U.S. patent application number 17/731432 was filed with the patent office on 2022-09-15 for led-filaments and led-filament lamps.
The applicant listed for this patent is Intematix Corporation. Invention is credited to Yi-Qun Li, Gang Wang, Jun-Gang Zhao.
Application Number | 20220293571 17/731432 |
Document ID | / |
Family ID | 1000006362496 |
Filed Date | 2022-09-15 |
United States Patent
Application |
20220293571 |
Kind Code |
A1 |
Wang; Gang ; et al. |
September 15, 2022 |
LED-Filaments and LED-Filament Lamps
Abstract
An LED-filament includes a partially light-transmissive
substrate; blue LED chips mounted on a front face of the substrate;
first broad-band green to red photoluminescence materials and a
first narrow-band manganese-activated fluoride red
photoluminescence material covering the blue LED chips and the
front face of the substrate; and second broad-band green to red
photoluminescence materials covering the back face of the
substrate. The LED-filament may further include a second
narrow-band manganese-activated fluoride red photoluminescence
material on the back face of the substrate in an amount that is
less than 5 wt % of a total red photoluminescence material content
on the back face of the substrate.
Inventors: |
Wang; Gang; (Sunnyvale,
CA) ; Zhao; Jun-Gang; (Fremont, CA) ; Li;
Yi-Qun; (Danville, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Intematix Corporation |
Fremont |
CA |
US |
|
|
Family ID: |
1000006362496 |
Appl. No.: |
17/731432 |
Filed: |
April 28, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16540019 |
Aug 13, 2019 |
11342311 |
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17731432 |
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62831699 |
Apr 9, 2019 |
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62820249 |
Mar 18, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F21Y 2103/10 20160801;
H01L 2933/0091 20130101; H01L 33/507 20130101; F21K 9/232 20160801;
H01L 25/0753 20130101; H01L 33/504 20130101; F21Y 2115/10
20160801 |
International
Class: |
H01L 25/075 20060101
H01L025/075; H01L 33/50 20060101 H01L033/50 |
Claims
1. (canceled)
2. An LED-filament comprising: an at least partially
light-transmissive substrate; an array of LED chips on a front face
of the substrate; a first layer containing a narrow-band red
phosphor, wherein the first layer is in direct contact with and
covers all of the LED chips of the array; a second layer containing
a first broad-band green phosphor and a first broad-band red
phosphor, wherein the second layer is in direct contact with and
covers the first layer; and a third layer containing a second
broad-band green phosphor and a second broad-band red phosphor
covering a back face of the substrate.
3. The LED-filament of claim 2, wherein the third layer contains no
narrow-band red phosphor, or wherein the third layer contains a
narrow-band red phosphor in an amount up to 5 wt % of a total red
phosphor content of the third layer.
4. The LED-filament of claim 2, wherein a content ratio of the
first broad-band red phosphor with respect to the total of the
narrow-band red phosphor and the first broad-band red phosphor is
at least one of: at least 20 wt %; at least 30 wt %; and at least
40 wt %.
5. The LED-filament of claim 2, wherein the peak emission
wavelength of the first broad-band red phosphor is shorter than at
least one of: the peak emission wavelength of the second broad-band
red phosphor, and the peak emission wavelength of the narrow-band
red phosphor.
6. The LED-filament of claim 5, wherein the peak emission
wavelength of the first broad-band red phosphor is about 615
nm.
7. The LED-filament of claim 5, wherein the peak emission
wavelength of the second broad-band red phosphor is from about 620
nm to about 650 nm.
8. The LED-filament of claim 2, further comprising a layer
containing particles of a light scattering material, wherein the
layer is in contact with at least one of: the first layer, the
second layer, and the third layer.
9. The LED-filament of claim 8, wherein light scattering material
is selected from the group consisting of: zinc oxide, titanium
dioxide, barium sulfate, magnesium oxide, silicon dioxide, aluminum
oxide, zirconium oxide, and mixtures thereof.
10. The LED-filament of claim 2, wherein the narrow-band red
phosphor is at least 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+.
11. The LED-filament of claim 2, wherein the substrate has a
transmittance of one of: from 20% to 100%, from 2% to 70%, from 30%
to 50%, and from 10% to 30%.
12. The LED-filament of claim 2, wherein the LED-filament has a
luminous efficacy of at least 150 lm/W.
13. The LED-filament of claim 2, wherein the first layer is on at
least one light emitting face of the LED chips, or is on each light
emitting face of the LED chips.
14. The LED-filament of claim 2, wherein at least one of the first
layer, the second layer, and the third layer comprises particles of
a light scattering material.
15. The LED-filament of claim 14, wherein light scattering material
is selected from the group consisting of: zinc oxide, titanium
dioxide, barium sulfate, magnesium oxide, silicon dioxide, aluminum
oxide, zirconium oxide, and mixtures thereof.
16. An LED-filament lamp comprising an LED-filament, wherein the
LED-filament comprises: an at least partially light-transmissive
substrate; an array of LED chips on a front face of the substrate;
a first layer containing a narrow-band red phosphor, wherein the
first layer is in direct contact with and covers all of the LED
chips of the array; a second layer containing a first broad-band
green phosphor and a first broad-band red phosphor, wherein the
second layer is in direct contact with and covers the first layer;
and a third layer on a back face of the substrate containing a
second broad-band green phosphor and a second broad-band red
phosphor.
17. The LED-filament lamp of claim 16, wherein the third layer
contains no narrow-band red phosphor or wherein the third layer
contains a narrow-band red phosphor in an amount up to 5 wt % of a
total red phosphor content of the third layer.
18. The LED-filament lamp of claim 16, wherein the peak emission
wavelength of the first broad-band red phosphor is shorter than at
least one of: the peak emission wavelength of the second broad-band
red phosphor, and the peak emission wavelength of the narrow-band
red phosphor.
19. The LED-filament lamp of claim 16, wherein the peak emission
wavelength of the first broad-band red phosphor is about 615 nm
and/or the peak emission wavelength of the second broad-band red
phosphor is from about 620 nm to about 650 nm.
20. The LED-filament lamp of claim 16, further comprising a layer
containing particles of a light scattering material, wherein the
layer is in contact with at least one of: the first layer, the
second layer, and the third layer.
