LED filament providing a soft light

Abstract

The present invention relates to a light emitting diode, LED, filament (100) configured to, in an on-state of the LED filament, emit LED filament light. The LED filament (100) comprises an elongated carrier (101) comprising a first major surface (101´) and a second major surface (101´´) opposite to the first major surface (101´), and an array of a plurality of LEDs (102) arranged on the first major surface of the elongated carrier (101), wherein each LED (102) of the plurality of LEDs is configured to, in the on-state, emit LED light. The LED filament (100) further comprises a first elongated encapsulant (104) at least partly enclosing the plurality of LEDs and at least partly covering the first major surface (101´), the first elongated encapsulant (104) comprising a first luminescent material comprising first green-yellow luminescent particles (104´) and configured to convert at least part of the LED light into first green-yellow converted light, and a second elongated encapsulant (105) enclosing the first elongated encapsulant (104), the second elongated encapsulant (105) comprising a second luminescent material configured to, in the on-state, at least partly convert the LED light and / or part of the first green-yellow converted light into a second orange-red converted light, wherein the second luminescent material comprises first orange-red luminescent particles (105´), and wherein the second elongated encapsulant further comprises first white pigment particles (105´´). The LED filament light at least comprises the first green-yellow converted light and the second orange-red converted light. 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 70. The second elongated encapsulant (105) has, in an off-state of the LED filament, a terracotta appearance.

Description

[0001] LED filament providing a soft light

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to a LED filament providing a soft light in an on-state while having a terracotta appearance in an off-state.

[0004] BACKGROUND OF THE INVENTION

[0005] The use of phosphor-based luminescent LED filaments is continuing to attract attention. In particular, such luminescent LED filaments may be incorporated in lighting devices due to its high energy and cost efficiency, and because they have shown to be useful in many applications. The LED filament comprises an array of light emitting diodes arranged on a carrier. The LED filament is often encapsulated by a phosphor-based luminescent encapsulant which converts the light emitted by the LEDs to a certain desired light. In such an embodiment, the desired light directed to the user is chosen after parameters such as color temperature and brightness, and often has a terracotta colored appearance. The reason for this is that terracotta colored lamps are both energy-efficient and appreciated by the user because it provides a color that is perceived as intimate and cozy.

[0006] However, a problem often perceived in relation to LED filaments used in lighting devices is that the phosphor color can be seen by the user at certain distances from the LED filament. In particular, the user may observe the phosphor color of the LED filament and thus the illuminating light might not be perceived as homogeneous. Rather, the illuminating light may in some cases be perceived as inhomogeneous light or dots originating from the individual light sources, which is truly the individual LEDs arranged in the LED filament.

[0007] In embodiment known in the art red-orange and green-yellow phosphor is used, especially in the dispensed encapsulant enclosing the lighting device to diffuse the LED light emitted from the LED filaments. Typically, the top and bottom dispensed elongated encapsulants have a different phosphor composition and concentration. In the known art, the top encapsulant usually comprises a stack of top encapsulant layers, wherein a green-yellow phosphor is typically dispersed in the outer top encapsulant layer while an orange-red phosphor is typically dispersed in the inner top encapsulant layer. In the known art, a particular drawback arise since manufacturing dispensed elongated encapsulants as described above is both costly and requires complex manufacturing processes. Further, another drawback of such dispensed elongated encapsulants is that they are not energy efficient.

[0008] Considering the above, there is a need to provide a LED filament providing a soft light with improved homogeneity of the light emitted by the LED filament, while being energy and cost efficient.

[0009] US 2019 / 280168 discloses an optoelectronic component and a lighting apparatus.. In an embodiment an optoelectronic component includes a carrier having an upper side and an underside opposite the upper side, an optoelectronic semiconductor chip arranged on the upper side of the carrier, the semiconductor chip configured to emit primary radiation during operation via one or more sides. The component further includes a first conversion layer having an inorganic phosphor on the semiconductor chip, the first conversion layer covering at least all radiation-emitting sides of the semiconductor chip not facing the carrier and a solid body in which an organic phosphor is distributed.

[0010] US 11674644 provides a LED filament lamp which comprises a LED filament with a light transmissive, elongated substrate . The substrate has a first main surface at a first side (105) and a second main surface at a second side (106') opposite to the first side. A plurality of LEDs is mounted only onto the first main surface and configured to emit LED light . An encapsulant covers the plurality of LEDs and at least part of said first main surface. The LED filament by a specific distribution of beam modifying material, comprises at least a luminescent material provided in the encapsulant, and is configured to emit first LED filament light in a first main direction away from the first main surface and having a first color point xl,yl, and to emit second LED filament light in a second main direction away from the second main surface having a second color point x2,y2. The first main direction is opposite to the second main direction, and, wherein (i) |xl-x2| greater than or equal to 0.05 and / or (ii) |y 1 -y2| greater than or equal to 0.05 applies.

