Light emitting device with at least two alternately driven light emitting diodes

• US 7,659,544 B2
• Filed: 12/23/2005
• Issued: 02/09/2010
• Est. Priority Date: 12/23/2005
• Status: Active Grant

• Current Assignee: Hong Kong Applied Science And Technology Research Institute Co., Ltd.
• Original Assignee: Hong Kong Applied Science And Technology Research Institute Co., Ltd.
• Inventors: Leung, Lap-Wei, Lu, Ming, Shuy, Geoffrey Wen Tai
• Primary Examiner(s): Soward; Ida M
• Application Number:
  US11/317,937
• Publication Number:
  US 20070145349A1
• Time in Patent Office: 1,509 Days
• Field of Search: 257 88- 89, 257 98- 99, 257/E31.099, 257/E31.105, 257/E33.001
• US Class Current: 257/88
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 45/44 with an active control inside an LED matrix

Abstract

A light emitting device includes a first light emitting diode (LED) emitting a first light emission of at least a first wavelength, and a second light emitting diode emitting a second light emission of at least a second wavelength. The second LED is placed in close proximity to the first LED such that after a mixing length from the first and second LEDs, a combination of the first and second lights is perceived as one color in the human vision. In use, the first and second LEDs are alternately driven by a power source in the time domain.

Claims

1. A light emitting device, comprising:

a first light emitting diode (LED) emitting a first light emission of at least a first wavelength, and

a second light emitting diode emitting a second light emission of at least a second wavelength, the second LED being placed in close proximity to the first LED such that after a mixing length from the first and second LEDs, a combination of the first and second lights is perceived as one color in the human vision; and

a power source which outputs a plurality of periodic discontinuous pulses for alternately driving the first and second LEDs in the time domain.

2. The light emitting device of claim 1, wherein the power source repeatedly and sequentially drives the first LED and the second LED.

3. The light emitting device of claim 1, wherein the first LED and the second LED are electrically connected in parallel.

4. The light emitting device of claim 1, wherein the pulses includes a first and a second set of pulses each set being of a first and second number of pulses within a predetermined period of time, and wherein the color perceived in the human vision can be determined and controlled by controlling a ratio of the first number to the second number.

5. The light emitting device of claim 1, wherein the pulses include a first and a second set of pulses, and wherein the color perceived in the human vision can be determined and controlled by controlling a ratio of the pulse width of the first set to the pulse width of the second set.

6. The light emitting device of claim 1, wherein the output of the power source drives at least one of the first LED and the second LED at a frequency of at least 20 Hz.

7. The light emitting device of claim 1, wherein the first and second wavelengths are different.

8. The light emitting device of claim 1, wherein the first and second wavelengths are the same, the device further comprising a phosphor materials coating on at least one of the first and second LEDs for generating a light of different wavelength.

9. The light emitting device of claim 1, further comprising a diffuser for diffusing at least one of the first and second lights so as to reduce the mixing length.

10. The light emitting device of claim 1, wherein at least one of the first and second LEDs is coated with a phosphor of a different color for reducing the mixing length.

11. The light emitting device of claim 1, wherein the one color perceived in the human vision is any desired color in the color spectrum.

12. The light emitting device of claim 1, wherein the one color perceived in the human vision is the color white.

13. The light emitting device of claim 1, wherein the first LED emitting a first light of a first wavelength is one of a first plurality of LEDs emitting a first light of a first wavelength;

the second LED emitting a second light of a second wavelength is one of a second plurality of LEDs emitting a second light of a second wavelength;

there being no other LED other than the first and second plurality of LEDs involved in generating the one color perceived in the human vision.

14. The light emitting device of claim 1, wherein the power source is an alternate current power source.

15. The light emitting device of claim 14, further comprising a rectifying circuit electrically connected between the power source and at least one of the first LED and the second LED.

16. The light emitting device of claim 1, further comprising a control mechanism for controlling at least a character of one of first LED and the second LED for altering the color perceived in the human vision.

17. The light emitting device of claim 16, wherein the control mechanism includes an adjustable resistor for controlling the voltage amplitude applied to the at least one of the first and second LEDs.

18. The light emitting device of claim 16, wherein the control mechanism includes means for controlling the frequency of the power signals applied to the at least one of the first and second LEDs.

19. The light emitting device of claim 1, further comprising a time delay mechanism in electrical connection with the power source for delaying the power signal by a predetermined period of time so as to drive at least a third LED.

20. The light emitting device of claim 19, wherein the time delay mechanism includes a phase shifter for shifting the phase of the power signal by a predetermined amount.

21. The light emitting device of claim 1, wherein the first and second LEDs are stacked for reducing the mixing length.

22. The light emitting device of claim 21, wherein the first and second LEDs are stacked by using flip-chip technology.

23. The light emitting device of claim 22, wherein the first and second LEDs are firstly adhered by using epoxy materials.

24. The light emitting device of claim 21, wherein the first and second LEDs are stacked by using a wire bonding process.

25. A light emitting device, comprising:

a first light emitting diode (LED) emitting blue light;

a second light emitting diode emitting amber light, the second light emitting diode being placed in close proximity to the first light emitting diode such that the combination of the blue and amber light form white light; and

an alternate current power source which outputs a plurality of periodic discontinuous pulses for alternately, repeatedly and sequentially driving the first LED and the second LED in the time domain, wherein the pulses includes a first and a second set of pulses each set being of a first and second number of pulses within a predetermined period of time, and wherein the color perceived can be determined and controlled by controlling a ratio of the first number to the second number and/or by controlling a ratio of the pulse width of the first set to the pulse width of the second set.

26. The light emitting device of claim 25, wherein at least one of the first LED and the second LED has a phosphor materials coating for converting the emission of at least one of the first LED and the second LED.