ELECTRIC LAMP

Abstract: The electric lamp has a lamp vessel (1) provided with a pinched seal (2), in which a metal foil (4) is accommodated, which is connected to an external current conductor (7, 7′) and to an internal current conductor (11). The metal foil (4) has a welding connec­ tion (10) with the internal current conductor (11) on its first major surface (8). A metal auxiliary foil (12) is welded against the second major surface (9) of the metal foil (4) and is welded against the internal current conductor (11) (weld 17). The lamp has a simple construction and has never­ theless during operation a comparatively low temperature of the pinched seal (2).

Description: The invention relates to an electric lamp comprising: a lamp vessel sealed in a vacuum-tight manner and made of glass having an SiO₂ content of at least 95% by weight, said lamp vessel having a pinched seal at an end thereof; a light source within the lamp vessel; at least one metal foil having a first and a second end included as a current lead-through conductor in the said pinched seal, said metal foil being connected near its first end to at least one external current conductor, which is passed to the exterior from the said pinched seal, and said metal foil having a first and a second major surface and having near its second end on a first major surface a welding connection with an internal current conductor extending to the light source; a metal auxiliary foil near the second end of the said metal foil, which forms an additional connection between the metal foil and said internal current conductor. Such an electric lamp is known as an incandescent lamp from JP UM Application No. 51-137898. In the known lamp, the internal current conductor is enclosed, as far as it overlaps the metal foil, between said metal foil and the metal auxiliary foil. This construction has a number of great disadvantages. The end of the internal current conductor welded to the metal foil should be bevelled in order that the metal auxiliary foil can follow exactly the surface of the internal current conductor. Without this measure, there is a risk that, when the pinched seal is formed, the metal auxiliary foil is subjected to tensile stress and breaks. Another disadvantage is that cavities are formed between the two foils on either side of the internal current conductor. The foils are consequently subjected to a considerable extent to the atmosphere prevailing in the lamp. A further disadvantage is that the assembly of the current conduction to the light source can be manufactured only with great difficulty. Certain electric lamps are very heavily loaded during operation. A high current of, for example, several tens of amperes flows through these lamps, which leads to high current densities in the pinched seal especially at the transition from the metal foil to the internal current conductor. This results in a strong development of heat in the pinched seal. The maximum permissible temperature of the pinched seal can thus be readily exceeded. Exceeding of this temperature causes the metal foil and the external current conductor to oxidize so rapidly that the pinched seal bursts and that the lamp becomes leaky before the calculated life of the lamp is attained. Therefore, it is of major importance that a lamp is available having a construction which keeps the temperature of the pinched seal sufficiently low during operation, i.e . so low that the oxidation in the pinched seal does not determine the lifetime. A contribution to a temperature reduction is obtained by a suitable construction of the transition from the metal foil to the external current conductor. It is known, for example, to weld several external current conductors to the first end of the metal foil and to interconnect these current conductors outside the lamp. The temperature reduction thus obtained is insufficient, however, with heavily loaded lamps. A similar construction of the transition from the metal foil to the internal current conductors generally cannot be realized in practice. The invention has for its object to provide a lamp of the kind described in the opening paragraph having a construction which can be readily manufactured and prevents the temperature of the pinched seal from rising excessively during operation. According to the invention, this object is achieved in a lamp of the kind described in the opening paragraph in that the metal auxiliary foil is welded against the second major surface of the metal foil and against the said internal current conductor. In view of the high currents through the lamp, the internal current conductor has a large diameter, for example of 1 mm or larger, while the metal foil, in order that a vacuum-tight seal of the lamp vessel can be attained, has a thickness of only a few tens of microns, for example 40 µm. In spite of this large and small thickness respectively, the current conduction means of the lamp according to the invention can be readily assembled. As also appears from the drawing, not the internal current conductor is located between the metal foil and the metal auxiliary foil, but the metal foil is located between the metal auxiliary foil and the internal current conductor. The welding connections between these components can be readily formed, for example in a welding jig. Deformation of the metal foils substantially does not occur. Furthermore, the metal foil and the metal auxiliary foil are firmly pressed against each other when the pinched seal is formed, while they then come into a more intimate physical and electrical contact with one another. It is further important that the glass of the pinched seal is in intimate contact with the metal foil and with the metal auxiliary foil. The heat transfer to the glass of the pinched seal and thence to its environment is thus improved. Due to this simple construction, the electric current is introduced more gradually and with a larger spread from the internal current conductor into the metal foil, and conversely. This results in a smaller development of heat. The lamp according to the invention may have two pinched seals, each of which accommodates its own metal oil and an internal and an external current conductor secured thereto, or this lamp may be such that one pinched seal accommodates these two metal foils. In order to further reduce the temperature, the external current conductors may each consist of several wires alternatively, a respective metal auxiliary foil may be used with the external current conductors. The electric lamp may be a gas discharge lamp, in which event the light source is a pair of electrodes in an ionizable medium, or this lamp may be an incandescent lamp, for example a halogen incandescent lamp, in which event the light source is a filament. It is common practice that metal foils have between their first and second ends side edges which are etched (feathered edges), in order to ensure that the glass of the pinched seal satisfactorily adjoins the metal foil and hence vacuum-tightness is obtained. It has proved to be favourable, in order to avoid stresses in the pinched seal, that the metal auxiliary foil is also provided with etched side edges. An embodiment of the lamp according to the invention is shown in the drawing. In the drawing: Fig. 1 is a front elevation of an incandescent lamp with a lamp cap partly broken away, Fig. 2 shows a detail of the lamp shown in Fig. 1 in side elevation on a strongly enlarged scale. In Fig. 1, the electric incandescent lamp has a lamp vessel 1 sealed in a vacuum-tight manner and made of glass having an SiO₂ content of at least 95% by weight, for example quartz glass, which has at one end a pinched seal 2. A filament 3 is arranged as a light source within the lamp vessel 1. At least one metal foil 4 of, for example, molybdenum is accommodated in the pinched seal 2 and has a first and a second end 5 and 6, respectively, serving as an current lead-through conductor. The metal foil 4 is connected near a first end 5 thereof ― in the embodiment shown by welding ― to an external current conductor 7, which is passed to the exterior from said pinched seal 2. In the embodiment shown, there are several external current conductors 7, 7′. The metal foil 4 has a first major surface 8 and a second major surface 9 (Fig. 2). Near its second end 6, the metal foil 4 has on the first major surface 8 a welding connection 10 with an internal current conductor 11 extending to the light source 3. A metal auxiliary foil 12 of, for example, molybenum near the second end 6 of the metal foil 4 forms an additional connection between the metal foil 4 and the internal current conductor 11. The metal auxiliary foil 12 is welded against the second major surface 9 (Fig. 2) of the metal foil (welds 10) and is welded against the internal current conductor 11 (weld 17). In the drawing, the pinched seal 2 has a second metal foil 4′, which is connected to a second internal current conductor 11′ with the use of a metal auxiliary foil 12′. The external current conductors 7, 7′ are all connected to a contact 13 of a lamp cap 14. The lamp cap 14 is filled partly with sand 15 and partly with cement 16, which ensures that the lamp vessel 1 is fixed in the lamp cap 14. In a lamp according to the invention, the internal current conductors 11 of tungsten had a diameter of 1,5 mm, while the metal foil 4 and the metal auxiliary foil 12 had a thickness of 45 µm. The lamp used as film studio lamp consumed during operation at 120 V a power of 5 kW so that the current through the lamp was about 42 A. The lamp reached the calculated lifetime without the pinched seal being damaged. In Fig. 2, the detail of the lamp of Fig. 1 shows that the metal foil 4 is in intimate contact with the metal auxiliary foil 12 and with the internal current conductor 11. The side edges shown of the two foils 4, 12 and the side edges extending parallel thereto are etched in order to make said foils thinner along said side edges and to cause their major surfaces (8, 9 with the foil 4) to enclose at these side edges an acute angle with each other. Due to the construction shown, the current is introduced more satisfactorily from the internal current conductor 11 gradually into the foil 4, and conversely. The current conduction 11, 4, 12 is thicker at the area of the welds 10 than without a metal auxiliary foil 12. Nevertheless, the glass of the pinched seal 2 adjoins very satisfactorily especially the foils 4, 12. Due to the construction of the lamp, development of heat in the pinched seal 2 is counteracted and developed heat is transferred excellently to the glass of the pinched seal 2 and is thence dissipated to the ambient atmosphere. The lamp can be readily manufactured.

