LED filament comprising a plurality of leds and a substrate

Abstract

: A light emitting diode, LED, filament (100) configured to provide, in an on- state, LED filament light (110), is provided. The LED filament comprises an elongated substrate (120), an array of a plurality of light emitting diodes, LEDs (130), configured to, in operation, emit LED light (140), and an elongated encapsulant (150) covering the plurality of LEDs and at least partially covering a first major surface (160) of the elongated substrate, wherein the plurality of LEDs is at least partly recessed in the elongated substrate.

Description

[0001] LED filament comprising a plurality of LEDs and a substrate

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to a light emitting diode, LED, filament. More specifically, the present invention relates to a LED filament comprising a plurality of light emitting diodes, LEDs, and a substrate.

[0004] BACKGROUND OF THE INVENTION

[0005] The use of light emitting diodes, LEDs, for illumination purposes continues to attract attention. Compared to incandescent lamps, fluorescent lamps, neon tube lamps, etc., LEDs provide numerous advantages such as a longer operational life, a reduced power consumption, and an increased efficiency related to the ratio between light energy and heat energy.

[0006] Due to the advantageous aspects of the use of LEDs, the interest has rapidly increased to replace conventional light sources with LEDs in many lighting arrangements. It will be appreciated that this replacement, also called retrofitting, is appreciated and desired by users who wish to have the look of an incandescent bulb. The light source replacement (retrofitting) is often performed by removing the conventional light source(s) from the luminaire (e.g. a lamp holder) of the lighting arrangement and attaching the LEDs, LED arrangement(s) or LED device(s) into the luminaire. One of these concepts is based on LED filaments which are placed in a bulb. The visible LED filament(s) may provide a light distribution which is effective and decorative at the same time, whilst taking advantage of LED technology.

[0007] It is desired to even further improve the assembly (e.g., easy pick-and-place, reliable fixation, etc.), performance (e.g., optical and / or thermal performance), functionality and / or appearance (e.g., more slim) of LED filaments and / or LED filament devices comprising one or more LED filaments. More specifically, there is a wish to provide an augmented aesthetical appearance of the LED filament(s) and / or the emitted LED filament light, whilst still providing an efficient LED filament lighting during operation, and an improved performance and / or functionality of the light emission and / or light distribution from the LED filament(s). In US 2020 / 105724 an LED filament is disclosed that includes a carrier composed of a material transparent to electromagnetic radiation, two electrical terminals located on the carrier and at least two radiation-emitting semiconductor chips arranged on the carrier, wherein the semiconductor chips are electrically connected to the electrical terminals, wherein undersides of the semiconductor chips are connected by way of an adhesive layer to the carrier, wherein the adhesive layers comprise a first conversion material, wherein the first conversion material is configured to shift at least a portion of a wavelength of radiation from the semiconductor chips, wherein the semiconductor chips comprise a conversion layer on upper sides and on lateral areas, wherein the conversion layers are configured to shift at least a portion of the wavelength of the radiation from the semiconductor chips, wherein a transparent matrix material mixed with a second conversion material covers the semiconductor chips, and wherein sedimented conversion layers with an increased concentration of the second conversion material cover the upper sides and lateral areas of the semiconductor chips.

[0008] WO 2017 / 085063 discloses an LED filament comprising a substrate element that has a reflective first main surface to which a plurality of LED chips is applied in a row along a main direction of extension, and a first electric contact point in a first end region on the first main surface of the substrate element. The LED chips are electrically connected in series. Also disclosed are another LED filament, two methods for producing an LED filament, and a retrofitted lamp comprising an LED filament.

[0009] SUMMARY OF THE INVENTION

[0010] It is of interest to explore the possibility of combining one or more of the numerous advantages of LED filaments comprising LEDs, whilst improving the assembly, performance, functionality and / or appearance of the LED filaments.

[0011] This and other objects are achieved by providing a LED filament having the features in the independent claim. Preferred embodiments are defined in the dependent claims.

[0012] According to the present invention, there is provided a LED filament configured to provide, in an on-state, LED filament light. The LED filament comprises an elongated substrate, an array of a plurality of LEDs configured to, in operation, emit LED light, and an elongated encapsulant covering the plurality of LEDs and at least partially covering a first major surface of the elongated substrate. The plurality of LEDs is at least partly recessed in the elongated substrate. Thus, the present invention is based on the idea of providing a LED filament comprising an elongated substrate, an array of a plurality of LEDs, and an elongated encapsulant covering the plurality of LEDs and at least partially covering a first major surface of the elongated substrate, wherein the plurality of LEDs is at least partly recessed in the elongated substrate. By the recessed arrangement or provision of the plurality of LEDs at least partly within the elongated substrate, the LED filament provides numerous advantages related to its assembly, performance, functionality and / or appearance.

[0013] The present invention is particularly advantageous concerning the recessed arrangement or provision of the plurality of LEDs within the elongated substrate, resulting in a slimmer LED filament compared to LED filaments of the prior art. The relatively slim LED filament thus provided consequently leads to an efficient saving of space, and further provides the benefit of a more appealing appearance of the LED filament.

[0014] The present invention is further advantageous concerning the embedding and / or placement of the plurality of LEDs in the elongated substrate, leading to a facilitated assembly of the LED filament (e.g., by a pick-and-place process). Thus, in embodiments the plurality of LEDs may be embedded in the elongated substrate. The wording embedded means fully enclosed. Thus, in embodiments the plurality of LEDs may be fully enclosed in / by the elongated substrate.