[0011] SUMMARY OF THE INVENTION

[0012] The object of the present invention is thus to solve at least the above-identified problems. To this end, the present invention provides a light-emitting diode (LED) filament configured to, in an on-state of the LED filament, emit LED filament light. The LED filament comprises an elongated carrier. The term “elongated” is in the context of the present invention intended to mean having an extension in one direction being significantly greater than extension in any other direction. The elongated carrier comprises a first major surface and a second major surface opposite to the first major surface. The elongated carrier may have a flat surface, or may have other geometrical shapes such as a round surface, or an ellipsoid surface, or a diamond shaped surface.

[0013] The first major surface and the second major surface face opposite directions such that there is an angle 180° between each of the directions of the first major surface and the second major surface.

[0014] An array of a plurality of LEDs is arranged on the first major surface of the elongated carrier such that the plurality of LEDs is carried by the elongated carrier. Alternatively, or additionally, the LEDs my be arranged in the carrier. Each LED of the plurality of LEDs is configured to, in the on-state, emit LED light. The elongated carrier may further be a transparent carrier. In such an embodiment, the LED light emitted by the plurality of LEDs may be emitted in all directions, such that the light emission profile of each LED of the plurality of LEDs is spherical. Further, the joint emission profile of the LED filament may also be spherical.

[0015] The LED filament according to the present invention further comprises a first elongated encapsulant at least partly enclosing the plurality of LEDs and at least partly covering the first major surface. In other words, the first major surface may be fully encapsulated by the first elongated encapsulant. Alternatively, a part of the first major surface may be encapsulated by the first elongated encapsulant and another part of the first major surface may be free from the first elongated encapsulant. If the first major surface is fully encapsulated by the first elongated encapsulant, it implies that all of the LEDs of the plurality of LEDs are encapsulated by the first elongated encapsulant. If the first major surface is not fully encapsulated by the first elongated encapsulant, it may imply that a part the LEDs of the plurality of LEDs is free from the first elongated encapsulant.

[0016] The first elongated encapsulant comprises a first luminescent material comprising first green-yellow luminescent particles and configured to, in the on-state, convert at least part of the LED light into a first green-yellow converted light. Put differently, all of the LED light diffusing through the first elongated encapsulant may be converted by the first luminescent material into a first green-yellow converted light. Alternatively, a part of the LED light diffusing through the first elongated encapsulant will be converted by the first luminescent material into first green-yellow converted light, while a second part of the LED light diffusing through the first elongated encapsulant may not be converted into first greenyellow converted light. The LED filament according to the present invention further comprises a second elongated encapsulant enclosing the first elongated encapsulant. The second elongated encapsulant may also fully encapsulate the first major surface.

[0017] The second elongated encapsulant comprises a second luminescent material, wherein the second luminescent material may comprise second green-yellow luminescent particles. The second luminescent material comprises first orange-red luminescent particles and the second elongated encapsulant comprises first white pigment particles. The second luminescent material is configured to, in the on-state, at least partly convert the LED light and / or part of the first green-yellow converted light into a second orange-red converted light. Put differently, a part of the LED light diffusing through the second elongated encapsulant will be converted into a second orange-red converted light, while a second part of the LED light diffusing through the second elongated encapsulant may not be converted into a second orange-red converted light. Further, a part of the first green-yellow converted light diffusing through the second elongated encapsulant will be converted into a second orange-red converted light, while a second part of the first green-yellow converted light may not be converted into a second orange-red converted light. In such an embodiment, the LED filament light comprises LED light, first green-yellow converted light and second orange-red converted light.

[0018] As mentioned above, the second luminescent material may comprise second green-yellow luminescent particles. In such an embodiment, at least a part of the LED light diffusing through the second elongated encapsulant may be converted by the second luminescent material into second green-yellow converted light. The concentration of the second green-yellow luminescent particles in the second elongated encapsulant may be (much) lower than the concentration of the first green-yellow luminescent particles in the first elongated encapsulant, e.g. at least 0.5 times lower or at least 0.1 times lower. Because the sufficient green light in the white LED filament is needed, the (major) contribution to the green light in the LED filament light is established by the first green-yellow luminescent particles. Put differently, a higher ratio of the LED light passing through the first elongated encapsulant may be converted into first green-yellow converted light compared to a ratio of LED light passing through the second elongated encapsulant being converted to second green-yellow converted light. The second green-yellow luminescent particles may further finetune the terracotta (coloured) appearance of the LED filament, especially when provided in a relative low concentration. In an embodiment, the second elongated encapsulant and / or the third elongated encapsulant only comprises orange-red luminescent particles and green-yellow luminescent particles as luminescent material. Such a composition further improves the terracotta (coloured) appearance of the LED filament.

