Snap-on LED filament cover for improved off-state appearance

Abstract

The present invention relates to a LED filament (200) having a length axis (LA), the LED filament(200) comprising: a carrier (201) extending along the length axis and a plurality of LEDs (202) arranged on a first major surface (205) of the carrier (201)., The plurality of LEDs (202) is arranged to emit LED light. The LED filament (100) further comprises an encapsulant (203) extending along the length axis, at least partially covering the carrier (201) and at least partially enclosing the plurality of LEDs (202), the encapsulant having an outer diameter, D1. The encapsulant (203) comprises a luminescent material (210) arranged to at least partly convert the LED light into converted light. The LED filament (200) further comprises an elongated sleeve (204) enclosing at least 80% of the encapsulant (203). The elongated sleeve (204) has an inner sleeve surface (204') facing towards the encapsulant (203) and being in physical contact with the encapsulant (203). The elongated sleeve (204) further has an outer sleeve surface (204") facing away from the encapsulant (203). The elongated sleeve (204) is arranged to reflect part of the converted light, to transmit part of the converted light, and to provide the LED filament (200) with a white or metallic off-state appearance. The elongated sleeve (204) comprises one of the following: (i) a heat shrink, and (ii) a flexible plastic sheet extending along the length axis and being curled around the length axis.

Description

[0001] 2024PF80039

[0002] 1

[0003] SNAP-ON LED FILAMENT COVER FOR IMPROVED OFF-STATE APPEARANCE

[0004] FIELD OF THE INVENTION

[0005] The present invention generally relates to a LED filament comprising an elongated sleeve that can be removably engaged with an encapsulant by snapping it on or snapping it of the encapsulant.

[0006] BACKGROUND OF THE INVENTION

[0007] LED filaments have been developed for the use in LED lightning devices and is continuing to attract attention. In particular, such LED filaments may be incorporated in lighting devices due to its high energy and cost efficiency, and because they have shown to be useful in many applications. The LED filament comprises an array of light emitting diodes arranged on a carrier. The LED filament is often encapsulated by an encapsulant comprising a phosphor-based luminescent material which at least partly converts the light emitted by the LEDs into converted light to obtain a certain desired light (spectrum). In such an embodiment, the desired light directed to the end-user is chosen after parameters such as color temperature and brightness.

[0008] However, a problem often perceived in relation to LED filaments used in lighting devices is that, in an off-state, the LED filament often has a yellow-orange appearance due to the phosphor-based luminescent material comprised in the encapsulant. This yellow-orange appearance in an off-state is undesired by the end-user, since it may disturb the all-around impression of the interior in which the LED filament is arranged.

[0009] Therefore, there is a need to provide an alternative LED filament in particular for use in a lighting device which at least partly alleviate one or more of above-described drawbacks.

[0010] SUMMARY OF THE INVENTION

[0011] It is therefore an object of the present invention to overcome at least some of the above-mentioned drawbacks. This and other objects are achieved by means of a LED filament as defined in the appended independent claim(s). Other embodiments are defined by the dependent claims. It is noted that other embodiments using all possible combinations of 2024PF80039

[0012] 2 features recited in the above-described embodiments may be envisaged. Thus, the present disclosure also relates to all possible combinations of features mentioned herein.

[0013] Considering the above, the present invention provides a LED filament, having a length axis. The LED filament of the present invention comprises a carrier extending along the length axis and a plurality of LEDs arranged on a first major surface of the carrier. The plurality of LEDs is arranged to emit LED light.

[0014] The first major surface of the carrier may be flat or may have other geometrical shapes such as a round surface, or an ellipsoid surface, or a diamond shaped surface. The carrier may further be a light transmissive carrier. The term “transmissive” shall not be construed to be limiting, rather it shall be interpreted broadly to include terms such as “translucent” and “transparent”. In such an embodiment as described, the LED filament light may be emitted in all directions, such that the light emission profile is preferably omnidirectional.

[0015] The LED filament further comprises an encapsulant extending along the length axis, at least partially covering the carrier and at least partially enclosing the plurality of LEDs. The encapsulant has an outer diameter, DI. The encapsulant comprises a luminescent material arranged to at least partly convert the LED light into converted light,

[0016] The luminescent material may be any of an inorganic luminescent particles, quantum dots, quantum rods, an organic luminescent material or a combination of two or more of these luminescent particles. The first luminescent material may also comprise other types of luminescent particles.

