Patent Application
20090302784
The present invention relates to a high-pressure discharge lamp.
High-pressure discharge lamps, in particular so-called HID lamps, have long been known. They are used for various purposes, primarily also for applications in which relatively good color rendering and a very good luminous efficiency are required. These two variables are in this case usually interrelated, i.e. an improvement in one variable impairs the other, and vice versa. In general lighting applications, the color rendering is generally more important, but in street lighting, for example, the reverse is true.
High-pressure discharge lamps are also characterized by a high power in comparison with the size of the lamp or with the size of the light-emitting region of the lamp.
Here and in the text below, high-pressure discharge lamps are understood to mean only those lamps which have electrodes within the discharge vessel. There is a very large number of publications and an immense amount of patent literature relating to high-pressure discharge lamps, for example WO 99/05699, WO 98/25294, and Born, M., Plasma Sources Sci. Technol., 11, 2002, A55.
Individual fill components have also been investigated in microwave discharges, for example in the BMBF (Federal Ministry of Education and Research) project, Final Report, FKZ: 13N 7412/6, 2001, pages 3-8, pages 86-87 and pages 89-90. In this case, microwave discharges demonstrate the difference in comparison with discharges using electrodes that the heating of the discharge gas is carried out from the peripheral region out instead of from the inside out. Different temperature profiles are therefore set than in the case of discharges using electrodes.
As regards these properties, high-pressure discharge lamps have for some time been the subject of constant improvements. The present invention also has the aim of specifying a high-pressure discharge lamp which is improved as regards a good overall combination of luminous efficiency and color rendering properties.
The invention is directed to a high-pressure discharge lamp with a discharge vessel which contains: electrodes, at least one noble gas as starting gas, at least one element selected from the group consisting of Al, Tn, Mg, Tl, Hg, Zn for arc transfer and discharge vessel wall heating and at least one rare-earth halide for the generation of radiation, which is designed in such a way that the light generated is dominated by molecular radiation.
Preferred configurations are specified in the dependent claims and will be likewise explained in more detail below. In this case, the invention relates in particular also to a lighting system comprising the high-pressure discharge lamp together with an appropriate electronic ballast for the operation thereof.
The basic concept of the invention consists in the radiation generated by molecules in the discharge medium being utilized in very dominant fashion in the generation of light of the high-pressure discharge lamp. For this purpose, the rare-earth halide for the radiation generation is provided, with naturally also other constituents of the discharge plasma being capable of being involved in the radiation generation.
Conventional high-pressure discharge lamps are dominated by atomic radiation. Molecular radiation conventionally occurs to a subordinate extent and in this case has a broader-band spectral distribution in comparison with atomic radiation, i.e. can completely fill broader wavelength segments with radiation. In contrast to this, atomic radiation is naturally line radiation, in which, in conventional lamps, a certain improvement in the fundamentally restricted color rendering properties of line radiation is nevertheless achieved as a result of a large number of lines and various broadening mechanisms. In general, however, the segments generated by such mechanisms are markedly smaller than in the case of molecular radiation and, in addition, the line widths of atoms are fixedly correlated with further particle densities in a complicated manner, it being very difficult for particle densities in the lamp to be influenced.
Placing the emphasis on molecules for the radiation economy of the lamp in this case has at the same time the effect of making good absorption properties and therefore greater thermalization possible. The term thermalization is in this case to be understood locally. One refers to local thermodynamic equilibrium since in fact there is naturally no homogeneous temperature distribution.
