Lighting device with optimized color scale

Abstract

To provide a lighting device or a light conversion unit for the lighting device, having optimal color properties for electronic equipment such as a projector or screen.SOLUTION: A lighting device includes: a light source emitting primary light particularly with a wavelength of 400 nm to 460 nm; and a light conversion element illuminated by the primary light and adjusted so as to emit secondary light with a wavelength changed to the primary light. The light conversion element is configured to emit the secondary light characterized by a spectrum which defines that a radial distance from dots in the CIE1931 color space, that is, (i) blue dots and red dots of the REC709 window as well as dots defining an area covering at least 95% of the REC709 window and / or (ii) green dots of the REC709 window, is 0.02 at maximum, during illumination by the primary light.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an illumination device comprising a light source that emits primary light and a light conversion element that receives the primary light and emits secondary light with a shifted color position. [Background technology]

[0002] The color coordinates of light are often specified in the CIE 1931 color space, which describes the totality of colors that can be perceived by humans in an xy coordinate system. For color reproduction by electronic devices, such as projectors or screens, the color locations for red, green, and blue can also be specified in the CIE 1931 color space, which correspond to the red point, green point, or blue point.

[0003] Thus, depending on the material of the light-converting element and the irradiated primary light, a certain color position in the CIE color space can be targeted or achieved for the emitted secondary light. However, in practice, in this case, it is difficult to avoid deviations between the target setting and the color position actually achieved. Color correction can be performed by filtering out part of the emitted secondary light using optical filters. However, this can put a strain on the efficiency or consumption efficiency of the lighting device. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention is therefore based on the problem of providing a lighting device or a light conversion unit for a lighting device with optimal color characteristics for electronic devices such as projectors or screens. In particular, a sufficiently good conversion characteristic, a high efficiency or consumption efficiency, and a not too strong negative thermal quenching (NQT) during heating are targeted here. Furthermore, according to one aspect of the problem, it should be possible to dispense with optical filters for color correction. [Means for solving the problem]

[0005] To achieve this object, according to the present invention an illumination device is disclosed which comprises a light source, in particular configured as a laser, for emitting primary light, wherein the light source is configured to emit primary light having a wavelength preferably in the range of 400 nm to 460 nm, particularly preferably in the range of 448 nm to 455 nm, e.g. 450 nm.

[0006] The lighting device according to the invention further comprises a light-converting unit formed by or including a light-converting element having a front face and a rear face, which may therefore in the simplest case be formed as the light-converting element itself or may possibly comprise further components, as will be explained in more detail below.

[0007] In any case, the light-converting element is illuminated by the primary light and is adapted to emit secondary light, which preferably has at least one wavelength and in particular a color locus that is changed relative to the primary light.

[0008] When illuminated with primary light, in particular having a wavelength in the range of 400 nm to 460 nm, particularly preferably in the range of 448 nm to 455 nm, for example 450 nm, secondary light can be emitted from the light-converting element, which is preferably characterized by a spectrum that defines a given point in the CIE 1931 color space.

[0009] Preferably, the dot (i) together with the blue dot and the red dot of the REC709 window defines a surface covering at least 95% of the REC709 window, preferably at least 96%, particularly preferably at least 97%, and / or (ii) is characterised by a radial distance from the green dot of the REC709 window of at most 0.02, preferably at most 0.015, particularly preferably at most 0.01.

[0010] The REC709 window or color gamut defines a certain range within the CIE1931 color space. For this purpose, three color positions within the range, blue, red and green, are defined as corner points of the range. This REC709 range is shown in FIG. 3 and will be explained in more detail subsequently below.

[0011] The secondary light that the light-converting element can emit when illuminated by the primary light can be experimentally detected. To determine the color locus, the light-converting element can be excited by the primary light, in particular with a wavelength in the range of 400 nm to 460 nm, particularly preferably in the range of 448 nm to 455 nm, for example 450 nm, and the emitted light can be spectroscopically measured using a spectrometer.