21. The LED-filament lamp of claim 16, wherein the narrow-band red
phosphor is at least 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
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/540,019, filed Aug. 13, 2019, which in turn
claims the benefit of priority to U.S. provisional application Ser.
No. 62/831,699, filed Apr. 9, 2019, each of which is hereby
incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] Embodiments of the present invention are directed to
LED-filaments and LED-filament lamps. More particularly, although
not exclusively, the invention concerns LED-filaments and
LED-filament lamps that generate light having a General Color
Rendering Index CRI Ra of at least 80.
BACKGROUND OF THE INVENTION
[0003] White light emitting LEDs ("white LEDs") include one or more
photoluminescence materials (typically inorganic phosphor
materials), which absorb a portion of the blue light emitted by the
LED and re-emit light of a different color (wavelength). The
portion of the blue light generated by the LED that is not absorbed
by the phosphor material combined with the light emitted by the
phosphor provides light which appears to the eye as being white in
color. Due to their long operating life expectancy (>50,000
hours) and high luminous efficacy (100 lm/W and higher), white LEDs
are rapidly being used to replace conventional fluorescent, compact
fluorescent and incandescent lamps.
[0004] Recently, LED-filament lamps have been developed comprising
LED-filaments whose visual appearance resemble the filament of a
traditional incandescent lamp. The LED-filaments, which are
typically 2 inches (52 mm) long, comprise COG (Chip-On-Glass)
devices having a plurality of low-power LED chips mounted on one
face of a light-transmissive glass substrate. Front and back faces
of the light-transmissive substrate are coated with a
phosphor-impregnated encapsulant, such as silicone. Typically, the
phosphor comprises a mixture of green and red light emitting
phosphors for generating warm white light and to increase General
Color Rendering Index (CRI Ra) of light generated by the filament.
The same phosphor-impregnated encapsulant is applied to both faces
of the substrate to ensure that the filament generates the same
color of light in forward and backward directions.
[0005] Narrow-band red phosphors such as, for example,
manganese-activated fluoride phosphors such as
K.sub.2SiF.sub.6:Mn.sup.4+(KSF), K.sub.2TiF.sub.6:Mn.sup.4+(KTF),
and K.sub.2GeF.sub.6:Mn.sup.4+(KGF) have a very narrow red spectrum
(Full Width Half Maximum of less than 10 nm for their main emission
line spectrum) which makes them highly desirable for attaining high
brightness (about 25% brighter than broad-band red phosphors such
as europium-activated red nitride phosphor materials such as
CASN--CaAlSiN.sub.3:Eu) and high CRI Ra in general lighting
applications. While manganese-activated fluoride photoluminescence
materials are highly desirable, there are drawbacks that make their
use in LED-filaments challenging. For example, the absorption
capability of manganese-activated fluoride phosphors is
substantially lower (typically about a tenth) than that of
europium-activated red nitride phosphor materials are currently
used in LED-filaments. Therefore, in order to achieve the same
target color point, the usage amount of manganese-activated
fluoride phosphors typically can be from 5 to 20 times greater than
the usage amount of a corresponding europium-activated red nitride
phosphor. The increased amount of phosphor usage significantly
increases the cost of manufacture since manganese-activated
fluoride phosphors are significantly more expensive than
europium-activated red nitride phosphors (at least five times more
expensive). Moreover, compared with packaged LEDs, since equal
amounts of phosphor are required on each side of the filament, this
doubles usage amount of manganese-activated fluoride
photoluminescence material. As a result of the higher usage and
higher cost, use of narrow-band manganese-activated fluoride red
phosphors is prohibitively expensive for LED-filaments.
[0006] Embodiments of the invention 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 through
innovative phosphor packaging structures to improve the blue
absorption efficiency of manganese-activated fluoride
photoluminescence material.
SUMMARY OF THE INVENTION
[0007] Some embodiments of the invention concern LED-filaments that
are configured to generate a majority (e.g. at least 70% of the
total) of light in a forward direction away from a front face of
the substrate on which the LED chips are mounted and a small
proportion of light in a backward direction away from the back face
of the substrate. More particularly, the substrate and LED chips
are configured such that the proportion of total blue excitation
light generated by the blue LED chips on (emanates from) the front
face side of the substrate is substantially greater (e.g. at least
70% of the total) than on (emanates from) the opposite back face
side. Such a configuration enables use of a higher brightness
narrow-band red phosphor on the front face of the substrate only
and a less expensive red phosphor other than a manganese-activated
fluoride phosphor ("non-manganese-activated fluoride
photoluminescence material" also referred to as a broad-band red
photoluminescence material) on the back face of the substrate while
still providing substantially most of the superior brightness
benefit of using narrow-band manganese activated fluoride on both
faces, but using only half (50% by weight) the quantity of
narrow-band red photoluminescence material. This is to be
contrasted with known LED-filaments which use the same
photoluminescence materials on the front and back faces of the
substrate to ensure a uniform color emission in forward and
backward directions. In accordance with the invention, the
LED-filament can be configured in the above way by, for example,
using: (i) a partially light-transmissive substrate, (ii) LED chips
that generate more light from a top face in a forward/upward
direction than in a backward/downward direction from a bottom face
(base) towards the substrate, (iii) providing a reflector, or
partial reflector, on the base of one or more of the LED chips or a
combination thereof. The present invention finds particular utility
in LED-filaments that use an at least partially light-transmissive
substrate.
[0008] In some embodiments, an LED-filament comprises a partially
light-transmissive substrate having a plurality of blue LED chips
mounted on a front face of the substrate; narrow-band red and first
broad-band green to red photoluminescence materials disposed on and
covering the front face of the substrate and the plurality of blue
LED chips; and second broad-band green to red photoluminescence
materials covering the opposite back face of the substrate, there
being only a small quantity or no narrow-band photoluminescence
material present on the back face. The narrow-band and broad-band
red photoluminescence materials typically have different crystal
structures--that is the red photoluminescence material covering the
front face has a different crystal structure to that of the red
photoluminescence material covering the back face. In an
embodiment, the narrow-band red photoluminescence material
comprises a manganese-activated fluoride photoluminescence material
(e.g. KSF), and the broad-band red photoluminescence material
comprises rare-earth activated red photoluminescence material, for
example, CASN. In this patent specification "broad-band red
photoluminescence material" and "non manganese-activated fluoride
photoluminescence material" denotes a red photoluminescence
material whose crystal structure is other than that of a
manganese-activated fluoride red photoluminescence material, such
as for example rare-earth-activated red photoluminescence materials
including for example a red emitting nitride-based phosphor, a
Group selenide sulfide or silicate-based photoluminescence
(phosphor) material.