A lamp according to the invention has a noble gas or noble gas mixture as the starting or buffer gas, with the noble gases Xe, Ar, Kr, and of these very particularly Xe, being preferred. Typical coldfilling partial pressures of the starting gas are in the range of from 10 mbar to 15 bar and preferably between 50 mbar and 10 bar, further preferably between 500 mbar and 5 bar and very particularly preferably between 500 mbar and 2 bar. In addition, an arc transfer and vessel wall heating component is provided which has at least one element from the group consisting of Al, Tn, Mg, Tl, Hg, Zn. In this case, these elements may be present in the form of halides, in particular iodides or bromides, and can also be introduced in this form, for example as AlI3 or TlI. The starting and buffer gas ensures the coldstarting ability and coldstart ignition of the discharge. After sufficient heating, the arc transfer and vessel wall heating elements, which are present as a chemical compound or, in the case of Al, Mg, In, Hg and Zn, possibly also in elemental form, evaporate The corresponding chemical components in the resultant plasma take on the arc. As a result of the changed plasma properties, the wall temperature increases, and therefore the at least one rare-earth halide also transfers to the vapor phase This rare-earth halide is preferably formed with an element from the group consisting of Tm, Dy, Ce, Ho, Gd, preferably the group consisting of Tm, Dy, and very particularly preferably Tm. As above, these are preferably iodides or bromides. An example is TmI3. The components which are important for the starting process, i.e. the starting gas and the arc transfer and vessel wall heating elements, now possibly only play a subordinate role in the emission.
In contrast to conventional high-pressure discharge lamps, an arc is now produced which is dominated by the molecular emission in particular of the rare-earth halides. In particular thulium monoiodide TmI comes into consideration, which is formed from the introduced triiodide TmI3.
In principle, rare-earth elements can be introduced in particular as triiodides, which become diiodides and finally monoiodides as a function of temperature. Particularly effective for the invention are the temporarily formed rare-earth monoiodides or generally monohalides.
The role of the rare-earth halides is not restricted to the generation of the desired continuous radiation. They are at the same time used for arc contraction, i.e. for reducing the temperature in the contraction regions and correspondingly changing the nonreactive resistance of the plasma.
In conventional high-pressure discharge lamps, a distinction is traditionally drawn between so-called voltage formers and light formers. The addition of a special voltage former in the present context is not absolutely necessary and can, in any case above certain quantities, also be counterproductive. Owing to the special formation of the temperature profile in the form of the contracted arc, species contained in the discharge core nevertheless obviously take on a suitable resistance formation of the plasma. In particular, it is also possible to entirely or partially dispense with the conventional voltage formers Hg and Zn, with the invention not being restricted to Hg-free or Zn-free lamps. To be able to omit or at least reduce the Hg constituent forms a marked advantage already in terms of environmental points of view.
The constituents Hg and Zn can, however, play a positive role, for example, even in connection with wall interactions and may nevertheless be desirable for further increasing the lamp voltage and therefore may be included despite the fact that a voltage former can actually be dispensed with.
In order to achieve very good radiation yields, it has conventionally been usual to use atomic radiation, in particular that of Tl and Na. The need to use atomic radiation for achieving high luminous efficiencies is not only not necessary in the present context but, owing to the color rendering properties, is also not desirable in the case of Tl and Na primarily owing to the undesired arc cooling. In particular, the introduction of Na should be refrained from entirely or markedly restricted. The Na radiation in the infrared at approximately 819 nm and further infrared lines of the Na can leave the plasma largely unimpeded, since it is often optically very thin above a limit wavelength, for example above approximately 630 nm, and can cool the arc. Even if the spectral range about the Na resonance line at 589 nm cannot be designated as optically thin, this radiation would also result in undesirable cooling of the central arc regions. Thus, the temperatures in the arc would be reduced in an undesirable manner.
Similar arguments also apply to other species which have significant emission capabilities in the wavelength range of above 580 nm, in particular K and Ca. The constituents Na, K and Ca should therefore preferably be present at most in those quantities which are not relevant to the emissions properties and which do not disrupt the mentioned domination by molecular radiation.
According to the invention, the plasma should be optically thick over a visible spectral range which is as broad as possible. This means that there is further-reaching thermalization of the radiation in comparison with conventional high-pressure discharge lamps prior to the exit of said radiation from the lamp, which produces a desirable approximation to a Planckian spectral distribution. The Planckian spectral distribution corresponds to the idealized blackbody radiator and is found to be “natural” in human sensory perception.
Moreover, the pronounced radiation contributions of the additives Na, K and Ca “bend” the spectra and impair the approximation to the Planckian spectral response. Lines at wavelengths over 600 nm can, however, in principle barely be avoided since in this case the rare-earth halides no longer absorb to a notable extent and also there are no other absorbers available.