[0012] In order to determine the color position from the measurable spectrum in this way, in particular, only the measured spectrum portion from a wavelength of 465 nm is used.Therefore, in particular, in the context of the present invention, the spectrum with which the secondary light is characterized should be understood as the spectrum from a wavelength of 465 nm.Furthermore, this definition of the emission spectrum preferably makes it possible to avoid including diffusely reflected primary light in the secondary light during measurement, as will be explained in more detail below.

[0013] Surprisingly, it has been found that the color position of the secondary light can depend on the thickness of the light-converting element, the thickness of which is understood to mean its dimension extending from the front surface to the rear surface.

[0014] In a preferred embodiment, this thickness is between 50 μm and 250 μm, particularly preferably between 70 μm and 250 μm, and even more preferably between 80 μm and 150 μm or between 70 μm and 115 μm.

[0015] The colour locus of the secondary light also depends inter alia on the material of the light-converting element.

[0016] In a preferred embodiment, the light-converting element comprises a light-converting ceramic material.

[0017] In a preferred embodiment, the light conversion element contains the material (Lu 1-x Ce x )3(Al 1-y Ga y ) 5 O 12 , where 0 < x < 0.01 and 0 < y < 0.2, preferably 0 < x < 0.007 and 0 < y < 0.15 apply. The light conversion element preferably consists mainly of this material and particularly preferably consists entirely of this material.

[0018] The lighting device according to the invention is particularly suitable for a re-emission geometry but can also be used as a transmission geometry.

[0019] Thus, for example, it may be assumed that the front surface of the light conversion element is illuminated by the primary light and the front surface of the light conversion element is adjusted to emit secondary light. In this case, it can be understood as a re-emission geometry.

[0020] Optionally, the light conversion unit can further include, in addition to the light conversion element, a substrate that is directly or indirectly connected to the rear surface of the light conversion element and is preferably formed as a cooling body.

[0021] Furthermore, the light conversion unit can optionally include a connector that exists between the light conversion element and the substrate and interconnects them.

[0022] For example, it may also be assumed that the rear surface of the light conversion element is illuminated by the primary light and the front surface of the light conversion element is adjusted to emit secondary light. In this case, it can be understood as a transmission geometry.

[0023] In some embodiments, the light conversion unit and / or the light conversion element may be configured as a ring or a ring segment, particularly preferably as a ring wafer.

[0024] The light-converting unit and / or the light-converting element may preferably have an outer diameter greater than 30 mm, preferably less than 120 mm.

[0025] In some embodiments, the light conversion unit may have at least one highly reflective coating, where the highly reflective coating is preferably a metal coating and / or a dielectric coating, and particularly preferably an Ag coating or an Ag-containing coating.

[0026] In some embodiments, the connector may be formed as a metal solder or as a sintered sinter paste or adhesive, where the solder preferably has a melting point of less than 300° C. and preferably includes or consists of Au / Sn solder and / or AuSn8020.

[0027] In some embodiments, the light conversion element comprises a plurality of pores.

[0028] This light-converting element can in particular have a porosity lying between 2% and 12%, preferably between 4% and 8%.

[0029] The present invention further relates to a light-conversion unit having a front surface and a rear surface, formed by or including a light-conversion element that is illuminated by primary light and adapted to emit secondary light having at least one wavelength that is altered relative to the primary light.

[0030] The light conversion element is preferably configured to emit secondary light, characterized by a spectrum defining a given point in the CIE 1931 color space, upon illumination with primary light, in particular having a wavelength in the range of 400 nm to 460 nm, particularly preferably having a wavelength in the range of 448 nm to 455 nm, for example a wavelength of 450 nm.

[0031] Preferably, this dot defines an area that covers at least 95%, preferably at least 96%, particularly preferably at least 97% of the REC709 window, together with the blue dots and red dots of the REC709 window, and / or (ii) is characterized in that the radial distance from the green dots of the REC709 window is at most 0.02, preferably at most 0.015, particularly preferably at most 0.01.

[0032] The light conversion unit optionally includes a substrate that is directly or indirectly connected to the rear surface of the light conversion element and is preferably formed as a cooling body.

[0033] Furthermore, the light conversion unit optionally includes a connector that exists between the light conversion element and the substrate and interconnects them.

