LED filament with light-reflecting particles for providing flicker

Abstract

The present disclosure relates to a light emitting diode (LED) filament (110). According to one embodiment, the LED filament comprises an elongated substrate (111) and a plurality of light emitting diodes (LEDs) (112) mechanically coupled to the substrate. According to one embodiment, the LED filament further comprises: an at least partially light transmissive encapsulation (114) encapsulating the plurality of LEDs and at least partially encapsulating the substrate; and a plurality of at least partially light reflective particles (115) arranged on an outer surface of the encapsulation.

Description

Technical Field

[0001] This disclosure relates to light-emitting diode filaments for use in lighting equipment. Background Technology

[0002] Incandescent lamps are rapidly being replaced by lighting solutions based on light-emitting diodes (LEDs). Compared to incandescent, fluorescent, and gas discharge lamps, solid-state light sources offer numerous advantages, such as extended operating life, reduced power consumption, higher efficiency, less heat generation, and being environmentally friendly (i.e., mercury-free). Solid-state lighting devices, such as LEDs, are used in a wide range of lighting applications, including general lighting.

[0003] Solid-state lighting devices have been developed as retrofit lights to resemble incandescent bulbs. However, there is always a need for more decorative solid-state lighting devices.

[0004] Furthermore, the color of the light provided by LED lights typically varies depending on the angle at which the light is emitted. This color-with-angle (COA) effect is sometimes significant and can result in a yellow ring at large angles in the far field of a white LED. LED retrofit lights often also provide more directional light than their incandescent counterparts. As a result, the light from these lights can cause a more pronounced contrast between illuminated and shadowed areas and make objects appear flat.

[0005] US 2017 / 227169 discloses an LED bulb comprising a bulb housing, a bulb base, a rod, a conductive support, an LED filament, and a support arm. The LED filament includes a plurality of LED chips, at least two conductive electrodes, and a light conversion coating. The plurality of LED chips and the conductive electrodes are electrically connected therebetween. The light conversion coating is applied to at least two sides of the conductive electrodes and the LED chips. The light conversion coating exposes a portion of two of the conductive electrodes. The light conversion coating includes a binder, a plurality of inorganic oxide nanoparticles, and a plurality of phosphors. Summary of the Invention

[0006] Therefore, one object of this disclosure is to overcome some of the disadvantages mentioned above and to provide an improved LED filament.

[0007] This and other objectives are achieved by means of an LED filament as described in the independent claim. Other embodiments are defined by the dependent claims.

[0008] According to one aspect of this disclosure, an LED filament is provided. The LED filament includes an elongated substrate, a plurality of light-emitting diodes (LEDs), an encapsulation portion, and a plurality of at least partially light-reflecting particles. The LEDs are mechanically coupled to the substrate, and the encapsulation portion encapsulates at least a portion of the substrate and the LEDs. At least partially light-reflecting particles (e.g., flashers or sheets) are arranged on the outer surface of the encapsulation portion. The at least partially light-reflecting particles may, for example, have a high aspect ratio, and they may in particular be flat particles.

[0009] According to some embodiments, at least a portion of the light-reflecting particles (or flash sheets) may include a first surface and a second surface. The first surface may abut against the encapsulation portion, thereby facing the substrate and the LED. The second surface may be opposite to the first surface and may be pointed away from the encapsulation portion. The second surface may, for example, face the environment surrounding the filament.

[0010] The encapsulation portion includes a certain volume of material that encapsulates at least a portion of the substrate and the LED. The outer surface of the encapsulation portion is the surface of the encapsulation portion volume facing outwards. In other words, it faces away from the encapsulation portion and the LED, and faces the surrounding environment of the encapsulation portion.

[0011] At least some of the light-reflecting particles on the outer surface of the package can give the LED filament a flickering appearance when it is in the OFF state (i.e., when the LED filament is not turned on) by reflecting ambient light (external light, surrounding light, i.e., light from other sources) in various directions. This flickering appearance can enhance the decorative characteristics of the LED filament.

[0012] Furthermore, at least some of the light-reflecting particles on the surface of the package can redirect the light emitted by the LED in the ON state (i.e., when the LED filament is turned on) at a different angle. This redirection can result in a more omnidirectional dispersion of the emitted light, which in turn can give the light a softer appearance and reduce the harsh contrast typically caused by conventional LED filaments.

