A LED filament arrangement

Abstract

A light emitting diode, LED, filament (1) configured to, in an on-state, emit LED filament light (2) and comprising an elongated carrier (3), an array of a plurality of LEDs (4) configured to, in an on-state, emit LED light (41) and being arranged on a first major surface (31) of the elongated carrier (3), a first elongated encapsulant (5) enclosing the plurality of LEDs (4), covering the first major surface (31), and comprising a first luminescent material (51), a second elongated encapsulant (6) enclosing the first elongated encapsulant (5) and comprising a second luminescent material (61), a third elongated encapsulant (7) covering a second major surface (32) of the elongated carrier (3) and comprising a third luminescent material (71). The second luminescent material (61) has a green color and is configured to convert LED light into first green converted light (62). The third luminescent material (71) has a green color and is configured to convert LED light and / or first green converted light (62) into second green converted light (72). The first luminescent material (51) has an orange-red color and is configured to convert one or more of the LED light, the first green converted light and the second green converted light into first orange-red converted light (52).

Description

[0001] A LED filament arrangement

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a light emitting diode, LED, filament configured to, in operation, emit LED filament light. The invention further relates to a lamp and a luminaire comprising such a LED filament.

[0004] As used herein, the term “blue light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 430 nm to 500 nm.

[0005] As used herein, the term “green light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 500 nm to 550 nm.

[0006] As used herein, the term “yellow light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 550 nm to 570 nm.

[0007] As used herein, the term “orange light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 570 nm to 600 nm.

[0008] As used herein, the term “red light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 600 to 680 nm.

[0009] BACKGROUND OF THE INVENTION

[0010] A trend in lighting is LED filament lamps. An LED filament lamp is an LED lamp which is designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes, but with the high efficiency of lightemitting diodes.

[0011] A LED filament is providing LED filament light and comprises a plurality of light emitting diodes (LEDs) arranged in a linear array. Preferably, the LED filament has a length L and a width W, wherein L > 5W. The LED filament may be arranged in a straight configuration or in a non-straight configuration such as for example a curved configuration, a 2D / 3D spiral, or a helix. Preferably, the LEDs are arranged on an elongated carrier like for instance a carrier, that may be rigid (made from, e.g., a polymer, glass, quartz, metal, or sapphire) or flexible (e.g., made of a polymer or metal, e.g., a film or foil). In case the elongated carrier comprises a first major surface and an opposite second major surface, the LEDs are arranged on at least one of these surfaces. The elongated carrier may be reflective or light transmissive, such as translucent and preferably transparent.

[0012] As used herein, the terms carrier and elongated carrier may be used interchangeably, such that the elongated carrier may also simply be denoted carrier.

[0013] The LED filament may comprise an encapsulant at least partly covering at least part of the plurality of LEDs. The encapsulant may also at least partly cover at least one of the first major surface and second major surface. The encapsulant may be a polymer material which may be flexible such as for example a silicone. Further, the LEDs may be arranged for emitting LED light, e.g., of different colors or spectrums. The encapsulant may comprise a luminescent material that is configured to convert at least a part of the LED light into converted light. The luminescent material may be a phosphor such as an inorganic phosphor and / or quantum dots or rods (QDs). The term ‘luminescent material’ may also refer to a combination of two or more luminescent materials.

[0014] The LED filament may comprise multiple sub-filaments.

[0015] US 2020 / 0058835 Al discloses an LED filament which includes a carrier, a plurality of LEDs, an underlying layer exhibiting a first appearance at a first temperature, and an over-coated layer comprising a thermochromic material that exhibits at the first temperature, a preselected appearance other than the first appearance, and at a second temperature, a transparent or translucent appearance. Both layers enclose the plurality of LEDs and both sides of the carrier.

[0016] It is desired to improve the optical performance (such as light quality and correlated color temperature, CCT, control and so forth) and / or the appearance (such as light mixing) of LED filaments.

[0017] SUMMARY OF THE INVENTION

[0018] It is an object of the present invention to overcome this problem, and to provide a LED filament which comprise an improved optical performance and / or an improved optical appearance.

[0019] It is a further object of the invention to provide a LED filament with one or more of an improved light quality, an improved CCT control and an improved light mixing.

