FIELD OF THE INVENTION

The present invention generally relates to lighting arrangements comprising one or more light emitting diodes (LEDs). More specifically, the present invention is related to a LED filament arrangement.

BACKGROUND OF THE INVENTION

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.

In particular, there is currently a very large interest in lighting devices and/or arrangements (such as lamps) provided with LEDs, and incandescent lamps are rapidly being replaced by LED-based lighting solutions. It is nevertheless appreciated and desired to have retrofit lighting devices (e.g. lamps) which have the look of an incandescent bulb. For this purpose, it is possible to make use of the infrastructure for producing incandescent lamps based on LED filaments arranged in such a bulb. In particular, LED filament lamps are highly appreciated as they are very decorative.

However, there is a wish to provide alternatives to existing LED filament lamps in order to even further improve the decorative aspect of the light emitted therefrom. More specifically, it is highly desirable to achieve a glowing and/or sparkling appearance of the light emitted from the LED filament lamps during operation.

Hence, it is an object of the present invention to provide alternatives to existing LED filament lamps of the prior art in order to obtain a more decorative lighting.

DE 10 2016 206896 discloses an arrangement of a plurality of light-emitting semiconductor chip on a carrier. The elongated carrier is divided in equally sized adjoining imaginary rectangular areas, wherein each area comprises at least one light-emitting semiconductor chip, and the number of chips increases per area when going from the centre of the carrier towards the edge in the longitudinal direction. Therewith, thermal power dissipation increases from the centre to the edge in such a way that the temperature is nearly constant over the entire arrangement.

SUMMARY OF THE INVENTION

It is of interest to provide alternatives to LED filament lamps of the prior art in order to improve the decorative aspect of the light emitted from the LED filaments of the LED filament lamps during operation.

Within the context of the present application, a LED filament is understood for providing LED filament light and comprises a plurality of light emitting diodes (LEDs) arranged in a linear array. Preferably, the LED filament has a length L and a width W, wherein L>5W. The LED filament may be arranged in a straight configuration or in a non straight configuration such as for example a curved configuration, a 2D/3D spiral or a helix. Preferably, the LEDs are arranged on an elongated carrier like for instance a substrate, that may be rigid (made from e.g. a polymer, glass, quartz, metal or sapphire) or flexible (e.g. made of a polymer or metal e.g. a film or foil).

In case the carrier comprises a first major surface and an opposite second major surface, the LEDs are arranged on at least one of these surfaces. The carrier may be reflective or light transmissive, such as translucent and preferably transparent.

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

The LED filament may comprise multiple sub-filaments.

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

Hence, according to the present invention, there is provided a LED filament arrangement. The LED filament arrangement comprises at least one LED filament comprising a plurality of LEDs, arranged on an elongated substrate. The LED filament extends along a first axis A, wherein the plurality of LEDs has a distribution essentially in the direction of the first axis A. The distribution is subdivided in a plurality of subsets oriented in the direction of the first axis A, wherein adjacent subsets differ in one of the following properties: pitch of the LEDs in the direction of the first axis A, distance of at least one LED to the first axis A, number of LEDs in a direction orthogonal to the first axis A, a rotation of at least one LED, and/or in a combination of said properties.

Thus, the present invention is based on the idea of providing a LED filament arrangement wherein the LED filament(s) thereof comprise(s) LEDs having different arrangements in order to achieve a sparkling and/or glowing effect during operation of the LED filament arrangement. The light emitted from LED filament may hereby be perceived as more vivid and/or that the light may resemble light emitted from a light source such as a candle. In other words, the arrangement of the LEDs may provide a light distribution pattern of the LED filament arrangement during operation which may be perceived as randomized and/or irregular. The LED filament arrangement may hereby provide a sparkling and/or glowing effect of the light during operation of the LED filament arrangement.

Under sparkling and/or glowing should be understood that this effect is in general best obtained with a LED density that is higher in the central part of the LED filament compared to the outer parts.

These effects can be realized by various arrangements of subsets on the LED filaments. For instance, adjacent subsets may differ in brightness in an alternating way. In case there are e.g. four adjacent subsets, starting from the first subset the brightness increases in the second subset, decreases in the third one and finally increase in the fourth one. In the remainder of this application the words brightness and luminance can be interchanged.

