Light emitting diode, LED, based filament lamp as well as a luminaire comprising at least one LED based filament lamp

Abstract

A Light Emitting Diode, LED, based filament lamp, comprising an LED filament comprising: (i) a first sub-filament having a first plurality of LEDs, and (ii) a second sub-filament having a second plurality of LEDs, wherein said first sub-filament and said second sub-filament are positioned to ensure that light emitted by each of said first plurality of LEDs is mixed with light emitted by any of said second plurality of LEDs, respectively, such that said combination of light emitted by said first sub-filament and light emitted by said second sub-filament is perceived as light emitted by a single filament, a first driver arranged for driving said first plurality of LEDs of said first sub-filament, a second driver, different from said first driver, arranged for driving said second plurality of LEDs of said second sub-filament.

Description

[0001] Light Emitting Diode, LED, based filament lamp as well as a luminaire comprising at least one LED based filament lamp.

[0002] FIELD OF THE INVENTION

[0003] The present disclosure generally relates to the field of lighting and, more specifically, to Light Emitting Diode, LED, based filament lamps that comprise a plurality of LEDs arranged in a filament-like pattern.

[0004] BACKGROUND OF THE INVENTION

[0005] A Light Emitting Diode, LED, based filament lamp, also known as an LED filament bulb, is a type of light bulb that combines the energy efficiency and longevity of LEDs with the aesthetic appeal of traditional incandescent filament bulbs.

[0006] Unlike traditional incandescent bulbs that use a filament wire to produce light, LED filament lamps use multiple LEDs arranged in a filament-like pattern. These LEDs emit light when an electric current passes through them, providing illumination in a similar manner to traditional bulbs.

[0007] LED filament lamps may be designed to mimic the warm glow and appearance of incandescent bulbs. The LEDs are typically housed within a transparent or frosted glass envelope, often shaped like a traditional bulb, to create a familiar and nostalgic look. The filament-like arrangement of LEDs helps to distribute the light more evenly and create a pleasant, omnidirectional illumination.

[0008] LED filament lamps may offer several advantages over traditional incandescent bulbs. They are highly energy-efficient, consuming significantly less electricity and producing less heat. LED technology also enables these bulbs to have a much longer lifespan compared to incandescent bulbs. LED filament lamps can last tens of thousands of hours, reducing the frequency of bulb replacements and lowering maintenance costs.

[0009] Furthermore, LED filament lamps are available in various shapes, sizes, and colour temperatures, allowing users to choose the right ambiance for their space. They are also compatible with standard bulb sockets, making it easy to retrofit existing fixtures with LED technology. An LED-based filament lamp typically comprises a filament that incorporates multiple LEDs, along with a driver responsible for powering these LEDs. If a fault condition were to occur in either the driver, the filament, or both, the LED-based filament lamp would be considered broken.

[0010] SUMMARY OF THE INVENTION

[0011] It would be advantageous to achieve an LED based filament lamp that is designed in such a way that, even when a fault condition would arise in either the driver or the filament, the LED based filament lamp would still function normally to a certain extent.

[0012] It would further be advantageous to achieve a luminaire comprising such an LED based filament lamp.

[0013] In a first aspect of the present disclosure, there is provided a Light Emitting Diode, LED, based filament lamp, comprising: an LED filament comprising:

[0014] (i) a first sub-filament having a first plurality of LEDs, and

[0015] (ii) a second sub-filament having a second plurality of LEDs, a first driver arranged for driving said first plurality of LEDs of said first sub- filament; a second driver, different from said first driver, arranged for driving said second plurality of LEDs of said second sub-filament.

[0016] The first sub-filament and the second sub-filament may be positioned to ensure that light emitted by each of said first plurality of LEDs is mixed with light emitted by any of said second plurality of LEDs, respectively, such that said combination of light emitted by said first sub-filament and light emitted by said second sub-filament is perceived as light emitted by a single filament at a target distance.

