A stretchable LED filament

Abstract

A stretchable LED filament (1) configured to, in operation, provide LED filament light, the stretchable LED filament (1) comprising an elongated carrier (2) comprising a longitudinal direction (L), a transversal direction (T), a first major surface (21), a second major surface (22), a first longitudinal edge (23) and a second longitudinal edge (24), the first and the second longitudinal edge (23 and 24) being mutually opposing edges connecting the first and second major surface (21 and 22), a plurality of LEDs (3) configured to, in operation, provide LED light and being arranged on the first major surface (21), an elongated encapsulant (4) encapsulating the plurality of LEDs (3) and covering at least a portion of the first major surface (21), the elongated carrier (2) being flexible and comprising a meandering shape, the elongated encapsulant (4) being flexible, the first longitudinal edge (23) comprising first recesses (25) and the second longitudinal edge (24) comprises second recesses (26), where each of the first recesses (25) comprise a first extension (27) in the longitudinal direction and each of the second recesses (26) comprise a second extension (28) in the longitudinal direction (L) and are arranged such that the first extension (27) of each first recess (25) forms an overlap (29) with the second extension (28) of at least one directly opposing second recess (26).

Description

[0001] A STRETCHABLE LED FILAMENT

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a stretchable LED filament configured to, in operation, provide LED filament light, the stretchable LED filament comprising an elongated carrier comprising a longitudinal direction, a transversal direction extending perpendicular to the longitudinal direction, a height direction extending perpendicular to both the transversal direction and the longitudinal direction, a first major surface, a second major surface, a first longitudinal edge and a second longitudinal edge, the first longitudinal edge and the second longitudinal edge being mutually opposing longitudinal edges connecting the first major surface and the second major surface, a plurality of LEDs configured to, in operation, provide LED light and being arranged on the first major surface of the elongated carrier, and an elongated encapsulant encapsulating the plurality of LEDs and covering at least a portion of the first major surface. The invention further relates to a luminaire and a lamp comprising such a stretchable LED filament.

[0004] BACKGROUND OF THE INVENTION

[0005] A trend in lighting is LED filament lamps. A LED filament lamp is a LED lamp which is designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes, but with the high efficiency of lightemitting diodes. A recent trend within LED filament lamps is arranging LED filaments in luminaires.

[0006] CN 205447297 U discloses a LED filament which is stretchable in the length direction. The LED filament comprises a metal substrate and a plurality of LEDs. The metal substrate comprises an upper connecting part and a lower connecting part. LEDs are connected with the upper connecting part and the lower connecting part. Z-shaped metal connecting parts are arranged between the upper connecting parts and the lower connecting parts. In other words, spring like parts are inserted between the upper connecting parts and a lower connecting parts. The light emitting surface of the LEDs may further be coated with a fluorescent glue. It is desired to improve the performance, functionality and / or appearance of LED filaments.

[0007] SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to overcome this problem, and to provide a stretchable LED filament with an improved performance, functionality and / or appearance.

[0009] According to a first aspect of the invention, this and other objects are achieved by means of a stretchable LED filament configured to, in operation, provide LED filament light, the stretchable LED filament comprising:

[0010] ■ an elongated carrier comprising a longitudinal direction, a transversal direction extending perpendicular to the longitudinal direction, a height direction extending perpendicular to both the transversal direction and the longitudinal direction, a first major surface, a second major surface, a first longitudinal edge and a second longitudinal edge, the first longitudinal edge and the second longitudinal edge being mutually opposing longitudinal edges connecting the first major surface and the second major surface,

[0011] ■ a plurality of LEDs configured to, in operation, provide LED light and being arranged on the first major surface of the elongated carrier, and

[0012] ■ an elongated encapsulant encapsulating the plurality of LEDs and covering at least a portion of the first major surface, where the elongated carrier is flexible and comprises a meandering shape with bends pointing in the transversal direction, where the elongated encapsulant is flexible, where the first longitudinal edge comprises first recesses and the second longitudinal edge comprises second recesses, where each of the first recesses comprise a first extension in the longitudinal direction and each of the second recesses comprise a second extension in the longitudinal direction, where the first recesses and the second recesses are arranged such that the first extension of each first recess forms an overlap with the second extension of at least one directly opposing second recess, where the LED filament comprises a first length, LI, in an unstretched configuration, the unstretched configuration being achieved when no external forces are applied to the LED filament, where the LED filament comprises a second length, L2, in a stretched configuration, the stretched configuration being achieved when a stretch force is applied to the LED filament, and where the second length is larger than the first length.