[0015] The present invention is further advantageous in that the recessed embedding of the plurality of LEDs in the elongated substrate achieves a reliable fixation of the plurality of LEDs, consequently leading to an improved overall mechanical stability and / or operational reliability of the LED filament.

[0016] The present invention is further advantageous in that the recessed arrangement or provision of the plurality of LEDs at least partly within the elongated substrate improves the optical and / or thermal performance of the LED filament. Concerning the optical performance, the LED filament may achieve a particularly appealing lighting effect from the plurality of LEDs at least partly recessed in the elongated substrate. Furthermore, the thermal performance of the LED filament may be improved as the heat-generating LEDs may efficiently dissipate its heat to the elongated substrate at least partially enclosing the plurality of LEDs, thereby achieving an improved thermal management.

[0017] The present invention is further advantageous in that the LED filament may achieve less spottiness by its arrangement of the LEDs at least partly recessed in the elongated substrate. The present invention is further advantageous in that the numerous advantages of using LED technology may be combined with the attractiveness and the appealing properties of the LED filament as disclosed.

[0018] The present invention is further advantageous in that the LED filament of the present invention comprises relatively few components. The low number of components is advantageous in that the LED filament is relatively inexpensive to fabricate. Moreover, the low number of components of the LED filament implies an easier recycling, especially compared to devices or arrangements comprising a relatively high number of components which impede an easy disassembling and / or recycling operation.

[0019] There is provided a LED filament configured to provide, in an on-state, LED filament light. Preferably, the LED filament has a length, LF, and a width, WF, wherein LF > 5WF. 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. The LED filament may extend along a length axis, LX. The LED filament comprises an elongated substrate. The elongated substrate (carrier) may, for instance, 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). The elongated substrate may be reflective or light transmissive, such as translucent and preferably transparent. The LED filament comprises an array of a plurality of LEDs configured to, in operation, emit LED light. By the term “array”, it is here meant that the plurality of LEDs may be provided in a configuration that extends linearly, or substantially linearly, e.g. as an arrangement or chain of LEDs, or the like. The LED filament further comprises an elongated encapsulant covering the plurality of LEDs and at least partially covering a first major surface of the elongated substrate. By the term “encapsulant”, it is here meant an elongated material, element, arrangement, or the like, which in the present context is configured or arranged to cover, surround, encapsulate and / or enclose the plurality of LEDs and at least partially cover, surround, encapsulate and / or enclose a first major surface of the elongated substrate. The elongated encapsulant may be flexible. The plurality of LEDs is at least partly recessed in the elongated substrate. Hence, the elongated substrate is configured or arranged to at least partly enclose or accommodate the plurality of LEDs. In other words, the plurality of LEDs is arranged at least partly within the elongated substrate.

[0020] According to an embodiment of the present invention, the LED filament light may be white light having a correlated color temperature, CCT, in a range of 1700 - 6500 K and e.g. a color rendering index, CRI, of least 80 or at least 85. According to an embodiment of the present invention, the elongated substrate may comprise a plurality of recesses, and wherein each recess of the plurality of recesses at least partly accommodates a respective LED of the plurality of LEDs. By “recess”, it is here meant a cavity, accommodation, or the like, of the elongated substrate. In case of a number, N, of LEDs of the LED filament, the number of recesses, N, may be the same according to the embodiment. The present embodiment of the one-to-one relationship between the number of LEDs and the number of recesses is particularly advantageous concerning the assembly, performance, functionality and / or appearance of the LED filament. In embodiments, each recess of the plurality of recesses may be conformal to the LED recessed in the recess, i.e. that the recesses and LEDs may have (about) the same shape and dimensions.

[0021] According to an embodiment of the present invention, the plurality of LEDs may be completely recessed in the elongated substrate. Hence, the dimensions of the recess(es) or cavity(ies) of the elongated substrate may be larger than the dimension(s) of the plurality of LEDs. Alternatively, the dimensions of the recess(es) or cavity(ies) of the elongated substrate may correspond to the dimension(s) of the plurality of LEDs, such that the plurality of LEDs is arranged flush with the first major surface of the elongated substrate.

[0022] According to an embodiment of the present invention, the plurality of LEDs may be arranged flush with the first major surface of the elongated substrate. Hence, the plurality of LEDs is recessed in the elongated substrate such that a top portion or surface of the plurality of LEDs is arranged flush with the first major surface of the elongated substrate.

[0023] According to an embodiment of the present invention, neighboring LEDs of the plurality of LEDs may be electrically connected by at least one wire bond e.g. embedded in the elongated encapsulant. By “wire bond” it is here meant an interconnection in the form of one or more wires arranged or configured for electrical connection between neighboring LEDs of the array of the plurality of LEDs. The present embodiment is advantageous in that the wire bonds provide a convenient electrical interconnection between the neighboring LEDs. The present embodiment is further advantageous in that the wire bonds may provide a mechanical connection and / or stability between the plurality of LEDs and the elongated encapsulant in which the wire bond(s) is (are) embedded. It will be appreciated that this effect may be attained considering the relatively high flexibility of the elongated substrate (e.g., if the elongated substrate comprises a silicone polymer), thereby even further contributing to the mechanical stability of the LED filament. It should be noted, however, that in order to safeguard the electrical operational reliability of the LED filament, the wire bond(s) may be configured, arranged and / or designed such that the wire bond(s) minimize(s) any impact on the flexibility of the elongated substrate and / or the elongated encapsulant. In other words, the wire bond(s) may be configured, arranged and / or designed to minimize detrimental mechanical stress to one or more components or constituents of the LED filament, as mechanical stress, in turn, could lead to failure of the electrical connection of the array of the plurality of LEDs. The wire bond(s) hereby provided may accordingly improve the (mechanical and / or electrical) operational stability of the LED filament to an even further extent.

