EP2177078B1 - Device and method for controlling light emission - Google Patents

Description

The present invention relates to a device for controlling the light output of a plurality of light sources according to the preamble of claim 1 and a corresponding method thereof. With the device according to the invention and the method according to the invention, in particular a possibility for effective and accurate color control for LED lights is provided. The device and the method basically work according to the principle of a so-called feed-back loop.

Prior art can be found in the document DE 10 2005 049 579 A1 being found. This document discloses a light source (10) emitting mixed-color light containing light of at least two different colors emitted by a plurality of primary light sources (1) in which the primary light source (1) is divided into groups and the brightness values of primary light sources (1) within a group are separately detected and controlled by colors so that the color location of the mixed-color light is within a predetermined range of the CIE standard color chart. Furthermore, a method for controlling such a light source (10) and a lighting device with such a light source (10), for example, for the backlighting of a display.

Furthermore, prior art of the document EP 1482 770 A1 which discloses a light-emitting device, a display unit having such a light-emitting device, and a reader.

LEDs or general semiconductor light-emitting elements are increasingly being used in lighting technology recently, since the achievable with such light sources achievements are sufficiently high even for larger lighting applications. LEDs have the advantage of higher efficiency over other types of light sources. Furthermore, the power and thus the brightness of a LED can be adjusted relatively easily, so that light can be generated in almost any hue by an appropriate mixture of different colors.

A problem of such LED lights, which have different colored LEDs, however, is that these lights are not stable color without a corresponding regulation or control due to thermal influences or aging influences. Further away Even production-related deviations in the light output of individual LEDs may be present, this means that expensive measures must be taken to adjust the performance of the individual LEDs. Otherwise, there would be the danger that ultimately the color tone of the mixed light emitted by the luminaire does not correspond to the wishes of the user.

In this context, it is known from the prior art to detect the light emitted by the various light sources with the aid of a sensor and then to carry out a control in the control of the LEDs which is coordinated with the measurement result. Since information about the light of each individual light source must be available to achieve accurate color control, special measures are taken to obtain this information. For example. will be at one in the EP 1 056 993 B1 described method for operating light sources during operation made a calibration. In this case, the light sources are temporarily controlled during a calibration phase such that only a single light source is active in a sequence of individual measuring periods. In each case, the brightness information about the currently active light source can then be obtained via the sensor, with a corresponding activation of the LEDs overall being carried out on the basis of this information. The individual measuring periods are preferably dimensioned so short that the regular operation of the lamp is influenced as little as possible.

That in the EP 1056 993 B1 Although described method is often used for color control of LED lights, but has been found to be problematic that during the calibration phases, the various LEDs are each activated individually. This has the consequence that, despite the relatively short measuring periods in which each light of a single LED or a single color is emitted, there are slight color changes in the light output of the lamp as a whole, which for an observer - albeit small - perceptible , This effect is additionally reinforced by the fact that these color sequences required for calibration occur regularly. Furthermore, a shortening of the individual measurement periods are limited, since at a too short on and off again individual light sources may occur peaks that distort the measurement result.

The present invention is therefore based on the object to open up a novel possibility for driving LED lights, in which measurements made during operation or calibrations of the individual light sources for a viewer are not or at least significantly less noticeable.

The object is achieved by a device for emitting light, which has the features of claim 1, and by a method for controlling the light emission according to claim 7. Advantageous developments of the invention are the subject of the dependent claims.

In principle, the solution according to the invention is again based on the already known idea of controlling the light sources during operation in recurring calibration phases in such a way that the light emitted by the light sources is detected and evaluated in a sequence of individual measurement periods. In contrast to the prior art, however, in which the light sources to be evaluated are each activated separately in the individual measuring periods, it is provided in the procedure according to the invention that light from several light sources is detected simultaneously in at least one of the measuring periods. The fact that the light sources are no longer individually activated but that the mixed light emitted by the light sources is also used at least in part means that the temporary deviations in the light output are much more difficult to discern for a viewer of the luminaire. Finally, the light emitted in comparison with the regular operation is changed relatively slightly in the calibration phase, although, despite all, an exact determination of the light intensity of the individual light sources is made possible. Accordingly, the procedure according to the invention in turn leads to the fact that the color control can be performed in a reliable manner, but for this less or not at all must be intervened in the ongoing operation of the lamp. The measurements for calibration can thus be performed permanently during normal operation of the luminaire, without this being associated with an impairment of the light output in the desired manner.

