Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
2001-04-06
2003-06-10
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S226000, C356S405000
Reexamination Certificate
active
06576881
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to controlling a luminary. The present invention specifically relates to sensing tri-stimulus values for a feedback control of a light output illuminating from a luminary including a plurality of light emitting diodes (LEDs) illuminating various colors of light.
2. Description of the Related Art
White light generation based on a Red LED, Green LED, and Blue LED (RGB LED) is well known in the art. It is also known that, even when produced from the same fabrication process, the optical characteristics of individual RGB LED can significantly vary in a batch. In addition, the characteristics of the LEDs vary with the forward current, ambient temperature, and aging. As a result, the quality of white light produced by each individual RGB LED based luminary will vary. Thus, to minimize, if not to eliminate, the quality variance of white light produced by a RGB LED based luminary, a feedback control system is required to establish and constantly maintain both a color (defined by a standard calorimetric system such as Commission International de l'Eclairage (CIE) 1931 chromaticity coordinates) and a lighting level of the RGB LED based luminary at standard levels.
Accordingly, the feedback control system must receive signals indicative of an actual color and an actual lighting level of a RGB LED based luminary in order to control the color temperature and the lighting level. Sensors including filters and photo diodes, which matches the color matching functions in a standard calorimetric system such as CIE 1931 xy color space, can produce such signals for the feedback control system. However, such sensors are extremely difficult and very expensive to manufacture, and are therefore commercially unfeasible. Thus, prior to the present invention, the realization of a required feedback control system for RGB LED based luminary was not attainable.
SUMMARY OF THE INVENTION
The present invention relates to a method and system for sensing the tri-stimulus values for controlling a luminary including LEDs, particularly RGB LEDs. Various aspects of the invention are novel, non-obvious, and provide various advantages. While the actual nature of the present invention covered herein can only be determined with reference to the claims appended hereto, certain features, which are characteristic of the embodiments disclosed herein, are described briefly as follows.
A first form of the present invention is a method for controlling a light output illuminating from a luminary including two or more light emitting diodes. A first set of tri-stimulus values of the light output is sensed. The first set of tri-stimulus values is transformed into a second set of tri-stimulus values. The second set of tri-stimulus values are representative of a standard calorimetric system. The light output are controlled as a function of the second set of tri-stimulus values.
A second form of the present invention is a method of selectively employing a set of sensors within a light output control system. A first set of tri-stimulus values and a first set of xy coordinates and lumens of light output illuminating from a luminary including two or more light emitting diodes is measured. The standard color space such as CIE 1931 color space is used for this purpose. A second set of tri-stimulus values of the light outputs are sensed by a plurality of sensors. Coefficients of a transformation matrix are computed as a function of the first set of tri-stimulus values and the second set of tri-stimulus values. The sensors are rejected when the transformation matrix contains complex numbers. The first set of xy coordinates and lumens and a second set of xy coordinates and lumens, which are determined by an application of the transformation matrix on the second set of tri-stimulus values, are compared when the transformation matrix is linear. The sensors are rejected when a differential error between the first set of xy coordinates and lumens and the second set of xy coordinates and lumens exceeds a maximum error limit. The set of sensors is employed in the light output control system when the transformation matrix is linear and the differential error between the first set of xy coordinates and the second set of xy coordinates is within the maximum error limit.
A third form of the present invention is a system for controlling a light output illuminating from a luminary including one or more light emitting diodes. The system comprises a plurality of sensors, and a controller. The sensors are operable to sense a first set of tri-stimulus values of the light output and to provide a plurality of signals indicative of the first set of tri-stimulus values to the controller. The controller is operable to transform the first set of tri-stimulus values to a second set of tri-stimulus values and to determine a set of xy coordinates and lumens of the light output as a function of the second set of tri-stimulus values.
The foregoing forms and other forms, features and advantages of the present invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the present invention rather than limiting, the scope of the present invention being defined by the appended claims and equivalents thereof.
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Muthu Subramanian
Van Der Sijde Arjen
Koninklijke Philips Electronics , N.V.
Le Que T.
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