[0024] According to an embodiment of the present invention, the LEDs of the plurality of LEDs may be flip-chip LEDs electrically connected by at least one interconnecting element e.g. embedded in the elongated encapsulant. By the term “flip-chip LED”, it is here meant a LED which may be arranged or mounted upside down in the LED filament (arrangement). By “interconnecting element”, it is here meant substantially any element arranged or configured for electrical connection between the flip-chip LEDs of the plurality of LEDs. The present embodiment of flip-chip LEDs is particularly advantageous concerning the heat management properties of the LED filament, and the energy consumption of the LED filament may hereby be even further decreased.

[0025] According to an embodiment of the present invention, the flip-chip LEDs of the plurality of LEDs may be arranged back-to-back and partly superimposed. Hence, the flip-chip LEDs of the plurality of LEDs may be arranged so that they are at least partly overlapping, and in a back-to-back manner. It should be noted that the flip-chip LEDs are at least partly recessed in the elongated substrate, e.g. by every second flip-chip LED being recessed in the elongated substrate.

[0026] According to an embodiment of the present invention, the elongated substrate may be an elongated polymer substrate e.g. comprising a (cross-linked) silicone polymer.

[0027] According to an embodiment of the present invention, the elongated substrate may comprise a (crosslinked) silicone polymer e.g. selected from the group consisting of polydimethylsiloxane, PDMS, polymethylphenyl siloxane, PMPS, and polydiphenylsiloxane, PDPS or combinations thereof.

[0028] According to an embodiment of the present invention, the elongated encapsulant may comprise a (crosslinked) silicone polymer e.g. selected from the group consisting of polydimethylsiloxane, PDMS, polymethylphenylsiloxane, PMPS, and polydiphenylsiloxane, PDPS or combinations thereof.

[0029] According to an embodiment of the present invention, the elongated encapsulant may comprise a silicone polymer, and wherein the silicone polymer of the elongated polymer substrate and the silicone polymer of the elongated encapsulant may comprise a crosslinked silicone selected from the group consisting of polydimethylsiloxane, PDMS, polymethylphenyl siloxane, PMPS, and polydiphenylsiloxane, PDPS or combinations thereof. This implies that the crosslinked silicone comprises at least one of polydimethylsiloxane, PDMS, polymethylphenylsiloxane, PMPS, and polydiphenylsiloxane, PDPS. The present embodiment is advantageous in that these mentioned materials are optimal concerning the ability to withstand high (levels of) flux of the emitted LED light. Hence, the selection of this (these) material(s) may increase the service life of the LED filament and / or promotes the operation of the LED filament, thereby even further increasing the reliability of the LED filament.

[0030] According to an example of the present invention, the elongated substrate may further comprise transparent beads. For example, the transparent beads may constitute (small) glass beads, e.g. with the same or similar refractive index as silicone. The present example is advantageous in that the transparent beads increase the thermal conductivity of the elongated substrate, thereby improving the thermal management of the LED filament during operation. The present example is further advantageous in that the transparent beads provide higher efficiency because of less back scattering.

[0031] According to an embodiment of the present invention, the elongated substrate may be manufactured by polymer molding e.g. injection molding or extrusion molding. The present embodiment is advantageous in that the polymer molding is convenient as well as time and / or cost-efficient.

[0032] According to an embodiment of the present invention, the elongated substrate may have a rectangular (cross-sectional) shape (i.e. in a cross-section measured in a plane perpendicular to a length axis of the LED filament).

[0033] According to an embodiment of the present invention, the elongated encapsulant may have a non-polygonal / non-rectangular (cross-sectional) shape (i.e. in a cross-section measured in a plane perpendicular to a length axis of the LED filament). The cross-sectional shape of the encapsulant may have rounded edges or may be half-oval shaped.

[0034] According to an embodiment of the present invention, the elongated encapsulant may be dispensed on top of the first major surface of the elongated substrate.

[0035] According to an embodiment of the present invention, the elongated encapsulant may comprise a (crosslinked) silicone polymer.

[0036] According to an embodiment of the present invention, the elongated encapsulant may comprise at least one of a first luminescent material configured to at least partly convert the emitted LED light into first converted light, and a first light-scattering material configured to at least partly scatter the emitted LED light into first scattered light. Hence, the elongated encapsulant may comprise a first luminescent material configured to at least partly convert the emitted LED light into first converted light and / or a first lightscattering material configured to at least partly scatter the emitted LED light into first scattered light. In embodiments, the first luminescent material may comprise a first greenyellow phosphor and / or a first orange / red phosphor.