According to the invention, therefore, a device for emitting light is proposed which has at least three light sources, means for supplying energy to the light sources, a sensor for detecting the light emitted by the light sources in their entirety and a control unit for controlling the means for supplying energy, wherein the control unit is designed for this purpose in a calibration phase, to control the means for supplying energy in such a way that the light emitted by the light sources is detected by the sensor in a sequence of measurement periods, and to calculate the brightness of each individual light source on the basis of the information obtained from the sensor. According to the invention, it is provided here that the light detected by the sensor originates from a plurality of the light sources in at least one measurement period.

Furthermore, a method for controlling the light output of at least three light sources is proposed, wherein during a calibration phase in a sequence of measurement periods, the light emitted by the light sources detected and based on the information obtained in the measurement periods, the brightness of each individual light source is calculated, and wherein the method according to the invention is characterized in that in at least one of the measurement periods the detected light originates from a plurality of the light sources.

There are different possibilities with regard to the control of the different light sources in the calibration phase.

Thus, for example, it may be provided that in the individual measurement periods the light sources are controlled such that in each case exactly one light source is deactivated during a measurement period. This procedure leads to a particularly low influence or modification of the emitted light in comparison to a regular operation of the lamp, although, however, despite all the light intensity of each individual light source can be determined very accurately. Alternatively, it would also be possible to deactivate the light sources one after the other in a sequence of individual measuring periods, so that the total light output decreases stepwise and only the light of a single light source remains in the last measuring period. In this case as well, the light intensity of the light source can be deduced individually from the signals detected in the individual measurement periods. In addition, it is also possible to vary the order in which the light sources are deactivated, which is ultimately additionally to avoid noticeable light effects for a viewer of the luminaire.

In connection with the aforementioned two variants, it should be noted with respect to the present invention that as an alternative to completely deactivating individual light sources, it is provided according to the invention to reduce or dimming their power in such a way that they emit light below a threshold perceptible for the sensor , This can still be deduced in the right way to the light intensity of the individual light sources, however, since the human eye is relatively sensitive at low light levels, this affects Dimming down the light sources for a viewer of the light less strong.

In the two above-mentioned embodiments according to the invention, in which alternative to a complete deactivation of individual light sources according to the invention is intended to reduce or dim those in their power so that they emit light below a detectable threshold for the sensor, can be provided for the sake of simplicity be that the measurement periods each have the same duration. In a third variant, which brings with it special advantages, however, the length of the measurement periods can be adjusted in a suitable manner. This procedure is particularly suitable when the brightness control of the light sources takes place in that they are operated with pulse width modulated (PWM) signals. The duration of the measuring periods is in each case matched to the differences between the respective pulse widths for the light sources, which ultimately means that the brightness of the individual light sources can be determined during ongoing operation, without there being a deviation in the control during the calibration phase. This means that no flickering or intensity or color changes occur during calibration.

The light sources of the device according to the invention are preferably formed by light-emitting semiconductor elements or LEDs. It can of course also be provided that in each case a single light source is represented by a plurality of LEDs that emit light of the same color.

After, according to the procedure of the invention, the brightness was determined for each individual light source, then a change in the intensity, the Aging is due to be compensated by the control unit. For this purpose, it is preferably connected to storage means or has storage means in which reference values for the brightness of the respective light source are stored. Based on a comparison between the brightness values determined in the calibration phase and the reference values, the currents supplied to the light sources can then be adjusted during operation in order to compensate for corresponding deviations.

Fig. 1

den schematischen Ausbau eines Ausführungsbeispiels einer erfindungsgemäßen Vorrichtung zur Lichtabgabe;

Fig. 2

ein erstes Beispiel eines Schemas zur Ansteuerung der Lichtquellen zur Durchführung einer Kalibrierung;

Fig. 3

ein weiteres Beispiel eines Schemas zur Ansteuerung der Lichtquellen zur Durchführung einer Kalibrierung.

Fig. 4

ein erfindungsgemäßes Ausführungsbeispiel eines Schemas zur Ansteuerung der Lichtquellen zur Durchführung einer Kalibrierung.

