EP2701464B1 - Apparatus and method for producing light of a predetermined spectrum with at least four light sources of different colours - Google Patents

Description

The invention relates to a lighting device with a light unit, which comprises a plurality of light sources of different color spectra, with a sensor for determining the spectral power distribution (SPD) emitted by the light unit, a control unit which acts on a drive unit as a function of a predetermined spectral power distribution measured by the sensor , which individually controls the light sources of the lighting unit, so that the emitted light has the predetermined spectral power distribution. Color spectrum in this context refers to the electro-magnetic waves of a range of defined bandwidth and intensity in the visually perceptible by man color space.

The invention further relates to a method for operating a lighting device with a light unit, which comprises at least four light sources of different color spectra, with a sensor for determining the emitted from the light unit spectral power distribution (SPD), a control unit, which depends on a given and the sensor measured spectral power distribution, a drive unit acted upon, which controls the light sources of the lighting unit individually, so that the emitted light has the predetermined spectral power distribution.

With semiconductor-based lighting elements such as LEDs, the color spectrum and the brightness (intensity) change with increasing operating time, which can be distracting without compensation. In addition, LEDs have a scattering of their technical properties in terms of brightness and color during manufacture. This is compensated by the manufacturer by so-called "binning", in which semiconductor elements are sorted according to a given scattering. The narrower the scattering selection, the more expensive the LEDs are.

A device according to the preamble of claim 1 is known from EP 1 461 982 B1 in which a desired light color of three LED light sources with red, green and blue color spectra is generated. In this case, the light emitted by the three LEDs is detected by means of a tristimulus filter, which converts the measured RGB value into the so-called CIE standardized XYZ color space (CIE = Commission Internationale de l'eclairage). This measured value vector is used in a control unit operating as a P-controller compared with an XYZ setpoint, which acts as a function of the error, a drive unit which controls the light sources supplied to the electrical power accordingly. By means of such a device, such changes in brightness and color can be compensated.

The disadvantage here is that on the one hand, the sensor must be tuned to the frequency spectrums of the LEDs, so that the control loop works sufficiently. Furthermore, with this system, a lighting device with more than 3 light sources of different color spectrums - for example, a yellow or white LED as the fourth LED - no longer regulate because the result of this scheme is no longer unambiguous, since several luminous intensity settings of the four light sources the same color in XYZ color space can generate.

In the DE 10 2007 044 556 describes a method for determining the luminous flux components of individual LEDs via a v (lambda) matched sensor. The operational color and brightness changes of the individual LED are determined by measuring the spectral component with the aid of a v (lambda) fitted sensor and measuring the operating temperature of the LED (board and junction temperature). These measured values are determined individually for the respectively activated LED. The measured values then flow as input parameters for the determination of the individual emission spectra of the LED, which can then be optimized with regard to luminous flux, so that the entire luminaire achieves a defined color and brightness. The disadvantage here is that only one single light source can be considered by the measuring method used. Also, a detection of the color shift of a single light source can be determined only indirectly via the information of the temperature and the v (lambda) measurement. Non-temperature-dependent color changes of the light source can hereby not be distinguished from a change in brightness. Another disadvantage is that the described adjustments of the color and brightness values of the luminaire only work in an operating state in which the individual light sources are individually adjusted. This is equivalent to interrupting the operation.

The object of the invention is to provide a generic lighting device, which is characterized in that more than 3 lighting elements of different color spectrums and brightness values can be integrated and thereby largely any desired color spectrum can be used. It should be a structural simple three-channel sensor be used. It is also an object to provide a method for controlling a generic lighting device with more than three light sources of different color spectrums. The sensor should measure all the light sources simultaneously and determine a valid for the totality of the light sources used color and brightness measurement.

The solution of these objects results from the features of the independent claims. Advantageous developments and refinements are the subject of the dependent claims. Other features, applications and advantages of the invention will become apparent from the following description, as well as the explanation of embodiments of the invention, which are illustrated in the figures.

The first object is achieved in that the lighting unit comprises at least four light sources and the control unit is set up to use an optimization algorithm that maximizes as a main condition a calculated weighting criterion such as in particular color rendering index (CRI), which can be calculated from the individual control data of the light sources and as a termination criterion has the error between the predetermined and the measured spectral power distribution is smaller than a limit value.

