DE102016212086B4 - LIGHTING DEVICE WITH A LIGHT SOURCE FOR EMISSION OF ILLUMINATION LIGHT - Google Patents

Abstract

Lighting device with
a light source (2) for the emission of an illumination light (23),
a micromirror array with a multitude of matrix-arranged micromirror actuators (1) and an illumination optic (6),
wherein the light source (2) and the micromirror array are arranged relative to each other such that, during operation, a supply beam (3) containing the illumination light (23) is directed from the light source (2) onto the micromirror actuators (1) of the micromirror array and reflected off them, with the reflection in the time integral
- a single beam of light (8) is reflected from the micromirror actuators (1) in a respective tilting position beyond the lighting optics (6) to a lighting application and
- an outgoing beam (9) is reflected from the micromirror actuators (1) in a respective tilted position next to the illumination optics (6), furthermore with a recycling mirror (15) onto which at least a part of the outgoing beam (9) falls in such a way that a part of the illumination light contained in the outgoing beam (9) is reflected at least partially back to the light source (2) by the recycling mirror (15),
wherein the reflection behavior of the recycling mirror (15) is adjustable.

Description

Technical field

The present invention relates to a lighting device comprising a light source for emitting illumination light, a micromirror array and illumination optics.

State of the art

A micromirror array consists of a large number of micromirrors arranged in a matrix, which can be independently switched and thus tilted. In projection applications, such micromirror arrays are used as image transmitters. Each micromirror actuator corresponds to a pixel, whereby, depending on its tilt position, the light of a specific color (e.g., red, green, and blue) falling on it at a given time is either transmitted for image formation or not.

Various approaches are known from the state of the art to reuse this non-transmitted light (light recycling) in order to increase efficiency.

The US 2008/0 246 705 A1 It reveals a display system in which the "OFF-state light" of a spatial light modulator is captured and routed back to the modulator's pixels for recycling. DE 10 2016 200 586 A1 Describes a lighting device for a vehicle in which light not required for projection is fed back into the original luminous flux. CN 1 02 705 767 A The figure shows a headlight arrangement in which light reflected to the side by a micromirror element is focused and fed back to a first light guide via a second light guide for reuse within the system. US 2002/0 149 852 A1 It describes a projection system with a DMD in which "off-state light" is recycled and fed back into the lamp. Furthermore, a system with two color wheels for improving recycling is shown. US 2009/0 009 730 A1 It reveals a projection system in which "off"-pixel light is captured and recycled by directing it back to the light source via a light integrator. WO 2005/074 267 A1 This shows a projection system with light recycling, where light reflected from a light valve is reflected back into the system's light path to increase the image brightness. And the US 2015/0 377 446 A1 The document reveals an illumination system with a DMD and laser-modulated adaptive beam shaping. This system uses a multitude of laser light sources that shine onto a phosphor, the light from which is then directed onto the DMD.

Description of the invention

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

According to the invention, this problem is solved by a lighting device having the features of claim 1.

• - ein Ein-Strahlenbündel von den Mikrospiegelaktoren in einer jeweiligen Ein-Kippstellung über die Beleuchtungsoptik zu einer Beleuchtungsanwendung hinaus reflektiert wird und
• - ein Aus-Strahlenbündel von den Mikrospiegelaktoren in einer jeweiligen Aus-Kippstellung neben die Beleuchtungsoptik reflektiert wird,

ferner mit einem Recycling-Spiegel, auf welchen zumindest ein Teil des Aus-Strahlenbündels derart fällt, dass ein in dem Aus-Strahlenbündel enthaltene Teil des Beleuchtungslichts an dem Recycling-Spiegel zumindest anteilig zurück zu der Lichtquelle reflektiert wird,
wobei ein Reflexionsverhalten des Recycling-Spiegels einstellbar ist.A lighting device is proposed comprising a light source for emitting illumination light, a micromirror array with a plurality of matrix-arranged micromirror actuators, and illumination optics, wherein the light source and the micromirror array are arranged relative to each other such that, during operation, a beam of light from the light source is directed onto the micromirror actuators of the micromirror array and reflected by them, with the reflection occurring in the time integral

• - a single beam of light from the micromirror actuators in a respective tilting position is reflected beyond the lighting optics to a lighting application and
• - an out-ray beam is reflected from the micromirror actuators in a respective tilted position next to the lighting optics,

furthermore, with a recycling mirror onto which at least part of the emitted beam falls in such a way that a part of the illumination contained in the emitted beam is reflected at least partially back to the light source by the recycling mirror,
where the reflection behavior of the recycled mirror is adjustable.

Preferred embodiments are found in the dependent claims and the entire disclosure, whereby the presentation does not always differentiate in detail between apparatus and method or use aspects; in any case, the disclosure is to be read implicitly with regard to all claim categories.

