Patent Application
20100213867
The present invention relates to a high-pressure discharge lamp.
High-pressure discharge lamps, in particular so-called HID lamps, have been known for a long time. They are used for various purposes, and above all for applications in which relatively good color rendering and very good luminous efficiency are required. These two properties are usually in conflict, i.e. improving one property degrades the other, and vice versa. The color rendering is generally more important for general lighting applications, but the situation is reversed for example in street lighting.
High-pressure discharge lamps are furthermore distinguished by a high power in relation to the size of the lamp or the size of the light-emitting region.
Here and in what follows, high-pressure discharge lamps are intended to mean only those lamps which have electrodes inside the discharge vessel. There are very many publications and an enormous amount of patent literature on the subject of high-pressure discharge lamps, for example WO 99/05699, WO 98/25294, and Born, M., Plasma Sources Sci. Technol., 11, 2002, A55.
DE Application 10 2006 034 833.8, which has not yet been published, discloses a molecular radiation-dominated high-pressure discharge lamp. With noncritical selection of the rare earth iodides, however, the problem of a sensitive power dependency of the color distance ΔC(P) in the event of a power variation often arises. The color distance is also referred to as the color difference or color deviation. Minor differences in the power from the working point with ΔC=0 lead to sizable ΔC values, which change very rapidly with an increasing power from positive to negative values or vice versa.
It is an object of the present invention to provide a molecular radiation-dominated high-pressure discharge lamp, which is distinguished by good color rendering over a large power range. It is also an object to achieve a maximally high efficiency of such a lamp.
This object is achieved by the characterizing features of claim 1.
Particularly advantageous configurations may be found in the dependent claims.
The aim of the present invention is to provide a high-pressure discharge lamp which is improved in respect of a good overall combination of luminous efficiency and color-rendering properties, and which is distinguished in particular by high consistency of the color rendering and by a small color deviation over a large power range. It has been found that this can expediently be achieved by combining at least two groups of rare earths as a constituent of the filling, the first group having the property that the color distance ΔC(P) decreases with a power increase when the power P of the lamp is increased in a predetermined power interval, and the second group having the property that the color distance ΔC(P) increases with a power increase when the power P of the lamp is increased in this predetermined power interval, so that a suitable combination of members of the two groups leads to a flat profile close to zero of the color distance ΔC(P) with a power increase. The change in the power may be regarded on the one hand from the perspective of dimmability, and on the other hand from the aspect of variation of the power in a sizable assembly of lamps and their variance of properties.
The invention relates to a high-pressure discharge lamp having a discharge vessel, which contains: electrodes, at least one noble gas as a start gas, at least one element selected from the group consisting of Al, In, 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 configured such that the generated light is dominated by molecular radiation.
Preferred configurations are specified in the dependent claims and will also be explained in more detail below. The invention relates in particular to a lighting system consisting of the high-pressure discharge lamp together with a suitable electronic ballast device for operating it.
The basic concept of the invention, as explained in DE Application 10 2006 034 833.8, is to utilize the radiation generated by molecules in the discharge medium very dominantly for the generation of light by the high-pressure discharge lamp. To this end the rare earth halide is provided for the generation of radiation, although other constituents of the discharge plasma may naturally also be involved in the generation of radiation.
Conventional high-pressure discharge lamps are dominated by atomic radiation. Molecular radiation conventionally occurs secondarily and has a broader-band spectral distribution compared with atomic radiation, and can thus entirely fill wider wavelength segments with radiation. In contrast to this, atomic radiation is inherently line radiation, although some broadening of the basically restricted color rendering properties of line radiation has been achieved in conventional lamps by a multiplicity of lines and various broadening mechanisms. Generally, however, the segments generated by such mechanisms are much smaller than in molecular radiation and the linewidths of atoms are closely correlated with other particle densities in a complicated way, and it is very difficult to influence particle densities in the lamp.
Here, promoting molecules in the radiation balance of the lamp also has the effect of allowing good absorption properties and therefore stronger thermalization. The term thermalization is in this case to be understood locally. The concept of local thermodynamic equilibrium is used, because naturally there is not in fact a homogeneous temperature distribution.
