Control of correlated color temperature

Abstract

There is provided a lighting device (1) comprising a first (111), a second (112) and a third (113) light source. The first light source emits a first light output, being a white light output having a first correlated color temperature (104) and a first color point located above the black body locus (103) in a CIE 1931 xy chromaticity diagram. The second light source emits a second light output, being a white light output having a second correlated color temperature and a second color point located above the black body locus. The second correlated color temperature is at least 500 K higher than the first correlated color temperature. The third light source emits a third light output having a third color point with an x-value in a range of 0.28 to 0.38 and a y-value in a range of 0.13 to 0.23.

Description

[0001] 2024PF80037

[0002] 1

[0003] Control of correlated color temperature

[0004] FIELD OF THE INVENTION

[0005] The present invention generally relates to control of properties of device light. More specifically, the present invention is related to control of a device correlated color temperature and a device color point.

[0006] BACKGROUND OF THE INVENTION

[0007] The use of solid-state light emitting devices for illumination purposes and the relative ease of adjusting its light properties has contributed to an increased interest in procedures for adapting light properties of light emitting devices. The adaptations may be performed statically, resulting in a light having constant properties, but by mixing different light sources, also dynamically changing light properties may be obtained. The light properties may then be adapted according to a user’s request or be controlled based on e.g. environmental quantities.

[0008] The original inherent solid-state light may provide a light output having a certain correlated color temperature and a certain color point in a CIE 1931 xy chromaticity diagram. This original light may then be converted by use of e.g. luminescent elements to a light having a different correlated color temperature and color point in the CIE 1931 xy chromaticity diagram. By then also combining different such original and / or converted light sources, a device light with further different correlated color temperature and color point in the CIE 1931 xy chromaticity can be obtained. Depending on the original light source, the luminescence elements, and the relative mixing of the light source light, almost any point in the CIE 1931 xy chromaticity diagram can be obtained, and in particular in the vicinity of the blackbody locus (BBL). The adaptation may be performed in order to increase the efficiency, which normally ends up at a color point above the BBL. Alternatively, if a good color rendering index (CRI) is requested, a color point below the BBL is normally used. In many applications, possibilities to change between such preferred light properties are requested.

[0009] In order to allow adaptations over an area within the CIE 1931 xy chromaticity diagram, at least three light sources with different color points have to be provided and their 2024PF80037

[0010] 2 relative intensities have to be controllable. This task is, however, difficult to perform if a well-defined compose light is to be achieved.

[0011] Hence, it is an object of the present invention to improve and simplify the possibilities for adjustments of color points of device light. In particular are adjustments between points on opposite sides of the BBL requested.

[0012] SUMMARY OF THE INVENTION

[0013] It is of interest to simplify adjustment of color points of device light, and in particular adjustments across the BBL.

[0014] This and other objects are achieved by providing a lighting device and a method for controlling the lighting device having the features in the independent claim. Preferred embodiments are defined in the dependent claims.

[0015] Hence, according to the present invention, there is in a first aspect provided a lighting device comprising a first light source, a second light source and a third light source. The first light source is configured to emit a first light output, being a white light output having a first correlated color temperature and a first color point located above the black body locus in a CIE 1931 xy chromaticity diagram. The second light source is configured to emit a second light output, being a white light output having a second correlated color temperature and a second color point located above the black body locus in the CIE 1931 xy chromaticity diagram. The second correlated color temperature is at least 500 K higher than the first correlated color temperature. The third light source is configured to emit a third light output having a third color point with an x-value in a range of 0.28 to 0.38 and a y-value in a range of 0.13 to 0.23 in the CIE 1931 xy chromaticity diagram.

[0016] In one embodiment, the third light source is configured to emit a third light output having a third color point with an x-value in a range of 0.31 to 0.36 and a y-value in a range of 0.16 to 0.21 in the CIE 1931 xy chromaticity diagram.

[0017] In one embodiment, the second correlated color temperature is at least 1000 K higher than the first correlated color temperature.

[0018] In one embodiment, the second correlated color temperature is at least 1500 K higher than the first correlated color temperature.

[0019] Thus, the present technology is based on the discovery of that at least most of the extensions of isotherms in the CIE 1931 xy chromaticity diagram pass through a limited area in the magenta zone. This area is defined by the x value range of 0.28 to 0.38 and the y value range of 0.13 to 0.23. By selecting one of the light sources to have a color point within 2024PF80037

[0020] 3 this area, control of the device light output along an isotherm is highly facilitated by keeping a ratio between the intensities of the first and second light sources constant.

