WO2005124824A2 - Discharge lamp and method for running up such a discharge lamp - Google Patents

Abstract

Discharge lamp, such as a neon sign, a germicidal and tanning lamp, photographic electronic flash and strobe or an arc lamp for industry and A/V projectors, or a gas discharge automotive headlight, for the environment in residences, office buildings, commercial and industrial buildings, streets, vehicles and parking lots. The invention relates to a discharge lamp comprising at least one burner containing a ionisable substance, and multiple electrodes connected to said burner for ionising said substance. The invention also relates to a method for running up such a discharge lamp. The discharge lamp comprises at least one antenna connected to at least one electric conductor for stimulating ignition in said burner, the antenna further being as a heathing wire during lamp run-up.

Description

Discharge lamp and method for running up such a discharge lamp

The invention relates to a discharge lamp, comprising: at least one burner containing a ionisable substance, and in which multiple electrodes are present between which a discharge extends during lamp operation, at least one sealing portion retaining gastightness of said burner, said sealing portion incorporating at least one electric conductor connected to one of said electrodes, and at least one antenna connected to an electric conductor for stimulating ignition in said burner. The invention also relates to a method for running up such a discharge lamp. Discharge lamps, such as neon signs, germicidal and tanning lamps, photographic electronic flashes and strobes, arc lamps for industry and A V projectors, and gas discharge automotive headlights, are found throughout our environment in residences, office buildings, commercial and industrial buildings, streets, vehicles and parking lots. They are energy efficient and virtually indispensable. These discharge lamps pass an electric current through a rare gas or metal vapour to produce light. The electrons collide with gas atoms, exciting them to higher energy levels which then decay to lower levels by emitting light. Low-pressure lamps thereby have sharp line emission characteristic of the atoms in the lamp, and high-pressure lamps have broadened lines superimposed on a continuum. A discharge lamp according to the preamble, in particular a high pressure discharge lamp, is disclosed in the international application WO 00/77826, wherein the antenna is provided to promote ionisation of the substance in the burner. However, besides the wide application of these known gas discharge lamps and its advantageous properties of efficient light production, the known discharge lamps have also several drawbacks, in particular during runup of the discharge lamps. For example, an important limitation of Ultra Jligh Performance (UHP) discharge lamps is the relatively low maximum pressure that can be obtained in the burner of the lamp. At higher pressures most importantly the lumen output and colour rendering will commonly improve. The limitation in maximum pressure is due to the explosion sensitivity at higher pressures. The phenomenon of early explosion is due to the presence of a considerable amount of tension in the lamp at cold start. The total tension in the lamp is caused by a latent tension in the cold burner and tension in the lamp due to the internal pressure. A second major drawback of these UHP lamps also relates to the running up stage of the lamp. After breakdown of the burner of the UHP lamp, the discharge is an arc, characterised by a relatively low arc voltage, commonly about 20 Volt, due to a relatively low pressure of mercury droplets contained in the burner. This relatively low pressure is caused by a relatively slow evaporation of mercury droplets present on the inner wall of said burner, in particular in the coldest region of the burner, id est close to the sealing portion. Only during evaporation of these droplets the internal pressure will increase resulting in a (significant) increase of arc voltage and thus a higher power dissipating in the burner. Choosing for a high current in the burner just after breakdown is no solution in this situation, since the tungsten electrode (winding) is deformed by this temperature increase. Moreover, this temperature increase will lead to a relatively high sputter rate of the tungsten electrode, resulting in a possible