Fig. 5

ein weiteres Beispiel eines Schemas zur Ansteuerung der Lichtquellen zur Durchführung einer Kalibrierung.

The invention will be explained in more detail with reference to the accompanying drawings. Show it:

Fig. 1

the schematic expansion of an embodiment of a device according to the invention for emitting light;

Fig. 2

a first example of a scheme for controlling the light sources to perform a calibration;

Fig. 3

another example of a scheme for controlling the light sources to perform a calibration.

Fig. 4

an inventive embodiment of a scheme for controlling the light sources to perform a calibration.

Fig. 5

another example of a scheme for controlling the light sources to perform a calibration.

In the Fig. 1 illustrated and generally provided with the reference numeral 1 device for light output initially has three light sources 2 ₁ to 2 ₃ , which are designed to emit light in the colors red (L _R ), green (L _G ) and blue (L _B ). The light sources 2 ₁ to 2 ₃ can each be set independently in their brightness, which opens the possibility to provide mixed light of almost any hue and in a desired intensity. The optical elements required for mixing the light are not shown for the sake of simplicity of illustration, but are already known from the prior art. The independent control of the light sources 2 ₁ to 2 ₃ is achieved by three driver circuits 3 ₁ to 3 ₃ , which supply their respective assigned light source 2 ₁ to 2 ₃ with a corresponding power. The control of the light sources 2 ₁ to 2 ₃ by the driver circuits 3 ₁ to 3 ₃ takes place in accordance with the driver circuits 3 ₁ to 3 ₃ supplied control signals, which are generated by a control unit 4 of the device for emitting light.

The control of the light sources 2 ₁ to 2 ₃ by the driver circuits 3 ₁ to 3 ₃ to adjust their brightness, can be done in different ways. Thus, on the one hand, it is possible to supply the light sources 2 ₁ to 2 ₃ with a variable in height direct current. Alternatively, it is also possible to operate the light sources 2 ₁ to 2 ₃ in the PWM mode, with pulse-width-modulated supply currents being supplied to them and an adjustment of the intensity via a change in the pulse width. Both methods described above are particularly suitable for the case that the light sources 2 ₁ to 2 ₃ are formed by LEDs, each light source can also be formed in each case from a number of multiple LEDs of the same color.

In order now to carry out a color control for the light emitted from the light sources 2 ₁ to 2 ₃ mixed light emitted from the light sources 2 ₁ to 2 ₃ Light in its entirety from a sensor 5 of a photodiode, for example. Detected, a corresponding signal S is transmitted to the control unit 4. As will be explained in detail later, a suitable control of the light sources 2 ₁ to 2 _{3 is} carried out in a calibration phase, in which case the brightness for the individual light sources 2 ₁ to 2 _{3 is selected} from the signals S delivered by the sensor 5 by the control unit 4 is calculated. The information obtained here is compared with reference values which are stored in a memory 6. The memory 6 can either be connected to the control unit 4 or be part of the control unit 4. Based on the comparison values, a corresponding modification of the control of the light sources 2 ₁ to 2 ₃ can then be made in order to compensate for deviations in the light intensity of the individual light sources that occur over time, for example due to signs of aging.

The previously generally described procedure for compensating for aging phenomena in the control of LED light sources, which is also referred to as a feed-back loop, was already known in principle from the prior art. Compared to the known procedures, however, the device 1 according to the invention differs now in the way in which the light sources 2 ₁ to 2 _{3 are driven} during the calibration phase and in which way the Information obtained thereby, which are supplied by the sensor 5, are evaluated by the control unit 4. This will be explained below with reference to FIGS. 2 to 5 be explained.

