Efficient and reliable blue-free white LED lighting device using an over-dimensioned concentration of ksif phosphor

Abstract

The invention provides a light generating system (1000) comprising a light source (10), a first luminescent layer (2100), and a second luminescent layer (2200), wherein: (i) the light source (10) is configured to generate light source light (11); (ii) the first luminescent layer (2100) is configured downstream of the light source (10), wherein the first luminescent layer (2100) comprises a first layer luminescent material (2110) comprising a first luminescent material (210), wherein the first luminescent material (210) is configured to convert a first part of the light source light (11) received by the first luminescent material (210) into first luminescent material light (211); (iii) the second luminescent layer (2200) is configured downstream of the first luminescent layer (2100), wherein the second luminescent layer (2200) comprises a second layer luminescent material (2220) comprising a second luminescent material (220), wherein the second luminescent material (220) comprises M'XM2-2XAX6 doped with tetravalent manganese, wherein M' comprises an alkaline earth cation, wherein M comprises an alkaline cation, wherein A comprises a tetravalent cation, and wherein X comprises a monovalent anion, at least comprising fluorine (F); wherein the second luminescent material (220) is configured to convert a second part of the light source light (11) received by the second luminescent material (220) into second luminescent material light (221); and wherein the second luminescent layer (2200) comprises at least 1.2 times an amount of the second layer luminescent material (2220) needed to transmit at most 2% of the light source light (10) received by the second luminescent layer (2200); and (iv) the light generating system (1000) is configured to generate, in a first operational mode of the light generating system (1000), system light (1001) comprising the first luminescent material light (211) and the second luminescent material light (221), wherein the system light (1001) has a correlated color temperature selected from the range of 1300-2700 K.

Description

[0001] Efficient and reliable blue-free white LED lighting device using an over-dimensioned concentration of KSiF phosphor

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a light generating system. The invention further relates to a lighting device comprising the light generating system.

[0004] BACKGROUND OF THE INVENTION

[0005] Light generating systems comprising luminescent materials are known in the art. For instance, US2019067532A1 describes a light emitting device which emits a secondary light with high color purity and has a fast response speed. A KSF phosphor which absorbs a part of blue light and emits red light and a CASN phosphor are distributed in a resin which seals an LED chip which emits the blue light. The KSF phosphor absorbs the blue light and emits the red light by forbidden transition, and the CASN phosphor absorbs the blue light and emits the red light by allowed transition.

[0006] SUMMARY OF THE INVENTION

[0007] Blue-free LED lighting may be desired for e.g. cleanroom lighting. To produce blue-free LED light, a luminescent converter comprising multiple types of phosphor, such as a yellow and a red phosphor, may be used. However, prior art solutions may have problems to provide efficient, reliable, and / or stable solutions. Hence, it is an aspect of the invention to provide an alternative light generating system, which preferably further at least partly obviates one or more of above-described drawbacks. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0008] According to a first aspect, the invention provides a light generating system (“system”) comprising a light source, a first luminescent layer, and a second luminescent layer. The light source may be configured to generate light source light. In embodiments, the light source light may have a first peak wavelength kpi selected from the wavelength range of 400-490 nm. Further, the light source may comprise a solid state light source. In embodiments, the first luminescent layer may be configured downstream of the light source. Further, the first luminescent layer may comprise a first layer luminescent material comprising a first luminescent material. The first luminescent material may be configured to convert a first part of the light source light received by the first luminescent material into first luminescent material light. In embodiments, the first luminescent material light may have an emission band having a first centroid wavelength ci selected from the wavelength range of 505-590 nm. Further, the first luminescent material light may have an emission band having a first full width half maximum (FWHM1) of at least 50 nm (at room temperature). In embodiments, the second luminescent layer may be configured downstream of the first luminescent layer (and the light source). Especially, the second luminescent layer may comprise a second layer luminescent material comprising a second luminescent material. In embodiments, the second luminescent material may comprise M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, wherein M comprises an alkaline cation, wherein A comprises a tetravalent cation, and wherein X comprises a monovalent anion, at least comprising fluorine (F). Further, the second luminescent material may be configured to convert a second part of the light source light received by the second luminescent material into second luminescent material light. The second luminescent material light may in embodiments have at least one emission band (in the wavelength range of 620-640 nm) having a second full width half maximum (FWHM2) of up to 40 nm (at room temperature). Further, in embodiments, the second luminescent material light may have a second centroid wavelength Zc2 selected from the wavelength range of 620-640 nm. In embodiments, the second luminescent layer may comprise at least 1.2 times an amount of the second layer luminescent material (that is) needed to transmit at most 2% of the light source light (at the first peak wavelength kpi) received by the second luminescent layer. In embodiments, the light generating system may be configured to generate, in a first operational mode of the light generating system, system light comprising the first luminescent material light and the second luminescent material light. The system light may in embodiments have a correlated color temperature selected from the range of 1300-2700 K. Hence, in specific embodiments, the invention provides a light generating system comprising a light source, a first luminescent layer, and a second luminescent layer, wherein: (i) the light source is configured to generate light source light, wherein the light source light has a first peak wavelength kpi selected from the wavelength range of 400-490 nm; and wherein the light source comprises a solid state light source; (ii) the first luminescent layer is configured downstream of the light source, wherein the first luminescent layer comprises a first layer luminescent material comprising a first luminescent material, wherein the first luminescent material is configured to convert a first part of the light source light received by the first luminescent material into first luminescent material light, wherein the first luminescent material light has an emission band having a first centroid wavelength ci selected from the wavelength range of 505-590 nm and a first full width half maximum (FWHM1) of at least 50 nm; (iii) the second luminescent layer is configured downstream of the first luminescent layer, wherein the second luminescent layer comprises a second layer luminescent material comprising a second luminescent material, wherein the second luminescent material comprises M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, wherein M comprises an alkaline cation, wherein A comprises a tetravalent cation, and wherein X comprises a monovalent anion, at least comprising fluorine (F); wherein the second luminescent material is configured to convert a second part of the light source light received by the second luminescent material into second luminescent material light having at least one emission band having a second full width half maximum (FWHM2) of up to 40 nm, wherein the second luminescent material light has a second centroid wavelength ( C2) selected from the wavelength range of 620-640 nm; and wherein the second luminescent layer comprises at least 1.2 times an amount of the second layer luminescent material needed to transmit at most 2% of the light source light received by the second luminescent layer; and (iv) the light generating system is configured to generate, in a first operational mode of the light generating system, system light comprising the first luminescent material light and the second luminescent material light, wherein the system light has a correlated color temperature selected from the range of 1300-2700 K.

[0009] With such a light generating system, essentially blue-free system light may be provided. Especially, as the amount of second layer luminescent material may be higher than needed to transmit at most 2% of the blue light source light incident on the second luminescent layer (after already partial conversion of the light source light in the first luminescent layer), the light generating system may provide blue-free light without the use of additional filters, thereby increasing the efficiency of the light generating system. Further yet, as the second layer luminescent material may be over-dimensioned (i.e., selected such that the amount of second layer luminescent material is higher than needed to transmit <2 % of the incident light) for the light source light, a potential degradation of the second layer luminescent material over time may not (significantly) affect the amount of blue light source light transmitted by the second luminescent layer (or only after a relatively long operation period). Hence, the light generating system may be stable and / or reliable, and may therefore have an improved lifespan and / or performance. The light generating system may generate efficient and reliable (white) light. Especially, the light generating system may generate efficient and reliable (essentially) blue-free (white) light.

[0010] In embodiments, the light generating system may comprise a light source. Especially, the light source may comprise a solid state light source. Further, the light source may be configured the generate light source light. In embodiments, the light source light may comprise violet light, i.e., light having a wavelength in the range of about 380-440 nm. Additionally or alternatively, in embodiments, the light source light may comprise, such as be, blue light, i.e., light having a wavelength in the range of about 440-490 nm. Especially, the light source light may have a first peak wavelength kpi selected from the wavelength range of 380-490 nm, such as selected from the wavelength range of 400-490 nm, more especially from the wavelength range of 420-475 nm. Hence, in specific embodiments, the first peak wavelength kpi may be selected from the wavelength range of 420-475 nm. Light source light having a first peak wavelength kpi selected from the wavelength range of 420- 475 nm may provide light source light having a highest intensity at a wavelength near an excitation maximum of the first (layer) luminescent material and / or of the second (layer) luminescent material. As such, such light source light (wherein 420 nm < kpi < 475 nm) may be especially beneficial to (efficiently) excite the first (layer) luminescent material and / or the second (layer) luminescent material (with relatively low thermalization losses). Further embodiments relating to the light source are provided below.

[0011] In embodiments, downstream of the light source, the light generating system may comprise a first luminescent layer. The terms “downstream” and “upstream” relate to an arrangement of items or features relative to the propagation of the light from a light generating means (here especially the light source), wherein relative to a first position within a beam of light from the light generating means, a second position in the beam of light closer to the light generating means is “upstream”, and a third position within the beam of light further away from the light generating means is “downstream”. In embodiments, the first luminescent layer may thus be configured downstream of the light source. Further, in embodiments, the second luminescent layer may be configured downstream of the first luminescent layer (and the light source). Here, some general embodiments relating to the first luminescent layer and / or second luminescent layer are provided.

[0012] In embodiments, the luminescent layer may be a self-supporting layer. Further, in embodiments, the luminescent layer may be a coating. In embodiments, the luminescent layer may comprise a light transmissive matrix, wherein the luminescent material is embedded. For instance, the luminescent layer may comprise a polymeric (e.g. a silicone, such as PDMS) matrix, with luminescent material embedded therein.

[0013] The luminescent layer may have any shape. In general, however, the luminescent layer may comprise two essentially parallel faces (i.e. a first side and a second side), defining a height (of the luminescent layer). Further, the luminescent layer may comprise a third side (or “edge face”), bridging the first side and second side. The edge face may be curved in one or two dimensions. The edge face may be planar. The luminescent layer may have a rectangular or circular cross-section, though other cross-sections may also be possible, like e.g. hexagonal, octagonal, etc. Hence, the luminescent layer may have an n- gonal cross-section, wherein n is at least 3, like 4 (square or rectangular cross-section), 5 (pentagonal cross-section), 6 (hexagonal cross-section), 8 (octagonal cross-section) or higher, such as up to 24. The first side and second side may also be indicated as “main faces”, as they may especially provide the largest external area of the luminescent layer. Perpendicular to the afore-mentioned cross-section, may be another cross-section, which may in embodiments be rectangular. Hence, the luminescent layer may e.g. have a cubic shape, a (non-cubic) cuboid shape, an n-gonal prism shape with n being at least 5 (such as pentagonal prism, hexagonal prism), and a cylindrical shape. Other shapes, however, may also be possible. In embodiments, the luminescent layer has lateral dimensions width or length (W or L) or diameter (D) and a thickness or height (H). In embodiments, (i) D > H or (ii) W > H and / or L> H. Especially, the lateral dimensions like length, width, and diameter are at least 2 times, like at least 5 times, larger than the height. In specific embodiments, the luminescent layer has a length L, a height H, and a width W, wherein H< 0.5*L and H< 0.5*W. In specific embodiments, the luminescent body may be a (small) tile. Further, the luminescent layer may be transparent or light scattering.

[0014] Focusing on the first luminescent layer, in embodiments, the first luminescent layer may be configured (directly) on top of a light exit surface of the light source. That is, in embodiments, the distance between (the light exit surface of) the light source and (a first side of) the first luminescent layer may be (essentially) zero. Hence, the first luminescent layer may be configured in physical contact with the light source. Alternatively, (the first side of) the first luminescent layer may be configured at a non-zero distance di from (the light exit surface of) the light source (“remote configuration”). That is, the first luminescent layer may be configured physically separated from the light source. For example, the one or more light sources may be configured on a (bottom) inner surface of a housing unit, wherein the first luminescent layer is comprised by a light exit window comprised by a second (top) surface of said housing unit. In embodiments, the distance di may be selected from the range of > 5 gm, such as from the range of > 15 gm, especially from the range of > 50 gm. Further, the distance di may be selected from the range of < 50 cm, such as from the range of < 30 cm, especially from the range of < 10 cm. Hence, in specific embodiments, the first luminescent layer may be configured at a non-zero distance di from the light source. Configuring the first luminescent layer at a non-zero distance di from the light source may reduce a surface temperature of the first luminescent layer, as the surface of the first luminescent layer may be physically separated from the (heat-generating) light source. Hence, the first luminescent layer may have improved thermal management, and consequently an improved lifespan and / or performance.

[0015] In embodiments, the first luminescent layer may comprise a first layer luminescent material comprising a first luminescent material. Especially, the first layer luminescent material may be a luminescent material comprised by (such as embedded in) the first luminescent layer. The first layer luminescent material may (at least) comprise the first luminescent material. In embodiments, the first luminescent material may especially be a broadband emitter. Herein, a broadband emitter may refer to a light emitting element configured to provide emission having an emission band having a full width half maximum bandwidth of > 50 nm, such as a bandwidth of > 60 nm, especially a bandwidth of > 70 nm. Further, the first luminescent material may be configured to convert a first part of the light source light received by the first luminescent material into first luminescent material light. In embodiment, the first part of the light source light may have a spectral power selected from the range > 10%, such as from the range of > 20%, especially from the range of > 30%, of a spectral power of the (overall) light source light. Further, in embodiments, the first part of the light source light may have a spectral power selected from the range of < 65%, such as from the range of < 55%, especially from the range of < 45%, of a spectral power of the (overall) light source light. Hence, the first luminescent material may in embodiments be configured to convert 10-65%, such as 20-55%, especially 30-45%, of the light source light into first luminescent material light.