starting of an undesired crystallisation process of the quartz wall. It is an object of the invention to provide an improved discharge lamp which can be run up in a relatively quick and efficient way. The object of the invention can be achieved by a discharge lamp according to the preamble, characterised in that, the antenna is further adapted to be heated during run-up of the lamp to heat up the sealing portion and the burner at least partially. In the discharge lamp according to the invention the antenna is thus given an additional functionality, namely to heat up critical parts of the lamp, id est the sealing portion and the burner, resulting in the ability to run-up the discharge lamp in a relatively efficient manner. By heating the critical region of the discharge lamp the tension in this critical region can be decreased significantly resulting in an improved capacity of the burner to withstand the increasing internal pressures present in the burner. In this manner an increased explosion sensitivity during run-up of the discharge lamp can be eliminated. This improved capacity therefore leads to a relatively high maximum internal pressure which can be achieved during run-up and normal operation of the lamp, thereby improving the lumen output and colour rendering of the emitted light. As it is known that a fully cold sealing portion (pinch) lowers the maximum achievable internal pressure by about 80 bar a pre-heated pinch will enable a discharge lamp with a internal pressure that is some fraction of 80 bar higher than conventional operation. Heating the sealing portion of the discharge lamp and (parts of the) burner will commonly lead to a significantly accelerated evaporation of droplets to be ionised which are present on the inner wall of the burner. This improved evaporation of ionisable droplets leads to an accelerated internal pressure increase resulting in a accelerated increase of the arc voltage generated in said burner, and therefore to a higher power dissipation in the burner. Since efficient and effective, accelerated evaporation of the droplets is established, the run-up process can be shortened, wherein the maximum lumen output and a relatively high internal pressure are achieved in relatively short time. Noted is that heating the sealing portions, or at least one of them, is in particular advantageous in Ultra High Performance (UHP) discharge lamps, but can also be applied in other kind of discharge lamps being sensitive for explosions during run-up as a result of a conflict between a relatively high internal tension, which has not yet relaxed (wherein the burner, electrodes and sealing portion are not yet at a final temperature), and a relatively high internal lamp pressure, the latter due to the run-up of the discharge. Heating the burner during (or just before) run-up of the discharge lamp is in particular advantageous in situations where the ionisable substance sticks as a film or in droplets to the inner wall of the burner, in particular in relatively cold regions of the burner near the sealing portion(s), resulting in a (considerable) delay in the running up of the discharge lamp. Particular advantage of the discharge lamp is thus that the antenna per se, prima facie applied to improve the initiation of the ionisation process within the burner, is also used as heating means to heat up critical parts of the lamp during (or just before) run-up to further improve the running up of the discharge lamp. No relative complex and expensive additional means are necessary to heat up the sealing portion and the burner at least partially. Preferably, the lamp comprises two sealing portions positioned opposite one to one another. In this embodiment the burner is positioned in between said sealing portions. In a preferred embodiment said antenna is wound around at least one sealing portion at least partially. In this way a surround heat can be generated around the critical region of the lamp, resulting in a steady heating of the critical region. This winding is preferably helically shaped, resulting in a heating coil wound around the sealing portion to heat up the correspondent sealing portion and (commonly indirectly) the burner. In a particular embodiment said antenna is at least wound around the sealing portion opposite to the sealing portion incorporating the electric conductor to which the antenna is connected. However, in another particular