A LED filament lighting device

Abstract

A light-emitting diode, LED, filament lighting device (1) is disclosed. The LED filament lighting device (1) comprises an elongated carrier substrate (2) comprising at least one ceramic material, wherein the carrier substrate (2) has at least a first surface (6) and a second surface (7) opposite to the first surface (6). The LED filament lighting device (1) comprises a plurality of solid-state light sources (3, 4, 5) configured to, in operation, emit light, wherein the plurality of solid-state light sources (3, 4, 5) is arranged in an array on the second surface (7) of the carrier substrate (2). The LED filament lighting device (1) comprises a thermally conductive layer (8) arranged at at least a portion of the first surface (6) of the carrier substrate (2), wherein at least a portion of the thermally conductive layer (8) comprises a first material that is graphene-based and a second material that is metal-based.

Description

[0001] A LED FILAMENT LIGHTING DEVICE

[0002] TECHNICAL FIELD

[0003] The present invention relates to a light-emitting diode (LED) filament lighting device.

[0004] BACKGROUND

[0005] Efforts have been made to make solid state-based lighting devices, e.g., lightemitting diode (LED) based lighting devices, mimic or resemble traditional incandescent lighting devices, e.g., with respect to light distribution and / or color temperature. In bulb lighting devices based on LEDs, commonly referred to as “retrofit lamps” since these LED lamps are often designed to have the appearance of a traditional incandescent light bulb and to be mounted in conventional sockets, etc., the light-emitting filament wire is replaced with one or more LEDs. Such bulb lighting devices based on LEDs may also be referred to as LED bulbs. A LED bulb may for example comprise one or more so-called LED filaments, wherein each LED filament may include multiple LEDs which may be connected in series to form a light-emitting filament. A LED filament lamp, which may be referred to simply as a LED filament, is hence a LED-based lamp which is designed to resemble a traditional incandescent light bulb with one or more visible filaments for aesthetic and light distribution purposes, but with the high efficiency of LEDs. It is desired to improve the performance, functionality and / or appearance of LED filament lamps.

[0006] EP3514440B1 discloses a method of making a LED light bulb with thermal radiation filaments comprising molding LED chips and phosphors on a front face of a substrate made of any one of metal, ceramic, glass and plastic; forming a thermal radiation dissipation film on a back face of the substrate; and cutting the substrate into the thermal radiation dissipation filaments.

[0007] SUMMARY

[0008] For example, it is desired to improve the efficiency of LED filament lamps or LED bulbs capable of providing light having a high luminous flux. Such improvement of efficiency may be realized by means of improving cooling of the LEDs. Solutions for cooling of the LEDs usually involve employing a metal core printed circuit board (MCPCB), whereby temperatures of LEDs in operation may be kept relatively low. However, it is desired to further improve the efficiency of lighting devices such as LED filament lamps or LED bulbs.

[0009] In view of the above, a concern of the present invention is to provide a LED filament lighting device having a relatively high efficiency.

[0010] A further concern of the present invention is to provide a LED filament lighting device configured so as to facilitate or allow for an efficient cooling of solid-state light sources such as LEDs in the LED filament lighting device to keep temperatures of the solid-state light sources in operation relatively low.

[0011] According to a first aspect of the present invention, a light-emitting diode (LED) filament lighting device is provided. The lighting device comprises an elongated carrier substrate, which comprises at least one ceramic material. The carrier substrate may also be referred to as carrier. The carrier substrate has at least a first surface and a second surface opposite to the first surface. The lighting device comprises a plurality of solid-state light sources, which are configured to, in operation, emit light. The plurality of solid-state light sources are arranged in an array (or arranged in a group) on the second surface of the carrier substrate. The lighting device comprises a thermally conductive layer. The thermally conductive layer is arranged at at least a portion of the first surface of the carrier substrate. At least a portion of the thermally conductive layer comprises a first material that is graphenebased and a second material that is metal-based.

[0012] By the carrier substrate comprising at least one ceramic material, an efficient transfer of thermal energy (e.g., heat) from the plurality of solid-state light sources on the second surface of the carrier substrate may be achieved via the carrier substrate. Further, by the thermally conductive layer being arranged at at least a portion of the first surface of the carrier substrate, an efficient transfer of thermal energy from the plurality of solid-state light sources and the carrier substrate may be achieved via the thermally conductive layer. As mentioned, at least a portion of the thermally conductive layer comprises a first material that is graphene-based. It has been found by the inventor that by the providing of the thermally conductive layer having incorporated the graphene-based first material therein, a significant reduction in temperature of the solid-state light sources in operation may be achieved.

