Light emitting device

Abstract

A LED filament comprises an array of a plurality of LEDs arranged on a first major surface of an elongated light-transmissive carrier. The plurality of LEDs is arranged to emit LED light having an emission peak wavelength between 430nm and 490nm. A first encapsulant covers the array of the plurality of LEDs. A second encapsulant covers at least part of a second major surface, opposite to the first major surface, of the carrier. The encapsulants comprise a respective luminescent material comprising a respective green phosphor of different types, arranged to convert at least part of the LED light into respective green phosphor light having different emission peak wavelengths. An emission spectrum of the first green phosphor at least partly overlaps an excitation spectrum of the second phosphor.

Description

[0001] Light emitting device

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to light emitting devices. More specifically, the present invention is related to a light emitting diode (LED) filament comprising an array of a plurality of LEDs arranged on an elongated carrier.

[0004] BACKGROUND OF THE INVENTION

[0005] A trend in the development of light emitting devices is LED filament lamps. A LED filament lamp is a lamp comprising LEDs which is designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes. In addition to the advantage that LED filament lamps may be configured such that they resemble traditional light bulbs, a further advantage of LED filament lamps is the inherent high energy efficiency of light-emitting diodes. However, there remain aspects of LED filament lamps that allow for further improvements. For example, there is a strong desire to improve the light quality in terms of factors like color rendering index (CRI) and / or having light with a more / improved continuous spectrum and / or improved spectrum that more resembles the spectrum of natural sunlight, as well as improving the energy efficiency of LED filament lamps.

[0006] US 2020 / 303355 discloses a. LED-filament includes a partially light- transmissive substrate; blue LED chips mounted on a front face of the substrate; first broadband green to red photoluminescence materials and a first narrow-band manganese-activated fluoride red photoluminescence material covering the blue LED chips and the front face of the substrate; and second broad-band green to red photoluminescence materials covering the back face of the substrate. The LED-filament can further include a second narrow-band manganese-activated fluoride red photoluminescence material on the back face of the substrate in an amount that is less than 5 wt percent of a total red photoluminescence material content on the back face of the substrate.

[0007] SUMMARY OF THE INVENTION It is of interest to provide a LED filament that is capable of overcoming drawbacks with prior art LED filaments.

[0008] This and other objects are achieved in a first aspect by providing a LED filament having the features of the appended independent claim. Preferred embodiments are defined in the appended dependent claims.

[0009] Hence, according to the present invention, there is provided a LED filament arranged to provide LED filament light. The LED filament comprises an array of a plurality of LEDs arranged on a first major surface of an elongated light-transmissive carrier. The plurality of LEDs is arranged to emit LED light having an emission peak, e.g. a dominant emission peak, wavelength in a wavelength range from 430nm to 490nm. The LED filament comprises a first encapsulant covering the array of the plurality of LEDs and covering at least part of the first major surface of the carrier. A second encapsulant is covering at least part of a second major surface, opposite to the first major surface, of the carrier.

[0010] The first encapsulant comprises a first luminescent material comprising a first green phosphor of a first phosphor type. The first green phosphor is arranged to convert at least part of the LED light into first green phosphor light, e.g. in the wavelength range 510- 580nm, having a first emission peak, e.g. a dominant emission peak, wavelength, XL The second encapsulant comprises a second luminescent material comprising a second green phosphor of a second phosphor type that is different from the first green phosphor type. The second green phosphor is arranged to convert at least part of the LED light into second green phosphor light, e.g. in the wavelength range 510-580nm, having a second emission peak, e.g. a dominant emission peak, wavelength, X2, where X2 is different from XL An emission spectrum of the first green phosphor at least partly overlaps an excitation spectrum of the second phosphor.

