EP4680886A1 - Led filament - Google Patents

Led filament

Info

Publication number
EP4680886A1
EP4680886A1 EP24709740.5A EP24709740A EP4680886A1 EP 4680886 A1 EP4680886 A1 EP 4680886A1 EP 24709740 A EP24709740 A EP 24709740A EP 4680886 A1 EP4680886 A1 EP 4680886A1
Authority
EP
European Patent Office
Prior art keywords
light
led filament
led
semi
reflecting mirror
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP24709740.5A
Other languages
German (de)
French (fr)
Inventor
Ties Van Bommel
Rifat Ata Mustafa Hikmet
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Signify Holding BV
Original Assignee
Signify Holding BV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Signify Holding BV filed Critical Signify Holding BV
Publication of EP4680886A1 publication Critical patent/EP4680886A1/en
Pending legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
    • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
    • F21K9/20—Light sources comprising attachment means
    • F21K9/23—Retrofit light sources for lighting devices with a single fitting for each light source, e.g. for substitution of incandescent lamps with bayonet or threaded fittings
    • F21K9/232—Retrofit light sources for lighting devices with a single fitting for each light source, e.g. for substitution of incandescent lamps with bayonet or threaded fittings specially adapted for generating an essentially omnidirectional light distribution, e.g. with a glass bulb
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V7/00—Reflectors for light sources
    • F21V7/04—Optical design
    • F21V7/043—Optical design with cylindrical surface
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V7/00—Reflectors for light sources
    • F21V7/22—Reflectors for light sources characterised by materials, surface treatments or coatings, e.g. dichroic reflectors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V9/00—Elements for modifying spectral properties, polarisation or intensity of the light emitted, e.g. filters
    • F21V9/20—Dichroic filters, i.e. devices operating on the principle of wave interference to pass specific ranges of wavelengths while cancelling others
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2103/00—Elongate light sources, e.g. fluorescent tubes
    • F21Y2103/10—Elongate light sources, e.g. fluorescent tubes comprising a linear array of point-like light-generating elements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2115/00—Light-generating elements of semiconductor light sources
    • F21Y2115/10—Light-emitting diodes [LED]
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/85—Packages
    • H10H20/851—Wavelength conversion means
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/85—Packages
    • H10H20/855—Optical field-shaping means, e.g. lenses
    • H10H20/856—Reflecting means
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
    • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
    • H10H20/80—Constructional details
    • H10H20/882—Scattering means
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
    • H10W90/00—Package configurations

Definitions

  • the present invention relates to a light emitting diode (LED) filament.
  • the present invention also relates to an LED filament lamp comprising at least one such LED filament.
  • An LED filament lamp is an LED lamp which is designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes, but with the high efficiency of lightemitting diodes.
  • US2022186889A1 discloses an LED filament, which comprises an elongated substrate and a plurality of LEDs mechanically coupled to the substrate.
  • the LED filament in US2022186889A1 further comprises an at least in part light-transmissive encapsulation which encapsulate the plurality of LEDs and at least partially encapsulates the substrate, and a plurality of at least partially light-reflective particles which are arranged on an outer surface of the encapsulation.
  • the at least partially light-reflective particles on the outer surface of the encapsulation may give the LED filament a sparkling appearance in the OFF-state (i.e.
  • the at least partially light reflective particles on the encapsulation surface may redirect light emitted by the LEDs in the ON-state (i.e. when the LEDs of the filament are turned on) at other angles. This redirection may lead to a more omnidirectional spreading of the emitted light, which may in turn give the light a softer appearance, and lessen the sharp contrast often caused by conventional LED filaments.
  • a light emitting diode (LED) filament providing LED filament light
  • the LED filament comprising: an LED filament arrangement comprising a plurality of LEDs adapted to emit LED light arranged on a first major surface of an elongated carrier and a first encapsulant at least partly enclosing said plurality of LEDs and at least partly covering the first major surface of said elongated carrier, said first encapsulant comprising at least one of a light scattering material adapted to scatter at least part of said LED light into scattered light and a light converting material adapted to convert at least part of said LED light into converted light for providing LED filament arrangement light comprising said scattered light and/or said converted light and optionally said LED light; and a semi-reflective specular-reflecting mirror (fully) enclosing said LED filament arrangement, wherein said semi-reflective specular-reflecting
  • the LED filament arrangement is here construed as being a subset of the LED filament. Furthermore, ‘specular-reflecting’ should be construed as providing mirror-like reflection of light, as opposed e.g. to diffuse reflection. Furthermore, said transmitted LED filament arrangement light may form (at least part of) said LED filament light.
  • the present invention is at least partly based on the understanding that by enclosing the LED filament arrangement with a semi-reflective specular-reflecting mirror, which LED filament arrangement could correspond to a conventional LED filament, a nice LED filament providing a decorative light effect may be provided. Furthermore, the semi- reflective specular-reflecting mirror may beneficially hide the usually yellow/orange color of the underlying LED filament arrangement. In other words, the LED filament arrangement, which as mentioned above may correspond to a conventional LED filament, may be hidden by the semi-reflective specular-reflecting mirror.
  • Said LED filament arrangement light may be white light.
  • the plurality of LEDs may for example be blue LEDs, and the light converting material may comprise phosphor e.g. a green-yellow phosphor (converting part of the blue LED light into green-yellow converted light) and a red phosphor (converting part of the blue LED light into red converted light).
  • This white light may have a first correlated color temperature (CCT1) in a range from 1500K to 6500K (preferably in a range from 1600K to 3000K, more preferably in a range from 1700K to 2700K, most preferably in a range from 1800 to 2500K) and a first color rendering index (CRI1) of at least 80.
  • CCT1 first correlated color temperature
  • the obtained effect is improved transmitted LED filament arrangement light. The reason is by starting with a high quality of light, also the transmitted light has likely a higher quality although part of the spectrum is reflected.
  • the provided LED filament light may have a second color rendering index (CRI2),
  • the reflectivity of the semi-reflective specular-reflecting mirror may be > 30%, and/or the transmissivity of the semi-reflective specular-reflecting mirror may be > 30 %.
  • the reflectivity and transmissivity may be an averaged reflectivity and transmission over the visible wavelength range from 400 nm to 800 nm.
  • the reflectivity of > 30%, in particular > 40%, is needed for a nice appearance and/or decorative light.
  • the transmissivity of > 30 %, in particular > 40 %, is needed to have a good efficiency. Too much reflection will result in too much light loss.
  • the absorption of the semi-reflective specular-reflecting mirror may be less than 10%, preferably less than 5%, more preferably less than 3%, most preferably less than 2% such as for example 1% or 0%.
  • the semi-reflective specular-reflecting mirror may have a constant reflectivity of light, with respect to wavelength, over the wavelength range of from 400 nm to 800 nm. That is, the semi-reflective specular-reflecting mirror reflects the LED filament arrangement light in the same way regardless of the color/wavelength of the LED filament arrangement light. In this way, a relatively simple/inexpensive semi-reflective specular-reflecting mirror may be used, while still being able to hide the usually yellow/orange underlying LED filament arrangement. When the semi-reflective specular-reflecting mirror has this constant reflectivity, the LED filament may have a silver appearance (when OFF).
  • the semi-reflective specular-reflecting mirror has a non-constant reflectivity of light and a non-constant transmissivity (T) of light, with respect to wavelength, over a wavelength range of from 400 nm to 800 nm.
  • T non-constant transmissivity
  • the semi-reflective specular-reflecting mirror has a reflectivity of at least 70% (and preferably ⁇ 95%, i.e. 70 ⁇ R% ⁇ 95), wherein for one or more further sub wavelength ranges in the wavelength range of from 400 nm to 800 nm the semi-reflective specular-reflecting mirror has a transmissivity of at least 70%.
  • the semi-reflective specular-reflecting mirror may be configured to: (i) dominantly reflect blue light by having a reflectivity R of at least 70% in the blue wavelength range and dominantly transmit green and red light by having a transmissivity T of at least 70% in the green and red wavelength ranges; or (ii) dominantly reflect green light by having a reflectivity R of at least 70% in the green wavelength range and dominantly transmit blue and red light by having a transmissivity T of at least 70% in the blue and red wavelength ranges; or (iii) dominantly reflect light by having a reflectivity R of at least 70% in the red wavelength range and dominantly transmit blue and green light by having a transmissivity T of at least 70% in the blue and green wavelength ranges.