[0013] A thickness of the thermally conductive layer may be in a range between 10 pm and 200 pm. The first material may comprise or be constituted by graphene. The second, metal-based material may comprise or be constituted by copper and / or aluminum. Simulations have been made by the inventor, e.g., for a case where for the LED filament lighting device the first material is graphene and the second material is copper, and with a thickness of the thermally conductive layer being 200 pm and with the solid-state light sources being LEDs. Such simulations have shown that for such LED filament lighting devices, the temperature of the solid-state light sources can be further reduced by a factor of up to two or even three or possibly more compared to a case where the solid-state light sources are arranged on a MCPCB or on a ceramic printed circuit board (PCB) (i.e., a configuration without the thermally conductive layer in accordance with the first aspect of the present invention).

[0014] The first and second surfaces of the carrier substrate may for example be referred to as first and second major surfaces of the carrier substrate.

[0015] The thermally conductive layer may be coupled to the at least a portion of the first surface of the carrier substrate.

[0016] As mentioned, the elongated carrier substrate comprises at least one ceramic material. The carrier substrate may for example comprise a PCB and / or some other appropriate type of substrate, which may have the at least one ceramic material as a base material. The at least one ceramic material may be embodied as a layer (e.g., a dielectric layer) included in the PCB or other type of substrate, which layer might have a thickness between a few micrometers and a few millimeters. The at least one ceramic material may comprise one or more of alumina, aluminum nitride and beryllium oxide, and / or another (e.g., highly) thermally conductive material.

[0017] The second surface of the carrier substrate may be included in or be constituted by a metallic layer, by which electrical tracing may be provided to which, e.g., the plurality of solid-state light sources may be coupled. The metallic layer may for example comprise copper, silver, gold, tungsten, molybdenum, and / or sheet metal with gold.

[0018] As mentioned, the first material may comprise or be constituted by graphene. The graphene may be comprised in a graphene layer.

[0019] As mentioned, at least a portion of the thermally conductive layer comprises a first material that is graphene-based and a second material that is metal-based.

[0020] According to one implementation example and in accordance with one or more embodiments of the present invention, the first material and the second material may be included in a single layer. Thus, the first material and the second material may not necessarily be provided in different (separate) layers, but the first material and the second material may be combined (e.g., mixed) in a single layer. For example, the thermally conductive layer may comprise a layer in which, e.g., graphene, is combined (e.g., mixed) with, e.g., copper.

[0021] According to another implementation example and in accordance with one or more embodiments of the present invention, the thermally conductive layer may comprise (e.g., at least) a first sub-layer and a second sub-layer. The second sub-layer may be coupled with the first sub-layer. The first sub-layer may comprise the first material, and the second sub-layer may comprise the second material.

[0022] The thermally conductive layer may be configured such that the first sub-layer (comprising the first material) is arranged between the second sub-layer and the carrier substrate. Thereby, the first sub-layer comprising the first material may be arranged at the at least a portion of the first surface of the carrier substrate and may possibly be coupled to the at least a portion of the first surface of the carrier substrate.

[0023] In alternative, the thermally conductive layer may be configured such that the second sub-layer is arranged between the first sub-layer and the carrier substrate. This alternative configuration may however be less preferred compared to the above-described example configuration wherein the first sub-layer is arranged between the second sub-layer and the carrier substrate.

[0024] A thickness of each of the first sub-layer and the second sub-layer may be in a range between 10 pm and 30 pm.

[0025] The thermally conductive layer may comprise a reflective sub-layer. The reflective sub-layer may be reflective to light. The reflective sub-layer may be a peripheral sub-layer. That is, the reflective sub-layer may be arranged in the thermally conductive layer so that a surface of the reflective sub-layer constitutes an outer surface of the thermally conductive layer. The reflective sub-layer may be a non-metallic layer. The reflective sublayer may be embodied as a coating. The reflective sub-layer may comprise titanium oxide, boron nitride, and / or composite mixed with silicone, polycarbonate, fluoropolymer, etc. In alternative or in addition, the reflective sub-layer may comprise silver-based mirror layer(s). The reflective sub-layer may have a thickness between a few micrometers and a few hundred micrometers.

[0026] Particularly, a light-emitting diode (LED) filament lighting device, also simply referred to as LED filament, is a light-emitting device that has a plurality of light emitting diodes (LEDs) arranged in a linear array. The LEDs may be arranged to emit light of different colors or spectral distributions. A LED filament has a length, a width, and an axis of elongation along the length. The length may be more than five times the width, such as more than ten times the width. A LED filament has a light-emitting surface that extends along the length, and preferably at least partly around the axis of elongation. The light-emitting surface is preferably arranged to homogenously emit light and / or to emit light omnidirectionally. A LED filament may be arranged in a straight configuration or in a non-straight configuration, such as a curved configuration, a spiral or a helix. The LEDs are preferably arranged on an elongated carrier substrate, that may be made from a polymer, glass, quartz, metal, or sapphire. The carrier substrate may be rigid or flexible. When the carrier substrate has a first major surface and an opposite second major surface, the LEDs are arranged on at least one of these surfaces. The carrier substrate may be reflective or transmissive for light, such as translucent, or transparent. A LED filament may comprise an encapsulant that at least partly covers one or more of the LEDs. The encapsulant may also at least partly cover one or more of the first and second major surfaces of the carrier. For optimum performance of the thermally conductive layer, the encapsulant preferably may not cover the thermally conductive layer. However, in examples the encapsulant may also at least partly cover the thermally conductive layer. The encapsulant may comprise a polymer, which may be flexible, such as a silicone. The encapsulant may comprise a luminescent material for converting the light emitted by the LEDs. A LED filament may be used to mimic the filament of an incandescent light bulb. A LED filament may comprise multiple sub-filaments.