The lighting device according to the invention thus comprises a light source and a micromirror array (hereinafter also referred to as "array"), wherein the supply beam containing the illumination light falls from the light source onto the array. The illumination light is reflected at the micromirror actuators of the array (hereinafter also referred to as "actuators"), i.e., each micromirror actuator reflects a partial beam. Depending on the tilt position of the respective micromirror actuator, the respective partial beam is reflected via the illumination optics to the illumination application (tilt position) or next to the illumination optics (tilt position). In the latter case, it is therefore not supplied to the lighting application. The tilting position of the actuators allows for targeted adjustment of the light distribution in the far field (however, a particular tilting position does not have to be held permanently; for example, oscillating back-and-forth tilting is also possible, e.g., to implement dimming states; see below for details). One possible application is adaptive road lighting with a vehicle headlight; see also below for details.

The sum of all partial beams reflected by the actuators in their tilted positions constitutes the "in beam"; the sum of all partial beams reflected by the actuators in their respective tilted positions constitutes the "out beam." The in beam and the out beam are each derived from the time integral because typically not all actuators are in the same tilted position simultaneously, and the actuators are generally operated in oscillation mode. A time integral can encompass a duration in the microsecond range, millisecond range, second range, minute range, and/or longer. In projection applications (video projection, etc.), micromirror arrays are used as image sources, as described above. The out beam is then "absorbed" in a beam dump.

In the lighting device according to the invention, at least a portion of the illumination light contained in the emitted beam (hereinafter also referred to simply as "light") is preferably directed back to the light source. This is advantageous insofar as it can then, at least partially, reach the array again and thus ultimately be used for illumination purposes (this portion of the illumination light is "recycled," hereinafter also referred to as "recycled illumination light"). Preferably, the recycled illumination light reaches the array via the same path as the originally emitted illumination light, i.e., in the feed beam. As explained in detail below, the illumination light returned to the light source preferably travels back in the opposite direction, thus requiring a reversal of direction for recycling. This can be particularly well achieved in the case of a light source with a pump-excited phosphor element, as described in detail below, because in this element the illumination light is scattered or absorbed and re-emitted, and with this scattering undergoes a partial reversal of direction (back towards the array).

In general, such recycling with reversal of direction can also be possible, for example, in the case of a halogen or gas discharge lamp as the light source; the returned illumination light can be reflected, for instance, by a reflector of the lamp and thus brought into the incoming beam and recycled. Furthermore, absorption is also possible here, or the light does not necessarily have to be scattered only (e.g., in a halogen lamp, the filament can be heated by reflected IR light, and this power then no longer needs to be supplied electrically). Moreover, the illumination light can also be returned to the light source in such a way that it already arrives there with a directional component that coincides with a main emission direction of the illumination light originally directed away from the light source.

The illumination light can generally be guided back to the light source via a light guide, such as an optical fiber. This allows for relatively free selection of the directional component of the illumination light at the light source (through appropriate orientation of the light guide exit, or through additional optical elements such as mirrors and/or dichroic elements and/or lenses and/or further light guides). The light guide can also be associated with a wavelength-dependent mirror, which, for example, in the case of a light source with a fluorescent element, can be preferably transmissive for the pump radiation and reflective for the conversion light, so that only the pump radiation is guided back to the fluorescent element.

The micromirror array is configured with lighting optics such that the illumination light, guided through the optics by different micromirror actuators in a tilted position, is directed in different spatial directions. The light distribution in the spatial plane of the array is thus translated into a light distribution in the angular space of the far field. By selectively switching a particular actuator on or off, a specific spatial direction or angular area can be selectively illuminated, or not illuminated.

From a light cone that is maximally accessible downstream of the lighting optics, specific solid angle areas can be selectively added to and removed, which can be used, for example, for adaptive road illumination. A vehicle ahead or approaching, detected by, for example, a camera system in a motor vehicle, can thus be selectively excluded from the light cone by switching off the respective micromirror actuators (moving them into a corresponding tilting position). This is intended to illustrate an advantageous and, in this respect, also preferred field of application of the invention. but not limit it to its generality.

The illumination optics can generally also include a reflector; a purely refractive illumination optics is preferred. A non-imaging illumination optics is also generally conceivable, but an imaging optics is preferred. The illumination optics can, for example, include a lens, preferably a converging lens, which can also be constructed as a lens system consisting of several individual lenses (arranged sequentially with respect to the transmission). An arrangement such that the illumination optics image the micromirror array, i.e., the actuators, to infinity is preferred.

The "micromirror array" (also known as a digital micromirror device, DMD) can, for example, comprise at least 10, 100, 500, 1,000, 5,000, 10,000, or 30,000 micromirror actuators and (independently thereof) no more than, for example, 1 × ^10⁸ , 1 × ^10⁷ , or 1 × ^10⁶ micromirror actuators (in increasing order of preference). The micromirror actuators are preferably part of the same semiconductor component (chip). They are not necessarily completely independently switchable, but can, for example, be grouped together on the chip itself. Thus, for example, several adjacent micromirror actuators can jointly supply a solid angle range, or not, i.e., all be switched on or off. This also applies to certain operating modes, such as... For example, high beam, low beam, daytime running lights, etc., it is also possible to group them together in an original way.