The lamp includes a noble gas or noble gas mixture as a start or a buffer gas, the noble gases Xe, Ar, Kr being preferred, and among these more particularly Xe. Typical cold fill partial pressures of the start gas lie in the range of from 10 mbar to 15 bar and preferably between 50 mbar and 10 bar, more preferably between 500 mbar and 5 bar and more particularly preferably between 500 mbar and 2 bar. An arc transfer and vessel wall heating component is furthermore provided, which includes at least one element selected from the group consisting of Al, In, Mg, Tl, Hg, Zn. These elements may be present as halides, in particular iodides or bromides, and the lamp may also be filled with them in this form, for instance as AlI3 or TlI. The start or buffer gas ensures cold startability and cold ignition of the discharge. Sufficient heating leads to evaporation of the arc transfer and vessel wall heating elements present in a chemical compound, or in the case of Al, Mg, In, Hg and Zn possibly also an elementary form. The corresponding chemical components in the resulting plasma carry the arc. The wall temperature increases owing to the modified plasma properties, so that the at least one rare earth halide also enters the vapor phase. This rare earth halide is preferably formed with an element from the group consisting of Tm, Dy, Ce, Ho, Gd, preferably from the group consisting of Tm, Dy, and more particularly preferably Tm. Here, as above, iodides or bromides are preferred. One example is TmI3. The components important for the start process, i.e. the start gas and the arc transfer and vessel wall heating elements, may now possibly play only a secondary role in the emission.
In contrast to conventional high-pressure discharge lamps, an arc is now created which is dominated by the molecular emission, in particular by the rare earth halides. Thulium iodide TmI may in particular be envisaged, since this is formed from the triiodide TmI3 with which the lamp is filled.
In principle, the lamp may in particular be filled with rare earth elements as triiodides, which become diiodides and finally monoiodides as a function of the temperature. Temporarily formed rare earth monoiodides, or in general monohalides, are particularly effective for the invention.
The role of the rare earth halides is not limited to generating the desired continuous radiation. They are also used for arc contraction, i.e. to reduce the temperature in the contraction regions and correspondingly change the ohmic impedance of the plasma.
In conventional high-pressure discharge lamps, distinction is traditionally made between so-called voltage gradient generators and light generators. The addition of a special voltage gradient generator is not categorically necessary in the present context and may even be counterproductive, at least beyond certain amounts. Owing to the special design of the temperature profile in the form of the contracted arc, species contained in the discharge core in any event clearly provide suitable formation of the plasma impedance. In particular, the classical voltage gradient generators Hg and Zn may be entirely or partially obviated, although the invention is not restricted to Hg— and Zn-free lamps. Merely the possibility of omitting or at least reducing the constituent Hg offers a significant advantage in environmental terms.
The constituents Hg and Zn may however also play a positive role for example in connection with wall interactions, or may even be desirable in order to increase the lamp voltage further, and the lamp may therefore contain a voltage gradient generator despite the option of obviating them per se.
In order to achieve very good radiation efficiencies, it has conventionally been usual to employ atomic radiation, and in particular that of Tl and Na. Not only is the use of atomic radiation in order to achieve high luminous efficiencies no longer necessary in the present context, but it is not even desirable owing to the color rendering properties, and in the case of Tl and Na above all owing to undesirable arc cooling. In particular, the introduction of Na should be entirely avoided or significantly restricted. The Na radiation in the infrared range at about 819 nm and other infrared lines of Na can leave the plasma substantially unimpeded because it is often optically very thin above a threshold wavelength, for instance above about 630 nm, and can cool the arc. Even though the spectral range around the Na resonance line at 589 nm cannot be regarded as optically thin, this radiation would also lead to undesirable cooling of the central arc regions. The temperatures in the arc would therefore be reduced undesirably.
A similar argument also applies for other species which have significant emissivities in the wavelength range of more than 580 nm, in particular K and Ca. The constituents Na, K and Ca should thus preferably be present at most in amounts which are not relevant for the emission properties and do not interfere with said domination by molecular radiation.
According to the invention, the plasma should be optically thick over a visible spectral range which is as wide as possible. This means that there is more substantial thermalization of the radiation before it emerges from the lamp, in comparison with conventional high-pressure discharge lamps, which creates a desirable approximation of a Planck-like spectral distribution. The Planckian radiation distribution corresponds to the idealized black-body radiator, and is interpreted as “natural” in human sensory perception.