[0009] According to an embodiment, an LED-filament comprises: a
partially light-transmissive substrate; a plurality of blue LED
chips mounted on a front face of the substrate; first broad-band
green to red photoluminescence materials and a first narrow-band
manganese-activated fluoride red photoluminescence material
covering the plurality of blue LED chips and the front face of the
substrate; and second broad-band green to red photoluminescence
materials covering the back face of the substrate. The inventors
have discovered that by providing the narrow-band
manganese-activated fluoride red photoluminescence on only the
front face of the substrate and a less expensive second broad-band
photoluminescence material on the back face of the substrate
provides substantially the same brightness increase benefit but
uses only half (50% by weight) the quantity of manganese-activated
fluoride photoluminescence material. In embodiments, the
LED-filament can further comprises a second narrow-band
manganese-activated fluoride red photoluminescence material on the
back face of the substrate in an amount that is less than 5 wt % of
a total red photoluminescence material content on the back face of
the substrate. Embodiments of the invention comprise 0 wt % of the
second narrow-band manganese-activated fluoride red
photoluminescence material on the back face of the substrate.
[0010] In embodiments, the substrate has a transmittance of at
least one of: 2% to 70%, 30% to 50% and 10% to 30%. In embodiments,
at least one of: at least 70%, at least 80%, and at least 90% of
the total blue light generated by the LED chips is on the front
face side of the substrate. Since, in embodiments of the invention,
the substrate is only partially light-transmissive and/or the LED
chips have a reflector covering their base, a greater proportion of
the total blue excitation light generated by the blue LED chips
will be on (emanates from) the front face side of the substrate
than on the back face side of the substrate. It will be appreciated
that this is true even when the LED chips generate equal amounts of
blue excitation light in forward (i.e. away from the front face of
the substrate) and backward (i.e. towards the front face substrate)
directions since the substrate will allow passage of only a
proportion of blue excitation light to pass and reflect the
remainder resulting in greater proportion of blue excitation light
on the front face side of the substrate. Due to this difference in
the proportion of total blue excitation light on opposite faces of
the substrate, it enables use of a less expensive broad-band red
photoluminescence material (e.g. CASN) on a back face of the
substrate, thereby substantially reducing costs while increasing
brightness.
[0011] The LED-filament can comprise a single-layer structure
comprising a layer comprising a mixture of the narrow-band red
photoluminescence material and the first broad-band green to red
photoluminescence materials. To further reduce narrow-band red
photoluminescence material usage, the layer can further comprise
particles of a light scattering material such as for example
particles of zinc oxide; silicon dioxide; titanium dioxide;
magnesium oxide; barium sulfate; aluminum oxide and combinations
thereof. A single-layer structure may be more robust and also
enhance ease of manufacture due the different photoluminescence
materials being comprised in the same layer. This may reduce cost
and time of manufacture, and also help eradicate errors during
manufacture since there are less steps involved in the creation of
the single-layer structure.
[0012] Alternatively, in order to further improve the blue
absorption efficiency of the narrow-band red photoluminescence
material, the LED-filament can comprise a double-layer structure in
which the narrow-band red photoluminescence material is located in
a separate layer from the broad-band green to red photoluminescence
materials with the separate layer being disposed on top of the LED
chips in, for example, the form of a conformal coating. In such
embodiments, an LED-filament can comprise a first layer comprising
the first narrow-band red photoluminescence material disposed on
the plurality of blue LED chips, and a second layer comprising the
first broad-band green to red photoluminescence material disposed
on the first layer. In embodiments, the first layer can comprise a
uniform thickness layer (film) on at least the principle light
emitting face of at least one of the LED chips, that is the
LED-filament comprises CSP (Chip Scale Packaged) LEDs containing
the narrow-band red photoluminescence material. The first layer can
comprise a uniform thickness layer on all light emitting faces of
the LED chips in the form of a conformal coating layer. To further
reduce narrow-band red photoluminescence material usage, the first
layer can further comprise particles of a light scattering material
such as for example particles of zinc oxide; silicon dioxide;
titanium dioxide; magnesium oxide; barium sulfate; aluminum oxide
and combinations thereof. The inventors have discovered that
compared with a LED-filament comprising a single-layer structure, a
double-layer structure can provide a substantial further reduction,
up to 80% by weight reduction, in manganese-activated fluoride red
photoluminescence material usage. Compared with known LED-filaments
having manganese-activated fluoride red photoluminescence material
on both front and back faces a double-layer structure can provide a
90% by weight reduction in manganese-activated fluoride red
photoluminescence material usage. By providing the narrow-band red
photoluminescence material in a respective layer disposed on the
plurality of LED chips this increases the concentration of
narrow-band red photoluminescence material in immediate proximity
to LED chips and improves the blue absorption efficiency of the
narrow-band red photoluminescence material, thereby reducing
narrow-band red photoluminescence material usage.
[0013] In embodiments, where the first broad-band green to red
photoluminescence materials comprises a first broad-band red
photoluminescence material, a content ratio of the first broad-band
red photoluminescence material with respect to the total of the
first narrow-band red photoluminescence material and the first
broad-band red photoluminescence material is at least one of: at
least 20 wt %; at least 30 wt %; at least 40 wt %; and in a range
from about 20 wt % to less than 60 wt %.
[0014] The narrow-band red photoluminescence material(s) such as a
manganese-activated fluoride red photoluminescence material can
have a peak emission wavelength ranging from 630 nm to 633 nm and
may comprise at least one of: K.sub.2SiF.sub.6:Mn.sup.4+(KSF),
K.sub.2GeF.sub.6:Mn.sup.4+(KGF), and
K.sub.2TiF.sub.6:Mn.sup.4+(KTF).