[0027] According to an implementation example and in accordance with one or more embodiments of the present invention, at least one of the plurality of solid-state light sources may comprise a LED configured to, in operation, emit light having a peak wavelength (e.g., a dominant peak wavelength) in a blue wavelength range from 420 nm to 500 nm, preferably in a range of 430 nm to 490 nm, more preferably in a range of 440 - 480 nm. However, LEDs or other types of solid-state light sources capble of emitting light within another or other wavelength ranges are possible. At least part of the blue light emitted by the LED may be converted by one or more luminescent material to light having a green and / or yellow and / or orange, and / or red wavelength range, for generating white light.

[0028] 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 540 nm. As used herein, the term “yellow light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 540 nm to 580 nm. As used herein, the term “orange light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 580 to 600 nm. 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 700 nm. As used herein, the terms “upstream” and “downstream” are intended to be understood relative to the direction of propagation of light through the light generation system.

[0029] In an embodiment the light-emitting diode (LED) filament lighting device is configured to generate white light. The term “white light”, and similar terms, herein, is known to the person skilled in the art. In general, if a light source is indicated to generate white light, it may especially relate to light having a correlated color temperature (CCT) between about 1500 K and 20000 K, such as between 2000 and 20000 K, especially 2700- 20000 K, for general lighting especially in the range of about 2000-7000 K, such as in the range of 2700 K and 6500 K. More especially, in embodiments, in an operational mode the system light may be white light having a correlated color temperature selected from the range of 1500-10000 K, such as selected from the range of 1500-8000 K, like selected from the range of 1700-6500 K. Additionally or alternatively, in such embodiments, the system light may be white light having a color rendering index of at least 70, especially at least 80, such as at least 90. Such embodiments may be beneficial for applications where high brightness light sources may be desired, such as e.g. spots, stage-lighting, headlamps, home and office lighting, and automotive lighting.

[0030] The plurality of solid-state light sources may be (e..g, completely) enclosed by means of wavelength-converting material or wavelength-converting encapsulant. The wavelength-converting material or wavelength-converting encapsulant may be configured to modify the wavelength of at least some of the light emitted by the plurality of solid-state light sources and impinging on the wavelength-converting material or wavelength-converting encapsulant. Possibly, of the carrier substrate, the thermally conductive layer and the plurality of solid-state light sources, only the plurality of solid-state light sources may be (e.g., completely) enclosed by means of the wavelength-converting material or wavelengthconverting encapsulant. That is, the plurality of solid-state light sources may be enclosed by means of the wavelength-converting material or wavelength-converting encapsulant but not the carrier substrate or the thermally conductive layer (but one or both of them could be).

[0031] The wavelength-converting material or wavelength-converting encapsulant may be configured to at least partly convert at least some of the light emitted by the plurality of solid-state light sources, which light may have a peak wavelength (e.g., a dominant peak wavelength) in a certain wavelength range, into converted light having a peak wavelength (e.g., a dominant peak wavelength) in another wavelength range. The wavelength-converting material may for example comprise one or more luminescent materials such as, for example, a phosphor such as an inorganic phosphor, and / or quantum dots or rods. In an embodiment, the luminescent material is of the type AsBsO 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.

[0032] In an embodiment, the luminescent material comprises I hSisNs Eu2, or MAlSiNs:Eu2+or Ca2AlSi3O2Ns:Eu2+, etc., wherein M comprises one or more of Ba, Sr, and Ca, especially in embodiments at least Sr.

[0033] In an embodiment, the luminescent material 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. 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’xM2-2xAX6 luminescent material has the hexagonal phase. In yet another embodiment, the M’xM2-2xAX6 luminescent material has the cubic phase. For x=0, the composition is M2AX6.

