JP2015167105A - visible light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a visible light source having high conversion efficiency.SOLUTION: The vicinity of a filament 1 made of tungsten (W) is covered with a transparent silica tube with respect to visible light and infrared light, the outer surface of the silica tube 2 is covered with a high refractive index layer 3 having a refractive index nwhich is larger than the refractive index nof the silica tube 2, and the outer surface of the high refractive index layer 3 is covered with infrared light reflective multilayer 4. The infrared light reflective multilayer 4 transmits the visible light therethrough. At the end of the silica tube 2, a while scattering body (or a mirror) 5 is provided which totally reflects the visible light and the infrared light.

Description

  The present invention relates to a visible light source used as various light sources such as an illumination light source, an automobile lamp, a projector light source, and a liquid crystal (LCD) backlight light source.

  A visible light source is widely used in which an electric current is passed through a filament such as tungsten (W) to heat the filament and use it as a light source.

  FIG. 6 is a graph showing a radiation spectrum of a general visible light source. As shown in FIG. 6, for example, since the infrared light component at a filament temperature of 3000 K is 90% or more, the conversion efficiency of the filament input power into visible light is low, which is a low value of about 15 lm / W. In the case of a fluorescent lamp, the conversion efficiency from input power to visible light is about 90 lm / W. Therefore, although a visible light source has a good color rendering radiation spectrum close to that of sunlight, it is not being used from the viewpoint of environmental load.

  As shown in FIG. 6, in order to improve the conversion efficiency from the input power of the filament to visible light, the filament temperature may be increased. Therefore, there are the following conventional visible light sources as an attempt to increase the conversion efficiency, the brightness, and the lifetime of the visible light source.

  The first conventional visible light source is a halogen light bulb used as an automobile lamp in which an inert gas and a halogen gas are sealed inside the light source (see: Patent Documents 1 and 2). As a result, the filament temperature is raised to improve the conversion efficiency of the filament input power into visible light, and at the same time, the filament life is extended. In order to increase the conversion efficiency and extend the life, it is important to control the composition and pressure of the sealed gas.

  However, in the first conventional visible light source described above, it is possible to achieve a life extension effect using a halogen cycle, but it is difficult to improve the high conversion efficiency, and conversion of a fluorescent lamp at about 20 lm / W at most. The efficiency is far from 90 lm / W.

  In the second conventional visible light source, a fine structure is formed on the filament itself, and infrared light is suppressed by the physical effect of the fine structure (refer to Patent Documents 3, 4, 5, and 6). As a result, the filament temperature is increased to improve the conversion efficiency from the input power of the filament to visible light.

  However, in the above-described second conventional visible light source, the physical effect of the fine structure, that is, the suppression effect of the infrared light by the resonator structure, has the radiation enhancement and suppression effect for only a part of the infrared light spectrum. No (Ref: Non-Patent Document 1). That is, when one wavelength is suppressed, other wavelengths are enhanced. Therefore, the suppression effect over the wide infrared light is very difficult. As a result, it is still difficult to improve high conversion efficiency. In addition, when a fine structure is formed, since a high-level fine processing technique such as electron beam lithography is used, the manufacturing cost increases. Furthermore, a filament made of tungsten or the like, which is a high melting point material having a fine structure, melts and breaks at a heating temperature of about 1000 ° C.

  In the third conventional visible light source, the surface of the light source glass is coated with an infrared light reflecting multilayer film, and infrared light other than visible light is reflected by the infrared light reflecting multilayer film. The filament is absorbed and reheated (refer to Patent Documents 7, 8, and 9). This raises the filament temperature and improves the conversion efficiency of the filament input power into visible light.

JP-A-60-253146 Japanese Patent Laid-Open No. 62-10854 JP 2001-519079 JP-A-6-5263 JP-A-6-2167 JP 2006-205332 A JP 59-58752 A JP-T 62-501109 JP 2000-123795 A

F. Kusunoki et al., "Narrow-Band Thermal Radiation with Low Directivity by Resonant Modes inside Tungusten Microcavities", Japanese Journal of Applied Physics, Vol.43, No.8A, pp.5253-5258, 2004