[0019] Further, the LED filament light emitted by the LED filament of the present invention at least comprises the first green-yellow converted light, and the second orange-red converted light, and optionally further comprises part of the LED light (that is not converted and e.g. transmitted through the first and second elongated encapsulants). The LED filament light is white light having a correlated color temperature in a range from 1700K to 6500K (or in a range from 1700K to 3000K) and a color rendering index of at least 70, preferably at least 80, even more preferably at least 85.

[0020] The second elongated encapsulant has, in an off-state of the LED filament, a terracotta (colored) appearance. The terracotta (colored) appearance is obtained by a combination of the first orange-red luminescent particles and the first white pigment particles. The terracotta (colored) appearance of (the second elongated encapsulant of) LED filament is appreciated by the user because it provides an intimate / cosy atmosphere and / or gives an energy-saving impression.

[0021] The terracotta (coloured) appearance may be defined by a colour code range HEX #B35642 / RGB (179, 86, x), wherein x may be an integer having a value from 60 to 70.

[0022] The first luminescent material may further comprise third orange-red luminescent particles. The first luminescent material may thus be configured to, in the on- state, convert at least part of the LED light into a third orange-red converted light. Put differently, a part of the LED light passing through the first luminescent material will be converted into a third orange-red converted light, while a second part of the LED light passing through the first luminescent material may not be converted into a third orange-red converted light. The obtained effect is that the light properties of the LED filament light e.g. color point, CCT and / or CRI are further improved.

[0023] The first luminescent material may be any of an inorganic luminescent material, quantum dots, quantum rods, an organic luminescent material or a combination of two or more of these luminescent materials. The first luminescent material may also comprise other types of luminescent material.

[0024] The second luminescent material may further comprise green-yellow luminescent particles. The second luminescent material may thus be configured to, in the on- state, at least partly convert the LED light diffusing through the second luminescent material into a second green-yellow converted light. Put differently, a part of the LED light diffusing through the second elongated encapsulant will be converted into second green-yellow converted light, while a second part of the LED light diffusing through the second elongated encapsulant may not be converted into second green-yellow converted light.

[0025] The second luminescent material may be any of an inorganic luminescent material, quantum dots, quantum rods, an organic luminescent material or a combination of two or more of these luminescent materials. The second luminescent material may also comprise other types of luminescent material is not excluded.

[0026] The LED filament may further comprise a third elongated encapsulant covering at least a part of the second major surface. The third elongated encapsulant comprises a third luminescent material comprising second orange-red luminescent particles and the third encapsulant further comprises second white pigment particles. The third luminescent material is configured to, in the on-state, at least partly convert the LED light and / or part of the first green-yellow converted light into a fourth orange-red converted light. In other words, a part of the LED light diffusing through the third elongated encapsulant may be converted into a fourth orange-red converted light, while a second part of the LED light diffusing through the third elongated encapsulant may not be converted into a fourth orange- red converted light. Further, a part of the first green-yellow converted light diffusing through the third elongated encapsulant may be converted into a third green-yellow converted light, while a second part of the first green-yellow converted light diffusing through the third elongated encapsulant may not be converted into a third green-yellow converted light.

[0027] The third elongated encapsulant has, in an off-state of the LED filament, a terracotta (colored) appearance. The terracotta (colored) appearance is obtained by a combination of the second orange-red luminescent particles and the second white pigment particles. The terracotta (colored) appearance of (the third elongated encapsulant of) LED filament is further improved.

[0028] The terracotta (coloured) appearance may be defined by a colour code range HEX #B35642 / RGB (179, 86, x), wherein x is an integer having a value from 60 to 70.

[0029] The third luminescent material may be any of an inorganic luminescent material, quantum dots, quantum rods, an organic luminescent material or a combination of two or more of these luminescent materials. Further, the third luminescent material may also comprise other types of luminescent material. The first and / or second white pigment particles may comprise one or more of titanium dioxide (TiCE) particles, aluminium oxide (AI2O3) particles, barium sulphate (BaSCU) particles, and zirconium oxide (ZrCE) particles. However, it shall not be excluded that the white pigment particles may comprise other white particles. These white pigment particles have a relatively high reflectivity (for highly efficient LED filament light) and combined with the first orange-red luminescent particles provide a terracotta (color) appearance.

[0030] In the LED filament of the present invention, the concentration of the first orange-red luminescent particles in the second luminescent material may be higher than the concentration of the third orange-red luminescent particles in the first elongated encapsulant, e.g. at least two or at least three times higher. The higher concentration is needed for the terracotta (coloured) appearance, but the third orange-red luminescent particles in the first elongated encapsulant is needed to further improve the light quality of the LED filament light e.g. in terms of color point, CCT and or CRI. In other words, a higher ratio of the LED light diffusing through the second elongated encapsulant may be converted into second orange-red converted light compared to a ratio of LED light diffusing through the first elongated encapsulant being converted to third orange-red converted light.

