DE102018202144A1 - LIGHTING UNIT - Google Patents

Abstract

The present invention relates to a lighting unit (1) having a pump radiation source (2), a phosphor element (3) for converting pump radiation into a conversion light and having a mirror (9, 40), the phosphor element being operated in reflection, and the mirror in a reflection beam bundle which results from reflection of a pump radiation beam bundle (4) incident on the irradiation surface of the phosphor element, such that light reflected off the irradiation surface (20) and guided away from the irradiation surface in the reflection beam bundle (21) Pump radiation to the mirror is at least partially reflected back to the Einstrahlfläche.

Description

Technical area

The present invention relates to a lighting unit with a pump radiation source for emitting pump radiation and a phosphor element for the at least partial conversion of the pump radiation into a conversion light.

State of the art

With the combination of a pump radiation source of high power density, such as a laser, and a spaced apart arranged fluorescent element that emits light in response to the pump radiation towards conversion light, light sources high luminance can be realized. The pump radiation is incident on an irradiation surface of the phosphor element, and the conversion light is emitted at a radiating surface. When operated in transmission, the Einstrahl- and the radiating surface are opposite to each other in the present relevant operation in reflection they coincide. Not necessarily the entire pump radiation must be converted (full conversion), but also an unconverted part thereof with the conversion light in mixture can be used as illumination light (partial conversion).

Presentation of the invention

The present invention is based on the technical problem of specifying a particularly advantageous lighting unit.

This is achieved according to the invention with a lighting unit according to claim 1, which has a mirror in addition to the pump radiation source and the phosphor element. The pump radiation falls in a pump radiation beam on the irradiation surface of the phosphor element (which is at the same time radiating surface), and the inventor has found that not the entire pump radiation is converted or scattered in the phosphor element, but it also proportionally a somewhat specular (Fresnel ' reflection) (even when irradiating near or at the Brewster angle). Accordingly, there is a reflection beam, which results from a geometric reflection of the pump radiation beam at the Einstrahlfläche and in which pump radiation propagates away from the emission surface during operation. In the case of a partial conversion, it is of course also possible for pump radiation to propagate away from the irradiation surface around the reflection beam bundle which has been scattered on the phosphor element.

In the reflection beam, however, more pump radiation is performed in proportion, the power density of the propagating away from the phosphor element pump radiation is therefore disproportionately high, compared with the other conversion light beam (in which the conversion light and in the case of partial conversion proportionately not converted, scattered pump radiation be removed from the radiating surface). With the mirror, which is arranged in the reflection beam, this reflection is now advantageously conducted back to the phosphor element, the pump radiation thus again reaches the phosphor element in order to be converted, in any case proportionally. On the one hand, the mirror is advantageous on the one hand with regard to efficient use of pump radiation; on the other hand, it can also help to reduce or prevent local elevation of the pump radiation density in the conversion light beam (at the location of the reflex), which may, for example, result in a more homogeneous illumination light. Furthermore, there may also be a safety aspect, see below in detail.

In general, the mirror can, for example, also be used for beam shaping, ie bundle or widen the pump radiation reflected back to the phosphor element, for example. Thus, for example, can also compensate for a part of the pump radiation source originally inhomogeneous irradiance distribution on the Einstrahlfläche, at least proportionately. The incidence or reflection surface of the mirror can therefore be curved convexly or concavely, for example, have a spherical, ellipsoidal or paraboloidal shape, but in general a free-form is also possible.

Nevertheless, a flat reflection or incidence surface is preferred because, for example, this can also simplify the adjustment and thus production. In general, for example, even a holographic structure as a mirror is conceivable or it could also be composed of a plurality of individual mirror surfaces, which can then be separately (tiltable) in particular as actuators respectively (which corresponds to a DMD array). However, a mirror with a inherently static mirror surface (which nevertheless is preferred) is preferred can be displaceable in the whole, see below), such as a metallic mirror (full mirror), or even a wavelength-dependent mirror.

Preferably, the radiating surface is associated with a lighting optical system, which "collects" the illuminating light emitted in a fanned-out manner, ie bundles (not necessarily the entire illuminating light, but as a rule a large part thereof). The illumination optics is preferably provided as an imaging, as a converging lens or collective lens system (from a plurality of individual lenses). Preferably, the pump radiation beam and / or the reflection beam enforce the illumination optics or at least a part thereof, the mirror or mirrors (see below) can thus be arranged between individual lenses of the optics in the latter case. As far as reference is made to an "optical axis", this refers to the optical axis of the illumination optical system, in particular the optical axis of the single lens which is closest to the phosphor element in the case of a multi-lens system.

Preferred embodiments can be found in the dependent claims and the entire disclosure, wherein in the representation of the features is not always distinguished in detail between device and process or use aspects; In any case, implicitly, the disclosure must be read with regard to all categories of claims.

In a preferred embodiment, the lighting unit has a light mixing agent. This is preferably arranged between the phosphor element and the mirror, so that the reflected back to the mirror to the phosphor element pump radiation passes through the light mixing agent at least twice (in reflex on the path to the mirror and then again after the reflection back to the phosphor element). The reflected back to the phosphor element pump radiation can thus advantageously be particularly uniform, so give on the Einstrahlfläche a uniform irradiance course. Due to the beam guidance, the same optical component is used twice (on the way there and back, relative to the mirror). In simple terms, therefore, with only one optical component, the double effect can be achieved by combining it with the mirror.

In a preferred embodiment, the light mixing agent is provided and arranged such that even the pump radiation guided from the pump radiation source to the phosphor element passes through the light mixing agent, ie the pump radiation beam. The pump radiation beam passes through the light mixing agent usually elsewhere than the reflection beam, because the pump radiation beam preferably eccentric, ie laterally or to the optical axis (see above) is guided on the phosphor element. Accordingly, then the reflection beam is eccentric or laterally offset, so fall the two beams so certainly not together. Even if they then enforce the light mixing agent in each case at a different location, these are merely different regions of the same optical body, ie the same component is irradiated. This may, for example, be advantageous insofar as only one component then has to be mounted or adjusted, which may simplify the design or the manufacture of the lighting unit.

