Method for operating a lighting device and lighting device

Abstract

Method for operating a lighting device comprising: a pump radiation source for emitting pump radiation and a phosphor wheel (1) on which a first phosphor (2a, 3a) for emitting first conversion light and a second phosphor (2b, 3b) for emitting second conversion light are arranged, wherein the first phosphor (2a, 3a) and the second phosphor (2b, 3b) are arranged spatially separated from one another on the phosphor wheel (1), wherein a first useful light based on the first conversion light and a second useful light based on the second conversion light have the same color but a different color location in the CIE standard color system, in which method the phosphor wheel (1) rotates about a rotation axis and is irradiated with the pump radiation in an irradiation area eccentric to the rotation axis in such a way that a circular track is irradiated as a result of the rotation of the phosphor wheel, wherein during a 360° rotation of the phosphor wheel (1) the first phosphor (2a, 3a) is irradiated with a first pump radiation power and the second phosphor (2b, 3b) is irradiated with a second pump radiation power which is different from the first pump radiation power, and the first pump radiation power and the second pump radiation power are greater than 0.

Description

Technical area

[0001] The present invention relates to a method for operating a lighting device with a pump radiation source and a phosphor wheel. State of the art

[0002] High-luminance light sources can be used, for example, in endoscopy or projection devices, although gas discharge lamps are currently the most widely used. Recent developments involve the combination of a high-luminance radiation source, such as a laser, with a phosphor element that converts the pump radiation emitted by it. The phosphor element is arranged at a distance from the pump radiation source. The phosphor element converts the pump radiation, for example, ultraviolet or blue, and emits conversion light of a longer wavelength.

[0003] A phosphor wheel can also be provided as the phosphor element, which rotates around a rotational axis and is irradiated with pump radiation along a circular track. Different phosphors can also be arranged consecutively on the phosphor wheel in the direction of rotation, so that the colors of the conversion light then, for example, sequentially span an RGB color gamut. The "color gamut" refers to the area spanned jointly by the colors, specifically their color locations in a color space.

[0004] DE 10 2012 209 426 A1 relates to a phosphor wheel for converting pump light to conversion light, on which a first phosphor is provided for emitting conversion light of a first color and a second phosphor is provided for emitting conversion light of a second color. The light from the first and second phosphors, which are spatially separated from each other on the phosphor wheel, has the same color tone. Depending on the requirements, either the first or the second phosphor can be selected.

[0005] DE 10 2012 211 837 A1 proposes simultaneously superimposing narrowband laser radiation of the same light color on the broadband colored light generated by phosphor conversion, with a light color corresponding to the phosphor used. This achieves a high luminous flux and high luminance for the respective light color, which is particularly required for projection applications. For example, the broadband red light generated by a red phosphor by irradiation with a blue-violet laser is simultaneously superimposed with narrowband red laser radiation (r) in an optical integrator.

[0006] The present invention is based on the technical problem of specifying a particularly advantageous method for operating a lighting device with a fluorescent wheel and a correspondingly configured lighting device. Description of the invention

[0007] According to the invention, this problem is solved by a method for operating a lighting device and a lighting device according to claims 1, 4 and 11.

[0008] Preferred embodiments can be found in the dependent claims and in the following description, whereby a distinction is not always made in detail between a representation of the method and a description of the lighting device; in any case, the disclosure is to be read implicitly with regard to all categories of claims.

[0009] The lighting device is therefore initially designed such that the first and second useful light do not differ in color. For example, they are not like R(ed) and G(reen) or G and B(lue) (or R and B), but rather have the same color but different color coordinates. Using the method according to the invention, the underlying phosphors—i.e., the first, which forms the basis of the first useful light, and the second, which forms the basis of the second useful light—are irradiated with different pump radiation powers.

[0010] The first and second pump radiation powers may differ, for example, in that the greater power may be, in this order, at least 25%, 50%, 75%, 100%, 125%, 150%, 175%, or 200% greater than the smaller power; to the extent that the pump radiation power per phosphor changes during one revolution, "pump radiation power" refers to an average value formed over the corresponding circumferential section (of the first or second phosphor).

[0011] During one revolution, the two phosphors are therefore irradiated differently, resulting in an effective color (perceived, for example, by a user) with an effective color location in the CIE standard color system (CIE 1931, throughout the disclosure) averaged over the revolution.