[0011] That is, such an arrangement of the first and second green phosphors provides an overlap between the emission spectrum of the first green phosphor and the excitation spectrum of the second phosphor such that the first green phosphor light is absorbed by the second green phosphor, which in turn emits the second green phosphor light having a different (dominant) emission peak wavelength. This re-absorption of light may result in increasing the amount of green light generated by the second green phosphor resulting in a more uniform light output of the LED filament in both directions. In addition, compared to mixing the first and second green phosphor in one layer, the efficiency is increased as less green light generated by the first green phosphor is absorbed by the second green phosphor, because only a part of the light generated by the first green phosphor is transmitted to the second green phosphor via the substrate. For example, the absolute difference between X2 and I may be greater than or equal to 20nm, preferably 25nm, more preferably 30nm, more preferably 35nm and more preferably 40nm.

[0012] In embodiments, the first luminescent material further comprises the second green phosphor, wherein the concentration of the first green phosphor in the first encapsulant is at least two times higher than the concentration of the second green phosphor in the first encapsulant, the second luminescent material further comprises the first green phosphor, the concentration of the second green phosphor in the second encapsulant is at least two times higher than the concentration of the first green phosphor in the second encapsulant, or, the first encapsulant does not comprise a second green phosphor and the second encapsulant does not comprise a first green phosphor.

[0013] In a further embodiment, I is at least 20 nm larger than X2. The effect of this choice is that less first green phosphor light is generated by the second green phosphor leading to an increase of the efficiency of the LED filament.

[0014] In embodiments, the LED filament light may be white light having a correlated color temperature in a range from 1700K to 6500K and preferably a color rendering index of at least 80, more preferably at least 85, most preferably at least 90. By using different green phosphors (with sufficient large difference between X2 and XI e.g. at least 25nm) (and different red phosphors) in the configuration according to the invention, an extreme high CRI value can be obtained such as >85 or even >90.

[0015] Moreover, the first green phosphor may be a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm, and the second phosphor may be a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm.

[0016] Furthermore, the first green phosphor may be a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm, and the second phosphor may be a narrowband phosphor having an emission peak with a full-width-half-maximum of less than 40 nm. Alternatively, the first green phosphor may be a narrowband phosphor having an emission peak with a full-width-half-maximum of less than 40 nm, and the second phosphor may be a broadband phosphor having an emission peak with a full-width-half- maximum of at least 70 nm.

[0017] In other words, in intervals in the spectrum where there is an overlap between the emission spectrum of the first green phosphor with the excitation spectrum of the second green phosphor there will occur a dip in the intensity of the LED filament light, i.e. decreasing the quality of the light because, e.g., these particular wavelengths are not present any more or present at low intensity and / or the CRI is lower. Thus, by spatially separating the first and second green phosphors the interaction between these two phosphors is reduced resulting in a reduced dip in the output spectrum. The first green phosphor may be a garnet class phosphor and the second green phosphor may be a garnet class phosphor.

[0018] In an embodiment, both of the first green phosphor and the second green phosphor comprises one or more of LuAG, LuY AG, YAG, or YGdAG.

[0019] In some embodiments, (at least 80% or 90% of) the first green phosphor comprises LuAG and (at least 80% or 90% ol) the second green phosphor comprises YAG.

[0020] In some embodiments, (at least 80% or 90% ol) the first luminescent material comprises LuAG and (at least 80% or 90% of) the second luminescent material comprises YAG

[0021] In some embodiments, (at least 80% or 90% of) the first green phosphor comprises YAG and (at least 80% or 90% of) the second green phosphor comprises LuAG.

[0022] In some embodiments, (at least 80% or 90% of) the first luminescent material comprises YAG and (at least 80% or 90% of) the second luminescent material comprises LuAG.

[0023] In embodiments, at least 80% or 90% of the first luminescent material comprises the first green phosphor and / or at least 80% or 90% of the second luminescent material comprises the second green phosphor.