[0013] Thereby, and particularly in virtue of that the first longitudinal edge comprises first recesses and the second longitudinal edge comprises second recesses, where each of the first recesses comprise a first extension in the longitudinal direction and each of the second recesses comprise a second extension in the longitudinal direction and are arranged such that the first extension of each first recess forms an overlap with the second extension of at least one directly opposing second recess, a LED filament is provided with which at least one of the performance, functionality and appearance is improved, both in the unstretched condition of the LED filament and in the stretched condition of the LED filament.

[0014] Furthermore, and also in virtue of that the elongated carrier is flexible and comprises a meandering shape with bends pointing in the transversal direction, and where the elongated encapsulant is flexible, a LED filament with an improved functionality, which a simpler and more durable constructions, and which may be fixed in, in principle, any stretched condition, is provided for.

[0015] The elongated encapsulant may be made of a silicone.

[0016] Practical use has shown that silicone is a particularly useful material for stretchable LED filaments as it is both flexible and stretchable and also resistant due to wear caused by the LED light emitted by the plurality of LEDs.

[0017] The stretchable LED filament may comprise a maximum stretching percentage, MS, the maximum stretching percentage being defined as MS = (L2 / L1 - 1)- 100 %, and MS being in a range from 3 % to 30 %. MS is depending on the design / configuration of the (meandering shape of the) elongated carrier. The required MS depends on the lighting application. In embodiments, MS may be at least 3% to obtain a reliable LED filament because LED filaments with no (or very low) stretching characteristics / properties are having a reduced reliability, especially if the LED filament is arranged between two points (exerting a force on the LED filament). In embodiments, MS may be at most 30% to obtain a reliable LED filament because LED filaments with too much stretching characteristics / properties are having a reduced reliability. Other ranges may be acceptable depending on the flexibility and / or reliability of the filament., for instance 3% to 10% for less flexible / reliable types of filaments and 3% to 50% for high flexible / relaible filaments.

[0018] On the one hand, some stretchability is of course needed to make the LED filament stretchable. On the other hand, the stretchability should not be too large since then the improved LED filament appearance and lighting effect may be lost. Furthermore, the amount of stretchability desired is related to the application of the stretchable LED filament. For instance, if it is desired to hang a long, stretchable LED filament between two points, a certain amount of stretchability is needed in order to keep the stretchable LED filament straight, especially over time. In view of these considerations a lower limit of 2 % and an upper limit of 20 % has been found to be particularly suitable.

[0019] The LED filament may be elastic. Thereby, after stretching when the force is removed the LED filament will revert back to its original shape. In the non-elastic case after stretching when the force is removed the LED filament will stay in the stretched configuration.

[0020] The plurality of LEDs may be arranged in a meandering pattern when the stretchable LED filament is in the unstretched configuration, and optionally also when stretchable LED filament is in the stretched configuration, and at least five LEDs may be arranged within a section of the elongated carrier corresponding to the first extension and at least five LEDs may be arranged within a section of the elongated carrier corresponding to the second extension.

[0021] Put in more general terms, the pitch of or gap between the LEDs of the plurality of LEDs may be chosen to be considerably smaller than the turn pitch of the meandering shape of the elongated carrier.

[0022] Thereby, a high quality of LED filament light as well as a particularly wellfunctioning mimicking of a filament is achieved.

[0023] The stretchable LED filament may further comprise electrical circuitry for providing the plurality of LEDs with electrical energy, where the electrical circuitry is arranged in a meandering pattern.

[0024] Thereby, and especially by providing the said meandering pattern of the electrical circuitry, short circuiting is prevented, and a stable electrical connection is obtained.

[0025] The LEDs of the plurality of LEDs may be arranged with a gap between the LEDs being equal to or smaller than 0.5 mm, preferably equal to or smaller than 0.3 mm, more preferably equal to or smaller than 0.2 mm, and most preferably equal to or smaller than 0.1 mm.

[0026] The elongated carrier may be continuous.

[0027] Thereby, especially the appearance of the LED filament is improved, both in the unstretched condition and in the stretched condition.

