LED lamp filament
By adopting a multi-layer LED structure and an independent controller on the LED filament, the problems of optical crosstalk and insufficient light distribution are solved, and pure blue light output and selective adjustment of multiple colors are achieved to meet different light distribution requirements.
Patent Information
- Application Number
- CN202480009614.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-01-30
- Filing Date
- 2024-01-17
- Publication Date
- 2025-09-05
AI Technical Summary
Existing LED filament lamps have deficiencies in optical crosstalk and light distribution, making it difficult to provide pure blue or efficient adjustment of multiple colors.
A multi-layer LED structure is adopted, including a first blue LED arranged on a carrier and a second blue LED string on the top surface. The emission of each LED is independently controlled by a controller, optical crosstalk is reduced, and a variety of light effects are provided by combining LEDs of different colors.
It achieves the output of pure blue light and reduces optical crosstalk, and provides selective adjustment of white light and colored light and a combination of multiple colors to meet different light distribution requirements.
Smart Images
Figure CN120604345A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a light emitting diode (LED) filament, a lamp or a lamp fixture comprising the LED filament, and a lighting system comprising the lamp or the lamp fixture. Background Art
[0002] One trend in lighting is the LED filament lamp. An LED filament lamp is an LED lamp designed to resemble a traditional incandescent bulb, with a visible filament for aesthetics and light distribution purposes, but with the high efficiency of a light-emitting diode. Summary of the Invention
[0003] It is an object of the present invention to improve the performance and / or functionality of LED filaments.
[0004] According to a first aspect of the present invention, this object and other objects are achieved by a light emitting diode (LED) filament, which includes: a carrier; a plurality of first blue LEDs suitable for emitting first blue light, wherein the plurality of first blue LEDs are arranged on the carrier; a first slender package, the first slender package covering the plurality of first blue LEDs and at least part of the carrier, wherein the first slender package includes a first luminescent material, the first luminescent material is configured to convert at least part of the first blue light into first converted light, and the first slender package has a top surface, wherein the LED filament also includes a string of second blue LEDs suitable for emitting second blue light, wherein the string of second blue LEDs is arranged on the top surface of the LED filament, and wherein the light output surface of the second blue LED faces away from the LED filament.
[0005] In this way, optical crosstalk (ie the effect whereby an operated blue LED excites the phosphor converter of an LED filament causing it to subsequently emit light of a different color) is reduced / absent, thereby providing a pure blue color.
[0006] Preferably, less than 5% of the second blue LED light is converted (by the first luminescent material), more preferably less than 3% of the second blue LED light is converted (by the first luminescent material), most preferably less than 1% (e.g. 0%) of the second blue LED light is converted (by the first luminescent material).
[0007] The top surface can have a top surface area (TSA), wherein the string of the second blue LEDs has a string area SA, and wherein SA<0.4TSA, in particular, SA<0.2TSA. In this way, the string of the second blue LEDs does not block and / or absorb (too much) the first blue light and / or the first converted light.
[0008] The LED filament may further include a controller configured to individually control the emission of first blue light by the plurality of first blue LEDs and the emission of second blue light by the string of second blue LEDs. In this manner, the LED filament may selectively provide white light, colored light, or a combination thereof.
[0009] The string of second blue LEDs can be arranged on a light-transmitting substrate or not. Thus, the first blue light and / or the first converted light can easily pass through the string of second blue LEDs arranged above the first blue LEDs. Although the second blue LEDs and their electrical tracks can still block some light, the first blue light and / or the converted light are transmitted through the light-transmitting substrate or only around the second blue LEDs and (one or more) electrical tracks.
[0010] The second string of blue LEDs can be covered by a second elongated package that is free of luminescent and light-scattering materials. In other words, the second elongated package does not contain any luminescent or light-scattering materials. In this way, the light distribution requirements of an optical LED filament can be met. The second elongated package can, for example, be dome-shaped.
