Step-wise intensity control of a solid state lighting system

• US 20080224025A1
• Filed: 03/13/2007
• Published: 09/18/2008
• Est. Priority Date: 03/13/2007
• Status: Active Grant

• Current Assignee: ABL IP Holding LLC (Acuity Brands, Inc.)
• Original Assignee: Renaissance Lighting Incorporated (Acuity Brands, Inc.)
• Inventors: Lyons, Steve S., Aldrich, Matthew H., Garbus, Michael E.
• Granted Patent: US 7,560,677 B2
• Time in Patent Office: Days
• US Class Current: 250/205
• CPC Class Codes: F21K 9/62 using mixing chambers, e.g. housings with reflective walls
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: G01J 1/32 adapted for automatic variation of the measured or reference value regulation of light intensity G05D25/00
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices

Abstract

A solid state lighting system controls overall light output level in a step-wise manner by discretely controlling the ON/OFF state of its light emitters. Solid state emitters that are ON at a given time are set and kept at a level intended to produce a desired output characteristic, e.g. at a level to produce a described color of light. The system utilizes optical processing of the generated light, for example by diffuse reflection in an optical integrating cavity, sufficient to convert the point source output(s) from the emitting elements into a uniform virtual source output. The virtual source output appears uniform regardless of how many emitters are ON or OFF, and only the perceptible intensity of the light output changes with the number of emitters that the system has ON.

Claims

1. A lighting system, comprising:

a first solid state light emitting element for emitting a color of light;

a second solid state light emitting element for emitting the color of light;

an optical processing element coupled to receive light emitted from the first and second solid state light emitting elements, for processing the received light to produce a virtual source of light of said color at a luminous output area of the lighting system; and

a control circuit connected to the first and second solid state light emitting elements, wherein the control circuit is configured for;

(a) driving each of the first and second solid state light emitting elements to operate at a respective predetermined level whenever each respective one of the first and second solid state light emitting elements is activated; and

(b) selectively activating and deactivating the first and second solid state light emitting elements at the respective predetermined levels, in such a manner as to provide a plurality of discrete intensity levels for the virtual source of light of said color at the luminous output area of the lighting system.

2. The lighting system of claim 1, wherein:

the first solid state light emitting element comprises a first plurality of solid state emitters of a type for emitting the color of light; and

the second solid state light emitting element comprises a second plurality of solid state emitters of a type for emitting the color of light.

3. The lighting system of claim 2, wherein the first plurality of solid state emitters is equal in number to the second plurality of solid state emitters.

4. The lighting system of claim 2, wherein the first plurality of solid state emitters is different in number from the second plurality of solid state emitters.

5. The lighting system of claim 4, wherein:

the first plurality of solid state emitters comprises a first string of light emitting diodes (LEDs) of a first number; and

the second plurality of solid state emitters comprises a second string of LEDs of a second number different from the first number.

6. The lighting system of claim 1, wherein the control circuit comprises:

at least one driver circuit, for providing at least one drive signal for the first and second solid state light emitting elements to drive the solid state light emitting elements at the respective levels; and

a programmable processor for receiving an input specifying a desired brightness and connected to control the at least one driver circuit in response to the received input.

7. The lighting system of claim 6, wherein the at least one driver circuit comprises:

a first driver circuit selectively activated and deactivated by the processor for providing a drive signal for the first solid state light emitting element; and

a second driver circuit selectively activated and deactivated by the processor for providing a drive signal for the second solid state light emitting element.

8. The lighting system of claim 7, wherein the first and second driver circuits comprise constant current sources.

9. The lighting system of claim 1, wherein the first and second solid state light emitting elements are connected in series, and the control circuit comprises:

a current source connected to supply current for the series connected first and second solid state light emitting elements;

a switch connected to a tap between the series connected first and second solid state light emitting elements, so as to disable one of the solid state light emitting elements when the switch is activated; and

means responsive to an input specifying a desired brightness for selectively turning the current source ON and OFF and selectively activating and deactivating the switch in such a manner as to select one of the discrete intensity levels for the virtual source of light of said color at the luminous output area of the lighting system corresponding to the desired brightness.

10. The lighting system of claim 9, wherein said means comprises a programmable micro-control unit.

11. The lighting system of claim 9, wherein said means comprises logic gates.

12. The lighting system of claim 1, wherein the first and second solid state light emitting elements are connected in series, and the control circuit comprises:

a first switch connected across the first solid state light emitting element, so as to disable the first solid state light emitting element when the first switch is activated;

a second switch connected across the second solid state light emitting element, so as to disable the second solid state light emitting element when the second switch is activated; and

means responsive to an input specifying a desired brightness for selectively activating and deactivating the first and second switches in such a manner as to select one of the discrete intensity levels for the virtual source of light of said color at the luminous output area of the lighting system corresponding to the desired brightness.

