Improved light emitting diode filament

Abstract

An LED filament (100) comprises an elongated carrier (102), an array of a plurality of LEDs (101) arranged on the carrier (102). An encapsulant (103) at least partly covers the first major surface (111) of the carrier (102) and at least partly enclosing the plurality of LEDs (101). The elongated carrier (102) and the elongated encapsulant (103) are transparent. At least one of the following i and ii applies: i: the first major surface of the carrier has a carrier surface area S1 comprising a covered surface area S2 being covered by the plurality of LEDs and electrical connections configured for electrically connecting the plurality of LEDs and an uncovered surface area, S3, wherein S3 ≥0.8S1, or ii: the first major surface of the carrier has a carrier surface area S1 comprising a covered surface area, S4, being covered by the plurality of LEDs, wherein S4 ≤0.15S1, and wherein connections configured for electrically connecting the plurality of LEDs are transparent.

Description

[0001] 2024PF80169

[0002] 1

[0003] Improved light emitting diode filament

[0004] FIELD OF THE INVENTION

[0005] The present invention generally relates to light emitting devices. More specifically, the present invention relates to a light emitting diode (LED) filament and a lamp or a luminaire comprising an LED filament.

[0006] BACKGROUND OF THE INVENTION

[0007] The original bulb lamps powered by electricity were of the type having metal wire filaments enclosed within more or less evacuated glass bulbs. These are also known as incandescent lamps. This type of bulb lamps was the ubiquitous choice of light source for more than a century until the introduction of LEDs. Light sources based on LEDs have now replaced the light bulb as a source of light in homes and in many other locations. Initially, mainly due to the inherent structural characteristics of LEDs, the early LED light sources (i.e. LED lamps) did not resemble the earlier light bulbs and in many cases were considered as aesthetically inferior to a light bulb of the earlier type. Thus, for aesthetic reasons, a desire for light sources having the look of the traditional bulb shaped filament lamp came back when it was found that this was technically feasible to make light sources using LED filaments. However, there still remain various aspects of such light sources using LED filaments. For example, there is still a need for improving the performance and / or the appearance of light sources using LED filaments.

[0008] WO 2023 / 174818 Al discloses an LED filament supporting increased efficiency and functionality.

[0009] SUMMARY OF THE INVENTION

[0010] It is of interest to provide an LED filament that is capable of overcoming drawbacks of prior art devices. This and other objects are achieved in a first aspect by providing an LED filament having the features of the appended independent claim. Preferred embodiments are defined in the appended dependent claims.

[0011] Hence, according to the present invention there is provided an LED filament configured to provide, in operation, LED filament light. The LED filament comprises an2024PF80169

[0012] 2

[0013] elongated carrier, an array of a plurality of LEDs arranged along an elongation direction on a first major surface of the elongated carrier. The plurality of LEDs is configured to emit, in operation, LED light. An elongated encapsulant is arranged along the elongation direction and at least partly covers the first major surface of the elongated carrier and at least partly enclosing the plurality of LEDs. The elongated carrier and the elongated encapsulant are transparent.

[0014] At least one of the following i and ii applies:

[0015] i: the first major surface of the elongated carrier has a carrier surface area, SI, the carrier surface area, SI, comprising a covered surface area, S2, being covered by the plurality of LEDs and electrical connections configured for electrically connecting the plurality of LEDs and an uncovered surface area, S3, wherein S3 >0.8Sl, or

[0016] ii: the first major surface of the elongated carrier has a carrier surface area, SI, the carrier surface area, SI, comprising a covered surface area, S4, being covered by the plurality of LEDs, wherein S4 <0.15Sl, and wherein electrical connections configured for electrically connecting the plurality of LEDs are transparent.

[0017] Such an LED filament has the advantageous effect of being less visible to the naked eye in comparison with prior art devices and thereby enabling an improved appearance of light sources using such an LED filament.