[0017] The luminescent material may comprise a green-yellow and / or red phosphor.

[0018] The luminescent material may comprise a luminescent material of the type AsBsOn Ce. A may comprise one or more of Lu, Y, La, Gd, Tb. B may comprise one or more of Al, Ga, In and Sc.

[0019] The luminescent material may comprise a luminescent material of the type AsBsOn Ce, wherein A may comprise 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 may comprise 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 2024PF80039

[0020] 3 aluminum. Such garnets may be doped with cerium (Ce), with praseodymium (Pr) or a combination of cerium and praseodymium, especially however with Ce. Especially, B may comprise aluminum (Al); however, in addition to aluminum, B may also partly comprise gallium (Ga) and / or scandium (Sc) and / or indium (In), especially up to about 20 % of B, more especially up to about 10 % of B (z.e., the B ions essentially consist of 90 or more mole % of Al and 10 or less mole % of one or more of Ga, Sc and In); B may especially comprise up to about 10% gallium. In another variant, B and O may at least partly be replaced by Si and N. The element A may especially be selected from the group consisting of yttrium (Y), gadolinium (Gd), terbium (Tb) and lutetium (Lu). Further, Gd and / or Tb are especially only present up to an amount of about 20 % of A. In a specific embodiment, the garnet luminescent material comprises (Yi-xLux)3B50i2:Ce, wherein x is equal to or larger than 0 and equal to or smaller than 1. The term “:Ce,” indicates that part of the metal ions (z.e., in the garnets: part of the “A” ions) in the luminescent material is replaced by Ce. For instance, in the case of (Yi-xLux)3AhOi2:Ce, part of Y and / or Lu is replaced by Ce. This is known to the person skilled in the art. Ce will replace A in general for not more than 10 %; in general, the Ce concentration will be in the range of 0.1 to 4%, especially 0.1 to 2 % (relative to A). Assuming 1 % Ce and 10% Y, the full correct formula could be (Yo.iLuo.sgCeo.o sALOn. Ce in garnets is substantially or only in the trivalent state, as is known to the person skilled in the art.

[0021] The LED filament is arranged to provide, in operation, LED filament light. The LED filament light comprises (i) converted light or (ii) a combination of part of the LED light and the converted light.

[0022] The LED filament light may be white light having a correlated color temperature in a range from 1800 K to 6500 K, preferably in a range from 1800 K to 2700 K, and for example a color rendering index of at least 80, or at least 85.

[0023] The LED filament further comprises an elongated sleeve enclosing at least 80% or at least 90% of the encapsulant. The term “elongated” is in the context of the present invention intended to mean having an extension in one direction being significantly greater than an extension in any other direction. The elongated sleeve has an inner sleeve surface facing towards the encapsulant and being in physical contact with the encapsulant. The elongated sleeve has an outer sleeve surface facing away from the encapsulant. The elongated sleeve is arranged to reflect, such as scatter or specularly reflect, part of the converted light, to transmit part of the converted light, and to provide the LED filament with a white or metallic off-state appearance. 2024PF80039

[0024] 4

[0025] The elongated sleeve comprises one of the following:

[0026] (i) a heat shrink, and

[0027] (ii) a flexible plastic sheet extending along the length axis and being curled around the length axis.

[0028] According to the present invention, the elongated sleeve provides, in the off state, the LED filament with a metallic or white appearance. Further, the elongated sleeve is arranged to reflect part of the converted light and to transmit part of the converted light.

[0029] Moreover, the end-user will perceive the elongated sleeve, in the off state, as having a white or a metallic appearance. It shall be noted that the white or metallic appearance of the elongated sleeve may also be a “white-ish” or a “metallic-ish”, or a white-metallic appearance. The terms “white-ish” and “metallic-ish” are in the context of the present invention intended to mean a color significantly close to the definition of white or significantly close to the definition of metallic, but not limited to being exactly white or exactly metallic. Furthermore, the term white-metallic is intended to mean a mixed color appearance of white and metallic.

