Light emitting diode filament arrangement

Abstract

The invention, in the field of light emitting diode, LED, lighting, relates to a color point tunable LED filament arrangement (1) with an off-state white appearance, with improved efficiency. A first and a second LED filament (10, 20) comprise a white encapsulant (17, 14). The white encapsulants (17, 14) comprise scattering material (18, 25) in a translucent material (19, 26). The concentrations of scattering material (18, 25) in the white encapsulants and / or the thicknesses of the white encapsulants are not the same for the first and second LED filament (10, 20). The invention also relates to a lighting device (100) and a luminaire comprising such a LED filament arrangement (1).

Description

[0001] Light emitting diode filament arrangement

[0002] FIELD OF THE INVENTION

[0003] The invention relates to the field of LED lighting, and more particularly to a color-point tunable light emitting diode, LED, filament arrangement.

[0004] BACKGROUND OF THE INVENTION

[0005] It is typical for a lighting apparatus, such as a light fixture, luminaire, decorative or general purpose lamp, to include one or more light emitting diode, LED, filaments, which are composed of a linear series of LEDs arranged on a carrier, supported or held in an envelope to give the appearance of an incandescent filament. The filaments are typically constructed with InGaN blue-emitting LED dies carried on a substantially linear glass or sapphire substrate and covered or encapsulated with a blend of silicone and phosphor. Often, the encapsulating blend may have a yellow color in an OFF-state. The appearance of the LED filaments may be considered disadvantageous due to the yellow color in the OFF-state.

[0006] US 2019 / 128481 discloses an overcoated LED filament including an LED filament comprising one or more LED dies coated with an underlying layer of a phosphor material exhibiting a colored appearance, and an over-coated layer comprising a resinous material loaded with a scattering agent that causes the LED filament to appear white. While this solution may solve the aforementioned problem, it is known that the scattering, caused by the scattering agent, reduces the luminous efficiency of the LED filament.

[0007] US 2022 / 349530 discloses LED filament lamp which provides LED filament lamp light. The LED filament lamp comprises at least one LED filament which has a LED filament length (L) which extends from a first end to a second end. The at least one LED filament provides LED filament light and comprises an array of a plurality of LEDs and an encapsulant. The array of a plurality of LEDs provides LED light and extend along the LED filament length (L). The encapsulant is at least partially enclosing the plurality of LEDs. The encapsulant comprises a light scattering material.

[0008] SUMMARY OF THE INVENTION The invention overcomes the aforementioned problems and provides a further development by providing a color-point tunable light emitting diode, LED, filament arrangement configured to, in an on-state, emit LED filament arrangement light. The LED filament arrangement comprises a first LED filament configured to provide, in an on-state, first LED filament light and the first LED filament comprises a plurality of first LEDs arranged on a first major surface of a first elongated carrier. Furthermore, the first LED filament comprises a first elongated light-converting encapsulant covering the plurality of first LEDs and at least a part of the first major surface, the first elongated light-converting encapsulant comprises a first luminescent material arranged in a first translucent material. The first luminescent material is configured to convert at least a part of first LED light, that is emitted by the plurality of first LEDs into a first converted light. The first LED filament also comprises a first elongated white encapsulant covering the first elongated light-converting encapsulant, the first elongated white encapsulant comprises a first light scattering material arranged in a second translucent material, the first light scattering material being configured to scatter at least a part of the first converted light and, optionally, first LED light emitted by the plurality of first LEDs into a first scattered light. The first elongated white encapsulant has a first thickness, Tl, and the first light scattering material comprises a first concentration, Cl, in the second translucent material.

[0009] The LED filament arrangement moreover comprises a second LED filament configured to provide, in an on-state, a second LED filament light and comprises a plurality of second LEDs arranged on a second major surface of a second elongated carrier. Furthermore, a second white elongated encapsulant covers the plurality of second LEDs and at least a part of the second major surface. The second elongated white encapsulant comprises a second light scattering material arranged in a third translucent material, the second light scattering material being configured to scatter at least a part of the second LED light emitted by the plurality of second LEDs into a second scattered light, the second elongated white encapsulant comprising a second thickness, T2, and the second light scattering material comprising a second concentration, C2, in the third translucent material. Additionally, the LED filament arrangement comprises a controller configured to individually control the first LED filament light provided by the first LED filament and the second LED filament light provided by the second LED filament. Also, Cl, C2, Tl and T2 are chosen such that Cl > C2 and / or Tl > T2.