[0016] In embodiments, the first luminescent material light may have an emission band having a first centroid wavelength ci selected from the wavelength range of 490-610 nm, such as from the wavelength range of 495-600 nm, like from the wavelength range of 500-595 nm, especially from the wavelength range of 505-590 nm, such as from the wavelength range of 535-590 nm. In specific embodiments, the first centroid wavelength ci may be selected from the wavelength range of 505-520 nm. In embodiments, the first luminescent material light may essentially consist of said emission band. Hence, in such embodiments, the (total) first luminescent material light may have a first luminescent material centroid wavelength Xcmiselected from the wavelength range of 490-610 nm, such as from the wavelength range of 500-600 nm, especially from the wavelength range of 505- 590 nm, like from the wavelength range of 535-590 nm. Alternatively, the first luminescent material light may comprise a plurality of emission bands.

[0017] The term “centroid wavelength”, also indicated as c, is known in the art, and refers to the wavelength value where half of the light energy is at shorter and half the energy is at longer wavelengths; the value is stated in nanometers (nm). It is the wavelength that divides the integral of a spectral power distribution into two equal parts as expressed by the formula Ac = X I(k) / (S I( A)), where the summation is over the wavelength range of interest, and I (A) is the spectral energy density (i.e. the integration of the product of the wavelength and the intensity over the emission band normalized to the integrated intensity). The centroid wavelength may e.g. be determined at operation conditions.

[0018] Further, in embodiments, the emission band (having the first centroid wavelength ci) of the first luminescent material light may have a first full width half maximum (FWHM1). That is, the first luminescent material light may have an emission band having a first full width half maximum (FWHM1). The full width half maximum (FWHM) of an emission band may especially be determined at room temperature. That is, the full width half maximum (FWHM) of an emission band from a luminescent material may be determined when said luminescent material has a temperature selected from the range of 20- 25 °C (i.e., room temperature). Further, the full width half maximum (FWHM) of an emission band may be determined from a spectral power distribution of said emission band, and may be defined as the width of the emission band (in nm) at half of the maximum intensity of the emission band. In embodiments, the first full width half maximum (FWHM1) may be selected from the range of at least 40 nm, such as from the range of at least 45 nm, especially from the range of at least 50 nm. Further, the first full width half maximum (FWHM1) may be selected from the range of at least 55 nm, such as from the range of at least 70 nm, especially from the range of at least 80 nm. Further yet, in embodiments, the first full width half maximum (FWHM1) may be selected from the range of at most 150 nm, such as from the range of at most 125 nm, especially from the range of at most 100 nm. Hence, in embodiments the first luminescent material light may have a first centroid wavelength ( ci) selected from the wavelength range of 505-590 nm (especially from the wavelength range of 535-590 nm) and a first full width half maximum (FWHM1) of at least 50 nm.

[0019] Further, in embodiments, the first layer luminescent material may be configured to convert at least part of the light source light into first layer luminescent material light. In embodiments, the first layer luminescent material may consist of the first luminescent material, and the first layer luminescent material may thus be configured to convert 10-65%, such as 20-55%, especially 30-45%, of the light source light into first layer luminescent material light. This would leave about 35-90%, such as 45-80%, especially 55- 70% of the light source light to be received by the second luminescent layer. Alternatively, in embodiments, the first layer luminescent material may comprise the first luminescent material and one or more further luminescent materials, different from the first luminescent material (e.g. differing in chemical composition). The optional one or more further luminescent materials from the first luminescent layer may (individually) be selected from a broadband emitter or a narrow-band emitter. Especially, the first layer luminescent material, comprising the first luminescent material and optionally one or more further luminescent materials comprised by the first luminescent layer, may be configured to convert 15-70%, such as 25-60%, especially 35-55%, of the light source light into first layer luminescent material light.

[0020] Further, the first layer luminescent material light may have a first layer centroid wavelength CLI. In embodiments, the first layer centroid wavelength may be equal to the first centroid wavelength, ci = CLI. Alternatively, the first layer centroid wavelength XCLI may be different than the first centroid wavelength ci. Especially, in embodiments, 0 nm < |XCI-XCLI| < 50 nm, especially 0 nm < |XCI-XCLI| < 40 nm.

[0021] Hence, in embodiments, the first layer luminescent material may comprise a first luminescent material, and optionally one or more further (different) luminescent materials. Likewise, the second luminescent material layer may comprise a second layer luminescent material, which comprises the second luminescent material, and optionally one or more further luminescent materials (comprised by the second luminescent material layer), see further also below. First some general aspects in relation to luminescent material are described below.

[0022] The term “luminescent material” may especially refer to a material that can convert first radiation, especially one or more of UV radiation and blue radiation, into second radiation. In general, the first radiation and second radiation have different spectral power distributions, with the second radiation generally having a spectral power distribution at larger wavelengths than the first radiation (i.e. “down-conversion”). In embodiments, the “luminescent material” may especially refer to a material that can convert radiation into e.g. visible and / or infrared light. For instance, in embodiments the luminescent material may be able to convert one or more of UV radiation and blue radiation, into visible light. The terms “visible”, “visible light” or “visible emission” and similar terms refer to light having one or more wavelengths in the range of about 380-780 nm. Herein, UV (ultraviolet) may especially refer to a wavelength selected from the range of 190-380 nm, such as 200-380 nm, though in specific embodiments other wavelengths may also be possible. Hence, upon excitation with radiation, the luminescent material may emit radiation. The terms “light” and “radiation” are herein interchangeably used, unless clear from the context that the term “light” only refers to visible light. The terms “light” and “radiation” may thus refer to UV radiation, visible light, and IR radiation. In specific embodiments, especially for lighting applications, the terms “light” and “radiation” refer to (at least) visible light. In embodiments, the term “luminescence” may refer to phosphorescence. In embodiments, the term “luminescence” may also refer to fluorescence. Instead of the term “luminescence”, also the term “luminescent material light” or “emission” may be applied. Hence, the terms “first radiation” and “second radiation” may refer to excitation radiation and emission (radiation), respectively. The term “luminescent material” may also refer to a plurality of different luminescent materials. Examples of possible luminescent materials are indicated below. Hence, the term “luminescent material” may in specific embodiments also refer to a luminescent material composition. Instead of the term “luminescent material” also the term “phosphor” may be applied. These terms are known to the person skilled in the art.

[0023] A non-limiting number of examples of luminescent materials are described below.

[0024] In embodiments, a luminescent material may be selected from garnets and nitrides, especially doped with trivalent cerium or divalent europium, respectively. The term “nitride” may also refer to oxynitride or nitridosilicate, etc. Alternatively or additionally, the luminescent material(s) may be selected from silicates, especially doped with divalent europium. In embodiments, the luminescent material may comprise a divalent europium comprising oxynitride luminescent material. Further, in embodiments, the luminescent material may comprise a divalent europium comprising nitride luminescent material.

[0025] In specific embodiments, a luminescent material may at least comprise a luminescent material of the type AsBsOnUe, wherein A comprises one or more of Y, La, Gd, Tb and Lu, and wherein B comprises one or more of Al, Ga, In and Sc; and wherein the light source light may comprise blue light source light. Especially, A may comprise one or more of Y, Gd and Lu, such as especially one or more of Y and Lu. Especially, B may comprise one or more of Al and Ga, more especially at least Al, such as essentially entirely Al. Hence, especially suitable luminescent materials are cerium comprising garnet materials. Embodiments of garnets especially include A3B5O12 garnets, wherein A comprises at least yttrium (Y) or lutetium (Lu) and wherein B comprises at least aluminum (Al). Such garnets may be doped with cerium (Ce), with praseodymium (Pr) or a combination of cerium and praseodymium; especially however with Ce. Especially, B may comprise aluminum (Al); however, in addition to aluminum, B may also partly comprise gallium (Ga) and / or scandium (Sc) and / or indium (In), especially up to about 20% of B, more especially up to about 10 % of B; B may especially comprise up to about 10% gallium. In another variant, B and O may at least partly be replaced by Si and N. The element A may especially be selected from the group consisting of yttrium (Y), gadolinium (Gd), terbium (Tb) and lutetium (Lu). Further, Gd and / or Tb are especially only present up to an amount of about 20% of A. In a specific embodiment, the garnet luminescent material comprises (Yi-xLux)3B50i2:Ce, wherein 0 < x < 1. The term “:Ce”, indicates that part of the metal ions (i.e. in the garnets: part of the “A” ions) in the luminescent material is replaced by Ce. For instance, in the case of (Yi-xLux)3A150i2:Ce, part of Y and / or Lu is replaced by Ce. This is known to the person skilled in the art. Ce will replace A in general for not more than 10%; in general, the Ce concentration will be in the range of 0.1 to 4%, especially 0.1 to 2% (relative to A). Assuming 1% Ce and 10% Y, the full correct formula could be (Yo.iLuo.sgCeo.o sALOn. Ce in garnets is substantially or only in the trivalent state, as is known to the person skilled in the art. In embodiments, such luminescent materials may have a suitable spectral distribution, have a relatively high efficiency, have a relatively high thermal stability, and allow a high CRI (optionally in combination with (the) light of other sources of light as described herein).

[0026] In specific embodiments, a luminescent material may only include a luminescent material selected from the type of cerium comprising garnets. In even further specific embodiments, the luminescent material may include a single type of luminescent material, such as (YxiA’X2CeX3)3(AlyiB’y2)5Oi2. Hence, in specific embodiments the luminescent material may comprise luminescent material, wherein at least 85 weight%, even more especially at least about 90 wt.%, such as yet even more especially at least about 95 weight % of the luminescent material comprises (YxiA’X2CeX3)3(AlyiB’y2)5Oi2. Here, A’ comprises one or more elements selected from the group consisting of lanthanides, and B’ comprises one or more elements selected from the group consisting of Ga, In and Sc, wherein xl+x2+x3=l, wherein x3>0, wherein 0<x2+x3<0.2, wherein yl+y2=l, wherein 0<y2<0.2. Especially, x3 is selected from the range of 0.001-0.1. Note that in embodiments x2=0. Alternatively or additionally, in embodiments y2=0.

[0027] A luminescent material may comprise a luminescent material of the type AsSieNiuCe3, wherein A comprises one or more of Y, La, Gd, Tb and Lu, such as in embodiments one or more of La and Y. In embodiments, the luminescent material may alternatively or additionally comprise one or more of MS:Eu2+and / or NfcSis Eu2and / or MAlSiNvEu2and / or Ca2AlSi3O2Ns:Eu2+, etc., wherein M comprises one or more of Ba, Sr and Ca, especially in embodiments at least Sr. Hence, in embodiments, the luminescent material may comprise one or more materials selected from the group consisting of (Ba,Sr,Ca)S:Eu, (Ba,Sr,Ca)AlSiN3:Eu and (Ba,Sr,Ca)2SisN8:Eu. In these compounds, europium (Eu) is substantially or only divalent, and replaces one or more of the indicated divalent cations, as is known to a person skilled in the art. In general, Eu will not be present in amounts larger than 10% of the cation; its presence will especially be in the range of about 0.5 to 10%, more especially in the range of about 0.5 to 5% relative to the cation(s) it replaces.

[0028] In embodiments, a luminescent material may comprise a luminescent material of the type M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, M comprises an alkaline cation, and x may be selected from the range of 0-1, wherein A comprises a tetravalent cation, for instance comprising one or more of silicon and titanium, wherein X comprises a monovalent anion, at least comprising fluorine. Especially, in embodiments, a luminescent material may comprise M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, wherein M comprises an alkaline cation, wherein A comprises a tetravalent cation, and wherein X comprises a monovalent anion, at least comprising fluorine (F). A luminescent material of the type M’XM2-2XAX6 doped with tetravalent manganese may herein also be indicated as “KSiF” or “KSF”, whether or not M comprises K or one or more other alkaline cations. A luminescent material of the type M’xM2-2xAX6 doped with tetravalent manganese is amongst others described in WO2013121355A1, which is herein incorporated by reference. Passages from WO2013121355A1 are also copied herein. Relevant alkaline earth cations (M’) are magnesium (Mg), strontium (Sr), calcium (Ca) and barium (Ba), especially one or more of Sr and Ba. Relevant alkaline cations (M) are sodium (Na), potassium (K) and rubidium (Rb). Optionally, also ammonium (NHC), lithium (Li) and / or cesium (Cs) may be applied. In a preferred embodiment, M comprises at least potassium. In yet another embodiment, M comprises at least rubidium. In another preferred embodiment, M comprises at least potassium and rubidium. In an embodiment, preferably at least 80% (i.e. 80% of all moles of the type M), even more preferably at least 90%, such as 95% of M consists of potassium and / or 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. In an embodiment, a combination of different alkaline cations may be applied. In yet another embodiment, a combination of different alkaline earth cations may be applied. In yet another embodiment, a combination of one or more alkaline cations and one or more alkaline earth cations may be applied. For instance, KRbo.sSro^sAXe might be applied, wherein x may be selected from the range of 0-1, especially x < 1. In specific embodiments, x = 0.