  • the semi-reflective specular-reflecting mirror may be configured to dominantly reflect light in a blue wavelength range such that LED light which is initially not converted by said light converting material is reflected back to said first encapsulant comprising said light converting material, whereby at least a portion of said LED light which was initially not converted by said light converting material is after reflection by the semi- reflective specular-reflecting mirror being converted by said light converting material, such that said LED filament light is white light having a second correlated color temperature (CCT2) lower than the first correlated color temperature CCT1 of the white LED filament arrangement light.
  • CCT2 second correlated color temperature
  • the lower CCT2 may for example be achieved as reflected blue LED light is absorbed by green phosphor light converting material in the first encapsulant to produce more green light and/or is absorbed by red phosphor light converting material in the first encapsulant to produce more red light.
  • CCT2 CCTl-500K.
  • the LED filament could alternatively have a thinner (first) encapsulant comprising light converting material while (substantially) maintaining the “original” correlated color temperature CCT1.
  • the LED filament will appear blue when OFF.
  • the semi-reflective specular-reflecting mirror is configured to dominantly reflect blue light, more red light may be generated by the light conversion material, which in turn may increase the CRI of the LED filament light (CRI2>CRI1).
  • the semi-reflective specular-reflecting mirror may be configured to dominantly reflect light in a green wavelength range (but transmit blue and red light) such that, when this LED filament is ON, at least part of converted light is reflected back to said first encapsulant comprising said first light converting material, whereby at least a portion of said converted light is after reflection by the semi-reflective specular-reflecting mirror being re-converted by said light converting material into reconverted light having a peak wavelength higher than the peak wavelength of said converted light, which in turn can result in white LED filament light with a correlated color temperature CCT3 different than CCT1.
  • This embodiment may also provide an environmental friendly color of the LED filament when OFF (i.e. when the plurality of LEDs are not emitting the LED light).
  • the semi-reflective specular-reflecting mirror may alternatively be configured to dominantly reflect red light, to provide a flame glowing effect of the LED filament when OFF. Furthermore, when this LED filament is ON, the semi-reflective specular-reflecting mirror will reflect red phosphor (light converting material) light which typically not will be (re)absorbed, hence not affecting the correlated color temperature of white LED filament light.
  • the semi-reflective specular-reflecting mirror is preferably (at least) partially transmissive for blue, green, and red, to make it possible to provide white LED filament light.
  • the semi-reflective specular-reflecting mirror (having the non-constant reflectivity of light) is a dichroic mirror.
  • the dichroic mirror may selectively reflect light of a (small/limited) range of colors/wavelengths while transmitting other colors/wavelengths.
  • the semi-reflective specular-reflecting mirror (having the non-constant reflectivity of light) is a cholesteric mirror.
  • cholesteric mirrors per se, please see Gao, Y.; Luo, Y.; Lu, J. High-Reflective Templated Cholesteric Liquid Crystal Filters. Molecules 2021, 26, 6889. https://doi.org/10.3390/molecules26226889, the contents of which herein/hereby is incorporated by reference.
  • the semi-reflective specular-reflecting mirror (having the non-constant reflectivity of light depending on wavelength of the light) may have a color-variable reflection over its length.
  • the LED filament may show different colors along its length when OFF, and there may also be different light colors (CCTs) along the length of the LED filament when ON.
  • the semi-reflective specular-reflecting mirror may for example have different regions with different color reflections along its length. The different regions may be discrete (stepped), or there can be a gradual transition between different color reflections (i.e. gradual change in color-variable reflection over the length of the filament). Also, the different regions could have the same or different lengths.
  • the different regions may for example include at least a first region with a first color reflection (e.g. dominantly reflecting blue light), a second region with a second, different color reflection (e.g. dominantly reflecting red light), and optionally a third region with third, different color reflection (e.g. dominantly reflecting green light).
  • a first color reflection e.g. dominantly reflecting blue light
  • a second region with a second, different color reflection e.g. dominantly reflecting red light
  • a third region with third, different color reflection e.g. dominantly reflecting green light.
  • the semi-reflective specular- reflecting mirror having a color-variable reflection over its length is a cholesteric mirror
  • the color-variable reflection of the cholesteric mirror can be tuned by the pitch of the molecular structure of the cholesteric mirror.
  • the semi-reflective specular-reflecting mirror may be flexible and/or arranged in a curved configuration around said LED filament arrangement, as seen in a cross-section of the LED filament perpendicular to the longitudinal axis of the LED filament.
  • the semi-reflective specular-reflecting mirror could be arranged in polygonal (e.g. rectangular) configuration around said LED filament arrangement, for example.
  • the LED filament arrangement may have a spiral or helix shape, wherein said semi-reflective specular-reflecting mirror has a corresponding spiral or helix shape, resulting in that the LED filament (overall) has a spiral or helix shape or configuration.
  • said LED filament arrangement has a linear (straight) shape, and wherein said semi-reflective specular-reflecting mirror has a cylindrical shape, e.g. a right circular or elliptical cylinder, resulting in that the LED filament (overall) has a liner/ straight shape or configuration.
  • the semi-reflective specular-reflecting mirror may be continuous and/or extend along (substantially) the complete length of the LED filament arrangement. In this way, the complete LED filament arrangement may be hidden by the semi-reflective specular- reflecting mirror, and the light effect provided by the semi-reflective specular-reflecting mirror may be provided all throughout the LED filament.
  • the semi-reflective specular-reflecting mirror may be in (physical/mechanical) contact with said encapsulant. This at least provides to a slim LED filament.
  • the semi-reflective specular-reflecting mirror may be arranged at a distance (e.g. ⁇ 7mm or ⁇ 3 mm) to said encapsulant, for example using an air gap or a transparent further encapsulant e.g. of silicone.
  • the transparent further encapsulant may for example be a silicone glue fixing the semi-reflective specular-reflecting mirror to (the outside of) the encapsulant of the LED filament arrangement.
  • the semi-reflective specular-reflecting mirror may be arranged on a foil, e.g. a sheet with a blue (or red or green) dichroic layer.
  • a foil e.g. a sheet with a blue (or red or green) dichroic layer.
  • an LED filament lamp comprising at least one light emitting diode filament (LED) according to the first aspect.
  • the LED filament lamp may for example comprise a single LED filament or dual LED filaments, typically but not necessarily in spiral or helix configuration.
  • the LED filament lamp may alternatively comprise multiple LED filaments (e.g. 2-8 LED filaments), typically in linear or straight configuration.
  • the LED filament lamp may further comprise an envelope inside which the at least one light emitting diode filament is arranged, and a cap (comprising a base) for electrically and mechanically connecting the LED filament lamp to an external socket, in particular a socket of a luminaire.
  • the envelope is preferable a light transmissive envelope.
  • the light transmissive envelope may for example be made of glass.
  • the light transmissive envelope may have various shapes, including bulb, candle, globe, etc.
  • the cap or base may for example be E14, E27, B22, etc.
  • the LED filament lamp may for example be a (retrofit) light bulb.
  • Fig. l is a schematic cross-sectional view of an LED filament according to one or more embodiments of the present invention.
  • Fig. 2 is a schematic side view of the LED filament of fig. 1.
  • Fig. 3 is a schematic side view of an LED filament arrangement of the LED filament of figs. 1-2.
  • Fig. 4 is a diagram of constant reflectivity of light.
  • Figs. 5a-c are diagrams of non-constant reflectivity of light.
  • Fig. 6 is a (CIE 1931) color space with various correlated color temperatures.
  • Figs. 7a-b are schematic cross-sectional view of an LED filament according to different embodiments.
  • Fig. 8a-b are side views of embodiments of the present LED filament, wherein the semi-reflective specular-reflecting mirror has a color-variable reflection over its length.
  • Figs. 9a-d are views of various LED filament lamps according to an aspect of the present invention. As illustrated in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.
  • Figs. 1-2 illustrate an LED filament 10 adapted to provide LED filament light 12 according to one or more embodiments of the present invention.
  • fig. 1 illustrates a cross-section of the LED filament 10 in a plane perpendicular to a longitudinal axis 14 of the LED filament 10, e.g. section A-A in fig. 2.
  • the LED filament 10 has a length L and a width W, wherein L>5W.
  • the width W may for example be in a range from 0.5 to 5 mm.
  • the LED filament 10 may be arranged in a straight configuration (as in figs. 2 and 9a) or in a non-straight configuration such as for example a curved configuration, a 2D/3D spiral or a helix (as in figs. 9b-c).
  • the LED filament 10 comprises an LED filament arrangement 16, shown separately in fig. 3.
  • the LED filament arrangement 16 should here be construed as being a subset of the LED filament 10. Consistent with the overall configuration of the LED filament 10, the LED filament arrangement 16 may have a linear (straight) shape, as in fig. 3, or a spiral or helix shape.