In general, the light-mixing agent may, for example, also be constructed in the manner of an integrator rod, that is, the pump radiation can be guided therein by reflection, in particular total reflection, and mixed on the basis of the (multiple) reflections. Furthermore, for example, a diffusing screen is also conceivable as a light-mixing agent which, for example, can scatter due to embedded scattering centers, for example embedded scattering particles, for example titanium dioxide particles, and / or due to a corresponding surface structuring, for example due to a roughened / etched surface. However, the mixing by means of scattering may, for example, be detrimental to the efficiency (scattering losses), and in the present case the scattering associated with the scattering beam (enlargement of the opening angle) may also be undesirable, because then, for example, the pump radiation reflected back to the phosphor element proportionally also on a Fluorescent element surrounding area falls (due to the expansion). The integrator rod can be disadvantageous because of its structural length and the associated space requirements.

In a preferred embodiment, a microlens array is therefore provided as a light mixing agent. This may preferably be formed as a monolithic body (free of material boundaries in the interior), for example as a casting, in particular injection molded part, or as a glass body.

The array can have, for example, at least 50, 100, 150 or 200 microlenses, with possible (independent) upper limits at, for example, at most 100,000, 10,000 or 1,000 (in each case in the order of naming increasingly preferred). The microlenses can, for example, each have a rectangular or a hexagonal shape in the direction of transmission.

It may be preferred that the microlenses of the array in the region (s) through which the pump radiation beam and / or the reflection radiation beam passes are smaller than in the remaining microlens array. In other words, the microlenses provided only for mixing the conversion light and the scattered pump radiation may be larger, for example at least 20%, 30% or 40%. It may be preferred that the microlenses interspersed by the pump radiation beam and / or the reflection beam are square, the remaining microlenses then being more preferably rectangular but not square. You can, for example, have an aspect ratio of 16: 9.

In absolute values, the microlenses interspersed by the pump radiation beam and / or the reflection beam may, for example, each have a size of 0.25 × 0.25 mm ² , the remaining microlenses may have a size of 0.44 × 0, for example. 25 mm ² have. A different aspect ratio for the microlenses interspersed by pump radiation / reflection beam bundles on the one hand and the remaining microlenses on the other hand may be advantageous insofar as the former in their aspect ratio can then be selected / optimized for the desired irradiance distribution on the phosphor element, the latter, on the other hand regarding the further use of the illumination light. The remaining microlenses can then be matched, for example, to a micromirror array arranged downstream of the illumination unit, which can also have, for example, an aspect ratio of 16: 9.

In general, the microlens array can, for example, also be provided with a through-hole through which the radiation passes without interaction with the microlenses. The array can then, for example, be taken in such a way that the pump radiation beam and / or the reflection beam each pass through microlenses, so that the pump radiation is well homogenized. On the other hand, a particularly central part of the conversion light beam can pass through the through-hole, because in this respect less homogenization may be required.

In a preferred embodiment, the mirror is oriented in such a way that the reflection, that is to say the reflection beam, is substantially perpendicular to an incident surface of the mirror. If, for example, a metallic mirror is provided, its incident surface coincides with the reflection surface. However, it is also possible to provide, for example, a wavelength-dependent mirror with a sequence of a plurality of dielectric layers, in which case the incident surface of the entrance surface corresponds to this multilayer system. The pump radiation reflected at the irradiation surface falls substantially perpendicular to the incident surface, ie, in concrete terms, a center beam of the reflection beam is substantially perpendicular to the incident surface.

This central ray is parallel to a main propagation direction of the pumping radiation propagating away from the phosphor element in the reflection beam (the direction in the respective section of the beam), and in the center of the beam, ie in a sectional plane perpendicular to the main propagation direction, in the centroid of the beam. The radiation incidence "substantially perpendicular" means that said center axis is tilted to a surface normal on the incident surface (where the center axis passes through the incident surface) by at most 10 °, 8 °, 6 °, 4 °, and 2 °, respectively (in FIG Order of naming increasingly preferred), with a technically usual accuracy exactly rectangular incidence is particularly preferred (0 °).

As far as generally referred to in this disclosure a "main propagation direction" of radiation or light, this refers to an average of all the directional vectors along which the corresponding radiation or light propagates in the corresponding beam at the corresponding location In this averaging, each direction vector is weighted with its associated beam strength.

In a preferred embodiment, the reflection beam and a back-reflection beam, in which the pump radiation reflected at the mirror is guided back to the phosphor element, are substantially congruent. In other words, therefore, the pump radiation reflected back to the phosphor element on the mirror is guided on the same path as the reflex, but only in the opposite direction. If one considers the reflection and the back-reflection beam bundles in each case as a volume (which is measured in each case according to the half-width, see below), the "essentially congruent" arrangement means, for example, that each of the volumes has a total volume which is Unification amount of the two volumes results in a proportion of at least 80%, 85%, 90% and 95% (in the order of naming increasingly preferred). Within the usual technical accuracy, the volumes are exactly congruent, ie each of the volumes corresponds to the total volume.

In a preferred embodiment, the mirror is arranged in the conversion light beam in which the conversion light is dissipated at the emission surface. In this case, the mirror fills the conversion light beam only partially, so goes proportionate conversion light also past the mirror, depending on the variant of a larger or smaller part, see below in detail. The conversion light is emitted at the emission surface typically Lambertsch, and it is then, for example, collected with an illumination optics at least a part thereof and fed to a lighting application. The entirety of the conversion light rays collected on the emission surface constitute the conversion light radiation beam. The light guided in the conversion light beam can then be supplied, for example, to a lighting application.

In general, two variants can be distinguished with regard to the mirror and its function. On the one hand, the mirror can actually only be used to return pump radiation guided in the reflection beam, and it can then be correspondingly small. On the other hand, he can also take over a further aperture or light redistribution function, cf. in particular the end of the description introduction. The only proportionate filling of the conversion light beam by the mirror can be quantified, for example, with reference to a cross-sectional area of the conversion light beam. This is perpendicular to a main propagation direction of the guided in the conversion light beam conversion light; the cross-sectional area is planar on its own, ie it extends in the whole direction perpendicular to the main propagation direction. Relative to their position along the main propagation direction, the cross-sectional area is placed in the conversion light beam so as to be in contact with, but not penetrate, the mirror on a side proximate to the phosphor element; it thus borders on the mirror like a tangential plane (it is on one side, the phosphor element on the other).

