Light emitting device

Abstract

A LED filament (1) provides LED filament light and comprises an array of LEDs (101) arranged along an elongation direction (150) on a first major surface (121) of an elongated carrier (102). A first elongated encapsulant (103) is 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). The first elongated encapsulant (103) comprises a first luminescent material configured to at least partly convert LED light emitted by the LEDs into first converted light and / or a first light scattering material configured to at least partly scatter the LED light into first scattered light. The elongated carrier has a first width (W1) and a first height (H1) in a plane transverse the direction of elongation. The first elongated encapsulant has a second width (W2) and a second height (H2) in the same plane. W2 / W1 ≥ 1.3, preferably W2 / W1 > 1.5.

Description

[0001] Light emitting device

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to light emitting devices. More specifically, the present invention is related to a light emitting diode (LED) filament comprising a plurality of LEDs arranged on an elongated carrier.

[0004] BACKGROUND OF THE INVENTION

[0005] A trend in the development of light emitting devices is LED filament lamps. An LED filament lamp is a lamp comprising LEDs which is designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes. In addition to the advantage that LED filament lamps may be configured such that they resemble traditional light bulbs, a further advantage of LED filament lamps is the inherent high energy efficiency of light-emitting diodes. However, there remain aspects of LED filament lamps that allow for further improvements. For example, there is a strong desire to improve the light quality in terms of the spatial distribution of the light emitted by the LED filament.

[0006] CN 203910855 discloses a LED lamp filament, comprising: a long stripshaped substrate, a plurality of light-emitting units arranged on a first surface of the substrate and distributed along the extending direction of the substrate, and a light-transmittable fluorescent glue layer covering the first surface and the plurality of light-emitting units. A plurality of bulges are provided on at least one side of the substrate, and the bulges are distributed along the extending direction of the substrate; one part of light excited by the fluorescent glue layer and emitted from the light-emitting units emits out in a direction towards a second surface, opposite to the first surface, of the substrate from a space between adjacent bulges.

[0007] SUMMARY OF THE INVENTION

[0008] It is of interest to provide a LED filament that is capable of overcoming drawbacks with prior art LED filaments. 2023PF80398

[0009] 2

[0010] This and other objects are achieved in a first aspect by providing a 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 a LED filament configured to provide, in operation, LED filament light. The LED filament comprises an elongated carrier and 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. A first elongated encapsulant is arranged along the elongation direction and at least partly covering the first major surface of the elongated carrier and at least partly enclosing the plurality of LEDs. The first elongated encapsulant comprises i: a first luminescent material configured to at least partly convert the LED light into first converted light and / or ii: a first light scattering material configured to at least partly scatter the LED light into first scattered light. The elongated carrier has a first width (Wl) and a first height (Hl) in a plane transverse the direction of elongation. The first elongated encapsulant has a second width (W2) and a second height (H2) in the plane transverse the direction of elongation and wherein W2 / W1 > 1.2, preferably W2 / W1 > 1.3, preferably W2 / W1 > 1.5. Embodiments include those where 0.3>Hl / Wl>0.05 and in various embodiments H2 > HL

[0012] Embodiments of such a LED filament may thus have a cross-sectional view in the plane transverse the direction of elongation of said elongated carrier and said first elongated encapsulant that has a mushroom shape.

[0013] Such a LED filament provides an improved light distribution in relation to prior art configurations. The reason is that inventors have found that LED filaments emit a major part of their light in a direction facing away from the first encapsulant and a minor part of their light in a direction facing away from the back surface of the carrier, resulting in an unequal light distribution. By using a configuration of encapsulant and carrier as summarized above, the amount of light emitted by the LED filament in the directions facing away from the first encapsulant and facing away from the back surface of the carrier obtains a more even distribution in relation to prior art configurations.

[0014] In various embodiments, H2 / W2<0.4, which provides a configuration of the LED filament that is compact while maintaining an improved light distribution.

[0015] In some embodiments, 0.6>H2 / W2>0.4, which provides an improved color over angle. The reason is that such H2 / W2 ratio ensures a similar path length of the (blue) light at different angles in the first elongated encapsulant, which is desired when luminescent material is used in the first elongated encapsulant. 2023PF80398

[0016] 3

[0017] A second elongated encapsulant may be arranged along the elongation direction and at least partly cover a second major surface, opposite said first major surface, of the elongated carrier. The second elongated encapsulant comprises i: a second luminescent material and / or ii: a second light scattering material. The second elongated encapsulant has a third width (W3) and a third height (H3) in the plane transverse the direction of elongation and W3 / W2 < 0.85, preferably W3 / W2 < 0.8.

