Abstract
A dimmable light source for emitting white overall radiation may include a dimmer and a light-emitting diode. The dimmer may vary a current intensity of a current for operating the light-emitting diode during the operation of the light source. The LED may include a semiconductor layer sequence to emit primary radiation, and the LED may further include a conversion element configured to at least partially convert the primary radiation into secondary radiation having a first emission band with a first emission maximum ranging from 400 nm to 500 nm and a second emission band with a second emission maximum ranging from 510 nm to 700 nm. A relative intensity of the first emission band may reduce with decreasing current intensity of the current for operating the LED, and a relative intensity of the second emission band may increase with decreasing current intensity of the current for operating the LED.
Claims
1. A dimmable light source for emitting white overall radiation, wherein the light source comprises: a dimmer; and two or more of the same light-emitting diodes, wherein: the dimmer is configured to vary a current intensity of a current for operating the two or more of the same light-emitting diodes during the operation of the light source; and each light-emitting diode of the two or more of the same light-emitting diodes comprises: a semiconductor layer sequence configured to emit primary electromagnetic radiation in the UV range of the electromagnetic spectrum during the operation of the light source; and a conversion element, comprising a converter material configured to at least partially convert, the primary electromagnetic radiation into secondary electromagnetic radiation, having a first emission band with a first emission maximum ranging from 400 nm to 500 nm and a second emission band with a second emission maximum of ranging from 510 nm to 700 nm; and wherein a relative intensity of the first emission band reduces with decreasing current intensity of the current for operating the two or more of the same light-emitting diodes, and a relative intensity of the second emission band increases with decreasing current intensity of the current for operating the two or more of the same light-emitting diodes; wherein the converter material comprises a first phosphor with the formula (MA)Si.sub.2O.sub.2N.sub.2:Eu with MA=Sr, Ca and/or Ba, and a second phosphor with the formula CaLu.sub.2Mg.sub.2Si.sub.3O.sub.12:Ce.
2. The dimmable light source as claimed in claim 1, wherein the converter material is configured to convert the primary electromagnetic radiation into the secondary electromagnetic radiation in full; and wherein the white overall radiation completely, corresponds to the secondary radiation.
3. The dimmable light source as claimed in claim 1, wherein a temperature of the converter material reduces with decreasing current intensity of the current for operating the two or more of the same light-emitting diodes.
4. The dimmable light source as claimed in claim 1, wherein the overall radiation has a correlated color temperature, which reduces with decreasing current intensity of the current for operating the two or more of the same light-emitting diodes.
5. The dimmable light source as claimed in claim 1, wherein the primary electromagnetic radiation has a wavelength ranging from 300 nm to 420 nm.
6. The dimmable light source as claimed in claim 1, wherein the converter material consists of the first phosphor with the formula (MA)Si.sub.2O.sub.2N.sub.2:Eu and the second phosphor with the formula CaLu.sub.2Mg.sub.2Si.sub.3O.sub.12:Ce.
7. The dimmable light source as claimed in claim 6, wherein the first phosphor has the formula (Sr.sub.xBa.sub.1-x)Si.sub.2O.sub.2N.sub.2:Eu with 0≤x≤0.5.
8. The dimmable light source as claimed in claim 6, wherein the first phosphor has the formula (Sr.sub.xBa.sub.1-x)Si.sub.2O.sub.2N.sub.2:Eu with x=0.25.
9. The dimmable light source as claimed in claim 1, wherein the first phosphor has the formula (Sr.sub.xBa.sub.1-x)Si.sub.2O.sub.2N.sub.2:Eu with 0≤x≤1.
10. The dimmable light source as claimed in claim 1, wherein the dimmer is a single dimmer.
11. The dimmable light source as claimed in claim 1, wherein the dimmer is configured to actuate the two or more of the same light-emitting diodes together.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Further advantageous embodiments and developments of the dimmable light source emerge from the exemplary embodiments described below in conjunction with the figures.
