EP0535311B1 - Low power, high pressure discharge lamp - Google Patents

Description

The invention relates to a high-pressure discharge lamp of low power. This means the range of around 35 - 200 W.

These are preferably metal halide lamps for general lighting, which are essentially characterized by a warm white light color (WDL) or neutral light color (NDL) corresponding to a color temperature of approximately 2600-4600 K.

Criteria for the suitability in general lighting are in particular a long lifespan of ≧ 6000 hours and the best possible color rendering, which is expressed in a high Ra index. A minimum value of Ra₈ = 80 is sought for the overall color rendering index. In addition, however, the individual index R9, which forms a yardstick for the reproduction in the red spectral range, is of particular importance. So far it has not been possible to find a satisfactory compromise between long service life and good color rendering.

DE-C-2 106 447 is one for the NDL light color developed filling from halides of sodium and various rare earth metals (SE) known. However, this filling is not suitable for the WDL light color, since too high a wall load would be required to achieve this light color, which, in connection with the fact that the major part of the rare earth material is present in the lamp as condensate, quickly becomes one chemical reaction of the filling substances with the quartz glass leads (devitrification), which significantly affects the service life.

Another system that has already been tried and tested specifically for the light color WDL is a Na-Sn filling (DE-C-26 55 167), with which, however, no satisfactory color rendering has yet been achieved and which, moreover, leads to severe electrode corrosion if incomplete removal of unwanted residual gases can.

Another alternative is the pure Na-Sc filling (EP-B-165 587), which has so far found widespread use particularly in the USA, the relatively poor color rendering properties of this system so far in favor of the long service life (over 6000 hours) Purchased were: a total color rendering index Ra₈ of only about 70 and an R9 of -90.

To improve the lamp behavior, various additives have been tested in the Na-Sc system, in particular halides (abbreviated to H.) of the thorium (for example EP-B-220 633) and the thallium. In US-A-4 866 342 for color temperatures between 3800 and 4600 K (corresponding to the light color NDL) and a high power (400 W) as a dosage a molar ratio between Na-H.:Sc-H. from 25: 1 to 50: 1 and accordingly a ratio between Na-H.:Tl-H. from 75: 1 to 280: 1.

A similar dosing regulation can be found in DE-C-3 341 846 for a motor vehicle discharge lamp, which have typical color temperatures of 4500 K (neutral white). The color rendering does not matter.

To improve the Na-Sc system, other tricks have also been tried, for example the addition of elemental scandium (EP-B-173 235), a coating on the discharge vessel (EP-B-220 633 and 173 235) or the evacuation of the Outer bulb using an additional heat accumulation tube (EP-B-165 587).

Special efforts are made in EP-B-215 524 to achieve a satisfactory lamp with good color rendering and low color temperature (corresponding to WDL). The lamp is based on a Na-Tl system, possibly with the help of rare earth additives (including Sc). However, the lamp must be operated with such a high wall load (> 25 W / cm², typically 60 W / cm²) that a ceramic discharge vessel must be used. In addition, several geometric relationships with regard to the discharge volume and the electrode arrangement must be maintained. This solution is theoretically interesting, but in practice unsatisfactory if only because the use of ceramic material is a completely new technology requires what is associated with significant additional costs and problems. This relates in particular to the permanent tightness of the implementation and the development of halogen-resistant glass solders.

It is an object of the present invention to provide a high-pressure discharge lamp with a low-power metal halide filling which is suitable for interior lighting and which is accordingly characterized by a relatively low color temperature, good color rendering and a long service life. Another task is to retain the quartz glass technology for the discharge vessel, which has proven itself per se, if possible.

This object is solved by the features of claim 1. Particularly advantageous embodiments of the invention can be found in the subclaims.

The desire to develop a discharge lamp of low wattage with good color rendering and a long service life for interior lighting has existed for many years without it being possible to find a fully satisfactory solution. The problem is that the two desired features are mutually exclusive and that the luminous efficiency deteriorates when the color rendering index is increased. A compromise that is as balanced as possible must therefore be found between conflicting demands. In principle, the individual technical features that come into question are known for a long time. However, they are so intricately linked that only practical attempts make it possible to find an optimal combination.

