WO2000002231A1 - Electric lamp - Google Patents
Electric lamp Download PDFInfo
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- WO2000002231A1 WO2000002231A1 PCT/IB1999/001195 IB9901195W WO0002231A1 WO 2000002231 A1 WO2000002231 A1 WO 2000002231A1 IB 9901195 W IB9901195 W IB 9901195W WO 0002231 A1 WO0002231 A1 WO 0002231A1
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- WO
- WIPO (PCT)
- Prior art keywords
- layer
- sub
- layers
- refractive index
- interference film
- Prior art date
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- 239000000463 material Substances 0.000 claims abstract description 60
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 25
- 230000003287 optical effect Effects 0.000 claims abstract description 23
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 18
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims description 17
- 229910000484 niobium oxide Inorganic materials 0.000 claims description 15
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 14
- URLJKFSTXLNXLG-UHFFFAOYSA-N niobium(5+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Nb+5].[Nb+5] URLJKFSTXLNXLG-UHFFFAOYSA-N 0.000 claims description 12
- BPUBBGLMJRNUCC-UHFFFAOYSA-N oxygen(2-);tantalum(5+) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ta+5].[Ta+5] BPUBBGLMJRNUCC-UHFFFAOYSA-N 0.000 claims description 8
- 229910001936 tantalum oxide Inorganic materials 0.000 claims description 8
- 229910000449 hafnium oxide Inorganic materials 0.000 claims description 2
- WIHZLLGSGQNAGK-UHFFFAOYSA-N hafnium(4+);oxygen(2-) Chemical compound [O-2].[O-2].[Hf+4] WIHZLLGSGQNAGK-UHFFFAOYSA-N 0.000 claims description 2
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 claims description 2
- 229910001928 zirconium oxide Inorganic materials 0.000 claims description 2
- 239000000377 silicon dioxide Substances 0.000 abstract description 5
- PBCFLUZVCVVTBY-UHFFFAOYSA-N tantalum pentoxide Inorganic materials O=[Ta](=O)O[Ta](=O)=O PBCFLUZVCVVTBY-UHFFFAOYSA-N 0.000 abstract description 4
- 239000010410 layer Substances 0.000 description 161
- 239000013078 crystal Substances 0.000 description 10
- 230000002349 favourable effect Effects 0.000 description 9
- 238000000411 transmission spectrum Methods 0.000 description 8
- 230000000694 effects Effects 0.000 description 6
- 238000005457 optimization Methods 0.000 description 5
- 238000004544 sputter deposition Methods 0.000 description 5
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 230000005855 radiation Effects 0.000 description 4
- 229910052681 coesite Inorganic materials 0.000 description 3
- 229910052906 cristobalite Inorganic materials 0.000 description 3
- 238000002425 crystallisation Methods 0.000 description 3
- 230000008025 crystallization Effects 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 239000010955 niobium Substances 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 230000003595 spectral effect Effects 0.000 description 3
- 238000001228 spectrum Methods 0.000 description 3
- 229910052682 stishovite Inorganic materials 0.000 description 3
- 230000007704 transition Effects 0.000 description 3
- 229910052905 tridymite Inorganic materials 0.000 description 3
- CPELXLSAUQHCOX-UHFFFAOYSA-N Hydrogen bromide Chemical compound Br CPELXLSAUQHCOX-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 229910052736 halogen Inorganic materials 0.000 description 2
- 150000002367 halogens Chemical class 0.000 description 2
- 230000000977 initiatory effect Effects 0.000 description 2
- 238000004518 low pressure chemical vapour deposition Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 238000005240 physical vapour deposition Methods 0.000 description 2
- 238000000623 plasma-assisted chemical vapour deposition Methods 0.000 description 2
- 238000005546 reactive sputtering Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 229910019704 Nb2O Inorganic materials 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000012790 adhesive layer Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000003618 dip coating Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- CJNBYAVZURUTKZ-UHFFFAOYSA-N hafnium(IV) oxide Inorganic materials O=[Hf]=O CJNBYAVZURUTKZ-UHFFFAOYSA-N 0.000 description 1
- 229910000042 hydrogen bromide Inorganic materials 0.000 description 1
- 239000011261 inert gas Substances 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
- 229910001507 metal halide Inorganic materials 0.000 description 1
- 150000005309 metal halides Chemical class 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000007740 vapor deposition Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/38—Devices for influencing the colour or wavelength of the light
- H01J61/40—Devices for influencing the colour or wavelength of the light by light filters; by coloured coatings in or on the envelope
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/28—Interference filters
- G02B5/281—Interference filters designed for the infrared light
- G02B5/282—Interference filters designed for the infrared light reflecting for infrared and transparent for visible light, e.g. heat reflectors, laser protection
Definitions
- the invention relates to an electric lamp comprising a light-transmitting lamp vessel which accommodates a light source, at least a part of the lamp vessel being provided with an interference film, said interference film including layers of alternately a first layer which is made predominantly of silicon oxide and a second layer which is made of a material having a refractive index which is high as compared to a refractive index of silicon oxide.
- the layers having a high refractive index are made of tantalum oxide.
- Said layers may alternatively consist of niobium oxide or titanium oxide.
- Said layers may also be composed of a combination of two layers, for example TiO 2 .ZrO 2 , TiO 2 .HfO 2 , TiO 2 .Nb 2 O 5 , TiO 2 .Ta 2 O 5 or Ta 2 O 5 .2TiO 2 .
- the lamp of the type described in the opening paragraph is characterized in that at least one of the second layers comprises an odd number of sub-layers of alternately a first sub-layer of the material with the high refractive index and a second sub-layer of a further material with a further high refractive index.
- Crystallization occurs of, in particular, the (high-refraction) material of the second layer of the interference film.
- the crystallization state of the material of the second layer may change.