Claims: 1. An electric lamp comprising: a lamp vessel (1) sealed in a vacuum-tight manner and made of glass having an SiO₂ content of at least 95% by weight, said lamp having a pinched seal at an end (2) thereof; a light source (3) within the lamp vessel; at least one metal foil (4, 4′) having a first and a second end (5, 6) included as a current lead-through conductor in the said pinched seal; said metal foil being connected near the first end (5) thereof to at least one external current conductor (7, 7′), which is passed to the exterior from the said pinched seal, and said metal foil having a first and a second major surface (8, 9) and having near its second end (6) on a first major surface (8) a welding connection with an internal current conductor (11, 11′), which extends to the light source; a metal auxiliary foil (12, 12′) near the second end (6) of the said metal foil (4, 4′), which forms an additional connection between the metal foil and the said internal current conductor (11, 11′), characterized in that the metal auxiliary foil (12, 12′) is welded against the second major surface (9) of the metal foil (4, 4′) and against the said internal current conductor (11, 11′). 2. An electric lamp as claimed in Claim 1, characterized in that the metal foil (4, 4′) is connected near its first end (5) to several external current conductors (7, 7′).

Inventors: OOMS, LEO FRANS MARIA
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1988
Main classification: H01K1
IPC codes: H01J5, H01K1