The choice of filling components and their relative proportions is of fundamental importance. Special advantages can be achieved with a suitable choice of the material and the geometric dimensions of the lamp bulb.

An important aspect of the invention is the consideration that with careful selection of the filling components, the wall load of a discharge vessel made of quartz glass can be chosen to be higher than the experts have assumed up to now. Up to now, a limit of 20 W / cm² has generally been regarded as the limit value, which can be seen, for example, in the "Technical and Scientific Treatments of the OSRAM Society" (TWAOG), Volume 12, Springer Verlag, Heidelberg 1986, page 11 et seq 15), is expressed. Another document is DE-A-40 13 039, page 3. The wall load increases with decreasing power level. This compensates for the heat losses that increase with the correspondingly small lamp dimensions. It is particularly critical for power levels below 100 W, which are particularly preferred for interior lighting.

On the basis of this basic consideration, a filling system was sought which forms little sediment (condensate) from aggressive materials when the lamp is in operation, because it has been found that this condensate additionally forms the vessel material and the lifespan is shortened due to increased devitrification. The obvious and usually tried and tested Na-SE system is unsuitable for this, because it has to be operated saturated in order to achieve a long service life, with about 90% (!) Of the filling material in the sediment. A saturated Na-Sc system as described in EP-B-220 633 is also unsuitable.

Surprisingly, however, it has now been shown that the Na-Sc system, which is already known per se for lamps with relatively poor color rendering (Ra = 70), has the best prerequisites for the above-mentioned. To achieve goals when Tl is added. However, this Na-Sc-Tl system is only able to meet the desired requirements if it deviates from the usual dosage (molar ratio Na-H.:Sc-H. = 25 ... 50: 1 or Na-H.:Tl-H. = 75 ... 280: 1) is used.

According to the invention, a molar ratio of Na-H.:Sc-H. from 5 ... 24: 1 (preferably from 5 ... 22: 1, particularly preferably from 5 ... 19: 1) and Na-H.:Tl-H. from 25 ... 73: 1 used. The sodium content is therefore reduced. A Na-Sc ratio below 25: 1 leads to an improvement in the service life, because then the Na-Sc-X₄ complex (X = halogen), which is equally important for the light generation and devitrification of the bulb and is known to form in lamp operation, becomes unsaturated is present. It has completely evaporated and is therefore not available in the form of condensate for a reaction between the wall and the filling, which leads to devitrification. On the other hand, there is a soil body of Na halide (especially NaI), which does not play a role in devitrification. The present invention is therefore essentially based on the knowledge of the different roles of these two sodium compounds in relation to the filling / wall reaction and on the consequences drawn from them. The result is a partially saturated lamp that is designed to be saturated with respect to the Na halides but unsaturated with respect to the complex compound and the Sc and Tl halides. If the Na-Sc ratio is below 5: 1, the desired color temperature cannot be achieved.

The reduction in the amount of sodium is compensated for by two measures: the first is a corresponding increase in the cold spot temperature in order to achieve the same warm white light color. This is done using a reflective coating. In particular, it is heat accumulation at the two ends of the two-sided squeezed discharge vessel. The heat accumulation behavior must be optimized so that the cold spot temperature Tc exceeds 800 ° C; Previously common Tc values were around 600-800 ° C for quartz glass, whereas higher Tc values were previously only possible with ceramic discharge tubes. This temperature is achieved particularly elegantly by a layer thickness of the heat accumulation covering which is considerably increased compared to previous versions. This effect can be intensified by evacuating the outer bulb. Under these conditions the sodium vapor density is so great that the Na resonance line at 589 nm is considerable in the spectrum of the lamp appears widened in pressure and self-absorbed in the middle. In this way, an additional improvement in red rendering (R9) is achieved by the emission in the long-wave wing of the resonance line. Particularly good results can be achieved if the operating conditions are chosen such that the distance between the maximum values (crests) of the two wings is approximately 7-12 nm.

