EP2433472B1 - Method for setting a chromaticity coordinate - Google Patents

Description

The invention relates to a method for adjusting a color location.

WO 2009/039132 A1 discloses a system for controlling the intensity and spectrum of a semiconductor lighting system.

For luminaires, it is advantageous if a light with a color locus on or near the Planckian curve, preferably with a color temperature between 2000K and 4000K or at a standard color location according to IEC 60081, can be efficiently generated. In particular, light-emitting diodes (LEDs) can be used for this purpose. One goal is to achieve a high color rendering or a nearly constant color fidelity in a wide range.

In particular, phosphor converted light emitting diodes can be used in a certain range in the Cx-Cy color diagram above the Planckian curve. In order to achieve a color location on the Planckian curve, red LEDs can also be used. This achieves a high color rendering index Ra (8)> 90.

Luminaires according to the prior art have the problem that the brightness and color locations of the LEDs used to migrate with a change in temperature. Also, the individual LEDs are subject to aging, so that changes over time the mediated by the lamp color impression. It is customary for the luminaire to have a temperature range of 20 ° C. (for example when the luminaire is switched on) up to 100 ° C. in a thermally stabilized state.

It is known a luminaire, which has red LEDs and in which the brightness of the red LEDs by means of a sensor is measured. The current through the light emitting diodes or a pulse width modulation (PWM) are tracked so that the Summenfarbort the lamp is approximately constant.

In this case, it is disadvantageous that the color locus migrates with increasing temperature (typically by + 0.07 nm / K) due to the shift of the dominant wavelength of the red LED. This results in a shift of the sum color location by about three MacAdams Threshold Units (SWE) from the original color location. In that regard, with changing temperature and the change of the color location of a user is perceptible.

The object of the invention is to avoid the above-mentioned disadvantages and in particular to provide an efficient way to keep the color location of a lamp (largely) constant.

This object is achieved according to the features of the independent claims. Further developments of the invention will become apparent from the dependent claims.

• bei dem ein Strom für die mindestens eine phosphorkonvertierte Leuchtdiode eingestellt wird;
• bei dem eine Pulsweitenmodulation für die mindestens eine phosphorkonvertierte Leuchtdiode eingestellt wird;
• bei dem ein Strom oder eine Pulsweitenmodulation für die mindestens eine monochromatische Leuchtdiode eingestellt wird.

To achieve the object, a method for setting a color locus of a luminaire comprising at least one phosphor-converted light-emitting diode and at least one monochromatic light-emitting diode is specified,

• in which a current for the at least one phosphor-converted light-emitting diode is set;
• in which a pulse width modulation for the at least one phosphor converted light emitting diode is set;
• in which a current or a pulse width modulation for the at least one monochromatic light-emitting diode is set.

The light-emitting diode may in each case be any semiconductor light-emitting element.

Thus, a number of the employed LED colors correspond to a number of lighting parameters to be controlled and / or controlled, e.g. brightness, CIE coordinates (Cx, Cy) or tristimulus coordinates (X, Y, Z) minus one. Thus, a regulation or control is not only about the brightness of the individual colors. Advantageously, the control or regulation is thus carried out via the mentioned combination of current and pulse width modulation of the individual types of light-emitting diodes.

In this case, setting the pulse width modulation means in particular that the duty cycle (active / inactive) per time interval for controlling the respective LED is adjustable. For example, a 50% pulse width modulation means that the LED is 50% active and 50% inactive within a given time interval.

The phosphor-converted LED has, for example, a wavelength-converting phosphor, for example based on garnets such as YAG: Ce. Such an LED can emit, for example, yellowish, greenish, blue-greenish or reddish light.

A further development is that the color location is set as a function of a desired color location, in particular as a function of a threshold value around the desired color location.

Thus, upon reaching the threshold value around the target color location, a correction of the color location can be initiated. The threshold value can be selected such that the human eye still (almost) does not perceive a change in the color location up to this threshold value.