- Crystallization is regarded as one of the causes of diffuse scattering occurring during the service life of a lamp provided with a lamp vessel covered with an interference film. It has been found that the crystals can grow bigger as the thickness of the layer of the high-refraction material is larger. The effect on diffuse scattering increases as the crystals become bigger.
- the (relatively thick) second layers of the high-refraction material in the interference film are built up of a stack of an odd number of sub-layers, whereby between two first sub-layers of the material with the high refractive index a second sub-layer of a further material with a further high refractive index is sandwiched, the possibilities of crystal growth in the second layer are effectively reduced by 50%.
- crystals developing in the odd sub-layers can only grow within said sub-layer and will consequently remain relatively small, so that the effect of such crystals on diffuse scattering is reduced.
- the relatively thick layer of the material with ' the high refractive index is interrupted as it were, which has a favorable effect on the reduction of undesirable diffuse scattering.
- the further material of the second sub-layer is selected from the group formed by tantalum oxide, zirconium oxide, hafnium oxide and combinations of said materials.
- the high-refraction optical material tantalum oxide exhibits favorable properties at higher temperatures.
- the refractive index of the further material forming the second sub-layer should correspond at least substantially to the refractive index of the material of the first sub-layer. If so, the spectrum of the interference film in accordance with the invention hardly differs from that of the known interference film.
- a suitable choice of the material of the second sub-layer (for example a combination of two high-refraction materials) enables the refractive indices of the materials of the first and the second sub-layer to be properly matched.
- Suitable combinations of high-refraction materials are TiO .ZrO 2 , TiO 2 .HfO and TiO .Nb 2 O 5 .
- a further suitable combination of high-refraction materials is TiO 2 .Nb 2 O > .
- the further material of the second sub-layer includes a combination of titanium oxide and tantalum oxide.
- Such a combination of materials (for example TiO 2 .Ta 2 O 5 or Ta 2 O 5 .2TiO 2 ) unites the favorable property that the refractive index of titanium oxide is relatively high relative to that of silicon oxide with the favorable behavior of tantalum oxide at relatively high temperatures.
- the stack of an odd number of alternately a first and a second sublayer comprises three sub-layers, namely two (first) sub-layers of the high-refraction material between which a (second) sub-layer of the further material with the further high refractive index is sandwiched.
- the lamp of the type described in the opening paragraph is characterized in that at least one of the second layers comprises an odd number of sub-layers of alternately a first sub-layer of the material with the high refractive index and a second sub-layer of silicon oxide, the optical layer thickness d oP of the second sub-layer lying in the range 1 ⁇ d op 20 nm.
- the relatively thick layer of the material with the high refractive index is interrupted as it were, which has a favorable effect on the reduction of undesirable diffuse scattering.
- QWOT Quadrater Wave Optical Thickness
- n x d p the product of the (complex) refractive index n and the physical layer thickness d p
- the optical layer thickness of the second sub-layer is smaller than or equal to 10 nm (d oP ⁇ 10 nm).
- Such relatively thin sub-layers with such a small optical layer thickness practically have no effect on the spectral characteristic of the interference film.
- An existing design of an interference film does not have to be adapted if the optical layer thickness of the second sub-layer is smaller than or equal to 5 nm (d op 5 nm).
- the stack of an odd number of alternately a first and a second sublayer comprises three sub-layers, that is two (first) sub-layers of the high- refraction material between which a relatively thin (second) sub-layer of silicon oxide with a relatively low refractive index is sandwiched.
- the interference film of the electric lamp in accordance with the invention keeps its initial properties to a large extent during the service life of the lamp.
- the physical layer thickness d pr ⁇ of the second sub-layer lies in the range 1 ⁇ d P h 25 nm. If the thickness of the second sub-layer exceeds 25 nm, then there is a substantial influence on the optical properties of the interference film, so that undesirable side-effects on the transmission or reflection properties of the interference film occur.
- a lower limit of 1 nm is desirable to ensure that at least one or a few monolayers of the second sub-layer are situated between the first sub-layers.
- the physical layer thickness d Ph of the second sub-layer lies in the range 2 ⁇ d P h ⁇ 12 nm.
- the effect of such layer thicknesses on the spectral characteristic of the interference film is small.
- Physical layer thicknesses of the second sub-layer below or equal to 5 nm (d p h 5 nm) are particularly favorable.
- the material of the first sub-layer comprises predominantly niobium oxide or titanium oxide.
- niobium oxide Nb 2 O 5
- various crystal forms are known: while in the course of a sputtering process an amorphous material is deposited, this material exhibits, at approximately 300°C, a transition to a so-called T-structure with a substantially hexagonal cation lattice. At approximately 500°C, a transition to a so-called TT- structure takes place. At approximately 700°C, a slow transition to a so-called H-structure, which causes diffuse scattering, occurs.
- the high-refraction titanium oxide (TiO 2 ) two crystal forms are known (anatase and rutile) which blend with each other at approximately 600°C. Particularly the high-temperature rutile form causes diffuse scattering. If said high- refraction materials ( b O b and TiO ) are incorporated in an interference film on a lamp vessel of an electric lamp, which lamp vessel during the service life of the lamp is subject to (frequent) temperature changes between room temperature and temperatures above 500°C (temperatures as high as 900°C are no exception), these materials are known to cause diffuse scattering of the interference film, thereby adversely affecting the action of the interference film. Particularly for materials of the second layer, such as niobium oxide or titanium oxide, the measure in accordance with the invention can be advantageously used.
- the light source of the lamp may be an incandescent body, for example in a halogen-containing gas, but it may alternatively be an electrode pair in an ionizable gas, for example an inert gas with metal halides, if necessary with, for example, mercury as the buffer gas.
- the light source may be surrounded by an innermost gastight envelope. It is alternatively possible that an outermost envelope surrounds the lamp vessel.
- the layers of the film are relatively thick, the optical layer thickness being a quarter of a wavelength in the LR-region of the spectrum.