[0017] The inventors have found that it may be beneficial to create an LED based filament lamp, wherein the LED filament is construed in such a way that it comprises at least two sub-filament. Both of the sub-filaments have a plurality of LEDs.

[0018] The underlying concept is based on the insight that the first sub-filament and the second sub-filament may be positioned in such a way that a user may perceive the subfilaments as a single filament. The user may not be able to distinguish the different subfilament from one another. The target distance is considered a distance between the LED based filament lamp and a user during normal operation. For example, the LED based filament lamp may be mounted on the ceiling. The LED based filament lamp may also be used in a floor lamp. Preferably, the target distance is larger than 30 cm, preferably larger than 50 cm.

[0019] To accomplish this technical effect, the first sub-filament and the second subfilament may be positioned in such a way that light emitted by each of the plurality of LEDs of the first sub-filament is mixed with respective light emitted by any of the second plurality of LEDs such that the combination of light emitted by the first and second sub-filament is perceived, by the user, as light emitted by a single filament.

[0020] A first driver is arranged for driving the plurality of LEDs of the first subfilament and the second driver is arranged for driving the plurality of LEDs of the second sub-filament.

[0021] Following the above, if a fault condition would occur in any of the subfilaments, then that particular sub-filament may break down. The other sub-filament may still function properly. The result is that a user may not see, or notice, the broken sub-filament. The LED based filament lamp may have reduced functionality as one of the sub-filaments has broken down, but the LED based filament lamp may still function properly. For example, the total amount of lux emitted by the LED based lighting lamp may be reduced.

[0022] Following the above, if a fault condition would occur in any of the two driver, then the corresponding sub-filament may no longer work properly. This particular scenario is the same as the one sketched above. A user is not able to see, or notice, the sub-filament that is no longer functioning properly. A user would have the impression that the LED based filament lamp is functioning properly, although the total amount of lux, or the colour range, may be reduced. The user is not able to see the non-working sub-filament, as the subfilaments as a whole are perceived as a single filament.

[0023] One of the advantages of the present disclosure is that the LED based filament lamp does not need to be replaced in case of a fault condition. The LED based filament lamp may still function above certain quality standards, thereby improving the life expectancy of the LED based filament lamp as a whole.

[0024] Summarizing the above, in other words, The positioning of the first subfilament and the second sub-filament is arranged in such a way that the light emitted by each LED in the first group blends with the light emitted by any LED in the second group. As a result, the combined light from the first sub-filament and the second sub-filament is perceived as if it were emitted by a single filament.

[0025] To ensure the above described effect, the first sub-filament and the second sub-filament may be strategically positioned. The LEDs in the first sub-filament may be arranged in a manner that allows their emitted light to mix with the light emitted by any LED in the second sub-filament. This can be achieved by placing the LEDs of the first group in close proximity to the LEDs of the second group.

[0026] The specific arrangement may involve interleaving the LEDs from both subfilaments, such that each LED from the first sub-filament is interspersed with LEDs from the second sub-filament along the length of the filament. Alternatively, the LEDs from each group may be positioned side by side, ensuring that the emitted light from adjacent LEDs in different sub-filaments overlaps and mixes.

[0027] Additionally, optical components such as diffusers or reflectors may be utilized to further enhance the blending of light. These components help to scatter and redirect the emitted light, ensuring that it interacts and merges effectively.

[0028] By positioning the LEDs and employing appropriate optical techniques, the combined effect of the light emitted by the first sub-filament and the second sub-filament creates the illusion of a single filament, resulting in a cohesive and uniform lighting appearance.

[0029] In an example, the first and second sub-filament are arranged in parallel and next to each other.

[0030] The above may entail that the LEDs in both sub-filaments are positioned side- by-side.

[0031] By arranging the sub-filaments in parallel, the LEDs in each sub-filament are aligned in a row or series, running alongside each other. This configuration ensures that the emitted light from adjacent LEDs in the first sub-filament overlaps and mixes with the light emitted by adjacent LEDs in the second sub-filament.