It is then considered a vertical projection of the mirror in the cross-sectional area, this should have, depending on the variant on the entire cross-sectional area an area ratio of, for example, at most 30%. Further advantageous upper limits may be at most 25%, 20%, 15% or 10%, with possible (independent) lower limits for example at least 1%, 2%, 3%, 4% and 5% (respectively in the Order of naming increasingly preferred). In general, and in particular in this case is based as a mirror, which can reflect the ability to the pump radiation in the desired manner, so it is, for example, not only considered an actually irradiated with pump radiation area (which may be smaller). If, on the other hand, the mirror is, for example, a layer / a layer system on a base body, the latter remains outside in these considerations. As a mirror so only considered, which (a corresponding irradiation assumed) reflects the pump radiation.

In a preferred embodiment, the mirror is mounted so displaceable that can be changed by the displacement of the mirror, the proportion to which the mirror fills the conversion light beam. Preferably, the storage is provided such that the path of the reflected back to the mirror to the phosphor element pump radiation remains unaffected, so in different displacement positions of the mirror is the same. The mirror is preferably offset parallel to its surface extension, particularly preferably exclusively parallel to it, thus therefore substantially or exactly perpendicular to the center beam of the reflection beam. The displacement can be, in particular, a straight-line displacement, for this purpose the mirror can, for example, be fastened to a linear bearing or provided as part thereof.

By displacing the mirror, the proportion of the above-mentioned projected area on the cross-sectional area can be changed, for example, reduced by at least 10%, 20%, 30%, 40%, 50% and 60%, respectively, and although starting from a maximum possible projection surface in storage (and in the order of naming increasingly preferred). Possible upper limits can be (independently of this), for example, at most 95% or 90%. Irrespective of this in detail, for example, in the case of a partial conversion with the displacement of the mirror, advantageously the spectral composition of the illumination light can be changed, in particular in the case of a wavelength-dependent mirror (see below).

In a preferred embodiment, a wavelength-dependent mirror is generally provided which is reflective only for the pump radiation but transmissive for the conversion light (in each case at least predominantly). Thus, for example, when viewing a spectral intensity distribution, the greater part of the conversion light is transmitted by the conversion light, that is to say more than 50%, 60%, 70% or 80% when viewed in an integral manner. For reasons of efficiency, a perfect transmission (100%) may be preferred, but for technical reasons upper limits can be, for example, at most 98% or 95%. This applies analogously to the reflectivity with respect to the pump radiation, although the pump radiation preferably has a narrow band and thus the reflected component is correspondingly higher, for example, can be at least 90% or 95% (with theoretical upper limits at 99.9% and 99.5%).

Irrespective of this, with the wavelength-dependent mirror, only the pump radiation is (essentially) reflected back, ie conversely, the conversion light is transmitted towards the illumination application. The wavelength-dependent reflective mirror can be constructed, for example, as an interference mirror (also called a "dichroic mirror"), ie as a multilayer system. This can be provided from at least two dielectric materials which differ in their refractive indices and are arranged alternately successively in the multilayer system. Such a multilayer system may, for example, be arranged on a base body, for example a transparent plate, in particular deposited thereon. The peculiarity lies in the present case but rather in the arrangement of the mirror relative to the other components. The substantially perpendicular incidence of radiation on the mirror (see above) may be of particular advantage in this regard, because such a multi-layer system works particularly well or reliable and loss-free with a substantially vertical radiation incidence. In fact, unlike an oblique incidence of radiation, the layer thicknesses of the layers are actually optically effective, ie, conversely, the desired reflection / transmission edge can be set relatively precisely.

In a preferred embodiment, an optical sensor is arranged on a rear side of the wavelength-dependent mirror, with which the conversion light transmitted at least partially by the mirror can be measured. Said back is opposite to the front of the mirror, on which the reflection beam falls, so opposed to the incident surface. The sensor arranged on the rear side of the mirror can advantageously enable monitoring of the transmitted conversion light, with which, for example, the mechanical integrity of the phosphor element can be monitored.

In general, the phosphor element is operated in a preferred embodiment in partial conversion, so the pump radiation is only partially converted and discharged an unconverted portion of it in the conversion light beam. The conversion is preferably a down-conversion, so the conversion light has a longer wavelength than the pump radiation. The pump radiation is preferably blue light and / or the conversion light yellow light, the illumination light is preferably white light. The wavelength-dependent mirror then reflects the blue light and is transmissive to the yellow light, which is why it is also called the "cold mirror" (the mirror reduces the blue component in the illumination light, which shifts it to lower color temperatures).

The phosphor element may be, for example, a phosphor applied in particle form, but it may also be a phosphor ceramic, which may in particular be monocrystalline. "Phosphor" is also to read on a mixture of several individual phosphors. A preferred single phosphor may be cerium doped yttrium aluminum garnet (YAG: Ce). The phosphor element can be antireflection-coated at the irradiation / emission surface, for example with a dichroic layer system. On one of the Einstrahl- / radiating surface opposite side surface of the phosphor element is preferably arranged a mirror and / or a heat sink, preferably both. The silvering can z. B. dichroic or metallic, particularly advantageous may be a combination thereof.

For example, the phosphor element may be exposed to a high load due to the high power density of the pump radiation. But it may also, for example, the environmental conditions, especially in automotive applications, cause mechanical stress (eg. Due to temperature fluctuations or vibrations etc.). Various damage or degradation mechanisms are possible, which can lead, for example, to tearing or breaking of the phosphor element; in the worst case scenario, this can also detach completely from a carrier, as a rule a heat sink. Also due to the mirroring back, the pump radiation would then conversion-free, so bundled and reflected high power density, and on the path of the conversion light beam (through lighting optics, etc.) to the lighting application, which may pose a significant photobiological risk for a viewer there , It can lead to damage to the retina, in the worst case a loss of vision.

