WO2011048517A1

WO2011048517A1 - High intensity discharge lamp

Info

Publication number: WO2011048517A1
Application number: PCT/IB2010/054337
Authority: WO
Inventors: Paulus A. H. J. Huijbrechts; Lars Dabringhausen
Original assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips Electronics NV
Current assignee: Philips Intellectual Property and Standards GmbH; Koninklijke Philips NV
Priority date: 2009-10-19
Filing date: 2010-09-27
Publication date: 2011-04-28
Anticipated expiration: 2012-04-19

Abstract

A high intensity discharge (HID) lamp or an ultra high intensity dis¬ charge (UHP) lamp is disclosed, which lamps are ignited by applying a high ignition voltage, and which are provided for an improved resistance against flashover discharge formations (9) outside or partly outside the discharge vessel (4) by dimensioning and/or shaping at least one of its plugs (5, 6) such that a creeping distance for the high ignition voltage is increased. The lamp is especially a two-sided lamp and suitable for use in automotive head light applications.

Description

HIGH INTENSITY DISCHARGE LAMP

FIELD OF THE INVENTION

The invention relates to a high intensity discharge (HID) lamp or an ultra high intensity discharge (UHP) lamp and especially a ceramic HID automotive lamp, which lamps are ignited by applying a high ignition voltage and which are provided for preventing discharge or flashover formations outside or partly outside the burner (or discharge vessel) of the lamp during the application of the high ignition voltage. The invention especially relates to such a lamp in the form of a two-sided lamp, i.e. a lamp having its electrical connection terminals on opposite sides of the lamp.

BACKGROUND OF THE INVENTION

Due to their high efficiency and superior radiation characteristics, high intensity discharge lamps have been provided for a great variety of applications and in very different configurations, shapes and sizes. One problem which has been observed with such discharge lamps is the occurrence of a flashover discharges during an ignition of the lamp in a cold or hot state especially if the lamp has been provided for a comparatively low ignition voltage. More in detail, it has revealed that the possibility of fla- shover discharges can increase when certain measures are taken for decreasing the ignition voltage of the discharge lamp. Such a decrease of the ignition voltage is often desired for increasing the ignition reliability of the lamp, especially in case of a lamp which is provided for automotive applications.

US 4,876,483 discloses a discharge lamp having both its connection ter- minals or lead wires for the electrodes on the same side of the lamp ("single- sided lamp"). The lamp shall be made resistant to surface path arcing by press sealing a dielectric barrier between the electrode roots. However, this solution is not applicable in case of a discharge lamp having its connection terminals or lead wires on opposite sides of the lamp ("two-sided lamp").

SUMMARY OF THE INVENTION

One object underlying the invention is to provide a high intensity discharge lamp as mentioned in the first paragraph above which has improved resistance properties against discharge or flashover formations outside or partly outside the burner (or discharge vessel) of the lamp during the application of a high ignition voltage, in comparison to known such lamps. Another object underlying the invention is to provide a high intensity discharge lamp as mentioned in the first paragraph above and in the form of a two-sided lamp, i.e. a lamp having its electrical connection terminals on opposite sides of the lamp, having the above improved flashover resistance properties.

Another object underlying the invention is to provide a high intensity discharge lamp as mentioned in the first paragraph above and which comprises an outer bulb which encloses an inner bulb or burner comprising the discharge vessel, and which lamp has the above improved flashover resistance properties.

Finally, an object underlying the invention is to provide a high intensity discharge lamp as mentioned in the first paragraph above and which lamp has been provided in a known manner with means (e.g. an antenna) for obtaining a comparatively low ignition voltage (which is of interest e.g. in order to improve the ignition reliability especially in case of a hot re- strike of the lamp), but at the same time the lamp having the above improved flashover resistance properties.

The above objects are solved according to claim 1 by a high intensity discharge lamp comprising a first bulb with a discharge vessel and a first and a second plug into which a first and a second connection lead, respectively, is entering for electrically supplying a first and a second electrode, respectively, of the lamp with an ignition voltage for igniting an arc discharge between the electrodes within the discharge vessel, wherein the plugs each comprise a length which extends between the entry position of the connection lead into the plug and the discharge vessel, and wherein at least one of the plugs comprises a first extension of its length and/or a second extension of its cross section or diameter, which at least one extension is dimensioned for lengthening a creeping path of the ignition voltage along an outside of the at least one plug such that flashover discharges along the outside of the at least one plug are prevented.