[0037] According to an embodiment of the present invention, the elongated encapsulant may be dispensed on top of the first major surface of the elongated substrate, wherein the elongated encapsulant comprises a silicone polymer, and wherein the elongated encapsulant comprises at least one of a first luminescent material configured to at least partly convert the emitted LED light into first converted light, and a first light-scattering material configured to at least partly scatter the emitted LED light into first scattered light. Hence, the elongated encapsulant, which may at least partly cover the first major surface of the elongated substrate, may be dispensed on top of the first major surface of the elongated substrate. Furthermore, the elongated encapsulant comprises a silicone polymer, and the elongated encapsulant comprises a first luminescent material configured to at least partly convert the emitted LED light into first converted light and / or a first light-scattering material configured to at least partly scatter the emitted LED light into first scattered light. The first luminescent material may be a phosphor such as an inorganic phosphor and / or quantum dots or rods. The present embodiment is advantageous in that the provision of the first luminescent material and / or the first light-scattering material in the elongated encapsulant may achieve a particularly efficient light distribution and / or a particularly appealing lighting effect from the LED filament during operation.

[0038] According to an embodiment of the present invention, at least one of (i) the elongated substrate comprises at least one of a second luminescent material configured to at least partly convert the emitted LED light (and / or the first converted light) into second converted light, and a second light-scattering material configured to at least partly scatter the emitted LED light (and / or the first scattered light) into second scattered light, and (ii) the LED filament comprises a further elongated encapsulant at least partially covering a second major surface, opposite the first major surface, of the elongated substrate, the further elongated encapsulant comprises at least one of a third luminescent material configured to at least partly convert the emitted LED light into third converted light, and a third lightscattering material configured to at least partly scatter the emitted LED light into third scattered light, is fulfilled. Hence, the elongated substrate of the LED filament may comprise a second luminescent material and / or a second light-scattering material for light-conversion and light-scattering purposes, respectively. Alternatively, or in combination n with this, the LED filament may comprise a further elongated encapsulant comprising a third luminescent material and / or a third light-scattering material for light-conversion and light-scattering purposes, respectively. The present embodiment is advantageous in that the second luminescent material and / or the second light-scattering material, on the one hand, and the further elongated encapsulant comprising a third luminescent material and / or a third lightscattering material, on the other hand, may even further improve the optical properties of the LED filament. The present embodiment is advantageous in that the second luminescent material, the second light-scattering material, the further elongated encapsulant, the third luminescent material and / or the third light-scattering material may be optimized (e.g. comprising different properties) in order to achieve desired (light distribution and / or aesthetical) properties of the LED filament light. In embodiments, the second luminescent material may comprise a second green-yellow phosphor and / or a second orange / red phosphor. In embodiments, the third luminescent material may comprise a third green-yellow phosphor and / or a third orange / red phosphor. In embodiments, the concentration, composition and / or type of the second luminescent material in the elongated substrate may be different from the concentration, composition and / or type of the first luminescent material in the elongated encapsulant. In embodiments, the concentration, composition and / or type of the second luminescent material in the elongated substrate may be different from the concentration, composition and / or type of the third luminescent material in the further elongated encapsulant. The obtained effect in improved spectral and / or spatial light distribution e.g. improved color over angle.

[0039] In embodiments, the further elongated encapsulant may be dispensed on top of the second major surface of the elongated substrate. The further elongated encapsulant may comprise a silicone polymer e.g. a crosslinked silicone polymer such as crosslinked PDMS, PDPS, PMPS or combinations / copolymers thereof.

[0040] According to an embodiment of the present invention, the elongated substrate may be light-transmissive and / or flexible. The present embodiment is advantageous in that the light-transmissive property of the elongated substrate may even further enhance the desired (light distribution and / or aesthetical) properties of the LED filament light. For example, the light-transmissive property of the elongated substrate may achieve (substantially) omnidirectional lighting. According to an embodiment of the present invention, the elongated substrate has a refractive index, m, and the elongated encapsulant has a refractive index, n2, wherein |ni - n2| < 0.2. Hence, the elongated substrate and the elongated encapsulant may have refractive indexes which are similar, almost the same or even the same. It will be appreciated that the elongated substrate and the elongated encapsulant may be formed of the same (base) material, optionally with different (concentrations) of luminescent material and / or lightscattering material. The elongated substrate and the elongated encapsulant may hereby have similar or the same mechanical properties. In embodiments, the further elongated encapsulant may have a refractive index, ns, wherein |m - ns| < 0.2 and / or |n2 - ns| < 0.2.

[0041] According to an example of the present invention, there is provided a LED filament arrangement comprising at least one LED filament according to any one of the preceding embodiments. The LED filament arrangement may further comprise a controller coupled to the at least one LED filament, wherein the controller is configured to control the LED light emitted from the plurality of LEDs. By “controller”, it is here meant any device, unit, or the like, which is able to control the LED light either by wire or via wireless technology. In case the LED filament arrangement comprises a plurality of LED filaments, the controller may control each LED filament individually. The present example is advantageous in that the controller may conveniently and efficiently control the emitted LED light, thereby even further ameliorating the light emission from the LED filament(s) and improving the appearance and / or the decorative aspect of the LED filament(s) and / or LED filament arrangement.