In a preferred embodiment, a recycling mirror is provided, by which the illumination light directed alongside the lighting optics is at least partially reflected back to the light source. The recycling mirror can generally have a diffusely or specularly diffusely reflecting surface; preferably, it is specularly reflective. Preferably, the reflective surface can be curved, particularly preferably a concavely curved surface; for example, a spherical curvature is also possible, preferably an aspherical, ellipsoidal, or even free-form shape, in each case at least partially.

In a preferred embodiment, the illumination light reflected by the recycled mirror is guided back to the light source via the micromirror array. While a separate path is generally conceivable, for example via an additional mirror next to the array, the light is preferably guided back and forth along the same path (from the light source to the recycled mirror and back). This can be advantageous, for example, because the same optical components are used, meaning, for instance, that no additional mirror next to the array is necessary. This can offer cost advantages and also help increase the integration depth, as well as being of interest with regard to installation space.

The inventors have determined that while guiding illumination light across the array may potentially be disadvantageous in the aforementioned projection applications, as it increases the likelihood of unwanted reflections being introduced into the single-beam beam, such reflections can occur not only at the actuators themselves but also, and especially, at mounting brackets, the chip metallization, or the surface in general. However, in the relevant headlight applications, particularly in the automotive sector, the aforementioned efficiency advantage outweighs any potentially slightly reduced contrast.

In a preferred embodiment, a recycling optic is arranged between the array and the recycling mirror. This optic can, for example, map a reflective surface of the recycling mirror onto the array or simply focus the outgoing beam, potentially allowing for a smaller recycling mirror. A 1:1 recycling process may be preferred, meaning a 1:1 mapping of the array (or a specific micromirror) back onto the array (or the respective micromirror) via the recycling mirror. However, it may also be preferable to focus on a specific area(s). For example, the outer areas of the array may be darker from the perspective of the lighting application, meaning the actuators are more frequently switched off. To effectively recycle this light, it is ideally reflected back to the center of the light source (not necessarily to the center of the array).

A converging lens is preferred as the recycling optic, which can, for example, also be constructed as a lens system consisting of several individual lenses (arranged sequentially with respect to the transmission). Preferably, all the illumination light directed from the array to the recycling mirror and back passes through the recycling optic, thus passing through it twice during a single recycling process. The recycling optic is preferably anti-reflective. In general, however, a separate recycling optic is not mandatory, and light shaping can also be achieved, for example, with a concave mirror as the recycling mirror, which can therefore be used as an alternative to, or in combination with, a recycling optic. In particular, if the array can be considered approximately point-like, a spherical concave mirror is sufficient; however, a freeform mirror can also be used.

A preferred embodiment relates to a recycled mirror whose reflection behavior is adjustable. "Adjustable" in this context can mean, for example, that the spatial distribution of the reflection is variable and/or the spectral composition of the reflected illumination is variable, perhaps via a wavelength-selective variable reflectance. The adjustability can also consist of an overall reflectance that varies across all wavelengths. Various implementation possibilities are discussed in detail below; generally, one approach is to provide a recycled mirror with varying reflection properties across its entire reflective surface. Depending on requirements, one or another area of the total reflective surface can then be used (preferably by repositioning the mirror).

The adjustable recycling mirror also allows the properties of the illuminating light that is ultimately directed through the lighting optics to the lighting application (taking the recycled light into account) to be influenced, either by targeted modification or by keeping it constant (through compensation). This can particularly affect the spectral properties, such as the color coordinates. Here, recycling can lead to a shift, for example, in the case of a light source with a fluorescent element, because recycling can change the ratio of pumped light to conversion light.

For example, in a fluorescent lamp operating in partial conversion mode, white illumination can be achieved by a mixture of partially unconverted pump radiation (blue light) and yellow conversion light, whereby recycling can shift the ratio in favor of the latter (the pump radiation still contained in the recycled illumination light is at least partially converted during recycling, which changes the ratio). The adjustable recycling mirror should therefore be viewed particularly in this context.

In a preferred embodiment, the adjustable reflection behavior is implemented with a reflective surface that is at least partially hinged. For example, the recycled mirror could also be a micromirror array, regarding whose possible configuration reference is expressly made to the preceding disclosure. However, macroscopic mirror elements are also conceivable in principle (which, for example, are not part of a common chip), each forming a portion of the reflective surface and switchable/hingable such that in one switching/hinging state the illumination light is directed from a respective mirror element back to the light source, and in another switching/hinging state it is not. Further switching/hinging states are also possible, which would allow, for example, the location to which the light is reflected back to be varied. The same functionality could of course also be achieved with a micromirror array as a recycling mirror, tending towards a finer spatial resolution (an array as a recycling mirror would preferably be arranged very close to the actual array or realized in conjunction with an imaging of the actual array onto the recycling mirror).

