WO2005096258A1

WO2005096258A1 - Method of calibrating an illumination system and an illumination system

Info

Publication number: WO2005096258A1
Application number: PCT/IB2005/050947
Authority: WO
Inventors: Peter H. F. Deurenberg; Christoph G. A. Hoelen
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-03-30
Filing date: 2005-03-18
Publication date: 2005-10-13
Also published as: TW200609877A

Abstract

A method of calibrating an illumination system including at least a first light emitter (1, 1', ...) of a first primary color and of at least a second light emitter (2, 2', ...) of a second primary color, the second primary color being distinct from the first primary color. The method comprises the steps of determining respective optical and/or electrical characteristics of the light emitters and coding the respective optical and/or electrical characteristics of the light emitters in a coding means (7) of the illumination system to enable a controller (5) of the illumination system to read the respective optical and/or electrical characteristics from the coding means and to control the light emission of the light emitters depending on the respective optical and/or electrical characteristics to obtain a light emission by the illumination system having a standard deviation of color-matching within in a predetermined range. In addition, the invention relates to an illumination system.

Description

Method of calibrating an illumination system and an illumination system

The invention relates to a method of calibrating an illumination system including at least a first light emitter of a first primary color and of at least a second light emitter of a second primary color, the second primary color being distinct from the first primary color. In addition, the invention relates to an illumination system comprising at least a first light emitter of a first primary color and at least a second light emitter of a second primary color, the second primary color being distinct from the first primary color. Such illumination systems are known per se. They are used, inter alia, as backlighting of (image) display devices, for example for television receivers and monitors. Such illumination systems can particularly suitably be used as a backlight for non-emissive displays, such as liquid crystal display devices, also referred to as LCD panels, which are used in (portable) computers or (cordless) telephones. In addition, such illumination systems are used for general lighting purposes, such as spot lights, flood lights and for large-area direct-view light emitting panels such as applied, for instance, in signage, contour lighting, and billboards. When light emitters of distinct primary colors are used for creating an illumination system, a problem of achieving a desired color point with a desired spread in the color point of the illumination system arises. The color point of a light emitter is normally characterized by the color coordinates or the so-called tristimulus values (x, y, z) according to the CIE 1931 color diagram, known in the art. In addition, the spread in the color point is normally characterized by the so-called "standard deviation of color-matching" (SDCM) according to the so-called MacAdam ellipses, known in the art. By way of example, with a SDCM of approximately 3 color differences are just discernable. The light emitters, for instance light-emitting diodes (LEDs), can be light sources of distinct primary colors, such as, for example the well-known red (R), green (G), or blue (B) light emitters. In addition, the light emitter can have, for example, amber or cyan as primary color. These primary colors may be either generated directly by a light emitting device such as a LED, or may be generated by a phosphor upon irradiance with light from a light emitting device such as an LED. In the latter case, also mixed colors or white light is possible as one of the primary colors. Because the optical properties of the light emitters change as a function of time, current and temperature, a controller is employed to obtain and maintain a pre- determined color accuracy. It is known in the art to employ a controller which uses sensors and a feedback algorithm in order to obtain a high color accuracy. In such systems the sensors measure, among others, the light distribution of the light emitters, the temperature and/or the level of the luminous flux of the light emitters. In addition, feed forward control systems are employed to manufacture illumination systems with even higher color accuracies. The extra technology in an illumination system needed to accurately control the color point in combination with a desired spread in the color point requires the use of sensors and a sophisticated controller. Such a controller incorporates relatively complicated feedback routines, consumes space and is relatively expensive.

European patent application EP-A 1 244 334 discloses a switching device for a light-emitting diode (LED). The switching system comprises an adjustable current supply for regulating the current of the LED. The nominal current of the LED is coded in a coding element. The current supply obtains the nominal current from the coding element to operate the LED at its nominal current. A drawback of the known illumination system is that the current supply is adjusting the current through the LED to the nominal current only.