[0030] It should be stressed that the white or metallic appearance of the elongated sleeve, in the off state, means the white or metallic color is not due to white or metallic light of, for example, the plurality of LEDs or a further luminescent encapsulant.

[0031] In embodiments, the heat shrink and / or flexible plastic sheet may enclose or cover at least 80 % or at least 90 % or at least 95 % such as 100 % of the encapsulant.

[0032] In embodiments, the elongated sleeve may be a snap-on LED filament cover.

[0033] In embodiments, the elongated sleeve may absorb less than 10 % or less than 5 % of the LED light and / or converted light.

[0034] Heat shrinking tubes are manufactured in various ways depending on the specific intended use of the heat shrink. Commonly a heat shrink is made of a polymer, which shrinks radially (but not longitudinally) when being heated. However, the chemical composition of the heat shrink may easily be adapted to the intended use in a certain application. In the context of the present invention, the heat shrink composition may be adapted to be fit for use on a LED filament.

[0035] The applying procedure of a heat shrink is commonly made in the following steps. Firstly, the LED filament need to be prepared to receive the heat shrink. With other words, the LED filament need to be clean and free from any type of debris. If needed a lubricant may be applied to the LED filament to ease the applying of the heat shrink to the 2024PF80039

[0036] 5

[0037] LED filament. Further, the heat shrink need to be measured and cut in the desired and correct length. The heat shrink is subsequently slid over the LED filament. When the heat shrink is arranged on the desired position heat is applied to the heat shrink. The applied heat will shrink the heat shrink, and thus the inner diameter of the heat shrink becomes smaller, such that the heat shrink encapsulates or covers the LED filament. Lastly, after the heat shrink has cooled down it is perfectly fitted around the LED filament.

[0038] In embodiments, the elongated sleeve (for example a heat shrink and / or a flexible plastic sheet) may fully enclosing or cover the encapsulant. In embodiments, the elongated sleeve (for example a heat shrink and / or a flexible plastic sheet) may fully enclosing or cover the encapsulant. In embodiments, the encapsulant may be an elongated encapsulant. In embodiments, the elongated sleeve and / or the (elongated) encapsulant may have a length of at least 40 mm or at least 50 mm, such as 70 mm. In embodiments, the (elongated) encapsulant may have a diameter (such as a thickness and / or width) in a range from 1 to 4 mm. In embodiments, the elongated sleeve may have a diameter (such as a thickness and / or width) in a range from 3 to 7 mm.

[0039] The elongated sleeve of the LED filament may comprise a heat shrink. Further, the heat shrink may comprise a heat shrink tubing comprising a shrinkable plastic. The shrinkable plastic of the elongated sleeve may comprise a thermoplastic material. Preferably, the thermoplastic material may comprise a polyolefin, a fluoropolymer, PVC, neoprene, a silicone elastomer, Viton™, or a combination thereof. The thermoplastic material may also comprise other types of polymers having thermodynamic properties which make them heat resistant or heat stable.

[0040] The elongated sleeve of the LED filament may comprise a flexible plastic sheet extending along the length axis and being curled around the length axis, such that the elongated sleeve is clamped around the encapsulant.

[0041] The elongated sleeve of the LED filament may be configured to be removably engaged with the encapsulant. In such an embodiment, the elongated sleeve is easily mounted on the LED filament, and the elongated sleeve is easily removed from the LED filament. Furthermore, exchange of the elongated sleeve is facilitated.

[0042] The elongated sleeve may have a tubular shape and a slit extending along the length axis. The slit may have a first end portion and a second end portion opposite the first end portion. The first and the second end portions extend along the length axis, and the slit is configured to enable the elongated sleeve to be removably engaged with the encapsulant. In 2024PF80039

[0043] 6 such an embodiment, the elongated sleeve is easily mounted on the LED filament, and the elongated sleeve is engaged tight against the encapsulant, such that the LED filament is kept slim. The term “slim” is in the context of the present invention intended to mean that even though the elongated sleeve is mounted on the encapsulant, the LED filament is not substantially broader or thicker compared to when the elongated sleeve is not mounted on the encapsulant.