[0021] In one embodiment, the first correlated color temperature is at most 3000 K.

[0022] In one embodiment, the second correlated color temperature is at most 4000 K.

[0023] By spreading out the color points of the first and second light source in temperature range, basically all temperatures between them are available to reach for the color point of a device light output. At the same time, a reasonable proximity of the first and second light sources is advantageous for achieving good mixing properties.

[0024] In one embodiment, at least one of the first color point and the second color point is situated at least 10 or at least 12 standard deviation color matching -SDCM - above the black body locus. Since the third light source color point is situated far below the black body locus, a mixing of the light sources may be performed to obtain device light color points below the black body locus as well as above the black body locus. For example, the device light may have a color point of at least 5 or at least 7 SDCM above and / or below the BBL.

[0025] In one embodiment, each of the first light source, the second light source, and the third light source comprises a light-emitting element configured to emit a primary light output, and a luminescent element configured to at least partly convert the primary light output into a converted light output. In a further embodiment, at least 90 % of the primary light output is in a range of 400 to 500 nm or in a range from 420 to 490 nm.

[0026] In embodiments, the first light source may comprise a first light-emitting element configured to emit a primary light output, and a first luminescent element configured to at least partly convert the primary light output into a converted light output. In embodiments, the second light source may comprise a second light-emitting element configured to emit a primary light output, and a second luminescent element configured to at least partly convert the primary light output into a converted light output. In embodiments, the third light source may comprise a third light-emitting element configured to emit a primary light output, and a third luminescent element configured to at least partly convert the primary light output into a converted light output.

[0027] The approach of having a primary light output that is subsequently modified by a luminescent element into a converted light output is well suited for achieving all the light sources, in particular when utilizing the above-indicated wavelength interval. 2024PF80037

[0028] 4

[0029] In embodiments, the third luminescent element may comprise a third luminescent material of the type M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, M comprises a monovalent cation, and x is in the range of 0-1, wherein A comprises a tetraval ent cation, and wherein X comprises a monovalent anion, at least comprising fluorine. Relevant alkaline cations (M) are sodium (Na), potassium (K) and rubidium (Rb). Optionally, also lithium and / or cesium may be applied. In a preferred embodiment, M comprises at least potassium. In yet another embodiment, M comprises at least rubidium. The phrase “wherein M comprises at least potassium” indicates for instance that of all M cations in a mole M’xM2-2xAX, a fraction comprises K+and an optionally remaining fraction comprises one or more other monovalent (alkaline) cations (see also below). In another preferred embodiment, M comprises at least potassium and rubidium. Optionally, the M’xM2-2xAX6 luminescent material has the hexagonal phase. In yet another embodiment, the M’xM2-2xAX6 luminescent material has the cubic phase. For x=0, the composition is M2AX6. Relevant alkaline earth cations (M’) are magnesium (Mg), strontium (Sr), calcium (Ca) and barium (Ba), especially one or more of Sr and Ba. The term “tetravalent manganese” refers to Mn4+. This is a well-known luminescent ion. In the formula as indicated above, part of the tetravalent cation A (such as Si) is being replaced by manganese. Hence, M’xM2-2xAX6 doped with tetravalent manganese may also be indicated as M’xM2-2xAi-mMnmX6. The mole percentage of manganese, i.e. the percentage it replaces the tetravalent cation A will in general be in the range of 0.1-15 %, especially 1-12 %, i.e. m is in the range of 0.001-0.15, especially in the range of 0.01-0.12. As indicated above, X relates to a monovalent anion, but at least comprises fluorine. Other monovalent anions that may optionally be present may be selected from the group consisting of chlorine (Cl), bromine (Br), and iodine (I). In an embodiment, M’xM2-2xAX6 comprises K2SiFe (indicated herein also as KSiF system). As indicated above, in another preferred embodiment, M’XM2-2XAX6 comprises KRbSiFe (herein also indicated as K,Rb system). As indicated above, part of silicon is replaced by manganese (i.e. the formula may also be described as K2Sii-mMnmF6 or KRbSii-mMnmFe, with m as indicated above, or as KRbSiFe:Mn and K2SiFe:Mn, respectively). As manganese replaces part of a host lattice ion and has a specific function, it is also indicated as “dopant” or “activator”. Hence, the hexafluorosilicate is doped or activated with manganese (Mn4+). In specific embodiments, the luminescent material may comprise (K,Rb)2SiF6:Mn4+. Alternatively or additionally, in embodiments the third luminescent material may comprise K2SiFe:Mn4+. Alternatively or additionally, in embodiments the third luminescent material may comprise K2TiFe:Mn4+. In embodiments, 2024PF80037