- the filter may also be a so-called "bandpass" filter, which transmits a part of the visible radiation and reflects other parts of the spectrum.
- the interference film in accordance with the measure of the invention was found to retain its favorable properties.
- the interference film may be provided in a customary manner, for example by vapor deposition (PVD: physical vapor deposition) or by (DC) (reactive) sputtering or by means of a dip-coating process or LP-CVD (Low Pressure Chemical Vapor Deposition), or PE-CVD (Plasma Enhanced CVD).
- PVD physical vapor deposition
- DC reactive chemical vapor deposition
- PE-CVD Pullasma Enhanced CVD
- Fig. 1 is a side view of an electric incandescent lamp
- Fig. 2 A shows a detail of the interference film in accordance with the known embodiment
- Fig. 2B shows a detail of an interference film in accordance with the invention
- Fig. 3 shows the known transmission spectrum of an infrared reflecting interference film
- Fig. 4 shows the transmission spectrum of an infrared reflecting interference film in accordance with a first aspect of the invention
- Fig. 5 shows the transmission spectrum of an infrared reflecting interference film in accordance with a second aspect of the invention.
- the electric lamp has a quartz glass lamp vessel 1 in which an incandescent body is arranged as the light source 2.
- Current conductors 3 are connected thereto and issue from the lamp vessel 1 to the exterior.
- the lamp vessel 1 is filled with a gas comprising halogen, for example hydrogen bromide.
- a gas comprising halogen for example hydrogen bromide.
- At least a portion of the lamp vessel 1 is coated with an interference film 5 which comprises layers (see Fig. 2 A) of alternately a first layer 51 of predominantly silicon oxide (refractive index, on average, approximately 1.45) and a second layer 52 of a material having a relatively high refractive index, in this example niobium oxide (refractive index, on average, approximately 2.35).
- the interference film transmits visible radiation and reflects infrared radiation.
- the lamp vessel 1 is mounted in an outer envelope 4 which supports a lamp cap 6 to which the current conductors 3 are electrically connected.
- the lamp shown is a 60 W mains voltage lamp with a rated life of at least substantially 2000 hours.
- FIG. 2 A schematically shows a detail of the structure of an interference film 5, shown in Fig. 1, in accordance with the known embodiment (for an enumeration of the layer thicknesses reference is made to columns 2 and 3 in Table I).
- Fig. 2B schematically shows a detail of the structure of an interference film 5' in accordance with a first aspect of the invention, relatively thick niobium oxide layers being divided into three sub-layers of alternately a first sub-layer 52a of niobium oxide, a second sub-layer 52b of tantalum oxide (refractive index, on average, approximately 2.15) and a third sub-layer 52c of niobium oxide (for an enumeration of the respective layer thicknesses reference is made to columns 4, 5 and 6 in Table I).
- the (physical) layer thicknesses of the first and the third sub-layer 52a, 52c are chosen so as to be equal to each other and each amount to less than 50% of the original layer thickness.
- Fig. 2B also schematically shows a detail of the structure of an interference film 5' in accordance with a second aspect of the invention, relatively thick niobium oxide layers being divided into three sub-layers of alternately a first sub-layer 52a of niobium oxide, a second sub-layer 52b of silicon (average refractive index approximately 1.45) and a third sub- layer 52c of niobium oxide (for an enumeration of the respective layer thicknesses reference is made to columns 7 and 8 in Table I).
- the (physical) layer thicknesses of the first and the third sub-layer 52a, 52c are chosen to be equal to each other and each amount to less than 50% of the original layer thickness.
- the relevant part of the lamp vessel 1 is coated with the interference film 5' in accordance with the invention by means of reactive sputtering.
- the layers of SiO 2 are obtained by sputtering Si in an environment of Ar and O 2 .
- Typical conditions are: an Ar-pressure of 400-1400 Pa (3-10 mtorr) and an O 2 -pressure of 25- 50 Pa (0.2-0.4 mtorr). Also the material with the high refractive index is obtained by sputtering the metallic material in an Ar/O 2 mixture.
- Typical conditions are: an Ar-pressure of 400-1400 Pa (3-10 mtorr) and an O 2 -pressure of 40-140 Pa (0.3-1.0 mtorr).
- the Ar pressure is controlled by means of a constant flow, and the oxygen is controlled by means of a specific oxygen sensor.
- the sputtering process takes place in a temperature range from 20 to 100°C.
- the interference film 5' in accordance with the invention remained in tact throughout the rated life of the lamp and retained its initial properties.
- Fig. 3 shows the transmission spectrum as a function of the wavelength ⁇ (in nm) of an infrared reflecting interference film 5, which is known per se, and which is built up of 47 alternate layers of SiO 2 and Nb O on a glass substrate (see columns 2 and 3 in Table I).
- the transmission of the known interference film is higher than at least 90% in the visible wavelength range from 400 to 770 nm, and said interference film exhibits, in the wavelength range from 800 to 1900 nm, a broad reflection band with an average reflection which is at least higher than 70%.
- the known interference film is composed of three so-called multiperiod stacks, which are known per se, and which spectrally border on each other.
- the interference film is the result of known computer optimizations of a design for an infrared reflecting optical interference film.
- the interference film 5 shown in Fig. 3 comprises a computer optimization of a design for an infrared reflecting interference film including three successive stacks of alternating high-refraction and low-refraction layers, which layers are referenced, respectively, H and L.
- a first stack has a design wavelength of 1700 nm (the design wavelength is the wavelength which corresponds to the center of the reflection band), so that the optical layer thickness for the material having a high refractive index and the material having a low refractive index is equal to 425 nm.
- a second stack has a design wavelength of 1300 nm with a corresponding optical layer thickness of 333 nm for the material having a high refractive index and the material having a low refractive index.