Alternatively, the brightness of at least some of the subsets differ, e.g. in case of three subsets which differ in brightness, this may be chosen as brightness of subset 1 > brightness subset 2 > brightness subset 3.

The difference in brightness of adjacent subsets may preferably be at least 30%, more preferably 40% and most preferably 50%.

Further, in the arrangements the subsets have preferably 3 different lengths, more preferably different lengths 4, and most preferably 5 different lengths.

The LED filament comprises a number of subsets with a relative high brightness with respect to the other subsets; preferably with at least two brightness levels.

By the wording“pitch of the LEDs in the direction of the first axis A”, it is here meant the number of LEDs along the first axis A per unit length, i.e. the concentration of LEDs along the first axis A. According to an embodiment of the present invention, the at least one LED filament comprises at least a first subset, Si, of LEDs, and at least a second subset, S ₂ , of LEDs. At least one of the at least one first subset, Si, of LEDs is different from at least one of the at least one second subset, S ₂ , of LEDs. A respective first arrangement, Sn, of at least one of the at least one first subset, Si, of LEDs, and a respective second arrangement, S ₂₁ , of at least one of the at least one second subset, S ₂ , of LEDs, are selected from a group of arrangements. The group of arrangements comprises

a first arrangement (i) of equidistantly arranged LEDs in an array along the first axis, A;

a second arrangement (ii) of arranged LEDs along the first axis, A, wherein a first distance, Di, between the LEDs of at least a first pair, Ci, of adjacently arranged LEDs is different from a second distance, D ₂ , between the LEDs of at least a second pair, C ₂ , of adjacently arranged LEDs, wherein the first pair, Ci, of adjacently arranged LEDs is different from the second pair, C ₂ , of adjacently arranged LEDs;

a third arrangement (iii) of arranged LEDs along the first axis, A, wherein the number of LEDs, dNi, per unit length, dLi, of the at least one LED filament, is dNi/dLi;

a fourth arrangement (iv) of arranged LEDs along the first axis, A, wherein the number of LEDs, dlNb, per unit length, dL ₂ , of the at least one LED filament, is dN ₂ /dL ₂ , wherein dNi/dLi ¹ dN ₂ /dL ₂ ;

a fifth arrangement (v) of at least one LED arranged in a first row, Fi, in parallel to the first axis, A, and at least one LED arranged in at least one second row, F ₂₁ , which is shifted with respect to the first row, Fi, and which is arranged in parallel to the first row, Fi;

a sixth arrangement (vi) arranged LEDs along the first axis, A, of which at least one first LED is arranged in a first orientation, Ri, and of which at least one second LED, different from the at least one first LED, is arranged in a second orientation, R ₂ , different from the first orientation, Ri;

a seventh arrangement (vii) of LEDs arranged in a semi-circular pattern, E, in a plane of the LED filament spanned by the first axis, A, and a second axis, B, perpendicular to the axis, A; and

an eighth arrangement (viii) of LEDs arranged along the first axis, A, of which at least one first LED has a first size, Zi, and of which at least one second LED, different from the at least one first LED, has a second size, Z ₂ , different from the first size, Zi. The selection of one or more of the arrangements is performed under the condition that at least one of the at least one first arrangement, Sn, selected for the LEDs of at least one of the at least one first subset, Si, from the group of arrangements (i)-(viii) is different from at least one of the at least one second arrangement S ₂₁ , selected for the LEDs of at least one of the at least one second subset, S ₂ , from the group of arrangements (i)-(viii).

Thus, the present embodiment provides a LED filament arrangement wherein the LED filament(s) thereof comprises at least two subsets of LEDs having a different arrangement in order to achieve a sparkling and/or glowing effect during operation of the LED filament arrangement. The different arrangements of the subsets of the LEDs may comprise equi distantly arranged LEDs (arrangement (i)); subsets of LEDs having different distances between adjacently arranged LEDs (arrangement (ii)); a specific concentration (density) of LEDs (third arrangement (iii)); subsets of LEDs having different concentrations (densities) (fourth arrangement (iv)); adjacently arranged rows of LEDs (fifth arrangement (v)); LEDs having different orientations (sixth arrangement (vi)); LEDs arranged in a semi circular pattern (seventh arrangement (vii)); and LEDs having different size (eighth arrangement (viii)).