In the third conventional visible light source described above, the design of the infrared light reflecting multilayer film is a combination of a low refractive index layer and a high refractive index layer having different thicknesses for a certain wavelength λ of the reflected infrared light. Are stacked. Therefore, if the wavelength λ has a range, _N sets of layers are required for the center wavelengths λ ₁ , λ ₂ ,. Further, if the incident angle θ has a range even at the same center wavelength λ, the number of stacked layers increases. For example, when it is desired to reflect 95% or more of infrared light having a wavelength λ = 0.8 μm to 3.0 μm at an incident angle θ ₁ = 0 ° to 30 °, as shown in FIG. 101, in a visible light source comprising a quartz tube 102 enclosing the filament 101 and an infrared light reflecting multilayer film 103A formed on the outer surface of the quartz tube 102, a set of 30 low refractive index layers and high refractive index layers having different thicknesses is provided. In this case, the infrared light reflectance from the filament 101 to the quartz tube 102 and the infrared light reflecting multilayer film 103A has an angle dependency. That is, when the incident angle θ ₁ is 0 to 30 °, the infrared light reflectance is large, but when the incident angle θ ₁ is 30 to 90 °, the infrared light reflectance is remarkably lowered. Infrared light leaks from the infrared light reflecting multilayer film 103A to the external space. As a result, it is still difficult to improve high conversion efficiency, and there is a problem that the conversion efficiency of fluorescent lamps is not far from 90 lm / W at most at about 20 lm / W. In FIG. 7A, the incident angle θ ₁ = 0 ° to 30 ° to the quartz tube 102 is an infrared light reflecting multilayer film if the refractive index n ₂ of the quartz tube 102 is 1.4. The incident angle to 103A is θ ₂ = 0 ° to 21 °. On the other hand, when it is desired to reflect 95% or more of infrared light having a wavelength λ = 0.8 μm to 3.0 μm at an incident angle θ ₁ = 0 ° to 90 °, as shown in FIG. 101, in a visible light source comprising a quartz tube 102 enclosing the filament 101 and an infrared light reflecting multilayer film 103B formed on the outer surface of the quartz tube 102, a set of a low refractive index layer and a high refractive index layer having different thicknesses is set to 100. In this case, the infrared light reflectance from the filament 101 to the quartz tube 102 and the infrared light reflecting multilayer film 103B has no angle dependency, and the incident angle θ1 is 0 to 90 °. Infrared light reflectance is large. However, there is a problem that the manufacturing cost is high due to the increase in the number of layers. In FIG. 7B, the incident angle θ ₁ = 0 ° to 90 ° to the quartz tube 102 is an infrared light reflecting multilayer film if the refractive index n ₂ of the quartz tube 102 is 1.4. The incident angle to 103B is θ ₂ = 0 ° to 45 °.

  Thus, in the third conventional visible light source described above, the conversion efficiency and the manufacturing cost are in a trade-off relationship.

  In order to solve the above-described problems, a visible light source according to the present invention covers a filament, a transparent base material transparent to visible light and infrared light surrounding the filament, and an outer surface of the transparent base material. A high refractive index layer having a refractive index larger than that of the substrate and an infrared light reflecting multilayer film covering the outer surface of the high refractive index layer are provided. The incident angle to the transparent substrate is converted to a smaller incident angle to the infrared light reflecting multilayer film, and the infrared light reflectance of the infrared light reflecting multilayer film is increased over a wide range of incident angles to the transparent substrate. . Therefore, the angle dependency of the infrared light reflectance with respect to the incident angle to the transparent substrate is reduced.

  According to the present invention, since the angle dependency of the infrared light reflectance with respect to the incident angle to the transparent base material is reduced, the infrared light reflectance can be increased, and accordingly, leakage of infrared light to the external space And the conversion efficiency of input power into visible light can be increased.

It is a graph which shows the emitted light spectrum for demonstrating the principle of the visible light source which concerns on this invention. It is sectional drawing which shows embodiment of the visible light source which concerns on this invention. It is a figure for demonstrating operation | movement of the visible light source of FIG. It is sectional drawing which shows the detail of the infrared light reflection multilayer film of FIG. FIG. 3 is a partially cutaway sectional view in which the visible light source of FIG. 2 is configured as an incandescent bulb. It is a graph which shows the emitted light spectrum of a common visible light source. It is a figure for demonstrating the subject of the 3rd conventional visible light source.

  The principle of the visible light source of the present invention will be described with reference to FIG. That is, a single infrared light reflection multilayer having reflectivity characteristics R (λ) that substantially falls to 1 in the infrared light region of 2 μm or more and suddenly drops to 0 in the visible light region of 0.8 μm to 0.35 μm. A film is formed in the vicinity of a filament in a vacuum so as to have a peak of radiation intensity in a visible light region of 0.35 to 0.8 μm. An efficient visible light source can be realized by creating such physical characteristics. At this time, in order to reduce the incident angle to the infrared light reflecting multilayer film, a high refractive index layer is newly provided on the light incident surface side of the infrared light reflecting multilayer film.

