CN210197064U

CN210197064U - LED filament

Info

Publication number: CN210197064U
Application number: CN201921178154.4U
Authority: CN
Inventors: Bommel T.Van; T·范博梅尔; R.A.M.Hikmet; R·A·M·希克梅特
Original assignee: Philips Lighting Holding BV
Current assignee: Signify Holding BV
Priority date: 2018-11-20
Filing date: 2019-07-25
Publication date: 2020-03-27
Anticipated expiration: 2029-07-25

Abstract

Embodiments of the present disclosure relate to Light Emitting Diode (LED) filaments. The utility model relates to a light emitting diode LED filament (10), this LED filament (10) include translucent long and thin base plate (12) and a plurality of LED (14) of being arranged on the base plate. The substrate comprises at least one light transmission interruption (20), the at least one light transmission interruption (20) being arranged to provide a non-uniform spatial light distribution from the LED filament, the light transmission interruption being electrically isolated from the plurality of LEDs.

Description

LED filament

Technical Field

The present invention relates generally to lighting devices including one or more light emitting diodes. More particularly, the lighting device relates to a Light Emitting Diode (LED) filament with configurable spatial light distribution and a lighting apparatus comprising such an LED filament.

Background

Incandescent lamps are rapidly being replaced by lighting solutions based on light emitting diodes, LEDs, because the fact proves that lighting solutions based on LEDs are more efficient than incandescent lamps, both in terms of energy consumption and in terms of lifetime. However, users appreciate and desire to have retrofit lamps that look like incandescent bulbs. For this purpose, the infrastructure for producing incandescent lamps based on glass can be used and the filament replaced by an LED. In addition to the reduced power consumption and increased service life they provide, the decorative appearance of this type of lamps is also highly appreciated.

US2018066811 discloses such a retrofit lamp, i.e. an LED lamp with a bulb or outer envelope, wherein a plurality of LEDs (such as filament LEDs) and associated LED drivers are placed in a position inside a nearby encapsulated bulb. To maintain an aesthetic appearance like an incandescent lamp, the circuit board placed inside the bulb is masked with a reflective coating or panel. The reflective coating or panel is arranged to create a different light illusion to the viewer, such as additional LEDs or even bright lines. However, the drawbacks of this solution are: the light distribution of filament LEDs is uniform and does not provide different levels of illumination in different directions.

SUMMERY OF THE UTILITY MODEL

It is an object to overcome at least some of the above disadvantages and to provide an improved LED filament.

In a first aspect, there is provided a light emitting diode, LED, filament comprising: a translucent elongated substrate, and a plurality of light emitting diodes, LEDs, arranged at the substrate, wherein the substrate comprises at least one light transmission interruption arranged to provide a non-uniform spatial light distribution from the light emitting diodes, LEDs, filament, the light transmission interruption being electrically isolated from the plurality of light emitting diodes, LEDs.

According to one embodiment, the at least one light transmission interruption is a non-transparent part of the substrate.

According to one embodiment, the at least one light transmission interruption covers 20% to 80% of the total surface of the substrate.

According to one embodiment, the at least one light transmission interruption covers 25% to 75% of the total surface of the substrate.

According to one embodiment, the at least one light transmission interruption covers 30% to 70% of the total surface of the substrate.

According to one embodiment, the at least one light transmission interruption portion comprises a reflector, the reflector being arranged at a portion of the substrate.

According to one embodiment, the reflectivity of the reflector is at least 80%.

According to one embodiment, the reflectivity of the reflector is at least 85%.

According to one embodiment, the reflectivity of the reflector is at least 88%.

According to one embodiment, the reflector comprises at least one of a layer and a coating.

According to one embodiment, the light transmission interruption part includes an absorber disposed at a portion of the substrate.

According to one embodiment, the substrate comprises several light transmission discontinuities arranged at different portions of the substrate.

According to one embodiment, the substrate comprises several light transmission discontinuities arranged at different portions of the substrate along the length of the substrate.