[0044] The elongated sleeve may have (in a relaxed or unmounted state) an inner diameter D2 which may be equal to the outer diameter DI of the encapsulant (D2 = DI), or less than DI (D2 < DI), or larger than DI (D2 > DI). In the first configuration the elongated sleeve may have a perfect fit onto the encapsulant. In the second configuration the elongated sleeve may (well) clamp around the encapsulant. In the third configuration the elongated sleeve may be easily fitted around the encapsulant.

[0045] In a mounted state of the sleeve, the first end portion and the second end portion of the slit may be in contact with each other. In such an embodiment, the inner diameter D2 of the elongated sleeve is equal to or slightly larger than the outer diameter DI of the encapsulant. By the term “slightly larger” is understood as being at maximum 3 % larger.

[0046] In a mounted state of the sleeve, the first end portion and the second end portion may overlap each other. In embodiments where the first and second end portions overlap, the inner diameter D2 of the elongated sleeve is larger than the outer diameter DI of the encapsulant, (D2 > DI). Further in such an embodiment, the elongated sleeve fully encloses the encapsulant. In such an embodiment, the elongated sleeve provides an optimal hiding effect. The term “hiding” in the context of the present invention is intended to mean covering such that the end-user may not, in the off state, perceive or view the encapsulant of the LED filament which the elongated sleeve encapsulates.

[0047] The first end portion and the second end portion may be configured , in a mounted state, to have a gap between each other. In such an embodiment, the inner diameter D2 of the elongated sleeve is less than the outer diameter DI of the encapsulant, (D2 < DI). Moreover, in such an embodiment the end-user may perceive or view a small part of the encapsulant of the LED filament. Such an embodiment offers the advantage of an improved arrangement on the encapsulant of the LED filament.

[0048] Alternatively, the inner diameter D2 of the elongated sleeve may be equal to or smaller than the outer diameter DI of the encapsulant, or D2 < (Dl+1 mm), or D2 < (DI +2 mm). 2024PF80039

[0049] 7

[0050] The slit may be arranged on a side of the encapsulant facing away from the first major surface of the carrier. In other words, the slit may be arranged such that it does not interfere with the LEDs being arranged on the first major surface of the carrier, thus offering the advantage of improved LED filament light provided by the LED filament of the present invention. In such an embodiment, the slit may be arranged anywhere on the back side of the LED filament, and may not be perceived, in the off state, from the frontside of the LED filament. Alternatively, the slit may be arranged in a plane of the carrier.

[0051] The elongated sleeve may act as a clamp configured to have a clamping function on the encapsulant. Thus, the engagement of the elongated sleeve and the encapsulant is improved. In the context of the present invention “improved engagement” is intended to mean that the elongated sleeve and the encapsulant are engaged such that there is no space in between the two.

[0052] The LED filament may have a first thickness, and the elongated sleeve may have a second thickness, and the second thickness is less than half of the first thickness. In such an embodiment, the LED filament is kept slim. The term “slim” is in the context of the present invention intended to mean that even though the elongated sleeve is mounted on the encapsulant, the LED filament is not substantially broader or thicker compared to when the elongated sleeve is not mounted on the encapsulant.

[0053] The elongated sleeve may comprise a polymer matrix comprising a crosslinked silicone. Preferably the crosslinked silicone may comprise one or more of crosslinked PDMS, PMPS and PDPS. Such an embodiment offers the advantage of improved reliability, for example improved optical performance over lifetime or lifetime as such.

[0054] In an off state of the LED filament, the elongated sleeve may have a white appearance. To this end, the elongated sleeve may comprise white pigment particles. In particular, the white pigment particles may comprise one or more of titanium dioxide (TiCL), barium sulphate (BaSCU), aluminum oxide (AI2O3) and zirconium oxide (ZrCh). However, it shall not be excluded that the white pigment particles may comprise other white particles. These white pigment particles have a relatively high reflectivity.

[0055] In an off state of the LED filament, the elongated sleeve may have a metallic appearance. To this end, the elongated sleeve may comprise metallic particles or a metallic layer. 2024PF80039

[0056] 8

[0057] In particular, the elongated sleeve may comprise a coating comprising one or more of aluminum (Al), silver (Ag), and gold (Au). However, it shall not be excluded that the metallic particles may comprise other metals.

