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(11) | EP 0 784 864 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
LOW-PRESSURE DISCHARGE LAMP NIEDERDRUCKENTLADUNGSLAMPE LAMPE A DECHARGE BASSE PRESSION |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The invention relates to a low-pressure discharge lamp, comprising
a tubular glass lamp vessel which is closed in a vacuumtight manner and which has end portions;
an ionizable filling comprising a rare gas in the lamp vessel;
hollow cylindrical electrodes which enter the lamp vessel each at a respective end portion and which each have an end inside and outside the lamp vessel.
[0003] The known lamp is of a simple construction which is easy to realise. The hollow cylindrical electrodes therein have a multiple function: they act as electrodes inside the lamp vessel, as current supply conductors and current lead-throughs inside the lamp vessel and in the lamp vessel wall, and also as tubes through which the lamp vessel can be cleaned and be provided with its filling. The lamp vessel may be closed in a vacuumtight manner in that a glass tube is fused to each of the electrodes outside the lamp vessel and is closed at its free end, for example by fusion.
[0004] The construction of the known lamp renders it easy to realise lamps of a comparatively small internal diameter, for example 1.5 to 7 mm, and of a comparatively great length of, for example, 1 m or more.
[0005] The ionizable filling may comprise a rare gas or a mixture of rare gases, or in addition a component capable of evaporation such as, for example, mercury. The lamp vessel wall may be provided with a fluorescent material. The lamp may be used for lighting purposes, or as a signal lamp, for example with a neon filling as a tail lamp or stop lamp in vehicles. In the latter application the lamp has the advantage over an incandescent lamp that it emits its full light after 10 ms already, instead of 300 ms after being energised.
[0007] It is an object of the invention to provide a low-pressure discharge lamp of the kind described in the opening paragraph which is capable of providing an increased luminous flux.
[0008] According to the invention, this object is realised in that a tube lies in the extended direction of at least one of the electrodes at a distance from an end thereof, which tube is coated with an electron emitter and is connected to the electrode by electrically conducting means of which the material in cross-sections transverse to the electrode has a surface area which is at most 25% of the surface area of the material of the electrode itself in cross-sections, and which tube is open at least at a side facing the electrode.
[0009] The lamp according to the invention was found to provide an increased luminous flux against the same consumed power.
[0010] The discharge arc is found to apply itself mainly to the inside of the electrode during starting of the lamp. The arc also hits the tube and raises its temperature. After some time the arc applies itself mainly to the tube and remains there.
[0011] The tube assumes a comparatively high temperature during lamp operation. This results in a good electron emission. The electrically conducting means provide the tube with a thermal insulation, so that the electrode itself remains comparatively cool, cooler than the electrode of the known lamp. This manifests itself in the temperature of the electrode at the area where it makes contact with the lamp vessel, and outside the lamp vessel. The lamp vessel and the electrode outside the lamp vessel as a result may be in contact with or in connection with materials which have a comparatively low resistance to heat during operation.
[0012] In general, the electrically conducting means form a heat resistance of 50-2000 K/W. If the heat resistance is considerably greater than indicated here, the tube may generally assume a temperature at which evaporation may start to occur. Given a resistance lower than indicated, the effect on the tube temperature is small. It is favourable when the heat resistance is 100-2000 K/W.
[0013] The lamp which has only one electrode provided with a tube is highly suitable for DC operation. The electrode with the tube is the cathode then. It is favourable, however, for example for AC operation, when both electrodes arc fitted with such a tube.
[0014] The electrically conducting means may be formed by a metal wire which is welded to the electrode and to the tube, for example with resistance welds or laser welds. Alternatively, however, said means may comprise two or more wires. This embodiment may be preferable in lamps which arc subjected to accelerations during operation, for example owing to shocks or vibrations.
[0015] In a favourable embodiment, the tube is integral with the electrode. In that case material has been removed from the shell of a cylinder from which the electrode and the tube were formed over a longitudinal portion thereof, for example by sawing, grinding, drilling, burning, or etching. One or several connections between the tube and the electrode may have been maintained then so as to serve as electrically conducting means. Three such connections distributed over the circumference provide a mechanically strong construction. The wall of the tube is formed, for example, from a solid material, for example the same material as the electrode, for example, the tube is integral with the electrode.
[0016] In a favourable embodiment, the wall of the tube is porous. The material from which the tube is made is a refractory metal such as Ni, Mo or Ta or an alloy thereof. This has the advantage that both the adhesion strength and the amount of emitter material that can be adhered to the tube arc improved. Furthermore, the heat capacity of the tube is relatively low, resulting in a fast warming-up of the electrode.