[0029] 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 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+).

[0030] In embodiments, A comprises a tetravalent cation, and preferably at least comprises silicon. A may optionally (further) comprise one or more of titanium (Ti), germanium (Ge), stannum (Sn) and zinc (Zn). Preferably, at least 80%, even more preferably at least 90%, such as at least 95% of A consists of silicon.

[0031] 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). Preferably, at least 80%, even more preferably at least 90%, such as 95% of X consists of fluorine. Especially, X may essentially consist of F (fluorine).

[0032] In an embodiment, M’xM2-2xAX6 comprises BGSiFe (indicated herein also as KSiF system). In another preferred embodiment, M’xM2-2xAX6 comprises KRbSiFe (herein also indicated as K,Rb system). In specific embodiments, the indication M’xM2-2xAX6 may refer to one or more of (K,Rb)2SiFe:Mn4+, (K,Rb)2TiFe:Mn4+, K2(Si,Ti)Fe:Mn4+, and Rb2(Si,Ti)Fe:Mn4+, such as one or more of K2TiFe:Mn4+, of K2SiFe:Mn4+, and of Rb2SiFe:Mn4+. In embodiments, a luminescent material may comprise (K,Rb)2SiFe:Mn4+. Additionally or alternatively, in embodiments, a luminescent material may comprise K2(Si,Ti)Fe:Mn4+. In specific embodiments, a luminescent material may especially comprise K2SiFe:Mn4+. As can be derived from the above, “(Si,Ti)” may indicate one or more of Si and Ti (and “(K,Rb)” may indicate one or more of K and Rb). Hence, in specific embodiments, a luminescent material may comprise one or more of (K,Rb)2SiFe:Mn4+and K2(Si,Ti)Fe:Mn4+. The luminescent material may also be coated, as also described in WO2013121355A1.

[0033] The term “luminescent material” herein especially relates to inorganic luminescent materials. Alternatively or additionally, also other luminescent materials may be applied. For instance quantum dots, (organic and / or inorganic) perovskites, and / or organic dyes may be applied and may optionally be embedded in transmissive matrices like e.g. polymers, like PMMA, or polysiloxanes, etc.

[0034] Further, in specific embodiments, the first luminescent material may comprises a luminescent material of the type AsBsOn Ce, wherein A comprises one or more of Y, La, Gd, Tb and Lu, and wherein B comprises one or more of Al, Ga, In and Sc.

[0035] Further, in embodiments, the first luminescent material may comprise at least two luminescent materials of the type AsBsOn Ce3, such as at least (YxiiLuxnA’xisCexi^sBsOn and (Yx2iLux22A’x23CeX24)3B5Oi2. In such embodiments, the first luminescent material may comprise a primary first luminescent material such as (YxiiLuxi2A’xi3Cexi4)3B5Oi2, wherein xn + X12 + X13 + xi4 = 1, xn + xn > 0, 0 < X13 < 1, 0.001

[0036] < xu < 0.1, wherein A’ comprises one or more of La, Gd, and Tb, and wherein B comprises one or more of Al, Ga, In, and Sc. Further, in such embodiments, the first luminescent material may comprise a secondary first luminescent material such as (Yx2iLux22A’x23CeX24)3B5Oi2, wherein X21 + X22 + X23 + X24=1, X21 + X22 > 0, 0 < X23 < 1, 0.001

[0037] < X24 < 0.1, wherein A’ comprises one or more of La, Gd, and Tb, and wherein B comprises one or more of Al, Ga, In, and Sc. In embodiments, the secondary first luminescent material may comprise on a molar basis more Lu than the primary first luminescent material, X22 > X12. Further, in embodiments, the primary first luminescent material may comprise on a molar basis more Y than the secondary first luminescent material, xn > X21. In embodiments, X12 may be equal to zero. Further, in embodiments, X21 may be equal to zero. Further yet, in embodiments, one or more of X12, X13, and X23 may be equal to zero. In embodiments, X14 may be equal to X24. Yet, in embodiments, X14 may be different from X24, wherein (both) X14 and X24 may be individually selected from the range of 0.001-0.1. Hence, in specific embodiments, the first luminescent material may comprise a primary first luminescent material of the type (YxiiLuxnA’xnCexu^BsOn and a secondary first luminescent material of the type (YX2iLux22A’X23CeX24)3B5Oi2, wherein A’ comprises one or more of La, Gd, and Tb, wherein B comprises one or more of Al, Ga, In and Sc; wherein (a) xn + X12 + XB + XI4 = 1; Xu + xn > 0; 0 < XB < 1; and 0.001 < xu< 0.1; (b) X21 + X22 + X23 + X24= 1; X21 + X22 > 0; 0 < X23 < 1; and 0.001 < X24< 0.1; and (c) xn > X21 and X22 > X12. Such a composition of first luminescent material may provide a broader spectral power distribution of the first luminescent material light, compared to a spectral power distribution of a first luminescent material light provided by a first luminescent material comprising (just) one type of first luminescent material (e.g., (YxnLuxi2A’xi3Cexi4)3B5Oi2 or (YX2iLuX22A’X23CeX24)3B5Oi2). For instance, in embodiments, the primary first luminescent material may be configured to provide primary first luminescent material light, and the secondary first luminescent material may be configured to provide secondary first luminescent material light, wherein (a wavelength range of) a spectral power distribution of the primary first luminescent material light may overlap (a wavelength range of) a spectral power distribution of the secondary first luminescent material light for < 90%.

[0038] In embodiments, the first luminescent layer may comprise the first layer luminescent material in a first layer luminescent material concentration Ci. The first layer luminescent material concentration Ci may in embodiments be selected from the range of > 2 v / v%, such as from the range of > 5 v / v%, especially from the range of > 10 v / v%. Additionally or alternatively, in embodiments, the first layer luminescent material concentration Ci may be selected from the range of < 25 v / v%, such as from the range of < 20 v / v%, especially from the range of < 15 v / v%. Here, the term “v / v%” indicates a ratio between the total volume of the first layer luminescent material and the total volume of the first luminescent layer (including the volume of the first layer luminescent material). The remainder of the first luminescent layer may essentially consist of a polymeric material, like silicone and / or PMMA.

[0039] Further, in embodiments, the first luminescent layer may have a first layer height Hi. The first layer height Hi may in embodiments be selected from the range of > 50 pm, such as from the range of > 75 pm, especially from the range of > 100 pm. Further, the first layer height Hi may be selected from the range of < 10 mm, such as from the range of < 5 mm, especially from the range of < 3 mm, like from the range of < 2 mm.

[0040] In embodiments, the first peak wavelength kpi and the first layer luminescent material concentration Ci (and the first layer height Hi) may be selected such that under perpendicular irradiation (of a first side of the first luminescent layer) a part of the light source light at the first peak wavelength kpi (received by the first luminescent layer) may be transmitted by the first luminescent layer. Especially, in embodiments, the part of the light source light (at the first peak wavelength kpi) transmitted by the first luminescent layer may be selected from the range of > 45%, such as from the range of > 50%, especially from the range of > 55%, of the (total) light source light (at the first peak wavelength kpi) received by the first luminescent layer (under perpendicular irradiation). Further, in embodiments, the part of the light source light (at the first peak wavelength kpi ) transmitted by the first luminescent layer may be selected from the range of > 60%, such as from the range of > 65%, especially from the range of > 70%, of the (total) light source light (at the first peak wavelength kpi ) received by the first luminescent layer (under perpendicular irradiation). Additionally or alternatively, in embodiments, the part of the light source light (at the first peak wavelength kpi) transmitted by the first luminescent layer may be selected from the range of < 80%, such as from the range of < 75%, especially from the range of < 70%, like from the range of < 65%, of the (total) light source light (at the first peak wavelength kpi ) received by the first luminescent layer (under perpendicular irradiation). Hence, in embodiments, the part of the light source light (at the first peak wavelength kpi ) transmitted by the first luminescent layer may be selected from the range of 45-80%, such as from the range of 50-75%, especially from the range of 55-70%, like from the range of 60-65%, of the (total) light source light (at the first peak wavelength kpi) received by the first luminescent layer (under perpendicular irradiation). Hence, in specific embodiments, the first luminescent layer may comprise the first layer luminescent material in a first layer luminescent material concentration Ci, wherein the first luminescent layer may have a first layer height Hi; wherein the first peak wavelength kpi and the first layer luminescent material concentration Ci may be selected such that under perpendicular irradiation selected from the range of 55- 70% of the light source light at the first peak wavelength kpi received by the first luminescent layer is transmitted by the first luminescent layer. A first luminescent layer configured to transmit 55-70% of the light source light at the first peak wavelength kpi received by said first luminescent layer may facilitate providing a substantial part of the light source light to the second luminescent layer, to facilitate the production of second (layer) luminescent material light.

[0041] In embodiments, the percentage of the light source light at the first peak wavelength kpi transmitted by the first luminescent layer may be different than the percentage of the (overall) light source light transmitted by the first luminescent layer. That is, the first luminescent layer may have an average absorption coefficient for the (wavelengths comprised by the) light source light, wherein a first absorption coefficient for the first peak wavelength kpi may be higher or lower than the average absorption coefficient. Further, in embodiments, the light source may not irradiate the first luminescent layer from a direction perpendicular to the first side of the first luminescent layer. For example, the (beam of) light source light may be divergent, such that the light source light may (at least partially) irradiate the first luminescent layer with an angle of 90° with respect to (the first side of) the first luminescent layer. In such embodiments, the (average) path length of the light source light in the first luminescent layer (i.e., the distance the light source light travels between entering the first luminescent layer and exiting the first luminescent layer) may be larger than for (fully) perpendicular irradiation. Hence, the first luminescent layer may further be configured to transmit a part of the (full spectral power distribution of the) light source light, especially under (at least partial) non-perpendicular irradiation. Especially, in embodiments, the first luminescent layer may be configured to transmit 50-85%, such as 55-80%, especially 55-70%, like 60-70%, of the light source light received by the first luminescent layer. Hence, in specific embodiments, the first luminescent layer may be configured to transmit selected from the range of 55-70% of the light source light received by the first luminescent layer.

[0042] In embodiments, the light source light transmitted by the first luminescent layer may be incident on the second luminescent layer. Especially, > 95%, such as > 99%, especially > 99.5%, like > 99.8%, including 100%, of the light source light transmitted by the first luminescent layer may be incident on the second luminescent layer. Further, in embodiments, > 95%, such as > 99%, especially > 99.5%, like > 99.8%, including 100%, of the first (layer) luminescent material light generated by the first (layer) luminescent material (and emitted from the second side of the first luminescent layer) may be incident on the second luminescent layer. Hence, in embodiments, the second luminescent layer may be configured downstream of the first luminescent layer. Further, in embodiments, (a first side of) the second luminescent layer may be configured in physical contact with (a second side of) the first luminescent layer, such as especially be configured at the second side of the first luminescent layer. Alternatively, (a first side of) the second luminescent layer may be configured at a second non-zero distance d? from (the second side of) the first luminescent layer. That is, the second luminescent layer may be physically separated from the first luminescent layer (by a second distance dz). In embodiments, the second distance dz may be selected from the range of > 5 pm, such as from the range of > 15 pm, especially from the range of > 50 pm. Further, the distance di may be selected from the range of < 100 mm, such as from the range of < 75 mm, especially from the range of < 50 mm. Configuring the second luminescent layer at a second (non-zero) distance dz from the first luminescent layer may provide improved thermal management for both the first luminescent layer and the second luminescent layer, e.g. by facilitating an airflow between the first and second luminescent layers. Additionally, configuring the second luminescent layer at a second distance d? from the first luminescent layer may facilitate (more easily) replacing the second luminescent layer upon e.g. degradation of the second layer luminescent material, with a lower risk of damaging the first luminescent layer during the replacement action.

[0043] In embodiments, the second luminescent layer may comprise a second layer luminescent material comprising a second luminescent material. In embodiments, the second luminescent material may especially be a tetravalent manganese based narrow-band emitter (see also above). That is, the second luminescent material may be a narrow-band emitter comprising, such as doped with, tetravalent manganese (Mn4+). Herein, a narrow-band emitter may refer to a light emitting element configured to provide emission having an emission band having a full width half maximum (FWHM) of < 50 nm, especially a bandwidth of < 40 nm, like up to 35 nm (at room temperature). Hence, in embodiments, the second luminescent material may be configured to convert (a second part of the) light source light received by the second luminescent material into second luminescent material light having at least one emission band having a second full width half maximum (FWHM2) of up to 50 nm, such as up to 45 nm, especially up to 40 nm, like up to 35 nm. Further, in embodiments, the second luminescent material light may have a plurality of emission bands. In embodiments, a plurality of the emission bands may have a second full width half maximum (FWHM2) of up to 50 nm, such as up to 45 nm, especially up to 40 nm, like up to 35 nm. Further, the at least one and / or the plurality of emission band(s) may have a second full width half maximum (FWHM2) of at least 5 nm, such as at least 10 nm, especially at least 15 nm.