[0013] At least some of the light-reflecting particles may have at least one flat surface and are characterized by a longest dimension length L1, a shortest dimension length L2, and another dimension length L3. The dimensions of the light-reflecting particles can be related by specifying an aspect ratio. A first aspect ratio AR1 is defined as the ratio between the longest dimension length and the shortest dimension length. Further, at least some of the light-reflecting particles may be characterized by a second aspect ratio AR2, which is defined as the ratio between the other dimension length and the shortest dimension length. At least some of the light-reflecting particles may be characterized by a third aspect ratio AR3, which is the ratio between the longest dimension length and the other dimension length.

[0014] In some embodiments, the length and ratio of at least some of the light-reflecting particles can meet certain requirements to provide an improved shimmering appearance. As an example, the longest dimension L1 can be in the range of 0.1 mm to 3 mm. Similarly, another dimension L3 can also be in the range of 0.1 mm to 3 mm. The shortest dimension L2 can be in the range of 10 μm to 300 μm.

[0015] In some embodiments, the first aspect ratio AR1 can be in the range of 10 to 300. The second aspect ratio AR2 can also be in the range of 10 to 300. The third aspect ratio AR3 can be in the range of 0.3 to 3.

[0016] According to some embodiments, the LED filament may have a diameter D. The longest dimension length L1 may be defined relative to this diameter. For example, the longest dimension length may be in the range of 0.1D to D (i.e., 0.1D). <L1<D)。

[0017] According to some embodiments, at least some of the light-reflecting particles can be rigid (e.g., cannot be bent or forced to deform; non-flexible), which further increases the reflectivity of the light-reflecting particles, allowing them to act as micro-mirrors.

[0018] According to some embodiments, at least some of the light-reflecting particles may be randomly distributed or randomly oriented, or both. The random distribution and / or arrangement of the particles can further enhance the flashing effect of the LED filament because ambient light is reflected in a more random manner. The random distribution and / or orientation of at least some of the light-reflecting particles can also increase the omnidirectional dispersion of the emitted light in the ON state, because the emitted light can be redirected more randomly.

[0019] Although at least some of the light-reflecting particles are described as randomly distributed and / or oriented, other embodiments are possible. For example, at least some of the light-reflecting particles may be uniformly distributed or concentrated in a certain area of ​​the package surface.

[0020] The LED filament coverage area, denoted by C, represents the coverage area of ​​at least a portion of the light-reflecting particles on the outer surface of the package. Certain sub-ranges of the LED filament coverage area have been shown to provide a better flicker appearance without blocking the light emitted by the LED.

[0021] According to some embodiments, it is denoted as C min The minimum LED filament coverage can be 3%.

[0022] According to some embodiments, at least some of the reflective particles may be opaque (non-transmissive). For these embodiments, the maximum LED filament coverage area C max It can be 30% to achieve the best flickering appearance.

[0023] According to some other embodiments, at least some of the light-reflecting particles may be transmissive, where the transmittance is expressed as T. According to some embodiments, the transmittance of these particles is less than 40%, i.e., T < 40%. Transmissive particles allow some of the light emitted by the LED to pass through the particles, resulting in a larger filament coverage area being possible. For these embodiments, the maximum LED filament coverage area C... max It can depend on the transmittance of the particles. However, the coverage should never be less than C. min =5%. Therefore, the maximum coverage area can be expressed as:

[0024]

[0025] According to some embodiments, at least a partially transparent encapsulation portion may include a wavelength conversion material. The encapsulation portion including the wavelength conversion material can extend the spectrum of light emitted by the LED filament. In most everyday lighting applications, white light is preferred. In the LED filament, the LED can be selected to emit blue light. By providing the encapsulation portion with a wavelength conversion material (e.g., different phosphors), some of the blue light can be absorbed by the wavelength conversion material. Some of the absorbed blue light can undergo a Stokes shift and be emitted as longer wavelengths (e.g., other blue, red, and green / yellow). Combinations of different wavelengths can give the impression of white light. By selecting the LED and the wavelength conversion material, the color and hue of the emitted light can be defined. The light emitted by the LED filament (LED filament light) can, for example, be within 15 standard deviations (SCDM) of color matching from the blackbody line (BBL). Furthermore, the LED filament light can further have a color rendering index (CRI) of at least 70.

[0026] In embodiments where wavelength conversion material is included in the encapsulation, at least some of the light-reflecting particles can positively influence the color change with angle of origin (COA). At large angles, blue light can propagate through the encapsulation for a longer period. Blue light passing through more wavelength conversion material results in more blue light absorption and therefore more green and red light emission. Consequently, the outer regions of the illuminated area can exhibit a more yellow hue. The light-reflecting particles on the outer surface of the encapsulation can redirect light of different wavelengths to more and different directions, which can mitigate the color change with angle.