[0031] The first luminescent material may comprise no third orange-red luminescent particles or at least less than 1% third orange-red particles relative to all particles in the first luminescent material.

[0032] The first elongated encapsulant may comprise no white pigment particles or at least less than 1 % white pigment particles relative to all particles in the first elongated encapsulant. In another embodiment the first elongated encapsulant may comprise up to 5 % white pigment particles relative to all particles in the first elongated. Each of the first elongated encapsulant, the second encapsulant, and the third encapsulant may further each comprise a first polymer matrix, a second polymer matrix and a third polymer matrix, respectively. In particular, the first elongated encapsulant may comprises a first polymer matrix, the first polymer matrix comprising a first cross-linked silicone polymer e.g. crosslinked PDMS, PMPS and / or PDPS; the second encapsulant may comprises a second polymer matrix, the second polymer matrix comprising a second cross-linked silicone polymer e.g. crosslinked PDMS, PMPS and / or PDPS; and if applicable, the third encapsulant may comprises a third polymer matrix, the third polymer matrix comprising a third crosslinked silicone polymer e.g. crosslinked PDMS, PMPS and / or PDPS. These materials have a high light transmission, a low light absorption and are very stable e.g. less browning during lifetime of the LED filament.

[0033] The first, second and third polymer matrices may comprise the same crosslinked polymer or different cross-linked polymers. The cross-linked polymers may be inorganic polymers or organic polymers. The cross-linked polymers provide physical properties such as strength, flexibility and light absorbance to the first, second and third encapsulants.

[0034] The first, second and third cross-linked silicone polymers may have the same chemical composition of cross-linked polymers or a different chemical composition of crosslinked polymers or a combination thereof. In other words, two of the first, second and third cross-linked polymers have the same chemical composition of cross-linked polymers and a third of the first, second and cross-linked polymers have a different chemical composition of cross-linked polymers.

[0035] The LED filament of the present invention may further comprise a fourth encapsulant arranged between the third elongated encapsulant and the second major surface. The fourth encapsulant may at least partly cover the second major surface. In other words, the second major surface may be fully encapsulated by the fourth encapsulant. Alternatively, a part of the second major surface may be encapsulated by the fourth encapsulant and a second part of the second major surface may be free from the fourth encapsulant.

[0036] The fourth encapsulant comprises a fourth luminescent material configured to, in the on-state, convert at least part of the LED light into a fourth green-yellow converted light. In other words, all of the LED light diffusing through the fourth encapsulant may be converted into a fourth green-yellow converted light. Alternatively, a part of the LED light diffusing through the fourth encapsulant will be converted into a fourth green-yellow converted light, while a second part of the LED light diffusing through the fourth luminescent material may not be converted into a fourth green-yellow converted light.

[0037] The first elongated encapsulant may comprise a first elongated encapsulant layer and a second encapsulant layer, wherein the first elongated encapsulant layer is arranged in contact with the first elongated encapsulant, and the second encapsulant layer is arranged in contact with the first elongated encapsulant layer. Further in such an embodiment, the first elongated encapsulant layer and the second encapsulant layer may comprise different luminescent materials. For example, the first elongated encapsulant layer may comprise a luminescent material comprising orange-red phosphor particles only, and the second encapsulant layer may comprise a luminescent material comprising green-yellow phosphor particles only. However, the first and second encapsulant layer may also comprise other luminescent materials.

[0038] In the present invention, the LED light emitted by the LEDs of the plurality of LEDs, the green-yellow converted light and the orange-red converted light may each have certain wavelengths. The LED light may be a blue light having a peak emission wavelength in the range of 430-490 nm. The green-yellow converted light may have a peak emission wavelength in the range of 500-590 nm. The orange-red converted light may have a peak emission wavelength in the range of 600-690 nm.

[0039] The first and / or the fourth luminescent material may comprise a luminescent material of the type AsBsOn Ce. A may comprise one or more of Lu, Y, La, Gd, Tb. B may comprise one or more of Al, Ga, In and Sc.

[0040] The Luminescent material of the type AsBsOn Ce, 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)3B50i2: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 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.

[0041] The second and / or the third luminescent material may comprise a luminescent material of the type nitrides, oxynitrides and / or M’xM2-2xAX6 doped with tetravalent manganese. M’ may comprise an alkaline earth cation. M may comprise an alkaline cation, x is in the range of 0-1. A may comprise a tetravalent cation, for instance comprising one or more of silicon and titanium. X may comprise a monovalent anion, at least comprising fluorine.

[0042] Luminescent material of the type M’xM2-2xAX6 doped with tetraval ent 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 tetravalent cation, for instance comprising one or more of silicon and titanium, wherein X comprises a monovalent anion, at least comprising fluorine.