The invention has for its object to eliminate the above disadvantage wholly or partly. According to the invention, a method of calibrating an illumination system of the kind mentioned in the opening paragraph for this purpose comprises the steps of: determining respective optical and/or electrical characteristics of the light emitters, and coding the respective optical and/or electrical characteristics of the light emitters in a coding means of the illumination system to enable a controller of the illumination system to read the respective optical and/or electrical characteristics from the coding means and to control the light emission of the light emitters depending on the respective optical and/or electrical characteristics to obtain a light emission by the illumination system having a standard deviation of color-matching within in a pre-determined range. By measuring the optical and/or electrical characteristics of the first and second light emitters and by coding the respective optical and/or electrical characteristics of the light emitters in the coding means of the illumination system, the illumination system is provided with the information relating to the optical and/or electrical characteristics of the light emitters. The controller of the illumination system reads the respective optical and/or electrical characteristics from the coding means and controls the light emission of the light emitters depending on the respective optical and/or electrical characteristics. Because the controller of the illumination system is provided with the information relating to the optical and/or electrical characteristics of the light emitters, the controller can be relatively simple. The light emitters in the illumination system according to the invention behave at least partly in a sufficiently well pre-determined and predictable manner. A controller provided with the respective optical and/or electrical characteristics of the light emitter employs a relatively simple control scheme and accordingly consumes relatively little space and is relatively inexpensive. If desired the optical and/or electrical characteristics of the light emitters can be combined with additional sensor signals that provide information on the light output or light output characteristics of the system. In this manner the light emission by the illumination system can be controlled by the controller in a relatively simple manner. In particular, a relatively accurate light emission of the illumination system having a standard deviation of color-matching (SDCM) within in a pre-determined range is obtained by the controller. According to a preferred embodiment of the method of calibrating an illumination system, after determining the optical and/or electrical characteristics of the first light emitter, the first light emitter is sorted to a first set of a plurality of bins, each bin corresponding to a disjunctive sub-range of the optical and/or electrical characteristics of the first light emitter, and after determining the optical and/or electrical characteristics of the second light emitter, the second light emitter is sorted to a second set of a plurality of bins, each bin corresponding to a disjunctive sub-range of the optical and/or electrical characteristics of the second light emitter. The determination of the optical and/or electrical characteristics of the first and second light emitters and sorting the light emitters to the first and the second sets of a plurality of bins can be performed by the manufacturer of the light emitters. In particular, a number of manufacturers of light emitters, for example manufactures of light-emitting diodes, label their products according to pre-determined disjunctive sub-ranges of optical and/or electrical characteristics. In addition, the light emitters can be obtained from the manufacturers of light emitters packaged in or sorted to so-called "bins" with specified optical and/or electrical characteristics. Alternatively, or in addition, characterization and sorting of the light emitters into bins suitable for lighting systems with a pre-defined maximum standard deviation of color-matching (SDCM) while employing LEDs with different electrical and/or optical characteristics can be performed prior to the assembly of the illumination system by e.g. the manufacturer of the lighting system. Upon selecting a light emitter from a particular bin for use in an illumination system, the optical and/or electrical characteristics corresponding to said bin is coded in the coding means. To this end, a preferred embodiment of the method of calibrating an illumination system, at least one coded first light emitter is selected from one of the bins of the first set of bins and coding the information corresponding to the selected bin in the coding means, and at least one coded second light emitter is selected from one of the bins of the second set of bins and coding the information corresponding to the selected bin in the coding means. Such pre-selected light emitters behave in a well-defined and predictable manner enabling to control the light emission by the illumination system by the controller in a relatively simple manner. Preferably, for an illumination system with a plurality of light emitters of the same primary color, the light emitters are selected from the same bin. By selecting the light emitters from the same bin for a particular illumination system, the coding means are provided with one set of optical and/or electrical characteristics for each of the primary colors. In an alternative embodiment, two or more bins are used for a primary color to obtain a combined set op optical and/or electrical characteristics that are uniquely identified by the appropriate coding means. In addition, to the method of calibrating an illumination system including a first and a second light emitter of a first and a second primary color, respectively, a preferred embodiment of the method, the illumination system includes at least a third light emitter of a third primary color, the third primary color being distinct from the first and the second primary color. In the method according to this preferred embodiment of the invention, the optical and/or electrical characteristics of the first, second and third light emitters are determined. In addition, the respective optical and/or electrical characteristics of the first, second and third light emitters are coded in the coding means of the illumination system. The controller of the illumination system reads the respective optical and/or electrical characteristics from the coding means and controls the light emission of the first, second and third light emitters depending on the respective optical and/or electrical characteristics. Because the first, second and third light emitters in the illumination system behave in a predetermined and predictable manner, the controller can control the light emission by the illumination system in a relatively simple manner. In particular, a relatively accurate light emission of the illumination system having a standard deviation of color-matching within in a pre-determined range is obtained by the controller. In a further preferred embodiment, the illumination system includes at least a fourth primary color. In this manner a larger area in the CIE 1931 color diagram can be spanned. In particular, this is advantageous if larger color temperature ranges are desired. Preferably, determining the optical and/or electrical characteristics of a light emitter includes measuring at least one of the following: peak wavelength, dominant wavelength, correlated color temperature, color point, luminous flux, radiant power, brightness, intensity, forward voltage, dissipated power of the light emitter. As mentioned above, a number of manufacturers of light emitters label their products according to predetermined disjunctive sub-ranges of such optical and/or electrical characteristics.