[0010] This LED filament arrangement thereby provides a color-tunable light source, that has a white appearance when it is in an OFF-state while at the same time having a high efficiency as the second scattering material concentration, C2, is less than the first scattering material concentration, Cl, and / or the second elongated white encapsulant thickness, T2, is less than the first elongated white encapsulant thickness, Tl. The inventor has found that covering phosphor-converted LED filaments with a white encapsulant has a high negative impact on the efficiency of the LED filament. Therefore, the proposal is to tune / tweak the concentration of the light scattering material and / or thickness of the white encapsulant to the type of LED filament.

[0011] One or both of the first elongated white encapsulant and the second elongated white encapsulant is free from luminescent material. Optionally, the second elongated white encapsulant is free from luminescent material. The first elongated white encapsulant causes the first elongated light-converting encapsulant to appear white when the LED filament arrangement is in an off-state. The first and / or second elongated white encapsulants being free from luminescent material contributes to the LED filaments to appear white as the luminescent material typically has a yellow or orange appearance.

[0012] Furthermore, one of the following may apply: the first light scattering material has a different average particle size than the second light scattering material; and / or the first light scattering material is a different material than the second light scattering material. This advantageously allows to choose a material suitable to create a uniform color appearance of the LED filament arrangement, as the need for hiding power of the first elongated white encapsulant and the second elongated white encapsulant may be different.

[0013] For the LED filament arrangement, Cl > C2 and Tl > T2, or Cl > C2 and Tl > T2 may apply. These features may be desirable as the first elongated white encapsulant thereby is provided with a higher hiding power than the second elongated white encapsulant. This in turn gives the first and second LED filaments the same white appearance while being highly efficient, as an overly light-absorbing layer of white encapsulant is avoided.

[0014] More specifically, Cl > C2 and Tl = T2 may apply. This advantageously provides a white encapsulant for the first LED filament to appear white in an OFF-state and provides a white encapsulant for the second LED filament to appear in the same white color. This may be particular advantageous as the LED filaments may be produced using similar processes, having only to vary the use of a different concentration of light scattering material.

[0015] Alternatively, Cl > C2 and Tl < T2 may apply. This may be desirable as the hiding power of the first elongated white encapsulant may be the same or higher than that of the second elongated white encapsulant while an overall thickness of the LED filaments may be the same and / or the overall thickness of the first LED filament is reduced. Specifically, one of the following may apply: Cl > 1.1 *C2 and 0.9 < T1 / T2 < 1.1; or 0.9 < C1 / C2 < 1.1 and T1 > 1.1*T2. More specifically one of the following may apply: Cl > 1.1*C2 and 0.95 < T1 / T2 < 1.05; or 0.95 < C1 / C2 < 1.05 and T1 > L PT2. This may be desirable as it causes the hiding power of the first elongated white encapsulant to be higher than that of the second elongated white encapsulant. One may use a same encapsulant material for manufacturing both the first and the second elongated white encapsulant but applying a different thickness. Alternatively, one may use a different encapsulant material for manufacturing the first and the second elongated white encapsulant but creating the same thickness.

[0016] The second LED filament comprises a first diameter, DI, and the second LED filament comprises a second diameter, D2, and 0.8 < D1 / D2 < 1.2 or 0.9 < D1 / D2 < 1.1 or 0.95 < D1 / D2 < 1.05 may apply. This advantageously causes the two LED filaments to be appreciated as having a very similar diameter.

[0017] The second LED filament may comprise a second elongated light-converting encapsulant covering the plurality of second LEDs and at least a part of the second major surface. The second elongated light-converting encapsulant may comprise a second luminescent material arranged in a fourth translucent material. The second luminescent material may be configured to convert at least a part of the second LED light emitted by the plurality of second LEDs into a second converted light, and wherein the second elongated white encapsulant is covering the second elongated light-converting encapsulant. Beneficially, the second elongated light-converting encapsulant allows to transform the first LED light to a second converted light while the second elongated white encapsulant is hiding the second elongated light-converting encapsulant / is providing the second elongated lightconverting encapsulant a white appearance in the off-state.

[0018] The first LED filament is configured to provide LED filament light with a first correlated color temperature, CCT1, and the second LED filament is configured to provide LED filament light with a second correlated color temperature, CCT2, and CCT2 > CCT1 + 500 K or CCT2 > CCT1 + 1000 K may apply. This may enable a defined range of CCT for the light that is emitted by the LED filament arrangement. The range may be at least 500 K wide. A phosphor converted LED filament having a higher CCT has a less orange / reddish appearance, e.g., a more yellow appearance / color. And therefore, the second elongated encapsulant only needs a lower thickness and / or a lower concentration of light scattering material because less hiding power is needed for yellow or orange / reddish color. The first luminescent material may comprise a first green-yellow phosphor having a first phosphor concentration, PCI, and a first red phosphor having a second phosphor concentration, PC2, the second luminescent material may comprise a second greenyellow phosphor having a third phosphor concentration, PC3, and a second red phosphor having a fourth phosphor concentration, PC4, and at least one of the following may apply: PC2 > PC4 and (PC1+PC2) > (PC3+PC4).

