EP3060624A1 - Photobiologically friendly phosphor converted light-emitting diode - Google Patents
Photobiologically friendly phosphor converted light-emitting diodeInfo
- Publication number
- EP3060624A1 EP3060624A1 EP14805690.6A EP14805690A EP3060624A1 EP 3060624 A1 EP3060624 A1 EP 3060624A1 EP 14805690 A EP14805690 A EP 14805690A EP 3060624 A1 EP3060624 A1 EP 3060624A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- phosphor
- light
- led
- wavelength
- luminance
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 title claims abstract description 79
- 239000004065 semiconductor Substances 0.000 claims abstract description 48
- 238000006243 chemical reaction Methods 0.000 claims abstract description 43
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- 230000000007 visual effect Effects 0.000 claims abstract description 25
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- 238000001228 spectrum Methods 0.000 claims abstract description 10
- 238000005424 photoluminescence Methods 0.000 claims abstract description 8
- YJPIGAIKUZMOQA-UHFFFAOYSA-N Melatonin Natural products COC1=CC=C2N(C(C)=O)C=C(CCN)C2=C1 YJPIGAIKUZMOQA-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229960003987 melatonin Drugs 0.000 claims abstract description 7
- DRLFMBDRBRZALE-UHFFFAOYSA-N melatonin Chemical compound COC1=CC=C2NC=C(CCNC(C)=O)C2=C1 DRLFMBDRBRZALE-UHFFFAOYSA-N 0.000 claims abstract description 7
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 abstract description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 abstract description 6
- 239000002223 garnet Substances 0.000 abstract description 6
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- 229910052581 Si3N4 Inorganic materials 0.000 abstract description 4
- KMWBBMXGHHLDKL-UHFFFAOYSA-N [AlH3].[Si] Chemical compound [AlH3].[Si] KMWBBMXGHHLDKL-UHFFFAOYSA-N 0.000 abstract description 4
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 abstract description 3
- GPXKZAAXSMEHPY-UHFFFAOYSA-N [Ca++].[Se--].[Se--].[Sr++] Chemical compound [Ca++].[Se--].[Se--].[Sr++] GPXKZAAXSMEHPY-UHFFFAOYSA-N 0.000 abstract description 3
- AGMGTXZBSQRRBN-UHFFFAOYSA-N [Sr++].[Ba++].[O-][Si]([O-])([O-])[O-] Chemical compound [Sr++].[Ba++].[O-][Si]([O-])([O-])[O-] AGMGTXZBSQRRBN-UHFFFAOYSA-N 0.000 abstract description 3
- NFRFIMNIYLSHNB-UHFFFAOYSA-N [Sr].[Ba].[Si] Chemical compound [Sr].[Ba].[Si] NFRFIMNIYLSHNB-UHFFFAOYSA-N 0.000 abstract description 3
- MIOQWPPQVGUZFD-UHFFFAOYSA-N magnesium yttrium Chemical compound [Mg].[Y] MIOQWPPQVGUZFD-UHFFFAOYSA-N 0.000 abstract description 3
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- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 5
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 5
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- OGPBJKLSAFTDLK-UHFFFAOYSA-N europium atom Chemical compound [Eu] OGPBJKLSAFTDLK-UHFFFAOYSA-N 0.000 description 4
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- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 2
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 210000004556 brain Anatomy 0.000 description 2
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- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 2
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- 150000002500 ions Chemical class 0.000 description 2
- 238000004020 luminiscence type Methods 0.000 description 2
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 2
- 230000033764 rhythmic process Effects 0.000 description 2
- 230000004296 scotopic vision Effects 0.000 description 2
- 210000000221 suprachiasmatic nucleus Anatomy 0.000 description 2
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- 101100512897 Caenorhabditis elegans mes-2 gene Proteins 0.000 description 1
- 229910052688 Gadolinium Inorganic materials 0.000 description 1
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 1
- 241000124008 Mammalia Species 0.000 description 1
- 206010052143 Ocular discomfort Diseases 0.000 description 1
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- 229910052733 gallium Inorganic materials 0.000 description 1
- 229910001195 gallium oxide Inorganic materials 0.000 description 1
- BVSHTEBQPBBCFT-UHFFFAOYSA-N gallium(iii) sulfide Chemical compound [S-2].[S-2].[S-2].[Ga+3].[Ga+3] BVSHTEBQPBBCFT-UHFFFAOYSA-N 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
- 229940088597 hormone Drugs 0.000 description 1
- 239000005556 hormone Substances 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
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- 230000000247 oncostatic effect Effects 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 238000005375 photometry Methods 0.000 description 1
- 229920001296 polysiloxane Polymers 0.000 description 1
- 229910002059 quaternary alloy Inorganic materials 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
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- 229920005989 resin Polymers 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 210000000964 retinal cone photoreceptor cell Anatomy 0.000 description 1
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 description 1
- XXCMBPUMZXRBTN-UHFFFAOYSA-N strontium sulfide Chemical compound [Sr]=S XXCMBPUMZXRBTN-UHFFFAOYSA-N 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
- H01L2224/4805—Shape
- H01L2224/4809—Loop shape
- H01L2224/48091—Arched
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
- H01L2224/481—Disposition
- H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
- H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
- H01L2224/48245—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic
- H01L2224/48247—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic connecting the wire to a bond pad of the item
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/73—Means for bonding being of different types provided for in two or more of groups H01L2224/10, H01L2224/18, H01L2224/26, H01L2224/34, H01L2224/42, H01L2224/50, H01L2224/63, H01L2224/71
- H01L2224/732—Location after the connecting process
- H01L2224/73251—Location after the connecting process on different surfaces
- H01L2224/73265—Layer and wire connectors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
- H01L33/50—Wavelength conversion elements
- H01L33/501—Wavelength conversion elements characterised by the materials, e.g. binder
- H01L33/502—Wavelength conversion materials
Definitions
- the present invention relates to light sources that are suitable for the use in outdoor lighting and only slightly disrupts the circadian rhythm of humans; more specifically the invention discloses light-emitting diodes that are composed of semiconductor short wavelength emitters that emit blue light due to electroluminescence and of inorganic phosphors that generate the orange components of spectral power distribution.
- CAF - circadian action factor the ratio of non-visual circadian efficacy to the luminous efficacy of radiation
- Phosphor - a certain material that converts light with a shorter wavelength to light with a longer wavelength
- Firelight - light that has a low correlated colour temperature ( ⁇ 2500 K) with the chromaticity that is similar to that of a black body radiation.
- High and low pressure sodium vapour lamps are distinguished by low CCT and small circadian action. However due to the scarce and structured spectrum they are characterized by extremely low colour rendering.
- a mercury vapour lamp is presented. The radiation of this lamp is characterized by a high radiation flux in the blue region and strongly affects the circadian rhythm of humans. Also under conditions of low luminance, the visual discomfort can appear due to the high CCT [A. A. ruithof, Tabular luminescence lamps for general illumination, Philips Tech. Rev. 6, p. 65-73 (1941)].
- the SPD of the optimal photobiologically friendly LED consists of two spectral components, whereas in the patent the LED with SPD consisting of three spectral components is described;
- the USA patent US 6,501, 102 discloses a trichromatic pcLED that contains a semiconductor chip emitting light with a wavelength shorter than 460 nm that is partially converted to a secondary and tertiary radiation in phosphors where at least one of those is composed of at least one of the following: yttrium aluminium oxide compound, strontium gallium sulphide, yttrium aluminium lanthanum oxide compound, yttrium aluminium gallium oxide compound, and strontium sulphide nitridosilicate. This blend of three colours is perceived by humans as white light. However, this kind of LED is not optimal for photobiologically friendly street lighting for the following reasons:
- the SPD of the optimal photobiologically friendly LED consists of two spectral components, whereas in the patent the LED with SPD consisting of three spectral components is described;
- the USA patent US 6,294,800 discloses a phosphor with the chemical composition of Ca8Mg(Si0 4 ) 4 Cl 2 :Eu 2+ ,Mn 2+ and a trichromatic pcLED that contains a semiconductor chip, which emits light in the 330 - 420 nm wavelength region, the mentioned Ca 8 Mg(Si0 4 ) 4 CI 2 :Eu 2+ ,Mn 2+ phosphor, in which a part of the primary radiation is converted to green light, Y 2 0 3 :Eu 3+ ,Bi 3+ phosphor, in which a part of the primary radiation is converted to red light, and BaMg 2 Al i 6 0 27 :Eu or (Sr,Ba,Ca) 5 (PO " 4)3Cl:Eu phosphor, in which a part of the primary radiation is converted to blue light.
- the chemical compositions of the phosphors used in the LED are not chosen such that their SPD would be optimal for outdoor lighting with the lowest circadian action factor.
- the USA patent 6,084,250 discloses a trichromatic pcLED that contains a GaN LED emitting radiation in the ultraviolet region with the emission peak between 300 and 370 nm, and blue BaMgAl ioOi 7 :Eu 2+ phosphor, in which the primary radiation is converted to radiation that peaks in the 430-490 nm region, green ZnS:Cu phosphor, in which the primary radiation is converted to radiation that peaks in the 520-570 nm region, and red Y 2 0 2 S phosphor, in which the primary radiation is converted to radiation, which peaks in the 590-630 nm region.
- This blend of three colours is perceived by humans as white light.
- this kind of LED is not optimal for photobiologically friendly street lighting for the following reasons:
- the SPD of the optimal photobiologically friendly LED consists of two spectral components, whereas in the patent the LED with SPD consisting of three spectral components is described;
- the US patent US 5,851 ,063 discloses an entirely electroluminescent array of different-colour LEDs, which can be used for obtaining a desired SPD of the light source.
- arrays require complex topology, which is needed for the layout of different groups of LEDs.
- direct-emission electroluminescent LEDs of different colours are driven by different currents, which requires a higher number of control channels and more complex electronic circuits than in the case of pcLEDs when the electroluminescent chip in all LEDs is the same.
- the LED described in this patent is composed of a semiconductor light emitting component and a phosphor.
- the semiconductor chip emits excitation light in the 400-530 nm wavelength region and the phosphor photoluminescence is chosen such that its peak wavelength would be longer than that of the excitation light.
- the following drawbacks are not avoided:
- the SPD of the LED is not optimized in such a way that the circadian action factor of radiated light is minimized, i.e., that during the evening or night the negative impact for the human organism would be as small as possible;
- phosphor converted firelight sources optimized for mesopic vision when the average luminance of the environment is between 0.01 and 10 cd/m 2 ) that are characterized by a several times smaller circadian action than that of common daylight LEDs [A. Zukauskas, R. Vaicekauskas, P. Vitta, Optimization of solid-state lamps for photobiologically friendly mesopic lighting, Appl. Optics 51(35), p. 8423-8432 (2012)] could be used.
- the present invention discloses a low CCT (firelight) LED, which has a spectral power distribution composed of a blue and an orange components. These components have such peak wavelengths and ratios of radiation fluxes that the ratio of the excitation of non-visual photoreceptors in the eye retina that are controlling the circadian rhythm and the excitation of visual photoreceptors causing the visual perception would be the lowest. In this way the minimal disruption of the human circadian rhythm is obtained.
- CCT firelight
- the ratio of radiant fluxes of the spectral components are set by adjusting the size and the concentration of phosphor particles, the thickness of the wavelength converter, the refraction index of the material of the wavelength converter, the distance between the wavelength converter and the electroluminescent chip, and the position of the wavelength converter within the housing of the LED or outside the package.