According to one embodiment, each of the light transmission interruption portions includes a reflector, and a reflectivity of at least one reflector disposed at one portion of the substrate is different from a reflectivity of at least one reflector disposed at another portion of the substrate.

According to one embodiment, the reflector is arranged to provide a reflectivity gradient along a portion of the substrate.

According to one embodiment, the reflector is arranged to provide a reflectivity gradient along a length of the substrate along a portion of the substrate.

According to an embodiment, the substrate comprises a first elongated side and an opposite second elongated side, wherein the plurality of light emitting diodes, LEDs, are arranged at the first elongated side and the at least one light transmission interruption is arranged at the second elongated side.

According to one embodiment, the at least one light transmission interruption completely covers the second side of the substrate.

Thus, according to the present invention, a light emitting diode, LED, filament is provided, comprising a translucent elongated substrate and a plurality of LEDs arranged at the substrate. The substrate comprises at least one light transmission interruption arranged to provide a non-uniform spatial light distribution from the LED filament, such light transmission interruption being electrically isolated from the plurality of LEDs.

Accordingly, the present invention is based on the idea of providing an LED filament configurable to provide different spatial light distributions while minimizing any obstruction of the light emitted from the plurality of LEDs. Arranging at least one light transmission interruption at a portion of the substrate will have the consequence that: the transmission of light emitted from the plurality of LEDs incident on the light transmission interruption portion is interrupted so that the light is not completely transmitted therethrough. In contrast, for example, light is reflected, resulting in an increase in light emissivity outside another portion of the substrate that does not include the at least one light transmission interruption, or light is absorbed, resulting in a reduction or elimination of transmission of light that passes through and exits the substrate on which the light transmission interruption is disposed. Thus, by arranging the light transmission discontinuities at specific portions of the substrate, the LED filament itself may be tailored to provide a specific non-uniform spatial light distribution. Depending on the arrangement of the light transmission interruption portions, the light distribution from the LED filament may vary along, for example, the length of the LED filament or around its circumference, and may be different around the circumference at one portion of the LED filament relative to its other peripheral portion. In other words, the LED filament does not emit light omnidirectionally. Thus, light emission in directions where no illumination is required can be avoided. In addition, increased levels of illumination in the desired direction may be provided.

The translucent substrate preferably comprises a material selected from the group consisting of glass, sapphire and quartz. Alternatively, a translucent ceramic material or foil is used as the substrate. The term "translucent substrate" refers herein to a material, compound and/or substance that is translucent and/or transparent to visible light and that is arranged to carry, support and/or secure a plurality of LEDs, typically at a surface thereof. Preferably, the light transmission through the substrate is at least 60%, more preferably at least 70%, most preferably at least 80%. The high light transmission capability of the substrate allows light from a plurality of LEDs arranged at the substrate to be transmitted through the substrate, thereby increasing the efficiency of the LED filament. In a preferred embodiment, the translucent substrate is transparent. The efficiency of the LED filament is improved because the transparent substrate provides less back reflection and therefore higher transmission.

The LED filament includes a plurality of LEDs, such as an LED array. The term "array" refers herein to a linear arrangement or chain of LEDs or the like arranged at the surface of a substrate.

The light transmission interruption portion is configured to interrupt transmission of light emitted from the LED incident on the light transmission interruption portion. For example, the light transmission interruption may include a reflective surface, an opaque material, or an increased opacity material. "reflective surface" refers herein to a surface configured, adapted and/or arranged to reflect incident light.

According to an embodiment of the invention, the at least one light transmission interruption is a non-transparent part of the substrate. The substrate of this embodiment thus comprises at least one portion that is translucent and at least another portion that is non-transparent. The non-transparent portion of the substrate is configured to interrupt transmission of any light incident on the non-transparent portion of the substrate that is emitted from, for example, an LED disposed at the same portion of the substrate. By "non-transparent portion" is meant herein a portion that provides less than 1%, such as 0.1% or more preferably 0%, light transmission. Thus, light from any LED arranged at the non-transparent part of the substrate will be emitted mainly in the opposite direction to the direction in which the substrate is arranged, resulting in a non-uniform spatial light distribution from the LED filament. The non-transparent portion preferably comprises an opaque material, a material comprising a reflective surface, or a material with increased opacity. The advantages of this embodiment are: the non-transparent portion of the substrate provides an efficient light transmission interruption allowing to obtain an apparently non-uniform spatial light distribution from the LED filament. Preferably, the non-transparent portion of the substrate constitutes 20% to 80% of the substrate, more preferably 25% to 75% of the substrate, and most preferably 30% to 70% of the substrate.

