LED-filaments and LED-filament lamps
11781714 · 2023-10-10
Assignee
Inventors
Cpc classification
H01L2933/0091
ELECTRICITY
F21K9/232
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
H01L33/504
ELECTRICITY
F21Y2115/10
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
International classification
C09K11/61
CHEMISTRY; METALLURGY
F21K9/232
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
Abstract
An LED-filament comprising: a partially light transmissive substrate; a plurality of LED chips on a front face of the substrate; a photoluminescence material that is in direct contact with and covers all of the plurality of LED chips; and a light scattering layer that is in direct contact with and covers at least the photoluminescence material, wherein the light scattering layer comprises particles of light scattering material, and wherein the photoluminescence material comprises broadband green to red photoluminescence materials and narrowband red photoluminescence material.
Claims
1. An LED-filament comprising: a partially light transmissive substrate; a plurality of LED chips on a front face of the substrate; a photoluminescence material layer that is in direct contact with and covers all of the plurality of LED chips; and a light scattering layer which is in direct contact with and covers at least the photoluminescence material layer and a back face of the substrate, wherein the light scattering layer contains particles of a light scattering material, wherein the photoluminescence material layer comprises broadband green to red photoluminescence material and narrowband red photoluminescence material, wherein there is no photoluminescence material layer on the back face of the substrate, and wherein light emitted from the LED-filament is emitted through the light scattering layer covering the photoluminescence material layer and the back face of the substrate.
2. The LED-filament of claim 1, wherein the photoluminescence material layer comprises a single—layer structure comprising a single layer containing the broadband green to red photoluminescence material and the narrowband red photoluminescence material.
3. The LED-filament of claim 2, wherein the single layer is in the form of a continuous strip that covers all of the LED chips and the region of the front face of the substrate between the LED chips.
4. The LED-filament of claim 1, wherein the photoluminescence material layer comprises a double—layer structure comprising: a first layer containing the narrowband red photoluminescence material that is in direct contact with and covers all of the plurality of LED chips; and a second layer containing the broadband green to red photoluminescence material that is in direct contact with and covers the first layer, and wherein the light scattering layer is in direct contact with and covers the second layer.
5. The LED-filament of claim 4, wherein the first layer is in the form of a continuous strip that covers all of the LED chips and the region of the front face of the substrate between the LED chips.
6. The LED-filament of claim 1, wherein the light scattering material is white in color.
7. The LED-filament of claim 1, wherein, in an off-state, the LED-filament appears white in color.
8. The LED-filament of claim 1, wherein the light scattering material is selected from the group consisting of: zinc oxide (ZnO), titanium dioxide (TiO.sub.2), barium sulfate (BaSO.sub.4), magnesium oxide (MgO), silicon dioxide (SiO.sub.2), aluminum oxide (A1.sub.2O.sub.3), zirconium dioxide (ZrO.sub.2) and mixtures thereof.
9. The LED-filament of claim 1, wherein the light scattering layer comprises a mixture of the particles of the light scattering material and a light transmissive binder, and wherein a weight loading of the light scattering material to the light transmissive binder is from 0.2 wt % to 5 wt %.
10. The LED-filament of claim 1, wherein the LED-filament has a luminous efficacy of at least 180 lm/W.
11. The LED-filament of claim 1, wherein the narrowband red photoluminescence material is one of: K.sub.2SiF.sub.6:Mn.sup.4+, and K.sub.2TiF.sub.6:Mn.sup.4+.
12. The LED-filament of claim 1, wherein the light scattering layer comprises a respective light scattering layer on the front and back faces of the substrate and wherein a thickness or weight loading of the particles of the light scattering material in the respective light scattering layers are different.
13. An LED-filament lamp comprising: an LED-filament comprising: a partially light transmissive substrate; a plurality of LED chips on a front face of the substrate; a photoluminescence material layer that is in direct contact with and covers all of the plurality of LED chips; and a light scattering layer that encapsulates the LED-filament and is in direct contact with and covers at least the photoluminescence material layer and a back face of the substrate, wherein the light scattering layer comprises particles of a light scattering material, and the photoluminescence material layer comprises broadband green to red photoluminescence material and narrowband red photoluminescence material, wherein there is no photoluminescence material layer on the back face of the substrate, wherein light emitted from the LED-filament is emitted through the light scattering layer covering the photoluminescence material layer and the back face of the substrate, and wherein, in an off-state, the LED-filament appears white in color.
14. The LED-filament lamp of claim 13, wherein the photoluminescence material layer comprises a single—layer structure comprising a single layer containing the broadband green to red photoluminescence material and the narrowband red photoluminescence material.
15. The LED-filament lamp of claim 13, wherein the photoluminescence material layer comprises a double—layer structure comprising: a first layer containing the narrowband red photoluminescence material that is in direct contact with and covers all of the plurality of LED chips; and a second layer containing the broadband green to red photoluminescence material that is in direct contact with and covers the first layer, and wherein the light scattering layer is in direct contact with and covers the second layer.
16. The LED-filament lamp of claim 13, wherein the light scattering material is white in color.
17. The LED-filament lamp of claim 13, wherein the light scattering material is selected from the group consisting of: zinc oxide (ZnO), titanium dioxide (TiO.sub.2), barium sulfate (BaSO.sub.4), magnesium oxide (MgO), silicon dioxide (SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3), zirconium dioxide (ZrO.sub.2) and mixtures thereof.
18. The LED-filament lamp of claim 13, wherein the light scattering layer comprises a mixture of the particles of the light scattering material and a light transmissive binder, and wherein a weight loading of the light scattering material to the light transmissive binder is from 0.2 wt % to 5 wt %.
19. The LED-filament lamp of claim 13, wherein the narrowband red photoluminescence material is one of: K.sub.2SiF.sub.6:Mn.sup.4+, K.sub.2GeF.sub.6:Mn.sup.4+, and K.sub.2TiF.sub.6:Mn.sup.4+.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures, in which:
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DETAILED DESCRIPTION OF THE INVENTION
(12) Embodiments of the present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the invention is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration.
(13) The LED-filament lamp 100 comprises a connector base 102, a light-transmissive envelope 104; an LED-filament support 106 and four LED-filaments 108a, 108b, 108c, 108d.
(14) In some embodiments, the LED-filament lamp 100 can be configured for operation with a 110V (r.m.s.) AC (60 Hz) mains power supply as used in North America. For example and as illustrated, the LED-filament lamp 100 can comprise an E26 (ϕ26 mm) connector base (Edison screw lamp base) 102 enabling the lamp to be directly connected to a mains power supply using a standard electrical lighting screw socket. It will be appreciated that depending on the intended application other connector bases can be used such as, for example, a double contact bayonet connector (i.e. B22d or BC) as is commonly used in the United Kingdom, Ireland, Australia, New Zealand and various parts of the British Commonwealth or an E27 (ϕ27 mm) screw base (Edison screw lamp base) as used in Europe. The connector base 102 can house rectifier or other driver circuitry (not shown) for operating the LED-filament lamp.
(15) The light-transmissive envelope 104 is attached to the connector 102. The light-transmissive envelope 104 and LED-filament support 106 can comprise glass. The envelope 104 defines a hermetically sealed volume 110 in which the LED-filaments 108a to 108d are located. The envelope 104 can additionally incorporate or include a layer of a light diffusive (scattering) material such as for example particles of zinc oxide (ZnO), titanium dioxide (TiO.sub.2), barium sulfate (BaSO.sub.4), magnesium oxide (MgO), silicon dioxide (SiO.sub.2) or aluminum oxide (Al.sub.2O.sub.3).
(16) The LED-filaments 108a to 108d, which are linear (strip or elongate) in form, are oriented such that their direction of elongation is generally parallel to an axis 112 of the lamp 100. In this embodiment, the LED-filaments 108a to 108d are equally circumferentially spaced around the glass filament support 106 (
(17) An LED-filament according to an embodiment of the invention is now described with reference to
(18) The substrate 224 can further comprise the respective electrical contacts 214, 218 on the front face 228 at the first and second ends of the substrate 224 for electrical connection to a respective one of the conducting wires 116, 120 (
(19) When the LED-filament 208 is used as a part of an energy efficient bulb an elongate configuration is typically preferred since the appearance and emission characteristics of the device more closely resembles a traditional filament of an incandescent bulb. It should be noted that the LED chips 226 are unpackaged and emit light from both their top and bottom (base) faces with the base surface of the LED chip mounted directly on the substrate 224.