This solution has the advantage that it is effective not only in case of a cold strike of the lamp, but also in case of a hot re-strike of the lamp. In the following description, a cold strike is defined to be a condition of the lamp, in which the lamp has been switched off for about 15 minutes or longer, so that the burner of the lamp and its content typically has the temperature of the surroundings. A hot re-strike is defined to be a condition of the lamp, in which the lamp has been switched off for less than about 15 minutes, especially for between a few micro-seconds and some minutes, so that the burner and its content is still hot and typically has a temperature between about 300K and about 1700K.

The dependent claims disclose advantageous embodiments of the invention. Claims 2 to 4 are related to preferred embodiments with respect to the first extension which have been proven to be especially effective.

Claims 5 to 7 are related to preferred embodiments with respect to the second extension which have been proven to be especially effective.

Claims 8 and 9 are related to certain materials which are selected for decreasing the risk of flashover discharges.

Claims 10 and 11 are related to lamps in which the (inner) bulb is enclosed by an outer bulb and disclose certain filling pressures of the gases within the outer bulb in order to prevent unwanted flashover discharges.

Finally, claims 12 and 13 are directed to preferred applications of the invention for certain types of discharge lamps.

Further details, features and advantages of the invention become apparent from the following description of exemplary and preferred embodiments of the invention with respect to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 schematically shows a known discharge lamp and a first flashover discharge path;

Fig. 2 schematically shows a known discharge lamp and a second flashover discharge path;

Fig. 3 schematically shows a preferred first embodiment of a discharge lamp according to the invention;

Fig. 4 shows a first graph of the ignition voltages of a hot re-strike over time for different embodiments of the invention;

Fig. 5 show a second graph of the ignition voltages of a hot re-strike over time for different embodiments of the invention; and

Fig. 6 schematically shows further embodiments of a discharge lamp according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 schematically shows substantial parts of a known high voltage discharge lamp comprising a first inner bulb or burner 1 which is enclosed by a second outer bulb 10. The inner bulb 1 comprises a discharge vessel 4 and a first and a second pinch or plug 5, 6. Further, a first and a second electrode 2, 3 are provided which are positioned opposite to each other and extend axially within the inner bulb 1. One of the ends of the electrodes 2, 3 extend with their free trips into the discharge vessel 4, whereas the other ends are connected within the first and the second pinch or plug 5, 6, respectively, with a first and a second connection lead or lead wire 7, 8, respectively. For this purpose, the connection lead 7, 8 enters into the free end of the first and the second plug 5, 6, respectively, for supplying an ignition voltage to the electrodes 2, 3 in order to ignite an arc discharge between the free tips of the electrodes 2, 3. The ignition voltage is typically a 23 kV triangular pulse voltage waveform, wherein it is assumed that the lamp is provided for applying the high voltage side or the positive potential of this ignition voltage at the first connection lead 7 and the first electrode 2, and the low voltage side or negative or mass potential is assumed to be applied at the second connection lead 8 and the second electrode 3.

Further, an operating voltage/current is applied usually at the same connection leads 7, 8 (and by this to the electrodes 2, 3) in order to maintain the arc dis- charge between the free tips of the electrodes 2, 3 during operation of the lamp.

The discharge vessel 4 contains a known discharge gas which is filled into the discharge vessel 4 e.g. via a feed-through 5a. The outer bulb 10 is usually filled with a certain filling pressure of nitrogen or comprises a vacuum.

Further, Figure 1 schematically shows a first possible flashover dis- charge path 9 extending from the first connection lead 7 (high voltage side) along the outer surface of the first plug 5, the outer surface of the discharge vessel 4, and the outer surface of the second plug 6 to the second connection lead 8 (low voltage side) when applying an ignition voltage.

In Figure 2, the same known high voltage discharge lamp is shown as in Figure 1, and the same components are denoted with the same reference signs, so that reference is made to Figure 1 with respect to the explanation of these components.

