EP1229567A1 - Discharge lamp with a starting gas - Google Patents

Abstract

The lamp (10) contains a radio active gas for firing the lamp. The gas is enclosed in a metal capsule having a wall which is transparent to radio active radiation. The capsule is positioned sufficiently close to the lamps anode so as to facilitate ignition when the lamp is supplied with direct current. The lamp has an intermediate metallic part soldered to an electrode (12). .

Description

The present invention relates to a discharge lamp containing a radioactive gas for starting said lamp.

It also relates to a glow type starter containing a radioactive gas and used for starting a discharge lamp.

The present invention finds its application, for example, in neon lamps or in miniature fluorescent lamps of the cold electrode type intended for the automotive industry or signaling, the reliability of the ignition being essential for these lamps.

U.S. Patent No. 2,930,872 describes a glow type starter used for ignition of elongated low-pressure discharge lamps such as lamps fluorescent. Said patent proposes a starter having characteristics of stable operation over time. For this, the starter type glow according to art previous includes an envelope containing, in addition to a filling gas, a tiny amount of radioactive krypton to provide an ionization source for remove the dark effect. In addition, said lamp contains a small proportion of impurities soft.

The object of the present invention is to provide a discharge lamp having a longer service life.

Indeed, if the addition of radioactive krypton to the filling gas contained in a glow type starter for discharge lamp or inside a discharge lamp itself initially improves the ignition of said lamp, this addition results in the following consumption of radioactive krypton over time. This drawback is due to the migration of electrons to the negative electrode, this phenomenon being known as cataphoresis, which, combined with the spraying of the electrodes, causes the disappearance of radioactive krypton. This point is all the more critical for lamps with discharge of elongated tubular type supplied by a direct current. Therefore, the radioactive krypton tends to become scarce and no longer allows the lamp to start after a few hundred hours, thereby limiting the life of said lamp.

In order to overcome these drawbacks, the discharge lamp according to the present invention is remarkable in that the radioactive gas which it contains is enclosed in a capsule whose a wall is transparent to radioactive radiation.

Said capsule having a wall transparent to radioactive radiation will favor the ignition of the discharge lamp by ionization of the filling gas while avoiding consumption of the radioactive gas it contains since it is isolated filling gas through the sealed walls of the capsule. The service life of the lamp discharge is thereby increased.

The use of such a capsule is also of considerable interest for the protection of the environment. Indeed, the capsule can be easily recycled or better still reused which considerably limits the environmental nuisance of such discharge lamps.

In addition, in the case of a lamp powered by direct current, the discharge has need for free electrons in the vicinity of the anode for the first ignition.

This is why the discharge lamp according to the present invention is remarkable in that the capsule is positioned close enough to an anode of the discharge lamp in order to facilitate its ignition, when said lamp is supplied with a direct current.

The present invention also relates to a starter of the light type intended for ignition of a discharge lamp, said starter being characterized in that the gas radioactive it contains is enclosed in a capsule whose wall is transparent to radioactive radiation.

• la Fig. 1 représente de façon très schématique une lampe à décharge selon l'invention,
• la Fig. 2 illustre une partie de lampe à décharge comprenant une capsule de gaz radioactif selon un premier mode de réalisation de l'invention,
• la Fig. 3 illustre une partie de lampe à décharge comprenant une capsule de gaz radioactif selon un second mode de réalisation de l'invention,
• la Fig. 4 illustre une partie de lampe à décharge comprenant une capsule de gaz radioactif selon un troisième mode de réalisation de l'invention, et
• la Fig. 5 illustre un starter de type à lueurs selon l'invention comprenant une capsule de gaz radioactif.

These aspects of the invention as well as other more detailed aspects will become more clearly apparent from the following description of several embodiments of the invention, given by way of nonlimiting examples and with reference to the appended drawings in which:

• Fig. 1 very schematically represents a discharge lamp according to the invention,
• Fig. 2 illustrates a part of a discharge lamp comprising a radioactive gas capsule according to a first embodiment of the invention,
• Fig. 3 illustrates a part of a discharge lamp comprising a radioactive gas capsule according to a second embodiment of the invention,
• Fig. 4 illustrates a part of a discharge lamp comprising a radioactive gas capsule according to a third embodiment of the invention, and
• Fig. 5 illustrates a starter of the glow type according to the invention comprising a radioactive gas capsule.