[0058] The encapsulant may further be configured to, in the on-state, diffuse at least part of the LED light and / or at least part of the converted light. In such an embodiment, the LED light and / or the converted light may be perceived as more homogenous by the end-user. Further, in such an embodiment, the LEDs of the plurality of LEDs are prevented from being perceived as dots or multiple light sources by the end-user. Rather, the plurality of LEDs may be perceived as a single light source.

[0059] The LED filament of the present invention may comprise an electrical circuitry to provide electrical power to the plurality of LEDs and connecting means for mechanically connecting the LED filament to a connector.

[0060] Further, the present invention may relate to a LED filament arrangement comprising a controller and a LED filament as described above. The controller may be configured to control the LED filament light emitted by the LED filament.

[0061] Finally, the present invention may relate to a luminaire or a lamp comprising the LED filament or LED filament arrangement described above.

[0062] It is noted that the invention relates to all possible combinations of features recited in the claims. Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following. This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

[0063] BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Exemplifying embodiments will now be described in more detail, with reference to the following appended drawings:

[0065] As illustrated in the figures, the sizes of the elements and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of the embodiments. Like reference numerals refer to like elements throughout.

[0066] Figure 1 A schematically shows a cross-sectional view of an exemplifying LED filament according to the prior art. 2024PF80039

[0067] 9

[0068] Fig. IB schematically shows a cross-sectional view of another exemplifying LED filament according to the prior art.

[0069] Fig. 2 schematically shows a cross-sectional view of a LED filament according to a second embodiment of the present invention.

[0070] Fig. 3 schematically shows a cross-sectional view of a LED filament according to a third embodiment of the present invention.

[0071] Fig. 4 schematically shows a cross-sectional view of a LED filament according to a fourth embodiment of the present invention.

[0072] Figs. 5A, 5B, and 5C schematically show a cross-sectional view of a LED filament according to an embodiment of the present invention, wherein the three figures illustrate the mounting of the elongated sleeve from its unmounted state to its mounted state.

[0073] Fig. 6A schematically shows a side-view of an exemplifying LED filament according without an elongated sleeve.

[0074] Fig. 6B schematically shows a side-view of an exemplifying embodiment of the LED filament according to the present invention.

[0075] Fig. 7 schematically shows a perspective-view of a lamp for illumination with incorporated LED filaments according to the present invention.

[0076] Fig. 8 schematically shows a perspective-view of a luminaire for illumination with incorporated LED filaments according to the present invention.

[0077] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0078] Exemplifying embodiments will now be described more fully hereinafter with reference to the accompanying drawings in which currently preferred embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

[0079] Figure 1 A shows a LED filament 100 according to the prior art. The LED filament 100 is arranged to provide, in operation, LED filament light. The LED filament 100 comprises a carrier 101 extending along the length axis and a plurality of LEDs 102 arranged on a first major surface 105 of the carrier 101. The first major surface 105 of the carrier 101 shown in Figure 1 A is flat. 2024PF80039

[0080] 10

[0081] The plurality of LEDs 102 is arranged to emit LED light. The LED filament 100 further comprising an encapsulant 103 extending along the length axis, partly covering the carrier 101 and fully enclosing the plurality of LEDs 102. The encapsulant 103 has an outer diameter, DI. The width of the carrier 101 is equal to the outer diameter, DI, of the encapsulant 103. Thus, the right and left end portion of the carrier 101 are not covered by the encapsulant 103. The encapsulant 103 comprises a luminescent material 110 arranged to at least partly convert the LED light into converted light. The encapsulant 103 in Figurel A, may be applied to the LED filament 100 by dispensing.

[0082] Figure IB shows another LED filament 100 according to the prior art. The LED filament 100 is arranged to provide, in operation, LED filament light. The LED filament 100 comprises a carrier 101 extending along the length axis and a plurality of LEDs 102 arranged on a first major surface 105 of the carrier 101. The first major surface 105 of the carrier 101 shown in Figure IB is flat.

[0083] The plurality of LEDs 102 is arranged to emit LED light. The LED filament 100 further comprising an encapsulant 103 extending along the length axis, fully covering the carrier 101 and fully enclosing the plurality of LEDs 102. The encapsulant 103 has an outer diameter, DI. The encapsulant 103 comprises a luminescent material 110 arranged to at least partly convert the LED light into converted light. The encapsulant 103 in Figure IB may be applied to the LED filament 100 by overmolding.