Generally, "at least partially foldable" means that a given reflective surface area can be pivoted or tilted around at least one axis of rotation. With a suitable design of the recycling mirror, different folding patterns can then be set as needed, for example, depending on the respective switching states of the micromirror array.

In a preferred embodiment, the recycled mirror is mounted so that it can be moved relative to the emitted beam, and its reflection behavior can be adjusted by moving it. Generally, this could also be combined with a partially hinged reflective surface; preferably, exactly one of the two alternatives is implemented (also for reasons of complexity). With the "movable" mounting, it is not necessary to change the overall position of the recycled mirror; for example, a rotatable mounting is also possible (comparable to a filter wheel), whereby the rotation allows switching between the different positions. Likewise, a sliding mounting is also possible, preferably with a sliding direction that is oblique, and particularly preferably perpendicular, to a main direction in which the illumination light strikes the recycled mirror. Alternatively, in general, variation could also be achieved not (only) by moving the recycled mirror, but alternatively/additionally also by tilting and/or rotating and/or sliding a recycled optic.

In general, within the framework of this disclosure, a "principal direction" of a given beam of rays (or part thereof) is determined as the mean of all direction vectors along which the radiation or light propagates in the given beam of rays (or part thereof), whereby in this averaging process each direction vector is weighted with its corresponding radiance.

A linearly movable recycled mirror is preferred, driven, for example, by a linear motor/actuator. As an alternative to inclined/vertical movement, a generally suitable alternative would be... I also believe that a displacement along the main direction is conceivable; in combination with convergent/divergent illumination hitting the recycling mirror, the illuminated area can be varied, which, combined with different reflection properties across the reflective surface, results in a changed reflection behavior.

In a preferred embodiment, a movable filter is provided, and the spectral properties of the illumination light reflected beyond the lighting application can be adjusted by moving the filter. This adjustability does not necessarily have to mean a change, but can also consist of keeping the properties constant; see the preceding explanations. The filter can, for example, be arranged between the array and the recycling mirror, or, in a solution where the recycled light is not returned via the array, between the array and the light source (ultimately, the arrangement also depends on the available installation space; ideally, the power density at the filter position should not be too high).

Preferably, the filter is movable relative to a beam of light returning to the light source, for example, by being rotatable and/or slidable. Reference is expressly made to the options mentioned regarding the mounting of the recycled mirror, which are also possible for mounting the filter (whereby the "main direction" of the returned light passing through the filter is taken into account). The filter can generally be an interference or absorption filter, e.g., a gray filter or neutral density filter with a filter strength that changes across the filter; however, wavelength-selective filtering is also possible, for example, with a dichroic filter. Thus, for example, the yellow component could be selectively reduced to compensate for the mixing ratio problem described above.

In a preferred embodiment, the light source comprises a pump radiation unit and a phosphor element, which is irradiated with the pump radiation during operation and subsequently emits conversion light. The conversion is preferably a down-conversion, meaning the conversion light has a longer wavelength than the pump radiation; the conversion light has at least a predominant component in the visible spectral range, preferably it lies entirely within the visible range. The conversion light can, for example, also be red or green light; yellow light is preferred.

The conversion light can constitute the illumination light on its own (full conversion); however, partial conversion is preferred, in which it forms the illumination light together with a portion of the unconverted pump radiation. The pump radiation is preferably blue light. Generally, the illumination light is preferably white light, the color coordinate of which can lie, for example, in the ECE white field according to UN-ECE Regulation 48 (e.g., current revision: ECE/324/Rev.1/Add.47/Reg.No.48/Rev.12) in a CIE standard colorimetric diagram (1931).

In this case, a light source with a fluorescent element can be particularly advantageous because the illumination light returned to the light source can be scattered by or within the fluorescent element and thus at least partially redirected to the array. This offers advantages in terms of efficiency.

Although in the preferred light source with a phosphor element the phosphor element can generally be positioned directly adjacent to an exit surface of the pump radiation unit (for example, in the case of an LED with an integrated phosphor element), the pump radiation unit and the phosphor element are preferably spaced apart. The pump radiation then passes through a fluid volume, preferably a gas volume, particularly preferably air, upstream of an irradiation surface of the phosphor element. With such a remote phosphor arrangement (also referred to as laser-activated remote phosphor, LARP), light sources with high luminance can be realized, for example. Laser-activated remote phosphor light sources can be operated in transmissive and/or reflective mode. In general, such a setup is also conceivable with, for example, an LED, halogen lamp, or gas discharge lamp as the pump radiation source; a laser source, which can be composed of one or more individual laser sources, is preferred. A laser diode is preferred as the individual laser source, for example, also because of the switching times it allows (see below for details).

In a preferred embodiment, a feed optic is associated with the emitting surface of the phosphor element, through which the feed beam of light is directed from the phosphor element to the array. Preferably, the feed optic projects the emitting surface of the phosphor element, from which the illumination light is emitted, onto the micromirror array.