The present invention relates to a discharge lamp intended for industry automotive or signaling. This discharge lamp can either be a neon lamp, or a miniature fluorescent lamp with cold electrodes.

• une première électrode (11), qui est par exemple l'électrode négative en courant continu ou cathode,
• une seconde électrode (12), qui est par exemple l'électrode positive en courant continu ou anode,
• un gaz de remplissage (13), du néon ou de l'argon par exemple, qui s'illumine à basse pression sous l'effet d'une tension électrique entre les deux électrodes, et
• une paroi périphérique (14) en verre, recouverte d'un enduit fluorescent dans le cas d'une lampe fluorescente.

Fig. 1 is a schematic representation of a discharge lamp according to the invention. Such a discharge lamp (10) mainly comprises:

• a first electrode (11), which is for example the negative direct current electrode or cathode,
• a second electrode (12), which is for example the positive direct current electrode or anode,
• a filling gas (13), for example neon or argon, which lights up at low pressure under the effect of an electric voltage between the two electrodes, and
• a peripheral wall (14) made of glass, covered with a fluorescent coating in the case of a fluorescent lamp.

The discharge lamp further comprises a capsule (15) containing a radioactive gas, a wall of said capsule being transparent to radioactive radiation in order to facilitate the ignition of the discharge lamp by ionization of the filling gas while avoiding consumption of the radioactive gas it contains. In the preferred embodiment, the radioactive gas is radioactive krypton ₃₆ Kr ⁸⁵ , but it will be apparent to those skilled in the art that any other radioactive gas may be suitable for our application.

• une source lumineuse placée dans le voisinage immédiat de l'anode de la lampe à décharge favorise son amorçage,
• la même source lumineuse placée au niveau de la cathode ne favorise pas l'amorçage de la lampe.

In addition, if the discharge lamp is powered by a direct current, the radioactive krypton capsule ₃₆ Kr ⁸⁵ is preferably placed at the level of the anode. Indeed, in this case, the discharge needs free electrons in the vicinity of the anode for the first ignition. This is confirmed by the following experiments:

• a light source placed in the immediate vicinity of the anode of the discharge lamp promotes its ignition,
• the same light source placed at the cathode does not favor the starting of the lamp.

In the preferred embodiment, the wall transparent to radioactive radiation of the capsule is made with a glass with a thickness of 0.5 mm. Such a capsule is not not completely transparent to radioactive radiation because it absorbs part of the radiation, but it still remains effective nonetheless.

• une épaisseur de fer de 30 µm environ est nécessaire,
• une épaisseur d'aluminium de 80 µm environ est nécessaire,
• une épaisseur de verre de 100 µm environ est nécessaire.

Le krypton radioactif émet également environ 1% de rayonnement gamma avec une énergie de 0.52 Mev. Ce rayonnement est plus pénétrant, de sorte qu'une épaisseur de l'ordre du centimètre fait décroítre le rayonnement gamma de moitié. En conséquence, l'épaisseur de la capsule est, de préférence inférieure aux valeurs citées plus haut, en référence au rayonnement Bêta, pour les différents matériaux envisagés afin de permettre l'amorçage de la lampe à décharge. Cependant des valeurs supérieures, de l'ordre du millimètre pour le verre par exemple, peuvent également convenir dans la mesure où le rayonnement gamma transmis est suffisamment énergétique pour favoriser l'amorçage.Other materials, such as iron, aluminum, nickel or steel, to name a few, can advantageously be used to manufacture the capsules. It is the thickness of the chosen material which makes it transparent to radioactive radiation. The radioactive krypton ₃₆ Kr ⁸⁵ essentially emits (around 99% of the radiation) beta radiation with an energy of 0.67 Mev. For example, to absorb the Beta radiation of 0.67 Mev:

• an iron thickness of around 30 µm is required,
• an aluminum thickness of around 80 µm is required,
• a glass thickness of approximately 100 µm is required.

Radioactive krypton also emits about 1% of gamma radiation with an energy of 0.52 Mev. This radiation is more penetrating, so that a thickness of the order of a centimeter decreases the gamma radiation by half. Consequently, the thickness of the capsule is preferably less than the values mentioned above, with reference to beta radiation, for the various materials envisaged in order to allow the discharge of the discharge lamp. However, higher values, of the order of a millimeter for glass for example, may also be suitable insofar as the gamma radiation transmitted is sufficiently energetic to promote ignition.