[0034] The thermally conductive layer may be provided with fins, which may be referred to as cooling fins. To that end, the thermally conductive layer may comprise a base portion extending parallel with the carrier substrate. The thermally conductive layer may be configured such that at least one lateral edge of the thermally conductive layer comprises a plurality of fins projecting from the base portion of the thermally conductive layer in the width direction. The plurality of fins may additionally extend at least partly beyond the carrier substrate. The plurality of fins may be arranged in spaced relation with each other. The carrier substrate may have a carrier substrate width Wc and each fin of the plurality of fins may have a fin width WF measured in a width direction of the LED filament lighting device. The fin width may be less than or equal to the carrier substrate width, such as less than or equal to 0.7 times the carrier substrate width, especially less than or equal to 0.5 times the carrier width. Hence, the filament width may be less or equal to three times the carrier width, being the carrier width plus the width of the plurality of fins on both lateral edges. By employing such fins, the temperature of the solid-state light sources in operation may be further reduced while keeping the appearance of a LED filament.

[0035] The thermally conductive layer may be configured such that a fin distance between adjacent fins of the plurality of fins is in a range between 0.5 mm and 6 mm, preferably between 1 mm and 4 mm, most preferably between 1.5 mm and 2.5mm. The fin distance is measured in an elongation direction of the LED filament. In alternative or in addition, the thermally conductive layer may be configured such that a fin length of each fin of the plurality of fins is in a range between 2 mm and 8 mm, preferably between 3 mm and 5 mm, most preferably between 4 mm and 6 mm. The fin length is measured in an elongation direction of the LED filament. In alternative or in addition, the thermally conductive layer may be configured such that a fin width of each fin of the plurality of fins is in a range between 1 mm and 7 mm, preferably between 2.5 mm and 5 mm, most preferably between 3 mm and 4 mm. The fin width is measured in a width direction of the filament, the width direction being oriented in a transversal direction perpendicular to the elongation direction. By means of simulations made by the inventor, the inventor has found out that such configurations of the fins may be particularly beneficial for further reducing the temperature of the solid-state light sources in operation.

[0036] A LED filament is a light-emitting device that has a plurality of solid-state light sources, such as a plurality of light emitting diodes (LEDs), which may be arranged in a linear array. The LEDs may be arranged to emit light of different colors or spectral distributions. A LED filament has a length, a width, and an axis of elongation along the length. The length may be more than five times the width, such as more than ten times the width. A LED filament has a light-emitting surface that extends along the length, and preferably at least partly around the axis of elongation. The light-emitting surface is preferably arranged to homogenously emit light and / or to emit light omnidirectionally. A LED filament may be arranged in a straight configuration or in a non-straight configuration, such as a curved configuration, a spiral or a helix. The LEDs are preferably arranged on an elongated carrier, such as a substrate, that may be made from a polymer, glass, quartz, metal, or sapphire. The carrier - to which the elongated carrier substrate described herein may correspond - may be rigid or flexible. When the carrier has a first major surface and an opposite second major surface, the LEDs are arranged on at least one of these surfaces. The carrier may be reflective or transmissive for light, such as translucent, or transparent. A LED filament may comprise an encapsulant that at least partly covers one or more of the LEDs. The encapsulant may also at least partly cover one or more of the first and second major surfaces of the carrier. The encapsulant may comprise a polymer, which may be flexible, such as a silicone. The encapsulant may comprise a luminescent material for converting the light emitted by the LEDs. A LED filament may be used to mimic the filament of an incandescent light bulb. A LED filament may comprise multiple sub-filaments.

[0037] Each or any one of the plurality of LEDs may for example include or be constituted by an inorganic LED and / or an organic LED (OLED). Solid-state light emitters or sources are relatively cost-efficient light sources since they in general are relatively inexpensive and have a relatively high optical efficiency and a relatively long lifetime. Examples of LEDs include semiconductor, organic, or polymer / polymeric LEDs, optically pumped phosphor coated LEDs, optically pumped nano-crystal LEDs or any other similar devices as would be readily understood by a person skilled in the art. For example, the term LED can encompass a bare LED die arranged in a housing, which may be referred to as a LED package. According to another example, the term LED can encompass a Chip Scale Package (CSP) LED, which may comprise a LED die directly attached to a substrate such as a PCB, and not via a sub-mount. The term LED can for example encompass a laser diode, because a laser diode is a diode which emits light.

[0038] Each or any of the solid-state light sources may be controllable, e.g., with respect to switching on and switching off the solid-state light source. One or more groups of solid-state light sources may be individually controllable, e.g., with respect to switching on and switching off the solid-state light sources of the group(s). The lighting device may comprise a controller. The controller may be configured to control operation of the solid-state light sources. The controller may be configured to control operation of the solid-state light sources at least with respect to switching on and switching off each or any of the solid-state light sources.

[0039] According to a second aspect of the present invention, a lamp or luminaire is provided. The lamp or luminaire comprises one or more lighting devices according to the first aspect of the present invention. The lamp may for example comprise a base for electrically and mechanically connecting the lamp to a socket of a luminaire and an envelope at least partly enclosing one or more lighting devices in accordance with the first aspect of the present invention.