[0043] 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’XM2- 2xAXe luminescent material has the hexagonal phase. In yet another embodiment, the M’XM2- 2xAXe luminescent material has the cubic phase. For x=0, the composition is M2AX6.

[0044] Relevant alkaline earth cations (M’) are magnesium (Mg), strontium (Sr), calcium (Ca) and barium (Ba), especially one or more of Sr and Ba.

[0045] 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.

[0046] As indicated above, X relates to a monovalent anion, but at least comprises fluorine. Other monovalent anions that may optionally be present may be selected from the group consisting of chlorine (Cl), bromine (Br), and iodine (I). In an embodiment, M’xM2-2xAX6 comprises K^SiFe (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-mMnmF6, 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+).

[0047] In specific embodiments, the luminescent material may comprise (K,Rb)2SiFe: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.

[0048] The luminescent material comprising NfcSis Eu2, or MAlSiXvEu2or 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 CaAlSi 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 NESis 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.sSis Eu (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 MAlSi 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.

[0049] The first, second and third orange-red luminescent particles may have the same chemical composition or different chemical compositions or a combination thereof. In other words, two of the first, second and third orange-red luminescent particles may have the same chemical composition and a third of the first, second and third orange-red luminescent particles material have a different chemical composition.

[0050] The first, second and third green-yellow luminescent particles may have the same chemical composition or a different chemical composition or a combination thereof. In other words, two of the first, second and third green-yellow luminescent particles may have the same chemical composition and a third of the first, second and third green-yellow luminescent particles may have a different chemical composition.

[0051] The first, second and third white pigment particles may have the same chemical composition or a different chemical composition or a combination thereof. In other words, two of the first, second and third white pigment particles may have the same chemical composition and a third of the first, second and third white pigment particles may have a different chemical composition.

[0052] In embodiments, the concentration of the second green-yellow luminescent particles in the second luminescent material less than 0.5 times the concentration of the first orange-red luminescent particles in the second luminescent material. The obtained is an improved terracotta color.

[0053] The concentration of the first white pigment particles in the second elongated encapsulant may be lower than the concentration of the first orange-red luminescent particles in the second luminescent material. The obtained effect is an improved terracotta color.

[0054] The LED filament according to the present invention may comprise electrical circuitry configured to, in operation, provide electrical power to the plurality of LEDs. The LED filament may further comprise connection means for mechanically connecting the LED filament to a connector.

[0055] Finally, the present invention relates to a lamp or a luminaire comprising a LED filament described above. The lamp may comprise at least one of an envelope at least partly enclosing the LED filament, a connector for mechanically and electrically connecting the lamp to a socket or a socket of a luminaire, and the luminaire may comprise a light exit window for exiting the LED filament light.

[0056] It is noted that the invention relates to all possible combinations of features recited in the claims. Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following. 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.

[0057] BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Fig. 1 schematically shows a cross-sectional view of a LED filament according to an exemplifying embodiment of the present invention;

[0059] Fig. 2 schematically shows a cross-sectional view of a LED filament according to a second embodiment of the present invention;

[0060] Fig. 3 schematically shows a cross-sectional view of a LED filament according to a third embodiment of the present invention;

[0061] Fig 4 schematically shows a cross-sectional view of a LED filament according to a fourth embodiment of the present invention;

[0062] Fig. 5 schematically shows a lamp comprising a LED filament according to the present invention.

[0063] DETAILED DESCRIPTION

[0064] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Fig. 1 shows an embodiment of the light-emitting diode (LED) filament (100) comprising an elongated carrier 101. The elongated carrier 101 comprises a first major surface 10L and a second major surface 101" opposite to the first major surface 10L. The elongated carrier 101 has a flat surface. The first major surface 10L and the second major surface 101" face opposite directions such that there is an angle 180° between each of the directions of the first major surface 10L and the second major surface 101". An array of a plurality of LEDs 102 is arranged on the first major surface 10L of the elongated carrier 101 such that the plurality of LEDs is carried by the elongated carrier 101. Alternatively, or additionally, the LEDs my be arranged in the carrier. Each LED 102 of the plurality of LEDs is configured to, in the on-state, emit LED light. The elongated carrier 101 is a transparent carrier. Thus, the LED light emitted by the plurality of LEDs 102 is emitted in all directions, such that the light emission profile of each LED 102 of the plurality of LEDs is spherical.

[0065] The LED filament 100 in Fig. 1 comprises a first elongated encapsulant 104 enclosing the plurality of LEDs 102 and covering the first major surface 101 . In other words, the first major surface 101 ' is fully encapsulated by the first elongated encapsulant 104. Since the first major surface 101 ' is fully encapsulated by the first elongated encapsulant 104, it implies that all of the LEDs 102 of the plurality of LEDs are encapsulated by the first elongated encapsulant 104.