  • the LED filament arrangement 16 includes an elongated carrier 18.
  • the elongated carrier 18 may have substantially the same length and width as the LED filament 10.
  • the elongated carrier 18 may for example be a substrate, such as a printed circuit board (PCB).
  • the elongated carrier 18 may be rigid (made from e.g. a polymer, glass, quartz, metal or sapphire) or flexible (e.g. made of a polymer or metal e.g. a film or foil).
  • the elongated carrier 18 comprises a first major surface 20a and an opposite second major surface 20b.
  • the carrier 18 may be reflective or light transmissive, such as translucent and preferably transparent.
  • the LED filament arrangement 16 further includes a plurality of light emitting diodes (LEDs) 22 arranged on the elongated carrier 16.
  • the plurality of LEDs 22 may be arranged on at least the first major surface 20a of the elongated carrier 18.
  • the plurality of LEDs 22 will typically be arranged in a linear array.
  • the plurality of LEDs 22 are adapted to emit LED light 24. That is, when the plurality of LEDs 22 are ON, they emit the LED light 24.
  • the plurality of LEDs 22 may for example be blue LEDs adapted to emit blue LED light 24.
  • the plurality of LEDs 22 may be or include red, green, and blue LEDs adapted to emit red, green, and blue LED light, respectively, wherein the red, green, and blue LED light together may form white light.
  • the number of LEDs 22 may for example be at least 10, preferably at least 15, more preferably at least 20, most preferably at least 25 such as 30 or 40 LEDs.
  • the LED filament arrangement 16 further includes an encapsulant 26a (at least partly) enclosing the plurality of LEDs 22 and (at least partly) covering the first major surface 22a of the elongated carrier 18.
  • the encapsulant 26a may be elongated, like the elongated carrier 18.
  • the encapsulant 26a comprises at least one of a light scattering material adapted to scatter at least part the said LED light 24 into scattered light and a light converting material adapted to convert at least part of said LED light 24 into converted light 28 for providing LED filament arrangement light 30 comprising said scattered light and/or said converted light 28 and optionally the LED light 24.
  • the light scattering material may for example be light scattering particles, such as for example BaS04, Ti02, and/or AI2O3.
  • the light converting material may be a luminescent material, for example phosphor such as an inorganic phosphor and/or quantum dots or rods.
  • the light converting material may include one or more of green phosphor, green-yellow phosphor, and red phosphor.
  • the encapsulant 26a can be made of a polymer material which may be flexible such as for example a silicone.
  • the LED filament arrangement light 30 will typically be white light, which for example may be realized by using the blue LEDs adapted to emit blue LED light 24 and the light converting material being phosphor.
  • This white LED filament arrangement light 30 may have a first correlated color temperature CCT1 in a range from 1500K to 6500K and a first color rendering index of at least 80.
  • the LED filament arrangement 16 may further include a second encapsulant 26b at least partly covering the second major surface 20b of the elongated carrier 18, in which case the aforementioned encapsulant 26a may be referred to as first encapsulant 26a.
  • the second encapsulant 26b may as well comprise at least one of a light scattering material and a light converting material.
  • the cross-section of the LED filament arrangement 16 with the first encapsulant 26a and the (optional) second encapsulant 26b as seen in fig. 1 may for example have circular or elliptical outer profile.
  • the LED filament 10 further comprises a semi-reflective specular-reflecting mirror 32 enclosing the LED filament arrangement 16.
  • the semi-reflective specular-reflecting mirror 32 configured to partly reflect the LED filament arrangement light 30 into reflected LED filament arrangement light 34, and to partly transmit the LED filament arrangement light 30 into transmitted LED filament arrangement light 36.
  • the transmitted LED filament arrangement light 36 may form (at least part of) the aforementioned LED filament light 12, whereas the reflected LED filament arrangement light 34 could be (re)absorbed by the light converting material.
  • the semi-reflective specular-reflecting mirror 32 By means of the semi-reflective specular-reflecting mirror 32 enclosing the LED filament arrangement 16, an LED filament 10 providing a decorative light effect may be realized, as will be exemplified hereinbelow. Furthermore, the semi-reflective specular- reflecting mirror 32 may beneficially hide the usually yellow/orange color of the underlying LED filament arrangement 16 (when the LEDs 22 are OFF). In other words, the LED filament arrangement 16, which could correspond to a conventional LED filament, may be hidden by the semi-reflective specular-reflecting mirror 32.
  • the semi-reflective specular-reflecting mirror 32 should fully encloses the LED filament arrangement 16, both in the circumferential direction (see fig. 1) and in the longitudinal direction (see fig. 2). To this end, the semi-reflective specular-reflecting mirror 32 may be continuous and arranged (e.g. in a curved configuration) around the complete outer profile of the LED filament arrangement 16 (fig. 1), and also extend along the complete length L’ of the LED filament arrangement 16 (fig. 2).
  • the semi-reflective specular-reflecting mirror 32 may have a corresponding cylindrical shape, e.g. a right circular or elliptical cylinder, as in figs. 1-2.
  • the semi-reflective specular-reflecting mirror 32 may have a corresponding spiral or helix shape, resulting in that the LED filament 10 (overall) has a spiral or helix shape or configuration, as in figs. 9b-c.
  • the semi-reflective specular-reflecting mirror 32 may be in direct contact with the encapsulant 26a and the optional second encapsulant 26b by using e.g. a glue.
  • the semi-reflective specular-reflecting mirror 32 may be arranged at a distance D to the encapsulant 26a and the optional second encapsulant 26b, for example using an air gap or a transparent further encapsulant 38 e.g. of silicone.
  • the air gap may be realized by using a holder (not shown). The holder may be attached e.g. to part of the electrodes at the ends of a LED filament 10.
  • the transparent further encapsulant 38 may for example be a silicone glue fixing the semi-reflective specular-reflecting mirror 32 to the encapsulant 26a and the optional second encapsulant 26b.
  • the distance D is preferably ⁇ 3 mm.
  • the thickness of the semi-reflective specular-reflecting mirror 32 may be in the range of 0.05-2 mm, typically 0.2 mm, whereby LED filament 10 may maintain a typical, slim appearance.
  • the reflectivity R of the semi-reflective specular-reflecting mirror 32 may be R> 30%, in particular R> 40%.
  • the transmissivity T of the semi-reflective specular-reflecting mirror 32 may be T> 30 %, in particular T> 40%.
  • the reflectivity R and transmissivity T may be an averaged reflectivity and transmission over the visible wavelength range from 400 nm to 800 nm.
  • the absorption of the semi-reflective specular-reflecting mirror 32 may be less than 10%, preferably less than 5%, more preferably less than 3%, most preferably less than 2% such as for example 1% or 0%.
  • the semi-reflective specular-reflecting mirror 32 may have a constant* reflectivity of light over the wavelength range of from 400 nm to 800 nm (*with respect to wavelength, here of the LED filament arrangement light 30 and/or of ambient light). This is exemplarily illustrated in fig. 4, wherein reflectivity R is on the vertical axis and wavelength is on the horizontal axis.
  • the semi-reflective specular-reflecting mirror 32 may have a non-constant reflectivity of light (and a non-constant transmissivity (T) of light), with respect to the light’s wavelength, over the wavelength range of from 400 nm to 800 nm, as exemplarily illustrated in figs. 5a-c.
  • T non-constant transmissivity
  • the semi- reflective specular-reflecting mirror 32 may have a reflectivity of at least 70%, wherein for further/other sub wavelength ranges (green and red ) the semi-reflective specular-reflecting mirror has a transmissivity of at least 70%, as in fig. 5a.
  • the semi-reflective specular-reflecting mirror has a transmissivity of at least 70%, as in fig. 5a.
  • the semi-reflective specular-reflecting mirror 32 is configured to dominantly reflect blue light, i.e. dominantly reflect light in a blue wavelength range.
  • the semi-reflective specular-reflecting mirror 32 having the non-constant reflectivity of light may for example be a dichroic mirror.
  • the LED light 24 is blue
  • the LED filament arrangement light 30 is white light with the first correlated color temperature CCT1
  • the semi- reflective specular-reflecting/dichroic mirror 32 is configured to dominantly reflect blue light (while transmitting other colors/wavelengths, see fig. 5a), such that the LED filament light 12 is white light having a second correlated color temperature CCT2 lower than CCT1.
  • CCT2 CCTl-500K, see fig. 6.