[0017] Advantageously, the porous material is a gauze as it is easy to handle and has a relatively high strength. The gauze is woven, for example, from a wire having a diameter of the order of a few tens of micrometers and with a density of a few wires per mm.
[0018] It is favourable when the tube is internally coated with emitter. Alternatively, however, the tube may be coated externally, or both internally and externally. The discharge arc preferentially applies itself to the inside of the tube in the case of internal coating. Any material detached from the tube then remains substantially inside the tube instead of depositing itself on the lamp vessel wall. A tube allows itself to be coated particularly easily both internally and externally when it is immersed in a suspension of emitter material. The external emitter may then act as a spare reservoir if the internal emitter stock should become exhausted towards the end of lamp life.
[0019] The thermal insulation of the tube may be chosen through the choice of the distance between the tube and the electrode, the number of connections between the tube and the electrode, and the average cross-section thereof. If the tube and the electrode arc an assembled unit, the insulation is also adjustable through the choice of the material of said means, in particular the heat conductivity thereof. Those skilled in the art may many make this choice in a small test series for each lamp type.
[0020] The emitter may be chosen, for example, from emitters known from lamps, for example low-pressure discharge lamps, or mixtures thereof. Highly suitable is an emitter of BaO, CaO, and SrO, for example obtained from equal molar parts of their carbonates. Alternatively, for example, BaxSr1-xY2O4 may be used, in which x is, for example, 0.75.
[0021] The electrode, and thus possibly the tube, may be made of a metal which has a coefficient of expansion which corresponds to that of the glass of the lamp vessel, for example a CrNiFe alloy in the case of time glass, for example Cr 6% by weight, Ni 42% by weight, and the rest Fe. For a hard-glass lamp vessel, for example of borosilicate glass, an electrode may be used, for example made of Ni/Fe or NiCoFe, for example Ni 29% by weight, Co 17% by weight, the rest Fe, for example with a diameter of 1.5 mm and a wall thickness of 0.12 mm.
[0022] Alternatively, the tube in an assembled unit of electrode and tube may consist of, for example, CrNiFe with 18% Cr by weight, 10% Ni by weight, and the rest Fe, or of Ni. The electrically conducting means may then be, for example, NiCr, for example Ni80Cx20 (weight/weight), for example in the form of wire of 0.125 or 0.250 mm diameter.
[0023] In an embodiment of the lamp according to the invention, the tube is open at both ends and is positioned inside the lamp vessel. Practically all radiation generated by the discharge arc is utilized in this embodiment, which is particularly attractive for a comparatively short lamp vessel.
[0024] Experiments leading to the invention have shown that the discharge arc enters the electrode around the tube in the case of an emitter applied in a tube arranged inside the discharge vessel, which tube is open at one side, the closed side either facing the electrode or being remote from the electrode. The lamp vessel then shows strong blackening near the tube.
[0025] The lamp vessel may be closed in that a glass tube was fused to one or both electrodes outside the lamp vessel and closed. It is alternatively possible, however, that a seal has been made in the electrode tube itself outside the lamp vessel. For this purpose, the tube may have been closed by fusion, for example with a laser, or pinched, or pinched and fused.
[0026] In another embodiment of the lamp according to the invention, the tube is positioned outside the lamp vessel in front of the electrode. This has the advantage that material detached from the tube during operation will end up substantially outside the lamp vessel, so that the lamp vessel itself remains clear. The lumen output accordingly remains high during lamp life. This embodiment is of particular importance for lamps whose filling comprises a component capable of evaporation. Since the discharge arc applies itself mainly to the tube during normal operation, the space outside the lamp vessel, where the tube is accommodated, assumes a comparatively high temperature. The evaporation component can thus have a comparatively high vapour pressure.
[0027] The opposite side facing away from the electrode may be open, as is the side facing the electrode, or it may alternatively be closed, for example in that it has been pinched.
[0028] A first embodiment of the low-pressure discharge lamp according to the invention is shown in Fig. 1 of the drawing in side elevation, partly broken away. Fig. 2 shows a second embodiment, also in side elevation and partly broken away.
[0029] The low-pressure discharge lamp in the drawing has a tubular glass lamp vessel 1 which is closed in a vacuumtight manner and has end portions 2. It has an ionizable filling comprising rare gas, in the drawing a filling of argon and mercury. A mixture of phosphors 8 covers the inner surface of the lamp vessel for the major part. Hollow cylindrical electrodes 3 enter the lamp vessel each at a respective end portion 2 and have ends 4A, 4B inside and outside the lamp vessel.