[0012] Regarding the "different color coordinates": In the CIE standard color system, the first useful light has a first color coordinate and the second useful light has a second, which are not identical; if the two color coordinates are in the green, they can be separated from each other by, for example, at least 0.02, 0.03, 0.04, or 0.05 in magnitude (the geometric distance is considered); possible upper limits are approximately 0.20 or 0.15, respectively.

[0013] If the two color locations are in the red, they can, for example, lie approximately on the spectral color line, i.e. be spaced from it by less than 0.07, 0.05, 0.03 or 0.01 (again in the CIE standard color system), and the first and second useful light can differ in their respective dominant wavelengths by, for example, at least 5 nm, preferably at least 10 nm, more preferably at least 15 nm.

[0014] With the proportionally different irradiation, the effective color location can now be shifted, i.e., adjusted, "between" the first and second color locations. The color (of the first and second useful light) can, for example, span an RGB color gamut with two additional colors, which can generally also be provided by one or more additional lighting devices. The area of ​​this color gamut, and thus the size of the addressable color gamut, can be adjusted using the method according to the invention.

[0015] For many phosphors, there is a correlation such that some offer advantages in terms of their color coordinates (e.g., spanning a wider color gamut), but have, for example, low conversion efficiency. Furthermore, saturation behavior is often observed at increased luminous flux, and conversion efficiency decreases further (the phosphors are less efficient at higher temperatures). Efficient phosphors, on the other hand, often have disadvantages in terms of their color coordinates.

[0016] To illustrate this specifically: the color gamut addressable with the second color location can, for example, be larger. If this is advantageous in an application, such as for displaying image content with a projection device, the first phosphor, which forms the basis of the first useful light, is irradiated to a correspondingly lesser extent than the second phosphor, so that the effective color location is shifted towards the second color location, and the color gamut is therefore correspondingly larger. If the first phosphor is then proportionally more irradiated in a different operating mode, the luminous flux increases, but the addressable color gamut is smaller because the effective color location moves closer to the first color location. Finally, in a "maximum luminous flux" operating mode, the two phosphors can also be irradiated with the same pump radiation power over a further numerous consecutive revolutions, thus allowing the maximum luminous flux to be achieved.

[0017] In the case of the "wide color gamut" operating mode, the first phosphor could theoretically no longer be irradiated at all, so that the first pump radiation power would be zero. Although the effective color coordinate would then be at the second color coordinate (the second color with a "wide color gamut"), the inventor has observed disadvantages in that with a pump radiation power repeatedly varying between 0% and 100%, the 100% value would have to be relatively large in order to achieve a desired average luminous flux. This would require a correspondingly large pump radiation source, thus requiring a relatively large technical effort for what would ultimately be a low average pump radiation. Against this background, a not fully optimized effective color coordinate is accepted in order to be able to realize an overall efficient lighting device, also in terms of manufacturing costs.

[0018] The first and second useful light have "the same color"; if the color is "green", the dominant wavelength of the first and second useful light can be, for example, at least 520 nm, preferably at least 530 nm, more preferably at least 535 nm, and (independent of the lower limits), for example, at most 570 nm, preferably at most 565 nm, more preferably at most 560 nm. If the color is "red", the dominant wavelength of the first and second useful light can be, for example, at least 590 nm, preferably at least 595 nm.

[0019] The term "fluorescent wheel" should not generally imply that it necessarily has to have a circular disk or ring-shaped geometry; it is generally a rotating body that is irradiated as a result of its rotation on a circular path. The arrangement can therefore, for example, also be a cone rotating around its axis of symmetry, in which case the incident light direction can be perpendicular to the axis of rotation and the conversion light can be discharged parallel to the axis of rotation, or vice versa.

[0020] Furthermore, it is also possible, for example, to arrange the phosphors on a cylindrical surface, preferably a circular cylindrical surface, such as the surface of a roller. However, the phosphor wheel is preferably a flat body designed for rotation about an axis of rotation extending transversely to the surface (in which the phosphors are arranged), preferably perpendicular to it.

[0021] A respective "phosphor" can also be a phosphor mixture, i.e., a mixture of several conversion materials; however, preferably, exactly one respective conversion material is provided for each phosphor. In general, in addition to the irradiation area in question, there can also be another irradiation area(s) on the phosphor wheel, i.e., one or more circular tracks can also be irradiated (e.g., for a different channel); however, exactly one irradiation area is preferred.