A special circumstance here is that the resulting control values of the individual light source are unknown. Only the color and brightness impression of the totality of the light sources is considered. This can be done without interruption in the operation of the lamp. It also ensures that all intrinsic and extrinsic influences on the color and brightness change can be compensated. In particular, as a result of the use of at least four light sources an over-determination with respect to the color impression is generated, which can be used as a compensation source. Furthermore, an intended control reserve serves as a source for further compensation of color and brightness changes. Third, color reduction can be achieved by reducing the overall brightness of the luminaire by performing the optimization instead of in a brightness-rich XYZ color space in a luminance-less color space such as CIE xy.

As far as in the context of this application of light sources is mentioned, any lighting element is detected, in particular any type of light-emitting diode including organic light emitting diodes (OLED). It is also possible to use light sources of different types together, in particular LEDs and light bulbs. While the main field of application of the invention is the range of visible light, it is expressly contemplated that the invention may be applied to the infrared or ultraviolet range. Thus, individual or all light sources may have frequency spectrums which are partly or wholly outside the range of visible light. Thus, in the infrared or in the UV range with a sensor channel number smaller than the number of manipulated variables using the optimization approach can be set to a defined target size.

The idea of the invention is not to make the adjustment of the light sources used via a conventional control loop but to apply an optimization method which has two or more optimization criteria. On the one hand, a coefficient of the weighted sensor values, in particular a color rendering index CRI (color rendering index), is to be maximized as the optimization target, which is not calculated from measured light values but rather from the control data for the individual light sources. As a second optimization criterion or as a secondary condition, the deviation measured in the color spectrum in the defined color space of the sensor is to be minimized by the sensor. Since the present luminaire example should have a high CRI as a requirement, the CRI was also used as an optimization criterion here. Depending on the requirements of the lighting system, other criteria for optimization can also be implemented. Further possible optimization criteria can be selected taking into account the properties of individual light sources. For example, the protection of particularly vulnerable light sources by minimizing the requested performance.

The drive data is typically transmitted in accordance with the DMX protocol or a similar protocol. The DMX protocol allows adjustment of the drive current for each light source with an accuracy of 8 bits (ie 256 different values). Of course, other protocols, such as those of higher accuracy, may be used instead of the DMX protocol. Preferably, a control reserve of, for example, an additional bit is provided in order to take due account of the decreasing brightness in the course of aging processes.

From the current DMX value of a light source is stored due to for the light source Data computes an associated spectrum that is added to the computed spectra of the other light sources to form a common computed, "predicted" or "virtual" total spectrum. From this calculated total spectrum, the CRI value R _{a is} calculated in the usual way as with measured spectral values. This calculation is preferably carried out in the CIE system. This calculated CRI value R _a uses the optimization system according to the invention as the main criterion. Since many algorithms can only minimize, but the negated minimum is the maximum, the main condition or objective function can also be defined as follows: $$\min (\left(-{\mathrm{R}}_{\mathrm{a}}\left(\mathrm{x}\right)\right)$$

As a constraint, the invention specifies that a difference vector from the measured color vector (preferably in the XYZ system) and a predetermined (target) vector is minimized. In order for the optimization system to reach a solution in a timely manner, it is predetermined as a termination condition that the magnitude of the difference vector falls below a limit value ε. The constraint can therefore be defined as follows: $$\left|{\overrightarrow{\mathit{XYZ}}}_{\mathit{actual}}-{\overrightarrow{\mathit{XYZ}}}_{\mathit{target}}\right|,\le \mathrm{\epsilon }$$

In this way, the production and aging-related color and brightness changes of the lighting device according to the invention can be compensated in order to ensure a uniform illumination quality over their entire operating time. The system according to the invention makes it possible to optimize the lighting for any number of light sources (LEDs). The constant adjustment of color and brightness allows the selection of cost-effective light sources (ie a cost-effective "Binnings") while increasing the quality of illumination. It should be noted that the optimization method may include further constraints, in particular high color saturation.