[0044] In embodiments, the second luminescent material may be configured to convert a part of the light source light received by the second luminescent material into second luminescent material light. This part (of the light source light) may herein also be indicated as “second part”. In embodiment, the second part of the light source light may have a spectral power corresponding to 35-90%, such as corresponding to 45-80%, especially corresponding to 55-70%, of a spectral power of the (overall) light source light (as generated by the light source). Further, in embodiments, the second part of the light source light may have a spectral power selected from the range > 99%, such as from the range of > 99.5%, especially from the range of > 99.8%, including (essentially) 100%, of a spectral power of the light source light received by the second luminescent material. Hence, in embodiments, the second luminescent material may be configured to convert > 99%, such as > 99.5%, especially > 99.8%, including (essentially) 100%, of the light source light received by the second luminescent material into second luminescent material light. In embodiments, the second luminescent material may (further) be configured to convert > 90%, such as > 95%, of the light source light received by the second luminescent layer into second luminescent material light. Further, in embodiments, the second luminescent material may be configured to convert < 10%, such as < 5%, especially < 1%, of the first layer luminescent material light received by the second luminescent material into second luminescent material light. In embodiments, the second luminescent material light may have a second centroid wavelength Xc2 selected from the wavelength range of 610-650 nm, such as from the wavelength range of 615-645 nm, especially from the wavelength range of 620-640 nm, like from the wavelength range of 625-635 nm.

[0045] In embodiments, the second layer luminescent material may consist of the second luminescent material. Alternatively, the second layer luminescent material may comprise the second luminescent material and one or more further luminescent materials, different from the second luminescent material. The optional one or more further luminescent materials from the second luminescent layer may (individually) be selected from a broadband emitter or a narrow-band emitter. In embodiments, the second layer luminescent material (comprising the second luminescent material and optionally one or more further luminescent materials) may be configured to convert > 99%, such as > 99.5%, especially > 99.8%, including (essentially) 100%, of the light source light received by the second layer luminescent material into second layer luminescent material light. Further, in embodiments, the second layer luminescent material may be configured to convert > 99%, such as > 99.5%, especially > 99.8%, including 100%, of the light source light received by the second luminescent layer into second layer luminescent material light. In embodiments, the second layer luminescent material light may have a second layer centroid wavelength ZCL2. In embodiments, the second layer centroid wavelength may be equal to the second centroid wavelength, Zc2 = XCL2. Alternatively, the second layer centroid wavelength ZCL2 may be different than the second centroid wavelength Zc2. Especially, in embodiments, 0 nm < |Zc2- kcL2| < 50 nm, especially 0 nm < |XC2-XCL2| < 40 nm.

[0046] Hence, in embodiments, the second layer luminescent material may comprise the second luminescent material, and optionally one or more further (especially different) luminescent materials. In embodiments, the second layer luminescent material may comprise a luminescent material selected from the luminescent materials described above. Especially, in embodiments, the second (layer) luminescent material may comprise a luminescent material of the type M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, M comprises an alkaline cation, and x may be selected from the range of 0-1, wherein A comprises a tetravalent cation, for instance comprising one or more of silicon and titanium, wherein X comprises a monovalent anion, at least comprising fluorine. In specific embodiments, the second luminescent material may comprise one or more of (K,Rb)2SiFe:Mn4+and K2(Si,Ti)Fe:Mn4+. Especially, in embodiments, the second luminescent material may comprise K2SiFe:Mn4+. A second luminescent material comprising M’xM2-2xAX6 may have a relatively high efficiency, and may increase the color rendering index (CRI) of the system light. Further, a second luminescent material comprising M’XM2- 2xAXe may (essentially) not absorb light in the wavelength range of 505-590 nm.

[0047] In embodiments, the second luminescent layer may comprise more of the second layer luminescent material than is needed to absorb at least 98% of the light source light (at the first peak wavelength kpi) received by the second luminescent layer. Hence, in embodiments, the second luminescent layer may comprise more of the second layer luminescent material than is needed to transmit at most 2% of the light source light (at the first peak wavelength kpi) received by the second luminescent layer. Especially, the second luminescent layer may comprises at least 1.1 times the amount of the second layer luminescent material that is needed to transmit (or absorb) at most 2% (or at least 98%) of the light source light (at the first peak wavelength kpi) received by the second luminescent layer, such as at least 1.2 times the amount, like at least 1.5 times the amount, especially at least 2 times the amount. Hence, in specific embodiments, the second luminescent layer may comprise at least 1.5 times an amount of the second layer luminescent material needed to transmit at most 2% of the light source light received by the second luminescent layer. A second luminescent layer comprising a higher amount of the second layer luminescent material than is needed to transmit at most 2% of the light source light may provide the benefit that (only) a negligible amount of light source light may be transmitted through the second luminescent layer, such as (essentially) no light source light. As such, the system light may be (essentially) free from light source light.

[0048] In embodiments, the second luminescent layer may (further) comprise at most 5 times the amount of the second layer luminescent material that is needed to transmit at most 2% of the light source light (at the first peak wavelength kpi) received by the second luminescent layer, such as at most 4 times the amount, like at most 3.5 times the amount, especially at most 3 times the amount. Hence, in embodiments, the second layer luminescent material may comprise at most 5 times the amount of the second layer luminescent material that is needed to absorb at least 98% of the light source light (at the first peak wavelength kpi) received by the second luminescent layer, such as at most 4 times the amount, like at most 3.5 times the amount, especially at most 3 times the amount.

[0049] In embodiments, the second luminescent layer may comprise the second layer luminescent material in a second layer luminescent material concentration C2. In embodiments, the second layer luminescent material concentration C2 may be selected from the range of > 3 v / v%, such as from the range of > 5 v / v%, especially from the range of > 10 v / v%. Additionally or alternatively, in embodiments, the second layer luminescent material concentration C2 may be selected from the range of < 30 v / v%, such as from the range of < 25 v / v%, especially from the range of < 20 v / v%. Hence, in embodiments, the second layer luminescent material concentration C2 may be selected from the range of 3-30 v / v%, such as from the range of 5-25 v / v%, especially from the range of 10-20 v / v%. In specific embodiments, the second layer luminescent material concentration C2 may be selected from the range of 5-25 v / v%. Such a second layer luminescent material concentration C2 may be high enough that the light source light received by the second luminescent layer may not travel along a (straight) path through the second luminescent layer without being incident on (a particle of) the second layer luminescent material. Hence, light source light incident on the second luminescent layer may not pass through the second luminescent layer without being incident on the second layer luminescent material. The remainder of the second luminescent layer may essentially consist of a polymeric material, like silicone and / or PMMA.

[0050] Further, in embodiments, the second luminescent layer may have a second layer height H2. The second layer height H2 may in embodiments be selected from the range of 50 pm-10 mm, such as from the range of 75 pm-5 mm, especially from the range of 100 pm-3 mm. In embodiments, the first peak wavelength kpi and the second layer luminescent material concentration C2 may be selected such that under perpendicular irradiation (of the first side of the second luminescent layer) at least 98% of the light source light at the first peak wavelength kpi received by the second luminescent layer may be absorbed over a second absorption height H2a. Hence, the first peak wavelength kpi and the second layer luminescent material concentration C2 may be selected such that under perpendicular irradiation (of the first side of the second luminescent layer) at maximum 2% of the light source light at the first peak wavelength kpi received by the second luminescent layer may be transmitted over a second absorption height H2a. In embodiments, the second absorption height H2a may be determined by H2a = 0.98 / (s2*C2), wherein £2 may be the absorption coefficient of the second layer luminescent material for the first peak wavelength kpi . Further, in embodiments, the second layer height H2 may be selected to be larger than the second absorption height H^a. Especially, in embodiments, H2 > 1.25*H2a, such as H2 > 1.5*H2a, especially H2 > 2*H2a, like H2 > 2.5*H2a. Further, in embodiments, H2 < 5*H2a, such as H2 < 4*H2a, especially H2 < 3.5*H2a, like H2 < 3*H2a. Hence, in specific embodiments, the second luminescent layer may comprise the second layer luminescent material in a second layer luminescent material concentration C2, wherein the second luminescent layer may have a second layer height H2; wherein the first peak wavelength kpi and the second layer luminescent material concentration C2 may be selected such that under perpendicular irradiation at maximum 2% of the light source light at the first peak wavelength kpi received by the second luminescent layer may be transmitted over a second absorption height H2a of the second luminescent layer, wherein H2 > 1.5*H2a. Selecting the second layer height H2 to be larger than the second absorption height H2a may facilitate the second layer luminescent material absorbing (essentially) all of the light source light (at the first peak wavelength kpi received by the second luminescent layer).

[0051] In embodiments, the second luminescent layer may further comprise a secondary second absorption height H2a,2. In embodiments, the secondary second absorption height H2a,2 may define a height of the second luminescent layer at which at maximum 2% of the (full spectral power distribution of the) light source light received by the second luminescent layer may be transmitted (by the second luminescent layer). In embodiments, 1.25*H2a,2 < H2 < 5*H2a,2, such as 1.5*H2a,2 < H2< 4*H2a.2, especially 2*H2a,2 < H2< 3.5*H2a,2, like 2.5*H2a,2 < H2 < 3*H2a,2. In embodiments, the transmission (or absorption) of light source light (at the first peak wavelength kpi) by the second luminescent layer may be decreased (or increased) by one or more of (i) increasing the second layer height H2, and (ii) increasing the second layer luminescent material concentration C2.

[0052] In embodiments, the second layer height H2 may be selected to be larger than the first layer height Hi. Hence, in embodiments, H2 > Hi, such as 0.9*H2 > Hi, especially 0.8*H2 > Hi. Additionally or alternatively, in embodiments, the second layer luminescent material concentration C2 may be selected to be higher than the first layer luminescent material concentration Ci. Especially, in embodiments, C2 > Ci, such as 0.9*C2 > Ci, especially 0.8*C2 > Ci. Hence, in specific embodiments, for (a) the first layer luminescent material concentration Ci and the first layer height Hi and (b) the second layer luminescent material concentration C2 and the second layer height H2 it may apply that (i) C2 > Ci and (ii) H2 > Hi. Selecting the second concentration C2 to be higher than the first concentration Ci and / or selecting the second layer height H2 to be larger than the first layer height Hi may provide the benefit that light source light may be partially transmitted by the first luminescent layer, yet may be (essentially) fully absorbed by the second luminescent layer.

[0053] Hence, the light source light may (thus) be (essentially) fully absorbed by the first layer luminescent material and the second layer luminescent material. As such, in embodiments, the system light may not comprise the light source light. Alternatively, in embodiments, the system light may comprise part of the light source light, wherein the light source light may provide at most 2%, such as at most 1%, especially at most 0.5%, like at most 0.2%, of a spectral power of the system light (in the wavelength range of 400-780 nm). In embodiments, the system light may comprise the first layer luminescent material light. Further, in embodiments, the system light may comprise the second layer luminescent material light. The first layer luminescent material light and the second layer luminescent material light may (together) provide at least 99%, such as at least 99.5%, especially at least 99.8%, like at least 99.95%, including 100%, of the spectral power of the system light. Further, in embodiments, the first layer luminescent material light and the second layer luminescent material light may each have a spectral power distribution in the visible wavelength range (i.e., the range of 380-780 nm), especially in the wavelength range of 400- 780 nm. Hence, in embodiments, the system light may have a spectral power distribution in the visible wavelength range, such as in the wavelength range of 400-780 nm. Especially, the system light may have a spectral power distribution in the wavelength range of 400-780 nm, with at least 95%, such as at least 97.5%, especially at least 99%, like at least 99.5%, including (essentially) 100%, of the spectral power provided by the first layer luminescent material light and the second layer luminescent material light. Hence, in specific embodiments, the system light may have a spectral power distribution in the wavelength range of 400-780 nm, wherein at least 97.5% of the spectral power in the wavelength range of 400-780 nm may be provided by (i) first layer luminescent material light generated by the first layer luminescent material, and (ii) second layer luminescent material light generated by the second layer luminescent material.

[0054] In embodiments, the first layer luminescent material light may (essentially) consist of the first luminescent material light. As indicated, the first luminescent material light may have a first centroid wavelength ci selected from the wavelength range of 505-590 nm, such as especially from the wavelength range of 535-590 nm. Hence, in embodiments, the first luminescent material light may be yellow light or green light (or a combination thereof). Further, in embodiments, the first layer luminescent material may comprise the first luminescent material and one (or more) further luminescent materials. In embodiments, the one (or more) further luminescent materials may be configured to provide orange and / or red luminescent material light. For example, the one (or more) further luminescent materials may be a nitride (see above). Hence, in embodiments, the first layer luminescent material light may be one or more of green light, yellow light, orange light, and red light. Further, in embodiments, the second layer luminescent material light may (essentially) consist of the second luminescent material light, having a second centroid wavelength Xc2 selected from the wavelength range of 620-640 nm, such as especially from the wavelength range of 625-635 nm. Hence, in embodiments, the second luminescent material light may be red light. Further, in embodiments, the first luminescent material light and the second luminescent material light may (together) provide at least 95%, such as at least 97.5%, especially at least 99%, like at least 99.5%, including (essentially) 100%, of the spectral power of the system light, especially in the wavelength range of 400-780 nm. Hence, in specific embodiments, the first luminescent material light may be yellow light or green light, the second luminescent material light may be red light, and the system light may have a spectral power distribution in the wavelength range of 400-780 nm, with at least 99% of a spectral power provided by the first luminescent material light and the second luminescent material light. System light wherein at least 99% of the spectral power is provided by the first luminescent material light and the second luminescent material light may provide yellow-orange system light. Such system light may e.g. be beneficial for applications in photolithography cleanrooms, wherein light with a blue (and / or violet) component would damage materials and / or cause unwanted reactions.