[0030] 5 the third luminescent material may comprise K2(Si,Ti)Fe:Mn4+. As can be derived from the above, “Si,Ti” may indicate one or more of Si and Ti. Preferably the converted light output emitted by the third luminescent element may have a peak emission wavelength, A3, selected from the range of 610-650 nm (or 620-640nm) and may have a full width at half maximum (FWHM1) of < 50 nm (or < 40 nm). The obtained effect is that the third light source is configured to emit a third light output at a very high efficiency. The reason is that the third luminescent material proposed above has a very high conversion efficiency, a superior narrow spectral distribution, and an optimal peak emission wavelength position.

[0031] In embodiments, at least 70% or at least 80% of the luminescent material in the third luminescent element may be the third luminescent material. The obtained effect next to a very high efficiency is a very high color quality. The reason is that the third light output may mainly be based on (part ol) the primary light output of the first light-emitting element and light emitted by the third luminescent material.

[0032] In embodiments, the primary light output emitted by the first light-emitting element may have a peak emission wavelength in a wavelength range 430-490nm or 440- 480nm.

[0033] In one embodiment, the lighting device is configured to emit a device light output. The device light output has a device correlated color temperature and a device color point. The lighting device further comprises a controller configured for individually controlling the first light output, the second light output, and the third light output to set at least one of the device color points and the device correlated color temperature. For example, the device correlated color temperature may be varied at least 500K or at least lOOOK. For example, the x coordinate of the device color point (x,y) can be varied at least Ax>0.05 or at least Ax>0.1. For example, the y coordinate of the device color point (x,y) can be varied at least Ay>0.05 or at least Ay>0.1.

[0034] The first light output, the second light output, and the third light output are preferably controlled by the controller for defining the present device light output.

[0035] In one embodiment, the controller is configured to operate the lighting device in at least one of a first operational mode and a second operational mode. In the first operational mode, the device color point is above the black body locus. In the second operational mode, the device color point is below the black body locus. In a further embodiment, the color point of the device light output in the first operational mode has a first y-coordinate and the color point of the device light in the second operational mode has a 2024PF80037

[0036] 6 second y-coordinate. The difference between the first y-coordinate and the second y- coordinate is preferably at least 0.05.

[0037] Color points on both sides of the black body locus are reachable, which enables operation of the lighting device with a selected compromise between efficiency or color rendering.

[0038] In one embodiment, the controller is configured for controlling at least one of the first light output, the second light output, and the third light output for changing the device color point along an isotherm of the device correlated color temperature in the CIE 1931 xy chromaticity diagram. This is particularly simplified by the location of the third light output in the diagram. The ratio between the first light output and the second light output may then preferably be kept essentially constant.

[0039] In one embodiment, the controller is configured for controlling at least one of the first light output, the second light output, and the third light output for changing the device correlated color temperature with a value of at least 500 K. Due to a separation in correlated color temperature between the first light output and the second light output, also control across the isotherms are possible.

[0040] In one embodiment, the controller is configured for individually controlling at least one of the first light output, the second light output, and the third light output based on one or more of a user interface, a clock module, and a sensor. The reasons for selecting different operation modes may thereby be decided by a user, using a user interface. The operation mode adjustments may also be automated, and a reading from a sensor or a clock may be used for governing such operation mode adjustments.

[0041] According to the present invention, there is in a second aspect provided a luminaire or a lamp comprising the lighting device according to the first aspect.

[0042] According to the present invention, there is in a third aspect provided a method for controlling the lighting device according to the first aspect. The lighting device is configured to emit a device light output having a device correlated color temperature and a device color point. The method comprises the step of controlling the third light output while keeping a ratio of the first light output and the second light output substantially constant to thereby change the device color point along an isotherm of the device correlated color temperature in the CIE 1931 xy chromaticity diagram.

[0043] Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present 2024PF80037

[0044] 7 invention can be combined to create embodiments other than those described in the following.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

[0047] Fig. 1 schematically show a CIE 1931 xy chromaticity diagram,

[0048] Fig. 2 schematically disclose a part of a CIE 1931 xy chromaticity diagram with color points of light sources according to an embodiment of a lighting device,

[0049] Fig. 3 schematically shows a schematic cross section of an embodiment of a lighting device,

[0050] Fig. 4 schematically disclose another part of a CIE 1931 xy chromaticity diagram with color points of light sources according to an embodiment of a lighting device, and

[0051] Fig. 5 is a flow diagram of steps of an embodiment of a method for controlling the lighting device.