[0018] Such a configuration with a second encapsulant on the opposite side of the carrier provides a further improvement of the light distribution from the LED filament. The reason is that because the width W3 of the second encapsulant is smaller than the width W2 of the first elongated encapsulant, less light that exits the first elongated encapsulant is blocked by the second elongated encapsulant.

[0019] The elongated carrier may be light transmissive and i: the second luminescent material may be configured to at least partly convert the LED light and / or the first converted light into second converted light and / or ii: the second light scattering material is configured to at least partly scatter the LED light and / or the first scattered light into second scattered light.

[0020] Such a configuration provides a further improvement of the light distribution from the LED filament.

[0021] In various embodiments, W3 < Wl, which even further improves the light distribution because the width of the second encapsulant is equal to or smaller than the width of the carrier.

[0022] In various embodiments, H3 < 0.8H2 or H3 < 0.6H2, which provides a configuration of the LED filament that is compact while maintaining an improved light distribution since it minimizes blocking of light by the second encapsulant.

[0023] In various embodiments, W2 / W1 < 3, which provides a compact LED filament.

[0024] The first elongated encapsulant may comprise a first layer having a fourth width (W4) arranged on the first major surface of the carrier and a second layer having a fifth width (W5) arranged on top of the first layer and wherein W5=W2 and W4<W5. The second layer may comprise a higher concentration of luminescent material than the first layer and / or the second layer may comprise a higher concentration of light scattering material than the first layer. In an example, the first and / or the second layer may be free from luminescent material. In another example, the first layer may (only e.g. at least for 90%) comprises a red phosphor converting the LED light to red phosphor light. In yet another example, the second 2023PF80398

[0025] 4 layer may (only e.g. at least for 90%) comprises a green-yellow phosphor converting the LED light to green-yellow phosphor light. The first converted light may comprises the red phosphor light and / or green-yellow phosphor light.

[0026] Such a dual-layer configuration provides an improved light distribution since most of the light conversion and / or light scattering ay happen in the outer layer.

[0027] The first layer may be a transparent layer, which further improves the light distribution because less light (almost) no light is converted and / or scattered close to the LEDs and most of the light conversion and / or light scattering ay happen in the outer layer.

[0028] The second layer may extend over the full second width (W2) of the first elongated encapsulant. Such a configuration further improves the light distribution and / or provides mechanical stability for the stack of layers.

[0029] In some embodiments, W4<W1, which increases the mechanical stability and / or light scattering / conversion in the first elongated encapsulant.

[0030] In some embodiments, the first layer is fully enclosed by the second layer and said elongated carrier. Such a configuration provides increased mechanical stability and / or light scattering / conversion in the first elongated encapsulant.

[0031] In various embodiments, a second concentration (C2) of the second lightscattering and / or second luminescent material in the second elongated encapsulant is lower than a first concentration (Cl) of the first light-scattering material and / or first luminescent material in the first elongated encapsulant, preferably C2 < 0.8C1.

[0032] The LED filament may be configured such that at least part of the first converted light and / or at least part of the first scattered light exit the first elongated encapsulant is in a direction facing away from the second major surface.

[0033] In a further aspect, there is provided a lamp or a luminaire comprising one or more LED filaments as summarized above.

[0034] Such a lamp or luminaire provide the effects and advantages as summarized above.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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.

[0037] Fig. la schematically illustrates an end view of a LED filament,

[0038] Fig. lb schematically illustrates a side view of the LED filament illustrated in figure la, 2023PF80398

[0039] 5

[0040] Fig. 2a schematically illustrates an end view of a LED filament,

[0041] Fig. 2b schematically illustrates a side view of the LED filament illustrated in figure 2a,

[0042] Fig. 3a schematically illustrates an end view of a LED filament,

[0043] Fig. 3b schematically illustrates a side view of the LED filament illustrated in figure 2a,

[0044] Fig. 4 schematically illustrates an end view of a LED filament,

[0045] Fig. 5 schematically illustrates an end view of a LED filament,

[0046] Fig. 6 schematically illustrates a lamp, and

[0047] Fig. 7 schematically illustrates a luminaire.