[0055] In embodiments, the system light may thus comprise a green and / or yellow component (provided in majority by the first (layer) luminescent material light), as well as a red component (provided in majority by the second (layer) luminescent material light). Further, the system light may comprise (essentially) no blue component. The terms “blue light” or “blue emission”, and similar terms, may especially relate to light having a wavelength in the range of about 440-490 nm. The terms “green light” or “green emission”, and similar terms, may especially relate to light having a wavelength in the range of about 490-560 nm. The terms “yellow light” or “yellow emission”, and similar terms, may especially relate to light having a wavelength in the range of about 560-590 nm. The terms “orange light” or “orange emission”, and similar terms, may especially relate to light having a wavelength in the range of about 590-620 nm. The terms “red light” or “red emission”, and similar terms, may especially relate to light having a wavelength in the range of about 620- 780 nm. The phrase “light having a wavelength in a wavelength range” and similar phrases may especially indicate that the indicated light (or radiation) has a spectral power distribution with at least an intensity or intensities at the wavelength in the indicated wavelength range. For instance, a blue emitting solid state light source will have a spectral power distribution with intensities at at least a wavelength in the 440-495 nm wavelength range. Hence, in embodiments, system light comprising (essentially) no blue (and / or violet) component may have a spectral power distribution with no or little intensity in the wavelength range of 400- 490 nm. Hence, in embodiments, the majority of a spectral power of the system light may be provided in the wavelength range of 490-780 nm, such as in the wavelength range of 500-780 nm, especially in the wavelength range of 505-780 nm. Especially, the system light may have a spectral power distribution in the wavelength range of 400-780 nm, with at least 95%, such as at least 97.5%, especially at least 98%, of the spectral power provided in the wavelength range of 490-780 nm. Further, in embodiments, the system light may have a spectral power distribution in the wavelength range of 400-780 nm, with at least 99%, such as at least 99.5%, especially at least 99.8%, including (essentially) 100%, of the spectral power provided in the wavelength range of 490-780 nm.

[0056] In embodiments, light comprising a (relatively) small blue component (i.e., relatively little spectral power provided in the wavelength range of 440-490 nm) may have a lower CCT than light having a (relatively) large blue component. Conversely, light comprising a (relatively) large red (and / or orange) component may have a lower CCT than light having a (relatively) small red (and / or orange) component. Hence, in embodiments, system light wherein > 95% of the spectral power of said system light is provided in the wavelength range of 490-780 nm may provide white light with a relatively low correlated color temperature (CCT) (small blue component). Especially, in embodiments, the system light may have a correlated color temperature selected from the range of < 2800 K, such as from the range of < 2700 K, especially from the range of < 2500 K, like from the range of < 2300 K. Further, as indicated above, the first luminescent material light may have an emission band having a first centroid wavelength ci selected from the wavelength range of 535-590 nm. Hence, in embodiments, the system light may comprise a green component. As such, the CCT of the system light may be selected from the range of > 1200 K, such as from the range of > 1300 K, especially from the range of > 1500 K, like from the range of > 1600 K. In specific embodiments, the CCT of the system light may be selected from the range of > 1700 K, such as from the range of > 1800 K. Further, in embodiments, the correlated color temperature of the system light may thus be selected from the range of 1200-2800 K, such as from the range of 1300-2700 K, especially from the range of 1500-2500 K, like from the range of 1500-2300 K. Hence, in specific embodiments, the first centroid wavelength ci may be selected from the wavelength range of 535-590 nm, and the system light may have a correlated color temperature selected from the range of 1500-2300 K. System light having a CCT in the range of 1500-2300 K may especially be beneficial in applications wherein blue light would be damaging to the environment. For example, in photolithography cleanrooms or specific chemical labs, blue light would degrade materials and / or cause unwanted reactions. Further, for e.g. street lighting, blue light contributes relatively more to light pollution, and may affect the (natural) behavior and rhythms of wildlife. Hence, a light generating system providing system light with a CCT of < 2300 K may have as advantage that it provides (reliable) (essentially) blue-free white light for such and other applications.

[0057] Further, in embodiments, the first luminescent material light may have an emission band having a first centroid wavelength ci selected from the wavelength range of 505-520 nm. In such embodiments, the system light may have a CCT selected from the range of 2000-2800 K, such as from the range of 2150-2750 K, especially from the range of 2350- 2700 K. Hence, in specific embodiments, the first centroid wavelength ci may be selected from the wavelength range of 505-520 nm, and the system light may have a correlated color temperature selected from the range of 2350-2700 K. Such system light may (still) provide blue-free lighting (i.e., light comprising 0-2% blue light), yet may have a higher correlated color temperature due to the green component in the system light. As such, such system light may appear less orange-red than system light having a CCT selected from the range of 1500- 2300 K.

[0058] In embodiments, the correlated color temperature of the system light may be (at least partially) determined by the percentage of the light source light absorbed (and converted) by the first (layer) luminescent material. Especially, as indicated above, the first (layer) luminescent material light may be yellow and / or green light, and the second (layer) luminescent material light may be red light. Further, in embodiments, > 98% of the light source light may be absorbed by the first (layer) luminescent material and the second (layer) luminescent material. Hence, by increasing the percentage of light source light absorbed (and converted) by the first (layer) luminescent material (providing yellow and / or green light), the correlated color temperature of the system light may be increased, as a smaller percentage of the light source light may (remain to) be absorbed (and converted) by the second (layer) luminescent material to provide red second (layer) luminescent material light. For instance, a light generating system wherein 30% of the light source light is absorbed by the first (layer) luminescent material, and > 68% of the light source light is absorbed by the second (layer) luminescent material, may provide system light having a CCT of 1750 K. Conversely, a light generating system wherein 39% of the light source light is absorbed by the first (layer) luminescent material, and > 59% of the light source light is absorbed by the second (layer) luminescent material, may provide system light having a CCT of 2000 K. Further yet, in embodiments, a light generating system wherein 49% of the light source light is absorbed by the first (layer) luminescent material, and > 49% of the light source light is absorbed by the second (layer) luminescent material, may provide system light having a CCT of 2500 K. In specific embodiments, the system light may have a CCT in a range from 1750 K to 2500 K, or even broader, like 1500-2500 K, such as 1300-2700 K.

[0059] In embodiments, the system light may further have a color rendering index (CRI) selected from the range of at least 35, such as from the range of at least 40, especially from the range of at least 45. Further, the system light may have a CRI selected from the range of at least 50, such as from the range of at least 55, especially from the range of at least 60. Hence, in specific embodiments, the system light may have a color rendering index of at least 50, and a correlated color temperature in a range from 1700K to 2500 K. In embodiments, the CRI may be determined using a plurality of Test Color Samples (TCSs), as is known to a person skilled in the art. In embodiments, the plurality of TCSs may include TCS09, which has a saturated red color. In embodiments, the TCS09 may be used to assess the reproduction of saturated red colors by a light source by calculating a CRI R9 value, wherein a higher (positive) number indicates a better reproduction of the saturated red (TCS09) color. In embodiments, light having a relatively large red component may have a (higher) positive R9 value, while light having a relatively low red component may have a negative R9 value. In embodiments, the system light may have a positive R9 value, especially in embodiments wherein the CCT is in a range from 1700K to 2500 K. Further, in embodiments, the system light may be within 20 Standard Deviation of Color Matching (SDCM) from the black body locus (BBL), such as within 15 SDCM from the BBL, especially within 10 SDCM from the BBL. In specific embodiments, the system light may be within 10 SDCM from the BBL, and have a CCT in a range from 1700K to 2500K.

[0060] As indicted above, the light generating system may comprise a light source configured to generate (blue or violet) light source light. Some general aspects related to the light source are described below.

[0061] The term “light source” may in principle relate to any light source known in the art. In a specific embodiment, the light source comprises a solid state light source (such as a light emitting diode (LED) or laser diode (or “diode laser”)). The term “light source” may also relate to a plurality of (essentially identical (or different)) light sources, such as 2-2000 (solid state) (LED) light sources. The phrases “different light sources” or “a plurality of different light sources”, and similar phrases, may in embodiments refer to a plurality of solid- state light sources selected from at least two different bins. Likewise, the phrases “identical light sources” or “a plurality of same light sources”, and similar phrases, may in embodiments refer to a plurality of solid-state light sources selected from the same bin. Hence, the term LED may also refer to a plurality of LEDs.

[0062] The light source may in embodiments comprise a solid state die (such as an LED). The die dimensions may be equal to or smaller than 2 mm, such as in the range of e.g. 0.2-2 mm. Herein, the term “light source” may also especially refer to a small solid state light source, such as having a mini size or micro size. For instance, the light sources may comprise one or more of mini LEDs and micro LEDs, such as especially micro LEDs or “microLEDs” or “pLEDs”. Herein, the term mini size or mini LED especially refers to solid state light sources having dimensions, such as die dimension, especially length and width, selected from the range of 100 pm - 1 mm. Herein, the term p size or micro LED especially refers to solid state light sources having dimensions, such as die dimension, especially length and width, selected from the range of 100 pm and smaller.

[0063] The light source may have a light escape surface. For LEDs it may for instance be the LED die, or when a resin is applied to the LED die, the outer surface of the resin. In principle, it may also be the terminal end of a fiber. The term escape surface especially relates to that part of the light source, where the light actually leaves or escapes from the light source. The light source is configured to provide a beam of light. This beam of light (thus) escapes from the light exit surface of the light source. Likewise, a light generating system may comprise a light escape surface, such as an end window.

[0064] The term “light source” may refer to a semiconductor light-emitting device, such as a light emitting diode (LEDs), a resonant cavity light emitting diode (RCLED), a vertical cavity laser diode (VCSELs), an edge emitting laser, etc... The term “light source” may also refer to an organic light-emitting diode (OLED), such as a passive-matrix (PMOLED) or an active-matrix (AMOLED). In an embodiment, the light source comprises an LED. The terms “light source” or “solid state light source” may also refer to a superluminescent diode (SLED). Further, the term “light source” or “solid state light source” may refer to a multi -junction light emitting diode (or “multi-junction LED”). A multijunction LED may be a single (LED) die comprising multiple junctions connected in series, which may be (directly) connected to a power supply providing an alternating current (AC). Especially, I term “solid state light source”, or “solid state material light source”, and similar terms, may refer to semiconductor light sources, such as a light emitting diode (LED), a laser diode, a superluminescent diode, or a multi -junction LED. Hence, in specific embodiments, the light source may be selected from the group of light emitting diodes, laser diodes, superluminescent diodes, and multi -junction light emitting diodes.

[0065] In embodiments, the light source may comprise one or more micro-optical elements (array of micro lenses) downstream of a single solid-state light source, such as an LED, or downstream of a plurality of solid-state light sources (i.e. e.g. shared by multiple LEDs). In embodiments, the light source may comprise an LED with on-chip optics. In embodiments, the light source comprises pixelated single LEDs (with or without optics) (offering in embodiments on-chip beam steering).

[0066] In embodiments, the light source may be configured to provide primary radiation, which is used as such, such as e.g. a blue light source, like a blue LED, or a green light source, such as a green LED, and a red light source, such as a red LED. Such LEDs, which may not comprise a luminescent material (“phosphor”) may be indicated as direct color LEDs. In embodiments, the light source may be a light source that during operation emits at least (blue) light at a wavelength selected from the range of 380-470 nm. However, other wavelengths may also be possible.

[0067] In embodiments, the light source may be selected from the group of laser diodes and superluminescent diodes. In other embodiments, the light source may comprise an LED. The light source may especially be configured to generate light source light having an optical axis (O), (a beam shape,) and a spectral power distribution. The light source light may in embodiments comprise one or more bands, having band widths as known for lasers.

[0068] The term “light source” may (thus) refer to a light generating element as such, like e.g. a solid state light source, or e.g. to a package of the light generating element, such as a solid state light source, and (other) optics, like a lens, a collimator. In embodiments, the term “light source” may thus also refer to a combination of a light source, like an LED, and an optical filter, which may change the spectral power distribution of the light generated by the light source. Especially, the term “light generating device” may be used to address a light source and further (optical components), like an optical filter and / or a beam shaping element, etc.