Moreover, the pronounced radiation contributions of the additives Na, K and Ca “bend” the spectra and degrade the approximation to Planckian spectral behavior. Lines at wavelengths of more than 600 nm, however, can in principle scarcely be avoided because the rare earth halides no longer absorb significantly here and no other absorbers are available.
The approximation to Planckian spectral behavior can be measured by the so-called color difference ΔC. The lamp according to the invention should have a good, i.e. small ΔC value. When using ceramic discharge vessels, values of |ΔC|<10−2 can very advantageously be achieved here for general lighting purposes.
Good luminous efficiencies can be achieved with the high-pressure discharge lamp according to the invention, and to be specific preferably more than 90 lm/W. The color rendering properties should at the same time be very good, preferably with a color rendering index Ra of at least 90.
In particular cases, however, one of the two aims mentioned above, i.e. the color rendering properties or the luminous efficiency, may more particularly be of greater importance for the embodiment of the invention, for instance the luminous efficiency in the case of street lighting. The preferred field of application of the invention is however high-quality general lighting, for which both values are in the end important.
In one configuration, the domination by molecular radiation is quantified by a parameter AL, which is referred to here as the “atomic line component”. Claim 13 gives a definition of this atomic line component AL. It is preferably at most 40%, more preferably 35%, 30% or even at most 25%, even in the case of quartz discharge vessels. For ceramic discharge vessels, it is particularly preferably at most 20%, more preferably 15% and even at most 10%.
The particular stability when there is a variation in the power is achieved by suitably combining a plurality of rare earth halides as molecular radiators. In this context, two groups of rare earth halides are used together. A first group has the property that minor differences in the power from the working point with ΔC=0 lead to sizable ΔC values, which change rapidly with an increasing power from positive to negative values. One particularly suitable member of this group is Tm halide, in particular TmI3. A second group has the property that minor differences in the power from the working point with ΔC=0 lead to sizable ΔC values, which change rapidly with an increasing power from negative to positive values. One particularly suitable member of this group is Dy halide, in particular DyI3. Another highly suitable member of this group is GdI3, which may in particular be used in addition to Dy halide. A mixture which contains approximately equal molar amounts of the first and second groups, in particular from 25 to 75 mol % of the first group, is particularly highly suitable. A proportion of from 45 to 55 mol % is particularly preferred for the first group.
The favorable properties of a lamp according to the invention may above all be exploited and optimized in conjunction with an electronic ballast device, for which reason the invention also relates to a lighting system consisting of a lamp according to the invention with a suitable electronic ballast device.
The characteristic dimensions of the discharge vessel are the length l, the internal diameter d and the electrode spacing a, which will be discussed in more detail below.
Both the ceramic discharge vessel and the quartz glass discharge vessel are respectively fitted in an outer bulb (not shown) made of quartz glass, as is known per se. The outer bulb is evacuated. The electrical leads are fed out from the outer bulb through pinches which seal the outer bulb in a leaktight fashion, and are used for connecting the lamp to the electronic ballast device (EBD). From the mains voltage, the latter generates the square-wave excitation typically used for operating high-pressure discharge lamps, with a frequency of typically from 100 Hz to 400 Hz at a power of from 35 W to 400 W (“alternating DC voltage”).
The discharge vessel contains a filling with Xe as a start gas and AlI3 and TlI as arc transfer and wall heating elements, as well as TmI3.
The fill quantities and the characteristic dimensions of the discharge vessel vary according to the embodiment of the lamp.
Typical examples A1 to A6 are given in Table 1. The Xe pressure indicated is the cold fill pressure. The iodide quantities indicated are the absolute amounts added. The aforementioned geometrical parameters l, d, a are also indicated. The ΔC data are given in thousandths (E-3).
The electronic ballast device may preferably be designed to excite acoustic resonances, by imposing a radiofrequency amplitude modulation in a frequency range of for instance between 20 and 60 kHz. For more detailed explanation, reference is made for example to the Patent EP-B 0 785 702 and the references given therein. Excitation of acoustic resonances in this form leads to active stabilization of the discharge arc in the plasma, which can in particular also be advantageous in connection with the present invention owing to the relatively constricted shape of the temperature profile.