Especially if the feed-through 5a is made of iridium, a second possible flashover discharge path 9 may occur which extends from the first connection lead 7 along the outer surface of the first plug 5, the outer surface of the discharge vessel 4, and into the feed-through 5a to the (nearest) second electrode 3 inside the discharge vessel 4 and then via the second electrode 3 inside the second plug 6 to the second connection lead 8 when applying an ignition voltage. In contrary to Figure 1, the second flashover discharge path 9 extends only partly outside the burner 1.

Also other flashover discharge paths can occur, especially if the (inner) bulb 1 comprises a known active or a passive antenna (not indicated) which is connected to one of the connection leads 7, 8 or other known measures have been taken in order to decrease the ignition voltage of the discharge lamp. (This is usually desired for improving the ignition reliability especially in case of a hot re-strike of the lamp as explained above).

If the lamp as usual comprises an outer bulb 10 which encloses the inner bulb 1, the risk of the occurrence of the above and other unwanted flashover discharges inside the outer bulb 10 also increases if e.g. the gas pressure within the outer bulb 10 has been decreased (or other known measures have been taken) again in order to decrease the ignition voltage of the discharge lamp.

For preventing the occurrence of the above flashover discharges, and es- pecially for providing a discharge lamp in which the risk of the above flashover discharges is at least not increased or even reduced when the above or other measures have been taken for reducing the ignition voltage of the lamp, several features are proposed according to the invention which can be applied separately or in any combination with each other, the selection of which is made substantially in dependence on a specific lamp, certain operating conditions and/or other.

As a first feature according to the invention, at least one of the plugs 5, 6 and preferably the first plug 5 adjacent to the first connection lead 7 at the high voltage side, comprises a first extension in the form of an extended length of the plug 5, 6 in comparison to the length of such plugs in known such discharge lamps. The length of the plugs 5, 6 is considered to be the distance between the entry position of the adjacent connection lead 7, 8 into the plug 5, 6 and the discharge vessel 4, especially the transition between the plug 5, 6 and the discharge vessel 4. This transition can be identified at the position or range, at which the diameter of the plug 5, 6 increases until it reaches the diameter of the discharge vessel 4.

Such an extended length can amount to a range between about 4 mm and about 6 mm, wherein the first plug 5 at the high voltage side preferably has a length of about 6 mm. If the second plug 6 at the low voltage side has an extended length at all, this length is preferably about 4 mm. Especially if a passive antenna is applied, preferably both plugs 5, 6 have an extended length of about 6 mm.

As a second feature, the feed-through 5a (if present) is extended with respect to its length in comparison to the length of such a feed-through in a known such discharge lamp, wherein the length is considered to be the distance between the free end and the entry location of the feed-through 5a into the discharge vessel 4. Such an extended length can also amount to a range between about 4 mm and about 6 mm. The material of the extended plugs 5, 6 and of the extended feed- through 5a can be the same as the material of the discharge vessel 4. Especially a ceramic material can be used for the plugs 5, 6 and the feed through 5a.

As a third feature, at least one of the plugs 5, 6 comprises a second ex- tension in the form of at least a portion of the related plug 5, 6 having an extended diameter or extended cross section, i.e. an extension in a direction perpendicularly to the length of the related plug 5, 6.

This second extension can be a disk or a plate which is closely attached around at least one of the plugs 5, 6 and preferably around the first plug 5 adjacent to the first connection lead 7 at the high voltage side. The diameter of such a disk or plate is preferably between about the outer diameter of the discharge vessel 4 and the inner diameter of the outer bulb 10. The material of the disk or plate can be a ceramic material or a quartz material.

As a fourth feature, the above second extension of at least one of the plugs 5, 6, and again preferably of the first plug 5 at the high voltage side of the lamp, can be provided by at least a portion having an increased cross section or increased diameter in relation to the related plug 5; 6, i.e. again in a direction perpendicularly to its length (and in comparison to the cross section or the diameter of such plugs in known such discharge lamps). The cross section or the diameter can increase along the length of the portion and e.g. can increase with increasing distance from the discharge vessel 4, or it can be constant along the length of the portion. The length of the portion can extend along the entire length or only along a part of the length of the related plug 5; 6. The cross section of the second extension is preferably circular or square.