  • the lower CCT2 can be achieved as blue LED light 24’ initially not converted by the light converting material is reflected back by the mirror 32 as reflected blue LED light 42, which reflected blue LED light 42 is absorbed by green phosphor light converting material in the first encapsulant 26a and in the optional encapsulant 26b to produce more green light 28 and by red phosphor light converting material in the first encapsulant and in the optional encapsulant 26b to produce more red light 28, see fig. 7a. Also when the semi-reflective specular-reflecting mirror 32 is configured to dominantly reflect blue light, the LED filament 10 will appear blue when in OFF state.
  • the semi-reflective specular-reflecting/dichroic mirror 32 is configured to dominantly reflect green light (see fig. 5b), to give the LED filament 10 an environmental friendly color (more green) when the LED filament 10 is OFF. Furthermore, when this LED filament 10 is ON, the semi-reflective specular-reflecting mirror 32 may reflect green phosphor (light converting material) light 44 (see fig. 7b) back to the first encapsulant 26a and/or the optional encapsulant 26b, whereby at least a portion of this light 44 is reconverted by the light converting material (e.g. green phosphor) in the first encapsulant 26a and/or the optional encapsulant 26b into reconverted light 28’.
  • the reconverted light 28’ may have a peak wavelength higher than the peak wavelength of the converted light 28, which in turn can result in white LED filament light 12 with a correlated color temperature CCT3 different than CCT1, see fig. 6.
  • the semi-reflective specular-reflecting/dichroic mirror 32 is configured to dominantly reflect red light (see fig. 5c), to give the LED filament 10 a flame glowing effect (more red) when the LED filament 10 is OFF. Furthermore, when this LED filament 10 is ON, the semi -reflective specular-reflecting mirror 32 will reflect red phosphor (light converting material) light which typically not will be (re)absorbed, hence not affecting the correlated color temperature of white LED filament light 12.
  • the semi-reflective specular-reflecting mirror 32 having the non-constant reflectivity may have a color-variable reflection over its length L”.
  • This mirror 32 may for example be a dichroic mirror or a cholesteric mirror.
  • the semi-reflective specular-reflecting mirror 32 has a first region 40a towards one end of the LED filament 10, a second region 40c towards the opposite end of the LED filament, and a third, intermediate region 40b between the first region 40a and the second region 40c.
  • the first region may for example be configured to dominantly reflect blue light
  • the second region 40c may be configured to dominantly reflect green light
  • the third region 40c may be configured to dominantly reflect red light.
  • the regions 40a-c in fig. 8a are discrete and have equal length. An observer will here see different colored effects on the LED filament 10 in the OFF state. And the observer may as well see differences in light colors (temperatures) in the ON state, at least in the near field.
  • the semi-reflective specular-reflecting mirror 32 is configured to dominantly reflect light of a first color at one end 46a of the LED filament 10, and is further configured to dominantly reflect light of a second color (different than the first color) at the opposite end 46b of the LED filament 10, with a gradual transition therebetween.
  • Figs. 9a-d are views of various LED filament lamps lOOa-d, each comprising at least one LED filament 10.
  • Fig. 9a is a perspective view
  • figs. 9b-d are side views.
  • the LED filament lamp 100a comprises multiple LED filaments 10, namely four LED filaments 10.
  • Each LED filaments 10 here has a linear or straight configuration.
  • the LED filaments 10 may be substantially vertically arranged, as seen in the view of fig. 4a.
  • the LED filaments 10 may be substantially parallel to each other.
  • the LED filaments 10 could have semi-reflective specular-reflecting mirrors 32 with the same or different reflective properties.
  • the semi -reflective specular-reflecting mirrors 32 of all the LED filaments 10 could for example be configured to dominantly reflect green light, so that they look green when OFF.
  • each LED filament lamp lOOb-c comprises only one LED filament 10.
  • the LED filament 10 here has a spiral or helix configuration.
  • the LED filament 10 may be substantially vertically arranged, as seen in the view of figs. 9b-c.
  • the semi-reflective specular-reflecting mirror 32 of the LED filament 10 in fig. 9b may for example be a dichroic mirror configured to dominantly reflect blue light.
  • the LED filament 10 in fig. 9b may look (more) blue when OFF, due to blue color in ambient light being reflected by the dichroic mirror 32, and also provide warmer/less cool (e.g. CCT2) white LED filament light 12 when ON, as discussed above.
  • CCT2 warmer/less cool
  • the semi-reflective specular-reflecting mirror 32 of the LED filament 10 in fig. 9c has color-variable reflection over its length L”.
  • the mirror 32 may for example have a blue lower region 40a (closer/proximal to cap 104) gradually transitioning to a top yellow region 40d (further from/distal of cap 104).
  • the LED filament lamp lOOd comprises only one LED filament 10 having a linear/ straight configuration.
  • the semi-reflective specular-reflecting mirror 32 of the LED filament 10 in fig. 9d has a color-variable reflection over its length L”, here with blue, red, and green regions 40a-c arranged in triplets after one another.
  • Each LED filament lamp lOOa-d may further comprise a light transmissive envelope 102 inside which the at least one LED filament 10 is arranged, and a cap (comprising a base) 104 for electrically and mechanically connecting the LED filament lamp lOOa-d to a socket of a luminaire (not shown).
  • the light transmissive envelope 102 may for example be made of glass.
  • the light transmissive envelope 102 may have various shapes, including bulb, candle, globe, etc.
  • the cap or base 104 may for example be E14, E27, B22, etc.
  • the LED filament lamp lOOa-d may for example be a (retrofit) light bulb.
  • the semi-reflective specular-reflecting mirror 32 may be arranged on a foil, e.g. a sheet with a blue (or red or green) dichroic layer.
  • the dichroic layer may be on the outer side, facing away from the first encapsulant 26a and optional second encapsulant 26b.
  • An advantage of having the dichroic layer on the outer side is less mechanical stress in the dichroic layer.
  • the dichroic layer may be on the inner side, facing the first encapsulant 26a and optional second encapsulant 26b.
  • An advantage of having the dichroic layer on the inner side is that the dichroic layer is better protected, e.g. against scratches.

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Abstract

The present invention relates to an LED filament (10), the comprising: an LED filament arrangement (16) comprising a plurality of LEDs (22) adapted to emit LED light (24) arranged on a first major surface (20a) of an elongated carrier (18) and a first encapsulant (26a) at least partly enclosing said LEDs and at least partly covering said first major surface (20a), said first encapsulant comprising at least one of a light scattering material adapted to scatter at least part of said LED light into scattered light and a light converting material adapted to convert at least part of said LED light into converted light (28) for providing LED filament arrangement light (30) comprising said scattered light and/or said converted light and optionally said LED light; and a semi-reflective specular-reflecting mirror (32) enclosing said LED filament arrangement, wherein said mirror has a reflectivity (R) configured to partly reflect said LED filament arrangement light into reflected LED filament arrangement light (34), and a transmissivity, T, configured to partly transmit said LED filament arrangement light into transmitted LED filament arrangement light (36).

Description

LED filament
FIELD OF THE INVENTION
The present invention relates to a light emitting diode (LED) filament. The present invention also relates to an LED filament lamp comprising at least one such LED filament.
BACKGROUND OF THE INVENTION
A trend in lighting is LED filament lamps. An LED filament lamp is an LED lamp which is designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes, but with the high efficiency of lightemitting diodes.
US2022186889A1 discloses an LED filament, which comprises an elongated substrate and a plurality of LEDs mechanically coupled to the substrate. The LED filament in US2022186889A1 further comprises an at least in part light-transmissive encapsulation which encapsulate the plurality of LEDs and at least partially encapsulates the substrate, and a plurality of at least partially light-reflective particles which are arranged on an outer surface of the encapsulation. According to US2022186889A1, the at least partially light-reflective particles on the outer surface of the encapsulation may give the LED filament a sparkling appearance in the OFF-state (i.e. when the LEDs of the filament are not turned on) by reflecting environmental light (outside light, surrounding light, i.e. light from other sources) in various directions. This sparkling appearance may increase the decorative character of the LED filament. Further, the at least partially light reflective particles on the encapsulation surface may redirect light emitted by the LEDs in the ON-state (i.e. when the LEDs of the filament are turned on) at other angles. This redirection may lead to a more omnidirectional spreading of the emitted light, which may in turn give the light a softer appearance, and lessen the sharp contrast often caused by conventional LED filaments.