[0030] A tube 5 lies in the extended direction of at least one of the electrodes 3, at a distance in front of one of the ends 4 thereof, i.e. 4A, which tube is open at least at a side facing the electrode, is coated with an electron emitter 6, and is connected to the electrode 3 by electrically conducting means 7 whose material in cross-sections transverse to the electrode has a surface area which is at most 25% of the surface area of the material of the electrode itself in cross-sections.
[0031] In the embodiment shown, the tube 5 is open at two sides and is positioned in front of the electrode 3, inside the lamp vessel 1.
[0032] The tube is coated with emitter internally and externally. The electrode and the tube form an integral whole. In the Figure, both electrodes have such an emitter-coated tube, and the tubes arc connected to the electrodes by three connections distributed over the circumference, covering approximately 10% of the circumference in the Figure and forming the electrically conducting means.
[0033] In a similar lamp having a lamp vessel of lime glass with an internal diameter of 3.5 mm and an external diameter of 5 mm, electrodes of Cr6Ni42Fe52 (weight/weight/weight) were used. The electrodes had an inner diameter of 1.5 mm and a wall thickness of 0.12 mm. A tube having a solid nickel wall open at two ends and of 4 mm length extended in front of each of the electrodes at a distance of 3 mm. The tubes were internally and externally coated with BaCaSrO3. The tubes were supported by a nickel wire of 0.4 mm diameter which in cross-section had a surface area amounting to approximately 6% of the material surface area of the electrode itself in cross-section, resulting in a heat resistance of 320 K/W.
[0034] The lamp was compared with a lamp (ref) which had no tubes at the electrodes, but which was identical in all other respects. The reference lamp was operated, as was the lamp according to the invention (inv 1) with 10 mA alternating current. The lamp according to the invention was also operated with 30 mA (Inv 2). The voltage across the harps V1a, the power consumption P1a, the luminous flux Φ, and the luminous efficacy η are listed in Table 1 below.
Table 1
| lamp | V1a [V] | P1a [W] | Φ [1m] | η [1m/W] |
| ref | 304 | 3.0 | 135 | 44 |
| inv 1 | 180 | 1.8 | 135 | 75 |
| inv 2 | 163 | 4.9 | 300 | 60 |
[0035] It is evident from Table 1 that the lamp according to the invention operated with the same current but taking up a lower power than the reference lamp yields the same luminous flux, and accordingly has a considerably higher luminous efficacy. When the lamp is operated at a higher power (inv 2), the luminous efficacy is higher than that of the reference lamp, as is the luminous flux.
[0036] An identical lamp vessel, but not coated with phosphors, and having the same electrodes, tubes with emitter, and electrically conducting means, was filled with 25 mbar neon to which 0.05% argon by volume was added. The lamp (inv 3) was operated with 10 mA direct current and compared with a reference lamp (ref 2) having electrodes without the tubes, but identical in all other respects.
[0037] The insults arc listed in Table 2.
Table 2
| lamp | V1a[V] | P1a[W] | Φ[1m] | η[1m/W] |
| ref 2 | 800 | 8 | 120 | 15 |
| inv 3 | 650 | 6.5 | 120 | 18,5 |
[0038] The higher luminous efficacy of the lamp according to the invention is evident from the Table, which leads to a higher luminous flux than that of the reference lamp when the same power is consumed as in the reference lamp.
[0039] The temperature of the lamp inv 3 was measured in the locations indicated in the Figure with a-g, the cathode being at location g. These temperatures arc listed with the corresponding temperatures of the reference lamp (ref 2) for comparison in Table 3 below.
Table 3
| temp. [°C] at: | a | b | c | d | e | f | g |
| inv 3 | 45 | 55 | 63 | 47 | 124 | 120 | 71 |
| ref 2 | 60 | 60 | 60 | 50 | 177 | 177 | 230 |
[0040] It is evident from Table 3 that the highest measured temperature (e) for the lamp inv 3 is more than 50° C lower than in the reference lamp. Since the lamp must certainly be held by the projecting portion of the electrode in order to supply it, it is of greater importance for the choice of materials with which the lamp is in connection during operation that the temperature near the cathode in location g is the lowest, and is much lower (71°C) than in the reference lamp. It is apparent from the temperatures at e-g that the lamp vessel of the reference lamp gets its temperatures mainly through conduction of heat originating from the electrode through the lamp vessel wall. The lamp vessel of lamp inv 3 gets its temperatures mainly through radiation originating from the tube at the electrode.
[0041] In an alternative embodiment, the wall of the tube is of a porous material, for example a gauze of a wire having a diameter. in the range of 50-100 µm and with a density of 3-5 wires per mm. Suitable materials are, for example, Ni, Mo and Ta. In an embodiment, the tube has a length and an internal diameter of 3 mm and of 1.5 mm, respectively.