(2) In the embodiments and figures, components which are the same or of the same type, or which have the same effect, are respectively provided with the same references. The elements represented and their size ratios with respect to one another are not to be regarded as to scale. Rather, individual elements, in particular layer thicknesses, may be represented exaggeratedly large for better understanding.
(3) FIGS. 1 and 12 show a light source integrated in an electric circuit;
(4) FIGS. 2, 4 and 6 show emission spectra at different temperatures;
(5) FIGS. 3, 5 and 7 show color points at different temperatures in the CIE standard diagram (1931);
(6) FIG. 8 shows the dependence of the color rendering index Ra on the temperature;
(7) FIG. 9 shows the dependence of the correlated color temperature on the temperature;
(8) FIG. 10 shows the distance of color points from the Planck curve at different temperatures.
(9) FIG. 11 shows the dependence of the light yield on the temperature.
DETAILED DESCRIPTION
(10) FIG. 1 shows a light source 1, which is integrated into an electric circuit. The light source 1 includes a plurality of light-emitting diodes 2 and a dimmer 3. The light source 1 is connected to a power source 4, which supplies the current required for operating the light source 1. A current with constant current intensity or current density emerges from the power source 4. The dimmer 3 is configured to vary the current intensity or current density of the current such that the light-emitting diodes 2 can be supplied with current with different current intensities. The change in the current intensity can be altered by a user by way of a manual control element 5 and the overall radiation of the light source 1 can consequently be “dimmed”. The light-emitting diodes 2 have the same structure and consequently emit the same, or virtually the same, secondary radiation. Same light-emitting diodes should be understood to mean, in particular, that the semiconductor layers are based on the same semiconductor material and the conversion element contains the same converter material or the same converter material and the same matrix material, in particular also in the same quantities, within the scope of manufacturing tolerances. Therefore, the light-emitting diodes 2 can advantageously be operated with the same current; a separate actuation is not required. Further light-emitting diodes 2 of the same type can be connected in series or else in parallel (not shown).
(11) The structure of the light-emitting diodes 2, which is not illustrated in FIG. 1 for reasons of clarity, is described below: the light-emitting diodes 2 include a semiconductor layer sequence on the basis of InGaAlN and emit primary electromagnetic radiation in the UV range of the electromagnetic spectrum, for example at 400 nm, during the operation of the light source 1. A conversion element including a converter material is disposed in the beam path of the primary electromagnetic radiation, wherein the converter material consists of a phosphor KLi.sub.3SiO.sub.4:Eu (AB1), a first phosphor Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and a second phosphor (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB.sub.2) or a first phosphor Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and a second phosphor (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB3). The primary electromagnetic radiation is absorbed by the converter material and converted, in full or virtually in full, into secondary radiation that is emitted to the outside by the light source 1 as white overall radiation.
(12) If the current intensity of the current is reduced proceeding from a maximum current intensity by means of the dimmer 3, there is a change in the temperature of the converter material and, as a result thereof, there is a change in the color point of the overall radiation to lower correlated color temperatures. Advantageously, the color point of the overall radiation at different temperatures and hence at different current intensities lies on or near the Planck curve such that the overall radiation always appears white.
(13) Advantageously, it is consequently possible to provide a dimmable light source 1, which contains only one type of light-emitting diode 2 or only the same light-emitting diodes 2. Moreover, only one phosphor or a combination of two phosphors as a converter material is required for the light-emitting diodes 2. The secondary radiation of the converter material has a first emission band with a first emission maximum in the range of 400 nm to 500 nm and a second emission band with a second emission maximum in the range of 510 nm to 700 nm. Expressed differently, the emission spectrum of the converter material exhibits a first emission band with a first emission maximum in the range of 400 nm to 500 nm and a second emission band with a second emission maximum in the range of 510 nm to 700 nm. The relative intensity of the first emission band reduces with decreasing current intensity and the relative intensity of the second emission band increases with decreasing current intensity of the current with which the light-emitting diodes are operated. In particular, a decreasing relative light output power is connected to a decreasing relative intensity and an increasing relative light output power is connected to an increasing relative intensity, and so the component of the secondary radiation of the first emission band in the overall radiation reduces with decreasing current intensity while the component of the secondary radiation of the second emission band in the overall radiation increases. The different relative intensities of the first emission band and the second emission band can be traced back to the surprisingly different thermal quenching behavior of the emission bands. Since the temperature of the converter material increases with increasing current intensity, the different thermal quenching behavior can be exploited to provide a dimmable light source and consequently to imitate a conventional incandescent lamp.