[0066] The first elongated encapsulant 104 in Fig. 1 comprises a first luminescent material comprising first green-yellow luminescent particles 104' and configured to, in the on-state, convert at least part of the LED light into a first green-yellow converted light. Put differently, all of the LED light diffusing through the first elongated encapsulant 104 may be converted by the first luminescent material into a first green-yellow converted light. Alternatively, a part of the LED light diffusing through the first elongated encapsulant 104 will be converted by the first luminescent material into first green-yellow converted light, while a second part of the LED light diffusing through the first elongated encapsulant 104 may not be converted into first green-yellow converted light.

[0067] The LED filament 100 in Fig. 1 further comprises a second elongated encapsulant 105 enclosing the first elongated encapsulant 104. The second elongated encapsulant 105 fully encapsulates the first major surface 10L. The second elongated encapsulant 105 comprises a second luminescent material. The second luminescent material comprises first orange-red luminescent particles 105', and the second encapsulant comprises white pigment particles 105". The second luminescent material is configured to, in the on- state, at least partly convert the LED light and / or part of the first green-yellow converted light into a second orange-red converted light . Thus, a part of the LED light diffusing through the second elongated encapsulant 105 will be converted into a second orange-red converted light, while a second part of the LED light diffusing through the second elongated encapsulant 105 may not be converted into a second orange-red converted light. Further, a part of the first green-yellow converted light diffusing through the second elongated encapsulant 105 will be converted into a second orange-red converted light, while a second part of the first greenyellow converted light may not be converted into a second orange-red converted light. The second elongated encapsulant 105 has, in an off-state of the LED filament 100, a terracotta appearance.

[0068] The LED filament 100 shown in Fig. 1 further comprises a third elongated encapsulant 103 covering the second major surface 101". The third elongated encapsulant 103 comprises a third luminescent material comprising fourth orange-red luminescent particles 103' and the third encapsulant comprises third white pigment particles 103". The third luminescent material is configured to, in the on-state, at least partly convert the LED light and / or part of the first green-yellow converted light into a third orange-red converted light. In other words, a part of the LED light diffusing through the third elongated encapsulant 103 will be converted into a third orange-red converted light, while a second part of the LED light diffusing through the third elongated encapsulant 103 may not be converted into a third orange-red converted light. Further, a part of the first green-yellow converted light diffusing through the third elongated encapsulant 103 will be converted into a third green-yellow converted light, while a second part of the first green-yellow converted light diffusing through the third elongated encapsulant 103 may not be converted into a third green-yellow converted light.

[0069] Fig. 2 illustrates another embodiment of the LED filament 200 of the present invention. The LED filament 200 shown in Fig. 2 comprises an array of a plurality of LEDs 202 arranged on the first major surface 20 L of the elongated carrier 201, a first elongated encapsulant 204 comprising a first elongated encapsulant layer 206 and a second encapsulant layer 207, wherein the first elongated encapsulant layer 206 is arranged in contact with the first major surface 201 ', and the second encapsulant layer 207 is arranged in contact with the first elongated encapsulant layer 206 and the second elongated encapsulant 205. Further in such an embodiment, the first elongated encapsulant layer 206 and the second encapsulant layer 207 comprise different luminescent materials. For example, the first elongated encapsulant layer 206 may comprise a luminescent material comprising orange-red phosphor particles 206' only, and the second encapsulant layer 207 may comprise a luminescent material comprising green-yellow phosphor particles 207' only. The LED filament 200 shown in Fig 2 further comprises a third elongated encapsulating 203 covering the second maj or surface 201".

[0070] Fig. 3 shows an embodiment of the light-emitting diode (LED) filament 300 comprising an elongated carrier 301. The elongated carrier 301 comprises a first major surface 30 L and a second major surface 301" opposite to the first major surface 30 L. The elongated carrier 301 has a flat surface. The first major surface 301’ and the second major surface 301" face opposite directions such that there is an angle 180° between each of the directions of the first major surface 30 Land the second major surface 301". An array of a plurality of LEDs 302 is arranged on the first major surface 30L of the elongated carrier 301 such that the plurality of LEDs is carried by the elongated carrier 301. Each LED 302 of the plurality of LEDs is configured to, in the on-state, emit LED light. The elongated carrier 301 is a transparent carrier. Thus, the LED light emitted by the plurality of LEDs 302 is emitted in all directions, such that the light emission profile of each LED 302 of the plurality of LEDs is spherical.

[0071] The LED filament 300 in Fig. 3 comprises a first elongated encapsulant 304 enclosing the plurality of LEDs 302 and covering the first major surface 30 L. In other words, the first major surface 30L is fully encapsulated by the first elongated encapsulant 304. Since the first major surface 30L is fully encapsulated by the first elongated encapsulant 304, it implies that all of the LEDs 302 of the plurality of LEDs are encapsulated by the first elongated encapsulant 304. The LED filament 300 shown in Fig 3 further comprises a third elongated encapsulant 303 covering the second major surface 30L.