[0019] The first elongated light-converting encapsulant may have a darker color than the second elongated light-converting encapsulant and / or the first elongated light-converting encapsulant may have a more orange-reddish color than the second elongated lightconverting encapsulant. In that case the hiding power of the first elongated white encapsulant thus needs to be higher than the second elongated white encapsulant to achieve the same white appearance of the first and second LED filaments in an OFF-state. A phosphor converted LED filament having a higher CCT has a less orange / reddish appearance, e.g., a more yellow appearance / color. Therefore, the second elongated encapsulant only needs a lower thickness and / or a lower concentration of light scattering material because less hiding power is needed for yellow or orange / reddish color.

[0020] The first elongated light-converting encapsulant and the first elongated white encapsulant may cover the first elongated carrier on a first backside, and the second elongated light-converting encapsulant and / or the second elongated white encapsulant further may cover the second elongated carrier on a second backside, and the first elongated carrier and the second elongated carrier may be light transmissive. This may be desirable as the first light converting encapsulant on the first major side of the first elongated carrier may reflect a part of the light back towards the first major side. This reflected light may then pass through the first elongated carrier and the encapsulants on the first backside to contribute to the luminous flux of the first LED filament. If the first elongated carrier is not transparent the reflected light may just turn into heat and would not contribute to the luminous flux of the first LED carrier. The same applies to the second LED filament.

[0021] A further aspect of the invention relates to a lighting device or a luminaire comprising a transparent cover (e.g., envelope) covering the first LED filament and the second LED filament of a color-point tunable LED filament arrangement according to the invention. This may provide a common platform (such as for example an E27 socket) to employ the LED filaments. Furthermore, the transparent cover may protect the LED filaments and the transparent cover may also be used to help mix the light emitted by the LED filaments by scattering and / or refraction. In a further aspect the lighting device or luminaire comprises a color-point tunable LED filament arrangement configured to, in an on-state, emit LED filament arrangement light, the LED filament arrangement comprising: a first LED filament configured to provide, in an on-state, first LED filament light and comprising: a plurality of first LEDs arranged on a first major surface of a first elongated carrier, a first elongated lightconverting encapsulant covering the plurality of first LEDs and at least a part of the first major surface, the first elongated light-converting encapsulant comprising a first luminescent material arranged in a first translucent material, the first luminescent material being configured to convert at least a part of first LED light emitted by the plurality of first LEDs into first converted light, and a first elongated white encapsulant covering the first elongated light-converting encapsulant, the first elongated white encapsulant comprising a first light scattering material arranged in a second translucent material, the first light scattering material being configured to scatter at least a part of the first converted light and optionally first LED light emitted by the plurality of first LEDs into first scattered light, the first elongated white encapsulant comprising a first thickness, Tl, and the first light scattering material comprising a first concentration (Cl) in the second translucent material. Furthermore the LED filament arrangement also comprises a second LED filament configured to provide, in an on-state, second LED filament light and comprising: a plurality of second LEDs arranged on a second major surface of a second elongated carrier, and a second elongated white encapsulant covering the plurality of second LEDs and at least part of the second major surface, the second elongated white encapsulant comprising a second light scattering material arranged in a third translucent material, the second light scattering material being configured to scatter at least a part of the second LED light emitted by the plurality of second LEDs into second scattered light, the second elongated white encapsulant comprising a second thickness, T2, and the second light scattering material comprising a second concentration, C2, in the third translucent material, and a second elongated light-converting encapsulant covering the plurality of second LEDs and at least a part of the second major surface, the second elongated light-converting encapsulant comprising a second luminescent material arranged in a fourth translucent material, the second luminescent material being configured to convert at least a part of second LED light emitted by the plurality of second LEDs into second converted light, and wherein the second elongated white encapsulant is covering the second elongated light-converting encapsulant. Moreover, the LED filament arrangement also comprises a controller configured to individually control the first LED filament light provided by the first LED filament and the second LED filament light provided by the second LED filament. Also, Cl, C2, T1 and T2 are chosen such that Cl > C2 and / or T1 > T2.

[0022] The first LED filament may be configured to provide LED filament light with a first correlated color temperature, CCT1, and the second LED filament may be configured to provide LED filament light with a second correlated color temperature, CCT2, wherein CCT2 > CCT1+500K, and / or wherein the first elongated light-converting encapsulant and the first elongated white encapsulant further cover the first elongated carrier on a first backside, and the second elongated light-converting encapsulant and / or the second elongated white encapsulant further cover the second elongated carrier on a second backside, and the first elongated carrier and the second elongated carrier are light transmissive.