(14) FIG. 12 shows a light source 1 from the prior art, which is integrated into an electric circuit. The light source 1 contains two types of light-emitting diodes 2a and 2b, which are connected in parallel and which are actuated separately. Accordingly, the light source 1 contains two dimmers 3. A microcontroller 6 is required for controlling the dimmers 3; said microcontroller not being required in the light source 1 as the latter contains only one dimmer 3. The light source 1 contains a sensor 7 for controlling the functionality of the microcontroller 6. The light-emitting diodes 2a emit white secondary radiation and the light-emitting diodes 2b emit red secondary radiation. The red and white secondary radiation are mixed by means of a diffusor 8 and yield the white overall radiation, which is emitted to the outside by the light source 1. In order to change the color point, the current intensity is modified separately by means of the dimmers 3 for the light-emitting diodes 2a and 2b, and so these are operated with current with different current intensities, and consequently the relative component of the secondary radiations of the light-emitting diodes 2a and 2b in the overall radiation is altered. Here, a higher component of red secondary radiation in the overall radiation results in a more warm white overall radiation, i.e., a lower correlated color temperature.
(15) Advantageously, in contrast to the known dimmable light source 1, only one type of light-emitting diodes 2 is required for changing the color point of the overall radiation and consequently for designing the light source 1 to be “dimmable” in the dimmable light source 1. Additionally, only one dimmer 3 is required in the light source and it is possible to dispense with further electronic components, such as a microcontroller 6 and a sensor 7, and also dispense with a diffusor 8 for mixing the secondary radiations.
(16) Consequently, the light source 1 is both more cost-effective and producible with less outlay than the dimmable light source 1 from the prior art. As a result of using the same light-emitting diodes 2 in the light source 1, the color point of the overall radiation in the case of a constant current intensity advantageously does not change over the service life of the light source 1. However, this occurs in the known light sources 1 with different light-emitting diode types 2a and 2b on account of the different aging stability of the different light-emitting diodes 2a and 2b.
(17) FIG. 2 shows the emission spectrum of the phosphor KLi.sub.3SiO.sub.4:Eu (AB1) at 25° C., 100° C., 150° C. and 200° C. Here, the wavelength λ in nanometers is plotted along the x-axis and the relative intensity rI in percent is plotted along the y-axis. For the purposes of measuring the emission spectra, the phosphor KLi.sub.3SiO.sub.4:Eu was applied to a heat-conducting substrate, brought to the corresponding temperature and excited by primary electromagnetic radiation in the UV range (400 nm). The emission spectrum of KLi.sub.3SiO.sub.4:Eu at the respective temperature exhibits a respective first emission band E1 with a first emission maximum, which is located in the range from approximately 440 nm to 470 nm, and a second emission band E2 with a second emission maximum, which is located in the range from approximately 570 to 630 nm. The first emission band E1 extends in each case from approximately 430 nm to 500 nm and the second emission band E2 extends in each case from approximately 500 nm to 730 nm. For reasons of clarity, the first emission band E1 and the second emission band E2 are only labeled for the emission spectrum at 25° C. in the figure. The emitted secondary radiation of the measured emission spectra at the different temperatures gives an observer an impression of shining in white. As is evident, the relative intensity of the first emission band E1 reduces in the case of decreasing temperature while the relative intensity of the second emission band E2 increases in the case of decreasing temperature. With a decreasing relative intensity of an emission band, the light output power from this emission band decreases and, with an increasing relative intensity of an emission band, the light output power from this emission band increases. Consequently, the component of secondary radiation in the wavelength range between 430 nm and 500 nm reduces with decreasing temperature and the component of secondary radiation in the wavelength range between 500 nm and 730 nm increases.