[0052] DETAILED DESCRIPTION

[0053] The present technology concerns a lighting device. This lighting device is advantageously comprised in a luminaire or a lamp.

[0054] The present technology is based on the behavior of the isotherms in the CIE 1931 xy chromaticity diagram. Figure 1 illustrates schematically the CIE 1931 xy chromaticity diagram, where the solid line 101 is the spectrum locus, the line 102 is the purple boundary and the line 103 indicates the black body locus (BBL). The blue and purple colors are appearing in the lower left part of the diagram, the green in the upper part of the diagram and the orange and red colors in the right parts of the diagram. White light is present in the center of the diagram. Some isotherms 104 are indicated in the vicinity of the BBL.

[0055] It was discovered that if extensions 104B were drawn on the isotherms 104 in the direction of decreasing x values, at least most of the extensions 104B of isotherms in pass through a limited area 105, somewhere around a magenta color. This area is defined by the x value range of 0.28 to 0.38 and the y value range of 0.13 to 0.23. Furthermore, it was also seen that the isotherms of the correlated color temperatures commonly used for illumination purposes, the crossing area could be reduced even more, as indicated by the dotted box 106. 2024PF80037

[0056] 8

[0057] This preferred area is defined by the x value range of 0.32 to 0.37 and the y value range of 0.17 to 0.22.

[0058] The extension of the isotherms hereby presented the same associated color points within these areas. In other words, a light source having a color point within the area 105 or preferably within the area 106, can be associated with “all” correlated color temperatures within a broad temperature range.

[0059] If two light sources have color points located at the same isotherm, a mix between the two light sources will also end up on the same isotherm. This means that a light control of a mixed light from these two light sources along the isotherm is easily obtained by simply controlling the relative intensities of the light sources.

[0060] If one of these light sources in turn is a mix of light output from two light sources, e.g. a first light source 111 and a second light source 112, the color point and correlated color temperature of this mix is determined by the relative intensities of these first and second light sources 111, 112. If then a third light source 113 is added, which has a color point in the above-described area 105, it can be associated with almost any correlated color temperature, for instance the correlated color temperature of the mix between the first and second light sources 111, 112. This becomes the situation regardless of which exact correlated color temperature the color mix has.

[0061] Thereby, by selecting one of the light sources, here denoted the third light source 113, to have a color point within the area 106, control of a device light output along an isotherm is highly facilitated by keeping a ratio between the intensities of the first and second light sources 111, 112 constant.

[0062] Similarly, a control of the color point transverse to the isotherms can easily be achieved by changing the relative intensities between the first and second light sources 111, 112.

[0063] In other words, an advantageous lighting device comprises a first light source 111, a second light source 112 and a third light source 113. The first light source 111 is configured to emit a first light output, being a white light output having a first correlated color temperature and a first color point located above the black body locus 103 in a CIE 1931 xy chromaticity diagram, wherein the second light source 112 is configured to emit a second light output, being a white light output having a second correlated color temperature and a second color point located above the black body locus 103 in a CIE 1931 xy chromaticity diagram, wherein the second correlated color temperature is at least 500 K higher than the first correlated color temperature, and wherein the third light source 113 is 2024PF80037

[0064] 9 configured to emit a third light output having a third color point with an x-value in a range of 0.28 to 0.38 and ay-value in a range of 0.13 to 0.23 in a CIE 1931 xy chromaticity diagram.

[0065] In one embodiment, the third light source 113 is configured to emit a third light output having a third color point with an x-value in a range of 0.31 to 0.36 and a y-value in a range of 0.16 to 0.21 in a CIE 1931 xy chromaticity diagram.

[0066] Figure 2 illustrates parts of the diagram of Fig. 1. The first light source 111, the second light source 112 and the third light sources 113 defines a triangle 117. By combining the three light sources 111-113 a resulting light with color points somewhere within the triangle can be obtained. If the light sources 111-113 are positioned further away from each other, the triangle 117 becomes larger and there are more theoretically reachable color points. However, mixing becomes more and more difficult upon increased distances within the diagram. In one embodiment the first correlated color temperature is lower than 3000 K. In one embodiment, the second correlated color temperature is higher than 4000 K. This gives some useful ranges for controlling the correlated color temperature of the mixed light within reasonable ranges.

[0067] It can be notice that the triangle 117 in Figure 2 is a relatively “wide” triangle without pronounced narrow comers. This indicates that the distances in the diagram space between the three light sources are relatively short, compared to e.g. mixing using a pure blue light source. This implies that another advantage of the present technology is very good light mixing and an excellent homogenous lighting.