[0020] According to a first aspect of the invention, this and other objects are achieved by means of a light emitting diode, LED, filament configured to, in an on-state, emit LED filament light, the LED filament comprising an elongated carrier comprising a first major surface and a second major surface opposite to the first major surface, an array of a plurality of LEDs configured to, in an on-state, emit LED light and being arranged on the first major surface of the elongated carrier, a first elongated encapsulant at least partly enclosing the plurality of LEDs and at least partly covering the first major surface, the first elongated encapsulant comprising a first luminescent material, a second elongated encapsulant enclosing the first elongated encapsulant, the second elongated encapsulant comprising a second luminescent material, a third elongated encapsulant covering at least a part of the second major surface, the third elongated encapsulant comprising a third luminescent material, where the second luminescent material has a green color and is configured to, at least partly, convert the LED light into first green converted light, where the third luminescent material has a green color and is configured to, at least partly, convert the LED light and / or first green converted light into second green converted light, where the first luminescent material is configured to, at least partly, convert one or more of the LED light, the first green converted light and the second green converted light into first orange-red converted light, where the LED filament light at least comprises the first green converted light, the second green converted light and the first orange-red converted light and optionally part of the LED light, where the LED filament light is white light having a correlated color temperature in a range from 1700 K to 6500 K and a color rendering index of at least 80, and where the second elongated encapsulant and the third elongated encapsulant have, in an off- state of the LED filament, a green appearance.

[0021] Thereby, a LED filament which comprises an improved optical performance and / or an improved optical appearance is obtained. Such a LED filament further provides for at least one of an improved light quality, an improved CCT control and an improved light mixing. It is noted that ‘appearance’ may mean color.

[0022] At least 90%, at least 95%, at least 98%, or at least 99% of the luminescent material in the second elongated encapsulant may be the second luminescent material.

[0023] At least 90%, at least 95%, at least 98%, or at least 99% of the luminescent material in the third elongated encapsulant may be the third luminescent material.

[0024] The first luminescent material may have an orange-red color. The LED light may be blue light.

[0025] The CCT may be in a range from 1700K to 2700K.

[0026] The LED filament may further comprise a fourth elongated encapsulant covering at least a part of the second major surface, the fourth elongated encapsulant comprising a fourth luminescent material, where the fourth luminescent material is configured to, at least partly, convert one or more of the LED light, the first green converted light and the second green converted light into second orange-red converted light, where the fourth elongated encapsulant is arranged between the second major surface and the third elongated encapsulant, the third elongated encapsulant encloses the fourth elongated encapsulant, and wherein the LED filament light further comprises the second orange-red converted light.

[0027] Thereby, a LED filament providing an improved quality of light, such as color over angle and / or color rendering index (CRI) is provided for.

[0028] The second luminescent material may have an orange-red color.

[0029] The second luminescent material and the third luminescent material may have the same chemical composition. The same chemical composition especially means the use of the same phosphor(s).

[0030] Thereby, an improved, i.e., similar, green appearance of the LED filament is obtained.

[0031] The concentration of the third luminescent material in the third elongated encapsulant may be lower that the concentration of the second luminescent material in the second elongated encapsulant. Further, the third elongated encapsulant may have a lower thickness than the second encapsulant.

[0032] Because (first and / or second) converted light is transmitted through the elongated carrier, it is thereby obtained that less blue light which is transmitted through the elongated carrier needs to be converted.

[0033] The first green converted light has a first dominant peak wavelength, I, and the second green converted light has a second dominant peak wavelength, X2, where XI and X2 may be in a wavelength range from 500 nm to 540 nm.

[0034] Thereby, a LED filament with an optimal green appearance is provided for. The first and second dominant peak wavelengths may fulfill the relation I XI- X2 I < 20nm.

[0035] Thereby, a LED filament with more uniformity in appearance is provided for. The first and second dominant peak wavelengths may fulfill the relation I XI- X2 I > 20nm.

[0036] Thereby, a LED filament providing an improved quality of LED filament light is provided for. The reason is that a broader spectrum is obtained, e.g., increasing the CRI. One or both of the second luminescent material and the third luminescent material may be of the type A3B5O72:Ce, where A comprises Lu and optionally one or more of Y, La, Gd, Tb, and where B in embodiments comprises one or more of Al, Ga, In and Sc, and where A comprises at least 30 % Lu.

[0037] One or both of the second luminescent material and the third luminescent material may be a KSiF phosphor.

[0038] Thereby, a LED filament with a good green appearance is provided for. Furthermore, such phosphors are stable and efficient phosphors.

[0039] The first luminescent material may comprise one or more of a narrowband-red type of phosphor, a Nitride phosphor and an Oxynitride phosphor.