- pcLEDs can be used for various outdoor lighting applications (lighting for streets, pedestrian and bicycle tracks, building facades, monuments, parks, car parking lots, and house yards) in the evening and the first part of the night.
- the aim of this invention is to develop a pcLED with a low non-visual photobiological effect, in which the partial conversion of blue light or the total conversion of near ultraviolet (UV) light in the wavelength converter would be realized in a such way that the obtained light would have a spectral component with a peak value in the 570-600 nm wavelength range and a spectral component with a peak value in the 400-500 nm wavelength range and that the ratio of the radiant fluxes of the components would be such that the chromaticity coordinates of the LED matched the black body radiation in the low CCT range ( 1 500 - 3000 ).
- the aim of the present invention is achieved by a dichromatic (blue-orange) LED that has a semiconductor chip, which emits radiation due to injection electroluminescence, and a photoluminescent converter, which is placed on the way of the photon flux emitted by the said chip.
- the converter is designed to convert the said radiation to longer wavelength radiation below 500 nm and has one type (in the case of partial conversion) or two types (in the case of complete conversion) of phosphor particles.
- the novelty is that the LED emits a blend of blue and orange light while the converter contains one of the orange phosphors listed below. This orange component together with the blue component composes a firelight SPD that is characterized by a low non-visual circadian action for humans.
- the mentioned phosphor radiating in the orange range of the spectrum can be such as: - yttrium magnesium aluminium silicon garnet, activated by trivalent cerium ions Y 3 g 2 AISi 2 0 12 :Ce 3+ ,
- the semiconductor chip generates blue light in the 400- 500 nm spectral range and the converter contains a phosphor that is characterized by the partial conversion of the said light to longer wavelength (orange) light.
- the active layer of the semiconductor chip is made of semiconductor alloy.
- the semiconductor chip In the case of complete conversion, the semiconductor chip generates near UV radiation or blue (violet) light, that has a wavelength shorter than 450 nm, and the converter contains a second phosphor which is characterized by luminescence in the 400-500 nm spectral range and that can be oxide, halo-oxide or nitride compound activated by divalent europium, divalent manganese, divalent tin or trivalent cerium ions.
- the active layer of the semiconductor chip is made of GaN semiconductor alloy or of ALGai - y N, or
- the radiant flux and the peak wavelength of each spectral component are chosen such that the final composition of the radiated light would be suitable for photobiologically friendly outdoor lighting, i.e., that its chromaticity would match that of the absolute black body radiation with a low temperature ( 1500 - 3000 K), and that the SPD would be characterized by a relatively small non-visual circadian action.
- the ratio of the radiant fluxes of the spectral components are set by adjusting the size and the concentration of phosphor particles, the width of the wavelength converter, the refraction index of the material of the wavelength converter, the distance between the wavelength converter and the electroluminescent chip, and the position of the wavelength converter within the housing of the LED or outside the package.
- the generated light spectral components have peak wavelengths as follows: ⁇ about 585 ⁇ 20 nm for the orange component,
- Fig. 1 photopic and scotopic spectral luminous efficiency functions and spectral circadian efficiency function
- Fig. 2 basic structure of LED (100) with the partial conversion of blue light for photobiologically friendly outdoor lighting;
- Fig. 3 basic structure of LED (200) with the complete conversion of near UV l ight for photobiologically friendly outdoor lighting;
- Fig. 4 typical electroluminescence spectra of a semiconductor chip containing the InGaN active layer: (a) blue 450 nm emitter; (b) near UV 365 nm emitter;
- Fig. 5 typical photoluminescence spectra of inorganic phosphors: (a) orange emitter; (b) blue emitter;
- Fig. 6 - SPDs of firelight pcLEDs for photobiologically friendly outdoor lighting (a) partial conversion LEDs with orange phosphors Y3Mg 2 AlSi 2 0i 2 :Ce 3+ , (Ba,Sr) 2 Si 5 N8:Eu 2+ , (Ba,Sr) 2 Si0 4 :Eu 2+ , Ca-a-SiAIOM:Eu 2+ , (Ca,Sr)Se:Eu 2+ ; (b) complete conversion LED with blue BaMg Al i 6 0 27 :Eu 2+ and orange Y 3 Mg 2 AlSi 2 0] 2 :Ce 3+ phosphors.
- LEDs While designing smart energy-saving lighting systems, semiconductor LEDs are more and more often applied in outdoor lighting. They are efficient and longevous, characterized by flexibility while choosing the desired SPD, suitable for rapidly switching on and off and for continuous dimming, feature no abrupt burn-out, and do not require high voltage supply; moreover they are compatible with computer-control technologies.
- the proposed two-component firelight chromaticity LED is characterized by a small non- visual circadian action and its SPD is optimized by taking into account the luminous efficacy of radiation. Since the luminous efficacy of a light source is the product of the luminous efficacy of the generated radiation and the radiant efficiency of the light source, the optimization by luminous efficacy of radiation, which depends only on SPD, is rather general. Meanwhile the radiant efficiency of LEDs depends on the injection efficiency, internal quantum efficiency, light extraction efficiency, and serial resistance, i.e. on the parameters that are gradually improving while developing LED technologies [P. Mottier, LEDs for Lighting Applications, John Wiley & Sons, Inc, London, (2009)].
- K Ko X J S(A)dA '
- S(X) is the SPD of an LED
- ⁇ is the wavelength
- V(X) is the spectral luminous efficiency function for photopic vision defined by the CIE in 1924
- KQ is the maximum possible value of luminous efficacy, which for photopic vision equals 683 Im/W.
- Photopic vision is typical for an environment where the average (adaption) luminance is above 10 cd/m . Under such conditions the sense of vision is dominated by three types of photoreceptors in the eye retina (cones) thus the photopic vision is chromatic. When the value of adaption luminance is below 0.01 cd/m 2 , the sense of vision is caused by one type of photoreceptors (rods), therefore under the conditions of low luminance humans lose the ability to distinguish colours. In this case the eye sensitivity function is described by the spectral luminous efficiency function of scotopic vision V' k), which was defined by the CIE in 1951. The maximum possible value of luminous efficacy for photopic vision is 1700 Im/W. The spectral luminous efficiency functions for photopic and scotopic vision are presented in Fig. 1.
- the proposed LED for outdoor lighting is optimized for the intermediate, i.e. mesopic, region, when the average luminance is in the range between 0.01 cd/m 2 and 10 cd/m 2 .
- This luminance range covers the interval used for the lighting of pedestrian tracks and streets which is between 0.1 cd/m 2 and 2 cd/m 2 .
- the sense of vision is determined by both cones and rods, the discrimination of colours is reduced, and the mesopic spectral luminous efficiency function Vmes ) depends on the luminance of the environment.
- the dependence of the spectral sensitivity of mesopic vision on adaption luminance is complex and is described by various models.
- the spectral luminous efficiency function is defined as:
- VmesW Mimr mVm + (1 - m)V X)
- the luminous efficacy of radiation is estimated as: where the maximum possible mesopic luminous efficacy ⁇ r mes o depends on the luminance of the environment and varies from 1700 lm/W to 683 lm/W.
- the ganglion cells that are responsible for non-visual circadian action of light are characterized by spectral sensitivity similarly to the visual receptors.
- This spectral sensitivity is described by the circadian efficiency function C(k) that is presented in Fig. 1.
- the peak of this function is seen to be at about 460 nm, thus the circadian rhythm is mostly affected by blue light [D. Gall, Circadiane Lichtgrosen und deren messtechnische Ermittlung, Licht 54, p. 1292-1297 (2002)].
- the non-visual circadian action of the proposed LED for outdoor lighting is evaluated by calculating the circadian action factor (CAF) o mes .
- This factor is defined as the ratio of the non-visual circadian efficacy of radiation to the mesopic luminous efficacy of radiation:
- K c o is equaled to 683 lm/W [A. Zukauskas, R. Vaicekauskas, P. Vitta, Optimization of solid-state lamps for photobiologically friendly mesopic lighting, Appl. Optics 51(35), p. 8423-8432 (2012)].
- the value of CAF is suitable for the comparison of the non-visual circadian action of light sources. For lighting in the evening, as low as possible Cimes value is desired since in this case a higher luminous efficacy and a lower circadian efficacy is required.
- the dichromatic light source with a short wavelength component that peaks at about 440-460 nm and with a long wavelength component that peaks at about 570-600 nm is characterized by a minimum CAF value [A. Zukauskas, R. Vaicekauskas, P. Vitta, Optimization of solid-state lamps for photobiologically friendly mesopic lighting, Appl. Optics 51(35), p. 8423-8432 (2012)].
- the SPD of the proposed LED was optimized by searching for the minimum value of CAF.
- the proposed LED for outdoor lighting is superior to common outdoor lighting sources (high and low pressure sodium vapour lamps) in colour rendering properties.
- the colour rendering can be evaluated by the general colour rendering index (CRI) R a that was introduced by CIE in 1965 and the evaluation procedure was updated in 1995 [Commission Internationale de l' Eclairage, Method of measuring and specifying colour rendering properties of light sources, Pub. CIE 13.3 : 1995].
- CRI colour rendering index
- eight main colour test samples are used; each sample is illuminated by a reference and a test light sources. After the analysis of the spectra of the reflected light, the colour differences are calculated and the special colour rendering index is found for each sample.
- the general CRI is estimated as the average of the special colour rendering indices:
- ⁇ is the average of the colour shifts of the eight samples in the CIE 1964 uniform colour space [Commission Internationale de PEclairage, Method of measuring and specifying colour rendering properties of light sources, pub. CIE 13.3: 1995].
- the maximum CRI value is 100; this value is typical of incandescent and halogen lamps.
- mesopic luminance conditions the ability of humans to distinguish colours is known to become poorer [W. R. J. Brown, The influence of luminance level on visual sensitivity to color differences, J. Opt. Soc. Am. 41, p. 684-688 (1951 )]; thus the mesopic CRI R ⁇ mes could be described somewhat differently depending on the luminance [A. Zukauskas, R. Vaicekauskas, P. Vitta, Optimization of solid-state lamps for photobiologically friendly mesopic lighting, Appl. Optics 5 1 (35), p. 8423-8432 (2012)]:
- R a ,mes 100 - A.e Y ⁇ L mes )AE, where ⁇ is the coefficient that depends on the luminance of the environment L mes .
- the proposed LED (100, 200) comprises a semiconductor chip (1 , 1 1 ) generating short- wavelength radiation with a shorter than 500 nm wavelength due to injection electroluminescence, which is placed in a reflector cup (2, 12) and is connected to terminals (3, 13) by bonded wires (4, 14).
- the chip ( 1 , 1 1 ) is covered by a wavelength converter (5, 15), which is encapsulated in a transparent package (6, 16).
- the said converter is designed for the conversion of short wavelength radiation to longer wavelength radiation due to photoluminescence for obtaining photons (10, 20, 22) and it has one type of phosphor particles (7) and two types of phosphor particles ( 17, 18) in the cases of partial conversion and complete conversion, respectively.
- the proposed LED ( 100) with the partial conversion of blue light in phosphor has a semiconductor chip ( 1 ) emitting blue light in the 400-500 nm spectral range, which is matched to the absorption spectrum of phosphor in the converter (5). A certain part of the primary flux is converted to orange light in the 570-600 nm region by an appropriate phosphor (7).