[0042] According to an embodiment of the present invention, there is provided a LED lighting device comprising at least one LED filament according to any one of the preceding embodiments. Alternatively, the LED lighting device may comprise a LED filament arrangement according to the previous example. The LED lighting device further comprises a controller configured to control the LED filament light provided by the LED filament e.g. the controller may be configured to individually control subsets of the plurality of LEDs. The present embodiment is advantageous in that the LED lighting device, comprising the LED filament(s), combines the aspects of a desired light emission and aesthetical appearance provided via the LED filament(s) and / or via the feature(s) of the LED lighting device. For example, the controller may be configured to alter / change the color point (e.g. change color) and / or color temperature (e.g. at least 500K difference) of the LED filament light.

[0043] According to an embodiment of the present invention, there is provided a LED filament lamp comprising at least one LED filament or the LED lighting device according to the previously described embodiment. The LED filament lamp may comprise a light- transmissive (e.g. transparent) envelope (or cover) at least partly enclosing the at least one LED filament. The LED filament lamp may (further) comprise a connector configured to electrically and mechanically connect the LED filament to a socket or a socket of a luminaire.

[0044] According to an embodiment of the present invention, there is provided a LED filament luminaire comprising at least one LED filament or the LED lighting device or the LED filament lamp according to any one of the preceding embodiments. The LED filament luminaire may comprise a light exit window configured to exit LED filament light as luminaire light.

[0045] According to an embodiment of the present invention, there is provided a method of producing a LED filament (configured to provide, in an on-state, LED filament light).

[0046] The method may comprise the following steps: (A) providing an elongated substrate (according to any one of the preceding embodiments), (B) providing an array of a plurality of light emitting diodes, LEDs, (configured to, in operation, emit LED light), and at least partly recessing the plurality of LEDs in the elongated substrate, and (C) covering the plurality of LEDs, and at least partially covering a first major surface of the elongated substrate, by an elongated encapsulant. The elongated substrate may be made by (polymer) molding e.g. injection molding or extrusion. The plurality of LEDs may be attached to the elongated substrate e.g. using a glue.

[0047] Alternatively, the method may comprise the following steps: (A) providing an array of a plurality of light emitting diodes, LEDs, (configured to, in operation, emit LED light) e.g. onto a surface and / or in a (elongated) mold, (B) providing a polymerizable liquid onto the plurality of LEDs, (C) solidifying (i.e. polymerizing) the polymerizable liquid obtaining a (solid) elongated substrate (according to any one of the preceding embodiments) such that the plurality of LEDs are at least partly recessed in the elongated substrate, (D) covering the plurality of LEDs, and at least partially covering a first major surface of the elongated substrate, by an elongated encapsulant. The elongated encapsulant may be applied by e.g. dispensing a (fluid) polymer material which may be crosslinked afterwards. Polymerization / curing / solidifying may be done by using suitable (photo / heat) initiators (in combination with (UV) light and / or heat).

[0048] According to an embodiment of the present invention, the method of producing a LED filament may further comprise the step of electrically connecting neighboring LEDs of the plurality of LEDs by at least one wire bond. It will be appreciated that after a (subsequent) step of the method of covering the plurality of LEDs with an encapsulant, the wire bond(s) become(s) embedded in the elongated encapsulant.

[0049] According to an embodiment of the present invention, the method of producing a LED filament may further comprise the steps of providing the LEDs of the plurality of LEDs as flip-chip LEDs, and electrically connecting the flip-chip LEDs by at least one interconnecting element. It will be appreciated that after a (subsequent) step of the method of covering the plurality of LEDs with an encapsulant, the interconnecting element(s) become(s) embedded in the elongated encapsulant.

[0050] Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following.

[0051] BRIEF DESCRIPTION OF THE DRAWINGS

[0052] 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.

[0053] Fig. 1 shows a LED filament lamp according to the prior art,

[0054] Figs. 2-8 schematically show cross-sections of LED filaments according to exemplifying embodiments of the present invention,

[0055] Fig. 9 schematically shows a LED lighting device according to an exemplifying embodiment of the present invention, and

[0056] Figs. 10-12 schematically show methods of producing a LED filament according to examples of the present invention.

[0057] DETAILED DESCRIPTION

[0058] Fig. 1 shows a LED filament lamp 10 according to the prior art, comprising a plurality of LED filaments 20. LED filament lamps 10 of this kind are highly appreciated as they are very decorative, as well as providing numerous advantages compared to incandescent lamps such as a longer operational life, a reduced power consumption, and an increased efficiency related to the ratio between light energy and heat energy. However, it is of interest to improve the properties of the light distribution emitted from the LED filaments 20, and to even further augment the decorative appearance and / or aspect of the LED filaments 20 and / or the LED filament lamps 10. It is further of interest to improve the assembly, performance and / or functionality of the LED filaments 20.

[0059] Fig. 2 schematically shows a cross-section of a LED filament 100 according to an exemplifying embodiment of the present invention. The LED filament 100 is configured to provide (emit) LED filament light 110 in an on-state of the LED filament 100. The LED filament light 110 may, for example, be white light having a correlated color temperature, CCT, in a range of 1700 - 6500 K and a color rendering index, CRI, of least 80. The LED filament 100 extends along a length axis, LX. Preferably, the LED filament 100 has a length, LF, and a width, WF, wherein LF > 5WF. The LED filament 100 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.