- the first and the second stack each comprise seven layers of alternately high-refraction and low-refraction material of the type: ai L bi xH a 2 ⁇ L b 2 ⁇ H a 2 ⁇ L bi xH ai xL), which is known per se, and wherein the coefficients ai, a , bi and b are the result of the computer optimization.
- a third stack has a design wavelength of 930 nm with an optical layer thickness of the high-refraction and low-refraction material of 233 nm.
- the third stack comprises three layers of alternately high-refraction and low-refraction material of the type:
- the infrared reflecting interference film (L/2 H L/2), which is known per se.
- the infrared reflecting interference film successively comprises three times the first stack of layers (layers 1-7, layers 7-13, layers 13-19), followed by three times the second stack of layers (layers 19-25, layers 25-31, layers 31-37) and subsequently five times the third stack of layers (layers 37-39, layers 39-41, layers 41-43, layers 43-45, layers 45-47).
- Fig. 4 shows the transmission spectrum as a function of the wavelength ⁇ (in nm) of an infrared reflecting interference film 5' in accordance with a first aspect of the invention, which is built up according to the same principle as the interference film 5 shown in Fig. 3.
- each of the (eleven) relatively thick Nb O 5 layers 52 (having a layer thickness beyond 50 nm) is divided into three sub-layers 52a, 52b, 52c comprising a first sub-layer 52a and a third sub-layer 52c of Nb 2 O 5 , between which a second, relatively thin sub-layer 52b of Ta 2 O 5 is sandwiched (see Fig. 2B).
- an interference film 5' is obtained which includes 69 layers (see columns 4, 5 and 6 of Table I).
- the layer thicknesses of the first and the third sub-layers 52a, 52c are less than half the layer thickness of the (original) layer 52 (cf. columns 3 and 5 in Table I).
- the physical layer thickness d pn of the second sub- layer 52b amounts to 10 nm (see column 6 in Table I).
- the other layer thicknesses of the layers are kept the same.
- the transmission spectrum as shown in Fig. 4 exhibits a small decline in the visible region near approximately 490 nm. Further computer optimization of the interference film reduces the influence of this decline.
- Fig. 5 shows the transmission spectrum as a function of the wavelength ⁇ (in nm) of an infrared reflecting interference film 5' in accordance with a second aspect of the invention, which interference film is built up according to the same principle as the interference film 5 shown in Fig. 3.
- each of the (eleven) relatively thick Nb 2 O layers 52 (having a layer thickness above 50 nm) is divided into three sub-layers 52a, 52b, 52c comprising a first sub-layer 52a and a third sublayer 52c of Nb 2 O 5 , between which a second, relatively thin sub-layer 52b of SiO 2 is sandwiched (see Fig. 2B).
- an interference film 5' is obtained which comprises 69 layers (see columns 7 and 8 in Table I).
- the layer thicknesses of the first and the third sub-layer 52a, 52c are less than half the layer thickness of the (original) layer 52 (cf. columns 3 and 8 of Table I).
- the physical layer thickness d ph of the second sub-layer 52b is 5 nm (see column 7 in Table I).
- the other layer thicknesses of the layers are kept the same for clarity.
- the transmission spectrum as shown in Fig. 5, exhibits a small decline in the visible range at approximately 490 nm. Further computer optimization of the interference film reduces the influence of this decline.
- d pr of the second layer 52b of 2 nm, no optical influence of the interposed second sub-layers is noticeable in the spectral characteristic of the interference film.
- the invention is embodied in each novel characteristic and each combination of characteristics.
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Filters (AREA)
- Vessels And Coating Films For Discharge Lamps (AREA)
Abstract
The electric lamp comprises a lamp vessel (1) which is transparent to visible light, and which lamp vessel accommodates a light source. The lamp vessel (1) is covered with an optical interference film (5; 5') which includes layers of alternately a first layer (51, 53) of silica and a second layer (52) of a material having a relatively high refractive index. According to a first aspect of the invention, one of the second layers (52) includes an odd number of sub-layers (52a, 52b, 52c) of alternately a first sub-layer (52a, 52c) of the material with a relatively high refractive index and a second sub-layer (52b) of a further material with a further relatively high refractive index. Preferably, the material of the second sub-layer (52b) is Ta2O5. According to a second aspect of the invention, one of the second layers (52) includes an odd number of sub-layers (52a, 52b, 52c) of alternately a first sub-layer (52a, 52c) of the material with the relatively high refractive index and a second sub-layer (52b) of silica with an optical layer thickness smaller than 20 nm. Preferably, the physical layer thickness dph of the second sub-layer (52b) is less than 25 nm. Preferably, each high-refractive index layer (52) includes three sub-layers (52a, 52b, 52c). The electric lamp according to the invention exhibits reduced diffuse scattering.
Description
Electric lamp.
Description
The invention relates to an electric lamp comprising a light-transmitting lamp vessel which accommodates a light source, at least a part of the lamp vessel being provided with an interference film, said interference film including layers of alternately a first layer which is made predominantly of silicon oxide and a second layer which is made of a material having a refractive index which is high as compared to a refractive index of silicon oxide.
An electric lamp of the type mentioned in the opening paragraph is known from US 5 138 219. In the known discharge lamp, the layers having a high refractive index are made of tantalum oxide. Said layers may alternatively consist of niobium oxide or titanium oxide. Said layers may also be composed of a combination of two layers, for example TiO2.ZrO2, TiO2.HfO2, TiO2.Nb2O5, TiO2.Ta2O5 or Ta2O5.2TiO2.
It is a drawback of lamps having an interference film on the lamp vessel that said film is exposed to substantially varying temperatures (above 500°C). As a result, diffuse scattering of the interference film during the service life of the electric lamp increases. Diffuse scattering leads to an unclear transparent lamp. Diffuse scattering additionally causes the direction in which (for example infrared) radiation is reflected by the interference film to be changed relative to the desired direction, thus causing the efficacy of the lamp to be reduced. It is an object of the invention to provide an electric lamp of the type described in the opening paragraph, in which diffuse scattering of the interference film is reduced.