The second measure is the use of Tl in the dosage according to the invention. The task of the Tl is not so much in its direct contribution to improving color rendering. The focus is rather on the fact that it partially takes on the function of Na as an electron supplier. As a result, the degree of ionization of the Na vapor phase is reduced accordingly. A large part of the sodium is therefore present as a neutral atom, which supports the broadening of the Na resonance line. The thallium additive is dimensioned so that the lamp, when baked (after approx. 100 hours), lies almost exactly on the Planck curve and thus harmonises well with other light sources. A Na-Tl ratio below 25: 1 would give the lamp a green tinge. A ratio above 73: 1 would have an unfavorable effect on the burning voltage and the reignition behavior.

In the case of warm white light colors, it has proven to be particularly advantageous to use a Na / Tl ratio between 25: 1 and 50: 1 if iodine is used exclusively as the halide. For neutral white light colors, a Na-Tl ratio of 40: 1 to 73: 1, in particular from 50: 1 to 73: 1, is preferably suitable. This applies to pure iodine fillings as well as to mixed fillings made from iodine and bromine.

In particular, it has been shown that the heat accumulation behavior can be influenced favorably by carefully designing the heat accumulation coating in the form of two calottes. The decisive factor here is the thickness of the covering, its purity and the distance between the two covering domes. Zirconium oxide or aluminum oxide with a purity of at least 97% according to DE-OS 38 32 643 is advantageously used. With regard to the layer thickness, the dimensioning of which has so far been given no particular attention, care must be taken that it is sufficiently large, namely optically thick. The thickness of an aluminum or zirconium oxide layer must be at least 0.15 mm. The distance between the two spherical caps of the covering should advantageously be chosen so that it is approximately 90 to 105% of the electrode distance.

The absolute dosage of the Na-Sc-Tl system is preferably 2.5 to 5.5 mg / cm³, based on the internal volume of the discharge vessel, so that the system is just at the limit of saturation. Iodine, possibly with a certain proportion of bromine, can be used as halogen.

As a result of a certain loss of filling substance in the first 100 hours of operation, the Sc partial pressure decreases, since the Sc, unlike Na, has no replenishment from the soil. This is associated with a shift towards lower color temperatures. It is therefore advisable to add a small amount of elemental scandium as a compensation, which can reduce the color drift at the start of the burning time.

Another or additional possibility for reducing the color drift is the partial use of bromine as the halide, whereby the amount of iodine can be replaced by bromine up to 70%. Typical values are 30%, regardless of the light color. The use of bromine is already known as a theoretical alternative to pure iodine fillings from US Pat. No. 4,866,342, but it has not yet been used in the lamps according to the invention. Only now has the behavior of a mixed filling of iodine and bromine been clarified to such an extent that their use appears to be particularly advantageous.

As a result of the greater binding energy of the ScBr₃ compared to ScI₃, the undesired interaction of the scandium halide with the quartz wall of the discharge vessel with formation of scandium oxide turns out to be significantly weaker with a mixed filling. Although the bromine is introduced as NaBr₃, an equilibrium is established after the dissociation during operation, so that ScBr₃ is formed in addition to the original ScI₃. The combination of a scandium dosing with a bromine-containing mixed filling, especially with high wall loads (small-watt types and / or extremely good color rendering) is recommended, since the scandium loss mechanism runs faster at higher temperatures.

The addition of bromine causes the decrease in luminous flux (previously up to 30%), the decrease in color temperature (previously up to 600 K) and the drift of the color locus (decrease in the y-coordinate up to 10 hundredths of a point) during the first 100 to 500 Operating hours is improved by more than 50%.

While the Na-Sc ratio 5 ... 13: 1 (based on the halides) is preferred for the exclusive addition of iodine as the halide, in the case of an I / Br mixed filling a higher value, in particular up to 22: 1 , possibly even up to 24: 1, recommended. The reason is that the addition of bromine causes a higher color temperature due to the partial elimination of the iodine-related absorption in the blue spectral range. This must be compensated for by increasing the Na-Sc ratio.

To further improve the color rendering values, zirconium and / or hafnium halides can also be used in a total amount of up to 4 mol% of the metal halide filling.

While both Hf and Zr improve ignition and emission behavior, Zr is also suitable for improving the R9 index because it also emits in the red spectral range.