[0032] The close proximity and parallel arrangement enable the two sub-filaments to work together in producing a cohesive and uniform lighting appearance, giving the perception of a single filament.

[0033] In a further example, the first sub-filament and said second sub-filament are positioned such that a largest distance between said second sub-filament and said first subfilament is equal to or smaller than 5 mm, preferably equal to or smaller than 3 mm, more preferably equal to or smaller than 1 mm, most preferably 0 mm.

[0034] The distance between the sub-filaments may affect how well the light emitted by the LEDs in one sub-filament mixes with the light emitted by the LEDs in the other subfilament. When the sub-filaments are positioned closer together, the emitted light has a higher chance of overlapping and interacting, resulting in better blending. This proximity allows the light from adjacent LEDs in different sub-filaments to combine effectively creating a uniform and cohesive lighting appearance.

[0035] The distance between the sub-filaments may also influence the visual perception of the emitted light. By keeping the sub-filaments closer, a human eye may perceive the combined light as if it were emitted by a single filament. This visual illusion may be of importance for achieving the desired effect of replicating the appearance of a traditional incandescent filament bulb.

[0036] Ensuring an appropriate distance between the sub-filaments may help to maintain uniformity in the emitted light. If the sub-filaments are positioned too far apart, there may be gaps or inconsistencies in the lighting pattern, resulting in an uneven appearance. By minimizing the distance between the sub-filaments, the light distribution becomes more consistent, creating a smoother and more balanced illumination.

[0037] In a further example, each of said LEDs in said first plurality of LEDs has a distance to a LED in said second plurality of LEDs smaller than 5 mm, preferably smaller than 3 mm, more preferably equal to or smaller than 1 mm, most preferably 0 mm.

[0038] The inventors have found that it may be beneficial to ensure that the distance between the LEDs in the different sub-filaments are spaced apart with a maximum distance of 5mm. Preferably, the distance between these LEDs is smaller, for example smaller than 3 mm.

[0039] In another example, the LED based filament lamp comprises an elongated carrier, said elongated carrier comprising said first sub-filament and said second subfilament. Preferably, said elongated carrier may be a monolithic carrier.

[0040] The sub-filaments may be positioned on the same elongated carrier, for example a Printed Circuit Board, PCB, or any other type of carrier. The sub-filaments may still be driven by different drivers, such that the sub-filaments are isolated from one another. In an example, the PCB may be a metal-core PCB.

[0041] In a further example, the first sub-filament is connected in series with said second sub-filament.

[0042] In another example, the first sub-filament is connected in parallel with said second sub-filament.

[0043] In yet another example, the filament comprises: a first elongated encapsulant covering the first plurality of LEDs, said first elongated encapsulant comprises a first luminescent material configured to at least partly convert LED light emitted by said first plurality of LEDs into first converted light and / or a first scattering material configured to at least partly scatter LED light emitted by said first plurality of LEDs into first scattered light; and a second luminescent material configured to at least partly convert LED light emitted by said second plurality of LEDs into second converted light and / or a second scattering material configured to at least partly scatter LED light emitted by said second plurality of LEDs into second scattered light.

[0044] In yet another example, the filament comprises: a first elongated encapsulant covering the first plurality of LEDs, said first elongated encapsulant comprises a first luminescent material configured to at least partly convert LED light emitted by said first plurality of LEDs into first converted light and / or a first scattering material configured to at least partly scatter LED light emitted by said first plurality of LEDs into first scattered light; and a second luminescent material configured to at least partly convert LED light emitted by said second plurality of LEDs into second converted light and / or a second scattering material configured to at least partly scatter LED light emitted by said second plurality of LEDs into second scattered light wherein said first elongated encapsulant is in physical contact with said second elongated encapsulant.

[0045] The inventors have found that it may be beneficial to cover the first plurality of LEDs and the second plurality of LEDs with a luminescent material and / or a scattering material. This further improves the effect that the sub-filaments are perceived as a single filament.