但し、α ＝ ３．７４７×１０^８ Ｗ・μｍ^４／ｍ^２
β ＝ １．４３８７×１０^４ μｍ・Ｋ When the filament is made of a material whose emissivity does not depend on the wavelength, for example, a black body or a gray body made of W, the emitted light spectrum E _B (λ) of the filament follows Planck's radiation law. That is, it is expressed by the following equation (1).

However, α = 3.747 × 10 ⁸ W ・ μm ⁴ / m ²
β = 1.4387 × 10 ⁴ μm ・ K

In this case, as shown by E _B (λ) in FIG. 1, almost all of the input power (90% or more) is converted into infrared light.

By the way, when a structure having reflectivity as shown in FIG. 1 R (λ) is formed around the filament, the emitted light spectrum at the wavelength λ is expressed by ε (λ) · E _B (λ). Therefore, it is expressed by Equation 2.

Here, since the emissivity ε (λ) and the reflectivity R (λ) follow Kirchhoff's law below, a desired radiated light spectrum can be obtained by considering the reflectivity characteristics.
ε (λ) = 1-R (λ)

As shown by ε (λ) · E _B (λ) in FIG. 1, in this case, almost all of the input power is converted into visible light, and an efficient light source is formed from the viewpoint of visible light emission. I can do it. At that time, the total energy P _R of the radiation of the visible light source obtained by the present invention is represented by the integral value of ε (λ) · E B 1 a _(lambda) at a wavelength lambda. That is, it is expressed by the following formula 3.

  That is, by covering the vicinity of the filament with the above-mentioned infrared light reflecting multilayer film, the necessary visible light is transmitted, while unnecessary infrared light other than visible light is reflected and absorbed by the filament again to reheat it. To do. This realizes a visible light source that suppresses the emission of infrared light to the external space and increases the conversion efficiency from input power to visible light. At this time, the angle dependency of the infrared light reflectance is reduced by providing a high refractive index layer in the infrared light reflecting multilayer film to reduce the incident angle to the infrared light reflecting multilayer film.

  FIG. 2 is a sectional view showing an embodiment of a visible light source according to the present invention.

In FIG. 2, the vicinity of the filament 1 is covered with a tube made of a transparent base material transparent to visible light and infrared light, for example, a quartz tube 2 from a refractory metal such as tungsten (W), and the outer surface of the quartz tube 2 is covered. The quartz tube 2 is covered with a high refractive index layer 3 having a refractive index n ₃ greater than the refractive index n ₂ , and the outer surface of the high refractive index layer 3 is covered with an infrared light reflecting multilayer film 4. The infrared light reflecting multilayer film 4 transmits visible light. A white scatterer (or mirror) 5 that totally reflects visible light and infrared light is provided at the end of the quartz tube 2.

FIG. 3 is a cross-sectional view for explaining the operation of the visible light source of FIG. In FIG. 3, the following equation is established by Snell's law.
n ₁ sin θ ₁ = n ₂ sin θ ₂ = n ₃ sin θ ₃
However, _{n 1} is a refractive index in vacuum filament 1 exists, 1.0,
n ₂ is the refractive index of quartz (SiO ₂ ) of the quartz tube 2 and is 1.4,
n ₃ is the refractive index of the high refractive index layer 3, for example, a refractive index of zirconium oxide (ZrO ₂ ) or haonium oxide (HfO ₂ ) of 2.0,
θ ₁ is the angle of incidence on the quartz tube 2,
θ ₂ is an incident angle to the high refractive index layer 3,
θ ₃ is an incident angle to the infrared light reflective multilayer film 4. Therefore, when the incident angle θ ₁ to the quartz tube 2 is 0 to 90 °, the incident angle θ ₃ to the infrared light reflecting multilayer film 4 is 0 to 30 °. In other words, light emitted in a solid angle 2π (90 ° hemispherical direction) in a vacuum is converted into light having a solid angle π / 6 (30 ° direction) in the high refractive index layer 3. In this case, the solid angle in the quartz tube 2 is π / 4 (45 ° direction). In this way, by inserting the high refractive index layer 3 between the quartz tube 2 and the infrared light reflecting multilayer film 4, the radiation to the infrared light reflecting multilayer film 4 is gathered within a narrow solid angle. Thereby, high visible light transmissivity and infrared light reflectivity can be achieved with the infrared light reflective multilayer film 4. As a result, infrared light having a large incident angle θ ₁ (for example, 0 ° to 90 °) can be reflected by the infrared light reflecting multilayer film 4 having a smaller number of layers.