Another development is that an actual value is determined by means of at least one sensor, wherein a deviation between the actual value and the target color location is determined and according to the color location is set so that the target color location is reached.

Here, the target color location can be set exactly or with a predetermined blur. For example, it is possible to determine the target color location within a MacAdams ellipse with a predetermined number of MacAdams threshold units.

In particular, it is a further development that the at least one sensor comprises an optical sensor.

• gemäß einem CIE CxCy-Farbraum,
• gemäß einem CIE uv-Farbraum,
• gemäß einem CIE u'v'-Farbraum und/oder
• gemäß einem Tristimulus XYZ-Raum.

It is also a development that the actual value is determined

• according to a CIE CxCy color space,
• according to a CIE uv color space,
• according to a CIE u'v 'color space and / or
• according to a tristimulus XYZ space.

In particular, any color spaces can be provided.

• den Strom für die mindestens eine phosphorkonvertierte Leuchtdiode;
• die Pulsweitenmodulation für die mindestens eine phosphorkonvertierte Leuchtdiode;
• den Strom für die mindestens eine monochromatische Leuchtdiode.

Furthermore, it is a development that the actual value is converted into the following control parameters for setting the color locus:

• the current for the at least one phosphor converted light emitting diode;
• the pulse width modulation for the at least one phosphor converted light emitting diode;
• the current for the at least one monochromatic light emitting diode.

• den Strom für die mindestens eine phosphorkonvertierte Leuchtdiode;
• die Pulsweitenmodulation für die mindestens eine phosphorkonvertierte Leuchtdiode;
• die Pulsweitenmodulation für die mindestens eine monochromatische Leuchtdiode.

It is also possible that the actual value is converted into the following control parameters for setting the color locus:

• the current for the at least one phosphor converted light emitting diode;
• the pulse width modulation for the at least one phosphor converted light emitting diode;
• the pulse width modulation for the at least one monochromatic light emitting diode.

Thus, the color space of the actual value is converted into a target color space, which is determined on the basis of the described control parameters.

In the context of an additional development, the setting of the color space is done by means of a lookup table.

Thus, the determination of the control parameters of the target color space can be calculated or the control parameters can be determined from a structure of pre-stored values on the basis of the actual values without separate calculation or transformation.

• Weißes Licht,
• violettes Licht,
• grünliches Licht,
• rötliches Licht.

A next development is that the phosphor-converted LED emits light in at least one of the following colors:

• White light,
• violet light,
• greenish light,
• reddish light.

One embodiment is that the monochromatic light-emitting diode is a red light-emitting diode.

Embodiments of the invention are illustrated and explained below with reference to the drawings.

Fig.1

eine schematische Darstellung einer Vorrichtung für eine Leuchte mit zwei phosphorkonvertierten LEDs und einer monochromatischen LED;

Fig.2

ein schematisches Ablaufdiagramm mit Schritten zur Einstellung des Farborts der Leuchte;

Fig.3A

ein Diagramm zur Visualisierung eines relativen Lichtstroms als Funktion der Temperatur für eine rote LED;

Fig.3B

ein Diagramm zur Visualisierung einer Veränderung der Dominantwellenlänge über die Temperatur für eine rote LED;

Fig.4A

ein Diagramm mit einer Farbortverschiebung abhängig von einem Strom durch eine weiße LED;

Fig.4B

ein Diagramm mit einer Farbortverschiebung abhängig von der Temperatur für eine weiße LED;

Fig.5

ein Diagramm mit einem Sollfarbort, der in etwa inmitten einer Ellipse liegt, wobei Schritte zur Regelung auf diesen Sollfarbort erläutert werden.

Show it:

Fig.1

a schematic representation of a device for a lamp with two phosphor-converted LEDs and a monochromatic LED;

Fig.2

a schematic flow diagram with steps to adjust the color locus of the lamp;

3A

a diagram for visualizing a relative luminous flux as a function of temperature for a red LED;

3B

a diagram for visualizing a change of the dominant wavelength over the temperature for a red LED;

4A

a diagram with a color locus shift dependent on a current through a white LED;

4B

a diagram with a color locus shift depending on the temperature for a white LED;

Figure 5

a diagram with a target color location, which is located approximately in the middle of an ellipse, with steps to control this target color location will be explained.