The above first to fourth features have the effect that the length of the high-voltage creeping path along the related plug 5, 6 (or along the feed-through 5a in case of the second feature) and by this the total creeping path from the first connection lead or lead wire 7 to the second connection lead or lead wire 8 is increased. By this, the voltage at which a flashover discharge can occur is increased as well. Accordingly, the above dimensioning and shaping etc. of the first to fourth feature is selected and the features are combined, if necessary, such that a desired resistance against flashover discharges is obtained under given operating conditions including a hot re- strike (if desired) of the lamp.

As a fifth feature, at least one of the first and the second connection lead or lead wire 7, 8 and again preferably the first connection lead or lead wire 7 at the high voltage side is completely insulated by an insulating layer or coating. The material of such a layer or coating has to be selected on the one hand such that it is sufficiently electrically insulating for obtaining or supporting the above resistance against flashover discharges and on the other hand that it can withstand the high temperatures which are generated during operation of the lamp. As an example, such a material can be silicon- oxide or aluminum-oxide, however, other appropriate materials are available in the prior art.

As a sixth feature, the feed through 5a (if provided) can be electrically insulated by a ceramic tube (especially if the feed through 5a is made of iridium), or the feed through 5a itself is made of a ceramic material.

In contrary to the above first to sixth features, the following seventh fea- ture is applicable only in case that the lamp comprises an outer bulb 10. According to this seventh feature, the gas pressure within the outer bulb 10 is increased in comparison to the gas pressure of such prior art discharge lamps, and is especially between about 800 mbar and 1000 mbar or more, wherein the gas is preferably nitrogen.

Figure 3 shows a preferred first embodiment of the relevant parts of a discharge lamp comprising the above first feature of the invention. The same or corresponding components and parts as in Figures 1 and 2 are again denoted with the same reference signs, so that a reference is made to the related explanations above.

According to this first embodiment, the first plug 5 at the high voltage side of the lamp comprises a first extension 51 as explained above in the form of an extension of the length of the first plug 5 in comparison to the length of the second plug 6 at the low voltage side which has the length as in a known discharge lamp as shown in Figures 1 and 2. The first plug 5 especially has a total length of about 6 mm.

Alternatively, also the second plug 6 at the low voltage side of the lamp can be provided with such a first extension 51, and the first plug 5 at the high voltage side can have the usual length as in a known discharge lamp. This can also result in an improved resistance against flash over discharges, however, it has revealed that it is more effective if the first plug 5 at the high voltage side is provided with the first extension 51.

According to a second embodiment of the invention, the first and the second plug 5, 6 is provided with the above first extension 51. In such an embodiment, both plugs 5, 6 can have the same extended length of for example about 4 mm to about 6 mm each in total, or the first plug 5 is longer than the second plug 6. In this case, the first plug 5 preferably has an extended length of about 6 mm in total whereas the second plug 6 has an extended length of about 4 mm in total. Preferably, in the embodiments above, the gas filling within the outer bulb 10 surrounding the inner bulb 1 has a pressure of about 800 mbar of nitrogen or higher, especially 1000 mbar of nitrogen or higher.

Measurements have been made with a discharge lamp in which the first plug 5 at the high voltage side has a total length of 6 mm and the second plug 6 at the low voltage side has a total length of 4 mm. Further, a Xenon gas filling pressure within the discharge vessel 4 was 12 bar and instead of an iridium feed-through 5a, a PCA (poly crystalline aluminum) feed-through 5a was used, and no antenna was applied. With such a discharge lamp, no flashover discharges outside the inner bulb 1 occurred in case of a nitrogen filling pressure within the outer bulb 10 of between about 800 and about 1000 mbar and higher, as well as in case of a vacuum within the outer bulb 10, both for a cold strike and a hot re- strike of the lamp. If in contrast to this the nitrogen filling pressure within the outer bulb 10 is between about 200 and below 800 mbar, flashover discharges can occur.

Figure 4 shows a diagram in which on the vertical axis the ignition voltage for a hot re- strike in percentage of the standard maximum D4 ignition voltage (which is usually a 23kV triangular pulse voltage waveform) of such a lamp, and on the horizontal axis the time in seconds is indicated.

Each of the curves A, B, C has been established by connecting measured values (which are each marked by a square or triangular dot) of the breakdown voltage of a discharge lamp upon applying an ignition voltage every 10 seconds for obtaining a hot re-strike of the lamp.