[0040] The first luminescent material may comprise (i) a narrowband-red type of phosphor and (ii) at least one of a Nitride phosphor and an Oxynitride phosphor.

[0041] The narrowband red type of phosphor may be of the type M’xM2-2xAX6 doped with tetravalent manganese, where M’ comprises an alkaline earth cation, M comprises an alkaline cation, and x is in the range of 0-1, where A comprises a tetravalent cation, for instance comprising one or more of silicon and titanium, and where X comprises a monovalent anion, at least comprising fluorine.

[0042] Thereby, a LED filament with a good green appearance is provided for. Furthermore, such phosphors are stable and efficient phosphors.

[0043] The fourth luminescent material may be free from a KSiF phosphor (i.e. less than 1% of the luminescent material used in the fourth elongated encapsulant may be a KSif Phosphor).

[0044] The chemical composition of the first luminescent material in the first elongated encapsulant may be different from the chemical composition of the fourth luminescent material in the fourth elongated encapsulant.

[0045] Thereby a LED filament with an improved green appearance in the off state is provided for.

[0046] The concentration of the fourth luminescent material in the fourth elongated encapsulant may be lower than the concentration of the first luminescent material in the first elongated encapsulant.

[0047] Thereby a LED filament with an improved green appearance in the off state is provided for.

[0048] The layer thickness of the second elongated encapsulant may be larger than the layer thickness of the first elongated encapsulant and / or the concentration of the second luminescent material in the second elongated encapsulant may be higher than a concentration of the first luminescent material in the first elongated encapsulant.

[0049] Thereby a LED filament with a sufficient green appearance in the off state is provided for.

[0050] The LED filament may have a green appearance in the off state of the LED filament. At least 80 %, or at least 90 %, of the surface of the LED filament may have a green appearance.

[0051] At least 90 %, or at least 95 %, or at least 98 %, or at least 99 %, or even 100 % of the second luminescent material in the second elongated encapsulant may have a green color.

[0052] At least 90 %, or at least 95 %, or at least 98 %, or at least 99 %, or even 100 % of the third luminescent material in the third elongated encapsulant may have green color.

[0053] The first elongated encapsulant and, where provided, the fourth elongated encapsulant are not visible in an off state of the LED filament.

[0054] One or both of the first luminescent material and the fourth luminescent material may have a peak emission wavelength in a wavelength range from 560 nm to 600 nm.

[0055] Thereby, a LED filament with a good green appearance is provided for.

[0056] The invention further relates to a LED filament lamp comprising a LED filament according to the invention.

[0057] The LED filament lamp may further comprise a light transmissive envelope at least partly enclosing the LED filament and a base for electrically and mechanically connecting the LED filament lamp to a socket or a socket of a luminaire.

[0058] The invention still further relates to a luminaire comprising a LED filament lamp according to the invention.

[0059] The invention still further relates to a luminaire comprising a LED filament according to the invention.

[0060] It is noted that the invention relates to all possible combinations of features recited in the claims.

[0061] BRIEF DESCRIPTION OF THE DRAWINGS

[0062] 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. Fig. 1 shows a cross-sectional schematic view of a light emitting diode, LED, filament according to the invention.

[0063] Fig. 2 shows a cross-sectional schematic view of another light emitting diode, LED, filament according to the invention.

[0064] Fig. 3 shows a graph of the intensity in arbitrary units as a function of the wavelength of emission (Em; solid line) and excitation (Ex; dashed line), respectively, for a LuAG phosphor.

[0065] Fig. 4 shows a graph of the intensity in arbitrary units as a function of the wavelength of emission (Em; solid line) and excitation (Ex; dashed line), respectively, for a nitride phosphor.

[0066] Fig. 5 shows a graph of the intensity in arbitrary units as a function of the wavelength of emission (Em; solid line) and excitation (Ex; dashed line), respectively, for an oxynitride phosphor.

[0067] Fig. 6 shows a graph of the intensity in arbitrary units as a function of the wavelength of emission (Em; solid line) and excitation (Ex; dashed line), respectively, for a KSiF phosphor.

[0068] Fig. 7 shows a graph of the intensity in arbitrary units as a function of the wavelength of emission (Em; solid line) and excitation (Ex; dashed line), respectively, for a YAG phosphor.

[0069] Fig. 8 shows a schematical side view of a lamp comprising a LED filament according to the invention.

