Illumination – Light source or light source support and luminescent material
Reexamination Certificate
1999-12-01
2002-03-19
Husar, Stephen (Department: 2875)
Illumination
Light source or light source support and luminescent material
C362S230000, C362S231000, C362S235000, C362S260000, C362S293000, C362S542000, C362S249070, C313S512000
Reexamination Certificate
active
06357889
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the illumination arts. More particularly, this invention relates to a color-tunable lighting system incorporating a plurality of phosphors and light emitting diodes (LEDs) or laser diodes (LDs) which is capable of producing visible light of different color temperatures.
Light emitting diodes and lasers have been produced from Group III-V alloys, such as gallium nitride (GaN)-based LEDs. To form the LEDs, layers of the GaN-based alloys are typically deposited epitaxially on a substrate, such as a silicon carbide or sapphire substrate, and may be doped with a variety of n and p-type dopants to improve properties, such as light emission efficiency. Such GaN-based LEDs generally emit light in the UV and blue range of the electromagnetic spectrum. As used herein, the term “UV/blue” LED or LD means an LED or laser diode emitting in the UV range, or in the blue range, or both the UV and the blue ranges of the electromagnetic spectrum.
Recently, techniques have been developed for converting the light emitted from LEDs to useful light for illumination purposes. By interposing a phosphor in the beam produced from a UV/blue LED, for example, light of longer wavelength, in the visible range of the spectrum (e.g., green, red, or white light), may be generated.
The wavelength of the light emitted by the phosphor is dependent on the particular phosphor material used. For example, a blue absorbing, yellow emitting phosphor, such as an yttrium-aluminum-gallium phosphor, commonly referred to as a YAG phosphor, can be used to generate yellow light. Examples of such phosphors include a Y
3
(Al/Ga)
5
O
12
:Ce phosphor having a garnet structure, as disclosed in EP 0 936 682, to Nichia Chemical Ind. Light sources produced in this manner are suited to a wide variety of applications, including lamps, displays, back light sources, traffic signals, illuminating switches, and the like.
In some cases, it is desirable to change the color of light. For example, certain light tones are suited for working, yet are considered too harsh for other activities. At present, this need is satisfied with discharge-based fluorescent lights by changing the relative proportions of phosphors in the phosphor coatings in order to attain a specified color coordinate. Thus, the light source is set at the factory to emit light of a particular wavelength or wavelengths and could not be adjusted by the consumer to emit light of a different tone. To change color temperature, the light source could be replaced by one of a different tone. This is time consuming and not practical for changing the tone at frequent intervals. Alternatively, one light could be switched off and another switched on. This option is not practical for most purposes, since multiple lights and electrical connections are required.
The present invention provides a new and improved color tunable light source and method of use, which overcomes the above-referenced problems and others.
SUMMARY OF THE INVENTION
In an exemplary embodiment of the present invention, a light source is provided. The light source includes a first light emitting component, which emits light at a first wavelength, a second light emitting component, which emits light at a second wavelength different from that of the first wavelength, and phosphors positioned to receive the light emitted by the first and second light emitting components. The phosphors include a first phosphor which is capable of absorbing a part of the light from the first light emitting component and emitting light of a third wavelength, and a second phosphor which is capable of absorbing a part of the light from the second light emitting component and emitting light of a fourth wavelength. The second phosphor is excited relatively less by light of the first wavelength than by light of the second wavelength.
In another exemplary embodiment of the present invention, a method of changing the color of light is provided. The method includes providing first and second light emitting component which emit light of first and second wavelengths, a first phosphor which is capable of absorbing a part of the light from the first light emitting component and emitting light of a longer wavelength, and a second phosphor which is capable of absorbing a part of the light from the second light emitting component and emitting light of a longer wavelength different from the wavelength of the light emitted by the first phosphor. The second phosphor is relatively less affected by light of the first wavelength than by light of the second wavelength. The method further includes adjusting power supplied to at least one of the first and second light emitting components separately from the other of the first and second light emitting components such that the amount of light emitted by the at least one the first and second light emitting components is adjusted. Further, the method includes combining the light emitted by the first phosphor and the second phosphor.
One advantage of the present invention is the provision of a light source which is tunable to more than one color for mood or for functional purposes.
Another advantage of the present invention is that the light emitted by the light source is infinitely variable over a range of wavelengths.
Another advantage of the present invention is that it enables the light source to be adjusted to an optimum color for performing a particular activity.
Another advantage of the present invention is that it enables a single manufacturing process to be used to produce lamps which are then utilized in a variety of potential markets.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.
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Duclos Steven J.
Duggal Anil R.
Levinson Lionel M.
Srivastava Alok M.
Fay, Sharpe, Fagan, Minnich & Mckee, LLP
General Electric Company
Ton Anabel
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