- This phosphor could be yttrium magnesium aluminium silicon garnet activated by trivalent cerium ions (Y3Mg 2 AlSi 2 0i 2 :Ce 3+ ), barium strontium silicon nitride activated by divalent europium
- the proposed LED (200) with the complete conversion of near UV light has a semiconductor chip (1 1 ) emitting near UV, violet or blue light with the wavelength shorter than 450 nm. This light is matched to the absorption spectra of phosphors and is completely absorbed in the wavelength converter.
- the converter ( 15) contains a phosphor ( 17) that converts the short-wavelength radiation to orange light in the 570-600 nm spectral range.
- the converter ( 1 5) contains another phosphor ( 18) that converts the short-wavelength radiation to blue light in the 400-500 nm spectral range.
- This phosphor could be oxide, halo-oxide or nitride compound activated by divalent europium, divalent manganese, divalent tin, or trivalent cerium ions.
- the blue component could be generated by inorganic phosphors like CaMgSi 2 0 6 :Eu 2+ , Ba 5 Si0 4 Cl 6 :Eu 2+ , Mg 3 Ca 3 (P0 4 ) 4 :Eu 2+ , (Ca,Sr,Ba) 5 (P0 4 ) 3 CI:Eu 2+ , Ca 2 B 5 0 9 (Br,Cl):Eu 2+ , BaMgAl , 0 O, 7 :Eu 2+ ,Mn 2+ ,
- the blue and the orange components are mixed with the ratio of radiant fluxes of about 1 : 15, the spectrum matching the black body radiation chromaticity is obtained, which is perceived by the human eye as a low CCT white light or firelight.
- PcLED ( 100, 200) has a semiconductor chip ( 1 , 1 1 ) of common design that is composed of a p type cladding layer, which is connected to the anode terminal, and an n type cladding layer, which is connected to the cathode terminal (3, 13).
- the electrons injected form the n type cladding layer recombine with holes injected from the p type cladding layer.
- the semiconductor chip (1 , 1 1) of the disclosed pcLEDs (100, 200) has an active layer that emits blue or near UV light.
- group III nitride compounds with the general formula A ⁇ y ⁇ n x Ga. ⁇ - ⁇ x ⁇ yN are the most convenient to use.
- the energy band-structure (side valleys are far apart) and the properties of carrier recombination in these semiconductors determine a weak dependence of the output flux on temperature.
- the most appropriate material for the active layer is the ternary alloy.
- the active layer of the proposed LED (200) with a semiconductor chip ( 1 1 ) emitting light with a wavelength shorter than 450 nm could be made of a ternary alloy (wavelength range 370 ⁇ 150 nm), a binary GaN compound (wavelength about 360 nm), or a ternary ALXjai -yN alloy (wavelength shorter than 360 nm). Also in the entire range of wavelengths, a quaternary alloy - x -yN can be used.
- the chip (1 , 1 1 ) of the LEDs (100, 200) is mounted on the reflector cup (2, 12) and using wires (4, 14) is connected to metal terminals (3, 13), through which the chip ( 1 , 1 1 ) is supplied by the driving current.
- the wavelength converter (5, 15) which is a layer of resin or silicone, a crystal or ceramic plate, or a casting of plastic that contains phosphor particles, is mounted next to the said silicon chip ( 1 , 1 1 ) in such a way that a part of or the entire photon flux generated in the semiconductor chip would be absorbed by phosphor particles.
- the converter (5, 1 5) could also be placed outside the LED package, for instance, a transparent cover of LED containing phosphor particles could also serve as a converter.
- the wavelength converter (5, 15) is designed in such a way that the wavelengths and radiant fluxes of the spectral components of LED radiation would be the most suitable for the photobiologically friendly outdoor lighting with low non-visual circadian action.
- the optimal composition of the spectrum can vary depending on a certain application (illumination of streets, car parking lots, pedestrian and bicycle tracks, building facades, monuments, parks or house yards) and on the luminance requirements.
- the radiant fluxes of each spectral component of two-spectral-component LEDs for photobiologically friendly outdoor lighting can be set by several ways.
- this is achieved by adjusting the size and concentration of the phosphor particles, the thickness of the wavelength converter, the refraction index of the material of the wavelength converter, the distance between the wavelength converter and the electroluminescent chip, and the position of the wavelength converter within the housing of the LED or outside the package.
- the optimal photobiologically friendly street lighting can be achieved when the chromaticity of LEDs matches the chromaticity of black body radiation.
- the spectral components are selected with mesopic spectral luminous efficiency and spectral circadian efficiency functions taken into account.
- the optimal peaks of the spectral components of the LED characterized by a low non-visual circadian action are at about 450 nm and 585 nm. Since the mentioned spectral efficiency functions are broadened, the indicated optimal wavelength values can differ within the ⁇ 15 nm range. Examples
- a pcLED with the partial conversion of blue light (100) for photobiologically friendly outdoor lighting is presented.
- the LED contains a semiconductor chip ( 1 ) that generates blue light due to injection electroluminescence.
- the chip is placed in a reflector cup (2) and is connected to terminals (3) by bonded wires (4).
- the chip is covered by a wavelength converter (5).
- the chip ( 1 ) and converter (5) are encapsulated within a transparent package (6) such as a plastic or silicon casting.
- the common semiconductor chip contains a p type cladding layer, which is connected to the anode terminal, and an n type cladding layer, which is connected to the cathode terminal.
- the electrons injected from the n type cladding layer recombine radiatively with the holes injected from the p type cladding layer.
- a common material for the active layer is a ternary In Gal -xN alloy with the width of the active layer and the molar fraction of indium x in the alloy chosen in such a way that the radiation band would have the peak in the 430-470 nm spectral range.
- the light generated in the semiconductor chip (1 ) passes through the wavelength converter (5), which contains phosphor particles (7).
- One part of the photons (8) emitted from the semiconductor chip are not absorbed by the phosphor particles and escape from the chip to the environment through the transparent packaging.
- Another part of the photons (9) emitted from the semiconductor chip are absorbed by the phosphor particles (7) and are converted to the photons (10) with the wavelength that matches the spectral component with the peak in the 570-600 nm (orange) spectral range.
- This kind of LED emits two-component blue-orange (low-CCT white or firelight) light.
- a pcLED (200) with the complete conversion of near UV light for photobiologically friendly outdoor lighting is presented.
- the mentioned LED (200) contains a semiconductor chip (1 1 ) that generates near UV light due to injection electroluminescence.
- the chip is placed in a reflector cup (12) and is connected to terminals ( 13) by bonded wires (14).
- the chip is covered by a wavelength converter ( 15).
- the chip ( 14) and converter (15) are encapsulated within a transparent package (16).
- the common semiconductor chip contains a p type cladding layer, which is connected to the anode terminal, and an n type cladding layer, which is connected to the cathode terminal.
- a common material for the active layer is a binary GaN semiconductor compound, or ternary IruGal -xN or AlyGal - N alloys, or a quaternary ⁇ nxA ⁇ yGa ⁇ -x-yN alloy with the width of the active layer and the molar fractions of indium x or of aluminium y in the alloy chosen in such a way, that the radiation band would have the peak with the wavelength shorter than 450 nm.
- the light generated in the semiconductor chip ( 1 1 ) passes through the wavelength converter (15), which contains the phosphor particles (17) of first type and additionally the phosphor particles ( 1 8) of second type. All photons that are emitted from the semiconductor chip are absorbed by the phosphor particles. One part of the photons ( 19) are absorbed by the first type phosphor particles ( 17) and converted to the photons (20) with the wavelength that matches the spectral component with the peak in the 570-600 nm (orange) spectral range.
- the other part of the photons (21 ) is absorbed by the second type phosphor particles (18) and is converted to the photons (22) with a wavelength that falls within 430-470 nm (blue) spectral range.
- This kind of dichromatic LED emits blue-orange (low CCT white or firelight) light.
- the possible electroluminescence spectra of semiconductor chips that are proposed for the use in pcLEDs for photobiologically friendly outdoor lighting are presented (Fig. 4).
- the electroluminescence spectra of LEDs are required to match the absorption spectra of phosphors.
- the electroluminescence spectrum of the LED has to be matched with the orange phosphor in such a way that the overall SPD would match the chromaticity of black body radiation.
- Fig. 4(a) displays the electroluminescence spectrum that corresponds to the semiconductor chip containing the active layer made of ternary In x Gai. x N alloy with the width of the active layer and indium molar fraction in the layer chosen in a such way that the radiation band peaks at 445 nm in the blue spectral range.
- This kind of chip can be used in the partial conversion LED for photobiologically friendly outdoor lighting.
- Figure 4(b) displays the electroluminescence spectrum that corresponds to the semiconductor chip containing an active layer made of ternary ln x Gai- x N alloy with the width of the active layer and indium molar fraction in the layer chosen in a such way that the radiation band peaks at 380 nm in the near UV range.
- This kind of chip can be used in the complete conversion LED for photobiologically friendly outdoor lighting.
- Fig. 5(a) displays the photoluminescence spectra that correspond to yttrium magnesium aluminium silicon garnet activated by trivalent cerium ions (Y 3 Mg 2 AISi 2 012:Ce 3+ ), barium strontium silicon nitride activated by divalent europium ions ((Ba,Sr) 2 Si 5 Ng:Eu 2+ ), barium strontium orthosilicate, activated by divalent europium ions ((Ba,Sr)Si0 4 :Eu 2+ ), calcium - alpha silicon aluminium oxynitride, activated by divalent europium ions (Ca-a-SiA10N:Eu 2+ ), or calcium strontium selenide, activated by divalent europium ions (
- phosphors can be used in the partial conversion or complete conversion pcLEDs for the photobiologically friendly outdoor lighting in order to generate the orange spectral component.
- Fig. 5(b) displays the photoluminescence spectrum that corresponds to aluminate phosphor activated by divalent europium ions (BaMgAlioO
- divalent europium ions BaMgAlioO
- Such phosphor can be used in the complete conversion pcLEDs for the photobiologically friendly outdoor lighting for the generation of the blue spectral component.
- the SPDs of the partial and complete conversion pcLEDs for photobiologically friendly outdoor lighting are presented in Fig. 6.
- the spectra have the blue component with the peak in the 430-470 nm range that is generated by the InGaN semiconductor chip due to injection electroluminescence or by the wavelength converter due to photoluminescence and the orange component generated due to the photoluminescence of the wavelength converter.
- the radiation fluxes of residual blue light and of light that is generated by each phosphor are set by adjusting the concentration of the phosphor particles, the width of the wavelength converter, the refraction index of the material of the wavelength converter, and the position of the wavelength converter within the housing of the LED or outside the package. Accordingly, Fig.
- 6(a) presents the SPDs that correspond to two-component light that has the firelight chromaticity and that is generated using the partial conversion of blue light with the spectral component that peaks at 445- ⁇ 50 nm in Y 3 Mg 2 AISi 2 0 12 :Ce 3+ , (Ba,Sr) 2 Si 5 N 8 :Eu 2+ , (Ba,Sr) 2 Si0 4 :Eu 2+ , Ca-a-SiA10N:Eu 2+ and (Ca,Sr)Se:Eu 2+ phosphors emitting orange light with the spectral component due to the photoluminescence that peaks at 570-600 nm. Accordingly, Fig.