In a preferred embodiment, a mirror is provided on a side surface opposite the emissive surface, i.e., the rear surface, and optionally also on one or more of the adjacent side surfaces of the fluorescent element. This can, for example, be particularly advantageous in the present case. This offers advantages, as the recirculated light enters the fluorescent element at its emitting surface, is reflected by the mirror, and can thus be directed back to the array. Compared to light recycling based solely on scattering processes (see above), this ideally increases the proportion of recycled light. In a reflecting fluorescent element, where the incident and emitting surfaces coincide, the mirror can, for example, be a solid metallic mirror.

Even independently of mirroring the side surface of the phosphor element opposite the emitting surface, those side surfaces of the phosphor element that lie outside with respect to directions perpendicular to the direction of illumination can generally also be mirrored. This can further improve efficiency. In a preferred embodiment, the phosphor element is operated in transmission mode, meaning the incident and emitting surfaces are opposite each other, with the mirror arranged on the incident surface and also being transmissive depending on the wavelength. The wavelength-dependent mirror does not necessarily have to cover the entire side surface; for example, it could also be provided only in a portion of the incident surface, with the remaining side surface being fully mirrored. Preferably, it covers the entire incident surface. Regardless of the specifics, the wavelength-dependent mirror is then transmissive for the pump radiation and reflective for the conversion light. A corresponding dichroic layer system can preferably also be applied directly to the incident surface, for example, as a coating.

In a preferred embodiment, the lighting device is configured to vary the output power of the pump radiation unit depending on the proportion of the illumination light reflected back to the phosphor element. The greater the reflected proportion, the more the output power can be reduced, thus contributing to an energy-efficient lighting device. In the simplest case, such an adjustment of the output power can be achieved using one or more threshold values, i.e., in steps, or it can be continuous.

The aforementioned semiconductor sources, namely a laser diode or an LED, can also be advantageous in that relatively rapid changes are possible on the timescale of the micromirror movements, allowing even comparatively small changes (changes in the tilt position of a few actuators) to be tracked. However, particularly with relatively slow changes, such as those involving fundamentally different operating modes (e.g., city driving lights versus high beams), a halogen or gas discharge lamp can also be used as a pump radiation unit for appropriate adjustment.

When the lighting device is generally described as being "set up," this means, for example, that during operation the pump radiation/illumination light propagates accordingly and/or the micromirror array is appropriately wired or illuminated. Regarding beam guidance, the individual components are arranged relative to each other in such a way that the pump radiation and conversion/illumination light propagate accordingly. Preferably, the lighting device includes a control unit that controls the wiring of the micromirror actuators (switching them on/off) and/or controls the light source accordingly.

In general, pulsed operation may be preferred for the pump radiation unit or its individual sources (especially laser diodes and/or LEDs). The output power can then be adjusted by amplitude and/or pulse-width modulation; the latter is preferred.

Regarding the micromirror array, an operation such that the actuators are repeatedly flipped from one tilt position (corresponding to the actual switching state) to the other of the two maximum possible tilt positions at a flip frequency that is many times greater than the actual switching frequency (and then usually immediately flipped back to the actual tilt position) can be preferred. Such an intermittent operation between two tilt positions can offer advantages over a static circuit, for example, with regard to the service life of the actuators.

The actuators of the micromirror array can be operated at very high flip frequencies. These flip frequencies can be, for example, at least 100 Hz, or even at least 500 or 1,000 Hz; possible upper limits are, for example, 1 MHz, 100 kHz, or 10 kHz. In conjunction with intelligent control, any desired brightness can be set individually for each pixel, since the gray value or dimming is determined by the ratio, averaged over a certain period, of the time the actuator is in the on state to the time it is in the off state. Thus, any desired gray value can be set on the micromirror array, depending on location and time, in order to modify the light distribution spatially and temporally as desired. Dimming This allows for smoother transitions when changing between different light distributions, e.g., when switching from low beam to high beam and vice versa. Furthermore, dimming enables a smoother transition between areas of different brightness, e.g., at the light-dark boundary of the light distribution on the road.

In a preferred embodiment, the pump radiation unit comprises a first and a second, and optionally further, pump radiation sources (preferably laser diodes and/or light-emitting diodes, LEDs) that are operated such that their output powers are in a different relative ratio to each other at the first time points than at the second time points (which differ from the first). For example, the output power of one pump radiation source can be kept constant while that of the other is reduced or increased, or an opposing change in both output powers is also possible. As a result, the irradiance distribution generated by the pump radiation sources on the irradiation surface of the phosphor element is different at the first time points than at the second time points. Thus, for example, an adjustment can also be made location-dependent, depending on the recycled illumination light at the respective time points.

In general, for example, with precise knowledge of the conversion and scattering properties of the phosphor element, a profile can be stored for predefined switching patterns of the array to adjust the output power of the pump radiation unit or to adjust the irradiance distribution on the phosphor element's radiating surface, e.g., a reduced or increased radiant power of the light source used. In the preferred case of a vehicle headlight, there can be predefined switching patterns for certain operating modes (e.g., low beam, daytime running lights, city driving lights), meaning the matrix-like distribution of the actuators' on and off states is known. Particularly with a highly scattering phosphor element, which essentially eliminates spatial resolution of the recycled illuminant, a correlation of the dimming based solely on the number of deactivated actuators is also conceivable.