In accordance with a first aspect of the invention, the lamp of the type described in the opening paragraph is characterized in that at least one of the second layers comprises an odd number of sub-layers of alternately a first sub-layer of the material with the high refractive index and a second sub-layer of a further material with a further high refractive index.
During the service life of the electric lamp, the lamp vessel of which is provided with an optical interference film, crystallization occurs of, in particular, the (high-refraction) material of the second layer of the interference film. In addition, as a result of temperature changes, the crystallization state of the material of the second layer may change.
Crystallization is regarded as one of the causes of diffuse scattering occurring during the service life of a lamp provided with a lamp vessel covered with an interference film. It has been found that the crystals can grow bigger as the thickness of the layer of the high-refraction material is larger. The effect on diffuse scattering increases as the crystals become bigger. If, in accordance with a first aspect of the invention, the (relatively thick) second layers of the high-refraction material in the interference film are built up of a stack of an odd number of sub-layers, whereby between two first sub-layers of the material with the high refractive index a second sub-layer of a further material with a further high refractive index is sandwiched, the possibilities of crystal growth in the second layer are effectively reduced by 50%. By virtue of the measure in accordance with the invention, crystals developing in the odd sub-layers can only grow within said sub-layer and will consequently remain relatively small, so that the effect of such crystals on diffuse scattering is reduced. By sandwiching a (second) sub-layer of the further material with the further high refractive index between two (first) sub-layers of the material with the high refractive index, the relatively thick layer of the material with' the high refractive index is interrupted as it were, which has a favorable effect on the reduction of undesirable diffuse scattering.
Preferably, the further material of the second sub-layer is selected from the group formed by tantalum oxide, zirconium oxide, hafnium oxide and combinations of said materials. Particularly the high-refraction optical material tantalum oxide exhibits favorable properties at higher temperatures. It is further desirable that the refractive index of the further material forming the second sub-layer should correspond at least substantially to the refractive index of the material of the first sub-layer. If so, the spectrum of the interference film in accordance with the invention hardly differs from that of the known interference film. A suitable choice of the material of the second sub-layer (for example a combination of two high-refraction materials) enables the refractive indices of the materials of the first and the second sub-layer to be properly matched. Suitable combinations of high-refraction materials are TiO .ZrO2, TiO2.HfO and TiO .Nb2O5. A further suitable combination of high-refraction materials is TiO2.Nb2O>. In a very favorable, alternative embodiment of the electric lamp in accordance with a first aspect of the invention, the further material of the second sub-layer includes a combination of titanium oxide and tantalum oxide. Such a combination of materials (for example TiO2.Ta2O5 or Ta2O5.2TiO2) unites the favorable property that the refractive index of titanium oxide is relatively high relative to that of silicon oxide with the favorable behavior of tantalum oxide at relatively high temperatures.
Preferably, the stack of an odd number of alternately a first and a second sublayer comprises three sub-layers, namely two (first) sub-layers of the high-refraction material between which a (second) sub-layer of the further material with the further high refractive index is sandwiched. In accordance with a second aspect of the invention, the lamp of the type described in the opening paragraph is characterized in that at least one of the second layers comprises an odd number of sub-layers of alternately a first sub-layer of the material with the high refractive index and a second sub-layer of silicon oxide, the optical layer thickness doP of the second sub-layer lying in the range 1 < dop 20 nm. By incorporating such a second sub-layer of silicon oxide having a relatively low refractive index, the optical layer thickness of which is chosen so that these second sublayers contribute little, or not at all, to the optical effect of the interference film, the possibilities of crystal growth in the second (high-refraction) layer are effectively reduced by 50%. By virtue of the measure in accordance with the invention, crystals which develop in the odd sub-layers can grow only within said sub-layer and, as a result, will remain relatively small, so that the effect of such crystals on diffuse scattering is reduced. By sandwiching a (second) sub-layer of silicon oxide between two (first) sub-layers of the material with the high refractive index, the relatively thick layer of the material with the high refractive index is interrupted as it were, which has a favorable effect on the reduction of undesirable diffuse scattering.
An expression which in connection with the term optical layer thickness is known to those skilled in the art is QWOT (= "Quarter Wave Optical Thickness"), which is defined as the wavelength at which the optical thickness of a layer is equal to a quarter (0.25) of the design wavelength of the stack of the interference film, that is: QWOT = 4ndphcos a where n x dp is the product of the (complex) refractive index n and the physical layer thickness dp , and α is the angle at which the light is incident on the interference film (if light is incident transversely to the stack of layers, then α = 0°). As a result of the relative simplicity of stacks of such so-called "quarter- wave" optical layer thicknesses, designs of interference films are often referred to in terms of fractions of "quarter-waves" at a reference wavelength. Preferably, the optical layer thickness of the second sub-layer is smaller than or equal to 10 nm (doP < 10 nm). Such relatively thin sub-layers with such a small optical layer thickness practically have no effect on the spectral characteristic of the interference film. An
existing design of an interference film does not have to be adapted if the optical layer thickness of the second sub-layer is smaller than or equal to 5 nm (dop 5 nm).
Preferably, the stack of an odd number of alternately a first and a second sublayer comprises three sub-layers, that is two (first) sub-layers of the high- refraction material between which a relatively thin (second) sub-layer of silicon oxide with a relatively low refractive index is sandwiched.
It has been found that the interference film of the electric lamp in accordance with the invention keeps its initial properties to a large extent during the service life of the lamp. In a favorable embodiment of the electric lamp in accordance with the invention, the physical layer thickness dprι of the second sub-layer lies in the range 1 < dPh 25 nm. If the thickness of the second sub-layer exceeds 25 nm, then there is a substantial influence on the optical properties of the interference film, so that undesirable side-effects on the transmission or reflection properties of the interference film occur. A lower limit of 1 nm is desirable to ensure that at least one or a few monolayers of the second sub-layer are situated between the first sub-layers.