[0027] According to some embodiments, at least some of the light-reflecting particles may have a wavelength-dependent reflectivity. In the OFF state, the light-reflecting particles with a wavelength-dependent reflectivity can provide a colored flickering effect, which can further enhance the decorative properties of the LED filament.

[0028] According to some embodiments, at least some of the light-reflecting particles may include multilayer reflectors.

[0029] According to some embodiments, at least some of the light-reflecting particles may include dichroic mirrors.

[0030] In some embodiments of this disclosure, at least one LED filament, as described with respect to any of the foregoing embodiments, may be part of a lighting device. The lighting device may further include a light-transmitting housing that at least partially surrounds at least one LED filament. The lighting device may also include a base on which the light-transmitting housing may be mounted. The base may include an electrical connector for connection to a luminaire socket for electrically connecting the lighting device.

[0031] The base can be configured, for example, to allow the lighting device to function as a retrofit lamp. Furthermore, at least partially translucent housings can have a pear shape similar to that of a conventional incandescent light bulb.

[0032] According to some embodiments, a lighting device including at least one LED filament, as described above, can be connected to a luminaire. The luminaire may include a socket and a lighting device connected to the socket, the socket being an electrical connector for connection to the lighting device.

[0033] It should be noted that other embodiments using all possible combinations of the features described in the embodiments described above are conceivable. Therefore, this disclosure also relates to all possible combinations of the features mentioned herein. Any embodiment described herein can be combined with other embodiments also described herein, and this disclosure relates to all combinations of features. Attached Figure Description

[0034] This and other aspects of the invention will now be described in more detail with reference to the accompanying drawings, which illustrate embodiments of the invention. The drawings should not be construed as limiting the invention to the specific embodiments; rather, they are intended to explain and understand the invention.

[0035] As shown in the figures, the dimensions of the layers and regions are exaggerated for illustrative purposes and are therefore provided to illustrate the general structure of embodiments of the invention. The same reference numerals throughout refer to the same elements.

[0036] Figures 1a to 1b A schematic side view of an LED filament according to some embodiments is shown.

[0037] Figures 2a to 2b Schematic cross-sectional views of an LED filament according to some embodiments are shown. These figures illustrate the cross-section of the LED filament in a plane perpendicular to the elongated axis of the LED filament.

[0038] Figure 3 The illustration shows at least a portion of light-reflecting particles according to some embodiments.

[0039] Figure 4 A lighting device according to some embodiments is shown.

[0040] Figure 5 The illustration shows a illuminator according to some embodiments. Detailed Implementation

[0041] Exemplary embodiments will now be described more fully with reference to the accompanying drawings, in which currently preferred embodiments are illustrated. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness and to fully convey the scope of the invention to those skilled in the art.

[0042] refer to Figure 1a and Figure 1b The LED filament according to some embodiments will be described.

[0043] Figure 1a and Figure 1b Both show schematic side views of an LED filament according to some embodiments.

[0044] like Figure 1a As shown, the LED filament 110 according to this embodiment includes an elongated substrate 111, a plurality of light-emitting diodes (LEDs) 112, and a package 114 that is at least partially transparent. It may also include wiring 113 for supplying power to the LEDs. Figure 1b As shown, the LED filament 110 may further include a plurality of at least partially light-reflecting particles 115, which are arranged on the outer surface of the package portion 114.

[0045] The substrate 111 can be light-transmitting, such as translucent or transparent. For example, the substrate 111 can be made of one or a combination of the following materials: glass, sapphire, quartz, and ceramic. A light-transmitting, translucent, or transparent substrate allows emitted light to escape from the LED filament at all angles.

[0046] The substrate 111 can be rigid. Alternatively, the substrate 111 can be flexible, which allows for an aesthetically pleasing non-rigid configuration.

[0047] The substrate may include an elongated body extending along an elongated axis A. The elongated axis A may be at least partially straight or substantially straight. However, it will be appreciated that the elongated axis of the substrate may be at least partially curved. For example, the substrate, and therefore the LED filament, may be shaped according to a coil. The substrate may be arranged such that it includes: one or more portions or segments wherein the elongated axis of the substrate is straight or substantially straight; and one or more other portions or segments wherein the elongated axis of the substrate is curved.