[0024] More specifically, regarding garnet class phosphor, this refers to a luminescent material of the type AsELOnX'e. wherein A in embodiments comprises one or more of Y, La, Gd, Tb and Lu, especially (at least) one or more of Y, Gd, Tb and Lu, and wherein B in embodiments comprises one or more of Al, Ga, In and Sc. 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 or lutetium and wherein B comprises at least aluminum. 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 (i.e. the B ions essentially consist of 90 or more mole % of Al and 10 or less mole % of one or more of Ga, Sc and In); 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)3BsOi2:Ce, wherein x is equal to or larger than 0 and equal to or smaller than 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 ofY 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.89Ceo.oi)3A150i2. Ce in garnets is substantially or only in the trivalent state, as is known to the person skilled in the art.

[0025] The first luminescent material may further comprise a first red phosphor arranged to convert at least part of said LED light and / or at least part of the first green phosphor light into first red phosphor light, and / or the second luminescent material may further comprise a second red phosphor arranged to convert at least part of said LED light and / or at least part of the second green phosphor light into second red phosphor light.

[0026] In other words, by arranging red phosphors in such manner, absorption of only blue light occurs and no absorption of green light takes place. Thus the generation of red light by the red phosphor is not impacted and the red light will make the spectrum even more continuous and / or improve the CRI.

[0027] For example, the first red phosphor and / or the second red phosphor may be selected from the Mn-activated narrow-band class red phosphors. Such a red phosphor may be a KSiF phosphor. In some embodiments, the first red phosphor and the second red phosphor are different, with an effect of further improved light quality. In some embodiments, the first red phosphor and the second red phosphor is a Nitride class phosphor and / or an Oxynitride class phosphor, with an effect of further improved light quality.

[0028] With regard to (oxy)nitride class phosphors, this refers to a luminescent material comprising M2SisN8:Eu2+, or MAlSiN3:Eu2+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 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. 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. The term “:Eu”, indicates that part of the metal ions is replaced by Eu (in these examples by Eu2+). For instance, assuming 2% Eu in CaAlSiN3:Eu, the correct formula could be (Cao.98Euo.o2)AlSiN3. Divalent europium will in general replace divalent cations, such as the above divalent alkaline earth cations, especially Ca, Sr, or Ba. The material (Ba,Sr,Ca)S:Eu can also be indicated as MS:Eu, wherein M is one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca); especially, M comprises in this compound calcium or strontium, or calcium and strontium, more especially calcium. Here, Eu is introduced and replaces at least part of M (i.e. one or more of Ba, Sr, and Ca). Further, the material (Ba,Sr,Ca)2SisN8:Eu can also be indicated as NfcSis Eu, wherein M is one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca); especially, M comprises in this compound Sr and / or Ba. In a further specific embodiment, M consists of Sr and / or Ba (not taking into account the presence of Eu), especially 50 to 100%, more especially 50 to 90% Ba and 50 to 0%, especially 50 to 10% Sr, such as Bai.sSro.sSisNs^u (i.e. 75 % Ba; 25% Sr). Here, Eu is introduced and replaces at least part of M, i.e. one or more of Ba, Sr, and Ca). Likewise, the material (Ba,Sr,Ca)AlSiN3:Eu can also be indicated as MAlSiN3:Eu, wherein M is one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca); especially, M comprises in this compound calcium or strontium, or calcium and strontium, more especially calcium. Here, Eu is introduced and replaces at least part of M (i.e. one or more of Ba, Sr, and Ca). Eu in the above indicated luminescent materials is substantially or only in the divalent state, as is known to the person skilled in the art.

[0029] With regard to Mn-activated narrow-band class red phosphors, this refers to 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 is in the range of 0-1, wherein A comprises a tetraval ent cation, for instance comprising one or more of silicon and titanium, wherein X comprises a monovalent anion, at least comprising fluorine.