Preferably, the physical layer thickness dPh of the second sub-layer lies in the range 2 < dPh < 12 nm. The effect of such layer thicknesses on the spectral characteristic of the interference film is small. Physical layer thicknesses of the second sub-layer below or equal to 5 nm (dph 5 nm) are particularly favorable.
Preferably, the material of the first sub-layer comprises predominantly niobium oxide or titanium oxide. Of the high-refraction niobium oxide (Nb2O5) various crystal forms are known: while in the course of a sputtering process an amorphous material is deposited, this material exhibits, at approximately 300°C, a transition to a so-called T-structure with a substantially hexagonal cation lattice. At approximately 500°C, a transition to a so-called TT- structure takes place. At approximately 700°C, a slow transition to a so-called H-structure, which causes diffuse scattering, occurs. Of the high-refraction titanium oxide (TiO2) two crystal forms are known (anatase and rutile) which blend with each other at approximately 600°C. Particularly the high-temperature rutile form causes diffuse scattering. If said high- refraction materials ( b Ob and TiO ) are incorporated in an interference film on a lamp vessel of an electric lamp, which lamp vessel during the service life of the lamp is subject to (frequent) temperature changes between room temperature and temperatures above 500°C (temperatures as high as 900°C are no exception), these materials are known to cause diffuse
scattering of the interference film, thereby adversely affecting the action of the interference film. Particularly for materials of the second layer, such as niobium oxide or titanium oxide, the measure in accordance with the invention can be advantageously used.
The light source of the lamp may be an incandescent body, for example in a halogen-containing gas, but it may alternatively be an electrode pair in an ionizable gas, for example an inert gas with metal halides, if necessary with, for example, mercury as the buffer gas. The light source may be surrounded by an innermost gastight envelope. It is alternatively possible that an outermost envelope surrounds the lamp vessel.
The interference film may transmit visible light and reflect LR (= infrared) light. In this case, the layers of the film are relatively thick, the optical layer thickness being a quarter of a wavelength in the LR-region of the spectrum. It is alternatively possible for the film to reflect UV (= ultraviolet) light and transmit visible light, or conversely. The filter may also be a so-called "bandpass" filter, which transmits a part of the visible radiation and reflects other parts of the spectrum. In the case of an LR-reflecting filter having relatively thick layers, and also if a relatively large number of layers are stacked and the interference film has a relatively large thickness of, for example, 3.5 to 4 μm, the interference film in accordance with the measure of the invention was found to retain its favorable properties.
The interference film may be provided in a customary manner, for example by vapor deposition (PVD: physical vapor deposition) or by (DC) (reactive) sputtering or by means of a dip-coating process or LP-CVD (Low Pressure Chemical Vapor Deposition), or PE-CVD (Plasma Enhanced CVD).
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
In the drawings:
Fig. 1 is a side view of an electric incandescent lamp;
Fig. 2 A shows a detail of the interference film in accordance with the known embodiment; Fig. 2B shows a detail of an interference film in accordance with the invention;
Fig. 3 shows the known transmission spectrum of an infrared reflecting interference film;
Fig. 4 shows the transmission spectrum of an infrared reflecting interference film in accordance with a first aspect of the invention, and
Fig. 5 shows the transmission spectrum of an infrared reflecting interference film in accordance with a second aspect of the invention.
The Figures are purely schematic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly. In the Figures, like reference numerals refer to like parts whenever possible.
In Fig. 1, the electric lamp has a quartz glass lamp vessel 1 in which an incandescent body is arranged as the light source 2. Current conductors 3 are connected thereto and issue from the lamp vessel 1 to the exterior. The lamp vessel 1 is filled with a gas comprising halogen, for example hydrogen bromide. At least a portion of the lamp vessel 1 is coated with an interference film 5 which comprises layers (see Fig. 2 A) of alternately a first layer 51 of predominantly silicon oxide (refractive index, on average, approximately 1.45) and a second layer 52 of a material having a relatively high refractive index, in this example niobium oxide (refractive index, on average, approximately 2.35). In this example, the interference film 5 further comprises a silicon oxide-containing adhesive layer 53, by means of which the adhesion of the interference film 5 to the substrate (= the above-mentioned part of the lamp vessel 1) is enhanced. The interference film transmits visible radiation and reflects infrared radiation.
The lamp vessel 1 is mounted in an outer envelope 4 which supports a lamp cap 6 to which the current conductors 3 are electrically connected. The lamp shown is a 60 W mains voltage lamp with a rated life of at least substantially 2000 hours.
Fig. 2 A schematically shows a detail of the structure of an interference film 5, shown in Fig. 1, in accordance with the known embodiment (for an enumeration of the layer thicknesses reference is made to columns 2 and 3 in Table I).
Fig. 2B schematically shows a detail of the structure of an interference film 5' in accordance with a first aspect of the invention, relatively thick niobium oxide layers being divided into three sub-layers of alternately a first sub-layer 52a of niobium oxide, a second sub-layer 52b of tantalum oxide (refractive index, on average, approximately 2.15) and a third sub-layer 52c of niobium oxide (for an enumeration of the respective layer thicknesses reference is made to columns 4, 5 and 6 in Table I). In this example, the (physical) layer thicknesses of the first and the third sub-layer 52a, 52c are chosen so as to be equal to each other and each amount to less than 50% of the original layer thickness. The physical layer thickness of the second sub-layer 52b is indicated by dprι and is preferably equal to or smaller than 5 nm (dop = n x dprι).