According to an advantageous embodiment of the invention, the lighting unit 4 light sources with different spectral emission, particularly preferably with a selection of the colors red, green, yellow, blue, white. The selection of the light sources will be made depending on the application of the lighting device. Alternatively, five or more light sources in all mentioned colors or spectral values can be used.

According to an advantageous development of the invention, the control algorithm is standardized in CIE X, Y, Z color space feasible. This has the advantage that with a simple three-channel sensor, which is provided with suitable standardized filters, the entire color space perceivable by humans can be detected. Alternatively, other color spaces, eg RGB, LUV, HSL, LMS, RG may be used, taking into account the respective restriction of the gamut.

According to an advantageous development of the invention, the sensor is a three-channel sensor which preferably provides data in RGB or XYZ format. By means of a very simple and inexpensive sensor, the optimization according to the invention can be carried out. This sensor determines the luminous flux and the color location of all the light sources used in the luminaire.

The object underlying the invention is further achieved by a method for operating a lighting device with a light unit comprising at least four light sources of different color spectra, with a sensor for determining the emitted from the light unit spectral power distribution (SPD), a control unit, in dependence a predetermined and measured by the sensor spectral power distribution a drive unit is applied, which controls the light sources of the lighting unit individually, so that the emitted light has the predetermined spectral power distribution, the method is designed as an optimization algorithm that maximizes a calculated color rendering index (CRI) as the main condition, is calculated from the individual drive data of the light sources, and as a side condition the optimization is aborted if the error between the predetermined and the measured spectral power values ilung falls below a threshold. The mode of operation and advantages of the method have already been explained above in connection with the device.

According to an advantageous development, the so-called simplex method is used as the optimization method. This is a proven optimization method for solving linear optimization problems. Alternatively, other optimization methods can also be used.

According to an advantageous development of the color rendering index (CRI) is calculated from stored data on the spectra of the individual light sources and the driving data of the light sources.

Preferably, a function between the respective maximum of a spectrum and the radiation intensity is used, from which a multiplication factor is determined, with which the radiation spectrum of a light source at the current control value of the light source is determined, from the radiation spectra of all light sources a total virtual radiation spectrum is added, and this results in the calculated color rendering index (CRI) of the total virtual radiation spectrum.

The documents DE 10 2008 050818 A1 and WO 2010/122312 A1 disclose a lighting device according to the preamble of claim 1.

Further advantages, features and details will become apparent from the following description in which - with reference to the drawings - at least one embodiment is described in detail. The same, similar and / or functionally identical parts are provided with the same reference numerals.

Figur 1:

eine schematische Blockbilddarstellung der erfindungsgemäßen Vorrichtung;

Figur 2:

eine schematische Blockbilddarstellung der CRI-Wert-Berechnungseinheit.

Show it:

FIG. 1:

a schematic block diagram representation of the device according to the invention;

FIG. 2:

a schematic block diagram representation of the CRI value calculation unit.

The device 10 according to the invention comprises according to FIG. 1 a lighting unit 12 comprising four or more light sources 14 having different color spectrums. For example, a red LED (620 nm), a green LED (520 nm), a blue LED (460 nm) and a yellow LED (590 nm) may be provided. It can also be provided to increase the light intensity of multiple light sources of the same color spectrum, which are preferably driven together (in parallel or in series) but are considered in the context of this embodiment as a light source or LED. These light sources radiate essentially in the same, unspecified direction here. It is essential that in the radiation field of all light sources, a sensor 16 is arranged, which is preferably designed as an RGB or XYZ sensor and transmits corresponding data from the received radiation spectrum to an optimization unit 18. The optimization unit 18 also receives as input signal a desired radiation value 20 as a spectral power distribution (SPD), here as a vector in the XYZ color space. Further, the optimization unit 18 obtains a calculated CRI value which should correspond to the current actual CRI value of the lighting unit 12 and is provided by a CRI value calculation unit 22. The operation of the CRI value calculation unit 22 will be in FIG. 2 explained in more detail. The optimization unit 18 carries out an optimization process on the basis of said data inputs, preferably according to the so-called simplex method, and calculates drive values (preferably in the DMX protocol) which are transferred in asynchronous serial operation to a drive unit 24 based on the driving values, the light sources 14 of the lighting unit 12 individually controls.