- 6(b) displays the SPD that corresponds to two-component light that has firelight chromaticity and that is generated using the complete conversion of near UV light in BaMgAl mOnrEu 2 " and Y 3 Mg 2 AlSi 2 0
- Such firelight pcLEDs can be used in the evening illumination of streets, car parking lots, pedestrian and bicycle tracks, buildings, monuments, parks and house yards in order to avoid the disruption of the human circadian rhythm.
- Table 1 presents photometric, chromatic, and photobiological parameters of the pcLED.
- Table 1 presents parameters of the pcLED examples that are compared to the parameters of commercial warm white and cool white LEDs and of the standard CIE illuminant A: CCT (correlated colour temperature), CAF (circadian action factor), LER (luminous efficacy of radiation), CRI (colour rendering index), CRI mes (mesopic colour rendering index), and rj (maximum efficiency that is determined by the wavelength difference of light emitted by the semiconductor chip and phosphor (Stokes shift).
- the parameters of the pcLEDs presented in Table 1 are also compared to the parameters of the widely used high pressure sodium (HPS) lamp.
- HPS high pressure sodium
- the values are given for the luminance of the environment of 0.3 and 2 cd/m 2 (the lowest class ME6 and the highest class ME 1 of street lighting standards, respectively).
- the CAF values normalized to the CIE standard illuminant A 2856 black body radiation
- Table 1 shows that the parameters of light sources strongly depend on the selected phosphor. However, the common tendency is that for increased CCT values, the CAF is also increasing.
- the values of the luminous efficacy of radiation for the SPDs of the proposed LEDs are somewhat lower than those of commercial LEDs and HPS lamps.
- the CAF of the proposed LEDs when the luminance of the environment is 2 cd/m 2 , the CAF of the proposed LEDs is by about 0.1-0.25 blm/lm lower than that of the commercial warm white LEDs and even by 0.3-0.45 blm/lm lower than that of the commercial cool white LEDs.
- the CAF value of the proposed LEDs normalized to that of the CIE standard illuminant A is no larger than 0.6
- the normalized CAF is about 0.85 and 1 .4, respectively.
- the colour rendering properties of the proposed LEDs are comparable to those of the commercial LEDs and significantly surpass those of the HPS lamp.
- the maximum efficiency values of the commercial warm white LED and of the proposed LEDs are very similar. However, due to the smaller Stokes shift, the commercial cool white LED is characterized by a higher maximum efficiency.
- the short wavelength and long wavelength components of light generated by the proposed partial conversion LEDs have partial radiant flux ratios as follows:
- the used phosphor is Y3Mg 2 AlSi 2 0i2:Ce 3+
- the light emitted by the InGaN chip has a spectral peak at 440 nm
- the CCT of the obtained SPD is 2088
- the CAF normalized to the CIE standard illuminant A equals 0.379 for the luminance of the environment 2 cd/m 2 ;
- the short wavelength and the long wavelength components of light generated by the proposed complete conversion LEDs have partial radiant flux ratios as follows: - about 1 : 19, when the used phosphor is Y 3 Mg 2 AlSi 2 0 I 2 :Ce 3+ , the CCT of the obtained SPD is 2100 , and the CAF normalized to the CIE standard illuminant A equals 0.398 for the luminance of the environment 2 cd/m 2 ;
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Abstract
The proposed low correlated colour temperature phosphor converted LED is characterized by a small non-visual photobiological action to humans, which manifests itself as the suppression of melatonin secretion in the pineal gland, and can be used for the illumination of streets, car parking lots, pedestrian and bicycle tracks, building facades, monuments, parks and house yards that only slightly disrupts the circadian rhythm of humans. The LED has a semiconductor chip that emits short wavelength light in the blue, violet or near UV region due to the injection electroluminescence and a wavelength converter which converts the said short wavelength light due to photoluminescence to longer wavelength light having an orange component with the spectrum peaking in the range of about from 570 nm to 600 nm. In the case of partial conversion LED, the chip generates blue light that is partially converted to orange light by one phosphor (for instance, yttrium magnesium aluminium silicon garnet activated by trivalent cerium ions (Y3Mg2AISi2012:Ce3+), barium strontium silicon nitride activated by divalent europium ions ((Ba,Sr)2Si5N8:Eu2+), barium strontium orthosilicate, activated by divalent europium ions ((Ba,Sr)SiO4:Eu2+), calcium - alpha silicon aluminium oxynitride, activated by divalent europium ions (Ca-α-SiAlON:Eu2+), or calcium strontium selenide, activated by divalent europium ions ((Ca,Sr)Se:Eu2+)) contained in the converter. In the case of complete conversion LED, the chip generates near UV light that is completely absorbed in the converter and converted by a blue phosphor (for instance, CaMgSi2O6:Eu2+, Ba5SiO4Cl6:Eu2+, Mg3Ca3(PO4)4:Eu2+, (Ca,Sr,Ba)5(PO4)3CI :Eu2+, Ca2B5O9(Br,Cl):Eu2+, BaMgAl10O17:Eu2+,Mn2+, BaMg2Al16O27:Eu2+, (Lu,Gd)2SiO5:Ce3+, Sr2P2O7:Sn2+, SrSiAI2O3N2:Ce3+ or La3Si6N11 :Ce3+) and the orange phosphors mentioned above.
Description
PHOTOBIOLOGICALLY FRIENDLY PHOSPHOR CONVERTED LIGHT- EMITTING DIODE
Technical field
The present invention relates to light sources that are suitable for the use in outdoor lighting and only slightly disrupts the circadian rhythm of humans; more specifically the invention discloses light-emitting diodes that are composed of semiconductor short wavelength emitters that emit blue light due to electroluminescence and of inorganic phosphors that generate the orange components of spectral power distribution.
Definitions
CIE - (fr. Commission Internationale de VEclairage) the International Commission on Illumination;
CIE standard illuminant A - the spectral power distribution that matches the radiation of a 2856 temperature black body;
CAF - circadian action factor (the ratio of non-visual circadian efficacy to the luminous efficacy of radiation);
Phosphor - a certain material that converts light with a shorter wavelength to light with a longer wavelength;
Firelight - light that has a low correlated colour temperature (<2500 K) with the chromaticity that is similar to that of a black body radiation.
CRI - colour rendering index;
SPD - spectral power distribution;
CCT - correlated colour temperature;
LED - light emitting diode;
pcLED - phosphor converted LED.
Background of the Invention
When using outdoor lighting at night, the impact of light on the biological day-night (circadian) rhythm of humans is to be taken into account. Like other mammals, humans have their own circadian rhythm, which controls the phases of sleep and alertness [D. Lang, Energy
efficient illumination for the biological clock, Proc. of SPIE 7954, p. 795402-1-12 (201 1 )]. Already in the past century, the circadian rhythm of humans was related to lighting and in 2001 this rhythm was found to be controlled by ganglion cells that are located in the lower part of the eye retina [G. C. Brainard, J. P Hanifin, J. M. Greeson, B. Byrne, G. Glickman, E. Gerner, M. D. Rollag, Action spectrum for melatonin regulation in humans: Evidence for a novel circadian photoreceptor, J. Neurosci. 21 (16), p. 6405-6412 (2001 ); K. Thapan, J. Arendt, D. J . Skene, An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans, J. Physiol. 535(1 ), p. 261 -267 (2001 )]. These cells are non- visual photoreceptors, which form the non-visual path for the control of the circadian rhythm along with the suprachiasmatic nucleus and pineal gland, which are located in the brain.
When an eye is illuminated by blue light, especially that falling from above, the aforementioned ganglion cells generate a signal to the brain suprachiasmatic nucleus, which then starts suppressing the secretion of melatonin (sleep hormone and natural oncostatic agent) in the pineal gland. Due to this reason, humans feel alert under bright light conditions during the daytime or in the morning, whereas in the evening, when the sun sets down, the secretion of melatonin is not suppressed and humans are preparing for sleep. The disruption of the circadian rhythm and the suppression of melatonin secretion are proven by scientific research to increase the risk of cancerous diseases [S. Davis, D. K. Mirick, Circadian disruption, shift work and the risk of cancer: a summary of the evidence and studies in Seattle, Cancer Causes Control 17(4), p. 539-545 (2006)]. Therefore it is important to ensure that in the evening and during the first part of the night, light with high circadian action would be avoided for the illumination of streets, car parking lots, pedestrian and bicycle tracks, facades of buildings, monuments, parks, and yards of houses. In the USA patents US 6,498,429 and US 4,401 ,914, high pressure sodium vapour lamp and low pressure sodium vapour lamp are presented, respectively. These discharge lamps are breakable, are characterized by a long warm up time and relatively low luminous efficacy; moreover they contain toxic and chemically aggressive compounds. High and low pressure sodium vapour lamps are distinguished by low CCT and small circadian action. However due to the scarce and structured spectrum they are characterized by extremely low colour rendering. In the USA patent US 2,001 ,501 , a mercury vapour lamp is presented. The radiation of this lamp is characterized by a high radiation flux in the blue region and strongly affects the circadian rhythm of humans. Also under conditions of low luminance, the visual discomfort
can appear due to the high CCT [A. A. ruithof, Tabular luminescence lamps for general illumination, Philips Tech. Rev. 6, p. 65-73 (1941)].
In the USA patent US 6,504,179 a trichromatic pcLED that contains a semiconductor chip emitting light in the 300 - 470 nm wavelength region that is partially converted to green light by a europium activated calcium magnesium chlorsilicate phosphor and to yellow light by a cerium activated rare earth metal garnet phosphor is presented. This blend of three colours is perceived by humans as white light. However, this kind of LED is not optimal for photobiologically friendly street lighting for the following reasons:
• The SPD of the optimal photobiologically friendly LED consists of two spectral components, whereas in the patent the LED with SPD consisting of three spectral components is described;
• The chemical compositions of the phosphors used in the LED are not chosen such that their SPD would be optimal for outdoor lighting with the lowest circadian action factor.
The USA patent US 6,501, 102 discloses a trichromatic pcLED that contains a semiconductor chip emitting light with a wavelength shorter than 460 nm that is partially converted to a secondary and tertiary radiation in phosphors where at least one of those is composed of at least one of the following: yttrium aluminium oxide compound, strontium gallium sulphide, yttrium aluminium lanthanum oxide compound, yttrium aluminium gallium oxide compound, and strontium sulphide nitridosilicate. This blend of three colours is perceived by humans as white light. However, this kind of LED is not optimal for photobiologically friendly street lighting for the following reasons:
• The SPD of the optimal photobiologically friendly LED consists of two spectral components, whereas in the patent the LED with SPD consisting of three spectral components is described;
· The chemical compositions of the phosphors used in the LED are not chosen such that their SPD would be optimal for outdoor lighting with the lowest circadian action factor.
