32 by the synchronization line 24. The clock signal is used to maintain synchronization between the drive controllers 32 and to provide each drive controller 32 with a fixed time base used. to drive the respective LED modules 50, 80. In this regard, the clock signal directly triggers two internal timers within each drive controller 32. The first internal timer of each drive controller 32 is associated with a first drive output 34 (drive output A) and the second timer. The internal control of each drive controller 32 is associated with a second drive output 34 (drive output B). Internal timers allow the two drive outputs 34 (that is, drive output A and drive output B) to provide drive output signals that are out of phase with each other, thus preventing large fluctuations in current draw when The lighting device is activated. According to a preferred embodiment of the present invention, the phase is different for each drive output 34 of all drive controllers 32. Thus, drive output A of drive controller 1, drive output B of drive controller 1,

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8/14 drive output A of drive controller 2 and drive output B of drive controller 2 provide drive output signals that are out of phase with each other.

Trigger output signals associated with preferably triggered outputs 34 have a fixed frequency of 300 Hz. The frequency of 300 Hz is selected because it is a multiple of 50 Hz (the scan rate of PAL camcorders) and 60 Hz (the scan rate of NTSC camcorders). When using an optional camcorder with the lighting device associated with the present invention, the camera will detect a noticeable flicker in the light if the output frequency of LEDs 52, 82 is not a multiple of the camera scan rate.

Primary controller 20 sends multiple commands to each drive controller 32 to activate ”LED modules 50, 80 (ie enable LEDs 52, 82). Commands include a command indicating a selected duty cycle (also called a “target duty cycle”) for drive output signals from drive outputs 34, a command indicating “phase shift” for each drive output 34, and a command indicating activation of LED modules 50, 80, called the "start" command. The operating activity cycle is indicated by a number of pulses of the clock signal output by the primary controller 20. As will be explained in more detail below, the number of clock signal pulses of the primary controller 20 will set the "on period" for each period of the drive output signal produced by the drive outputs 34.

Operational duty cycle is the ratio of the drive output signal ON time to the drive output signal period for drive outputs 34. As indicated above, each drive output signal preferably has , a fixed frequency of 300 Hz, and therefore has a period of 3.33 msec. In the illustrated embodiment, LED modules 50, 80 are activated (i.e. illuminated) during the ON time of the drive output signals. The internal timers of each drive controller 32 count a predetermined number of clock signal pulses provided by the primary controller 20 to establish the on time for each period of the drive output signals. Thus, the predetermined number of counted pulses corresponds to the operating duty cycle selected for the drive output signals. For example, in a selected operating duty cycle of 40%, 40 clock signal pulses are counted to establish the on time for the trigger output signals period.

In addition, a phase shift is generated in units of the clock signal emitted by the primary controller 20. The start command indicates to the drive controllers 32 that the associated LED modules 40, 80 are about to be activated (that is, activate the lights

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9/14

LED). Drive controllers 32 use the start command to initialize their respective internal timers and prepare for the start of the clock signal generated by primary controller 20. Primary controller 20 can also send a “stop” command to drive controllers 32 of informing drive controllers 32 to disable the associated drive outputs 34 and interrupt their respective internal timers.

As discussed above, the primary controller clock signal 20 triggers the two internal timers within each drive controller 32, thereby enabling drive controllers 32 to control the associated LED modules 50, 80 in the duty cycle by means of of the drive output signals from the drive outputs 34. The values ​​for the various operating activity cycles provided by the primary controller 20 are set to correspond to a plurality of user selectable predetermined LED intensity levels. The duty cycle values ​​associated with each intensity level can be pre-stored in a lookup table in primary controller memory 20. By way of example, and not limitation, the illustrated embodiment may include the nine intensity levels shown in TABLE 1:

TABLE 1

<td>Intensity level</td><td>Activity Cycle</td>

<td> 1</td><td> 40%</td>

<td> 2</td><td> 50%</td>

<td> 3</td><td> 60%</td>

<td> 4</td><td> 70%</td>

<td> 5</td><td> 80%</td>

<td> 6</td><td> 90%</td>

<td> 7</td><td> 100%</td>

<td>Maintenance</td><td> 25%</td>

<td>Calibration</td><td> 100%</td>

The duty cycle value for the maintenance intensity level provides a low duty cycle for low light intensity to make it easier to inspect faulty 50 LED modules 50, 80 with less visual discomfort. The duty cycle value for the calibration intensity level provides a maximum duty cycle that allows convenient adjustment of power supplies until the lowest drive current output is at the target drive current, thereby distributing output current. sufficient drive to all LED modules 50, 80

As will be described in more detail below, the primary controller 20 is also

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10/14 programmed to operate LED modules 50, 80 during a warm-up mode, so that the light output provided by LED modules 50, 80 does not exceed a predetermined maximum light output level and so that a light output uniformly maintained.