According to an embodiment of the invention, the at least one light transmission interruption covers 20% to 80%, preferably 25% to 75%, more preferably 30% to 70% of the total surface of the substrate. For example, in one embodiment, the light transmission discontinuities completely cover a surface of the substrate, such as an elongated surface thereof. In an alternative embodiment, the light transmission interruption partially covers the surface of the substrate.

According to an embodiment of the invention, the at least one light transmission interruption comprises a reflector arranged at a portion of the substrate. In one embodiment, at least one reflector is a semi-reflective reflector. In another embodiment, at least one reflector is a total reflection reflector. The at least one reflector preferably comprises a coating or layer for diffuse or specular reflection of the light emitted from the plurality of LEDs. Alternatively, or in combination with one or more coatings and/or arrangement of layers, according to a further embodiment of the invention, the at least one reflector comprises at least one mirror for specular reflection of light emitted from the plurality of LEDs. Alternatively or in combination, the reflector comprises at least one surface that has been treated for diffuse reflection of light emitted from the LED 14. The reflectivity of the at least one reflector is preferably at least 80%, more preferably at least 85% and most preferably at least 88%. Prioritizing the higher reflectivity generates increased efficiency of the reflector and thus of the LED filament. Typically, at least one reflector may be configured to reflect different wavelengths. In a preferred embodiment, the reflector is configured to reflect incident visible light. Furthermore, the reflectivity is preferably constant over the entire visible spectrum of light.

The advantages of this embodiment are: the reflector may be configured to provide varying degrees of light transmission interruption by adapting the reflectivity of the reflector used. In addition, the reflector may advantageously be used by providing a highly reflective reflector at a portion of the substrate corresponding to the opposite portion thereof, in order to provide increased light in a direction from a specific portion of the LED filament. This provides an efficient LED filament, considering that the arrangement of the reflector at one part of the substrate allows light reflected there to be transmitted through another part of the substrate without significant light loss.

According to an embodiment of the present invention, the light transmission interruption portion includes an absorber disposed at a portion of the substrate. The absorber is configured to absorb any incident light emitted from the LED disposed at the nearby portion of the substrate. The absorber preferably comprises a light absorbing material. The advantages of this embodiment are: this embodiment allows a significant interruption of the light emitted from the LED filament at the portion of the substrate corresponding to the portion where the absorber is arranged.

According to an embodiment of the invention, the substrate comprises several light transmission discontinuities arranged at different parts of the substrate, e.g. along the length of the substrate. According to one embodiment, the light transmission discontinuities are adjacently arranged along the length of the substrate, and the light transmission disrupting power is preferably different between different light transmission discontinuities. According to another embodiment, the light transmission discontinuities are further arranged to cover the entire width of the substrate and are distributed along its length with spaces between each light transmission discontinuity. The advantages of this embodiment are: this embodiment allows for a customized flexibility of the non-uniform spatial light distribution of the LED filament, thereby meeting the lighting requirements arranged therefor.

According to an embodiment of the present invention, each light transmission interruption portion includes a reflector, and a reflectance of at least one reflector disposed at a portion of the substrate is different from a reflectance of at least one reflector disposed at another portion of the substrate. The advantages of this embodiment are: this embodiment allows tailoring the emissivity of the light from the LED filament to be increased in some parts and reduced or eliminated altogether in other parts.