[0072] The LED filament 300 in Fig. 3 further comprises a second elongated encapsulant 305 enclosing the first elongated encapsulant 304. The second elongated encapsulant 305 fully encapsulates the first major surface 30L. The second elongated encapsulant 305 comprises a second luminescent material. The second luminescent material comprises second orange-red luminescent particles 305'. The second luminescent material is configured to, in the on-state, at least partly convert the LED light and / or part of the first green-yellow converted light into a second orange-red converted light. Thus, a part of the LED light diffusing through the second elongated encapsulant 305 will be converted into a second orange-red converted light, while a second part of the LED light diffusing through the second elongated encapsulant 305 may not be converted into a second orange-red converted light. Further, a part of the first green-yellow converted light diffusing through the second elongated encapsulant 305 will be converted into a second orange-red converted light, while a second part of the first green-yellow converted light may not be converted into a second orange-red converted light. The second elongated encapsulant 305 has, in an off-state of the LED filament 300, a terracotta appearance.

[0073] The LED filament 300 further comprises a fourth encapsulant 312 arranged between the third elongated encapsulant 303 and the second major surface 301". The fourth encapsulant 312 partly covers the second major surface 301".

[0074] The fourth encapsulant comprises a fourth luminescent material configured to, in the on-state, convert at least part of the LED light into a fourth green-yellow converted light. In other words, all of the LED light diffusing through the fourth encapsulant 312 may be converted into a fourth green-yellow converted light. Alternatively, a part of the LED light diffusing through the fourth encapsulant 312 will be converted into a fourth green-yellow converted light, while a second part of the LED light diffusing through the fourth encapsulant 312 may not be converted into a fourth green-yellow converted light.

[0075] Fig. 4 shows an embodiment of the light-emitting diode (LED) filament 400 comprising an elongated carrier 401. The elongated carrier 401 comprises a first major surface 40 L and a second major surface 401 " opposite to the first major surface 40 L. The elongated carrier 401 has a flat surface. The first major surface 40 L and the second major surface 401" face opposite directions such that there is an angle 180° between each of the directions of the first major surface 40 L and the second major surface 401 ". An array of a plurality of LEDs 402 is arranged on the first major surface 40 L of the elongated carrier 401 such that the plurality of LEDs is carried by the elongated carrier 401. Each LED 402 of the plurality of LEDs is configured to, in the on-state, emit LED light. The elongated carrier 401 is a transparent carrier. Thus, the LED light emitted by the plurality of LEDs 402 is emitted in all directions, such that the light emission profile of each LED 402 of the plurality of LEDs is spherical.

[0076] The LED filament 400 in Fig. 4 comprises a first elongated encapsulant 404 enclosing the plurality of LEDs 402 and covering the first major surface 40 L. In other words, the first major surface 40 L is fully encapsulated by the first elongated encapsulant 404. Since the first major surface 40 L is fully encapsulated by the first elongated encapsulant 404, it implies that all of the LEDs 402 of the plurality of LEDs are encapsulated by the first elongated encapsulant 404.

[0077] The LED filament 400 in Fig. 4 further comprises a second elongated encapsulant 405 enclosing the first elongated encapsulant 404. The second elongated encapsulant 405 fully encapsulates the first major surface 401 '. The second elongated encapsulant 405 has, in an off-state of the LED filament 400, a terracotta appearance.

[0078] The LED filament 400 shown in Fig. 4 further comprises a third elongated encapsulant 403 covering the second major surface 401". Fig. 5 illustrates an exemplifying embodiment of the present invention of the

[0079] LED filament 500, where the LED filament 500 is part of a lamp for illumination.

Claims

CLAIMS:

1. A light emitting diode, LED, filament (100) configured to, in an on-state of the LED filament, emit LED filament light, the LED filament comprising: an elongated carrier (101) comprising a first major surface (10L) and a second major surface (101") opposite to the first major surface (10L), an array of a plurality of LEDs (102) arranged on the first major surface of the elongated carrier (101) or arranged in the carrier, wherein each LED (102) of the plurality of LEDs is configured to, in the on-state, emit LED light, a first elongated encapsulant (104) at least partly enclosing the plurality of LEDs and at least partly covering the first major surface (10L), the first elongated encapsulant (104) comprising a first luminescent material comprising first green-yellow luminescent particles (104') and configured to convert at least part of the LED light into first green-yellow converted light, the first elongated encapsulant further comprising white pigment particles less than 5 % relative to all particles in the first elongated encapsulant and a second elongated encapsulant (105) enclosing the first elongated encapsulant (104), the second elongated encapsulant (105) comprising a second luminescent material configured to, in the on-state, at least partly convert the LED light and / or part of the first green-yellow converted light into a second orange-red converted light, wherein the second luminescent material comprises first orange-red luminescent particles (105'), and wherein the second elongated encapsulant further comprises first white pigment particles (105"), and wherein the LED filament light at least comprises the first green-yellow converted light, the second orange-red converted light; and 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 70; and wherein the second elongated encapsulant (105) has, in an off-state of the LED filament, a terracotta appearance.

