EP0834905B1 - Low power high pressure sodium lamp - Google Patents

Description

Technical area

The invention is based on a high-pressure sodium discharge lamp according to the preamble of claim 1.

These are in particular high-pressure sodium discharge lamps with a power of at most 100 W and very high xenon pressure. Typically, such lamps have a circular cylindrical discharge vessel of alumina, which is housed in a translucent outer bulb.

State of the art

The basic features of the construction of high-pressure sodium discharge lamps have been known for a long time. Likewise, it has long been known to use xenon at relatively high pressure to increase the luminous efficacy in these lamps. For example, in the relevant monograph " The High-Pressure Sodium Lamp "by DE GROOT / VAN VLIET (Philips Technical Library, Deventer, 1986) on page 299 and 300 stated that an increase in the luminous efficacy of 10 to 15% can be achieved if - in so-called SUPER lamps - a cold filling pressure of xenon from 20 to 40 kPa (200 to 400 mb) instead of the standard filling pressure of about 30 mb is used.

At the same time, it is pointed out on page 299 that the luminous efficacy in high-pressure sodium discharge lamps decreases with decreasing lamp power decreases sharply. Even at elevated xenon pressure, it is at most 85 lm / W for 50 W lamp power, while at approximately 400 W lamp power a light output of approximately 138 lm / W can be achieved.

In the DE-PS 26 00 351 describes a Hg-free sodium _{high-pressure lamp} suitable for so-called self- _stabilizing operation with a sodium _{operating pressure} p _NaB = 4 to 93 mb, a xenon operating pressure p _{Xe (hot)} ≥ 800 mb and a pressure ratio p _NaB / p _{Xe (hot)} ≤ 1 / 20th Taking into account the usual factor 8 (see DE-AS 28 14 882 , Sp. 2, middle) for the conversion between xenon operating pressure and Xenonkaltfülldruck p _{XeK thus} results in a pressure ratio p _XeK / p _NaB ≥ 2.5. In self-stabilizing operation, the aim is to operate a high-pressure sodium lamp without a ballast. For this mode of operation a long disintegration time of the plasma formed from the filling gas is necessary. In order to achieve this long disintegration time, a relatively high xenon pressure and a relatively large inside diameter of the discharge vessel are used, as known per se (see also the abovementioned relevant monograph by DE GROOT / VAN VLIET on page 126 and 154). According to DE GROOT / VAN VLIET, p. 155, the self-stabilizing operation of high-pressure sodium lamps has not found any practical application due to problems with ignition and sudden changes in the mains voltage.

empfohlen (pNaB = Natriumbetriebsdruck). Dieser Wert für das Druckverhältnis pXeK / pNaB stimmt im übrigen wieder gut mit dem in DE-PS 26 00 351 beschriebenen überein. Es wird aber in DE-AS 28 14 882 (Sp. 3, Z. 41f) von einer weiteren Erhöhung des Xenon-Drucks über diese obere Grenze abgeraten, da sich der Nachteil der erschwerten Zündung ergibt, "ohne dass dem ein Zuwachs an Lichtausbeute gegenübersteht". Bei den Ausführungsbeispielen mit kleiner Lampenleistung von 70 und 100 W ist pNaB = 230 mb, der Xenonkaltfülldruck liegt bei ca. 500 mb. Dies entspricht einem Druckverhältnis pXeK / pNaB von etwa 2 bis 2,5. Damit wird eine Lichtausbeute von 97 bzw. 105 lm/W bei 70 bzw. 100 W Leistung erzielt. Diese Werte sind zum Vergleich als Kreuze in Fig. 3 (s.u.) eingetragen.In the DE-PS 26 00 351 Sodium high-pressure discharge lamp described by way of example has a high power of 400 W and a very large inner diameter of 7.6 mm. The xenon cold filling pressure is 260 mb and the pressure ratio p _XeK / p _NaB is about 3.5. This achieves a rather moderate light output of only 110 lm / W at the high power of 400 W. In this document, a particularly bohe luminous efficacy in comparison to other high-pressure sodium lamps is neither sought nor achieved. According to FIG. 10.18 of DE GROOT / VAN VLIET (page 299), at 400 W power, rather, light outputs of up to 138 lm / W can be achieved. This principle dependence of the luminous efficacy on the lamp power is here again for comparison purposes Fig. 3 shown (see below). In the DE-AS 28 14 882 describes a Hg-free high pressure sodium lamp without self-stabilization. In this case, based on the sodium operating pressure, a value between the xenon cold filling pressure PXeK $$1.25<\mathrm{p\; XeK}/\mathrm{NaB}<6\mathrm{with\; pNaB}=150\mathrm{to}500\mathrm{mb}$$