(20) In accordance the invention, the light-transmissive substrate 224 can comprise any material which is partially light-transmissive and preferably has a transmittance to visible light from 2% to 70% (reflectance of 98% to 30%). The substrate can comprise a glass, ceramic material or a plastics material such as polypropylene, silicone or an acrylic. Typically, in embodiments the light-transmissive substrate comprises a porous ceramic substrate composed of alumina that has a transmittance of about 40%. To aid in the dissipation of heat generated by the LED chips 226, the substrate 224 can not only be light-transmissive, but can also be thermally conductive to aid in the dissipation of heat generated by the LED chips. Examples of suitable light-transmissive thermally conductive materials include: magnesium oxide, sapphire, aluminum oxide, quartz glass, and diamond. The transmittance of the thermally conductive substrate can be increased by making the substrate thin. To increase mechanical strength, the substrate can comprise a laminated structure with the thermally conductive layer mounted on a light-transmissive support such as a glass or plastics material. To further assist in the dissipation of heat, the volume 110 (
(21) In accordance with embodiments of the invention, the LED-filament 208 further comprises a first photoluminescence wavelength conversion material 236 applied to and covering the LED chips 226 and front face 228 of the substrate 224 and a second different photoluminescence wavelength conversion material 238 applied to and covering the second back (opposite) face 234 of the substrate 224. The first photoluminescence wavelength conversion material 236 is applied directly to the LEDs chips 226 and covers the front face of the substrate in the form of an encapsulating layer.
(22) In accordance with the invention, the first photoluminescence wavelength conversion material 236 comprises a mixture of a first broadband green photoluminescence material having a peak emission wavelength ranging from 520 nm to 560 nm (preferably 540 nm to 545 nm), a first broadband red photoluminescence material having a peak emission wavelength ranging from 620 nm to 650 nm and a narrowband red photoluminescence material typically a manganese-activated fluoride phosphor. Collectively, the first broadband green and red photoluminescence materials will be referred to as first broadband green to red photoluminescence materials. Since in this embodiment both the narrowband red and broadband green to red photoluminescence materials are provided as a mixture in a single layer, the LED-filament will be referred to as a “single-layer” structured filament.
(23) The second photoluminescence wavelength conversion material 238 comprises a mixture of only a second broadband green photoluminescence material having a peak emission wavelength ranging from 520 nm to 560 nm (preferably 520 nm to 540 nm) and a second broadband red (non-manganese-activated fluoride) photoluminescence material having a peak emission wavelength ranging from 620 nm to 650 nm. Collectively, the second broadband green and red photoluminescence materials will be referred to as second broadband green to red photoluminescence materials.
(24) In contrast, in known LED-filaments, the same photoluminescence material composition (narrowband and broadband red photoluminescence materials) is provided on the front and back faces of the filament. Suitable broadband green photoluminescence materials, narrowband red photoluminescence materials and broadband red photoluminescence materials are discussed below.
(25) In the embodiment illustrated in
(26) In operation, blue excitation light generated by the LED chips 210 excites the green-emitting and red emitting photoluminescence materials to generate green and red light. The emission product of the LED-filament 208 which appears white in color comprises the combined photoluminescence light and unconverted blue LED light. Since the photoluminescence light generation process is isotropic, phosphor light is generated equally in all directions and light emitted in a direction towards the substrate 224 can pass through the substrate and be emitted from the back of the LED-Filament 208. It will be appreciated that the use of a partially light-transmissive substrate 224 enables the LED-filament to achieve an emission characteristic in which light is emitted in a direction away from both the front face 228 and back face 234 of the substrate. Additionally, particles of a light scattering material can be combined with the phosphor material to reduce the quantity of phosphor required to generate a given emission product color.
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(28) Referring to
(29) TABLE-US-00001 TABLE 1 Effect of substrate transmittance/reflectance on the proportion of blue excitation light on the front and back face sides of the substrate and LED-filament brightness Substrate % of total blue excitation light on: LED-Filament Transmittance Reflectance Front face side of Back face side of Brightness (%) (%) substrate substrate (%) 5 95 97.5 2.5 124.4 10 90 95.0 5.0 123.8 20 80 90.0 10.0 122.5 40 60 80.0 20.0 120.0 50 50 75.0 25.0 118.8 60 40 70.0 30.0 117.5 70 30 65.0 35.0 116.3
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(31) The double-layer LED-filament of
(32) In the double-layer LED-filament of
(33) The inventors have discovered that providing the narrowband red photoluminescence material as a respective individual layer 450 (double-layer structure) is found to further substantially reduce (up to a further 80% by weight reduction) the usage amount of the narrowband red photoluminescence material compared with an LED-filament in which the narrowband red and broadband green photoluminescence materials comprise a mixture in a single layer (
(34) It is believed that the reason for this reduction in usage amount, is that in an LED-filament (
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(36) The double-layer double-sided LED-filament of
(37) In the double-layer double-sided LED-filament of
(38) The inventors have discovered LED-filaments having a double-sided double-layer structure can substantially reduce (as much as 80% by weight reduction for a substrate with a transmittance of 100%) the usage amount of the narrowband red photoluminescence material compared with known LED-filaments comprising narrowband and broadband red photoluminescence materials on front and back faces.
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(40) In various embodiments of the invention, and to reduce photoluminescence material usage, in particular to further reduce narrowband red photoluminescence material usage, the LED-filament can further comprise particles of a light scattering material such as for example particles of zinc oxide (ZnO), titanium dioxide (TiO.sub.2) barium sulfate (BaSO.sub.4), magnesium oxide (MgO), silicon dioxide (SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3), zirconium dioxide (ZrO.sub.2) or mixtures thereof. The particles of light scattering material can be provided as a mixture with any of the photoluminescence materials and/or in a separate layer in contact with a photoluminescence material layer. Preferably, the particles of light scattering material are incorporated with the narrowband red photoluminescence material to further reduce narrowband red photoluminescence material usage. For example, for a single-layer structured LED-filament the particles of light scattering material can be incorporated in the first photoluminescence wavelength conversion material 236 as part of the mixture of the first broadband green to red photoluminescence materials and the narrowband red photoluminescence material (
(41) Alternatively and/or in addition, the particles of light scattering material can be provided in a separate layer that is in contact with a photoluminescence layer such as for example a layer containing the narrowband red photoluminescence material to further reduce narrowband red photoluminescence usage.
(42) The inclusion of particles of a light scattering material with the photoluminescence material increases the number of collisions of LED generated excitation light with particles of the photoluminescence material enhancing photoluminescence light generation which decreases the amount of photoluminescence material usage. It is believed that on average as little as 1 in 10,000 interactions of a photon with a photoluminescence material results in absorption and generation of photoluminescence light. The majority, about 99.99%, of interactions of photons with a photoluminescence material particle result in scattering of the photon. Since the inclusion of the light scattering materials increases the number of collisions this increases the probability of photoluminescence light generation, which decreases the amount of photoluminescence material usage to generate a selected emission intensity/color.
(43)
(44) As shown in
(45) As shown in
(46) The light scattering material may comprise particles of titanium dioxide (TiO.sub.2), though it can comprise other materials such as barium sulfate (BaSO.sub.4), magnesium oxide (MgO), silicon dioxide (SiO.sub.2) or aluminum oxide (Al.sub.2O.sub.3). In some arrangements, particles of the light scattering material have an average particle size from 1 μm to 50 μm and more preferably from 10 μm to 20 μm. In other arrangements, the light scattering material has a particle size that is selected such that the particles will scatter blue light relatively more than they will scatter green to red light generated by the photoluminescence material(s). In such arrangements, the light scattering material particle size can be selected such that the particles will Rayleigh scatter blue light at least twice as much as they will scatter light generated by the photoluminescence materials. Such a configuration ensures that a higher proportion of blue light will be scattered by the light scattering material layer 762 in a direction back towards and into the first and second photoluminescence wavelength conversion materials 736, 738 thereby increasing the probability of blue photons interacting with a photoluminescence material particles and resulting in the generation of photoluminescence light. At the same time, photoluminescence light generated by the photoluminescence materials can pass through the light scattering material layer with a lower probability of being scattered compared with the blue light. Since the light scattering material layer 762 increases the probability of blue photons interacting with photoluminescence material particles, less photoluminescence material can be used to generate a selected emission color of light.