[0022] The phosphor wheel is constructed, for example, from a substrate different from the phosphor, such as metal or glass, to which the phosphors are applied, for example by dispensing, sprinkling, doctoring, brushing, or spraying a phosphor suspension. Due to its suitability for rotation, the substrate is preferably circular or disk-shaped, and a rotating shaft is connected to the substrate; the rotating shaft can also be connected to a circular substrate or extend through it.

[0023] Such a substrate is typically flat, meaning it has a greater extension in the surface direction than perpendicular to it, approximately at least 2, 5, 10, or 20 times larger (in the case of a non-circular geometry, based on the average of the shortest and longest extensions). The same applies to the phosphor layer provided on the substrate, so that the phosphor wheel is flat overall (apart from, for example, fastening means for a rotating shaft or the like). The phosphor wheel can be operated in transmission and / or reflection.

[0024] During a 360° rotation, the first phosphor is irradiated with a first pump radiation power and the second phosphor is irradiated with a different, second pump radiation power. This variation between the first pump radiation power and the second pump radiation power is preferably repeated over a first plurality of successive 360° rotations, for example over, increasingly preferably, at least 50, 250, 500, 750 or 1000 successive rotations in this order. Preferably, over the first plurality of rotations, the first and / or the second pump radiation power are each the same from rotation to rotation, i.e., if the first and second pump radiation powers differ from one another per rotation, the first pump radiation power in a subsequent rotation is always the same as the first pump radiation power in the previous rotation, and this also applies analogously to the second pump radiation power.

[0025] In a preferred embodiment, the first plurality of successive revolutions, i.e. the “large color gamut” operating mode, is followed by a second plurality of successive revolutions, during which the first and second phosphors are irradiated with the same pump radiation power in a “maximum luminous flux” operating mode.

[0026] [The first / second (hereinafter "respective") useful light is "based" on the respective conversion light. This means that the respective useful light is either identical to the respective conversion light or is provided by filtering the respective conversion light. In other words, the respective useful light should correspond to the respective conversion light in at least one spectral sub-range (which is not filtered out), but can also correspond to the respective conversion light across the entire spectral range, meaning the respective conversion light can also be used without filtering. The term "useful light" is not intended to imply that this light must necessarily be supplied to an application without further modification; rather, it refers to the light emitted by the lighting device, which, for example, can also have further optical components downstream of it in a projection device.

[0027] With regard to a causal relationship, the relationship between the respective phosphor, the respective conversion light, and the respective useful light can be specified in such a way that if the respective phosphor is not irradiated and thus does not emit the respective conversion light, the respective useful light is also not available (regardless of whether this is the respective conversion light itself or an unfiltered portion thereof); the respective useful light and the respective conversion light are directly proportional to one another.

[0028] Preferably, at least one of the first and second useful light is filtered conversion light. "Filtering" in this respect means that the luminous flux in a spectral range, which can extend, for example, over at least 50 nm or at least 100 nm, is reduced in any case, for example by at least 50% or 75% (in each case on average), but preferably equal to zero. A so-called edge filter, which transmits the light below a cutoff wavelength and blocks it above it (for example by reflection), or vice versa, can be particularly preferred. The filter can, for example, be provided on the phosphor wheel itself, for example applied to the respective phosphor, or can also be arranged on a separate filter wheel or generally provided downstream of the phosphor wheel (at a distance from it).

[0029] In a preferred embodiment, the first and second phosphors are the same phosphor, thus the first and second conversion light have identical spectral properties, and the different colors are then adjusted solely by filtering. In this case, only a single light can be filtered from the first and second useful light, which may be preferred, for example, if the "same color" is green.

[0030] For example, the unfiltered green phosphor may be more efficient as the first phosphor, but have a poorer color coordinate (the light from the first phosphor). In contrast, in the case of the second phosphor, the light from the green phosphor may be filtered, thus adjusting the second color to a better color coordinate. However, filtering reduces the luminous efficacy.

[0031] Furthermore, if the first and second phosphors are the same, both the first and second useful light can be filtered conversion light. For example, if the color is red, a yellow phosphor can be provided as the first and second phosphors, whose originally yellow conversion light is then filtered differently to produce the red first and red second useful light.

[0032] The dependence of luminous efficacy / color location has already been discussed. A preferred embodiment generally relates to first useful light, which is provided with a first luminous efficacy, and second useful light, which is provided with a second luminous efficacy, wherein the first luminous efficacy is, in this order, preferably at least 20%, 30%, 40%, 50%, 60%, 70%, or 80% greater than the second luminous efficacy.

