DE102012204786A1 - LIGHTING DEVICE WITH FLUORESCENT BODY ON COOLING BODY - Google Patents

Abstract

The lighting device has a heat sink (12) and at least one phosphor body (13), wherein the at least one phosphor body (13) is arranged with its rear side (14) on the heat sink (12) and at its front side (15) to be irradiated with a transparent layer (16) is occupied, which has at least the same high thermal conductivity as the phosphor body (13).

Description

The invention relates to a lighting device which has a heat sink and at least one phosphor body, wherein the at least one phosphor body is arranged with its rear side on the heat sink and is provided for irradiation on its front side. The lighting device is particularly applicable as a light-generating unit in a projector, e.g. for video projectors or as a vehicle light, e.g. for motor vehicles.

For efficient generation of long-wavelength (secondary) light (e.g., green, yellow, red, infrared, etc. colors), phosphor is often used which converts blue (primary) light from light-emitting diodes (LEDs) or laser diodes to wavelengths. The phosphor is usually in layer form with its back on a heat sink and is irradiated on the front side with the blue primary light.

Already in the first 10 to 30 micrometers, the majority of the blue primary light is converted and the resulting energy difference is converted into heat ('Stokes heat'). With typical layer thicknesses of the phosphor layer of 20 to 100 micrometers, this heat must first be transported through the phosphor layer to the heat sink. However, the phosphor layer usually has a poor thermal conductivity, so that the heat can be dissipated only insufficient. This affects a conversion efficiency and limits the achievable luminance.

So far, the insufficient heat dissipation is achieved by applying the phosphor to a rotating color wheel to reduce the thermal load of the phosphor by using a larger irradiated area. However, this is technically complex and prevents a compact design.

If no color wheel is used, the power density of the irradiated blue primary light is kept so small that the accumulated heat can still be dissipated. However, this happens at the expense of luminance.

Another possibility is to thin the phosphor layer so that the heat is still well dissipated. However, this happens at the expense of conversion efficiency.

It is the object of the present invention to at least partially overcome the disadvantages of the prior art, and in particular to provide a lighting device which enables improved heat dissipation from a phosphor without a significant reduction in luminance and / or conversion efficiency.

This object is achieved according to the features of the independent claims. Preferred embodiments are in particular the dependent claims.

The object is achieved by a lighting device, comprising a heat sink and at least one phosphor body, wherein the at least one phosphor body is arranged with its back on the heat sink and is occupied at its front to be irradiated with a transparent layer, which has at least the same high thermal conductivity as the phosphor body.

As a result, improved heat spreading and / or heat dissipation is achieved on the front side of the phosphor body, where most of the waste heat is generated. Already the more extensive distribution of the heat and thus also the heat dissipation surface (for example by convection) results in a considerable cooling effect. In addition, a thickness of the phosphor body does not need to be reduced, so that the conversion efficiency does not suffer. Also, an intensity of an irradiated light need not be reduced. In addition, the lighting device comes without movement mechanics and can therefore maintain a compact design.

It is a particularly preferred for effective heat dissipation development that the translucent layer has a higher thermal conductivity than the phosphor body. However, a transparent layer having the same or similar thermal conductivity as that of the phosphor body may be sufficient, since this layer is not warmed up directly by the phosphor and is thus available for a more effective heat spreading.

In particular, the heat sink may be a metallic heat sink, e.g. made of aluminum and / or copper.

It is a development that the phosphor body is a layered or sheet-like phosphor body.

It is yet another development that the phosphor body has a light-permeable matrix material which has phosphor (particles) as filling material. The matrix material is in particular a transparent material, but may also be translucent or opaque. The translucent material may e.g. have non-converting scattering particles.

The matrix material may be, for example, silicone, ABS or PC. It is particularly preferred that the matrix material is water glass, as this is higher temperature resistant.

The phosphor body may have one or more phosphors.