The operation of LED module 50 (module A) will now be described in detail with reference to FIG. 3. Temperature compensation circuit 60 adjusts the total voltage drop across LED module pairs 50, 80 as the direct voltage characteristics of LEDs 52, 82 change with LED temperature. As LEDs 52, 82 heat up, their direct voltage drops. Reductions in direct voltage lead to an increase in current flowing through LEDs 52, 82. The total voltage drop across the six LEDs connected in series 52, 82 of LED modules 50, 80 is high enough to require some form of temperature compensation that keeps the LED drive current at the target drive current and prevents the modules from LED 50, 80 suffer overcurrent shutdown.

The temperature compensation circuit 60 of LED module 50 (LED module A, for example) includes a FET Q2 which is polarized so that when LED modules 50, 80 are cold, FET Q2 is fully activated. This makes the direct resistance of the FET Q2 very low, so there is a relatively small amount of voltage drop across the FET Q2 when cold. As LED modules 50, 80 begin to heat, thermistor 62 acts to reduce the gate voltage on the FET Q2 and increase its direct resistance. This action effectively absorbs the reduction in direct voltage as the LEDs 52, 82 heat up. As LEDs 52, 82 begin to warm, thermistor 62 in the FET Q2 bias network acts to reduce the gate voltage on the FET Q2 and increase its direct resistance. This action effectively absorbs the direct voltage reduction as the LEDs 52, 82 heat up. As the resistance of thermistor 62 gets smaller and smaller, the gate voltage for FET Q2 becomes sufficiently low, making the FET Q2 resistance much larger than that of the pair of low value parallel power resistors R1, R2. . At this point, virtually all current flowing through the temperature compensation circuit 60 passes through parallel resistors R1 and R2, effectively shutting down FET Q2. Turning off FET Q2 and turning on fixed resistors R1 and R2 allows FET Q2 to be smaller and less expensive, as FET Q2 does not need to be set to manage total current at higher temperatures. Temperature compensation circuit 60 is an independent circuit which has no feedback to drive controller 32 or primary controller 20.

As indicated above, the temperature sensor circuit 70 provides data for the primary controller 20 for display only and indicates the operating temperature in specifications 870190021964 of 3/7/2019, p. 22/33

11/14 limits of LED module 50.

The operation of LED module 80 (module B) will now be described in detail with reference to FIG. 4. LED 80 module compensation circuit 90 offers the ability to insert an adjustable fixed voltage drop in series with six LEDs 52 and 82 to calibrate the pair of LED modules 50 and 80 to a fixed input voltage used to power all LED modules 50 and 80 on the lighting device. An adjustable voltage drop in series with LEDs 52 and 82 allows the electrical voltage of each pair of modules 50 and 80 to be adjusted to a common electrical voltage to a specified electrical current. This feature allows module pairs 50 and 80 to be driven in parallel.

Each drive output 34 drives two pairs of electrically connected LED modules 50 and 80 in parallel. If the two parallel pairs of LED modules 50 and 80 do not have substantially similar direct voltage drops, the currents across the two pairs of LED modules 50 and 80 are not equivalent, and thus the light output of the two parallel pairs of LED modules. 50 and 80 will not vary accordingly. Compensating circuit 90 amplifier 96 generates the FET Q1 gate voltage based on the difference between the positive FET drain input and the negative input that is set using digital POT 92. When digital POT 92 is being set to a appropriate resistance value, the FET Q1 acts as a resistor fixed in series with LEDs 52 and 82. Adjusting the direct resistance of the FET Q1 effectively suppresses the direct voltage variations of LED modules 50 and 80 caused by the different direct voltages of LEDs 52 and 82.

POT 92 is adjusted and programmed as part of the LED module production process by connecting the J5 connector to a programming tool (for example, a test and calibration instrument) that records a setpoint value for POT 92. POT 92 adjustment is performed during a test and production process when the modules are

LEDs 50 and 80 are electrically connected together. During the production process of LED modules 50 and 80, approximately 24V is applied by a test and calibration instrument to LED module 50 via connector J1. POT 92 is then adjusted so that the drive current through LEDs 52 and 82 is a predetermined drive current target value. Compensating circuit 90 is a stand-alone circuit and has no feedback to drive controller 32 or primary controller 20.

It should be noted that LED modules 50 and 80 can be overridden to account for optical losses during mounting of the lighting fixture. In this regard, the LED drive current control target is defined as a predetermined fixed deviation above the LED direct drive current rating. Consequently, manufacturing personnel will be able to increase the intensity of LEDs 52 and 82 by adjusting the drive current to a value within the permissible range of the LED manufacturer, thereby achieving a desired lux reading of the lighting device. 03/07/2019, p. 23/33

12/14 tion.

A calibration function is provided by primary controller 20 to allow additional adjustment to be made to “tune” the drive current so that it is closer to the target drive current. 24VDC adjustable output power supplies to be supplied to luminaires including 50 and 80 LED modules can have their outputs adjusted up or down to increase or decrease drive current readings.