The LED filament arrangement according to the embodiment of the present invention comprises at least one LED filament. The at least one LED filament, in its turn, comprises an array of LEDs. By the term“array”, it is here meant a linear arrangement or chain of LEDs, or the like, arranged on the LED filament(s). The at least one LED filament comprises at least a first subset, Si, of LEDs, and at least a second subset, S ₂ , of LEDs, wherein at least one of the at least one first subset, Si, of LEDs is different from at least one of the at least one second subset, S ₂ , of LEDs. In other words, the LED filament comprises at least two distinctive subsets of LEDs which are not the same. A respective first arrangement, Sn, of at least one of the at least one first subset, Si, of LEDs, and a respective second arrangement, S ₂₁ , of at least one of the at least one second subset, S ₂ , of LEDs, are selected from a group of arrangements. Hence, the LEDs of the respective subsets of LEDs may be arranged according to one or more arrangements, including equidistantly arranged LEDs; LEDs having different distances between adjacently arranged LEDs; a specific concentration (density) of LEDs; subsets of LEDs having different concentrations (densities); adjacently arranged rows of LEDs; LEDs having different orientations; and LEDs arranged in a semi circular pattern. Hence, by arranging the LEDs of the two or more subset of LEDs of the LED filament of the LED filament arrangement according to one or more of the above- mentioned arrangements, a sparkling and/or glowing effect of the light during operation of the LED filament arrangement may be achieved.

According to an embodiment of the present invention, the arrangement may further comprise a single LED arranged in the at least one second row, F ₂₁ . Hence, at least one of the subsets of LEDs of the LED filament(s) may comprise a single LED in one or more second rows F _2i arranged adjacently to the first row Fi. In this embodiment, the LEDs may, for example, be arranged in a“T”-shape wherein a single LED of a second row F ₂₁ may be arranged adjacent an array of LEDs arranged in a first row Fi.

According to an embodiment of the present invention, the LED filament arrangement may further comprise a pair of LEDs arranged in the at least one second row, F _2i . Hence, at least one of the subsets of LEDs of the LED filament(s) may comprise two LEDs in one or more second rows F ₂₁ arranged adjacently to the first row Fi. In this embodiment, the LEDs may, for example, be arranged in a rectangular shape. For example, an array of linearly arranged LEDs of the LED filament(s) in the first row Fi may be intervened by a formation of LEDs in a rectangular shape of a second row F ₂₁ .

According to an embodiment of the present invention, the LED filament arrangement may further comprise a pair of LEDs respectively arranged in each of two second rows, F ₂₁ . In this embodiment, the LEDs in the second rows F ₂₁ are arranged in a quadratic (square) shape. For example, an array of linearly arranged LEDs of the LED filament(s) in the first row Fi may be intervened by a square-shaped formation or

arrangement of LEDs of a second row F ₂₁ .

According to an embodiment of the present invention, at least one of the at least one first arrangement, Sn, of the at least one first subset, Si, of LEDs, may comprise arranged LEDs along the first axis, A, wherein the number of LEDs, dNi, per unit length, dLi, of the at least one LED filament, is dNi/dLi; and at least one of the at least one second arrangement, S ₂₁ , of the at least one second subset, S ₂₁ , of LEDs, comprises arranged LEDs along the first axis, A, wherein the number of LEDs, dN ₂ , per unit length, dL ₂ , of the at least one LED filament, is dN ₂ /dL ₂ , wherein dNi/dLi ¹ dN ₂ /dL ₂ . In other words, the LEDs of the first subset(s) Si may have a concentration or density of LEDs, dNi/dLi, which is different from the concentration or density of LEDs, dNi/dLi, of the second subset(s) S ₂ . For example, the LEDs of the first subset(s) Si may be arranged in a close vicinity of each other, such that the concentration or density of LEDs, dNi/dLi, of the first subset(s) Si is relatively high, whereas the LEDs of the second subset(s) Si may be have a longer distance with respect to each other, compared to the LEDs of the first subset(s) Si, such that the concentration or density of LEDs, dN ₂ /dL ₂ , of the first subset(s) S ₂ is relatively low.