[0060] The LED filament 100 comprises an elongated substrate 120. The elongated substrate 120 (carrier) may, for instance, 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). The elongated substrate 120 may be reflective or light transmissive, such as translucent and preferably transparent. The elongated substrate 120 may be an elongated polymer substrate comprising a silicone polymer. Furthermore, the silicone polymer may comprise a crosslinked silicone selected from the group consisting of polydimethylsiloxane, PDMS, polymethylphenylsiloxane, PMPS, and polydiphenylsiloxane, PDPS. The elongated substrate 120 may be manufactured by polymer molding. Furthermore, the elongated substrate may comprise transparent beads, e.g. (small) glass beads.

[0061] The LED filament 100 comprises an array of a plurality of LEDs 130 configured to, in operation, emit LED light 140. It should be noted that the LED filament 100 may comprise substantially any number of LEDs of the plurality of LEDs 130. The plurality of LEDs 130 preferably comprises more than 5 LEDs, more preferably more than 8 LEDs, and even more preferred more than 10 LEDs. The plurality of LEDs 130 may be direct emitting LEDs which provide a color.

[0062] The LED filament 100 further comprises an elongated encapsulant 150 covering the plurality of LEDs 130 and at least partially covering a first major surface 160 of the elongated substrate 120. The elongated encapsulant 150 may be dispensed on top of the first major surface 160 of the elongated substrate 120. The elongated encapsulant 150 may comprise a silicone polymer. The silicone polymer may comprise a crosslinked silicone such as polydimethylsiloxane, PDMS, polymethylphenylsiloxane, PMPS, or polydiphenylsiloxane, PDPS. The silicone polymer of the elongated substrate 120 and the silicone polymer of the elongated encapsulant 150 may comprise the same material.

[0063] The elongated encapsulant 150 may furthermore comprise a first luminescent material configured to at least partly convert the emitted LED light 140 into first converted light, and / or a first light-scattering material configured to at least partly scatter the emitted LED light 140 into first scattered light. The first luminescent material of the elongated encapsulant 150 may be a phosphor such as an inorganic phosphor (e.g. YAG, LuAG, EC AS, KSiF, etc.) and / or quantum dots or rods. The first light-scattering material may, e.g., be a polymer matrix comprising BaSCU, AI2O3 and / or TiCL particles.

[0064] The LED filament 100, in this exemplifying embodiment of Fig. 2, further comprises a pair of electric pins 165, extending from the LED filament 100 on either side thereof.

[0065] The plurality of LEDs 130 of the LED filament 100 is at least partly recessed in the elongated substrate 120. Hence, the elongated substrate 120 is configured or arranged to at least partly enclose or accommodate the plurality of LEDs 130. According to the example of Fig. 2, the plurality of LEDs 130 is recessed in the elongated substrate 120 such that the top surface or part of the plurality of LEDs 130 is arranged flush with the first major surface 160 of the elongated substrate 120.

[0066] Fig. 3 schematically shows a cross-section of a LED filament 100 according to an exemplifying embodiment of the present invention. Compared to the LED filament shown in Fig. 2, the LED filament 100 is shown along the length axis, LX, i.e. that the cross-section is perpendicular to the length axis, LX. The LED filament 100 in Fig. 3 has many features in common with the LED filament 100 shown in Fig. 2, and it is hereby also referred to Fig. 2 for an increased understanding of the features and / or functions of the LED filament 100. In Fig. 3, the view of the elongated substrate 120 shows a (single) recess 170, but it will be appreciated that the elongated substrate 120 may comprise a plurality of recesses 170. By this arrangement, each recess 170 at least partly accommodates a respective LED of the plurality of LEDs 130. As exemplified in Fig. 3, the (width) dimension of the recess 170 is larger than the width (dimension) of the LED 130. Alternatively, the (width) dimension of the recess 170 may correspond to the width (dimension) of the LED 130, such that the LED 130 is (tightly) fitted in the recess 170. Furthermore, as exemplified in Fig. 3, the (depth) dimension of the recess 170 corresponds to the height (dimension) of the LED 130, such that the LED 130 is arranged flush with the first major surface 160. Alternatively, the (depth) dimension of the recess 170 may be smaller or larger than the height (dimension) of the LED 130. Fig. 4 schematically shows a cross-section of a LED filament 100 according to an exemplifying embodiment of the present invention. The LED filament 100 comprises wire bonds 180, wherein neighboring LEDs of the plurality of LEDs 130 are electrically connected by these wire bonds 180 being embedded in the elongated encapsulant 150. The wire bonds 180 are shaped as brackets, extending from the neighboring LEDs into the elongated encapsulant 180.

[0067] Fig. 5 schematically shows a cross-section of a LED filament 100 according to an exemplifying embodiment of the present invention. Here, the LEDs of the plurality of LEDs are flip-chip LEDs 190. Furthermore, the flip-chip LEDs 190 are electrically connected by at least one interconnecting element 200 embedded in the elongated encapsulant 150. In Fig. 5, it is shown that neighboring flip-chip LEDs 190 are electrically connected by these interconnecting elements 200 being embedded in the elongated encapsulant 150.

[0068] Fig. 6 schematically shows a cross-section of a LED filament 100 according to an exemplifying embodiment of the present invention. The LEDs of the plurality of LEDs are flip-chip LEDs 190 which are arranged back-to-back and partly superimposed. Hence, the flip-chip LEDs 190 are arranged so as to partly overlap, and in a back-to-back manner, whereby the array of the flip-chip LEDs 190 is arranged in an alternating manner of the flipchip LEDs 190.