[0011] The LED pitch of the string of second blue LEDs may be 1000 μm or less, preferably 800 μm or less, more preferably 600 μm or less, and most preferably 500 μm or less.“LED pitch” may be the center-to-center distance between adjacent second blue LEDs of a string.
[0012] The LED filament may also include a plurality of red LEDs adapted to emit red light, and optionally, a plurality of green LEDs adapted to emit green light, wherein the plurality of red LEDs and the optional plurality of green LEDs are arranged on the top surface of the LED filament. Alternatively, the plurality of red LEDs and the optional plurality of green LEDs may be arranged on a carrier of the LED filament, for example, below or adjacent to the first elongated package. The plurality of red LEDs and the optional plurality of green LEDs allow the LED filament to provide light of various colors. Therefore, the controller may also be configured to independently control the emission of red light from the plurality of red LEDs and the emission of green light from any plurality of green LEDs.
[0013] The plurality of red LEDs and optionally the plurality of green LEDs can be arranged in at least one string, such as a string of red LEDs and a string of green LEDs, or a combination string of a second blue LED, a red LED, and optionally a green LED. Thus, in one or more embodiments, the string of the second blue LED includes only the second blue LED. In one or more other embodiments, the string of the second blue LED also includes a plurality of red LEDs and optionally a plurality of green LEDs.
[0014] The first luminescent material can be configured to convert at least a portion of the first blue light into first converted light, the first converted light including first green / yellow light and first red light, the first converted light, together with unconverted first blue light emitted by the plurality of first blue LEDs, forming first white light having a first correlated color temperature (CCT1). Preferably, CCT1 is ≤ 2500K.
[0015] The LED filament may further include: a plurality of third blue LEDs adapted to emit a third blue light, wherein the plurality of third blue LEDs are arranged on a carrier; and a third elongated encapsulation covering the plurality of third blue LEDs and a portion of the carrier, wherein the third elongated encapsulation includes a second luminescent material configured to convert at least a portion of the third blue light into second converted light. In this manner, the LED filament can provide white light having different color temperatures while still reducing or avoiding optical crosstalk.
[0016] The string of second blue LEDs may be arranged at the interface between the first and third elongated packages to reduce or minimize the impact on the first blue / converted light and the third blue / second converted light.
[0017] The second luminescent material can be configured to convert at least a portion of the third blue light into second converted light, the second converted light comprising a second green / yellow light and a second red light, the second converted light, together with unconverted third blue light emitted by the plurality of third blue LEDs, forming a second white light having a second correlated color temperature (CCT2), the second correlated color temperature being higher than the first correlated color temperature. Preferably, CCT2-CCT1 is ≥ 500K, and more preferably, CCT2-CCT1 is ≥ 1000K. Typically, CCT2 is ≥ 3500K. Furthermore, the color rendering index (CRI) of the first and second white lights can be at least 80.
[0018] According to a second aspect of the present invention, a lamp or luminaire is provided, comprising an LED filament according to the first aspect and an antenna functionally coupled to a controller for the LED filament. The antenna allows remote control of the lamp or luminaire. The lamp may be, for example, a (retrofit) light bulb.
[0019] According to a third aspect of the invention, there is provided a lighting system comprising: a lamp or luminaire according to the second aspect; and at least one (remote) user interface for providing user input and / or at least one (remote) sensor for sensing data, wherein a controller is configured to control, based on the user input and / or data, a plurality of first blue LEDs, a plurality of second blue LEDs, and optionally a plurality of red LEDs, a plurality of green LEDs and a plurality of third blue LEDs.
[0020] It is noted that the invention relates to all possible combinations of features recited in the claims. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] These and other aspects of the present invention will now be described in more detail, with reference to the accompanying drawings showing embodiments of the invention.
[0022] Figure 1a is a cross-sectional view of an LED filament according to an embodiment of the present invention.
[0023] Figure 1b yes Figure 1a Side view of an LED filament.
[0024] Figure 1c yes Figure 1a A top view of an LED filament.