The approach presented here makes it possible to set a (nearly) constant color location in a lamp or luminaire comprising a plurality of light-emitting diodes and to hold it (largely) upright.

It should be noted that a light-emitting diode may also comprise any semiconductor light-emitting element.

The proposed luminaire comprises at least one monochrome LED (e.g., red in color or reddish tint) and at least one "white" LED. The "white" LED is a phosphor converted LED. It should be noted that the phosphor converted LED is not limited to the emission of "white" light. Rather, there are also phosphors, e.g. allow emission of violet, greenish or even reddish light.

1. (a) PWM der monochromen LED (rot) und
   Stromregelung der weißen LED und
   PWM der weißen LED;
2. (b) Stromregelung der monochromen LED (rot) und Stromregelung der weißen LED und
   PWM der weißen LED.

The following options for regulation and / or control are proposed:

1. (a) PWM of the monochrome LED (red) and
   Current control of the white LED and
   White LED PWM;
2. (b) Current control of the monochrome LED (red) and current control of the white LED and
   White LED PWM.

Thus, current control and PWM are performed for the phosphor converted LED (here also referred to as "white" LED), while current control or PWM is performed for the monochrome LED.

It is therefore exploited that shifts the color of the phosphor converted LED with the current, in a PWM control but not.

Thus, in the above-mentioned approaches (a) and (b), there are each three independent controlled variables which cause linearly independent changes in a (three-dimensional) color space. This allows control of the color location and brightness (within the scope of measurement and control accuracies).

By means of the three control variables, the brightness and color location of the luminaire can be tracked without the need for additional LEDs or additional control effort would be necessary.

Fig.1 shows a schematic representation of a device for a lamp 110th

The luminaire 110 comprises a luminous element 109 with an optionally multistage mixing optics 101, 102, a red LED 104 and two white LEDs 103, 105. A sensor 106 is arranged on the luminous element 109. The sensor 106 is an optical sensor. The sensor 106 is connected to a microcontroller 107 which, depending on the signal detected by means of the sensor 106, drives an LED driver 108. The LEDs 103 to 105 are connected to the LED driver 108, respectively.

The LED driver 108 includes a current source for the red LED 104 with current regulation or PWM control. Further, the LED driver 108 includes a power source for the white LEDs 103, 105 with current regulation and PWM control.

It should be noted that several (even different) sensors can be provided at different locations in the lamp 110 and / or outside the lamp 110.

The regulation of the color locus of the luminaire 110 can be effected, for example, by a correction of the values detected via the sensor 106. This correction comprises a transformation of the deviation vectors (Cx, Cy, brightness) into a coordinate system of the change vectors of the control parameters (PWM red, current white and PWM white). The microcontroller 107 controls e.g. via a PID control in each control parameter the sum color location and the brightness to the setpoint. The deviation from the setpoint may be e.g. well below 1 SWE and thus invisible to the human eye.

Fig.2 shows a schematic flow diagram with steps to adjust the color location of the lamp.

In a step 201, the LEDs are applied with a predetermined current or PWM value. This is the default setting before the actual control.

• der Summenfarbort der Leuchte oder
• die Helligkeiten der LEDs

gemessen. Der Summenfarbort entspricht einem IST-Zustand. In der letztgenannten Option wird der Summenfarbort anhand der gemessenen Helligkeiten berechnet.In a step 202 will / will be

• the zoom color place of the light or
• the brightness of the LEDs

measured. The sum color location corresponds to an actual state. In the latter option, the Sum color location calculated on the basis of the measured brightnesses.