For operation of the lighting device, primary light (e.g., blue light or UV light) is irradiated on the front of the phosphor body through the transparent sheet. This light is at least partially converted by the phosphor into secondary light of typically longer wavelength and isotropically emitted. As a result, the secondary light and possibly an unconverted primary light component emerge again from the front side. To increase the efficiency, at least one contact surface of the heat sink with the phosphor can be designed to be reflective, so that light incident on the heat sink can also be emitted from the front side after renewed passage through the phosphor.

It is an embodiment that the translucent layer is connected to the heat sink. As a result, an even more effective heat removal from the front side of the phosphor body is achieved.

It is a particularly simple embodiment of the fact that the translucent layer has an edge region projecting beyond the at least one phosphor body and is connected to the heat sink via the edge region. As a result, the phosphor body, for example, need not have recesses.

Also, such a production can be simplified, for example, by a mounted on the heat sink phosphor body in a step on the front side and edge with suitable material for a translucent layer potted, sprayed or otherwise can be occupied.

A further advantage is, in particular in a fastening of the translucent layer by means of non-translucent means, e.g. good thermal conductive mechanical fastener, e.g. metal, that the attachment (s) of the phosphor body does not block or shade light. The at least one fastening means may comprise, for example, a snap means or a latching means.

It is still an embodiment that the phosphor body has water glass as a base material or matrix material and the translucent layer of glass material (glass, quartz, water glass or similar). The translucent layer consequently has a similar refractive index as the matrix material of the phosphor body, so that light losses due to reflection at the boundary layer between the phosphor body and the transparent layer can be avoided.

It is generally preferred to reduce reflections at (internal) interfaces such that a refractive index of the transmissive layer is at least similar, in particular equal, to a refractive index of a matrix material of the phosphor body.

It is yet another embodiment that the translucent layer is a diamond or sapphire plate. This is particularly heat-conducting and thus allows a particularly effective cooling.

It is also an embodiment that the translucent layer is a glass material plate (made of glass, quartz or the like), which is coated with a light-transmitting, electrically conductive material. The translucent, electrically conductive material is typically particularly highly thermally conductive, so that there is a further improved cooling of the phosphor body.

It is a development of the fact that the translucent, electrically conductive material is located at least on one side of the translucent layer facing the phosphor body and in particular is in contact with the phosphor body.

The translucent layer may in particular be made prior to application to the phosphor body, e.g. be coated with the translucent, electrically conductive material.

It is also an embodiment that the translucent, electrically conductive material is a TCO (Transparent Conducting Oxide) material, ie a transparent, electrically conductive oxide material. The TCO material may be e.g. Indium-tin-oxide (ITO), fluorine-tin-oxide (FTO), aluminum-tin-oxide (AZO) and / or antimony-tin-oxide (ATO).

It is also an embodiment that the material is a material having an anisotropic thermal conductivity, e.g. with embedded graphene or carbon nanotubes.

It is also an embodiment that the translucent layer has an antireflection coating. In particular, this can suppress reflections on the front side, at which the primary light is irradiated, and consequently increase a luminous efficacy and support precise color mixing.

A particularly preferred development consists in that the phosphor body comprises water glass as the matrix material, the translucent layer likewise consists of water glass and the light-permeable layer has an antireflection coating on the free surface facing away from the phosphor body. An advantage in this case is that the application process of the antireflection coating does not or only slightly influences the phosphor particles.

In addition, it is a further development that at least one optic is applied or integrated on the phosphor body and / or on the light-permeable layer, e.g. by immersion. The optics may e.g. be a lens or a concentrator. The optics can be anti-reflective.

It is also a development that the heat sink is a stationary heat sink. This lighting device has the advantage that it allows a simple and compact design and yet the (at least one) phosphor is well cooled.

Alternatively, the heat sink may be a movable heat sink, e.g. a rotatable disc of a light wheel or color wheel. The movable heat sink may provide even better cooling and / or distribution of the incident primary light.