Fig. 2B also schematically shows a detail of the structure of an interference film 5' in accordance with a second aspect of the invention, relatively thick niobium oxide layers being divided into three sub-layers of alternately a first sub-layer 52a of niobium oxide, a second sub-layer 52b of silicon (average refractive index approximately 1.45) and a third sub- layer 52c of niobium oxide (for an enumeration of the respective layer thicknesses reference is made to columns 7 and 8 in Table I). In this example, the (physical) layer thicknesses of the first and the third sub-layer 52a, 52c are chosen to be equal to each other and each amount to less than 50% of the original layer thickness. The physical layer thickness of the second sublayer 52b is indicated by dPh and is preferably equal to or smaller than 5 nm (dop = n x dPh). The relevant part of the lamp vessel 1 is coated with the interference film 5' in accordance with the invention by means of reactive sputtering. In the case of reactive sputtering, the layers of SiO2 are obtained by sputtering Si in an environment of Ar and O2. Typical conditions are: an Ar-pressure of 400-1400 Pa (3-10 mtorr) and an O2-pressure of 25- 50 Pa (0.2-0.4 mtorr). Also the material with the high refractive index is obtained by sputtering the metallic material in an Ar/O2 mixture. Typical conditions are: an Ar-pressure of 400-1400 Pa (3-10 mtorr) and an O2-pressure of 40-140 Pa (0.3-1.0 mtorr). In general, for both materials the Ar pressure is controlled by means of a constant flow, and the oxygen is controlled by means of a specific oxygen sensor. The sputtering process takes place in a temperature range from 20 to 100°C. The interference film 5' in accordance with the invention remained in tact throughout the rated life of the lamp and retained its initial properties.
Tabel I Interference films with physical layer thicknesses
Fig. 3 shows the transmission spectrum as a function of the wavelength λ (in nm) of an infrared reflecting interference film 5, which is known per se, and which is built up of 47 alternate layers of SiO2 and Nb O on a glass substrate (see columns 2 and 3 in Table I). In general, the transmission of the known interference film is higher than at least 90% in the visible wavelength range from 400 to 770 nm, and said interference film exhibits, in the wavelength range from 800 to 1900 nm, a broad reflection band with an average reflection which is at least higher than 70%. In this example, the known interference film is composed of three so-called multiperiod stacks, which are known per se, and which spectrally border on
each other. In general, the interference film is the result of known computer optimizations of a design for an infrared reflecting optical interference film.
The interference film 5 shown in Fig. 3 comprises a computer optimization of a design for an infrared reflecting interference film including three successive stacks of alternating high-refraction and low-refraction layers, which layers are referenced, respectively, H and L. A first stack has a design wavelength of 1700 nm (the design wavelength is the wavelength which corresponds to the center of the reflection band), so that the optical layer thickness for the material having a high refractive index and the material having a low refractive index is equal to 425 nm. A second stack has a design wavelength of 1300 nm with a corresponding optical layer thickness of 333 nm for the material having a high refractive index and the material having a low refractive index. The first and the second stack each comprise seven layers of alternately high-refraction and low-refraction material of the type: ai L bi xH a2 χL b2 χH a2 χL bi xH ai xL), which is known per se, and wherein the coefficients ai, a , bi and b are the result of the computer optimization. A third stack has a design wavelength of 930 nm with an optical layer thickness of the high-refraction and low-refraction material of 233 nm. The third stack comprises three layers of alternately high-refraction and low-refraction material of the type:
(L/2 H L/2), which is known per se. The infrared reflecting interference film, the physical layer thicknesses of which are shown in columns 2 and 3 of Table I, successively comprises three times the first stack of layers (layers 1-7, layers 7-13, layers 13-19), followed by three times the second stack of layers (layers 19-25, layers 25-31, layers 31-37) and subsequently five times the third stack of layers (layers 37-39, layers 39-41, layers 41-43, layers 43-45, layers 45-47).
Fig. 4 shows the transmission spectrum as a function of the wavelength λ (in nm) of an infrared reflecting interference film 5' in accordance with a first aspect of the invention, which is built up according to the same principle as the interference film 5 shown in Fig. 3. However, in accordance with the measure of the invention, each of the (eleven) relatively thick Nb O5 layers 52 (having a layer thickness beyond 50 nm) is divided into three sub-layers 52a, 52b, 52c comprising a first sub-layer 52a and a third sub-layer 52c of Nb2O5, between which a second, relatively thin sub-layer 52b of Ta2O5 is sandwiched (see Fig. 2B). Instead of the known 47-layer infrared reflecting interference film 5, an interference film 5' is obtained which includes 69 layers (see columns 4, 5 and 6 of Table I). The layer thicknesses of the first and the third sub-layers 52a, 52c are less than half the layer thickness of the (original) layer 52 (cf. columns 3 and 5 in Table I). The physical layer thickness dpn of the second sub-
layer 52b amounts to 10 nm (see column 6 in Table I). For clarity, in the example of Table I the other layer thicknesses of the layers are kept the same. As a result, the transmission spectrum, as shown in Fig. 4, exhibits a small decline in the visible region near approximately 490 nm. Further computer optimization of the interference film reduces the influence of this decline.
Fig. 5 shows the transmission spectrum as a function of the wavelength λ (in nm) of an infrared reflecting interference film 5' in accordance with a second aspect of the invention, which interference film is built up according to the same principle as the interference film 5 shown in Fig. 3. However, in accordance with the measure of the invention, each of the (eleven) relatively thick Nb2O layers 52 (having a layer thickness above 50 nm) is divided into three sub-layers 52a, 52b, 52c comprising a first sub-layer 52a and a third sublayer 52c of Nb2O5, between which a second, relatively thin sub-layer 52b of SiO2 is sandwiched (see Fig. 2B). Instead of the known 47-layer infrared reflecting interference film 5, an interference film 5' is obtained which comprises 69 layers (see columns 7 and 8 in Table I). The layer thicknesses of the first and the third sub-layer 52a, 52c are less than half the layer thickness of the (original) layer 52 (cf. columns 3 and 8 of Table I). In this example, the physical layer thickness dph of the second sub-layer 52b is 5 nm (see column 7 in Table I). In the example of Table I, the other layer thicknesses of the layers are kept the same for clarity. As a result, the transmission spectrum, as shown in Fig. 5, exhibits a small decline in the visible range at approximately 490 nm. Further computer optimization of the interference film reduces the influence of this decline. At a physical layer thickness dpr, of the second layer 52b of 2 nm, no optical influence of the interposed second sub-layers is noticeable in the spectral characteristic of the interference film.