[0068] In Figure 2, the square 115 illustrates a color point of a mix between the first light source 111 and the second light source 112, corresponding to a correlated color temperature 104. By also mixing with the light output from the third light source 113, the color point may be controlled to move along the correlate color temperature 104 towards the third light source 113 by increasing the relative intensity of the third light source compared to the combination of the light from the first light source 111 and the light from the second light source. 112. The resulting color point 116 may even end up below the BBL 103.

[0069] Since the mixing with the third light source 113 always tends to move the color point downwards, the only possibility to have a final color point above the BBL 103 is to have at least on of the first light source 111 and the second light source above the BBL 103. Preferably, such a positioning is made with a reasonable distance from the BBL. In a preferred embodiment at least one of the first color point and the second color point is situated at least 10 Standard Deviation Color Matching (SDCM) above the black body locus 2024PF80037

[0070] 10

[0071] 103. By such a distance above the BBL 103, it will be possible to reach color points above the BBL 103 for most correlated color temperatures.

[0072] SDCM is a standard term in the lighting field, used to define a distance, in this case from the BBL 103. A 1-step SDCM defines an elliptic zone in the CIE 1931 xy chromaticity diagram within which the human eye cannot discern color differences. The definition relies upon visual observation of the so-called Just Noticeable Colour Difference (JND) between two very similar colored lights, in turn defined as the color difference where 50% of observers see a difference and 50% of observers do not see a difference. The ellipses vary size and orientation depending upon the actual location in the CIE 1931 xy chromaticity diagram. The ellipses are largest in the green areas and smallest in the red and blue areas.

[0073] The light sources can in a general case be of any kind, capable of emitting light with the required correlated color temperature and color point. In a preferred embodiment each of the first light source, the second light source, and the third light source comprises a light-emitting element configured to emit a primary light output. Typically, today solid-state based light sources, such as light emitting diodes (LED) are used in most cases. If the light-emitting element does not provide the requested correlated color temperature and color point, a luminescent element can be combined with each light-emitting element. The luminescent element is configured to at least partly convert the primary light output into a converted light output. Typically, the luminescent element is different for the three different light sources.

[0074] With reference to Figure 1, and in a preferred embodiment, at least 90 % of the primary light output is in a range of 400 to 500 nm, and even more preferably having a peak primary wavelength ( / .p l ) in a range of 430 to 490 nm.

[0075] Figure 3 illustrates schematically a part of an embodiment of a lighting device 1. A first light source 111 comprises a light-emitting element 10. The light-emitting element 10 is configured to emit a primary light output. Typically, the light-emitting element 10 is a light-emitting diode (LED). The first light source 111 further comprises a first luminescent element 11. The first luminescent element 11 is configured to at least partly convert the primary light output from the light-emitting element 10 into a first converted light output 21. The first converted light output 21 thus in this embodiment constitutes the light output of the first light source 111. The primary light output and the first luminescent element 11 are selected in such a way that the light output of the first light source 111 becomes a white light output having the first correlated color temperature and the first color point located above the 2024PF80037

[0076] 11 black body locus 103 in a CIE 1931 xy chromaticity diagram. Such choices are, as such, well-known by any person skilled in the art.

[0077] Analogously, a second light source 112 also comprises a light-emitting element 10. The light-emitting element 10 is configured to emit a primary light output. This primary light output may or may not be of a same character as for the first light source 111. The second light source 112 further comprises a second luminescent element 12. The second luminescent element 12 is configured to at least partly convert the primary light output from the light-emitting element 10 of the second light source 112 into a second converted light output 22. The second converted light output 22 thus in this embodiment constitutes the light output of the second light source 112. The primary light output and the second luminescent element 12 are selected in such a way that the light output of the second light source 112 becomes a white light output having the second correlated color temperature and the second color point located above the black body locus 103 in a CIE 1931 xy chromaticity diagram. Such choices are, as such, well-known by any person skilled in the art.