(18) Expressed differently, the long-wavelength, predominantly red component of the secondary radiation increases while the short-wavelength, predominantly blue component decreases, leading to a change in the color point of the secondary radiation. Since the temperature of the phosphor likewise decreases with a decreasing current intensity of a current with which a light-emitting diode with a conversion element containing the phosphor KLi.sub.3SiO.sub.4:Eu is operated, a light source containing such a light-emitting diode may surprisingly change the color point by varying the current intensity by means of a dimmer and hence said light source can be dimmed, wherein the overall radiation appears white both in the dimmed state and in the non-dimmed state.
(19) FIG. 3 shows the CIE standard diagram (1931), wherein the CIE x-component of the primary color red is plotted along the x-axis and the CIE y-component of the primary color green is plotted along the y-axis. In the CIE standard diagram, the color points of the secondary radiation of KLi.sub.3SiO.sub.4:Eu (AB1) are shown in the case of an excitation with primary electromagnetic radiation in the UV range (400 nm) at different temperatures. In the case of a decreasing temperature, the color points move on or along the Planck curve P to higher CIE x-values, and hence to a higher red component of the secondary radiation and lower correlated color temperatures. At 225° C., the correlated color temperature of the secondary radiation is at approximately 5400 K (cold white) and, at 25° C., it is at approximately 2860 K (warm white). As is evident, the color points of the secondary radiation are located at or near the Planck curve and the second radiation consequently appears white. A light source including a light-emitting diode with a conversion element containing the phosphor KLi.sub.3SiO.sub.4:Eu can consequently change the color point to lower correlated color temperatures by reducing the current intensity by means of a dimmer.
(20) FIG. 4 shows the emission spectrum of a combination of the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB2) at 25° C., 125° C., 175° C. and 225° C. Here, the wavelength λ in nanometers is plotted along the x-axis and the relative intensity rI in percent is plotted along the y-axis. For the purposes of measuring the emission spectra, the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce were mixed in a ratio to obtain a color point of the secondary radiation of the phosphors at or near the Planck curve such that an impression of shining in white is raised. The phosphors are applied to a heat-conducting substrate, brought to the corresponding temperature and excited by primary electromagnetic radiation in the UV range. The emission spectrum of the combination of the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce at the respective temperature exhibits a respective first emission band E1 with a first emission maximum in the range from approximately 460 nm to 490 nm and a second emission band E2 with a second emission maximum in the range from approximately 560 nm to 630 nm. For reasons of clarity, the first emission band E1 and the second emission band E2 are only labeled for the emission spectrum at 25° C. in the figure. The emitted secondary radiation of the measured emission spectra at the different temperatures gives an observer an impression of shining in white. As is evident, the relative intensity of the first emission band E1 reduces in the case of decreasing temperature while the relative intensity of the second emission band E2 increases in the case of decreasing temperature. Consequently, with a decreasing temperature, the component of secondary radiation in the wavelength range of the first emission band E1 decreases and the component of the secondary radiation of the second emission band E2 increases. Expressed differently, the long-wavelength, predominantly red component of the secondary radiation increases while the short-wavelength, predominantly blue component decreases, leading to a change in the color point of the secondary radiation. Since the temperature of the phosphors likewise decreases with a decreasing current intensity of a current with which a light-emitting diode with a conversion element containing the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce is operated, a light source containing such a light-emitting diode may surprisingly change the color point by varying the current intensity by means of a dimmer and hence said light source can be dimmed, wherein the overall radiation appears white both in the dimmed state and in the non-dimmed state.
(21) FIG. 5 shows the CIE standard diagram (1931), wherein the CIE x-component of the primary color red is plotted along the x-axis and the CIE y-component of the primary color green is plotted along the y-axis. In the CIE standard diagram, the color points of the secondary radiation of a combination of the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB2) are shown in the case of an excitation with primary electromagnetic radiation in the UV range at different temperatures. In the case of a decreasing temperature, the color points move on or along the Planck curve P to higher CIE x-values, and hence to a higher red component of the secondary radiation and lower correlated color temperatures. At 225° C., the correlated color temperature of the secondary radiation is at approximately 4800 K and, at 25° C., it is at approximately 3750 K. As is evident, the color points of the secondary radiation are located at or near the Planck curve and consequently appears white. A light source including a light-emitting diode with a conversion element containing the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce can consequently change the color point to lower correlated color temperatures by reducing the current intensity by means of a dimmer.