[0046] In another example, the second sub-filament light has a first correlated colour temperature and second sub-filament light has a second correlated colour temperature, wherein

[0047] The inventors have found that it is desired that the first and second sub LED filaments emit (substantially) the same CCT but the first sub LED filament is optimized for the first driver and the second sub LED filament is optimized for the second driver. As an example, turning off the first driver and operating the second driver at full power allows simple dimming to 50%, while operating at high efficiency. Therefore, the LED based filament lamp may receive a dimming signal and may determine to turn on or off the first driver or the second driver in dependence of the dimming level. Preferably, when the dimming signal is below a threshold, the first driver is disabled, while keeping the second driver active. Under disabled, it could be understood that the power stage of the driver is turned off such that no power can be provided to the corresponding sub-filament, while the driver consumes only a very small standby power.

[0048] In an example, the first and second luminescent material may be the same e.g. in terms of phosphor composition and / or phosphor concentration.

[0049] In another example, the second sub-filament light has a first correlated colour temperature and second sub-filament light has a second correlated colour temperature, wherein | CCT2-CCT1 | >500K.

[0050] In an example, the first and second luminescent material may be different e.g. in terms of phosphor composition and / or phosphor concentration.

[0051] In a further example, the LED based lighting lamp further comprises a light- transmissive envelope at least partially enclosing said LED filament.

[0052] In an example, a length of said first sub-filament is substantially equal to a length of said second sub-filament.

[0053] The advantage of this particular example is that it is more straightforward to create two sub-filaments that together appear as a single filament.

[0054] As an alternative, the first sub-filament may be longer that the second subfilament. Even in this particular case, the technical effect is obtained albeit not necessary over the entire range. In case of a malfunction in the second sub-filament, the user may not perceive any fault condition in the LED based filament lamp. In case of a malfunction in the first sub-filament, the user may perceive a fault condition in a small part of the first subfilament.

[0055] In an example, the first driver and said second driver are any of: a buck converter; a boost converter.

[0056] The first driver and the second driver may have the same primary input, for example 230 volts Alternating Current, AC. The converters may have isolated outputs.

[0057] The driver may thus encompass a switched mode power supply. A switched- mode power supply, SMPS, is an electronic circuit that efficiently converts electrical power from one form to another using switching devices, such as transistors or MOSFETs. It is commonly used to regulate and convert electrical energy from a source, such as the mains power supply, to provide a stable and specific output voltage or current for LEDs.

[0058] In a further example, the first driver and said second driver are at least partly enclosed by a base of said LED based filament lamp. In another example, the first driver is galvanic isolated from said second driver.

[0059] In an example, the first driver may be arranged for only driving said first plurality of LEDs of said first sub-filament and the second driver may be arranged for only driving said second plurality of LEDs of said first sub-filament.

[0060] In an example, the second driver may be different from said first driver in terms of (maximum) output power.

[0061] In an example, a maximum output power (Pl) of the second driver may be different from a maximum output power (P2) of the first driver. For example, the electronic component arrangement of the first and second drivers may be different. In an example, the first driver may provide a maximum output power (Pl) of 3W, while the second driver may provide a maximum output power (P2) of 12W.

[0062] In an example, in a first operation mode the light emitted by said first subfilament may have a higher luminous flux and / or intensity than the light emitted by said second sub-filament.

[0063] In an example, in a second operation mode said first sub-filament may emit light, while the said second sub-filament does not emit light.

[0064] In an example, in a third operation mode said second sub-filament may emit light, while the said first sub-filament does not emit light.

[0065] In a second aspect of the present disclosure, there is provided a luminaire comprising at least one LED based filament lamp in accordance with any of the previous examples.

[0066] It is noted that the advantages as explained with respect to the first aspect, being the Light Emitting Diode, LED, based filament lamp, are also applicable to the second aspect, being the luminaire comprising such a LED based filament lamp.