[0028] The elongated carrier may be made of a polymer. A polymer is a suitable material for the carrier due to the combination of the flexibility and robustness of such materials.

[0029] The meandering shape of the elongated carrier may comprise a sinusoidal pattern or may be free from sharp cuts.

[0030] Thereby, especially the appearance and performance of the LED filament is improved, both in the unstretched condition and in the stretched condition.

[0031] The elongated carrier comprises a width W, and the first recesses and the second recesses each comprise a width WR, and WR may be larger than 0.5 W, or WR may be smaller than or equal to 0.7 W.

[0032] Thereby, the LED filament becomes particularly stretchable.

[0033] The meandering shape of the elongated carrier has a meander width, WM, the first recesses and the second recesses each comprise a length, LR, and LR may be larger than 0.5-WM.

[0034] Thereby it is ensured that each recess extends further than the meander width, which in turn ensures that the LED filament is optimally stretchable.

[0035] The elongated encapsulant may further cover at least part of the first recesses and at least part of the second recesses. Alternatively, or additionally, the elongated encapsulant may be straight.

[0036] Thereby, a stretchable LED filament with an improved stretchability is obtained.

[0037] Parts of the elongated encapsulant covering the recesses may be more flexible than the remaining part of the elongated encapsulant. Alternatively, or additionally, parts of the elongated encapsulant covering the recesses may be thinner as measured in the height direction of the LED filament than the remaining part of the elongated encapsulant. Alternatively, or additionally, parts of the elongated encapsulant covering the recesses may be made of a material being softer than the material of which the remaining part of the elongated encapsulant is made.

[0038] Each of these embodiments ensure that a stretchable LED filament with an improved stretchability is obtained.

[0039] The stretchable LED filament may further comprise a further elongated encapsulant which is flexible, and which covers at least a portion of the second major surface, where the further elongated encapsulant is in physical contact with the elongated encapsulant. Thereby, a stretchable LED filament with an improved stretchability is obtained.

[0040] The plurality of LEDs may be configured to, in operation, provide LED light having a blue color, and the elongated encapsulant may comprise a luminescent material configured to, at least partly, convert the LED light into converted light. Alternatively, or additionally the elongated encapsulant may comprise a light scattering material configured to, at least partly, scatter the LED light into scattered light.

[0041] Each of these embodiments provide for a stretchable LED filament comprising an improved LED filament light or lighting effect and an improved capability of convincingly mimicking a filament.

[0042] The luminescent material may be a green-yellow and red phosphor. Such phosphor are particularly suitable for use in combination with LEDs providing LED light having a blue color.

[0043] The stretchable LED filament may further comprise two mechanical connectors, the two mechanical connectors being attached to the LED filament at opposite ends of the LED filament, and the two mechanical connectors being configured to fix the LED filament in the stretched configuration of the LED filament.

[0044] Thereby, a stretchable LED filament which may be fixed in its stretched condition in a particularly simple manner, and which is particularly simple to attach, e.g., to a luminaire or in a lamp, is provided for.

[0045] The stretchable LED filament may further comprise two electrical connectors, where the two mechanical connectors are arranged next to the two electrical connectors. Alternatively, or additionally, the stretchable LED filament may further comprise two electrical connectors, where the two mechanical connectors comprises the two electrical connectors.

[0046] Each of these two embodiments provide for a stretchable LED filament which may be fixed in its stretched condition in a particularly simple manner, and which is particularly simple to attach, e.g., to a luminaire or in a lamp. In the latter case, the stretchable LED filament is further provided with a particularly simple structure.

[0047] The LED filament may provide LED filament light with a first intensity, II, and a first correlated color temperature, CCT1, in the unstretched configuration, and the LED filament may provide LED filament light with a second intensity, 12, and a second correlated color temperature, CCT2, in the stretched configuration, where II 12, preferably where II > 12, and / or where CCT1 CCT2, preferably where CCT2 > CCT1. In embodiments, I CCT2-

[0048] Thereby a LED filament is provided which comprises at least two different appearances in terms of intensity and / or correlate color temperature of the LED filament light emitted depending on the condition (stretched or unstretched) of the LED filament.

[0049] The invention further relates to a LED lamp or a luminaire comprising a stretchable LED filament according to the invention.