(47) The use of a separate light scattering material layer 762 that covers (encapsulates), or at least substantially covers, the photoluminescence wavelength conversion material layers 736, 738 can substantially reduce the quantity of photoluminescence materials required to generate a selected color of emitted light. As described herein, it is estimated that on average as little as 1 in 10,000 interactions of a photon with a photoluminescence material particle results in absorption and generation of photoluminescence light. The majority, about 99.99%, of interactions of photons with a photoluminescence material particle result in scattering of the photon (without absorption and generation of photoluminescence light). Due to the isotropic nature of the scattering process on average about half of the photons will be scattered in a direction towards the light scattering material layer. It is believed that the light scattering material layer 762 increases the probability that a photon will result in the generation of photoluminescence light by scattering light back towards and into the photoluminescence wavelength conversion material layers 736, 738 where it can interact the photoluminescence material. As a result of the increased probability of photons interacting with and exciting the photoluminescence material, the quantity of photoluminescence material required to generate a selected color of light can be reduced. Tests indicate that inclusion of a light scattering material layer in direct contact with the photoluminescence layer can substantially reduce the quantity of photoluminescence material (in particular narrowband red photoluminescence material) required to generate a given color emission product with only a minimal reduction in intensity of generated light. For example, a single-layer LED-filament in accordance with the invention that comprises a light scattering material layer this can reduce the use of manganese-activated fluoride red photoluminescence material by up to about 35% and overall phosphor usage by up to about 35% with only a 2% reduction in emitted intensity/luminous efficacy compared with the same single-layer LED-filament without a light scattering material layer.
(48) A further benefit of a separate light scattering material layer 762 that at least substantially encapsulates the LED-filament, is that it can improve the visual appearance, “white appearance”, of the LED-filament 708 in the “off-state” (“off-state” white appearance). The light scattering material layer will scatter light 764 originating from external sources 766, for example daylight, which reduces the amount of light reaching the underlying photoluminescence material layers 736, 738 and exciting photoluminescence materials therein. Due to the reduction in photoluminescence light generated by the photoluminescence material(s), the color appearance of the filament 708 to an observer 768 will have a color that more closely resembles the color of the light scattering material (rather than that of the photoluminescence material, for example, which is undesirable). In embodiments, the particles of light scattering material comprise a material that is white in color (i.e. an achromatic material that reflects or scatters all the visible wavelengths of light) such that in an “off-state” the LED-filament 708 has an appearance that is white in color.
(49) The inventors have discovered that a yet further benefit of a light scattering layer 762 that at least covers the back face 734 of the LED-filament 708, is that this can improve the color uniformity of emitted light to an extent that the LED-filament 708 no longer requires photoluminescence materials 738 on the back face 734 of the substrate 724, thereby further reducing overall photoluminescence material usage. As shown in
(50) Tests indicate that a single-layer LED-filament in accordance with the invention, that includes a light scattering layer and has no photoluminescence materials on the back face 734, can reduce the use of manganese-activated fluoride red photoluminescence material by up to about 35% and overall phosphor usage by up to about 60% with only a 2% reduction in emitted intensity compared with an single-layer LED-filament without a light scattering material layer (see TABLES 13A, 13B and 14—Dev. 6 compared with Dev.5).
(51) The single-layer LED-filament 708 of
(52) The single-layer LED-filament 708 of
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(54) The first photoluminescence layer 850, comprising the narrowband red photoluminescence material, is disposed on and covers each of the LED chip 826 and front face 828 of the substrate 824 between the LED chips 826 and can be in the form of an encapsulating layer. The first photoluminescence layer 850 can comprise a mixture of particles of narrowband red photoluminescence material and a light transmissive binder material.
(55) The second photoluminescence layer 852, comprising the first broadband green to red photoluminescence materials (that is first broadband green and first broadband red photoluminescence materials), is disposed on and covers the first photoluminescence layer 850 and front face 828 of the substrate 824 not already covered by the first photoluminescence layer 850 (that is the first photoluminescence layer 850 is in closer proximity to the LED chips 826 than the second photoluminescence layer 850). The second photoluminescence layer 852 may be in the form of an encapsulating layer and can comprise a mixture of particles of first broadband green to red photoluminescence materials and a light transmissive binder material.
(56) As described herein, a benefit of a double-layer structure comprising a respective layer (first photoluminescence layer 850) comprising substantially only a narrowband red photoluminescence material compared with a single-layer arrangement is a substantial reduction in the amount of narrowband red photoluminescence material required to a selected color of emitted light. This can provide a substantial cost saving as narrowband red photoluminescence materials are typically many times more expensive than broadband green to red photoluminescence materials.
(57) As shown in
(58) As shown in
(59) As described herein, the provision of a separate light scattering material layer 862 that covers (encapsulates), or at least substantially covers, the photoluminescence materials on the front and back faces 828, 834 of the LED-filament, are that it can: (i) substantially reduce the quantity of photoluminescence materials required to generate a selected color of emitted light and (ii) improve the visual appearance, white appearance, of the LED-filament 808 in the “off-state” (“off-state” white appearance). A further benefit of the light scattering layer 862 that covers at least the back face 834 of the LED-filament, is that it can eliminate the need to provide photoluminescence materials 838 on the back face 834 of the substrate 824 thereby further reducing the overall photoluminescence material usage. As shown in
(60) The double-layer LED-filament 808 of
(61) The double-layer LED-filament 808 of
(62) Broadband Green Photoluminescence Materials
(63) In this patent specification, a broadband green photoluminescence material refers to a material which generates light having a peak emission wavelength (λ.sub.pe) in a range ˜520 nm to ˜560 nm, that is in the yellow/green to green region of the visible spectrum. Preferably, the green photoluminescence material has a broad emission characteristic and preferably has a FWHM (Full Width Half Maximum) of between about 50 nm and about 120 nm. The green photoluminescence material can comprise any photoluminescence material, such as for example, garnet-based inorganic phosphor materials, silicate phosphor materials and oxynitride phosphor materials. Examples of suitable green phosphors are given in TABLE 2.
(64) In some embodiments, the green photoluminescence materials comprises a cerium-activated yttrium aluminum garnet phosphor of general composition Y.sub.3(Al.sub.1-yGa.sub.y).sub.5O.sub.12:Ce (YAG) where 0<y<1 such as for example a YAG series phosphor from Intematix Corporation, Fremont Calif., USA which have a peak emission wavelength of in a range 520 nm to 543 nm and a FWHM of ˜120 nm. In this patent specification, the notation YAG # represents the phosphor type—YAG—based phosphors—followed by the peak emission wavelength in nanometers (#). For example, YAG535 denotes a YAG phosphor with a peak emission wavelength of 535 nm. The green photoluminescence material may comprise a cerium-activated yttrium aluminum garnet phosphor of general composition (Y,Ba).sub.3(Al,Ga).sub.5O.sub.12:Ce (YAG) such as for example a GNYAG series phosphor from Intematix Corporation, Fremont Calif., USA. In some embodiments, the green photoluminescence material can comprise an aluminate (LuAG) phosphor of general composition Lu.sub.3Al.sub.5O.sub.12:Ce (GAL). Examples of such phosphors include for example the GAL series of phosphor from Intematix Corporation, Fremont Calif., USA which have a peak emission wavelength of 516 nm to 560 nm and a FWHM of ˜120 nm. In this patent specification, the notation GAL # represents the phosphor type (GAL)—LuAG—based phosphors—followed by the peak emission wavelength in nanometers (#). For example, GAL520 denotes a GAL phosphor with a peak emission wavelength of 520 nm. Suitable green phosphors are given in TABLE 2.
(65) Examples of green silicate phosphors include europium activated ortho-silicate phosphors of general composition (Ba, Sr).sub.2SiO.sub.4: Eu such as for example G, EG, Y and EY series of phosphors from Intematix Corporation, Fremont Calif., USA which have a peak emission wavelength in a range 507 nm to 570 nm and a FWHM of ˜70 nm to ˜80 nm. Suitable green phosphors are given in TABLE 2.