[0030] Relevant alkaline cations (M) are sodium (Na), potassium (K) and rubidium (Rb). Optionally, also lithium and / or cesium may be applied. In a preferred embodiment, M comprises at least potassium. In yet another embodiment, M comprises at least rubidium. The phrase “wherein M comprises at least potassium” indicates for instance that of all M cations in a mole M’xM2-2xAX6 , a fraction comprises K+and an optionally remaining fraction comprises one or more other monovalent (alkaline) cations (see also below). In another preferred embodiment, M comprises at least potassium and rubidium. Optionally, the M’xNfc- 2xAXe luminescent material has the hexagonal phase. In yet another embodiment, the M’xNfc- 2xAXe luminescent material has the cubic phase. For x=0, the composition is M2AX6.

[0031] Relevant alkaline earth cations (M’) are magnesium (Mg), strontium (Sr), calcium (Ca) and barium (Ba), especially one or more of Sr and Ba.

[0032] 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 tetraval ent 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.

[0033] 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).

[0034] In an embodiment, M’xM2-2xAX6 comprises K2SiFe (indicated herein also as KSiF system). As indicated above, in another preferred embodiment, M’xM2-2xAX6 comprises KRbSiFe (herein also indicated as K,Rb system). As indicated above, part of silicon is replaced by manganese (i.e. the formula may also be described as K2Sii-mMnmF6 or KRbSii-mMnmFe, with m as indicated above, or as KRbSiFe:Mn and K2SiFe:Mn, respectively). As manganese replaces part of a host lattice ion and has a specific function, it is also indicated as “dopant” or “activator”. Hence, the hexafluorosilicate is doped or activated with manganese (Mn4+).

[0035] In specific embodiments, the luminescent material may comprise (K,Rb)2SiF6:Mn4+. Alternatively or additionally, in embodiments the third luminescent material may comprise K2SiFe:Mn4+. Alternatively or additionally, in embodiments the third luminescent material may comprise K2TiFe:Mn4+. In embodiments, the third luminescent material may comprise K2(Si,Ti)Fe:Mn4+. As can be derived from the above, “Si,Ti” may indicate one or more of Si and Ti.

[0036] In embodiments, the first green phosphor has a first concentration (Cl) in the first encapsulant and the second green phosphor has a second concentration (C2) in the second encapsulant which may be different from the first concentration (Cl) e.g. C2 may be lower than Cl. In embodiments, the first red phosphor has a third concentration (C3) in the first encapsulant and the second red phosphor has a fourth concentration (C4) in the second encapsulant which may be different from the third concentration (C3) e.g. C4 may be lower than C3.

[0037] The concentration can be expressed in volume percent (v / v%) or weight precent (w / w%).

[0038] In a further aspect, there is provided a lighting arrangement comprising at least one LED filament as summarized above and a controller configured to control the array of the plurality of LEDs. In yet a further aspect, there is provided a lamp or a luminaire comprising at least one LED filament as summarized above or the at least one lighting arrangement as summarized above. These further aspects provide the same effects and advantages as summarized above.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0040] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

[0041] Fig. la schematically illustrates a top view of a LED filament,

[0042] Fig. lb schematically illustrates a side view of the LED filament illustrated in figure la,

[0043] Fig. 1c schematically illustrates a cross-sectional view of the LED filament illustrated in figure la and figure lb,

[0044] Fig. 2a illustrates an emission spectra of a first green phosphor,

[0045] Fig. 2b illustrates an absorption spectra of a second green phosphor,

[0046] Fig. 3 schematically illustrates a lighting arrangement, and

[0047] Fig. 4 schematically illustrates a luminaire.

[0048] DETAILED DESCRIPTION

[0049] As illustrated in figures la-c and with reference to figures 2a and 2b, an embodiment of a LED filament 100 that is arranged to provide LED filament light comprises an array of a plurality of LEDs 101 arranged on a first maj or surface 111 of an elongated light-transmissive carrier 102. The plurality of LEDs 101 are arranged to emit LED light having an emission peak wavelength in a wavelength range from 430nm to 490nm. A first encapsulant 103 covers the array of the plurality of LEDs 101 and covers at least part of the first major surface 111 of the carrier 102. A second encapsulant 104 covers at least part of a second major surface 112, opposite to the first major surface 111, of the carrier 102.