[0042] In Fig. 2, components corresponding to those of Fig. 1 have reference numerals which arc 10 higher. Lamp properties were measured for lamps of the embodiments of Fig. 1 and Fig. 2, referred to below as inv 4 and inv 5, respectively, after 1 h and 2000 h of operation. The distance between the tubes in lamp inv 4 is 12 cm. Its construction is identical to that of lamp inv 1 in all other respects. The construction of lamp inv 5 differs from that of lamp inv 4 only in that the tube is placed outside the lamp vessel. The distance between the tubes in lamp inv 5 is 14 cm. Lamp construction is the same in other respects, i.e. materials and dimensions of the tubes, electrically conducting means, and electrodes. The lamps inv 4 and inv 5 were filled with 40 mbar Ar and 2 mg Hg. The following lamp properties were measured at a lamp current of 40 mA after a lamp life T (h) of 1 bond 2000 h of operation:
lamp voltage V1a in V, power consumed by the lamp P1a in W, luminous flux φ of the lamp in 1m, and luminous efficacy η in 1m/W, as listed in Table 4 below. The ratio of the luminous efficacy after 2000 hours of operation η2000 to the luminous efficacy after 1 hour of operation η1 is also shown in the Table.
Table 4
| lamp | T[h] | V1a[V] | P1a[W] | φ[1m] | η[1m/W] | η2000/η1 |
| inv 4 | 1 | 76 | 3.0 | 130 | 43.3 | - |
| 2000 | 82 | 3.3 | 108 | 32.7 | 75.7 | |
| inv 5 | 1 | 98 | 3.9 | 162 | 41.5 | - |
| 2000 | 100 | 4.0 | 138 | 34.5 | 83.1 |
[0043] The luminous efficacy of lamp inv 5 after 2000 hours of operation is found to be higher than that of lamp inv 4 in spite of the fact that the radiation generated by the discharge arc in lamp inv 5 is partly intercepted by the electrode because the discharge arc passes through the hollow electrode and applies itself to the tube.
1. A low-pressure discharge lamp, comprising
a tubular glass lamp vessel (1) which is closed in a vacuumtight manner and which has end portions (2);
an ionizable filling comprising a rare gas in the lamp vessel;
hollow cylindrical electrodes (3) which enter the lamp vessel each at a respective end portion (2) and which each have an end (4A) inside and an end (4B) outside the lamp vessel,
characterized in that a tube (5) lies in the extended direction of at least one of the electrodes (3) at a distance from an end (4A) thereof, which tube (5) is coated with an electron emitter (6) and is connected to the electrode (3) by electrically conducting means (7) of which the material in cross-sections transverse to the electrode has a surface area which is at most 25% of the surface area of the material of the electrode itself in cross-sections, and which tube (5) is open at least at a side facing the electrode (3).2. A low-pressure discharge lamp as claimed in Claim 1, characterised in that the wall
of the tube (15) is made of a porous material.
3. A low-pressure discharge lamp as claimed in Claim 2, characterised in that the porous
material is a gauze.
4. A low-pressure discharge lamp as claimed in Claim 1, 2 or 3, characterized in that
the tube (5) is open at both sides and is positioned inside the lamp vessel (1) in
front of the electrode (3).
5. A low-pressure discharge lamp as claimed in Claim 1, or 3, characterized in that the
tube (15) is positioned outside the lamp vessel (11) in front of the electrode (13).
6. A low-pressure discharge lamp as claimed in Claim 1, 2, 3, 4, or 5, characterized
in that the tube (5) is internally coated with emitter (6).
7. A low-pressure discharge lamp as claimed in Claim 6, characterized in that the tube
(5) is coated with emitter (6) internally and externally.
8. A low-pressure discharge lamp as claimed in one of the Claims 1 or 4 to 7, characterized
in that the electrode (3) and the tube (5) arc integral.
9. A low-pressure discharge lamp as claimed in one of the preceding Claims, characterized
in that both electrodes (3) have a tube (5).