SUMMARY OF THE INVENTION
It is an object of the present invention to improve the performance, functionality and/or appearance of LED filaments. According to a first aspect of the invention, this and other objects are achieved by a light emitting diode (LED) filament providing LED filament light, the LED filament comprising: an LED filament arrangement comprising a plurality of LEDs adapted to emit LED light arranged on a first major surface of an elongated carrier and a first encapsulant at least partly enclosing said plurality of LEDs and at least partly covering the first major surface of said elongated carrier, said first encapsulant comprising at least one of a light scattering material adapted to scatter at least part of said LED light into scattered light and a light converting material adapted to convert at least part of said LED light into converted light for providing LED filament arrangement light comprising said scattered light and/or said converted light and optionally said LED light; and a semi-reflective specular-reflecting mirror (fully) enclosing said LED filament arrangement, wherein said semi-reflective specular-reflecting mirror has a reflectivity (R) configured to partly reflect said LED filament arrangement light provided by said LED filament arrangement into reflected LED filament arrangement light, and a transmissivity (T) configured to partly transmit said LED filament arrangement light provided by said LED filament arrangement into transmitted LED filament arrangement light.
The LED filament arrangement is here construed as being a subset of the LED filament. Furthermore, ‘specular-reflecting’ should be construed as providing mirror-like reflection of light, as opposed e.g. to diffuse reflection. Furthermore, said transmitted LED filament arrangement light may form (at least part of) said LED filament light.
The present invention is at least partly based on the understanding that by enclosing the LED filament arrangement with a semi-reflective specular-reflecting mirror, which LED filament arrangement could correspond to a conventional LED filament, a nice LED filament providing a decorative light effect may be provided. Furthermore, the semi- reflective specular-reflecting mirror may beneficially hide the usually yellow/orange color of the underlying LED filament arrangement. In other words, the LED filament arrangement, which as mentioned above may correspond to a conventional LED filament, may be hidden by the semi-reflective specular-reflecting mirror.
Said LED filament arrangement light may be white light. To this end, the plurality of LEDs may for example be blue LEDs, and the light converting material may comprise phosphor e.g. a green-yellow phosphor (converting part of the blue LED light into green-yellow converted light) and a red phosphor (converting part of the blue LED light into red converted light). This white light may have a first correlated color temperature (CCT1) in a range from 1500K to 6500K (preferably in a range from 1600K to 3000K, more preferably in a range from 1700K to 2700K, most preferably in a range from 1800 to 2500K) and a first color rendering index (CRI1) of at least 80. The obtained effect is improved transmitted LED filament arrangement light. The reason is by starting with a high quality of light, also the transmitted light has likely a higher quality although part of the spectrum is reflected. The provided LED filament light may have a second color rendering index (CRI2), which may be higher than CRIl.
The reflectivity of the semi-reflective specular-reflecting mirror may be > 30%, and/or the transmissivity of the semi-reflective specular-reflecting mirror may be > 30 %. The reflectivity and transmissivity may be an averaged reflectivity and transmission over the visible wavelength range from 400 nm to 800 nm. The reflectivity of > 30%, in particular > 40%, is needed for a nice appearance and/or decorative light. The transmissivity of > 30 %, in particular > 40 %, is needed to have a good efficiency. Too much reflection will result in too much light loss. Furthermore, the absorption of the semi-reflective specular-reflecting mirror may be less than 10%, preferably less than 5%, more preferably less than 3%, most preferably less than 2% such as for example 1% or 0%.
The semi-reflective specular-reflecting mirror may have a constant reflectivity of light, with respect to wavelength, over the wavelength range of from 400 nm to 800 nm. That is, the semi-reflective specular-reflecting mirror reflects the LED filament arrangement light in the same way regardless of the color/wavelength of the LED filament arrangement light. In this way, a relatively simple/inexpensive semi-reflective specular-reflecting mirror may be used, while still being able to hide the usually yellow/orange underlying LED filament arrangement. When the semi-reflective specular-reflecting mirror has this constant reflectivity, the LED filament may have a silver appearance (when OFF).
Alternatively, the semi-reflective specular-reflecting mirror has a non-constant reflectivity of light and a non-constant transmissivity (T) of light, with respect to wavelength, over a wavelength range of from 400 nm to 800 nm. In this way, various optical effects may be achieved. Preferably, for one or more sub wavelength ranges in the wavelength range of from 400 nm to 800 nm the semi-reflective specular-reflecting mirror has a reflectivity of at least 70% (and preferably < 95%, i.e. 70<R%< 95), wherein for one or more further sub wavelength ranges in the wavelength range of from 400 nm to 800 nm the semi-reflective specular-reflecting mirror has a transmissivity of at least 70%.
The semi-reflective specular-reflecting mirror may be configured to: (i) dominantly reflect blue light by having a reflectivity R of at least 70% in the blue wavelength range and dominantly transmit green and red light by having a transmissivity T of at least 70% in the green and red wavelength ranges; or (ii) dominantly reflect green light by having a reflectivity R of at least 70% in the green wavelength range and dominantly transmit blue and red light by having a transmissivity T of at least 70% in the blue and red wavelength ranges; or (iii) dominantly reflect light by having a reflectivity R of at least 70% in the red wavelength range and dominantly transmit blue and green light by having a transmissivity T of at least 70% in the blue and green wavelength ranges.
In an embodiment wherein said LED filament arrangement light is white light having the first correlated color temperature CCT1 and wherein said first encapsulant comprises the light converting material adapted to convert at least part of said LED light into converted light, the semi-reflective specular-reflecting mirror may be configured to dominantly reflect light in a blue wavelength range such that LED light which is initially not converted by said light converting material is reflected back to said first encapsulant comprising said light converting material, whereby at least a portion of said LED light which was initially not converted by said light converting material is after reflection by the semi- reflective specular-reflecting mirror being converted by said light converting material, such that said LED filament light is white light having a second correlated color temperature (CCT2) lower than the first correlated color temperature CCT1 of the white LED filament arrangement light. The lower CCT2 may for example be achieved as reflected blue LED light is absorbed by green phosphor light converting material in the first encapsulant to produce more green light and/or is absorbed by red phosphor light converting material in the first encapsulant to produce more red light. For example, CCT2=CCTl-500K.
Also when the semi-reflective specular-reflecting mirror is configured to dominantly reflect blue light, the LED filament could alternatively have a thinner (first) encapsulant comprising light converting material while (substantially) maintaining the “original” correlated color temperature CCT1.
Also when the semi-reflective specular-reflecting mirror is configured to dominantly reflect blue light, the LED filament will appear blue when OFF.
Also when the semi-reflective specular-reflecting mirror is configured to dominantly reflect blue light, more red light may be generated by the light conversion material, which in turn may increase the CRI of the LED filament light (CRI2>CRI1).
In another embodiment wherein said first encapsulant comprises the light converting material adapted to convert at least part of said LED light into converted light, the semi-reflective specular-reflecting mirror may be configured to dominantly reflect light in a green wavelength range (but transmit blue and red light) such that, when this LED filament is ON, at least part of converted light is reflected back to said first encapsulant comprising said first light converting material, whereby at least a portion of said converted light is after reflection by the semi-reflective specular-reflecting mirror being re-converted by said light converting material into reconverted light having a peak wavelength higher than the peak wavelength of said converted light, which in turn can result in white LED filament light with a correlated color temperature CCT3 different than CCT1. This embodiment may also provide an environmental friendly color of the LED filament when OFF (i.e. when the plurality of LEDs are not emitting the LED light).
The semi-reflective specular-reflecting mirror may alternatively be configured to dominantly reflect red light, to provide a flame glowing effect of the LED filament when OFF. Furthermore, when this LED filament is ON, the semi-reflective specular-reflecting mirror will reflect red phosphor (light converting material) light which typically not will be (re)absorbed, hence not affecting the correlated color temperature of white LED filament light.
Notwithstanding the above, the semi-reflective specular-reflecting mirror is preferably (at least) partially transmissive for blue, green, and red, to make it possible to provide white LED filament light.
In one embodiment the semi-reflective specular-reflecting mirror (having the non-constant reflectivity of light) is a dichroic mirror. The dichroic mirror may selectively reflect light of a (small/limited) range of colors/wavelengths while transmitting other colors/wavelengths.
In another embodiment, the semi-reflective specular-reflecting mirror (having the non-constant reflectivity of light) is a cholesteric mirror. For possible details of cholesteric mirrors per se, please see Gao, Y.; Luo, Y.; Lu, J. High-Reflective Templated Cholesteric Liquid Crystal Filters. Molecules 2021, 26, 6889. https://doi.org/10.3390/molecules26226889, the contents of which herein/hereby is incorporated by reference.