With the rear side of the mirror arranged sensor, any damage or a drop of the phosphor element can be detected via a change in the conversion light, namely a proportionately lower conversion light component. If the phosphor element completely precipitates, is not converted at all, so the sensor measures no more radiation power, although the pump radiation source is operated. This can then be output by an evaluation to a control unit of the pump radiation source, so that, for example, a shutdown of the pump radiation source is caused (or at least one Power reduction). Ideally, however, not only the extreme case ("dropped-down phosphor element") can be detected with the sensor, but also a certain conversion light drop can be used in connection with threshold values for fault detection, namely, for example, displaying an interrupted / broken phosphor element which converts correspondingly less.

In connection with the above-described degradation / damage mechanisms, the mirror arranged according to the invention in the reflection beam can also generally be advantageous, ie also independent of a sensor arranged on the rear side. If, in fact, the phosphor element falls away from the carrier or breaks or breaks, ie the pump radiation is reflected at least partially directly on the carrier (largely specular), the pump radiation propagates in this error case essentially on the same path as that guided in normal operation in the reflex pump radiation. With the mirror, not only in normal operation, the efficiency can be increased (see the front), but at the same time a backup is created, namely, the bundled pump radiation high power density is "intercepted" in case of failure. This pump radiation is then reflected back to the damaged phosphor element or the carrier, and from there to the path of the original pump radiation irradiation (in the opposite direction), that is, as a result, for example. Back to the pump radiation source. In any case, an escape of the pump radiation is avoided for lighting application, which is a significant safety advantage.

In a preferred embodiment, the mirror has a polarization-dependent reflectivity, which is larger than for s-polarized incident pump radiation for p-polarized incident pump radiation. The pump radiation guided in the pump radiation beam from the pump radiation source to the irradiation surface of the phosphor element is substantially p-polarized. In the case of partial conversion, that is to say when proportional pump radiation is not converted, but is scattered at the phosphor element, this scattered pump radiation is not polarized. For these non-polarized radiation, the polarization-dependent mirror is less or only 50% reflective, the pump radiation guided in the conversion light beam is therefore less "shadowed" locally by the mirror, as far as scattered pump radiation is concerned.

However, if the pump radiation radiation beam incident p-polarized pump radiation on the irradiation surface of the phosphor element (proportionally) to a certain extent specularly reflected and / or reflected in an error case (see the front) on the carrier, the polarization does not change, the pump radiation is in any case largely p -polarized on the mirror. Its reflectivity is high for p-polarized pump radiation, the pump radiation is reflected back for re-conversion (normal operation), or it is prevented from leaking to the illumination application (error).

In the case of the "substantially p-polarized" incident pump radiation, the planes of polarization formed by the vectors of the electric field are no more than 20 ° with respect to the plane of incidence on the irradiation surface, and increasingly preferably no more than 15 °, 10 °, 5 ° or more in the order of entry. 2 ° tilted. Particularly preferably, the planes coincide (angle of 0 °), so the pump radiation falls exactly p-polarized on the Einstrahlfläche. The plane of incidence is spanned by a surface normal on the irradiation surface and a center axis of the pump radiation beam where the center axis intersects the irradiation surface. A prerequisite for the p-polarized radiation is that the pump radiation guided in the pump radiation beam is linearly polarized. Preferably, it is already emitted by the pump radiation source originally linearly polarized.

In a preferred embodiment, which represents an alternative to a wavelength- or polarization-dependent reflector designed mirror, the mirror is provided metallic reflective. This may be particularly, although not exclusively, in connection with the ring-type mirror discussed in detail below. In general, a metallic mirror, for example, be advantageous insofar as it can be made relatively solid and thus can be thermally optimized for heat dissipation out. The metallic mirror, which may, for example, comprise silver and / or aluminum, may i. A. also additionally have a dichroic layer, which can achieve very high reflectivities (despite the dichroic layer, the reflection is not wavelength-dependent, but metallic).

The metallic mirror is also called a full mirror because it is not wavelength dependent (at least in the visible). The metallic mirror may preferably have a reflectivity of at least 80%, 85%, 90%, 95%, and 98%, respectively (increasingly preferred in the order of designation); Possible upper limits can (independently of), for example, be at most 99.9% or 99.5% and ultimately be technically conditioned.

In a preferred embodiment, in the pump radiation beam of the irradiation surface upstream of a beam compression optics is arranged, which reduces the cross section of the pump radiation beam. At the outlet side of the compression optics, for example, this cross section can make up at most 80%, 70%, 60%, 50% or 40% of a cross section on the inlet side, with possible (independent) lower limits for example at least 5% or 10% (in each case in the Order of naming increasingly preferred). Preferably, a further mirror is provided, via which the pump radiation beam is guided onto the irradiation surface (see below), wherein the compression optics is then further preferably arranged between the pump radiation source and the further mirror.

The cross sections are each taken in a direction perpendicular to the main propagation direction of the pump radiation plane directly to an entrance surface of the compression optics ("inlet side") and an exit surface ("exit side"). The cross sections are dimensioned in the respective plane after an increase of the irradiance to half of the maximum value of the irradiance in the plane. The reference to the "rise" means that the outer peripheral surface in the plane is determined from the outside inwards (towards the centroid); figuratively speaking, a line (a closed curve) is placed around the beam and each time moved inwards until half the maximum value is reached for the first time.

The compression optics can, for example, be provided such that they leave the aperture angle of the pump radiation beam essentially unchanged. On the other hand, however, it can also bundle the pump radiation, for example, starting from a previously collimated pump radiation beam. A compression optics can be constructed, for example, from staircase mirrors or reflection prisms, preferably a lens system. As the lens system, a combination of a positive lens and a downstream diverging lens may be preferable, see the embodiment for illustration. In general, the pump radiation beam can be homogenized upstream of the irradiation surface, which is preferably carried out downstream with the compression optics present; For example, a microlens array provided for homogenization can be correspondingly smaller, which can also offer cost advantages.