[0048] LED 112 is mechanically coupled to substrate 111. In some embodiments, LED 112 may be arranged only on a first surface of the substrate, which is the main surface or large surface compared to the other surfaces of the substrate.

[0049] The LEDs can be arranged along an elongated axis A. The LEDs 112 are configured to emit light when operated or activated (i.e., in an ON state). The LEDs 112 can be further configured to emit light having substantially the same spectral distribution. Alternatively, the LEDs 112 can be adapted to emit light with different spectral distributions. Multiple LEDs 112 can be powered via wiring 113. Wiring 113 can, for example, include conductive tracks.

[0050] At least a portion of the encapsulation portion 114 that is at least partially transparent to light, the encapsulation substrate 111, and the LED 112.

[0051] In some embodiments, the encapsulation portion 114 may encapsulate at least a portion of the first main surface of the substrate.

[0052] In some embodiments, the encapsulation portion 114 may encapsulate at least a portion of the first main surface of the substrate and at least a portion of the second main surface of the substrate. The second main surface of the substrate may be opposite to the first main surface of the substrate.

[0053] According to some embodiments, the encapsulation portion can completely encapsulate the first surface of the substrate.

[0054] In some embodiments, the encapsulation portion may completely encapsulate both the first and second main surfaces of the substrate.

[0055] In some embodiments, the encapsulation portion can completely encapsulate all surfaces of the substrate (i.e., the entire substrate).

[0056] The encapsulation portion may include light-diffusing elements, such as scattering particles, to disperse light and prevent non-uniform illumination. Alternatively, the encapsulation portion 114 may include a scattering material.

[0057] Within the concept of this invention, an LED filament provides LED filament light and comprises a plurality of light-emitting diodes (LEDs) arranged in a linear array. Preferably, the LED filament has a length L and a width W, where L > 5W. The LED filament can be arranged in a straight configuration or a non-straight configuration (such as, for example, a curved configuration, a 2D / 3D spiral, or a helix). Preferably, the LEDs are arranged on an elongated carrier, such as a substrate, which can be rigid (made of, for example, polymers, glass, quartz, metal, or sapphire) or flexible (e.g., made of polymers or metals, for example, a film or foil).

[0058] In the case where the carrier comprises a first main surface and an opposing second main surface, the LED is disposed on at least one of these surfaces. The carrier may be reflective or translucent, such as translucent and preferably transparent.

[0059] LED filaments may include an encapsulant that at least partially covers at least a portion of a plurality of LEDs. The encapsulant may also at least partially cover at least one of a first main surface or a second main surface. The encapsulant may be a polymeric material, which may be flexible, such as, for example, silicone. Furthermore, the LEDs may be arranged to emit LED light, for example, different colors or spectra. The encapsulant may include a light-emitting material configured to at least partially convert the LED light into converted light. The light-emitting material may be a phosphor (such as an inorganic phosphor) and / or quantum dots or rods.

[0060] LED filaments can include multiple sub-filaments.

[0061] refer to Figure 2a and Figure 2b An embodiment of an LED filament having at least a plurality of partially reflective particles 115 will be described.

[0062] Figure 2a and Figure 2b Both figures show schematic cross-sectional views of an LED filament according to some embodiments. These figures illustrate the relationship between the filament and the elongated axis of the LED filament (such as about...). Figure 1a and Figure 1b The cross-section of the LED filament in a plane perpendicular to the slender axis A mentioned above.

[0063] like Figure 2a As shown, at least some of the light-reflecting particles 115 may include a first surface 216 and a second surface 217. The first surface 216 may abut against the encapsulation portion 114, thereby facing the encapsulation portion 114 and the substrate 111. The second surface 217 may be opposite to the first surface 216 and point away from the encapsulation portion 114.

[0064] At least some of the light-reflecting particles 115 are disposed outside the encapsulation portion 114, i.e., they are not embedded in the encapsulation portion. The particles 115 can be attached to the encapsulation portion using an adhesive. In some embodiments, the adhesive can form part of the encapsulation portion, for example, the particles 115 can be attached using the encapsulation portion itself. In some embodiments, the particles 115 can be attached to the encapsulation portion 114 using a second encapsulation portion (not depicted) that at least partially encapsulates the first encapsulation portion 114.

[0065] Alternatively, this could include: partially imprinting particle 115 in encapsulation portion 114, thereby freeing second surface 217.

[0066] The reflectivity of at least partially light-reflecting particles 115 can be at least 75%. More specifically, the reflectivity of particles 115 can be at least 80%. Even more specifically, the reflectivity of particles 115 can be at least 85%.