The invention also relates to an illumination system. According to the invention, an illumination system comprises: at least a first light emitter of a first primary color, the first light emitter being sorted to a disjunctive sub-range of optical and/or electrical characteristics of the first light emitter, at least a second light emitter of a second primary color, the second primary color being distinct from the first primary color, the second light emitter being sorted to a disjunctive sub-range of optical and/or electrical characteristics of the second light emitter, a coding means for coding the information corresponding to the first and second light emitters, and a controller for obtaining the bin-coded information corresponding to the first and the second light emitters from the coding means and to control the light emission of the first and the second light emitters depending on the information of the first and the second light emitters to obtain a light emission by the illumination system having a standard deviation of color-matching within a pre-determined range. By coding the respective optical and/or electrical characteristics of the light emitters in the coding means of the illumination system, the illumination system is provided with the information relating to the optical and/or electrical characteristics of the light emitters. The controller of the illumination system reads the respective optical and/or electrical characteristics from the coding means and controls the light emission of the light emitters depending on the respective optical and/or electrical characteristics. Because the controller of the illumination system is provided with the information relating to the optical and/or electrical characteristics of the light emitters, a relatively simple controller can be employed. The light emitters in the illumination system according to the invention behave in a pre-determined and predictable manner. The controller provided with the respective optical and/or electrical characteristics of the light emitter employs a relatively simple control scheme and accordingly consumes relatively little space and is relatively inexpensive. In this manner the light emission by the illumination system can be controlled by the controller in a relatively simple manner. In particular, a relatively accurate light emission of the illumination system having a standard deviation of color-matching within in a pre-determined range is obtained by the controller. A preferred embodiment of the illumination system according to the invention is characterized in that the illumination system comprises two or more light emitters of the same primary color, each light emitter having the same bin-coded information. By selecting the light emitters for a primary color from the same bin for a particular illumination system, the coding means are provided with one set of optical and/or electrical characteristics for each of the primary colors. In an alternative embodiment of the illumination system, at least two bins are used for at least one of the primary colors in an illumination system comprising at least two primary colors, the combination of the two bins being uniquely identified by the coding means. Preferably, the illumination system further comprises: at least a third light emitter of a third primary color, the third primary color being distinct from the first and the second primary color, the third light emitter being bin coded to a disjunctive sub-range of optical and/or electrical characteristics of the third light emitter, the information corresponding to the third light emitter being coded in the coding means, the bin-coded information corresponding to the third light emitter being obtained from the coding means by the controller. According to this preferred embodiment of the illumination system, the optical and/or electrical characteristics of the first, second and third light emitters are coded in the coding means of the illumination system. The controller of the illumination system reads the respective optical and/or electrical characteristics from the coding means and controls the light emission of the first, second and third light emitters depending on the respective optical and/or electrical characteristics. Because the first, second and third light emitters in the illumination system behave in a pre-determined and predictable manner, the controller can control the light emission by the illumination system in a relatively simple manner. In particular, a relatively accurate light emission of the illumination system having a standard deviation of color-matching within in a pre-determined range is obtained by the controller. In an alternative embodiment of the illumination system, three primary colors are used, but these are addressed using only two driving channels. The resulting two groups of light emitters are uniquely identified by the coding means. In a further alternative embodiment of the illumination system, at least four primary colors are used with three drive channels. The three groups of light emitters are uniquely identified by the coding means. In yet a further alternative embodiment of the illumination system, at least two primary colors are used with two drive channels. The two groups of light emitters are uniquely identified by the coding means. Preferably, the optical and/or electrical characteristics of the light emitters are selected from the group formed by the peak wavelength, the dominant wavelength, the correlated color temperature, the color point, the luminous flux, the radiant power, the brightness, the intensity, the forward voltage, and/or the dissipated power of the light emitter. A number of manufacturers of light emitters label their products according to pre-determined disjunctive sub-ranges of such optical and/or electrical characteristics. A preferred embodiment of the illumination system according to the invention is characterized in that the coding means comprises a non-volatile memory. Preferably, the coding is written into EPROM or other electronic coding means. Preferably, the coding means is selected from the group formed by jumpers, dipswitches and notches. The controller and coding means can communicate with each other in many ways. Preferably, the controller communicates with the coding means via electrical/electronic communication. Preferably, the controller communicates with the coding means via electrical means or via mechanical or optical sensors. In an alternative embodiment of the illumination system, optical feed back info from at least one optical sensor is included and combined with the coded information to further enhance the stability and/or predictability of the light output of the system. In a further alternative embodiment of the illumination system, thermal feed back info from at least one thermal sensor is included and combined with the coded information to further enhance the stability and/or predictability of the light output of the system. In yet a further alternative embodiment of the illumination system, combined optical and thermal feed back info from at least one optical sensor and at least one thermal sensor is included and combined with the coded information to further enhance the stability and/or predictability of the light output of the system.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings: Figure 1 is a cross-sectional view of an illumination system according to the invention, and Figure 2 shows an embodiment of a first and a second set of bins. The Figures are purely diagrammatic and not drawn to scale. Notably, some dimensions are shown in a strongly exaggerated form for the sake of clarity. Similar components in the Figures are denoted as much as possible by the same reference numerals.

