GB2178230A

GB2178230A - Discharge lamp with noble gas filling, especially for pulse operation

Info

Publication number: GB2178230A
Application number: GB08615913A
Authority: GB
Inventors: Miklos Csapody; Ferenc Nagel; Gabor Varga
Original assignee: Tungsram Rt
Current assignee: Tungsram Rt
Priority date: 1985-07-02
Filing date: 1986-06-30
Publication date: 1987-02-04
Also published as: DE3618573C2; JPS6231938A; GB8615913D0; HUT52894A; DE3618573A1; NL8601430A; HU202013B; BE904993A

Abstract

A discharge lamp with noble gas filling, especially for pulse operation at high power, comprises a cylindrical discharge vessel /1/ having walls made of ceramic translucent alumina, an anode /4/ and a cathode /5/ arranged in the inner space of the discharge vessel /1/, current inlet means /6, 7/ connected respectively to the anode /4/ and the cathode /5/ and a filling disposed in the inner space of the discharge vessel /1/, the filling consisting of one noble gas mixture of the noble gases and if necessary, of mercury, wherein the filling has a gas pressure of at least 10 millibars. <IMAGE>

Description

SPECIFICATION Discharge lamp with noble gas filling, especially for pulse operating BACKGROUND OF THE INVENTION The invention relates to a discharge lamp with noble gas filling, especially for pulse operating wherein high specific power is required.

The discharge lamps with noble gas filling comprising a cylindrical shaped discharge vessel, an anode and a cathode arranged in the discharge vessel and connected to current inlet means embedded in the end parts of the discharge vessel, and a gas filling having a gas pressure at least 10 millibars consisting of one or more noble gases and, if necessary, mercury are very advantageous for pulse operating required in many industrial and professional fields of use, especially in the photography and the motor car repairing service works.

The discharge vessel of the known light sources operated in pulses as flashgun type discharge light sources comprising a filling consisting of noble gases is made of glass or quartz glass. In the technology of production it is important that at the end portions of the cylindrical discharge vessel cut out from a tube and having the necessary dimensions respective electrode means should be soldered or arranged in other way, and the electrode means are flattened or made with glass. The gas discharge lamps intended to be used as flashguns for taking photos and giving low specific power the construction shown above is applicable and the lamp can be produced by the well known steps of the industrial technologies.

Pulse operation causes shock waves, however, and this is true especially of the lamps of higher specific output; this produces high mechanical loads on the end portions of the discharge vessel. This is to be taken into account because the consequence is the erosion of the electrodes and thereby shortened life period of the light sources equipped with lamps of the type mentioned.

Many different inventions has been elaborated for increasing the life period of the light sources characterized above. The German patent specification DE-PS 28 48 891 proposes for example to close the end portions of the discharge vessels by flat soldering and applying a metallic plate. The U.S. Letters Patent 4 315187 shows the coupling of the electrodes with a special protective plate arranged in a given distance from the walls of gas discharge vessel. The German Offenlegungsschrift DE-OS 32 27 280 includes a solution whereby the closing of the discharge vessel should be realised by the use of disc made of glass or glass based ceramics.

The solutions shown above are intended to create in the discharge vessel a meeting region of increased mechanical strength wherein the longitudinal shock waves of the discharge meet the material of the vessel. Another intention of the mentioned inventions is to create a discharge vessel, wherein the shock waves are not capable of reaching the end regions of the discharge vessel. The known solutions are, however, not capable of ensuring both the high specific power and the high reliability of the work.

SUMMARY OF THE INVENTION The object of this invention is to overcome the mentioned drawbacks and to create a discharge lamp with noble gas filling, which is capable of ensuring high specific power and can be operated in pulses and characterized by long life and high reliability. The life period should be many times longer than that of the known light sources.

The present invention is based on the recognition that in the production of gas discharge lamps intended for ensuring high specific power and assuring the conditions of pulse operating it is very important to solder in the discharge vessel without causing any remaining stress, to prepare the end regions of the discharge vessel from a basic material of necessary mechanical strength and to make the walls of the discharge vessel from a material of high enough mechanical strength.

These three conditions can be fulfilled by ceramic alumina which is translucent. It should be mentioned that alumina is well known as basic material of ceramic vessels to high-pressure sodium vapour lamps wherein glass and quartz glass are not acceptable as basic material because of the presence of sodium therein, which results in undesirable recrystallisation of the wall regions.

The invention relates therefore to a discharge lamp with noble gas filling, especially for pulse operating at high specific power comprising a cylindrical discharge vessel, an anode and a cathode arranged in the inner space of the cylindrical discharge vessel and connected to respective current inlet means, and a filling consisted of noble gases/argon, xenon, krypton, helium or neon or a mixture of desired composition of these gases/exclu sively having gas pressure at least 10 milli bars, wherein the improvement lies in applying translucent ceramic alumina for preparing the walls of the discharge vessel. The gas discharge light source proposed by the invention is constructed similarly to the different types of the sodium vapour lamps, however, it com prises a filling consisting of noble gases and no sodium or other metals are required therein.

