EP2499883B1 - Led lighting device and method for operating an led lighting device - Google Patents

Description

The invention relates to a method for operating an LED lighting device and an LED lighting device.

WO 2006/063552 A1 relates to a motor vehicle headlight element which has at least one light-emitting diode (LED) and at least one control device which is suitable for processing a signal that is dependent on a measured variable and for impressing a current corresponding to the signal in the light-emitting diode, the control device and the light-emitting diode on one common carrier are arranged.

US 2004/0036418 A1 relates to a circuit and a method for providing a closed control loop using continuous current switching techniques. By controlling the current supplied to light emitting diodes (LEDs), the LEDs can be operated at or near their maximum capacity without the risk of overloading the LEDs and without using excessive amounts of current. A circuit has several high-side switches, each of which is connected to an LED array. The LED arrays are connected via a coil to a power switching control point, which switches power to ground or feeds the power back in order to maintain an LED current flow in a desired area.

US 2006/0006821 A1 relates to a system and method for implementing an LED-based luminaire that contains one or more color channels. The luminaire includes a controller that uses optical sensing and feedback to control LEDs in each channel to provide consistent luminosity and / or color output. The luminaire controller likes the optical feedback loop Provide uniform luminosity and / or color of the luminaire output. The controller may then set a current and / or a pulse width modulation (PWM) duty cycle, which separate color channels are fed to the luminaire in order to obtain the desired luminosity and / or color.

US 2002/0097000 A1 relates to an LED luminaire system for providing power for LED light sources in order to provide a desired light color, which system has a power supply stage which is configured to provide a direct current signal. A light mixing circuit is coupled to the power supply stage and includes a plurality of LED light sources of red, green and blue colors to produce light of various desired color temperatures. A control system is coupled to the power supply stage and is configured to provide the power supply stage with control signals to maintain the DC signal at a desired level to the desired. Maintain light output. The control system is further configured to estimate lumen output fractions associated with the LED light sources based on a transition temperature of the LED light sources and chromaticity coordinates of the desired light to be generated at the light mixing circuit. The light mixing circuit further includes a temperature sensor for measuring the temperature associated with the LED light sources and a light detector for measuring a lumen output level of light generated by the LED light sources. Based on the measured temperatures, the control system determines the amount of output lumens that each of the LED light sources must produce in order to achieve the desired mixed light output, and the light detector in conjunction with a feedback loop maintains the required lumen output for each of the LED light sources.

the EP 1 898 677 A2 shows a color control for a luminaire in which only the light source to be measured and therefore the color to be measured is active during the measurement of a light source.

The publication WO 02/23954 A1 discloses a lamp with an array of red, green and blue light emitting diodes and a control system. The control system is set up to operate the individual components in such a way that a desired color impression can be permanently maintained.

DE 10 2005 049 579 A1 relates to a light source that emits mixed-colored light that contains light at least two different colors that is emitted by a plurality of primary light sources, in which: the primary light sources are divided into groups and the brightness values of the primary light sources within a group are determined separately according to color and are controlled so that the color locus of the mixed-colored light lies in a predetermined range of the CIE standard color table. Furthermore, a method for controlling such a light source is specified, as well as a lighting device with such a light source, for example for backlighting a display.

It is the object of the present invention to provide a particularly user-friendly and easily realizable possibility of an adjustment of an LED lighting device with at least two color channels.

This object is achieved according to the features of the independent claims. Preferred embodiments can be inferred in particular from the dependent claims.

• mindestens zwei Farbkanäle, insbesondere unterschiedlicher Farbe, wobei jeder Farbkanal mindestens eine Leuchtdiode (LED) gleicher Farbe umfasst und wobei jeder Farbkanal getrennt oder individuell ansteuerbar ist, und
• mindestens einen Photodetektor, welcher dazu eingerichtet und angeordnet ist, einen Anteil eines von den LEDs abgestrahlten Lichts zu detektieren,

wobei das Verfahren mindestens die folgenden Schritte aufweist:

• Umschalten der LED-Leuchtvorrichtung von einer Betriebsphase in eine Messphase;
• zeitlich nacheinander folgendes (sequenzielles) Ansteuern oder Aktivieren der Farbkanäle so, dass ein während der Messphase von den LEDs abgestrahltes Licht eine (integrale) Farbmischung aufweist, welche im Wesentlichen einer Farbmischung der Betriebsphase entspricht.

