TWO-WIRE DIMMER CIRCUIT FOR A SCREW-IN COMPACT FLUORESCENT LAMP

• US 20090108765A1
• Filed: 10/31/2007
• Published: 04/30/2009
• Est. Priority Date: 10/31/2007
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Taipale, Mark S., Weightman, Russell
• Granted Patent: US 7,868,561 B2
• Time in Patent Office: Days
• US Class Current: 315/224
• CPC Class Codes: H05B 39/08 by shifting phase of trigger voltage applied to gas-filled controlling tubes also in controlled semiconductor devices in converters H02M5/00; with regulation G05F1/44
• CPC Class Codes: H05B 41/3924 by phase control, e.g. using a triac H05B41/3922 takes precedence
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y10S 315/04 Dimming circuit for fluorescent lamps

Abstract

A dimmer switch for controlling the intensity of a dimmable screw-in compact fluorescent lamp provides smooth dimming of the fluorescent lamp and prevents flickering of the lamp due to multiple re-strikes. The dimmer switch prevents multiple re-strikes by avoiding multiple firings of a controllably conductive switching device of the dimmer circuit by limiting the high-end light intensity of the fluorescent lamp. Specifically, the dimmer switch limits the length of a conduction interval of the controllably conductive switching device to less than approximately 75% of each half-cycle. The dimmer switch may include a user-accessible adjustment actuator for changing the dimmer switch between an incandescent operating mode and a screw-in compact fluorescent mode. The dimmer switch may also be operable to automatically change the dimmer switch between the incandescent operating mode and the screw-in compact fluorescent mode by detecting the occurrence of the multiple firings of the controllably conductive switching device.

Claims

1. A two-wire dimmer control circuit for a fluorescent lamp load including a ballast circuit, said two-wire dimmer control circuit adapted to be coupled in series electrical connection between an AC power source and said ballast circuit, said two-wire dimmer control circuit comprising:

a controllably conductive switching device adapted to be coupled in series electrical connection between said AC power source and said ballast circuit, and having a control electrode;

a phase-cut AC drive circuit connected to said control electrode of said controllably conductive switching device for rendering said controllably conductive switching device conductive for a conductive interval each half-cycle of said AC power source, said phase-cut AC drive circuit operable to control the length of said conduction interval of said controllably conductive switching device each half-cycle; and

a high-end intensity regulation circuit for limiting the length of said conduction interval of said controllably conductive switching device to less than approximately 75% of each half-cycle.

2. The circuit of claim 1, wherein said controllably conductive switching device is a triac with a low holding current rating.

3. The circuit of claim 2, wherein said low holding current rating is less than approximately 35 mA.

4. The circuit of claim 3, wherein said two wire control circuit is further adapted to be coupled between an AC power source and an incandescent lamp for dimming said incandescent lamp.

5. The circuit of claim 4, wherein said fluorescent lamp load includes a dimmable screw-in compact fluorescent lamp load, and said ballast circuit is integral to said fluorescent lamp load.

6. The circuit of claim 1, wherein said high-end intensity regulation circuit contains a high-end resistor having a resistance of greater than approximately 22 kΩ

.

7. The circuit of claim 1, wherein said phase-cut circuit further includes:

a potentiometer for adjusting the intensity of said fluorescent lamp;

a low-end calibration resistor coupled in parallel with said potentiometer for setting a low-end intensity setting of said fluorescent lamp; and

an input voltage compensation circuit for adjusting for variations in an output voltage of said AC power source.

8. The circuit of claim 1, wherein said high-end intensity regulation circuit limits the length of said conduction interval of said controllably conductive switching device to less than approximately 70% of each half-cycle.

9. A phase-cut circuit for controlling the amount of power delivered from an AC power source to an incandescent lamp, said phase-cut circuit modified to drive a fluorescent ballast for a fluorescent lamp, said phase-cut circuit including a triac which has a lower holding current than that used for said incandescent lamp, and providing a reduced high-end intensity setting as compared to that used for said incandescent lamp.

10. The modified phase-cut circuit of claim 9, wherein said phase-cut circuit limits a conduction time of said triac to less than approximately 75% of each half-cycle.