[0025] Figures 2a to 2e An LED filament according to another embodiment of the present invention is shown.
[0026] Figure 3 is a side view of aspects of the present invention including a lamp.
[0027] As shown in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, therefore, are provided to illustrate the general structure of embodiments of the present invention. Like reference numerals refer to like elements throughout. DETAILED DESCRIPTION
[0028] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that they will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.
[0029] Figures 1a to 1c An LED filament 10 is shown according to an embodiment of the present invention. The LED filament 10 may provide an LED filament (device) lamp 12.
[0030] The LED filament 10 includes an LED filament 14. The LED filament 14 may be rigid or flexible.
[0031] The LED filament 14 includes a carrier 16. The carrier 16 is typically a substrate. The carrier 16 is typically elongated. Preferably, the LED filament 14 has a length L, where L>5D. The distance D corresponds to the width of the carrier 16 and can be, for example, in the range of 0.5 mm to 5 mm. The carrier 16 can include two elongated edge portions 18a-18b spaced apart from each other by a distance D, a first (major) surface 20a, and a second (major) surface 20b disposed opposite the first surface 20a. The carrier 16 can be rigid (e.g., made of a polymer, glass, quartz, metal, or sapphire) or flexible (e.g., made of a polymer or, for example, a metal film or foil).
[0032] The LED filament 14 further includes a plurality of first blue LEDs 22 adapted to emit a first blue light 24. The first blue light 24 may, for example, have a dominant peak wavelength within a wavelength range of 450 nm to 490 nm. The plurality of first blue LEDs 22 are arranged on the carrier 16. Specifically, the plurality of first blue LEDs 22 may be mounted on the first surface 20 a of the carrier 16. Furthermore, the plurality of first blue LEDs 22 are preferably arranged in a linear array, string, or single column, in this case, along the longitudinal centerline of the carrier 16. The number of first blue LEDs 22 may, for example, be at least ten or at least twenty first blue LEDs 22.
[0033] The LED filament 14 also includes a first elongated encapsulant 26 that covers the plurality of first blue LEDs 22 and at least a portion of the carrier 16. The first elongated encapsulant 26 includes a first luminescent material 28 that is configured to convert at least a portion of the first blue light 24 into first converted light 30. Specifically, the first luminescent material 28 can be configured to convert at least a portion of the first blue light 24 into first converted light 30, which includes first green / yellow light and first red light, and together with the unconverted first blue light 24, forms first white light 32 having a first correlated color temperature (CCT1). Preferably, CCT1 is ≤ 2500K (warm white light). Furthermore, the color rendering index (CRI) of the first white light 32 is preferably at least 80. The first luminescent material 28 can be a phosphor, and the first elongated encapsulant 26 can be made of, for example, silicone. The plurality of first blue LEDs 22 with the first elongated encapsulant 26 and the first luminescent material 28 can be referred to as a first white light source.
[0034] The LED filament 14 further comprises a top surface 34, here the top surface 34 of the first elongated encapsulation 26. The top surface 34 is opposite to the bottom surface (= second (carrier) surface 20b) of the LED filament 14. The top surface 34 and the bottom surface 20b may be surrounded by an edge surface. Figure 1c As shown, the top surface 34 has a top surface area TSA, typically, TSA = L x D.
[0035] The LED filament 10 also includes a second light source comprising a string 36 of second blue LEDs 38 adapted to emit a second blue light 40. Here, the string 36 of second blue LEDs 38 includes only the second blue LEDs 38. The string of second blue LEDs 38 is arranged on the top surface 34 of the LED filament 14, either directly or by being arranged on a light transmissive substrate (not shown), such that light output surfaces 42 of the second blue LEDs 38 face away from the LED filament 14. That is, the second blue light 40 is emitted away from the first package 26 comprising the luminescent material 28 in operation. Each light output surface 42 may be a top surface of the blue LED 38, while an opposing bottom surface 44 of the blue LED 38 faces towards (and may be mounted to) the top surface 34 (of the first elongated package 26) of the LED filament 14. Thus, the second blue LEDs 38 may be referred to as top-emitting second blue LEDs 38. Preferably, the string 36 of second blue LEDs 38 is arranged at the longitudinal centerline of the top surface 34 of the LED filament 14, as shown in FIG. Figure 1c That is, the first and second blue LEDs 22, 42 can be arranged in a stack facing the same direction. The number of second blue LEDs 38 can be, for example, at least ten or at least twenty second blue LEDs 38.