The object is achieved by a method for operating an LED lighting device, the LED lighting device having at least:

• at least two color channels, in particular of different colors, each color channel comprising at least one light-emitting diode (LED) of the same color and each color channel being separately or individually controllable, and
• at least one photodetector which is set up and arranged to detect a portion of a light emitted by the LEDs,

wherein the method comprises at least the following steps:

• Switching the LED lighting device from an operating phase to a measuring phase;
• Sequential control or activation of the color channels following one another in time so that a light emitted by the LEDs during the measurement phase has an (integral) color mixture which essentially corresponds to a color mixture of the operating phase.

The at least two color channels can also include different color channels of the same color. Each color channel comprises one or more LEDs of the same color, e.g. connected in series or connected in parallel.

A portion or fraction of the light emitted by the (in particular all) LEDs is detected or sensed by means of the at least one photodetector, in particular a single photodetector. The photodetector can comprise, for example, a photodiode or a phototransistor.

The operating phase corresponds to normal operation of the LED lighting device.

Color mixing or integral color mixing of the measurement phase can in particular be understood to mean an addition of the light emitted from the color channels during the measurement phase.

The order of the successively controlled color channels is fundamentally not restricted. The order of the successively controlled color channels can be the same or different for several measurement phases.

The above method has the advantage that the luminous flux detected by the photodetector can be assigned unambiguously and with high accuracy to a specific color channel through the successive (sequential) control of the color channels. This eliminates the need for faulty separation or reconstruction of the luminous fluxes of the individual color channels. This can be used, for example, to determine a correlation between a current through a color channel and the luminous intensity or luminous flux of this color channel resulting therefrom. In this way, for example, a desired color location and / or a desired light intensity can be set or regulated more precisely during the operating phases.

Because a light emitted by the LEDs during the measurement phase has a color mixture which essentially corresponds to a color mixture of the operating phase, a color impression from the previous operating phase is continued at the same time, so that an observer cannot distinguish the measurement phase from the operating phase in terms of color and so the Measurement phase does not perceive as disturbing.

It is an embodiment that during the measurement phase each color channel is controlled separately by means of a pulse width modulation so that a ratio of pulse widths of the color channels during the measurement phase essentially corresponds to a ratio of the pulse widths of the color channels during the operating phase. The color impression that is the same as in the operating phase is thus achieved by setting a similar or the same pulse width, which is particularly easy to achieve.

It is a particularly advantageous embodiment for generating an identical or similar color impression that a deviation of a ratio of the pulse widths of two color channels during the measurement phase by no more than 10%, in particular does not deviate by more than 1% from the ratio of the pulse widths of these two color channels during the operating phase.

It is an alternative or additional embodiment that a flow level is set separately for each of the color channels so that a ratio of current levels of the color channels during the measurement phase essentially corresponds to a ratio of the current levels of the color channels during the operating phase. As a result, an identical or similar color impression can be achieved in the operating phase and measurement phase by maintaining the current level ratios, e.g. if the color channels are controlled in continuous operation.

It is a further development that an amount of light during the measurement cycle is brought to a value by setting a current level at which a signal level or level of a sensor signal of the at least one photodetector is in a range between 75% and less than 100%, e.g. 99.5 %, of its maximum signal level. In this way, on the one hand, a sufficiently high signal level with a high signal-to-noise ratio (SNR) can be achieved and, at the same time, saturation of the photodetector can be avoided.

It is an advantageous embodiment for quickly setting the level of the sensor signal in the range between 75% and less than 100% of its maximum signal height that the amount of light is brought to the value or in the range by means of a search algorithm. The search algorithm can be, for example, a linear search algorithm. To set the level quickly, a search algorithm can be used which works faster than the linear search algorithm, in particular a binary search algorithm or an interval search.