(22) FIG. 6 shows the emission spectrum of a combination of the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB.sub.3) at 25° C., 125° C., 175° C. and 225° C. Here, the wavelength λ in nanometers is plotted along the x-axis and the relative intensity rI in percent is plotted along the y-axis. For the purposes of measuring the emission spectra, the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce were mixed in a ratio to obtain a color point of the secondary radiation of the phosphors at or near the Planck curve such that an impression of shining in white is raised. The phosphors are applied to a heat-conducting substrate, brought to the corresponding temperature and excited by primary electromagnetic radiation in the UV range. The emission spectrum of the combination of Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce at the respective temperature exhibits a respective first emission band E1 with a first emission maximum in the range from approximately 460 nm to 490 nm and a second emission band E2 with a second emission maximum in the range from approximately 560 nm to 630 nm. The emitted secondary radiation of the measured emission spectra at the different temperatures gives an observer an impression of shining in white. As is evident, the relative intensity of the first emission band E1 reduces in the case of decreasing temperature while the relative intensity of the second emission band E2 increases in the case of decreasing temperature. Consequently, with a decreasing temperature, the component of secondary radiation of the first emission band decreases and the component of secondary radiation of the second emission band increases. Expressed differently, the long-wavelength, predominantly red component of the secondary radiation increases while the short-wavelength, predominantly blue component decreases, leading to a change in the color point of the secondary radiation. Since the temperature of the phosphors likewise decreases with a decreasing current intensity of a current with which a light-emitting diode with a conversion element containing the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce is operated, a light source containing such a light-emitting diode may surprisingly change the color point by varying the current intensity by means of a dimmer and hence said light source can be dimmed, wherein the overall radiation appears white both in the dimmed state and in the non-dimmed state.
(23) FIG. 7 shows the CIE standard diagram (1931), wherein the CIE x-component of the primary color red is plotted along the x-axis and the CIE y-component of the primary color green is plotted along the y-axis. In the CIE standard diagram, the color points of the secondary radiation of a combination of the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB3) are shown in the case of an excitation with primary electromagnetic radiation in the UV range at different temperatures. In the case of a decreasing temperature, the color points move on or along the Planck curve P to higher CIE x-values, and hence to a higher red component of the secondary radiation and lower correlated color temperatures. At 225° C., the correlated color temperature of the secondary radiation is at approximately 4200 K and, at 25° C., it is at approximately 3300 K. As is evident, the color points of the secondary radiation are located at or near the Planck curve and consequently the secondary radiation appears white. The distance of the color point from the Planck curve can be observed to increase with increasing temperature. A light source including a light-emitting diode with a conversion element containing the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce can consequently change the color point to lower correlated color temperatures by reducing the current intensity by means of a dimmer.
(24) FIG. 8 shows the dependence of the color rendering index Ra of the secondary radiation of the phosphor KLi.sub.3SiO.sub.4:Eu (AB1), a combination of the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB2) and a combination of the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB3) on the temperature during an excitation with primary electromagnetic radiation in the UV range. The color rendering index Ra is a measure for the quality of the rendering of colors of radiation and its maximum can be 100.
(25) AB1 exhibits an Ra of more than 80 over the entire temperature range. A radiation with an Ra of 80 or more is desirable for general illumination. Advantageously, Ra increases with increasing temperature. The light output power of the light source increases with increasing temperature since this has a higher emission of the primary electromagnetic radiation, which is provided for the conversion into the second radiation, as a consequence. High color rendering with a simultaneously high light output power is desirable, particularly in the case of cold white overall radiation of a light source, i.e., at high correlated color temperatures. By way of example, this overall radiation is suitable when good color rendering is required, for example one observing or creating pieces of art, while the requirements on the color rendering index of the overall radiation of the light source are lower in the dimmed state.