[0070] Fig. 9 shows a schematical side view of a luminaire comprising a lamp and a LED filament according to the invention.

[0071] As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.

[0072] DETAILED DESCRIPTION

[0073] 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.

[0074] Fig. 1 shows a cross-sectional schematic view of a light emitting diode, LED, filament 1 according to the invention. Generally, and irrespective of the embodiment, the LED filament 1 comprises an elongated carrier 3, an array of a plurality of LEDs 4, a first elongated encapsulant 5, a second elongated encapsulant 6 and a third elongated encapsulant 7.

[0075] The elongated carrier 3 comprises a first major surface 31 and a second major surface 32 opposite to the first major surface 31. The elongated carrier 3 is a substrate such as a printed circuit board, PCB. The elongated carrier 3 comprises electrical wiring configured to supply the array of a plurality of LEDs 4 with electrical energy.

[0076] The array of a plurality of LEDs 4 is configured to, in an on-state, emit LED light 41. The LED light 41 may be blue light. The array of a plurality of LEDs 4 is arranged on the first major surface 31 of the elongated carrier 3.

[0077] The first elongated encapsulant 5 encloses the plurality of LEDs 4 at least partly and optionally fully. The first elongated encapsulant 5 further covers the first major surface 31 of the elongated carrier 3 at least partly and optionally fully. The first elongated encapsulant 5 comprises a layer thickness Tl. The first elongated encapsulant 5 comprises a first luminescent material 51. The first luminescent material 51 may have an orange-red color. The first luminescent material 51 is configured to, at least partly and optionally fully, convert one or more of the LED light 41, the first green converted light 62 and the second green converted light 72 into first orange-red converted light 52. The first luminescent material 51 may have a peak emission wavelength in a wavelength range from 570 nm to 600 nm. The first elongated encapsulant 5 comprises a concentration Cl of the first luminescent material 51. The first luminescent material 51 may comprise one or more of a narrowband- red type of phosphor, a Nitride phosphor and an Oxynitride phosphor. Alternatively, the first luminescent material 51 may comprise a narrowband-red type of phosphor and one or both of a Nitride phosphor and an Oxynitride phosphor. In both cases, the narrowband red type of phosphor is 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.

[0078] The second elongated encapsulant 6 encloses the first elongated encapsulant 5. The second elongated encapsulant 6 comprises a layer thickness T2. The layer thickness T2 of the second elongated encapsulant 6 may be larger than the layer thickness T1 of the first elongated encapsulant 5. The second elongated encapsulant 6 comprises a second luminescent material 61. The second luminescent material 61 has a green color. Particularly, at least 90 %, or at least 95 %, or at least 98 %, or at least 99 %, or even 100 % of the second luminescent material 61 has a green color. The second luminescent material 61 may be configured to, at least partly and optionally fully, convert the LED light 41 into first green converted light 62. The second luminescent material 61 may be of the type A3B5O72:Ce, where A comprises Lu and optionally one or more of Y, La, Gd, Tb, and where B in embodiments comprises one or more of Al, Ga, In and Sc, and where A constitutes at least 30 % of the second luminescent material 61. The second elongated encapsulant 6 comprises a concentration C2 of the second luminescent material 61. The concentration C2 of the second luminescent material 61 in the second elongated encapsulant 6 may be higher than the concentration Cl of the first luminescent material 51 in the first elongated encapsulant 5.

[0079] The third elongated encapsulant 7 covers at least a part, and optionally all, of the second major surface 32 of the elongated carrier 3. The third elongated encapsulant 7 comprises a third luminescent material 71. The third luminescent material 71 has a green color. Particularly, at least 90 %, or at least 95 %, or at least 98 %, or at least 99 %, or even 100 % of the third luminescent material 71 has a green color. The third luminescent material 71 is configured to, at least partly and optionally fully, convert one or both of the LED light 41 and the first green converted light 62 into second green converted light 72. The third luminescent material 71 may be of the type A3B5O72:Ce, where A comprises Lu and optionally one or more of Y, La, Gd, Tb, and where B in embodiments comprises one or more of Al, Ga, In and Sc, and where A constitutes at least 30 % of the third luminescent material 71. The third elongated encapsulant 7 comprises a concentration C3 of the third luminescent material 71.

[0080] The second luminescent material 61 and the third luminescent material 71 may have different chemical compositions, or they may have the same chemical composition. The concentration C3 of the third luminescent material 71 in the third elongated encapsulant 7 may be lower that the concentration C2 of the second luminescent material 61 in the second elongated encapsulant 6.