For example, it may be desirable to reduce the level of the sensor signal if a lot of light is reflected back into the photodetector and / or irradiated from the surroundings. This can be the case, for example, when the LED lighting device a light mixer such as a diffuser, beam-shaping optics, etc. is connected downstream, which reflects a comparatively large amount of light. As a result, the photodetector can be saturated, so that in the measurement phase there is no longer any meaningful correlation between a control signal of a color channel and its luminous flux.

In another embodiment, in addition to the step of activating the color channels, the measurement phase has a step of not activating all of the color channels. In this “dark phase”, an effect of ambient light incident on the LED lighting device on the sensor signal can be determined.

It is still a further embodiment that the measurement phase additionally has compensation sections, during which the color channels are controlled as during an operating phase. In this way, the color channels can also be operated simultaneously during the compensation sections. As a result, an impression of brightness for a user during the measurement phase can be matched to an impression of brightness during an operating phase.

If, due to the different on-times or activation times of the individual channels, more measurements can be carried out than are necessary for the control, these measurements can be omitted or specifically shortened in subsequent measurement phases in order to reduce the time required for the measurement phase. In this embodiment, the error caused by the omitted measurements can be corrected, for example, by the compensation sections.

For integral color mixing, in which the sequential control of the color channels is perceived by a user as simultaneous light emission due to eye sluggishness, it is an advantageous embodiment that a measurement phase does not last longer than approx. 40 ms, in particular no longer than 20 ms, in particular no longer than 10 ms. In particular, the duration of the measurement phase in which a color channel is activated can last as long as is necessary for the measurement value acquisition of the individual channels, that is, for example, even without a dark phase.

It is also an embodiment that a period of time between two measurement phases is not constant. As a result, it can be suppressed that a plurality of LED lighting devices, in particular several times one behind the other, are simultaneously (collectively) in their measurement phase and thus reinforce a difference to an impression from an operating phase for a viewer. This effect can be suppressed particularly effectively if a period of time between two measurement phases is non-deterministic, e.g. determined randomly or pseudo-randomly.

It is also an embodiment that a sensor signal output by the at least one photodetector during the measurement phase is used, at least in sections, to adapt a control in a subsequent operating phase. This can take the form of feedback, for example. For example, the result can be used to calculate and / or readjust the amount of light required to reach the color location in a control loop.

It is advantageous to control the color channels in the measurement phase in the order of the brightness of the color channels, preferably in descending order. If the brightness is adjusted by activating the current source, the period of time that the current source needs to achieve the desired power value is decisive for the duration of the measurement. Depending on the power source, this can be different in terms of increase or decrease. It has proven to be advantageous to select the "slow" step at the beginning of the measurement and then to follow the "fast" direction for the adjustments in the individual steps.

Most power sources allow a rapid reduction in power and thus current strength, but only a slow increase. It is therefore particularly advantageous to control the color channels in descending order of brightness, i.e. first the color channel with the greatest brightness, then the one with the second largest, etc. up to the channel with the lowest brightness. As a conclusion, the dark phase is advantageous if one is provided. This results in a particularly fast measurement and thus a short measurement phase, which minimizes the risk of brightness fluctuations that are visible to the observer.

• mindestens zwei Farbkanäle, insbesondere unterschiedlicher Farbe, wobei jeder Farbkanal mindestens eine LED gleicher Farbe umfasst und wobei jeder Farbkanal getrennt ansteuerbar ist,
• mindestens einen Photodetektor, welcher dazu eingerichtet und angeordnet ist, einen Anteil eines von den LEDs abgestrahlten Lichts zu detektieren,
• eine Umschalteinrichtung zum Umschalten der LED-Leuchtvorrichtung von einer Betriebsphase in eine Messphase und
• eine Messphasenablaufsteuerung, die dazu eingerichtet ist, die Farbkanäle nacheinander so anzusteuern, dass ein während der Messphase von den LEDs abgestrahltes Licht eine integrale Farbmischung aufweist, welche im Wesentlichen einer Farbmischung der Betriebsphase entspricht.