In a preferred embodiment, however, a sensor unit is provided that is configured to measure the radiant power and/or wavelength distribution and/or color coordinates of a portion of the illumination light. The "wavelength distribution" can, for example, refer to the measurement of an actual spectrum (transmission, absorption, and/or reflection), but it can also simply measure the distribution or ratio at specific wavelengths/"colors" (e.g., blue/yellow or RGB, etc.). Detecting a wavelength distribution or color coordinate can be particularly important in the case of partial conversion, i.e., when the illumination light results from a mixture of the converted light and the partially unconverted pump radiation. The pump radiation still contained in the illumination light returned to the phosphor element is then at least partially converted, which shifts the ratio of unconverted pump radiation to converted light in favor of the latter after recycling. For example, if a light source with two pump light sources of slightly different wavelengths is used, whose respective pump radiation can be converted differently well by the phosphor element, a change in the ratio of the output powers of the light sources can offer a degree of freedom for adjustment.

For example, in the case of blue/yellow mixing, the reconversion increases the yellow component, which may necessitate readjustment. The sensor unit is preferably coupled to a control unit that, for example, controls the pump radiation unit; a separate light source specifically for color correction is also conceivable.

In a preferred embodiment, the phosphor element is mounted in a position relative to the pump radiation unit such that the conversion properties of the phosphor element differ in a first offset position from those in a second offset position (which differs from the first). Regarding the "movable" mounting, reference is made to the preceding disclosure concerning the mounting options for the recycling mirror; the same options are also suitable for the phosphor element (the "principal direction" being that of the incident pump radiation). For example, a rotatable mounting is possible, whereby the rotation allows switching between the offset positions. A sliding mounting is also possible, whereby the direction of movement can be inclined, preferably perpendicular, to a principal direction of the pump radiation on the irradiation surface. Linear sliding, for example via a linear motor/actuator, is preferred. In general, in combination with non-collimated pump radiation (which therefore strikes convergently or divergently), displacement along the aforementioned main direction would also be conceivable, thus changing (enlarging/reducing) the irradiated area.

In a preferred embodiment, the feed, inlet, and outlet beams fill a The total angular range accessible by the array is covered to at least 80%, more preferably at least 90% or 95%, and most preferably completely. This means that the transient flat state of the actuators is also utilized. This is a transition state between the two maximum tilt positions of a given actuator, which is the state the actuator assumes when not deflected or when it is not in operation. The mirror surfaces of the actuators are then at least approximately parallel to the chip plane. The transient flat state is therefore not used, for example, in the projection applications mentioned at the beginning, because unwanted reflections from the rest of the chip surface (connecting bridges, metallization, etc.) can occur in the associated solid angle range.

In this case, utilizing the transition region allows the angular range per beam to be increased, possibly at the cost of slightly reduced contrast. With a larger angular range, for example, more light can be guided across the array, or a more widely distributed light (from a light source with lower luminance) can be used. Whenever reference is made to an "angular range" per beam, or in this case to a "total angular range," this refers to a view in a plane perpendicular to the mirror surface of a respective actuator, in which the tilt of the actuator and the extent of the beams are at their maximum.

In a preferred embodiment, the micromirror actuators each have a possible deflection angle of at least 10°, preferably at least 12°, and particularly preferably at least 15° (possible upper limits may be, for example, 30°, 25°, or 20°). This deflection angle is taken between the 0° axis and a maximum tilt position; preferably, it is the same on both sides of the 0° axis, thus being, for example, +/- 10°, +/- 12°, or +/- 15°.

The invention also relates to a motor vehicle headlight and/or a motor vehicle signal light, in particular a car headlight and/or a front headlight with a lighting device disclosed herein.

The invention also relates to the use of a lighting device disclosed herein, or a vehicle headlight with such a device for illumination, in particular for adaptive road illumination and/or for projecting (additional) information onto the road or the vehicle's surroundings. Reference is expressly made to the preceding information, which is also intended to disclose a corresponding use or the vehicle headlight. In general, however, the lighting device could also be used, for example, in an effect light headlight, or more generally in the entertainment sector or in the field of entertainment lighting.

In the application category relating to automotive lighting, a lighting device disclosed herein can be of interest even independently of the fact that a portion of the illumination contained in the outgoing beam is returned to the light source. The illumination contained in the outgoing beam can then be used, at least partially, for a different lighting function than the light contained in the incoming beam; the latter can, for example, be used to illuminate the road (headlights), while the former can be used, for example, for signal lights or even in the interior. This light used for other purposes can, for example, be guided to the respective light of the other function via a light guide.

Brief description of the drawings

The invention will be explained in more detail below using exemplary embodiments, whereby the individual features within the scope of the dependent claims may also be essential to the invention in other combinations and no distinction will be made in detail between the claim categories.