[0067] For example, at least some of the light-reflecting particles can have a high aspect ratio, and they can in particular include flat particles.

[0068] When the LED filament 110 is de-energized (not activated, in its OFF state), at least some of the light-reflecting particles 115 on the outer surface of the substrate 111 can give the LED filament a flickering appearance. At least the second surface 217 can be adapted to reflect external light 218 in various directions, i.e., light from a source different from the LED of the LED filament 110.

[0069] like Figure 2b As shown, at least some of the light-reflecting particles 115 can also redirect light emitted by the LED when it is in the ON state (i.e., when the LED filament is energized and activated). For example, at least some of the light-reflecting particles 115 can reflect light emitted by the LED 112 along light path 220, or refract the emitted light along another light path 219. This redirection of light can result in a more omnidirectional dispersion of the light emitted by the LED filament. Dispersing light in more directions and angles can mitigate the problem of sharp lines between bright areas and shadows (as caused by conventional LED light sources).

[0070] The package 114 may include a wavelength conversion material. The wavelength conversion material may be configured to at least partially convert light emitted by the LED at a first wavelength (LED light) into light emitted at a second wavelength, which is different from the first wavelength. The wavelength conversion material may impart a broader spectrum of light to the LED filament.

[0071] As an example, the LED 112 of the LED filament 110 can emit UV light or blue light. The wavelength conversion material can be a phosphor, such as, for example, a yttrium aluminum garnet (YAG)-based phosphor and / or a lutetium aluminum garnet (LuAG)-based phosphor. The wavelength conversion material in the package 114 can be adapted to absorb blue light and re-emit the light as radiation 221 with a longer wavelength, such as other blue, green / yellow, or red light. For example, the wavelength conversion material can be adapted to convert LED light into blue and / or green / yellow and / or red light. The combination of LED light and converted light forms the light emitted by the LED filament (LED filament light). Combinations of different wavelengths can give the appearance of white light. For example, the resulting white light can be within 15 standard deviations (SCDM) of color matching from the blackbody line (BBL). In particular, the resulting white light can be within 10 SCDM of the BBL. More specifically, the resulting white light can be within 7 SCDM of the BBL, such as within 5 SCDM or 3 SCDM of the BBL.

[0072] The resulting white light may further have a color rendering index (CRI) of at least 70. In particular, the resulting white light may have a CRI of at least 75. The resulting white light may have a CRI of at least 80, such as 85 or 90.

[0073] Compared to blue light emitted from the substrate at a small angle, blue light emitted in a more perpendicular direction can travel a longer distance through the substrate. Light traveling a longer distance through the package encounters more wavelength-converting material, meaning a larger portion of the light can be converted into longer wavelengths. This can cause a non-uniform distribution of different wavelengths, known as color as a function of angle (CoA). The redirection of emitted light by light-reflecting particles on the outer surface of the package can produce light with a more uniform color.

[0074] refer to Figure 3 The particles (flash plates) in at least some of the light-reflecting particles will be described.

[0075] Figure 3 A light-reflecting particle 115, at least partially in the shape of a flattened cuboid, is shown. This specific shape of particle 115 is for illustrative purposes only. Particle 115 can have any shape of a flattened polyhedron, or any other flat particle with a high aspect ratio and at least one flat surface. For example, other examples could include different prisms. Figure 3 The diagram illustrates the longest dimension length L1, the shortest dimension length L2, and another dimension length L3 to characterize particle 115. The dimension lengths can be related by aspect ratio. The first aspect ratio (AR1) can be the ratio between the longest dimension length L1 and the shortest dimension length L2:

[0076]

[0077] The second aspect ratio (AR2) can be the ratio between the other dimension length L3 and the shortest dimension length L2:

[0078]

[0079] The third aspect ratio (AR3) can be the ratio between the longest dimension length L1 and the other dimension length L3:

[0080]

[0081] To provide a decorative, shimmering appearance, the dimension length and ratio 115 can meet certain requirements. For example, the dimension length can be within certain ranges or intervals defining the appropriate size of the particles. The longest dimension length L1 can be in the range of 0.1 mm to 3 mm. In particular, the longest dimension length L1 can be in the range of 0.15 mm to 2 mm. More particularly, the longest dimension length L1 can be in the range of 0.2 mm to 1 mm, such as, for example, 0.25 mm or 0.3 mm.