[0078] Also, a third light source 113 comprises a light-emitting element 10. The lightemitting element 10 is configured to emit a primary light output. This primary light output may or may not be of a same character as for the first light source 111 and / or the second light source 112. The third light source 113 further comprises a third luminescent element 13. The third luminescent element 13 is configured to at least partly convert the primary light output from the light-emitting element 10 of the third light source 113 into a third converted light output 23. The third converted light output 23 thus in this embodiment constitutes the light output of the second light source 112. The primary light output and the third luminescent element 13 are selected in such a way that the light output of the third light source 113 has a third color point with an x-value in a range of 0.28 to 0.38 and a y-value in a range of 0.13 to 0.23 in a CIE 1931 xy chromaticity diagram. Such choices are, as such, known by any person skilled in the art. One non-limiting example of such an arrangement may e.g. the use of a phosphor converted LED comprising a blue LED chip, e.g. giving light of 450 nm, as a lightemitting element 10 of the third light source 113 covered by a green phosphor, e.g. YAG / LuAG, and a red phosphor, e.g. KSiF, in the third luminescent element 13.

[0079] The lighting device 1 of Figure 3 also comprises a mixing element 30, in which the first converted light output 21, the second converted light output 22 and the third converted light output 23 are combined into a device light output 31. The lighting device 1 is thereby configured to emit a device light output 31 having a device correlated color temperature and a device color point. 2024PF80037

[0080] 12

[0081] The lighting device 1 furthermore comprises a controller 40 configured for individually controlling the first light output, the second light output, and the third light output, e.g. the first converted light output 21, the second converted light output 22, and the third converted light output 23 to set at least one of the device color points and the device correlated color temperature. This is typically performed by individually controlling the intensities emitted from the different light-emitting elements 10 of the light sources 111-113. By changing the emission from the different light-emitting elements 10, different device color points and the device correlated color temperatures can be achieved.

[0082] For instance, the controller 40 may be configured to control the device light output 31 in at least two different operational modes. In a first operational mode of the lighting device 1, first white device light may be provided. Such first white device light has a first correlated color temperature CCT1. The first white device light comprises a spectral power distribution comprising the first light output, the second light output and typically also the third light output. In a device as schematically illustrated in Figure 3, the first white device light comprises a spectral power distribution comprising the primary light, and the first, second and third luminescent material arrangement light. In a second operational mode of the lighting device 1, second white device light may be provided. Such second white device light has a second correlated color temperature CCT2. The second white device light comprises a spectral power distribution comprising the first light output, the second light output and typically also the third light output. In a device as schematically illustrated in Figure 3, the first white device light comprises a spectral power distribution comprising the primary light, and the first, second and third luminescent material arrangement light.

[0083] When varying the color point, it is often requested to do so along an isotherm. A person watching the change will typically not experience any drastic changes. At the same time, the compromise between efficiency and color rendering may be adapted. Color point changes along an isotherm is therefore often considered as a requested property.

[0084] Figure 4 illustrates a part of the CIE 1931 xy chromaticity diagram. In this figure, an operational mode device color point 118 and the corresponding operational mode device correlated color temperature are illustrated. This operational mode corresponds to a certain intensity mix of the first light output of the first light source 111, the second light output of the second light source 112 and the third light output of the third light source 113. Another operational mode device color point 119 and the corresponding operational mode device correlated color temperature are illustrated. This operational mode corresponds to another certain intensity mix of the first light output of the first light source 111, the second 2024PF80037

[0085] 13 light output of the second light source 112 and the third light output of the third light source 113. The two operational mode device color points 118 and 119 share the same device correlated color temperature 104A. A motion 121 along the device correlated color temperature 104A is caused by a change of the relative intensity of the third light output of the third light source 113, compared to the first light output of the first light source 111, the second light output of the second light source 112. However, the relative intensity of the first light output of the first light source 111 compared to the second light output of the second light source 112 is unchanged. This condition makes it very easy to control.

[0086] In one embodiment, the controller is thus configured for controlling at least one of the first light output, the second light output, and the third light output for changing the device color point along an isotherm of the device correlated color temperature in the CIE 1931 xy chromaticity diagram.

[0087] In devices using a mix of two light outputs, a change along an isotherm is only possible if the light outputs are situated at the same isotherm. By using three light outputs, a more flexible tuning of the color point can be achieved. However, for an arbitrary set of three light outputs, changes along an isotherm are typically complex, requiring simultaneous detailed control of each of the three light outputs. Such control requires typically complex look-up tables or software.

[0088] In the present technology, the control efforts to move the device color point along an isotherm is far less complex, since it can be performed by changing the relative intensity of one light output, the third light output of the third light source 113.

[0089] In one embodiment, the controller is configured to operate the lighting device in at least one of a first operational mode wherein the device color point is above the black body locus, and a second operational mode wherein the device color point is below the black body locus.