According to an embodiment of the invention, the at least one reflector is arranged to provide a reflectivity gradient along a portion of the substrate. According to one embodiment, the at least one reflector is arranged to provide a reflectivity gradient along a length of the substrate or along a width of the substrate. The at least one reflector may alternatively be arranged to provide a reflectivity gradient along a portion of the length of the substrate. The reflectivity gradient is typically formed by several reflectors of different reflectivity arranged adjacently along the length of the substrate, such that the reflectivity decreases or increases along the substrate. Alternatively, the reflectivity gradient is formed by one reflector having a reflectivity gradient along its length or width.

An advantage of this embodiment is that it provides an LED filament with a portion of gradually increasing or decreasing light emissivity.

According to an embodiment of the invention, the substrate comprises a first elongated side and an opposite second elongated side, wherein the plurality of LEDs are arranged at the first elongated side and the light transmission discontinuities are arranged at the second elongated side. The plurality of LEDs is preferably arranged at a surface of the first elongated side of the substrate. In one embodiment, the light transmission interruption is arranged at a surface of the second elongated side of the substrate. In an alternative embodiment, the light transmission interruption is formed by a portion of the substrate comprising the second elongated side. According to a further embodiment, the at least one light transmission interruption completely covers the second side of the substrate.

The second side of the substrate and any reflective surfaces arranged thereon are preferably flat. This facilitates the transmission of light reflected at the light transmission interruption through another part of the substrate, such as the first side of the substrate, without significant light loss due to the light being reflected several times.

An advantage of this embodiment is that light emitted from the plurality of LEDs arranged at the first side of the substrate and incident on the light transmission discontinuities is at least partially reflected and transmitted outwardly from the LED filament through the first side of the substrate. Alternatively, the light transmission interruption portion absorbs incident light emitted from a plurality of LEDs arranged at the substrate. In any event, the amount of light emitted from the first side of the substrate is greater than the amount of light emitted from the second side of the substrate, thereby providing a non-uniform spatial light distribution or non-omnidirectional light emissivity from the LED filament. Due to the arrangement of the light transmission interruption at the second side of the substrate, no non-absorbed light may be trapped in the substrate, since the non-absorbed light may reflect off the first side of the substrate, thereby providing an efficient LED filament.

According to an embodiment of the invention, the LED filament is flexible. Thus, in this embodiment, the substrate is flexible. The flexible LED filament allows for the same bending into the desired shape at different portions. An advantage of this embodiment is that the LED filament may be configured to provide an efficient spatial light distribution for the shape in which the LED filament is arranged. For example, the LED filament may be configured to provide an increased emissivity of light towards the outside of the shape enclosing the two-dimensional space by arranging light transmission interruptions at respective portions of the substrate pointing towards the center of such enclosed space. Providing a flexible LED filament with a configurable spatial light distribution is particularly advantageous for applications requiring different lighting in a particular direction, such as, for example, illuminated text or shapes.

According to a second aspect of the present invention, there is provided a lighting device comprising at least one LED filament according to any one of the embodiments disclosed herein. The lighting device further comprises a cover comprising an at least partially transmissive material, wherein the cover at least partially surrounds the LED filament. "cover" herein refers to an enclosing element comprising an at least partially translucent and/or transparent material, such as a cover, an envelope, etc. Furthermore, the lighting device comprises electrical connections connected to the LED filament for supplying power to the plurality of LEDs of the LED filament. An advantage of this embodiment is that the LED filament according to the present invention can be conveniently arranged in substantially any lighting device, such as an LED filament lamp, a luminaire, a lighting system, etc. The lighting device typically further comprises a driver for powering the plurality of LEDs of the LED filament.

According to an embodiment of the present invention, there is provided a lighting apparatus including two or more LED filaments, wherein a spatial light distribution of at least one LED filament is different from a spatial light distribution of at least another LED filament. As one example, the lighting device comprises two LED filaments, one of which has a uniform spatial light distribution and the other has a non-uniform spatial light distribution. Thus, according to one embodiment, the first LED filament provides light in a first direction and the second LED filament provides light in both the first direction and a second direction. Alternatively, the first LED filament provides light in a first direction and the second LED filament provides light in a second direction. Further, the lighting device may alternatively comprise more than two LED filaments, some of the more than two LED filaments having different non-uniform spatial light distributions and some of the LED filaments having uniform spatial light distributions, or all of the more than two LED filaments having non-uniform spatial light distributions.