11. The modified phase-cut circuit of claim 10, wherein said fluorescent lamp is a dimmable screw-in compact fluorescent lamp.

12. The modified phase-cut circuit of claim 10, wherein said phase-cut circuit comprises a high-end resistor having a resistance greater than approximately 22 kΩ

.

13. A method of controlling a fluorescent lamp load including a ballast circuit, the method comprising the steps of:

conducting a load current from an AC power source to the ballast circuit for a conduction interval each half-cycle of the AC power source;

controlling the length of the conduction interval each half-cycle; and

limiting the length of the conduction interval to less than approximately 75% of each half-cycle.

14. A two-wire dimmer control circuit for a fluorescent lamp load including a ballast circuit, the two-wire dimmer control circuit adapted to be coupled in series electrical connection between an AC power source and the ballast circuit, the two-wire dimmer control circuit comprising:

means for conducting a load current from the AC power source to the ballast circuit for a conduction interval each half-cycle of the AC power source; and

means for controlling the length of the conduction interval each half-cycle;

wherein the improvement comprises means for limiting the length of the conduction interval to less than approximately 75% of each half-cycle.

15. A two-wire dimmer circuit for a fluorescent lamp load including a ballast circuit, the two-wire dimmer circuit adapted to be coupled in series electrical connection between an AC power source and the ballast circuit, the two-wire dimmer control circuit comprising:

a bi-directional semiconductor switch adapted to be coupled in series electrical connection between the AC power source and the ballast circuit for controlling the amount of power delivered to the ballast circuit, the bi-directional semiconductor switch having a control input;

a timing circuit operatively coupled in parallel electrical connection with the bi-directional semiconductor switch, the timing circuit having an output for generating a timing voltage representative of a desired intensity of the fluorescent lamp; and

a trigger circuit operatively coupled between the output of the timing circuit and the control input of the bi-directional semiconductor switch, the trigger circuit operable to render the bi-directional semiconductor switch conductive in response to the timing voltage, such that the bi-directional semiconductor switch is conductive for a conduction interval each half-cycle;

wherein the improvement comprises the timing circuit being adapted to limit the conduction interval to less than approximately 75% of each half-cycle.

16. The dimmer circuit of claim 15, wherein the bi-directional semiconductor switch comprises a triac having a holding current rating of less than 35 mA.

17. The dimmer circuit of claim 16, wherein the timing circuit is adapted to limit the conduction interval to greater than approximately 31% of each half-cycle.

18. The dimmer circuit of claim 17, further comprising:

a voltage compensation circuit coupled in series electrical connection with the timing circuit, such that the series combination of the timing circuit and the voltage compensation circuit are coupled in parallel electrical connection with the bi-directional semiconductor switch, the voltage compensation circuit operable to compensate for voltage fluctuations of the AC power source.

19. The dimmer circuit of claim 17, further comprising:

a filter circuit coupled in parallel electrical connection with the bi-directional semiconductor switch, the filter circuit comprising a resistor in series with a capacitor, the filter circuit operable to minimize ringing in a dimmed-hot voltage produced across the fluorescent lamp load.

20. The dimmer circuit of claim 19, wherein the timing circuit comprises:

a potentiometer having two main terminals and a wiper terminal coupled to one of the main terminals, such that the resistance of the potentiometer between the two main terminals ranges from approximately 0Ω

to 300 kΩ

;

a high-end resistor coupled in series electrical connection with the main terminals of the potentiometer, the high-end resistor having a resistance greater than approximately 22 kΩ

; and

a firing capacitor coupled to the output of the timing circuit for generating the timing voltage, the firing capacitor adapted to charge through the potentiometer and the high-end resistor.

21. The dimmer circuit of claim 20, wherein the timing circuit further comprises a calibration resistor coupled in parallel electrical connection with the two main terminals of the potentiometer and having a resistance of approximately 110 kΩ

.

22. The dimmer circuit of claim 21, wherein the firing capacitor of the timing circuit has a capacitance of approximately 0.047 μ

F, and the trigger circuit comprises a diac having a break-over voltage of approximately 30 V.