recommended (pNaB = sodium operating pressure). This value for the pressure ratio pXeK / pNaB agrees otherwise well with the in DE-PS 26 00 351 described match. It will be in DE-AS 28 14 882 (Sp. 3, Z. 41f) discouraged from further increasing the xenon pressure above this upper limit, since there is the disadvantage of difficult ignition "without any increase in light output". In the embodiments with a small lamp power of 70 and 100 W pNaB = 230 mb, the Xenonkaltfülldruck is about 500 mb. This corresponds to a pressure ratio pXeK / pNaB of about 2 to 2.5. This achieves a luminous efficacy of 97 or 105 lm / W at 70 and 100 W power respectively. These values are for comparison as crosses in Fig. 3 (see below).

From the US 4,260,929 is a sodium high-pressure lamp is known which contains sodium and xenon, wherein the Na operating pressure of 50 to 200 Torr is disclosed, corresponding to 67 to 267 mbar. The disclosed Xe cold fill pressure is 50 to 1000 Torr, corresponding to 67 to 1333 mbar. A metal halide lamp that uses sodium iodide together with xenon as a buffer gas with no mercury is out EP-A 183 247 previously known, wherein the Na partial pressure between 10 and 100 Torr and 13 to 133 mbar and the Xenonkaltfülldruck between 60 and 1000 Torr and 80 to 1333 mbar. A conventional metal halide lamp with sodium iodide shows EP-A 374 678 ,

Presentation of the invention

It is an object of the present invention to provide a low-pressure sodium high-pressure discharge lamp according to the preamble of claim 1 which has a high luminous efficacy.

This object is solved by the characterizing features of claim 1. Particularly advantageous embodiments can be found in the dependent claims.

The low-pressure sodium high-pressure discharge lamp according to the invention has a discharge vessel which contains at least sodium and xenon. Low power is understood to mean a lamp power of less than or equal to 100W.

Here, p _{NaB is} the operating pressure of sodium and p _{XeK is} the cold pressure of the xenon. Surprisingly, at low powers, contrary to the previous doctrine, a further increase in the luminous efficacy of typically 20% can be achieved if p _NaB = 20 to 100 mb and p _XeK = 1 to 5 bar is selected and if, at the same time, the condition p _XeK / p _NaB ≥ 10 is maintained. Advantageously, the pressure ratio p _XeK / p _{NaB is} between 10 and 30.

To increase the burning voltage, mercury may be added to the lamp filling.

The xenon pressure exceeds the usual with conventional high pressure sodium discharge lamps with high xenon pressure (for example, the NAV SUPER lamps from. OSRAM) by three to ten times. Compared to these NAV-SUPER lamps, this results in a typically 20% increase in luminous efficacy.

The already mentioned previously known increase in the luminous efficacy of high-pressure sodium lamps with increasing xenon pressure (see DE GROOT / VAN VLIET, p. 153 and p. 299-300) is used commercially in so-called NAV SUPER lamps. The light output increase achieved with the present invention with a further increase in xenon pressure over the However, values in NAV-SUPER lamps are unexpectedly high and were unknown to this extent. For example, in DE GROOT / VAN VLIET, p. 300, a luminous efficacy increased by 10 to 15% compared to so-called standard lamps (with 30 mb xenon cold filling pressure) with increase of the xenon filling pressure (cold) to 200 to 400 mb. A further pressure increase is excluded because of the complicated ignition.