[0069] In embodiments, the light generating system may comprise a plurality of (the) light sources, such as > 2 light sources, like > 4 light sources, especially > 6 light sources. Further, in embodiments, the light generating system may comprise (a plurality of) < 2000 light sources, such as < 1500 light sources, especially < 1000 light sources. In embodiments, the plurality of (the) light sources may be arranged in a Chip-on-Board (CoB) system. Hence, in embodiments, the light generating system may comprise a Chip-on-Board (CoB). The term “CoB” especially refers to LED chips in the form of a semiconductor chip that is neither encased nor connected but directly mounted onto a substrate, such as a printed circuit board (PCB). Hence, a plurality of light emitting semiconductor light source may be configured on the same substrate. In embodiments, a CoB is a multi LED chip configured together as a single lighting module. Hence, in embodiments, the CoB may comprise a plurality of (the) light sources. Further, in embodiments, the CoB may comprise the first luminescent layer. The first luminescent layer may especially be configured on top of the plurality of (the) light sources. In specific embodiments, the first luminescent layer may be (at least partially) configured in physical contact with the plurality of (the) light sources (of the CoB). Further, in embodiments, the CoB may comprise the second luminescent layer. The second luminescent layer may in such embodiments especially be configured on top of (and in physical contact with) the first luminescent layer. Alternatively, the first luminescent layer may be configured on top of (and in physical contact with) the plurality of light sources, and the second luminescent layer may be configured at a non-zero second distance d? from (the second side of) the first luminescent layer. Yet, in other embodiments, the (first side of the) second luminescent layer may be configured in physical contact with the (second side of the) first luminescent layer. Hence, in specific embodiments, the light generating system may comprise a Chip-on-Board (CoB), wherein the Chip-on-Board (CoB) may comprise (i) a plurality of light sources, (ii) the first luminescent layer, and (iii) the second luminescent layer, wherein the first luminescent layer may be configured on top of the plurality of light sources, and wherein the second luminescent layer may be configured on top of the first luminescent layer. A light generating system comprising a CoB may provide the advantage that a single first (and second) luminescent layer may be configured covering the plurality of light sources. This may have as benefit that no separate first (and second) luminescent layer has to be provided for each (of the plurality of) light source(s). Further, as the first luminescent layer may be configured (directly) on top of the plurality of light sources, the risk of light source light being transmitted (or “leaking”) past the first luminescent layer may be (further) reduced.

[0070] Further, in embodiments, the light generating system may comprise a LED filament. LED filaments as such are known, and are e.g. described in US 8,400,051 B2, W02020016058, WO2019197394, etc., which are herein incorporated by reference. In general, a LED filament may in embodiments comprise (i) a plurality of light emitting diodes (LEDs), especially arranged in a (linear) array, arranged on (at least) a first major surface of an elongated carrier, and (ii) an elongated encapsulant covering the plurality of LEDs and at least part of the elongated carrier. Hence in embodiments, the LED filament may comprise a plurality of (the) light sources (of the light generating system), wherein the plurality of (the) light sources may especially be light emitting diodes (LEDs). In embodiments, the plurality of (the) light sources may be configured in an array (see further below). Further, the LED filament may comprise the first luminescent layer. The first luminescent layer may especially be configured as a first elongated encapsulant. Hence, the first luminescent layer may be configured surrounding the plurality of (the) light sources, such as especially covering the plurality of (the) light sources. Further, in embodiments, the LED filament may comprise the second luminescent layer. The second luminescent may in embodiments be configured as a second elongated encapsulant covering the first luminescent layer (i.e., the first elongated encapsulant). Hence, the second luminescent layer may be configured surrounding (at least part of) the first luminescent layer. Alternatively, in embodiments, the first luminescent layer may be configured as a first elongated encapsulant covering the plurality of light sources, and the second luminescent layer may be configured remote (i.e., at a non-zero second distance dz) from the first luminescent layer, e.g., the second luminescent layer may be configured in and / or at the light escape surface of the light generating system. Hence, in specific embodiments, the light generating system may comprise a LED filament, wherein the LED filament may comprise (i) a plurality of light sources, wherein the plurality of light sources may be configured in an array, and wherein the plurality of light sources may be light emitting diodes (LEDs), (ii) the first luminescent layer, and (iii) the second luminescent layer, wherein the first luminescent layer may be configured surrounding the plurality of light sources, and wherein the second luminescent layer may be configured surrounding the first luminescent layer. A light generating system comprising a LED filament may have as advantage that the light generating system may be easily incorporated into and / or used in existing light bulbs, lamps, luminaires, etc. Further, a LED filament may be configured to provide (system) light in all directions, thereby allowing a larger area to be illuminated with a single light generating system.

[0071] In embodiments, the LED filament may be defined by a filament length LF, a filament width WF, and a filament thickness TF. The LED filament may further comprise a filament axis of elongation AF. The filament axis of elongation AF may especially be a straight axis centered on the direction along which the LED filament is elongated. The filament axis of elongation AF may define an axis length LA, wherein the axis length LA may be the length of the LED filament along the filament axis of elongation AF. In some embodiments, the LED filament may be straight. In straight embodiments, the filament length LF may (essentially) be equivalent to the axis length LA. In other embodiments, the LED filament may be curved. For instance, the filament may have a (2D or 3D) spiraling shape, (like) a helical shape, or another curved shape. In curved embodiments, the axis length LA may be smaller than the filament length LF, such as LA / LF < 0.95, especially LA / LF < 0.75, more especially LA / LF < 0.55. Further, the LED filament may have relatively high aspect ratios (LF / WF or LF / TF), like at least 5, such as at least 10, especially at least 15, such as at least 20, more especially at least 50. Large aspect ratios may better mimic a filament. Yet, in embodiments, the aspect ratio (LF / WF and / or LF / TF) may be at most 900, such as at most 650, especially at most 500. Hence, in specific embodiments, 5*WF < LF < 900*WF, and 5*TF < LF < 900*TF. In embodiments, the LED filament may have a light-emitting surface that may extend along the filament length LF, and preferably at least partly around the axis of elongation. The light-emitting surface may in embodiments preferably be arranged to homogenously emit light and / or to emit light omnidirectionally.

[0072] Further, as indicated, the LED filament may comprise an elongated carrier, solid state light sources, and an encapsulant. Especially, the elongated carrier may support the solid state light sources. The elongated carrier may e.g. comprise glass, quartz, metal, or sapphire. In other embodiments, the elongated carrier may e.g. comprise a polymeric material or (flexible) metal, e.g., a film or foil. The elongated carrier may be rigid (self-supporting), but may (in polymeric embodiments) also be flexible. In embodiments, the elongated carrier may be light transmissive, translucent, or transparent for light, especially visible light. Alternatively, in embodiments, the carrier may be light reflective, especially reflective for one or more of the light source light and the LED filament light (see below), such as reflective for at least the light source light and the LED filament light. In specific embodiments, the carrier may be diffuse reflective. The elongated carrier may have (essentially) similar dimensions to the LED filament. Especially, the elongated carrier may (essentially) define the filament length LF and axis length LA of the LED filament. The width WF and thickness TF of the LED filament may be defined by the elongated carrier as well as other components of the LED filament, e.g., the solid state light sources and the (first and second) encapsulant. In embodiments, the (elongated) carrier may comprise a first major surface at a first side of the carrier and a second major surface at a second side of the carrier, opposite to the first side. In embodiments, the solid state light sources may be arranged on at least one of these surfaces. Hence, in embodiments, at least part of, such as all of, the (plurality of) solid state light sources may be mounted onto the first major surface. Additionally or alternatively, at least part of the solid state light sources may be mounted onto the second major surface. Hence, in embodiments, the solid state light sources may be arranged, mounted and / or mechanically coupled on / to the carrier, wherein the carrier may especially be configured to mechanically and / or electrically support the LEDs.

[0073] In embodiments, the solid state light sources may comprise LEDs. Alternatively or additionally, in embodiments, the solid state light sources may comprise diode lasers. Further, the LED filament may comprise one or more of LEDs, laser diodes, and superluminescent diodes. Especially, the LED filament may comprise a plurality of light emitting diodes (LEDs). The (plurality of) solid state light sources may be arranged in an array (on the elongated carrier), especially over (at least part of) the filament length LF. The number of solid state light sources in the array may be at least 4, such as at least 8, even more especially at least 12, and may e.g. be up to 100, or yet even larger. Especially, in embodiments the number of solid state light sources in the array may be selected from the range of 10-2000, such as from the range of 10-1500, especially from the range of 10-1000. In embodiments, the solid state light sources may be configured in a ID (linear) array over at least part of the filament length LF. A first and a last solid state light source may, when measured along the LED filament, have a mutual distance of at least 0.5*LF, even more especially at least 0.7*LF. Further, in embodiments, the solid state light sources may be configured in two ID arrays, one on the first major surface of the elongated carrier and one on the second major surface. A 2D array of solid state light sources of n*m LEDs may also be possible. In embodiments, n may be selected from the range of 1-4, such as 1-3, like 1-2, such as in embodiments 1 or in embodiments 2, and m may be selected from the range of larger than n, such as especially selected from the range of at least 4 (when n<4), like at least 6, such as at least 8. Hence, a 2D array of solid state light sources may especially have a (much) smaller number of rows (n) than the number of solid state light sources in those respective rows (m), such as n / m <0.2, like n / m <0.1, especially n / m <0.05.

[0074] In embodiments, the LED filament may comprise a (first) encapsulant. The (first) encapsulant may especially (at least partly) cover the plurality of solid state light sources. Further, the (first) encapsulant may (at least partly) cover at least part of the elongated carrier, such as at least (part of) one of the first major and second major surface. In general, the (first) encapsulant may be in contact with the elongated carrier and may cover all of the solid state light sources. Hence, in embodiments the (first) encapsulant may be configured over a substantial part of the filament length LF of the LED filament (such as over more than 70% of the filament length LF). The (first) encapsulant may be a continuous coating along the filament length LF, at one or both of the first major and the second major surface (of the elongated carrier). Further, the encapsulant may at least partly cover the solid state light sources, such as in embodiments at least 50% of the total number of solid state light sources in the array, such as at least 75%, especially at least 95%, up to 100%.

[0075] In embodiments, the (first) encapsulant may comprise one or more of a luminescent material (especially the first layer luminescent material) and a light scattering material. The one or more of the luminescent material and the light scattering material may especially be configured embedded in an encapsulant material, e.g. a (flexible) polymer material (such as a silicone). Further, in embodiments, the light scattering material may be configured to scatter (or “diffuse”) the light source light (and / or the first layer luminescent material light), especially in a direction transverse to a normal of the (first and / or second) major surface. In specific embodiments, the light scattering material may comprise light scattering particles, such as e.g. at least one of BaSCU, A12O3 and TiCL particles.

[0076] In embodiments, the LED filament may further comprise a second encapsulant, wherein the second encapsulant may especially comprise (such as be) the second luminescent layer. The second encapsulant may be configured (at least partly) covering the first encapsulant. Hence, in embodiments, the second encapsulant may be configured over a substantial part of the filament length LF of the LED filament (such as over > 70%, like over > 80%, especially over > 90%, including (essentially) 100%, of the filament length LF). The second encapsulant may be a continuous coating along the filament length LF, at one or both of the first major and the second major surface. Further, the encapsulant may at least partly cover the first encapsulant (comprising the first luminescent layer), such as in embodiments at least 50% of the total surface area of the first encapsulant, such as at least 75%, especially at least 95%, up to 100%.

[0077] In embodiments, the LED filament may be configured to generate filament light, which may comprise one or more of (scattered) first layer luminescent material light and second layer luminescent material light. The term “LED filament light” may refer to the light emitted by the LED filament during operation of the LED filament. In embodiments, the system light may comprise the LED filament light. Further, in embodiments, the system light may consist of the LED filament light. Especially, the LED filament light may be the system light. Further, the solid state light sources, comprised by the LED filament, may be configured to generate light source light. In embodiments, at least two, such as all, of the solid state light sources may be configured to emit light source light having different spectral power distributions. In other embodiments, at least two, such as all, of the solid state light sources may be configured to provide light source light having essentially the same spectral power distribution. In embodiments, the LED filament may comprise multiple sub-filaments.

[0078] In embodiments, the light generating system may comprise a plurality of (solid state) light sources. The plurality of light sources may comprise a first subset of one or more light sources, a second subset of one or more light sources, a third subset of one or more light sources, etc.. In embodiments, the subsets of one or more light sources may be individually controllable. Further, in embodiments, the subsets of one or more light sources may be configured in e.g. different CoB systems and / or different sub-filaments. Especially, in embodiments, each subset of one or more light sources may be configured in a lightproviding relationship with a (separate) first luminescent layer and / or a (separate) second luminescent layer. Hence, the first luminescent layer may comprise a plurality of first luminescent layer sections, wherein each first luminescent layer section is configured in a light-receiving relationship with one of the subsets of one or more light sources. Similarly, the second luminescent layer may comprise a plurality of second luminescent layer sections, wherein each second luminescent layer section is configured in a light-receiving relationship with one of the subsets of one or more light sources. In embodiments, each of the first luminescent layer sections and / or each of the second luminescent layer sections may be configured to generate (upon irradiation with light source light) first and / or second layer luminescent material light having different optical properties. For example, a primary first luminescent layer section may comprise a different composition and / or concentration of first layer luminescent material than a secondary first luminescent layer section. Similarly, a primary second luminescent layer section may comprise a different composition (and / or concentration) of second layer luminescent material than a secondary second luminescent layer section. Hence, in embodiments, the light generating system may comprise a plurality of light generating modules, wherein each light generating module comprises (i) one or more light sources, (ii) a first luminescent layer section, and (iii) a second luminescent layer section; and wherein each light generating module is configured to generate module light. In embodiments, the light generating system may comprise 2-10 light generating modules, such as 2-8 light generating modules, especially 2-6 light generating modules.