23. The dimmer circuit of claim 22, wherein the voltage compensation circuit comprises a resistor coupled in series electrical connection with two series-coupled diacs, the resistor having a resistance of approximately 27 kΩ

, and the diacs both having break-over voltages of approximately 30 V, the junction of the resistor and the two series-coupled diacs connected to the timing circuit, and further wherein the resistor of the filter circuit has a resistance of approximately 220Ω and

the capacitor of the filter circuit has a capacitance of approximately 0.047 μ

F.

24. The dimmer circuit of claim 20, wherein the high-end resistor has a resistance of approximately 44 kΩ

.

25. The dimmer circuit of claim 19, wherein the low holding current rating is approximately 15 mA.

26. A dimmer switch adapted to be coupled between an AC power source generating an AC line voltage and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

a controllably conductive switching device adapted to be coupled in series electrical connection between the AC power source and the lighting load for controlling the amount of power delivered to the lighting load;

a drive circuit coupled to a control input of the controllably conductive switching device for controlling the controllably conductive switching device to be conductive for a conduction interval each half-cycle of the AC power source; and

a user interface operable to receive a user input for changing the dimmer switch between first and second operating modes, such that the drive circuit is operable to adjust the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value in the first operating mode, and to adjust the high-end intensity setting to a second high-end intensity setting value and the low-end intensity setting to a second low-end intensity setting value in the second operating mode.

27. The dimmer switch of claim 26, wherein the second high-end intensity setting value is less than the first high-end intensity setting value, and the second low-end intensity setting value is greater than the first low-end intensity setting value.

28. The dimmer switch of claim 27, wherein the drive circuit comprises a controller operatively coupled to the control input of the controllably conductive switching device, and a zero-crossing detector operable to provide a signal representative of a zero-crossing of the AC line voltage to the controller.

29. The dimmer switch of claim 28, wherein the user interface comprises a control actuator and an intensity adjustment actuator, the controller operable to change the dimmer switch between the first and second operating modes in response to actuations of the control actuator and the intensity adjustment actuator.

30. The dimmer switch of claim 29, wherein the controller is operable to change the dimmer switch between the first and second operating modes as part of an advanced programming mode.

31. The dimmer switch of claim 27, wherein the user interface comprises a user-accessible adjustment actuator coupled to the drive circuit for changing the dimmer switch between the first and second operating modes.

32. The dimmer switch of claim 27, wherein the first and second operating modes comprise an incandescent operating mode and a screw-in compact fluorescent operating mode, respectively.

33. A dimmer switch adapted to be coupled between an AC power source and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

a user-accessible adjustment actuator for changing the dimmer switch between first and second operating modes, such that the high-end intensity setting is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, and the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode.

34. The dimmer switch of claim 33, wherein the second high-end intensity setting value is less than the first high-end intensity setting value, and the second low-end intensity setting value is greater than the first low-end intensity setting value.

35. The dimmer switch of claim 34, further comprising:

a controllably conductive switching device adapted to be coupled in series electrical connection between the AC power source and the lighting load, the controllably conductive switching device having a control input for controlling the controllably conductive switching device;

a trigger circuit coupled to the control input of the controllably conductive switching device for rendering the controllably conductive switching device conductive each half-cycle of the AC power source; and

a timing circuit operatively coupled in parallel electrical connection with the controllably conductive switching device for generating a timing voltage;

wherein the trigger circuit is operable to control the semiconductor switch in response to the timing voltage.

36. The dimmer switch of claim 35, wherein the timing circuit comprises:

a potentiometer for providing a variable resistance;

a firing capacitor coupled to the output of the timing circuit for generating the timing voltage, the firing capacitor adapted to charge through the potentiometer; and

a mechanical switch mechanically coupled to the user-accessible adjustment actuator, and electrically coupled such that the dimmer switch operates in the first operating mode when the mechanical switch is in a first position, and the dimmer switch operates in the second operating mode when the mechanical switch is in a second position.

37. The dimmer switch of claim 36, wherein the timing circuit further comprises:

a high-end resistor coupled in series electrical connection with the potentiometer, the firing capacitor adapted to charge through the potentiometer and the high-end resistor;

wherein the mechanical switch is electrically coupled to the high-end resistor, such that a first resistance is provided in series with the potentiometer when the mechanical switch is in a first position, and a second resistance is provided in series with the potentiometer when the mechanical switch is in a second position.