[0048] DETAILED DESCRIPTION

[0049] As illustrated in figures la-b, 2a-b, 3a-b, 4 and figure 5, a LED filament 1 arranged to provide, in operation, LED filament light may comprise an elongated carrier 102 and an array of a plurality of LEDs 101 arranged along an elongation direction 150 on a first major surface 121 of the elongated carrier 102. The plurality of LEDs 101 is configured to emit, in operation, LED light.

[0050] A first 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 first elongated encapsulant 103 comprises i: a first luminescent material configured to at least partly convert the LED light into first converted light and / or ii: a first light scattering material configured to at least partly scatter the LED light into first scattered light.

[0051] The elongated carrier 102 has a first width (Wl) and a first height (Hl), in a plane 151 transverse the direction of elongation 150. The first elongated encapsulant 103 has a second width (W2) and a second height (H2) in the plane 151 transverse the direction of elongation 150. The ratio W2 / W1 > 1.2, preferably W2 / W1 > 1.3, preferably W2 / W1 > 1.5.

[0052] In embodiments, the LED filament light may be white light having a correlated color temperature in a range from 1700K to 6500K and / or a color rendering index of at least 80 (or at least 90).

[0053] In embodiments, the elongated carrier 102 may have a first length (LI), wherein LI may be at least 10 times Wl and / or LI may be at least 20 times HL For example, W 1 may be in a range from 1 to 6 mm, W 1 may be in a range from 1 to 6 mm, and / or Hl may be in a range from 0.4 to 2 mm, and / or LI may be in a range from 3 to 15 cm. 2023PF80398

[0054] 6

[0055] In embodiments, the first elongated encapsulant 103 may extend the elongated carrier 102 on both sides, e.g. the first elongated encapsulant 103 may centrally / symmetrically arranged with respect to the elongated carrier 102.

[0056] The LED filament 1 may be configured such that at least part of the first converted light and / or at least part of the first scattered light exit the first elongated encapsulant is in a direction facing away from the second major surface 122.

[0057] As illustrated in figures 2a-b, 4 and figure 5, a second elongated encapsulant 108 may be arranged along the elongation direction 150 and at least partly cover a second major surface 122, opposite the first major surface 121, of the elongated carrier 102. The second elongated encapsulant 108 may comprise i: a second luminescent material and / or ii: a second light scattering material. The second elongated encapsulant 108 has a third width (W3) and a third height (H3) in the plane 151 transverse the direction of elongation 150. W3 / W2 < 0.85, preferably W3 / W2 < 0.8.

[0058] In embodiments, the second major surface 122 may be free from LEDs.

[0059] In embodiments, the elongated carrier 102 may be rigid or flexible. In case of the latter, the first elongated encapsulant 103 and / or second elongated encapsulant 108 may provide sufficient mechanical strength to the LED filament 1, e.g. such that the LED filament 1 may become rigid.

[0060] In various embodiments, a second concentration (C2) of the second lightscattering and / or second luminescent material in said second elongated encapsulant 108 is lower than a first concentration (Cl) of the first light-scattering material and / or first luminescent material in said first elongated encapsulant 103, preferably C2 < 0.8C1.

[0061] The elongated carrier 102 may be light transmissive, and i: the second luminescent material may be configured to at least partly convert the LED light and / or the first converted light into second converted light and / or ii: the second light scattering material may be configured to at least partly scatter the LED light and / or the first scattered light into second scattered light. For example, W3 < Wl. For example, H3 < 0.8H2. For example, W2 / W1 < 3.

[0062] As illustrated in figures 3a-b and figure 5, the first elongated encapsulant 103 may comprise a first layer 1031 having a fourth width (W4) arranged on the first major surface 121 of the elongated carrier 102 and a second layer 1032 having a fifth width (W5) arranged on top of the first layer 1031, and wherein W4<W5. The second layer 1032 may comprise a higher concentration of luminescent material than the first layer 1031 and / or the second layer 1032 may comprise a higher concentration of light scattering material than the 2023PF80398

[0063] 7 first layer 1031. The first layer 1031 may be a transparent layer. The second layer 1032 may extend over the full second width (W2) of the first elongated encapsulant 103. In some embodiments, W4<W1. As illustrated in figures 3a-b and figure 5, the first layer 1031 may be fully enclosed by the second layer 1032 and the elongated carrier 102. As illustrated in figure 4, in some embodiments the LED filament 1 may be configured such that the first elongated encapsulant 103 at least partly encloses the plurality of LEDs 101 such that there exists a void 1033 between the first elongated encapsulant 103 and the plurality of LEDs 101 and the elongated carrier 102. Such a void 1033 provides an effect of improving the light distribution because the void 1033 will act as a light mixing chamber that diffuses the output of light.