[0023] The invention, in the field of light emitting diode, LED, lighting, relates to a color point tunable LED filament arrangement with an off-state white appearance, with improved efficiency. A first and a second LED filament comprise a white encapsulant. The white encapsulants comprises scattering material in a translucent material. The concentrations of scattering material in the white encapsulants and / or the thicknesses of the white encapsulants are not the same for the first and second LED filament. The invention also relates to a lighting device and a luminaire comprising such a LED filament arrangement.

[0024] In a further aspect the plurality of second LEDs may comprise a plurality of red light emitting diodes, a plurality of green light emitting diodes, and a plurality of blue light emitting diodes. The red, green, and blue light emitting diodes may repeat periodically on the elongated carrier in order to create a homogenous white light, (e.g. arranged in an RGB alternating fashion).

[0025] In a particular embodiment the lamp or a luminaire comprises a color-point tunable light emitting diode, LED, filament arrangement configured to, in an on-state, emit LED filament arrangement light, the LED filament arrangement comprising: a first LED filament configured to provide, in an on-state, first LED filament light and comprising: a plurality of first LEDs arranged on a first major surface of a first elongated carrier, a first elongated light-converting encapsulant covering the plurality of first LEDs and at least a part of the first major surface, the first elongated light-converting encapsulant comprising a first luminescent material arranged in a first translucent material, the first luminescent material being configured to convert at least a part of first LED light emitted by the plurality of first LEDs into first converted light, and a first elongated white encapsulant covering the first elongated light-converting encapsulant, the first elongated white encapsulant comprising a first light scattering material arranged in a second translucent material the first light scattering material being configured to scatter at least a part of the first converted light and optionally first LED light emitted by the plurality of first LEDs into first scattered light, the first elongated white encapsulant comprising a first thickness and the first light scattering material comprising a first concentration in the second translucent material; a second LED filament configured to provide, in an on-state, second LED filament light and comprising: a plurality of second LEDs arranged on a second major surface of a second elongated carrier, and a second elongated light-converting encapsulant covering the plurality of second LEDs and at least a part of the second major surface, the second elongated light-converting encapsulant comprising a second luminescent material arranged in a fourth translucent material, the second luminescent material being configured to convert at least a part of second LED light emitted by the plurality of second LEDs into second converted light, and wherein the second elongated white encapsulant is covering the second elongated lightconverting encapsulant, and a second elongated white encapsulant covering the second elongated light-converting encapsulant and at least part of the second major surface, the second elongated white encapsulant comprising a second light scattering material arranged in a third translucent material, the second light scattering material being configured to scatter at least a part of the second converted light into the second scattered light, the second elongated white encapsulant comprising a second thickness and the second light scattering material comprising a second concentration in the third translucent material; and a controller configured to individually control the first LED filament light provided by the first LED filament and the second LED filament light provided by the second LED filament, and wherein Cl > C2 and / or T1 > T2.

[0026] BRIEF DESCRIPTION OF DRAWINGS

[0027] Fig. l is a cross-sectional view of an LED filament arrangement. Fig. 2 is a cross-sectional view of an LED filament arrangement. Fig. 3 is a cross-sectional view of a lighting device.

[0028] Fig. 4A is a partial cross-sectional view of an LED filament arrangement. Fig. 4B is a partial cross-sectional view of an LED filament arrangement.

[0029] DETAILED DESCRIPTION OF EMBODIMENTS

[0030] Starting out with Fig. 1 a color-point tunable light emitting diode, LED, filament arrangement 1 configured to, in an on-state, emit LED filament arrangement light LI is shown. The LED filament arrangement 1 comprises a first LED filament 10 configured to provide, in an on-state, first LED filament light LIO and comprising a plurality of first LEDs 11 arranged on a first major surface 12 of a first elongated carrier 13. The first elongated light-converting encapsulant 14 may have, in an off-state of the first LED filament, an orange appearance. The elongated carrier 13 may be made from a polymer, glass, quartz, metal, or sapphire. The carrier 13 may be translucent or transparent. The carrier 13 may be rigid or flexible. Moreover, the first LED filament 10 comprises a first elongated lightconverting encapsulant 14 covering the plurality of first LEDs 11 and at least a part of the first major surface 12. The first elongated light-converting encapsulant comprises a first luminescent material 15 arranged in a first translucent material 16. The first luminescent material 15 is configured to convert at least a part of first LED light LI 1 emitted by the plurality of first LEDs into first converted light L12. Furthermore, the first LED filament comprises a first elongated white encapsulant 17 covering the first elongated light-converting encapsulant 14. The first elongated white encapsulant 17 has, in an off-state of the first LED filament 10, a white or whitish appearance. Preferably, the first elongated white encapsulant may fully cover (e.g. enclosing) the first elongated light-converting encapsulant. The first elongated white encapsulant 17 comprises a first light scattering material 18 arranged in a second translucent material 19. The first elongated white encapsulant may be white or whitish. The first light scattering material 18 is configured to scatter at least a part of the first converted light L 12 and optionally first LED light LI 1 emitted by the plurality of first LEDs into first scattered light LI 3. The first elongated white encapsulant 17 comprises a first thickness T1 and the first light scattering material 18 comprises a first concentration Cl in the second translucent material 19. Furthermore, the first elongated light-converting encapsulant 14 and the first elongated white encapsulant 17 cover the first elongated carrier on a first backside 12’. The first backside 12’ is a major surface of the elongated carrier 13 opposite to the first major surface 12. The first elongated white encapsulant is above the light-converting encapsulant on both the first major surface and the first backside.