Figure 1 schematically shows a cross-sectional view of an illumination system in accordance with the invention. The illumination system comprises at least a first light emitter 1, 1 ', ... of a first primary color and at least a of second light emitter 2, 2', ..., of a second primary color, the second primary color being distinct from the first primary color. In the example of Figure 1, the illumination system comprises a plurality of first light emitters 1, 1 ', ... and a plurality of second light emitter 2, 2'. ... Preferably, the light emitters 1 , 1 ', ...; 2, 2', ... are light-emitting diodes (LEDs). In general, the LEDs have a relatively high source brightness. Preferably, each of the LEDs has a radiant power output of at least 100 mW when driven a nominal power. LEDs having such a high output are also referred to as LED power packages. The use of such high-efficiency, high-output LEDs has the specific advantage that, at a desired, comparatively high light output, the number of LEDs may be comparatively small. This has a positive effect on the compactness and the efficiency of the illumination system to be manufactured. The first light emitters 1, 1 ', ... are sorted to a disjunctive sub-range of optical and/or electrical characteristics of the first light emitter 1, 1 ', ..., whereas the second light emitters 2, 2', ... are sorted to a disjunctive sub-range of optical and/or electrical characteristics of the second light emitter 2, 2', .... In the example of Figure 1, power stages 11, 21, 31 are included for powering the light emitters 1 , 1 ', ...; 2, 2', .... The illumination system further comprises a coding means 7 for coding the information corresponding to the first and second light emitters 1, 1 ', ...; 2, 2' In the coding means 7 the optical and/or electrical characteristics of the respective light emitters 1, 1 ', ...; 2, 2', ... are bin-coded. In addition, the illumination system comprises a controller 5 for obtaining the bin-coded information corresponding to the first and the second light emitters 1, 1 ', ...; 2, 2', ... from the coding means 7. The controller controls the light emission of the first and the second light emitters 1, 1 ', ...; 2, 2', ... depending on the information of the first and the second light emitters 1, 1 ', ...; 2, 2', .... In this manner a light emission by the illumination system is obtained having a standard deviation of color- matching within a pre-determined range. The discernability and acceptability of color-point differences are limited by ellipsoidal areas in the x,y chromaticity diagram, the form and the size of the areas are determined by (MacAdam):