7E−3
The last four columns in Table 1 will be discussed in more detail below.
First, emission spectrum of the lamps will be presented for exemplary embodiments A1, A2 and A3. The way in which the atomic line component AL is determined will also be explained.
Superimposed on the serrated line which can be seen, corresponding to the resolution, there is in each case a curve for determining the continuous background, which is determined according to the following method. In particular, reference is made in this regard to the additional graphical explanations in
A further function Ih2(λ) is determined on the basis of this, intervals with the same width in turn being used around each individual wavelength value, i.e. with a total of 100 measurement points. In this case, however, the maxima of the function Ih1(λ) in these intervals are respectively used as function values Ih2. This creates a second function which lies somewhat closer to the measured profile, i.e. it extends between the measured profile Im(λ) and the function Ih1(λ) with the minima.
A third function Iu(λ) is determined on the basis of this, this time the average values of Ih2(λ) being determined again in the 30 nm width intervals around the respective wavelength values. This smooths the curve Ih2 considerably and leads in this example to the smooth lines indicated in
Essentially, this is only a relatively simple model procedure for determining a realistic continuous background, although it is objective and reproducible. With the background function Iu(λ) which has been found and the spectral distribution Im(λ) which has been measured, the atomic line component AL can then be determined as:
Here, the bright-adapted sensitivity of the human eye is jointly taken into account as a weighting function, and therefore at the same time also restricts the integration to the visible spectral range. The eye's spectral sensitivity V(λ) is shown in
In order to carry out the individual steps of determining Ih1(λ), Ih2(λ) and Iu(λ) as presented, with the full interval width of 30 nm, measurement values above 380 nm and below 780 nm are also required at the edge of the wavelength range.
However, weighting with the eye sensitivity V(λ), which is equal to zero outside the wavelength range of from 380 nm to 780 nm, means that carrying out the measurement only between 380 nm and 780 nm is sufficient in order to determine the atomic line component AL. When determining Ih1(λ), Ih2(λ) and Iu(λ), the interval size in the individual steps may then need to be restricted to the range available in the measurement values. In order to determine the values of Ih1(390 nm), Ih2(390 nm) and Iu(390 nm), for example, only the interval of from 380 nm to 405 nm is used instead of the interval of from 375 nm to 405 nm, corresponding to the interval width of 30 nm.
As may be seen for example in
If these troughs lie closer together than the interval width of 30 nm, then the background curve Iu(λ) determined in said way will be falsely pulled downward. In order to prevent this, the spectral resolution for measuring Im(λ) should be restricted to the range of from 0.25 nm to 0.35 nm.
The upper limit derives from the need to select the resolution high enough so that the atomic lines can actually be resolved.
If measurement is carried out with a spectral resolution higher than 0.25 nm, then the measurement Im(λ) must be converted to a spectral resolution within the limits of from 0.25 nm to 0.35 nm before determining Ih1(λ), Ih2(λ) and Iu(λ). This may, for example, be done by averaging over a plurality of neighboring measurement points.
Simply speaking, the atomic line component integrally describes the part of the measurement curve remaining above the background curve constructed as described above. It measures an area ratio relative to the area below the measurement curve overall.
In the present exemplary embodiments, the atomic line components are 4% for the ceramic lamps according to exemplary embodiments A1 and A2, and 12% for the quartz lamp according to exemplary embodiment A3. This shows that there is a relatively very large continuous background owing to the molecular dominance according to the invention in the emission, which greatly reduces the relative importance of the atomic line emission.
It can be seen that the spectrum behaves in a very Planck-like fashion until the red wavelength range of about 600 nm upward. Quantitatively, this means a color difference value ΔC of 3×10−4. The luminous efficiency was 94 lm/W with a color rendering index of Ra=92. This exemplary embodiment is therefore outstandingly suitable for general lighting.