[0040] Further objects and advantages of the present invention are described in the following by means of exemplifying embodiments. It is noted that the present invention relates to all possible combinations of features recited in the claims. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the description herein. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described herein.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Exemplifying embodiments of the invention will be described below with reference to the accompanying drawings.

[0043] Fig. l is a schematic sectional view of a light-emitting diode (LED) filament lighting device according to an embodiment of the present invention.

[0044] Fig. 2 is a perspective view of a LED filament lighting device according to an embodiment of the present invention.

[0045] Each of Figs. 3 and 4 is a schematic sectional view of a LED filament lighting device according to an embodiment of the present invention.

[0046] Fig. 5 is a perspective view of a LED filament lighting device according to an embodiment of the present invention.

[0047] Fig. 6 is a schematic view of a lamp according to an embodiment of the present invention.

[0048] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate embodiments of the present invention, wherein other parts may be omitted or merely suggested.

[0049] DESCRIPTION WITH REFERENCE TO THE DRAWINGS

[0050] The present invention will now be described hereinafter with reference to the accompanying drawings, in which exemplifying embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments of the present invention set forth herein; rather, these embodiments of the present invention are provided by way of example so that this disclosure will convey the scope of the invention to those skilled in the art. In the drawings, identical reference numerals denote the same or similar components having a same or similar function, unless specifically stated otherwise.

[0051] Figure l is a schematic sectional view of a light-emitting diode (LED) filament lighting device 1 according to an embodiment of the present invention. The LED filament lighting device 1 comprises an elongated carrier substrate 2, which comprises at least one ceramic material. The carrier substrate 2 has at least a first surface 6 and a second surface 7 opposite to the first surface 6. The carrier substrate 2 may for example comprise a printed circuit board (PCB) and / or some other appropriate type of substrate, which may have the at least one ceramic material as a base material. The at least one ceramic material may be embodied as a layer (e.g., a dielectric layer) included in the PCB or other type of substrate.

[0052] The LED filament lighting device 1 comprises a plurality of solid-state light sources 3, 4, 5. The solid-state light sources 3, 4, 5 are configured to, in operation, emit light. The plurality of solid-state light sources 3, 4, 5 may be arranged in an array, or group, on the second surface 7 of the carrier substrate 2. The plurality of solid-state light sources 3, 4, 5 may for example comprise or be constituted by a plurality of light emitting diodes (LEDs).

[0053] The plurality of solid-state light sources 3, 4, 5 may for example be arranged in a linear array, or in a succession, which may extend generally along a longitudinal axis of the carrier substrate 2 or of the LED filament lighting device 1. Such a configuration of the plurality of solid-state light sources 3, 4, 5 is illustrated in Figure 2, which is a perspective view of a LED filament lighting device 1 according to an embodiment of the present invention. The LED filament lighting device 1 illustrated in Figure 2 is similar to the LED filament lighting device 1 illustrated in Figure 1, and the same reference numerals in Figures 1 and 2 indicate the same or similar components having the same or similar function or functionality.

[0054] The LED filament lighting device has a filament length L and a filament width W. The filament length is more than five times the filament width. The carrier substrate has a carrier substrate width Wc measured in a width direction of the LED filament lighting device. The carrier substrate width may be smaller than the filament width.

[0055] It is to be understood that the number of solid-state light sources illustrated in Figures 1 and 2 is according to an example, and that the number of solid-state light sources comprised in each of the LED filament lighting devices 1 illustrated in Figures 1 and 2 could be more or fewer than illustrated in Figures 1 and 2. Each of the LED filament lighting devices 1 illustrated in Figures 1 and 2 could comprise, in principle, any number of solid- state light sources. Also, while in particular Figure 2 illustrates a configuration of the plurality of solid-state light sources 3, 4, 5 in which the solid-state light sources 3, 4, 5 are arranged in a linear array, or in a succession, which may extend generally along a longitudinal axis of the carrier substrate 2 or of the LED filament lighting device 1, it is to be understood that this is exemplifying and that other configurations of the plurality of solid-state light sources 3, 4, 5 are possible. For example, the plurality of solid-state light sources could be arranged in two or more successions or linear arrays of solid-state light sources wherein the successions or linear arrays of solid-state light sources are spaced from each other and may be extending in parallel or substantially in parallel with each other.

[0056] With reference to each of the LED filament lighting devices 1 illustrated in Figures 1 and 2, the LED filament lighting device 1 comprises a thermally conductive layer 8. According to the embodiments of the present invention illustrated in Figures 1 and 2, the thermally conductive layer 8 is arranged at a portion of the first surface 6 of the carrier substrate 2. At least a portion of the thermally conductive layer 8 comprises a first material that is graphene-based and a second material that is metal-based.