[0050] In embodiments, the LED filament light may be white light, e.g., having a correlated color temperature in a range from 1700K to 6500K and / or a CRI of at least 80. The LED lamp or luminaire may further comprise at least two attachment points, and the stretchable LED filament may comprise at least two mechanical connectors, the two mechanical connectors being attached to the stretchable LED filament at opposite ends of the LED filament, and the two mechanical connectors being configured to be attached to the at least two attachment points in a stretched condition of the stretchable LED filament.

[0051] Such a configuration may be more reliable particularly when the filament becomes hot due to heat generation when the LEDs emit LED light. Such a configuration may further keep the stretchable LED filament straighter, such as during use or over its lifetime. The latter is especially relevant for long stretchable LED filaments, such as stretchable LED filaments with a length in the unstretched condition being larger than 10 cm or larger than 20 cm.

[0052] The at least two attachment points of the LED lamp or luminaire may comprise two end attachment points arranged to enable fixing the stretchable LED filament in a maximally stretched condition.

[0053] The at least two attachment points of the LED lamp or luminaire may further comprise one or more intermediate attachment points arranged between the end attachment points such as to enable fixing the stretchable LED filament in a stretched condition where the stretchable LED filament is less stretched than in the maximally stretched condition.

[0054] Thereby it becomes possible to attach the stretchable LED filament to the luminaire or lamp in any desired stretched condition.

[0055] It is noted that the invention relates to all possible combinations of features recited in the claims.

[0056] BRIEF DESCRIPTION OF THE DRAWINGS This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

[0057] Fig. 1 shows a top view of an embodiment of a stretchable LED filament according to the invention in an unstretched condition.

[0058] Fig. 2 shows a top view of the stretchable LED filament according to Fig. 1 and further comprising an encapsulant, which for simplicity is not shown in Fig. 1.

[0059] Fig. 3 shows a bottom view of the stretchable LED filament according to Fig. 2.

[0060] Fig. 4 shows a top view of the stretchable LED filament according to Fig. 1 in a stretched condition.

[0061] Fig. 5 shows a schematical side view of a luminaire comprising a LED filament according to the invention.

[0062] As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.

[0063] DETAILED DESCRIPTION

[0064] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

[0065] As used herein, the term “unstretched condition” in relation to a given feature or element, for instance a LED filament 1 according to the invention, is intended to mean a condition in which no stretching force is applied to the said given feature or element.

[0066] As used herein, the term “stretched condition” in relation to a given feature or element, for instance a LED filament 1 according to the invention, is intended to mean a condition in which a stretching force is applied to the said given feature or element. The term “stretched condition” is intended to apply irrespective of the magnitude of the stretching force is applied.

[0067] As used herein, the terms “fully stretched condition” and “maximally stretched condition” of a given feature or element, for instance a LED filament 1 according to the invention, is intended to mean a condition in which a stretching force is applied to the said given feature or element, the stretching force being of such a magnitude that any further stretching force applied would cause plastic deformation of the given feature or element.

[0068] Referring first to Figs. 1-4, a stretchable LED filament 1 according to the invention is shown. More specifically, Figs. 1 and 2 shows a top view of an embodiment of a stretchable LED filament 1 according to the invention in an unstretched condition and without and with an encapsulant 4, respectively, Fig. 3 shows a bottom view of the stretchable LED filament 1, and Fig. 4 shows a top view of the stretchable LED filament 1 in a stretched condition.

[0069] Generally, and irrespective of the embodiment, the stretchable LED filament 1 comprises an elongated carrier 2, a plurality of LEDs 3 and an elongated encapsulant 4. The stretchable LED filament 1 is configured to, in operation, provide LED filament light.

[0070] The elongated carrier 2 is flexible, thus enabling that the stretchable LED filament 1 is stretchable between an unstretched condition as is shown in Figs. 1 and 2 and a stretched condition as is shown in Fig. 4, especially in a longitudinal direction L of the elongated carrier 2. The LED filament 1 is in the unstretched configuration when no external forces are applied to the LED filament 1. The LED filament is in a stretched configuration when a stretch force is applied to the LED filament 1. The LED filament 1 comprises a first length LI in the unstretched configuration. The LED filament 1 comprises a second length L2 in a stretched configuration. The second length L2 is dependent on the magnitude of the stretch force which is applied to the LED filament 1. Generally, L2 is larger than LI. The stretchable LED filament 1 comprises a maximum stretching percentage, MS. The maximum stretching percentage MS is defined as MS = (L2 / L1 - 1)- 100 %. The maximum stretching percentage MS may be in a range from 3 % to 30 %.

