Deriving a white-point for use in a multi-color light scene

Abstract

When a light scene comprises multiple colors of light, not all white light is suitable for matching the scene. A method is provided such that a white point is determined for each color in a set of colors, to create a set of white points. A single white point is then determined based on the set of white points. This allows, for example, a user to select a light scene (e.g. a romantic scene featuring red colors) for a living room, such that lighting devices contributing to the scene emit colored light. A functional lighting device (e.g. reading light) can then emit white light, determined according to the method, to provide more functional light (e.g. light suitable for reading) that matches the scene (e.g. warm white instead of cold white).

Claims

1. A method of controlling a first lighting device, the method comprising: receiving a set of colors, selected by a user and rendered by further lighting devices, determining a set of white points comprising a white point for each of a plurality of colors in the set of colors previously selected by the user, the selection comprising selecting the set of colors via selecting an image from which the plurality of colors are extracted, determining a single white point based on the set of white points, and controlling the first lighting device to emit white light according to the determined single white point.

2. The method according to claim 1, wherein determining a white point for at least one color in the set of colors comprises: desaturating, in a predetermined color space comprising a black body line, the at least one color along a first path according to a first function; and determining as a white point, for the at least one color, a color point along the first path at a predetermined distance from the black body line.

3. The method according to claim 2, wherein the first function is a transfer function avoiding a predetermined region of color space.

4. The method according to claim 1, wherein determining a white point for at least one color in the set of colors comprises: desaturating, in a predetermined color space comprising a black body line, the at least one color along a first path according to a first function, determining as an intermediate color point, for the at least one color, a color point along the first path at a predetermined distance from the black body line, desaturating, in the predetermined color space, the intermediate color point along a second path according to a second function, and determining as a white point, for the at least one color, a color point along the second path at a further predetermined distance from the black body line.

5. The method according to claim 4, wherein the second function is arranged such that the second path is perpendicular to the black body line.

6. The method according to claim 1, wherein the predetermined color space is the UV color space.

7. The method according to claim 1, wherein determining a single white point based on the set of white points comprises: determining as a single white point, the average white point of the set of white points.

8. The method according to claim 7, the method further comprising: determining an intensity level for each color of the set of colors, wherein the average of the set of white points is a weighted average based on the determined intensity level.

9. The method according to claim 1, the method further comprising: storing the determined single white point and/or the received set of colors in a memory.

10. The method according to claim 1, the method further comprising: controlling the further lighting devices to emit colored light according to the received set of colors.

11. A non-transitory computer-readable medium comprising a computer program product arranged for performing the method according to claim 1 when run on one or more processors.

12. The method according to claim 1, wherein said set of colors are colors of light present in an environment, and wherein the image is an image of the environment.

13. The method according to claim 12, wherein the controlling the first lighting device to emit the white light comprises controlling the first lighting device to emit said white light in said environment.

14. A controller for controlling a first lighting device, the controller comprising: a first interface arranged for receiving a set of colors, selected by a user and rendered by further lighting devices, a second interface arranged for controlling the first lighting device, and a processor coupled to the first and second interface, wherein the processor is arranged for: determining a set of white points comprising a white point for each of a plurality of colors in the set of colors previously selected by the user, the selection comprising selecting the set of colors via selecting an image from which the plurality of colors are extracted, determining a single white point based on the set of white points, and controlling the first lighting device to emit white light according to the determined single white point.

15. The controller according to claim 14, comprising a third interface for controlling the further lighting devices, and wherein the processor is further arranged for controlling the further lighting devices to emit colored light according to the received set of colors.

16. A lighting system comprising the controller according to claim 15, the lighting system further comprising the first lighting device.

17. The controller according to claim 14, wherein said set of colors are colors of light present in an environment, and wherein the image is an image of the environment.

18. The controller according to claim 17, wherein the controlling the first lighting device to emit the white light comprises controlling the first lighting device to emit said white light in said environment.