The minimum thickness of the high refractive index layer 3 described above is determined by the minimum film thickness to which Snell's law can be applied. Specifically, when the light to be reflected is considered at a wavelength of 1 μm of infrared light, the value obtained by multiplying the refractive index of the high refractive index layer 3 and the film thickness is twice or more than 1 μm, that is, about 2 μm or more. To. Considering a film having a refractive index of 2 of the high refractive index layer 3, the film thickness finally becomes 1 μm or more. Further, the maximum thickness of the high refractive index layer 3 is limited to about 100 μm in view of manufacturing by a vapor phase growth process such as vacuum deposition and prevention of cracks. In the case of forming the high refractive index layer 3 made of ZrO ₂ having a large thickness, for example, a liquid phase growth process using ZrO ₂ nanoparticles or the like, for example, sol-gel and Nanoparticle solvent sintering is used.

  If the quartz tube 2 is made of a material having a higher refractive index, for example, a tube made of sapphire having a refractive index of 1.8, instead of inserting the high refractive index layer 3, radiation to the infrared light reflecting multilayer film 4 is emitted. It can be gathered within a narrower solid angle. However, such a high refractive index material tube has problems such as poor transparency to visible light, high manufacturing cost, poor heat resistance (for example, 1500 K or less), and poor flatness. Therefore, in the present invention, a relatively thick low refractive index 1.4 quartz tube 2 without these problems is used, and a relatively thin high refractive index layer 3 is coated thereon.

  FIG. 4 is a cross-sectional view showing details of the infrared light reflective multilayer film 4 of FIG.

In FIG. 4, the infrared light reflecting multilayer film 4 includes a set 4-1, 4-2,... Composed of a low refractive index layer 41 that is a high heat resistant dielectric layer that transmits infrared light, and a high refractive index layer 42. , 4-N are laminated. Each set 4-i (i = 1, 2,..., N) reflects infrared light having a predetermined center wavelength λ _i using light interference. The reflection condition at this time is
n ₄₁ · d ₄₁ = n ₄₂ · d ₄₂ = λ _i / 4
_{However, n 41} is the refractive index of the low refractive index layer 41,
d ₄₁ is the thickness of the low refractive index layer 41,
n ₄₂ is the refractive index of the high refractive index layer 42,
d ₄₂ is the thickness of the high refractive index layer 42. That is, in order to reflect infrared light in a wide wavelength range, a plurality of sets 4-1, 4-2,..., 4-N having slightly different center wavelengths λ _i are required. In this case, the greater the difference in refractive index between the low refractive index layer 41 and the high refractive index layer 42, the greater the wavelength width of the infrared light that can be reflected. Therefore, the low refractive index is reduced according to the wavelength width of the infrared light that is desired to be reflected. The material of the layer 41 and the high refractive index layer 42 is selected.

For example, the low refractive index layer 41 is a silicon oxide (SiO ₂ ) layer having a refractive index of 1.4, and the high refractive index layer 42 is a ZrO ₂ layer having a refractive index of 2.0. As shown in FIG. 6, since the black body radiation at 2500 K has a peak at a wavelength of 1200 nm, the luminous efficiency can be improved by increasing the infrared reflection in the wavelength band in which the wavelength near this peak is selected. For example, the number N of sets of the SiO ₂ layer 41 and the ZrO ₂ layer 42 is 26, and a total of 52 layers are laminated. In this case, the thickness d ₄₁ of the SiO ₂ layer 41 is gradually changed from 200 nm to 50 nm, the thickness _{d 42} of the ZrO ₂ layer 42 and gradually different value from 180nm to 30 nm. In this way, the infrared light reflecting multilayer film 4 having a small number of layers 52 allows the central wavelengths λ ₁ , λ ₂ ,..., Λ _{26 to} be in the range of ₁ μm to 4 μm and the incident angle to the infrared light reflecting multilayer film 4. theta ₃ can be obtained an excellent infrared reflection properties at 0 ° to 30 °.

As the low refractive index layer 41, a high temperature heat resistant low refractive index material such as MgO, MgF ₂ or Al ₂ O ₃ can be used instead of SiO ₂ . Further, as the high refractive index layer 42, instead of ZrO ₂ , oxide-based materials such as Ta ₂ O ₅ , TiO ₂ , and HfO ₂ , carbohydrate-based materials such as diamond and SiC, and nitride-based materials such as BN and GaN. Materials can also be used.