[0071] The LED filament 1 may for instance be configured to provide LED filament light with a first intensity, II, and first correlated color temperature, CCT1, in the unstretched configuration, and to provide LED filament light with a second intensity, 12, and a second correlated color temperature, CCT2 in the stretched configuration. The first intensity II may be different from the second intensity 12 or larger than second intensity 12. The first correlated color temperature CCT1 may be different from the second correlated color temperature CCT2 or larger than the second correlated color temperature CCT2. The LED filament may also be configured to provide LED filament light with a second intensity, 12, and a second correlated color temperature, CCT2 in the stretched configuration, where the second intensity, 12, and the second correlated color temperature, CCT2, is dependent on the magnitude of the stretch force applied to the stretchable LED filament 1.

[0072] The elongated carrier 2 comprises a meandering shape. The meandering shape may have a sinusoidal pattern. The meandering shape may be free from sharp cuts. Alternatively, or additionally the meandering shape may have a square pattern, a triangular pattern and / or a sawtooth pattern. The elongated carrier 2 may be continuous, that is be in one piece. The elongated carrier 2 may be made of a suitable polymer. The meandering shape of the elongated carrier 2 comprises a meander width, WM and the first recesses 25 and the second recesses 26 each comprise a length, LR. The length LR may be larger than 0.5 times the meander width WM.

[0073] The elongated carrier 2 comprises a longitudinal direction L, a transversal direction T and a height direction H. The transversal direction T and the longitudinal direction L are mutually perpendicular and extend in the same plane. The height direction H extends perpendicular to both the transversal direction T and the longitudinal direction L. The elongated carrier 2 further comprises a first major surface 21, a second major surface 22, a first longitudinal edge 23 and a second longitudinal edge 24. The first major surface 21 and the second major surface 22 are mutually opposing surfaces. The first longitudinal edge 23 and the second longitudinal edge 24 are mutually opposing longitudinal edges. The first longitudinal edge 23 and the second longitudinal edge 24 connect the first major surface 21 and the second major surface 22.

[0074] The first longitudinal edge 23 comprises one or more first recesses 25. The second longitudinal edge 24 comprises one or more second recesses 26. Each of the first recesses 25 and each of the second recesses 26 comprise a length LR measured in the longitudinal direction L. Each of the first recesses 25 comprise a first extension 27 in the longitudinal direction L. Each of the second recesses 26 comprise a second extension 28 in the longitudinal direction L. The first extension 27 of each first recess 25 forms an overlap 29 with the second extension 28 of at least one directly opposing second recess 26, as is illustrated by the hatched area in Fig. 1. In the embodiment illustrated on Fig. 1, the size of the overlap 29 is in the order of half of the length LR of the recesses 25 and 26. In other embodiments, the overlap may be smaller than half of the length LR of the recesses 25 and 26, such that for instance a quarter of the length LR of the recesses 25 and 26, or 0.1 *LR.

[0075] The elongated carrier 2 further comprises a width W. The width W is measured as the shortest distance between the first and second longitudinal edges 23 and 24, or in other words the distance between the first and second longitudinal edges 23 and 24 as measured in the transversal direction T of the elongated carrier 2. The first recesses 25 and the second recesses 26 each comprise a width WR. The size of the width W of the elongated carrier and the width WR of the respective recesses 25 and 26 may be chosen such that WR > 0.5 W, or such that WR < 0.7 W.

[0076] The plurality of LEDs 3 are configured to, in operation, provide LED light. The plurality of LEDs 3 may for instance be configured to, in operation, provide LED light having a blue color. The plurality of LEDs 3 are arranged on the first major surface 21 of the elongated carrier 2. The plurality of LEDs 3 may be attached to the elongated carrier 2 in an unstretched configuration of the stretchable LED filament 1. The plurality of LEDs 3 may be arranged in a meandering pattern, at least in an unstretched configuration of the stretchable LED filament 1, but optionally also in a stretched configuration of the stretchable LED filament 1. At least five, eight or ten LEDs may be arranged within a section of the elongated carrier 2 corresponding to the first extension 27 of a first recess 25. Similarly, at least five, eight or ten LEDs may be arranged within a section of the elongated carrier 2 corresponding to the second extension 28 of a second recess 26.