[0031] The LED filament arrangement 1 further comprises a second LED filament 20 configured to provide, in an on-state, second LED filament light L20. The second LED filament 20 comprises a plurality of second LEDs 21. The plurality of second LEDs 21 may be of a different type of LEDs than the plurality of first LEDs 11. The plurality of second LEDs 21 may be LEDs that are configured to emit either, red, blue, green, or ultraviolet light. The plurality of second LEDs 21 may be arranged in a periodic pattern, and this periodic pattern may contribute to a more homogenous light color over all directions the second LED filament 20 emits light towards. The second plurality of LEDs 21 are arranged on a second major surface 22 of a second elongated carrier 23. A second elongated white encapsulant 24 covers (e.g. enclosing) the plurality of second LEDs and at least part of the second major surface. The second elongated white encapsulant 24 has, in an off-state of the second LED filament, a white or whitish appearance. The second elongated white encapsulant may be white or whitish. Preferably, the second elongated white encapsulant may fully cover the second elongated light-converting encapsulant. The second elongated white encapsulant 24 comprises a second light scattering material 25 arranged in a third translucent material 26. The second light scattering material 25 is configured to scatter at least a part of the second LED light L21 emitted by the plurality of second LEDs 21 into second scattered light L22. The second elongated white encapsulant 24 comprises a second thickness T2 and the second light scattering material 25 comprises a second concentration C2 in the third translucent material 26. Preferably, the first light scattering material has a higher refractive index than the second light scattering material. More preferably the difference in refractive index between the first light scattering material and the second translucent material is higher than the difference between the second light scattering material and the third translucent material.

[0032] The arrangement also comprises a controller 2. The controller 2 is configured to individually control the first LED filament light LIO provided by the first LED filament 10 and the second LED filament light L20 provided by the second LED filament 20, thereby achieving a controlled LED arrangement light. The controller 2 may be configured to maintain luminous flux or electric power consumption of the LED filament arrangement 1 constant during tuning of the color-point. The controller 2 may control the current that flows through the first and second LED filament 10 and 20, respectively. The first LED filament light L10 has a first correlated color temperature, CCT1, and the second LED filament has a second correlated color temperature, CCT2. The CCT1 may be lower than the CCT2. For example, CCT1 may be at least 500 K, 1000 K, 2000 K, or 3000 K lower than the CCT2. The controller 2 may be incorporated into the same unit as the LED filament arrangement. The controller 2 may be implemented in the form of dedicated hardware circuitry, or configurable or reconfigurable circuitry, such as a PGA or FPGA, or any combination of these. Regarding the various communication involved in implementing the functionality discussed above, the controller 2 may be able to receive a signal from a user and to control the LED filament light L10, L20 accordingly. The communicative abilities of the controller 2 may be implemented by any suitable wired and / or wireless means, for example, by means of a wired network, such as an ethernet network, a DMX network, or the Internet, or by means of a wireless network, such as a local (short range) RF network, for example, a Wi-Fi, ZigBee or Bluetooth network, or any combination of these and / or other means. Moreover, Cl > C2 and / or T1 > T2. Alternatively, Cl > C2 and T1 < T2. The concentrations may be expressed in volume percent, v / v%.