[0018] In embodiments, the elongated carrier may comprise quartz, sapphire or glass. In embodiments, the elongated encapsulant comprises a crosslinked silicone e.g. comprising one or more of crosslinked poly-dimethyl siloxane (PDMS), crosslinked poly-diphenyl siloxane (PDPS), crosslinked poly -methylphenyl siloxane (PMPS) or copolymers thereof.

[0019] In embodiments, the elongated encapsulant may at least partly cover a second major surface, opposite the first major surface, of the elongated carrier.

[0020] In embodiments, preferably S3 >0.85Sl, more preferably S3 >0.88Sl, most preferably S3 >O.9S1.

[0021] In embodiments, preferably S4 <O.12S1, more preferably S4 <0.10Sl, most preferably S4 <0.08Sl.

[0022] In various embodiments, each LED of the plurality of LEDs comprise a respective die that has a surface area, SA, having a largest spatial extent, SE, where SE < 100 pm.

[0023] In embodiments, preferably SE < 80 micron, more preferably SE < 60 micron, most preferably SE < 50 micron.2024PF80169

[0024] 3

[0025] That is, such embodiments utilize so-called microLEDs. An advantageous effect of using microLEDs is that microLEDs are not visible in the OFF mode by the human eye, thereby providing an improved appearance of light sources using such an LED filament. Thus, the obtained effect is further reducing the visibility of the LED filament.

[0026] In various embodiments, the LED light has one or more peak emission wavelength in an ultraviolet UV wavelength range from 280 nm to 380 nm and / or in a violet wavelength range from 380 nm to 420 nm.

[0027] That is, UV and violet light of such LED point sources is not visible by the human eye. Thus, the obtained effect is further reducing the visibility of the LED filament.

[0028] Alternatively, the LED light may have one or more peak emission wavelength in a blue wavelength range from 420 nm to 490 nm.

[0029] In some embodiments, the elongated encapsulant may be free from a luminescent material.

[0030] In some embodiments, the LED filament may be free from a luminescent material.

[0031] In some embodiments, the plurality of LEDs may emit white LED light, e.g., having a CCT in a range from 1700K to 6500K (or in a range from 1700K to 2500K) and optionally a CRI of at least 80 or at least 85.

[0032] In some embodiments, the plurality of LEDs may comprise a plurality of RGB LEDs, e.g., a plurality of red LEDs, a plurality of green LEDs and a plurality of blue LEDs. The plurality of RGB LEDs may comprise at least 10 or at least 20 clusters of RGB LEDs. The obtained effect is that such cluster of microLEDs may appear as a white LED (due to the small size of the LEDs). The distance between RGB LEDs in a cluster may be at most 0.7 or at most 0.4 times the (closest) distance between clusters.

[0033] In various embodiments, the transparent elongated encapsulant comprises a luminescent material configured to at least partly convert the LED light into converted light. The LED filament light may comprise one or more of the converted light and (part of) the LED light. For example, the luminescent material comprises a transparent luminescent material. Most luminescent materials are non-transparent e.g. scattering and are thus visible. Therefore, in embodiments, the transparent elongated encapsulant may be free from nontransparent luminescent material.

[0034] This is advantageous in that, although the elongated encapsulant comprises a luminescent material, it is still transparent and thereby provides an improved appearance of light sources using such an LED filament. Very good transparency of a luminescent2024PF80169

[0035] 4

[0036] elongated encapsulant can be obtained with a transparent photoluminescent phosphor, for example in the form of lanthanide luminescent complexes. In some of these embodiments, although the elongated encapsulant comprises a luminescent material, next to being transparent, it may also be colorless under visible light. It is to be noted that the concept of colorless refers to a state of lacking color. It may not absorb any visible light i.e. <5% or <3%. Such embodiments further illustrate the advantageous effect of improved appearance of light sources using such an LED filament. In embodiments, the elongated carrier and / or the elongated encapsulant may be colorless.