Fig. 2 In this case, a first example of the procedure for controlling the light sources for carrying out a calibration is shown, wherein the time profile of the signals transmitted by the sensor 5 to the control unit 4 is shown. It should first be pointed out once again that the sensor 5 does not differentiate according to the colors of the light emitted by the light sources but only detects the total brightness. During normal operation, the sensor thus detects a signal S which represents the sum of the brightness values L1, L2 and L3 of the three light sources.

$$S2=L1+L3$$

$$S3=L2+L3$$

During a calibration phase, the light sources are now driven in successive measurement periods such that one of the three light sources is selectively deactivated in each case. Thus, in a first measuring period the third light source is deactivated, in a second measuring period the second light source and in a third measuring period the first light source. The signals detected by the sensor during these three measurement periods are then composed as follows: $$S1=L1+L2$$

$$\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}2=L1+L3$$

$$\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}3=\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}2+\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}3$$

$$L2=\left(S1-S2+S3\right)/2$$

$$L3=\left(-S1+S2+S3\right)/2$$

On the basis of these measurement signals S1, S2, S3 can then easily by the control unit, the brightness for each single light source, as follows from the three equations above: $$L1=\left(S1+S2-\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}3\right)/2$$

$$\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}2=\left(S1-\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}2+\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}3\right)/2$$

$$\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}3=\left(-S1+\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}2+\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}3\right)/2$$

The individual brightness information L1, L2 and L3 obtained in this way are then compared by the control unit with the reference values stored in the memory. The current or power for each of the three light sources can then be adjusted in a corresponding manner to correspond to the respective reference value, whereby aging phenomena are compensated. After completion of the calibration phase is then transferred back to a conventional operation.

The procedure described above is characterized in that in each of the three measuring periods only one single light source is deactivated or the sensor evaluates a mixed light instead of a single color. This has the consequence that in the individual measurement periods compared to the light signal during normal operation significantly lower deviations occur, as would be the case if only a single light source would be activated. The deviations in the light emitted by the entire device relative to the normal operation are correspondingly much less perceptible to an observer. This also brings, for example, the advantage that the measurement periods are relatively long can be, without this effect would be recognizable to a viewer. As a result, the accuracy in determining the individual light levels is significantly increased, in particular because there is no risk that due to short-term on and off effects that can lead to voltage spikes, distortions in the measurement result. Thus, the measurements during the calibration phase can be carried out without problems in the range of about 100 Hz, which of course would also be possible to make measurements in the KHz range.

$$S2=L1+L2$$

$$S3=L1$$

A variant to that on the basis of Fig. 2 explained procedure is in Fig. 3 and consists in the fact that in the three measuring periods of the calibration phase, the light sources are deactivated one after the other, so that the following measurement signals result: $$S1=L1+\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}2+L3$$

$$\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}2=L1+L2$$

$$\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}3=L1$$

$$L2=S2-S3$$

$$L3=S1-S2$$

In this case as well, the control unit can easily deduce the individual brightness since now the following applies: $$L1=S3$$

$$\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}2=S2-S3$$

$$\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}3=S1-\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}2$$

Again, in the first two measuring periods compared to the light signals during normal operation lower deviations occur, so that no disturbing Light effects arise. In addition, this method can be further optimized by varying the order in which the light sources are deactivated in the individual measurement periods in successive calibration phases. In this way, the repetitive emergence of similar light or color sequences is avoided, with such a variation of the order also in the method according to Fig. 2 could be used.

One way to do that in Fig. 3 To complete the illustrated method is in Fig. 4 shown in FIG Fig. 4 illustrated method represents an inventive embodiment. In this case, the LEDs are not completely deactivated during the individual measuring periods but - as indicated schematically - dimmed down to a level which is below a perceptible by the sensor threshold. The contribution of this light source to the sensor signal is negligible in this case, which is why the previously mentioned equations still apply and, in turn, the intensity of each individual light source can be determined. On the other hand, since the sensitivity of the human eye at low brightness levels is relatively high, the intensity change compared to the conventional operation for a viewer is again lower, which is why this measure - of course, according to a further embodiment of the invention in the method according to Fig. 2 be used - in addition to helping to avoid interference by calibrating the light sources.

However, the level below a threshold that can be dimmed during the calibration phase may also be above the threshold perceivable by the sensor. The calibration phase may include at least one measurement period in which the LEDs are not deactivated or not completely activated in the sense of the previous calibration steps, but at which at least one LED, several LEDs or even all LEDs are dimmed down to the level below a threshold value. The measurement of this at least one measurement period can be used as calibration information in order to evaluate the information obtained during the calibration phase, taking into account the knowledge of the levels of the LED below a threshold, in such a way that the information obtained is corrected for this calibration information during the further measurement phases.

