Light-emitting device and lamp

Abstract

A light-emitting device (1) comprises at least two LED units (Li, i = 1, 2, 3), each with at least one LED chip (Ci) for generating primary light (Pi) with a primary spectrum and a conversion component (Ki) for converting the primary light (Pi) into secondary light (Si) with a secondary spectrum that has a broader spectral range than the primary spectrum. The secondary spectra of different LED units (Li) are distinct.

Description

The present invention relates to a light-emitting device, in particular in the form of an LED package. The invention also relates to a luminaire having at least one such light-emitting device.Light emitting devices in the form of LED packages are known by prior use. These use one or more LED chips to generate light. Due to the narrow-band emission characteristic of LED chips, the generation of white light and mixed colors requires special measures. For example, it is known to combine LED chips of different colors. In particular, the use of red, green and blue LEDs in an LED package for generating white light is known. These so-called RGB LED packages or RGB LEDs for short, however, have an inhomogeneous spectrum, which leads to poorer color rendering values.In particular for generating white light, it is also known to convert primary light of an LED chip into, for example, white secondary light with the aid of a light-converting material. However, the resulting spectrum is predefined by the light-converting material used in each case and is therefore not adjustable.It is an object of the present invention to improve a light emitting device, particularly to provide a light emitting device having a radiation spectrum with high color rendering quality and high flexibility in radiation spectrum.This object is achieved by a light-emitting device according to claim 1. It has at least two LED units. The at least two LED units each have at least one LED chip for generating primary light having a primary spectrum and a conversion component for converting the primary light into a secondary light having a secondary spectrum, wherein the secondary spectrum has a greater spectral width than the primary spectrum. The secondary spectra of different ones of the at least two LED units are different. The device combines the advantages of individual LED units with the broadband emission characteristic of the respective conversion component. This enables more homogeneous and thus more color-fidelity color mixtures without being restricted to the spectrum of a light-converting material.The secondary light of the at least two LED units is superimposed to form emission light of the light-emitting device. In other words, the secondary spectra of the at least two LED units are superimposed to form an emission spectrum. The emission light with the emission spectrum is the light emitted by the device and ultimately perceived by the user. The emission spectrum covers in particular at least a part of the visible light. The emission spectrum can also comprise parts of the infrared range and / or UV range, depending on the application. The emission spectrum is preferably in the visible wavelength range, in particular between 380 nm and 780 nm. In particular for generating white light, the emission spectrum preferably covers at least 50% of the visible wavelength range, in particular at least 75% of the visible wavelength range.The secondary spectra differ. They cover different partial regions of the wavelength range covered by the emission spectrum. The secondary spectra are preferably in the visible wave range, in particular between 380 nm and 780 nm.The primary light may be visible light (in particular between 380 nm and 780 nm). The primary light can also have other wavelengths, in particular in the UV wavelength range. The primary light of an LED unit is converted into the secondary light by the respective conversion components. The wavelengths of the primary light are preferably selected in such a way that good absorption and reemission is provided by the respective conversion component. It is also possible to choose the primary light in such a way that the primary spectrum lies completely in the spectral range of the secondary spectrum. False colors in the emission spectrum, which are due to unconverted primary light, are thereby particularly reliably avoided.The spectral width of the secondary spectrum is greater than that of the respective primary spectrum. The spectral width is in particular an emission line width, in particular a full width at half maximum (narrow. Full Width at Half Maximum, FWHM). Due to the use of LED chips, the primary light is in particular narrowband. The respective primary spectra can have, for example, a full width at half maximum between 5 nm and 20 nm, for example a full width at half maximum of approximately 15 nm. The spectral width, in particular the full width at half maximum, of the secondary spectra is preferably greater than 15 nm, in particular greater than 20 nm, in particular greater than 30 nm. A particularly suitable range for the spectral width, in particular the full width at half maximum, of the respective secondary spectra is between 15 nm and 120 nm.The conversion components comprise in particular at least one light-converting material. In order to achieve different secondary spectra, the conversion components of the respective LED units, in particular