AS² = g_u (Ax)² + 2 g Ax Ay + g₂₂ (Ay)²

wherein

ΔS Standard deviation of color-matching (SDCM) according to a MacAdam ellipse. By way of example, with a SDCM of approximately 3 color differences are just discernable;

Δx, Δy Difference value with respect to the center of the MacAdam ellipse; gl 1 , gl2, gl3 Coefficient, the value of which is determined by the place in the chromaticity diagram.

The illumination system may be provided with a sensor (not shown in Figure 1) for measuring one or more optical properties of the light which, in operation, is emitted by the light emitters 1, 1 ', ...; 2, 2', .... Such a sensor may be coupled to control electronics in the controller 7 for suitably adapting the luminous flux of the light emitters 1, 1 ', ...; 2, 2', .... By means of the sensor and the control electronics in the controller 5, a feedback mechanism can be formed which is used in combination with the data from the coding means 7 to influence the quality and the quantity of the light emitted by the illumination system. In an alternative embodiment, the illumination system may be provided with a temperature sensor for measuring the temperature of the system, the light emitting devices or at some other location in the system. By means of the temperature sensor and the control electronics in the controller 5, a feedback and/or feed forward mechanism can be formed which is used in combination with the data from the coding means to influence the quality and the quantity of the light emitted by the illumination system. In the example of Figure 1 the illumination system further comprises at least a third light emitter 3, 3', ... of a third primary color, the third primary color being distinct from the first and the second primary color. Similar to the first and the second light emittersl, 1 ', ...; 2, 2', ..., the third light emitter 3, 3', ... is bin coded to a disjunctive sub-range of optical and/or electrical characteristics of the third light emitter 3, 3', .... The information corresponding to the third light emitter 3, 3', ... is coded in the coding means 7. The bin- coded information corresponding to the third light emitter 3, 3', ... being obtained from the coding means 7 by the controller 5. In the example of Figure 1 the illumination system comprises two or more light emitters 1, 1 ', ...; 2, 2', ...; 3, 3', ... of the same primary color, each light emitter having the same bin-coded information. By selecting the light emitters from the same bin for a particular illumination system, the coding means 7 are provided with one set of optical and/or electrical characteristics for each of the primary colors. The optical and/or electrical characteristics of the light emitters 1, 1 ', ...; 2, 2',

...; 3, 3', ... are selected from the group formed by, e.g., the peak wavelength, the dominant wavelength, the correlated color temperature, the color point, the luminous flux, the radiant power, the brightness, the intensity, the forward voltage, and/or the dissipated power of the light emitter (also see Figure 2). Preferably, the coding means 7 comprises a non-volatile memory. Preferably, the coding means 7 is selected from the group formed by (soldered) jumpers, dipswitches and notches. The controller 5 and coding means 7 can communicate with each other in many ways. Preferably, the controller 5 communicates electronically with the coding means 7. Preferably, the controller 5 communicates with the coding means 7 via electrical means or via mechanical or optical sensors.