But it can also be one or more LED or the optics of the LED itself or the optics of the LED light designed so that only at a certain dimming level (brightness value of the LED) light is emitted to the environment and the sensor and thus the be defined for the sensor perceptible threshold. The level below a threshold value can thus also be below the threshold perceptible by the sensor,

The sensor may also have a defined filter defining the threshold for visibility. This threshold value can have different values or the same value for different wavelengths. The threshold may be adjustable, for example, depending on the calibration information.

An advantage of the previously described variants of the procedure according to the invention consists, as already mentioned, in the fact that, as part of the calibration phase, the intensity deviations from normal operation are lower, so that no flicker phenomena occur for a viewer of the luminaire. Based on Fig. 5 Now, another example of the procedure for controlling the light sources for performing a calibration will be described, which is applicable for the case that the light sources are operated with pulse width modulated signals. This type of control of LEDs is particularly useful when LEDs are to be changed in intensity, for example, to achieve mixed light of a desired hue. The LEDs are switched on and off alternately, whereby the time relationship between the switch-on time and switch-off time influences the average intensity of the respective LED. By changing this duty cycle, accordingly, the intensity of the corresponding light source can be adjusted almost continuously.

Fig. 5 now shows the time course of the signals received by the sensor in such a PWM operation, the signal sequence represents the normal operation of the LED light.

The peculiarity of the method now described is that the light signals generated during normal operation can also be used to determine the intensities L1, L2 and L3 of the individual light sources. This is possible because the pulse widths for the individual light sources known (da predetermined by the control unit) and from this the time intervals Δt1, Δt2 and Δt3 can be determined.

$$S2*=L1\cdot \mathrm{\Delta }\mathit{t}2/\mathit{PW}+L2\cdot \mathrm{\Delta }\mathit{t}2/\mathit{PW}$$

$$S3*=L1\cdot \mathrm{\Delta }\mathit{t}3/\mathit{PW}$$

It would then be possible to determine the total intensity of the light emitted by the light sources within the three time periods, in each case briefly by the sensor, and then, as explained above, to determine the intensity of each light source individually. However, the accuracy of the measurements can be further increased by integrating the signal detected by the sensor over the duration of the respective measurement period. The peculiarity consists in the fact that the measuring periods for a calibration of the light sources are adapted to these time intervals, whereby the following results for the signals integrated over the three measuring periods and normalized to the pulse width duration PW: $$S1*=L1\times \mathrm{\Delta }\mathit{t}1/\mathit{PW}+\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}2\cdot \mathit{.delta.t}1/\mathit{PW}+\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}3\cdot \mathrm{\Delta }\mathrm{t}1/\mathit{<figure-callout\; id="2"\; label="PW\; S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">PW\; </figure-callout>}$$

$$S$$$$2*=L1\cdot \mathrm{<figure-callout\; id="2"\; label="\Delta \; t"\; filenames="imgf0003.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}\mathit{t}\mathit{}2/\mathit{PW}+\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}2\cdot \mathrm{<figure-callout\; id="2"\; label="\Delta \; t"\; filenames="imgf0003.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}\mathit{t}\mathit{}2/\mathit{<figure-callout\; id="3"\; label="PW\; S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">PW\; </figure-callout>}$$

$$S$$$$3*=L1\cdot \mathrm{<figure-callout\; id="3"\; label="\Delta \; t"\; filenames="imgf0003.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}\mathit{t}\mathit{}3/\mathit{PW}$$

$$L2=\left(S2*-S3*\cdot \mathrm{\Delta }\mathit{t}2/\mathrm{\Delta }\mathit{t}3\right)\cdot \mathit{PW}/\mathrm{\Delta }\mathit{t}2$$

$$L3=\left(S1*-S3*\cdot \mathrm{\Delta }\mathit{t}1/\mathrm{\Delta }\mathit{t}3-\left(S2*-S3*\cdot \mathrm{\Delta }\mathrm{t}\mathit{2}/\mathrm{\Delta }\mathit{t}3\right)\cdot \mathit{PW}/\mathrm{\Delta }\mathit{t}2\right)\cdot \mathit{PW}/\mathrm{\Delta }\mathit{t}1$$

