Light source emitting mixed-colored light and method for controlling the color locus of such a light source

1. A method for controlling the color locus of a light source ( 10 ) emitting mixed-colored light containing light of at least two different colors which is emitted by a plurality of primary light sources comprising:

dividing the primary light sources into groups,

determining and controlling the brightness values of the primary light sources within a group separately according to colors, such that the color locus of the mixed-colored light lies in a predetermined region of the CIE Standard chromaticity diagram, wherein the brightness values of the primary light sources are determined and controlled by:

setting the brightness of the primary light source using pulse-width-modulated signals which are switched on with a fixed basic period for a specific length of time;

phase-shifting the first switch-on time of the primary light source of a first color relative to the switch-on time of the remaining colors such that only the primary light sources of the first color are switched-on during a first time interval, wherein the phase-shifting of the first switch-on time of the primary light source of a first color is distributed over a plurality of basic periods, the plurality of basic periods continuing until the beginning of the first switch-on time is substantially congruent with the beginning of the first time interval; and

at least partially overlapping the switch-on times of all of the primary light sources of the light source in a second time interval which is adjacent to the first time interval.

2. The method as claimed in claim 1 , wherein the primary light sources of a group are selected with respect to one another such that the brightness values of their light are within a predetermined range.

3. The method as claimed in claim 1 , wherein the primary light sources of a color within a group are selected with respect to one another such that the dominant wavelengths of their light lie within a predetermined range.

4. The method as claimed in claim 1 , wherein semiconductor light emitting diodes (LEDs), organic light emitting diodes (OLEDs), lasers or electroluminescent films are used as primary light sources.

5. The method as claimed in claim 1 , wherein the primary light sources of a color within a group are driven with a respective pulse-width-modulated signal having a modified basic period such that only the primary light sources of one color are switched on during a first time interval of the basic period, and the brightness value of said color is determined during the first time interval (t 1 ).

6. The method as claimed in claim 5 , wherein a total period of the pulse-width-modulated signal contains at least one basic period modified such that no primary light source of a group is switched on within a time interval of the basic period and the brightness value of the background light is determined within the time interval.

7. The method as claimed in claim 1 , wherein the brightness values are determined by means of a sensor, the sensitivity of which is adapted to the sensitivity of the human eye.

8. The method as claimed in claim 1 , wherein a photodiode is used for determining the brightness values.

9. The method as claimed in claim 1 , wherein the brightness values of the primary light sources of a color within a group are determined sequentially with the aid of a photodiode.

10. The method as claimed in claim 1 , wherein the brightness values of the primary light sources of a color within a group are corrected by a background brightness.

11. The method as claimed in claim 1 , wherein the light source emits mixed-colored light comprising the colors red, green and blue.

12. The method as claimed in claim 1 , wherein the mixed-colored light has a color locus in the white region of the CIE standard chromaticity diagram.

13. A light source emitting mixed-colored light containing light of at least two different colors which is emitted by a plurality of primary light sources wherein:

the primary light sources are divided into groups, and the brightness values of the primary light sources within a group are determined and controlled separately according to colors, such that the color locus of the mixed-colored light lies in a predetermined region of the CIE Standard chromaticity diagram;

the brightness of the primary light source are set using pulse-width-modulated signals which are switched on with a fixed basic period for a specific length of time;

the first switch-on time of the primary light source of a first color are phase-shifted relative to the switch-on time of the remaining colors such that only the primary light sources of the first color are switched-on during a first time interval, wherein the phase-shifting of the first switch-on time of the primary light source of a first color is distributed over a plurality of basic periods, the plurality of basic continuing until the be inning of the first switch-on time is substantially congruent with the beginning of the first time interval; and

the switch-on times of all of the primary light sources of the light source at least partially overlap in a second time interval which is adjacent to the first time interval.

14. The light source as claimed in claim 13 , wherein the primary light sources of a color within a group are selected with respect to one another such that the brightness values of their light are within a predetermined range.

15. The light source as claimed in claim 13 , wherein the primary light sources of a color within a group are selected with respect to one another such that the dominant wavelengths of their light lie within a predetermined range.

16. The light source as claimed in claim 13 , which has semiconductor light emitting diodes (LEDs), organic light emitting diodes (OLEDs), lasers or electroluminescent films as primary light sources.

17. The light source as claimed in claim 13 , which comprises a sensor, the sensitivity of which is adapted to the sensitivity of the human eye, for determining the brightness values.

18. The light source as claimed in claim 13 , which comprises a photodiode for determining the brightness values.

19. The light source as claimed in claim 13 which emits mixed-colored light comprising red, green and blue light.

20. The light source as claimed in claim 13 , which emits mixed-colored light having a color locus in the white region of the CIE Standard chromaticity diagram.

21. An illumination device for backlighting a display comprising a light source as claimed in claim 13 .