38. The dimmer switch of claim 37, wherein the timing circuit further comprises:

a low-end resistor coupled in parallel electrical connection with the potentiometer;

wherein the mechanical switch is electrically coupled to the low-end resistor, such that a third resistance is provided in parallel with the potentiometer when the mechanical switch is in the first position, and a fourth resistance is provided in parallel with the potentiometer when the mechanical switch is in the second position.

39. The dimmer switch of claim 36, wherein the timing circuit further comprises:

first and second high-end resistors coupled in series, the series combination of the first and second high-end resistors coupled in series with the potentiometer; and

first and second low-end resistors coupled in series, the series combination of the first and second low-end resistors coupled in parallel with the potentiometer;

wherein the mechanical switch is coupled such that one of the first and second high-end resistors is electrically shorted when the mechanical switch is in a first position, and one of the first and second low-end resistors is electrically shorted when the mechanical switch is in a second position.

40. The dimmer switch of claim 39, wherein the mechanical switch comprises a single-pole double-throw switch.

41. The dimmer switch of claim 34, further comprising:

an intensity adjustment actuator mechanically coupled to the potentiometer, such that the variable resistance of the potentiometer is responsive to the intensity adjustment actuator.

42. A dimmer switch adapted to be coupled between an AC power source and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

a controllably conductive switching device adapted to be coupled in series electrical connection between the AC power source and the lighting load for controlling the amount of power delivered to the lighting load;

a controller coupled to a control input of the controllably conductive switching device for controlling the controllably conductive switching device to be conductive for a conduction interval each half-cycle of the AC power source; and

a user interface operable to receive a user input;

wherein the controller is operable to change the dimmer switch between first and second operating modes in response to the user interface, such that the high-end intensity setting is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, and the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode, the second high-end intensity setting value less than the first high-end intensity setting value, and the second low-end intensity setting value greater than the first low-end intensity setting value.

43. The dimmer switch of claim 42, wherein the user interface comprises a control actuator and an intensity adjustment actuator, the controller operable to change the dimmer switch between the first and second operating modes in response to actuations of the control actuator and the intensity adjustment actuator.

44. The dimmer switch of claim 43, wherein the controller is operable to change the dimmer switch between the first and second operating modes as part of an advanced programming mode.

45. The dimmer switch of claim 43, wherein the controller is operable to adjust the low-end intensity setting to a third low-end intensity setting value in response to actuations of the control actuator and the intensity adjustment actuator.

46. The dimmer switch of claim 42, further comprising:

a hot terminal adapted to be coupled to a hot side of the AC power source;

a dimmed hot terminal adapted to be coupled to the electrical load;

a neutral terminal adapted to be coupled to a neutral side of the AC power source;

a power supply coupled between the hot terminal and the neutral terminal, the power supply operable to provide a DC voltage for powering the controller; and

a zero-crossing detector operable to provide a signal representative of a zero-crossing of the AC power source to the controller, the controller operable to control the controllably conductive switching device in response to the zero-crossing detector.

47. A drive circuit for a controllably conductive switching device of a dimmer switch adapted to be coupled between an AC power source and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the drive circuit comprising:

a potentiometer for providing a variable resistance;

a firing capacitor coupled to an output of the potentiometer for generating a timing voltage, the firing capacitor adapted to charge through the potentiometer such that the timing voltage is responsive to the variable resistance of the potentiometer; and

a mechanical switch for changing the dimmer switch between first and second operating modes, such that the high-end intensity setting is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, and the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode, the second high-end intensity setting value less than the first high-end intensity setting value, and the second low-end intensity setting value greater than the first low-end intensity setting value.

48. The drive circuit of claim 47, further comprising:

first and second high-end resistors coupled in series, such that the series combination of the first and second high-end resistors are coupled in series with the potentiometer; and

first and second low-end resistors coupled in series, such that the series combination of the first and second low-end resistors are coupled in parallel with the potentiometer;

wherein the mechanical switch is coupled such that one of the first and second high-end resistors is electrically shorted when the mechanical switch is in a first position, and one of the first and second low-end resistors is electrically shorted when the mechanical switch is in a second position.