Further improvements are possible by optimizing the geometric dimensions. Surprisingly, it has been found that in the lamp type according to the invention there is a non-linear relationship between the electrode spacing (in mm) and the power level (in W) for different power levels. So far, one had always assumed a linear relationship. However, the best results are achieved if the electrode spacing is selected proportionally to the root of the power level. The proportionality factor is 0.85 with a tolerance range of ± 0.1.

Another important dimensioning is the ratio of the maximum inside diameter of the Discharge vessel to the electrode gap. It is advantageously about 1.1 to 1.4 and is thus significantly higher than the previously usual values of typically 0.9. The term maximum inner diameter also indicates that the discharge vessel should preferably be bulged in the middle. In particular, a barrel body has proven itself. Another option is an ellipsoid. The degree of bulging is chosen in particular so that the so-called effective average inner diameter is approximately 0.9 to 1.2 times the electrode spacing. The effective mean inner diameter is defined by the root of the inner volume that has been divided by the electrode spacing (cf. EP-B-215 524).

A particular advantage of the lamp according to the invention is that the operating voltage of 100 V remains constant over a good approximation.

In addition, the spread of the color temperature is reduced. The lamp can be operated in any burning position without any significant change in the color values. This makes the lamp particularly suitable for illuminating large areas (e.g. halls), since the individual lamps have only slightly different color values.

The invention creates high-pressure discharge lamps of low power which are suitable for interior lighting. With a lifespan of 6000 hours, a color rendering index Ra₈ ≧ 80 and an R₉ of ≧ -30 are created. The proportion of red increases from 15% to more than 20%.

Figur 1

zeigt den Aufbau einer zweiseitig gesockelten Hochdruckentladungslampe mit zweiseitig gequetschtem Entladungsgefäß

Figur 2

zeigt einen Vergleich zwischen dem Spektrum einer 75 W-Lampe mit vorbekannter (gestrichelt) und erfindungsgemäßer (durchgezogen) Füllung

The invention is explained in more detail below with the aid of several exemplary embodiments.

Figure 1

shows the structure of a double-ended high-pressure discharge lamp with a two-sided squeezed discharge vessel

Figure 2

shows a comparison between the spectrum of a 75 W lamp with previously known (dashed) and inventive (solid) filling

The 75 W high-pressure discharge lamp 1 shown in FIG. 1 consists of a discharge vessel 2 made of quartz glass, which is squeezed on both sides and is enclosed by an evacuated outer bulb 3, which has a base on both sides. The electrodes 4, 5 - shown schematically - are melted gas-tight into the discharge vessel 2 by means of foils 6, 7 and via the current leads 8, 9, the sealing foils 10, 11 of the outer bulb 3 and via further short current leads with the electrical connections of the ceramic base (R7s ) 12, 13 connected. The current leads 8, 9 are encased by a fabric made of quartz fibers (not visible), which suppresses the formation of photoelectrons in the outer bulb. As a result, the lifespan can be significantly extended over 6000 hours.

In a pinch of the outer bulb 3, a getter material 14 applied to a metal plate is additionally melted potential-free via a piece of wire. The ends of the discharge vessel 2 are provided with a heat-reflecting coating 15, 16 made of zirconium dioxide with a layer thickness of provided about 0.2 mm, so that the cold spot temperature is kept well above 800 ° C. The coating forms two domes, the inner edges of which are arranged at the level of the electrode tips. The electrode distance of 7 mm also corresponds to the distance between the inner edges.

The discharge vessel 2 is bulged in a barrel shape. The generatrix of the barrel body is a circular arc with a radius of 11.1 mm. The inside length of the discharge vessel is 14 mm, its inside volume is 0.69 m³ with a wall load of up to 22 W / cm². The quartz glass is about 1.3 mm thick.

The discharge vessel 2 contains a total of 2 mg of the following metal halides (molar fraction in% of the total metal halides): 89% NaI, 8.3 in order to achieve a warm white light color (WDL) with a color temperature of 3000 K in addition to 16 mg of mercury and 120 mbar argon % ScI₃ and 2.7% TlI. This corresponds to a molar ratio of sodium halide to scandium halide of 11: 1 and to thallium halide of 33: 1. The luminous flux (100 hours value) increases by 20% to 6000 lm compared to a lamp with a known filling with the halides of sodium, tin, thallium, indium and lithium. The luminous efficacy is 77 lm / W instead of 67 lm / W (15% increase). The overall color rendering index is Ra₈ = 82 instead of the previous Ra₈ = 76. The index R9 improves from -90 to -20, with the red component increasing from 15 to 21%. The service life is 6000 hours. The color scatter is reduced from ± 300 K to ± 130 K. The standard color value components are x = 0.418 and y = 0.400.