The surprising behavior of the lamps according to the invention is based on the targeted utilization of a previously not considered by experts in the facts. Although it is known that the luminous efficacy of high-pressure sodium lamps to small lamp powers decreases significantly (DE GROOT / VAN VLIET, p 299, see below Fig. 3 ). The statement given there that is responsible for this law, the fact that at low lamp power, the efficiency of the radiation is lower and the electrode losses are greater than with larger lamp power, but is not correct. Rather, the main reason is that the relative contribution of heat loss in the arc to the lamp power increases with decreasing lamp power. However, this heat loss can be reduced by the low thermal conductivity of xenon when used at sufficiently high pressure as a buffer gas. This effect affects the more favorable the light output, the smaller the lamp power is. Crucial importance comes here to the pressure ratio between xenon and sodium, because sodium, in contrast to xenon has a high thermal conductivity. The higher the xenon pressure against the sodium pressure, the better the heat losses can be contained. This ultimately results in the observed additional increase in light output at low powers.

1. 1. Durch die geringeren Wärmeverluste kann eine niedrigere Wandtemperatur des Entladungsgefäßes erreicht werden. Dies kann beispielsweise zu einer Verlängerung der Lebensdauer ausgenutzt werden. Alternativ kann das Entladungsgefäß verkleinert werden, so daß die ursprünglich vorhandene Wandtemperatur wieder erreicht wird. Durch die höhere Leistungsdichte erhöht sich dabei die Lichtausbeute noch weiter.
2. 2. Der hohe Xenondruck behindert die Diffusion. Dies mindert die Abdampfung von Elektrodenbestandteilen während des Zündvorgangs und reduziert die daraus folgende Schwärzung der Wand des Entladungsgefäßes im Bereich der Elektroden. Dieser Effekt ist qualitativ von NAV SUPER-Lampen her bekannt. Bei sehr hohem Xenon-Druck ist er noch stärker ausgeprägt, wodurch die Lebensdauer weiter vergrößert wird.
3. 3. Bei den erfindungsgemäßen Lampen liefert Xenon wegen seines sehr hohen Drucks einen erheblichen Beitrag zur Brennspannung. Dieser Beitrag ist unabhängig von der Temperatur des Entladungsgefäßes, da das Xenon im Gegensatz zu Natrium auch bei Zimmertemperatur gasförmig vorliegt. Dies wirkt stabilisierend gegenüber Schwankungen der Netzspannung oder Fertigungsstreuungen. Im Gegensatz dazu ist bei allen vorbekannten Lampen (beispielsweise gemäß DE-AS 28 14 882 ) der Beitrag der Xenon-Atome zur Brennspannung unerheblich. Die Brennspannung wird dort fast allein durch die Anzahl der Natrium-Atome bestimmt, die stark von der Temperatur des kältesten Punktes (cold spot) und damit von Schwankungen der Netzspannung oder Fertigungsstreuungen beeinflußt wird. Im Falle eines Quecksilberzusatzes wirkt auch dieser bei der Einstellung der Brennspannung mit.
4. 4. Durch den sehr hohen Xenondruck ergibt sich eine besonders niedrige Wiederzündspitze im Betrieb der Lampe. Dies verlängert die Lebensdauer wegen der geringeren Belastung der Elektroden und gibt größere Sicherheit vor Verlöschen bei plötzlichen Netzspannungsschwankungen.
5. 5. Xenon bewirkt im Natriumspektrum eine Verbreiterung des Kuppenabstands im spektralen Profil der druckverbreiterten, in ihrer Mitte selbstabsorbierten Natrium-Resonanzlinie (D-Linie). Dieser Effekt ist im Prinzip bekannt (siehe DE GROOT/VAN VLIET, insbes. S. 16a, Plate 1c). Dadurch kann der Natriumdruck bei gleicher Farbtemperatur und Farbwiedergabe erniedrigt werden. Dieser Effekt wirkt sich bei sehr hohem Xenon-Druck von mindestens 1 bar (kalt) durchgreifend aus. Bei der vorliegenden Erfindung wird der Natriumdruck im Verhältnis zum Xenondruck besonders bevorzugt so niedrig eingestellt, daß sich ein Kuppenabstand der beiden Flügel der Resonanzlinie von typisch 10 nm, höchstens 12 nm, ergibt. Dabei ist eine wesentliche Voraussetzung, daß das Verhältnis p_XeK /p_NaB ≥ 10 und p_NaB = 20 bis 100 mb gewählt wird. Es hat sich herausgestellt, daß unter diesen Bedingungen optimale Lichtausbeuten entstehen. Dagegen liegt bei den in DE-AS 28 14 882 angegebenen Verhältnissen ein Kuppenabstand der beiden Flügel der Natrium-D-Linie von mindestens 15 bis 20 nm vor, da p_NaB dort relativ hoch ist (s.o.). Dies läßt sich mit Hilfe der in DE GROOT/VAN VLIET, S. 87, angegebenen Gleichung (3.28) abschätzen.