[0015] At least one of the first broad-band green to red
photoluminescence material and the second broad-band green to red
photoluminescence materials can comprise a rare-earth-activated red
photoluminescence material. The rare-earth-activated red
photoluminescence materials can have a peak emission wavelength
ranging from 620 nm to 650 nm and may comprise at least one of a
nitride-based phosphor material having a general composition
AAlSiN.sub.3:Eu.sup.2+ where A is at least one of Ca, Sr or Ba; a
sulfur-based phosphor material having a general composition
(Ca.sub.1-xSr.sub.x)(Se.sub.1-yS.sub.y):Eu.sup.2+ where
0.ltoreq.x.ltoreq.1 and 0<y.ltoreq.1 and a silicate-based
phosphor material having a general composition
(Ba.sub.1-xSr.sub.x).sub.3SiO.sub.5:Eu.sup.2+ where
0.ltoreq.x.ltoreq.1.
[0016] In embodiments, the first broad-band green to red
photoluminescence materials comprises a first broad-band green
photoluminescence material and the second broad-band green to red
photoluminescence materials comprises a second broad-band green
photoluminescence material. The first broad-band green
photoluminescence material can have a peak emission wavelength
ranging from 530 nm to 550 nm while the second broad-band green
photoluminescence material can have a peak emission wavelength
ranging from 520 nm to 540 nm. The first and/or second broad-band
green photoluminescence materials can comprise a cerium-activated
garnet phosphor having a general composition
(Lu.sub.1-xY.sub.x).sub.3(Al.sub.1-yGa.sub.y).sub.5O.sub.12:Ce
where 0.ltoreq.x.ltoreq.1 and 0.ltoreq.y.ltoreq.1.
[0017] The partially light-transmissive substrate can comprise a
material selected from the group consisting of: alumina, silica,
magnesium oxide, sapphire, quartz glass, diamond, silicon oxide and
mixtures thereof.
[0018] The LED-filament can be operable to generate white light
with a correlated color temperature from 2700K to 6500K. The
LED-filament can be operable to generate white light with a general
color rendering index CRI Ra of at least 80 and optionally at least
90.
[0019] According to further embodiments, an LED-filament comprises:
a partially light-transmissive substrate; a plurality of blue LED
chips mounted on a front face of the substrate; a broad-band green
photoluminescence material, a broad-band red photoluminescence
material, and a narrow-band manganese-activated fluoride red
photoluminescence material covering the plurality of blue LED chips
and the front face of the substrate; and wherein a content ratio of
the broad-band red photoluminescence material with respect to the
total of the narrow-band red photoluminescence material and
broad-band red photoluminescence material is at least 20 wt %. In
embodiments, a content ratio of the broad-band red
photoluminescence material with respect to the total of the
narrow-band manganese-activated fluoride red photoluminescence
material and broad-band red photoluminescence material is at least
one of: at least 30 wt %; and at least 40 wt %.
[0020] In embodiments, the LED-filament can comprise a first layer
having the narrow-band red photoluminescence material disposed on
the plurality of blue LED chips; and a second layer having the
broad-band green photoluminescence material disposed on the first
layer; and the broad-band red photoluminescence material is in at
least one of: the first layer and the second layer.
[0021] In further embodiments, LED-filaments can comprise a
double-layer structure on the front and back faces of the
substrate, a so called "double-sided double-layer" structure.
According to embodiments, an LED-filament comprises: a partially
light-transmissive substrate; a plurality of blue LED chips mounted
on a front face of the substrate; a first photoluminescence layer
comprising a first narrow-band manganese-activated fluoride red
photoluminescence material disposed on the plurality of blue LED
chips; a second photoluminescence layer comprising a first
broad-band green to red photoluminescence materials disposed on the
first photoluminescence layer; a third photoluminescence layer
comprising a second narrow-band manganese-activated fluoride red
photoluminescence material disposed on the back face of the
substrate; and a fourth photoluminescence layer comprising a second
broad-band green to red photoluminescence material disposed on the
third photoluminescence layer. In embodiments, the first layer can
comprise a uniform thickness layer (film) on at least the principle
light emitting face of at least one of the LED chips, that is the
LED-filament comprises CSP (Chip Scale Packaged) LEDs containing
the narrow-band red photoluminescence material. The first layer can
comprise a uniform thickness layer on all light emitting faces of
the LED chips in the form of a conformal coating layer. To reduce
narrow-band red photoluminescence material usage, at least one of
the first photoluminescence layer and the third photoluminescence
layer further comprises particles of a light scattering material
selected from the group comprising: zinc oxide; silicon dioxide;
titanium dioxide; magnesium oxide; barium sulfate; aluminum oxide;
and combinations thereof. The inventors have discovered such a
double-sided double-layer structure can substantially reduce (as
much as 80% by weight for a substrate with a transmittance of 100%)
the usage amount of the narrow-band red photoluminescence material
compared with known LED-filaments comprising narrow-band and
broad-band red photoluminescence materials on front and back faces
of the substrate. In such embodiments, the substrate can have a
transmittance in a range from 20% to 100%.
[0022] According to a further embodiment, an LED-filament
comprises: a partially light-transmissive substrate; a plurality of
blue LED chips mounted on a front face of the substrate; first
broad-band green to red photoluminescence materials and a
narrow-band manganese-activated fluoride red photoluminescence
material covering the plurality of blue LED chips and the front
face of the substrate; and second broad-band green to red
photoluminescence materials covering the back face of the
substrate, wherein at least 70% of the total blue light generated
by the LED chips is on the front face side of the substrate.
[0023] According to an aspect of the invention, an LED-filament
lamp comprises: a light-transmissive envelope; and at least one
LED-filament as described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] 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:
[0025] FIGS. 1A and 1B respectively illustrate partial
cross-sectional A-A side and plan views of a four LED-filament
A-Series (A19) lamp in accordance with an embodiment of the
invention;
[0026] FIGS. 2A, 2B and 2C respectively illustrate schematic
cross-sectional B-B side, partial cutaway plan and cross-sectional
C-C end views of a single-layer LED-filament in accordance with an
embodiment of the invention for use in the lamp of FIGS. 1A and
1B;
[0027] FIGS. 3A and 3B are respectively a schematic representation
of an LED chip showing its emission characteristics in forward and
backward directions and a schematic exploded representation of an
LED chip and substrate indicating the distribution of blue
excitation light present at front and back face sides of the
substrate;
[0028] FIGS. 4A and 4B are schematic cross-sectional end views of
double-layer LED-filaments in accordance with embodiments of the
invention;
[0029] FIGS. 5A and 5B are schematic cross-sectional end views of
double-sided double-layer LED-filaments in accordance with
embodiments of the invention; and
[0030] FIG. 6 is a schematic cross-sectional end view of an
LED-filament in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] 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.