The semi-reflective specular-reflecting mirror (having the non-constant reflectivity of light depending on wavelength of the light) may have a color-variable reflection over its length. In this way, the LED filament may show different colors along its length when OFF, and there may also be different light colors (CCTs) along the length of the LED filament when ON. The semi-reflective specular-reflecting mirror may for example have different regions with different color reflections along its length. The different regions may be discrete (stepped), or there can be a gradual transition between different color reflections (i.e. gradual change in color-variable reflection over the length of the filament). Also, the different regions could have the same or different lengths. The different regions may for example include at least a first region with a first color reflection (e.g. dominantly reflecting blue light), a second region with a second, different color reflection (e.g. dominantly reflecting red light), and optionally a third region with third, different color reflection (e.g. dominantly reflecting green light). In case the semi-reflective specular- reflecting mirror having a color-variable reflection over its length is a cholesteric mirror, the color-variable reflection of the cholesteric mirror can be tuned by the pitch of the molecular structure of the cholesteric mirror.
The semi-reflective specular-reflecting mirror may be flexible and/or arranged in a curved configuration around said LED filament arrangement, as seen in a cross-section of the LED filament perpendicular to the longitudinal axis of the LED filament. Alternatively, the semi-reflective specular-reflecting mirror could be arranged in polygonal (e.g. rectangular) configuration around said LED filament arrangement, for example.
The LED filament arrangement may have a spiral or helix shape, wherein said semi-reflective specular-reflecting mirror has a corresponding spiral or helix shape, resulting in that the LED filament (overall) has a spiral or helix shape or configuration. Alternatively, said LED filament arrangement has a linear (straight) shape, and wherein said semi-reflective specular-reflecting mirror has a cylindrical shape, e.g. a right circular or elliptical cylinder, resulting in that the LED filament (overall) has a liner/ straight shape or configuration.
The semi-reflective specular-reflecting mirror may be continuous and/or extend along (substantially) the complete length of the LED filament arrangement. In this way, the complete LED filament arrangement may be hidden by the semi-reflective specular- reflecting mirror, and the light effect provided by the semi-reflective specular-reflecting mirror may be provided all throughout the LED filament.
The semi-reflective specular-reflecting mirror may be in (physical/mechanical) contact with said encapsulant. This at least provides to a slim LED filament. Alternatively, the semi-reflective specular-reflecting mirror may be arranged at a distance (e.g. <7mm or <3 mm) to said encapsulant, for example using an air gap or a transparent further encapsulant e.g. of silicone. The transparent further encapsulant may for example be a silicone glue fixing the semi-reflective specular-reflecting mirror to (the outside of) the encapsulant of the LED filament arrangement.
The semi-reflective specular-reflecting mirror may be arranged on a foil, e.g. a sheet with a blue (or red or green) dichroic layer. According to a second aspect of the invention, there is provided an LED filament lamp comprising at least one light emitting diode filament (LED) according to the first aspect. The LED filament lamp may for example comprise a single LED filament or dual LED filaments, typically but not necessarily in spiral or helix configuration. The LED filament lamp may alternatively comprise multiple LED filaments (e.g. 2-8 LED filaments), typically in linear or straight configuration. The LED filament lamp may further comprise an envelope inside which the at least one light emitting diode filament is arranged, and a cap (comprising a base) for electrically and mechanically connecting the LED filament lamp to an external socket, in particular a socket of a luminaire. The envelope is preferable a light transmissive envelope. The light transmissive envelope may for example be made of glass. The light transmissive envelope may have various shapes, including bulb, candle, globe, etc. The cap or base may for example be E14, E27, B22, etc. The LED filament lamp may for example be a (retrofit) light bulb.
It is noted that the invention relates to all possible combinations of features recited in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
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.
Fig. l is a schematic cross-sectional view of an LED filament according to one or more embodiments of the present invention.
Fig. 2 is a schematic side view of the LED filament of fig. 1.
Fig. 3 is a schematic side view of an LED filament arrangement of the LED filament of figs. 1-2.
Fig. 4 is a diagram of constant reflectivity of light. Figs. 5a-c are diagrams of non-constant reflectivity of light. Fig. 6 is a (CIE 1931) color space with various correlated color temperatures. Figs. 7a-b are schematic cross-sectional view of an LED filament according to different embodiments.
Fig. 8a-b are side views of embodiments of the present LED filament, wherein the semi-reflective specular-reflecting mirror has a color-variable reflection over its length.
Figs. 9a-d are views of various LED filament lamps according to an aspect of the present invention. As illustrated in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.
DETAILED DESCRIPTION
The present invention will now 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 for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.
Figs. 1-2 illustrate an LED filament 10 adapted to provide LED filament light 12 according to one or more embodiments of the present invention. In particular, fig. 1 illustrates a cross-section of the LED filament 10 in a plane perpendicular to a longitudinal axis 14 of the LED filament 10, e.g. section A-A in fig. 2.
Preferably, the LED filament 10 has a length L and a width W, wherein L>5W. The width W may for example be in a range from 0.5 to 5 mm. The LED filament 10 may be arranged in a straight configuration (as in figs. 2 and 9a) or in a non-straight configuration such as for example a curved configuration, a 2D/3D spiral or a helix (as in figs. 9b-c).
The LED filament 10 comprises an LED filament arrangement 16, shown separately in fig. 3. The LED filament arrangement 16 should here be construed as being a subset of the LED filament 10. Consistent with the overall configuration of the LED filament 10, the LED filament arrangement 16 may have a linear (straight) shape, as in fig. 3, or a spiral or helix shape.
LED filament arrangement 16 includes an elongated carrier 18. The elongated carrier 18 may have substantially the same length and width as the LED filament 10. The elongated carrier 18 may for example be a substrate, such as a printed circuit board (PCB). The elongated carrier 18 may be rigid (made from e.g. a polymer, glass, quartz, metal or sapphire) or flexible (e.g. made of a polymer or metal e.g. a film or foil). The elongated carrier 18 comprises a first major surface 20a and an opposite second major surface 20b. The carrier 18 may be reflective or light transmissive, such as translucent and preferably transparent. The LED filament arrangement 16 further includes a plurality of light emitting diodes (LEDs) 22 arranged on the elongated carrier 16. Specifically, the plurality of LEDs 22 may be arranged on at least the first major surface 20a of the elongated carrier 18. The plurality of LEDs 22 will typically be arranged in a linear array. The plurality of LEDs 22 are adapted to emit LED light 24. That is, when the plurality of LEDs 22 are ON, they emit the LED light 24. The plurality of LEDs 22 may for example be blue LEDs adapted to emit blue LED light 24. Alternatively, the plurality of LEDs 22 may be or include red, green, and blue LEDs adapted to emit red, green, and blue LED light, respectively, wherein the red, green, and blue LED light together may form white light. The number of LEDs 22 may for example be at least 10, preferably at least 15, more preferably at least 20, most preferably at least 25 such as 30 or 40 LEDs.
The LED filament arrangement 16 further includes an encapsulant 26a (at least partly) enclosing the plurality of LEDs 22 and (at least partly) covering the first major surface 22a of the elongated carrier 18. The encapsulant 26a may be elongated, like the elongated carrier 18. The encapsulant 26a comprises at least one of a light scattering material adapted to scatter at least part the said LED light 24 into scattered light and a light converting material adapted to convert at least part of said LED light 24 into converted light 28 for providing LED filament arrangement light 30 comprising said scattered light and/or said converted light 28 and optionally the LED light 24. The light scattering material may for example be light scattering particles, such as for example BaS04, Ti02, and/or AI2O3. The light converting material may be a luminescent material, for example phosphor such as an inorganic phosphor and/or quantum dots or rods. In particular, the light converting material may include one or more of green phosphor, green-yellow phosphor, and red phosphor. Apart from the light scattering material and/or the light converting material, the encapsulant 26a can be made of a polymer material which may be flexible such as for example a silicone.
The LED filament arrangement light 30 will typically be white light, which for example may be realized by using the blue LEDs adapted to emit blue LED light 24 and the light converting material being phosphor. This white LED filament arrangement light 30 may have a first correlated color temperature CCT1 in a range from 1500K to 6500K and a first color rendering index of at least 80.
The LED filament arrangement 16 may further include a second encapsulant 26b at least partly covering the second major surface 20b of the elongated carrier 18, in which case the aforementioned encapsulant 26a may be referred to as first encapsulant 26a. The second encapsulant 26b may as well comprise at least one of a light scattering material and a light converting material. The cross-section of the LED filament arrangement 16 with the first encapsulant 26a and the (optional) second encapsulant 26b as seen in fig. 1 may for example have circular or elliptical outer profile.