Drive controller 32 is programmed to sample the LED drive current and determine if the LED drive current is within the target drive current value plus / minus a preset tolerance to provide fault messages to the display medium. If the LED drive current is outside the allowable tolerance, an audible or visual alarm may be used to indicate to the user that power supplies need to be adjusted, or that LED modules 50 and 80 (or the associated harness) need to be replaced.

Primary controller 20 is programmed to monitor drive current

Trigger output LEDs 34 to determine if one or both of the associated pairs of LED modules 50 and 80 have failed (ie open circuit) to provide a fault message to the display medium. If an LED module 50 and 80 of the pair of LED modules have failed to open, the drive current will be approximately 50% of a target drive current setting. If both pairs of LED modules have failed, the drive current reading will be approximately 0 mA. Fault conditions are detected by the primary controller 20 and indicator alarms are generated on the user interfaces. A portion of each drive output 34 determines whether an LED module 50 and 80 has failed due to a short circuit. In this regard, drive output 34 detects the presence of a short circuit and generates an overcurrent indication for the associated drive controller 32. This drive controller 32 then shuts off drive output 34 associated with LED module 50, 80 short-circuit, and prevents drive output 34 from being switched on until the short-circuit fault condition has been eliminated. A failure message may also be displayed to the user.

As discussed above, primary controller 20 is programmed to operate according to a heating mode, as will be explained in detail with reference to FIGS. 5A and 5B. FIGS. 5A and 5B show a flow chart of a lighting control method for operating LEDs during a heating mode. Warm-up mode starts when LED modules 50, 80 are initially powered on at startup, as long as the ambient temperature of the electronics for the LED light source is below a predefined setpoint temperature (Tsetpoint), for example, in

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13/14

38^OC. Ambient temperature is checked in step 105. Primary controller 20 recovers the predetermined setpoint (Dsp) activity cycle corresponding to a user-selected light intensity level (Step 110). For example, intensity levels 1 through 7 may correspond respectively to setpoint activity (Dsp) cycles of 40%, 50%, 60%, 70%, 80%, 90%, and 100%. After this, the primary controller 20 retrieves a pre-stored Duty Cycle Compensation (Dtrim) value associated with the selected light intensity level (Step 120). Primary controller 20 is also programmed to determine if a gradual shift activity cycle function has been activated (Step 120). The gradual change activity cycle function is described in detail below.

In step 130, the operating activity cycle (D) is established in the setpoint activity cycle (DSP), corresponding to the selected intensity level as compensated by Dtrim, thus for a first time interval (eg 15 minutes), LED modules 50, 80 are operated at an operating duty cycle (D) equal to the Dtrim reduced setpoint activity cycle (Dsp) (Step 140). As discussed above, the duty cycle (D) refers to the duty cycle of the drive output signals of the drive outputs 34. After the first time interval has elapsed, primary controller 20 determines whether gradual change activity cycle has been activated (Step 145). If the gradual shift activity cycle function has not been activated, then the heating mode is terminated. Alternatively, if the gradual change activity cycle has been activated, then the gradual change activity cycle function is started (Step 150).

At step 160, primary controller 20 retrieves pre-stored values ​​for the incremental time (Tr) and duty cycle increment (Dstep) value. The duty cycle increment (Dstep) value is a percentage value (for example, 2%). The duty cycle tap change value (Dramp) is initially set equal to Dstep (Step 170). At Step 180, LED modules 50, 80 are operated for a period of time (for example, 5 minutes) at a defined duty cycle (D) equal to Dsp - Dtrim + Dramp. At the end of the time interval, the primary controller 20 determines whether the incremental time (Tr) has already elapsed, whether the operating duty cycle (D) has reached the setpoint activity cycle Dsp to the intensity level of light selected or if a new light intensity level has been manually selected by the user, thus resulting in a new operating activity cycle (Step 185). If any of these conditions have been met, then the heating mode is terminated. If none of these conditions have been met, then primary controller 20 increases the current Dramp by Dstep (Step 190). Primary controller 20 then operates LED modules 50, 80 for the subsequent time interval in the newly opened operating duty cycle (D).

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14/14 established, which is equal to Dsp - Dtrim + Dramp (Step 180). Once Dramp has been increased at Step 190, the duty cycle (D) will be increased at Step 180. This gradual staggered increase in duty cycle (D) will continue for subsequent time intervals until one of the conditions at step 185 is satisfied, thus ending the heating mode.

Further modifications and changes will be designed after reading and understanding the descriptive report. It should be understood that it is contemplated that the present invention may have many alternative embodiments. For example, in one configuration, 28 LED modules are grouped into 14 pairs of LED modules. Thus, four drive controllers are connected to the primary controller. In another configuration, 56 LED modules are grouped into 28 pairs of LED modules. Thus, seven drive controllers are connected to the primary controller. In addition, it is contemplated that multi-color LEDs may be used in place of single-color LEDs of the illustrated embodiment. All such modifications and alterations are intended to be included to the extent that they fall within the scope of the invention as claimed or its equivalents. Having described the invention, the following is claimed.