Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2000-04-19
2001-12-11
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S20000A, C315S360000, C362S800000
Reexamination Certificate
active
06329764
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and apparatus to improve the colour rendering of a solid state light source and, in particular, solid state lamps or light sources such as LEDs.
BACKGROUND TO THE INVENTION
A number of different types of light sources ate used to provide general lighting. General lighting for offices, residences or similar has been provided by incandescent lighting or fluorescent light in the past. One of the reasons for favouring such light sources is the improved colour rendering that can be provided by light sources that produce light over a broad bandwidth.
Solid state lighting usually involves the use of LEDs hat, upon application of a relatively constant forward current, produce a relatively stable quantity of light at a particular dominant wavelength. Although such light sources have advantages in reliability and efficiency over other light sources such as incandescent lighting, they have generally been unable to provide the variety of wavelengths necessary to produce white light cost effectively.
To produce white light from LEDs, it is possible to combine two or more LEDs having different dominant wavelengths that complement each other to produce white light. However, the cost of each individual light source is increased with each additional different coloured LED provided. Although white light can be produced by as few as two complementary LEDs, such light will not produce good colour rendering as many of the wavelengths from the spectrum of light are missing or insufficiently provided to provide accurate colour rendering over a reasonable range.
Various attempts have been to produce white light from a single LED or to alter the wavelength of light generated from LED sources.
One category of solutions has sought to alter the wavelength of the light emitted by the lamp subsequent to its production by the LED through the use of surrounding apparatus. This may include the use of an LED to stimulate a phosphor-based colour conversion system as is described in U.S. Pat. No. 6,028,694 or the use of a surrounding reflector to alter the emitted wavelength as is described in U.S. Pat. No. 5,743,629. The difficulty with such methods is that it requires fair more expensive production or installation for the individual light sources as each LED or a small group of LEDs requires provision with additional items to produce the desired light, With the phosphor based solutions, the use of phosphor Creates extra variation in the light produced by each LED, A consistent colour between LEDs is difficult
Another method to try and produce some variation in emitted wavelengths involved producing LEDs having a graded band gap active region that is graded between two materials of different centre wavelengths of light emission. Such an LED is disclosed in U.S. Pat. No. 5,045,896. However, the production of such LEDs is difficult to provide any accuracy in the emissions of the light source.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a method and apparatus to improve the colour rendering of a solid state light source including at least one at LED to overcome some of the disadvantages of the prior art or at least provide the public with a useful choice.
In particular, it is an object of the present invention to reduce the need for extraneous items to alter the wavelength of light once emitted.
SUMMARY OF THE INVENTION
Accordingly, in the first aspect, the invention consists in a method for improving the colour rendering of a solid state light source comprising:
providing at least one LED;
providing a current including a modulated driving signal to said LED; and
altering the forward current with the modulated driving signal to provide at least two dominant emitted wavelengths from said at least one LED.
Accordingly, in a second aspect, the invention may broadly be said to consist a solid state light source comprising:
at least one LED;
a current signal generator to generate a modulated driving signal to said LED; and
said modulated driving signal including at least one portion at a higher current and at least one portion of said signal at a lower current within a cycle of said driving signal.
Preferably said driving signal comprises a pulse width modulated signal.
Preferably said at least one pulse of higher current is of shorter duration than said at least one pulse at said lower current.
REFERENCES:
patent: 5045896 (1991-09-01), Ash et al.
patent: 5743629 (1998-04-01), Helstern et al.
patent: 5783909 (1998-07-01), Hochstein
patent: 6016038 (2000-01-01), Mueller et al.
patent: 6028694 (2000-02-01), Schmidt
patent: 6095661 (2000-08-01), Lebens et al.
Jacobson & Holman PLLC
Lee Wilson
Wong Don
LandOfFree
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