the at least one light-converting material contained therein, preferably differ.The conversion component, in particular light-converting material contained therein, absorbs the primary light and emits the secondary light. Suitable conversion components have, in particular, light-converting material which exhibits luminescence, in particular photoluminescence, for example fluorescence or phosphorescence. Such materials are also referred to as phosphors. Depending on the desired secondary spectrum, suitable light-converting materials can be selected.Exemplary suitable phosphors are in particular: CaAlSiN 3: Eu 2+, ( Sr, Ca)AlSiN 3: Eu 2+, Lu 2 O 3: Eu 3+, ( Sr 2-x La x)( Ce 1-x Eux)O4, Sr2Sr1-xEuxO4, Sr 2-x Eu x CeO 4, SrTiO 3: Pr 3+, Ga 3+, Sr 2 Si 5 N 8: Eu 2+, CaSc2O4:Ce3+, CaSc2O4:Ce3+, Y3(Al, Ga) 5 O 12 Ce 3+, Lu 3 Al 5 O 12: Ce 3+, YAG: Ce 3+, La 3 Si 6 N11:Ce3+and / or (La, Y)3Si6N11:Ce3+.Particularly suitable conversion components comprise light-converting material in the form of so-called quantum dots, for example cadmium-containing or cadmium-free quantum dots. Exemplary suitable materials for the quantum dots are CdSe / ZnS, InP / ZnS, ZnSe / ZnS and / or perovskites, in particular CsPbX 3, wherein X is selected from the group consisting of Cl, Br and / or I. Quantum dots are nanoparticles which have different emission spectra depending on their diameter and / or starting material. The diameter can be, for example, between 1 nm and 20 nm, in particular for quantum dots based on CdSe. Depending on the size and / or starting material, the emission spectrum, in particular a maximum position and / or spectral width, can thus be adjusted easily and efficiently. By suitable mixtures of quantum dots of different diameters, in particular the spectral width of the secondary spectrum obtained can be adjusted.The light emitting device includes at least two LED units. The light-emitting device can have more than two LED units, in particular three, in particular four, in particular five or more LED units.An LED unit has at least one LED chip for generating primary light. An LED unit may also have more than one LED chip. Different LED chips of an LED unit may generate primary light having a same primary spectrum or primary light having different primary spectra. The generation of different primary spectra can be used, for example, to excite different light-converting materials of the corresponding conversion component.The secondary spectra of different ones of the at least two LED units differ. The secondary spectra of different LED units can have, in particular, different maximum wavelengths and / or different center wavelengths. The secondary spectra can cover in particular different regions of the emission spectrum. Different secondary spectra may have overlapping spectral ranges. It is also possible for different secondary spectra to have closely spaced or identical maximum and / or center wavelengths. Different secondary spectra can have in particular the same color valence. If appropriate, the secondary spectra can differ in their respective spectral width. In this way, it is possible to cover spectral ranges of different widths with the respective secondary spectra.A device according to claim 2 is particularly advantageous with regard to the colour mixtures which can be achieved. Different color values of the secondary spectra of the LED units allow a mixing of the respective corresponding colors. Different color values are to be understood in particular in such a way that the respective secondary spectra correspond to different colors perceptively for a viewer, in particular different primary colors. Different color values can be caused by different spectral characteristics. In particular, the respective secondary spectra can have different maximum and / or center wavelengths.A device according to claim 3 enables particularly flexible mixtures of the secondary spectra. In particular, any desired color mixtures of different color values of the respective secondary spectra can be achieved. The independent control of the respective LED units can be effected, for example, with the aid of an externally controlled power supply of the respective connections of the LED units, in particular their LED chips. The device, in particular the LED package, preferably has an integrated circuit (IC) for driving the respective LED units.A device according to claim 4 is particularly advantageous and flexible. By means of the at least three LED units which cover the primary colors of a color system, the colors of the respective color system can be produced with high quality. In particular, high-quality white light generation is possible. Particularly preferably, the at least three LED units can be controlled independently, whereby the color generated here can be flexibly adjusted within the color space of the respective color system.The generated color of the color system and / or generated white light has a homogeneous mixture. This improves characteristic variables of the color system, in particular a correlated color temperature (engl. Correlated Color Temperature, CCT) and / or a color rendering index (IC). Color Rendering Index, CRI).The primary colors respectively covered by the secondary spectra can be the primary colors of any desired color systems. For example, these may be the primary colors of the RGB color system red, green and blue. The imaging