[0082] The shortest dimension length L2 can be in the range of 10 μm to 300 μm. In some embodiments, the shortest dimension length L2 can be in the range of 10 μm to 200 μm. In particular, the shortest dimension length L2 can be in the range of 10 μm to 100 μm, such as, for example, 12 μm or 20 μm.

[0083] The other dimension length L3 can be in the range of 0.1 mm to 3 mm. In particular, the other dimension length L3 can be in the range of 0.15 mm to 2 mm. More particularly, the other dimension length L3 can be in the range of 0.2 mm to 1 mm, such as, for example, 0.25 mm or 0.3 mm.

[0084] Furthermore, the aspect ratio that relates the lengths of the dimensions can also be within a specified interval or range, which defines a suitable shape for improving the shimmering appearance. For example, the aspect ratio can ensure that the particles have a larger reflective surface to reflect external light. The first aspect ratio AR1 that defines the relationship between the longest and shortest dimension lengths can be in the range of 10 to 300. In particular, the first aspect ratio can be in the range of 15 to 270. More particularly, AR1 can be in the range of 20 to 250, such as, for example, 25 or 30.

[0085] The second aspect ratio (AR2) defining the relationship between the other dimension length and the shortest dimension length can be in the range of 10 to 300. In particular, the second aspect ratio can be in the range of 15 to 270. More particularly, the second aspect ratio can be in the range of 20 to 250, such as, for example, 25 or 30.

[0086] The third aspect ratio AR3 that defines the relationship between the length of the longest dimension and the length of another dimension can be in the range of 0.3 to 3. In some embodiments, the third aspect ratio can be in the range of 0.5 to 1.5. In particular, the third aspect ratio can be in the range of 0.9 to 1.1, such as, for example, 1. In embodiments where the third aspect ratio AR3 is 1, the largest surface of at least some of the light-reflecting particles 115 can have a square or hexagonal shape. Such particles (sheets) can be produced using a high-precision cutting process.

[0087] According to some embodiments, the surface of at least some of the light-reflecting particles 115 can have a surface area of at least 250 μm 2 . In particular, the surface area can be at least 500 μm 2 . More particularly, the surface area can be at least 1000 μm 2 .

[0088] According to some embodiments, the cross-section of the LED filament can have a diameter D. The diameter D can be in the range of 1 mm to 10 mm. In particular, the diameter D can be in the range of 1.5 mm to 7 mm. More particularly, D can be in the range of 2 mm to 5 mm.

[0089] Furthermore, there can be a relationship between the diameter D and the size of the particles 115. For example, according to some embodiments, the length of the longest dimension L1 can be in the range of 0.05D to D (i.e., 0.05D < L1 < D). In particular, the length of the longest dimension L1 can be in the range of 0.1D to 0.8D (i.e., 0.1D < L1 < 0.8D). More particularly, L'1 can be in the range of 0.1D to 0.7D (i.e., 0.1D < L1 < 0.7D).

[0090] According to some embodiments, the length of another dimension L3 can also be limited by the length of the diameter D. For example, the length of another dimension L3 can be in the range of 0.05D to D (i.e., 0.05D < L3 < D). In particular, the length of another dimension L3 can be in the range of 0.1D to 0.8D (i.e., 0.1D < L3 < 0.8D). More particularly, L3 can be in the range of 0.1D to 0.7D (i.e., 0.1D < L3 < 0.7D).

[0091] At least some of the light-reflecting particles 115 can be rigid. The stiffness of the particles 115 can help to flatten the particles. The combination of stiffness and the flat surfaces of the particles can enable them to act as micro-mirrors.

[0092] At least some of the light-reflecting particles 115 may have a wavelength reflectance coefficient, causing them to exhibit wavelength-dependent reflectance behavior. In some embodiments, wavelength-dependent reflectance may be non-linear. For example, reflectance may be high in the blue visible light region and low in the green / yellow and red regions. This can further improve the color-angle performance of the LED filament. Furthermore, if the reflection of the light-reflecting particles varies with different wavelengths of light, the particles can provide a colored flickering effect.

[0093] Furthermore, at least some of the light-reflecting particles 115 may include multilayer mirrors. Alternatively or additionally, at least some of the light-reflecting particles 115 may include dichroic mirrors.

[0094] Return to reference Figure 1b At least some of the light-reflecting particles 115 may be randomly distributed and / or randomly oriented on the outer surface of the package. For example, the particles 115 may be arranged in at least three different orientations and without a regular pattern.

