Calibrated LED light module

• US 20070034775A1
• Filed: 08/15/2005
• Published: 02/15/2007
• Est. Priority Date: 08/15/2005
• Status: Active Grant

• Current Assignee: Document Security Systems, Inc.
• Original Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Inventors: Cheng, Heng, Ng, Kee, Lee, Joon
• Granted Patent: US 7,230,222 B2
• Time in Patent Office: Days
• US Class Current: 250/205
• CPC Class Codes: H01L 25/167 comprising optoelectronic devices, e.g. LED, photodiodes
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/24 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/40 Details of LED load circuits

Abstract

A light source and method for making the same are disclosed. The light source includes a plurality of LEDs mounted on a substrate and a sensor for measuring light from the LEDs. Each LED emits light having a different spectrum from the other LEDs, the average intensity of light from that LED being determined by a drive signal coupled to that LED. The sensor generates a plurality of signals, each signal being characterized by a sensor value that is proportional to the intensity of light emitted by a corresponding one of the LEDs. A controller generates the drive signals and stores a current target value for each LED. The drive signals for each of the LEDs is generated such that the sensor value for that LED matches the stored current target value for that LED.

Claims

1. A light source comprising:

a substrate;

a plurality of LEDs mounted on said substrate and encapsulated in a transparent cap, each LED emitting light having a different spectrum from said other LEDs, each LED generating light of an average intensity that is determined by a drive signal connected to that LED;

a sensor that generates a plurality of signals, each signal being characterized by a sensor value that is indicative of the intensity of light emitted by a corresponding one of said LEDs and independent of the intensity of light emitted by any other LED in said light source, said sensor comprising at least one photodetector that is encapsulated in said transparent cap; and

a controller that generates said drive signals and stores a current target value for each LED, wherein

said light source operates in a calibration phase and an operation phase, wherein during said operation phase said controller generates said drive signals for each of said LEDs such that said sensor value for that LED matches said stored current target value for that LED, and wherein during said calibration phase, said controller stores said current target values.

2. The light source of claim 1 wherein said controller stores the current values of said sensor values as said current target values in response to an external control signal being coupled to said controller during said calibration phase.

3. The light source of claim 1 wherein said sensor is mounted on said substrate.

4. The light source of claim 1 wherein said sensor measures light leaving a sidewall of a die that includes one of said LEDs.

5. The light source of claim 1 wherein said sensor measures light reflected from a boundary of said transparent cap.

6. The light source of claim 1 wherein said transparent cap comprises a lens.

7. The light source of claim 1 wherein said controller stores a plurality of sets of target values, and wherein said controller selects one of said sets of target values for said current target value in response to an external signal being connected thereto.

8. A method for fabricating a light source, said method comprising:

attaching a plurality of LEDs to a substrate, each LED emitting light having a different spectrum from said other LEDs, each LED generating light of an average intensity that is determined by a drive signal connected to that LED; and

providing a sensor that generates a plurality of signals, each signal being characterized by a sensor value that is indicative of the intensity of light emitted by a corresponding one of said LEDs and independent of the intensity of light emitted by any other LED in said light source;

encapsulating said LEDs and said sensor in a transparent cap;

attaching a controller to said substrate, said controller being connected to said LEDs and said sensor, said controller generating said drive signals and storing a current target value for each LED wherein said light source operates in a calibration phase and an operation phase, wherein during said operation phase said controller generates said drive signals for each of said LEDs such that said sensor value for that LED matches said stored current target value for that LED, and wherein during said calibration phase, said controller stores said current target values;

causing said LEDs to generate light corresponding to a predetermined color point during said operation phase;

causing said controller to store said sensor values as said target values when said LEDs generate light of said predetermined color point during said calibration phase.

9. The method of claim 8 wherein said LEDs are caused to generate light corresponding to said predetermined color point by measuring light from said light source in a calibrated light detector separate from said light source and varying said drive signals until said calibrated light detector indicates that said light generated by said LEDs matches said predetermined color point to within a predetermined accuracy.

10. The method of claim 9 wherein said calibrated light detector receives light from all of said LEDs during said measurement.