The object is also achieved by an LED lighting device, the LED lighting device having at least:

• at least two color channels, in particular of different colors, each color channel comprising at least one LED of the same color and each color channel being separately controllable,
• at least one photodetector which is set up and arranged to detect a portion of a light emitted by the LEDs,
• a switching device for switching the LED lighting device from an operating phase to a measuring phase and
• a measurement phase sequence control which is set up to control the color channels one after the other in such a way that a light emitted by the LEDs during the measurement phase has an integral color mixture, which essentially corresponds to a color mixture of the operating phase.

The switching device can, for example, be a functional part of a general control device of the LED lighting device.

It is a further development that the LED lighting device is set up to carry out a method as described above.

Fig.1

zeigt in drei Reihen jeweils einen Ausschnitt aus einem ersten, einem zweiten bzw. einem dritten Ansteuersignal für einen jeweils zugehörigen Farbkanal einer LED-Leuchtvorrichtung. Das Ansteuersignal ist als eine Auftragung eines Strompegels eines in den jeweiligen Farbkanal eingeprägten Stroms I gegen die Zeit T dargestellt;

Fig.2

skizziert eine möglich Ausgestaltung einer LEDLeuchtvorrichtung zur Durchführung der in Fig.1 gezeigten Abläufe.

In the following figures, the invention is described schematically in more detail using an exemplary embodiment.

Fig. 1

shows, in three rows, a section of a first, a second or a third control signal for a respective associated color channel of an LED lighting device. The control signal is shown as a plot of a current level of a current I impressed in the respective color channel against time T;

Fig. 2

outlines a possible configuration of an LED lighting device for carrying out the in Fig. 1 shown processes.

The first row off Fig. 1 shows an excerpt from a first control signal S1 for a first color channel Ch1 of an LED lighting device. The first color channel Ch1 contains all light emitting diodes (LEDs) of a first color, for example red, which are controlled jointly by means of the common control signal S1. The red light-emitting diodes of the first, red color channel Ch1 can be connected in series, for example.

The second row shows an excerpt from a second control signal S2 for a second color channel Ch2 of an LED lighting device. The second color channel Ch2 contains all light emitting diodes (LEDs) of a second color, e.g. green, which are controlled by means of the common control signal S2. The green light-emitting diodes of the second, green color channel Ch2 can be connected in series, for example.

The third row shows a section from a third control signal S3 for a third color channel Ch3 of an LED lighting device. The third color channel Ch3 contains all light-emitting diodes (LEDs) of a third color, for example blue, which are controlled jointly by means of the common control signal S3. The blue light-emitting diodes of the third, blue color channel Ch3 can be connected in series, for example.

Fig. 1 each shows simultaneous excerpts of the control signals S1, S2 and S3. The sections each show a first operating phase BP1, which is followed by a measurement phase MP, which is followed by a second operating phase BP2.

In the operating phases BP1, BP2, the LED lighting device is operated normally. The operating phases BP1, BP2 consist of a sequence of activation cycles of duration tba, of which an activation cycle is shown by way of example in the first operating phase BP1 between a point in time tb0 = 0 and a point in time tba.

In the activation cycle shown, all three color channels Ch1, Ch2, Ch3 are initially controlled or activated from time tb0, but within the activation cycle. ration cycle 'mostly for a different duration. In other words, a pulse, in particular a current pulse, is applied to all three color channels Ch1, Ch2, Ch3 in an activation cycle, wherein a pulse width PB1, PB2, PB3 of the color channels Ch1, Ch2, Ch3 can differ. The pulse width PB1, PB2, PB3 can be set by the LED lighting device and can, for example, be based on a desired color temperature. For example, a specific color or color location of the light emitted by the LED lighting device, e.g. warm-white or cold-white, can be assigned a specific ratio of the pulse widths PB1, PB2, PB3 and thus activation times of the color channels Ch1, Ch2, Ch3. This makes use of the fact that the duration tba of an activation cycle is so short that, due to eye sluggishness, the light emitted by all color channels Ch1, Ch2, Ch3 is seen by an observer as light emitted practically at the same time, i.e. as mixed light from the three color channels Ch1, Ch2, Ch3 , is perceived.