In a preferred embodiment, a further mirror is provided, via which the pump radiation beam is guided on the Einstrahlfläche. This further mirror is arranged in the conversion light beam, but fills this only partially. A vertical projection of the further mirror into a cross-sectional surface of the conversion light beam, which is perpendicular to the main propagation direction of the conversion light and tangent to the other mirror, may have at the cross-sectional area, for example, an area ratio of at most 50%, with at most 45%, 40% or ., 35% are increasingly preferred in the order of entry. Lower limits may (independently of), for example, be at least 5%, 10% and 15%.

Even if the further mirror only partially fills the conversion light beam, it is preferably (additionally) wavelength-dependent and / or polarization-dependent reflective. The further mirror can therefore be reflective, for example, of pump radiation, but transmissive for the conversion light (at least largely), reference is made expressly to the disclosure of the mirror in the reflection beam with respect to a quantification of the reflection / transmittance and further details. Alternatively or additionally, the further mirror can also have a higher reflectivity for p-polarized pump radiation than for s-polarized pump radiation, the pump radiation then being guided essentially p-polarized onto the further mirror. The pump radiation is then reflected at the other mirror to the phosphor element, but conversely, the scattered and therefore unpolarized radiation is reflected only half.

A preferred embodiment relates to an annular mirror. This is arranged in the conversion light beam and extends around the main beam at least partially encircling. The annular mirror preferably describes a closed ring shape (see below), but in general the ring shape can also be (partially) opened. With reference to the circulation around the main jet, the annular mirror can, for example, extend over an angular range of at least 200 °, 250 °, 300 °, 320 ° or 340 ° (increasingly preferred in the order in which they are mentioned), more preferably 360 ° ,

The main beam of the conversion light beam, in the same way as the above-discussed center beam of the reflection beam, lies centrally in the conversion light beam. Viewed in the direction of the main direction of propagation of the conversion light beam bundle cutting planes he interspersed in each case the centroid of the beam. Preferably, the main beam coincides with an optical axis of the illumination optics associated with the emission surface.

In a preferred embodiment, the annular mirror with a further mirror (see front) combined provided. The latter can be arranged, for example, in a gap of the annular mirror; He may also be arranged downstream of the annular mirror based on the conversion light (behind) and the pump radiation z. B. reflect through a corresponding recess in the annular mirror on the phosphor element. Conversely, however, the annular mirror is preferably arranged downstream of the further mirror. The latter relates to the conversion light propagation away from the emission surface of the phosphor element (any reflected light that is converted in the opposite direction, that is to say in the conversion radiation bundle, is ignored).

In general, the annular mirror, as already mentioned above, preferably designed as a metallic mirror, so it is equally reflective for the pump radiation and the conversion light. Preferably, the annular mirror, specifically its mirror surface, plan; Particularly preferably, the flat mirror surface lies in a plane perpendicular to the main beam of the conversion light beam. The annular mirror is preferably provided statically (not displaceable).

In a preferred embodiment of the annular mirror forms a closed ring shape (circulation by 360 °, see the front). The reference to a "ring" does not have to imply a circular ring shape; although such is generally also possible, a deviating ring shape is even preferred, in particular an elliptical shape (see below).

In a preferred embodiment, that part of the conversion light which is guided away from the emission surface in the conversion light beam and impinges on the annular mirror is reflected there at least partially back to the emission surface. This can offer an efficiency advantage. Namely, the inventor has found that this back-reflected conversion light is scattered on or in the phosphor element to a good, if not the larger part, so with some probability re-enters the conversion light beam and then passes the mirror to the illumination application (on it passes). It is thus redistributed with the annular mirror conversion light from an outer region of the conversion light beam in a central region.

In a preferred embodiment, the annular mirror limits the conversion light beam as a diaphragm. The ring-shaped mirror therefore delimits the ray bundle, thus shades it inwards from the edge and defines an aperture. The conversion light beam has considered in sectional planes, each containing the main beam, upstream of the aperture in each case a larger opening angle than the diaphragm or an aperture-imaging optics downstream. This is preferably true for all cutting planes, thus limiting a reflector with a closed ring shape completely circulating the beam.

In general, the mirror can thus advantageously also be used for beam shaping, for example for adaptation to a downstream area light modulator (see below). A particularly advantageous interaction may result with the partial reflection back of the conversion light to the phosphor element, that is, the redistribution discussed above in a central region of the conversion light beam. The part of the conversion light beam is then cut away on the one hand with the annular reflector on the one hand, the downstream is not usable anyway (aperture function), but this part of the light is then at least partially redistributed and can be used in the result. Thus, a light source with adapted etendue can be provided with the annular mirror.

In a preferred embodiment, a vertical projection of the annular mirror into a cross-sectional area of the conversion light beam has an area fraction of at least 20%, further and particularly preferably at least 25% or 30%. Possible upper limits may be (independently of), for example, at most 80% or 75% or 70%. The cross-sectional area is perpendicular to the main beam and contacts the mirror at its end closer to the phosphor element. If, for example, a plane mirror is provided which is in any case perpendicular to the main beam (which is preferred), this lies in the cross-sectional area and corresponds to the area of the vertical projection of that of the mirror.

In a preferred embodiment, an inner edge of the annular mirror facing the main beam of the conversion light beam describes an elliptical shape. In other words, then in particular the aperture has at least in sections, preferably in total the shape of an ellipse. Preferably, the beam is thus adjusted from a round or equiaxial cross-sectional shape to a specific aspect ratio (with unequal sides).

In a preferred embodiment, in the underlying ellipse, a ratio of small to large semiaxis is at least 4: 9, further and more preferably at least 5: 9 or 11:18. Preferred upper limits, which in general may also be of interest independently of the lower limits, are increasingly preferably no more than 7: 9 or 13:18 in the order in which they are mentioned. Particularly preferred is a ratio of about 2: 3.

In a preferred embodiment, a surface light modulator is arranged downstream of the mirror in the conversion light beam. In the case of the annular mirror provided as a diaphragm, therefore, that portion of the conversion light which passes through the diaphragm opening falls on this surface light modulator. In general, not all conversion light "passing through" the aperture is required to be incident on the area light modulator, but this is preferred.