[0084] Figure 2 shows a first embodiment of the LED filament 200. The LED filament 200 is arranged to provide, in operation, LED filament light. The LED filament 200 comprises a carrier 201 extending along the length axis, and a plurality of LEDs 202 arranged on a first major surface 205 of the carrier 201. The first major surface 205 of the carrier 201 is flat. The plurality of LEDs 202 is arranged to emit LED light. The LED filament 200 further comprising an encapsulant 203 extending along the length axis, and (fully) covering the carrier 201 and also (fully) enclosing the plurality of LEDs 202. The encapsulant has an outer diameter, DI. The encapsulant 203 comprises a luminescent material 210 arranged to at least partly convert the LED light into converted light.

[0085] The LED filament 200 further comprises an elongated sleeve 204 enclosing at least 80% of the encapsulant 203. The elongated sleeve 204 has an inner sleeve surface 204’ facing towards the encapsulant 203 and being in physical contact with the encapsulant 203. The elongated sleeve 204 has an outer sleeve surface 204” facing away from the encapsulant 203. The elongated sleeve 204 has a slit 208 extending along the length axis. The slit 208 has 2024PF80039

[0086] 11 a first end portion 206 and a second end portion 207 opposite the first end portion 206. The first and the second end portions 206, 207 extend along the length axis. In Figure 2, the inner diameter D2 of the elongated sleeve 204 is equal to the outer diameter DI of the elongated encapsulant 203, such that the elongated sleeve 204 perfectly fits the shape of the elongated encapsulant 203. The slit 208 is small and positioned on the backside of the LED filament 200, z.e., facing the direction being opposite to the first major surface of the carrier 205.

[0087] Figure 3 shows a second embodiment of the LED filament 300. The LED filament 300 comprises a carrier 301 extending along the length axis, and a plurality of LEDs 302 arranged on a first major surface 305 of the carrier 301. The first major surface 305 of the carrier 301 is flat. The plurality of LEDs 302 is arranged to emit LED light. The LED filament 300 further comprises an encapsulant 303 extending along the length axis, and fully covering the carrier 301 and fully enclosing the plurality of LEDs 302. The encapsulant has an outer diameter, DI. The encapsulant 303 comprises a luminescent material 310 arranged to at least partly convert the LED light into converted light.

[0088] The LED filament 300 further comprises an elongated sleeve 304 enclosing at least 80 % of the encapsulant 303. The elongated sleeve 304 has an inner sleeve surface 304’ facing towards the encapsulant 303 and being in physical contact with the encapsulant 303. The elongated sleeve 304 has an outer sleeve surface 304” facing away from the encapsulant 303. The elongated sleeve 304 has a slit 308 extending along the length axis. The slit 308 has a first end portion 306 and a second end portion 307 opposite the first end portion 306. The first and the second end portions 306, 307 extend along the length axis. In the embodiment shown in Figure 3, the first and second end portions 306, 307 are configured to overlap each other, thus providing optimal coverage of the encapsulant 303. In Figure 3, the inner diameter D2 of the elongated sleeve 204 is greater than the outer diameter DI of the elongated encapsulant 303, such that an overlap between the first and second end portions 306, 307 is formed.

[0089] Figure 4 shows a third embodiment of the LED filament 400. The LED filament 400 comprises a carrier 401 extending along the length axis, and a plurality of LEDs 402 arranged on a first major surface 405 of the carrier 401. The first major surface 405 of the carrier 401 is flat. The plurality of LEDs 402 is arranged to emit LED light. The LED filament 400 further comprises an encapsulant 403 extending along the length axis, and fully covering the carrier 401 and the plurality of LEDs 402. The encapsulant has an outer diameter, DI. The 2024PF80039

[0090] 12 encapsulant 403 comprises a luminescent material 410 arranged to at least partly convert the LED light into converted light.