[0081] The first green converted light 62 has a first dominant peak wavelength, XL The second green converted light 72 has a second dominant peak wavelength, X2. The first dominant peak wavelength XI and the second dominant peak wavelength X2 may be in a wavelength range from 500 nm to 540 nm. The first dominant peak wavelength XI and the second dominant peak wavelength X2 may be chosen such that I 1- 2 I < 20 nm. Alternatively, the first dominant peak wavelength XI and the second dominant peak wavelength X2 may be chosen such that I X1-X2 I > 20 nm.

[0082] The LED filament 1 is configured to, in an on-state, emit LED filament light 2. The LED filament light 2 comprises at least the first green converted light 62, the second green converted light 72 and the first orange-red converted light 52. The LED filament light 2 may further comprise a part of the LED light 41. The LED filament light 2 is white light having a correlated color temperature in a range from 1700 K to 6500 K, or in a range from 1700 K to 2700 K. The LED filament light 2 may further have a color rendering index of at least 80.

[0083] The LED filament 1 has a green appearance in the off state of the LED filament 1. Particularly, at least 80 %, or at least 90 %, of the surface of the LED filament 1 may have a green appearance. Alternatively, or additionally, the first elongated encapsulant 5 is not visible in an off state of the LED filament 1.

[0084] Referring now to Fig. 2, a cross-sectional schematic view of another LED filament 100 according to the invention is shown. The LED filament 100 differs from the LED filament 1 described above with reference to Fig. 1 in virtue of the following features.

[0085] The second luminescent material 61 and the third luminescent material 71 have the same chemical composition, and thereby the same green color G.

[0086] The LED filament 100 comprises a fourth elongated encapsulant 8. The fourth elongated encapsulant 8 covers at least part, and optionally all, of the second major surface 32 of the elongated carrier. The fourth elongated encapsulant 8 comprises a fourth luminescent material 81. The fourth luminescent material 81 may have an orange-red color. The fourth luminescent material 81 is configured to, at least partly and optionally fully, convert one or more of the LED light 41, the first green converted light 62 and the second green converted light 72 into second orange-red converted light 82. The fourth elongated encapsulant 8 is arranged between the second major surface 32 of the elongated carrier 3 and the third elongated encapsulant 7. The third elongated encapsulant 7 encloses the fourth elongated encapsulant 5. Thus, the LED filament light 2 further comprises the second orange- red converted light 82.

[0087] The fourth luminescent material 81 may be free from a KSiF phosphor. The phosphor composition of the first elongated encapsulant 5 may be different from a phosphor composition of the fourth elongated encapsulant 8. For instance, the phosphor concentration of the fourth elongated encapsulant 8 may be lower than a phosphor concentration of the first elongated encapsulant 5. One or both of the first luminescent material 51 and the fourth luminescent material 81 may have a peak emission wavelength in a wavelength range from 570 nm to 600 nm. One or both of the first elongated encapsulant 5 and the fourth elongated encapsulant 8 are not visible in an off state of the LED filament 100.

[0088] The first luminescent material 41 and the fourth luminescent material 81 may have the same chemical composition, or they may have different chemical compositions. As indicated on Fig. 2, the first luminescent material 41 and the fourth luminescent material 81 have different chemical compositions, thus resulting in different orange-red colors XI and X2.

[0089] Referring now to Figs. 3 to 7, different suitable phosphors for a LED filament 1 or 100 according to the invention will be described. Garnet class

[0090] Generally, garnet class phosphors are suitable for use as one or both of the second luminescent material 61 and the third luminescent material 71. Garnet class phosphors are luminescent materials 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 sAhOn. Ce in garnets is substantially or only in the trivalent state, as is known to the person skilled in the art.

[0091] Fig. 3 shows a graph of the intensity in arbitrary units as a function of the wavelength of emission (Em; solid line) and excitation (Ex; dashed line), respectively, for one suitable garnet class phosphor, namely a Lutetium Aluminum Garnet (LuAG) phosphor. LuAG phosphors offer performance comparable to YAG phosphors. LuAG phosphors may have dominant emission wavelengths ranging from 520nm to 540 nm. LuAG phosphors are generally used in conjunction with red phosphors for high CRI full spectrum coverage. LuAG phosphors can be effectively excited by a 450nm blue LED with an emission peak wavelength in the 510-540 nm range. Combined with nitride red phosphor, a high CRI spectrum with Ra above 95 can be achieved. LuAG phosphors are particularly suitable for use as one or both of the second luminescent material 61 and the third luminescent material 71.