(26) In AB2 and AB3, Ra drops with increasing temperature. Light sources including a light-emitting diode with a conversion element containing combination of the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce or Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce are therefore predominantly suitable for applications in which warm white overall radiation is desired and the light source is consequently operated predominantly in the dimmed state and consequently at a comparatively low current intensity.
(27) FIG. 9 shows the dependence of the correlated color temperature CCT in K of the secondary radiation of the phosphor KLi.sub.3SiO.sub.4:Eu (AB1), a combination of the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB2) and a combination of the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB3) on the temperature in the case of an excitation with primary electromagnetic radiation in the UV range. The correlated color temperature is a measure as to whether white radiation is perceived as warm white or cold white. Usually, warm white radiation has a correlated color temperature below 3500 K and cold white radiation has a correlated color temperature above 3500 K. The correlated color temperature increases with increasing temperature in AB1, AB2 and AB3. Transferred to a light source, the correlated color temperature increases with increasing current intensity of the current with which the light source is operated. KLi.sub.3SiO.sub.4:Eu (AB1), a combination of the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB2) and a combination of the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB3) are consequently suitable for a dimmable light source including a light-emitting diode with a conversion element containing KLi.sub.3SiO.sub.4:Eu (AB1), a combination of the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB2) or a combination of the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB3). Advantageously, such light sources can change the color point to lower correlated color temperatures by reducing the current intensity by means of a dimmer.
(28) FIG. 10 shows the distance of the color points of the secondary radiation of the phosphor KLi.sub.3SiO.sub.4:Eu (AB1), a combination of the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB2) and a combination of the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB3) from the Planck curve in the case of excitation with primary electromagnetic radiation in the UV range, in SDCM units (“standard deviation of color matching” or “MacAdam ellipse steps” or threshold units) at different temperatures. All color points lie on or near the Planck curve and generate an impression of shining in white. The color points of the secondary radiation of AB1 exhibit a very small distance from the Planck curve, particularly in the range between 75 and 175° C., with a minimum distance at approximately 125° C.
(29) FIG. 11 specifies the light yield LER in lm/W of the secondary radiation of the phosphor KLi.sub.3SiO.sub.4:Eu (AB1), a combination of the phosphors Sr.sub.0.25Ba.sub.0.75Si.sub.2O.sub.2N.sub.2:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB2) and a combination of the phosphors Rb.sub.0.25Na.sub.0.75Li.sub.3SiO.sub.4:Eu and (CaLu.sub.2)Mg.sub.2Si.sub.3O.sub.12:Ce (AB3) in the case of excitation with primary electromagnetic radiation in the UV range, as a function of the temperature. It is evident that a light yield of more than 280 lm/W is reached for AB1 over the entire temperature range, with, at 304 lm/W, the highest light yield being obtained at approximately 125° C. At 125° C., the smallest distance of the color point from the Planck curve, and hence the “purest” white, is also obtained for the secondary radiation of AB1 (see FIG. 10). The secondary radiation of AB2 and AB3 exhibit a drop in the light yield with increasing temperature. Therefore, an application of a light source with AB2 and AB3 tends to find use in the dimmed state, and hence during operation with a current with a reduced current intensity.
(30) The description on the basis of the exemplary embodiments does not restrict the invention thereto. Rather, the invention includes every novel feature and every combination of features, containing every combination of features in the patent claims, in particular, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.
LIST OF REFERENCE SIGNS
(31) λ Wavelength AB Exemplary embodiment P Planck curve rI Relative intensity lm Lumen W Watt LER Light yield LED Light-emitting diode CCT Correlated color temperature Ra Color rendering index K Kelvin nm Nanometer T Temperature ° C. Degrees Celsius E1 First emission band E2 Second emission band 1 Dimmable light source 2 Light-emitting diode 3 Dimmer 4 Power source 5 Manual control element 6 Microcontroller 7 Sensor 8 Diffusor