In the exemplary activation cycle shown, the LEDs of the first color channel Ch1 are continuously energized, which is a Pulse width PB1 corresponds to 100% of the activation cycle, i.e. PB1 = tba. The LEDs of the second color channel Ch2 are energized 55% of the time of the activation cycle (PB2 = 55% tba), and the LEDs of the third color channel Ch3 are energized 18% of the time of the activation cycle (PB3 = 18% tba). The pulse widths PB1, PB2 or PB3 can depend, for example, on the desired color location of the LED lighting device, the luminosity, the color and the number of LED (s) per color channel, etc. The pulse widths PB1, PB2, PB3 can be varied, for example in order to change a color location and / or a light intensity of the mixed light.

In the example shown, the three color channels Ch1, Ch2, Ch3 can be controlled independently of one another, so that, for example, simultaneous control, in particular energization, of the three color channels Ch1, Ch2, Ch3 can be achieved particularly easily. However, a sequential control can also be used in which no two color channels Ch1, Ch2, Ch3 are controlled at the same time.

Also, only two color channels may be used, e.g. with red LED (S) or mint green LED (s) to generate a white mixed light. More than three color channels can also be used, e.g. additionally with amber-colored LED (s) ('amber') to generate a warm-white mixed light.

A portion of the light emitted by the LEDs of the color channels Ch1, Ch2, Ch3 is captured by means of at least one photodetector. The at least one photodetector is at least able to detect a luminous flux of the LEDs and output a corresponding sensor signal, e.g. to an evaluation logic of the LED control device.

The operating phase BP1 changes to the measurement phase MP at a point in time tm0 for all three color channels Ch1, Ch2, Ch3. In the measurement phase MP, the three color channels Ch1, Ch2, Ch3 are controlled one after the other or sequentially and not contemporaneous. As a result, a sensor signal of the at least one photodetector can be easily and unambiguously assigned to a specific color channel Ch1, Ch2, Ch3 and evaluated, for example for determining and / or setting the light intensity or the color location of the mixed light.

So that the measurement phase MP is not noticeable to an observer, a time for activating the color channels Ch1, Ch2, Ch3 preferably does not last more than 40 ms, in particular not more than 20 ms, in particular not more than 10 ms. It is particularly preferred if the total duration tm of the measurement phase MP does not last more than 40 ms, in particular not more than 20 ms, in particular not more than 10 ms.

In order not to change a color impression for a viewer during the measurement phase MP in comparison to the previous operating phase BP1, the color channels Ch1, Ch2, Ch3 are controlled in such a way that light emitted by the LEDs during the measurement phase has an integral color mixture, which is essentially one Color mix corresponds to the operating phase. An integral color mixture can be understood to mean, in particular, an accumulation, in particular addition, of the light emitted by the LEDs during the measurement phase. For this purpose, in this exemplary embodiment, a ratio of the pulse widths PM1, PM2, PM3 of the color channels Ch1, Ch2, Ch3 during the measurement phase MP essentially corresponds to a ratio of the pulse widths PB1, PB2, PB3 of the color channels Ch1, Ch2, Ch3 during the operating phase BP1, even if whose absolute width or duration in the measurement phase MP and the previous operating phase BP1 need not match. Because of the inertia of the eyes, an observer then perceives the same color impression in the measurement phase MP as in the operating phase BP1.

The LED lighting device can use the sensor signals, for example for each of the color channels Ch1, Ch2, Ch3, to create a correlation between an associated control signal S1, S2, S3, for example a current, and a color-specific light intensity and if there is a deviation from a setpoint value, for example the light intensity, modify the control signal accordingly. For example, if it is determined that a light intensity for a specific color channel Ch1, Ch2, Ch3 is lower than a value of the light intensity stored for the pulse width PM1, PM2 or PM3 used, the pulse width PB1, PB2, PB3 for this color channel Ch1, Ch2, Ch3 are increased in a subsequent operating phase BP2. A lower luminous intensity can be caused, for example, by aging of the LEDs, temperature effects or by failure of an LED.