[0057] The first material may comprise or be constituted by graphene. The first material may be comprised in a graphene layer. The second material may comprise or be constituted by at least one of copper and aluminum.

[0058] Different configurations of the thermally conductive layer 8 are possible. For example, the first material and the second material may be included in respective (sub-)layers of the thermally conductive layer 8. According to another example, the first material and the second material may be included in a single layer. For example, the first material and the second material may be combined (e.g., mixed) in a single layer. For example, the thermally conductive layer 8 may comprise a layer in which, e.g., graphene, is combined (e.g., mixed) with, e.g., copper.

[0059] Further to the description in the foregoing section, by a LED filament lighting devices 1 such illustrated in Figures 1 and 2, the temperature of the solid-state light sources 3, 4, 5 can be further reduced by a factor of up to two or even more compared to a case where the solid-state light sources are arranged on a MCPCB or on a ceramic printed circuit board PCB (i.e., a configuration without the thermally conductive layer 8).

[0060] Figure 3 is a schematic sectional view of a LED filament lighting device 1 according to an embodiment of the present invention. The LED filament lighting device 1 illustrated in Figure 3 is similar to the LED filament lighting device 1 illustrated in Figure 1, and the same reference numerals in Figures 1 and 3 indicate the same or similar components having the same or similar function or functionality.

[0061] As mentioned, different configurations of the thermally conductive layer 8 are possible and the first material and the second material may for example be included in respective (sub-)layers of the thermally conductive layer 8. Such a configuration is illustrated in Figure 3. In particular, according to the embodiment of the present invention illustrated in Figure 3, the thermally conductive layer 8 comprises (e.g., at least) a first sub-layer 9 and a second sub-layer 10 coupled with the first sub-layer 9. The first sub-layer 9 may comprises the first material and the second sub-layer comprises the second material.

[0062] Further according to the embodiment of the present invention illustrated in Figure 3, the thermally conductive layer 8 is configured such that the first sub-layer 9 is arranged between the second sub-layer 10 and the carrier substrate 2. In alternative, the second sub-layer 10 could however instead be arranged between the first sub-layer 9 and the carrier substrate 2.

[0063] However, it is to be understood that a configuration of the thermally conductive layer 8 with first and sub-layers 9, 10 as illustrated in Figure 3 is not required but optional, and another or other configurations are possible, such as with the first material and the second material being included in a single layer and with the first material and the second material possibly being combined (e.g., mixed) in a single layer, as described in the foregoing.

[0064] Further according to the embodiment of the present invention illustrated in Figure 3, the plurality of solid-state light sources 3, 4, 5 is enclosed by means of wavelengthconverting material 12 configured to modify the wavelength of at least some of the light emitted by the plurality of solid-state light sources 3, 4, 5 and impinging on the wavelengthconverting material 12. For example, the solid-state light sources 3, 4, 5 may be arranged to emit light generally in a direction upwards in Figure 3, such that all of most of the light emitted by the solid-state light sources 3, 4, 5 impinges on the wavelength-converting material 12. The wavelength-converting material 12 may for example be realized as an encapsulation of the plurality of solid-state light sources 3, 4, 5 by the wavelength-converting material. The wavelength-converting material may for example comprise a luminescent material such as, for example, a phosphor such as an inorganic phosphor, and / or quantum dots or rods. Possibly, the plurality of solid-state light sources 3, 4, 5 may be enclosed by means of the wavelength-converting material 12, but not the carrier substrate 2 or the thermally conductive layer 8. As illustrated in Figure 3, the plurality of solid-state light sources 3, 4, 5 are enclosed (e.g., completely enclosed) by means of the wavelengthconverting material 12, by the plurality of solid-state light sources 3, 4, 5 being enclosed by the wavelength-converting material 12 together with the carrier substrate 2 (e.g., the second surface 7 of the carrier substrate 2).

[0065] Figure 4 is a schematic sectional view of a LED filament lighting device 1 according to an embodiment of the present invention. The LED filament lighting device 1 illustrated in Figure 4 is similar to the LED filament lighting device 1 illustrated in Figure 1, and the same reference numerals in Figures 1 and 4 indicate the same or similar components having the same or similar function or functionality. According to the embodiment of the present invention illustrated in Figure 4, the thermally conductive layer 8 comprises a reflective sub-layer 11. The reflective sub-layer 11 may be reflective to light. As illustrated in Figure 4, the reflective sub-layer 11 may be a peripheral sub-layer (in relation to other part(s) or portion(s) of the thermally conductive layer 8), such that the reflective sub-layer 11 is arranged in the thermally conductive layer 8 so that a surface of the reflective sub-layer 11 constitutes an outer surface of the thermally conductive layer 8 (in the illustrated embodiment, that outer surface is facing towards the first surface 6 of the carrier substrate 2). The reflective sub-layer 11 may be a non-metallic layer. The reflective sub-layer 11 may be embodied as a coating.