The USA patent US 6,294,800 discloses a phosphor with the chemical composition of Ca8Mg(Si04)4Cl2:Eu2+,Mn2+ and a trichromatic pcLED that contains a semiconductor chip, which emits light in the 330 - 420 nm wavelength region, the mentioned Ca8Mg(Si04)4CI2:Eu2+,Mn2+ phosphor, in which a part of the primary radiation is converted to green light, Y203:Eu3+,Bi3+ phosphor, in which a part of the primary radiation is converted to
red light, and BaMg2Al i6027:Eu or (Sr,Ba,Ca)5(PO"4)3Cl:Eu phosphor, in which a part of the primary radiation is converted to blue light. This blend of three colours is perceived by humans as white light. However, this kind of LED is not optimal for photobiologically friendly street lighting for the following reasons: · The SPD of the optimal photobiologically friendly LED consists of two spectral components, whereas in the patent the LED with SPD consisting of three spectral components is described;
• The chemical compositions of the phosphors used in the LED are not chosen such that their SPD would be optimal for outdoor lighting with the lowest circadian action factor. The USA patent 6,084,250 discloses a trichromatic pcLED that contains a GaN LED emitting radiation in the ultraviolet region with the emission peak between 300 and 370 nm, and blue BaMgAl ioOi7:Eu2+ phosphor, in which the primary radiation is converted to radiation that peaks in the 430-490 nm region, green ZnS:Cu phosphor, in which the primary radiation is converted to radiation that peaks in the 520-570 nm region, and red Y202S phosphor, in which the primary radiation is converted to radiation, which peaks in the 590-630 nm region. This blend of three colours is perceived by humans as white light. However, this kind of LED is not optimal for photobiologically friendly street lighting for the following reasons:
• The SPD of the optimal photobiologically friendly LED consists of two spectral components, whereas in the patent the LED with SPD consisting of three spectral components is described;
• The chemical compositions of the phosphors used in the LED are not chosen such that their SPD would be optimal for outdoor lighting with the lowest circadian action factor.
The US patent US 5,851 ,063 discloses an entirely electroluminescent array of different-colour LEDs, which can be used for obtaining a desired SPD of the light source. However, such arrays require complex topology, which is needed for the layout of different groups of LEDs. Moreover, direct-emission electroluminescent LEDs of different colours are driven by different currents, which requires a higher number of control channels and more complex electronic circuits than in the case of pcLEDs when the electroluminescent chip in all LEDs is the same.
The main prototype of this invention is disclosed in the USA patent US 5,998,925. The LED described in this patent is composed of a semiconductor light emitting component and a phosphor. In this case the semiconductor chip is composed of In,Ga,A N (0 < , 0 < j, 0 < k,
and / + j + k = 1 ), and the phosphor is a cerium activated garnet structure material, which is composed of at least one element of two groups that consist of Y, Lu, Se, La, Gd, and Sm and Al, Ga, and In elements, respectively. The semiconductor chip emits excitation light in the 400-530 nm wavelength region and the phosphor photoluminescence is chosen such that its peak wavelength would be longer than that of the excitation light. However, while using such LEDs in outdoor lighting the following drawbacks are not avoided:
• The SPD of the LED is not optimized in such a way that the circadian action factor of radiated light is minimized, i.e., that during the evening or night the negative impact for the human organism would be as small as possible;
· The chemical compositions of the phosphors used in the LED are not chosen such that their SPD would be optimal for outdoor lighting with the lowest circadian action factor.
In order to reduce the non-visual effect of outdoor lighting and to avoid complex design and electronics, phosphor converted firelight sources optimized for mesopic vision (when the average luminance of the environment is between 0.01 and 10 cd/m2) that are characterized by a several times smaller circadian action than that of common daylight LEDs [A. Zukauskas, R. Vaicekauskas, P. Vitta, Optimization of solid-state lamps for photobiologically friendly mesopic lighting, Appl. Optics 51(35), p. 8423-8432 (2012)] could be used. In the aforementioned reference, a concept of a dichromatic light source is presented, in which the model SPDs of LEDs are optimized to have the smallest non-visual circadian action and the highest luminous efficacy of radiation in the mesopic region. These light sources are characterized by a modest colour rendering which is appropriate for the majority of outdoor lighting applications due to the reduced ability to discriminate colours in dim light.
The present invention discloses a low CCT (firelight) LED, which has a spectral power distribution composed of a blue and an orange components. These components have such peak wavelengths and ratios of radiation fluxes that the ratio of the excitation of non-visual photoreceptors in the eye retina that are controlling the circadian rhythm and the excitation of visual photoreceptors causing the visual perception would be the lowest. In this way the minimal disruption of the human circadian rhythm is obtained. The ratio of radiant fluxes of the spectral components are set by adjusting the size and the concentration of phosphor particles, the thickness of the wavelength converter, the refraction index of the material of the wavelength converter, the distance between the wavelength converter and the
electroluminescent chip, and the position of the wavelength converter within the housing of the LED or outside the package.
These pcLEDs can be used for various outdoor lighting applications (lighting for streets, pedestrian and bicycle tracks, building facades, monuments, parks, car parking lots, and house yards) in the evening and the first part of the night.
Summary of the Invention
The aim of this invention is to develop a pcLED with a low non-visual photobiological effect, in which the partial conversion of blue light or the total conversion of near ultraviolet (UV) light in the wavelength converter would be realized in a such way that the obtained light would have a spectral component with a peak value in the 570-600 nm wavelength range and a spectral component with a peak value in the 400-500 nm wavelength range and that the ratio of the radiant fluxes of the components would be such that the chromaticity coordinates of the LED matched the black body radiation in the low CCT range ( 1 500 - 3000 ). The aim of the present invention is achieved by a dichromatic (blue-orange) LED that has a semiconductor chip, which emits radiation due to injection electroluminescence, and a photoluminescent converter, which is placed on the way of the photon flux emitted by the said chip. The converter is designed to convert the said radiation to longer wavelength radiation below 500 nm and has one type (in the case of partial conversion) or two types (in the case of complete conversion) of phosphor particles. The novelty is that the LED emits a blend of blue and orange light while the converter contains one of the orange phosphors listed below. This orange component together with the blue component composes a firelight SPD that is characterized by a low non-visual circadian action for humans. The mentioned phosphor radiating in the orange range of the spectrum can be such as: - yttrium magnesium aluminium silicon garnet, activated by trivalent cerium ions Y3 g2AISi2012:Ce3+,
2+
- barium strontium silicon nitride activated by divalent europium ions (Ba,Sr)2Si5N8:Eu , +
- barium strontium orthosilicate, activated by divalent europium ions (Ba,Sr)Si04:Eu ,
- calcium - alpha silicon aluminium oxynitride, doped with divalent europium ions Ca-a- SiA10N:Eu2+,
- calcium strontium selenide, doped with divalent europium ions (Ca,Sr)Se:Eu2+.
In the case of partial conversion, the semiconductor chip generates blue light in the 400- 500 nm spectral range and the converter contains a phosphor that is characterized by the partial conversion of the said light to longer wavelength (orange) light. In this case, the active layer of the semiconductor chip is made of
semiconductor alloy. In the case of complete conversion, the semiconductor chip generates near UV radiation or blue (violet) light, that has a wavelength shorter than 450 nm, and the converter contains a second phosphor which is characterized by luminescence in the 400-500 nm spectral range and that can be oxide, halo-oxide or nitride compound activated by divalent europium, divalent manganese, divalent tin or trivalent cerium ions. In this case the active layer of the semiconductor chip is made of GaN semiconductor alloy or of
ALGai -yN, or
-j-yN semiconductor alloy.
In any of the mentioned cases, when the LED is emitting several spectral components, the radiant flux and the peak wavelength of each spectral component are chosen such that the final composition of the radiated light would be suitable for photobiologically friendly outdoor lighting, i.e., that its chromaticity would match that of the absolute black body radiation with a low temperature ( 1500 - 3000 K), and that the SPD would be characterized by a relatively small non-visual circadian action.
A small non-visual circadian action SPD is such that the radiant flux of the blue component and the radiant flux of the orange component have the ratio of not larger than 1 : 17 and 1 : 15 in the cases of partial conversion LED and complete conversion LED, respectively, when CCT = 2000 , and has the ratio not larger than 1 :5 and 1 :4 in the cases of partial conversion LED and complete conversion LED, respectively, when CCT = 3000 K.
The ratio of the radiant fluxes of the spectral components are set by adjusting the size and the concentration of phosphor particles, the width of the wavelength converter, the refraction index of the material of the wavelength converter, the distance between the wavelength converter and the electroluminescent chip, and the position of the wavelength converter within the housing of the LED or outside the package.
In the case of optimal LED characterized by a low non-visual action, the generated light spectral components have peak wavelengths as follows: · about 585±20 nm for the orange component,
• about 450±20 nm for the blue component.
Brief Description of the Drawings
Fig. 1 - photopic and scotopic spectral luminous efficiency functions and spectral circadian efficiency function;
Fig. 2 - basic structure of LED (100) with the partial conversion of blue light for photobiologically friendly outdoor lighting;
Fig. 3 - basic structure of LED (200) with the complete conversion of near UV l ight for photobiologically friendly outdoor lighting;
Fig. 4 - typical electroluminescence spectra of a semiconductor chip containing the InGaN active layer: (a) blue 450 nm emitter; (b) near UV 365 nm emitter;
Fig. 5 - typical photoluminescence spectra of inorganic phosphors: (a) orange emitter; (b) blue emitter;
Fig. 6 - SPDs of firelight pcLEDs for photobiologically friendly outdoor lighting: (a) partial conversion LEDs with orange phosphors Y3Mg2AlSi20i2:Ce3+, (Ba,Sr)2Si5N8:Eu2+, (Ba,Sr)2Si04:Eu2+, Ca-a-SiAIOM:Eu2+, (Ca,Sr)Se:Eu2+; (b) complete conversion LED with blue BaMg Al i6027:Eu2+ and orange Y3Mg2AlSi20]2:Ce3+ phosphors.
Detailed description of the invention
While designing smart energy-saving lighting systems, semiconductor LEDs are more and more often applied in outdoor lighting. They are efficient and longevous, characterized by flexibility while choosing the desired SPD, suitable for rapidly switching on and off and for continuous dimming, feature no abrupt burn-out, and do not require high voltage supply; moreover they are compatible with computer-control technologies.
The proposed two-component firelight chromaticity LED is characterized by a small non- visual circadian action and its SPD is optimized by taking into account the luminous efficacy of radiation. Since the luminous efficacy of a light source is the product of the luminous efficacy of the generated radiation and the radiant efficiency of the light source, the optimization by luminous efficacy of radiation, which depends only on SPD, is rather general. Meanwhile the radiant efficiency of LEDs depends on the injection efficiency, internal quantum efficiency, light extraction efficiency, and serial resistance, i.e. on the parameters that are gradually improving while developing LED technologies [P. Mottier, LEDs for Lighting Applications, John Wiley & Sons, Inc, London, (2009)].
For photopic (daytime) vision, the luminous efficacy of radiation is:
K = Ko X J S(A)dA ' where S(X) is the SPD of an LED, λ is the wavelength, V(X) is the spectral luminous efficiency function for photopic vision defined by the CIE in 1924, KQ is the maximum possible value of luminous efficacy, which for photopic vision equals 683 Im/W.
Photopic vision is typical for an environment where the average (adaption) luminance is above 10 cd/m . Under such conditions the sense of vision is dominated by three types of photoreceptors in the eye retina (cones) thus the photopic vision is chromatic. When the value of adaption luminance is below 0.01 cd/m2, the sense of vision is caused by one type of photoreceptors (rods), therefore under the conditions of low luminance humans lose the ability to distinguish colours. In this case the eye sensitivity function is described by the spectral luminous efficiency function of scotopic vision V' k), which was defined by the CIE in 1951. The maximum possible value of luminous efficacy for photopic vision is 1700 Im/W. The spectral luminous efficiency functions for photopic and scotopic vision are presented in Fig. 1.