[0079] Herein the phrase “in a first operational mode of the light generating system, system”, and similar phrases, may refer to embodiments (of the light generating system) wherein the light generating system may only have single operational mode and may also refer to embodiments wherein the light generating system may also have one or more other operational modes. In another operational mode, the system light may or may not comprise both the first luminescent material light and the second luminescent material light. The phrase “system light comprising the first luminescent material light and the second luminescent material light” may refer to embodiments (of the light generating system) wherein the system light essentially consist of the first luminescent material light and the second luminescent material light but may also refer to embodiments (of the light generating system) wherein the system light comprises in addition to the first luminescent material light and the second luminescent material light one or more other types of light.

[0080] In embodiments, the module light from each of the light generating modules may differ in one or more of radiant flux, color point, spectral power distribution, and correlated color temperature. Further, in embodiments, the system light may comprise the module light. Further yet, in embodiments, the light generating system may comprise a control system. The control system may be configured to control the plurality of light generating modules. Hence, in embodiments, the control system may be configured to control the system light, by adjusting the module light generated by each of the light generating modules. Especially, the control system may be configured to control one or more of the radiant flux, color point, CCT, and spectral power distribution of the system light.

[0081] In embodiments, the control system may further be configured to monitor a spectral power distribution of the system light. Especially, in embodiments, the control system may be configured to monitor a spectral power of the system light in the wavelength range of 400-490 nm. Further, in embodiments, the control system may be configured to provide a warning and / or switch off the light generating system when a preset threshold for the spectral power (provided in the wavelength range of 400-490 nm) is exceeded. The term “controlling” and similar terms especially refer at least to determining the behavior or supervising the running of an element. Hence, herein “controlling” and similar terms may e.g. refer to imposing behavior on the element, such as e.g. measuring, displaying, actuating, opening, shifting, changing temperature, etc.. Beyond that, the term “controlling” and similar terms may additionally include monitoring. Hence, the term “controlling” and similar terms may include imposing behavior on an element and monitoring the element. The controlling of the element can be done with a control system, which may also be indicated as “controller”. The control system and the element may thus at least temporarily, or permanently, functionally be coupled. The element may comprise the control system. In embodiments, the control system and element may not be physically coupled. Control can be done via wired and / or wireless control. The term “control system” may also refer to a plurality of different control systems, which especially are functionally coupled, and of which e.g. one control system may be a master control system and one or more others may be slave control systems. A control system may comprise or may be functionally coupled to a user interface.

[0082] The control system may also be configured to receive and execute instructions from a remote control. In embodiments, the control system may be controlled via an App on a device, such as a portable device, like a Smartphone or I-phone, a tablet, etc.. The device is thus not necessarily coupled to the lighting system, but may be (temporarily) functionally coupled to the lighting system. In such embodiments the control system of the lighting system may be a slave control system or control in a slave mode.

[0083] The system, or apparatus, or device may execute an action in a “mode” or “operation mode” or “mode of operation” or “operational mode”. The term “operational mode may also be indicated as “controlling mode”. Likewise, in a method an action or stage, or step may be executed in a “mode” or “operation mode” or “mode of operation” or “operational mode”. This does not exclude that the system, or apparatus, or device may also be adapted for providing another controlling mode, or a plurality of other controlling modes. Likewise, this may not exclude that before executing the mode and / or after executing the mode one or more other modes may be executed.

[0084] However, in embodiments a control system may be available, that is adapted to provide at least the controlling mode. Would other modes be available, the choice of such modes may especially be executed via a user interface, though other options, like executing a mode in dependence of a sensor signal or a (time) scheme, may also be possible. The operation mode may in embodiments also refer to a system, or apparatus, or device, that can only operate in a single operation mode (i.e. “on”, without further tunability). Hence, in embodiments, the control system may control in dependence of one or more of an input signal of a user interface, a sensor signal (of a sensor), and a timer. The term “timer” may refer to a clock and / or a predetermined time scheme.

[0085] The light generating system may be part of or may be applied in e.g. office lighting systems, household application systems, shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-optics application systems, projection systems, self-lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, decorative lighting systems, portable systems, automotive applications, (outdoor) road lighting systems, urban lighting systems, green house lighting systems, horticulture lighting, digital projection, or LCD backlighting. The light generating system (or luminaire) may be part of or may be applied in e.g. optical communication systems. Hence, in yet a further aspect, the invention also provides a lamp or a luminaire comprising the light generating system as defined herein. The luminaire may further comprise a housing, optical elements, louvres, etc.. The lamp or luminaire may further comprise a housing enclosing the light generating system. The lamp or luminaire may comprise a light window in the housing or a housing opening, through which the system light may escape from the housing. In yet a further aspect, the invention also provides a projection device comprising the light generating system as defined herein. Especially, a projection device or “projector” or “image projector” may be an optical device that projects an image (or moving images) onto a surface, such as e.g. a projection screen. The projection device may include one or more light generating systems such as described herein. Hence, in an aspect the invention also provides a lighting device selected from the group of a lamp and a luminaire, comprising the light generating system as defined herein. Further, in embodiments, the lighting device may be selected from the group of a lamp, a luminaire, a projector device, a photochemical reactor, and an optical wireless communication device, wherein the lighting device may comprise the light generating system as defined herein. The lighting device may comprise a housing or a carrier, configured to house or support, one or more elements of the light generating system. In specific embodiments, the lighting device may be a lamp or luminaire for cleanroom applications.

[0086] BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0088] Fig. 1 schematically depicts an embodiment of the light generating system; Fig. 2 schematically depicts embodiments of a LED filament and an CoB comprising the light generating system;

[0089] Fig. 3 schematically depicts a further embodiment of the light generating system;

[0090] Fig. 4 schematically depicts an embodiment of the system light; and

[0091] Fig. 5 schematically depicts an embodiment of the lighting device.

[0092] The schematic drawings are not necessarily to scale. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0093] Fig. 1 schematically depicts an embodiment of the light generating system 1000 of the invention. In embodiments, the light generating system 1000 may comprise a light source 10, a first luminescent layer 2100, and a second luminescent layer 2200. The light source 10 may especially be configured to generate light source light 11. In embodiments, the light source light 11 may have a first peak wavelength kpi selected from the wavelength range of 400-490 nm. Especially, the first peak wavelength kpi may be selected from the wavelength range of 420-475 nm. Further, the light source 10 may comprise a solid state light source. Especially, the light source 10 may be selected from the group of light emitting diodes, laser diodes, superluminescent diodes, and multi -junction light emitting diodes. In embodiments, the first luminescent layer 2100 may be configured downstream of the light source 10. Further, the first luminescent layer 2100 may comprise a first layer luminescent material 2110 comprising a first luminescent material 210. The first luminescent material 210 may be configured to convert a first part of the light source light 11 received by the first luminescent material 210 into first luminescent material light 211. The first luminescent material light 211 may in embodiments have an emission band having a first centroid wavelength ci selected from the wavelength range of 505-590 nm. Further, in embodiments, the first luminescent material light 211 may have an emission band having a first full width half maximum (FWHM1) of at least 50 nm. In embodiments, the second luminescent layer 2200 may be configured downstream of the first luminescent layer 2100 (and the light source 10). In embodiments, the second luminescent layer 2200 may comprise a second layer luminescent material 2220 comprising a second luminescent material 220. The second luminescent material 220 may especially comprise M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, wherein M comprises an alkaline cation, wherein A comprises a tetravalent cation, and wherein X comprises a monovalent anion, at least comprising fluorine (F). Especially, the second luminescent material 220 may comprise one or more of (K,Rb)2SiFe:Mn4+and K2(Si,Ti)Fe:Mn4+(, wherein the second luminescent material 220 especially comprises K2SiFe:Mn4+). Further, the second luminescent material 220 may be configured to convert a second part of the light source light 11 received by the second luminescent material 220 into second luminescent material light 221. The second luminescent material light 221 may have at least one emission band having a second full width half maximum (FWHM2) of up to 40 nm. Further, the second luminescent material light 221 may have a second centroid wavelength Zc2 selected from the wavelength range of 620-640 nm. In embodiments, the second luminescent layer 2200 may comprise at least 1.2 times an amount of the second layer luminescent material 2220 (that is) needed to transmit at most 2% of the light source light 11 (at the first peak wavelength kpi) received by the second luminescent layer 2200. Especially, the second luminescent layer 2200 may comprise at least 1.5 times an amount of the second layer luminescent material 2220 (that is) needed to transmit at most 2% of the light source light 10 (at the first peak wavelength kpi) received by the second luminescent layer 2200. In embodiments, the light generating system 1000 may be configured to generate, in a first operational mode of the light generating system 1000, system light 1001 comprising the first luminescent material light 211 and the second luminescent material light 221. In embodiments, the system light 1001 may have a correlated color temperature selected from the range of 1300-2700 K.

[0094] In embodiments, the first luminescent material 210 may comprise a luminescent material of the type AsEEOn Ce, wherein A comprises one or more of Y, La, Gd, Tb and Lu, and wherein B comprises one or more of Al, Ga, In and Sc. Further, in embodiments, the first luminescent material 210 may comprise a primary first luminescent material of the type (YxiiLuxnA’xisCexu^BsOn and a secondary first luminescent material of the type (Yx2iLux22A’x23CeX24)3B5Oi2, wherein A’ comprises one or more of La, Gd, and Tb, wherein B comprises one or more of Al, Ga, In and Sc. In such embodiments, xn + X12 + X13 + xu= 1; xn + xn > 0; 0 < X13 < 1; and 0.001 < xu< 0.1. Further, in such embodiments, X21 + X22 + X23 + X24 = 1; X21 + X22 > 0; 0 < X23 < 1; and 0.001 < X24 < 0.1. Further yet, in embodiments, xn > X21 and X22 > X12. In embodiments, the first luminescent layer 2100 may comprise the first layer luminescent material 2110 in a first layer luminescent material concentration Ci. Additionally, the first luminescent layer 2100 may have a first layer height Hi. The first peak wavelength kpi and the first layer luminescent material concentration Ci may be selected such that under perpendicular irradiation (selected from the range of) 55- 70% of the light source light 11 at the first peak wavelength kpi received by the first luminescent layer 2100 may be transmitted by the first luminescent layer 2100. Further, the first luminescent layer 2100 may be configured to transmit (selected from the range of) 55- 70% of the light source light 11 received by the first luminescent layer 2100 (regardless of wavelength and / or angle of irradiation).

[0095] Similarly, the second luminescent layer 2200 may comprise the second layer luminescent material 2220 in a second layer luminescent material concentration C2. In embodiments, the second layer luminescent material concentration C2 may be selected from the range of 5-25 v / v%. Further, the second luminescent layer 2200 may have a second layer height H2. In embodiments, the first peak wavelength kpi and the second layer luminescent material concentration C2 may be selected such that under perpendicular irradiation at maximum 2% of the light source light 11 at the first peak wavelength kpi received by the second luminescent layer 2200 may be transmitted over a second absorption height Fka of the second luminescent layer 2200. Especially, H2 > 1.5*H2a. Hence, the absorption of light source light 11 by the second luminescent layer 2200 may be adjusted by adjusting one or more of the second layer height H2 and the second layer luminescent material concentration C2. In embodiments, for (a) the first layer luminescent material concentration Ci and the first layer height Hi, and (b) the second layer luminescent material concentration C2 and the second layer height H2, it may apply that (i) C2 > Ci and( / or) (ii) H2 > Hi. Hence, the second layer luminescent material concentration C2 may be selected to be higher than the first layer luminescent material concentration Ci. Additionally or alternatively, the second layer height H2 may be selected to be higher than the first layer height Hi.

[0096] Fig. 2A schematically depicts a further embodiment of the light generating system 1000. The light generating system 1000 may comprise a LED filament 4000. The LED filament 4000 may comprise a plurality of (the) light sources 10. The plurality of (the) light sources 10 may be configured in an array 100. Further, the plurality of (the) light sources 10 may be light emitting diodes (LEDs). The light sources 10 may especially be configured on one or more of a first major surface and second major surface of an (elongated) carrier 5. Here, the plurality of light sources 10 are configured on both the first major surface and second major surface of the (elongated) carrier 5. Further, the LED filament 4000 may comprise the first luminescent layer 2100. The first luminescent layer 2100 may especially be configured as an elongated encapsulant configured covering the plurality of light sources 10. Hence, the first luminescent layer 2100 is configured surrounding the plurality of (the) light sources 10. Further, the LED filament 4000 may comprise the second luminescent layer 2200. The second luminescent layer 2200 may be configured as an elongated encapsulant configured covering the first luminescent layer 2100. Hence, the second luminescent layer 2200 is configured surrounding the first luminescent layer 2100. In embodiments, the plurality of (the) light sources 10 may be configured on one of the first major surface and second major surface of the carrier 5. In such embodiments, the first luminescent layer 2100 and second luminescent layer 2200 may (only) be configured on said one of the first major surface and second major surface, and may not be configured on the other of said one of the first major surface and second major surface. Alternatively, the plurality of (the) light sources 10 may be configured on one of the first major surface and second major surface of the carrier 5, and the first luminescent layer 2100 and second luminescent layer 2200 may be configured on both of the first major surface and second major surface. Further, the light generating system 1000 may comprise a control system 300. The control system 300 may be configured to control one or more of the radiant flux, color point, CCT, and spectral power distribution of the system light.