[0033] The different luminous efficacy can be caused, for example, by different filtering, such as when the first useful light is not filtered at all or at least less than the second useful light. On the other hand, the luminous efficacy can also vary due to the respective phosphors themselves (i.e., when the first and second phosphors are not the same phosphor), because phosphors can differ not only in their spectral properties but also in their efficiency. "Luminous efficacy" in the context of this disclosure refers to the luminous flux of the respective useful light per pump radiation power radiated onto the respective phosphor, i.e., lumens per watt.

[0034] Reference has already been made above to the dominant wavelength of a particular useful light, which is determined by the intersection of a half-line extending from the white point and passing through the respective color location with the spectral color line. The first useful light then has a first dominant wavelength, and the second useful light has a second dominant wavelength.

[0035] If, on the one hand, “the same color” is preferably red, the second dominant wavelength is preferably greater than the first dominant wavelength, for example by at least 5 nm, preferably at least 10 nm, more preferably at least 15 nm; possible upper limits can be, for example, at most 30 nm, 25 nm or 20 nm. On the other hand, if “the same color” is green in a preferred embodiment, the second dominant wavelength is preferably smaller than the first dominant wavelength, for example by at least 5 nm, preferably at least 10 nm, more preferably at least 15 nm; possible upper limits can be, for example, at most 70 nm, 50 nm, 30 nm or 20 nm.

[0036] Typically, a smaller dominant wavelength in the green or a larger dominant wavelength in the red correlates with a larger color gamut (which is referred to as a "better color location"), but at the same time the luminous efficacy is lower, either due to a lower efficiency phosphor or due to filter losses.

[0037] As discussed at the beginning, the respective color coordinates of the first and second useful light, in a preferred embodiment, together with a third and fourth color, span an RGB color gamut. The first color coordinates then span an RGB color gamut with the third and fourth color coordinates, and the second color coordinates do the same together with the third and fourth color coordinates, with these two RGB color gamuts differing in their area in the CIE standard color system by at least 5%, preferably at least 10%, and more preferably at least 15%. Possible upper limits could be around 50% or 30%, respectively. The RGB color gamut with the second color of the "better color coordinate" would then have a correspondingly larger area (due to the greater distance of the second color coordinate from the white point).

[0038] The third and / or fourth useful light can generally also be provided separately from the fluorescent wheel with its own light source(s), such as an LED light source(s). Furthermore, it is also possible to provide multiple fluorescent wheels.

[0039] Preferably, however, the third and fourth useful light is based on the same phosphor wheel as the first and second useful light, i.e., a third and / or fourth phosphor is also provided on it. The third and / or fourth useful light is then "based" on the third and fourth phosphor in the sense described above, so the respective conversion light can be direct or filtered. Alternatively, the third or fourth useful light can also be pump radiation used without conversion, i.e., blue pump light (see below for details).

[0040] Although the RGB color gamut has been discussed so far in the context of color gamut, this can of course also be supplemented by another color, such as yellow and / or white. In other words, a fifth useful light of a fifth color (or another useful light of a further color) can also be provided—the corresponding fifth or further color coordinates can then lie either within the RGB triangle or outside it.

[0041] In the former case, the corresponding useful light can then serve, for example, to increase the luminous flux, whereas in the latter case, the color gamut is enlarged, for example, a quadrilateral (or, more generally, a higher-order polygon). Therefore, on the one hand, all specifications regarding an RGB color gamut should also be explicitly interpreted as referring to an RGBY, RGBYW, or generally higher-order RGB color gamut. On the other hand, an RGB color gamut composed exclusively of the three RGB channels may, of course, also be preferred.

[0042] In the case of an RGB color gamut, it can generally be preferred that the blue channel is guided over the phosphor wheel, but that this is not conversion light, but rather the pump radiation itself, i.e. blue pump light. The blue pump light then falls onto the phosphor wheel, whereby a transmission window, for example, can be provided in a section intended to provide the blue channel, so that the pump light passes through the phosphor wheel. The window can, for example, be a transparent section of the substrate, or a corresponding area can simply be cut out. On the other hand, it is also possible to reflect and / or scatter the pump light in the region of the blue channel, for example by providing a mirror coating or a scatterer with high remission.