The advantages of this embodiment are: this embodiment provides a lighting device that can be tailored to provide an efficient light distribution such that light is not emitted in directions where illumination is not required and/or such that the light emissivity can be increased in a particular direction. In addition, the lighting device may further include a controller for individually controlling two or more LED filaments (such as the first LED filament, the second LED filament, etc.) disposed therein.

Further objects, features and advantages of the present invention will become apparent upon a study of the following detailed disclosure, the drawings and the appended claims. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following.

Drawings

These and other aspects of the invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

Figure 1 schematically shows a cross-sectional view of an LED filament according to the prior art,

figure 2 schematically shows a cross-sectional view of an LED filament according to an embodiment of the invention,

figures 3a to 3e schematically show cross-sectional views of LED filaments according to exemplary embodiments of the present invention,

fig. 4 schematically shows a perspective view of an LED filament according to an embodiment of the invention, an

Fig. 5 schematically shows a lighting device according to an embodiment of the invention.

Detailed Description

The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

Fig. 1 shows a cross-sectional view of an LED filament 1 according to the prior art, the LED filament 1 comprising a plurality of LEDs 4, the plurality of LEDs 4 being arranged at an elongated substrate 2 distributed along its longitudinal axis. The use of such LED filaments in lamps is highly appreciated because such LED filaments are decorative and additionally because such LED filaments offer numerous advantages over incandescent lamps, such as longer service life, reduced power consumption and increased efficiency with respect to the ratio of light energy to heat energy.

Fig. 2 schematically shows a cross-section of an LED filament 10 comprising an elongated substrate 12, the elongated substrate 12 having a width W and a length L, wherein L > W and the length extends along an axis a. The length is preferably at least 20mm, more preferably at least 30mm, most preferably at least 40mm, such as, for example, 45mm or 50 mm. The width is preferably at least 1mm, more preferably at least 2mm, most preferably at least 3mm, such as, for example, 4mm or 5 mm. The aspect ratio L/W is preferably at least 5, more preferably at least 8, most preferably at least 10, such as, for example, 15 or 20.

The substrate 12 is preferably substantially flat, i.e. has a rectangular or square cross-section.

The substrate 12 is translucent and may, for example, comprise glass, sapphire and/or quartz. In a preferred embodiment, the substrate 12 is transparent. The translucency or transparency of the substrate 12 is illustrated in the figures by the unfilled regions of the element.

The LED filament 10 further comprises a plurality of LEDs 14, the plurality of LEDs 14 being arranged adjacently at the substrate 12 along the length of the substrate, forming an array or chain of LEDs 14. Each pair of adjacent LEDs is arranged with wiring (not shown) arranged to supply each LED. The plurality of LEDs 14 preferably comprises more than 5 LEDs, more preferably more than 8 LEDs, and most preferably more than 10 LEDs. The plurality of LEDs 14 may be direct emitting LEDs that provide color. The LED14 is preferably a blue LED. The LED14 may also be a UV LED. A combination of LEDs 14 (e.g. UV LEDs and blue LEDs) is also possible within the concept of the invention, since LEDs 14 comprising laser diodes are provided.