The photochemical applications require sometimes the use of a gas discharge lamp with noble gas filling which is capable of en suring high specific power and pulse operating in ultraviolet. The required spectral composition of the ultraviolet light emitted by such light sources can be ensured, as it is known, by adding mercury to the noble gas filling because mercury causes shifting of the frequency range of the emitted light in the direction of the ultraviolet.

The basic recognition of the invention can be applied in this case, too. The invention relates therefore also to a discharge lamp with noble gas filling, especially or pulse operating at high specific power comprising a cylindrical discharge vessel, an anode and a cathode arranged in the inner space of the cylindrical discharge vessel and connected to respective current inlet means, and a filling consisted of noble gases/argon, xenon, krypton, helium or neon or a mixture of desired composition of these gases/ and mercury having gas pressure at least 10 millibars, wherein the improvement lies in applying translucent ceramic alumina for preparing the walls of the discharge vessel.

The control measurements gave a proof that the translucent ceramic material consisting of alumina is translucent also for the ultraviolet rays.

As for the reliability and life period of the invented discharge lamp with noble gas filling they are many times higher than those of the known gas discharge light sources intended for flashgun type operating The walls of the discharge vessel made according to the invention can bear very high loads and this is especially advantageous while also enabling the reduction of the dimensions of the high power pulse light sources with gas filling in comparison to the light source of the art.

It is considered as an advantageous feature for ensuring relatively high load of the end regions of the discharge vessel if the end regions of the vessel-similarly to the highpressure sodium vapour lamps-plug type closing elements made of alumina are applied and the current inlet means are made of a material having thermal expansion coefficient in the same range as the closing elements wherein the closing elements and the discharge vessel are connected to each other by a vacuum proof seal prepared from an appropriate sealing material. The sealing material can be an enamel of known composition applicable in the production of the high-pressure sodium vapour lamps. The basic component of this enamel is the alumina and it should comprise oxides of other trivalent metals, possibly of some alkaline earth metals.The mentioned metal components are intended for ensuring the necessary thermal expansion and melting features of the enamel.

The basic material of the current inlet means is advantageously niobium, tantalum or an alloy of the mentioned metals. After control some other alloys can be applied, too, for example the iron base alloys.

The lamps intended for giving high specific powers it seems to be very advantageous to compose the current inlet means from a higher number of parallel wires embedded into the respective closing elements separately and united before and after crossing the closing element of the discharge vessel. At specific power ranges it is also acceptable to apply current inlet means shaped as a tube instead of parallel wires and this tube should be embedded into the closing element.

The manner in which the current inlet means are arranged in the closing elements can be a basis for asymmetric arrangement of the electrode/cathode and anode/whereby the negative influence of the shock waves can be diminished in the inner space of the discharge vessel. In this asymmetric arrangement it is especially advantageous to apply electrodes with peaks in the inner space of the discharge vessel, wherein the distance of the peaks is less than 0.35 times the distance of.the.two end regions of the discharge vessel and the asymmetry of the arrangement includes the feature that the bisecting point of the distance between the two electrode peaks and the bisecting point of the two end regions of the discharge vessel are shifted by at most 0.03 times the distance of the two end portions.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail by way of example and with reference to preferred embodiments illustrated in the drawings, wherein Figure 1 is a proposed embodiment of the light source of the invention with a gas filling, and Figure 2 shows an embodiment of the proposed light source with noble gas filling arranged in an outer vessel.

DESCRIPTION OF THE PREFERRED EMBODI MENTS The power range, the field of application and other requirements are the basid conditions for determining the composition of the gas filling of the light sources with noble gas filling intended for pulse operating at high specific power. The gas filling consists of exclusively noble gases and, if required, mercury.

The noble gases applicable usually are xenon, crypton, neon and helium. The quality and kind of the gas filling has no influence on the structural shape of the lamp, and the dimensions depend, of course on the power range.

The proposed light source, as shown in Fig.

1 can be built up without outer vessel, however, in specific fields of application or other conditions the outer vessel as shown in Fig 2 can be advantageous. The outer vessel seems to be advantageous when the end regions of the discharge vessel are heated up to temperature in range 200 to 300"C or higher and/or in a space with high content of moisture in the atmosphere.

As an example a gas discharge light source will be shown featured by energy of pulses in range 500 W.s. and by supply voltage 1500 V. This is a light source with noble gas filling.

The discharge lamp of the invention is equipped with a discharge vessel 1 which is cylindrical shaped and closed by plug-type closing element 2 and 3. The discharge vessel 1 and the closing elements 2 are made of ceramic alumina, wherein the length of the discharge vessel 1 is 80 mm and its inner diameter is 4.8 mm. The closing elements 2 and 3 comprise the electrode means composed of an anode 4 or a cathode 5 and a corresponding current inlet means 6 or 7. The current inlet means 6 and 7 are advantageously made of niobium, either pure or including about 1% zirconium. The current inlet means 6 and 7 include wires of 0.7 mm diameter. The anode 4 is an unactivated block shape element made of tungsten or a tungsten wire surrounding a cylindrical element.