[0090] This is an often-expressed request. There are LED light sources providing white light above the BBL e.g. for obtaining a higher efficiency. There are also LED light sources providing white light below the BBL e.g. for having a better color rendering index or R9 value (red content). Light sources are thus provided, providing below / above BBL white light. Research reveals the deviation from the BBL of white also depends on the correlated color temperature (CCT). A controller can thus be used to vary such a deviation as function of the CCT. In addition, the intensity of a light source can be varied during the day. The higher energy usage at high intensities can e.g. be compensated by shifting the color point upwards along the isotherm at the same CCT. 2024PF80037

[0091] 14

[0092] In one preferred embodiment, the color point of the device light output in the first operational mode has a first y-coordinate and the color point of the device light in the second operational mode has a second y-coordinate. The difference between the first y- coordinate and the second y-coordinate is at least 0,05.

[0093] The present set of light sources 111, 112, 113 also enables variations 122 of the color points between different device correlated color temperatures. An operational mode device color point 120 corresponds to yet another certain intensity mix of the first light output of the first light source 111, the second light output of the second light source 112 and the third light output of the third light source 113. This operational mode is associated with a correlated color temperature 104B different compared to the operational mode device color points 118 and 119. Expressed differently, the CCT1 may be different from CCT2.

[0094] In one embodiment, the controller is configured for controlling at least one of the first light output, the second light output, and the third light output for changing the device correlated color temperature. The change of the device correlated color temperature is preferably performed with a value of at least 500 K. That can be expressed as CCT2-CCT1 > 500 K.

[0095] The change of correlated color temperature transverse to the isotherms is achieved by changing the ratio of the intensities of the first light source 111 relative the second light source 112.

[0096] The adaptations in the direction of the isotherms and in the direction transverse to the isotherms can of course also be combined. The change of the relative intensity of the third light source 113 can be performed before, after, or at least partly simultaneous to the changes of the first light source 111 relative the second light source 112.

[0097] Simulations have been performed to verify the operability. The table 1 color points obtained above and below the BBL. Points above the BBL are obtained by simply mixing LEDs with CCT 2500K and CCT 5000K. It can be seen in the table that by adding magenta to these points above BBL, they are brought down to be below BBL, and each point simply moves along isotherms and the CCT of each point remains almost the same. 2024PF80037

[0098] 15

[0099] Table 1. Simulations of color pints above and below BBL.

[0100] As indicated above, the different color points may be requested at different occasions or conditions, or simply as a choice of a user. Preferably to this end, a user interface may be provided, with which a user can initiate changes of the color points of the lighting device. This user interface may provide means for selecting certain correlated color temperatures and / or certain distances above / below the BBL. Alternatively, or in combination, such a user interface may also provide a number of predetermined color point settings, among which the user can choose.

[0101] The request for certain preferred color points may also be dependent on different conditions around the lighting device. For instance, if a high surrounding light intensity is provided from elsewhere, the color rendering may be of less importance and a high-efficiency state of the lighting device may be preferred. All kinds of environmental conditions may influence the requested / preferred settings. In one embodiment, one or more sensors may be provided, being arranged for sensing environmental conditions of interest. An output from the sensor(s) may then be used for selecting an appropriate color point of the lighting device.

[0102] The requested or preferred color point may also be dependent on time. A lighting device operating at nights may for instance have a different preferred color point compared to the same lighting device operating during daytime. A clock module may therefore be useful for governing changes based on time.

[0103] In other words, in one embodiment, the controller is configured for individually controlling at least one of the first light output, the second light output, and the third light output based on one or more of a user interface, a clock module, and a sensor. 2024PF80037

[0104] 16

[0105] Figure 5 illustrates an embodiment of a method for controlling a lighting device. In step S10, a lighting device is provided. The lighting device is a device according to the above presented technology. The lighting device is configured to emit a device light output having a device correlated color temperature and a device color point. In step S20, the third light output is controlled, while keeping a ratio of the first light output and the second light output substantially constant. Thereby the device color point is changed along an isotherm of the device correlated color temperature in the CIE 1931 xy chromaticity diagram.

