EP2351376A1

EP2351376A1 - Method and device for adjusting the color point of a lighting unit

Info

Publication number: EP2351376A1
Application number: EP09752789A
Authority: EP
Inventors: Jan Oliver Drumm; Jens Richter; Claus Seibert
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2008-11-28
Filing date: 2009-11-06
Publication date: 2011-08-03
Also published as: CN102301722A; WO2010060775A1; US20110279494A1; KR20110099022A; DE102008059639A1; KR101334239B1; US9106878B2

Abstract

The invention relates to a method and to a device for adjusting the color point of a lighting unit, wherein the lighting unit comprises semiconductor-based lasers for producing an RGB signal. At least one component of the RGB signal, particularly a light ray originating from a semiconductor-based laser, is fed through a filter to a sensor, and at least one of the semiconductor-based lasers is controlled based on the signal detected by the sensor.

Description

description

Method and device for color balance of a light unit

The invention relates to a method and a device for color point matching a lighting unit.

In an RGB laser module for so-called embedded projection applications, semiconductor-based laser beam sources (laser sources or lasers) are used to generate light. The optical output power of the laser source is often dependent on the temperature. The emitted wavelength of the laser source can also be influenced by the temperature.

These two temperature dependencies lead to significant changes in a mixed color produced by a plurality of laser sources in the operation of the RGB laser module at different ambient temperatures and thus prevent color-accurate reproduction of image information, for example, an RGB laser projector.

The object of the invention is to avoid the above-mentioned disadvantages and in particular a comparatively color-true reproduction of

To enable image information, wherein the image information is achieved by the mixture of different light sources, at least one semiconductor-based light source.

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

To achieve the object, a method for color balance of a lighting unit is specified, wherein the Light unit has semiconductor-based laser for generating an RGB signal. At least one component of the RGB signal, in particular a light beam originating from a semiconductor-based laser, is fed via a filter to a sensor, and based on the signal detected by the sensor, at least one of the semiconductor-based lasers is driven.

It should be noted that the color point adjustment may comprise a color point adjustment or a continuous or iterative control of a set color point. In particular, the method can be used as a control method for the continuous or discrete-time adjustment or control of the color point.

It should also be noted that semiconductor-based laser sources can be used. Also, LEDs of different colors and / or semiconductor lasers can be used as light sources.

It should also be noted that the component of the RGB signal may comprise a light beam of the red semiconductor-based laser, the green semiconductor-based laser, and / or the blue semiconductor-based laser.

The filter may in particular be an optical filter.

An advantage of the proposed solution is that an efficient and application-dependent scalable possibility of setting or adjusting the

Color point is created. In particular, the color point may be around a white point, e.g. "D65", act.

The presented approach enables the reduction or compensation of a drift of the color point, in particular as a function of the temperature. Thus, effective wavelength drifts or power drifts of the semiconductor-based laser while maintaining a substantially stable appearing color point can be compensated.

A further development is that a plurality of semiconductor-based lasers are sequentially controlled on the basis of the respectively associated detected signal.

For example, color for color may be from the sensor, e.g. from a photodiode detected signal from a controller or by a control electronics (which may be implemented, for example, in the form of an ASIC) read and adapted to the performance of the corresponding laser. Accordingly, processing in such time slots (e.g., one time slot for driving a laser) is efficient using only one sensor for all components of the RGB signal, i. for all light beams of the semiconductor-based laser possible.

It is also a possibility that all components of the RGB signal are fed via the filter to the sensor.

Another refinement is that a plurality of components of the RGB signal are each supplied to a sensor and, based on the signal detected by the respective sensor, the at least one semiconductor-based laser is activated.

In particular, it is a development that several filters are provided for a plurality of components of the RGB signal.

In particular, at least one filter can be provided per component or light beam of the RGB signal. It is also a development that the sensor comprises a photodiode, wherein the photodiode is arranged in particular in the vicinity of a laser Rückfacette.