• Helligkeit (Strom und PWM-Wert) der roten LED,
• Strom für die weißen LEDs,
• PWM-Wert für die weißen LEDs

berechnet.In a subsequent step 203, a comparison is made between the actual state with a desired color location and / or a setpoint brightness. In a step 204, a correction in the direction of the setpoint values (target color location and / or setpoint brightness) is determined. These are control parameters

• Brightness (current and PWM value) of the red LED,
• Current for the white LEDs,
• PWM value for the white LEDs

calculated.

Finally, in a step 205, a change of the control parameters is carried out, and thus a color location change of the luminaire is corrected.

This control can be performed automatically at certain times (e.g., iterative every n minutes). It is also possible for the regulation to be started over an extent of a change; such as e.g. a change detected by the sensor may be the cause of the control. For this purpose a threshold value comparison can be used and e.g. upon reaching or exceeding the setpoint, the control can be started.

3A shows a relative luminous flux φ _v / φ _{v (250 ° C} ) as a function of temperature for a red LED. 3B shows the change of a dominant wavelength λ over the temperature for the red LED.

It turns out that the red LED loses its brightness as the temperature rises. $$\frac{d{\mathrm{\Phi }}_V}{dT}={\mathrm{\Phi }}_{V\left(25\mathrm{°\; C}\right)}\cdot \left(-0.66\%/K\right)\mathrm{,}$$

At the same time, the dominant wavelength λ changes with the temperature $$\frac{d\lambda }{dT}=+0.07\mathit{nm}/K\mathrm{,}$$

und $$\frac{d\mathit{Cy}}{dT}=-1,384\cdot {10}^{-4}/K\mathrm{.}$$

In CIE 1931 coordinates, this roughly corresponds to $$\frac{d\mathit{cx}}{dT}=1.390\cdot {10}^{-4}/K$$

and $$\frac{d\mathit{Cy}}{dT}=-1.384\cdot {10}^{-4}/K\mathrm{,}$$

The brightness of the red LED can be adjusted via the duty cycle of a PWM. Alternatively, the current through the red LED can be increased, causing a nonlinear change in the flux of light with the current. In both cases (changing the current through the red LED or changing the PWM value) there is no significant change in the dominant wavelength and thus the color location of the red LED.

By way of example, in the following, a PWM control of the brightness can be assumed, ie $$\frac{d{\mathrm{\Phi }}_V}{d\mathrm{PWM}}={\mathrm{\Phi }}_V\left(\mathrm{PWM}=100\%\right)\mathrm{,}$$

White LEDs also show changes in brightness and color (see Fig.4A and Fig.4B ).

$$\frac{d\mathit{Cx}}{dT}=\frac{d\mathit{Cy}}{dT}=-1,25\cdot {10}^{-5}/K\mathrm{.}$$

Out 4A follows for the Farbortverschiebung the white LED in a temperature range of 20 ° C to 100 ° C approximately $${\mathrm{\Phi }}_V={\mathrm{\Phi }}_{V\left(25\mathrm{°\; C}\right)}\cdot \left(-0.2\%/K\right)\cdot T;$$

$$\frac{d\mathit{cx}}{dT}=\frac{d\mathit{Cy}}{dT}=-1.25\cdot {10}^{-5}/K\mathrm{,}$$

$$\mathrm{\Delta }\mathit{Cy}=0,00375\mathrm{pro}100\mathrm{mA}$$

For example, for ultra-white LEDs, there is roughly a shift of $$\mathrm{\Delta }\mathit{cx}=0.0015\mathrm{Per}100\mathrm{mA}$$

$$\mathrm{\Delta }\mathit{Cy}=0.00375\mathrm{Per}100\mathrm{mA}$$

Corresponding to the red LED also applies to the white LED: $$\frac{d{\mathrm{\Phi }}_V}{d\mathrm{PWM}}={\mathrm{\Phi }}_V\left(\mathrm{PWM}=100\%\right)$$

mit
a = 1,53 und I_s = 0,38A.Used white LEDs can change their brightness with the current roughly as follows: $$\frac{d{\mathrm{\Phi }}_V}{dI}={\mathrm{\Phi }}_{V0}\cdot a\cdot \frac{1}{I+\mathit{is}}.$$

With
a = 1.53 and I _s = 0.38A.