[0067] In the appended figures, similar components and / or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

[0068] The above and other aspects of the disclosure will be apparent from and elucidated with reference to the examples described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Fig. 1 discloses an example of a Light Emitting Diode, LED, based filament lamp in accordance with the present disclosure;

[0070] Fig. 2 discloses another example of an LED based filament lamp in accordance with the present disclosure;

[0071] Fig. 3 discloses a luminaire in accordance with the present disclosure.

[0072] DETAILED DESCRIPTION

[0073] It is noted that in the description of the figures, same reference numerals refer to the same or similar components performing a same or essentially similar function.

[0074] A more detailed description is made with reference to particular examples, some of which are illustrated in the appended drawings, such that the manner in which the features of the present disclosure may be understood in more detail. It is noted that the drawings only illustrate typical examples and are therefore not to be considered to limit the scope of the subject matter of the claims. The drawings are incorporated for facilitating an understanding of the disclosure and are thus not necessarily drawn to scale. Advantages of the subject matter as claimed will become apparent to those skilled in the art upon reading the description in conjunction with the accompanying drawings.

[0075] The ensuing description above provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the disclosure, it being understood that various changes may be made in the function and arrangement of elements, including combinations of features from different embodiments, without departing from the scope of the disclosure.

[0076] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof. Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

[0077] These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

[0078] Fig. 1 discloses an example 1 of a Light Emitting Diode, LED, based filament lamp in accordance with the present disclosure.

[0079] The LED based filament lamp 1 comprises a LED filament 7. The LED filament comprises a first sub-filament 4 and a second sub-filament 3. Both sub-filaments 3, 4 comprise a plurality of LEDs. The first sub-filament 4 comprises a first plurality of LEDs. The second sub-filament 3 comprises a second plurality of LEDs.

[0080] The first and second sub-filaments are integrated on a substrate 2. The substrate may be a Printed Circuit Board, PCB. A PCB is typically a board made of a non- conductive material that serves as a base for mounting electronic components, like LEDs, and provides interconnections between them.

[0081] Another option is that the LEDs are mounted on a so-called Flex PCB. Such a type of PCB may be made of a flexible material such as polyimide or polyester. They offer the advantage of being able to bend and conform to different shapes, making them suitable for applications that require flexibility or space constraints. Flex PCBs can be used to mount LEDs and provide electrical connections in applications where rigid PCBs may not be suitable. Another option is related to ceramic substrates. These kind of substrates may, for example, be used in LED-based filament lamps with a helix-shaped filament. Ceramic substrates may offer improved thermal conductivity and insulation properties. They can efficiently dissipate heat generated by the LEDs and help maintain a stable operating temperature.

[0082] In accordance with the present disclosure, the first sub-filament and the second sub-filament may be positioned such to ensure that light emitted by each of the first plurality of LEDs, i.e. located on the first sub-filament, is mixed with light emitted by any of the second plurality of LED, i.e. located on the second sub-filament. This accomplishes that the combination of light emitted by the first sub-filament and light emitted by the second subfilament is perceived as light emitted by a single filament.

[0083] The LEDs of the different sub-filaments may be placed in close proximity to each other. The closer they are, the more effective their emitted light will blend together, creating the illusion of a single filament. Positioning them side by side or very close together helps to minimize any perceived separation between the two sources of light, i.e. the two subfilaments.

[0084] Optics or diffusers may be incorporated to blend the light from the two subfilaments. Optical elements such as lenses or light diffusing materials can help scatter and mix the light, reducing any distinct boundaries between the two sources. This can result in a more uniform and blended illumination, making it appear as if it's coming from a single filament.

[0085] The inventors have found that it might also be beneficial to align the direction of the light paths from the two sub-filaments. Ensuring that the light emitted by both subfilaments is directed towards the same focal point or general area. This alignment may help to create a convergence of the light and reduces the perception of multiple light sources.

[0086] Another criteria might be related to the viewing angle. The LEDs of the subfilaments may be positioned in a way that improves the viewing angle for the desired effect. Consider the perspective from which the light will be observed and adjust the LED placement accordingly.