[0034] In a preferred embodiment, the light conversion element has a thickness between 50 μm and 250 μm, particularly preferably between 70 μm and 250 μm, more preferably between 80 μm and 150 μm or between 70 μm and 115 μm.

[0035] In a preferred embodiment, the light conversion element includes a light conversion ceramic material.

[0036] In a preferred embodiment, the light conversion element is made of the material (Lu 1-x Ce x )3(Al 1-y Ga y ) 5 O 12 where 0 < x < 0.01 and 0 < y < 0.2, preferably 0 < x < 0.007 and 0 < y < 0.15. The light conversion element preferably consists mainly of this material and particularly preferably consists entirely of this material.

[0037] The front surface of the light conversion element may be illuminated by the primary light and adjusted to emit secondary light from its front surface.

[0038] However, it may also be envisaged that the light-converting element is arranged such that its rear face is illuminated by primary light and its front face emits secondary light.

[0039] In some embodiments, the light-converting units and / or light-converting elements may be formed as rings or ring segments, in particular as ring wafers.

[0040] The light-converting unit and / or the light-converting element may preferably have an outer diameter greater than 30 mm, preferably less than 120 mm.

[0041] In some embodiments, the light conversion unit may have at least one highly reflective coating, where the highly reflective coating is preferably a metal coating and / or a dielectric coating, and particularly preferably an Ag coating or an Ag-containing coating.

[0042] In some embodiments, the connector may be formed as a metal solder or as a sintered sinter paste or adhesive, where the solder preferably has a melting point of less than 300° C. and preferably includes or consists of Au / Sn solder and / or AuSn8020.

[0043] In some embodiments, the light conversion element comprises a plurality of pores.

[0044] This light-converting element can in particular have a porosity lying between 2% and 12%, preferably between 4% and 8%.

[0045] The invention will now be explained in more detail with reference to the following drawings, in which: [Brief description of the drawings]

[0046] [Figure 1]FIG. 2 is a schematic cross-sectional view of an illumination device further showing measurements with a detector for the diffuse luminescence converted beam and a detector for the specularly reflected beam. [Diagram 2] 1 is a schematic cross-sectional view of a light conversion unit having a substrate and a connector. [Diagram 3] FIG. 2 shows the CIE1931 color space and the REC709 window as well as two color positions A, B of the emitted secondary light for two different light conversion elements. [Figure 4] FIG. 2 shows the CIE1931 color space and the REC709 window, as well as two color positions A, B of emitted secondary light for two different light conversion elements and an area showing the coverage of the REC709 window. [Diagram 5] FIG. 2 shows the CIE1931 color space and the REC709 window, as well as two color positions A, B of emitted secondary light for two different light conversion elements and an area showing the coverage of the REC709 window. [Figure 6] FIG. 7 shows the CIE1931 color space and the REC709 window, as well as the three color positions A, B, and C of the emitted secondary light for three different light conversion elements, and, unlike in FIGS. 4 and 5, the area showing the coverage of the REC709 window only for color position C (FIG. 7). [Figure 7] FIG. 7 shows the CIE1931 color space and the REC709 window, as well as the three color positions A, B, and C of the emitted secondary light for three different light conversion elements, and, unlike in FIGS. 4 and 5, the area showing the coverage of the REC709 window only for color position C (FIG. 7). [Figure 8] FIG. 1 shows the color locus for emission color positions of various Ce-doped ceramic garnet materials of given thicknesses relative to the REC709 window. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] FIG. 1 shows the illumination device 100 together with a measurement setup having detectors 9 and 10 , which are described in more detail below, although these detectors should not be understood as part of the illumination device 100 .

[0048] The lighting device 100 in this case comprises a light-converting unit 200 with a light-converting element 1 and a substrate 3 formed, for example, as a mirror, and a primary light source 5, for example a blue laser beam source, in particular with a beam shaping, arranged to emit a laser beam 6 which is incident on the front surface of the light-converting element 1, whereby a secondary beam 7 is generated in the form of a diffusely emitting converted beam. Furthermore, a specular Fresnel-reflected laser beam 6 can be generated.