In the measurement phase MP shown, the section for which the color channels Ch1, Ch2, Ch3 are sequentially controlled or activated is followed by an optional section during which none of the color channels is controlled or activated, a so-called dark phase DP. In the dark phase DP, a black value can be measured which, for example, takes into account ambient light radiated into the LED device, in particular the photodetector.

After the measurement phase MP, a switch is made to a second operating phase BP2, in which the control signals S1, S2, S3 can be modified in comparison to the control signals S1, S2, S3 of the first operating phase BP1 on the basis of knowledge gained from the measurement phase MP.

The time interval between two measurement phases MP can be predetermined, for example a measurement phase MP can be carried out every n activation cycles. However, when several LED lighting devices are used, which are switched on at the same time, for example, the measurement phases MP of the several LED lighting devices occur essentially at the same time or only slightly offset in time. A viewer can then possibly perceive these measurement phases MP collectively. To a perception of the measuring phases MP of several LED lighting devices To suppress, the time interval (duration) of two measurement phases MP of an LED lighting device can be non-deterministic, for example random or pseudo-random, in particular within a predetermined time interval.

Fig. 2 outlines an LED lighting device L which, among other things, has a control device T, in particular a driver, for operating light-emitting diodes LD1, LD2 and LD3. The light-emitting diodes are divided into three strings, which correspond to a respective color channel Ch1, Ch2 or Ch3. Each color channel contains one or more light-emitting diodes LD1, LD2 or LD3 of the same color, for example the color channel Ch1 the red light-emitting diodes LD1, the color channel Ch2 the green light-emitting diodes LD1 and the color channel Ch3 the blue light-emitting diodes LD3. The color channels Ch1, Ch2 and Ch3 can be controlled separately or individually by means of the control device T. The color channels Ch1, Ch2 and Ch3 can, for example, contain the light-emitting diodes LD1, LD2 and LD3 in a series connection. The number of LEDs LD1, LD2 and LD3 can differ.

An LED LD1, LD2, LD3 can be understood as an individually housed LED or an LED chip. Light-emitting diodes LD1, LD2, LD3 designed as LED chips can for example be arranged on a common substrate. The LEDs LD1, LD2, LD3 can be, for example, inorganic LEDs, e.g. with InGAIP, or organic LEDs (OLEDs).

While a large proportion of the light emitted by the LEDs LD1, LD2 and LD3 is emitted to the outside, a smaller proportion falls on a photodetector D. A signal output of the photodetector D is functionally connected to the control device T, where a sensor signal output via the signal output is evaluated can be.

During an operating phase BP1, BP2, the sensor signal of the photodetector D can be used, for example, to to regulate the currents that flow through the color channels Ch1, Ch2 and Ch3 in such a way that a setpoint value of a luminous flux can be maintained. Alternatively, the photodetector D cannot be used in the operating phase BP1, BP2.

In particular, the measurement phase MP can be used for calibrating the LED lighting device L. For example, a correlation between a current through a color channel Ch1, Ch2 and Ch3 and the resulting light intensity or luminous flux of this color channel Ch1, Ch2 or Ch3 can be determined. In this way, in turn, a desired color location and / or a desired light intensity can be set or regulated more precisely during the operating phases BP1, BP2.

The control device T can functionally comprise a switching device for switching the LED lighting device from the operating phase BP1, BP2 into the measurement phase MP and back, as well as a measurement phase sequence control.

Of course, the present invention is not restricted to the exemplary embodiment shown.

Thus, instead of or in addition to a pulse-width-modulated control of the color channels, a current-level-modulated or current-intensity-modulated control of the color channels can also take place.

In one possible variant, the color channels can then each be operated in continuous operation, with their light intensity being able to be set via a current level or current level of an operating current impressed on the respective color channel.

Then, in the measurement phase, the color channels can be controlled one after the other with the same current strength or current level as in the operating phase, with different color channels can then preferably also be activated for the same length of time for a color impression that is uniform in relation to the operating phase. This also enables a particularly short measurement phase.

Furthermore, PWM control of the color channels with variable current levels is possible, i.e. PWM control in which the current level or current intensity can also be varied.

If a current level can be set (with or without PWM control), it can also be varied during the measurement phase in order to optimize the sensor signal of the at least one photodetector.