[0033] The first light scattering material 18 and / or the second light scattering material 25 may have a particle size being between 10 micrometer and 0,1 micrometer. Alternatively, the particle size of the first and second scattering material may be less than 1 micrometer. A further alternative is that the particle size of the first light scattering material may be less than 2 micrometer and the particle size of the second scattering material may be less than 1 micrometer. The particle size may be the average particle size. The first light scattering material 18 and / or the second light scattering material 25 may be any of A12O3, TiO2, BaSO4, or a combination thereof. E.g., the first light scattering material may be selected from one or more of: TiO2, BaSO4, A12O3 particles, and the second light scattering material may be selected from one or more of: glass or polymer particles. The materials mentioned for the first light scattering material have a higher reflective index and thus a higher refractive index mismatch with its surrounding. The first light scattering material 18 may have a different average particle size than the second light scattering material 25. The first light scattering material 18 may be a different material than the second light scattering material 25. Preferably the first light scattering material has a larger average particle size than the second light scattering material. Preferably the first light scattering material has a higher refractive index than the second light scattering material. Preferably the first light scattering material has a higher reflectivity than the second light scattering material

[0034] In Fig. 1 the first and the second elongated white encapsulant 17, 24 are free from luminescent material. The first and the second elongated white encapsulant 17, 24 contribute to a white appearance of the first and the second LED filament 10, 20.

[0035] In Fig. 2 a LED filament arrangement 1 is shown. The first LED filament 10 is similar in structure to the first LED filament of Fig. 1. The second LED filament 20 comprises LEDs 21 configured to emit blue or ultraviolet light which in turn is converted into converted light by a second elongated light-converting encapsulant 27. The second elongated light-converting encapsulant 27 and / or the second elongated white encapsulant 24 further cover the second elongated carrier 23 on a second backside 22’. The second backside 22’ is a major surface of the second elongated carrier 23 opposite to the second major surface 22. The second light converting encapsulant 27 comprises a second luminescent material 28 and a fourth translucent material 29. The second elongated light-converting encapsulant 27 is covered by the second elongated white encapsulant 24. The first luminescent material 15 may comprise a first green-yellow phosphor having a first phosphor concentration PCI and a first red phosphor having a second phosphor concentration PC2. The second luminescent material 28 may comprise a second green-yellow phosphor having a third phosphor concentration PC3 and a second red phosphor having a fourth phosphor concentration PC4. For example, PC2 > PC4 and / or PC1+PC2 > PC3+PC4 may apply. More specifically, PC2>1.2xPC4;

[0036] PCl>1.2xPC3; and (PCl+PC2)>1.2x(PC3+PC4) may apply. A phosphor converted LED filament having a higher CCT has a less orange / reddish appearance, e.g., a more yellow appearance / color. And therefore, the second elongated encapsulant only needs a lower thickness and / or a lower concentration of light scattering material because less hiding power is needed for yellow or orange / reddish color. This especially applies when PC2 > PC4 and / or PC1+PC2 > PC3+PC4. The phosphor concentrations may be interpreted as volume percent, v / v%, The first translucent material 16 and the second translucent material 19 may be the same translucent material. The third translucent material 26 and the fourth translucent material 29 may be the same translucent material. At least one of the first translucent material 15, the second translucent material 19, the third translucent material 26 and the fourth translucent material 29 is a silicone.

[0037] In Fig. 3 a lighting device 100 comprising an LED filament arrangement 1 according to the invention is shown. The lighting device 100 comprises a transparent cover 101 that protects the LED filament arrangement 1. Alternatively, the lighting device may comprise a translucent cover that covers the first and the second LED filament 10, 20. The lighting device 100 further comprises a threading 104, a terminal 102, and a cap 103. As shown in Fig. 3, the controller 2 is arranged within the cap 103. The threading 104 provides mechanical and electrical connection to a socket, and the terminal 102 provides electrical connection to a source of electrical energy. The controller 2 is in wired connection with the first and second LED filament 10, 20. The light paths shown in Fig. 3 are exemplary and many other paths are perceivable as well without departing from the invention. The first LED filament 10 produces first LED filament light L10 and the second LED filament 20 produces second LED filament light L20. Furthermore, LED filament arrangement light LI is shown. The LED filament arrangement light LI may be the result of the combination of first and second LED filament light, L10, L20.

[0038] In Fig. 4A a partial cross-section of an LED filament arrangement 1 is shown. The first thickness T1 and the second thickness T2 are similar or identical, but the first concentration Cl of first light scattering material 18 in the first elongated white encapsulant 17 is higher than the second concentration C2 of second light scattering material 25 in the second elongated white encapsulant 24. In this case the first elongated white encapsulant 17 provides a higher hiding power than the second elongated white encapsulant 24. This may be desirable as the color of the first light converting encapsulant 14 may be darker than the second light converting encapsulant 27 and necessitates therefore more hiding power to achieve an overall white appearance. In the following different light paths are discussed, they are not shown in all the figures in order to maintain a clear appearance of the drawings. The light paths shown in Fig. 4A are exemplary and many other paths are perceivable as well without departing from the invention. Shown is the first LED light LI 1 which is the light emitted by the plurality of first LEDs 11. The first LED light LI 1 is then converted by the first elongated light-converting encapsulant 14 to first converted light L12. The first converted light L12 is then at least partly scattered by the first elongated white encapsulant 17 leading to first scattered light L13. The second LED light L21 which is the light emitted by the plurality of second LEDs 21. The second LED light L21 is then converted by the second elongated light-converting encapsulant 27 to second converted light L23. The second converted light L23 is then at least partly scattered by the second elongated white encapsulant 24 leading to second scattered light L22.