Here, the main condition of the optimization method is to maximize the calculated CRI value R _a provided by the CRI value calculation unit 22. : $$\mathrm{Max}\left({\mathrm{R}}_{\mathrm{a}}\right)$$

As a constraint, a difference vector is minimized from the color vector measured by the sensor 16 (preferably in the XYZ system) and a given (target) vector 20. In order for the optimization system to reach a solution in a timely manner, it is predetermined as a termination condition that the magnitude of the difference vector falls below a limit value ε: $$\left|{\overrightarrow{\mathit{XYZ}}}_{\mathit{actual}}-{\overrightarrow{\mathit{XYZ}}}_{t\mathrm{bad}\mathit{et}}\right|,\le \mathrm{\epsilon }$$

gespeichert sind (DMX steht für die unabhängige Variable, also den zugehörigen DMX-Wert der Lichtquelle). Alternativ kann die Beziehung zwischen DMX-Wert und dem Maximum des Spektrums auch als Lookup-Tabelle ausgebildet sein, um die Beziehung noch genauer abzubilden. Die Koeffizienten a, b, c und d werden im Zuge der Auslegung der gesamten Leuchteneinheit für den jeweiligen verwendeten Leuchtentyp (Lichtquelle) individuell mit Hilfe von Spektralvermessung oder auf Basis der Datenblätter bestimmt.In FIG. 2 the operation of the CRI value calculation unit 22 will be explained in more detail. This takes as input the current drive data 25 for the light sources, of which in FIG. 2 only one will be shown further. Since the data transmission is serial, the drive data of the other light sources are supplied in chronological order and processed in the CRI value calculation unit 22. In a memory unit 26, a relationship between the maximum of the spectrum of a light source in relation to the relevant drive value (DMX value) is stored for each light source in a first memory area 28. In a first approximation, this is a straight line, but to increase the accuracy, this can be approximated by a polynomial function of the third degree, to which the four coefficients a, b, c, d as the relevant data for the relevant light source $$\mathrm{k}={\mathrm{a\; DMX}}^3+{\mathrm{b\; DMX}}^2+\mathrm{c\; DMX}+\mathrm{d}$$

are stored (DMX stands for the independent variable, ie the associated DMX value of the light source). Alternatively, the relationship between the DMX value and the maximum of the spectrum may also be formed as a look-up table to more accurately map the relationship. The coefficients a, b, c and d are used in the course of the interpretation of entire luminaire unit for the respective luminaire type (light source) used, individually determined by means of spectral measurement or on the basis of the data sheets.

A polynomial function calculation unit 30 calculates a multiplier k (k <1) from the DMX drive value 25 of the light source and the coefficients in the first storage area 28 according to the above formula.

The memory unit 26 contains for each light source a second memory area 32, in which the spectrum of the light source is stored at maximum illuminance as a look-up table. A multiplier unit 34 multiplies, from the multiplier k determined in the polynomial function calculation unit 30 and the light spectrum of the relevant light source stored in the second memory area 32, the current individual spectrum of the light source 36a, which corresponds to the individually calculated spectra of the other light source 36b-36d in the addition unit 38 Total spectrum is added. The total spectrum of all the light sources 14 thus calculated is converted in the CRI unit 40 according to a known algorithm into the color rendering index value CRI. This value will then be in FIG. 1 shown optimization unit 18 supplied.

LIST OF REFERENCE NUMBERS

10

device

12

light unit

14

light sources

16

sensor

18

optimization unit

20

Radiation setpoint

22

CRI value calculation unit

24

control unit

25

DMX control data

26

storage unit

28

first storage area

30

Polynomfunktionsberechnungseinheit

32

second memory area

34

multiplier unit

36a-d

Single spectrum

38

addition unit

40

CRI unit

Claims (12)