• 1 am Beispiel einer Projektionsanwendung ein nicht erfindungsgemäß genutztes Mikrospiegel-Array, bei dem zeitweilig nicht benötigtes Licht in einem Absorber vernichtet wird;
• 2 eine erfindungsgemäße Beleuchtungsvorrichtung, bei der zeitweilig nicht genutztes Beleuchtungslicht recycelt wird.

In detail, it shows

• 1 Using the example of a projection application, a micromirror array not used according to the invention, in which temporarily unneeded light is destroyed in an absorber;
• 2 a lighting device according to the invention in which temporarily unused lighting light is recycled.

Preferred embodiment of the invention

1 Figure 1 illustrates a micromirror array not operated according to the invention, using the example of a projection application. A micromirror actuator 1 is shown. A light source 2 is assigned to the micromirror array such that a feed beam 3 with illumination light emitted from the light source 2 falls onto the micromirror array.

For illustrative purposes, only the one micromirror actuator 1 of the array is shown (onto which only a partial beam actually falls), but the supplied/reflected light is illustrated by the “beams”, i.e., in relation to the array as a whole.

The micromirror actuator 1 is shown in its neutral state. It can be tilted back and forth between two maximum tilt positions, indicated by dashed lines. The neutral state is called the transient flat state, and in this case, one maximum tilt position corresponds to the tilt-in position and the other to the tilt-out position. In the tilt-out position, the micromirror actuator 1 reflects the illumination light incident on its mirror surface 4 onto an absorber 5; the illumination light is therefore not used further. In the tilt-in position, however, the illumination light is guided through an illumination optic 6 (a lens system) and thus used for imaging in the case of projection applications.

1 Figure 1 further illustrates how a total angular range of 96°, accessible by the tiltability of the micromirror actuators 1 by +/- 12°, can be divided. Within this total angular range, in addition to the feed beam 3, the input beam 8 (to the illumination optics 6), the output beam 9 (into the absorber 5), and the transient beam 10 are shown. The input beam 8 and the output beam 9 are spaced apart from each other by the transient beam 10 to minimize unintended reflections from the input beam 8 and thus ensure good contrast. These reflections can occur more frequently in the transient flat state because the mirror surfaces of the actuators are parallel to the chip plane, allowing reflections from the rest of the chip surface (connecting bridges, metallization, etc.) to be introduced.

2 shows a lighting device according to the invention, which differs from that according to 1 The first difference is that the emitted beam 9 is not guided into an absorber 5. Instead, a recycling mirror 15 is provided, at whose reflective surface 16 the illumination light contained in the emitted beam 9 at the respective times is reflected back to the micromirror array and thus via this back to the light source 2. Optionally, a recycling optic 17 (shown schematically here as a single converging lens) is arranged between the recycling mirror 15 and the micromirror array, which images the reflective surface 16 onto the array.

The recycled mirror 15 can be planar when using recycled optics, but depending on the optical design, it can also have a spherical or freeform reflection surface 16. A portion of the light returned via actuators that are in the "on" state could also strike outside the supply beam 3 and thus next to the light source 2, which could impair the image quality; this could then be prevented by an optional absorber (e.g., a riffle plate) at this point.

Instead of dissipating the unused illumination light in an absorber, the lighting device according to the invention directs at least some of it back to the light source 2. As will become clear from the detailed description of the light source 2 below, it can then be directed, at least partially, back towards the micromirror array and thus ultimately used for illumination purposes. This increases efficiency, which can be of particular interest in the automotive sector. The light source 2 will now be explained in more detail, followed by a description of the array's functionality in the application area of "vehicle headlights".

The light source 2 of the lighting device according to the invention comprises a pump radiation unit 20, in this case an array of several laser diodes (not shown in detail). The pump radiation 21 emitted by it, in this case blue laser light, strikes a phosphor element 22, which in this case comprises yttrium aluminum garnet (YAG:Ce) as the phosphor. Upon excitation with the pump radiation 21, this emits a conversion light, which together with the partially unconverted pump radiation 21 forms an illumination light 23.

The illumination light 23 is directed at an emission surface 25 opposite the emission surface 24 of the phosphor element 22 and reaches the micromirror array via a feed optic 26. At specific times, illumination light is reflected from the recycling mirror 15 back across the array to the light source 2, striking the phosphor element 22 through the feed optic 26. From there, it is partially redirected (recycled) towards the micromirror array due to scattering and absorption-emission processes. Furthermore, a mirror 27, namely a dichroic coating, is arranged on the emission surface 24 of the phosphor element 22. This coating is transmissive to the pump radiation 21 but reflects the conversion light. This further increases the proportion of the total recycled light.

The illumination optics 6 project the micromirror array to infinity; thus, from each actuator 1, a respective partial beam of light is collimated and directed downstream of the illumination optics 6 in a specific spatial direction. The illumination optics 6 translates the matrix-like arrangement of the actuators 1 (spatial distribution) into a solid angular distribution, allowing illumination to be directed precisely to specific spatial directions (incoming-outgoing). Tilt position of the respective actuator 1) or not (off tilt position of the respective actuator 1). A preferred application is adaptive road lighting with a vehicle headlight; see also the detailed introductory description.