[0039] An alternative solution is shown in Fig. 4B wherein the concentrations, Cl and C2 are the same but the first thickness T1 is larger than the second thickness T2. Thereby, the hiding power of the first elongated white encapsulant 17 is higher than the hiding power of the second elongated white encapsulant 24. Even though T1 and T2 may not be the same, the diameter DI of the first LED filament and the diameter D2 of the second LED filament may be similar. For example, 0.95 < D1 / D2 < 1.05. Moreover, the following may apply: Cl > C2 and T1 > T2; or Cl > C2 and T1 > T2. For example, Cl > 1.1 *C2 and 0.95 < T1 / T2 < 1.05; or 0.95 < C1 / C2 < 1.05 and Tl > L PT2.

[0040] The thicknesses may be the average thickness of the corresponding encapsulant. The thicknesses may be the average of the minimal distance from a point on the innermost surface of the encapsulant to a point on the outermost surface of said encapsulant. LIST OF REFERENCE NUMERALS

[0041] 1 LED filament arrangement

[0042] 2 controller

[0043] 10 first LED filament

[0044] 11 plurality of first LEDs

[0045] 12 first major surface

[0046] 12’ first backside

[0047] 13 first elongated carrier

[0048] 14 first elongated light-converting encapsulant

[0049] 15 first luminescent material

[0050] 16 first translucent material

[0051] 17 first elongated white encapsulant

[0052] 18 first light scattering material

[0053] 19 second translucent material

[0054] 20 second LED filament

[0055] 21 plurality of second LEDs

[0056] 22 second major surface

[0057] 22’ second backside

[0058] 23 second elongated carrier

[0059] 24 second elongated white encapsulant

[0060] 25 second light scattering material

[0061] 26 third translucent material

[0062] 27 second elongated light-converting encapsulant

[0063] 28 second light luminescent material

[0064] 29 fourth translucent material

[0065] 100 lighting device

[0066] 101 transparent cover

[0067] 102 terminal

[0068] 103 cap

[0069] 104 threading Cl first concentration

[0070] C2 second concentration

[0071] T1 first thickness T2 second thickness

[0072] LI arrangement light

[0073] LIO first LED filament light

[0074] Li l first LED light L12 first converted light

[0075] LI 3 first scattered light

[0076] L20 second LED filament light

[0077] L21 second LED light

[0078] L22 second scattered light L23 second converted light

Claims

CLAIMS:

1. A color-point tunable light emitting diode, LED, filament arrangement (1) configured to, in an on-state, emit LED filament arrangement light (LI), the LED filament arrangement (1) comprising: a first LED filament (10) configured to provide, in an on-state, first LED filament light (LIO) and comprising: a plurality of first LEDs (11) arranged on a first major surface (12) of a first elongated carrier (13), a first elongated light-converting encapsulant (14) covering the plurality of first LEDs (11) and at least a part of the first major surface (12), the first elongated light-converting encapsulant comprising a first luminescent material (15) arranged in a first translucent material (16), the first luminescent material being configured to convert at least a part of first LED light (LI 1) emitted by the plurality of first LEDs into first converted light (LI 2), and a first elongated white encapsulant (17) covering the first elongated light-converting encapsulant, the first elongated white encapsulant comprising a first light scattering material (18) arranged in a second translucent material (19), the first light scattering material being configured to scatter at least a part of the first converted light (LI 2) and optionally first LED light (LI 1) emitted by the plurality of first LEDs into first scattered light (L13), the first elongated white encapsulant comprising a first thickness (Tl) and the first light scattering material comprising a first concentration (Cl) in the second translucent material; a second LED filament (20) configured to provide, in an on-state, second LED filament light (L20) and comprising: a plurality of second LEDs (21) arranged on a second major surface (22) of a second elongated carrier (23), and a second elongated white encapsulant (24) covering the plurality of second LEDs and at least part of the second major surface, the second elongated white encapsulant comprising a second light scattering material (25) arranged in a third translucent material (26), the second light scattering material being configured to scatter at least a part ofthe second LED light (L21) emitted by the plurality of second LEDs into second scattered light (L22), the second elongated white encapsulant comprising a second thickness (T2) and the second light scattering material comprising a second concentration (C2) in the third translucent material; and a controller (2) configured to individually control the first LED filament light (LIO) provided by the first LED filament (10) and the second LED filament light (L20) provided by the second LED filament (20); wherein one or both of the following relations are fulfilled: Cl > C2 and T1 > T2; and wherein at least one of the following applies: (i) the first light scattering material has a different average particle size than the second light scattering material; (ii) the first light scattering material has a different refractive index than the second light scattering material; and (iii) the first light scattering material is a different material than the second light scattering material.