The proposed LED for outdoor lighting is optimized for the intermediate, i.e. mesopic, region, when the average luminance is in the range between 0.01 cd/m2 and 10 cd/m2. This luminance range covers the interval used for the lighting of pedestrian tracks and streets which is between 0.1 cd/m2 and 2 cd/m2. In this case the sense of vision is determined by both cones and rods, the discrimination of colours is reduced, and the mesopic spectral luminous efficiency function Vmes ) depends on the luminance of the environment. The dependence of the spectral sensitivity of mesopic vision on adaption luminance is complex and is described by various models. Here we refer to the photometric system MES-2 recommended by the CIE [Commission Internationale de PEclairage, Recommended system for mesopic photometry based on visual performance, Pub. CIE 191 :2010]. According to this system, the spectral luminous efficiency function is defined as:
VmesW = Mimr mVm + (1 - m)V X)
where M(m) is the normalization function and m is the multiplier that depends on the luminance of the environment. In the case of mesopic vision, the luminous efficacy of radiation is estimated as:
where the maximum possible mesopic luminous efficacy ^rmeso depends on the luminance of the environment and varies from 1700 lm/W to 683 lm/W.
The ganglion cells that are responsible for non-visual circadian action of light are characterized by spectral sensitivity similarly to the visual receptors. This spectral sensitivity is described by the circadian efficiency function C(k) that is presented in Fig. 1. The peak of this function is seen to be at about 460 nm, thus the circadian rhythm is mostly affected by blue light [D. Gall, Circadiane Lichtgrosen und deren messtechnische Ermittlung, Licht 54, p. 1292-1297 (2002)]. Under mesopic conditions that are typical of artificial outdoor lighting, the non-visual circadian action of the proposed LED for outdoor lighting is evaluated by calculating the circadian action factor (CAF) omes. This factor is defined as the ratio of the non-visual circadian efficacy of radiation to the mesopic luminous efficacy of radiation:
Kc Kc0 J C {X)S{X)dX
Kmes KmesO / nes ( )5(A)dA
where Kco is equaled to 683 lm/W [A. Zukauskas, R. Vaicekauskas, P. Vitta, Optimization of solid-state lamps for photobiologically friendly mesopic lighting, Appl. Optics 51(35), p. 8423-8432 (2012)]. The value of CAF is suitable for the comparison of the non-visual circadian action of light sources. For lighting in the evening, as low as possible Cimes value is desired since in this case a higher luminous efficacy and a lower circadian efficacy is required. The dichromatic light source with a short wavelength component that peaks at about 440-460 nm and with a long wavelength component that peaks at about 570-600 nm is characterized by a minimum CAF value [A. Zukauskas, R. Vaicekauskas, P. Vitta, Optimization of solid-state lamps for photobiologically friendly mesopic lighting, Appl. Optics 51(35), p. 8423-8432 (2012)]. The SPD of the proposed LED was optimized by searching for the minimum value of CAF.
The proposed LED for outdoor lighting is superior to common outdoor lighting sources (high and low pressure sodium vapour lamps) in colour rendering properties. The colour rendering can be evaluated by the general colour rendering index (CRI) Ra that was introduced by CIE in 1965 and the evaluation procedure was updated in 1995 [Commission Internationale de l' Eclairage, Method of measuring and specifying colour rendering properties of light sources, Pub. CIE 13.3 : 1995]. In this procedure, eight main colour test samples are used; each sample is illuminated by a reference and a test light sources. After the analysis of the spectra of the reflected light, the colour differences are calculated and the special colour rendering index is
found for each sample. The general CRI is estimated as the average of the special colour rendering indices:
Λα = 100 - 4.6ΔΕ,
where ΔΕ is the average of the colour shifts of the eight samples in the CIE 1964 uniform colour space [Commission Internationale de PEclairage, Method of measuring and specifying colour rendering properties of light sources, pub. CIE 13.3: 1995]. The maximum CRI value is 100; this value is typical of incandescent and halogen lamps. Under mesopic luminance conditions the ability of humans to distinguish colours is known to become poorer [W. R. J. Brown, The influence of luminance level on visual sensitivity to color differences, J. Opt. Soc. Am. 41, p. 684-688 (1951 )]; thus the mesopic CRI R^mes could be described somewhat differently depending on the luminance [A. Zukauskas, R. Vaicekauskas, P. Vitta, Optimization of solid-state lamps for photobiologically friendly mesopic lighting, Appl. Optics 5 1 (35), p. 8423-8432 (2012)]:
Ra,mes = 100 - A.eY{Lmes)AE, where γ is the coefficient that depends on the luminance of the environment Lmes.
The proposed LED (100, 200) comprises a semiconductor chip (1 , 1 1 ) generating short- wavelength radiation with a shorter than 500 nm wavelength due to injection electroluminescence, which is placed in a reflector cup (2, 12) and is connected to terminals (3, 13) by bonded wires (4, 14). The chip ( 1 , 1 1 ) is covered by a wavelength converter (5, 15), which is encapsulated in a transparent package (6, 16). The said converter is designed for the conversion of short wavelength radiation to longer wavelength radiation due to photoluminescence for obtaining photons (10, 20, 22) and it has one type of phosphor particles (7) and two types of phosphor particles ( 17, 18) in the cases of partial conversion and complete conversion, respectively.
The proposed LED ( 100) with the partial conversion of blue light in phosphor has a semiconductor chip ( 1 ) emitting blue light in the 400-500 nm spectral range, which is matched to the absorption spectrum of phosphor in the converter (5). A certain part of the primary flux is converted to orange light in the 570-600 nm region by an appropriate phosphor (7). This phosphor could be yttrium magnesium aluminium silicon garnet activated by trivalent cerium ions (Y3Mg2AlSi20i2:Ce3+), barium strontium silicon nitride activated by divalent europium
* 2"†"
ions (Ba,Sr)2Si5N8:Eu , barium strontium orthosilicate activated by divalent europium ions (Ba,Sr)Si04:Eu2+, calcium - alpha silicon aluminium oxynitride doped with divalent europium
ions Ca-a-SiAION:Eu , or calcium strontium selenide doped with divalent europium ions (Ca,Sr)Se:Eu2+. The remaining part of the blue light is not absorbed. When the blue and the orange components are mixed with the ratio of radiant fluxes of about 1 : 17, the spectrum matching the black body radiation chromaticity is obtained, which is perceived by the human eye as a low CCT white light or firelight.
The proposed LED (200) with the complete conversion of near UV light has a semiconductor chip (1 1 ) emitting near UV, violet or blue light with the wavelength shorter than 450 nm. This light is matched to the absorption spectra of phosphors and is completely absorbed in the wavelength converter. As well as in the case of partial conversion, the converter ( 15) contains a phosphor ( 17) that converts the short-wavelength radiation to orange light in the 570-600 nm spectral range. Moreover, the converter ( 1 5) contains another phosphor ( 18) that converts the short-wavelength radiation to blue light in the 400-500 nm spectral range. This phosphor could be oxide, halo-oxide or nitride compound activated by divalent europium, divalent manganese, divalent tin, or trivalent cerium ions. For example, the blue component could be generated by inorganic phosphors like CaMgSi206:Eu2+, Ba5Si04Cl6:Eu2+, Mg3Ca3(P04)4:Eu2+, (Ca,Sr,Ba)5(P04)3CI:Eu2+, Ca2B509(Br,Cl):Eu2+, BaMgAl ,0O,7:Eu2+,Mn2+,
BaMg2AI,6027:Eu2+, (Lu,Gd)2Si05:Ce3+, Sr2P207:Sn2+, SrSiAI203N2:Ce3+, or La3Si6Nn :Ce3+. When the blue and the orange components are mixed with the ratio of radiant fluxes of about 1 : 15, the spectrum matching the black body radiation chromaticity is obtained, which is perceived by the human eye as a low CCT white light or firelight.
PcLED ( 100, 200) has a semiconductor chip ( 1 , 1 1 ) of common design that is composed of a p type cladding layer, which is connected to the anode terminal, and an n type cladding layer, which is connected to the cathode terminal (3, 13). In the active layer, the electrons injected form the n type cladding layer recombine with holes injected from the p type cladding layer. The semiconductor chip (1 , 1 1) of the disclosed pcLEDs (100, 200) has an active layer that emits blue or near UV light. For the active layer, group III nitride compounds with the general formula A\y\nxGa.\ -~x~yN are the most convenient to use. These materials are highly chemically and photochemical ly inert, which results in the long life of LEDs. The energy band-structure (side valleys are far apart) and the properties of carrier recombination in these semiconductors determine a weak dependence of the output flux on temperature. The width of the active layer and the molar fractions of indium and (or) aluminium x and y, respectively, are chosen such that the peak of the radiation band would be at the requ ired wavelength.
For the proposed LED (100) with partial conversion in phosphor, which has the semiconductor chip ( 1 ) emitting in the 400-500 nm range, the most appropriate material for the active layer is the ternary alloy.
The active layer of the proposed LED (200) with a semiconductor chip ( 1 1 ) emitting light with a wavelength shorter than 450 nm could be made of a ternary
alloy (wavelength range 370^150 nm), a binary GaN compound (wavelength about 360 nm), or a ternary ALXjai -yN alloy (wavelength shorter than 360 nm). Also in the entire range of wavelengths, a quaternary alloy
-x-yN can be used.
Typically the chip (1 , 1 1 ) of the LEDs (100, 200) is mounted on the reflector cup (2, 12) and using wires (4, 14) is connected to metal terminals (3, 13), through which the chip ( 1 , 1 1 ) is supplied by the driving current. The wavelength converter (5, 15), which is a layer of resin or silicone, a crystal or ceramic plate, or a casting of plastic that contains phosphor particles, is mounted next to the said silicon chip ( 1 , 1 1 ) in such a way that a part of or the entire photon flux generated in the semiconductor chip would be absorbed by phosphor particles. The converter (5, 1 5) could also be placed outside the LED package, for instance, a transparent cover of LED containing phosphor particles could also serve as a converter.
The wavelength converter (5, 15) is designed in such a way that the wavelengths and radiant fluxes of the spectral components of LED radiation would be the most suitable for the photobiologically friendly outdoor lighting with low non-visual circadian action. The optimal composition of the spectrum can vary depending on a certain application (illumination of streets, car parking lots, pedestrian and bicycle tracks, building facades, monuments, parks or house yards) and on the luminance requirements.
The average optimal composition of dichromatic light matching the chromaticity of black body radiation with a low non-visual circadian action, is achieved when the spectral power distribution is composed of about 94-95% of orange light and of about 5-6% of blue light for CCT = 2000 and of about 75-80% of orange light and of about 20-25% of blue light for CCT = 3000 K. For this reason, the wide-application pcLEDs are proposed to have the blue and orange spectral components of the radiation with the radiant flux ratio matching these proportions, i.e., no larger than 1 : 17 and 1 : 15 in the case of partial conversion LEDs and complete conversion LEDs, respectively, for CCT = 2000 K and no larger than 1 :4 and 1 :5 in the case of partial conversion LEDs and complete conversion LEDs, respectively, for CCT = 3000 .