[0049] With the measurement setup shown it is possible, inter alia, to measure the emission spectrum and therefrom to determine the emission colour position. Detector 9 is a detector for the specularly reflected beam. Detector 10 is a detector for the diffusely luminous converted beam.

[0050] According to one example, a conversion material of a given thickness, for example polished on both sides, can be placed on a mirror with a reflectance of 95% or more in the visible spectrum. Excitation can be performed by blue light having a wavelength of 448-455 nm. The emitted light can be spectroscopically measured using a spectrometer. To determine the color position from the spectrum, in particular the range from a wavelength of 465 nm can be used.

[0051] Therefore, the spectrum emitted from a wavelength of 465 nm can be considered the emission spectrum. This definition can ensure, among other things, that specularly or diffusely reflected excitation light is not included in the emission spectrum.

[0052] By using an experimental setup, in particular the consumption efficiency can also be determined. For this purpose, in one example, a double-sided polished wafer or wafer ring of a given thickness can be placed on a mirror with a reflectivity of at least 95% in the visible spectrum. The conversion material is selected so that it is not heated significantly (a few mW / mm2 It can be irradiated by a blue laser beam with a small power or irradiance of I 0 The irradiation is particularly oblique, so the intensity I Fre The specularly reflected Fresnel beam of I can be measured. 0 is also known by a separate measurement. Em The intensity of (465 nm~) can be measured by an additional detector. The consumption efficiency η is η = J Em / (I 0 -I Fre ), where J Em I Em is the photometric luminous flux corresponding to

[0053] 2 shows a light-converting unit 200 with a light-converting element 1, a substrate 3 and a connector 2. The light-converting element 1 may in particular be configured as a ceramic converter. The connector may be formed, for example, as a solder, glue or a sintered sinter paste. The substrate may be formed, for example, as a heat sink ("heatsink") containing or made of copper or as a so-called "wheel" containing or made of aluminum.

[0054] FIG. 3 shows the measured emission color positions of two Ce-doped ceramic garnet materials that can be used for light conversion, e.g. in projectors, in the form of thin rings of a given thickness (here 225 μm) deposited on a mirrored substrate and polished on both sides, whose positions relative to the REC709 window are shown in the CIE1931 color space.

[0055] The two materials are (Y 1-x Ce x ) 3 Al 5 O 12 (YAG:Ce) or (Lu 1-x Ce x ) 3 Al 5 O 12(LuAG:Ce). The emission color position of these converters is more or less red-shifted relative to the green dot of the REC709 window.

[0056] In other words, the pure unfiltered emission spectra from these Ce-doped garnet materials have emission color positions that are more or less far from the green dot of the REC709 window, which leads to a suboptimal filling of this color space. It is possible to possibly filter parts of the spectrum to shift the color position closer to the green dot, but further solutions are implemented below.

[0057] 4 and 5 show only partial filling of the REC709 window by the aforementioned converter as indicated by the hatched area.

[0058] In particular, the standard of what proportion the REC709 gamut in the CIE1931 color space is filled by the color gamut (green dot) determined by the actual conversion material can be set broadly, which is hereinafter referred to as the area filling factor FF. According to this definition, this FF is at most equal to 1. The red dot and the blue dot are hereinafter specifically the corresponding color positions of the REC709 window.

[0059] As a further measure, the radial distance of the emitting color position in the CIE1931 color space from the green dot of the REC709 window is provided. This distance is referred to herein as GD (green distance) and is expressed by the relationship GD = ((cx 709 -cx em ) 2 +(cy 709 -cy em ) 2 ) 0.5 where cx 709 Or cy 709 represents the color coordinate of the green REC709 corner point, and cx em Or cy em represents the color coordinates of the converter.

[0060] The solution according to the invention is that upon excitation by a blue laser having a wavelength at 450 nm, the position of the already unfiltered emission color is as close as possible to the green dot of the REC709 window.

[0061] Both the efficiency or dissipation efficiency at high temperatures and the negative thermal quenching (NQT) affect the so-called "irradiance limit", i.e. the maximum possible excitation intensity from a blue laser.

[0062] In a preferred embodiment, a ceramic garnet material of a given composition and thickness has been demonstrated when the garnet lattice is doped with a given amount of gallium while tailoring the Ce content as well as the thickness of the transducer.