The cathode 5 consists of activated tungsten arranged in cylindrical windings. The electrode means are shaped in different manner at the anode and the cathode sides. This means that for example a longer part of the current inlet means 7 is embedded in the discharge vessel 1 than that of the current inlet means 6.

Thereby asymmetry of the electrodes is given and in the case of the discharge vessel shown above this results in a difference of about 3 mm. The current inlet means 7 are fixed in the closing element 3 by an enamel of appropriate composition and this enamel is used in form of a ring for hermetic sealing the coupling region of the discharge vessel 1 and the closing element 3. The enamel comprises a composition of alumina and alkali earth metals having melting point adjusted to 13500C. The enamel should be heated up and melted in vacuum or a protective gas atmosphere, then the light source arranged in a fitting is turned over. In this position the closing element 2 and the anode 4 can be arranged on the discharge vessel 1 carrying the enamel ring.This ring is heated up to the melting point and in this time the inner space of the discharge vessel is pumped out up to vacuum. Before soldering and sealing the gas filling of desired pressure composed e.g. by xenon should be fed into the discharge vessel which is closed by cooling. After soldering in the discharge vessel 1 shown in the drawing the gas pressure is 300 millibars in the discharge vessel 1, wherein the distance of the peaks of the electrodes is 43 mm.

The construction described above is that of a gas discharge light source without an exhaust tube. /It is important to note that the two ends of the discharge vessel can be sealed and soldered simultaneously./ In the case of light sources with an exhaust tube-wherein a tube made of niobium constitutes the exhaust tube and current inlet means-the operations of soldering and pumping and filling up with gas can be carried out separately. The application of the exhaust tube, tipped off after filling up the inner space with gas, is especially desirable when higher gas pressure range should be ensured. This is the more expensive solution selected at higher pressure values.

The construction of Fig. 2 comprises carrier means 8 or 9 for fixing the gas discharge vessel and a cylindrical outer vessel 10 made of hardened borosilicate glass. After exhausting the interior of the outer vessel 10 the inner space thereof should be filled with argon up to pressure in the range of atmospheric values, then soldered and equipped with head 11 of Edison-type (screw type).

The flashgun type light sources applicable at photopolymerisation processes have to generate light in ultraviolet. For ensuring these ultraviolet rays four gas discharge lamps connected in series are supplied over a capacitor of 15 ,uF from a voltage source 1500 V. The discharge lamps have an inner diameter 8 mm and the distance between the peaks. of the electrodes is 46 mm. The noble gas filling consists of xenon with gas pressure in 160 millibar range and of mercury in a quantity which is required for ensuring the saturated vapour pressure.

On applying technologies similar to described above it is possible to ensure light sources of different dimensions having other gas filling than the described above. Of course, the discharge lamp according to the invention can be produced by technological processes different from the characterized in the foregoing, however, such lamps will be in the scope of protection defined by the at

Claims

tached claims. CLAIMS

1. A discharge lamp with noble gas filling, especially for pulse operation comprising a discharge vessel, an anode and a cathode arranged in the inner space of the discharge vessel, current inlet means connected respectively to the anode and cathode and a filling in the inner space of the discharge vessel consisting of at least one gas selected from the group of the noble gases, the filling having a gas pressure of at least 10 millibars, the wall(s) of the discharge vessel being substantially of ceramic translucent alumina.

2. A discharge lamp with noble gas filling, especially for pulse operation, comprising a discharge vessel, an anode and a cathode arranged in the inner space of the discharge vessel, current inlet means connected respectively to the anode and cathode and a filling in the inner space of the discharge vessel consisting of mercury and at least one gas selected from the group of the noble gases, the filling having a gas pressure of at least 10 millibars, in which the wall(s) of the discharge vessel being substantially of ceramic translucent alumina.

3. A discharge lamp according to claim 1 or 2, in which at the end parts of the discharge vessel closing elements made of ceramic translucent alumina are arranged, the closing elements and the current inlet means having essentially similar thermal expansion coefficients, and wherein the closing elements and the discharge vessel are connected by a vacuum seal.

4. A discharge lamp according to any of claims 1 to 3, in which the current inlet means are made of a metal selected from the group of niobium and its alloys.

5. A discharge lamp according to any of claims 1 to 3, in which the current inlet means are made of a metal selected from the group of tantalum and its alloys.

6. A discharge lamp according to any of claims 1 to 5, in which the current inlet means consist of parallel current wires.

7. A discharge lamp according to any of claims 3 to 5, in which the current inlet means consist of a cylindrical tube element embedded in the closing elements.

8. A discharge lamp according to any of claims 1 to 7, in which the distance between the parts of the anode and the cathode lying in the inner space of the discharge vessel is at most the 0.35 times the distance between the end parts of the discharge vessel, wherein preferably the anode and the cathode are arranged asymmetrically in the inner space of the discharge vessel such that the bisecting point of the distance between the anode and cathode and the bisecting point of the distance between the end parts of the discharge vessel are disposed in a distance of at least the 0.03 times of the distance between the end parts of the discharge vessel.

9. A discharge lamp substantially as herein described with reference to and as shown in Fig. 1 or Fig. 2 of the accompanying drawing.