49. The drive circuit of claim 48, wherein the mechanical switch comprises a single-pole double-throw switch.

50. A dimmer switch adapted to be coupled between an AC power source generating an AC line voltage and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising a controllably conductive switching device adapted to be coupled in series electrical connection between the AC power source and the lighting load for controlling the amount of power delivered to the lighting load, and a user interface operable to receive a user input, the improvement comprising:

a drive circuit responsive to the user interface to change the dimmer switch between first and second operating modes, the drive circuit operable to adjust the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value in the first operating mode, and to adjust the high-end intensity setting to a second high-end intensity setting value and the low-end intensity setting to a second low-end intensity setting value in the second operating mode.

51. A dimmer switch adapted to be coupled between an AC power source generating an AC line voltage and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

a controllably conductive switching device adapted to be coupled in series electrical connection between the AC line voltage and the lighting load for controlling the amount of power delivered to the lighting load, the controllably conductive switching device having a conductive state and a non-conductive state;

a controller operable to drive the controllably conductive switching device to change the controllably conductive switching device from the non-conductive state to the conductive state each half-cycle of the AC power source, the controller operable to render the controllably conductive switching device conductive after a minimum off time following a zero-crossing of the AC line voltage, and to subsequently determine whether the controllably conductive switching device is conducting a load current to the lighting load;

wherein the controller is operable to adjust the dimmer switch to one of a first operating mode and a second operating mode in response to whether the controllably conductive switching device is conducting current to the load, the controller operable to adjust the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value in the first operating mode, and to set the high-end intensity setting to a second high-end intensity setting value and the low-end intensity setting to a second low-end intensity setting value in the second operating mode.

52. The dimmer switch of claim 51, wherein the second high-end intensity setting value is less than the first high-end intensity setting value, and the second low-end intensity setting value is greater than the first low-end intensity setting value.

53. The dimmer switch of claim 52, further comprising:

a voltage detect circuit coupled in parallel electrical connection with the controllably conductive switching device, the voltage detect circuit operable to provide a control signal representative of the magnitude of a voltage across the controllably conductive switching device to the controller.

54. The dimmer switch of claim 53, wherein the controller is operable to determine the magnitude of the voltage across the controllably conductive switching device at a predetermined time after the controller renders the controllably conductive switching device conductive.

55. The dimmer switch of claim 54, wherein the controller is operable to adjust the dimmer switch to the second operating mode if the voltage across the controllably conductive switching device is greater than a predetermined voltage threshold at the predetermined time after the controller renders the controllably conductive switching device conductive.

56. The dimmer switch of claim 55, wherein the predetermined voltage threshold comprises approximately 2 volts.

57. The dimmer switch of claim 55, wherein the first and second operating modes comprise an incandescent operating mode and a screw-in compact fluorescent operating mode, respectively.

58. The dimmer switch of claim 54, wherein the controller is operable to adjust the dimmer switch to the first operating mode if the voltage across the controllably conductive switching device is less than a predetermined voltage threshold.

59. The dimmer switch of claim 54, wherein the predetermined time comprises 400 μ

sec.

60. The dimmer switch of claim 52, further comprising:

a sensing circuit operable to sense an electrical characteristic representative of a magnitude of the load current, the controller coupled to the sensing circuit, such that the controller is operable to adjust the dimmer switch to one of the first operating mode and the second operating mode in response to the electrical characteristic.

61. The dimmer switch of claim 52, wherein the controller is operable to adjust the dimmer switch to one of the first operating mode and the second operating mode at power-up of the controller.

62. The dimmer switch of claim 61, further comprising:

a memory coupled to the controller for storing a desired intensity of the lighting load;

wherein the controller is operable to determine the desired intensity from the memory at power-up of the controller, and to adjust the dimmer switch to one of the first operating mode and the second operating mode at power-up if the desired intensity is greater than zero.

63. The dimmer switch of claim 62, further comprising:

a control actuator coupled to the controller, the controller operable to turn the lighting load on in response to an actuation of the control actuator;

wherein, if the desired intensity is determined to be off at power-up, the controller is operable to adjust the dimmer switch to one of the first operating mode and the second operating mode when the lighting load is turned on.