The surface light modulator is quite generally an electrically or electronically adjustable component which has an active surface, the reflection or transmission properties of which are individually adjustable in segments (pixelated), which results in an imager function. In general, for example, an LCD or LCoS array can also be provided; a micromirror array is preferred. Its micro-mirror actuators can be adjusted individually so that the light is pixelated either for illumination purposes or, for example, on an absorber (beam dump). Particularly advantageous can thus be achieved with a motor vehicle headlight active street lighting, so one of example. Other road users dependent selective street lighting (to avoid glare, for example, the opposite lane is not illuminated when a vehicle comes to meet).

In a preferred embodiment, the active surface of the surface light modulator has a rectangular shape, so it has an aspect ratio not equal to 1. This aspect ratio preferably corresponds to the above-discussed ratio of the semi-axes of the ellipse. With the annular mirror as the aperture, exactly that part of the conversion light is then guided onto the surface light modulator, which actually "fits" it. The invention also relates to the use of a lighting unit disclosed herein for lighting, in particular for automotive lighting, in particular automotive. Outdoor lighting, preferably in a headlight. In general, the lighting unit can, for example, be used as a light source in the stage or entertainment area, also in the field of architecture applications are possible. It is also an outdoor lighting of aircraft (helicopters / aircraft) possible, or even ships. A use in a road vehicle, for example, also a motorcycle or a truck, particularly preferably in a passenger car (car) is preferred.

A preferred use relates to the illumination unit with displaceably mounted mirror, which is then offset to adjust the spectral composition of the illumination light. The adaptation of the spectral composition is preferably an adaptation of the color locus, that is, the illuminating light is white light. The latter is generally preferred.

list of figures

In the following, the invention will be explained in more detail with reference to an exemplary embodiment, wherein the individual features in the context of the independent claims in another combination may be essential to the invention and continue to distinguish not in detail between the different claim categories.

• 1 eine erfindungsgemäße Beleuchtungseinheit in einer Schrägansicht;
• 2 einen Teil der Beleuchtungseinheit gemäß 1 in einer Seitenansicht;
• 3 eine alternative Beleuchtungseinheit mit einem ringförmigen Spiegel;
• 4 den ringförmigen Spiegel der Beleuchtungseinheit gemäß 3 in einer Aufsicht.

In detail shows

• 1 a lighting unit according to the invention in an oblique view;
• 2 a part of the lighting unit according to 1 in a side view;
• 3 an alternative lighting unit with an annular mirror;
• 4 the annular mirror of the lighting unit according to 3 in a supervision.

Preferred embodiment of the invention

1 shows a lighting unit according to the invention 1 with a pumping radiation source 2 and a phosphor element 3 in an oblique view. The pump radiation source 2 emits a pump radiation beam 4 with pump radiation, in the present case blue laser light. This intersperses a beam compression optics 5 namely, a condenser lens 5a and a downstream diverging lens 5b , The pump radiation beam 4 it is reduced in its cross section and at the same time bundled.

The beam compression optics 5 downstream is the pump radiation beam 4 in a manner explained in more detail below on the phosphor element 3 guided. The phosphor element 3 has YAG: Ce as a phosphor, the conversion light is yellow light. The pump radiation is in the phosphor element 3 only partially converted, an unconverted part thereof becomes, together with the conversion light in the conversion light beam 7 dissipated (shown in dotted lines). The blended illumination light is white light.

How out 1 can be seen, there are in the conversion light beam in addition to various lenses for beam shaping or homogenization (see. 2 in detail) also a mirror 9 , as well as another mirror 10 , About the other mirror 10 becomes the pump radiation beam 4 to the phosphor element 3 reflected. This further mirror 10 is wavelength-dependent, namely reflective for the pump radiation, but transmissive for the conversion light. The same applies to the mirror 9 whose function is described below in particular with reference to 2 is explained.

The pump radiation falls in the pump radiation beam 4 over the further mirror 10 on the Einstrahlfläche 20 of the phosphor element 3 , There, the entire pump radiation is not converted or scattered, but it is proportionally pump radiation at the Einstrahlfläche 20 reflected. This pump radiation propagates in a reflection beam 21 from the irradiation surface 20 away. This reflection beam 21 results from Fresnel reflection of the pump radiation beam 4 at the Einstrahlfläche 20 , For the sake of clarity, both beams are 4 . 21 indicated in dashed lines in their respective extent only in one section and is otherwise only the main beam 4a the pump radiation beam 4 or the main beam 21a of the reflection beam 21 shown. The reflection beam 21 results as a specular reflection of the pump radiation beam 4 at the Einstrahlfläche 20 ,

In the reflection beam 21 the pump radiation density is much higher than in the other conversion light beam 7 (shown dotted), so there is much more pump radiation per solid angle range than otherwise in the interspersed by the scattering solid angle ranges. That is why in the reflection beam 21 the mirror 9 arranged at the in the reflection beam 21 guided pump radiation (arrow up) reflected and thus back to the Einstrahlfläche 20 is guided (arrow down). This can on the one hand in the conversion light beam 7 Preventing a local increase in pump radiation relative to the conversion light, the illumination light must then, for example, less "mixed" before use, which can have efficiency advantages. In addition, the pump radiation is returned to the phosphor element 3 led, it can then at least then largely converted or scattered and thus be used, which generally offers an efficiency advantage.

How out 2 is apparent, between the mirrors 9 . 10 and the phosphor element 3 a light-mixing agent 30 arranged, namely a microlens array. Its side surfaces 30a, b are each with a variety of each other between side surface 30a and side surface 30b each paired associated microlenses shaped (shown schematically). The conversion light or the pump radiation passes through the microlens array and is thereby homogenized, the radiation or the light is thus mixed. In the process, the light-mixing agent becomes 30 in the present case advantageously used multiple times, namely on the one hand for mixing the illumination light, namely in the conversion light beam 7 guided conversion light and the proportionately scattered pump radiation, which also propagates in the conversion light beam for lighting application down.