19. A method of controlling a first lighting device, the method comprising: receiving a set of color coordinate points, selected by a user and rendered by further lighting devices; determining a set of white points comprising a respective white point for each corresponding color coordinate point of a plurality of color coordinate points in the set of color coordinate points previously selected by the user, wherein each respective white point, of said set of white points, is calculated by applying a function to the corresponding color coordinate point such that the calculated respective white point is independent of each other user-selected color coordinate point and such that the function approaches a black body line from said corresponding color coordinate point; determining a single white point based on the set of white points; and controlling the first lighting device to emit white light according to the determined single white point.

20. The method of claim 19, wherein said single white point is different from each white point of said set of white points.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 shows schematically and exemplarily a method of controlling a lighting device,

(3) FIG. 2 shows schematically and exemplarily a color space diagram illustrating the method, and

(4) FIG. 3 shows schematically and exemplarily determining a white point for a first color point according to an embodiment of the method.

DETAILED DESCRIPTION OF EMBODIMENTS

(5) In FIG. 1 a method 100 of controlling a lighting device is shown. The method 100 comprises: receiving a set of colors 110, determining a set of white points 120, determining a single white point 130, and controlling the lighting device 140. A user may select a set of colors, for example, through a user interface allowing the user to select an image from which colors are automatically extracted. This set of colors is then received as part of the method. For each color (or at least multiple colors) in this set of colors, a white point is determined. For a saturated red color, a reddish-white white point can be determined and for a yellow color, a yellowish-white point can be determined. As a single white point, a warm white can then be determined instead of a cold white, as the warm white will better fit a scene comprising the saturated red and the yellow color of the set of colors.

(6) In a larger lighting system, or a lighting system spanning a large area, the method can be applied to individual groups of lighting devices such that multiple white points are determined. As an example, when a dining room and kitchen are situated in the same open space, then warm colors (e.g. red) creating an atmosphere in the living room can be complemented with white point that is warm, and cold colors (e.g. blue) creating a different atmosphere in the kitchen can be complemented with a white point that is cold.

(7) In FIG. 2a CIE 1931 XY chromatic color diagram 200 is shown. Within a color space 210 lies the black body line 220. From a first color point A using a first function a path 230 leads to color point B which is a predetermined distance 240 from the black body line 220. From the second color point B a second function provides a path 260 to color point C which is on the black body line 220.

(8) The first function can, as an example, comprise a correlated color temperature calculation. This is beneficial when the first color point lies close to the black body line. Such a calculation in a U V color space creates a path perpendicular to the black body line. As a further example, a different function can be used to accommodate a first color point far from the black body line. Such a different function can comprise defining areas in the color space that are associated with specific point on the black body line. Continuing these examples, in an implementation of the method the correlated color temperature calculation is used when the first color point is less than a predetermined value away from the black body line (e.g. less than 0.001 units in the color space in which the calculation is performed) and the further function is used when the first color point is more than said predetermined value away from the black body line. As another example, an intermediate blending function can be used such that a first color point further away from the black body line (e.g. more than 0.01 units) is leads to a predetermined point being selected on the black body line based on the area of the color space the first color point is in; and a white point for a first color point that is at a medium distance from the black body line (in this example, more than 0.001 and less than 0.01 units) is determined using both functions, the outcome of which is averaged. For such a first color point at a medium distance from the black body line, a first white point is then calculated based on a correlated color temperature calculation and a second white point is then determined based on the area in the color space that the first color point is in, to which a white point on the black body line is associated. This first and second white point are then averaged, such that one white point is added to the set of white points for this first color point.

(9) As yet another example, multiple predetermined paths, in a color space, leading to the black body line can be predetermined. For each first color point the nearest path can then be used to determine an appropriate white point to add to the set of white points. In a more advanced implementation, shown in FIG. 3, two such paths 310, 320 are selected from multiple such predetermined paths 310, 320, 330, 340, 350. The selection is based on which paths the first color point A lies in between. The two white points 315, 325 associated with these two paths 310, 320 are then averaged to determine a white point C to add to the set of white points.

(10) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.