The very high xenon pressure of at least 1 bar (cold) has, in addition to the increase in the light output, further advantages:

1. 1. Due to the lower heat losses, a lower wall temperature of the discharge vessel can be achieved. This can for example be exploited to extend the life. Alternatively, the discharge vessel can be reduced, so that the original wall temperature is reached again. Due to the higher power density, the light output increases even further.
2. 2. The high xenon pressure hinders the diffusion. This reduces the evaporation of electrode components during the ignition process and reduces the consequent blackening of the wall of the discharge vessel in the region of the electrodes. This effect is qualitatively known from NAV SUPER lamps. At very high xenon pressure, it is even more pronounced, which further increases the service life.
3. 3. In the lamps according to the invention xenon provides a significant contribution to the burning voltage because of its very high pressure. This contribution is independent of the temperature of the discharge vessel, since the xenon, in contrast to sodium, is also gaseous at room temperature. This has a stabilizing effect on fluctuations in the mains voltage or production spreads. In contrast, in all previously known lamps (for example, according to DE-AS 28 14 882 ) the contribution of xenon atoms to the burning voltage irrelevant. The burning voltage is determined there almost exclusively by the number of sodium atoms, which is strongly influenced by the temperature of the coldest point and thus by fluctuations of the mains voltage or manufacturing dispersions. In the case of mercury addition, this also contributes to the setting of the burning voltage.
4. 4. The very high xenon pressure results in a particularly low Wiederzündspitze during operation of the lamp. This extends the life because of the lower load on the electrodes and gives greater security against extinction in case of sudden mains voltage fluctuations.
5. 5. Xenon causes in the sodium spectrum broadening of the dome spacing in the spectral profile of the pressure-broadened, in its center self-absorbed sodium resonance line (D-line). This effect is known in principle (see DE GROOT / VAN VLIET, esp. P. 16a, Plate 1c). As a result, the sodium pressure can be lowered at the same color temperature and color rendering. This effect has a dramatic effect at very high xenon pressure of at least 1 bar (cold). In the present invention, the sodium pressure relative to the xenon pressure is more preferably set so low as to give a pitch of the two wings of the resonance line of typically 10 nm, at most 12 nm. An essential prerequisite is that the ratio p _XeK / p _NaB ≥ 10 and p _NaB = 20 to 100 mb is selected. It has been found that optimal light efficiencies result under these conditions. In contrast, lies in the in DE-AS 28 14 882 given ratios a pitch of the two wings of the sodium D-line of at least 15 to 20 nm, since p _NaB there is relatively high ( _{see above} ). This can be estimated using the equation (3.28) given in DE GROOT / VAN VLIET, p. 87.