A method of calibrating an illumination system comprises a number of steps. As a first step the respective optical and/or electrical characteristics of the light emitters 1, 1 ', ...; 2, 2', ..., 3, 3', ... are determined . These respective optical and/or electrical characteristics are coded in a coding means 7 of the illumination system. A controller 5 of the illumination system obtains the respective optical and/or electrical characteristics from the coding means 7. The controller 5 controls the light emission of the light emitters 1, 1 ', ...; 2, 2', ..., 3, 3', ... depending on the respective optical and/or electrical characteristics. In this manner a light emission by the illumination system is obtained having a standard deviation of color-matching within in a pre-determined range. Preferably, after determining the optical and/or electrical characteristics of the first light emitter 1, 1', ..., the first light emitter 1, 1', ... is sorted to a first set of a plurality of bins 101 , 102, 103 ; 1 11 , 112; 121 , 122, 123 (see Figure 2), each bin corresponding to a disjunctive sub-range of the optical and/or electrical characteristics of the first light emitter 1, 1 ', .... In addition, after determining the optical and/or electrical characteristics of the second light emitter 2, 2', ..., the second light emitter 2, 2', ... are sorted to a second set of a plurality of bins 201, 202, 203, 204; 21 1, 212; 221, 222, 223, 224 (see Figure 2), each bin corresponding to a disjunctive sub-range of the optical and/or electrical characteristics of the second light emitter 2, 2', .... Additional sets of a plurality of bins may be provided in case a third or further light emitter is used in the illumination system. Figure 2 shows very schematically an embodiment of a first and a second set of bins. The first set of bins comprises a plurality of bins indicated with reference numerals 101 , 102, 103 ; 11 1 , 1 12; 121 , 122 and 123. The second set of bins comprises a plurality of bins indicated with reference numerals 201, 202, 203, 204; 21 1, 212; 221, 222, 223 and 224. By way of example, bins 101, 102 and 103 of the first set of bins and bins 201, 202, 203, 204 correspond to so-called color bins, each bin representing a disjunctive sub-range of the peak wavelength of the respective light emitter. In case the first light emitter 1, 1 ', ... is a red light emitter, the bin with reference numeral 101 corresponds to a peak wavelength in the range from 621 to 630 nm, the bin with reference numeral 102 corresponds to a peak wavelength in the range from 631 to 640 nm and the bin with reference numeral 103 corresponds to a peak wavelength in the range from 641 to 650 nm. In case the second light emitter 2, 2', ... is an amber light emitter, the bin with reference numeral 201 corresponds to a peak wavelength in the range from 581 to 585 nm, the bin with reference numeral 202 corresponds to a peak wavelength in the range from 586 to 590 nm, the bin with reference numeral 203 corresponds to a peak wavelength in the range from 591 to 595 nm and the bin with reference numeral 204 corresponds to a peak wavelength in the range from 596 to 600 nm. In a similar manner the other bins relate to other optical and/or electrical characteristics of the light emitters. For instance, the bins with reference numerals 1 1 1 and 112 may correspond to disjunctive subranges of the luminous flux of the first light emitter 1, 1 ', ... and the bins with reference numerals 121, 122 and 123 may correspond to disjunctive sub-ranges of the forward voltage of the first light emitter 1, 1 ', ... In addition, the bins with reference numerals 21 1 and 212 may correspond to disjunctive sub-ranges of the luminous flux of the second light emitter 2, 2', ... and the bins with reference numerals 221, 222, 223 and 224 may correspond to disjunctive sub-ranges of the forward voltage of the second light emitter 2, 2', ... Figure 2 only shows a simplified manner of bin-coding the optical and/or electrical characteristics of the light emitters. In practice for each of the light emitters, combinations of optical and/or electrical characteristics; this may give rise to bin-coding according to bins in two or more dimensions. By way of example, for each of the bins with a particular sub-range of the luminous flux of a light emitter, there may be a number of disjunctive sub-ranges of the forward voltage of this light emitter. Preferably, determining the optical and/or electrical characteristics of a light emitter includes measuring at least one of the following: peak wavelength, correlated color temperature, luminous flux, forward voltage of the light emitter. Upon calibrating the illumination system, at least one coded first light emitter 1, 1 ', ... is selected from one of the bins of the first set of bins 101, 102, 103; 1 11, 1 12; 121, 122, 123. The information corresponding to the selected bin is coded in the coding means 7. In addition, at least one coded second light emitter 2, 2', ... is selected from one of the bins of the second set of bins 201, 202, 203, 204; 21 1, 212; 221, 222, 223, 224. The information corresponding to the selected bin is coded in the coding means 7. Similar selecting and coding is performed in case a third or further light emitter is used in the illumination system. In the examples given above, the illumination system comprises a plurality of light emitters 1, 1 ', ...; 2, 2', ...; 