According to an embodiment of the present invention, at least one of the at least a first subset, Si, of LEDs may be arranged at a central portion, K, of the at least one LED filament, and the respective first arrangement, Sn, of the LEDs of the at least a first subset, Si, comprises equidistantly arranged LEDs in an array along the first axis, A, wherein the number of LEDs, dNi, per unit length of the at least one LED filament, dLi, is dNi/dLi; and at least two of the at least a second subset, S ₂ , of LEDs is arranged at respective end portions of the at least one LED filament, and the respective second arrangement, S ₂₁ , of the LEDs of the second subset, S ₂ , comprises equidistantly arranged LEDs in an array along the first axis, A, wherein the number of LEDs, dN ₂ , per unit length of the at least one LED filament, dL ₂ , is dN ₂ /dL ₂ , wherein dNi/dLi > dN ₂ /dL ₂ . In other words, at least one LED filament of the LED filament arrangement may comprise a centrally arranged first subset, Si, wherein the equidistantly arranged LEDs of the first subset, Si, may further be arranged in a close vicinity of each other, such that the concentration or density of LEDs, dNi/dLi, of the first subset Si is relatively high. This first subset, Si, may be arranged between two second subsets, S ₂ , of LEDs, wherein each of these second subsets, S ₂ , comprises equidistantly arranged LEDs in an array having a longer distance with respect to each other, compared to the LEDs of the first subset Si, such that the concentration or density of LEDs, dN ₂ /dL ₂ , of the second subsets, S ₂ , is relatively low.

According to an embodiment of the present invention, dN ₂ /dL ₂ may increase in a direction from either of the end portions towards the central portion. Hence, the

concentration or density dN ₂ /dL ₂ of the number of LEDs, of the second subset(s) Su of the at least one LED filament may increase from a direction from the end (peripheral) portions of the LED filament(s) towards the central portion thereof.

According to an embodiment of the present invention, at least one of the at least a first subset, Si, of LEDs may be arranged at a central portion, K, of the at least one LED filament, and the respective first arrangement, Sn, of the LEDs of the at least a first subset, Si, may comprise at least one LED arranged in a first row, Fi, parallel to the first axis, A, and at least one LED arranged in at least one second row, F ₂₁ , which is shifted with respect to the first row, Fi, and which is arranged in parallel to the first row, Fi, and at least two of the at least a second subset, S ₂ , of LEDs may be arranged at respective end portions of the at least one LED filament, and the respective second arrangement, S ₂₁ , of the LEDs of the second subset, S ₂ , may comprise equidistantly arranged LEDs in an array along the first axis, A. Hence, the LED filament arrangement may comprise two or more rows of LEDs at a central portion, K, of the LED filament(s) as a“block” or“area” of LEDs. On either side of this central portion, K, of the LED filament(s) is at least a respective second subset, S2, of LEDs arranged as a“linear” arrangement of LEDs. The present embodiment is advantageous in that the LED filament achieves a glowing appearance during operation of the LED filament arrangement.

According to an embodiment of the present invention, each of the first arrangements, Sn, of the LEDs of the at least a first subset, Si, may comprise a pair of LEDs arranged in the first row, Fi, and a pair of LEDs respectively arranged in each of two second rows, F _2i. In other words, each“block” or“area” of LEDs of the previous embodiment may be arranged as a square of four LEDs in a 2x2 matrix, whereas the respective second subset, S2, of LEDs may be arranged as a“linear” arrangement of LEDs on either side of the first subset, Si.

According to an embodiment of the present invention, each of the first arrangements, Sn, of the LEDs of the at least a first subset, Si, may comprise a single LED arranged in the first row, Fi, and one single LED arranged in one of the at least one second row, F2 _1. In this embodiment, the LEDs are arranged in a“T”-shape wherein the single LED of the second row, F _2i , is arranged adjacent an array of LEDs arranged in the first row Fi.