[0106] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Claims

2024PF8003717CLAIMS1. A lighting device (1) configured to emit a device light output (31) having a device correlated color temperature and a device color point, the lighting device (1) comprising a first light source (111), a second light source (112) and a third light source (113), wherein the first light source (111) is configured to emit a first light output (21), being a white light output having a first correlated color temperature and a first color point located above the black body locus (103) in a CIE 1931 xy chromaticity diagram, wherein the second light source (112) is configured to emit a second light output (22), being a white light output having a second correlated color temperature and a second color point located above the black body locus (103) in a CIE 1931 xy chromaticity diagram, wherein the second correlated color temperature is at least 500 K higher than the first correlated color temperature, wherein the third light source (113) is configured to emit a third light output (23) having a third color point with an x-value in a range of 0.28 to 0.38 and ay-value in a range of 0.13 to 0.23 in a CIE 1931 xy chromaticity diagram, wherein the lighting device (1) further comprises a controller (40) configured to control the third light output (23) while keeping a ratio of the first light output (21) and the second light output (22) substantially constant to thereby change the device color point along an isotherm (104) of the device correlated color temperature in the CIE 1931 xy chromaticity diagram.

2. The lighting device (1) according to claim 1, wherein the first correlated color temperature is at most 3000 K, and wherein the second correlated color temperature is at most 4000 K.

3. The lighting device (1) according to claim 1 or 2, wherein at least one of the first color point and the second color point is situated at least 10 SDCM above the black body locus (103).2024PF80037184. The lighting device (1) according to any one of the claims 1 to 3, wherein (i) the first light source (111) comprises a first light-emitting element (10) configured to emit a primary light output, and a first luminescent element (11) configured to at least partly convert the primary light output into a converted light output (21), (ii) the second light source (112) comprises a second light-emitting element (10) configured to emit a primary light output, and a second luminescent element (12) configured to at least partly convert the primary light output into a converted light output (22), and (iii) the third light source (113) comprises a third light-emitting element (10) configured to emit a primary light output, and a third luminescent element (13) configured to at least partly convert the primary light output into a converted light output (23).

5. The lighting device (1) according to claim 4, wherein at least 90 % of the primary light output is in a range of 400 to 500 nm.

6. The lighting device (1) according to claim 4 or 5, wherein the third luminescent element comprises a third luminescent material of the type M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, M comprises a monovalent cation, and x is in the range of 0-1, wherein A comprises a tetravalent cation, and wherein X comprises a monovalent anion, at least comprising fluorine; and wherein the converted light output (23) emitted by the third luminescent element (13) has (i) a peak emission wavelength (X.3) selected from the range of 610-650 nm and (ii) a full width at half maximum (FWHM1) of < 50 nm.

7. The lighting device (1) according to claim 6, wherein at least 70% of the luminescent material in the third luminescent element may be the third luminescent material; wherein the converted light output (23) emitted by the third luminescent element (13) has (i) a peak emission wavelength (X.3) selected from the range of 620-640 nm and (ii) a full width at half maximum (FWHM1) of < 40 nm.

8. The lighting device (1) according to any one of the claims 1 to 7, wherein the controller (40) is further configured for individually controlling the first light output (21), the second light output (22), and the third light output (23) to set at least one of the device color point and the device correlated color temperature.2024PF80037199. The lighting device (1) according to claim 8, wherein the controller (40) is configured to operate the lighting device (1) in at least one of a first operational mode (118) wherein the device color point is above the black body locus (103), and a second operational mode (119) wherein the device color point is below the black body locus (103).

10. The lighting device (1) according to claim 9, wherein the color point of the device light output (31) in the first operational mode (118) has a first y-coordinate and the color point of the device light in the second operational mode (119) has a second y- coordinate, and wherein the difference between the first y-coordinate and the second y- coordinate is at least 0,05.

11. The lighting device (1) according to any one of the claims 8 to 10, wherein the controller (40) is configured for controlling at least one of the first light output (21), the second light output (22), and the third light output (23) for changing the device color point along an isotherm (104) of the device correlated color temperature in the CIE 1931 xy chromaticity diagram.

12. The lighting device (1) according to any one of the claims 8 to 11, wherein the controller (40) is configured for controlling at least one of the first light output (21), the second light output (22), and the third light output (23) for changing the device correlated color temperature with a value of at least 500 K.

13. The lighting device (1) according to any one of the claims 8 to 12, wherein the controller (40) is configured for individually controlling at least one of the first light output (21), the second light output (22), and the third light output (23) based on one or more of a user interface, a clock module, and a sensor.

14. A luminaire or a lamp comprising the lighting device (1) according to any one of the preceding claims.

15. A method for controlling the lighting device (1) according to any one of the claims 1 to 13, wherein the lighting device (1) is configured to emit a device light output (31) having a device correlated color temperature and a device color point, and wherein the2024PF8003720 method comprises the step controlling (S20) the third light output (23) while keeping a ratio of the first light output (21) and the second light output (22) substantially constant to thereby change the device color point along an isotherm (104) of the device correlated color temperature in the CIE 1931 xy chromaticity diagram.

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