FIGS. 1A and 1B respectively illustrate a partial cross-sectional
side view through A-A and a partial cutaway plan view of an
LED-filament A-Series lamp (bulb) 100 formed in accordance with an
embodiment of the invention. The LED-filament lamp (bulb) 100 is
intended to be an energy efficient replacement for a traditional
incandescent A19 light bulb and can be configured to generate 550
lm of light with a CCT (Correlated Color Temperature) of 2700 K and
a general color rendering index CRI Ra of at least 80. The
LED-filament lamp is nominally rated at 4 W. As is known, an
A-series lamp is the most common lamp type and an A19 lamp is 23/8
inches (19/8 inches) wide at its widest point and approximately
43/8 inches in length.
[0032] 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.
[0033] 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 (.PHI.26
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 (.PHI.27 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.
[0034] 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).
[0035] 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
(FIG. 1B), although it will be appreciated that in other
embodiments the LED-filaments may not be equally spaced around the
glass support. A first electrical contact 114a to 114d on a first
end of each LED-filament 108a to 108d distal to the connector base
102 is electrically and mechanically connected to a first
conducting wire 116 that passes down an axis of the LED filament
support 106 to the connector base 102. A second electrical contact
118a to 118d on a second end of each LED-filament 108a to 108d
proximal to the connector base 102 is electrically and mechanically
connected to a second conducting wire 120 that passes through a
base portion 122 of the LED filament support 106 to the connector
base 102. As illustrated, the LED filaments 108a to 108d can be
electrically connected in parallel.
[0036] An LED-filament according to an embodiment of the invention
is now described with reference to FIGS. 2A, 2B and 2C which
respectively show a cross-sectional side view through B-B, a
partial cut-away plan and a cross-sectional C-C end view of a
single-layer LED-filament 208. Throughout this specification, like
reference numerals preceded by the figure number are used to denote
like parts. The LED-filament 208 comprises a partially
light-transmissive substrate 224 having an array of blue emitting
(465 nm) unpackaged LED chips (dies) 226 mounted directly to a
front (first) face 228. Typically each LED-filament has a total
nominal power of about 0.7 to 1 W.
[0037] 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 (FIG. 1A) to
provide electrical power to operate the LED-filament. The
electrical contacts 214, 218 can comprise copper, silver or other
metal or a transparent electrical conductor such as indium tin
oxide (ITO). In the embodiment, illustrated the substrate 224 is
planar and has an elongate form (strip) with the LED chips 226
being configured as a linear array (string) and equally spaced
along the length (direction of elongation) of the substrate. As
indicated in FIGS. 2A and 2B the LED chips 226 can be electrically
connected in series by bond wires 230 between adjacent the LED
chips of the string and wire bonds 232 between the LED chips at the
distal ends of the substrate and their respective electrical
contact 214, 218.
[0038] 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.
[0039] 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 (FIG. 1A) within the glass envelope 104 (FIG. 1A) is preferably
filled with a thermally conductive gas such as helium, hydrogen or
a mixture thereof.
[0040] 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.
[0041] In accordance with the invention, the first
photoluminescence wavelength conversion material 236 comprises a
mixture of a first broad-band green photoluminescence material
having a peak emission wavelength ranging from 520 nm to 560 nm
(preferably 540 nm to 545 nm), a first broad-band red
photoluminescence material having a peak emission wavelength
ranging from 620 nm to 650 nm and a narrow-band red
photoluminescence material typically a manganese-activated fluoride
phosphor. Collectively, the first broad-band green and red
photoluminescence materials will be referred to as first broad-band
green to red photoluminescence materials. Since in this embodiment
both the narrow-band red and broad-band 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.
[0042] The second photoluminescence wavelength conversion material
238 comprises a mixture of only a second broad-band green
photoluminescence material having a peak emission wavelength
ranging from 520 nm to 560 nm (preferably 520 nm to 540 nm) and a
second broad-band red (non-manganese-activated fluoride)
photoluminescence material having a peak emission wavelength
ranging from 620 nm to 650 nm. Collectively, the second broad-band
green and red photoluminescence materials will be referred to as
second broad-band green to red photoluminescence materials.
[0043] In contrast, in known LED-filaments, the same
photoluminescence material composition (narrow-band and broad-band
red photoluminescence materials) is provided on the front and back
faces of the filament. Suitable broad-band green photoluminescence
materials, narrow-band red photoluminescence materials and
broad-band red photoluminescence materials are discussed below.
[0044] In the embodiment illustrated in FIGS. 2A and 2B, the first
and second photoluminescence conversion materials 236 and 238 are
constituted as a single layer comprising a mixture of broad-band
green and red photoluminescence materials.
[0045] 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.
[0046] FIG. 3A is a schematic representation of an LED chip 326
showing its emission characteristics in forward/upward 340 and
backward/downward 342 directions and FIG. 3B is a schematic
exploded representation of the LED chip 326 and a partially
light-transmissive substrate 324 indicating the distribution of
blue excitation light on opposite face sides 328 and 334 of the
substrate 324.
[0047] Referring to FIG. 3A and assuming that the blue LED chip 326
emits equal amounts of blue light from its top surface 344 and its
base 346, then 50% of the total blue light generated by the LED
chip is emitted in a forward direction 340 away from the front face
of the substrate and 50% of the total blue light generated by the
LED chip is emitted in a backward direction 342 towards the front
face of the substrate. Referring to FIG. 3B and assuming that the
partially light-transmissive substrate 324 has a transmittance of
40% and a reflectance of 60%, only 40% of the blue light 342 (i.e.