On the other hand, even the pump radiation beam penetrates the light mixing agent 30 , So the pump radiation is mixed, what a homogeneous or at least more homogeneous irradiance distribution on the Einstrahlfläche 20 results. This is of particular advantage insofar as the pump radiation source 2 preferably composed of several laser sources, which is in 1 can be seen on the corresponding arrayed arranged Kollimationslinsen (in the present case 20 laser diodes are provided, each of which is associated with a separate collimating lens).

Furthermore, also penetrates the reflection beam 21 the light-mixing agent 30 , Part of the pump radiation is so even twice or three times (taking into account the pump radiation beam 4 ) through the light-mixing agent 30 guided. This is used very efficiently, cf. also the comments in the introduction to the description.

Both mirrors 9 . 10 are reflective depending on the wavelength, namely reflective for the pump radiation, but transmissive for the conversion light. Such a dichroic mirror may be constructed of a system of dielectric layers that differ in their refractive indices, the transmission and reflection edge then being adjustable over the layer thicknesses. Furthermore, both mirrors are also reflective dependent on polarization, namely reflective for p-polarized incident pump radiation, but transmissive for s-polarized pump radiation.

As explained in detail in the introduction, the pump radiation in the pump radiation beam p-polarized falls on the other mirror 10 and becomes corresponding to the phosphor element 3 reflected. The portion not scattered there, but scattered, is not polarized and is reflected both by the mirror 9 as well as the other mirror 10 transmitted in half. The at the Einstrahlfläche 20 reflected part of the pump radiation, however, falls p-polarized on the mirror 9 and will return to the phosphor element accordingly 3 reflected. The same applies to pump radiation that in case of failure (broken / from the carrier 31 dropped phosphor element 3 ) on the carrier 31 is reflected.

As can be seen from the figures, the mirrors are 9 . 10 although in the conversion light beam 7 arranged, but they fill out only partially. Relative to a cross-sectional area 32 the conversion light beam 7 has a vertical projection of the mirror 9 in this cross-sectional area only a fraction of less than 10%. The same applies analogously to the other mirror 10 , Although the mirrors 9 . 10 already dependent on wavelength and polarization anyway, the efficiency can be further improved.

In 2 is also a lens system 35 to recognize (that in 1 only schematically shown), with which of the phosphor element 3 Lambertsch emitted conversion light and the scattered pump radiation are bundled. The lens system 35 has a first converging lens 35a and a second condenser lens 35b on. Both the pump radiation beam 4 as well as the reflection beam 21 be through the lens system 35 guided.

How out 2 As can be seen, both are mirrors 9 . 10 stored displaceable, which can change the proportion of shading (especially if the mirror 9 . 10 slightly larger than shown). There is a certain color setting or adaptation of the color temperature possible, cf. also the comments in the introduction to the description.

In 1 is the light-mixing agent 30 for the sake of clarity not shown, but one is the light mixing agent 30 downstream lens 38 shown, with which the illumination light is led to the lighting application. The lens 38 downstream is a surface light modulator 39 arranged, specifically a micromirror array (DMD Digital Mirror Array). This is shown only schematically in the present case, also with regard to the orientation to the rest of the lighting unit 1 , Functionally, the micromirror array allows pixelization of that in the conversion light beam 7 guided light, so depending on the position of the micro-mirror actuators lighting side individual solid angle ranges optionally light can be supplied, see. also the description introduction in detail. Depending on the position of the actuator, a respective spatial direction (see the three arrows shown schematically) is then optionally supplied with light or not.

In 3 is a to the arrangement according to 2 in many parts comparable construction shown. The same parts or parts having the same function are denoted by the same reference numerals, and reference is also made to the description of the respective other figure. For the sake of clarity, is in 3 no light mixing agent shown - the variant according to 3 can be analogous to that according to 2 be provided with a light mixing agent, although this is not mandatory.

A significant difference to the variant according to 2 lies in the mirror 40 , the gem. 3 forms a closed ring shape. This ring shape is in 3 only to be seen in section, so also on 4 is referenced. This shows the mirror 40 in a plan view, so along a main beam 7a the conversion light beam 7 looking at it.

The annular mirror 40 acts as a stop in the conversion light beam 7 thus cuts out a part of the conversion light beam. How out 4 can be seen, is the aperture 41 elliptical, so has a main beam 7a facing inner edge 40a of the mirror 40 an elliptical shape. Here is the ratio of small semi-axis 42 too big half-axis 43 at 2: 3, bringing the conversion light beam 7 on the aspect ratio of the active surface of the downstream surface light modulator 39 is adjusted. So only that part of the light penetrates the mirror 40 through the aperture 41 pointing to the active surface of the surface light modulator 39 fits (either fits exactly or is slightly larger).

In 4 is shown by dashed lines, where the outer edge 7b the conversion light beam 7 lies. The degree of coverage by the mirror 40 is around 70%. But this is the part of the light that is not through the aperture 41 goes, but on the mirror 40 falls, on the mirror surface 40b reflected.

This part of the light is thus returned to the phosphor element 3 guided. There, the back-reflected light is at least partially scattered and then (re) emitted at such an angle that it passes through the aperture 41 fits. Of course, a part of the reflected back light is again on the mirror 40 however, the proportion of light with matching etendue is increased.