Curve A shows the resulting breakdown voltages for a filling pressure of about 800 mbar of nitrogen within the outer bulb 10. During the measurements of the breakdown voltages no flashover discharges could be observed outside the inner bulb 1.

Curves B and C show the resulting breakdown voltages for a filling pressure of about 600 mbar of nitrogen within the outer bulb 10. The measurements of the breakdown voltages according to curve B, i.e. after 10 and 20 seconds, showed a flashover discharge outside the inner bulb 1, whereas during the other measurements of the breakdown voltages according to curve C, again no flashover discharges could be observed outside the inner bulb 1. This means that only at a filling pressure of about 600 mbar, a certain risk of the occurrence of flashover discharges exists.

Figure 5 shows a diagram in which on the vertical axis again the ignition voltage for a hot re- strike in percentage of the standard maximum D4 ignition voltage (which is usually a 23kV triangular pulse voltage waveform), and on the horizontal axis the time in seconds is indicated. The curves A and B in Figure 5 have been established in the same way and for the same discharge lamp as the curves in Figure 4, however, with the following exceptions:

Curve A shows the breakdown voltages for a filling pressure of about 1000 mbar of nitrogen within the outer bulb 10. During the measurements of the breakdown voltages no flashover discharges could be observed outside the inner bulb 1.

Curve B has been established for a discharge lamp again with a filling pressure of about 1000 mbar of nitrogen within the outer bulb 10, however, comprising a passive antenna on the burner 1 in contrast to the discharge lamp of curve A and the discharge lamps of Figure 4. Again, during the measurements of the breakdown voltag- es no flashover discharges could be observed outside the inner bulb 1.

Further experiments with such a discharge lamp with a passive antenna have shown that flashovers would occur at filling pressures within the outer bulb 10 of between 200 and 800 mbar of nitrogen, whereas in case of a vacuum or a pressure of 1000 mbar of nitrogen (as indicated in curve B of Figure 5) within the outer bulb 10 no flashovers are observed.

Figure 6 schematically shows a discharge lamp with two exemplary embodiments 52, 61 of the second extension according to the above fourth feature (i.e. an extension in a direction perpendicularly to the length of the related plug 5, 6).

In Figure 6, the same components and parts as in Figures 1 to 3 are again denoted with the same reference signs, so that reference is made to the explanations above.

More in detail, the first plug 5 is provided according to Figure 6 with a first alternative of the second extension 52 which has a constant cross section or diameter along its length (and accordingly along the length of the first plug 5). The length of this second extension 52 (which is measured in the direction of the length extension of the related plug 5) can be smaller than or equal to the length of the first plug 5. This second extension 52 can have the shape of a box or a cylinder.

The second plug 6 is provided according to Figure 6 with a second alternative of the second extension 61 which has a non-constant, i.e. an increasing cross section or diameter along its length (and accordingly along the length of the second plug 6). The length of this second extension 61 (which is again measured in the direction of the length extension of the related plug 6) can be smaller than or equal to the length of the second plug 6. Further, according to Figure 6, the diameter of the second extension 61 increases along its length, and preferably increases as the distance from the discharge vessel 4 increases (i.e. the diameter increases with decreasing distance from the connected lead wire 8). This second extension 61 can have a trumpet like shape as shown in Figure 6 or a pyramidal or a similar shape with a stepwise or continuously increasing cross section or diameter.

If the cross section/diameter and/or the length of the second modification 52, 61 is dimensioned large enough, the length of the plugs 5, 6 possibly need not to be extended as explained above with respect to Figure 3, or at least one of the plugs, preferably the first plug 5 at the high voltage side only, is extended with respect to its length as indicated in and explained with reference to Figure 3, however, a shorter extension of the length (i.e. below 6 mm, especially about 4 mm) may be sufficient in order to obtain a desired increased resistance against flashover discharges.

Preferably the first plug 5 at the high voltage side of the lamp is provided with at least one of the first and the second extensions 51; 52, 61, however, also both plugs 5, 6 can be modified with the same or different extensions 51; 52, 61 as shown in Figure 6.

Finally, at least one of the plugs 5, 6 can be provided with extensions which are formed or shaped in another way than those shown in Figure 6, by which forms or shapes the creeping distance for the high voltage between the two connection leads 7, 8 is increased.