In the case where the substrate 12 includes a conductive material, the substrate is electrically isolated from the wiring of the LEDs 14. This provides improved safety for the LED filament 10. It should also be understood by the present disclosure that the light transmission discontinuity does not include an antenna. Due to the transparency and/or translucency of the substrate 12, light emitted from the LED14 during operation is transmitted through the substrate 12 such that the light is emitted omnidirectionally in a plane perpendicular to the axis a, thereby providing a uniform light distribution from the LED filament. In some cases, however, it is desirable to provide a non-uniform spatial light distribution from the LED filament such that the LED filament emits light non-omnidirectionally in a plane perpendicular to the axis a at least at a portion of the LED filament, e.g., for improving decorative effects or increasing the efficiency of the emitted light. To facilitate this non-uniform spatial light distribution from the LED filament, the substrate further comprises at least one light transmission interruption 20. In the embodiment shown in fig. 2, the light transmission interruption portion 20 is a non-transparent portion of the substrate 12. The substrate 12 thus comprises one portion that is translucent (e.g. transparent) and one portion that is non-transmissive for at least a part of the visible wavelength range. The non-transparent portion 20 here extends along the axis a from the middle of the LED filament 10 to its ends, whereas the transparent or translucent portion of the substrate 12 extends along the axis a from the middle of the LED filament 10 to its opposite ends. It is also possible within the concept of the present invention to arrange the non-transparent portions 20 in different ways and to provide non-transparent portions 20 of different sizes (e.g., the length corresponds to the length of the substrate 12 or a portion of the substrate, such as a quarter or otherwise).

The non-transparent portion 20 typically comprises one of an opaque material and a material having some degree of opacity, such as an optical fiber.

Some of the LEDs 14 arranged along the length of the substrate 12 are thus arranged at the light transmission discontinuities 20. The light emitted from these LEDs will therefore not travel through the light transmission interruption 20 in the operational situation, since it travels through the translucent portion of the substrate 12, but will be at least partially absorbed or reflected, resulting in a modified spatial light distribution from the LED filament 10.

The LED filament 10 further comprises an encapsulant 16, the encapsulant 16 comprising a translucent material. Here, the encapsulant 16 extends around the substrate 12 and the plurality of LEDs 14 disposed thereon, thereby completely surrounding the plurality of LEDs 14. However, it is also conceivable within the concept of the present invention to provide an encapsulant 16 that partially surrounds the substrate 12 and the plurality of LEDs 14. The term "encapsulant" refers herein to a material, element, device, etc. that is configured or arranged to surround, encapsulate, and/or enclose a plurality of LEDs of an LED filament. The term "translucent material" refers herein to materials, composites, and/or substances that are translucent and/or transparent to visible light.

According to one embodiment, the encapsulant 16 includes a luminescent material configured to emit light under excitation by external energy. For example, the luminescent material includes a fluorescent material. Alternatively, the fluorescent material comprises inorganic and organic phosphorus and/or quantum dots/rods. The UV/blue LED light may be partially or completely absorbed by the luminescent material and converted into light of another color, e.g. green, yellow, orange and/or red. The cross-section of the encapsulant 16 perpendicular to the longitudinal axis a may have generally any shape, such as circular, rectangular, etc.

The LED filament 10 further comprises electrical contact portions 18 arranged at opposite ends of the elongated substrate 12, through which electrical contact portions 18 the plurality of LEDs 14 of the LED filament 10 can be powered.

During operation, the light emitted from the LED filament 10 is preferably white light. The white light is preferably within 15SDCM of the black body curve (BBL). The color temperature of the white light is preferably in the range of 2000K to 6000K, more preferably in the range of 2100K to 5000K, most preferably in the range of 2200K to 4000K, such as, for example, 2300K or 2700K. The white light preferably has a CRI of at least 75, more preferably at least 80, most preferably at least 85, such as, for example, 90 or 92.

Fig. 3a to 3e schematically show embodiments of an LED filament 10, the LED filament 10 comprising an elongated substrate and a plurality of LEDs 14 distributed along the length of the substrate. The light transmitting portion 20 here comprises one or more reflectors 20, the one or more reflectors 20 being arranged at the substrate 12 for reflecting incident light from the LEDs 14 during operation. In fig. 3a, the LEDs are arranged at a first surface 12 'of the substrate 12 and the reflector 20 is arranged at a second surface 12 "of the substrate 12, which second surface 12" is opposite to the first surface 12'. The reflector 20 extends along the length of the second surface 12 "and comprises a semi-reflective reflector configured to transmit at least a portion of incident light traveling from the LEDs 14 through the substrate 12 and reflect at least a portion of incident light emitted from the LEDs such that the at least a portion of incident light travels back through the substrate 12 toward the first surface 12' of the substrate. The spatial distribution of the light emitted from the LED filament will thus increase near the first side 12' of the substrate 12 (i.e. in one direction), resulting in a non-uniform light distribution.