20% of the total blue light generated by the blue LED chip 346)
will pass through the substrate 324 and emanate 346 from the back
face side 334 of the substrate 324. The remaining 60% of blue light
342 (i.e. 30% of the total blue light generated by the blue LED
chip) will be reflected by the substrate 324 in a forward direction
and emanate from the front face side 328 of the substrate. It will
appreciated that the net effect is that approximately 80% of the
total blue light generated by the blue LED chip 348 will be on
(emanates from) the front face side of the substrate and only 20%
of the total blue light generated by the blue LED chip 348 will be
on (emanates from) the back face side of the substrate. Clearly,
when the photoluminescence materials are present these figures may
change due to scattering of blue light by the photoluminescence
materials. As described above, by configuring the proportion of
total blue excitation light generated by the blue LED chips present
at the front face side of the substrate to be substantially greater
(typically at least 70% of the total) than at the opposite back
face side this enables use of the higher brightness
manganese-activated fluoride phosphor on the front face of the
substrate only and a less expensive non manganese-activated
fluoride phosphor on the back face of the substrate while still
providing substantially most of the increase in brightness benefit
but using only half (50% by weight) the quantity of
manganese-activated fluoride photoluminescence material. TABLE 1
tabulates the effect of substrate transmittance/reflectance on the
proportion of total blue excitation light on (emanates from) the
front face and back face sides of the substrate and the relative
overall brightness of the LED-filament. The data assumes that each
blue LED chip generates equal amounts of blue excitation light in
forward and backward directions. The overall relative brightness is
relative to a known LED-filament having CASN on the front and back
faces of the substrate. For comparison, the relative brightness for
an LED-filament having KSF on both faces of the substrate is 120%
though it will be appreciated that uses twice the amount of KSF
than the LED-filaments of the invention.
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 % of total blue Substrate excitation light
on: LED- Trans- Front face Back face Filament mittance Reflectance
side side Brightness (%) (%) of substrate of 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
[0048] FIGS. 4A and 4B are schematic cross-sectional end views of
double-layer LED-filaments 408 in accordance with embodiments of
the invention. In these embodiments, the first photoluminescence
wavelength conversion material 436 covering the LED chips comprises
a "double-layer" structure comprising first and second
photoluminescence layers 450 and 452 that respectively contain
narrow-band red and first broad-band green to red photoluminescence
materials. As illustrated in FIGS. 4A and 4B, the first
photoluminescence layer 450, containing the narrow-band red
photoluminescence material, is disposed on and covers the LED chips
426 and the second photoluminescence layer 452, containing the
first broad-band green to red photoluminescence materials (that is
first broad-band green and first broad-band red photoluminescence
materials), is disposed on and covers the first photoluminescence
layer 450 (that is the first photoluminescence layer 450 is in
closer proximity to the LED chips than the second photoluminescence
layer).
[0049] The double-layer LED-filament of FIG. 4A can be manufactured
by firstly depositing the first photoluminescence layer 450 onto
the LED chips 426 and then depositing the second photoluminescence
layer 452 on the first photoluminescence layer 450. As illustrated
the first photoluminescence layer 450 can have a cross section that
is generally semi-circular in profile.
[0050] In the double-layer LED-filament of FIG. 4B the first
photoluminescence layer 450 comprises a uniform thickness coating
layer that is applied to the light emitting faces of individual LED
chips. LED chips with a uniform thickness layer (film) of phosphor
on their light emitting faces are often referred to as CSP (Chip
Scale Packaged) LEDs. As illustrated in FIG. 4B the LED chip 426
has a uniform thickness layer applied to the top light emitting and
four side light emitting faces and is in the form of a conformal
coating. In embodiments (not shown) the LED chip 426 has a uniform
thickness first photoluminescence layer 450 applied to the
principle (top) light emitting face only. The double-layer
LED-filament can be manufactured by first applying the first
photoluminescence layer 450 to at least the principle light
emitting face of individual LED chips 426, for example using a
uniform thickness (typically 20 .mu.m to 300 .mu.m)
photoluminescence film comprising the narrow-band red
photoluminescence material. The LED chips 426 are then mounted on
the substrate 424 and the second photoluminescence layer 452 then
deposited to cover the substrate and LED chips. Compared with the
double-layer LED-filament of FIG. 4A a uniform thickness coating
layer can be preferred as it concentrates all of the narrow-band
red photoluminescence material as close to the LED chip as possible
and ensures that, regardless of physical location within the layer,
all of the narrow-band red photoluminescence material receives
exposure to substantially the same excitation light photon density.
Such an arrangement can maximize the reduction in narrow-band red
photoluminescence material usage.
[0051] The inventors have discovered that providing the narrow-band
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
narrow-band red photoluminescence material compared with an
LED-filament in which the narrow-band red and broad-band green
photoluminescence materials comprise a mixture in a single layer
(FIG. 2C). Moreover, compared with a known LED-filament in which
narrow-band red photoluminescence material is provided on both
faces of the substrate, a double-layer structured LED-filament
reduces the usage amount of narrow-band red photoluminescence
material by as much as 90% by weight.
[0052] It is believed that the reason for this reduction in usage
amount, is that in an LED-filament (FIG. 2C) in which the
photoluminescence material 236 comprises a single photoluminescence
layer comprising a mixture of a narrow-band red photoluminescence
material and broadband green to red photoluminescence materials,
the photoluminescence materials have equal exposure to blue
excitation light. Since narrow-band red photoluminescence
materials, especially manganese-activated fluoride
photoluminescence materials, have a much lower blue light
absorption capability than the broad-band green photoluminescence
materials a greater amount of narrow-band red photoluminescence
material is necessary to convert enough blue light to the required
red emission. By contrast, in the LED-filaments 408 of FIGS. 4A and
4B, the narrow-band red photoluminescence material in its separate
respective layer 450 is exposed to blue excitation light
individually; thus, more of the blue excitation light can be
absorbed by the narrow-band red photoluminescence material and the
remaining blue excitation light can penetrate through to the second
photoluminescence layer 452 containing the broad-band green to red
photoluminescence materials. Advantageously, in this structure the
narrow-band red photoluminescence material can more effectively
convert the blue excitation light to red emission without
competition from the green to red photoluminescence materials.
Therefore, the amount (usage) of a narrow-band 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.