According to an embodiment of the present invention, the LED filament arrangement may further comprise an encapsulant at least partially enclosing the plurality of LEDs, wherein the encapsulant comprises a luminescent material and is configured to at least partly convert the light emitted by the plurality of LEDs. By the term“encapsulant”, it is here meant a material, element, arrangement, or the like, which is configured or arranged to surround, encapsulate and/or enclose the plurality of LEDs of the LED filament(s). The luminescent material of the encapsulant is configured to emit light under external energy excitation. For example, the luminescent material may comprise a fluorescent material. The luminescent material may comprise an inorganic phosphor, and organic phosphor and/or quantum dots/rods. The encapsulant is configured to at least partly convert the light emitted by the plurality of LEDs into converted light. For example, a UV/blue LED light may be partially or fully absorbed by the luminescent material and converted to light of another color e.g. green, yellow, orange and/or red.

According to an embodiment of the present invention, the plurality of LEDs may be connected in series. According to an embodiment of the present invention, there is provided a lighting device. The lighting device may comprise a light source comprising at least one LED filament arrangement according to any one of the preceding embodiments of the present invention. The lighting device may further comprise a cover comprising an at least partially transparent material, wherein the cover at least partially encloses the light source. The lighting device may further comprise an electrical connection connected to the light source for a supply of power to the plurality of LEDs of the light source. By the term“cover”, it is here meant an enclosing element, such as a cap, cover, envelope, or the like, comprising an at least partial translucent and/or transparent material. The present embodiment is advantageous in that the LED arrangement according to the invention may be conveniently arranged in substantially any lighting device, such as a LED filament lamp, luminaire, lighting system, or the like. The lighting device may further comprise a driver for supplying power the LEDs of the LED filament arrangement. Additionally, the lighting device may further comprise a controller for individual control of the subsets of LEDs of the LED filament arrangement.

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.

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.

Fig. 1 schematically shows a LED filament lamp according to the prior art, comprising LED filaments,

Fig. 2 schematically shows a LED filament according to the prior art,

Figs. 3-7 schematically shows LED filaments of LED filament arrangements according to exemplifying embodiments of the present invention,

Fig. 8 schematically shows a LED filament device according to an exemplifying embodiment of the present invention, and

Fig. 9 schematically shows a lighting device comprising a LED filament arrangement according to an exemplifying embodiment of the present invention.

DETAILED DESCRIPTION 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.

Fig. 2 schematically shows a LED filament 50 according to the prior art, wherein one or more of these LED filaments 50 may be arranged in a LED filament lamp 10 of Fig. 1. The LED filament 50 comprises a plurality of LEDs 60 which are arranged on a substrate 70. There is a wish to provide alternatives to existing LED filaments of this kind in order to even further improve the decorative aspect of the LED filaments and, consequently, of the LED filament arrangements. More specifically, it is highly desirable to achieve a glowing and/or sparkling appearance of the light emitted from the LED filament lamps during operation.

Fig. 3 schematically shows a LED filament arrangement 100 according to an exemplifying embodiment of the present invention. It will be appreciated that the LED filament arrangement 100 may be provided in a LED filament lamp according to Fig. 1 or in substantially any other LED lighting device, arrangement or luminaire. The LED filament arrangement 100 comprises a LED filament 120. It should be noted that there may be a plurality of LED filaments, whereas only one LED filament 120 is shown in Fig. 3 for an increased understanding. The LED filament 120 comprises a plurality of LEDs 140 arranged on an elongated substrate (70), and an encapsulant 145 which encloses the plurality of LEDs 140. The LED filament 120, elongating along an axis A, may preferably have a length L in the range from 1 cm to 20 cm, more preferably 2 cm to 12 cm, and most preferred 3 cm to 10 cm. The LED filament 120 may preferably have a width W in the range from 0.5 mm to 10 mm, more preferably 0.8 mm to 8 mm, and most preferred 1 to 5 mm. The aspect ratio L/W is preferably at least 5, more preferably at least 8, and most preferred at least 10.