[0043] A preferred embodiment relates to a phosphor wheel on which not only a first and a second phosphor, but also a second and a second phosphor are provided. One phosphor pair consisting of the first and second phosphors is provided for green (first and second) useful light, and the second phosphor pair is provided for red (first and second) useful light.

[0044] During operation, for example, either one phosphor pair or the other phosphor pair can be irradiated with different power levels during one rotation in the manner according to the invention. In other words, the effective color location can be set in the red or the effective color location in the green.

[0045] However, it is preferred that during one revolution, both the green first and the green second phosphors are irradiated with different pump radiation power, as are the red first and the red second phosphors (during the same revolution). In other words, in the case of two phosphor pairs each consisting of a first and a second phosphor, namely a "green" and a "red" phosphor pair, each phosphor pair is preferably operated in the manner according to the invention; in this respect, all of the information provided above generally regarding "first and second phosphors, conversion light, useful light, etc." is also expressly intended to be disclosed for a phosphor wheel with two phosphor pairs, each of which is operated accordingly.

[0046] As already mentioned at the beginning, the invention also relates to a lighting device comprising a pump radiation source, a phosphor wheel, and a control unit, the latter being provided for controlling the pump radiation source and configured for a method according to the invention. Although the method according to the invention, specifically the pump radiation power changing during rotation, could generally also be implemented by optical means, for example by filtering or (partially) reflecting the pump radiation from the irradiation path, the pump radiation power incident on the respective phosphor is preferably adjusted by varying the output power of the pump radiation source itself.The implementation can be simplified because no complex optical components are required; on the other hand, it is also advantageous for energy efficiency reasons if the pump radiation source only provides the output power actually required.

[0047] The pump radiation emitted by the pump radiation source falls onto the phosphor wheel in the irradiation region, and the various segments thereof, i.e., at least the first and second phosphors, are rotated as the phosphor wheel rotates through the irradiation region. Expressed in an orbital angle (relating to the rotation around the rotation axis), the irradiation region can, for example, extend over no more than 30°, preferably no more than 20°, more preferably no more than 10°.

[0048] The fluorescent wheel can generally rotate at, for example, 3600 revolutions per minute (rpm), 7200 rpm, 10800 rpm or 14400 rpm.

[0049] In general, a respective (first or second) average pump radiation power can also be achieved via pulsed pump radiation, i.e., by pulse-width modulation. However, amplitude modulation is preferred; in general, irradiation does not necessarily have to be applied across the entire respective segment; rather, the segment can also be irradiated individually, for example, only in sections (the average is what matters). Preferably, however, the pump radiation is applied across the segment of the respective phosphor (i.e., when the phosphor is moved through the irradiation area) with a constant pump radiation power, possibly excluding a decrease or increase at the beginning or end of the respective segment.

[0050] In general, the wavelength of the pump radiation can also be changed segment-by-segment (from the first to the second phosphor) during a 360° rotation, for example by using an array of laser diodes as the pump radiation source. These laser diodes differ in wavelength and are specifically switched on and off. An array of laser diodes may generally be preferred as the pump radiation source. Preferably, the wavelength of the pump radiation remains constant throughout the 360° rotation, and only the pump radiation power is changed.

[0051] Preferably, the control unit changes the amplitude of the pump radiation in a timed manner with the phosphor wheel, ensuring a specific pump radiation output for each phosphor. Generally, the control unit and the phosphor wheel can be synchronized, for example, via a zero sensor, which indicates to the control unit that a specific position has been reached with each rotation of the phosphor wheel.

[0052] As already mentioned at the beginning, the entire disclosure is expressly intended to be readable also in relation to a corresponding lighting device, wherein either the control unit is set up for a corresponding control of the pump radiation source, i.e. is not only suitable but also configured accordingly, for example provided or supplied with a corresponding data set which can, for example, contain pump radiation patterns for different effective color locations (of the useful light).

[0053] However, the remaining components of the lighting device can also be configured for a method described here, for example the phosphor wheel can be designed accordingly, for example equipped with a third or fourth phosphor.

[0054] Finally, the invention also relates to the use of a corresponding lighting device as a light source of a projection device or endoscope or for room lighting purposes or, in general terms, for industrial and / or medical applications.

[0055] In the case of a projection device, for example, its image quality can also be customized or adjusted depending on the situation by changing the ratio of the first and second pump radiation power. "Situation-dependent" can mean, for example, that, depending on the ambient brightness, the effective color coordinate is shifted closer to the first color coordinate, thus increasing the luminous efficacy when the ambient brightness is high, for example, in daylight conditions.