[0036] By arranging the string 36 of the second blue LED 38 above / in front of the first elongated package 26 / first luminescent material 28, and emitting the second blue LED light 40 away from the first elongated package 26 / first luminescent material 28 during operation, optical crosstalk (i.e., the effect of the operated blue LED 38 exciting the phosphor converter / luminescent material 28 of the LED filament causing it to subsequently emit light of a different color) is reduced / non-existent, thereby enabling a pure blue color to be provided.
[0037] The string 36 of the second blue LEDs 38 may have a string area SA. The string area SA may be the sum of the areas of the light output surface 42 of the second blue LEDs 38 and the associated electrical tracks. Figure 1c , the (approximate) string area SA is indicated by diagonal stripes. Preferably, SA is less than 0.2 TSA, so that the second blue LED 38 does not block too much of the first blue light 24 and / or the first converted light 30. For example, the electrical track can include copper wires / tracks. Furthermore, the string 36 of the second blue LEDs 36 can have an ultra-low LED pitch P of less than 1000 μm.
[0038] The LED filament 10 may further include a second elongated encapsulation member 46 covering the string 36 of second blue LEDs 38. The second elongated encapsulation member 46 is free of luminescent material and light scattering material. The second elongated encapsulation member 46 may be transparent, for example. The second elongated encapsulation member 46 may be made of silicone, for example. The second elongated encapsulation member 46 may have a dome-shaped cross-section relative to the width D, such as Figure 1a The dome-shaped cross-section may be uniform over substantially the entire length of the second elongated encapsulating member 46 .
[0039] The LED filament 10 may also include an electronic controller 48. The controller 48 is configured to individually control the emission of the first blue light 24 of the plurality of first blue LEDs 22 and the emission of the second blue light 40 of the string of second blue LEDs 38. Thus, in operation, Figures 1a to 1c The LED filament 10 can selectively provide white light 32, blue light 40, or a combination thereof.
[0040] Figure 2a is a cross-sectional view of an LED filament 10 according to another embodiment. Figure 2a LED filament 10 with Figures 1a to 1c Similarly, the LED filament 14 further includes a plurality of red LEDs 50 adapted to emit red light 52, and a plurality of green LEDs 54 adapted to emit green light 56. The plurality of red LEDs 50 and the plurality of green LEDs 54 are arranged on the top surface 34 of the LED filament 14, either directly or by being arranged on a light-transmitting substrate (not shown), with their light output surfaces 42′ facing away from the LED filament 14. The plurality of red LEDs 50 are arranged in a string on one side of the string 36 of the second blue LEDs 38, wherein the string of red LEDs 50 is parallel to the string 36 of the second blue LEDs 38. The plurality of green LEDs 54 are arranged in another string on the other side of the string 36 of the second blue LEDs 38, wherein the string of green LEDs 54 is also parallel to the string 36 of the second blue LEDs 38. The number of red LEDs 50 can be, for example, at least ten or at least twenty red LEDs 50. The number of green LEDs 54 can be, for example, at least ten or at least twenty green LEDs 54. The plurality of red LEDs 50 may be covered by an elongated package 58 similar to the second elongated package 46. Likewise, the plurality of green LEDs 54 may be covered by an elongated package 60 similar to the second elongated package 46. Alternatively, the second elongated package 46 may extend to cover both the red and green LEDs 50, 54 ( Figure 2a Here, the controller 48 may be configured to also individually control the emission of red light 52 from the plurality of red LEDs 50 and the emission of green light 56 from any plurality of green LEDs 54. Thus, in operation, Figure 2aThe LED filament 10 can selectively provide white light 32, blue light 40, red light 50, green light 54, or a combination thereof.