In accordance with the present invention, the LED filament 10 further comprises a semi-reflective specular-reflecting mirror 32 enclosing the LED filament arrangement 16. The semi-reflective specular-reflecting mirror 32 configured to partly reflect the LED filament arrangement light 30 into reflected LED filament arrangement light 34, and to partly transmit the LED filament arrangement light 30 into transmitted LED filament arrangement light 36. The transmitted LED filament arrangement light 36 may form (at least part of) the aforementioned LED filament light 12, whereas the reflected LED filament arrangement light 34 could be (re)absorbed by the light converting material.
By means of the semi-reflective specular-reflecting mirror 32 enclosing the LED filament arrangement 16, an LED filament 10 providing a decorative light effect may be realized, as will be exemplified hereinbelow. Furthermore, the semi-reflective specular- reflecting mirror 32 may beneficially hide the usually yellow/orange color of the underlying LED filament arrangement 16 (when the LEDs 22 are OFF). In other words, the LED filament arrangement 16, which could correspond to a conventional LED filament, may be hidden by the semi-reflective specular-reflecting mirror 32.
The semi-reflective specular-reflecting mirror 32 should fully encloses the LED filament arrangement 16, both in the circumferential direction (see fig. 1) and in the longitudinal direction (see fig. 2). To this end, the semi-reflective specular-reflecting mirror 32 may be continuous and arranged (e.g. in a curved configuration) around the complete outer profile of the LED filament arrangement 16 (fig. 1), and also extend along the complete length L’ of the LED filament arrangement 16 (fig. 2).
Furthermore, in case the LED filament arrangement 16 has a linear (straight) shape, the semi-reflective specular-reflecting mirror 32 may have a corresponding cylindrical shape, e.g. a right circular or elliptical cylinder, as in figs. 1-2. Alternatively, in case the LED filament arrangement 16 has a spiral or helix shape, the semi-reflective specular-reflecting mirror 32 may have a corresponding spiral or helix shape, resulting in that the LED filament 10 (overall) has a spiral or helix shape or configuration, as in figs. 9b-c.
Furthermore, the semi-reflective specular-reflecting mirror 32 may be in direct contact with the encapsulant 26a and the optional second encapsulant 26b by using e.g. a glue. Alternatively, the semi-reflective specular-reflecting mirror 32 may be arranged at a distance D to the encapsulant 26a and the optional second encapsulant 26b, for example using an air gap or a transparent further encapsulant 38 e.g. of silicone. The air gap may be realized by using a holder (not shown). The holder may be attached e.g. to part of the electrodes at the ends of a LED filament 10. The transparent further encapsulant 38 may for example be a silicone glue fixing the semi-reflective specular-reflecting mirror 32 to the encapsulant 26a and the optional second encapsulant 26b. The distance D is preferably <3 mm. The thickness of the semi-reflective specular-reflecting mirror 32 may be in the range of 0.05-2 mm, typically 0.2 mm, whereby LED filament 10 may maintain a typical, slim appearance.
The reflectivity R of the semi-reflective specular-reflecting mirror 32 may be R> 30%, in particular R> 40%. The transmissivity T of the semi-reflective specular-reflecting mirror 32 may be T> 30 %, in particular T> 40%. The reflectivity R and transmissivity T may be an averaged reflectivity and transmission over the visible wavelength range from 400 nm to 800 nm. The absorption of the semi-reflective specular-reflecting mirror 32 may be less than 10%, preferably less than 5%, more preferably less than 3%, most preferably less than 2% such as for example 1% or 0%.
The semi-reflective specular-reflecting mirror 32 may have a constant* reflectivity of light over the wavelength range of from 400 nm to 800 nm (*with respect to wavelength, here of the LED filament arrangement light 30 and/or of ambient light). This is exemplarily illustrated in fig. 4, wherein reflectivity R is on the vertical axis and wavelength is on the horizontal axis.
Alternatively, the semi-reflective specular-reflecting mirror 32 may have a non-constant reflectivity of light (and a non-constant transmissivity (T) of light), with respect to the light’s wavelength, over the wavelength range of from 400 nm to 800 nm, as exemplarily illustrated in figs. 5a-c. For example, for a blue sub wavelength range the semi- reflective specular-reflecting mirror 32 may have a reflectivity of at least 70%, wherein for further/other sub wavelength ranges (green and red ) the semi-reflective specular-reflecting mirror has a transmissivity of at least 70%, as in fig. 5a. Hence, in fig. 5a, the semi-reflective specular-reflecting mirror 32 is configured to dominantly reflect blue light, i.e. dominantly reflect light in a blue wavelength range. The semi-reflective specular-reflecting mirror 32 having the non-constant reflectivity of light may for example be a dichroic mirror.
In one embodiment, the LED light 24 is blue, the LED filament arrangement light 30 is white light with the first correlated color temperature CCT1, and the semi- reflective specular-reflecting/dichroic mirror 32 is configured to dominantly reflect blue light (while transmitting other colors/wavelengths, see fig. 5a), such that the LED filament light 12 is white light having a second correlated color temperature CCT2 lower than CCT1. For example, CCT2=CCTl-500K, see fig. 6. The lower CCT2 can be achieved as blue LED light 24’ initially not converted by the light converting material is reflected back by the mirror 32 as reflected blue LED light 42, which reflected blue LED light 42 is absorbed by green phosphor light converting material in the first encapsulant 26a and in the optional encapsulant 26b to produce more green light 28 and by red phosphor light converting material in the first encapsulant and in the optional encapsulant 26b to produce more red light 28, see fig. 7a. Also when the semi-reflective specular-reflecting mirror 32 is configured to dominantly reflect blue light, the LED filament 10 will appear blue when in OFF state.
In another embodiment, the semi-reflective specular-reflecting/dichroic mirror 32 is configured to dominantly reflect green light (see fig. 5b), to give the LED filament 10 an environmental friendly color (more green) when the LED filament 10 is OFF. Furthermore, when this LED filament 10 is ON, the semi-reflective specular-reflecting mirror 32 may reflect green phosphor (light converting material) light 44 (see fig. 7b) back to the first encapsulant 26a and/or the optional encapsulant 26b, whereby at least a portion of this light 44 is reconverted by the light converting material (e.g. green phosphor) in the first encapsulant 26a and/or the optional encapsulant 26b into reconverted light 28’. The reconverted light 28’ may have a peak wavelength higher than the peak wavelength of the converted light 28, which in turn can result in white LED filament light 12 with a correlated color temperature CCT3 different than CCT1, see fig. 6.
In yet another embodiment, the semi-reflective specular-reflecting/dichroic mirror 32 is configured to dominantly reflect red light (see fig. 5c), to give the LED filament 10 a flame glowing effect (more red) when the LED filament 10 is OFF. Furthermore, when this LED filament 10 is ON, the semi -reflective specular-reflecting mirror 32 will reflect red phosphor (light converting material) light which typically not will be (re)absorbed, hence not affecting the correlated color temperature of white LED filament light 12.
Moving to figs. 8a-b, the semi-reflective specular-reflecting mirror 32 having the non-constant reflectivity may have a color-variable reflection over its length L”. This mirror 32 may for example be a dichroic mirror or a cholesteric mirror.
In fig. 8a, the semi-reflective specular-reflecting mirror 32 has a first region 40a towards one end of the LED filament 10, a second region 40c towards the opposite end of the LED filament, and a third, intermediate region 40b between the first region 40a and the second region 40c. The first region may for example be configured to dominantly reflect blue light, the second region 40c may be configured to dominantly reflect green light, and the third region 40c may be configured to dominantly reflect red light. Furthermore, the regions 40a-c in fig. 8a are discrete and have equal length. An observer will here see different colored effects on the LED filament 10 in the OFF state. And the observer may as well see differences in light colors (temperatures) in the ON state, at least in the near field.
In fig. 8b, the semi-reflective specular-reflecting mirror 32 is configured to dominantly reflect light of a first color at one end 46a of the LED filament 10, and is further configured to dominantly reflect light of a second color (different than the first color) at the opposite end 46b of the LED filament 10, with a gradual transition therebetween.
Figs. 9a-d are views of various LED filament lamps lOOa-d, each comprising at least one LED filament 10. Fig. 9a is a perspective view, and figs. 9b-d are side views.
In fig. 9a, the LED filament lamp 100a comprises multiple LED filaments 10, namely four LED filaments 10. Each LED filaments 10 here has a linear or straight configuration. The LED filaments 10 may be substantially vertically arranged, as seen in the view of fig. 4a. The LED filaments 10 may be substantially parallel to each other. The LED filaments 10 could have semi-reflective specular-reflecting mirrors 32 with the same or different reflective properties. The semi -reflective specular-reflecting mirrors 32 of all the LED filaments 10 could for example be configured to dominantly reflect green light, so that they look green when OFF.