Furthermore, it is a development that a scheme for

Activation of the at least one semiconductor-based laser is provided.

This regulation can be realized in the form of a computer. In particular, the control may include hardware and / or software components. For example, the control can be implemented in the form of an ASIC.

In the context of an additional development, the color point adjustment comprises a white point adjustment or a white point adjustment or a white point control.

A next development is that the color point adjustment takes place within the framework of a predetermined tolerance, wherein the predetermined tolerance is / are determined in particular on the basis of a MacAdams distance.

One embodiment is that the lighting unit comprises a red semiconductor-based laser, a green semiconductor-based laser and a blue semiconductor-based laser.

An alternative embodiment is that the green semiconductor-based laser is an optically or electrically pumped infrared semiconductor laser, in particular with a frequency doubling.

This can be a frequency doubling within the resonator (inter-cavity frequency doubling) or a doubling of the frequency outside the resonator (extra-cavity doubling). A next embodiment is that the filter comprises one of the following filters:

a V-lambda filter;

an absorption filter; - a transmission filter.

It is also an embodiment that the filter is designed such that at least one further dependence of a color locus on a wavelength of at least one other light source is taken into account.

Thus, it is possible that only with a single filter, the wavelength change over the temperature for several lasers is taken into account, wherein the filter can be arranged only in a beam path of a laser. The signal detected by the sensor on the basis of the filter thus not only permits conclusions about the wavelength drift of the current light beam, but also about the wavelength drift of another light beam (not detected by the filter). This is e.g. in the context of the evaluation, the correlation between wavelength drifts is determined and, depending on the result, a plurality of semiconductor-based lasers are set.

Accordingly, a change in brightness with variable temperature can be detected and (at least partially) compensated.

A further development consists in that the semiconductor-based laser comprises a laser diode.

It is also a development that the filter is designed for a given wavelength range, in particular in a visible spectrum. Thus, the filter can be advantageously designed for a specific wavelength range of a light beam or a component of the RGB signal. This allows a simplified and cost-effective production of the filter.

Furthermore, to solve the above object, a device for color balance of a light unit is proposed - with semiconductor-based lasers to produce a

RGB signal,

- With at least one filter on the at least one component of the RGB signal is fed to at least one sensor, - with a control that controls based on a signal detected by the sensor at least one of the semiconductor-based laser.

Also, in order to achieve the above object, there is provided a device comprising a processor unit and / or an at least partially hard-wired or logical circuit arrangement arranged such that the method can be carried out as described herein.

Said processor unit may be or include any type of processor or computer or computer with correspondingly necessary peripherals (memory, input / output interfaces, input devices, etc.).

Furthermore, a hard-wired or logical

Circuit unit, e.g. an FPGA or an ASIC or other integrated circuit e.g. be provided as a control or regulation.

In particular, the device may thus comprise a unit for parallel processing of signals and / or a unit for serial processing of signals. Embodiments of the invention are illustrated and explained below with reference to the drawings.

Show it:

Fig.l an equation for describing a white point

[w], an equation 102 for describing the colors red, green, blue and a white point stability equation 103;

Fig.2 dependencies of tristimulus values of the RGB laser as a function of the wavelength in the form of so-called "color matching functions";

3 shows an equation 104 for illustrating the

Linking the tristimulus values of the RGB laser with the wavelengths;

4 shows an equation 105 for the resolution of the white point stability equation 103;

5 shows an equation 106 comprising filter functions and an equation 107 for illustrating the control circuits;

Fig. 6 is a graph showing exemplary changes in wavelengths for a red, a green and a blue laser as a function of temperature;

Fig. 7 is a CIE standard color chart illustrating a color locus change of a white point toward turquoise;

8 shows a diagram with exemplary laser powers for a red, a green and a blue laser as a function of the temperature; 9 is a block diagram for setting and regulation to a nearly constant color point, wherein each beam of an RGB light source is detected with its own photodiode and based on the signals detected by the photodiodes the RGB light source is driven, wherein additionally in the red light beam before the photodiode is arranged an optical filter;

10 shows a block diagram of an alternative adjustment and regulation to a nearly constant color point, wherein the RGB signal of an RGB light source is also detected via a filter by means of a photodiode and based on the signal of the

Photodiode the three light sources are driven;

11 shows an equation 108 for describing a wavelength-dependent transmission.