Referring again to FIG. 3, the radiation incident on the quartz tube 2 with the incident angle θ ₁ of 0 ° to 90 ° enters the infrared light reflective multilayer film 4 with the incident angle θ ₃ of 0 ° to 30 °. As a result, infrared light having a wavelength longer than 0.7 μm is reflected by the infrared light reflecting multilayer film 4, while visible light having a wavelength of 0.4 μm to 0.7 μm is emitted to the outside. Further, the infrared light reflected by the infrared light reflecting multilayer film 4 passes through the high refractive index layer 3 and the quartz tube 2 and is absorbed by the filament 1 to reheat it. At that time, a part of the above-mentioned infrared light is not absorbed by the filament 1 and goes to the end of the quartz tube 2, but this infrared light part is totally reflected by the white scatterer (or mirror) 5 and is then filamented. Head for one. As a result, the filament 1 is efficiently reheated, so that the temperature of the filament 1 becomes higher, and the conversion efficiency of input power into visible light can be improved.

  FIG. 5 is a partially cutaway sectional view in which the visible light source of FIG. 2 is configured as an incandescent bulb.

  In FIG. 5, a filament 1, a quartz tube 2, a high refractive index layer 3, an infrared light reflecting multilayer film 4 and a white color are contained in a light-transmitting hermetic container 51 composed of a hard glass bulb transparent to at least visible light. A structure including a scatterer (mirror) 5 is provided. The filament 1 is electrically connected between the lead wires 52a and 52b. A base 53 is joined to the sealing portion of the translucent airtight container 51. The base 53 includes a center electrode 531 connected to the lead wire 52a, a side electrode 532 connected to the lead wire 52b, and an insulating portion 533 that insulates the center electrode 531 from the side electrode 532.

The inside of the translucent airtight container 51 is in a high vacuum of 10 ⁻¹ to 10 ⁻⁶ Pa. However, 10 ⁵ to 10 ⁻¹ Pa of oxygen (0 ₂ ), hydrogen (H ₂ ), halogen gas, carbide gas, or a mixed gas thereof can be introduced. In this case, similarly to the halogen light bulb, sublimation and deterioration of the infrared light reflective multilayer film 4 can be controlled, and the life of the incandescent light bulb can be increased.

  Furthermore, the quartz tube 2 may be formed of other transparent material that is transparent to visible light and infrared light, such as sapphire, instead of quartz.

  Furthermore, the filament 1 made of W can be replaced with a black body filament having a lower reflectance, such as a carbon-based filament. The black body filament absorbs more infrared light reflected by the infrared light reflecting multilayer film 4 without reflecting it again. Therefore, the temperature of the filament itself is raised, and as a result, a visible light source with higher luminous flux efficiency can be realized. The reflectivity at the black body filament is 0 for both light wavelengths λ = 2 μm and 0.6 μm. Therefore, the output of visible light to the external space is attenuated by 25%, while infrared light is suppressed by 50% or more. The As a result, when the black body filament is used as the total, the luminous efficiency can be improved by two times or more as compared with the case of the W filament.

  Furthermore, the present invention can be applied to any modifications within the obvious scope of the above-described embodiments.

1: Filament 2: Quartz tube 3: High refractive index layer 4: Infrared light reflecting multilayer film 5: White scatterer (mirror)
51: Translucent airtight container 52a, 52b: Lead wire 53: Base 531: Center electrode 532: Side electrode 533: Insulating part 101: Filament 102: Quartz tube 103: Infrared light reflecting multilayer film

Claims (7)

Filament,
A transparent substrate transparent to visible light and infrared light that encloses the filament;
A high refractive index layer that coats the outer surface of the transparent substrate and has a refractive index greater than the refractive index of the transparent substrate;
A visible light source comprising: an infrared light reflective multilayer film covering an outer surface of the high refractive index layer.   The visible light source according to claim 1, wherein the high refractive index layer has a thickness of 1 μm to 100 μm. The transparent substrate is tubular;
Furthermore, the visible light source of Claim 1 which comprises the white scatterer or mirror which reflects visible light and infrared light in the edge part of the said transparent base material.   The visible light source according to claim 1, wherein the transparent substrate is quartz.   The visible light source according to claim 1, wherein the transparent substrate is sapphire.   The visible light source according to claim 1, wherein the filament is made of a refractory metal. The visible light source according to claim 1, wherein the filament is made of a carbon-based material.

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