[0095] Alternatively, the particles can be uniformly distributed, concentrated in a specific area of ​​the outer surface of the package, or arranged in a specific pattern. However, random distribution and / or orientation allows the particles 115 to redirect light (not only from an external source but also emitted by LED 112) in a more arbitrary manner. In the OFF state, this can contribute to a more pleasing flickering appearance and therefore a more decorative look. In the ON state, random distribution and / or orientation can contribute to a more omnidirectional distribution of the emitted light and / or any light converted by wavelength-converting materials in the package. In applications including wavelength-converting materials, a more omnidirectional distribution of light can improve color as a function of angle (CoA) because different wavelengths of light can be distributed more evenly. A more random distribution of the emitted light can also give a softer light, where the contrast is less sharp, because the light can reach a new surface, be reflected by that new surface, and spread further. Softer light can provide better depth perception and less glare.

[0096] According to some embodiments, the coverage area of ​​at least a portion of the light-reflecting particles on the outer surface of the package portion can be limited to certain ranges. The coverage area (LED filament coverage area) of the particles 115 on the outer surface of the package portion 114 can be represented as C. C min It can be the minimum coverage area, and C max This can be the maximum coverage area. Too small a coverage area may result in a loss of flashing effect, while too large a coverage area may block the light emitted by the LED. The minimum LED filament coverage area can be C. min =3%. Specifically, the minimum LED filament coverage area can be C. min=5%. More specifically, the minimum LED filament coverage can be C. min =6%, such as, for example, 7% or 9%.

[0097] In some embodiments, at least a portion of the light-reflecting particles 115 may be opaque (i.e., non-transmissive). In such embodiments, the particles can provide very good reflective behavior, but may also block light emitted by the LED from escaping the package 114. In these embodiments, the maximum LED filament coverage may be less than C. max =40%. Specifically, the maximum LED filament coverage area can be less than C. max =30%. More specifically, the maximum LED filament coverage area can be less than C. max =25%, such as, for example, 12% or 15%.

[0098] In other embodiments, at least some of the light-reflecting particles 115 may be transmissive. The transmittance of the particles may be expressed as T. In some embodiments, the transmittance T is less than 40%. In these embodiments, some light will be allowed to pass through the particles 115, meaning a larger coverage area can be achieved without blocking the light emitted by the LED. For these embodiments, the LED filament coverage area may depend on the transmittance of the particles 115. However, the maximum coverage area should not be less than the minimum coverage area C. min =5%. For example, the maximum LED filament coverage can be described as:

[0099]

[0100] In some embodiments, at least some of the light-reflecting particles may include both opaque particles and transmissive particles.

[0101] refer to Figure 4 The lighting device 430 according to some embodiments will be described.

[0102] The lighting device 430 may include one or more LED filaments 110 according to any embodiment described above. The lighting device 430 may further include a at least partially light-transmitting housing 431 that at least partially surrounds one or more LED filaments 110. The housing 431 may have a pear-shaped shape, such as... Figure 4 As shown. However, it will be understood that the housing 431 can have any shape, such as spherical or tubular. Light emitted from or reflected by at least one LED filament 110 can be output through the housing 431.

[0103] Lighting device 430 may be included in, or constitute an LED bulb or retrofit lamp. Lighting device 430 may include a base 432 on which housing 43 may be mounted. Base 432 may further include an electrical connector 433 for connection to lighting fixture 540. Figure 5 The socket 541 (as shown) may be an example of an Edison thread, bayonet adapter, or any other type of connector known in the art for connecting lighting equipment to a lamp or illuminator, which may form part of the base.

[0104] refer to Figure 5 The illuminator 540 according to some embodiments will now be described.

[0105] Lighting fixture 540 may include a socket 541 that is compatible with electrical connector 433 of lighting device 430. Figure 4 (As shown) connection. Further, the illuminator may include a lighting device 430, which is connected to the illuminator socket 541 via its electrical connector 433.

[0106] As a non-limiting example of the LED filament 110 according to some embodiments, the substrate can be made of glass, for example. The substrate 111 can be 50 mm long, the substrate 110 can be 3 mm wide, and the substrate can be 1 mm thick.

[0107] The plurality of LEDs 115 mechanically attached to the substrate 111 can be, for example, forty (40) LEDs emitting blue light. The package 114 can package both the first and second main surfaces of the substrate 111, as well as the forty LEDs. The package may include wavelength conversion materials, such as yellow phosphors and red phosphors.

[0108] The diameter D, measured above the cross-section of the LED filament, can be 3 mm.