[0092] Fig. 7 shows a graph of the intensity in arbitrary units as a function of the wavelength of emission (Em; solid line) and excitation (Ex; dashed line), respectively, for another suitable garnet class phosphor, namely a Yttrium Aluminum Garnet (YAG) phosphor. YAG phosphors are efficient and suitable for creating a high correlated color temperature (CCT). YAG phosphors exhibit absorption peaks at 450 nm, and dominant emission wavelengths range from 540 nm - 560 nm. YAG phosphors can be effectively excited by a 450 nm blue LED chip with an emission peak wavelength in the 540 nm - 560 nm range. YAG phosphors are mainly used for increasing luminous efficiency. By adding a small amount of a YAG yellow phosphor to an Ra80 LED, the luminous flux will increase dramatically. YAG phosphors are particularly suitable for use as one or both of the second luminescent material 61 and the third luminescent material 71. (Oxy)nitride class

[0093] Generally, phosphors of the (oxy)nitride class are suitable for use as a part of or all of the first luminescent material 51 and the fourth luminescent material 81.

[0094] (Oxy)niotride phosphors are luminescent materials comprising NfcSis 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 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 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.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.

[0095] Fig. 4 shows a graph of the intensity in arbitrary units as a function of the wavelength of emission (Em; solid line) and excitation (Ex; dashed line), respectively, for a nitride phosphor. Nitride phosphors are very suitable for obtaining high CRI and low correlated color temperature (CCT) white LEDs. Dominant emission wavelengths range from 605 nm to 660 nm. Nitride phosphors can also be applied in plant growth light LEDs where wide and stable red spectrum coverage is required. Nitride phosphors can be effectively excited by 400 nm - 460 nm violet LED or blue LED with an emission peak wavelength in the 600 nm - 660 nm range. When combined with blue LED chip and aluminosilicate green phosphor, nitride phosphors can produce a white LED light with Ra 95 or above. When combined with a violet LED chip, phosphate blue phosphor and a P-SiAION green phosphor, nitride phosphors can achieve a full spectrum of white light with R1-R15 all above 95. Nitride phosphors are particularly suitable for use as a part of or all of the first luminescent material 51 and the fourth luminescent material 81.

[0096] Fig. 5 shows a graph of the intensity in arbitrary units as a function of the wavelength of emission (Em; solid line) and excitation (Ex; dashed line), respectively, for an oxynitride phosphor. Oxynitride phosphors can be used to package high CRI LEDs which require full spectrum coverage. Dominant emission wavelengths range from 500 nm to 650 nm. Oxynitride phosphors are particularly suitable for use as a part of or all of the first luminescent material 51 and the fourth luminescent material 81.

[0097] KSiF class

[0098] Generally, KSiF class phosphors are suitable for use as a part of or all of the first luminescent material 51. The fourth luminescent material 81 may or may not comprise a KSiF class phosphor.

[0099] KSiF class phosphors are luminescent materials 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 tetravalent cation, for instance comprising one or more of silicon and titanium, wherein X comprises a monovalent anion, at least comprising fluorine.

[0100] 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.

[0101] Relevant alkaline earth cations (M’) are magnesium (Mg), strontium (Sr), calcium (Ca) and barium (Ba), especially one or more of Sr and Ba.

[0102] 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.

[0103] 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).

[0104] 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+).

[0105] 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.

[0106] Fig. 6 shows a graph of the intensity in arbitrary units as a function of the wavelength of emission (Em; solid line) and excitation (Ex; dashed line), respectively, for a KSiF phosphor. KSiF phosphors can be effectively excited by a 460 nm blue LED with a strongest emission peak wavelength at near 631 nm, full width at half maxima (FWHM) smaller than 60nm with comparatively high color purity. Combined with P-SIAION green phosphor for a backlight, NTSC can be improved to above 100 %. KSiF phosphors are particularly suitable for use as a part of or all of the first luminescent material 51. The fourth luminescent material 81 may or may not comprise a KSiF phosphor.