The LED filament 120 of the LED filament arrangement 100 comprises an array or“chain” of LEDs 140 which is arranged on the LED filament 120. For example, the array or“chain” of LEDs 140 may comprise a plurality of adjacently arranged LEDs 140 wherein a respective wiring is provided between each pair of LEDs 140. The plurality of LEDs 140 preferably comprises more than 5 LEDs, more preferably more than 8 LEDs, and even more preferred more than 10 LEDs. The plurality of LEDs 140 may be direct emitting LEDs which provide a color. The LEDs 140 are preferably blue LEDs. The LEDs 140 may also be UV LEDs. A combination of LEDs 140, e.g. UV LEDs and blue light LEDs, may be used. The LEDs 140 may comprise laser diodes. The light emitted from the LED filament 120 during operation is preferably white light. The white light is preferably within 15 SDCM (standard deviation of color matching) from the black body locus (BBL). The color temperature of the white light is preferably in the range of 2000 to 6000 K, more preferably in the range from 2100 to 5000 K, most preferably in the range from 2200 to 4000 K such as for example 2300 K or 2700 K. The white light has preferably a CRI of at least 75, more preferably at least 80, most preferably at least 85 such as for example 90 or 92.

The LED filament 120 of the LED filament arrangement 100 may further comprise an encapsulant 145 comprising a translucent material, wherein the encapsulant 145 at least partially encloses the plurality of LEDs 140. For example, the encapsulant 145 may fully enclose the plurality of LEDs 140. The encapsulant 145 may comprise a luminescent material, which is configured to emit light under external energy excitation. For example, the luminescent material may comprise a fluorescent material. The luminescent material may comprise an inorganic phosphor, and organic phosphor and/or quantum dots/rods. The UV/blue LED light may be partially or fully absorbed by the luminescent material and converted to light of another color e.g. green, yellow, orange and/or red.

The LED filament 120 comprises a plurality of first subsets, Si, of LEDs 140, and a plurality of second subsets, S2, of LEDs 140. It should be noted that the number of LEDs 140 of each of the first and second subsets, Si and S2, is arbitrary. Also, the number of the first and second subsets, Si and S2, is arbitrary. In Fig. 3, two first subsets, Si, of LEDs 140 are explicitly indicated, and they are different (separate) from the plurality of second subsets, S2, of LEDs 140. The first subsets, Si, of LEDs 140 are arranged according to a first arrangement, Sn, comprising equidistantly arranged LEDs 140 in an array along the first axis, A. The second subsets, S2, of LEDs 140 are arranged in an alternating manner in between the first subsets, Si, of LEDs 140. The second subsets, S2, of LEDs 140 are arranged according to a respective second arrangement, of which examples are provided in the following.

At the leftmost portion of the LED filament 120 of the LED filament arrangement 100 in Fig. 3, a second arrangement S21 of the second subset S2 comprises a single LED 140a arranged in a second row, F21, arranged adjacently to a first row Fi of the LED filament 120. Hence, at least one of the subsets of LEDs of the LED filament 120 may comprise a single LED 140a in one second row F21 arranged adjacently to the first row Fi. In this embodiment, the LEDs 140 of the second arrangement S21 of the second subset S2 are arranged in a“T”-shape wherein the single LED 140a of the second row F21 is arranged adjacent an array of LEDs 140 arranged in the first row Fi.

According to another configuration of LEDs 140 of the LED filament 120 of Fig. 3, a second arrangement, S22, of the LEDs 140 of the at least a second subset, S2, comprises a pair of LEDs 140b, 140c arranged in the first row, Fi, and a pair of LEDs 140d, 140e arranged in the second row, F21. In other words, the LEDs 140 of the second subset, S2 _, are arranged according to the arrangement S22 as a square of four LEDs 140d-e in a 2x2 matrix. Alternatively, and according to another configuration of LEDs 140 of the LED filament 120, a second arrangement, S23, of the LEDs 140 of the second subset, S2, comprises a single LED 140f arranged in a second row, F22, and a single LED 140g arranged in another second row, F23, wherein the second rows F22 and F23 are parallel to the first row Fi.