(66) In some embodiments, the green phosphor can comprise a green-emitting oxynitride phosphor as taught in U.S. Pat. No. 8,679,367 entitled “Green-Emitting (Oxy) Nitride-Based Phosphors and Light Emitting Devices Using the Same” which is hereby incorporated in its entirety. Such a green-emitting oxynitride (ON) phosphor can have a general composition Eu.sup.2+:M.sup.2+Si.sub.4AlO.sub.xN.sub.(7-2x/3) where 0.1≤x≤1.0 and M.sup.2+ is one or more divalent metal selected from the group consisting of Mg, Ca, Sr, Ba, and Zn. In this patent specification, the notation ON # represents the phosphor type (oxynitride) followed by the peak emission wavelength (λ.sub.pe) in nanometers (#). For example ON495 denotes a green oxynitride phosphor with a peak emission wavelength of 495 nm.
(67) TABLE-US-00002 TABLE 2 Example broadband green photoluminescence materials Wavelength Phosphor General Composition λ.sub.p (nm) YAG Y.sub.3-x(Al.sub.1-yGa.sub.y).sub.5O.sub.12:Ce.sub.x 0.01 < x < 0.2 & 0 < y < 2.5 520-550 (YAG #) GNYAG (Y,Ba).sub.3-x(Al.sub.1-yGa.sub.y).sub.5O.sub.12:Ce.sub.x 0.01 < x < 0.2 & 0 < y < 2.5 520-550 (YAG #) LuAG Lu.sub.3-x(Al.sub.1-yM.sub.y).sub.5O.sub.12:Ce.sub.x 0.01 < x < 0.2 & 0 < y < 1.5M = 500-550 (GAL #) Mg, Ca, Sr, Ba, Ga, LuAG Lu.sub.3-x(Al.sub.1-yGa.sub.y).sub.5O.sub.12:Ce.sub.x 0.01 < x < 0.2 & 0 < y < 1.5 500-550 (GAL #) Silicate A.sub.2SiO.sub.4:Eu A= Mg, Ca, Sr, Ba 500-550 Silicate (Sr.sub.1-xBa.sub.x).sub.2SiO.sub.4:Eu 0.3 < x < 0.9 500-550 Oxynitride Eu.sup.2+:M.sup.2+Si.sub.4AlO.sub.xN.sub.(7-2x/3) M.sup.2+ = Mg, Ca, Sr, Ba, Zn 500-550 (ON #) 0.1 ≤ x ≤ 1.0
(68) Red Photoluminescence Materials
(69) Narrowband Red Photoluminescence Materials
(70) In this patent specification, a narrowband red photoluminescence material refers to a photoluminescence material which, in response to stimulation by excitation light, generates light having a peak emission wavelength in a range 610 nm to 655 nm; that is light in the red region of the visible spectrum and which has a narrow emission characteristic with a Full Width at Half Maximum (FWHM) emission intensity of between about 5 nm and about 50 nm (less than about 50 nm). As described above, the narrowband red photoluminescence can comprise a manganese-activated fluoride red photoluminescence material that is disposed on and covers the front face of the substrate on which the LED chips are mounted. An example of a narrowband red manganese-activated fluoride photoluminescence material is manganese-activated potassium hexafluorosilicate phosphor (KSF)—K.sub.2SiF.sub.6:Mn.sup.4+ (KSF). An example of such a KSF phosphor is NR6931 KSF phosphor from Intematix Corporation, Fremont Calif., USA which has a peak emission wavelength of about 632 nm. Other manganese-activated phosphors can include: manganese-activated potassium hexafluorogermate phosphor (KGF)—K.sub.2GeF.sub.6:Mn.sup.4+ and manganese-activated potassium hexafluorotitanate phosphor (KTF)—K.sub.2TiF.sub.6:Mn.sup.4+.
(71) Broadband Red Photoluminescence Materials
(72) In this patent specification, a broadband red photoluminescence material (also referred to as a non-manganese-activated fluoride red photoluminescence material) refers to a photoluminescence material which, in response to stimulation by excitation light, generates light having a peak emission wavelength in a range 600 nm to 640 nm; that is light in the orange to red region of the visible spectrum and which has a broad emission characteristic with a full width at half maximum (FWHM) emission intensity of greater than about 50 nm. As described above, the broadband red photoluminescence can comprise rare-earth activated red photoluminescence materials. A broadband red photoluminescence material (non-manganese-activated fluoride red photoluminescence material) denotes a red photoluminescence material whose crystal structure is other than that of a narrowband red photoluminescence material (manganese-activated fluoride photoluminescence material), such as for example rare-earth-activated red photoluminescence materials and can comprise any such red photoluminescence material that is excitable by blue light and operable to emit light with a peak emission wavelength λ.sub.p in a range about 600 nm to about 640 nm. Rare-earth-activated red photoluminescence material can include, for example, a europium activated silicon nitride-based phosphor, α-SiAlON, Group IIA/IIB selenide sulfide-based phosphor or silicate-based phosphors. Examples of red phosphors are given in TABLE 3.
(73) In some embodiments, the europium activated silicon nitride-based phosphor comprises a Calcium Aluminum Silicon Nitride phosphor (CASN) of general formula CaAlSiN.sub.3:Eu.sup.2+. The CASN phosphor can be doped with other elements such as strontium (Sr), general formula (Sr,Ca)AlSiN.sub.3:Eu.sup.2+. In this patent specification, the notation CASN # represents the phosphor type (CASN) followed by the peak emission wavelength (λ.sub.pe) in nanometers (#). For example, CASN625 denotes a red CASN phosphor with a peak emission wavelength of 625 nm.
(74) In an embodiment, the rare-earth-activated red phosphor can comprise a red-emitting phosphor as taught in U.S. Pat. No. 8,597,545 entitled “Red-Emitting Nitride-Based Calcium-Stabilized Phosphors” which is hereby incorporated in its entirety. Such a red emitting phosphor comprises a nitride-based composition represented by the chemical formula M.sub.aSr.sub.bSi.sub.cAl.sub.dN.sub.eEu.sub.f, wherein: M is Ca, and 0.1≤a≤0.4; 1.5<b<2.5; 4.0≤c≤5.0; 0.1≤d≤0.15; 7.5<e<8.5; and 0<f<0.1; wherein a+b+f>2+d/v and v is the valence of M.
(75) Alternatively, the rare-earth-activated red phosphor can comprise a red emitting nitride-based phosphor as taught in U.S. Pat. No. 8,663,502 entitled “Red-Emitting Nitride-Based Phosphors” which is hereby incorporated in its entirety. Such a red emitting phosphor comprising a nitride-based composition represented by the chemical formula M.sub.(x/v)M′.sub.2Si.sub.5-xAl.sub.xN.sub.8:RE, wherein: M is at least one monovalent, divalent or trivalent metal with valence v; M′ is at least one of Mg, Ca, Sr, Ba, and Zn; and RE is at least one of Eu, Ce, Tb, Pr, and Mn; wherein x satisfies 0.1≤x<0.4, and wherein said red-emitting phosphor has the general crystalline structure of M′.sub.2Si.sub.5N.sub.8:RE, Al substitutes for Si within said general crystalline structure, and M is located within said general crystalline structure substantially at the interstitial sites. An example of one such a phosphor is XR610 red nitride phosphor from Intematix Corporation, Fremont Calif., USA which has a peak emission wavelength of 610 nm.
(76) Rare-earth-activated red phosphors can also include Group IIA/IIB selenide sulfide-based phosphors. A first example of a Group IIA/IM selenide sulfide-based phosphor material has a composition MSe.sub.1-xS.sub.x:Eu, wherein M is at least one of Mg, Ca, Sr, Ba and Zn and 0<x<1.0. A particular example of this phosphor material is CSS phosphor (CaSe.sub.1-xS.sub.x:Eu). Details of CSS phosphors are provided in co-pending United States patent application Publication Number US2017/0145309 filed 30 Sep. 2016, which is hereby incorporated by reference in its entirety. The CSS red phosphors described in United States patent publication US2017/0145309 can be used in the present invention. The emission peak wavelength of the CSS phosphor can be tuned from 600 nm to 650 nm by altering the S/Se ratio in the composition and exhibits a narrowband red emission spectrum with FWHM in the range ˜48 nm to ˜60 nm (longer peak emission wavelength typically has a larger FWHM value). In this patent specification, the notation CSS # represents the phosphor type (CSS) followed by the peak emission wavelength in nanometers (#). For example, CSS615 denotes a CSS phosphor with a peak emission wavelength of 615 nm.