[0077] The LEDs of the plurality of LEDs 3 are arranged on the elongated carrier 2 with a pitch 31. The pitch 31 may be defined as the center-to-center distance between two neighboring LEDs of the plurality of LEDs 3. Generally, the pitch 31 may be chosen such as to be smaller or even much smaller than the pitch of LEDs in traditional prior art LED strips. The pitch 31 may be smaller than 0.5 mm, equal to or smaller than 0.3 mm, equal to or smaller than 0.2 mm, or even equal to or smaller than 0.1 mm.

[0078] The elongated encapsulant 4 is arranged to encapsulate the plurality of LEDs 3. The elongated encapsulant 4 further covers at least a portion of the first major surface 21 of the elongated carrier. The elongated encapsulant 4 is flexible. For instance, the elongated encapsulant 4 may be made of a silicone, particularly an optical grade silicone. The elongated encapsulant 4 may be straight. The elongated encapsulant 4 may further cover the first recesses 25 or the second recesses 26 or both of the first and second recesses 25 and 26. Parts 41 of the elongated encapsulant 4 bridging or covering the first recesses 25 or the second recesses 26 or both of the first and second recesses 25 and 26 are shown in Fig. 2. The parts 41 may be more flexible than the remaining part of the elongated encapsulant 4. Alternatively, or additionally, the parts 41 may be thinner, or have a smaller thickness, than the remaining part of the elongated encapsulant 4, where the thickness is measured in the height direction H of the stretchable LED filament 1. Alternatively, or additionally, the parts 41 may be made of a material being softer than the material of which the remaining part of the elongated encapsulant 4 is made.

[0079] The elongated encapsulant 4 may comprise a luminescent material configured to, at least partly, convert the LED light into converted light. The luminescent material may for instance be a green-yellow phosphor and red phosphor. Alternatively, or additionally, the elongated encapsulant 4 may comprise a light scattering material configured to, at least partly, scatter the LED light such as to produce scattered light.

[0080] Referring particularly to Fig. 3, the stretchable LED filament 1 may further comprise electrical circuitry 5 for providing the plurality of LEDs 3 with electrical energy. The electrical circuitry 5 may be arranged on the elongated carrier 2. The electrical circuitry 5 may be arranged in a meandering pattern. The electrical circuitry 5 may comprise one or more electrical tracks or lines.

[0081] The stretchable LED filament 1 may further comprise two mechanical connectors 8 (cf. Figs. 2 and 4). The two mechanical connectors 8 are attached to the stretchable LED filament 1, particularly at opposite ends 11, 12 of the stretchable LED filament 1. The two mechanical connectors 8 may be attached to the elongated carrier 2, or to the encapsulant 4 or to both thereof. The two mechanical connectors 8 are configured to fix the stretchable LED filament 1 in a stretched condition of the stretchable LED filament 1. In principle, more than two electrical connectors 8 may be provided. For instance, as shown schematically in Fig. 5, the stretchable LED filament 1 may comprise four mechanical connectors 8, 8’, namely one mechanical connector 8 at each of the opposite ends 11 and 12, and two intermediately arranged mechanical connectors 8’. Mechanical connectors 8, 8’ may in principle be attached to the stretchable LED filament 1 at another position than at the opposite ends 11 and 12 to allow for fixing the stretchable LED filament 1 in one or more intermediate and partially stretched conditions.

[0082] The stretchable LED filament 1 may further comprise two electrical connectors 7. The two electrical connectors 7 are configured to connect the plurality of LEDs 3 and / or the circuitry 5 to a source of electrical energy, such as mains. The two mechanical connectors 8 and the two electrical connectors 7 may be arranged pairwise next to one another. Alternatively, the two mechanical connectors 8 and the two electrical connectors 7 may pairwise be integrated in one and the same connector.

[0083] The stretchable LED filament 1 may further optionally comprise a further elongated encapsulant 6 - cf. Fig. 3. The further elongated encapsulant 6 may be flexible. The further elongated encapsulant 6 may be made of a flexible material, such as for instance a silicone. The further elongated encapsulant 6 is arranged to cover at least a portion of the second major surface 22. The further elongated encapsulant 6 is in physical contact with the elongated encapsulant 4 along at least a part of the stretchable LED filament 1.