The approach proposed here allows a (nearly) constant white point by means of a setting or regulation of a power of at least one semiconductor-based laser source. In particular, the power can be set separately for a plurality of semiconductor-based laser sources.

In this case, a product of the power of the semiconductor-based laser source (hereinafter referred to as "laser") and a filter function derived from colorimetry can be kept constant as a controlled variable, in particular (for example independently) for a plurality of light sources of the RGB module.

The filter function takes into account a temperature dependence of the wavelength and a resulting resulting necessary adjustment of the optical output power of the laser, so that a stable white point can be achieved. It should be noted that a stable or constant white point is, for example, a white point with a predetermined tolerance, for example a white point within a predetermined deviation. In particular, such a tolerance can be predetermined product-specifically.

The form of the filter function is derived from a so-called white point stability equation.

For example, it is possible to provide a control loop for the three colors red, green and blue as follows:

S_R (T) = P_R * f_R (λ_R (T)) S_G (T) = P_G * f_G (λ_G (T)) S_B (T) = P_B * f_B (λ_B (T))

Denote: S_R (T), S_G (T), S_B (T) controlled variables,

P R, P G, P B optical output powers of the respective RGB laser as manipulated variables, λ_R (T), λ_G (T), λ_B (T) temperature-dependent wavelengths of the RGB laser.

The control circuits set the manipulated variables P_R, P_G, P_B such that the controlled variables S_R (T), S_G (T), S_B (T) are stable on the values

S_R (Tcal)

S_G (Tcal)

S_B (Tcal)

being held. These values S_R (Tcal), S_G (Tcal),

S_B (Tcal) can be determined by means of a calibration at a temperature Tcal. Thus, the optical output powers P_R, P_G, P_B can be set so that a predetermined white point [w] (eg, "D65") and a predetermined luminous flux L are achieved.

For example, the filter functions fR (λR (T)), f_G (λ_G (T)), f_B (λ_B (T)) may be in the form of an optical filter, e.g. as a transmission filter.

In the following, an option for the filter functions f_R (λ_R (T)), f_G (λ_G (T)), f_B (λ_B (T)) is explained by way of example. Colorimetric formulas refer, for example, to the CIE 1931 standard ("CIE standard valence system").

To generate a constant white point [w] according to equation 101 (see FIG. 1), with the tristimulus values Xw, Yw, Zw, three laser beams with the colors red [R], green [G] and blue [B] according to equation 102 (see FIG. 1) and the radiometric powers P_R (λ_R (T)), P_G (λ_G (T)), P_B (λ_B (T)) are superimposed to equation 103 (FIG. Equation 103 will also be referred to hereinafter as the "white point stability equation".

FIG. 2 shows dependencies of tristimulus values of the RGB lasers as a function of the wavelength as so-called "color matching functions" 201 to 203 according to CIE 1931.

Accordingly, the tristimulus values of the RGB lasers according to equation 104 (see FIG. 3) can be linked to the wavelengths λ_R (T), λ_G (T), λ_B (T).

The white point stability equation described above can be resolved according to the radiometric performances according to equation 105 (see FIG. 4). For a clearer Representation was omitted in the transformation to an explicit representation of the wavelength and temperature dependencies.

The white point stability equation 105 can be interpreted as follows: If the radiometric powers P_R (λ_R (T)), P_G (λ_G (T)), P_B (λ_B (T)) are set according to the above rule, the white point [w] also becomes kept stable at temperature-related wavelength fluctuations of the laser.