[0063] Partial substitution of Ga for Al in YAG, LuAG or similar garnet host lattices can affect the energy levels of Ce3+ in the host lattice, with respect to which the emission spectrum shows a more or less strong blue shift, although this measure may not be sufficient in some cases to achieve an optimal approximation to the green dot in REC709.

[0064] Surprisingly, it was found that the exact shape and position of the emission spectrum (and thus the emission colour position) of this type of conversion material depends not only on the composition of the host material but also on the Ce concentration and even on the thickness of the converter.

[0065] A preferred embodiment is, for example, a material having a predetermined range for x and y and a predetermined thickness (Lu 1-x Ce x )3(Al 1-y Ga y ) 5 O 12 Includes.

[0066] In Figures 6 and 7, this example is shown as color location C. The measured emission color locations A and B of the two Ce-doped ceramic garnet materials mentioned above are shown in the form of thin rings of a given thickness (here 225 μm) deposited on a mirror substrate and polished on both sides, as well as the composition (Lu 1-x Ce x )3(Al 1-y Ga y ) 5 O 12 7 and their position in REC709 expressed in the CIE 1931 color space. In FIG. 7 a particularly good filling of the REC709 window by converter C can be discerned.

[0067] Figure 8 shows a section of the CIE1931 color space with the location of the green corner of the REC709 window and various example emission color locations from the following table, which includes examples of measured emission color locations for various Ce-doped ceramic garnet materials of a given thickness, along with the distance GD from the REC709 green dot and the fill factor FF, as well as examples of measured power consumption. Additionally, the color coordinates of the REC709 window are also listed.

[0068] [Table 1]

[0069] From figure 4 it can be seen that example C is closest to the green dot of REC709. Example G differs from C by a small thickness of 80 μm compared to 225 μm. To approach the green dot of REC709 again at this small thickness, for example the Ga content y can be reduced and / or the Ce content x can be increased.

[0070] For the preparation of Example C, pure lutetium oxide, aluminum oxide, gallium oxide and cerium oxide powders were each mixed with the compounds listed in Table 1 (Lu 0.9964 Ce 0.0036 ) 3(Al 0.9 Ga 0.1 ) 5 O 12 The mixture was mixed according to the composition of 10 ...

[0071] For the measurement of the emission spectrum, a double-sided polished wafer or wafer ring of a given thickness was placed on a mirror with a reflectivity of more than 95% in the visible spectrum. Excitation was performed by blue laser light with a wavelength of 450 nm. The emitted light was spectroscopically measured using a spectrometer, and a range from a wavelength of 465 nm was used to determine the color position from the spectrum. For the measurement of the power consumption, a double-sided polished wafer or wafer ring of a given thickness was placed on a mirror with a reflectivity of about 98% in the visible spectrum. Excitation was performed by blue laser light with a wavelength of 450 nm and a power of 3 mW.

[0072] For the preparation of Example G, pure lutetium oxide, aluminum oxide, gallium oxide and cerium oxide powders were each mixed with the compounds listed in Table 1 (Lu 0.9964 Ce 0.0036 ) 3 (Al 0.9 Ga 0.1 ) 5 O 12The mixture was mixed according to the composition of 10 ...

[0073] For the measurement of the emission spectrum, a double-sided polished wafer or wafer ring of a given thickness was placed on a mirror with a reflectivity of more than 95% in the visible spectrum. Excitation was performed by blue laser light with a wavelength of 450 nm. The emitted light was spectroscopically measured using a spectrometer, and a range from a wavelength of 465 nm was used to determine the color position from the spectrum. For the measurement of the power consumption, a double-sided polished wafer or wafer ring of a given thickness was placed on a mirror with a reflectivity of about 98% in the visible spectrum. Excitation was performed by blue laser light with a wavelength of 450 nm and a power of 3 mW.