1. 1. Bei einem Natriumdampfdruck von 20 bis 100 mb beträgt die Temperatur des Entladungsgefäßes an der kältesten Stelle (cold spot) nur 840 bis 950 K. Diese kälteste Stelle liegt immer in der Nähe der Einschmelzung. Daher ist die Einschmelzung jetzt typisch um 150 K kälter als bei vorbekannten Lampen (siehe DE-AS 28 14 882 ), woraus eine Verringerung der Lampenausfälle durch Lecks im Bereich der Einschmelzung folgt.
2. 2. Die durch Natrium bedingte Korrosion der Wand des Entladungsgefäßes, die bevorzugt in der Mitte des Gefäßes auftritt, wird wegen des niedrigen Natriumpartialdrucks verringert. Dadurch ergibt sich eine zusätzliche Verbesserung der Lebensdauer.

From points 3 and 5 there is an additional justification for choosing the low operating pressure of sodium vapor of 20 to 100 mb typical for the present invention. This low sodium pressure in turn has several advantages:

1. 1. At a sodium vapor pressure of 20 to 100 mb, the temperature of the discharge vessel at the coldest point (cold spot) is only 840 to 950 K. This coldest point is always in the vicinity of the meltdown. Therefore, the melting is now typically 150 K colder than in previously known Lamps (see DE-AS 28 14 882 ), which results in a reduction in lamp failures due to leaks in the area of the meltdown.
2. 2. The sodium-induced corrosion of the wall of the discharge vessel, which preferably occurs in the center of the vessel, is reduced because of the low sodium partial pressure. This results in an additional improvement in the life.

The in DE-AS 28 14 882 mentioned disadvantage of difficult ignitability can be counteracted effectively, especially with small lamp powers (≤ 100 W) by the use of improved, commercially available sockets, sockets and ignitors, as long as the xenon pressure is not too high (over 5 bar) is selected. Advantageously, the xenon pressure is limited to values up to 3 bar. These improved parts are already used in commercially available metal halide lamps from OSRAM (eg HQI-E 100 W / NDL and WDL). Ignition of conventional ignitors for low power NAV lamps, however, is not possible with lamps according to the invention.

The lamps described here are in contrast to DE-PS 26 00 351 neither intended nor suitable for self-stabilizing operation. The xenon operating pressure achieved according to the invention at 8 to 24 bar is also substantially higher than the typical value of 1.8 bar given there.

This in DE-PS 26 00 351 described heating the discharge vessel, which is necessary there to start (alternatively, a conventional ballast can be used) is not required in the discharge vessel according to the invention. The discharge vessel according to the invention preferably has an appendix (initially open niobium tube) through which xenon can be filled at high pressure in a manner known per se and which is closed after the filling process.

In addition to sodium and xenon, the lamps according to the invention may additionally contain mercury in the filling. The increase in the light output is similar for lamps with and without mercury addition.

A typical mercury-added lamp fill uses an amalgam of 18% by weight Na.

Preferably, the inner diameter of the discharge vessel is between 2.5 and 5 mm, in particular at most 4 mm. With these dimensions self-stabilization is excluded from the outset. For comparison: the in DE-PS 26 00 351 given inside diameter are larger by a whole power of ten. In general, although the discharge vessel is circular cylindrical, but it may also have a different geometry, for example, be bulged in the middle.

Advantageously, the sodium high-pressure discharge lamps additionally have a capacitive starting aid, for example a wire along the discharge vessel. In contrast to DE-PS 26 00 351 However, the lamps of the invention require no preheating.

These lamps often have a niobium appendage, as described for example in DE GROOT / VAN VLIET on page 251, Fig. 8.30.

The operation of such lamps is possible on a conventional or often also on an electronic ballast.

The discharge vessels described here are preferably used in circular-cylindrical or elliptical outer pistons.