[0037] In some of the embodiments wherein the transparent elongated encapsulant comprises a luminescent material, the converted light has one or more peak emission wavelength in a green-yellow wavelength range from 500 nm to 580 nm and / or in an orange-red wavelength range from 580 nm to 660 nm. Thus, in embodiments, the luminescent material may comprise a green-yellow phosphor and an orange-red phosphor. The greenyellow phosphor and the orange-red phosphor may both be transparent and / or colorless.

[0038] In various embodiments, the elongated encapsulant comprises a polymer matrix having a first refractive index, nl, and the elongated carrier has a second refractive index, n2, wherein I nl-n2 I <0.10 or I nl-n2 I <0.05, preferably I nl-n2 I <0.03.

[0039] Such embodiments are advantageous in that almost no reflection of light takes place at the interface between the elongated carrier and the elongated encapsulant and thereby improving the appearance of light sources using such an LED filament.

[0040] In various embodiments, the electrical connections configured for electrically connecting the plurality of LEDs are transparent, for example made from Indium Tin Oxide (ITO).

[0041] Such embodiments are advantageous in that they further improve the invisibility of the LED filament.

[0042] In various embodiments, the encapsulant has a rounded cross-section transverse the elongation direction of the encapsulant. The elongated encapsulant and / or the elongated may comprise rounded edges. The obtained effect is further reduced visibility of the LED filament. The reason is that rounded edges are less visible compared to sharp edges.

[0043] In various embodiments, the elongated encapsulant comprises nano-particles having an (equivalent) diameter <500nm and / or structures having a size (e.g. pitch) <500nm. In embodiments, the nano-particles may have an (equivalent) diameter <300nm or <100nm. In embodiments, the structures may have a size (e.g. pitch) <300nm or <100nm.2024PF80169

[0044] 5

[0045] Such embodiments are advantageous in that the nano-particles are able to out-couple light out of the LED filament, while at the same time this type of particles and structures are not (or hardly) visible and thus improves the appearance of light sources using such an LED filament.

[0046] In various embodiments, the LED filament light is white light having a correlated color temperature in a range from 1700 K to 6500 K (or in a range from 1700 K to 2500 K) and a color rendering index of at least 80 (or at least 85).

[0047] Such embodiments are advantageous in that they provide high quality white light which can be used for general lighting applications.

[0048] In a further aspect there is provided an LED filament arrangement comprising a controller, at least one of a user interface and a sensor providing controller input, and an LED filament as summarized above, wherein the controller is configured to control the plurality of LEDs based on the controller input.

[0049] In yet a further aspect there is provided a lamp or a luminaire comprising a transparent light exit window and an LED filament as summarized above or the LED filament arrangement as summarized above. In some embodiments, the transparent light exit window comprises a transparent partially light-absorbing layer.

[0050] These further aspects provide effects and advantages that correspond to those summarized above in connection with the first aspect.

[0051] BRIEF DESCRIPTION OF THE DRAWINGS

[0052] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention where:

[0053] Fig. la schematically illustrates a perspective view of an LED filament, Fig. lb schematically illustrates a cross-section of the LED filament illustrated in Fig. la,

[0054] Fig. 2 schematically illustrates a cross-section view of a LED filament, Fig. 3 schematically illustrates a LED filament arrangement comprising a controller, and

[0055] Fig. 4 schematically illustrates a lamp or a luminaire.

[0056] DETAILED DESCRIPTION

[0057] As illustrated in Figure la and Figurelb, an embodiment of an LED filament2024PF80169

[0058] 6

[0059] 100 configured to provide, in operation, LED filament light. For example, the LED filament light may be white light having a correlated color temperature in a range from 1700 K to 6500 K (or in a range from 1700 K to 2500 K) and a color rendering index of at least 80 (or at least 85). The LED filament 100 comprises an elongated carrier 102, an array of a plurality of LEDs 101 arranged along an elongation direction 150 on a first maj or surface 111 of the elongated carrier 102. The plurality of LEDs 101 is configured to emit, in operation, LED light. An elongated encapsulant 103 is arranged along the elongation direction 150 and at least partly covers the first major surface 121 of the elongated carrier 102 and at least partly enclosing the plurality of LEDs 101. The elongated carrier 102 and the elongated encapsulant 103 are transparent.

