[0001] The invention relates to a copless electric lamp provided with a lamp vessel of quartz
glass which is sealed in a vacuum-tight manner and in which an electric element is
arranged, metal foils being incorporated in the wall of the lamp vessel, to each of
which foils are welded a respective internal current conductor connected to the electric
element and a respective external current conductor which serves to make direct electrical
contact with a lamp holder. Such a lamp is known, from US-PS 4,015,165 (PHX.7884).
[0002] Such external current conductors conventionally consist of molybdenum. This metal
has the disadvantage that it is susceptible to corrosion, as a result of which the
lamp is in poor electrical contact with the connection terminals of the lamp holder.
This results in electrical losses and may even lead to the lamp being not capable
of operating. In order to avoid this, in the lamp according to the aforementioned
United States Patent Specification, the external current conductors consist of molybdenum
wires which are incorporated in tubes of, for example, nickel. Thus, a good electrical
contact with a lamp holder is ensured. A disadvantage of the known construction, however,
is that the cost of the lamp is considerably higher due to the fact that additional
component parts are used.
[0003] The invention has for its object to provide an electric lamp having external current
conductors which are sufficiently resistant to corrosion and which nevertheless have
a non-composite structure.
[0004] In accordance with the invention, this object is achieved in the lamp described in
the opening paragraph in that the external current conductors consist of niobium or
tantalum.
[0005] The electric element in the lamp according to the invention may be a pair of electrodes
in an ionizable gas or may be a filament, for example in a halogen-containing gas.
[0006] The lamp vessel of quartz glass, the term "quartz glass" being understood to mean
glass having an Si0
2 content of at least 95% by weight, has a very small thermal coefficient of expansion.
Therefore, the current conductors generally consist of molybdenum or tungsten where
they are embedded in the wall of the lamp vessel in a vacuum-tight manner and are
in the form of a foil. As compared with other metals, the said metals have a low coefficient
of expansion. It is necessary to use foil-shaped conductors in order to ensure that
the conductors are embedded in a vacuum-tight manner. Niobium and tantalum in the
form of a foil do not ensure a vacuum-tight embedding in quartz glass. In the lamp
according to the invention, the external current conductors of niobium or tantalum
are therefore welded to the foils. The foils can be incorporated each in a respective
seal of the lamp vessel or together in one seal of the lamp vessel.
[0007] It has been found that the external conductors of the lamp according to the invention
had a high resistance to corrosion. The lamp with niobium external conductors is to
be preferred if a high power lamp is concerned because niobium is a better heat conductor
than tantalum. The external current conductors may contain the impurities usual for
niobium and tantalum, respectively.
[0008] An embodiment of the lamp according to the invention is shown in the drawing in side
elevation.
[0009] Molybdenum foils 3 are embedded in the wall 2 of the quartz glass lamp vessel 1 in
a vacuum-tight manner. Inside the lamp vessel a filament 4 is arranged as the electric
element with internal current conductors 5 connected to the foil 3. Each of the foils
3 has welded to it an external current conductor 6 of tantalum or niobium. The lamp
vessel is filled with a mixture of inert gas and hydrobromide and consumes at 12 V
a power of 100 W.
A copless electric lamp provided with a quartz glass lamp vessel which is sealed in
a vacuum-tight manner and in which an electric element is arranged, metal foils being
incorporated in the wall of the lamp vessel, to each of which foils are welded a respective
internal current conductor connected to the electric element and a respective external
current conductor which serves to make direct electrical contact with a lamp holder,
characterized in that the external current conductors consist of niobium or tantalum.