[0041] Figure 2b to Figure 2c is a cross-sectional view of an LED filament 10 according to another embodiment. Figure 2b to Figure 2c The LED filament 10 are with Figure 2a Similarly, here, a plurality of red LEDs 50 and a plurality of green LEDs 56 are arranged on the carrier 16 of the LED filament 14. Specifically, the plurality of red LEDs 50 can be mounted on the first surface 20a of the carrier 16 (on one side of the plurality of first blue LEDs 22), and the plurality of green LEDs 54 can also be mounted on the first surface 20a of the carrier 16 (but on the opposite side of the plurality of first blue LEDs 22). In other words, the plurality of red LEDs 50 can be arranged in a string parallel to the linear array / string / single column of the first blue LEDs 22. Similarly, the plurality of green LEDs 54 can be arranged in another string parallel to the linear array / string / single column of the first blue LEDs 22.
[0042] exist Figure 2b In FIG, the first elongated package 26 covers the first plurality of blue LEDs 22 and the plurality of red LEDs 50, as well as the plurality of green LEDs 54 and at least a portion of the carrier 16. Figure 2c In the embodiment, the first elongated package member, indicated by reference numeral 26', has a limited extension in the width direction and covers (only) the plurality of first blue LEDs 22 and part of the carrier 16, but does not cover the plurality of red LEDs 50 and the plurality of green LEDs 54. The plurality of red LEDs 50 and the plurality of green LEDs 54 may be uncovered or may be provided with Figure 2a Similar elongated packaging members 58, 60 ( Figure 2c not shown).
[0043] Figure 2d FIG. 1 is a top view of an LED filament 10 according to another embodiment. Figure 2d LED filament 10 with Figure 2a Similarly, the string with the second blue LED 38 also includes a plurality of red LEDs 50 and a plurality of green LEDs 54. That is, the plurality of second blue LEDs 38, the plurality of red LEDs 50, and the plurality of green LEDs 54 are arranged in a single string / line / column 36', preferably arranged at the longitudinal centerline of the top surface 34 of the LED filament 14. The LEDs 38, 50, 54 can be arranged in the string 36' in an alternating color sequence (e.g., RGBRGB, etc., i.e., (RGB)n, where n ≥ 5 is preferred), although other arrangements, such as batches, are also possible. Here, the second elongated encapsulation member 46 can also cover the red and green LEDs 50, 54.
[0044] Figure 2e is a cross-sectional view of an LED filament 10 according to another embodiment. Figure 2e LED filament 10 with Figure 2a Similarly, the LED filament 14 here also includes a plurality of third blue LEDs 62 adapted to emit a third blue light 64. The plurality of third blue LEDs 62 are arranged on the carrier 16. Specifically, the plurality of third blue LEDs 62 can be mounted on the first surface 20a of the carrier 16. Furthermore, preferably, the plurality of third blue LEDs 62 are arranged in a linear array / string / single column. The strings of third blue LEDs 62 can be arranged parallel to the strings of first blue LEDs 22 described above. These strings can be mounted on either side of the longitudinal centerline of the carrier 16, such as Figure 2e The number of the third blue LEDs 62 may be, for example, at least ten or at least twenty third blue LEDs 62 .