In the beam 9, a filter 28 can optionally be arranged between the recycling optics 17 and the recycling mirror 15. This filter allows the spectral properties of the portion of the illumination light returned to the light source 2, and thus ultimately also of the portion supplied to the lighting application, to be adjusted. For this purpose, the filter 28 can, for example, have a wavelength-dependent filter grade and/or be relocatable; see the introductory description.

At the in 2 The total angular range of the arrangement shown in the lighting device is as follows: 1 The array is subdivided into four beams 3, 8-10. Since the contrast requirements for the aforementioned automotive applications are generally not so high, the transient flat state can also be used for the actual light guidance. Therefore, the incoming beam 8 and the outgoing beam 9 can be positioned directly adjacent to each other, thus dividing the total angular range into only three beams, each with a correspondingly larger opening angle. In simpler terms, this allows more light, or light collected from a wider angular range, to be guided across the array.

REFERENCE MARK LIST

1

Micromirror actuator

2

light source

3

Feed beam

4

Mirror surface

5

absorber

6

Lighting optics

8

Beams of rays

9

Outward beams

10

Transient beam

15

Recycling mirror

16

Reflective surface

17

Recycled look

20

Pump radiation unit

21

Pump radiation

22

Fluorescent element

23

Lighting light

24

Radiation surface

25

Radiating surface

26

Feed optics

27

Mirror (ichroitic)

28

filter

Claims (13)

Lighting device comprising: a light source (2) for emitting illumination light (23), a micromirror array with a plurality of matrix-arranged micromirror actuators (1) and an illumination optic (6), the light source (2) and the micromirror array being arranged such that, during operation, a supply beam (3) containing the illumination light (23) is directed from the light source (2) onto the micromirror actuators (1) of the micromirror array and reflected by them, wherein, with the reflection in the time integral: - an incoming beam (8) is reflected from the micromirror actuators (1) in a respective tilted position beyond the illumination optic (6) to a lighting application, and - an outgoing beam (9) is reflected from the micromirror actuators (1) in a respective tilted position next to the illumination optic (6), further comprising a recycling mirror (15) onto which at least a part of the outgoing beam (9) falls in such a way that that a portion of the illumination contained in the beam (9) is reflected at least partially back to the light source (2) by the recycling mirror (15), whereby the reflection behavior of the recycling mirror (15) is adjustable. Lighting device according to Claim 1 , in which the micromirror array and the recycling mirror (15) are arranged such that the part of the illumination light reflected by the recycling mirror (15) back to the light source (2) is reflected by the recycling mirror (15) onto the micromirror array and from there to the light source (2). Lighting device according to Claim 2 with a recycling optic (17) which is preferably arranged between the recycling mirror (15) and the micromirror array such that it maps a reflective surface (16) of the recycling mirror (15) onto the micromirror array. Lighting device according to one of the preceding claims, in which a reflective surface (16) of the recycling mirror (15) is at least partially foldable and with which The reflection behavior of the recycling mirror (15) can be adjusted by flaps. Lighting device according to one of the preceding claims, in which the recycling mirror (15) is mounted so as to be displaceable relative to the emitting beam (9) that the reflection behavior of the recycling mirror (15) can be adjusted by displacing the recycling mirror (15). Lighting device according to one of the preceding claims with a filter (28) which is mounted in such a way that the spectral properties of the part of the illumination light reflected to the lighting application can be adjusted by moving the filter. Lighting device according to one of the preceding claims, in which the light source (2) has a pump radiation unit (20) for emitting pump radiation (21) and a phosphor element (22) for at least partially converting the pump radiation (21) into a conversion light, which conversion light forms at least a proportion of the illumination light (23). Lighting device according to Claim 7 , which is set up to change the output power of the pump radiation unit (20) depending on a proportion of the illumination light (23) returned to the light source (2) at respective times. Lighting device according to Claim 7 or 8 , in which the pump radiation unit (20) has a first and a second pump radiation source and is set up for operation of the pump radiation sources such that their output powers at first times are in a different relative ratio to each other than at second times, whereby at first times an irradiance distribution on a radiant surface (24) of the phosphor element (22) is different than at second times. Lighting device according to one of the preceding claims with a sensor unit configured to measure at least one of an optical power, a wavelength distribution and a color coordinate of a part of the illumination light (23). Lighting device according to one of the preceding claims, in which a respective tiltability of the micromirror actuators (1) between the tilt-in and tilt-out positions defines a maximum accessible total angular range (30) of the micromirror array, which total angular range (30) is filled jointly to at least 80% by the supply beam (3), the input beam (8) and the output beam (9). Automotive headlights with a lighting device according to one of the preceding claims. Use of a lighting device according to one of the Claims 1 until 12 or a vehicle headlight for illumination, especially for adaptive road illumination.