[0064] As illustrated in figures la, 2a, 3a, 4 and figure 5, a cross-sectional view in the plane 151 transverse the direction of elongation 150 of the elongated carrier 102 and the first elongated encapsulant 103 may have a mushroom shape.

[0065] A lamp 200 or a luminaire 300 may comprise the LED filament 1 as described above. This is exemplified in figures 6 and 7. Figure 6 illustrates a lamp 200 comprising one LED filament 1 and a base 202 for electrically and mechanically connecting the lamp 200 to, e.g., a socket 302 of a luminaire 300 (as illustrated in figure 7) and an envelope 203 at least partly enclosing the LED filament 1.

Claims

2023PF803988CLAIMS:

1. A light emitting diode, LED, filament (1) 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 (121) of the elongated carrier (102), wherein the plurality of LEDs (101) is configured to emit, in operation, LED light; a first 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), the first elongated encapsulant (103) comprising i: a first luminescent material configured to at least partly convert the LED light into first converted light and / or ii: a first light scattering material configured to at least partly scatter the LED light into first scattered light; a second elongated encapsulant (108) arranged along the elongation direction (150) and at least partly covering a second major surface (122), opposite said first major surface (121), of the elongated carrier (102), the second elongated encapsulant (108) comprising i: a second luminescent material and / or ii: a second light scattering material; wherein the elongated carrier (102) has a first width, Wl, and a first height, Hl, in a plane (151) transverse the direction of elongation (150); wherein the first elongated encapsulant (103) has a second width, W2, and a second height, H2, in the plane (151) transverse the direction of elongation (150); wherein W2 / W1 > 1.3, preferably W2 / W1 > 1.5, wherein the second elongated encapsulant (108) has a third width, W3, and a third height, H3, in the plane (151) transverse the direction of elongation (150); and wherein W3 / W2 < 0.85, preferably W3 / W2 < 0.8.

2. The LED filament (1) according to claim 1, wherein the elongated carrier (102) is light transmissive, and wherein i: the second luminescent material is configured to at least partly convert the LED light and / or the first converted light into second converted light2023PF803989 and / or ii: the second light scattering material is configured to at least partly scatter the LED light and / or the first scattered light into second scattered light.

3. The LED filament (1) according to claim 1 or 2, wherein W3 < W1.

4. The LED filament (1) according to any one of claims 1 to 3, wherein H3 < 0.8H2.

5. The LED filament (1) according to any one of claims 1 to 4, wherein W2 / W1 < 3.

6. The LED filament (1) according to any one of claims 1 to 4, wherein: the first elongated encapsulant (103) comprises a first layer (1031) having a fourth width, W4, arranged on the first major surface (121) of the elongated carrier (102) and a second layer (1032) having a fifth width, W5, arranged on top of the first layer (1031), wherein W5=W2 and W4<W5.

7. The LED filament (1) according to claim 6, wherein the second layer (1032) comprises a higher concentration of luminescent material than the first layer (1031) and / or the second layer (1032) comprises a higher concentration of light scattering material than the first layer (1031).

8. The LED filament (1) according to claim 6 or 7, wherein the first layer (1031) is a transparent layer.

9. The LED filament (1) according to any one of the claims 6 to 8, wherein W4<W1.

10. The LED filament (1) according to any one of the claims 6 to 8, wherein the first layer (1031) is fully enclosed by said second layer (1032) and said elongated carrier (102).

11. The LED filament (1) according to any one of claims 1 to 9, wherein: a second concentration, C2, of said second light-scattering and / or second2023PF8039810 luminescent material in said second elongated encapsulant (108) is lower than a first concentration, Cl, of said first light-scattering material and / or first luminescent material in said first elongated encapsulant (103), preferably C2 < 0.8C1.

12. The LED filament (1) according to any one of the preceding claims, wherein in a cross-sectional view in the plane (151) transverse the direction of elongation (150) of said elongated carrier (102) and said first elongated encapsulant (103) has a mushroom shape.

13. The LED filament (1) according to any one of the preceding claims, wherein the LED filament (1) is configured such that at least part of the first converted light and / or at least part of the first scattered light exit the first elongated encapsulant is in a direction facing away from the second major surface (122).

14. A lamp (200) or a luminaire (300) comprising a LED filament (1) according to any one of the preceding claims.

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