[0109] Multiple light-reflecting particles 115 may be based on polyethylene terephthalate (PET) with an aluminum layer. Particles 115 may have a hexagonal shape. The longest dimension L1 may be 250 μm, another dimension L3 may be 250 μm, and the shortest dimension L2 (thickness) may be 14 μm. The coverage area of ​​at least a portion of the light-reflecting particles 115 on the encapsulation may be 5%.

[0110] Those skilled in the art will recognize that the present invention is by no means limited to the preferred embodiments described above. Rather, many modifications and variations are possible within the scope of the appended claims.

[0111] Although the features and elements have been described above in specific combinations, each feature or element may be used alone without other features and elements, or in various combinations with or without other features and elements.

[0112] Additionally, by studying the accompanying drawings, the disclosure, and the appended claims, a person skilled in the art can understand and implement variations of the disclosed embodiments in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements, and the indefinite articles "a" or "an" do not exclude a plurality. The simple fact that certain features are recited in mutually different dependent claims does not imply that combinations of these features cannot be advantageously used.

Claims

1. A light emitting diode, LED, filament (110), comprising: an elongated substrate (111); a plurality of light emitting diodes, LEDs (112), mechanically coupled to the substrate; an at least partially light transmissive encapsulation (114) encapsulating the plurality of LEDs and at least partially encapsulating the substrate; and a plurality of at least partially light reflective particles (115) arranged on an outer surface of the encapsulation, wherein a particle of the at least partially light reflective particles (115) comprises: a first face (216) abutting the encapsulation; and a second face (217) opposite the first face, the second face facing away from the encapsulation, wherein a particle of the at least partially light reflective particles (115) has at least one flat surface and is characterized by a longest dimension length (LI), a shortest dimension length (L2), and a further dimension length (L3), and wherein a first aspect ratio AR1 = LI / L2 between the longest dimension length and the shortest dimension length is in a range of 10 to 300, wherein a second aspect ratio AR2 = L3 / L2 between the further dimension length and the shortest dimension length is in a range of 10 to 300, and wherein a third aspect ratio AR3 = LI / L3 between the longest dimension length and the further dimension length is in a range of 0.3 to 3.

2. The LED filament according to claim 1, wherein the longest dimension length (LI) is in a range of 0.1 mm to 3 mm, the further dimension length (L3) is in a range of 0.1 mm to 3 mm, and wherein the shortest dimension length (L2) is in a range of 10 pm to 300 pm.

3. The LED filament according to claim 1 or 2, wherein the LED filament has a diameter D, and wherein the longest dimension length LI is in a range of 0.1D to D.

4. The LED filament according to any one of the preceding claims, wherein the at least partially light reflective particles are rigid.

5. The LED filament according to any one of the preceding claims, wherein the at least partially light reflective particles are randomly distributed over the encapsulation, and / or wherein the at least partially light reflective particles are randomly oriented.

8. The LED filament according to any one of the preceding claims, wherein the at least partially light transmissive encapsulation comprises a wavelength conversion material.

9. The LED filament according to any one of the preceding claims, wherein a particle of the at least partially light reflective particles has a wavelength dependent reflectance.

6. The LED-filament of any of the preceding claims, wherein a minimum LED-filament coverage C min min is 3%, said minimum LED-filament coverage C min min denotes a minimum coverage of said at least partial light-reflective particles on said outer surface of said encapsulation.

7. The LED-filament according to any one of the preceding claims, wherein a maximum LED-filament coverage C max is C max = (T / 50) x 100, the maximum LED-filament coverage C max denotes a maximum coverage of the at least partially light-reflective particles on the outer surface of the encapsulation, wherein the at least partially light-reflective particles are transmissive and the transmissivity T of the at least partially light-reflective particles is less than 40%, or wherein the maximum LED-filament coverage C max is 30%, wherein the at least partially light-reflective particles are opaque.

10. The LED filament according to any one of the preceding claims, wherein a particle of the at least partially light reflective particles comprises a multilayer reflector or a dichroic mirror.

11. A lighting device (430), comprising: at least one LED filament (110) according to any one of the preceding claims; an at least partially light transmissive housing (431) at least partially enclosing the at least one LED filament; and an electrical driver (432) electrically coupled to the at least one LED filament. ​ a base (432) on which the at least partly light-transmissive envelope is mounted, the base comprising electrical connectors for connecting the lighting device to a luminaire socket (541).

12. A luminaire (540) comprising: a socket (541); and and the lighting device (430) of claim 11, the lighting device being connected to the socket.

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