In figs. 9b-c, each LED filament lamp lOOb-c comprises only one LED filament 10. The LED filament 10 here has a spiral or helix configuration. The LED filament 10 may be substantially vertically arranged, as seen in the view of figs. 9b-c.
The semi-reflective specular-reflecting mirror 32 of the LED filament 10 in fig. 9b may for example be a dichroic mirror configured to dominantly reflect blue light. In this way, the LED filament 10 in fig. 9b may look (more) blue when OFF, due to blue color in ambient light being reflected by the dichroic mirror 32, and also provide warmer/less cool (e.g. CCT2) white LED filament light 12 when ON, as discussed above.
The semi-reflective specular-reflecting mirror 32 of the LED filament 10 in fig. 9c has color-variable reflection over its length L”. The mirror 32 may for example have a blue lower region 40a (closer/proximal to cap 104) gradually transitioning to a top yellow region 40d (further from/distal of cap 104).
In fig. 9d, the LED filament lamp lOOd comprises only one LED filament 10 having a linear/ straight configuration. The semi-reflective specular-reflecting mirror 32 of the LED filament 10 in fig. 9d has a color-variable reflection over its length L”, here with blue, red, and green regions 40a-c arranged in triplets after one another. Each LED filament lamp lOOa-d may further comprise a light transmissive envelope 102 inside which the at least one LED filament 10 is arranged, and a cap (comprising a base) 104 for electrically and mechanically connecting the LED filament lamp lOOa-d to a socket of a luminaire (not shown). The light transmissive envelope 102 may for example be made of glass. The light transmissive envelope 102 may have various shapes, including bulb, candle, globe, etc. The cap or base 104 may for example be E14, E27, B22, etc. The LED filament lamp lOOa-d may for example be a (retrofit) light bulb.
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 semi-reflective specular-reflecting mirror 32 may be arranged on a foil, e.g. a sheet with a blue (or red or green) dichroic layer. The dichroic layer may be on the outer side, facing away from the first encapsulant 26a and optional second encapsulant 26b. An advantage of having the dichroic layer on the outer side is less mechanical stress in the dichroic layer. Alternatively the dichroic layer may be on the inner side, facing the first encapsulant 26a and optional second encapsulant 26b. An advantage of having the dichroic layer on the inner side is that the dichroic layer is better protected, e.g. against scratches.
Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person 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 measured cannot be used to advantage.

Claims

CLAIMS:
1. A light emitting diode, LED, filament (10) providing LED filament light (12), the LED filament comprising: an LED filament arrangement (16) comprising a plurality of LEDs (22) adapted to emit LED light (24) arranged on a first major surface (20a) of an elongated carrier (18) and a first encapsulant (26a) at least partly enclosing said plurality of LEDs and at least partly covering the first major surface (20a) of said elongated carrier, said first encapsulant comprising at least one of a light scattering material adapted to scatter at least part of said LED light into scattered light and a light converting material adapted to convert at least part of said LED light into converted light (28) for providing LED filament arrangement light (30) comprising said scattered light and/or said converted light and optionally said LED light; and a semi-reflective specular-reflecting mirror (32) enclosing said LED filament arrangement, wherein said semi-reflective specular-reflecting mirror has a reflectivity (R) configured to partly reflect said LED filament arrangement light provided by said LED filament arrangement into reflected LED filament arrangement light (34), and a transmissivity, T, configured to partly transmit said LED filament arrangement light provided by said LED filament arrangement into transmitted LED filament arrangement light (36), wherein said first encapsulant (26a) comprises the light converting material adapted to convert at least part of said LED light into converted light (28), and wherein said semi-reflective specular-reflecting mirror is configured to dominantly reflect light in a green wavelength range such that at least part (44) of converted light is reflected back to said first encapsulant comprising said first light converting material, whereby at least a portion of said converted light is after reflection by the semi-reflective specular-reflecting mirror being reconverted by said light converting material into reconverted light (28’) having a peak wavelength higher than the peak wavelength of said converted light.
2. A light emitting diode filament according to claim 1, wherein said LED filament arrangement light is white light having a first correlated color temperature, CCT1, in a range from 1500K to 6500K and a first color rendering index, CRI1, of at least 80.
RECTIFIED SHEET (RULE 91) ISA/EP
3. A light emitting diode fdament according to claim 1 or 2, wherein the reflectivity (R) of the semi-reflective specular-reflecting mirror is > 30%, and wherein the transmissivity (T) of the semi-reflective specular-reflecting mirror is > 30%.
4. A light emitting diode filament according to any one of the preceding claims, wherein the semi-reflective specular-reflecting mirror has a non-constant reflectivity (R) of light and a non-constant transmissivity, T, of light, with respect to wavelength, over a wavelength range of from 400 nm to 800 nm, wherein for one or more sub wavelength ranges in the wavelength range of from 400 nm to 800 nm the semi-reflective specular-reflecting mirror has a reflectivity of at least 70%, and wherein for one or more further sub wavelength ranges in the wavelength range of from 400 nm to 800 nm the semi-reflective specular- reflecting minor has a transmissivity of at least 70%.
5. A light emitting diode filament according to claim 4, wherein said semi- reflective specular-reflecting mirror is configured to: (i) dominantly reflect blue light by having a reflectivity (R) of at least 70% in the blue wavelength range and dominantly transmit green and red light by having a transmissivity, T, of at least 70% in the green and red wavelength ranges; or (ii) dominantly reflect green light by having a reflectivity (R) of at least 70% in the green wavelength range and dominantly transmit blue and red light by having a transmissivity, T, of at least 70% in the blue and red wavelength ranges; or (iii) dominantly reflect red light by having a reflectivity (R) of at least 70% in the red wavelength range and dominantly transmit blue and green light by having a transmissivity, T, of at least 70% in the blue and green wavelength ranges.
6. A light emitting diode according to claim 2 and 5, wherein said first encapsulant comprises the light converting material adapted to convert at least part of said LED light into converted light (28), and wherein said semi-reflective specular-reflecting mirror is configured to dominantly reflect light in a blue wavelength range such that LED light (24’) which is initially not converted by said light converting material is reflected back to said first encapsulant comprising said light converting material, whereby at least a portion of said LED light which was initially not converted by said light converting material is after reflection by the semi-reflective specular-reflecting mirror being converted by said light converting material, such that said LED filament light is white light having a second correlated color temperature, CCT2, lower than said first correlated color temperature.
RECTIFIED SHEET (RULE 91) ISA/EP
7. A light emiting diode filament according to any one of the preceding claims, wherein the semi-reflective specular-reflecting mirror is a dichroic mirror.
8. A light emiting diode filament according to any one of the preceding claims, wherein said semi-reflective specular-reflecting mirror has a col or- variable reflection over its length (L”).
9. A light emiting diode filament according to any one of the preceding claims, wherein the semi-reflective specular-reflecting mirror is flexible and arranged in a curved configuration around said LED filament arrangement.
10. A light emiting diode filament according to any one of the preceding claims, wherein said LED filament arrangement has a spiral or helix shape, and wherein said semi- reflective specular-reflecting mirror has a corresponding spiral or helix shape.
11. A light emiting diode filament according to any one of the claims 1 to 8, wherein said LED filament arrangement has a linear shape, and wherein said semi-reflective specular-reflecting mirror has a cylindrical shape.
12. A light emiting diode filament according to any one of the preceding claims, wherein semi-reflective specular-reflecting minor is continuous and extends along the complete length (L’) of the LED filament arrangement.
13. A light emiting diode filament according to any one of the preceding claims, wherein the semi-reflective specular-reflecting mirror is in contact with said encapsulant or arranged at a distance <3mm to said encapsulant.
14. An LED filament lamp (lOOa-d) comprising at least one light emiting diode filament (10) according to any one of the preceding claims; an envelope inside which the at least one light emitting diode filament is arranged; and
RECTIFIED SHEET (RULE 91) ISA/EP a base for electrically and mechanically connecting said LED filament lamp to a socket of a luminaire.
RECTIFIED SHEET (RULE 91) ISA/EP
EP24709740.5A 2023-03-14 2024-03-07 Led filament Pending EP4680886A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP23161838 2023-03-14
PCT/EP2024/056002 WO2024188799A1 (en) 2023-03-14 2024-03-07 Led filament

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EP4680886A1 true EP4680886A1 (en) 2026-01-21

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JP7546592B2 (en) 2019-04-11 2024-09-06 シグニファイ ホールディング ビー ヴィ LED filament with light-reflective particles that provide sparkle
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