In the event that a luminous flux incident on the at least one photodetector is comparatively low and therefore the signal-to-noise ratio (SNR) of the sensor signal is often low, the current level for this color channel can be increased until the sensor signal has a has lower noise error or a higher SNR.

The current level can also be reduced in the event that a light current incident on the at least one photodetector is comparatively high and is in particular in the saturation range of the at least one photodetector. In other words, the luminous flux here is already so high that the photodetector is saturated and if the luminous flux is increased further, its sensor signal is no longer amplified. An indication that the photosensor is being operated above its saturation limit is the presence of a maximum sensor signal, e.g. a maximum sensor voltage.

If the luminous flux is too high, the current level of the color channel can be reduced until the associated sensor signal is in a range between a value just below the maximum sensor signal (as the upper limit) and above a value with an already favorable SNR. It has proven to be advantageous that the current level of the color channel is reduced until the associated sensor signal is in a range between 50% and below, in particular 99.5%, of the maximum sensor signal, in particular between 75% and below, in particular 99.5%, of the maximum sensor signal.

The search for a favorable sensor area can be carried out using any suitable search algorithm. A linear search algorithm can be carried out in which the current level is increased step-by-step (linearly) (if the sensor signal is initially too weak) or decreased (if the sensor signal is initially too strong or saturated). Such a search algorithm has (in Landau notation) a complexity class O (n).

An even faster adaptation, e.g. with the complexity class O (log n), can be achieved using other search algorithms, e.g. a binary search algorithm or an interpolation search or an interval search.

In addition, the order of the color channels activated one after the other is basically not restricted. The sequence can be the same for several measurement phases (eg always Ch1, Ch2, Ch3) or differ (eg Ch1, Ch2, Ch3 for one measurement phase and, for example, Ch3, Ch1, Ch2 for another measurement phase). In general, the sequence is preferably chosen so that the measurement phase is as short as possible. With the power sources that are commonly used, this is particularly the case when the color channels are controlled one after the other in the measuring phase in descending order of brightness, i.e. first the color channel with the greatest brightness, then the one with the second largest, etc. up to the channel with the lowest brightness , since the usual power sources require considerably more time for a power increase than for a power decrease. As a conclusion, the dark phase is advantageous if one is provided is. This results in a particularly fast measurement and thus a short measurement phase, which minimizes the risk of brightness fluctuations that are visible to the observer. If a power source is used that reacts faster when rising than when falling, a measurement in the reverse order, ie from the darkest to the lightest color channel, is of course advantageous.

In general, each of the color channels can be activated once or several times in a measurement phase. In this way, at least one of the channels can be activated twice in a measurement phase; For example, the red, green and blue color channels can be activated twice in a measurement phase, for example in the order Ch1, Ch2, Ch3, Ch1, Ch2, Ch3. The control signals for the color channels can follow one another directly or be spaced apart in time.

List of reference symbols

BP1

first phase of operation

BP2

second operating phase

Ch1

first color channel

Ch2

second color channel

Ch3

third color channel

D.

Photodetector

DP

Dark phase

I.

current

L.

LED lighting device

LD1

Light emitting diode of the first color channel

LD2

Light-emitting diode of the second color channel

LD3

Light-emitting diode of the third color channel

MP

Measurement phase

PB1

Pulse width of a signal pulse of the first color channel during an activation cycle in an operating phase;

PB2

Pulse width of a signal pulse of the second color channel during an activation cycle in an operating phase;

PB3

Pulse width of a signal pulse of the third color channel during an activation cycle in an operating phase;

PM1

Pulse width of a signal pulse of the first color channel during a measurement phase

PM2

Pulse width of a signal pulse of the second color channel during a measurement phase

PM3

Pulse width of a signal pulse of the third color channel during a measurement phase

S1

Control signal of the first color channel

S2

Control signal of the second color channel

S3

Control signal of the third color channel

t

Time

T

Control device

tb0

Start of an activation cycle

tba

Duration of an activation cycle

tm0

Beginning of the measurement phase

Claims (12)