[0087] Yet another criteria is related to brightness matching. The brightness of the sub-filaments may be matched to one another closely. By ensuring that both sub-filaments have similar brightness levels, it helps to further enhance the illusion of a single filament. This can be achieved by adjusting the current or voltage supplied to each LED or by selecting LEDs with similar specifications. The LED-based filament lamp further comprises a first driver 5 and a second driver 6. The first driver is arranged for driving the first plurality of LEDs of the first subfilament 4. The second driver is arranged for driving the second plurality of LEDs of the second sub-filament.

[0088] The drivers are separated from one another. They may be connected to the same primary source, i.e. a mains voltage like 230V. The secondary side of the drivers 5, 6 is electrically isolated from one another.

[0089] Fig. 2 discloses another example of an LED based filament lamp in accordance with the present disclosure.

[0090] The filament is indicated with reference numeral 26. The sub-filaments are indicated with reference numerals 22 and 23. The difference between the example shown in figure 2 and the example shown in figure 1 is that the sub-filaments 22, 23 are each positioned on a separate substrate 24, 25.

[0091] Fig. 3 discloses a luminaire 31 in accordance with the present disclosure. The two sub-filaments are indicated with reference numerals 32 and 33, and the two drivers are indicated with reference numerals 34 and 35.

[0092] In accordance with the present disclosure, the LEDs of the different subfilaments may be positioned close to one another, typically within a few millimeters, to ensure that the emitted light overlaps and creates the desired mixing effect. The precise distance and angle of the LEDs may vary depending on the specific design and application, and can be determined through experimentation and testing.

[0093] If the second sub-filament fails, then the user would not able to “see” that second sub-filament. The lamp has reduced functionality, for example less light output, or reduced colour palette, or anything alike, but a user will not “see” that a particular subfilament is not operating properly.

[0094] It is further noted that the LED-based filament lamp in accordance with the present disclosure may comprise a third sub-filament. The third sub-filament may be accompanied by a third driver. All sub-filaments may be positioned such that it appears as if there is one filament in the LED-based filament lamp.

[0095] Another advantage of the present disclosure is related to the drivers of the respective sub-filaments. The sub-filaments may be heterogeneous of nature, such that they have different electrical properties. The load encountered by the first driver may thus be different to the load encountered by the second driver. In accordance with the solution provided by the present disclosure, the drivers may be tailored to the specific load. It is further noted that, for energy efficiency purposes, it may be decided to switch of a particular load. This reduces energy consumption, while maintaining a properly working lamp. As explained above, a fault-condition may arise in any of the driver or the sub-filament but there might thus also be a conscious decision to turn down one of the subfilaments. This is possible as a user will not perceive the lamp as being broken, but will assume the lamp is working properly.

[0096] To reduce the number of claims, certain aspects of the technology are presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of claim forms. For example, while some aspect of the technology may be recited as a computer-readable medium claim, other aspects may likewise be embodied as a computer-readable medium claim, or in other forms, such as being embodied in a means-plus-function claim.

[0097] In the description above, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

[0098] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

CLAIMS:

1. A Light Emitting Diode, LED, based filament lamp (1, 21 31), comprising: an LED filament (7, 26) comprising:(i) a first sub-filament (3, 4, 22, 23, 32, 33) having a first plurality of LEDs, and(ii) a second sub-filament (3, 4, 22, 23, 32, 33) having a second plurality of LEDs, wherein said first sub-filament (3, 4, 22, 23, 32, 33) and said second subfilament (3, 4, 22, 23, 32, 33) are positioned to ensure that light emitted by each of said first plurality of LEDs is mixed with light emitted by any of said second plurality of LEDs, respectively, such that said combination of light emitted by said first sub-filament (3, 4, 22, 23, 32, 33) and light emitted by said second sub-filament (3, 4, 22, 23, 32, 33) is perceived as light emitted by a single filament at a target distance; a first driver (5, 34) arranged for driving said first plurality of LEDs of said first sub-filament (3, 4, 22, 23, 32, 33), wherein the first driver (5, 34) is any of a buck converter or a boost converter; a second driver (6, 35), different from said first driver (5, 34), arranged for driving said second plurality of LEDs of said second sub-filament (3, 4, 22, 23, 32, 33), wherein the second driver (6, 35) is any of a buck converter or a boost converter.