It is yet another embodiment that the lighting device has at least one light source, in particular a semiconductor light source, for irradiating a front side of the phosphor body. Thus, advantageously, a high-energy, efficiently coordinated to the (at least one) phosphor primary light beam can be provided with a relatively low cost.

The at least one light source in particular has at least one ultraviolet and / or blue light emitting light source. However, this spectral range is not meant to be limiting.

It is also a development that the at least one light source has at least one laser. Such a laser can be made particularly bright and narrow and may be particularly efficiently matched to a phosphor. The laser may be formed, for example in the form of a laser diode as a semiconductor light source. Such a development is particularly suitable as a light-generating unit in a projector, such as video projector.

It is furthermore a development that the at least one light source has at least one light-emitting diode as a semiconductor light source.

However, the lighting device is not limited thereto and may, for example, also have a different type of light source, e.g. a fluorescent tube. The light source may be followed by a spectral filter.

It is also a development that the lighting device is a vehicle light device or a part thereof. The vehicle lighting device may in particular be a headlight. For example, land vehicles (e.g., cars, trucks, motorcycles, e-bikes, bicycles, etc.) may be considered as vehicles, but also aircraft or ships, etc.

The above-described characteristics, features, and advantages of this invention, as well as the manner in which they will be achieved, will become clearer and more clearly understood in connection with the following schematic description of exemplary embodiments which will be described in detail in conjunction with the drawings. In this case, the same or equivalent elements may be provided with the same reference numerals for clarity.

1 shows a sectional side view of a lighting device according to a first embodiment;

2 shows a sectional side view of a lighting device according to a second embodiment; and

3 shows a sectional side view of a lighting device according to a third embodiment.

1 shows a lighting device 11 according to a first embodiment with a heat sink 12 and a sheet-like phosphor body 13 , A typical layer thickness of the phosphor body 13 is about 20 to 100 microns, especially 50 to 100 microns.

The phosphor body 13 is with his back 14 on the heat sink 12 arranged and on his front to be irradiated 15 with a translucent layer 16 busy. The translucent layer 16 has at least the same high thermal conductivity as the phosphor body 13 ,

The heat sink 12 For example, consists of aluminum, while the phosphor body 13 Water glass as matrix material 17 has, in the phosphor particle 18 embedded as filling material.

Front side of the phosphor body 13 is a semiconductor light source in the form of a blue primary light P emitting ('blue') laser 19 , in particular laser diode attached. The blue primary light P passes through the translucent layer 16 , then hits the sheet-like phosphor body 13 and is at least partially converted into secondary light S of shorter wavelength, eg in yellow secondary light S. In the first 10 to 30 micrometers, a large part of the blue primary light P is converted and the resulting energy difference is converted into heat ('Stokes heat'). , The phosphor body 13 however, has one with respect to the thickness of the phosphor body 13 only comparatively poor thermal conductivity, so that the heat without the translucent layer 16 insufficient due to the heat sink 12 would be dissipated.

By means of the translucent layer 16 however, it may be in a region of the phosphor body 13 near the front 15 generated Stokes heat are spread (eg at a comparatively small focal spot) and also on the translucent layer 16 be dissipated more strongly, for example, by convection into the environment. This improves cooling of this near-side area.

The translucent layer 16 exists like the matrix material 17 of the phosphor body 13 made of water glass. Thus, advantageously, a refraction of light and reflection at the interface between the phosphor body 13 and the translucent layer 16 be prevented. In addition, a precisely fitting, firm connection without mechanical or thermal mismatch results.

To improve the luminous efficacy and a color deviation by reflection on a free (front) surface 20 the translucent layer 16 To suppress this, this can be done with an antireflective coating 21 be provided. An additional advantage of the translucent layer 16 made of water glass here is that the application process of the anti-reflection coating 21 the phosphor particles 18 not or only slightly influenced and thus, for example, can protect against thermal decomposition or chemical destruction.