Figur 1

eine Natriumhochdruckentladungslampe

Figur 2

einen Vergleich der Lichtausbeute verschiedener Natrium- hochdrucklampen (mit jeweils einer Leistung von 50 W) mit unterschiedlichem Xenondruck (mit und ohne Hg)

Figur 3

einen Vergleich der Lichtausbeute verschiedener Natrium- hochdrucklampen für unterschiedliche Lampenleistungen und unterschiedlichem Xenondruck

In the following the invention will be explained in more detail with reference to several embodiments. Show it:

FIG. 1

a high pressure sodium discharge lamp

FIG. 2

a comparison of the luminous efficacy of various high-pressure sodium lamps (each with a power of 50 W) with different xenon pressure (with and without Hg)

FIG. 3

a comparison of the light output of various high-pressure sodium lamps for different lamp powers and different xenon pressure

Description of the drawings

In the Fig. 1 shown sodium high-pressure discharge lamp with a power of 50 W has a discharge vessel 1 made of alumina. It is arranged in a cylindrical outer bulb 2 made of hard glass, which is closed at its first end with a screw base 3 and at its second end with a dome 9. The outer bulb 2 is evacuated.

In the discharge vessel 1 with an inner diameter of 3.3 mm, two electrodes 4 face each other, which have an electrode spacing EA of 30 mm. The socket-remote first electrode 4 is connected via a tubular niobium feedthrough 5 with appendix 6 to a feed line 7, which is connected to a solid external power supply 8, which leads along the discharge vessel to contact in the screw base 3.

The second electrode 4 is also connected to a metal wire 15 via a niobium feedthrough 5 (but without the appendix). This is connected via a further conductor 16 to a second contact in the base 3.

The discharge vessel is equipped with a capacitive starting aid, which is formed by an ignition wire 17 along the discharge vessel. The ignition wire 17 is electrically conductively connected to the second electrode 4.

The lamp is connected, for example via an ignition circuit in the lamp socket to an AC power supply with 220 V. The ignition voltage is 4 kV.

The discharge vessel 2 contains a filling comprising only sodium and xenon. The cold pressure of the xenon (p _XeK ) is 3 bar, the operating pressure of the sodium (p _NaB ) is 100 mb, so that P _XeK / p _NaB = 30.

This lamp achieves a luminous flux of 5100 lm and a luminous efficacy of 102 lm / W (see FIG. 2 , triangular full measuring point # 1 at 3000 mb xenon cold filling pressure). In comparison, previous 50 W lamps with a xenon cold filling pressure of 300 mb (type SUPER) only achieved a luminous flux of 4200 lm, corresponding to a luminous efficacy of 81 lm / W (see FIG. 2 triangular outlined measuring point). In Fig. 2 is also the light output for other lamps with the usual low xenon pressure of 100 mb (standard) specified. It is about 70 lm / W at 30 mb (see FIG. 2 triangular outlined measuring point).

In Fig. 3 the dependence of the light yield on the lamp power is shown schematically in accordance with DE GROOT / VAN VLIET. The value achieved with the above embodiment (102 lm / W at 50 W lamp power) is entered as a diamond-shaped measuring point. He is well above the state of the art.

In a SECOND embodiment, a lamp of the same type is operated only with 1 bar xenon pressure and 50 mb sodium pressure. Here is the ratio p _XeK / p _NaB = 20. The luminous efficacy is 95 lm / W (see Fig. 2 , triangular full measuring point # 2 at 1000 mb Xenonkaltfülldruck) still significantly higher than in the prior art lamps. Because of the lower xenon pressure, ignition is easier than the first embodiment. The ignition voltage is 3 kV.

These two lamps are particularly suitable for new systems with stronger ignitor.

In a THIRD embodiment, the identical 50 W lamp is additionally filled with mercury. For this purpose, an amalgam with 18 wt .-% sodium, balance mercury, is used. This lamp shows a luminous efficacy of 105 lm / W (circular full point # 3 in Fig. 2 ) at 2 bar xenon cold filling pressure, 80 mb sodium _operating pressure and a pressure ratio p _XeK / p _NaB = 25.0.

Accordingly, a FOURTH embodiment (50 W) with 1 bar xenon cold filling pressure at the same Na / Hg ratio shows a luminous efficacy of 93 lm / W (circular full measuring point # 4 in FIG Fig. 2 ).