[0053] FIGS. 5A and 5B are schematic cross-sectional end views of a
double-sided double-layer LED-filaments in accordance with
embodiments of the invention. In these embodiments, both the first
536 and second 538 photoluminescence wavelength conversion
materials covering the front and back face of the substrate
comprise a "double-layer" structure. On the front face of the
substrate, the first photoluminescence material 536 covering the
LED chips comprises first and second photoluminescence layers 550
and 552 that respectively contain first narrow-band red and first
broad-band green to red photoluminescence materials. As
illustrated, the first photoluminescence layer 550, containing the
first narrow-band red photoluminescence material, is disposed on
and covers the LED chips 526 and the second photoluminescence layer
552, containing the first broad-band green to red photoluminescence
materials, is disposed on and covers the first photoluminescence
layer 550 (that is the first photoluminescence layer 550 is in
closer proximity to the LED chips than the second photoluminescence
layer). On the back face of the substrate, the second
photoluminescence material 538 covering the back face of the
substrate 524 comprises third and fourth photoluminescence layers
554 and 556 that respectively contain second narrow-band red and
second broad-band green to red photoluminescence materials. As
illustrated, the third photoluminescence layer 554, containing the
second narrow-band red photoluminescence material, is disposed on
and cover a part of the substrate corresponding with the LED chips
526 and the fourth photoluminescence layer 556, containing the
second broad-band green to red photoluminescence materials, is
disposed on and covers the third photoluminescence layer 554 (that
is the third photoluminescence layer 554 is in closer proximity to
the back face of the substrate than the fourth photoluminescence
layer).
[0054] The double-layer double-sided LED-filament of FIG. 5A can be
manufactured by firstly depositing the first photoluminescence
layer 550 onto the LED chips 526 and then depositing the second
photoluminescence layer 552 on the first photoluminescence layer
550. As illustrated the first photoluminescence layer 550 can have
a cross section that is generally semi-circular in profile. The
third photoluminescence layer 554 is deposited on the back face of
the substrate corresponding with the LED chips 526, for example as
a strip, and the fourth photoluminescence layer 556 then deposited
on and covers the third photoluminescence layer 554. As illustrated
the third photoluminescence layer 554 can have a cross section that
is generally semi-circular in profile.
[0055] In the double-layer double-sided LED-filament of FIG. 5B the
first photoluminescence layer 550 comprises a uniform thickness
layer applied to at least the principle light emitting face of
individual LED chips, that is the LED-filament comprises CSP LEDs.
As illustrated in FIG. 5B the LED chip 526 has a uniform thickness
layer applied to the top light emitting and four side light
emitting faces and is in the form of a conformal coating. In
embodiments (not shown) the LED chip 526 has a uniform thickness
first photoluminescence layer 550 applied to the principle (top)
light emitting face only. The double-layer LED-filament can be
manufactured by first applying the first photoluminescence layer
550 to at least the principle light emitting face of individual LED
chips 526, for example using a uniform thickness (typically 20
.mu.m to 300 .mu.m) photoluminescence film comprising the
narrow-band red photoluminescence material. The LED chips 526 are
then mounted on the substrate 524 and the second photoluminescence
layer 552 then deposited to cover the substrate and LED chips. The
third photoluminescence layer 554 is deposited of the back face of
the substrate corresponding with the LED chips 526, for example as
a strip, and the fourth photoluminescence layer 556 then deposited
on, and covers, the third photoluminescence layer 554.
[0056] 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 narrow-band red
photoluminescence material compared with known LED-filaments
comprising narrow-band and broad-band red photoluminescence
materials on front and back faces.
[0057] FIG. 6 is a schematic cross-sectional end view of an
LED-filament in accordance with an embodiment of the invention. In
this embodiment, one or more of the LED chips 624 has a reflector
660 on its base. The reflector 660 reduces blue light emission from
the base of the LED chip and reflect such light in a forward/upward
direction. The reflector can be 100% light reflective or partially
light reflective. It will be appreciated that the invention
contemplates that other embodiments disclosed herein may also
include reflector(s) on the base(s) of the LED chips.
[0058] In various embodiments of the invention, and to reduce
photoluminescence material usage, in particular to further reduce
narrow-band 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
narrow-band red photoluminescence material to further reduce
narrow-band red photoluminescence 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 broad-band green to red photoluminescence
materials and the narrow-band red photoluminescence material (FIG.
2C). For a double-layer structured LED filament, the particles of
light scattering material can be incorporated as a mixture with the
narrow-band red photoluminescence material in the first
photoluminescence layer 450 (FIG. 4). For a double-sided
double-layer LED-filament, the particles of light scattering
material can be incorporated as a mixture with the narrow-band red
photoluminescence material in the first and/or third
photoluminescence layers 550, 554 (FIG. 5).
[0059] Alternatively and/or in addition, the particles of light
scattering material can be provided in a separate layer that is in
contact with the layer containing the narrow-band red
photoluminescence material to further reduce narrow-band red
photoluminescence usage.
[0060] 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.
[0061] Broad-Band Green Photoluminescence Materials
[0062] In this patent specification, a broad-band green
photoluminescence material refers to a material which generates
light having a peak emission wavelength (.lamda..sub.pe) in a range
.about.520 nm to .about.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.
[0063] 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
.about.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 .about.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.
[0064] 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 .about.70 nm to .about.80 nm. Suitable green phosphors are
given in TABLE 2.
[0065] 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.ltoreq.x.ltoreq.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
(.lamda..sub.pe) in nanometers (#). For example ON495 denotes a
green oxynitride phosphor with a peak emission wavelength of 495
nm.
TABLE-US-00002 TABLE 2 Example broad-band green photoluminescence
materials General Wavelength Phosphor Composition .lamda..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 & 520-550 (YAG#) 0 < y < 2.5 GNYAG
(Y,Ba).sub.3-x(Al.sub.1-yGa.sub.y).sub.5O.sub.12:Ce.sub.x 0.01 <
x < 0.2 & 520-550 (YAG#) 0 < y < 2.5 LuAG
Lu.sub.3-x(Al.sub.1-yM.sub.y).sub.5O.sub.12:Ce.sub.x 0.01 < x
< 0.2 & 500-550 (GAL#) 0 < y < 1.5 M = 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 & 500-550 (GAL#) 0 < y < 1.5 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, 500-550 (ON#) Sr, Ba, Zn 0.1 .ltoreq. x .ltoreq.
1.0
[0066] Red Photoluminescence Materials
[0067] Narrow-Band Red Photoluminescence Materials
[0068] In this patent specification, a narrow-band 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
narrow-band 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 narrow-band 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:
K.sub.2GeF.sub.6:Mn.sup.4+(KGF) and
K.sub.2TiF.sub.6:Mn.sup.4+(KTF).