2. An LED based filament lamp (1, 21 31) according to claim 1, wherein said first and second sub-filament (3, 4, 22, 23, 32, 33) are arranged in parallel and next to each other.

3. An LED based filament lamp (1, 21 31) according to any of the previous claims, wherein said first sub-filament (3, 4, 22, 23, 32, 33) and said second sub-filament (3,4. 22, 23, 32, 33) are positioned such that a largest distance between said second sub-filament (3, 4, 22, 23, 32, 33) and said first sub-filament (3, 4, 22, 23, 32, 33) is equal to or smaller than 5 mm, preferably equal to or smaller than 3 mm.

4. An LED based filament lamp (1, 21 31) according to any of the previous claims, wherein each of said LEDs in said first plurality of LEDs has a distance to a LED in said second plurality of LEDs smaller than 5 mm, preferably smaller than 3 mm.

5. An LED based filament lamp (1, 21 31) according to any of the previous claims, wherein said LED based filament lamp (1, 21 31) comprises an elongated carrier, said elongated carrier comprising said first sub-filament (3, 4, 22, 23, 32, 33) and said second subfilament (3, 4, 22, 23, 32, 33).

6. An LED based filament lamp (1, 21 31) according to any of the previous claims, wherein said first sub-filament (3, 4, 22, 23, 32, 33) is electrically connected in series with said second sub-filament (3, 4, 22, 23, 32, 33).

7. An LED based filament lamp (1, 21 31) according to any of the claims 1 - 5, wherein said first sub-filament (3, 4, 22, 23, 32, 33) is electrically connected in parallel with said second sub-filament (3, 4, 22, 23, 32, 33).

8. An LED based filament lamp (1, 21 31) according to any of the previous claims, wherein said filament further comprises: a first elongated encapsulant covering the first plurality of LEDs, said first elongated encapsulant comprises a first luminescent material configured to at least partly convert LED light emitted by said first plurality of LEDs into first converted light and / or a first scattering material configured to at least partly scatter LED light emitted by said first plurality of LEDs into first scattered light; and a second luminescent material configured to at least partly convert LED light emitted by said second plurality of LEDs into second converted light and / or a second scattering material configured to at least partly scatter LED light emitted by said second plurality of LEDs into second scattered light; wherein said first elongated encapsulant is in physical contact with said second elongated encapsulant.

9. An LED based filament lamp (1, 21 31) according to any of the previous claims, wherein said first sub-filament (3, 4, 22, 23, 32, 33) light has a first correlated colortemperature and said second sub-filament (3, 4, 22, 23, 32, 33) light has a second correlated color temperature, wherein I CCT2-CCT1 I <300K.

10. An LED based filament lamp (1, 21 31) according to any of the claims 1-8, wherein said second sub-filament (3, 4, 22, 23, 32, 33) light has a first correlated color temperature and second sub-filament (3, 4, 22, 23, 32, 33) light has a second correlated color temperature, wherein11. An LED based filament lamp (1, 21 31) in accordance with any of the previous claims, wherein a length of said first sub-filament (3, 4, 22, 23, 32, 33) is substantially equal to a length of said second sub-filament (3, 4, 22, 23, 32, 33).

12. An LED based filament lamp (1, 21 31) in accordance with any of the previous claims, wherein a maximum output power of the second driver (6, 35) is different from a maximum output power of the first driver (5, 34).

13. An LED based filament lamp (1, 21 31) in accordance with any of the previous claims, wherein said first driver (5, 34) is galvanic isolated from said second driver (6, 35).

14. A luminaire comprising at least one LED based filament lamp (1, 21 31) in accordance with any of the previous claims.

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