1. Method of operating an LED lighting device (L), wherein the LED lighting device (L) comprises at least:

   - at least two color channels (Ch1, Ch2, Ch3), wherein each color channel (Ch1, Ch2, Ch3) comprises at least one LED (LD1, LD2, LD3), wherein the LEDs (LD1, LD2, LD3) of a color channel (CH1, CH2, CH3) each include the same color, and wherein each color channel (CH1, CH2, CH3) can be separately energized, and

   - at least one photodetector (D) configured and arranged to detect a portion of a light irradiated from the LEDs (LD1, LD2, LD3),

   wherein the method comprises at least the following steps:

   - switching the LED lighting device (L) from an operation phase (BP1) into a measurement phase (MP), wherein an amount of light from the respective LEDs (LD1, LD2, LD3) during the measurement phase (MP) is brought to a value by adjusting a current level of the color channels, at which value a signal level of a signal of the at least one photodetector (D) ranges between 75% and below its maximum signal level;

   - sequential and non-simultaneous energizing channels (CH1, CH2, CH3) such that light irradiated during the measurement phase (MP) includes an integral color mixture, which substantially corresponds to a color mixture of the operation phase (BP1), characterized in that

   - during the measurement phase (MP) each color channel is separately energized by means of a pulse width modulation, such that a ratio of pulse widths of the color channels during the measurement phase (MP) substantially corresponds to a ratio of the pulse widths of the color channels during the operation phase.
2. Method according to claim 1, wherein a deviation of the ratio of the pulse widths of two color channels during the measurement phase (MP) deviates not more than 10%, in particular not more than 1%, from the ratio of pulse widths of these two color channels during the operation phase.
3. Method according to 1 of the preceding claims, wherein the current level is adjusted separately for each of the color channels, such that the ratio of current levels of the color channels during the measurement phase (MP) corresponds to a ratio of current levels of the color channels during the operation phase.
4. Method according to claim 3, wherein the amount of light is brought to the value by means of a search algorithm, in particular by means of a binary search algorithm.
5. Method according to one of the preceding claims, wherein the measurement phase (MP) includes a step of non-energizing all color channels in addition to the step of energizing the color channels.
6. Method according to one of the preceding claims, wherein the measurement phase (MP) additionally includes compensation sections, during which the color channels are energized like during the operation phase..
7. Method according to one of the preceding claims, wherein a measurement phase (MP) has a duration of no longer than about 40 ms, in particular no longer than 20 ms, more particular no longer than 10 ms.
8. Method according to one of the preceding claims, wherein a duration in time between two measurement phases is not constant, in particular non-deterministic.
9. Method according to one of the preceding claims, wherein a sensor signal output during the measurement phase (MP) from the at least one photodetector is used at least in sections to adjust and an energization in a subsequent operation phase.
10. Method according to one of the preceding claims, wherein the color channels are energized during the measurement phase in the sequence of brightness of the color channels, preferably in descending order.
11. LED lighting device, wherein the LED lighting device (L) at least includes:

    - at least two color channels, wherein each color channel comprises at least one LED of the same color, and wherein each color channel can be separately energized,

    - at least one photodetector configured and arranged to detect a portion of a light irradiated from the LEDs,

    - a switching device for switching the LED-lighting device (L) from an operation phase into a measurement phase (MP), wherein during the measurement phase (MP) an amount of light is brought to a value by adjusting a current level of the color channels, at which value a signal level of a signal of the at least one photodetector (D) ranges between 75% and below its maximum signal level, and

    - a measurement flow control configured to energize the color channels sequentially and non-simultaneously such that light irradiated during the measurement phase (MP) includes an integral color mixture, which substantially corresponds to a color mixture of the operation phase,

    - characterized in that

    - the measurement flow control is configured to energize each color channel separately during the measurement phase (MP) by means of a pulse width modulation, such that a ratio of pulse widths of the color channels during the measurement phase (MP) substantially corresponds to a ratio of the pulse widths of the color channels during the operation phase.
12. LED lighting device (L) according to claim 11, wherein the LED lighting device (L) is configured to execute the method according to one of claims 1 through 10.

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