[0056] In otherwise low ambient light, such as in a darkened room, the effective color coordinate system can be shifted closer to the second color coordinate system with the larger color gamut. "Situation-dependent" can also or alternatively refer to the displayed content, so that, for example, high luminous flux can be selected for text content and high color saturation for image content.

[0057] In general, use of the illumination device as a light source of a projection device is preferred, particularly preferably a projection device with a DLP (Digital Light Processing), LCoS (Liquid Crystal on Silicon) or LCD (Liquid Crystal Display) imager.

[0058] In a projection device, the lighting device according to the invention can also be provided for 3D reproduction, for example, so it can reproduce two color spaces, which are then selectively filtered for each eye using appropriate glasses. Short description of the drawings

[0059] In the following, the invention is explained in more detail using an exemplary embodiment, whereby no distinction is made in detail between the claim categories and the features within the scope of the independent claims can also be essential to the invention in other combinations.

[0060] In detail: Fig. 1 a fluorescent wheel of a lighting device according to the invention in a schematic oblique view; Fig. 2 a tabular overview of the light intensity applied to the fluorescent wheel during a 360° rotation according to Fig. 1 radiated pump radiation power; Fig. 3 a CIE standard colour system to illustrate the different colours obtained with a phosphor wheel according to Fig. 1 accessible color gamut. Preferred embodiment of the invention

[0061] In Fig. 1 schematically illustrates the structure of a phosphor wheel 1 of a lighting device according to the invention. A red first phosphor 2a and a red second phosphor 2b are arranged on the phosphor wheel 1, which provide red first useful light and red second useful light. The respective color locations are determined using Fig. 3 are explained in more detail and are in Fig. 2 are listed in a table.

[0062] To summarize, the red second useful light with the remaining colors spans a wider color gamut than the red first useful light with the same remaining colors. On the other hand, the red first useful light can be provided with a higher luminous efficacy, thus resulting in a higher luminous flux with the same pump radiation power. The luminous efficacy of the red first useful light is almost twice that of the red second useful light.

[0063] The reason for this is that in the case of the red second useful light, a larger spectral range is filtered out in order to shift the color coordinate further into the red. In principle, however, filtering occurs in both cases, so the respective useful light is not the same as the conversion light emitted by the respective phosphor. In the case of the red first and second phosphors, the underlying phosphor is the same, namely a yellow phosphor. The filtering ultimately sets the respective color coordinate.

[0064] This is possible, for example, with the following setup: Fluorescent wheel 1 is operated in reflection mode, meaning that blue pump light is irradiated from one side (in the irradiation area) and the conversion light is discharged from the same side. Appropriate filters are then arranged downstream of the fluorescent wheel, relative to the propagation path of the conversion light, on a filter wheel (not shown) whose segmentation and rotation (speed and phase) are matched to the fluorescent wheel.

[0065] The filters downstream of the phosphor wheel 1 can each be multilayer systems, whereby the transmission properties can be adjusted via the dielectric properties of the layer sequence and the layer thicknesses. Furthermore, the filter wheel also has transmission windows through which the conversion light or reflected pump light (see below) passes without interaction in the corresponding segments.

[0066] The yellow phosphor underlying the red first and second useful light is a cerium-doped yttrium aluminum garnet.

[0067] Furthermore, a green first phosphor 3a and a green second phosphor 3b are arranged on the phosphor wheel 1, specifically for emitting green first and green second useful light. The green second useful light has a better color coordinate, namely, it spans a larger color gamut; however, the green first useful light can be provided with a higher luminous efficacy, which is approximately 15% higher.

[0068] The green first useful light is unfiltered conversion light emitted by the green first phosphor 3a, namely the conversion light of a green phosphor. In this case, a cerium-doped lutetium aluminum garnet is provided as the green phosphor. The green second phosphor 3b is the same green phosphor, but the green second useful light is provided by filtering the green second conversion light. This results in a better color coordinate on the one hand, but also in a reduced luminous efficacy on the other.

[0069] Furthermore, two yellow segments 4a, b and two blue segments 5a, b are provided on the phosphor wheel 1. The aforementioned yellow phosphor is arranged in the first segment, the conversion light of which is not filtered in this case. The useful yellow light of both segments is the same.