According to yet another configuration of LEDs 140 of the LED filament 120 of Fig. 3, a second arrangement, S24, of the LEDs 140 of the second subset, S2, comprises a single LED 140h which is arranged in a second orientation, R2, which is different from a first orientation, Ri, of adjacently arranged LEDs 140 along the first axis, A. For example, a first arrangement Sn of LEDs 140 of the first subset, Si, of LEDs may comprise LEDs 140 which (all) may have a first orientation, Ri, wherein the single LED 140h is arranged in a second orientation, R2, which is shifted (rotated) by 45° with respect to Ri.

According to yet another configuration of LEDs 140 of the LED filament 120, a second arrangement, S25, of the LEDs of the at least a second subset, S2, comprises LEDs 140i-k. These LEDs 140i-k are arranged in a semi-circular pattern in a plane of the LED filament spanned by the first axis, A, and a second axis, B, perpendicular to the axis, A.

Furthermore, and according to yet another configuration of LEDs 140 of the LED filament 120, a first arrangement, Sn, of the LEDs of the first subset, Si, comprises equi distantly arranged LEDs in an array along the first axis, A, wherein the number of LEDs 140, dNi, per unit length, dLi, of the LED filament 120, is dNi/dLi. The second arrangement, S26, of the LEDs 140 of the at least a second subset, S2, comprises LEDs 1401-p arranged along the first axis, A, wherein the number of LEDs 140, dlNri, per unit length, dL2, of the at least one LED filament, is dN2/dL2, wherein dNi/dLi > dN2/dL2. Hence, in this example, the LEDs 140 of the first subset(s) Si are arranged in a close vicinity of each other, such that the pitch, concentration or density of LEDs 140, dNi/dLi, of the first subset Si is relatively high. In contrast, the LEDs 140 of the second subset S2 has longer distance with respect to each other, compared to the LEDs of the first subset Si, such that the pitch, concentration or density of LEDs 140, dN2/dL2, of the second subset S2 is relatively low. According to yet another configuration of LEDs 140 of the LED filament 120, at least one first LED has a first size, Zi, and at least one second LED, different from the at least one first LED, has a second size, Z2, different from the first size, Zi. Here, Zi > Z2, but it should be noted that the reverse relationship could be feasible according to other exemplifying embodiments, i.e. Zi < Z2.

It will be appreciated that the first and second arrangements of LEDs 140 of the first subset, Si, and second subset, S2, of LEDs 140 according to Fig. 3 are presented as examples of the LEDs 140 of the LED filament 120 of the LED filament arrangement 100 according to the present invention. Hence, the purpose of Fig. 3 is to visualize some of the possible arrangements of the LEDs 140 of the LED filament 120. In other words, the LED filament 120 may comprise only a few of these possible arrangements as exemplified.

Fig. 4 schematically shows a LED filament arrangement 100 according to an exemplifying embodiment of the present invention. A first subset, Si, of LEDs 140 is arranged at a central portion, K, of the LED filament 120. A first arrangement, Sn, of the LEDs 140 of the first subset, Si, comprises equidistantly arranged LEDs 140 in an array along the first axis, A. The number of LEDs 140, dNi, per unit length of the LED filament 120, dLi, is dNi/dLi. Two second subsets, S2, of LEDs 140 are arranged at respective end portions of the LED filament 120. The respective second arrangement, S26, of the LEDs 140 of the second subsets, S2, comprises equidistantly arranged LEDs 140 in an array along the first axis, A. The number of LEDs 140, dN2, per unit length of the LED filament 120, dL2, is dN2/dL2, wherein dNi/dLi > dN2/dL2. Hence, the concentration or density of LEDs 140, dNi/dLi, of the first subset Si is higher than the concentration or density of LEDs 140, dN2/dL2, of the second subset S2 of the LED filament 120 of the LED filament arrangement 100

Fig. 5 schematically shows a LED filament arrangement 100 according to an exemplifying embodiment of the present invention. Similar to Fig. 4, a first subset, Si, of LEDs 140 is arranged at a central portion, K, of the LED filament 120. A first arrangement, Sn, of the LEDs 140 of the first subset, Si, comprises equidistantly arranged LEDs 140 in an array along the first axis, A. The number of LEDs 140, dNi, per unit length of the LED filament 120, dLi, is dNi/dLi. Two second subsets, S2, of LEDs 140 are arranged at respective end portions of the LED filament 120 according to a second arrangement, S26. Compared to the embodiment of Fig. 4, the second arrangement, S26, of LEDs 140 implies that the concentration dN2/dL2 increases in a direction from either of the end portions towards the central portion K of the LED filament 1230. Hence, the concentration or density dN2/dL2 of the number of LEDs 140 of the second subsets S2 increases from a direction from the end (peripheral) portions of the LED filament 120 towards the central portion K thereof.