According to another embodiment and referring to fig. 3b, the reflector 20 is a total reflection reflector configured to reflect all incident light, arranged at the second surface 12 "of the substrate 12 and extending along the length of the substrate. Thus, no light is emitted from the substrate 12 at the portion covered by the reflector 20 (i.e. the second surface 12 "), resulting in a non-uniform spatial light distribution from the LED filament 10. Alternatively, according to another embodiment, the reflector 20 is arranged to extend along a portion of the length L of the substrate 12, see fig. 3 c. According to a further embodiment, the substrate comprises several light transmission discontinuities 20, wherein, for example, a first light transmission discontinuity 20' comprises a half extending along a portion of the length L of the substrate 12A reflective reflector 120 and the second light-transmission breaking portion 20 "comprises a total-reflection reflector extending along the portion of the second surface 12" of the substrate 12 not covered by the first light-transmission breaking portion 20'. This provides a varying light distribution from the LED filament 10 along its circumference and along its length. In another exemplary embodiment (not shown), the substrate 12 includes a light transmission discontinuity 20 that provides a reflectivity gradient along the length of the substrate 12. This is achieved by e.g. adjacently arranging reflectors of increasing reflectivity along the length of the substrate 12 or by providing elongated reflectors along the length of the substrate 12 having a decreasing or increasing reflectivity along its longitudinal extension. Alternatively, the reflectivity gradient is achieved by using a reflector whose thickness gradually increases along its extension (e.g., length). For example, according to one embodiment, the reflector comprises a mirror applied to the substrate by evaporation, the thickness of the mirror gradually increasing from 20nm to 70nm along the length of the substrate 12. According to another embodiment, the reflector is a coating comprising a polymer and reflective particles, such as Al, distributed in the polymer₂O₃、BaSO₄And/or TiO₂. The reflectivity gradient of the reflector is here achieved by providing a coating of increasing thickness along, for example, the length of the substrate or by providing a concentration of reflecting particles that increases along the substrate.

Fig. 3e shows another exemplary embodiment according to which the substrate 12 comprises several light transmission discontinuities 20 (e.g. reflectors) arranged at the second surface 12 "of the substrate 12, the several light transmission discontinuities 20 being distributed along the length of the substrate with spaces between them. The reflectors 20 may have the same reflectivity or different reflectivities, and may, for example, include total reflection reflectors or semi-reflection reflectors.

The at least one reflector 20 typically comprises a reflective coating or a high reflectivity layer. The coating and/or layer is applied to the substrate 12 by at least one of spraying, coating, painting, printing, and evaporation. In one embodiment, the coating includes a polymer (e.g., silica gel) that includes reflective particles (such as TiO)₂、Al₂O₃And/or BaSO₃) And flakes, such as aluminum (Al) and/or silver (Ag).

According to other embodiments of the present invention, the reflectors described with reference to fig. 3a to 3e are exchanged for absorbers.

Fig. 4 schematically shows an LED filament 10, which LED filament 10 is flexible and bent in several sections such that the LED filament 10 almost encloses a rectangular shape. The substrate of this embodiment is thus flexible. However, providing a rigid substrate is also possible within the concept of the invention. The LED filament 10 here comprises light transmission interruptions at opposite longitudinal side portions 11 of the bent LED filament 10, so that no light is emitted from the LED filament at these portions towards the enclosed rectangular space. It is also possible within the concept of the invention to bend the flexible LED filament into other shapes and to provide a non-uniform spatial light distribution configured in a different way.