64. The dimmer switch of claim 52, wherein the controllably conductive switching device comprises a bi-directional semiconductor switch.

65. The dimmer switch of claim 64, wherein the bi-directional semiconductor switch comprises a triac.

66. A dimmer switch adapted to be coupled between an AC power source and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

a first load terminal adapted to be coupled to the AC power source;

a second load terminal adapted to be coupled to the lighting load;

a controllably conductive switching device adapted to be coupled in series electrical connection between the first and second load terminals for controlling the amount of power delivered to the lighting load;

a controller coupled to a control input of the controllably conductive switching device for controlling the controllably conductive switching device to be conductive for a conduction interval each half-cycle of the AC power source; and

a sensing circuit coupled such that the sensing circuit is operable to sense an electrical characteristic of the second load terminal and adapted to provide a control signal representative of the electrical characteristic to the controller;

wherein the controller is operable to change the dimmer switch between first and second operating modes in response to the control signal from the sensing circuit, such that the high-end intensity setting is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, and the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode.

67. The dimmer switch of claim 66, wherein the second high-end intensity setting value is less than the first high-end intensity setting value, and the second low-end intensity setting value is greater than the first low-end intensity setting value.

68. The dimmer switch of claim 66, wherein the sensing circuit comprises a voltage sense circuit coupled in parallel electrical connection with the controllably conductive switching device.

69. A dimmer switch adapted to be coupled between an AC power source and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

a first load terminal adapted to be coupled to the AC power source;

a second load terminal adapted to be coupled to the lighting load;

a controllably conductive switching device adapted to be coupled in series electrical connection between the first and second load terminals for controlling the amount of power delivered to the lighting load;

a controller coupled to a control input of the controllably conductive switching device for controlling the controllably conductive switching device to be conductive for a conduction interval each half-cycle of the AC power source, the controller operable to automatically adjust the dimmer switch to one of a first operating mode and a second operating mode, such that the high-end intensity setting is adjusted to a first high-end intensity setting value and the low-end intensity setting is adjusted to a first low-end intensity setting value in the first operating mode, and the high-end intensity setting is adjusted to a second high-end intensity setting value and the low-end intensity setting is adjusted to a second low-end intensity setting value in the second operating mode.

70. The dimmer switch of claim 69, wherein the second high-end intensity setting value is less than the first high-end intensity setting value, and the second low-end intensity setting value is greater than the first low-end intensity setting value.

71. The dimmer switch of claim 69, wherein the controller is operable to automatically adjust the dimmer switch to one of the first and second operating modes at power up.

72. A method of controlling a dimmer switch adapted to be coupled between an AC power source and a lighting load, the dimmer switch adapted to control the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the method comprising the steps of:

conducting a load current from the AC power source to the lighting load for a conduction interval each half-cycle of the AC power source;

controlling the length of the conduction interval each half-cycle;

automatically changing the dimmer switch to one of first and second operating modes;

adjusting the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value when operating in the first operating mode; and

adjusting the high-end intensity setting to a second high-end intensity setting value and the low-end intensity setting to a second low-end intensity setting value when operating in the second operating mode;

wherein the second high-end intensity setting value is less than the first high-end intensity setting value, and the second low-end intensity setting value is greater than the first low-end intensity setting value.

73. A dimmer switch adapted to be coupled between an AC power source and a lighting load for controlling the intensity of the lighting load between a high-end intensity setting and a low-end intensity setting, the dimmer switch comprising:

means for conducting a load current from the AC power source to the lighting load for a conduction interval each half-cycle of the AC power source; and

means for controlling the length of the conduction interval each half-cycle;

wherein the improvement comprises;

means for automatically changing the dimmer switch to one of first and second operating modes;

means for adjusting the high-end intensity setting to a first high-end intensity setting value and the low-end intensity setting to a first low-end intensity setting value when operating in the first operating mode; and

means for adjusting the high-end intensity setting to a second high-end intensity setting value and the low-end intensity setting to a second low-end intensity setting value when operating in the second operating mode, the second high-end intensity setting value less than the first high-end intensity setting value, and the second low-end intensity setting value greater than the first low-end intensity setting value.