Based on the filter functions f_R (λ_R (T)), f_G (λ_G (T)), f_B (λ_B (T)) shown in equation 106 (see FIG. 5), the RGB power values resulting from the white point stability equation can be determined for the power control.

Thus, the filter functions according to Equation 106 can be used in the control loops according to Equation 107 (see FIG. 5). Thus, the respective control loop can provide a temperature-dependent or a wavelength-dependent power of at least one laser according to the white point stability equation.

Accordingly, it is possible that the present here

Approach at least one, in particular for each laser own control circuit provides that converts at least one filter function according to Equation 106 and thus effectively reduces or compensates for temperature fluctuations and allows a substantially stable white point.

In the context of an advantageous embodiment, to adapt the optical output power of at least one laser (or several RGB lasers), an initially set white point (eg "D65") can be kept stable independently of temperature changes in a predetermined range. For example, a red laser (with a wavelength of about 640 nm) may be provided whose wavelength changes by about 0.25 nm per Kelvin due to the semiconductor material properties. In a blue laser used by way of example (with a wavelength of about 440 nm), the wavelength changes due to the

Semiconductor material properties by about 0.05 nm per K. Preferably, a green laser (with a wavelength of about 528 nm) may be provided, whose wavelength is largely independent of temperature changes due to the arrangement with an intra-cavity frequency doubling.

6 shows exemplary changes in the wavelengths for the red laser 601, for the green laser 602 and for the blue laser 603 as a function of the temperature.

Due to the change of the laser wavelengths with the temperature, the tristimulus values of the RGB lasers change according to the color matching functions. Values for the color matching functions are e.g. can be taken from the literature in tabular form.

Thus, tristimulus values of the resulting white light can be determined by adding the RGB tristimulus values:

TX_w = TX_R + TX_G + TX_B

TY_w = TY_R + TY_G + TY_B TZ_w = TZ_R + TZ_G + TZ_B

CIE color coordinates x, y of the white light result

x = TX / (TX + TY + TZ) and y = TY / (TX + TY + TZ) FIG. 7 shows the color location change of the white light calculated from the abovementioned formulas under the boundary condition that the optical output power of the RGB lasers is kept substantially constant. Due to the temperature-dependent drifts of the wavelengths shown in FIG. 2, the color impression changes from original white (eg D65) (in the calibrated state) to turquoise.

This change in white point color location occurs e.g. at

Temperature changes in a range of 20 ⁰ C to 60 ⁰ C. This corresponds to a typical temperature in the housings of the laser components.

A distance in the color space between the color location in a calibrated state (e.g., D65) and an elevated temperature state without the compensation presented herein is a multiple of MacAdam's defined maximum distance between two color locations perceived by the human eye as distinguishable colors. Thus, the approach presented here, for example, allows to keep the temperature drift of the laser within the MacAdams distance and thus a substantially true color reproduction of image content.

Due to the linear superimposition of color impressions, it is possible to calculate the RGB laser power with which the o.g. Color locus change can be reduced or compensated:

[w] = [TX_w; TY_w; TZ_w]! =

ι ₌ p _R ( _T ) * [TX_R (λ_R (T)); TY (λ_R (T)) _R; TZ_R (λ_R (T))] + + PG (T) * [TX_G; TY_G; TZ_G] + + PB (T) * [TX_B (λ_B (T)); TY_B (λ_B (T)); TZ_B (λ_B () T))]:

=: A * [PR (T); PG (T); PB (T)] O [PR (T); PG (T); PB (T)] = A ^Λ (-1) * [TX_w; TY_w; TZ_w]! = [Eg D65]

The resulting performance (for 20 lumens in eg D65 and at a housing temperature in a range of 20 ⁰ C to 60 ⁰ C) are shown in Figure 8 for the red laser 801, for the green laser 802 and for the blue laser 803 depending on the temperature.

Accordingly, it can be seen that an adjustment of the powers for each laser is different in order to achieve a stable white point over a certain temperature range.