The color space can be described eg with coordinates according to CIE 1931 as φ _v - Cx-Cy. Alternatively, the tristimulus (X, Y, Z) space can be used.

durch Änderungsvektoren $$\left(\sum _i\frac{d{\mathit{Cx}}_i}{d{\mathrm{PWM}}_i}\right)+\frac{d{\mathit{Cx}}_{\mathit{\omega ei}\mathrm{ß}}}{d{I}_{\mathit{\omega ei}\mathrm{ß}}};$$

$$\left(\sum _i\frac{d{\mathit{Cy}}_i}{d{\mathrm{PWM}}_i}\right)+\frac{d{\mathit{Cy}}_{\mathit{\omega ei}\mathrm{ß}}}{d{I}_{\mathit{\omega ei}\mathrm{ß}}};$$

$$\left(\sum _i\frac{d{\mathrm{\Phi }}_{\mathit{Vi}}}{d{\mathrm{PWM}}_i}\right)+\frac{d{\mathrm{\Phi }}_{V_{\mathit{\omega ei}\mathrm{ß}}}}{d{I}_{\mathit{\omega ei}\mathrm{ß}}}$$

aufgehoben oder näherungsweise aufgehoben werden.Preferably, the control is designed so that the change vectors of the Sumfarbortortes $$\underset{i}{\Sigma }\frac{d{\mathit{cx}}_i}{dT}.\underset{i}{\Sigma }\frac{d{\mathit{Cy}}_i}{dT}.\underset{i}{\Sigma }\frac{d{\mathrm{\Phi }}_{\mathit{vi}}}{dT}$$

by change vectors $$\left(\underset{i}{\Sigma }\frac{d{\mathit{cx}}_i}{d{\mathrm{PWM}}_i}\right)+\frac{d{\mathit{cx}}_{\mathit{\omega ei}\mathrm{ß}}}{d{I}_{\mathit{\omega ei}\mathrm{ß}}};$$

$$\left(\underset{i}{\Sigma }\frac{d{\mathit{Cy}}_i}{d{\mathrm{PWM}}_i}\right)+\frac{d{\mathit{Cy}}_{\mathit{\omega ei}\mathrm{ß}}}{d{I}_{\mathit{\omega ei}\mathrm{ß}}};$$

$$\left(\underset{i}{\Sigma }\frac{d{\mathrm{\Phi }}_{\mathit{vi}}}{d{\mathrm{PWM}}_i}\right)+\frac{d{\mathrm{\Phi }}_{V_{\mathit{\omega ei}\mathrm{ß}}}}{d{I}_{\mathit{\omega ei}\mathrm{ß}}}$$

canceled or approximately canceled.

Alternatively, this correction can also be realized via a control with the aid of a lookup table.

Figure 5 shows a diagram with a target color location 502, which lies approximately in the middle of an ellipse 501. The Ellipse 501 exemplifies a color temperature of 2700K, the color temperature is on the Planckian curve and has a diameter of 3 SWE. Changes within this ellipse 501 are not perceived (or disturbed) by the untrained human eye.

• Weiße LEDs: I_max = 700mA; 60% PWM;
• Rote LED: 350mA konstant.