of primary colors of other color systems with the aid of the secondary spectra is also possible. For example, the CMY color system with the primary colors cyan, magenta and yellow can be used. Depending on the dimensionality of the color space associated with the color system, three or more LED units may be provided.It is also possible to provide at least six LED units which cover the primary colors of at least two color systems. In this way, a primary color system or a secondary color system can be covered, which further enhances the quality of color reproduction. For example, there may be LED units for covering the basic colors of the RGB color system and the CMY color system.A device according to claim 5 is distinguished by a particularly good color reproduction. The color rendering index can be determined, for example, according to the CIE Normvalence System 13.3 (1995). The color rendering index that can be achieved can be dependent in particular on the respective spectral width of the secondary spectra of the LED units.The improved color rendering index becomes particularly clear when compared to using conventional RGB LEDs. These have a lower color rendering index of less than 70 on account of the narrowband spectrum of the respective LED chips. In particular, the color rendering index of the emission spectrum of the device is improved by at least 5%, in particular by at least 10%, in particular by at least 20%, compared to the emission characteristic when using LED chips of the corresponding primary color of the color system without respective conversion components.Alternatively or additionally, the emission spectrum of the device preferably has a correlated color temperature which is below the correlated color temperature of RGB LEDs with a high, in particular corresponding color rendering index. In RGB LEDs, typically, the color temperature and a high color rendering index cannot be set simultaneously. If a high color rendering index is to be achieved with RGB LEDs, usually only a cool light of 7,000 K or more can be achieved.The emission spectrum of the device can have, in particular, a correlated color temperature between 2.700 K and 6,500 K. The correlated color temperature can depend in particular on a spectral width of the respective secondary spectra. This makes it possible to easily adapt the correlated color temperature. In particular, the generation of neutral white light or warm white light is possible.A device according to claim 6 has a particularly good color reproduction, in particular a particularly good white light quality. The spectral width can be, in particular, a half-width of the secondary spectra. By adjusting the spectral width, in particular the desired correlated color temperature and / or the color rendering index to be achieved can be influenced. The higher the spectral width, the more homogeneous the color mixture achieved, in particular with regard to the generation of white light. However, too high spectral widths lead to an overlap of the respective secondary spectra, so that a controlled generation of individual colors is made more difficult. The range of the spectral width of the secondary spectra between 15 nm and 120 nm, in particular between 20 nm and 120 nm, has proven to be particularly suitable. For the generation of white light, a spectral width of the secondary spectra between 60 nm and 120 nm is particularly advantageous. For the generation of color light, a spectral width of the secondary spectra between 20 nm and 60 nm is particularly advantageous.A device according to claim 7 has proved to be particularly advantageous. The use of quantum dots as light-converting material is particularly suitable with regard to the adjustability of the spectral width of the secondary spectrum. By using quantum dots of different diameters, the spectral width of the respective secondary spectra can be adapted flexibly and precisely to the respective application. For example, different groups of quantum dots with respective average diameters can be used, wherein the average diameters of different groups are in particular different. The respective proportions of the groups of quantum dots in the conversion component can in particular make it possible to adjust their respective contribution to the light conversion.An apparatus according to claim 8 enables a particularly flexible and precise adjustment of the mixture of the different secondary spectra. The respective shielding of the LED units prevents crosstalk (crosstalk). Excitation of the conversion component of other LED units by primary light and / or secondary light of an LED unit is reliably avoided. In this way, it is possible in particular to use individual ones of the LED units for generating the emission light, for example by corresponding individual actuation.A device according to claim 9 particularly effectively avoids crosstalk from different LED units. The arrangement of the LED units in the respective recesses or cavities of the substrate enables effective shielding without other structural measures, in particular separate shielding elements, being necessary. In addition, the LED units are mechanically protected in the recesses of the substrate. The device is robust.An apparatus according to claim 10 is robust and has a simple structure. Because the conversion component itself is an encapsulation for the respective LED chip, a separate encapsulation