Advantageously, three independent control loops can be used to control the o.g. Realize performance adjustments by using special filter functions in a sufficiently good approximation.

These control loops can be expressed by the following equations:

P_R (λ_R (T)) * f_R (λ_R (T)) = constant = S_R (Tcal)

P_G (λ_G (T)) * f_G (λ_G (T)) = constant = S_G (Tcal)

P_B (λ_B (T)) * f_B (λ_B (T)) = constant = S_B (Tcal)

Where P_R, P_G, P_B are the manipulated variables and S_R (Tcal), S_G (Tcal), S_B (Tcal) are the controlled variables.

The value of the respective control variable results from the calibration of the white point at the temperature Tcal.

The functions f_R (λ_R (T)), f_G (λ_G (T)), f_B (λ_B (T)) can be implemented as special filter functions. In particular, the filter functions can be selected such that, with active control, the adaptation of the RGB laser powers shown in FIG. 8 is achieved to a sufficiently good approximation.

Such an approximation can be achieved if the current color locus of the white point despite temperature changes over the exemplary range of 20 ⁰ C to 60 ⁰ C within an ellipse, for example with a 5-fold axis length of the corresponding MacAdams ellipse to the color location of the calibrated white point. Thus, by the invention, a faithful reproduction of image information can be achieved even with changes in the ambient temperature.

Further embodiments:

The following explanations are examples, which may be combined in combination with the above explanations or at least parts thereof.

9 shows a block diagram for a

Embodiment in which the filter function is implemented as an optical transmission filter.

An RGB laser module comprises a red laser diode 902, a blue laser diode 903 and a largely temperature-independent green laser 904. The green laser 904 emits a green light beam, which from a triple beam combination mirror 910 with a specific transmission and reflection on the one hand to a photodiode PD G 908 deflected for green light and on the other hand to a spatially superimposed RGB laser beam 909 is combined. The blue laser diode 903 emits a blue laser beam, which is supplied via a mirror on the one hand to the beam combination mirror 910 and thus to the RGB laser beam 909, on the other hand to a Photodiode PD B 907 is directed for blue light. The red laser diode 902 emits a red laser beam, which is supplied via a mirror on the one hand to the beam combination mirror 910 and thus the RGB laser beam 909, on the other hand is directed via a filter 905 to a photodiode PD R 906 for red light.

The filter 905 can be arranged in particular in one light beam or in a plurality of light beams of the RGB laser module. In particular, each light beam may have a separate filter. Preferably, filter 905 is a filter that allows for wavelength dependent transmission. The filter 905 is thus e.g. a V-lambda filter, a transmission filter or an absorption filter.

In particular, it is possible that the filter 905 is provided in the light beam having the highest temperature drift.

An exemplary embodiment for the filter 905 is that it is designed such that at least one further dependency of the color locus on the wavelength is taken into account for at least one further light source. Thus, for example, for the filter 905 arranged in the red beam path, a corresponding drift of the blue (and / or green) light can also be taken into account, to a certain extent by the drift of the red light. Thus, only by means of a single filter 905 in front of the photodiode PD R 906, the control can be supplied with information that enable a drive not only of the red laser 902, but also the blue laser 903 and the green laser 904. In such an embodiment, the sensors 907 and 908 and the associated expense can be eliminated accordingly. Accordingly, the filter 905 may be embodied as a V-lambda filter, by means of which, for example, a brightness sensitivity is determined only in a single beam path and the brightnesses for a part or for all lasers are set as a function of a change by means of the control 901.

In each case, electrically pumped semiconductor lasers (diode lasers) can be used in particular for the red or blue light beam. For example, have a red

Diode laser has a wavelength drift of 0.25 nm / K and a blue diode laser has a wavelength drift of 0.05 nm / K. To generate the green radiation component, an optically pumped infrared semiconductor laser with intra-cavity frequency doubling can be used. Such an infrared semiconductor laser is largely temperature independent, i. it shows no significant change in emitted wavelength over temperature.