[0107] Fig. 8 shows an exemplary lamp 300 comprising a LED filament 1, 100 according to any embodiment of the invention. In the embodiment shown, the LED filament 1, 100 comprises a substantially straight LED filament. The LED filament of such a lamp may in other embodiments be a LED filament with another shape, such as, but not limited to, spiral-shaped, helix-shaped, meandering, twisted, flat and combinations thereof. The lamp 300 further comprises a driver or controller 305 configured for controlling the plurality of LEDs 4 of the LED filament 1, 100. The controller 305 is configured to power the plurality of LEDs 4 via electrical circuitry (not visible on the figures) of the LED filament 1, 100. The LED filament 1 may also comprise a controller, which may or may not be separate from the controller 305. In other words, the controller 305 and the controller of the LED filament 1 may be integrated into one and the same driver or controller, or they may be mutually separate units.

[0108] The lamp 300 further comprises an envelope 301 at least partially enveloping the at least one LED filament 1, 100. The lamp 300 further comprises a cap 303. As shown in Fig. 8, the controller 305 is arranged within the envelope 301. When comprising a cap 303, the controller 305 may also be arranged inside the cap 303 such that it is hidden from view. The lamp 300 further comprises threading 302 for connection to a socket, and a terminal 304 for connection to a source of electrical energy.

[0109] The envelope 301 of the lamp 300 may further and optionally be provided with a coating (not shown), such as a reflective coating, covering at least a part of the envelope 301.

[0110] Turning finally to Fig. 9, an exemplary luminaire in the form of a pendant 400 is shown. The pendant 400 comprises a LED filament 1, 100 according to any embodiment of the invention. The LED filament 1, 100 is as shown in Fig. 9 provided within a lamp 300 in the form of a light bulb. The LED filament 1, 100 as shown in Fig. 9 comprises a substantially straight LED filament.

[0111] As is also mentioned above, the light bulb further comprises a transparent envelope (cf. transparent envelope 301 of lamp 300) at least partially enveloping the at least one LED filament 1, 100. The transparent envelope may be shaped in any feasible shape, for example such as to resemble the shape of any one of a standard light bulb, a globe light bulb, a candlelight bulb, a customized light bulb and even a spiral light bulb. The transparent envelope may comprise a luminescent material. The transparent envelope may be a glass envelope.

[0112] The pendant 400 further comprises a socket 401 for connecting the lamp 300, and thereby the LED filament 1, 100, to the pendant 400. The socket 401 is adapted to cooperate with the base 303 of the lamp 300. The socket 401 may comprise a threading adapted to cooperate with the threading 302 of the lamp 300. The socket 401 may comprise a terminal adapted to cooperate with the terminal 304 of the lamp 300. The pendant 400 further comprises a reflector or screen 403. The pendant 400 may further comprise a driver 402 configured for controlling the LED filament 1, 100. The driver 402 may or may not be the same unit as the controller 305 described above. In other words, the driver 402 and the controller 305 may be integrated into one and the same driver or controller, or they may be mutually separate units. Alternatively, or additionally, the LED filament 1, 100 may also comprise a controller, which may or may not be separate from one or both of the driver 402 and the controller 305.

[0113] As shown in Fig. 9, the driver 402 is arranged on a reflector or screen 403 of the pendant 400. The driver may also be arranged within or incorporated into the reflector or screen 403. The pendant 400 further comprises an electrical wiring 404 for connection to a source of electricity, such as a mains.

[0114] It is noted that the pendant 400 shown in Fig. 9 is only one example of a luminaire according to the invention. Any suitable type of luminaire may be envisaged, such as but not limited to, a standing luminaire, a wall hung luminaire, a chandelier, a reading luminaire, an outdoor luminaire, and a table luminaire.

[0115] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0116] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

CLAIMS:

1. A light emitting diode, LED, filament (1) configured to, in an on-state, emitLED filament light (2), the LED filament comprising: an elongated carrier (3) comprising a first major surface (31) and a second major surface (32) opposite to the first major surface, an array of a plurality of LEDs (4) configured to, in an on-state, emit LED light (41) and being arranged on the first major surface (31) of the elongated carrier, a first elongated encapsulant (5) at least partly enclosing the plurality of LEDs and at least partly covering the first major surface, the first elongated encapsulant (5) comprising a first luminescent material (51), a second elongated encapsulant (6) enclosing the first elongated encapsulant (5), the second elongated encapsulant (6) comprising a second luminescent material (61), a third elongated encapsulant (7) covering at least a part of the second major surface, the third elongated encapsulant (7) comprising a third luminescent material (71), wherein the second luminescent material (61) has a green color and is configured to, at least partly, convert the LED light into first green converted light (62), wherein the third luminescent material (71) has a green color and is configured to, at least partly, convert the LED light and / or the first green converted light (62) into second green converted light (72), wherein the first luminescent material (51) is configured to, at least partly, convert one or more of the LED light, the first green converted light and the second green converted light into first orange-red converted light (52), wherein the LED filament light (2) at least comprises the first green converted light (62), the second green converted light (72) and the first orange-red converted light (52) and optionally part of the LED light, wherein the LED filament light (2) is white light having a correlated color temperature in a range from 1700 K to 6500 K and a color rendering index of at least 80; and wherein the second elongated encapsulant (6) and third elongated encapsulant (7) have, in an off-state of the LED filament, a green appearance, andwherein the concentration of the third luminescent material (71) in the third elongated encapsulant (7) is lower than the concentration of the second luminescent material (61) in the second elongated encapsulant (6).