[0069] Broad-Band Red Photoluminescence Materials
[0070] In this patent specification, a broad-band 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 broad-band red photoluminescence can comprise rare-earth
activated red photoluminescence materials. A broad-band red
photoluminescence material (non-manganese-activated fluoride red
photoluminescence material) denotes a red photoluminescence
material whose crystal structure is other than that of a
narrow-band 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 .lamda..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,
.alpha.-SiAlON, Group IIA/BB selenide sulfide-based phosphor or
silicate-based phosphors. Examples of red phosphors are given in
TABLE 3.
[0071] 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 (.lamda..sub.pe) in
nanometers (#). For example, CASN625 denotes a red CASN phosphor
with a peak emission wavelength of 625 nm.
[0072] 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.ltoreq.a.ltoreq.0.4; 1.5<b<2.5;
4.0.ltoreq.c.ltoreq.5.0; 0.1.ltoreq.d.ltoreq.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.
[0073] 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.ltoreq.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.
[0074] Rare-earth-activated red phosphors can also include Group
IIA/IM 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
narrow-band red emission spectrum with FWHM in the range .about.48
nm to .about.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.
[0075] 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.ltoreq.0.5, 2.6.ltoreq.y.ltoreq.3.3,
0.001.ltoreq.z.ltoreq.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
(.lamda..sub.pe) in nanometers (#). For example, O600 denotes an
orange silicate phosphor with a peak emission wavelength of 600
nm.
TABLE-US-00003 TABLE 3 Example broad-band red photoluminescence
materials General Wavelength Phosphor Composition .lamda..sub.p
(nm) CASN (Ca.sub.1-xSr.sub.x) 0.5 < x .ltoreq. 1 600-650
(CASN#) AlSiN.sub.3:Eu 258 nitride
Ba.sub.2-xSr.sub.xSi.sub.5N.sub.8:Eu 0 .ltoreq. x .ltoreq. 2
580-650 Group IIA/IIB M = Mg, Ca, Sr, Ba, Zn Selenide Sulfide
MSe.sub.1-xS.sub.x:Eu 0 < x < 1.0 600-650 (CSS#) CSS
CaSe.sub.1-xS.sub.x:Eu 0 < x < 1.0 600-650 (CSS#) Silicate
(Sr.sub.1-xM.sub.x).sub.yEu.sub.zSiO.sub.5 M = Ba, Mg, Ca, Zn
565-650 (O#) 0 < x .ltoreq. 0.5 2.6 .ltoreq. y .ltoreq. 3.3
0.001 .ltoreq. z .ltoreq. 0.5
NOMENCLATURE
[0076] 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
narrow-band red (manganese-activated fluoride) photoluminescence
material on the front face of the substrate and a broad-band red
photoluminescence material on a back face of the substrate.
[0077] Experimental Data--Single-Layer Structure LED-Filament
[0078] 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
.apprxeq.40% having twenty four serially connected 1025 (10
mil.times.25 mil) blue LED chips of dominant wavelength
.lamda..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.
[0079] 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 .lamda..sub.pe.apprxeq.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 .lamda..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
.lamda..sub.pe.apprxeq.535 nm).
[0080] The red and green phosphors were mixed in a phenyl silicone
and the mixture dispensed onto the front and back faces of the
substrate.
[0081] 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.
[0082] 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.
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
[0083] 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 (narrow-band 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 (narrow-band 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.
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 Filament (1 m) (%) Forward
Backward x y CCT (K) CRI 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
[0084] Experimental Data--Double-Layer Structured LED-Filament
[0085] As discussed above, double-layer structured LED-filaments
(FIGS. 4A and 4B) compared with a single-layer structured
LED-filament (FIG. 2C) can provide a substantial reduction in usage
amount of narrow-band red photoluminescence material. Dev.2 is a
single-layer LED-filament in accordance with the invention Dev.2
and Dev.3 is a double-layer LED-filament (FIG. 4A) in accordance
with the invention.
[0086] Dev.2 and Dev.3 each comprise a 38 mm by 1.5 mm porous
silica substrate with a transmittance .apprxeq.40% having twenty
four serially connected 714 (7 mil.times.14 mil) blue LED chips of
dominant wavelength .lamda..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.
[0087] 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 .lamda..sub.pe.apprxeq.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 .lamda..sub.pe=543 nm and 550 nm).
[0088] 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.
[0089] 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.
[0090] 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.
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
[0091] 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.
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
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
[0092] 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.about.0.0942 compared with 0.0302 and 84% by
weight increase on back face.about.0.0963 compared with 0.0524) and
YAG (182% by weight increase on front face.about.0.9070 compared
with 0.3219 and 84% by weight increase on back face.about.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 1/5 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.
[0093] 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 (narrow-band 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.
[0094] As will be further noted from TABLE 7A, the content ratio of
the CASN (broad-band red photoluminescence material) with respect
to the total of the KSF (narrow-band red photoluminescence
material) and CASN in the double-layer LED-filament Dev.3 is
greater than about 30 wt %.
TABLE-US-00009 TABLE 8 Measured optical characteristics of 150 l m,
2700 K LED-filaments Dev.2 and Dev.3 Flux Br CIE CRI Ra Filament (1
m) (%) Lm/W x y CCT (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
[0095] 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 FIGS. 1A and 1B. LED-filament
Dev.4 comprises a 52 mm by 3.0 mm porous silica substrate with a
transmittance .apprxeq.40% having twenty five serially connected
714 (8 mil.times.27 mil) blue LED chips of dominant wavelength
.lamda..sub.d=454 nm mounted on a front face.
[0096] 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.
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 7.56 9.4 9.19 0.9
[0097] 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 (broad-band red photoluminescence
material) with respect to the total of the KSF (narrow-band red
photoluminescence material) and CASN in the double-layer
LED-filament Dev.4 is about 25 wt %.
TABLE-US-00011 TABLE 10A Phosphor amount of 250 l m double-layer
LED-filament Dev.4 Front face-Phosphor amount CASN/ KSF CASN615
YAG543 Total (CASN + Filament weight % weight weight weight KSF)
(wt %) Dev.4 0.1956 19.6 0.0642 0.7012 0.9610 24.7
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
[0098] 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.
TABLE-US-00013 TABLE 11 Measured optical characteristics of a
nominal 250 l m, 2700 K double-layer LED-filament Dev.4 I.sub.F
Flux CIE CRI Ra Test Condition (mA) V.sub.F (V) (1 m) Lm/W x y CCT
(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 .DELTA. 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
[0099] 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.
* * * * *