The controller 901 may be embodied, for example, in the form of an ASIC. The light beams emitted by the individual lasers 902 to 904 can generally be detected via any desired sensors, in particular via the photodiodes 906 to 908 shown. In addition to changing the wavelength, a change in the brightness can also be detected and compensated (at least in part) by means of the control 901. The controller 901 can set the respective laser current or the respective laser power so that the photocurrent of the photodiodes is substantially constant.

For example, separate filters (not shown) may be provided for the green laser 904 and for the blue laser diode 903, if separately determining separately the change in wavelength versus temperature determined and / or (at least partially) to be compensated.

In the example according to FIG. 9, the filter functions for the green and the blue light beam can be set as constant in a defined spectral range, ie.

f_G (λ_G) = constant (i.e., the control realizes a constant output power), f B (λ B) = constant (i.e., the control realizes a constant output power).

The filter function f_R (λ_R (T)) for the red light beam may be realized as an optical transmission filter, i. Depending on the wavelength, different amounts of light impinge on the photodiode 906. The transmission can depend in particular linearly on the wavelength:

f_R (λ_R) = Tr0 * (l- (λ_R-λ_R_0) * s)

Thus, effectively, the effect of ambient temperature changes on the color mixing parameters of optical power and wavelength can be determined by the

Control electronics detected and (at least partially) compensated accordingly.

The value Tr0 indicates the transmission of the filter at the reference wavelength λ_R. TrO is preferably to be dimensioned depending on the sensitivity of the respective photodiode.

For example, it is thus possible to stabilize the color locus drift of the white point with a deviation from a desired color locus (eg D65) in the CIE color space. A criterion for whether the deviation is visible to the human eye can be determined by the position of the current white point color locus relative to the MacAdams ellipse around the reference white point (eg D65). Color loci lying within an ellipse of, for example, 5 times the length of the half axes of the MacAdams ellipse are perceived by the human eye to be identical to the reference white point. Thus, this measure based on the MacAdams ellipse can be used to allow some tolerance for color drift. Depending on the respectively required accuracy, a more or less stable white point can be predetermined, for example, depending on the application and / or quality of a product. Accordingly, the regulation or the necessary components in connection with the regulation are scalable with regard to effort and thus costs.

The range of values for the above-mentioned parameter s of the transmission filter may preferably be chosen such that the above-mentioned. MacAdams criterion is met. For this purpose, e.g. the parameter s within an interval [4%; 4.8%] per nm.

10 shows a further block diagram for an exemplary embodiment in which the filter function is implemented as an optical transmission filter, wherein, in contrast to FIG. 9, only a single photodiode is used.

An RGB laser module comprises a red laser diode 1002, a blue laser diode 1003 and a largely temperature-independent green laser 1004. The green laser emits a green light beam, which is deflected by a triple beam combination mirror 1008 with a specific transmission and reflection on the one hand to a photodiode PD 1007 and on the other hand to a spatially superimposed RGB laser beam 1006 is combined. The blue laser diode 1003 emits a blue laser beam, which is supplied via a mirror to the beam combination mirror 1008 and thus to the RGB laser beam 1006 and to the photodiode PD 1007. The red laser diode 1002 emits a red laser beam, which is supplied via a mirror to the beam combination mirror 1008 and thus to the RGB laser beam 1006 and to the photodiode PD 1007.

In front of the photodiode PD 1007, a filter 1005 is arranged, in particular a V-lambda filter, a

Transmission filter or an absorption filter can be. The signal detected by the photodiode 1007 is passed to a controller 1001, which consequently drives the laser diodes 1002, 1003 and the laser 104.

In particular, the filter 1005 may be an optical transmission filter having a wavelength-dependent transmission, e.g. according to equation 108 (see FIG.

The optical transmission filter can be designed so that it in the three wavelength ranges red, green and blue o.g. Function realized by the wavelength. The regulation of the individual RGB lasers can be sequential, i. Color by color, the photodiode signal is read out by the control electronics (ASIC) and the power of the corresponding laser is adjusted.