2 shows a sectional view in side view of a lighting device 31 according to a second embodiment. At the lighting device 31 is the translucent layer 32 a self-supporting layer, eg of sapphire or diamond, which flat on the phosphor body 13 is hung up.

For mechanical attachment to the and thus also thermal connection to the heat sink 12 protrudes the translucent layer 32 laterally over the phosphor body 13 out. The translucent layer 32 thus has an edge over the phosphor body 13 protruding edge area 33 on, by means of which they are connected to the heat sink 12 connected is. The attachment is done for example via thermally conductive brackets 34 or locking elements, for example made of aluminum or copper, or via thermally conductive interface material (TIM material), for example via thermally conductive adhesive or thermal compound, etc.

3 shows a sectional view in side view of a lighting device 41 according to a third embodiment. The lighting device 41 differs from the lighting device 31 in that the translucent layer 42 to further increase the heat dissipation from the thermally stressed, front-side region of the phosphor body 13 on her the phosphor body 13 facing side a coating 43 of a transparent, electrically conductive material, in particular a TCO material such as indium tin oxide (ITO). The coating 43 So contacts the phosphor body 13 directly large area. The third embodiment is particularly advantageous if the translucent layer 42 itself has too low a thermal conductivity, which, for example, in a translucent layer 42 glass or other glass material such as quartz.

Although the invention has been further illustrated and described in detail by the illustrated embodiments, the invention is not so limited and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Thus features of the embodiments shown can be interchanged or combined. For example, a light-transmissive layer may have both a coating of a transparent, electrically conductive material and an anti-reflection coating.

Claims (11)

Lighting device ( 11 ; 31 ; 41 ), comprising a heat sink ( 12 ) and at least one phosphor body ( 13 ), wherein the at least one phosphor body ( 13 ) - with its back ( 14 ) on the heat sink ( 12 ) is arranged and - at its front to be irradiated ( 15 ) with a translucent layer ( 16 ; 32 ; 42 ) is occupied, which has at least the same high thermal conductivity as the phosphor body ( 13 ). Lighting device ( 31 ; 41 ) according to claim 1, wherein the translucent layer ( 32 ; 42 ) with the heat sink ( 12 ) connected is. Lighting device ( 31 ; 41 ) according to claim 2, wherein the translucent layer ( 32 ; 42 ) one at the edge over the at least one phosphor body ( 13 ) protruding edge region ( 33 ) and over the edge area ( 33 ) with the heat sink ( 12 ) connected is. Lighting device ( 11 ) according to one of claims 1 to 3, wherein the phosphor body ( 13 ) Has water glass as matrix material and the translucent layer ( 16 ) consists of glass material. Lighting device ( 31 ) according to one of claims 1 to 3, wherein the translucent layer ( 32 ) is a diamond or sapphire plate. Lighting device ( 41 ) according to one of claims 1 to 3, wherein the translucent layer ( 42 ) is a glass material plate which is coated with a transparent, electrically conductive material ( 43 ) is coated. Lighting device ( 41 ) according to claim 6, wherein the material ( 43 ) is a TCO material. Lighting device ( 41 ) according to claim 6, wherein the material ( 43 ) is a material with an anisotropic thermal conductivity. Lighting device ( 11 ) according to any one of the preceding claims, wherein the translucent layer ( 16 ) an antireflective coating ( 21 ) having. Lighting device ( 11 ; 31 ; 41 ) according to one of the preceding claims, wherein the lighting device ( 11 ; 31 ; 41 ) at least one semiconductor light source for irradiating a front side ( 15 ) of the phosphor body ( 13 ) having. Lighting device ( 11 ; 31 ; 41 ) according to one of the preceding claims, wherein the lighting device ( 11 ; 31 ; 41 ) is a vehicle lighting device.

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