FIG. 2 shows a comparison of the spectrum of a 75 W lamp with the known sodium-tin filling (dashed line) with a structurally identical lamp which contains the above sodium-scandium-thallium filling. The color temperature is set to 3300 K. The spectrum has additional single lines (a) that contribute to the improved color rendering index. They are caused by the addition of scandium. The uniformity of the spectrum is significantly improved. Strong single lines in the spectrum of the conventional lamp, such as the lines of sodium (b), lithium (c), indium (d), mercury (e) and thallium (f) are more or less leveled (lithium is still present as an impurity). Particularly striking is the significantly improved emission in the long-wave wing (b2) of the sodium resonance line, which above all increases the red component significantly (+ 40%). This means that all saturated colors are reproduced much more naturally. This is of particular interest for interior lighting, food lighting and shop window lighting.

Another embodiment is a similarly constructed 150 W lamp with warm white light color (WDL), the filling of which, in addition to mercury and argon, has a total of 4 mg of the same metal halide component as in the previous embodiment.

With a color temperature of 3000 K and a luminous efficacy of now 85 lm / W (formerly 75 lm / W), a luminous flux of approx. 12800 lm and a color rendering index of Ra₈ = 92 instead of Ra₈ = 85 were achieved. The color rendering is especially in red improved from R9 = -70 to R9 = 0. With a burner volume of 1.5 cm³ and an electrode spacing of 11.0 mm, the wall load is up to 18 W / cm².

This lamp also has a lifespan of at least 6000 hours. The color scatter decreases from ± 300 K to ± 130 K. The older comparison values relate to a filling that contains the iodides of dysprosium, holmium, thulium, sodium and thallium as metal halides.

A further exemplary embodiment of a WDL filling for a 75 W lamp additionally has a proportion of 1% HfI₄ or ZrI to improve the ignition behavior and further reduce the devitrification. Since Zr is also a red emitter, the addition of ZrI can even achieve a color rendering index of Ra₈ = 90 and a red component of 22%.

In addition, the NaI content can be partially (typically 30%) replaced by NaBr.

In the case of a WDL lamp with a color temperature of 3000 K and an output of 70 W, very good results can be achieved with the following filling (total amount 2 mg) (data in mol%): 58.8% NaI, 34.3% NaBr, 4.9% ScI₃, 1.3% TlI and 0.7% HfI₄. An alternative is the following hafnium-free filling: 59.2% NaI, 34.5% NaBr, 4.9% ScI₃ and 1.4% TlI. With these fillings, the Na-Sc ratio is about 19: 1, while the Na-Tl ratio is about 70: 1. The bromine fraction is approximately 31% of the halides. With these fillings one Luminous efficacy of 77 lm / W achieved with a total color index Ra₈ = 82 and a red index R9 = -20. The decrease in luminous flux of this lamp was only 15% (previously 30%) in the first 100 hours, the decrease in color temperature was reduced to 200 K (previously 600 K), while the decrease in the y coordinate of the color locus was only 4 hundredths of a point (previously 11).

Finally, elemental Sc in an amount of 0.03 mg can be added to the Na-Sc-Tl filling of the first exemplary embodiment. This compensates for the inevitable loss of filling quantity in the first 100 hours, so that the constancy of the color values and also the burning voltage is improved. Another scandium compound that releases Sc in substoichiometric amounts is suitable for this, e.g. ScI₂.

The dimensions of the discharge vessels mentioned above are particularly advantageous because they avoid acoustic resonances when operating on high-frequency ballasts.

An example of a HPS filling (color temperature 4000 K) is generated in a 75 W lamp by the following metal halide component (proportions in mol%): 81.9% NaI, 14% ScI₃, 2.7% HfI₄ and 1 , 4% TlI. With this filling the molar ratio NaI / ScI₃ is 6: 1 and the ratio NaJ / TlJ is 58: 1.