[0066] Figure 5 is a perspective view of a LED filament lighting device 1 according to an embodiment of the present invention. The LED filament lighting device 1 illustrated in Figure 5 is similar to the LED filament lighting device 1 illustrated in Figure 2, and the same reference numerals in Figures 2 and 5 indicate the same or similar components having the same or similar function or functionality. According to the embodiment of the present invention illustrated in Figure 5, the thermally conductive layer 8 comprises a base portion 31 which extends parallel with the carrier substrate 2. The base portion 31 of the thermally conductive layer 8 may thus have equal dimensions, especially the same width, as the carrier substrate 2. The thermally conductive layer 8 is configured such that each of two lateral edges 32 and 33 of the thermally conductive layer 8 comprises a plurality of fins 34 to 36 and 37 to 39, respectively, projecting from the base portion 31 of the thermally conductive layer 8. As illustrated in Figure 5, the plurality of fins 34 to 39 are arranged in spaced relation with each other. In particular, the fins 34 to 36 of the lateral edge 32 are arranged in spaced relation with each other, and the fins 37 to 39 of the lateral edge 33 are arranged in spaced relation with each other. By employing such fins, which may be referred to as cooling fins, the temperature of the solid-state light sources 3, 4, 5 in operation may be further reduced while maintaining the typical appearance of a LED filament.

[0067] It is to be understood that only some of the fins illustrated in Figure 5 are indicated by reference numerals. While reference is made herein to the fins 34 to 36 of the lateral edge 32 and to the fins 37 to 39 of the lateral edge 33, this may mean a reference to all of the fins of the lateral edge 32 and all of the fins of the lateral edge 33, respectively. Furthermore, it is to be understood the number of fins illustrated in Figure 5 is according to an example, and the LED filament lighting device 1 illustrated in Figure 5 may comprise fewer or more fins than what is illustrated in Figure 5. In particular, the lateral edge 32 may comprise fewer or more fins than illustrated in Figure 5, and the lateral edge 33 may comprise fewer or more fins than illustrated in Figure 5. Moreover, while Figure 5 illustrates the fins as having a (e.g., generally) rectangular shape, such a shape of the fins is according to an example, and one or more of the fins may have another or other shapes than illustrated in Figure 5 while still being able to further reduce the temperature of the solid-state light sources 3, 4, 5 in operation, as will be recognized by a person skilled in the art in the light of the disclosure of the fins herein.

[0068] The thermally conductive layer 8 may be configured such that a fin distance between adjacent fins of the plurality of fins is in a range between 1 mm and 4 mm. In particular, the fins 34 to 36 of the lateral edge 32 may be configured such that a fin distance between adjacent fins of the plurality of fins is in a range between 1 mm and 4 mm. In alternative or in addition, the fins 37 to 39 of the lateral edge 33 may be configured such that a fin distance between adjacent fins of the plurality of fins is in a range between 1 mm and

[0069] 4 mm.

[0070] In alternative or in addition, the thermally conductive layer 8 may be configured such that a fin width of each fin of the plurality of fins is in a range between 4 mm and 6 mm. In particular, the fins 34 to 36 of the lateral edge 32 may be configured such that a fin length of each fin of the plurality of fins is in a range between 4 mm and 6 mm. In alternative or in addition, the fins 37 to 39 of the lateral edge 33 may be configured such that a fin length of each fin of the plurality of fins is in a range between 4 mm and 6 mm.

[0071] In alternative or in addition, the thermally conductive layer 8 may be configured such that a fin width of each fin of the plurality of fins is in a range between 2.5 mm and 5 mm. In particular, the fins 34 to 36 of the lateral edge 32 may be configured such that a fin width of each fin of the plurality of fins is in a range between 2.5 mm and

[0072] 5 mm. In alternative or in addition, the fins 37 to 39 of the lateral edge 33 may be configured such that a fin width of each fin of the plurality of fins is in a range between 2.5 mm and

[0073] 5 mm.

[0074] Figure 6 is a schematic view of a lamp 20 according to an embodiment of the present invention. The lamp 20 comprises a plurality of LED filament lighting devices 1 according to an embodiment of present invention. Only one of the LED filament lighting devices 1 is indicated by a reference numeral in Figure 6. It is to be understood that the number of the LED filament lighting devices 1 illustrated in Figure 6 is according to an example, and that the lamp 20 may comprise fewer or more LED filament lighting devices 1 than what is illustrated in Figure 6.