Again, the intensity for the respective light source can then be calculated from the following equations: $$L1=\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}3*\cdot \mathit{PW}/\mathrm{\Delta }\mathit{t}3$$

$$\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}2=\left(\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}2*-\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}3*\cdot \mathrm{<figure-callout\; id="2"\; label="\Delta \; t"\; filenames="imgf0003.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}\mathit{t}\mathit{}2/\mathrm{<figure-callout\; id="3"\; label="\Delta \; t"\; filenames="imgf0003.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}\mathit{t}\mathit{}3\right)\cdot \mathit{PW}/\mathrm{\Delta }\mathit{t}2$$

$$\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="imgf0003.png"\; state="\{\{state\}\}">L</figure-callout>}3=\left(S1*-\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}3*\cdot \mathrm{\Delta }\mathit{t}1/\mathrm{\Delta }\mathit{t}3-\left(\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}2*-\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}3*\cdot \mathrm{<figure-callout\; id="2"\; label="\Delta \; t"\; filenames="imgf0003.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}\mathrm{t}\mathrm{}\mathit{2}/\mathrm{<figure-callout\; id="3"\; label="\Delta \; t"\; filenames="imgf0003.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}\mathit{t}\mathit{}3\right)\cdot \mathit{PW}/\mathrm{<figure-callout\; id="2"\; label="\Delta \; t"\; filenames="imgf0003.png"\; state="\{\{state\}\}">\Delta \; </figure-callout>}\mathit{t}\mathit{}2\right)\cdot \mathit{PW}/\mathrm{\Delta }\mathit{t}1$$

The advantage of this approach is that the intensities of the individual light source during the ongoing operation can be determined without that compared to the conventional operation, a deviation in the control of the light sources must be made. In other words, the measures for calibration of the light sources are no longer perceptible to a viewer. This, in turn, means that a corresponding readjustment of the LEDs can take place permanently during operation since calibration does not have to be carried out only in certain intermediate phases.

The method just described can also be modified in such a way that the times at which the LEDs operated in PWM mode are activated are selected differently. For different dimming levels then different start and stop times can be used, for example. Based on a table, to cause no regular intensity peaks. This measure in turn helps to reduce the externally noticeable effects when calibrating the light sources.

The method according to the invention is fundamentally applicable to devices for emitting light which have at least three light sources which can be controlled independently of one another, in particular LEDs. In the event that more than three light sources are used, the method can be easily extended accordingly. The resulting equations for determining the respective individual light intensities would then increase correspondingly, although in spite of everything a clear determination of the individual light intensities for each light source is possible. It is not mandatory here either required that the different light sources emit light of different colors. The only prerequisite for carrying out the method according to the invention is that at least two different colors are provided by the light source.

The above-described measures are used in particular to compensate for deviations in the intensities of the individual light sources, which are due to aging phenomena. Furthermore, in order to be able to take account of manufacturing tolerances in the manufacture of the LEDs, it can additionally be provided that the LEDs are measured once after assembly with the aid of a suitable color sensor and exactly determined for each light source, in which strength and color light emitted from the corresponding LEDs. This information can then be used during later operation to determine how much the light sources must be driven to produce light of a desired mixed color. This measure thus additionally contributes to ensuring that ultimately a mixed light is generated which lies exactly at the desired color location.

In the end, therefore, the present invention provides a possibility to readjust light sources during the normal operation of an LED light, without any intensity changes in the emitted light occurring, which are clearly perceptible to a viewer. The lighting properties of the device are significantly improved in this way.

Claims (10)

1. Device for light emission (1) with

   a) at least three light sources (2₁, 2₂, 2₃),

   b) means (3₁, 3₂, 3₃) for powering the light sources (2₁, 2₂, 2₃),

   c) a sensor (5) for detecting a measurement signal (S) that corresponds to the light emitted from the light sources (2₁, 2₂, 2₃) in its entirety, and

   d) a control unit (4) for controlling the means (3₁, 3₂, 3₃) for powering the light sources (2₁, 2₂, 2₃),

   wherein the control unit (4) is designed to,

   - so control the means (3₁, 3₂, 3₃) for the power supply in a calibration phase that a measuring signal (S1, S2, S3) is respectively detected in a sequence of at least three measurement periods by the sensor (5), wherein the light emitted from the light sources (S1, S2, S3) is reproduced in each measuring period and the individual brightness (L1, L2, L3) of each individual light source (2₁, 2₂, 2₃)is calculated on the basis of the measuring signals (S1, S2, S3) detected by the sensor (5),