It is also possible that the photodiodes of the red and blue lasers are positioned near the laser back facet and thus the laser back facet power is detected. From the back facet of the laser, an optical power is emitted whose value is proportional to the power emitted from the front facet of the laser. This arrangement allows an even more compact design of the RGB laser module.

The filter function can be realized both as a reflective and / or as an absorbing optical layer.

The values for TrO_R, TR0_G, TR0_B may be realized in the technical implementation of the filter as a neutral density filter (e.g., as an additional optical device) or as an integrated solution along with the wavelength dependent portion of the filter.

The approach presented here applies to any color points, in particular white points, in the color space. Because the size of the

MacAdam's ellipses vary according to the position of the selected color point in the color space, the tolerance for the filter slope s can be adjusted accordingly.

Other advantages:

The approach presented here allows the use of a control with a wavelength-dependent filter function in the control loop, taking into account the brightness perception of the human eye at different wavelengths. This allows for improved white point stability.

Another advantage is that the solution presented allows an efficient and cost-effective implementation. In particular, the cost of an otherwise complex and complex control electronics can be reduced.

It is also advantageous that no separate temperature measurement is needed.

Claims

claims

1. A method for color point matching of a light unit comprising semiconductor-based lasers (902, 903, 904) for generating an RGB signal (909),

- In which at least one component of the RGB signal (909) via a filter (905) is supplied to a sensor (906) and based on a detected by the sensor (906) signal at least one of the semiconductor-based laser (902, 903, 904) driven becomes.

2. The method of claim 1, wherein a plurality of semiconductor-based lasers are sequentially controlled based on the respective associated detected signal.

3. The method according to any one of the preceding claims, wherein a plurality of components of the RGB signal per a sensor (906, 907, 908) are supplied and based on the signal detected by the respective sensor, the at least one semiconductor-based laser (902, 903, 904) is controlled.

4. The method according to any one of the preceding claims, wherein a plurality of filters are provided for a plurality of components of the RGB signal.

5. The method according to any one of the preceding claims, wherein the sensor comprises a photodiode, wherein the

Photodiode is arranged in particular in the vicinity of a laser Rückfacette.

6. The method according to any one of the preceding claims, wherein a control (901) for driving the at least one semiconductor-based laser is provided.

7. The method according to any one of the preceding claims, wherein the color point adjustment comprises a white point adjustment or a white point adjustment or a white point control.

8. The method according to any one of the preceding claims, wherein the color point adjustment takes place within a predetermined tolerance, wherein the predetermined tolerance is determined in particular on the basis of a MacAdams distance.

The method of any one of the preceding claims, wherein the lighting unit comprises a red semiconductor-based laser, a green semiconductor-based laser, and a blue semiconductor-based laser.

10. The method of claim 9, wherein the green semiconductor-based laser is an optically or electrically pumped infrared semiconductor laser, in particular with a frequency doubling.

11. The method according to any one of the preceding claims, wherein the filter comprises one of the following filters:

a V-lambda filter; an absorption filter;

- a transmission filter.

12. The method according to any one of the preceding claims, wherein the filter is designed such that at least one further dependence of a color locus of a wavelength of at least one other light source is taken into account.

13. The method according to any one of the preceding claims, wherein the filter for a given

Wavelength range, especially in a visible spectrum, is designed.

14. Device for color balance of a lighting unit

with semiconductor-based lasers (902, 903, 904) for generating an RGB signal (909), with at least one filter (905) via which at least one component of the RGB signal can be supplied to at least one sensor (906),

- With a control (901), which controls at least one of the semiconductor-based laser (902, 903, 904) based on a signal detected by the sensor (906).

15. An apparatus for controlling at least one semiconductor-based laser with a processor unit and / or an at least partially hardwired or logical circuit arrangement, which is set up such that the method according to one of claims 1 to 12 can be carried out.