Fig. 5 schematically shows a lighting device 100 comprising a plurality of

LED filaments

1, 10. In this exemplary embodiment, the lighting device 100 comprises four

LED filaments

1, 10, two of which comprise a light transmission interruption arranged at a surface of the substrate and extending along the length of the substrate such that light is emitted from the respective LED filament 10 in only one direction. The other two LED filaments 1 do not comprise a light transmission interruption, the spatial light distribution from which is uniform. The lighting device 100 further comprises a cover 30, which cover 30 comprises an at least partially transparent material. Furthermore, the lighting device 100 comprises electrical connections connected to the LED filament for powering the plurality of LEDs 14 of the LED filament 10. The lighting device 100 further comprises a driver 40 and a cover 50, the driver 40 being for powering the plurality of LEDs 14 of the LED filament 10. Other configurations comprising different numbers of LED filaments and LED filaments 10 having differently configured spatial light distributions are also possible within the concept of the invention.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the light transmission discontinuities may have different shapes, sizes, and/or dimensions than the light transmission discontinuities described herein. Furthermore, according to one embodiment, the LED filament comprises a light transmission interruption in the form of a non-transparent part of the substrate in combination with a reflector or absorber arranged at a part of the substrate. The reflector and/or the absorber are here preferably arranged at the translucent portion of the substrate.

In addition, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A Light Emitting Diode (LED) filament, comprising:

a translucent elongated substrate, and

a plurality of Light Emitting Diodes (LEDs) arranged at the substrate,

wherein the substrate comprises at least one light transmission interruption arranged to provide a non-uniform spatial light distribution from the light emitting diode, LED, filament, the light transmission interruption being electrically isolated from the plurality of light emitting diode, LED, filaments.

2. The light emitting diode, LED, filament of claim 1, wherein said at least one light transmission discontinuity is a non-transparent portion of said substrate.

3. The light emitting diode, LED, filament of any of claims 1-2, wherein the at least one light transmission discontinuity covers 20% to 80% of the total surface of the substrate.

4. The light emitting diode, LED, filament of any of claims 1-2, wherein the at least one light transmission discontinuity covers 25% to 75% of the total surface of the substrate.

5. The light emitting diode, LED, filament of any of claims 1-2, wherein the at least one light transmission discontinuity covers 30% to 70% of the total surface of the substrate.

6. The light emitting diode, LED, filament of any of claims 1-2, wherein the at least one light transmission interruption comprises a reflector disposed at a portion of the substrate.

7. The light emitting diode, LED, filament of claim 6, wherein the reflector has a reflectivity of at least 80%.

8. The light emitting diode, LED, filament of claim 6, wherein the reflector has a reflectivity of at least 85%.

9. The light emitting diode, LED, filament of claim 6, wherein the reflector has a reflectivity of at least 88%.

10. The light emitting diode, LED, filament of claim 6, wherein said reflector comprises at least one of a layer and a coating.

11. The light emitting diode, LED, filament of any of claims 1 to 2, wherein the light transmission interruption comprises an absorber disposed at a portion of the substrate.

12. The light emitting diode, LED, filament of any of claims 1 to 2 and 7 to 10, wherein the substrate comprises several light transmission discontinuities arranged at different portions of the substrate.

13. The light emitting diode, LED, filament of any of claims 1 to 2 and 7 to 10, wherein the substrate comprises a plurality of light transmission discontinuities arranged at different portions of the substrate along the length of the substrate.

14. The Light Emitting Diode (LED) filament of claim 12, wherein each light transmission interruption comprises a reflector, and wherein the reflectivity of at least one reflector disposed at one portion of the substrate is different from the reflectivity of at least one reflector disposed at another portion of the substrate.

15. The light emitting diode, LED, filament of claim 6, wherein the reflector is arranged to provide a reflectivity gradient along a portion of the substrate.

16. The light emitting diode, LED, filament of claim 6, wherein the reflector is arranged to provide a reflectivity gradient along a length of the substrate along a portion of the substrate.

17. The light emitting diode, LED, filament of any of claims 1 to 2, 7 to 10 and 14 to 16, wherein the substrate comprises a first elongated side and an opposite second elongated side, wherein the plurality of light emitting diode, LEDs, are arranged at the first elongated side and the at least one light transmission interruption is arranged at the second elongated side.

18. The light emitting diode, LED, filament of claim 17, wherein said at least one light transmission discontinuity completely covers said second side of said substrate.