The radiant fluxes of each spectral component of two-spectral-component LEDs for photobiologically friendly outdoor lighting can be set by several ways. In the proposed LEDs, this is achieved by adjusting the size and concentration of the phosphor particles, the thickness of the wavelength converter, the refraction index of the material of the wavelength converter, the distance between the wavelength converter and the electroluminescent chip, and the position of the wavelength converter within the housing of the LED or outside the package.
The optimal photobiologically friendly street lighting can be achieved when the chromaticity of LEDs matches the chromaticity of black body radiation. The spectral components are selected with mesopic spectral luminous efficiency and spectral circadian efficiency functions taken into account. The optimal peaks of the spectral components of the LED characterized by a low non-visual circadian action are at about 450 nm and 585 nm. Since the mentioned spectral efficiency functions are broadened, the indicated optimal wavelength values can differ within the ±15 nm range. Examples
As an example, a pcLED with the partial conversion of blue light (100) for photobiologically friendly outdoor lighting is presented. The LED contains a semiconductor chip ( 1 ) that generates blue light due to injection electroluminescence. The chip is placed in a reflector cup (2) and is connected to terminals (3) by bonded wires (4). The chip is covered by a wavelength converter (5). The chip ( 1 ) and converter (5) are encapsulated within a transparent package (6) such as a plastic or silicon casting. The common semiconductor chip contains a p type cladding layer, which is connected to the anode terminal, and an n type cladding layer, which is connected to the cathode terminal. In the active layer, the electrons injected from the n type cladding layer recombine radiatively with the holes injected from the p type cladding layer. A common material for the active layer is a ternary In Gal -xN alloy with the width of the active layer and the molar fraction of indium x in the alloy chosen in such a way that the radiation band would have the peak in the 430-470 nm spectral range.
The light generated in the semiconductor chip (1 ) passes through the wavelength converter (5), which contains phosphor particles (7). One part of the photons (8) emitted from the semiconductor chip are not absorbed by the phosphor particles and escape from the chip to the environment through the transparent packaging. Another part of the photons (9) emitted from the semiconductor chip are absorbed by the phosphor particles (7) and are converted to the
photons (10) with the wavelength that matches the spectral component with the peak in the 570-600 nm (orange) spectral range. This kind of LED emits two-component blue-orange (low-CCT white or firelight) light.
Also as another example, a pcLED (200) with the complete conversion of near UV light for photobiologically friendly outdoor lighting is presented. The mentioned LED (200) contains a semiconductor chip (1 1 ) that generates near UV light due to injection electroluminescence. The chip is placed in a reflector cup (12) and is connected to terminals ( 13) by bonded wires (14). The chip is covered by a wavelength converter ( 15). The chip ( 14) and converter (15) are encapsulated within a transparent package (16). The common semiconductor chip contains a p type cladding layer, which is connected to the anode terminal, and an n type cladding layer, which is connected to the cathode terminal. In the active layer, the electrons injected from the n type cladding layer recombine radiatively with the holes injected from the p type cladding layer. A common material for the active layer is a binary GaN semiconductor compound, or ternary IruGal -xN or AlyGal - N alloys, or a quaternary \nxA\yGa\ -x-yN alloy with the width of the active layer and the molar fractions of indium x or of aluminium y in the alloy chosen in such a way, that the radiation band would have the peak with the wavelength shorter than 450 nm.
The light generated in the semiconductor chip ( 1 1 ) passes through the wavelength converter (15), which contains the phosphor particles (17) of first type and additionally the phosphor particles ( 1 8) of second type. All photons that are emitted from the semiconductor chip are absorbed by the phosphor particles. One part of the photons ( 19) are absorbed by the first type phosphor particles ( 17) and converted to the photons (20) with the wavelength that matches the spectral component with the peak in the 570-600 nm (orange) spectral range. Similarly, the other part of the photons (21 ) is absorbed by the second type phosphor particles (18) and is converted to the photons (22) with a wavelength that falls within 430-470 nm (blue) spectral range. This kind of dichromatic LED emits blue-orange (low CCT white or firelight) light.
As an example illustrating the invention, the possible electroluminescence spectra of semiconductor chips that are proposed for the use in pcLEDs for photobiologically friendly outdoor lighting are presented (Fig. 4). For the both cases of partial and complete conversion, the electroluminescence spectra of LEDs are required to match the absorption spectra of phosphors. Moreover in the case of partial conversion, the electroluminescence spectrum of the
LED has to be matched with the orange phosphor in such a way that the overall SPD would match the chromaticity of black body radiation.
Accordingly, Fig. 4(a) displays the electroluminescence spectrum that corresponds to the semiconductor chip containing the active layer made of ternary InxGai.xN alloy with the width of the active layer and indium molar fraction in the layer chosen in a such way that the radiation band peaks at 445 nm in the blue spectral range. This kind of chip can be used in the partial conversion LED for photobiologically friendly outdoor lighting. Accordingly, Figure 4(b) displays the electroluminescence spectrum that corresponds to the semiconductor chip containing an active layer made of ternary lnxGai-xN alloy with the width of the active layer and indium molar fraction in the layer chosen in a such way that the radiation band peaks at 380 nm in the near UV range. This kind of chip can be used in the complete conversion LED for photobiologically friendly outdoor lighting.
As an example illustrating the invention, the photoluminescence spectra corresponding to phosphors that are proposed for the use in photobiologically friendly pcLEDs for outdoor lighting are presented (Fig. 5). Accordingly, Fig. 5(a) displays the photoluminescence spectra that correspond to yttrium magnesium aluminium silicon garnet activated by trivalent cerium ions (Y3Mg2AISi2012:Ce3+), barium strontium silicon nitride activated by divalent europium ions ((Ba,Sr)2Si5Ng:Eu2+), barium strontium orthosilicate, activated by divalent europium ions ((Ba,Sr)Si04:Eu2+), calcium - alpha silicon aluminium oxynitride, activated by divalent europium ions (Ca-a-SiA10N:Eu2+), or calcium strontium selenide, activated by divalent europium ions ((Ca,Sr)Se:Eu2+) phosphors that absorb blue or near UV light and emit orange light with the spectral band that peaks at 570-600 nm. Such phosphors can be used in the partial conversion or complete conversion pcLEDs for the photobiologically friendly outdoor lighting in order to generate the orange spectral component. Accordingly, Fig. 5(b) displays the photoluminescence spectrum that corresponds to aluminate phosphor activated by divalent europium ions (BaMgAlioO|7:Eu2+) that absorbs near UV light and emits blue light with the spectral band that peaks at 446 nm. Such phosphor can be used in the complete conversion pcLEDs for the photobiologically friendly outdoor lighting for the generation of the blue spectral component. As an example illustrating the invention, the SPDs of the partial and complete conversion pcLEDs for photobiologically friendly outdoor lighting are presented in Fig. 6. The spectra have the blue component with the peak in the 430-470 nm range that is generated by the
InGaN semiconductor chip due to injection electroluminescence or by the wavelength converter due to photoluminescence and the orange component generated due to the photoluminescence of the wavelength converter. The radiation fluxes of residual blue light and of light that is generated by each phosphor are set by adjusting the concentration of the phosphor particles, the width of the wavelength converter, the refraction index of the material of the wavelength converter, and the position of the wavelength converter within the housing of the LED or outside the package. Accordingly, Fig. 6(a) presents the SPDs that correspond to two-component light that has the firelight chromaticity and that is generated using the partial conversion of blue light with the spectral component that peaks at 445-^50 nm in Y3Mg2AISi2012:Ce3+, (Ba,Sr)2Si5N8:Eu2+, (Ba,Sr)2Si04:Eu2+, Ca-a-SiA10N:Eu2+ and (Ca,Sr)Se:Eu2+ phosphors emitting orange light with the spectral component due to the photoluminescence that peaks at 570-600 nm. Accordingly, Fig. 6(b) displays the SPD that corresponds to two-component light that has firelight chromaticity and that is generated using the complete conversion of near UV light in BaMgAl mOnrEu2 " and Y3Mg2AlSi20|2:Ce3+ phosphors that emit blue light with the spectral component that peaks at 446 nm and orange light with the spectral component that peaks at 600 nm, respectively, due to photoluminescence.
Such firelight pcLEDs can be used in the evening illumination of streets, car parking lots, pedestrian and bicycle tracks, buildings, monuments, parks and house yards in order to avoid the disruption of the human circadian rhythm.
Table 1 presents photometric, chromatic, and photobiological parameters of the pcLED.
Table 1 presents parameters of the pcLED examples that are compared to the parameters of commercial warm white and cool white LEDs and of the standard CIE illuminant A: CCT (correlated colour temperature), CAF (circadian action factor), LER (luminous efficacy of radiation), CRI (colour rendering index), CRImes (mesopic colour rendering index), and rj (maximum efficiency that is determined by the wavelength difference of light emitted by the semiconductor chip and phosphor (Stokes shift). The parameters of the pcLEDs presented in Table 1 are also compared to the parameters of the widely used high pressure sodium (HPS)
lamp. The values are given for the luminance of the environment of 0.3 and 2 cd/m2 (the lowest class ME6 and the highest class ME 1 of street lighting standards, respectively). In the third column, the CAF values normalized to the CIE standard illuminant A (2856 black body radiation) are presented for the luminance of environment of 2 cd/m2. Table 1 shows that the parameters of light sources strongly depend on the selected phosphor. However, the common tendency is that for increased CCT values, the CAF is also increasing. The values of the luminous efficacy of radiation for the SPDs of the proposed LEDs are somewhat lower than those of commercial LEDs and HPS lamps. However, most of the proposed LED SPDs are characterized by a lower CAF: when the luminance of the environment is 2 cd/m2, the CAF of the proposed LEDs is by about 0.1-0.25 blm/lm lower than that of the commercial warm white LEDs and even by 0.3-0.45 blm/lm lower than that of the commercial cool white LEDs. When compared to the CIE standard illuminant A, the CAF value of the proposed LEDs normalized to that of the CIE standard illuminant A is no larger than 0.6, whereas for the warm white LED and cool white LED, which corresponds to the main prototype of this patent, the normalized CAF is about 0.85 and 1 .4, respectively.
The colour rendering properties of the proposed LEDs are comparable to those of the commercial LEDs and significantly surpass those of the HPS lamp. The maximum efficiency values of the commercial warm white LED and of the proposed LEDs are very similar. However, due to the smaller Stokes shift, the commercial cool white LED is characterized by a higher maximum efficiency.
The short wavelength and long wavelength components of light generated by the proposed partial conversion LEDs have partial radiant flux ratios as follows:
- about 1 :21 , when the used phosphor is Y3Mg2AlSi20i2:Ce3+, the light emitted by the InGaN chip has a spectral peak at 440 nm, the CCT of the obtained SPD is 2088 , and the CAF normalized to the CIE standard illuminant A equals 0.379 for the luminance of the environment 2 cd/m2;
- about 1 :37, when the used phosphor is (Ba,Sr)2Si5N8:Eu2+, the light emitted by the InGaN chip has a spectral peak at 443 nm, the CCT of the obtained SPD is 1 704 K, and the CAF normalized to the CIE standard illuminant A equals 0.185 for the luminance of the environment 2 cd/m2;
- about 1 : 10, when the used phosphor is (Ba,Sr)2Si0 :Eu , the light emitted by the InGaN chip has a spectral peak at 440 nm, the CCT of the obtained SPD is 2542 , and the CAF normalized to the CIE standard illuminant A equals 0.567 for the luminance of the environment 2 cd/m2; - about 1 : 14, when the used phosphor is (Ca,Sr)Se:Eu2+, the light emitted by the InGaN chip has a spectral peak at 443 nm, the CCT of the obtained SPD is 2101 , and the CAF normalized to the CIE standard illuminant A equals 0.31 1 for the luminance of the environment 2 cd/m2;
- about 1 : 1 1 , when the used phosphor is Ca-a-SiA10N:Eu +, the light emitted by the InGaN chip has a spectral peak at 443 nm, the CCT of the obtained SPD is 2426 , and the CAF normalized to the CIE standard illuminant A equals 0.507, for the luminance of the environment 2 cd/m2.