[0084] The further elongated encapsulant 6 may be straight. The further elongated encapsulant 6 may further cover the first recesses 25 or the second recesses 26 or both of the first and second recesses 25 and 26. Parts 61 of the further elongated encapsulant 6 bridging or covering the first recesses 25 or the second recesses 26 or both of the first and second recesses 25 and 26 are shown in Fig. 3. The parts 61 may be more flexible than the remaining part of the further elongated encapsulant 6. Alternatively, or additionally, the parts 61 may be thinner, or have a smaller thickness, than the remaining part of the further elongated encapsulant 6, where the thickness is measured in the height direction H of the stretchable LED filament 1. Alternatively, or additionally, the parts 61 may be made of a material being softer than the material of which the remaining part of the further elongated encapsulant 6 is made.

[0085] Turning now to Fig. 5, a schematical side view of a luminaire 50 comprising a stretchable LED filament 1 according to the invention is shown.

[0086] The luminaire 50 may comprise an electrical connection 56 and a terminal 57 for connecting the stretchable LED filament 1 to a source of electrical energy, such as mains.

[0087] The luminaire 50 may comprise a driver or controller 58 configured for controlling the plurality of LEDs 3 of the stretchable LED filament 1. The controller 58 is configured to power the plurality of LEDs 3 via the electrical circuitry 5 of the stretchable LED filament 1 and the electrical connection 56 of the luminaire 50. The controller 58 may further be configured for controlling at least one of the CCT of the LED filament light and the CRI of the LED filament light. The controller 58 may also be configured for controlling other parameters related to the plurality of LEDs 3, the stretchable LED filament 1 and the LED filament light.

[0088] The luminaire 50 further comprises an envelope 51 at least partially enveloping the at least one stretchable LED filament 1. The luminaire 50 further comprises a cap 52. As shown in Fig. 5, the controller 58 is arranged inside the cap 52 such that it is hidden from view. When not comprising a cap 52, the controller 58 may also be arranged within the envelope 51. The luminaire 50 may further comprise a threading 53 for connection to a socket.

[0089] The envelope 51 of the luminaire 50 may further and optionally be provided with a coating, such as a reflective coating, covering at least a part of the envelope. The luminaire 50 further comprises at least two end attachment points 54. Two mechanical connectors 8 provided on the stretchable LED filament 1 are configured to be attached to the at least two end attachment points 54 in a fully stretched condition of the stretchable LED filament 1. The luminaire 50 may further comprises at least one, in the embodiment shown two, intermediate attachment points 55. The intermediate attachment point(s) 55 is / are arranged between the at least two attachment points 54. Two intermediate mechanical connectors 8’ provided on the stretchable LED filament 1 are configured to be attached to the one or more intermediate attachment points 55 in a stretched condition, not necessarily being a fully stretched condition, of the stretchable LED filament 1.

[0090] 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.

[0091] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

CLAIMS:

1. A stretchable LED filament (1) configured to, in operation, provide LED filament light, the stretchable LED filament comprising:■ an elongated carrier (2) comprising a longitudinal direction (L), a transversal direction (T) extending perpendicular to the longitudinal direction, a height direction (H) extending perpendicular to both the transversal direction and the longitudinal direction, a first major surface (21), a second major surface (22), a first longitudinal edge (23) and a second longitudinal edge (24), the first longitudinal edge and the second longitudinal edge being mutually opposing longitudinal edges connecting the first major surface and the second major surface;■ a plurality of LEDs (3) configured to, in operation, provide LED light and being arranged on the first major surface (21) of the elongated carrier; and■ an elongated encapsulant (4) encapsulating the plurality of LEDs (3) and covering at least a portion of the first major surface (21); wherein the elongated carrier (2) is flexible and comprises a meandering shape with bends pointing in the transversal direction (T), wherein the elongated encapsulant (4) is flexible, wherein the first longitudinal edge (23) comprises first recesses (25) and the second longitudinal edge (24) comprises second recesses (26); wherein each of the first recesses (25) comprise a first extension (27) in the longitudinal direction and each of the second recesses (26) comprise a second extension (28) in the longitudinal direction, and wherein each of the first recesses (25) and each of the second recesses (26) are arranged such that the first extension of each first recess forms an overlap (29) with the second extension of at least one directly opposing second recess; and wherein the LED filament (1) has a first length (LI) in an unstretched configuration, the unstretched configuration being achieved when no external forces are applied to the LED filament, wherein the LED filament (1) has a second length (L2) in astretched configuration, the stretched configuration being achieved when a stretch force is applied to the LED filament, and wherein L2 > LI, wherein the stretchable LED filament (1) comprises a maximum stretching percentage (MS), wherein the maximum stretching percentage is defined as MS = (L2 / L1 - 1)- 100 %, and wherein MS is in a range from 3 % to 30 %.