[0070] For the two blue channels 5a, b, the phosphor wheel 1 is provided with two reflection segments, so the blue pump light is reflected by the phosphor wheel 1 without conversion and then used in the application as blue useful light.

[0071] In this case, a laser with a wavelength of 452 nm is used as the pump radiation source. Alternatively, a blue phosphor could be used for the blue channel and excited, for example, with UV or violet radiation at 405 nm; the blue conversion light would then have a wavelength of 460 nm, for example.

[0072] Counterclockwise, starting at 12 o'clock, the RGBY sequence is arranged twice on the phosphor wheel 1, with yellow (Y) and blue (B) being identical in the two sequences, but red (R) and green (G) being different.

[0073] Fig. Figure 2 uses a table to illustrate how the phosphor wheel is illuminated in a first operating mode. Namely, the red first phosphor 2a and the green first phosphor 3a are operated at a lower pump light power (P) than the red second phosphor 2b and the green second phosphor 3b. At the beginning of the 360° rotation, the pump light power is 25%, and then, after the green first phosphor 3a has passed the irradiation area, it is increased, initially to approximately 53% in the blue segment 5a and subsequently to 100% for the remainder of the rotation. As a result, the red first phosphor 2a and green first phosphor 3a are each illuminated with only 25% of their maximum power, while the red second phosphor 2b and green second phosphor 3b are illuminated with 100%. A correspondingly varying illumination is repeated over a large number of successive rotations.

[0074] Furthermore, the table shows the color coordinates of the respective useful light for each segment of phosphor wheel 1, i.e., coordinates in the CIE standard color system. The first row corresponds to the X value, and the second row to the Y value. Furthermore, the third row indicates the angle of rotation over which the respective segment extends.

[0075] Fig. Figure 3 illustrates the aforementioned color coordinates in a CIE standard color system. The first green color coordinate 31a and the second green color coordinate 31b are both in the green range. The second green useful light has a better color coordinate than the first green color coordinate; thus, the second green color coordinate 31b, together with the remaining color coordinates (RBY), forms a larger square than the first green color coordinate 31a.

[0076] In the Fig. In the operating mode explained in Figure 2, the green first phosphor 3a is pumped relatively less, so that an effective green color location (resulting from the average over the 360° rotation) lies close to the green second color location 31b. This operating mode is therefore suitable and designed for good color reproduction. A preferred application example is the reproduction of image content with a projection device.

[0077] However, since the green first phosphor 3a is only partially illuminated, the luminous flux (of the useful light) is lower. Therefore, if the projection device is to display text content and / or content in high ambient brightness, such as daylight conditions, it can be switched to a second operating mode in which all segments are illuminated with 100% pump light output.

[0078] The effective green color location is thereby shifted closer to the green first color location 31a, which means that the area of ​​the spanned quadrilateral becomes smaller.

[0079] This applies analogously to the red first color location 21a and the red second color location 21b. In the Fig. In the operating mode listed in Figure 2, the effective red color location resulting from averaging is shifted closer to the red second color location 21b. On the other hand, if the first red phosphor 2a is also operated with a pump light output of 100%, the effective red color location is shifted closer to the red first color location 21a. Thus, the color gamut is smaller, but the luminous flux is larger.