[0060] At least one of the following i and ii applies:

[0061] i: the first major surface 111 of the elongated carrier 102 has a carrier surface area, SI, the carrier surface area, SI, comprising a covered surface area, S2, being covered by the plurality of LEDs 101 and electrical connections 104 configured for electrically connecting the plurality of LEDs 101 and an uncovered surface area, S3, wherein S3 >0.8Sl, or

[0062] ii: the first major surface 111 of the elongated carrier 102 has a carrier surface area, SI, the carrier surface area, SI, comprising a covered surface area, S4, being covered by the plurality of LEDs 101, wherein S4 <0.15Sl, and wherein electrical connections 104 configured for electrically connecting the plurality of LEDs 101 are transparent.

[0063] As indicated in Figure lb, each LED of the plurality of LEDs 101 may comprise a respective die 106 that has a surface area, SA, having a largest spatial extent, SE, where SE < 100 pm.

[0064] As indicated in Figure lb, in some embodiments, the elongated encapsulant 103 may at least partly cover a second major surface 112, opposite the first major surface 111, of the elongated carrier 102.

[0065] The LED light emitted by the plurality of LEDs 101 may have one or more peak emission wavelength in an ultraviolet UV wavelength range from 280 nm to 380 nm and / or in a violet wavelength range from 380 nm to 420 nm.

[0066] The transparent elongated encapsulant 103 may comprise a luminescent material configured to at least partly convert the LED light into converted light. For example, such a luminescent material may comprise a transparent luminescent material. The luminescent material may be colorless. Where the transparent elongated encapsulant comprises a luminescent material, the converted light may have one or more peak emission2024PF80169

[0067] 7

[0068] wavelength in a green-yellow wavelength range from 500 nm to 580 nm and / or in an orange-red wavelength range from 580 nm to 660 nm.

[0069] The elongated encapsulant 103 may comprise a polymer matrix having a first refractive index, nl, and the elongated carrier 102 may have a second refractive index, n2, wherein I nl -n2 I <0.05.

[0070] The electrical connections 104 configured for electrically connecting the plurality of LEDs 101 may transparent and, e.g., made from Indium Tin Oxide (ITO).

[0071] As indicated in Figure lb, the encapsulant 103 may a rounded cross-section transverse the elongation direction 150 of the encapsulant 103.

[0072] The elongated encapsulant 103 may comprise nano-particles having an equivalent diameter <500nm and / or structures 105 having a size <500nm. Such structures 105 are schematically illustrated in Figure 2.

[0073] Figure 3 illustrates an LED filament arrangement 300 comprising a controller 301, at least one of a user interface 302 and a sensor 303 providing controller input. An LED filament 100 as exemplified above is connected to the controller 301, and the controller 301 is configured to control the plurality of LEDs 101 based on the controller input.

[0074] Figure 4 illustrates a lamp 400 or a luminaire 400 comprising a transparent light exit window 401 and an LED filament 100 as exemplified in connection with Figures 1 and 2 or the LED filament arrangement as exemplified in connection with Figure 3. Electric power may be provided to the lamp 400 or luminaire 400 via a power connection 402.

[0075] The transparent light exit window 401 may comprise a transparent partially light-absorbing layer. For example, the transparent light-absorbing layer may be configured to absorb less than 20% or less than 10% of the visible light. In embodiments, the transparent light-absorbing layer may be slightly yellow, slightly orange or slightly black. The transparent light-absorbing layer may have a yellow haze, an orange haze or a black haze.