1. Lighting device (10) comprising
   a luminous unit (12) comprising a plurality of light sources (14) of different colour spectra,
   a sensor (16) for determining the spectral power distribution emitted by the luminous unit (14),
   a control unit (18) configured to calculate drive values for the light sources (14) of the luminous unit (12) depending on a predefined spectral power distribution and the spectral power distribution measured by the sensor (16),
   a drive unit (24) configured to receive the drive values from the control unit (18) and to individually drive the light sources (14) of the luminous unit, such that the emitted light has the predefined spectral power distribution,
   characterized
   in that the luminous unit (12) comprises at least four light sources (14), wherein the control unit (18) is configured to apply an optimization algorithm which maximizes a colour rendering index determined on the basis of the drive values of the individual light sources (14) under a constraint, wherein, in accordance with the constraint, an error between the predefined spectral power distribution and the measured spectral power distribution is less than a predefined limit value, wherein the lighting device (10) furthermore has a colour rendering index calculation unit (22), which has a memory unit (26) comprising a first memory area (28) and a second memory area (32), wherein for each light source (14):

   - a relationship between the maximum of the spectrum of the respective light source (14) and the relevant drive value of the light source (14) is stored in the first memory area (28), and

   - a spectrum of the light source (14) in the case of maximum illuminance is stored as a look-up table in the second memory area (32),

   wherein the colour rendering index calculation unit (22) is configured

   - to calculate a multiplication factor from the relationship,

   - to determine a present individual spectrum for each light source (14) by multiplying the spectrum of the respective light source (14) in the case of maximum illuminance by the multiplication factor,

   - to add up the individual spectra determined for all the light sources (14) to form a virtual total radiation spectrum, and

   - to determine the colour rendering index from said total radiation spectrum.
2. Lighting device according to Claim 1, characterized in that the light sources (14) at least in part are semiconductor-based light sources.
3. Lighting device according to Claim 1, characterized in that the semiconductor-based light sources (14) at least in part are light-emitting diodes.
4. Lighting device according to Claim 1, characterized in that the luminous unit (12) has four light sources (14) having a different spectral emission.
5. Lighting device according to Claim 4, characterized in that the luminous unit (12) has four light sources (14) with a selection from the colours red, green, yellow, blue, white.
6. Lighting device according to Claim 1, characterized in that the luminous unit (12) has five light sources (14).
7. Lighting device according to any of the preceding claims, characterized in that the optimization algorithm is implementable in the CIE-standardized X, Y, Z colour space.
8. Lighting device according to any of the preceding claims, characterized in that the sensor (16) is a three-channel sensor, preferably an RGB or an XYZ sensor.
9. Lighting device according to any of the preceding claims, characterized in that the drive values are provided in the DMX system.
10. Method for operating a lighting device comprising a luminous unit (12) comprising at least four light sources (14) of different colour spectra, comprising a sensor (16) for determining the spectral power distribution emitted by the luminous unit, a control unit (18), which calculates drive values for the light sources (14) of the luminous unit (12) depending on a predefined spectral power distribution and the spectral power distribution measured by the sensor (16) and transfers the drive values to a drive unit (24), wherein the drive unit (24) individually drives the light sources (14) in order that the emitted light has the predefined spectral power distribution,
    characterized
    in that an optimization algorithm is carried out which optimizes a colour rendering index determined on the basis of the drive values of the individual light sources (14) under a constraint, wherein, according to the constraint, an error between the predefined spectral power distribution and the measured spectral power distribution is less than a predefined limit value, and
    in that a colour rendering index calculation unit (22) is present, which has a memory unit (26) comprising a first memory area (28) and a second memory area (32), wherein for each light source (14):

    - a relationship between the maximum of the spectrum of the respective light source (14) and the relevant drive value of the light source (14) is stored in the first memory area (28), and

    - a spectrum of the light source (14) in the case of maximum illuminance is stored as a look-up table in the second memory area (32),

    wherein:

    - a multiplication factor is calculated from the relationship,

    - a present individual spectrum for each light source (14) is determined by multiplying the spectrum of the respective light source (14) in the case of maximum illuminance by the multiplication factor,

    - the individual spectra determined for all the light sources (14) are added up to form a virtual total radiation spectrum, and

    - the colour rendering index is determined from said total radiation spectrum.
11. Method according to Claim 10, characterized in that the simplex method is used as optimization algorithm.
12. Method according to Claim 10 or 11, characterized in that the relationship is a third degree polynomial function whose coefficients are stored for each light source.

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