embodiment said antenna is wound around both sealing portions. In this way both relatively cold extremes of said burner can be heated during (or just before) run-up, resulting in stress relaxation within the sealing portions and the burner on the one side and evaporation of remaining droplets of the ionisable substance on the other side. These effects will lead to discharge lamp which can withstand an increased pressure within the burner resulting in an improved lumen output, and an improved power dissipation within said burner. In another preferred embodiment said burner is covered partially by said antenna. Preferably, this covering is such that the lumen output of the burner is not blocked substantially by the antenna. The covering of the burner by the antenna can be realised in different ways. The antenna can be wound around the burner, though commonly the covering of the burner will be minimised in order to maximise the lumen output, and thereby the antenna will preferably follow a substantially linear course in the region of the burner. Preferably, said antenna comprises at least one wire. Said wire can be relatively thin, but must be of sufficient thickness to stimulate ignition of the ionisable substance within the burner, and moreover to act as satisfying heating means to both sufficiently reduce material tensions of the discharge lamp and evaporate persevering substance droplets inside the burner. In another preferred embodiment said antenna comprises at least one heating strip. A heating strip can act as a relatively effective and efficient heating means to improve the run-up process of the discharge lamp as described above. The strip can be oriented near the burner and/or the one or more sealing portions. In a preferred embodiment at least one electrode comprises an element for compensating expansion and shrinking of said burner. Normally, a foil or thin sheet is used as element to establish this compensation. This compensation is often required to be able to connect the burner in a solid way to the electrodes, independent of the working temperature. Commonly, the burner is made of quartz in particular since this material has the highest melting point of all glass systems. One problem with quartz is that because it's coefficient of expansion is virtually negligible, it is difficult to make a gas tight seal with the molybdenum foil and at the same time to connect the lead out wire with the electrode. To abolish this problem, preferably etched molybdenum foil is applied as compensation element. These very thin molybdenum foils lead out through the "pinched" section of the lamp at the base. Within the lamp, the tungsten supports are welded to the foil and outside the bulb, short wires are connected to the lamp pins via said molybdenum foils. In another preferred embodiment the lamp is formed by a high pressure discharge lamp, more preferably an Ultra High Performance (UHP) lamp or a High Intensity Discharge (HID) lamp. It is imaginable that other kind of discharge lamps are used being sensitive for explosions during run-up as a result of a conflict between a relatively high internal tension, which has not yet relaxed (wherein the burner and sealing portions are not yet at a final temperature), and a relatively high internal lamp pressure, the latter is realised in steady state operation, after the run-up phase. The invention also relates to a method for ranning up a discharge lamp as described above, comprising the steps of: a) heating the antenna thereby heating at least one of the burner and at least one sealing portion at least partially, b) letting the antenna to cool down, and c) initiating ionising the substance within said burner by said antenna while applying a voltage between the electrodes. As aforementioned the antenna has subsequently different functionalities. At first the antenna is adapted to heat up critical regions of the lamp, in particular the sealing portion(s) and the region of the burner close to the sealing portion(s). Subsequently the antenna will be used to further support the starting up process of the discharge lamp, e.g. by generating free electrons by means of an UV enhancer, and by accelerating ionising collisions inside the burner by applying an electrical field inside the burner. A further elucidation of this advantageous method is given above. Preferably, step a) is carried out for a duration of between 0 and 60 seconds.