[0045] Figure 2e The LED filament 14 further includes a third elongated encapsulation member 66 covering the plurality of third blue LEDs and a portion of the carrier 16. The third elongated encapsulation member 66 includes a second luminescent material 68 configured to convert at least a portion of the third blue light 64 into second converted light 70. Specifically, the second luminescent material 68 can be configured to convert at least a portion of the third blue light 64 into second converted light 70. The second converted light 70 includes second green / yellow light and second red light, which, together with the unconverted third blue light 64, form a second white light 72 having a second correlated color temperature CCT2. The second correlated color temperature CCT2 is different from the first correlated color temperature CCT1. Preferably, CCT2-CCT1 is ≥ 500K, and more preferably, CCT2-CCT1 is ≥ 1000K. Typically, CCT2 is ≥ 3500K. Furthermore, the color rendering index (CRI) of the second white light 72 is preferably at least 80. The second luminescent material 68 may be a phosphor and the second elongated encapsulation 66 may otherwise be made of, for example, silicone.The plurality of second blue LEDs 62 with the third elongated encapsulation 66 and the third luminescent material 68 may be referred to as a third white light source.
[0046] As seen in the width direction, the first elongated package 26 and the third elongated package 66 can each cover approximately half of the carrier 16. In this way, the first and third elongated packages 26, 66 can be parallel to each other (in the length direction of the LED filament 12 / LED filament 14). And here, the top surface 34 of the LED filament 14 can be formed by the top surfaces of the first and third elongated packages 26, 66. In addition, the string of second blue LEDs 38 can be arranged at the interface 74 between the first elongated package 26 and the third elongated package 66 (at the top surface 34). The plurality of red LEDs 50 can be arranged on the first elongated package 26, and the plurality of green LEDs 54 can be arranged on the third elongated package 66. Alternatively, a single string of second blue LEDs 38, red LEDs 50, and green LEDs 54 (such as Figure 2d shown) may be arranged at the interface 74 (not shown).
[0047] Here, the controller 48 may also be configured to individually control the emission of the third blue light 64 of the plurality of third blue LEDs 62. Thus, in operation, Figure 2e The LED filament 10 can selectively provide the first white light 32, the second white light 72, the blue light 40, the red light 50, the green light 54 or a combination thereof. In addition, the second elongated package here can be a common elongated package 46', which covers the string 36 of the second blue LED 38, as well as the plurality of red LEDs 50 and any plurality of green LEDs 54. The common elongated package 46' can simplify the manufacture of the LED filament 10. Alternatively, Figure 2e The LED filament 10 may have, for example Figure 2a Individual elongated packaging members 46, 58, 60 are shown.
[0048] FIG4 illustrates a lamp 102 according to one aspect of the present invention. Lamp 102 includes at least one LED filament 10, a controller 48, and an antenna 104 functionally coupled to controller 48. Antenna 104 can be configured to receive user input from at least one user interface 106 and / or data from at least one sensor 108. Controller 54 can also be configured to control first plurality of blue LEDs 22, second plurality of blue LEDs 38, and any red LEDs 50, green LEDs 54, and third blue LED 62 based on user input from user interface 106 and / or (sensed) data from at least one sensor 108. Lamp 102 and user interface 106 and / or sensor(s) 108 can be referred to as lighting system 100. User interface 106 and / or sensor(s) 108 can be remote from lamp 102. User interface 106 can, for example, be implemented in a mobile phone. At least one sensor 108 can, for example, include at least one of the following: a camera, a light sensor, a presence sensor, and a proximity sensor.
[0049] The LED filament 14 / LED filament 10 is arranged here in a coiled configuration, but other configurations, such as a straight configuration, are also possible. The lamp 102 may also include a housing 110 for enclosing the LED filament 14 / LED filament 10; and a cap or base 112 for electrically and mechanically connecting the lamp 102 to an external socket (not shown). The lamp 102 may be, for example, a retrofit light bulb.
[0050] Those skilled in the art realize that the present invention is by no means limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.
[0051] Furthermore, variations to the disclosed embodiments may be understood and effected by those skilled in the art in practicing the claimed invention by studying the drawings, this 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 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.