Claims

1. A lighting device (100), wherein the lighting device (100) is A light source (5) configured as a laser in particular for emitting primary light (6), especially primary light having wavelengths in the range of 400 nm to 460 nm, A light conversion unit (200) is formed by or includes a light conversion element (1) having a front and a rear surface, which is illuminated by the primary light (6) and adjusted to emit secondary light (7) having a wavelength changed with respect to the primary light, Includes, The light conversion element (1), when illuminated by the primary light (6), produces the following dots in the CIE 1931 color space, i.e. (i) Dots that define an area covering at least 95%, preferably at least 96%, and particularly preferably at least 97% of the REC709 window, together with the blue and red dots of the REC709 window, and / or (ii) It is configured to emit secondary light (7) characterized by a spectrum that defines a point at a maximum radial distance of 0.02, preferably 0.015, and particularly preferably 0.01 from the green dot of the REC709 window, Lighting device (100).

2. The light conversion element (1) has a thickness t that extends from the front surface to the rear surface, The thickness is between 50 μm and 250 μm, preferably between 70 μm and 250 μm, particularly preferably between 80 μm and 150 μm, or between 70 μm and 115 μm. The lighting device according to claim 1.

3. The aforementioned light conversion element includes a light conversion ceramic material. The lighting device according to claim 1 or 2.

4. The aforementioned light conversion element (1) is made of material (Lu １－ｘ Ce ｘ )3(Al １－ｙ Ga ｙ ) ５ O １２ This includes, where 0 < x < 0.01 and 0 < y < 0.2, preferably 0 < x < 0.007 and 0 < y < 0.15, The aforementioned light conversion element (1) is preferably made mainly of this material, and particularly preferably made entirely of this material. The lighting device according to claim 3.

5. The light conversion element (1) is adjusted so that its front surface is illuminated by the primary light and its front surface emits the secondary light. The optical conversion unit (200) optionally includes a substrate (3) that is directly or indirectly connected to the rear surface of the optical conversion element and preferably formed as a cooling body. The optical conversion unit (200) optionally includes a connector (2) located between the optical conversion element (1) and the substrate, which connects them to each other. The lighting device according to claim 1 or 2.

6. The light conversion element (1) is configured such that its rear surface is illuminated by the primary light and its front surface emits the secondary light. The lighting device according to claim 1 or 2.

7. The optical conversion unit and / or the optical conversion element is formed as a ring or ring segment, and in particular as a ring wafer. The light conversion unit and / or the light conversion element preferably has an outer diameter greater than 30 mm and preferably less than 120 mm. The lighting device according to claim 1 or 2.

8. The light conversion unit has at least one highly reflective coating, the highly reflective coating is preferably a metal coating and / or a dielectric coating, and particularly preferably an Ag coating or an Ag-containing coating. The lighting device according to claim 1 or 2.

9. The connector is formed as metal solder, or as a sintered paste or adhesive. The aforementioned solder preferably has a melting point of less than 300°C, and preferably contains or consists of Au / Sn solder and / or AuSn8020. The lighting device according to claim 1 or 2.

10. The aforementioned light conversion element includes a plurality of pores, The lighting device according to claim 1 or 2.

11. The aforementioned light conversion element has a porosity between 2% and 12%, preferably between 4% and 8%. The lighting device according to claim 1 or 2.

12. A light conversion unit (200), wherein the light conversion unit (200) is A light conversion element (1) having a front and a rear surface, which is illuminated by primary light and adjusted to emit secondary light having a wavelength changed with respect to the primary light, A substrate (3) is optionally connected directly or indirectly to the rear surface of the light conversion element and preferably formed as a cooling body, Optionally, a connector (2) is provided between the optical conversion element and the substrate, and connects them to each other. Formed by or including them The aforementioned light conversion element, when illuminated by primary light (6) in the range of 400 nm to 460 nm, produces the following dots in the CIE 1931 color space, i.e. (i) Dots that define an area covering at least 95%, preferably at least 96%, and particularly preferably at least 97% of the REC709 window, together with the blue and red dots of the REC709 window, and / or (ii) It is configured to emit secondary light (7) characterized by a spectrum that defines a point at a maximum radial distance of 0.02, preferably at a maximum of 0.015, and particularly preferably at a maximum of 0.01 from the green dot of the REC709 window, Optical conversion unit (200).

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