[0050] The first encapsulant 103 comprises a first luminescent material comprising a first green phosphor of a first phosphor type. This first green phosphor is arranged to convert at least part of the LED light into first green phosphor light having a first (dominant) emission peak wavelength, XL The second encapsulant 104 comprises a second luminescent material comprising a second green phosphor of a second phosphor type that is different from the first green phosphor type. This second green phosphor is arranged to convert at least part of the LED light into second green phosphor light having a second (dominant) emission peak wavelength, X2, being different than XL

[0051] An emission spectrum 201 of the first green phosphor at least partly overlaps an excitation spectrum 203 of the second green phosphor. This is illustrated in figures 2a and 2b by an overlap wavelength interval 202. More specifically, as depicted in Fig.2a, four different emission spectra of four different green phosphors are shown. The four different green phosphors have different (dominant) emission peak wavelength. There is a maximum difference in emission between the phosphor showing the leftmost emission spectrum and the other spectra of the other phosphors. With reference also to figure 2b, there is also a difference between these phosphors with respect to their absorption. Part of the emission spectrum of a first phosphor 201 has the overlap wavelength interval 202 with the absorption / excitation spectrum of a second phosphor 203. This results in re-absorption of light thus decreasing the efficiency of the LED filament light.

[0052] For example,

[0053] The first green phosphor may be a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm, and the second green phosphor may be a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm.

[0054] The first green phosphor may be a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm, and the second green phosphor may be a narrowband phosphor having an emission peak with a full-width-half-maximum of less than 40 nm.

[0055] The first green phosphor may be a narrowband phosphor having an emission peak with a full-width-half-maximum of less than 40 nm, and the second green phosphor may be a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm. The first green phosphor may be a garnet class phosphor. The second green phosphor may be a garnet class phosphor.

[0056] Both of the first green phosphor and the second green phosphor may comprise one or more of: LuAG, LuYAG, YAG, or YGdAG.

[0057] The first green phosphor may comprise LuAG. The second green phosphor may comprise YAG.

[0058] The first luminescent material may comprise a first red phosphor arranged to convert at least part of said LED light and / or at least part of the first green phosphor light into first red phosphor light. The second luminescent material may comprise a second red phosphor arranged to convert at least part of said LED light and / or at least part of the second green phosphor light into second red phosphor light.

[0059] The first red phosphor may be selected from the Mn-activated narrow-band class red phosphors. The second red phosphor may be selected from the Mn-activated narrow-band class red phosphors.

[0060] The first red phosphor may be a KSiF phosphor. The second red phosphor may be a KSiF phosphor.

[0061] The first red phosphor and the second red phosphor may be different.

[0062] The first red phosphor may be a Nitride class phosphor and / or an Oxynitride class phosphor. The second red phosphor may be a Nitride class phosphor and / or an Oxynitride class phosphor.

[0063] Turning now to figure 3, and with continued reference to figures la-c, a lighting arrangement 300 comprises at least one LED filament 100 and a controller 302 configured to control the array of the plurality of LEDs 101 of the LED filament 100. The controller 302 is configured to be connected to a power supply and thereby control the at least one LED filament 100 to provide LED filament light as described herein.

[0064] A lamp or a luminaire 400, as illustrated in figure 4, may comprise at least one LED filament 100 or at least one lighting arrangement 300 as described herein.

[0065] The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the LED filament 100 may have different shapes, dimensions and / or sizes than those depicted / described.