The proximity to the Planckian radiation response can be calculated using the so-called chromaticity difference ΔC. The lamp according to the invention should have a good, i.e. a low, ΔC value. When using ceramic discharge vessels, very advantageous values of |ΔC|<10−2 can be achieved for general lighting purposes.
With the high-pressure discharge lamp according to the invention, good luminous efficiencies can be achieved, to be precise preferably over 90 lm/W. At the same time, the color rendering properties should be good, to be precise preferably with a color rendering index Ra of at least 90.
In specific cases, when implementing the invention, however, one of the two abovementioned aims, the color rendering properties or the luminous efficiency, can be very markedly in the foreground, for example the luminous efficiency in the case of streetlighting. The preferred sector of application of the invention, however, is high-quality general lighting, in which ultimately both variables are of relevance.
The domination by molecular radiation is quantified in a configuration of the invention by a parameter AL, which in this case is referred to as the “atom line component”. Claim 12 specifies the determination of this atom line component AL. It is preferably at most 40%, better 35%, 30% or even at most 25%, to be precise also in the case of quartz discharge vessels. In the case of ceramic discharge vessels, it is particularly preferably at most 20%, better 15% and even at most 10%.
Particular stability in terms of the variation of the power is achieved by a plurality of rare-earth halides being combined in a suitable manner as molecular radiators. In this case, two groups of rare-earth halides are used jointly. A first group has the property that small discrepancies in the power from the working point where ΔC=0 result in higher ΔC values, which transfer with a steep gradient from positive to negative values as the power increases. A particularly suitable representative of this group is Tm halide, in particular TmI3. A second group has the property that small discrepancies in the power from the working point where Δ=0 result in higher ΔC values, which transfer with a steep gradient from negative to positive values as the power increases. A particularly suitable representative of this group is Dy halide, in particular DyI3. A further well suited representative of this group is GdI3, with it being possible for the latter to be used in particular in addition to Dy halide. Particularly well suited is a mixture which contains approximately equal molar quantities of the first and second groups, in particular 25 to 75 mol % of the first group. Particularly preferred is a proportion of 45 to 55 mol % of the first group.
The favorable properties of a lamp according to the invention can be utilized and optimized primarily in conjunction with an electronic ballast, for which reason the invention also relates to a lighting system comprising a lamp according to the invention with an appropriate electronic ballast.
The characteristic dimensions of the discharge vessels are the length l, the inner diameter d and the electrode gap a, which will be described in more detail below.
Both the ceramic and the quartz glass discharge vessel are each introduced into an outer bulb (not illustrated) consisting of quartz glass, as is known per se. The outer bulb is evacuated. The power supply lines are passed to the outside from the outer bulb via pinch seals, which tightly seal the outer bulb, and are used for connecting the lamp to the electronic ballast (EB). Said electronic ballast generates from the system voltage the typical square-wave excitation for the operation of high-pressure discharge lamps with a frequency of typically 100 Hz to 400 Hz given a power of 35 W to 400 W (“alternating DC voltage”). A basic circuit diagram with the system voltage denoted by AC for short, the electronic ballast denoted by EB and the lamp is shown in
The discharge vessel contains a fill with Xe as the starting gas and AlI3 and TlI as the arc transfer and wall heating elements and TmI3.
The fill quantities and the characteristic dimensions of the discharge vessel vary depending on the embodiment of the lamp.
Typical examples A1 to A6 are listed in table 1. The Xe pressure specified is the coldfilling pressure. The iodide quantities specified are the absolute quantities added. The above geometry parameters l, d, a are also given. The figure for ΔC is given in thousandths (E-3).
Preferably, the electronic ballast can be designed to excite acoustic resonances by a radiofrequency amplitude modulation being applied in a frequency range of approximately between 20 and 60 kHz. For a more detailed explanation, reference is made by way of example to the patent EP-B 0 785 702 and the references therein. Excitation of acoustic resonances in this form results in the active stabilization of the discharge arc in the plasma, which may be advantageous in particular also in connection with the present invention as a result of the relatively constricted form of the temperature profile.
The four last columns in table 1 will be described in more detail below.
First, emission spectra of the lamps will be illustrated with respect to exemplary embodiments A1, A2 and A3. In this case, the determination of the atom line component AL will also be explained.