Commonly a duration of 30 seconds will be sufficient to sufficiently heat up the burner and the sealing portion(s) by the antenna to improve the run-up process of the discharge lamp significantly. In a preferred embodiment step b) and step c) are carried out simultaneously, more preferably after step a) has been completed. However, it is also conceivable that all steps a)-c) are carried out simultaneously. As aforementioned the conventional antenna can be used as heating wire as the presently applied antennae wire is already resistant against oxidation, as the discharge lamp according to the invention is (normally) operating in open air. Preferably, the antenna is electrically controlled by a control unit to control the functionality of the antenna at different stages of the run-up process.

The invention can be illustrated by way of the following, non-limitative embodiments, wherein: Figure 1 shows a side view of an embodiment of a discharge lamp according to the invention, Figure 2 shows a side view of an alternative embodiment of a discharge lamp according to the invention, and Figure 3 shows a side view of yet an alternative embodiment of a discharge lamp according to the invention.

Figure 1 shows a side view of an embodiment of a discharge lamp 1 according to the invention. The lamp 1 comprises a gastight burner 2 made of quartz glass containing a ionisable substance 3, such as mercury. In the burner 2 two electrodes 4 are present for generating a discharge arc during lamp operation. The burner 2 is sealed by two sealing portions 5, each comprising a conducting foil 6 connected to a correspondent electrode 4. Each conducting foil 6 is subsequently connected to a metal wire 7. One metal wire 7 is connected to an antenna 8 for both heating one sealing portion 5 and said burner 2, and subsequently stimulating ignition in said burner 2. The antenna 8 is thereby wounded helically around said sealing portion 5 and is connected by means of a closed loop 9 to a neck 10 of the burner 2 as discharge vessel. In the sealing portion 5 around which the antenna 8 is wounded a gas-filled cavity 11 is present. The available cavity 11 constitutes a start- promoting means as a source of UV radiation when applying an electric voltage across the cavity 11. However, during run-up, at first the antenna 8 is enforced by a control unit (not shown) to heat up the sealing portion 5 and one side of the burner 2. In this part of the lamp 1 the internal material stresses will be reduced by the heating, resulting in an increased maximum pressure to be obtained and an improved lumen output and colour rendering. Moreover, the heating up this critical region of the lamp 1 leads to an accelerated evaporation of mercury droplets stuck to the relatively cold inner wall of the burner 2 near the sealing portions 5. By giving the antenna 8 an additional functionality as heating means the run-up process of the discharge lamp 1 can further be improved in a significant way. Figure 2 shows a side view of an alternative embodiment of an ultra high discharge lamp 12 according to the invention. The lamp 12 has more or less the same structure as the lamp 1 shown in figure 1, distinctive in that the lamp 12 comprises an antenna 13 which is connected to a control unit (not shown) and a metal wire 14 connected to an electrode 15 via a molybdenum foil 16. The antenna 13 is wound helically around both pinches 17 incorporating said foils 16 thereby sealing a central discharge vessel 18. The antenna 13 is closed by a final loop 20. In this way the vessel 18 is encompassed de facto by two coils 19, which can among others be used to heat up both pinches 17 and the bilateral regions of the vessel 18 neighbouring said pinches 17. The bipartite effect of this heating is already elucidated above in a comprehensive way. Figure 3 shows a side view of yet an alternative embodiment of a discharge lamp 21 according to the invention. The structure of the lamp 21 is substantially equal to the structure of the lamp 1 as disclosed in figure 1. However, the lamp 21 is provided with a start-promoting antenna 22, which is also adapted to act as heating means to heat up both sealing portions 23 and a burner 24. To that end the antenna 22 is wound like a coil 25 around one sealing portion 23, and is moreover wound in a single winding 26 around said burner 24, and is secured around a neck 27 of an opposite sealing portion 23 by a final loop 28. The sophisticated plural functionality of the antenna is enunciated in the above- mentioned. It will be apparent that the invention is not limited to the exemplary embodiments shown and described here, but that numerous variants, which will be obvious to the skilled person in the field, are possible within the scope of the appended claims.

Claims

CLAIMS:

1. Discharge lamp, comprising: at least one burner containing a ionisable substance, and in which multiple electrodes are present between which a discharge extends during lamp operation, at least one sealing portion retaining gastightness of said burner, said sealing portion incorporating at least one electric conductor connected to one of said electrodes, and at least one antenna connected to the at least one electric conductor for stimulating ignition in said burner, characterised in that, the antenna is further used as a heating wire during run-up of the lamp to heat up the sealing portion and the burner at least partially.

2. Lamp according to claim 1, characterised in that the lamp comprises two sealing portions positioned opposite one to one another.

3. Lamp according to claim 1 or 2, characterised in that said antenna is wound around at least one sealing portion at least partially.

4. Lamp according to claims 2 and 3, characterised in that said antenna is at least wound around the sealing portion opposite to the sealing portion incorporating the electric conductor to which the antenna is connected.

5. Lamp according to claim 2 and one of claims 3 or 4, characterised in that said antenna is wound around both sealing portions.

6. Lamp according to one of the foregoing claims, characterised in that said burner is covered partially by said antenna.

7. Lamp according to one of the foregoing claims, characterised in that said antenna comprises at least one wire.

8. Lamp according to one of the foregoing claims, characterised in that said antenna comprises at least one heating strip.

9. Lamp according to one of the foregoing claims, characterised in that said electrical conductor is adapted for compensating expansion and shrinking of said burner.

10. Lamp according to one of the foregoing claims, characterised in that said lamp is formed by a high pressure discharge lamp.

11. Method for running up a discharge lamp according to one of claims 1-10, comprising the steps of: a) heating the antenna thereby heating at least one of the burner and at least one sealing portion at least partially, b) letting the antenna to cool down, and c) initiating ionising the substance within said burner by said antenna while applying a voltage between the electrodes.

12. Method according to claim 11, characterised in that step a) is carried out for a duration of between 0 and 60 seconds.

13. Method according to claim 11 or 12, characterised in that step b) and step c) are carried out simultaneously.