3, 3', ... of the same primary color. In case the coding depth is larger than the respective number of bins, also pre-defined bin combinations can be used by uniquely identifying this combination by the coding means. This is in particular advantageous to reduce output spread between products, to optimize the light quality and to optimize the logistics of applying a certain number of bins for a certain product. In the known illumination systems it is possible to combine light emitters with distinct primary colors (e.g. red, green, blue, amber and/or cyan) in order to obtain a variety of color points within the CIE 1931 color space as determined by the color coordinates or tristimulus values (x, y, z). Because the optical properties of the light emitters change over time, current and temperature, some sort of control may be necessary depending on the targeted color accuracy. To obtain a more predictable behavior of the light emitters, they are sorted in bins, which have certain specifications (e.g. peak wavelength, flux and forward voltage ranges). Investigations show that the light can be controlled using a feedback algorithm and sensors. In order to obtain relatively high color accuracy, such a sensor should detect either the light distribution, the temperature of the light emitters or of the illumination system, or both the temperature and the flux level of the illumination system. In certain applications, these parameters have to be measured for each of the primary colors. If relatively low color accuracy is sufficient, only a temperature sensor and/or a feed forward control can be used, or, alternatively, only a flux sensor and a feed-back system can be employed. A disadvantage of the known illumination systems is that extra technology is needed to control the color point with a relatively high accuracy. This results in expensive modules (feedback controlling means, sensors, development) and consumes valuable space (minimization of the module dimensions is of high importance), and/or hampers standardization or ease of application due to required additional components to be installed. According to the invention, additional information about the specific light emitters is used to decrease the complexity (number and type of sensors, complicated feed back controlling means) of the control loop as the light emitters behave in a more predictable manner. Instead of using only light emitters from a specific bin for all illumination systems, it is proposed to use all bins (which is the most economical use of the light emitters, resulting in reduced cost price of the illumination system, and may enable even further improvement of the light quality), as long as for a particular illumination system the light emitters of a specific primary color are all selected from the same bin or set of bins, as long as it is known how many are from which bin and this can be coded uniquely in the coding means. Upon introducing the light emitters in the illumination system, the information corresponding to the bins is coded electrically into a non-volatile electronic memory or hard- coded on the printed circuit board (PCB). The controller reads this non-volatile coded data and consults, by way of example, an internal look-up table for the optimal control strategy. This makes it possible to use cheaper light emitters or to apply a larger number of different types (bins) of light emitters, while still maintaining a relatively high color accuracy. In addition, it is possible to use a relatively simple control scheme (like feed forward) in combination with hard-coding of the binning information, to simplify the electronics in the controller and to reduce the costs of the illumination system while maintaining a relatively high color accuracy. The information can be hard-coded in several ways, for instance notches, (soldered) jumpers, dipswitches, EEPROM or other electronic coding means in the (MC)PCB (read out via electrical means or mechanical or optical sensors). A suitable way of hard-coding the information in the coding means is to use soldered jumpers, as the information can then be hard-coded and read very easily. The hard-coding can also be done when the light emitters are mounted in the illumination system, so when the binning information is available. The data could for instance be binary coded to save space. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A method of calibrating an illumination system including at least a first light emitter (1, 1 ', ...) of a first primary color and of at least a second light emitter (2, 2', ...) of a second primary color, the second primary color being distinct from the first primary color, the method comprising the steps of: determining respective optical and/or electrical characteristics of the light emitters (1, 1 ', ...; 2, 2', ...), and coding the respective optical and/or electrical characteristics of the light emitters (1, 1 ', ...; 2, 2', ...) in a coding means (7) of the illumination system to enable a controller (5) of the illumination system to read the respective optical and/or electrical characteristics from the coding means (7) and to control the light emission of the light emitters (1 , 1 ', ...; 2, 2', ...) depending on the respective optical and/or electrical characteristics to obtain a light emission by the illumination system having a standard deviation of color-matching within in a pre-determined range.