(77) In some embodiments, the rare-earth-activated red phosphor can comprise an orange-emitting silicate-based phosphor as taught in U.S. Pat. No. 7,655,156 entitled “Silicate-Based Orange Phosphors” which is hereby incorporated in its entirety. Such an orange-emitting silicate-based phosphor can have a general composition (Sr.sub.1-xM.sub.x).sub.yEu.sub.zSiO.sub.5 where 0<x≤0.5, 2.6≤y≤3.3, 0.001≤z≤0.5 and M is one or more divalent metal selected from the group consisting of Ba, Mg, Ca, and Zn. In this patent specification, the notation O # represents the phosphor type (orange silicate) followed by the peak emission wavelength (λ.sub.pe) in nanometers (#). For example, O600 denotes an orange silicate phosphor with a peak emission wavelength of 600 nm.
(78) TABLE-US-00003 TABLE 3 Example broadband red photoluminescence materials General Wavelength Phosphor Composition λ.sub.p (nm) CASN (Ca.sub.1-xSr.sub.x)AlSiN.sub.3: 0.5 < x ≤ 1 600-650 (CASN #) Eu 258 nitride Ba.sub.2-xSr.sub.xSi.sub.5N.sub.8:Eu 0 < x <2 580-650 Group IIA/BB MSe.sub.1-xS.sub.x:Eu M = Mg, 600-650 Selenide Sulfide Ca, Sr, Ba, Zn 0 < x < 1.0 (CSS #) CaSe.sub.1-xS.sub.x:Eu 0 < x < 1.0 600-650 CSS (CSS #) Silicate (Sr.sub.1-xM.sub.x).sub.yEu.sub.zSiO.sub.5 M = Ba, Mg, Ca, Zn 565-650 (O #) 0 < x ≤ 0.5 2.6 ≤ y ≤ 3.3 0.001 ≤ z ≤ 0.5
(79) Nomenclature
(80) In this specification, the following nomenclature is used to denote LED-filaments: Com. # denotes a comparative LED-filament having the same photoluminescence materials on the front and back faces of the substrate and Dev. # denotes an LED-filament (device) in accordance with an embodiment of the invention having a narrowband red (manganese-activated fluoride) photoluminescence material on the front face of the substrate and a broadband red photoluminescence material on a back face of the substrate.
(81) Experimental Data—Single-Layer Structure LED-Filament
(82) Comparative LED-filaments (Com.1 and Com.2) and single-layer LED-filament in accordance with the invention (Dev.1) each comprise a 52 mm by 1.5 mm porous silica substrate with a transmittance 40% having twenty four serially connected 1025 (10 mil×25 mil) blue LED chips of dominant wavelength λ.sub.d=456 nm mounted on a front face. Each LED-filament is a nominal 0.7 W device and is intended to generate white light with a target Correlated Color Temperature (CCT) of 2700K and a target general color rendering index CRI Ra of 90.
(83) The photoluminescence materials (phosphors) used in the test devices are KSF phosphor (K.sub.2SiF.sub.6:Mn.sup.4+) from Intematix Corporation, CASN phosphor (Ca.sub.1-xSr.sub.xAlSiN.sub.3:Eu λ.sub.pe≈640 nm), green YAG phosphor (Intematix NYAG4156—(Y, Ba).sub.3-x(Al.sub.1-yGa.sub.y).sub.5O.sub.12:Ce.sub.x Peak emission wavelength λ.sub.pe=550 nm) and green LuAG phosphor (Intematix GAL535—Lu.sub.3-x(Al.sub.1-yGa.sub.y).sub.5O.sub.12:Ce.sub.x λ.sub.pe≈535 nm).
(84) The red and green phosphors were mixed in a phenyl silicone and the mixture dispensed onto the front and back faces of the substrate.
(85) TABLE 4 tabulates phosphor composition of comparative LED-filaments Com.1 and Com.2 and an LED-filament Dev.1 in accordance with the invention.
(86) As can be seen from TABLE 4, in terms of phosphor composition: comparative LED-filament Com. 1 comprises the same phosphor composition on the front and back faces of the substrate and comprises a mixture of 7 wt % CASN640 and 93 wt % GAL535. Comparative LED-filament Com.2 comprises the same phosphor composition on the front and back faces of the substrate and comprises a mixture of 60 wt % KSF and 40 wt % YAG550. LED-filament Dev.1, in accordance with the invention, comprises on the front face of the substrate a mixture of 56 wt % KSF, 4 wt % CASN615 and 40 wt % YAG550 and on a back face of the substrate a mixture of 7 wt % CASN and 93 wt % GAL535.
(87) TABLE-US-00004 TABLE 4 Phosphor composition of comparative LED-filaments (Com. 1 and Com. 2) and an LED-filament in accordance with the invention (Dev. 1) wt % photoluminescence material Front face Back face Filament KSF CASN615 CASN640 YAG550 GAL535 KSF CASN640 YAG550 GAL535 Com. 1 — — 7 — 93 — 7 — 93 Com. 2 60 — — 40 — 60 — 40 — Dev. 1 56 4 — 40 — — 7 — 93
(88) TABLE 5 tabulates the measured optical performance of the LED-filaments Com.1, Com.2 and Dev.1. As can be seen from TABLE 5, the flux generated by Dev.1 is 22.2 lm greater (19% brighter: Brightness—Br) than LED-filament Com.1 that uses CASN on both front and back faces of the substrate. While LED-filament Com.2 generates a flux that is 33.5 lm greater (26% brighter: Brightness—Br) than LED-filament Com.1, this LED-filament uses double the amount of KSF (narrowband red photoluminescence material) as that of Dev.1. It will be appreciated that LED-filament Dev.1 achieves 94% (119/126) of the possible brightness gain of using KSF (narrowband red photoluminescence material) in place of CASN, but using only half (50% by weight) the amount of KSF. This is achieved, at least in part, due to the presence of the partially light transmissive substrate used in Dev.1. The invention thus discloses improvements relating to the LED-filaments and LED-filament lamps and in particular, although not exclusively, reducing the cost of manufacture of LED-filaments without compromising on brightness and CRI Ra.
(89) TABLE-US-00005 TABLE 5 Measured optical characteristics of 0.7 W, 2700 K nominal color temperature LED-filaments Com. 1, Com. 2 and Dev. 1 Flux Br Light emission (%) CIE CCT CRI Filament (lm) (%) Forward Backward x y (K) Ra Com. 1 115.5 100 84 16 0.4245 0.3952 3070 95.6 Com. 2 145.8 126 80 20 0.4391 0.4175 3148 90.5 Dev. 1 137.7 119 80 20 0.4821 0.4395 2624 85.0
(90) Experimental Data—Double-Layer Structured LED-Filament
(91) As discussed above, double-layer structured LED-filaments (
(92) Dev.2 and Dev.3 each comprise a 38 mm by 1.5 mm porous silica substrate with a transmittance≈40% having twenty four serially connected 714 (7 mil×14 mil) blue LED chips of dominant wavelength λ.sub.d=456 nm mounted on a front face. Each LED-filament is a nominal 150 lm (1 W) device and is intended to generate white light with a target Correlated Color Temperature (CCT) of 2700K and a target general color rendering index CRI Ra of 90. It will be appreciated that three of these LED-filaments can be used to provide a 450 lm LED-filament lamp.
(93) The photoluminescence materials (phosphors) used in the test devices are KSF phosphor (K.sub.2SiF.sub.6:Mn.sup.4+) from Intematix Corporation, CASN phosphors (Ca.sub.1-xSr.sub.xAlSiN.sub.3:Eu λ.sub.pe≈615 nm, 631 nm and 640 nm), and green YAG phosphors (Intematix GYAG4156 and GYAG543—(Y, Ba).sub.3-x(Al.sub.1-yGa.sub.y).sub.5O.sub.12:Ce.sub.x Peak emission wavelength λ.sub.pe=543 nm and 550 nm).
(94) For the single-layer LED-filament Dev.2 the red and green phosphors were mixed in a phenyl silicone and the mixture dispensed onto respective front and back faces of the substrate.
(95) For the two-layer LED-filament Dev.3, the KSF was mixed with a phenyl silicone and the mixture dispensed as a strip (first layer) onto the front face of the substrate covering the LED chips. The green phosphor and CASN was mixed in a phenyl silicone and the mixture dispensed as a second layer on the first layer on the front face of the substrate. On the back face, the green phosphor and CASN was mixed in a phenyl silicone and the mixture dispensed onto the back face of the substrate.