2. The LED filament (100) according to claim 1, wherein the first elongated encapsulant is free from white pigment particles or comprises at least less than 1 % white pigment particles relative to all particles in the first elongated encapsulant.

3. A LED filament (100) according to claim 1 or 2, further comprising a third elongated encapsulant (103) covering at least a part of the second major surface (101"), the third elongated encapsulant (103) comprising a third luminescent material configured to, in the on-state, at least partly convert the LED light and / or at least partly convert the first greenyellow converted light into a third orange-red converted light, wherein the third luminescent material comprises second orange-red luminescent particles (103'), and wherein the third elongated encapsulant further comprises second white pigment particles (103"), wherein the third elongated encapsulant (103) has, in the off-state of the LED filament, a terracotta appearance.

4. The LED filament (100) according to any of the preceding claims, wherein the second luminescent material is further configured to, in the on-state, at least partly convert the LED light into a second green-yellow converted light, wherein the second luminescent material further comprises second green-yellow luminescent particles (110).

5. The LED filament (100) according to any of the preceding claims, wherein the first luminescent material is further configured to, in the on-state, convert at least part of the LED light into a first orange-red converted light, and wherein the first luminescent material comprises third orange-red luminescent particles (111).

6. The LED filament (100) according to any one of the preceding claims, wherein the first and / or second white pigment particles (105", 103") comprise one or more of titanium dioxide (TiCL) particles, aluminium oxide (AI2O3) particles, barium sulphate (BaSCU) particles, and zirconium oxide (ZrCL) particles.

7. The LED filament (100) according to any one of claims 5-6, wherein the concentration of the first orange-red luminescent particles (105') in the second luminescent material is higher than the concentration of the third orange-red luminescent particles (111) in the first luminescent material.

8. The LED filament (100) according to any one of claims 4-7, wherein the concentration of the second green-yellow luminescent particles (110) in the secondluminescent material is lower than the concentration of the first green-yellow luminescent particles (104') in the first luminescent material.

9. The LED filament (100) according to any of the preceding claims, wherein one or more of the following applies: the first elongated encapsulant (104) comprises a first polymer matrix, the first polymer matrix comprises a first cross-linked silicone polymer; the second encapsulant (105) comprises a second polymer matrix, the second polymer matrix comprises a second cross-linked silicone polymer; and if applicable the third encapsulant (103) comprises a third polymer matrix, the third polymer matrix comprises a third cross-linked silicone polymer.

10. The LED filament (300) according to any one of claims 3-9, further comprising a fourth encapsulant (312) at least partly covering the second major surface (301"), the fourth encapsulant (312) comprising a fourth luminescent material configured to, in the on-state, convert at least part of the LED light into a fourth green-yellow converted light, and wherein the fourth encapsulant is arranged between the third elongated encapsulant (303) and the second major surface (301").

11. The LED filament (100) according to any of the preceding claims, wherein the LED light is blue light having a peak emission wavelength in the range of 430-490 nm, where the at least one of the green-yellow converted lights has a peak emission wavelength in the range of 500-590 nm, and wherein at least one of the orange-red converted lights has a peak emission wavelength in the range of 600-690 nm.

12. The LED filament (100) according to any of the preceding claims, wherein one or more of the green-yellow luminescent particles comprises a luminescent material of the type AsBsO Ce, wherein A comprises one or more of Lu, Y, La, Gd, Tb, and wherein B comprises one or more of Al, Ga, In and Sc, and wherein one or more of the orange-red luminescent particles comprises a luminescent material of the type nitrides, oxynitrides and / or 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 tetravalent cation, for instance comprising one or more of silicon and titanium, wherein X comprises a monovalent anion, at least comprising fluorine.

13. The LED filament (100) according to any one of the claims 4-12, wherein the concentration of the second green-yellow luminescent particles in the second luminescent material (105) is less than 0.5 times the concentration of the first orange-red luminescent particles in the second luminescent material (105).

14. The LED filament (100) according to any one of the preceding claims, wherein the concentration of the first white pigment particles in the second elongated encapsulant (105) is lower than the concentration of the first orange-red luminescent particles in the second luminescent material (105).

15. The LED filament (100) according to any of the preceding claims, wherein the terracotta appearance is defined by a colour code range HEX #B35642 / RGB (179, 86, x), wherein x is an integer having a value from 60 to 70.

16. A lamp or a luminaire comprising a LED filament (100) according to any of the preceding claims.

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