The above explain features of the invention are especially effective in case of a discharge lamp having its connection leads on opposite sides of the lamp, i.e. a so called "two-sided" lamp in contrary to a "single- sided" lamp.

Further, due to the fact that the above explained features of the invention are especially effective for preventing unwanted flashover discharges also in case the lamp has been provided for obtaining an especially low ignition voltage (in order to increase the ignition reliability, especially a hot re-strike of the lamp), the features ac- cording to the invention can advantageously be applied in case of a discharge lamp for automotive applications like headlight units.

LIST OF REFERENCE SIGNS

1 - first inner bulb or burner

2 - first electrode

3 - second electrode

4 - discharge vessel

5 - first plug

5a - feed- through

6 - second plug

7 - first lead wire or connection lead

8 - second lead wire or connection lead

9 - flashover discharge path

10 - second outer bulb

51 - first extension

52 - second extension, first alternative

61 - second extension, second alternative

Claims

CLAIMS:

1. High intensity discharge lamp comprising a first bulb (1) with a discharge vessel (4) and a first and a second plug (5, 6) into which a first and a second connection lead (7, 8), respectively, is entering for electrically supplying a first and a second electrode (2, 3), respectively, of the lamp with an ignition voltage for igniting an arc discharge between the electrodes (2, 3) within the discharge vessel (4), wherein the plugs (5, 6) each comprise a length which extends between the entry position of the connection lead (7, 8) into the plug (5, 6) and the discharge vessel (4), and wherein at least one of the plugs (5, 6) comprises a first extension (51) of its length and/or a second extension (52, 61) of its cross section or diameter, which at least one extension is dimensioned for lengthening a creeping path of the ignition voltage along an outside of the at least one plug (5, 6) such that flashover discharges along the outside of the at least one plug (5, 6) are prevented.

2. High intensity discharge lamp according to claim 1,

wherein the first extension (51) is provided in the form of a total length of at least one of the plugs (5, 6) of between about 4 mm and about 6 mm.

3. High intensity discharge lamp according to claim 1,

wherein the first connection lead (7) entering the first plug (5) is provided for applying a high voltage side of the ignition voltage and wherein the first and/or the second extension (51; 52, 61) is provided at the first plug (5) only.

4. High intensity discharge lamp according to claim 1,

wherein the first connection lead (7) entering the first plug (5) is provided for applying a high voltage side of the ignition voltage and wherein the first extension (51) is provided in the form of a total length of the first plug (5) of about 6 mm and of a total length of the second plug (6) of about 4 mm.

5. High intensity discharge lamp according to claim 1,

wherein the second extension (52, 61) is provided in the form of a disk or a plate which is attached around at least one of the plugs (5, 6).

6. High intensity discharge lamp according to claim 1, wherein the second extension (52, 61) is provided by at least a portion of one of the plugs (5, 6) having an increased diameter or cross section in comparison to the related plug (5, 6), wherein the portion extends over a part or over the whole length of the plug (5, 6).

7. High intensity discharge lamp according to claim 6,

wherein the diameter or cross section of the second extension (61) is increasing along the length of the plug (5, 6).

8. High intensity discharge lamp according to claim 1,

wherein at least one of the first and the second connection lead (7, 8) is electrically insulated by an insulating layer or coating.

9. High intensity discharge lamp according to claim 1,

wherein the discharge vessel (4) is provided with a feed-through (5a) which is made of ceramic material or polycrystalline aluminum or is electrically insulated by means of a ceramic tube.

10. High intensity discharge lamp according to claim 1,

comprising a second outer bulb (10) which encloses the first inner bulb (1) and an antenna, wherein the second bulb (10) contains a vacuum or a filling pressure of at least about 1000 mbar of nitrogen.

11. High intensity discharge lamp according to claim 1,

comprising a second outer bulb (10) which encloses the first inner bulb (1) without an antenna, wherein the second bulb (10) contains a vacuum or a filling pressure of about 800 mbar or higher of nitrogen.

12. High intensity discharge lamp according to claim 1,

which is provided in the form of a two-sided lamp having the first and the second connection lead (7, 8) on opposite sides of the lamp.

13. High intensity discharge lamp according to claim 1,

which is provided in the form of a HID automotive lamp.