(96) TABLE 6 tabulates phosphor compositions of the single-layer LED-filament Dev.2 and the double-layer LED-filament Dev.3. As can be seen from TABLE 6, in terms of phosphor composition the single-layer LED-filament Dev.2 comprises, on the front face of the substrate, a mixture of 74 wt % KSF, 2.2 wt % CASN615 and 23.8 wt % YAG543 and on a back face of the substrate a mixture of 5 wt % CASN (1.4 wt % CASN631+3.6 wt % CASN650) and 95 wt % YAG550. As can be seen from TABLE 6, in terms of phosphor composition the double-layer LED-filament Dev.3 comprises on the front face of the substrate a first layer comprising KSF only (17.0 wt % of the total phosphor content of the front face) and a second layer comprising a mixture of 7.8 wt % CASN615 and 75.2 wt % YAG543 and on a back face of the substrate a mixture of 5 wt % CASN (1.4 wt % CASN631+3.6 wt % CASN650) and 95 wt % YAG550. Dev.3 comprises on the back face of the substrate a mixture of 5 wt % CASN (1.4 wt % CASN631+3.6 wt % CASN650) and 95 wt % YAG550.
(97) TABLE-US-00006 TABLE 6 Phosphor composition of a single-layer (Dev. 2) and double-layer (Dev. 3) LED-filaments wt % photoluminescence material Back face Front face CASN Filament KSF CASN615 YAG543 CASN631 CASN650 YAG550 Dev. 2 74.0 2.2 23.8 1.4 3.6 95.0 Dev. 3 17.0 7.8 75.2 1.4 3.6 95.0
(98) TABLES 7A and 7B tabulate the phosphor amounts (usage) of the single-layer LED-filament Dev.2 and the double-layer LED-filament Dev.3. The phosphor weight values (weight) in TABLES 7A and 7B are normalized phosphor weight normalized to the weight of KSF of the single-layer LED-filament Dev.1.
(99) TABLE-US-00007 TABLE 7A Phosphor amount of single-layer (Dev. 2) and double-layer (Dev. 3) LED-filaments weight - phosphor weight normalized to weight of KSF of the single-layer LED-filament Dev. 1 Front face - Phosphor amount KSF CASN YAG Total CASN/(CASN + KSF) Filament weight % Weight % weight % weight % (wt %) Dev. 2 1.0000 100 0.0302 100 0.3219 100 1.3521 100 2.9 Dev. 3 0.2044 20 0.0942 312 0.9070 282 1.2056 89 31.5
(100) TABLE-US-00008 TABLE 7B Phosphor amount of single-layer (Dev. 2) and double-layer (Dev. 3) LED-filaments weight - phosphor weight normalized to weight of KSF of the single-layer LED-filament Dev. 1 Phosphor amount Back face Total CASN YAG Total (Front and Back) Filament weight % weight % weight % weight % Dev. 2 0.0524 100 0.9968 100 1.0492 100 2.4013 100 Dev. 3 0.0963 184 1.8350 184 1.9313 184 3.1369 131
(101) TABLE 8 tabulates the measured optical performance of the LED-filaments Dev.2 (single-layer) and Dev.3 (double-layer). The data are for a drive current I.sub.F=15 mA and drive voltage V.sub.F=68.7 V and are after 3 minutes of operation once the filament had reached thermal stability (Hot). As can be seen from TABLE 8, the color point of light generated by the LED-filaments are very similar with the General CRI Ra of the double-layer LED-filament Dev.3 being 93.1 compared with 90.5 of the single-layer LED-filament Dev.2. Moreover, the flux generated by the double-layer LED-filament Dev.3 being 4.7 lm greater (3.0% brighter: Brightness—Br) than the flux generated by the single-layer LED-filament Dev.2. Most significantly, while the two LED-filaments generate very similar light emissions, as can be seen from TABLE 8, compared with the single-layer LED-filament Dev.2, the double-layer LED-filament Dev.3 uses 80% by weight less KSF (0.2044 compared with 1.0000), as can be seen from TABLES 7A and 7B. Although the double-layer LED-filament Dev.3 compared with the single-layer LED-filament Dev.2 uses more CASN (212% by weight increase on front face—0.0942 compared with 0.0302 and 84% by weight increase on back face—0.0963 compared with 0.0524) and YAG (182% by weight increase on front face—0.9070 compared with 0.3219 and 84% by weight increase on back face—1.9313 compared with 1.0492), the double-layer structure still provides a substantial cost saving compared with a single-layer structure due to huge difference in costs of CASN (about a ⅕ of the cost of KSF) and YAG (about 1/100 to 1/150 of the cost of KSF) compared with KSF. It is believed that the reason for the increase in CASN and YAG usage is that due to less blue excitation light reaching the second phosphor layer, more CASN and YAG phosphor is required to generate red and green light to attain the required target color.
(102) As described above, the reduction in KSF usage is a result of locating the KSF in a separate layer that is in contact with (adjacent to) the LED chips. It is believed that the reason for this reduction in KSF usage amount, is that in a single-layer LED-filament Dev.2 comprising a single photoluminescence layer comprising a mixture of KSF (manganese-activated fluoride photoluminescence material), CASN and YAG, the various photoluminescence materials have equal exposure to blue excitation light. Since KSF has a much lower blue light absorption capability than YAG and CASN materials, a greater amount of KSF is necessary to convert enough blue light to the required red emission. By contrast, in the double-layer LED-filament Dev.3, the KSF (manganese-activated fluoride photoluminescence material) in its separate respective first layer is exposed to blue excitation light individually without competition from the YAG and CASN; thus, more of the blue excitation light can be absorbed by the KSF. Since the KSF can more effectively convert the blue excitation light to red emission, the amount (usage) of KSF (narrowband red photoluminescence material) required to achieve a target color point can be reduced compared with LED-filaments comprising a single-layer comprising a mixture of photoluminescence materials.
(103) As will be further noted from TABLE 7A, the content ratio of the CASN (broadband red photoluminescence material) with respect to the total of the KSF (narrowband red photoluminescence material) and CASN in the double-layer LED-filament Dev.3 is greater than about 30 wt %.
(104) TABLE-US-00009 TABLE 8 Measured optical characteristics of 150 lm, 2700 K LED-filaments Dev. 2 and Dev. 3 Flux Br lm/ CIE CCT CRI Ra Filament (lm) (%) W x y (K) Ra R8 R9 Dev. 2 154.5 100.0 150.0 0.4595 0.4103 2702 90.5 91.8 76.9 Dev. 3 159.2 103.0 154.3 0.4591 0.4113 2716 93.1 87.3 67.3
(105) Dev.4 is a further double-layer LED-filament in accordance with the invention and is a nominal 250 lm (1.5 W) device that is intended to generate white light with a target Correlated Color Temperature (CCT) of 2700K and a target general color rendering index CRI Ra of 90. It will be appreciated that four of these LED-filaments can be used to provide a 1000 lm LED-filament lamp using for example the embodiment of
(106) TABLE 9 tabulates phosphor compositions of the double-layer LED-filament Dev.4. As can be seen from TABLE 9, in terms of phosphor composition the double-layer LED-filament Dev.4 comprises on the front face of the substrate a first layer comprising KSF only (23.1 wt % of the total phosphor content of the front face) and a second layer comprising a mixture of 7.5 wt % CASN615 and 69.4 wt % YAG543. On a back face of the substrate a mixture of 9.1 wt % CASN615 and 90.9 wt % YAG535.
(107) TABLE-US-00010 TABLE 9 Phosphor composition of a 250 lm double-layer LED-filament Dev.4 wt % photoluminescence material Front face Back face Filament KSF CASN615 YAG543 CASN615 YAG535 Dev.4 23.1 7.5 69.4 9.1 90.9
TABLES 10A and 10B tabulate the phosphor amounts (mg) of the double-layer LED-filament Dev.4. The phosphor weight values (weight) in TABLES 10A and 10B are normalized phosphor weight normalized to the weight of KSF of a single-layer LED-filament using the same photoluminescence materials. As can be seen from TABLE 10A a double-layer structured LED-filament reduces KSF usage nearly 80% by weight (0.1956 compared with 1.0000) compared with a single-layer structured LED-filament and nearly 90% by weight compared with known LED-filaments that comprise KSF on the front and back faces. As will be further noted from TABLE 10A, the content ratio of the CASN (broadband red photoluminescence material) with respect to the total of the KSF (narrowband red photoluminescence material) and CASN in the double-layer LED-filament Dev.4 is about 25 wt %.