[0091] The LED filament 400 further comprises an elongated sleeve 404 enclosing at least 80 % of the encapsulant 403. The elongated sleeve 404 has an inner sleeve surface 404’ facing towards the encapsulant 403 and being in physical contact with the encapsulant 403. The elongated sleeve 404 has an outer sleeve surface 404” facing away from the encapsulant 403. The elongated sleeve 404 has a slit 408 extending along the length axis. The slit 408 has a first end portion 406 and a second end portion 407 opposite the first end portion 406. The first and the second end portions 406, 407 extend along the length axis. In Figure 4, the first end portion 406 and the second end portion 407 are configured to have a gap between each other such that the slit 408 may be perceived, in the mounted state, by the end-user. The slit 406 is arranged to be aligned in a plane of the carrier 401. Such an embodiment offers the advantage of facilitated mounting of the elongated sleeve 404. In Figure 4, the inner diameter D2 of the elongated sleeve 404 is smaller than the outer diameter DI of the elongated encapsulant 403, such that a gap is formed between the first and the second end portions 406, 407.

[0092] Figure 5A shows a fourth embodiment of the LED filament 500 arranged to provide, in operation, LED filament light. The LED filament 500 comprises a carrier 501 extending along the length axis, and a plurality of LEDs 502 arranged on a first major surface 505 of the carrier 501. The first major surface 505 of the carrier 501 is flat. The plurality of LEDs 502 is arranged to emit LED light. The LED filament 500 further comprises an encapsulant 503 extending along the length axis and covering the carrier 501 and the plurality of LEDs 502. The encapsulant 503 has an outer diameter, DI. The encapsulant 503 comprises a luminescent material 510 arranged to at least partly convert the LED light into converted light. The LED filament 500 in Figure 5A is arranged to receive a sleeve 504 to enclose the encapsulant 503. Further, the sleeve 504 to be received is a heat shrink.

[0093] In Figure 5B, a LED filament 500 with a heat shrink 504 being slid over the encapsulant 503 and enclosing the encapsulant 503 is shown. The inner diameter, D2, of the heat shrink 504 is larger than the diameter, DI, of the encapsulant 503.

[0094] Figure 5C shows a LED filament 500 where the heat shrink has been heated to tightly fit around the encapsulant 503.

[0095] The heat shrink 504 may be applied on the LED filament 500 by the following method steps. 2024PF80039

[0096] 13

[0097] At a first step, the LED filament 500 is prepared to receive the heat shrink 504. Such a preparation makes sure that the LED filament 500 is clean and free from any debris. The LED filament 500 is measured and a piece of the heat shrink 504 having a desired length is cut.

[0098] At a second step, the heat shrink 504 is arranged in its intended position by sliding the heat shrink 504 over the LED filament 500 and ensuring that the heat shrink 503 covers the entire length of the LED filament 500.

[0099] At a third step, the heat shrink 504 is heated, for example using a heat gun or a similar heat source, to evenly apply heat to the heat shrink 504. Heating may start from one end of the heat shrink 504 and gradually move to the other end of the heat shrink 504, to ensure that the heat shrink 504 shrinks uniformly around the LED filament 500.

[0100] At a fourth step, the heat shrink 504 is cooled and it is ensured that the heat shrink 504 is applied in the correct position and that the heat shrink 504 is securely fitted around the LED filament 500.

[0101] Figure 5C shows the result of the above method applied on LED filament 500 according to the present invention.

[0102] The above method to apply a heat shrink 504 on a LED filament 500 is only one exemplifying method, and it shall not be excluded that other methods may be used to apply a heat shrink 504 on a LED filament 500 in order to achieve the present invention.

[0103] Figure 6A shows a side-view of a LED filament according to the prior art. The LED filament in Figure 6A shows the main problem of the prior art, i.e., that the LED filament in an off-state has a yellow-orange appearance due to the phosphor-based luminescent material comprised in the encapsulant. This is shown by the dark grayscale of the encapsulant of the LED filament shown in Figure 6A.

[0104] Figure 6B illustrates a side-view of the LED filament according to the present invention. The outer surface of the LED filament shown in Figure 6B is covered by an elongated sleeve 604. Thereby, in contrast to the prior art shown in Figure 6A, the LED filament in Figure 6B does not show the characteristic yellow-orange appearance as the prior art. Instead, the LED filament according to the present invention shown in Figure 6B has a white or metallic appearance.