[0075] In accordance with the embodiment of the present invention illustrated in Figure 6, the lamp 20 comprises a base 15, which may be configured to electrically and mechanically connect the lamp 20 to a luminaire, e.g., to a socket of a luminaire. The lamp 20 comprises a transmissive envelope 14 (e.g., a light-transmissive envelope) that is coupled to the base 15 and is at least in part enclosing the LED filament lighting devices 1. The transmissive envelope 14 may for example be made of glass. The base 15 may include or be constituted by any suitable type of coupler or connector, for example an Edison screw base, a bayonet fitting, or any other type of connection which may be suitable for the particular type of luminaire. The lamp 20 may comprise one or more controllers, or control units (not shown in Figure 6), which may be configured to control operation of the solid-state light sources of each of the LED filament lighting devices 1. The one or more controllers or control units may be configured to control operation of the solid-state light source of each of the LED filament lighting devices 1 at least with respect to switching on and switching off each or any of the solid-state light source of the respective ones of the LED filament lighting devices 1.

[0076] As indicated in Figure 6, the LED filament lighting devices 1 may be suspended within the transmissive envelope 14 for example by means of some appropriate supporting structure 16, e.g., using any appropriate supporting structure as known in the art.

[0077] While the present invention has been illustrated in the appended drawings and the foregoing description, such illustration is to be considered illustrative or exemplifying and not restrictive; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the appended 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 measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A light-emitting diode, LED, filament lighting device (1) comprising: an elongated carrier substrate (2) comprising at least one ceramic material, wherein the carrier substrate has at least a first surface (6) and a second surface (7) opposite to the first surface, wherein the carrier substrate (2) has a carrier substrate width Wc measured in a width direction of the LED filament lighting device; a plurality of solid-state light sources (3, 4, 5) configured to, in operation, emit light, wherein the plurality of solid-state light sources is arranged in an array on the second surface of the carrier substrate; and a thermally conductive layer (8) arranged at at least a portion of the first surface of the carrier substrate, wherein at least a portion of the thermally conductive layer comprises a first material that is graphene-based and a second material that is metal-based; wherein the LED filament lighting device (1) has a filament length and a filament width, wherein the filament length is more than five times the filament width, wherein the thermally conductive layer comprises a base portion (31) extending in parallel with the carrier substrate, the thermally conductive layer being configured such that at least one lateral edge (32, 33) of the thermally conductive layer comprises a plurality of fins (34-39) projecting from the base portion of the thermally conductive layer in the width direction and extending at least partly beyond the carrier substrate (2), the plurality of fins being arranged in spaced relation with each other, wherein each fin of the plurality of fins has a fin width WF measured in the width direction, and wherein WF < Wc.

2. A lighting device according to claim 1, wherein the second material comprises or is constituted by at least one of copper and aluminum.

3. A lighting device according to any one of claims 1-2, wherein the first material and the second material are included in a single layer.

4. A lighting device according to any one of claims 1-2, wherein the thermally conductive layer comprises a first sub-layer (9) and a second sub-layer (10) coupled with the first sub-layer, wherein the first sub-layer comprises the first material and the second sublayer comprises the second material.

5. A lighting device according to claim 4, wherein the thermally conductive layer is configured such that the first sub-layer is arranged between the second sub-layer and the carrier substrate.

6. A lighting device according to claim 4, wherein the thermally conductive layer is configured such that the second sub-layer is arranged between the first sub-layer and the carrier substrate.

7. A lighting device according to any one of claims 4-6, wherein a thickness of the first sub-layer is in a range between 10 pm and 30 pm and / or a thickness of the second sub-layer is in a range between 10 pm and 30 pm.

8. A lighting device according to claim 7, wherein the first sub-layer comprises graphene comprised in a graphene layer.

9. A lighting device according to any one of claims 1-8, wherein the thermally conductive layer comprises a reflective sub-layer (11).

10. A lighting device according to any one of claims 1-9, wherein a thickness of the thermally conductive layer is in a range between 10 pm and 200 pm.

11. A lighting device according to any one of claims 1-10, wherein at least one of the plurality of solid-state light sources comprises a LED configured to, in operation, emit light having a peak wavelength in a blue wavelength range from 420 nm to 500 nm.

12. A lighting device according to any one of claims 1-11, wherein the plurality of solid-state light sources is enclosed by means of wavelength-converting material (12) configured to modify the wavelength of at least some of the light emitted by the plurality of solid-state light sources and impinging on the wavelength-converting material.

13. A lighting device according to claim 12, wherein of the carrier substrate, the thermally conductive layer and the plurality of solid-state light sources, only the plurality of solid-state light sources is enclosed by means of the wavelength-converting material.

14. A lighting device according to any one of claims 1-13, wherein the thermally conductive layer is configured such that: a fin distance DF between adjacent fins of the plurality of fins is in a range between 1 mm and 4 mm; a fin length LF of each fin of the plurality of fins is in a range between 4 mm and 6 mm; and / or the fin width WF of each fin of the plurality of fins is in a range between2.5 mm and 5 mm.

15. A lamp (20) or luminaire comprising a lighting device (1) according to any one of the preceding claims.

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