(108) TABLE-US-00011 TABLE 10A Phosphor amount of 250 lm double-layer LED-filament Dev. 4 Front face - Phosphor amount KSF CASN615 YAG543 Total CASN/(CASN + KSF) Filament weight % weight weight weight (wt %) Dev. 4 0.1956 19.6 0.0642 0.7012 0.9610 24.7
(109) TABLE-US-00012 TABLE 10B Phosphor amount of a double-layer LED-filament Dev.4 Phosphor amount Back face CASN615 YAG535 Total Total weight Filament weight weight weight Front & Back Dev.4 0.0493 0.3764 0.4257 1.3867
(110) TABLE 11 tabulates the measured optical performance of the double-layer LED-filament Dev.4. The data includes measurements immediately after switching the filament on (referred to as Instantaneous or COLD measurement) and after the filament has reached thermal stability (referred to as HOT measurement) after a period of about 3 minutes operation. Test data has shown that double-layer structured LED-filament enable production of LED-filaments having a CRI Ra greater than 90 and an optical performance which is greater (5% to 10%) than known LED-filament with a CRI Ra of only 80.
(111) TABLE-US-00013 TABLE 11 Measured optical characteristics of a nominal 250 lm, 2700 K double-layer LED-filament Dev. 4 I.sub.F V.sub.F Flux lm/ CIE CCT CRI Ra Test Condition (mA) (V) (lm) W x y (K) Ra R8 R9 Cold (C) 20.0 68.6 252.0 183.8 0.4556 0.4148 2793 92.5 83.5 59.3 Hot (H) 20.0 67.3 234.7 174.4 0.4553 0.4094 2756 93.4 83.6 61.2 Δ C to H for 0.0 −1.3 93% 95% −0.0004 −0.0054 −37 +0.9 +0.1 +1.9 I.sub.F = 20 mA Hot (H) 22.0 67.4 254.5 171.6 0.4552 0.4089 2753 93.4 83.5 61.1 Hot (H) 25.0 67.6 282.9 167.3 0.4552 0.4083 2748 93.4 83.4 61.0
(112) Experimental Data—Single-Layer Structured LED-Filament Inc. Light Scattering Layer
(113) Single-layer LED-filament (Dev.5—comparative device) and Single-layer LED-filaments including a light scattering layer in accordance with the invention (Dev.6 to Dev.8) each comprise a 52 mm by 1.5 mm porous silica substrate with a transmittance 40% having twenty five serially connected 1025 (10 mil×25 mil) blue LED chips of dominant wavelength λ.sub.d=456 nm mounted on a front face. Each LED-filament is a nominal 250 lm (1.5 W) device and is intended to generate white light with a target Correlated Color Temperature (CCT) of 3000K and a target general color rendering index CRI Ra of 90. LED-filament Dev.5 has the single-layer structure of
(114) The photoluminescence materials (phosphors) used in the test devices are KSF phosphor (K.sub.2SiF.sub.6:Mn.sup.4+) from Intematix Corporation, CASN phosphors (Ca.sub.1-xSr.sub.xAlSiN.sub.3:Eu λ.sub.pe≈615 nm, 631 nm and 650 nm), and green YAG phosphors (Intematix GYAG4156 and GYAG542—(Y, Ba).sub.3-x(Al.sub.1-yGa.sub.y).sub.5O.sub.12:Ce.sub.x Peak emission wavelength λ.sub.pe=542 nm and 550 nm).
(115) The red and green phosphors were mixed in a phenyl silicone and the mixture dispensed onto the substrate.
(116) TABLE 12 tabulates phosphor composition (wt % photoluminescence material) of comparative single-layer LED-filament without light scattering layer Dev.5 and single-layer LED-filaments including a light scattering layer Dev.6 to Dev.8.
(117) As can be seen from TABLE 12, in terms of phosphor composition LED-filament Dev.5 comprises, on the front face of the substrate, a mixture of 77.0 wt % KSF, 2.0 wt % CASN615 and 21.0 wt % YAG542 and on a back face of the substrate a mixture of 5 wt % CASN (1.4 wt % CASN631+3.6 wt % CASN650) and 95 wt % YAG550. Each of LED-filaments Dev.6 to Dev.8 comprise no phosphor on the back face of the substrate. As can be seen from TABLE 12, in terms of phosphor composition the LED-filament Dev.6 comprises on the front face of the substrate a mixture of 75.4 wt % KSF, 1.6 wt % CASN615 and 23.0 wt % YAG542; LED-filament Dev.7 comprises on the front face of the substrate a mixture of 76.0 wt % KSF, 1.4 wt % CASN615 and 22.6 wt % YAG542; and LED-filament Dev.8 comprises on the front face of the substrate a mixture of 77.7 wt % KSF, 0.7 wt % CASN615 and 21.6 wt % YAG542.
(118) TABLE-US-00014 TABLE 12 Phosphor composition of 250 lm single-layer LED-filaments Dev. 5 to Dev. 8 wt % photoluminescence material Back face Front face CASN Filament KSF CASN615 YAG542 CASN631 CASN650 YAG550 Dev. 5 77.0 2.0 21.0 1.4 3.6 95.0 Dev. 6 75.4 1.6 23.0 — — — Dev. 7 76.0 1.4 22.6 — — — Dev. 8 77.7 0.7 21.6 — — —
(119) TABLES 13A and 13B tabulate the phosphor amounts (usage) of the single-layer LED-filament without light scattering layer Dev.5 and the single-layer LED-filament including a light scattering layer Dev.6 to Dev.8. The phosphor weight values (weight) in TABLES 13A and 13B are normalized phosphor weights that are normalized to the weight of KSF of the single-layer LED-filament Dev.5.
(120) By comparing the phosphor amounts for single-layer LED-filaments Dev.6 to Dev.8 including a light scattering layer with those of single-layer LED-filament Dev.5, it is to be noted the inclusion of a light scattering layer substantially reduces not only KSF usage but also reduces CASN and YAG usage and that the magnitude of the reduction in phosphor usage is related to the wt % loading of light scattering material (TiO.sub.2) to light transmissive binder material in the light scattering layer. This result is to be compared with the double-layer LED-filament (Dev.3) that substantially reduced KSF usage but substantially increased CASN and YAG usage (TABLES 7A and 7B).
(121) As can be seen from TABLE 13A and comparing LED-filament Dev.6 with LED-filament Dev.5, the provision of a light scattering layer with a 0.4 wt % loading of TiO.sub.2 to silicone: (i) reduces KSF usage (front face) by about 36% by weight (0.6396 compared with 1.0000), (ii) reduces CASN usage (front face) by about 48% by weight (0.0133 compared with 0.0255), (iii) reduces YAG usage (front face) by about 28% by weight (0.1947 compared with 0.2721), and (iv) reduces total phosphor usage on the front face of the substrate by about 35% by weight (0.8476 compared with 1.2976). Moreover, it will be further noted from TABLE 13B that when taking into account that there is no phosphor on the back face of the substrate of Dev.6, the overall reduction in total phosphor usage (front and back faces) is about 60% by weight (0.8476 compared with 2.1122).
(122) As can be seen from the tables for an LED-filament Dev.7 with a 1.0% wt % loading of TiO.sub.2, this reduces KSF usage by about 59% by weight (0.4075 compared with 1.0000) and reduces total phosphor usage (front and back faces) by about 75% by weight (0.5297 compared with 2.1122) and for an LED-filament Dev.8 with a light scattering layer with a 2.0% wt % loading of TiO.sub.2 this reduces KSF usage by about 67% by weight (0.3308 compared with 1.0000) and reduces total phosphor usage (front and back faces) by about 67% by weight (0.4230 compared with 2.1122).