LIST OF REFERENCE NUMBERS

lighting unit 1 Pump radiation source 2 Fluorescent element 3 Pump radiation beam bundle 4 Of which main beam 4a Beam compression optics 5 Thereof collecting lens 5a Of which divining lens 5b Conversion light-ray bundle 7 Of which main beam 7a Of it outside edge 7b mirror 9 Another mirror 10 irradiation surface 20 Diffuse radiation beam 21 Of which main beam 21a Light mixing means 30 Of which side surface 30a Of which side surface 30b carrier 31 Cross sectional area 32 lens system 35 Lens (downstream of the light-mixing agent) 38 Spatial light modulator 39 Mirror (ring-shaped) 40 Of which inner edge 40a Of which mirror surface 40b aperture 41 Small half-axle 42 Big half-axle 43

Claims (26)

Illumination unit (1) for emitting illumination light, having a pump radiation source (2) for emitting a pump radiation, a phosphor element (3) for the at least partial conversion of the pump radiation into a conversion light which at least partially forms the illumination light, and a mirror (9, 40), the phosphor element (3) being operated in reflection, the irradiation surface (20) onto which the pump radiation in the form of a pump radiation beam (4) falls, so at the same time is a radiation surface, and wherein the mirror (9,40) in a reflection beam (21), which by reflection of the pump radiation beam (4) on the Einstrahlfläche (20) results, is arranged such that at the Einstrahlfläche (20) reflected, in the reflection beam (21) from the Einstrahlfläche (20) led away pump radiation to the mirror (9,40) at least partially back to the Einstrahlfläche ( 20) is reflected. Lighting unit after Claim 1 with a light mixing agent (30), which is arranged between the phosphor element (3) and the mirror (9,40) such that both in the reflection beam (21) from the Einstrahlfläche (20) guided away the pump radiation as well as on the Mirror (9,40) at least partially back reflected pump radiation passes through the light mixing means (30). Lighting unit (1) after Claim 2 in which the light mixing means (30) is arranged such that the pump radiation guided in the pump radiation beam bundle (4) onto the irradiation surface (20) of the phosphor element (3) passes through the light mixing means (30). Lighting unit (1) after Claim 2 or 3 in which the light mixing agent (30) is a microlens array. Lighting unit (1) according to one of the preceding claims, in which a main propagation direction with which the pumping radiation guided in the reflection beam (21) away from the irradiation surface (20) on an incident surface of the mirror (9,40), substantially perpendicular to the incidence surface stands. Illumination unit (1) according to one of the preceding claims, in which a back-reflection beam in which the pump radiation reflected at the mirror (9, 40) at least partially back to the irradiation surface (20) propagates to the irradiation surface (20) Reflection radiation beam (21) is substantially congruent. Lighting unit (1) according to one of the preceding claims, in which the mirror (9, 40) is also arranged in a conversion light beam (7) in which the conversion light is dissipated at the emitting surface of the phosphor element (3), the mirror (9,40) only partially fills the conversion light beam (7). Lighting unit (1) after Claim 7 in which the mirror (9, 40) is displaceably mounted such that when the mirror (9, 40) is displaced, a portion to which the mirror (9, 40) fills the conversion light beam (7) is variable. Lighting unit (1) according to one of the preceding claims, wherein the mirror is wavelength-dependent reflective, namely in each case at least predominantly reflective for the pump radiation, for the conversion light, however, is transmissive. Lighting unit (1) after Claim 9 in which at a rear side of the mirror (9, 40) which opposes a front side of the mirror onto which the pumping radiation reflected off the irradiation surface (20) and reflected by the irradiation surface (20) in the reflection beam (21) strikes is disposed, an optical sensor for detecting the at least partially transmitted by the mirror (9,40) conversion light. Lighting unit (1) according to one of the preceding claims, in which the pumping radiation incident on the radiation surface (20) in the pump radiation beam (4) is substantially p-polarized and the mirror (9, 40) has a polarization-dependent reflectivity which is greater for p-polarized pump radiation than for s-polarized pump radiation. Lighting unit (1) according to one of Claims 1 to 8th in which the mirror (9, 40) has a metallic reflective finish. Lighting unit (1) according to one of the preceding claims, wherein in the pump radiation beam (4) of the radiation surface (20) upstream of a beam compression optics (5) is arranged, with which a cross section of the pump radiation beam (4) is reduced. Lighting unit (1) according to one of the preceding claims, comprising a further mirror (10), via which the pump radiation guided in the pump radiation beam (4) is guided onto the phosphor element (3), the further mirror (10) being in a conversion light. Beam bundle (7), in which the conversion light is dissipated at the emission surface, is arranged, wherein the further mirror (10) only partially fills the conversion light beam (7). Lighting unit (1) according to one of the preceding claims, in which the mirror (40) is also arranged in a conversion light beam (7), in which the conversion light is dissipated at the emission surface of the phosphor element (3) and thereby annularly around a Main beam (7a) of the conversion light beam (7) extends at least partially circumferentially. Lighting unit (1) after the Claims 14 and 15 in which the annular mirror (40) is arranged downstream of the further mirror (10) with respect to a conversion light propagation away from the emission surface of the phosphor element (3). Lighting unit (1) after Claim 15 or 16 in which the annular mirror (40) extends completely circumferentially about the main beam (7a) of the conversion light beam (7), thus forms a closed ring shape. Lighting unit (1) according to one of Claims 15 to 17 in which in the conversion light beam (7) guided and on the annular mirror (7) falling conversion light at least partially back to the emission surface of the phosphor element (3) is guided. Lighting unit (1) according to one of Claims 15 to 18 in which the annular mirror (40) limits the conversion light beam (7) as a diaphragm. Lighting unit (1) according to one of Claims 15 to 19 in which a vertical projection of the annular mirror (40) into a cross-sectional area (32) of the conversion light beam (7), which cross-sectional area (32) is perpendicular to the main beam (7a) of the conversion beam (7), at the cross-sectional area has an area share of at least 20%. Lighting unit (1) according to one of Claims 15 to 20 in which an inner edge of the annular mirror (40) facing the main beam (7a) of the conversion light beam (7) describes an elliptical shape. Lighting unit (1) after Claim 21 in which, in the case of an ellipse on which the elliptic shape is based, a ratio of the minor semiaxis (42) to the large semiaxis (43) is at least 4: 9 and at most 7: 9. Lighting unit (1) according to one of the preceding claims, in which the conversion light beam (7) is incident on a surface light modulator (39), in particular a micromirror array. Lighting unit (1) after Claim 23 combined with Claim 21 or 22 in which an active area of the area light modulator (39) has a rectangular shape with an aspect ratio corresponding to a half-axis ratio of the ellipse underlying the elliptical shape. Use of a lighting unit (1) according to one of the preceding claims for lighting, in particular for vehicle lighting, in particular in a headlight. Use after Claim 25 a lighting unit (1) according to Claim 8 in which the mirror (9, 40) is displaced to change a spectral composition of the illumination light.

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