In each case one curve determined in accordance with the following method is superimposed on the line which, as can be seen, is zigzagged corresponding to the resolution, for determining the continuous background. Particularly, reference is made in this regard to the additional graphic explanations in
From this a further function Ih2(λ) is determined, with in turn intervals of the same width, i.e. with in total 100 measurement points, being used around each individual wavelength value. In this case, however, in each case the maxima of the function Ih1(λ) in these intervals are used as the function values Ih2. A second function results which comes slightly closer to the measured profile, i.e. runs between the measured profile Im(λ) and the function Th1(λ) with the minima.
From this, a third function Iu(λ) is determined, with in turn the means of Ih2(λ) this time being determined in the 30 nm width intervals around the respective wavelength values. This smoothes the curve Ih2 markedly and, in this example, results in the smooth lines illustrated in
In principle, this is a relatively simple procedure merely in the form of a model for determining a realistic continuous background, which is nevertheless objective and reproducible.
With the background function Iu(λ) determined and the spectral distribution Im(λ) measured, the atom line component AL can then be determined as:
In this case, the light-adapted sensitivity of the human eye is also taken into consideration as a weighting function and, as a result, at the same time the integration is also restricted to the visible spectral range. The spectral eye sensitivity V(λ) is shown in
In order to implement the individual steps for determining Ih1(λ), Ih2(λ) and Iu(λ) as illustrated with the full interval width of 30 nm, measured values below 380 nm and above 780 nm are also required at the edge of the wavelength range.
By means of weighting with the eye sensitivity V(λ), which is equal to zero outside of the wavelength range 380 nm to 780 nm, it is nevertheless sufficient to measure only between 380 nm and 780 nm in order to determine the atom line component AL. During the determination of Ih1(λ), Ih2(λ) and Iu(λ), the interval size then needs to be restricted possibly to the range provided in the measured values in the individual steps. In order to determine the value of Ih1 (390 nm), Ih2 (390 nm) and Iu(390 nm), for example, the interval 375 nm to 450 nm corresponding to the interval width of 30 nm is not used, but only the interval of 380 nm to 405 nm.
As can be seen, for example, in
If these dips are more dense than the interval width of 30 nm, the background curve Iu(λ) determined in the mentioned manner are erroneously drawn downwards. In order to prevent this, the spectral resolution in the measurement of Im(λ) can be restricted to the range 0.25 nm to 0.35 nm.
The upper limit results from the necessity to select the resolution to be so high that the atom lines can be resolved at all.
If the measurement takes place at a higher spectral resolution than 0.25 nm, the measurement of Im(λ) must be converted to a spectral resolution within the limits of 0.25 nm to 0.35 nm prior to the determination of Ih1(λ), Ih2(λ) and Iu(λ). This can take place, for example, by means of mean value generation over a plurality of adjacent measurement points.
By way of illustration, the atom line component describes, in integrated fashion, that part of the measurement curve which remains above the background curve constructed as described above. In this case, it calculates a relative area ratio with respect to the area below the measurement curve as a whole.
In the present exemplary embodiments, the atom line components are 4% for the ceramic lamps in accordance with exemplary embodiments A1 and A2 and 12% for the quartz lamp in accordance with exemplary embodiment A3. It is thereby demonstrated that, as a result of the molecule dominance according to the invention in the emission, a relatively very large continuous background exists which has significantly reduced the relative importance of the atomic line emission.
It can be seen that the spectrum up to in the red wavelength range of approximately above 600 nm has a very Planckian response. Quantitatively, this means a size of the chromaticity difference ΔC of 3×10−4. The luminous efficiency was 94 lm/W given a color rendering index of Ra=92. Thus, this exemplary embodiment is very suitable for general lighting.
Reference is additionally made to the CIE Technical Report 13.3 (1995) in relation to the variable “chromaticity difference ΔC”. This concerns the evaluation of the quality of the light color of a lamp as regards a sensory perception which is regarded as “natural” by humans. The chromaticity difference is a measure of the proximity of the lamp spectrum to the Planckian radiation response up to a color temperature of 5000 K or up to daylight spectra above this limit. There are application fields in which high values of the chromaticity difference do not have a disruptive effect, but the lamp according to the invention should preferably have a chromaticity difference value in an amount of below 10−2, better below 5×10−2 and better still below 2×10−3 for more demanding lighting tasks for example in general lighting.