Claims
1. A light emitting diode (LED) filament (10), comprising: carrier (16); a plurality of first blue LEDs (22) adapted to emit a first blue light (24), wherein the plurality of first blue LEDs are arranged on the carrier; a first elongated package (26) covering the plurality of first blue LEDs and at least a portion of the carrier, wherein the first elongated package comprises a first luminescent material (28) configured to convert at least a portion of the first blue light into first converted light (30); the first elongated package having a top surface (34), and A string (36, 36') of second blue LEDs (38) adapted to emit a second blue light (40), wherein the string of second blue LEDs is mounted directly on the top surface of the LED filament, and wherein light output surfaces (42) of the second blue LEDs face away from the top surface (34).
2. The LED filament according to claim 1, wherein The top surface has a top surface area TSA, wherein the string of second blue LEDs has a string area SA, and wherein SA<0.4TSA.
3. The LED filament according to any one of the preceding claims, further comprising a controller (48) configured to individually control the emission of the first blue light of the plurality of first blue LEDs and the emission of the second blue light of the string of second blue LEDs.
4. The LED filament according to any one of the preceding claims, wherein The string of the second blue LEDs is arranged on a light-transmitting substrate or is not arranged on a substrate.
5. The LED filament according to any one of the preceding claims, wherein The second string of blue LEDs is covered by a second elongated encapsulation (46) which is free of luminescent and light scattering materials.
6. The LED filament according to any one of the preceding claims, wherein The LED pitch of the second blue LED string is less than 1000 μm.
7. The LED filament according to any of the preceding claims, further comprising a plurality of red LEDs (50) adapted to emit red light (54), and optionally a plurality of green LEDs (54) adapted to emit green light (56), wherein The plurality of red LEDs and optionally the plurality of green LEDs are arranged on the top surface of the LED filament.
8. The LED filament according to claim 7, wherein: The plurality of red LEDs and optionally the plurality of green LEDs are arranged in at least one string.
9. The LED filament according to claim 7 or 8, wherein: The string (36) of second blue LEDs comprises only second blue LEDs.
10. The LED filament according to claim 7 or 8, wherein: The second string (36') of blue LEDs further comprises the plurality of red LEDs and optionally the plurality of green LEDs.
11. The LED filament according to any one of the preceding claims, wherein The first luminescent material is configured to convert at least a portion of the first blue light into first converted light, the first converted light including first green / yellow light and first red light, the first converted light together with the unconverted first blue light emitted by the plurality of first blue LEDs forming first white light having a first correlated color temperature CCT1, wherein CCT1 ≤ 2500K.
12. The LED filament according to any one of the preceding claims, wherein The LED filament further comprises: a plurality of third blue LEDs (62) adapted to emit a third blue light (64), wherein the plurality of third blue LEDs are arranged on the carrier; and A third elongated package (66) covering the plurality of third blue LEDs and a portion of the carrier, wherein the third elongated package includes a second luminescent material (68) configured to convert at least a portion of the third blue light into second converted light.
13. The LED filament according to claim 12, wherein: The string of the second blue LEDs is arranged at an interface (74) between the first elongated package and the third elongated package.
14. The LED filament according to claim 11 and 12, wherein: The second luminescent material is configured to convert at least a portion of the third blue light into second converted light, the second converted light including a second green / yellow light and a second red light, the second converted light together with the unconverted third blue light emitted by the plurality of third blue LEDs forming a second white light (72) having a second correlated color temperature CCT2, the second correlated color temperature being higher than the first correlated color temperature, wherein CCT2-CCT1≥500K, and wherein the color rendering index (CRI) of the first white light and the second white light is at least 80.
15. A lighting system (100), comprising: A lamp (102) or luminaire comprising an LED filament (10) according to any one of the preceding claims, and an antenna (104) functionally coupled to a controller (48) of the LED filament; and at least one user interface (106) for providing user input and / or at least one sensor (108) for sensing data, Wherein, the controller is configured to control the plurality of first blue LEDs, the plurality of second blue LEDs, and optionally the plurality of red LEDs, the plurality of green LEDs and the plurality of third blue LEDs based on the user input and / or the data.