It will be obvious that within the scope of the invention many variations are possible to those skilled in the art.
The invention is embodied in each novel characteristic and each combination of characteristics.
Claims
1. An electric lamp comprising a light-transmitting lamp vessel (1) which accommodates a light source (2), at least a part of the lamp vessel (2) being provided with an interference film
(5), said interference film (5) including layers (51 , 52, 53) of alternately a first layer
(51, 53) which is made predominantly of silicon oxide and a second layer (52) which is made of a material having a refractive index which is high as compared to a refractive index of silicon oxide, characterized in that at least one of the second layers (52) comprises an odd number of sub-layers (52a, 52b, 52c) of alternately a first sub-layer (52a, 52c) of the material with the high refractive index and a second sub-layer (52b) of a further material with a further high refractive index.
2. An electric lamp as claimed in claim 1, wherein the further material of the second sub-layer (52b) is selected from the group formed by tantalum oxide, zirconium oxide, hafnium oxide and combinations of said materials.
3. An electric lamp as claimed in claim 1, wherein the further material of the second sub-layer (52b) includes a combination of titanium oxide and tantalum oxide.
4. An electric lamp comprising a light-transmitting lamp vessel (1) which accommodates a light source (2), at least apart of the lamp vessel (2) being provided with an interference film
(5), said interference film (5) including layers (51 , 52, 53) of alternately a first layer
(51, 53) which is made predominantly of silicon oxide and a second layer (52) which is made of a material having a refractive index which is high as compared to a refractive index of silicon oxide, characterized in that at least one of the second layers (52) comprises an odd number of sub-layers (52a, 52b, 52c) of alternately a first sub-layer (52a, 52c) of the material with the high refractive index and a second sub-layer (52b) of silicon oxide, the optical layer thickness dop of the second sub-layer (52b) lying in the range 1 < dop < 20 nm.
5. An electric lamp as claimed in claim 4, wherein the optical layer thickness dop of the second sub-layer (52b) is smaller than or equal to 10 nm.
6. An electric lamp as claimed in any one of the claims 1 through 5, wherein the physical layer thickness dpr╬╣ of the second sub-layer (52b) lies in the range 1 < dpr╬╣ < 25 nm.
7. An electric lamp as claimed in claim 6, wherein the physical layer thickness dpr╬╣ of the second sub-layer (52b) lies in the range 2 < dPh < 12 nm.
8. An electric lamp as claimed in any one of claims 1 through 5, wherein the at least one second layer (52) comprises three sub-layers (52a, 52b, 52c).
9. An electric lamp as claimed in any one of claims 1 through 5, wherein the material of the first sub-layer (52a, 52c) comprises substantially niobium oxide or titanium oxide.
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE69930921T DE69930921T2 (en) | 1998-07-06 | 1999-06-24 | ELECTRIC LAMP |
JP2000558538A JP4434491B2 (en) | 1998-07-06 | 1999-06-24 | Electric lamp |
EP99925242A EP1036405B1 (en) | 1998-07-06 | 1999-06-24 | Electric lamp |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP98202270.9 | 1998-07-06 | ||
EP98202270 | 1998-07-06 |
Publications (1)
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WO2000002231A1 true WO2000002231A1 (en) | 2000-01-13 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/IB1999/001195 WO2000002231A1 (en) | 1998-07-06 | 1999-06-24 | Electric lamp |
Country Status (5)
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US (1) | US6356020B1 (en) |
EP (1) | EP1036405B1 (en) |
JP (1) | JP4434491B2 (en) |
DE (1) | DE69930921T2 (en) |
WO (1) | WO2000002231A1 (en) |
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WO2001057913A2 (en) * | 2000-02-03 | 2001-08-09 | Koninklijke Philips Electronics N.V. | Electric lamp and interference film |
WO2001071246A1 (en) * | 2000-03-20 | 2001-09-27 | Bartenbach, Christian | Device for guiding light for an elongated light source |
WO2001097253A1 (en) | 2000-06-16 | 2001-12-20 | Koninklijke Philips Electronics N.V. | Electric lamp comprising a light absorbing medium |
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CN102655075A (en) * | 2008-03-14 | 2012-09-05 | 芈振伟 | Luminous component |
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US20060226777A1 (en) * | 2005-04-07 | 2006-10-12 | Cunningham David W | Incandescent lamp incorporating extended high-reflectivity IR coating and lighting fixture incorporating such an incandescent lamp |
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US7919913B2 (en) | 2007-03-14 | 2011-04-05 | Mii Jenn-Wei | Light illuminating element |
EP1970939A3 (en) * | 2007-03-14 | 2012-02-29 | Jenn-Wei Mii | Light illuminating element |
CN102655075A (en) * | 2008-03-14 | 2012-09-05 | 芈振伟 | Luminous component |
Also Published As
Publication number | Publication date |
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DE69930921T2 (en) | 2006-12-21 |
EP1036405A1 (en) | 2000-09-20 |
US6356020B1 (en) | 2002-03-12 |
DE69930921D1 (en) | 2006-05-24 |
JP2002520774A (en) | 2002-07-09 |
EP1036405B1 (en) | 2006-04-19 |
JP4434491B2 (en) | 2010-03-17 |
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