Claims

[1] Method for operating a lighting device comprising: a pump radiation source for emitting pump radiation and a phosphor wheel (1) on which a first phosphor (2a, 3a) for emitting first conversion light and a second phosphor (2b, 3b) for emitting second conversion light are arranged, wherein the first phosphor (2a, 3a) and the second phosphor (2b, 3b) are arranged spatially separated from one another on the phosphor wheel (1), wherein a first useful light based on the first conversion light and a second useful light based on the second conversion light have the same color but a different color location in the CIE standard color system, in which method the phosphor wheel (1) rotates about a rotation axis and is irradiated with the pump radiation in an irradiation area eccentric to the rotation axis in such a way that a circular track is irradiated as a result of the rotation of the phosphor wheel, wherein during a 360° rotation of the phosphor wheel (1) the first phosphor (2a, 3a) is irradiated with a first pump radiation power and the second phosphor (2b, 3b) is irradiated with a second pump radiation power which is different from the first pump radiation power, and the first pump radiation power and the second pump radiation power are greater than 0. [2] Method according to claim 1, wherein said variation between the first pump radiation power and the second pump radiation power is repeated over a first plurality of successive 360° revolutions and during a second plurality of successive 360° revolutions of the phosphor wheel (1) following the first plurality of 360° revolutions, the first phosphor (2a, 3a) and the second phosphor (2b, 3b) are irradiated with the same pump radiation power. [3] Method according to claim 1 or 2, wherein the first useful light is provided by filtering the first conversion light and / or the second useful light is provided by filtering the second conversion light. [4] Method for operating a lighting device comprising: a pump radiation source for emitting pump radiation, and a phosphor wheel (1) on which a first phosphor (2a, 3a) for emitting first conversion light and a second phosphor (2b, 3b) for emitting second conversion light are arranged, wherein the first phosphor (2a, 3a) and the second phosphor (2b, 3b) are arranged spatially separated from one another on the phosphor wheel (1), wherein a first useful light based on the first conversion light and a second useful light based on the second conversion light have the same color but a different color location in the CIE standard color system, in which method the phosphor wheel rotates around a rotational axis and is irradiated with the pump radiation in an irradiation area eccentric to the rotational axis in such a way that a circular track is irradiated as a result of the rotation of the phosphor wheel, wherein during a 360° rotation of the phosphor wheel (1) the first phosphor (2a, 3a) is irradiated with a first pump radiation power and the second phosphor (2b, 3b) is irradiated with a second pump radiation power which is different from the first pump radiation power, wherein the first phosphor (2a, 3a) and the second phosphor (2b, 3b) are the same phosphor and the different color location is set solely by filtering. [5] Method according to one of claims 1 to 3, wherein the first useful light is provided with a first luminous efficacy and the second useful light is provided with a second luminous efficacy, wherein the first luminous efficacy is at least 20% greater than the second luminous efficacy. [6] A method according to any one of the preceding claims, wherein the same colour is red or green. [7] A method according to claim 6, wherein the first useful light has a first dominant wavelength and the second useful light has a second dominant wavelength, wherein in the case of red the second dominant wavelength is greater than the first dominant wavelength and in the case of green the second dominant wavelength is less than the first dominant wavelength. [8] Method according to one of the preceding claims, in which the first useful light has a first color location (21a, 31a) and the second useful light has a second color location (21b, 31b), wherein in addition at least a third useful light with a third color location and a fourth useful light with a fourth color location are provided, which third and fourth color locations together with the first (21a, 31a) or the second color location (21b, 31b) span at least one three-color RGB color gamut, wherein the two color gamuts differ in their area in the CIE standard color system by at least 5%. [9] Method according to one of the preceding claims, in which the color of the first and the second useful light is green, this useful light is therefore based on a green first phosphor (3a) and a green second phosphor (3b), wherein red first useful light and red second useful light are also provided, which differ in the color location but have the same color green, for which purpose a red first phosphor (2a) and a red second phosphor (2b) are additionally arranged spatially separated from one another on the phosphor wheel (1). [10] A method according to claim 9, wherein during one 360° rotation of the phosphor wheel (1) the green first phosphor (3a) is irradiated with a green first pump radiation power and the green second phosphor (3b) is irradiated with a green second pump radiation power which is different from the green first pump radiation power, and during the same 360° rotation the red first phosphor (2a) is irradiated with a red first pump radiation power and the red second phosphor (2b) is irradiated with a red second pump radiation power which is different from the green first pump radiation power, further wherein this variation between the pump radiation powers is repeated over the first plurality of successive 360° rotations. [11] Lighting device with: a pump radiation source for emitting pump radiation, a phosphor wheel (1) on which a first phosphor (2a, 3a) for emitting first conversion light and a second phosphor (2b, 3b) for emitting second conversion light are arranged, and a control unit for controlling the pump radiation source, wherein the first (2a, 3a) and the second phosphor (2b, 3b) are arranged spatially separated from one another on the phosphor wheel (1), and wherein a first useful light based on the first conversion light and a second useful light based on the second conversion light have the same color but a different color location in the CIE standard color system, wherein the control unit is further configured for a method according to claim 1. [12] Lighting device according to claim 11, which is adapted for a method according to any one of claims 2 to 10. [13] Use of a lighting device according to claim 11 or 12 for at least one of a projection device, an endoscope, room lighting purposes, industrial and medical applications. [14] Use according to claim 13 for a projection device, in which one of a DLP, LCoS and LCD unit is provided as the imaging element downstream of the illumination device.

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