[0069] Fig. 7 schematically shows a cross-section of a LED filament 100 according to an exemplifying embodiment of the present invention. The elongated encapsulant 150, which is dispensed on top of the first major surface 160 of the elongated substrate 120, comprises a silicone polymer and further comprises a first luminescent material 210 configured to at least partly convert the emitted LED light 140 into first converted light and / or a first lightscattering material 220 configured to at least partly scatter the emitted LED light 140 into first scattered light. In Fig. 7, the first luminescent material 210 and first light-scattering material 220 are schematically indicated by dashed ovals, and it should be noted that properties of the first luminescent material 210 and first light-scattering material 220 such as material, concentration, position, etc., may vary and / or be customized. The first luminescent material 210 may be a phosphor such as an inorganic phosphor and / or quantum dots or rods. According to this example, the elongated substrate 120 has a refractive index, m, and the elongated encapsulant 150 has a refractive index, n2, wherein |m - n2| < 0.2.

[0070] Fig. 8 schematically shows a cross-section of a LED filament 100 according to an exemplifying embodiment of the present invention. The light-transmissive, elongated substrate 120 may comprise a second luminescent material 230 configured to at least partly convert the emitted LED light 140 into second converted light and / or a second lightscattering material 240 configured to at least partly scatter the emitted LED light 140 into second scattered light. Alternatively, or in combination with the second luminescent material 230 and / or the second light-scattering material 240 of the elongated substrate 120, the LED filament 100 may further comprise a further elongated encapsulant 250 at least partially covering a second major surface 260, opposite the first major surface, of the elongated substrate 120. The further elongated encapsulant 250 comprises a third luminescent material 270 configured to at least partly convert the emitted LED light 140 into third converted light and / or a third light-scattering material 280 configured to at least partly scatter the emitted LED light 140 into third scattered light.

[0071] Fig. 9 schematically shows a LED lighting device 300 according to an embodiment of the present invention. The LED lighting device 300, which may constitute substantially any kind of lamp or luminaire, comprises one or more LED filaments 100 according to any one of the previously described embodiments. The LED filament lamp 300 further comprises a light-transmissive envelope 310, which is exemplified as being bulbshaped. The light-transmissive envelope 310 at least partially encloses the LED filament(s) 100. The LED filament lamp 300 further comprises a controller 320 (schematically indicated by a dashed rectangle) configured to control the luminous flux of the LED filament light. In case of a plurality of LED filaments 100, the controller 320 may control each LED filament 100 individually.

[0072] Fig. 10 schematically shows a method 400 for producing a LED filament, wherein the LED filament is configured to provide, in an on-state, LED filament light. The method 400 comprises the step of providing 410 an elongated substrate. The method further comprises the steps of providing 420 an array of a plurality of light emitting diodes, LEDs, configured to, in operation, emit LED light, and at least partly recessing 430 the plurality of LEDs in the elongated substrate. The method 400 further comprises the step of covering 440 the plurality of LEDs, and at least partially covering a first major surface of the elongated substrate, by an elongated encapsulant.

[0073] Alternatively, the method 400 of Fig. 10 may comprise the following steps:

[0074] (A) providing an array of a plurality of light emitting diodes, LEDs (configured to, in operation, emit LED light) e.g. onto a surface and / or in a (elongated) mold,

[0075] (B) providing a polymerizable liquid onto the plurality of LEDs, (C) solidifying (i.e. polymerizing) the polymerizable liquid obtaining a (solid) elongated substrate (according to any one of the preceding embodiments) such that the plurality of LEDs are at least partly recessed in the elongated substrate, and

[0076] (D) covering the plurality of LEDs, and at least partially covering a first major surface of the elongated substrate, by an elongated encapsulant. The elongated encapsulant may be applied by dispensing e.g. dispensing a (fluid) polymer material which may be crosslinked afterwards. Polymerization / curing / solidifying may be performed by using suitable (photo / heat) initiators (in combination with (UV) light and / or heat).

[0077] Fig. 11 schematically shows an example of a method 400 for producing a LED filament. The method 400 of Fig. 11 corresponds to the method of Fig. 10, and comprises the (same or corresponding) steps of the method 400 and / or one or more of the alternative method steps of A-D. In addition, the method 400 of Fig. 11 comprises the step of electrically connecting 435 neighboring LEDs of the plurality of LEDs by at least one wire bond, whereby the at least one wire bond, upon the subsequent step 440 of covering the plurality of LEDs with an encapsulant, become(s) embedded in the elongated encapsulant. Hence, the method 400 of Fig. 11 comprises providing 410 an elongated substrate, providing 420 an array of a plurality of light emitting diodes, LEDs, at least partly recessing 430 the plurality of LEDs in the elongated substrate, electrically connecting 435 neighboring LEDs of the plurality of LEDs by at least one wire bond and covering 440 the plurality of LEDs, and at least partially covering a first major surface of the elongated substrate, by an elongated encapsulant, whereby the wire bond(s) become(s) embedded in the elongated encapsulant. It will be appreciated that the step of electrically connecting 435 the plurality of LEDs may alternatively be performed before the step of at least partly recessing 430 the plurality of LEDs in the elongated substrate.

[0078] Alternatively, the step of electrically connecting 435 neighboring LEDs of the plurality of LEDs by at least one wire bond may be comprised in the alternative method according to the above, more specifically in association with step A (of the method steps A- D).