2. A LED filament according to claim 1, and further comprising a fourth elongated encapsulant (8) covering at least a part of the second major surface (32), the fourth elongated encapsulant (8) comprising a fourth luminescent material (81), wherein the fourth luminescent material is configured to, at least partly, convert one or more of the LED light, the first green converted light and the second green converted light into second orange-red converted light (82), wherein the fourth elongated encapsulant (8) is arranged between the second major surface (32) and the third elongated encapsulant (7), the third elongated encapsulant (7) encloses the fourth elongated encapsulant (5), and wherein the LED filament light (2) further comprises the second orange-red converted light.

3. A LED filament according to any one of the above claims, wherein the second luminescent material (61) and the third luminescent material (71) have the same chemical composition.

4. A LED filament according to any one of the above claims, wherein the first green converted light (62) has a first dominant peak wavelength (XI) and the second green converted light (72) has a second dominant peak wavelength (X2), wherein XI and X2 are in a wavelength range from 500 nm to 540 nm.

5. A LED filament according to claim 4, wherein I XI -X2 I < 20 nm.

6. A LED filament according to any one of the above claims, wherein one or both of the second luminescent material (61) and the third luminescent material (71) are of the type A3B5O72:Ce, wherein A comprises Lu and optionally one or more of Y, La, Gd, Tb, and wherein B in embodiments comprises one or more of Al, Ga, In and Sc, and wherein A comprises at least 30 % Lu.

7. A LED filament according to any one of the above claims, wherein the first luminescent material (51) comprises:one or more of a narrowband-red type of phosphor, a Nitride phosphor and an Oxynitride phosphor, or a narrowband-red type of phosphor and at least one of a Nitride phosphor and an Oxynitride phosphor, wherein the narrowband red type of phosphor is 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 tetravalent cation, for instance comprising one or more of silicon and titanium, wherein X comprises a monovalent anion, at least comprising fluorine.

8. A LED filament according to any one of the above claims 2-7, wherein the fourth luminescent material (81) is free from a KSiF phosphor.

9. A LED filament according to any one of the above claims 2-8, wherein one or more of the following apply: the chemical composition of the first luminescent material in the first elongated encapsulant (5) is different from the chemical composition of the fourth luminescent material in the fourth elongated encapsulant (8), and the concentration of the fourth luminescent material in the fourth elongated encapsulant (8) is lower than the concentration of the first luminescent material in the first elongated encapsulant (5).

10. A LED filament according to any one of the above claims, wherein one or more of the following apply: a layer thickness of the second elongated encapsulant (6) is larger than a layer thickness of the first elongated encapsulant (5), and a concentration of the second luminescent material (61) in the second elongated encapsulant (6) is higher than a concentration of the first luminescent material (51) in the first elongated encapsulant (5).

11. A LED filament according to any one of the above claims, wherein LED filament the first elongated encapsulant (5) and, where provided, the fourth elongated encapsulant (8) are not visible in the off-state of the LED filament (1).

12. A LED filament according to any one of the above claims 2-11, wherein one or both of the first luminescent material and the fourth luminescent material having a peak emission wavelength in a wavelength range from 560 nm to 600 nm.

13. A LED filament lamp (300) comprising a LED filament(l) according to any one of the preceding claims, and further comprising (i) a light transmissive envelope (301) at least partly enclosing the LED filament (1) and (ii) a base (303) for electrically and mechanically connecting the LED filament lamp to a socket or a socket of a luminaire.

14. A luminaire (400) comprising a LED filament lamp (300) according to claim13 or comprising a LED filament (1) according to any one of claims 1-12

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