In the preferred embodiment, the capsule is tubular in shape with a diameter ranging from 1 to 2 mm and a length ranging from 5 to 10 mm depending on the type of discharge lamp. The volume of radioactive krypton ₃₆ Kr ⁸⁵ is then from 4 to 30 mm ³ under a bar, its filling pressure varying from 0.75 to 1 bar. The radioactivity of krypton ₃₆ Kr ⁸⁵ being 11 million Becquerels per liter, the radioactivity of the capsule is at most 330 Becquerels. In addition to the fact that the capsule can be recycled or reused, the discharge lamp which contains it potentially presents a lesser nuisance for the environment than a neon tube currently manufactured which contains radioactive materials having a radioactivity of the order of 800 becquerels.

Fig. 2 shows the content of a discharge lamp according to the invention, the lamp comprising a radioactive gas capsule of the tubular type which is fixed according to a first method of attachment to an electrode. Said capsule (20) is made of glass and is held by a metal strip (21) formed by two fixing fins (21a, 21b) which pinch the capsule and a main part (21c) welded to an electrode, which is the anode (12) in direct current. A main glass tube (14) is sealed around the electrode. A second glass tube called closed pumping tube (23) is also shown in this Fig. This tube makes it possible to empty the lamp of the air which it contains then to fill it with the filling gas desired via the anode (12) which is hollow.

Fig. 3 shows the content of a discharge lamp according to the invention, the lamp comprising a closed cup-shaped radioactive gas capsule which is attached to a another method of attachment. Said capsule (30) is this time metallic and is welded to an electrode, which here is the anode (12), via a small plate metallic (30a).

Fig. 4 shows the content of a discharge lamp according to the invention, the lamp comprising a tube type radioactive gas capsule. The capsule (20) is this time the interior of the closed pumping tube (23) whose dimensions are adapted to limit the displacements of the capsule which it contains.

Fig. 5 illustrates a starter of the glow type (50) according to the invention comprising a radioactive gas capsule. Said starter comprises a bulb (51) filled with a rare gas (52) and two electrodes (53, 54), at least one of which is a bimetallic strip (54). This blade, composed of two metals with different coefficients of expansion, has the property of bending under the influence of heat. When voltage is applied to the choke, a light discharge occurs in the rare gas and the heat given off by the cathodic fall causes the blade to bend so that contacts are made and electrodes of the discharge lamp to which the choke is connected heat up. At the moment, the choke is short-circuited, which stops the discharge and causes cooling of the bimetallic blade and a reopening of the contacts. The voltage pulse that results from the power failure then starts the discharge lamp.

The above description with reference to Figs. 1 to 5 illustrates the invention more than it the limit. It is obvious that other forms of capsules are possible, associated with other fixing means to hold them.

No reference sign in parentheses in a claim should be interpreted restrictively. The verb "to understand" and its conjugations does not exclude the presence of other elements listed in a claim. The word "un" or "une" preceding an element does not exclude the presence of a plurality of these elements.

Claims (6)

Discharge lamp (10) containing a radioactive gas for igniting said lamp, characterized in that the radioactive gas is enclosed in a capsule whose wall is transparent to radioactive radiation. Discharge lamp (10) according to claim 1, characterized in that the capsule is positioned sufficiently close to an anode of the discharge lamp in order to facilitate its ignition when said lamp is supplied with direct current. Discharge lamp (10) according to claim 1 or 2, characterized in that the capsule (20) is made of glass and in that the discharge lamp comprises a metallic intermediate piece (21) welded to an electrode (12) and suitable to pinch the capsule. Discharge lamp (10) according to claim 1 or 2, characterized in that the capsule (30) is made of metal and in that it is welded to an electrode (12). Discharge lamp (10) according to claim 1 or 2, characterized in that the capsule is embedded in a closed pumping tube (23). Starter of the light type intended for starting a discharge lamp, said starter containing a radioactive gas and being characterized in that the radioactive gas which it contains is enclosed in a capsule whose wall is transparent to radioactive radiation.

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