2. A stretchable LED filament according to claim 1, wherein, in the unstretched configuration, and optionally also in the stretched configuration, of the LED filament (1), the plurality of LEDs (3) are arranged in a meandering pattern, wherein at least five LEDs are arranged within a section of the elongated carrier (2) corresponding to the first extension (27), and wherein at least five LEDs are arranged within a section of the elongated carrier (2) corresponding to the second extension (28).

3. A stretchable LED filament according to any one of the above claims, and further comprising electrical circuitry (5) for providing the plurality of LEDs (3) with electrical energy, wherein the electrical circuitry (5) is arranged in a meandering pattern.

4. A stretchable LED filament according to any one of the above claims, wherein the meandering shape of the elongated carrier (2) comprises a sinusoidal pattern or is free from sharp cuts.

5. A stretchable LED filament according to any one of the above claims, wherein the meandering shape of the elongated carrier has a meander width (WM), the wherein the first recesses (25) and the second recesses (26) each comprise a length (LR), wherein LR > 0.5-WM.

6. A stretchable LED filament according to any one of the above claims, wherein one or more of the following applies: the elongated encapsulant (4) further covers at least part of the first recesses (25) and at least part of the second recesses (26), and / or the elongated encapsulant (4) is straight.

7. A stretchable LED filament according to claim 6, wherein one or more of the following applies:■ parts (41) of the elongated encapsulant (4) covering the recesses are more flexible than the remaining part of the elongated encapsulant, and / or■ parts (41) of the elongated encapsulant (4) covering the recesses are thinner as measured in the height direction (H) of the LED filament (1) than the remaining part of the elongated encapsulant, and / or■ parts (41) of the elongated encapsulant (4) covering the recesses are made of a material being softer than the material of which the remaining part of the elongated encapsulant is made.

8. A stretchable LED filament according to any one of the above claims, and further comprising a further elongated encapsulant (6) which is flexible, and which covers at least a portion of the second major surface (22), wherein the further elongated encapsulant (6) is in physical contact with the elongated encapsulant (4).

9. A stretchable LED filament according to any one of the above claims, wherein one or more of the following applies:(i) the plurality of LEDs (3) are configured to, in operation, provide LED light having a blue color, and the elongated encapsulant (4) comprises a luminescent material configured to, at least partly, convert the LED light into converted light, and(ii) the elongated encapsulant (4) comprises a light scattering material configured to, at least partly, scatter the LED light into scattered light.

10. A stretchable LED filament according to any one of the above claims, and further comprising two mechanical connectors (8), the two mechanical connectors (8) being attached to the LED filament at opposite ends (11, 12) of the LED filament, and the two mechanical connectors (8) being configured to fix the LED filament (1) in the stretched configuration of the LED filament.

11. A stretchable LED filament according to claim 10, and further comprising two electrical connectors (7), wherein the two mechanical connectors (8) are arranged next to the two electrical connectors (7), or wherein the two mechanical connectors (8) comprises the two electrical connectors (7).

12. A stretchable LED filament according to any one of the above claims, wherein the LED filament is configured to provide LED filament light with a first intensity (II) and a first correlated color temperature (CCT1) in the unstretched configuration, wherein the LED filament is configured to provide LED filament light with a second intensity (12) and a second correlated color temperature (CCT2) in the stretched configuration, and wherein I I #12. and / or wherein CCT1 # CCT2.

13. A LED lamp or a luminaire (50) comprising a LED filament (1) according to any one of the above claims.

14. A LED lamp or a luminaire according to claim 13, wherein the LED lamp or luminaire (50) further comprises at least two attachment points (54), and wherein the LED filament (1) comprises at least two mechanical connectors (8), the two mechanical connectors (8) being attached to the LED filament at opposite ends (11, 12) of the LED filament, and the two mechanical connectors (8) being configured to be attached to the at least two attachment points (54) in a stretched condition of the LED filament (1).

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