Method and apparatus for producing untainted white light using off-white light emitting diodes

• US 20050135094A1
• Filed: 12/19/2003
• Published: 06/23/2005
• Est. Priority Date: 12/19/2003
• Status: Active Grant

• Current Assignee: Epistar Corporation
• Original Assignee: Avago Technologies ECBU IP Singapore Pte Limited (Broadcom, Inc.)
• Inventors: Ng, Kee Yean, Lee, Soo Ghee, Lee, Meng Ee
• Granted Patent: US 7,066,623 B2
• Time in Patent Office: Days
• US Class Current: 362/231
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/49175 Parallel arrangements
• CPC Class Codes: H01L 25/0753 the devices being arranged next to each other
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H05B 45/00 Circuit arrangements for operating light-emitting diodes [LED]
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/40 Details of LED load circuits

Abstract

A white light emitting device by using off-white light emitting diodes (LED'"'"'s). Rather than using just pure white LEDs, the white light emitting device arranges those LEDs which exhibit off-white colors in a manner such that the combination of light emanating from these off-white LEDs produces a radiation which appears substantially pure white to the human eye.

Claims

1. A light generating apparatus comprising:

a first light emitting diode which emits light in a first frequency band;

a second light emitting diode which emits light in a second frequency band, wherein a combination of light emanating from said first light emitting diode and said second light emitting appears substantially white to a human eye.

2. The apparatus of claim 1, wherein said first light emitting diode emits purplish-white light corresponding to said first frequency band and said second light emitting diode emits greenish-white light corresponding to said second frequency band.

3. The apparatus of claim 1, wherein said first light emitting diode has color coordinates which lie on one side of a black body curve and said second light emitting diode has color coordinates which line on the other side of said black body curve.

4. The apparatus of claim 1, wherein said combination of light from said first light emitting diode emanating said purplish-white light and from said second light emitting diode emanating said greenish-white light results in a pure white light.

5. The apparatus of claim 1 wherein said first light emitting diode comprise a blue light emitting diode covered with an encapsulant which contains a yellow phosphor wavelength converting material.

6. The apparatus of claim 1 wherein said second light emitting diode is covered with an encapsulant which contains said yellow phosphor wavelength converting material.

7. The apparatus of claim 2, wherein first light emitting diode comprise a wavelength of said purplish-blue light of between 460-465 nanometers.

8. The apparatus of claim 2, wherein second light emitting diode comprise a wavelength of said green-blue light of between 470-480 nanometers.

9. The apparatus of claim 1 further comprising a plurality of purplish-white light emitting diodes and an equal number of greenish-white light emitting diodes arranged in a manner to complement said plurality of purplish-white light to produce said pure white light.

10. The apparatus of claim 1, wherein the light generated by the first and second light emitting diodes are used to illuminate an object for an image capturing device.

11. A light emitting device, comprising:

an array of light emitting diodes arranged wherein a light emitting diode having color coordinates that lie on one side of a black body curve is placed near a light emitting diode having color coordinates that lie on the other side of the black body curve and wherein a resultant color lies along a locus of a straight line joining the color coordinates.

12. The light emitting device of claim 11, wherein the color coordinates conform to colorimetry standard as defined by CIE.

13. The light emitting device of claim 11, wherein the light produced by the light emitting diodes are complementary radiations.

14. The light emitting device of claim 11, wherein white light emitting diodes with greenish-white and purplish-white colors are arranged in said array to produce a radiation that appears substantially white to a human eye.

15. The light emitting device of claim 14, wherein white light has a color temperature which is approximately one of 6500 Kelvin or 9300 Kelvin.

16. The light emitting device of claim 11, wherein a greenish-white light emitting diode is comprised of a blue light emitting diode with 480 nm color and a purplish-white light emitting diode comprises a blue light emitting diode with 460 nm color.

17. The light emitting device of claim 16, wherein said greenish-white light emitting diode is comprised of a blue light emitting diode of more than 470 nm color and said purplish-white light emitting diode comprises a blue light emitting diode with less than 465 nm color.

18. The light emitting device of claim 11, wherein said array comprises a 1×

3 matrix of light emitting diodes having a first light emitting diode with a color coordinate that lies on a top side of the black body curve, a second light emitting diode with a color coordinate that lies close to the black body curve, and a third light emitting diode with a color coordinate that lies on the bottom of the black body curve.

19. The light emitting device of claim 11, wherein said array comprises at least a 1×

2 matrix of light emitting diodes having a first light emitting diode with a color coordinate that lies on a top side of a black body curve and a second light emitting diode with a color coordinate that lies on a bottom side of the black body curve.

20. The light emitting device of claim 11, wherein said array comprises LED device components.

21. The light emitting device of claim 11, wherein said array comprises a 2×

2 matrix of light emitting diodes having;

a first light emitting diode in an upper left corner with a color coordinate that lies on a top side of the black body curve;

a second light emitting diode in a bottom right corner with a color coordinate that lies on said top side of the black body curve;

a third light emitting diode in an upper right corner with a color coordinate that lies on the bottom of the black body curve;

a fourth light emitting diode in a bottom left corner with a color coordinate that lies on the bottom of the black body curve.

22. A light emitting device comprising an array of white light emitting diodes with color coordinates distal from a black body curve, wherein a composite light has a color coordinate less distal from the black body curve.

23. A white light emitting device comprising:

a substrate with electrically conductive traces;

an array comprising at least one green-blue LED and one purple-blue LED for each green-blue LED, wherein said green-blue LED and said purple-blue LED are attached to said substrate;

encapsulant containing yellow phosphor wavelength converting material, covering each LED;

a circuit for providing electric current to each LED.

24. The white light emitting device of claim 23, wherein said substrate has cavities onto which said green-blue LED and said purple-blue LED are disposed thereon, said cavities acting as a reflector in collecting and directing light out in a desired direction.

25. The white light emitting device of claim 23, wherein said encapsulant and said yellow phosphor wavelength converting material are shaped into a lens configuration to impart a desired radiation pattern of emitted light.

26. The white light emitting device of claim 23 further comprising an optical lens placed over said array of LEDs used to enhance a radiation pattern of emitted light.

27. The white light emitting device of claim 23, wherein light generated by the green-blue LED and the purple-blue LED are used to illuminate an object for an image capturing device.