The control of the LEDs (according to the example of Fig.1 : Two white LEDs and a red LED) is as follows:

• White LEDs: I _max = 700mA; 60% PWM;
• Red LED: 350mA constant.

verschiebt sich der Farbort der Leuchte in Richtung eines Pfeils 503 zu einem Farbort 504.At an increase in temperature without correction $$\frac{d{\lambda }_{\mathit{red}}}{dT};\frac{d{\mathrm{\Phi }}_{\mathit{vi}}}{dT}$$

the color location of the luminaire shifts in the direction of an arrow 503 to a color location 504.

in Richtung eines Pfeils 505 zu einem Farbort 506.Now the brightness of the red LED can be increased to 145% (corresponds to a current increase of approx. 170% to approx. 600mA), a correction is made $$\frac{d{\mathrm{\Phi }}_{\mathit{vrot}}}{d{\mathrm{PWM}}_{\mathit{red}}}$$

in the direction of an arrow 505 to a color location 506.

indem der Strom der weißen LEDs auf 350mA reduziert und die PWM für die weißen LEDs auf 100% angehoben wird. Dadurch wandert der Farbort in Richtung eines Pfeils 507 zum Sollfarbort 502.Now a correction is made $$\frac{d{\mathit{cx}}_{\mathit{\omega ei}\mathrm{ß}}}{d{I}_{\mathit{\omega ei}\mathrm{ß}}}.\frac{d{\mathit{Cy}}_{\mathit{\omega ei}\mathrm{ß}}}{d{I}_{\mathit{\omega ei}\mathrm{ß}}}.$$

by reducing the power of the white LEDs to 350mA and raising the PWM for the white LEDs to 100%. As a result, the color locus travels in the direction of an arrow 507 to the target color location 502.

List of abbreviations

cx

x-coordinate in the CIE 1931 color space

Cy

y-coordinate in the CIE 1931 color space

LED

led

PWM

Pulse Width Modulation

SWE

MacAdams Threshold Unit

LIST OF REFERENCE NUMBERS

101

optical component

102

optical component

103

white LED

104

red LED

105

white LED

106

Sensor (optical sensor)

107

microcontroller

108

LED driver

109

light element

110

lamp

201 to 205

Process steps for controlling the color locus of a luminaire

501

ellipse

502

Sollfarbort

503

arrow

504

color location

505

arrow

506

color location

507

arrow

Claims (7)

1. Method for setting a color locus of a luminaire (110) comprising at least one phosphor-converted light-emitting diode (103, 105) and at least one monochromatic light-emitting diode (104),

   - in which a current for the at least one phosphor-converted light-emitting diode (103, 105) is set;

   - in which a pulse width modulation for the at least one phosphor-converted light-emitting diode (103, 105) is set;

   characterized in that

   - in which method either a current or a pulse width modulation for the at least one monochromatic light-emitting diode (104) is set,

   - wherein the color locus is set depending on a setpoint color locus, in particular depending on a threshold value around the setpoint color locus, wherein an actual value is identified by means of the at least one sensor, wherein a discrepancy between the actual value and the setpoint color locus is determined and the color locus is set correspondingly in such a way that the setpoint color locus is achieved, and

   - in which the at least one sensor comprises an optical sensor.
2. Method according to Claim 1, in which the actual value is determined

   - in accordance with a CIE CxCy color space,

   - in accordance with a CIE uv color space,

   - in accordance with a CIE u'v' color space and/or

   - in accordance with a tristimulus XYZ space.
3. Method according to Claim 1, in which the actual value is converted into the following regulation parameters for setting the color locus:

   - the current for the at least one phosphor-converted light-emitting diode;

   - the pulse width modulation for the at least one phosphor-converted light-emitting diode;

   - the current for the at least one monochromatic light-emitting diode.
4. Method according to one of Claims 1 to 3, in which the actual value is converted into the following regulation parameters for setting the color locus:

   - the current for the at least one phosphor-converted light-emitting diode;

   - the pulse width modulation for the at least one phosphor-converted light-emitting diode;

   - the pulse width modulation for the at least one monochromatic light-emitting diode.
5. Method according to one of the preceding claims, in which the color locus is set by means of a lookup table.
6. Method according to one of the preceding claims, in which the phosphor-converted light-emitting diode emits light in at least one of the following colors:

   - white light,

   - violet light,

   - greenish light,

   - reddish light.
7. Method according to one of the preceding claims, in which the monochromatic light-emitting diode is a red light-emitting diode.

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