1. Niederdruck-Entladungslampe, mit
einem vakuumdicht verschlossenen, röhrenförmigen Lampengefäß aus Glas (1), das Endabschnitte (2) hat;
einer ionisierbaren Füllung mit einem Edelgas in dem Lampengefäß;
hohlzylindrischen Elektroden (3), die jeweils an einem jeweiligen Endabschnitt (2) in das Lampengefäß treten und die jeweils ein Ende (4A) innerhalb und ein Ende (4B) außerhalb des Lampengefäßes aufweisen,
dadurch gekennzeichnet, daß eine Röhre (5) in der Verlängerung zumindest einer der Elektroden (3) in einem Abstand zu einem Ende(4A) davon liegt, wobei die Röhre (5) mit einem Elektronenemitter (6) beschichtet ist und mit der Elektrode (3) mittels elektrisch leitender Mittel (7) verbunden ist, deren Material in Querschnitten quer zur Elektrode eine Oberfläche hat, die höchstens 25% der Oberfläche des Materials der Elektrode selbst in Querschnitten beträgt, und welche Röhre (5) zumindest an einer der Elektrode (3) zugewandten Seite offen ist.2. Niederdruck-Entladungslampe nach Anspruch 1, dadurch gekennzeichnet, daß die Wandung der Röhre (15) aus porösem Material besteht.
3. Niederdruck-Entladungslampe nach Anspruch 2, dadurch gekennzeichnet, daß das poröse Material eine Gaze ist.
4. Niederdruck-Entladungslampe nach Anspruch 1, 2 oder 3, dadurch gekennzeichnet, daß die Röhre (5) an beiden Seiten offen ist und innerhalb des Lampengefäßes (1)
vor der Elektrode (3) positioniert ist.
5. Niederdruck-Entladungslampe nach Anspruch 1, 2 oder 3, dadurch gekennzeichnet, daß die Röhre (15) außerhalb des Lampengefäßes (11) vor der Elektrode (13) positioniert
ist.
6. Niederdruck-Entladungslampe nach Anspruch 1, 2, 3, 4, oder 5, dadurch gekennzeichnet, daß die Röhre (5) innen mit Emitter (6) beschichtet ist.
7. Niederdruck-Entladungslampe nach Anspruch 6, dadurch gekennzeichnet, daß die Röhre (5) innen und außen mit Emitter (6) beschichtet ist.
8. Niederdruck-Entladungslampe nach einem der Ansprüche 1 oder 4 bis 7, dadurch gekennzeichnet, daß die Elektrode (3) und die Röhre (5) aus einem einzigen Stück bestehen.
9. Niederdruck-Entladungslampe nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß beide Elektroden (3) eine Röhre (5) haben.
1. Lampe à décharge à basse pression comportant
un récipient de lampe en verre tubulaire (1) qui est fermé d'une manière étanche au vide et qui présente des parties terminales (2);
un remplissage ionisable comportant un gaz rare dans le récipient de lampe;
des électrodes cylindriques creuses (3) qui entrent dans le récipient de lampe chacune à une propre partie terminale (2) et qui présentent chacune une extrémité (4A) à l'intérieur et une extrémité (4B) à l'extérieur du récipient de lampe,
caractérisée en ce qu'un tube (5) se situe dans la direction prolongée d'au moins une des électrodes (3) à une distance d'une extrémité (4A) de celle-ci, ledit tube (5) étant recouvert d'un émetteur d'électrons (6) et relié à l'électrode (3) par des moyens électriquement conducteurs (7) dont le matériau en coupes transversales à l'électrode présente une zone de surface qui est égale à tout au plus 25% de la zone de surface du matériau de l'électrode elle-même en coupes transversales, et ledit tube (5) étant ouvert au moins à un côté faisant face à l'électrode (3).2. Lampe à décharge à basse pression selon la revendication 1, caractérisée en ce que
la paroi du tube (15) est fabriquée à partir d'un matériau poreux.
3. Lampe à décharge à basse pression selon la revendication 2, caractérisée en ce que
le matériau poreux est une toile.
4. Lampe à décharge à basse pression selon la revendication 1, 2 ou 3, caractérisée en
ce que le tube (5) est ouvert aux deux côtés et est positionné à l'intérieur du récipient
de lampe (1) en face de l'électrode (3).
5. Lampe à décharge à basse pression selon la revendication 1, 2 ou 3, caractérisée en
ce que le tube (15) est positionné à l'extérieur du récipient de lampe (11) en face
de l'électrode (13).
6. Lampe à décharge à basse pression selon la revendication 1, 2, 3, 4 ou 5, caractérisée
en ce que le tube (5) est recouvert d'émetteur (6) intérieurement.
7. Lampe à décharge à basse pression selon la revendication 6, caractérisée en ce que
le tube (5) est recouvert d'émetteur (6) intérieurement et extérieurement.
8. Lampe à décharge à basse pression selon l'une quelconque des revendications 1 ou 4
à 7, caractérisée en ce que l'électrode (3) et le tube (5) font corps l'une avec l'autre.
9. Lampe à décharge à basse pression selon l'une quelconque des revendications précédentes,
caractérisée en ce que les deux électrodes (3) présentent un tube (5).