[0105] Figure 7. illustrates an exemplifying embodiment of the present invention of the LED filament 700, where the LED filament 700 is a part of a lamp for illumination. 2024PF80039

[0106] 14

[0107] Finally, Figure 8 illustrates another exemplifying embodiment of the present invention of the LED filament 800, where the LED filament 800 is part of a luminaire for illumination.

[0108] Although the present invention has been described with reference to various embodiments, those skilled in the art will recognize that changes may be made without departing from the scope of the invention. It is intended that the detailed description be regarded as illustrative and that the appended claims including all the equivalents are intended to define the scope of the invention.

Claims

2024PF8003915CLAIMS:

1. A LED filament (200) having a length axis, the LED filament (200) comprising: a carrier (201) extending along the length axis, a plurality of LEDs (202) arranged on a first major surface (205) of the carrier (201), the plurality of LEDs (202) being arranged to emit LED light, and an encapsulant (203) extending along the length axis, at least partially covering the carrier (201) and at least partially enclosing the plurality of LEDs (202), the encapsulant (203) having an outer diameter, wherein the encapsulant (203) comprises a luminescent material (210) arranged to at least partly convert the LED light into converted light, wherein the LED filament (200) further comprises an elongated sleeve (204) enclosing at least 80 % of the encapsulant (203), wherein the elongated sleeve (204) has an inner sleeve surface (204’) facing towards the encapsulant (203) and being in physical contact with the encapsulant (203), wherein the elongated sleeve (204) has an outer sleeve surface (204”) facing away from the encapsulant (203), wherein the elongated sleeve (204) is arranged to reflect part of the converted light, to transmit part of the converted light, and to provide the LED filament (200) with a white or metallic off-state appearance, wherein the elongated sleeve (204) comprises one of the following:(i) a heat shrink, and(ii) a flexible plastic sheet, the flexible sheet extending along the length axis and being curled around the length axis, and wherein, when the elongated sleeve (204) comprises the flexible plastic sheet, the elongated sleeve (204) has a tubular shape and a slit (308) extending along the length axis, wherein the slit (308) has a first end portion (306) and a second end portion (307) opposite the first end portion (306), the first end portion (306) and the second end portion (307) extending along the length axis, the slit (308) being configured to enable the elongated sleeve (204) to be removably engaged with the encapsulant (303).2024PF80039162. The LED filament (200) according to claim 1, wherein the heat shrink comprises a heat shrink tubing, and wherein the heat shrink tubing comprises a shrinkable plastic.

3. The LED filament (200) according to claim 2, wherein the shrinkable plastic comprises a thermoplastic material.

4. The LED filament (200) according to claim 1, wherein, when the elongated sleeve (204) comprises the flexible plastic sheet, the elongated sleeve (204) is clamped around the encapsulant (203).

5. The LED filament (300) according to any one of the preceding claims , wherein, in a mounted state, the first end portion (306) and the second end portion (307) overlap each other.

6. The LED filament (400) according to any one of the preceding claims , wherein, in a mounted state, the first end portion (406) and the second end portion (407) have a gap between each other.

7. The LED filament (400) according to any one of the preceding claims, wherein the slit (408) is arranged on a side of the encapsulant (403) facing away from the first major surface (405) of the carrier (401), or wherein the slit (408) is arranged in a plane of the carrier (401).

8. The LED filament (500) according to any of the preceding claims, wherein, when the elongated sleeve (204) comprises the flexible plastic sheet the elongated sleeve (504) has an inner diameter in an unmounted state, the inner diameter being equal to or less than the outer diameter of the encapsulant (403).

9. The LED filament (200) according to any of the preceding claims, wherein the elongated sleeve (204) comprises a polymer matrix comprising a crosslinked silicone.2024PF800391710. The LED filament (200) according to any of the preceding claims, wherein, in an off state of the LED filament:(i) the elongated sleeve (204) has a white appearance, wherein the elongated sleeve (204) comprises white pigment particles, or (ii) the elongated sleeve (204) has a metallic appearance, wherein the elongated sleeve comprises metallic particles or a metallic layer.

11. A LED filament arrangement comprising a controller and a LED filament according to any one of claims 1 to 10.

12. A luminaire or a lamp comprising the LED filament according to any one of claims 1 to 10, or the LED filament arrangement according to claim 11.

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