Claims

CLAIMS:

1. A light emitting diode, LED, filament (100) arranged to provide LED filament light and comprising: an array of a plurality of LEDs (101) arranged on a first major surface (111) of an elongated light-transmissive carrier (102), said plurality of LEDs arranged to emit LED light having an emission peak wavelength in a wavelength range from 430nm to 490nm; a first encapsulant (103) covering said array of said plurality of LEDs (101) and covering at least part of said first major surface (111) of the carrier (102); a second encapsulant (104) covering at least part of a second major surface (112), opposite to said first major surface (111), of the carrier (102); wherein: the first encapsulant (103) comprises a first luminescent material comprising a first green phosphor of a first phosphor type, said first green phosphor is arranged to convert at least part of said LED light into first green phosphor light having a first emission peak wavelength, I; the second encapsulant (104) comprises a second luminescent material comprising a second green phosphor of a second phosphor type that is different from the first green phosphor type, said second green phosphor being arranged to convert at least part of said LED light into second green phosphor light having a second emission peak wavelength, X2, being different from XI; and an emission spectrum (201) of the first green phosphor at least partly overlaps an excitation spectrum (203) of the second phosphor; and wherein: I X2 - XI I > 20nm.

2. The LED filament (100) of claim 1, wherein:(i) - the first luminescent material further comprises the second green phosphor, wherein the concentration of the first green phosphor in the first encapsulant is at least two times higher than the concentration of the second green phosphor in the first encapsulant,- the second luminescent material further comprises the first green phosphor, the concentration of the second green phosphor in the second encapsulant is at least two times higher than the concentration of the first green phosphor in the second encapsulant, or,(ii) the first encapsulant does not comprise a second green phosphor and the second encapsulant does not comprise a first green phosphor.

3. The LED filament (100) of any of claims 1 to 2, wherein: the first green phosphor is a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm and the second green phosphor is a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm, or the first green phosphor is a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm and the second green phosphor is a narrowband phosphor having an emission peak with a full-width-half-maximum of less than 40 nm, or the first green phosphor is a narrowband phosphor having an emission peak with a full-width-half-maximum of less than 40 nm and the second green phosphor is a broadband phosphor having an emission peak with a full-width-half-maximum of at least 70 nm.

4. The LED filament (100) of any of claims 1 to 3, wherein: the first green phosphor is a garnet class phosphor, and the second green phosphor is a garnet class phosphor.

5. The LED filament (100) of any of claims 1 to 4, wherein: both of the first green phosphor and the second green phosphor comprises one or more of:- LuAG,- LuYAG,- YAG, or- YGdAG.

6. The LED filament (100) of any of claims 1 to 5, wherein:XI is at least 20 nm larger than X2.

7. The LED filament (100) of any of claims 1 to 6, wherein: the first luminescent material further comprises a first red phosphor arrangedto convert at least part of said LED light and / or at least part of the first green phosphor light into first red phosphor light, and / or the second luminescent material further comprises a second red phosphor arranged to convert at least part of said LED light and / or at least part of the second green phosphor light into second red phosphor light.

8. The LED filament (100) of claim 7, wherein: the first red phosphor and / or the second red phosphor are selected from the Mn-activated narrow-band class red phosphors.

9. The LED filament (100) of claim 7 or 8, wherein: the first red phosphor and / or the second red phosphor is a KSiF phosphor.

10. The LED filament (100) of claim 7 to 9, wherein: the first red phosphor and the second red phosphor are different.

11. The LED filament (100) of claim 7 to 10, wherein: the first red phosphor is a Mn-activated narrow-band class red phosphors; and the second red phosphor is a Nitride class phosphor and / or an Oxynitride class phosphor.

12. The LED filament (100) according to any one of the preceding claims, wherein the LED filament light is white light having a correlated color temperature in a range from 1700K to 6500K and a color rendering index of at least 80.

13. The LED filament (100) according to any one of the preceding claims, wherein the first green phosphor has a first concentration (Cl) in the first encapsulant (103) and the second green has a second concentration (C2) in the second encapsulant (104) different from the first concentration (Cl).

14. A lighting arrangement (300) comprising at least one LED filament (100) of any of claims 1 to 13 and a controller (302) configured to control the array of the plurality of LEDs (101).

15. A lamp or a luminaire (400) comprising at least one LED filament (100) according to any one of claims 1 to 13 or the at least one lighting arrangement (300) of claim

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