Fig. 6 schematically shows a LED filament arrangement 100 according to an exemplifying embodiment of the present invention. A first subset, Si, of LEDs 140 is arranged at a central portion, K, of the LED filament 120. A first arrangement, S12, of the LEDs of the first subset, Si, comprises a plurality of LEDs 140 arranged in a first row, F22, parallel to the first axis, A. The first arrangement, S 12, of the LEDs of the first subset, S i, further comprises a plurality of LEDs 140 arranged in a second row, F23, which is shifted with respect to the first row, F22, and which is arranged in parallel to the first row, F22. Two second subsets, S2, of LEDs 140 are arranged at respective end portions of the LED filament 120. A second arrangement, S22, of the LEDs 140 of the two second subsets, S2, comprises equidistantly arranged LEDs 140 in an array along the first axis, A. Hence, the density or concentration of LEDs 140 at the central portion, K, of the LED filament 120, comprising two rows F22, F23, of LEDs 140, is higher than at the peripheral portions of the LED filament 120, comprising a (single) array of LEDs 140.

Fig. 7 schematically shows a LED filament arrangement 100 according to an exemplifying embodiment of the present invention. Three first subsets, Si, of LEDs 140 are arranged along the length of the LED filament 120, i.e. along the first axis, A. It should be noted that the number of the first subsets, Si, is arbitrary, and that substantially any number of first subsets, S i, may be feasible. According to a first arrangement, S 12, each of these first subsets, S i, comprises a pair of LEDs 140 arranged in a first row, F22, parallel to the first axis, A, and a pair of LEDs 140 arranged in a second row, F23, which is shifted with respect to the first row, F22, and which is arranged in parallel to the first row, F22. A plurality of second subsets, S2, of LEDs 140 are arranged in between the first subsets, S i, of LEDs 140. The second arrangement, S21, of the LEDs 140 of the two second subsets, S2, comprises equidistantly arranged LEDs 140 in an array along the first axis, A, of the LED filament 120.

Fig. 8 schematically shows a LED filament arrangement 100 according to an exemplifying embodiment of the present invention. The LED filament arrangement 100 as disclosed has many features in common with the LED filament arrangement 100 of Fig. 7, and it is referred to Fig. 7 for an increased understanding. In Fig. 8, three first subsets, Si, each comprises a single LED 140 of a first size Zi, whereas the LEDs 140 of the plurality of second subsets, S2, of LEDs have a second size Z2, different from the first size, Zi. In Fig. 8, Zi > Z2, but it should be noted that the reverse relationship could be feasible according to other exemplifying embodiments, i.e. Zi < Z2. Fig. 9 schematically shows a lighting device 800 according to an exemplifying embodiment of the present invention. The lighting device 800 comprises a LED filament arrangement 100 according to any one of the preceding Figs. 3-8. As exemplified in Fig. 9, the lighting device 800 comprises a LED filament arrangement 100 which in turn comprises a LED filament 120. However, it should be noted that the number of LED filaments 120 of the LED filament arrangement 100 is arbitrary, and that the lighting device 800 may comprises substantially any number of LED filaments 120. The lighting device 800 further comprises a cover 820 comprising an at least partially transparent material. The cover 820, which at least partially encloses the LED filament arrangement, is exemplified as being bulb-shaped. The lighting device 800 further comprises an electrical connection 830 connected to the LED filament arrangement for a supply of power to the plurality of LEDs of the LED filament 120

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(s) 120, the LEDs 140, the arrangements of the LEDs 140, etc., may have different shapes, dimensions and/or sizes than those depicted/described.