The constituents mentioned in the exemplary embodiment can be replaced in the context of the teaching of this invention by alternatives; for example Xe can also very easily be completely or partially replaced by Ar or else Kr or a noble gas mixture. AlI3 can be replaced, for example, by InI3, InI or else by MgI2, to be precise in turn completely or partially. The rare-earth halide TmT3 can also be replaced, in particular by CeI3 or else by other rare-earth iodides or bromides or mixtures.
One advantage of the invention is to be able to dispense with components such as Hg. However, these can also be included. The pronounced contributions to radiation of Na, K and Ca already mentioned should preferably be dispensed with entirely or in any case to such an extent that the described criterion for dominance of the molecular radiation is still met.
The exemplary embodiment contains a small quantity of thallium iodide TlI. Tl is used conventionally for increasing efficiency owing to its resonance line at 535 nm.
The conditions in the lamp should therefore be configured in such a way that the atomic line emission does not play a significant role in a spectral range of the continuum which is as large as possible in the visible range, i.e. the plasma is substantially optically thick in this wavelength range for this radiation or this radiation is generated to a lesser extent. At the same time, the molecular emission of rare-earth halides, in particular monohalides, from the plasma should be promoted to a maximum extent, in particular by virtue of the fact that arc cooling is minimized by emission in the spectral range in which the plasma is no longer sufficiently optically thick. In the present exemplary embodiment, this spectral range extends from 380 nm to approximately 600 nm and is therefore relatively large. Such large ranges are not absolutely essential, however.
Commercial lamps demonstrate line components of markedly above 20%. One example is shown in
Another high-pressure discharge lamp with a ceramic discharge vessel of the type CDM-TD 942 150 W (manufacturer Philips) with the spectral distribution as shown in
In a particularly preferred embodiment, the implementation of a molecular-radiation-dominated, preferably Hg-free high-pressure discharge lamp will be described below which is characterized by good efficiency and color rendering over a large power range.
Until now it has been demonstrated that the sole use of, for example, the TmI3 as the molecular radiator involves a relatively sensitive power dependency of the color gap ΔC. Small discrepancies in the power from the working point where ΔC=0 result in relatively large ΔC values, which transfer at a very steep gradient from positive to negative values as the power increases. A similar response is also found in the case of other rare earths. The use of, for example, DyI3, on the other hand, results in a ΔC(P) characteristic with which ΔC transfers from negative values to positive values, in sections, as the power increases—in opposition to the characteristic of TmI3. A similar dependency results for the color temperatures Tn(P). Spectra of the respective TmI3- or DyI3-containing lamps in the vicinity of the so-called working point (ΔC<2E-3) are illustrated by way of example in
Further exemplary embodiments are shown in
Specific exemplary embodiments which relate to HoI3 and also GdI3 are explained in
A suitable combination of TmT3 and DyT3 is particularly preferred since it allows the power dependency of ΔC and Tn to be set in a targeted manner given particularly high efficiency. A suitable combination is advantageously a mixture which contains from 25 to 75 mol % of TmI3, with the remainder being DyI3. Particularly preferred is a content of 45 to 55 mol % of TmI3. A specific example with a 1:1 mixture is illustrated in
A suitable combination of these two groups of molecular radiators results in spectra which are characterized by a particularly flat profile of ΔC(P) close to zero (ΔC<2E-3), as can be seen in
The most important parameters of the cylindrical ceramic discharge vessel used for the exemplary embodiment (see
The fills of the lamps all contained 1 bar of Xe (coldfilling pressure), 2 mg of AlI3 and 0.5 mg of TlI. In addition, in each case 4 mg of TmI3, 4 mg of DyI3 and, respectively, 2 mg of TmI3+2 mg of DyI3 as the dominant molecular radiator were added to the lamps. Instead of DyI3 or else in addition to DyI3, GdI3 can preferably be used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 034 833.8 | Jul 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP07/57316 | 7/16/2007 | WO | 00 | 8/13/2009 |