[0079] Fig. 12 schematically shows an example of a method 400 for producing a LED filament. The method 400 of Fig. 12 corresponds to the method of Fig. 10, and comprises the (same or corresponding) steps of the method 400 and / or one or more of the alternative method steps of A-D. In addition, the method 400 of Fig. 12 comprises the step of electrically connecting 435 the flip-chip LEDs by at least one interconnecting element in the elongated encapsulant, whereby the at least one interconnecting element, upon the subsequent step 440 of covering the plurality of LEDs with an encapsulant, become(s) embedded in the elongated encapsulant. Hence, the method of Fig. 12 comprises providing 410 an elongated substrate, providing 420 an array of a plurality of light emitting diodes, LEDs, wherein the LEDs of the plurality of LEDs are flip-chip LEDs, at least partly recessing 430 the plurality of (flip-chip) LEDs in the elongated substrate, electrically connecting 435 the flip-chip LEDs by at least one interconnecting element, and covering 440 the plurality of LEDs, and at least partially covering a first major surface of the elongated substrate, by an elongated encapsulant, whereby the interconnecting element(s) become(s) embedded in the elongated encapsulant. It will be appreciated that the step of electrically connecting 435 the plurality of LEDs may alternatively be performed before the step of at least partly recessing 430 the plurality of LEDs in the elongated substrate.

[0080] Alternatively, the step of electrically connecting 435 the flip-chip LEDs by at least interconnecting element may be comprised in the alternative method according to the above, more specifically in associated with step A (of steps A-D). 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. For example, one or more of the LED filament 100, the elongated substrate 120, the elongated encapsulant 150, etc., may have different shapes, dimensions and / or sizes than those depicted / described.

Claims

CLAIMS:

1. A light emitting diode, LED, filament (100) configured to provide, in an on- state, LED filament light (110), wherein the LED filament comprises an elongated substrate (120), an array of a plurality of light emitting diodes, LEDs (130), configured to, in operation, emit LED light (140), and an elongated encapsulant (150) covering the plurality of LEDs and at least partially covering a first major surface (160) of the elongated substrate, wherein the plurality of LEDs is at least partly recessed or embedded in the elongated substrate; wherein the elongated encapsulant comprises a first luminescent material configured to at least partly convert the emitted LED light into first converted light; wherein the elongated substrate comprises a second luminescent material (230) configured to at least partly convert the emitted LED light into second converted light.

2. The LED filament according to claim 1, wherein the elongated substrate comprises a plurality of recesses (170), and wherein each recess of the plurality of recesses accommodates a respective LED of the plurality of LEDs, and wherein (i) the width dimension of the recess corresponds to the width dimension of the LED and (ii) the depth dimension of the recess corresponds to the height dimension of the LED or the depth dimension of the recess is larger than the height dimension of the LED.

3. The LED filament according to claim 1 or 2, wherein at least one of the following applies: the plurality of LEDs is completely recessed in the elongated substrate; the plurality of LEDs is arranged flush with the first major surface of the elongated substrate.

4. The LED filament according to any one of the preceding claims, wherein the plurality of LEDs are embedded in the elongated substrate.

5. The LED filament according to any one of the preceding claims, wherein neighboring LEDs of the plurality of LEDs are electrically connected by at least one wire bond (180) embedded in the elongated encapsulant.

6. The LED filament according to any one of claims 1-4, wherein the LEDs of the plurality of LEDs are flip-chip LEDs (190) electrically connected by at least one interconnecting element (200) embedded in the elongated encapsulant.

7. The LED filament according to claim 6, wherein the flip-chip LEDs of the plurality of LEDs are arranged back-to-back and partly superimposed.

8. The LED filament according to any one of the preceding claims, wherein the elongated substrate is an elongated polymer substrate comprising a silicone polymer.

9. The LED filament according to claim 8, wherein the elongated encapsulant comprises a silicone polymer, and wherein the silicone polymer of the elongated polymer substrate and the silicone polymer of the elongated encapsulant comprise a crosslinked silicone selected from the group consisting of polydimethylsiloxane, PDMS, polymethylphenylsiloxane, PMPS, and polydiphenylsiloxane, PDPS or combinations thereof.

10. The LED filament according to any one of the preceding claims, wherein the elongated substrate is manufactured by polymer molding.

11. The LED filament according to any one of the preceding claims, wherein the elongated encapsulant is dispensed on top of the first major surface of the elongated substrate, wherein the elongated encapsulant comprises a silicone polymer.

12. The LED filament according to any one of the preceding claims, wherein the LED filament comprises a further elongated encapsulant (250) at least partially covering a second major surface (260), opposite the first major surface, of the elongated substrate, the further elongated encapsulant comprises at least one of a third luminescent material (270) configured to at least partly convert the emitted LED light into third converted light, anda third light-scattering material (280) configured to at least partly scatter the emitted LED light into third scattered light, is fulfilled.

13. The LED filament according to any one of the preceding claims, wherein the elongated substrate is light-transmissive and flexible.

14. The LED filament according to any one of the preceding claims, wherein the elongated substrate has a refractive index, m, and the elongated encapsulant has a refractive index, n2, wherein |m - n2| < 0.2.

15. A LED lighting device (300), comprising at least one LED filament according to any one of the preceding claims, and a controller (320) configured to control the LED filament light provided by the at least one LED filament.

Images