   wherein each of the measurement signals (S1, S2, 33) of a plurality of the light sources (2₁, 2₂, 2₃) detected by the sensor (5) originates in at least one of the measurement periods,
   wherein the light emission of each light emitting light source (2₁, 2₂, 2₃) remains constant in each measurement period, and wherein the light emitted from the respective light sources corresponds in its entirety to various combinations of light emissions from the light sources (2₁, 2₂, 2₃) in the various measurement periods, and
   wherein the control unit is designed to so control the means (3₁, 3₂, 3₃) for the power supply,

   - that exactly one of at least three light sources (2₁, 2₂, 2₃) is dimmed to a level in each measurement period of the at least three measurement periods, or

   - that the at least three light sources (2₁, 2₂, 2₃) are dimmed to a level in such a way in the at least three measurement periods, that

   - none of the at least three light sources (2₁, 2₂, 2₃) is dimmed to the level in a first measurement period,

   - a first light source of the at least three light sources (2₁, 2₂, 2₃) is dimmed to the level in a second measurement period, and

   - the first light source and a second light source of the at least three light sources (2₁, 2₂, 2₃) are dimmed to the level in a third measurement period,

   characterized in that,
   this level lies below a threshold value that is detectable by the sensor (5).
2. Device according to claim 1,
   characterized in that,
   the light sources (2₁, 2₂, 2₃) are configured to emit light of different colors.
3. Device according to claim 1 or 2,
   characterized in that,
   the light sources (2₁, 2₂, 2₃) are each formed by a plurality of LEDs.
4. Device according to one of the preceding claims,
   characterized in that,
   the control unit (4) comprises storage means (6) or is connected to storage means (6) in which reference values for the brightness of the respective light source (2₁, 2₂, 2₃) are stored.
5. Device according to claim 4,
   characterized in that,
   the control unit (4) is configured to adjust the power supplied to the light sources (2₁, 2₂, 2₃) based on a comparison between the brightness values determined in the calibration phase and the reference values.
6. Device according to one of the preceding claims,
   characterized in that,
   the measuring periods each have the same duration.
7. Method for controlling the light emission (1) of at least three light sources (2₁, 2₂, 2₃),
   wherein a measurement signal (S1, S2, S3), which reproduces the light emitted from the light sources (2₁, 2₂, 2₃), is detected in each case during a calibration phase in each measurement period in a sequence of at least three measurement periods, and calculates the individual brightness (L1, L2, L3) of each individual light source (2₁, 2₂, 2₃) on the basis of the detected measurement signals (S1, S2, S3),
   wherein the detected measurement signal (S1, S2, S3) of a plurality of the light sources (2₁, 2₂, 2₃) originates in at least one of the respective measurement periods,
   wherein the light emission of each light-emitting light source (2₁, 2₂, 2₃) in each measurement period remains constant, and wherein different combinations of the light sources (2₁, 2₂, 2₃) emit light in the different measurement periods,
   and wherein

   - exactly one of at least three light sources (2₁, 2₂, 2₃) is dimmed to a level in each measurement period of at least three measurement periods, or

   - the at least three light sources (2₁, 2₂, 2₃) are so dimmed to a level in the at least three measurement periods, that

   - none of the at least three light sources (2₁, 2₂, 2₃) is dimmed to the level in a first measurement period,

   - a first light source of the at least three light sources (2₁, 2₂, 2₃) is dimmed to the level in a second measurement period, and

   - the first light source and a second light source of the at least three light sources (2₁, 2₂, 2₃) are dimmed to the level in a third measurement period,

   characterized in that,
   this level is below a threshold value that is detectable by the sensor (5).
8. Method according to claim 7,
   characterized in that,
   the light sources (2₁, 2₂, 2₃) emit light of different colors.
9. Method according one of the claims 7 to 8,
   characterized in that,
   the power supplied to the light sources (2₁, 2₂, 2₃) is adjusted based on a comparison between the brightness values determined in the calibration phase and the reference values.
10. Method according to any one of the claims 7 to 9,
    characterized in that,
    the measuring periods each have the same duration.

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