For comparison, the corresponding luminous efficiencies of mercury-containing sodium lamps with lower xenon cold filling pressure (types SUPER and standard) are also indicated (circular outlined measuring points at 30 to 300 mb in Fig. 2 ).

In a FIFTH embodiment, a substantially similar lamp is operated at 63 W power. The filling contains 1 bar xenon and 50 mb sodium, but no mercury. The pressure ratio p _XeK / p _NaB = 20.

The luminous efficacy is 98 lm / W. This lamp is intended as a direct replacement for high-pressure 125W mercury lamps that have the same luminous flux. It has a power reduction circuit (phase control) and an ignition circuit in the lamp base.

In a SIXTH embodiment of a 35 W lamp, a discharge vessel having an inner diameter of 3.3 mm and an electrode spacing of 23 mm is filled only with sodium and xenon. The xenon cold filling pressure is p _XeK = 2 bar, the sodium _{operating pressure} is p _NaB = 90 mb.

Accordingly, the pressure ratio p _XeK / p _NaB = 22.2. The luminous efficacy is 98 lm / W (see Fig. 3 , diamond-shaped measuring point # 6) and is thus much higher than lamps of this power was previously expected.

In a seventh embodiment of a 70 W lamp, a discharge vessel having an inside diameter of 3.3 mm and an electrode spacing of 36 mm with sodium / mercury amalgam (see above) and xenon filled. The xenon cold filling pressure is p _XeK = 2 bar, the sodium _{operating pressure} is p _NaB = 75 mb. Accordingly, the pressure ratio p _XeK / p _NaB = 26.7. The luminous efficacy is 115 lm / W (see Fig. 3 , diamond-shaped measuring point # 7) and is therefore also significantly higher than was previously expected for lamps of this power.

In an EIGHT embodiment of a 70 W lamp, a discharge vessel having an inner diameter of 3.7 mm and an electrode spacing of 37 mm is filled with sodium / mercury and xenon. The xenon cold filling pressure is p _XeK = 1.5 bar, the sodium _{operating pressure} is p _NaB = 85 mb. Accordingly, the pressure ratio p _XeK / p _NaB = 17.6. The luminous efficacy is 108 lm / W

Claims (9)

1. Low-power high-pressure sodium discharge lamp having a discharge vessel (1) which contains sodium and xenon, p_NaB being the operating filling pressure of the sodium and p_XeK being the cold filling pressure of the xenon, characterized in that the lamp is constructed in such a way that the lamp power is less than or equal to 100 W and that: $${\mathrm{p}}_{\mathrm{NaB}}\mathrm{=}\mathrm{20}\mathrm{to}\mathrm{100}\mathrm{mb}\mathrm{,}$$

   

   $${\mathrm{p}}_{\mathrm{XeK}}\mathrm{=}\mathrm{1}\mathrm{to}\mathrm{5}\mathrm{bars}\mathrm{,}$$

   

   and $${\mathrm{p}}_{\mathrm{XeK}}\mathrm{/}{\mathrm{p}}_{\mathrm{NaB}}\mathrm{\ge }\mathrm{10}$$

   

   applies.
2. High-pressure sodium discharge lamp according to Claim 1, characterized in that p_XeK/p_NaB ≤ 30.
3. High-pressure sodium discharge lamp according to Claim 1, characterized in that p_XeK ≤ 3 bars.
4. High-pressure sodium discharge lamp according to Claim 1, characterized in that the discharge vessel (1) is a circular cylinder.
5. High-pressure sodium discharge lamp according to Claim 6, characterized in that the inside diameter of the discharge vessel (1) is between 2.5 and 5 mm.
6. High-pressure sodium discharge lamp according to Claim 7, characterized in that the inside diameter is at most 4 mm.
7. High-pressure sodium discharge lamp according to Claim 1, characterized in that the lamp additionally contains a capacitive starting aid (17).
8. High-pressure sodium discharge lamp according to Claim 1, characterized in that during operation the peak spacing of the two wings of the sodium D-line is at most
9. High-pressure sodium discharge lamp according to Claim 1, characterized in that the filling additionally contains mercury.

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