(123) As will be further seen from the tables the provision of a light scattering layer reduces the content ratio of the broadband red photoluminescence material (e.g. CASN) with respect to the total red photoluminescence material content (i.e. narrowband red photoluminescence material+broadband red photoluminescence material) in the LED-filament with the amount of reduction increasing with increasing TiO.sub.2 weight loading. For example, for Dev.5 the CASN content ratio is 2.5 wt %, for Dev.6 the content ratio is 2.0 wt % (TiO.sub.2 0.4 wt %), for Dev.7 the content ratio is 0.2 wt % (TiO.sub.2 1.0 wt %), and for Dev.8 the content ratio is 0.1 wt % (TiO.sub.2 2.0 wt %). This is to be contrasted with the double-layer structure LED-filament without a light scattering layer (Dev.3) which showed an increase in content ratio to 31.5 wt % compared with a content ratio of 2.9 wt % for a single-layer structured LED-filament (Dev.2)—TABLE 7A. In some embodiments, for a balance of off-state white visual appearance and optical performance, the content ratio of broadband red photoluminescence material with respect to the total red photoluminescence material in the LED-filament can be from about 0.1 wt % to about 0.5 wt %.
(124) As described herein, not only does the inclusion of a light scattering layer reduce overall phosphor usage, it also improves the off-state white appearance of the LED-filament. For example, in an off-state: LED-filament Dev.5 is bright yellow to orange in color; LED-filament Dev.6 is slightly yellowy white in color; LED-filament Dev.7 is slightly off-white in color; and LED-filament Dev.8 is white in color.
(125) TABLE-US-00015 TABLE 13A Phosphor/TiO.sub.2 amount of 250 lm single-layer LED-filaments Dev. 5 to Dev. 8 weight - weight normalized to weight of KSF of LED-filament Dev. 5 Front face - Phosphor amount KSF CASN615 YAG543 Total CASN/(CASN + KSF) TiO.sub.2 Filament Weight % Weight % Weight % Weight % Reduction (wt %) (wt %) Dev. 5 1.0000 100 0.0255 100 0.2721 100 1.2976 100 0% 2.5 0 Dev. 6 0.6396 64 0.0133 52 0.1947 72 0.8476 65 35% 2.0 0.4 Dev. 7 0.4075 41 0.0008 29 0.1214 45 0.5297 41 59% 0.2 1.0 Dev. 8 0.3308 33 0.0003 11 0.0919 34 0.4230 33 67% 0.1 2.0
(126) TABLE-US-00016 TABLE 13B Phosphor/TiO.sub.2 amount of 250 lm single-layer LED-filaments Dev. 5 to Dev. 8 weight - phosphor weight normalized to weight of KSF of LED-filament Dev. 5 Front and Back - Total Back face - Phosphor weight phosphor weight TiO.sub.2 Filament KSF CASN YAG535 Total Weight % reduction (wt %) Dev. 5 — 0.0408 0.7754 0.8162 2.1122 100 0 0 Dev. 6 — — — — 0.8476 40 60% 0.4 Dev. 7 — — — — 0.5297 25 75% 1.0 Dev. 8 — — — — 0.4230 20 80% 2.0
(127) TABLE 14 tabulates the measured optical performance of single-layer LED-filaments Dev.5 to Dev.8. The data are for a drive current I.sub.F=20 mA and drive voltage V.sub.F≈67 V and are after 3 minutes of operation once the filament had reached thermal stability.
(128) As described herein, while an increase in TiO.sub.2 loading in the light scattering layer increases the reduction in phosphor usage, it also decreases the light brightness.
(129) As can be seen by comparing each of LED-filaments Dev.6 to Dev.8 with Dev.5, each LED-filament generates light with substantially the same optical characteristics (CIE x, CIE y, CRI Ra, CRI R9). It will be noted that the brightness of light (BR), and luminous efficacy of LED-filaments Dev.6 to Dev.8 decreases with increasing TiO.sub.2 loading in the light scattering layer. For example, comparing LED-filament Dev.6 with Dev.5, Dev.6 generates light of substantially the same quality but with a reduction in brightness and luminous efficacy of about 2% (98.0% compared with 100.0%). It is to be noted that while LED-filament Dev.6 has a small 2% reduction in brightness and luminous efficacy, the provision of the light scattering layer with a 0.4 wt % loading of TiO.sub.2 has resulted in a substantial reduction in total phosphor usage of 60% and improvement in the visual appearance of the filament from bright yellow to orange in color to slightly yellowy white in color.
(130) Comparing LED-filament Dev.7 with Dev.5, Dev.7 generates light of substantially the same quality but with a reduction in brightness of about 6.4% (93.6% compared with 100.0%) and a reduction in luminous efficacy of about 5.5% (94.5% compared with 100.0%). It is to be noted that while LED-filament Dev.7 has a relatively small (about 6%) reduction in brightness and luminous efficacy, the provision of the light scattering layer with a 1.0 wt % loading of TiO.sub.2 has resulted in a vast 75% reduction in total phosphor usage and improvement in the visual appearance of the filament from bright yellow to orange in color to slightly off-white in color.
(131) Comparing LED-filament Dev.8 with Dev.5, Dev.8 generates light of substantially the same quality but with a reduction in brightness of about 17% (83.0% compared with 100.0%) and a reduction in luminous efficacy of about 16.1% (83.9% compared with 100.0%). It is to be noted that while LED-filament Dev.8 has about a 17% reduction in brightness and luminous efficacy, the provision of the light scattering layer with a 2.0 wt % loading of TiO.sub.2 has resulted in a massive 80% reduction in total phosphor usage and improvement in the visual appearance of the filament from bright yellow to orange in color to white in color.
(132) It will be appreciated that while the reduction in luminous efficacy is dependent on TiO.sub.2 loading in the light scattering layer, the reduction will also depend on the thickness of the light scattering layer. For example, a thinner light scattering layer with a higher loading of light scattering material can achieve a similar result and vice versa. It is anticipated that loading of light scattering material to light transmissive binder may be from 0.1 wt % to 5 wt %.
(133) TABLE-US-00017 TABLE 14 Measured optical characteristics of 250 lm, 3000 K LED-filaments Dev. 5 to Dev. 8 Flux Br Efficacy CIE CCT CRI TiO.sub.2 Filament (lm) (%) lm/W % x y (K) Ra R9 (wt %) Dev. 5 256.7 100.0 191.6 100 0.4359 0.4071 3043 92.9 72.1 0 Dev. 6 251.5 98.0 188.7 98.0 0.4317 0.4074 3118 90.4 67.9 0.4 Dev. 7 240.3 93.6 181.1 94.5 0.4387 0.4084 3006 90.4 67.8 1.0 Dev. 8 213.0 83.0 160.8 83.9 0.4401 0.4103 2998 92.3 82.9 2.0
(134) Preliminary tests suggest that a double-layer LED-filament including a light scattering layer (0.4 wt % TiO.sub.2) compared with a single-layer LED-filament without a light scattering layer (e.g. Dev.5) provide about an 80% reduction by weight in KSF and about a 100% increase by weight in green to red photoluminescence material (YAG, CASN) giving an overall reduction in phosphor usage of about 30% to 40% by weight. This is to be compared with the double-layer filament (Dev.4) without light scattering layer that compared with a single-layer LED-filament without a light scattering layer (Dev.2) used 80% by weight less KSF and about a 200% increase by weight in green to red photoluminescence material (YAG, CASN) giving an overall increase in phosphor usage of about 30% by weight.
(135) Embodiments of the invention thus concern improvements relating to the LED-filaments and LED-filament lamps and in particular, although not exclusively, reducing the cost of manufacture of LED-filaments without compromising on brightness and CRI Ra.
(136) As used in this document, and as customarily used in the art, terms of approximation, including the words “substantially” and “about,” are defined to mean normal variations in the dimensions and other properties of finished goods that result from manufacturing tolerances and other manufacturing imprecisions, and the normal variations in the measurement of such dimensions and other properties of finished goods.
(137) While the invention has been described in detail, it will be apparent to one skilled in the art that various changes and modifications can be made and equivalents employed, without departing from the present invention. It is to be understood that the invention is not limited to the details of construction, the arrangements of components, and/or the method set forth in the above description or illustrated in the drawings. Statements in the abstract of this document, and any summary statements in this document, are merely exemplary; they are not, and cannot be interpreted as, limiting the scope of the claims. Further, the figures are merely exemplary and not limiting. Topical headings and subheadings are for the convenience of the reader only. They should not and cannot be construed to have any substantive significance, meaning or interpretation, and should not and cannot be deemed to indicate that all of the information relating to any particular topic is to be found under or limited to any particular heading or subheading. Therefore, the invention is not to be restricted or limited except in accordance with the following claims and their legal equivalents.