is not required. The LED chip is protected in the encapsulant. In addition, the encapsulation prevents primary light of the respective LED chip from passing the conversion component to the outside and impairing the color mixture to be achieved.Particularly preferably, the at least one conversion component can form an encapsulation of the respective LED chip in a corresponding recess of the substrate. As a result, the LED chip and the encapsulation are securely embedded in the recess.A device according to claim 11 enables a particularly space-saving arrangement of the conversion component on the respective LED chips. The LED chip of an entire exposed surface is preferably coated with the conversion component. The coating prevents primary light of the LED chip from being able to escape past the conversion component.It is a further object of the invention to improve a luminaire.This object is achieved by the luminaire according to claim 12. The luminaire may include at least one or more corresponding LED packages. The advantages and optional features of the luminaire correspond to those of the device described above.Further features, advantages and details of the invention are evident from the following description of exemplary embodiments with reference to the figures. The following are shown: FIG. 1 schematically shows a first exemplary embodiment of a light-emitting device in the form of an LED package having three LED units, FIG. 2A shows an exemplary emission spectrum of a known RGB LED, FIG. 2B shows an exemplary emission spectrum of the LED package according to FIG. 1, FIG. 3A shows an example color temperature index depending on a spectral width of secondary spectra of the LED units of the LED package according to FIG. 1, FIG. 3B shows an example color rendering index as a function of a spectral width of the LED units of the LED package according to FIG. 1, FIG. 3C shows the color rendering index according to FIG. 3B as a percentage improvement over a color rendering index of a known RGB LED, FIG. 4 schematically shows a further exemplary embodiment of a light-emitting device in the form of an LED package, and FIG. 5 schematically shows a further exemplary embodiment of a light-emitting device in the form of an LED package.Corresponding parts, components and spectra and / or further variables are provided with the same reference numerals in FIGS. 1 to 5. Details of the exemplary embodiments explained in more detail below can also represent an invention per se or be part of an object of the invention.FIG. 1 schematically shows a first exemplary embodiment of a light-emitting device 1 in the form of an LED package. The LED package 1 has a substrate 2 on which a plurality of LED units L are arranged in i. The index i=1, 2,... here and in the following denotes different LED units and associated (partial) components, light spectra and / or characteristic variables. In the exemplary embodiment shown, three LED units L i are shown, namely L 1, L 2 and L 3 with respective (partial) components, light spectra and characteristic variables (with index i=1, 2, 3).The LED units L i have an LED chip C i for generating primary light P i. The LED units L i have a conversion component K i for converting the respective primary light P i into a secondary light S i.A primary spectrum of the primary light P i is narrow band. The secondary light S i generated with the aid of the respective conversion component K i has a secondary spectrum which has a greater spectral width than the primary spectrum. The resulting secondary spectra are therefore more broadband than the primary spectra that can be generated with the aid of the LED chips C i. The spectral width of the secondary spectra can be defined in particular as half width (narrow. Full Width at Half Maximum, FWHM). The full width at half maximum of the secondary spectra lies in particular in the range between 15 nm and 120 nm.The secondary light S i of the respective LED units L i has different secondary spectra, wherein the secondary spectra have color valences which correspond to the primary colors of a color system. In the exemplary embodiment shown, the color values of the respective secondary spectra correspond to the primary colors red, green and blue of the RGB color system. The secondary light S i of the LED units L i is superimposed to form an emission light A with an emission spectrum which corresponds to the superimposition of the respective secondary spectra.With the aid of an integrated circuit 3, the LED units L i can be controlled independently of one another. As a result, a mixture of the secondary spectra in the emission light A and thus the resulting emission spectrum can be set. By mixing the secondary light S i corresponding to the respective primary colors of the color system, the emission light A can be generated with arbitrary colors of the RGB color space, in particular white light.In the exemplary embodiment shown, the conversion components K i are embodied as encapsulation of the respective LED chips C i. A light converting material is contained in the encapsulant. For generating the respective, different secondary spectra of the secondary light S i the conversion components K i have different light-converting materials and / or different mixtures of light-converting materials. Suitable light-converting materials are, in particular, so-called quantum dots, which may or may