In summary, it can be said that the invention has its main advantages in those of particular interest for interior lighting Color temperatures in the range of about 3000 K unfolded, corresponding to a light color WDL. The addition of thallium is of very great importance here, corresponding to a halide ratio Na / Tl of 25 ... 50: 1 for pure iodine fillings or up to 73: 1 for mixed fillings. However, it has been shown that the principle of the invention can also be transferred to color temperatures of approximately 4300 K (corresponding to the light color NDL). The influence of thallium naturally decreases, so that in this case a halide ratio Na / Tl up to 70: 1 is recommended for pure iodine fillings; a ratio of 50: 1 ... 65: 1 is particularly advantageous. A ratio of 50: 1 ... 73: 1 is particularly suitable for mixed fillings.

Claims (14)

1. Low-power high-pressure discharge lamp having the following features:

   - a quartz-glass discharge vessel (2),

   - a translucent outer bulb (3) in which the discharge vessel (2) is disposed, a current supply system extending through the walls of the outer bulb and of the discharge vessel to two electrodes (4, 5) in the discharge vessel,

   - an ionizable filling in the discharge vessel, which filling contains noble gas, mercury and a metal-halide component which is essentially based on the metals sodium, scandium and thallium,

   - the molar ratio between the proportions of the sodium halide (Na.-H.) and of the scandium halide (Sc.-H.) is 5:1 to 24:1,

   - the molar ratio between sodium halide (Na.-H.) and thallium halide (Tl.-H.) is 25:1 to 73:1,

   - the discharge vessel (2) is provided with a reflective coating (15, 16) to improve the heat accumulation behaviour.
2. High-pressure discharge lamp according to Claim 1, characterized in that, to achieve a neutral-white light colour (NDL) corresponding to a colour temperature of typically 3,800 K to 4,600 K, the molar ratio between the proportions of the Na.-H. and the Tl.-H. is 50:1 to 73:1.
3. High-pressure discharge lamp according to Claim 1 or 2, characterized in that the filling contains iodine alone as halogen, the molar ratio of Na.-H. to Sc.-H. being 5:1 to 13:1.
4. High-pressure discharge lamp according to Claim 3, characterized in that, to achieve a warm-white light colour (WDL) corresponding to a colour temperature of typically 2,600 to 3,500 K, the molar ratio between the proportions of the Na.-H. and the Tl.-H. is 25:1 to 50:1.
5. High-pressure discharge lamp according to Claim 1 or 2, characterized in that the filling contains a mixture of iodine and bromine as halogen, the molar ratio of Na.-H. to Sc.-H. being 8:1 to 24:1.
6. High-pressure discharge lamp according to Claim 5, characterized in that the proportion of bromine in the halogen mixture is up to 70%.
7. High-pressure discharge lamp according to Claims 2 and 6, characterized in that, to achieve a warm-white light colour, the proportion of bromine in the halogen mixture is up to 40%.
8. High-pressure discharge lamp according to Claim 1, characterized in that the outer bulb (3) is evacuated.
9. High-pressure discharge lamp according to Claim 1, characterized in that the metal-halide component additionally contains compounds of hafnium and/or zirconium.
10. High-pressure discharge lamp according to Claim 1, characterized in that the filling additionally contains elemental scandium.
11. High-pressure discharge lamp according to Claim 1, characterized in that the discharge vessel (2) is pinched at both ends, the coating being formed in a cup-shaped manner at each end and the spacing between the two cups (15, 16) being about 105 to 90% of the electrode spacing.
12. High-pressure discharge lamp according to Claim 11, characterized in that the electrode spacing EA (in mm) is determined as a function of the power L (in watts) by the formula EA = 0.85 (± 0.1) x √L.
13. High-pressure discharge lamp according to Claim 1, characterized in that the coating comprises zirconium oxide having a layer thickness of at least 0.15 mm.
14. High-pressure discharge lamp according to Claim 1, characterized in that the sodium resonance line (b) appears self-absorbed and forms two lobes (bl, b2), the spacing between the maximum values (peaks) of the two lobes being about 7 to 12 nm.

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