Claims

2024PF80169CLAIMS:

1. A light emitting diode, LED, filament (100) configured to provide, in operation, LED filament light, the LED filament comprising:an elongated carrier (102);an array of a plurality of light emitting diodes, LEDs, (101) arranged along an elongation direction (150) on a first major surface (111) of the elongated carrier (102), wherein the plurality of LEDs (101) is configured to emit, in operation, LED light and wherein each LED of the plurality of LEDs (101) comprise a respective die (106) that has a surface area, SA, having a largest spatial extent, SE, where SE < 100 pm;an elongated encapsulant (103) arranged along the elongation direction (150) and at least partly covering the first major surface (121) of the elongated carrier (102) and at least partly enclosing the plurality of LEDs (101),wherein the elongated carrier (102) and the elongated encapsulant (103) are transparent; andwherein at least one of the following i and ii applies:i: wherein the first major surface (111) of the elongated carrier (102) has a carrier surface area, SI, the carrier surface area, SI, comprising a covered surface area, S2, being covered by the plurality of LEDs (101) and electrical connections (104) configured for electrically connecting the plurality of LEDs (101) and an uncovered surface area, S3, wherein S3 >0.8Sl, orii: wherein the first major surface (111) of the elongated carrier (102) has a carrier surface area, SI, the carrier surface area, SI, comprising a covered surface area, S4, being covered by the plurality of LEDs (101), wherein S4 <0.15Sl, and wherein electrical connections (104) configured for electrically connecting the plurality of LEDs (101) are transparent.

2. The LED filament (100) according to claim 1, wherein the LED light has one or more peak emission wavelength in a UV wavelength range from 280 nm to 380 nm and / or in a violet wavelength range from 380 nm to 420 nm.2024PF8016993. The LED filament (100) according to claim 1 or 2, wherein the transparent elongated encapsulant (103) comprises a luminescent material configured to at least partly convert the LED light into converted light.

4. The LED filament (100) according to claim 3, wherein the luminescent material comprises a transparent luminescent material.

5. The LED filament (100) according to claim 3 or 4, wherein the luminescent material is colorless.

6. The LED filament (100) according to any one of claims 3 to 5, wherein the converted light has one or more peak emission wavelength in a green-yellow wavelength range from 500 nm to 580 nm and / or in an orange-red wavelength range from 580 nm to 660 nm.

7. The LED filament (100) according to claim 1 or 2, wherein the elongated encapsulant (103) is free from a luminescent material, and wherein the plurality of LEDs (101) emits white light.

8. The LED filament (100) according to claim 1 or 2, wherein the elongated encapsulant (103) comprises a polymer matrix having a first refractive index, nl, and the elongated carrier (102) has a second refractive index, n2, wherein I nl-n2 I <0.05.

9. The LED filament (100) according to any one of the preceding claims, wherein the electrical connections (104) configured for electrically connecting the plurality of LEDs (101) are transparent.

10. The LED filament (100) according to any one of the preceding claims, wherein the encapsulant (103) has a rounded cross-section transverse the elongation direction (150) of the encapsulant (103).

11. The LED filament (100) according to any one of claims 1 to 4, wherein the elongated encapsulant (103) comprises nano-particles having an equivalent diameter <500nm and / or structures (105) having a size <500nm.2024PF801691012. The LED filament (100) according to any one of the preceding claims, wherein the LED filament light is white light having a correlated color temperature in a range from 1700 K to 6500 K and a color rendering index of at least 80.

13. A LED filament arrangement (300) comprising a controller (301), at least one of a user interface (302) and a sensor (303) providing controller input, and a LED filament (100) according to any one of the claims 1 to 12, wherein the controller (301) is configured to control the plurality of LEDs (101) based on the controller input.

14. A lamp (400) or a luminaire (400) comprising a transparent light exit window (401) and a LED filament (100) according to any one of the claims 1 to 12 or the LED filament arrangement according to claim 13.

15. The lamp (400) or the luminaire (400) according to claim 14, wherein the transparent light exit window (401) comprises a transparent partially light-absorbing layer.

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