[0097] Fig. 2B schematically depicts a further embodiment of the light generating system 1000. The light generating system 1000 may comprise a Chip-on-Board (CoB) 3000. The Chip-on-Board (CoB) 3000 may comprise a plurality of (the) light sources 10, especially configured directly mounted onto a substrate, such as a printed circuit board (PCB). Further, the CoB 3000 may comprise the first luminescent layer 2100. The first luminescent layer 2100 may be configured on top of the plurality of (the) light sources 10. In specific embodiments, the first luminescent layer 2100 may be configured in physical contact with the plurality of (the) light sources 10. Additionally, the CoB 3000 may comprise the second luminescent layer 2200. The second luminescent layer 2200 may especially be configured on top of the first luminescent layer 2100, such as in physical contact with the first luminescent layer 2100.

[0098] Fig. 3 schematically depicts a further embodiment of the light generating system 1000. In embodiments, the first luminescent layer 2100 may be configured at a nonzero distance di from (a face of) the light source 10. The non-zero distance di may in embodiments be selected from the range of 5 pm - 50 cm. Further, as depicted here, the first luminescent layer 2100 (and second luminescent layer 2200) may be configured as a light escape surface of the light generating system 1000. Further, though the second luminescent layer 2200 is depicted in Fig. 3 as being in (physical) contact with the first luminescent layer 2100, this need not be the case. For instance, the first luminescent layer 2100 may be configured at a non-zero distance di from (a face of) the light source 10, and the second luminescent layer 2200 may be configured at a second non-zero distance d? from (a side of) the first luminescent layer 2100. Alternatively, the first luminescent layer 2100 may be configured on top of the light source 10, and the second luminescent layer 2200 may be configured at a second non-zero distance d? from (a side of) the first luminescent layer 2100 (e.g. at or in the light escape surface of the light generating system 1000).

[0099] Fig. 4 schematically depicts an embodiment of the system light 1001. The system light 1001 may comprise the first layer luminescent material light 2111 comprising the first luminescent material light 211 and the second layer luminescent material light 2221 comprising the second luminescent material light 221. In embodiments, the first luminescent material light 211 may be yellow light or green light. Additionally or alternatively, the second luminescent material light 221 may be red light. In embodiments, the system light 1001 may not comprise the light source light 11. Hence, the system light 1001 may have a spectral power distribution in the wavelength range of 400-780 nm, with at least 99% of a spectral power provided by the first luminescent material light 211 and the second luminescent material light 221. Alternatively, the system light 1001 may have a spectral power distribution in the wavelength range of 400-780 nm, wherein at least 97.5% of the spectral power in the wavelength range of 400-780 nm is provided by (i) first layer luminescent material light 2111 generated by the first layer luminescent material 2110 and (ii) second layer luminescent material light 2211 generated by the second layer luminescent material 2210. Especially, the system light 1001 may have a spectral power distribution in the wavelength range of 400-780 nm, with at least 97.5% of the spectral power provided in the wavelength range of 490-780 nm. As indicated, the first centroid wavelength ci may be selected from the wavelength range of 505-590 nm, such as especially from the wavelength range of 535-590 nm. Further, the second centroid wavelength Xc2 may be selected from the wavelength range of 620-640 nm, such as especially from the wavelength range of 625-635 nm. Hence, in embodiments, the system light 1001 may have a correlated color temperature selected from the range of (1300-2700 K, such as especially from the range of) 1500-2300 K. Alternatively, in embodiments, the first centroid wavelength ci may be selected from the wavelength range of 505-520 nm, and the system light 1001 may have a correlated color temperature selected from the range of 2350-2700K.

[0100] As depicted in Fig. 4, the characteristic narrow band emissions of (some luminescent materials doped with) Mn4+(like the second luminescent material 220) may include a plurality of relatively narrow bands (sometimes also indicated as “line emissions”). Each of these narrow bands, centered about 632 nm may have a (second) FWHM(2) of at maximum 40 nm (at room temperature). Note that some of these narrow bands may partly overlap. Due to this effect, as well as apparatus related resolution aspects, the narrow bands may appear to be broader. However, when measured with enough resolution (at room temperature) and when deconvoluting overlapping bands, the FWHMs will in general be (well) below 40 nm.

[0101] Fig. 5 schematically depicts an embodiment of a luminaire 2 comprising the light generating system 1000 as described above. Reference 301 indicates a user interface which may be functionally coupled with the control system 300 comprised by or functionally coupled to the light generating system 1000. Fig. 5 also schematically depicts an embodiment of lamp 1 comprising the light generating system 1000. Reference 3 indicates a projector device or projector system, which may be used to project images, such as at a wall, which may also comprise the light generating system 1000. Hence, Fig. 5 schematically depicts embodiments of a lighting device 1200 selected from the group of a lamp 1 and a luminaire 2, comprising the light generating system 1000 as described herein. In embodiments, such lighting device may be a lamp 1, a luminaire 2, a projector device 3, (a disinfection device,) or an optical wireless communication device. Lighting device light escaping from the lighting device 1200 is indicated with reference 1201. Lighting device light 1201 may essentially consist of system light 1001, and may in specific embodiments thus be system light 1001. Reference 1300 refers to a space, such as a room.

[0102] The term “plurality” refers to two or more. The terms “substantially” or “essentially” herein, and similar terms, will be understood by the person skilled in the art. The terms “substantially” or “essentially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term “substantially” or the term “essentially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” also includes embodiments wherein the term “comprises” means “consists of’. The term “and / or” especially relates to one or more of the items mentioned before and after “and / or”. For instance, a phrase “item 1 and / or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term "comprising" may in an embodiment refer to "consisting of but may in another embodiment also refer to "containing at least the defined species and optionally one or more other species".

[0103] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. The devices, apparatus, or systems may herein amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation, or devices, apparatus, or systems in operation.

[0104] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

[0105] Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

[0106] The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim, or an apparatus claim, or a system claim, enumerating several means, several of these means may be embodied by one and the same item of hardware. 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. The invention also provides a control system that may control the device, apparatus, or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements of such device, apparatus, or system.

[0107] The invention further applies to a device, apparatus, or system comprising one or more of the characterizing features described in the description and / or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and / or shown in the attached drawings. The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.

Claims

CLAIMS:

1. A light generating system (1000) comprising a light source (10), a first luminescent layer (2100), and a second luminescent layer (2200), wherein: the light source (10) is configured to generate light source light (11), wherein the light source light (11) has a first peak wavelength (kpi ) selected from the wavelength range of 400-490 nm; and wherein the light source (10) comprises a solid state light source; the first luminescent layer (2100) is configured downstream of the light source (10), wherein the first luminescent layer (2100) comprises a first layer luminescent material (2110) comprising a first luminescent material (210), wherein the first luminescent material (210) is configured to convert a first part of the light source light (11) received by the first luminescent material (210) into first luminescent material light (211), wherein the first luminescent material light (211) has an emission band having a first centroid wavelength ( ci) selected from the wavelength range of 505-590 nm and a first full-width-half-maximum (FWHM1) of at least 50 nm; the second luminescent layer (2200) is configured downstream of the first luminescent layer (2100), wherein the second luminescent layer (2200) comprises a second layer luminescent material (2220) comprising a second luminescent material (220), wherein the second luminescent material (220) comprises M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, wherein M comprises an alkaline cation, wherein A comprises a tetravalent cation, and wherein X comprises a monovalent anion, at least comprising fluorine (F); wherein the second luminescent material (220) is configured to convert a second part of the light source light (11) received by the second luminescent material (220) into second luminescent material light (221) having at least one emission band having a second full width half maximum (FWHM2) of up to 40 nm, wherein the second luminescent material light (221) has a second centroid wavelength ( C2) selected from the wavelength range of 620-640 nm; and wherein the second luminescent layer (2200) comprises at least 1.2 times an amount of the second layer luminescent material (2220) needed to transmit at most 2% of the light source light (10) received by the second luminescent layer (2200); andthe light generating system (1000) is configured to generate, in a first operational mode of the light generating system (1000), system light (1001) comprising the first luminescent material light (211) and the second luminescent material light (221), wherein the system light (1001) has a correlated color temperature selected from the range of 1300-2700 K.

2. The light generating system (1000) according to claim 1, wherein the first peak wavelength (kpi) is selected from the wavelength range of 420-475 nm, and wherein the second luminescent material (220) comprises one or more of (K,Rb)2SiF6:Mn4+and K2(Si,Ti)F6:Mn4+.

3. The light generating system (1000) according to any one of the preceding claims, wherein the first centroid wavelength ( ci) is selected from the wavelength range of 535-590 nm; wherein the system light (1001) has a correlated color temperature selected from the range of 1500-2300 K.

4. The light generating system (1000) according to claim 1 or 2, wherein the first centroid wavelength ( ci) is selected from the wavelength range of 505-520 nm; wherein the system light (1001) has a correlated color temperature selected from the range of 2350-2700 K.

5. The light generating system (1000) according to any one of the preceding claims, wherein the second luminescent layer (2200) comprises at least 1.5 times an amount of the second layer luminescent material (2220) needed to transmit at most 2% of the light source light (10) received by the second luminescent layer (2200).

6. The light generating system (1000) according to any one of the preceding claims, wherein: the first luminescent material light (211) is yellow light or green light; the second luminescent material light (221) is red light; and the system light (1001) has a spectral power distribution in the wavelength range of 400-780 nm with at least 99% of a spectral power provided by the first luminescent material light (211) and the second luminescent material light (221).

7. The light generating system (1000) according to any one of the preceding claims, wherein the second luminescent layer (2200) comprises the second layer luminescent material (2220) in a second layer luminescent material concentration (C2), wherein the second luminescent layer (2200) has a second layer height (H2); wherein the first peak wavelength (kpi) and the second layer luminescent material concentration (C2) are selected such that under perpendicular irradiation at maximum 2% of the light source light (11) at the first peak wavelength (kpi) received by the second luminescent layer (2200) is transmitted over a second absorption height (H2a) of the second luminescent layer (2200), wherein H2 > 1.5*H2a.

8. The light generating system (1000) according to claim 7, wherein the second layer luminescent material concentration (C2) is selected from the range of 5-25 v / v%; and wherein the second luminescent material (220) comprises K2SiFe:Mn4+.

9. The light generating system (1000) according to any one of the preceding claims, wherein the first luminescent material (210) comprises a luminescent material of the type AsBsOn Ce, wherein A comprises one or more of Y, La, Gd, Tb and Lu, and wherein B comprises one or more of Al, Ga, In and Sc.

10. The light generating system (1000) according to any one of the preceding claims, wherein the first luminescent layer (2100) comprises the first layer luminescent material (2110) in a first layer luminescent material concentration (Ci), wherein the first luminescent layer (2100) has a first layer height (Hi); wherein the first peak wavelength (kpi) and the first layer luminescent material concentration (Ci) are selected such that under perpendicular irradiation selected from the range of 55-70% of the light source light (11) at the first peak wavelength (kpi) received by the first luminescent layer (2100) is transmitted by the first luminescent layer (2100).

11. The light generating system (1000) according to any one of the preceding claims, wherein for (a) the first layer luminescent material concentration (Ci) and the first layer height (Hi) as defined in claim 10 and (b) the second layer luminescent material concentration (C2) and the second layer height (H2) as defined in any one of claims 6-7 it applies that (i) C2 > Ci and (ii) H2 > Hi.

12. The light generating system (1000) according to any one of the preceding claims, wherein the first luminescent layer (2100) is configured at a non-zero distance (di) from the light source (10).

13. The light generating system (1000) according any one of the preceding claims 1-11, wherein the light generating system (1000) comprises a Chip-on-Board (CoB) (3000), wherein the Chip-on-Board (CoB) (3000) comprises (i) a plurality of light sources (10), (ii) the first luminescent layer (2100), and (iii) the second luminescent layer (2200), wherein the first luminescent layer (2100) is configured on top of the plurality of light sources (10), and wherein the second luminescent layer (2200) is configured on top of the first luminescent layer (2100).

14. The light generating system (1000) according to any one of the preceding claims 1-11, wherein the light generating system (1000) comprises a LED filament (4000), wherein the LED filament (4000) comprises (i) a plurality of light sources (10), wherein the plurality of light sources (10) are configured in an array (100), and wherein the plurality of light sources (10) are light emitting diodes (LED)s, (ii) the first luminescent layer (2100), and (iii) the second luminescent layer (2200), wherein the first luminescent layer (2100) is configured surrounding the plurality of light sources (10), and wherein the second luminescent layer (2200) is configured surrounding the first luminescent layer (2100).

15. A lighting device (1200) selected from the group of a lamp (1) and a luminaire (2), comprising the light generating system (1000) according to any one of the preceding claims.

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