In six individual diagrams,
Supplementarily, regarding the “color difference ΔC” reference is made to CIE Technical Report 13.3 (1995). This involves evaluating the quality of the light color of a lamp in respect of a sensory perception interpreted as “natural” by humans. The color difference is a measure of the closeness of the lamp spectrum to the Planckian radiation behavior up to a color temperature of 5000 K, or to daylight spectra above this limit. There are fields of application in which large values of the color difference are not problematic, although for more demanding lighting tasks, for example in general lighting, the lamp according to the invention should preferably have a color difference value with a magnitude of less than 10−2, more preferably less than 5×10−3 and even more preferably less than 2×10−3.
The constituents referred to in the exemplary embodiment may be replaced by alternatives in the scope of the teaching of this invention; for example, Xe may also very well be replaced fully or partially by Ar or Kr, or a noble gas mixture. AlI3 may for example be replaced by InI3, InI or MgI2, again fully or partially. The rare earth halide TmI3 may also be replaced, in particular by CeI3 or by other rare earth iodides or rare earth bromides or rare earth mixtures.
The ability to avoid components such as Hg constitutes an advantage of the invention. The lamp may however also contain some of them. The aforementioned pronounced radiation contributions of Na, K and Ca should be avoided, preferably fully or at least to such an extent that the described criterion for dominance of the molecular radiation remains fulfilled.
The exemplary embodiment contains a small amount of thallium iodide TlI. Owing to its resonance line at 535 nm, Tl is conventionally used to increase efficiency.
The conditions in the lamp should thus be configured so that the atomic line emission does not play an essential role in as large as possible a spectral range of the continuum in the visible range, i.e. the plasma is essentially optically thick in this wavelength range for this radiation, or this radiation is generated to a small extent. At the same time the molecular emission of rare earth halides, in particular monohalides, from the plasma should be a maximally promoted, in particular by minimizing the cooling due to emission in the spectral range in which the plasma is no longer optically thick enough. In the present exemplary embodiment, this spectral range extends from 380 nm to about 600 nm, and is therefore relatively large. Such large ranges are not however compulsory.
Commercial lamps exhibit line components of much more than 20%.
Another high-pressure discharge lamp with a ceramic discharge vessel of the type CMD-TD 942 150 W (manufacturer Philips) with a spectral distribution according to
The production of a molecular radiation-dominated, preferably Hg-free high-pressure discharge lamp, which is distinguished by good efficiency and color rendering over a large power range, will be described below in a particularly preferred embodiment.
So far, it has been shown that a relatively sensitive power dependency of the color distance ΔC must be tolerated when merely using for example TmI3 as a molecular radiator. Minor differences in the power from the working point with ΔC=0 lead to sizable ΔC values, which change very rapidly with an increasing power from positive to negative values. A similar behavior is also encountered when using other rare earths. The use of for example DyI3, on the other hand, leads to a ΔC(P) characteristic curve in which ΔC changes locally from negative values to positive values with an increasing power—which is the opposite to the characteristic curve of TmI3. A similar dependency is found for the color temperatures Tn(P). Spectra of lamps respectively containing TmI3 or DyI3 in the vicinity of the so-called working point (ΔC<2E-3) are represented by way of example in
Other exemplary embodiments are shown in
Specific exemplary embodiments, which relate to HoI3 and also GdI3, are explained in
A suitable combination of TmI3 and DyI3 is particularly preferred, because it allows the power dependency of ΔC and Tn to be adjusted deliberately with a particularly high efficiency. A suitable combination is advantageously a mixture which contains from 25 to 75 mol % TmI3, the remainder being DyI3. A TmI3 proportion of from 45 to 55 mol % is particularly preferred. A specific example with a 1:1 mixture is represented in
A suitable combination of these two groups of molecular radiators leads to spectra which are characterized by a particularly flat profile of ΔC(P) close to zero (ΔC<2E-3), as may be seen in
The most important parameters for the cylindrical discharge vessel used for the exemplary embodiment (see
All the fillings of the lamps contained 1 bar of Xe (cold fill pressure), 2 mg of AlI3 and 0.5 mg of TlI. The lamps were also provided with 4 mg of TmI3, 4 mg DyI3 or 2 mg of TmI3+2 mg of DyI3 as dominant molecular radiators. Instead of DyI3, or in addition to DyI3, GdI3 may preferably be used.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP07/57299 | 7/16/2007 | WO | 00 | 1/14/2010 |