2. A color-point tunable LED filament arrangement (1) according to claim 1, wherein one or both of the first elongated white encapsulant and the second elongated white encapsulant is free from luminescent material, and wherein the first elongated white encapsulant causes the first elongated light-converting encapsulant to appear white when the LED filament arrangement is in an off-state.

3. A color-point tunable LED filament arrangement (1) according to claim 1 or 2, wherein at least one of the following applies: (i) the average particle size of the first light scattering material is bigger than the average particle size of the second light scattering material; (ii) the first light scattering material has a higher mismatch in refractive index with respect to the second translucent material than the second light scattering material with respect to the third translucent material; (iii) the first light scattering material may be any one of: TiO2, BaSO4, A12O3 and the second light scattering material may be any one of: glass or polymer.

4. A color-point tunable LED filament arrangement (1) according to any one of the preceding claims, wherein Cl > C2 and T1 > T2, or wherein Cl > C2 and T1 > T2.

5. A color-point tunable LED filament arrangement (1) according to any one of claims 1 to 4, wherein Cl > C2 and T1 < T2.

6. A color-point tunable LED filament arrangement (1) according to claim 5, wherein the first LED filament (10) comprises a first diameter (DI), wherein the second LED filament (20) comprises a second diameter (D2), and wherein 0.8 < D1 / D2 < 1.2.

7. A color-point tunable LED filament arrangement (1) according to any one of the previous claims, and further comprising a second elongated light-converting encapsulant(27) covering the plurality of second LEDs and at least a part of the second major surface, the second elongated light-converting encapsulant (27) comprising a second luminescent material (28) arranged in a fourth translucent material (29), the second luminescent material(28) being configured to convert at least a part of second LED light (L21) emitted by the plurality of second LEDs into second converted light (L23), and wherein the second elongated white encapsulant is covering the second elongated light-converting encapsulant and the second light scattering material is configured to scatter at least a part of the second converted light into the second scattered light.

8. A color-point tunable LED filament arrangement (1) according to claim 7, wherein the first LED filament is configured to provide LED filament light with a first correlated color temperature, CCT1, wherein the second LED filament is configured to provide LED filament light with a second correlated color temperature, CCT2, wherein CCT2 > CCT1 + 500K.

9. A color-point tunable LED filament arrangement (1) according to claim 7 or 8, wherein the first luminescent material comprises a first green-yellow phosphor having a first phosphor concentration (PCI) and a first red phosphor having a second phosphor concentration (PC2), wherein the second luminescent material comprises a second greenyellow phosphor having a third phosphor concentration (PC3) and a second red phosphor having a fourth phosphor concentration (PC4), and wherein at least one of the following applies: PC2 > PC4; PC1>PC3; and (PC1+PC2) > (PC3+PC4).

10. A color-point tunable LED filament arrangement (1) according to claim 7 or 8 or 9, wherein the first elongated light-converting encapsulant has a darker color than thesecond elongated light-converting encapsulant and / or the first elongated light-converting encapsulant may have a more orange-reddish color than the second elongated lightconverting encapsulant.

11. A color-point tunable LED filament arrangement (1) according to any one of the preceding claims, wherein one of the following applies: Cl > 1.1 *C2 and 0.9 < T1 / T2 < 1.1; or 0.9 < C1 / C2 < 1.1 and Tl > L PT2.

12. A color-point tunable LED filament arrangement (1) according to any one of the preceding claims, wherein the first elongated light-converting encapsulant and the first elongated white encapsulant further cover the first elongated carrier on a first backside (12’), wherein the second elongated light-converting encapsulant and / or the second elongated white encapsulant further cover the second elongated carrier on a second backside (22’), and wherein the first elongated carrier and the second elongated carrier are light transmissive.

13. A color-point tunable LED filament arrangement (1) according to any one of claim 1 to 7, wherein the plurality of second LEDs comprise a plurality of red light emitting diodes, a plurality of green light emitting diodes, and a plurality of blue light emitting diodes.

14. A lamp (100) or a luminaire comprising a color-point tunable LED filament arrangement (1) according to any one of the previous claims and a transparent cover covering the first LED filament and the second LED filament of the color-point tunable LED filament arrangement (1).

Images