not contain cadmium, for example. Quantum dots are nanoparticles which absorb light and emit at a different wavelength. The emitted wavelength depends on the diameter and / or the starting material of the respective quantum dot. As a result, the secondary spectrum, in particular its spectral width, can be adjusted in a targeted and simple manner by the suitable selection of quantum dots of different diameters and / or different materials. The respective suitable diameter may depend on the material of the quantum dot. For example, the diameter can be selected from 1 nm to 20 nm, in particular for quantum dots based on CdSe.The primary spectra of the primary light P i of the respective LED chips C i are less relevant. The primary light P i can be selected to be the same or different for the different LED units L i. It is advantageous to choose corresponding LED chips C i whose primary light P i is absorbed particularly well by the light-converting material of the respective conversion component K i.A specific, purely exemplary example of a combination of LED chips C i and respective conversion components K i is specified below:The LED chip C 1 of the LED component L 1 has a primary spectrum of the generated primary light P 1 with a maximum at approximately 385 nm. The conversion component K 1 comprises a light-converting material in the form of quantum dots which have a good absorption below 450 nm, in particular an efficient absorption at 385 nm, and the secondary light S 1 of which has a secondary spectrum with a maximum of 450 nm. The half width is about 60 nm. The resulting color valence corresponds to blue light.The LED chip C 2 of the LED component L 2 has a primary spectrum of the generated primary light P 2 with a maximum at approximately 450 nm. The conversion component K 2 comprises a light-converting material in the form of quantum dots which have a good absorption below 500 nm, in particular an efficient absorption at 450 nm, and whose secondary light S 2 has a secondary spectrum with a maximum around 515 nm. The half width is about 60 nm. The resulting color valence corresponds to green light.The LED chip C 3 of the LED components L 3 has a primary spectrum of the generated primary light P 3 with a maximum at approximately 450 nm. The conversion component K 3 comprises a light-converting material in the form of quantum dots which have a good absorption below 650 nm, in particular an efficient absorption at 450 nm, and the secondary light S 3 of which has a secondary spectrum with a maximum of 640 nm. The half width is about 60 nm. The resulting color valence corresponds to red light.With reference to FIGS. 2A and 2B, the emission spectrum generated with the aid of the LED package 1 is illustrated in more detail. In this figure, the normalized intensity I is plotted over the wavelength λ in nm for different spectra.In FIG. 2A, the intensities of the spectra of individual LEDs of a known RGB LED package are shown. The respective spectra of the LEDs are marked with the respective colors blue (B), green (G) and red (R). The spectra of the RGB LEDs have a low half width. The total spectrum (dashed line) resulting from the superposition thereof is white light, which is however less homogeneous due to the low full width at half maximum of the individual spectra.In FIG. 2B, the secondary spectra of the secondary light S i corresponding to the respective LED units L i of the LED package 1 are shown. The respective conversion components K i broaden the full width at half maximum of the secondary spectra compared to the use of RGB LEDs. In the exemplary embodiment shown, the full width at half maximum is 60 nm in each case. The emission spectrum of the emission light A resulting from the superposition of the respective secondary light S i therefore has an intensity that is more homogeneous over the visible wavelength range (plotted from 380 nm to 780 nm). As a result, characteristic variables of the emission light, in particular a correlated color temperature and a color rendering index, are improved.The improvement of the characteristics of the emission light A will be explained in more detail with reference to FIGS. 3A, 3B, and 3C.In the figures, various characteristic variables are shown over the full width at half maximum FWHM of the secondary spectra of the respective LED units L i. FIG. 3 shows the correlated color temperature CCT (correlated color temperature) in Kelvin over the FWHM in nanometers of the secondary spectra. The cross "x" is the CCT of an overall spectrum of an RGB LED, as shown for example in FIG. 2A. In this case, the ratio of the intensities of the individual LEDs R, G and B to one another was chosen such that the color rendering index of the RGB LED is optimized. The half-width of the spectra of the RGB LED is typically about 15 nm. The solid curve shows the CCT of the output light A of the LED package 1. As the full width at half maximum increases, the CCT decreases with the ratio of the LEDs R, G, B remaining the same. While the RGB LED generates cold white light, neutral white and / or warm white output light A is generated in a simple manner by the LED package 1.In FIG. 3B, the color rendering index CRI (color rendering index) is shown over the full width at half maximum FWHM. The CRI of the RGB LED is again marked by a cross "x" at the corresponding half width of approximately 15 nm. The solid line shows the CRI