13. The lighting system of claim 9, wherein said means comprises a programmable micro-control unit.

14. The lighting system of claim 9, wherein said means comprises logic gates.

15. The lighting system of claim 1, further comprising:

a dimmer circuit for receiving an AC power signal and modifying a characteristic of the AC power signal in response to a user setting of the dimmer circuit;

a discriminator for discriminating a plurality of discrete states of the modified characteristic of the AC power signal from the dimmer circuit;

wherein the control circuit is responsive to the discrete states detected by the discriminator to implement the selective activation and deactivation of the first and second solid state light emitting elements, in such a manner as to provide a selected one of the discrete intensity levels for the virtual source of light of said color at the luminous output area of the lighting system responsive to the user setting of the dimmer circuit.

16. The lighting system of claim 1, wherein the optical processing element comprises:

an optical integrating cavity having a reflective interior surface, at least a portion of which exhibits a diffuse reflectivity, the optical integrating cavity being coupled for receiving the light emitted from the first and second solid state light emitting elements for diffuse reflective processing within the optical integrating cavity; and

an optical aperture for allowing emission of processed light from within the optical integrating cavity, wherein the diffuse reflective processing within the optical integrating cavity produces the virtual source of light of said color at the luminous output area of the lighting system at or downstream from the optical aperture.

17. The lighting system of claim 16, wherein the diffuse reflective processing within the optical integrating cavity produces the virtual source at the optical aperture.

18. The lighting system of claim 17, wherein:

each of the first and second solid state light emitting elements is coupled to emit light of said color into the optical integrating cavity from a location on a wall of the optical integrating cavity; and

the locations on the wall of the optical integrating cavity are such that substantially all light emissions entering the cavity from the emitting elements reflect at least once within the optical integrating cavity before emission via the virtual source.

19. The lighting system of claim 18, wherein diffuse reflection within the optical integrating cavity produces a substantially uniform intensity distribution across the entire optical aperture.

20. The lighting system of claim 19, wherein the intensity distribution across the entire optical aperture is substantially Lambertian.

21. The lighting system of claim 19, wherein the intensity distribution across the entire optical aperture is unpixelated.

22. The lighting system of claim 19, wherein the intensity distribution across the entire optical aperture exhibits a maximum-to-minimum ratio of 2:

1 or less.

23. The lighting system of claim 19, wherein area of the optical aperture is substantially larger than combined area of point source outputs of light emitted from the first and second solid state light emitting elements at the locations on the wall of the cavity.

24. In a solid state lighting system comprising a first solid state light emitting element for emitting a color of light and a second solid state light emitting element for emitting the color of light, a method of controlling intensity of light output from the system, the method including steps comprising:

receiving a first input representing a first desired brightness level;

in response to the first input, driving the first solid state light emitting element to emit light of a color at a predetermined intensity level for the first solid state light emitting element, while maintaining the second solid state light emitting element in an inactive state;

diffusely processing light emitted from the first solid state light emitting element to produce a virtual source of light of said color at a luminous output area of the lighting system, corresponding in intensity to the first desired brightness level;

receiving a second input representing a second desired brightness level higher than the first desired brightness level;

in response to the second input, driving the first solid state light emitting element to emit light of the color at the predetermined intensity level for the first solid state light emitting element and driving to the second solid state light emitting element to emit light of the color at a predetermined intensity level for the second solid state light emitting element; and

diffusely processing light emitted from the first and second solid state light emitting elements to produce a virtual source of light of said color at the luminous output area of the lighting system corresponding in intensity to the second desired brightness level.

25. The method of claim 24, wherein:

first solid state light emitting element comprises a first number of light emitting diodes (LEDs); and

the second solid state light emitting element comprises a second number of light emitting diodes (LEDs).

26. The method of claim 25, wherein:

the second number of LEDs is larger than the first number of LEDs; and

the method further comprises;

(a) receiving a third input representing a third desired brightness level between the first and second desired brightness levels;

(b) in response to the third input, driving the second solid state light emitting element to emit light of the color at the predetermined intensity level for the second solid state light emitting-element, while maintaining the first solid state light emitting element in an inactive state; and

(c) diffusely processing light emitted from the second solid state light emitting element to produce a virtual source of light of said color at the luminous output area of the lighting system corresponding in intensity to the third desired brightness level.

27. The method of claim 24, wherein each step of diffusely processing comprises:

receiving light from any and all active ones of the first and second solid state light emitting elements;

diffusely reflecting the received light within an optical cavity; and

emitting diffusely reflected light from the cavity via an optical aperture.

28. The method of claim 27, wherein the emitting of diffusely reflected light forms the virtual source of light of said color at the at the optical aperture forms.

29. The method of claim 24, wherein each step of receiving the first input or the second input comprises receiving a digital data input from a user interface device.

30. The method of claim 24, wherein each step of receiving the first input or the second input comprises receiving a signal representing a predetermined state of an AC signal from an AC dimmer circuit.

31. The method of claim 30, wherein each predetermined state relates to a threshold of phase of the AC signal from the AC dimmer circuit.