The short wavelength and the long wavelength components of light generated by the proposed complete conversion LEDs have partial radiant flux ratios as follows: - about 1 : 19, when the used phosphor is Y3Mg2AlSi20I 2:Ce3+, the CCT of the obtained SPD is 2100 , and the CAF normalized to the CIE standard illuminant A equals 0.398 for the luminance of the environment 2 cd/m2;
- about 1 :33, when the used phosphor is (Ba,Sr)2Si5N8:Eu2+, the CCT of the obtained SPD is 1708 K, and the CAF normalized to the CIE standard illuminant A equals 0.196, for the luminance of the environment 2 cd/m2;
- about 1 :9, when the used phosphor is (Ba,Sr)2Si04:Eu2+, the CCT of the obtained SPD is 2576 , and the CAF normalized to the CIE standard illuminant A equals 0.613 for the luminance of the environment 2 cd/m2;
- about 1 : 12, when the used phosphor is (Ca,Sr)Se:Eu2+, the CCT of the obtained SPD is 21 14 K, and the CAF normalized to the CIE standard illuminant A equals 0.338 for the luminance of the environment 2 cd/m ;
- about 1 : 10, when the used phosphor is Ca-a-SiA10N:Eu2+, the CCT of the obtained SPD is 2449 , and the CAF normalized to the CIE standard illuminant A equals 0.545 for the luminance of the environment 2 cd/m2.
Claims
The photobiologically friendly phosphor converted light-emitting diode (LED) with the spectral power distribution composed of at least two components, each of which has an individual spectral power distribution and relative partial radiant flux, characterized in that the spectral power distributions and the relative partial radiant fluxes of each component of the LED are set by choosing the respective phosphors with individual SPDs chosen in such way that the ratio of the non-visual circadian efficacy, which determines the suppression of the melatonin secretion in the human pineal gland, to the luminous efficacy of radiation would be no larger than 0.6 of that of the standard illuminant A, when the luminance of the environment is from 0.01 to 10 cd/m2.
The LED according to claim 1 , characterized in that the correlated colour temperature of the generated light is between 1500 K and 3000 .
The LED according to claims 1 and 2 that emits light due to the partial or complete conversion of the radiation with the spectrum peaking at a wavelength shorter than 500 nm generated within a semiconductor chip in the wavelength converter that is inside the housing or outside the package and has at least one type of phosphor characterized in that the said converter generates the radiation with the spectral peak in the orange range between about 570 nm and 600 nm due to photoluminescence in one type phosphor chosen from the group consisting of:
Y3Mg2AlSi20,2:Ce3+,
(Ba,Sr)2Si5N8:Eu2+,
(Ba,Sr)2Si04:Eu2+,
(Ca,Sr)Se:Eu2+, and
Ca-a-SiA10N:Eu2+.
The LED according to claim 3, characterized in that the semiconductor chip has an active layer made of In^Gai -^N semiconductor alloy that generates blue light in the 400-500 nm spectral range, which is partially converted to orange light in the converter.
5. The LED according to claim 3, characterized in that the semiconductor chip has an active layer made of GaN semiconductor compound or of In^Gai -^N, AlyGai -yN, or AlylnxGai -yN semiconductor alloy that generates near UV, blue or violet light with the wavelength shorter than 450 nm, which is completely converted in a converter having an additional phosphor emitting blue light in the 400-500 nm range that is chosen from a group consisting of: CaMgSi206:Eu2+, Ba5Si04CI6:Eu2+, Mg3Ca3(P04)4:Eu2+, (Ca,Sr,Ba)5(P04)3Cl:Eu2+, Ca2B509(Br,CI):Eu2+, BaMgA!10O17:Eu2+, n2+, BaMg2Al ,6027:Eu2+, (Lu,Gd)2Si05:Ce3+, Sr2P207:Sn2+, SrSiAl203N2:Ce3+ or La3Si6N, , :Ce +.
6. The LED according to claims 3 and 4, characterized in that the short wavelength and long wavelength components of the generated light have partial radiant flux ratios that are as follows:
- about 1 :21 , when the used phosphor is Y3Mg2AlSi20i2:Ce3+, the light emitted by the InGaN chip has a spectral peak at 440 nm, the CCT of the obtained SPD is 2088 , and the CAF normalized to the CIE standard illuminant A equals 0.379 for the luminance of the environment 2 cd/m2;
- about 1 :37, when the used phosphor is (Ba,Sr)2Si5N8:Eu2+, the light emitted by the InGaN chip has a spectral peak at 443 nm, the CCT of the obtained SPD is 1704 K, and the CAF normalized to the CIE standard illuminant A equals 0.185 for the luminance of the environment 2 cd/m2;
- about 1 : 10, when the used phosphor is (Ba,Sr)2Si04:Eu2+, the light emitted by the InGaN chip has a spectral peak at 440 nm, the CCT of the obtained SPD is 2542 K, and the CAF normalized to the CIE standard illuminant A equals 0.567 for the luminance of the environment 2 cd/m2;
- about 1 : 14, when the used phosphor is (Ca,Sr)Se:Eu +, the light emitted by the InGaN chip has a spectral peak at 443 nm, the CCT of the obtained SPD is 2101 K, and the CAF normalized to the CIE standard illuminant A equals 0.3 1 1 for the luminance of the environment 2 cd/m2;
- about 1 : 1 1 , when the used phosphor is Ca-a-SiA10N:Eu2+, the light emitted by the InGaN chip has a spectral peak at 443 nm, the CCT of the obtained SPD is 2426 K, and
the CAF normalized to the CIE standard illuminant A equals 0.507, for the luminance of the environment 2 cd/m2.
7. The LED according to claims 3 and 5, characterized in that the short wavelength component with the spectrum peaking at 446 nm wavelength is generated by the BaMg2Al ] 6027:Eu2+ phosphor and the short wavelength and long wavelength components have the partial radiant flux ratios as follows:
- about 1 : 19, when the used long wavelength phosphor is Y3Mg2AlSi20i2:Ce3+, the CCT of the obtained SPD is 2100 , and the CAF normalized to the CIE standard illuminant A equals 0.398 for the luminance of the environment 2 cd/m2;
- about 1 :33, when the used long wavelength phosphor is (Ba,Sr)2SisN8:Eu2+, the CCT of the obtained SPD is 1708 , and the CAF normalized to the CIE standard illuminant A equals 0.196 for the luminance of the environment 2 cd/m2;
- about 1 :9, when the used long wavelength phosphor is (Ba,Sr)2SiC>4:Eu2+, the CCT of the obtained SPD is 2576 , and the CAF normalized to the CIE standard illuminant A equals 0.613 for the luminance of the environment 2 cd/m2;
- about 1 : 12, when the used long wavelength phosphor is (Ca,Sr)Se:Eu2+, the CCT of the obtained SPD is 21 14 , and the CAF normalized to the CIE standard illuminant A equals 0.338 for the luminance of the environment 2 cd/m2;
- about 1 : 10, when the used long wavelength phosphor is Ca-a-SiA10N:Eu2+, the CCT of the obtained SPD is 2449 K, and the CAF normalized to the CIE standard illuminant A equals 0.545 for the luminance of the environment 2 cd/m2.
8. The LED according to any of the above claims, characterized in that the radiant fluxes of the each spectral component are set by adjusting the size and the concentration of the phosphor (7; 17; 18) particles, the thickness of the wavelength converter (5; 15), the refraction index of the material of the wavelength converter, the distance between the wavelength converter and the electroluminescent chip ( 1 ; 1 1), and the position of the wavelength converter within the housing of the LED or outside the package.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| LT2013122A LT6215B (en) | 2013-10-22 | 2013-10-22 | PHOTOBIOLOGICALLY FRIENDLY CONVERSION LEDs |
| PCT/LT2014/000012 WO2015060701A1 (en) | 2013-10-22 | 2014-10-20 | Photobiologically friendly phosphor converted light-emitting diode |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| EP3060624A1 true EP3060624A1 (en) | 2016-08-31 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP14805690.6A Withdrawn EP3060624A1 (en) | 2013-10-22 | 2014-10-20 | Photobiologically friendly phosphor converted light-emitting diode |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP3060624A1 (en) |
| LT (1) | LT6215B (en) |
| WO (1) | WO2015060701A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TWI756262B (en) * | 2016-09-12 | 2022-03-01 | 荷蘭商露明控股公司 | Lighting system having reduced melanopic spectral content |
| CN108513971B (en) * | 2018-03-17 | 2021-04-09 | 轻工业部南京电光源材料科学研究所 | Near ultraviolet LED mosquito repelling lamp and preparation method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2001501A (en) | 1933-03-10 | 1935-05-14 | Gen Electric | Gaseous electric discharge device |
| NL7801635A (en) | 1978-02-14 | 1979-08-16 | Philips Nv | LOW PRESSURE SODIUM VAPOR DISCHARGE LAMP. |
| US6294800B1 (en) | 1998-02-06 | 2001-09-25 | General Electric Company | Phosphors for white light generation from UV emitting diodes |
| KR100683364B1 (en) | 1999-09-27 | 2007-02-15 | 필립스 루미리즈 라이팅 캄파니 엘엘씨 | A light emitting diode device that produces white light by performing complete phosphor conversion |
| US6498429B1 (en) | 1999-11-15 | 2002-12-24 | General Electric Company | Sodium-xenon lamp with improved characteristics at end-of-life |
| KR100784573B1 (en) | 2000-05-29 | 2007-12-10 | 파텐트-트로이한트-게젤샤프트 퓌어 엘렉트리쉐 글뤼람펜 엠베하 | Led-based white-light emitting lighting unit |
| JP2008505477A (en) * | 2004-07-05 | 2008-02-21 | コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ | Illumination system including a radiation source and a fluorescent material |
| DE102005005263A1 (en) * | 2005-02-04 | 2006-08-10 | Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH | Yellow emitting phosphor and light source with such phosphor |
| KR100927154B1 (en) * | 2005-08-03 | 2009-11-18 | 인터매틱스 코포레이션 | Silicate-based orange phosphors |
| WO2007015542A1 (en) * | 2005-08-04 | 2007-02-08 | Nichia Corporation | Phosphor and light-emitting device |
-
2013
- 2013-10-22 LT LT2013122A patent/LT6215B/en not_active IP Right Cessation
-
2014
- 2014-10-20 WO PCT/LT2014/000012 patent/WO2015060701A1/en active Application Filing
- 2014-10-20 EP EP14805690.6A patent/EP3060624A1/en not_active Withdrawn
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| Title |
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| See also references of WO2015060701A1 * |
Also Published As
| Publication number | Publication date |
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| LT2013122A (en) | 2015-04-27 |
| WO2015060701A1 (en) | 2015-04-30 |
| LT6215B (en) | 2015-08-25 |
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