for the output light A of the LED package 1 as a function of the full width at half maximum FWHM of the respective secondary spectra. The CRI is significantly improved compared to the RGB LED. The CRI is above 70. A spectral width of 60 nm to 120 nm is particularly advantageous for generating white light. For the generation of color light, the spectral width can be selected in particular between 20 nm and 60 nm.FIG. 3C shows the relative improvement of the CRI over the RGB LED. The improvement is at least 5%. Depending on the FWHM, the improvement may be 20% or more.FIG. 4 schematically shows a further exemplary embodiment of an LED package 1 a. Components which have already been described with reference to the exemplary embodiment in FIG. 1 bear the same reference numerals and are not explained again in detail. Functionally corresponding, but structurally different, components bear corresponding reference numerals supplemented by "a".The conversion components Ka i of the LED units La i are formed as a coating of the LED chips C i. The LED units La i and the integrated circuit 3 are encapsulated in a common transparent encapsulation 4. The encapsulation 4 leads to a high structural integrity and stability of the LED package 1 a.FIG. 5 schematically shows a further exemplary embodiment of an LED package 1 b. Components which have already been described with reference to the preceding exemplary embodiments bear the same reference numerals and are not explained again in detail. Functionally corresponding, but structurally different, components bear corresponding reference numerals supplemented by "b".The LED units Lb i are introduced into corresponding recesses 5 of the substrate 2b. For this purpose, the LED chips C are arranged in i on the bottom of the respective recess 5. The respective light conversion component Kb i serves as encapsulation, which fills the recess 5. Due to the arrangement in the recesses 5, the LED units Lb i are shielded from one another, so that neither primary radiation P i nor secondary radiation S i can fall directly from one of the LED units Lb i into another. This prevents crosstalk (crosstalk). By appropriate actuation of the LED units Lb i the respective colors can be generated independently of one another without any mixing occurring as a result of the unwanted excitation of the light conversion components Kb i of other LED units Lb i. The color reproduction is particularly precise.

Claims

Light-emitting device, in particular an LED package, having at least two LED units (L i; La i; Lb i), each having - at least one LED chip (C i) for generating primary light (P i) having a primary spectrum and - a conversion component (K i; Ka i; Kb i) for converting the primary light (P i) into a secondary light (S i) having a secondary spectrum which has a greater spectral width than the primary spectrum, wherein the secondary spectra of different ones of the at least two LED units (L i; La i; Lb i) are different.Light emitting device according to claim 1, characterized in that the secondary spectra of the different LED units (L i; La i; Lb i) have different color values.Light-emitting device according to one of the preceding claims, characterized in that the at least two LED units (L i; La i; Lb i) can be controlled independently of one another in order to set a mixture of the secondary spectra of the at least two LED units (L i; La i; Lb i), in particular by means of an integrated circuit (3) of the light-emitting device (1; 1a; 1b).Light-emitting device according to one of the preceding claims, characterized byat least three LED units (L i; La i; Lb i), the secondary spectra of which have color values which correspond to the primary colors of a color system.Light emitting device according to Claim 4, characterized bya colour rendering index (CRI) of an emission spectrum obtained by superposition of the secondary spectra of more than 70, in particular more than 75, in particular more than 80.Light-emitting device according to one of the preceding claims, characterized in that a spectral width of the secondary spectra is in each case between 15 nm and 120 nm.Light-emitting device according to one of the preceding claims, characterized in that the conversion component (K i; Ka i; Kb i) has at least one LED unit (L i; La i; Lb i) quantum dots of different diameters.Light emitting device according to one of the preceding claims, characterized in that the LED units (L i; La i; Lb i) are shielded from one another in such a way that light of one LED unit (L i; La i; Lb i) cannot radiate directly into the conversion medium (K i; Ka i; Kb i) of another LED unit (L i; Lai; Lbi).Light emitting device according to claim 8, characterized in that the LED units (L i; La i; Lb i) are arranged in respective recesses (5) of a substrate (2b).Light-emitting device according to one of the preceding claims, characterized in that at least one of the conversion components (K i, Kb i) forms an encapsulation for the respective LED chip (C i) which encapsulation contains a light-converting material.Light-emitting device according to one of the preceding claims, characterized in that at least one of the conversion components (Ka i) is applied as a coating to the respective LED chip (C i).Luminaire comprising at least one light-emitting device (1; 1a; 1b) according to one of the preceding claims.

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