2. A method as claimed in claim 1, wherein after determining the optical and/or electrical characteristics of the first light emitter (1, 1 ', ...), sorting the first light emitter (1, 1 ', ...) to a first set of a plurality of bins (101, 102, 103; 1 11, 112; 121, 122, 123), each bin corresponding to a disjunctive sub-range of the optical and/or electrical characteristics of the first light emitter (1, 1 ', ...), and after determining the optical and/or electrical characteristics of the second light emitter (2, 2', ...), sorting the second light emitter (2, 2', ...) to a second set of a plurality of bins (201, 202, 203, 204; 211, 212; 221, 222, 223, 224), each bin corresponding to a disjunctive sub-range of the optical and/or electrical characteristics of the second light emitter (2, 2', ...).

3. A method as claimed in claim 2, wherein upon calibrating the illumination system selecting at least one coded first light emitter (1, 1 ', ...) from one of the bins of the first set of bins (101, 102, 103; 1 11, 1 12; 121, 122, 123) and coding the information corresponding to the selected bin in the coding means (7), and selecting at least one coded second light emitter (2, 2', ...) from one of the bins of the second set of bins (201, 202, 203, 204; 21 1, 212; 221, 222, 223, 224) and coding the information corresponding to the selected bin in the coding means (7).

4. A method as claimed in claim 2, wherein for an illumination system with a plurality of light emitters (1, 1 ', ...; 2, 2', ...) of the same primary color, selecting the light emitters from the same bin.

5. A method as claimed in claim 1 or 2, the illumination system including at least a third light emitter (3, 3', ...) of a third primary color, the third primary color being distinct from the first and the second primary color.

6. A method as claimed in claim 1 or 2, wherein determining the optical and/or electrical characteristics of a light emitter includes measuring at least one of the following: peak wavelength, dominant wavelength, correlated color temperature, color point, luminous flux, radiant power, brightness, intensity, forward voltage, dissipated power of the light emitter

7. An illumination system comprising: at least a first light emitter (1, 1 ', ...) of a first primary color, the first light emitter (1, 1 ', ...) being sorted to a disjunctive sub-range of optical and/or electrical characteristics of the first light emitter (1, 1 ', ...), at least a second light emitter (2, 2', ...) of a second primary color, the second primary color being distinct from the first primary color, the second light emitter (2, 2', ...) being sorted to a disjunctive sub-range of optical and/or electrical characteristics of the second light emitter (2, 2', ...), a coding means (7) for coding the information corresponding to the first and second light emitters (1, 1 ', ...; 2, 2', ...), and a controller (5) for obtaining the bin-coded information corresponding to the first and the second light emitters (1, 1 ', ...; 2, 2', ...) from the coding means (7) and to control the light emission of the first and the second light emitters (1, 1 ', ...; 2, 2', ...) depending on the information of the first and the second light emitters (1, 1 ', ...; 2, 2', ...) to obtain a light emission by the illumination system having a standard deviation of color- matching within a pre-determined range.

8. An illumination system as claimed in claim 7, wherein the illumination system comprises two or more light emitters (1 , 1 ', ...; 2, 2', ...) of the same primary color, each light emitter having the same bin-coded information.

9. An illumination system as claimed in claim 7 or 8, wherein the illumination system further comprises: at least a third light emitter (3, 3', ...) of a third primary color, the third primary color being distinct from the first and the second primary color, the third light emitter (3, 3', ...) being bin coded to a disjunctive sub-range of optical and/or electrical characteristics of the third light emitter (3, 3', ...), the information corresponding to the third light emitter (3, 3', ...) being coded in the coding means (7), the bin-coded information corresponding to the third light emitter (3, 3', ...) being obtained from the coding means (7) by the controller (5).

10. An illumination system as claimed in claim 7 or 8, wherein the optical and/or electrical characteristics of the light emitters (1, 1 ', ...; 2, 2', ...) are selected from the group formed by the peak wavelength, the dominant wavelength, the correlated color temperature, the color point, the luminous flux, the radiant power, the brightness, the intensity, the forward voltage, and/or the dissipated power of the light emitter.

11. An illumination system as claimed in claim 7 or 8, wherein the coding means

(7) comprises a non-volatile memory.

12. An illumination system as claimed in claim 1 1, wherein the coding means (7) is selected from the group formed by [soldered] jumpers, dipswitches and notches.

13. An illumination system as claimed in claim 7 or 8, wherein the controller (5) communicates with the coding means (7) via electrical means or via mechanical or optical sensors.