Electric incandescent lamps in which an incandescent filament is used as the light-generating element are lcnown. In halogen lamps, the incandescent filament is arranged in a sealed vessel having transparent walls. The ends of the incandescent filament are connected to electrical conductors that, to allow an electrical connection to be made, emerge from the vessel via a seal. The interior of the vessel is usually filled with an inert gas and halogen constituents.

The burner, i. e. the unit comprising the sealed vessel, the incandescent filament contained therein, and the electrical conductors emerging from the vessel, reaches high temperatures in operation. This causes problems due to the oxidation of the electrical conductors emerging from the vessel. There are different Icnown solutions to this problem.

The problem is addressed on the one hand in US A 6,239, 550. What is described there is a halogen incandescent lamp in which a coating that acts as a reflector of light in the infrared range is applied to the burner vessel. To counteract the oxidation of the electrical conductors emerging from the vessel, the infrared-reflecting coating is omitted in those regions of the vessel through which the electrical conductors extend. In this way, the temperature is brought down at these points.

Shown in US A 6,049, 169 is a lamp having a burner that is arranged in an outer vessel. The burner comprises a sealed inner vessel with transparent walls in which an incandescent filament is arranged. Emerging from the inner vessel with a seal at opposite ends of the vessel are electrical conductors to which the ends of the incandescent filament are connected. The interior of the outer vessel is filled with an inert gas.

It is an object of the invention to propose a lamp in which oxidation of the electrical conductors issuing out from the inner vessel is avoided in a particularly simple manner.

This object is achieved by a lamp as detailed in claim 1. Dependent claims relate to advantageous embodiments of the invention.

In accordance with the invention, the interior of the outer vessel is evacuated.

By this simple step, oxidation of the electrical conductors is very effectively prevented. The pressure within the outer vessel is preferably between 5 mbar and 500 mbar.

In a further embodiment of the invention, the protection against oxidation is further improved by introducing into the interior of the outer vessel a material that traps any oxygen that may still be present after manufacture. Materials of this kind are known per se and are referred to as getters. They contain a given amount of a substance that is activated after the outer vessel has been evacuated and sealed, by targeted exposure to heat for example, and then absorb and bind any oxygen left in the region of the outer vessel. In this way, any residual oxygen left in the outer vessel is further reduced. An example of a substance that may be used as a getter is ZrCo.

Burners of the double-ended type are preferred, that is to say ones where the electrical conductors emerge from the inner vessel at opposite ends thereof. The inner vessel is preferably approximately elliptical in shape in longitudinal section, with electrical conductors emerging from the vessel at opposite ends in the sealing regions. The electrical conductors are preferably composed of molybdenum.

In a yet further embodiment of the invention, a coating that is more reflective of light in the infrared range than of light in the visible range is applied. The use of such coatings is known per se to those skilled in the art. The wall of the inner vessel is preferably so shaped that the infrared radiation reflected from the coating is reflected back onto the filament. This increases the temperature of the filament and prevents losses of energy, which saves a considerable amount of energy.

To form the infrared-reflective coating, use is preferably made of successive layers of Si02 on the one hand and either mixtures of Nb205 and Taxons, or pure Ta205 or ZrO2, on the other. Layers of this kind are described in detail in US A 6, 049, 169. It has been found that infrared-reflective layers of this type-unlike other known layers of this kind- perform their function even in an evacuated outer vessel, i. e. when no oxygen is present.

The outer vessel has a transparent wall, preferably of quartz glass. A substantially cylindrical shape is preferred for the outer vessel. Electrical conductors to allow electrical contact to be made with the burner extend through the interior of the outer vessel.

These preferably emerge from the bulb-shaped outer vessel at one end thereof, mutually parallel and at a distance from one another.

In another embodiment of the invention, part of the outer vessel is provided with a layer that is impermeable to light. Where the outer vessel is of a bulb-like shape, the layer impermeable to light is preferably arranged in the region of the tip of the bulb that is formed. The layer impermeable to light may act as antiglare protection. As an alternative to or in addition to an antiglare cap of this kind, antiglare strips or regions of other shapes may also be formed.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings: Fig. 1 is a longitudinal section through one embodiment of a lamp according to the present invention.

Shown in Fig. 1 in longitudinal section is a lamp 10. Held in a substantially cylindrical outer vessel 12 is a halogen burner 14. The halogen burner 14 comprises a vessel 16 of quartz glass in whose interior is arranged an incandescent filament 18. The interior of the vessel 16 is filled with an inert gas (for example Kr, Xe, Ar) or a mixture of inert gases (for example 50% Xe, 50% Kr) and additional halogen constituents. Formed at opposite ends of the vessel 16 are sealing regions 20. In the region of the sealing regions 20, the incandescent filament 18 is connected to electrical conductors, flat strips 22 of molybdenum in the present case, that run out from the interior of the vessel 16. The wall of the vessel 16, which is composed of quartz glass, is compressed at the sealing regions 20, thus enclosing the molybdenum strip 22 with a seal. The vessel 16 is circular in cross-section. The sealed areas 20 are of a flat form and are also referred to as"pinches".

In its central region, the vessel 16 is approximately elliptical in shape in longitudinal section. In this region, a layer 24, which is shown here as relatively thick for the sake of clarity, is applied to the outside of the vessel 16. The layer 24 is a layer known per se that is largely transparent to light in the visible range but reflects light in the infrared range.

The layer 24 itself comprises a series of successive layers (not shown). The layer 24 is formed from, in each case, a layer of Si02 alternating with a layer of Ta205. Alternatively, the coating may comprise alternating layers of Si02 and ZrO2. Such layers are described in detail in US A 6,049, 169, to which explicit reference is made here.

Extending through the interior of the outer vessel 12 are wires 26 that hold the burner 14 in position mechanically in the interior of the outer vessel 12 and make electrical contact on the sealing regions 20. At the end of the outer vessel 12 that is at the bottom in the Figure is formed an outer sealing region 28 at which the wires 26 connect up with further strips of molybdenum, following on from which are wires 38 that emerge from the region of the outer vessel 12 with a seal. The ends of the wires 38 project downwards from the outer vessel 12 to form plug-in contacts.

At the other end of the outer vessel 12, there is a light-impermeable layer 30 applied in the region of the tip of the outer vessel 12. The layer 30 is produced by dipping after manufacture of the lamp 10 has been completed. The light-impermeable layer 30 forms an anti-dazzle cap in the region of the tip of the vessel 12. Alternatively or in addition, light- impermeable layers may also be applied to the outer vessel 12 at another point, for example in order to deliberately mask off given radiant areas or to avoid dazzle effects.

The interior of the outer vessel 12 is evacuated. The pressure in the interior of the outer vessel 12 is approximately 100 mbar. Also situated in the interior of the outer vessel 12, fastened to the wires 26 in this case, is a getter 32. The getter 32 is a metal vane 34 that contains a material 36 that is capable of absorbing and binding oxygen. In the example shown, the material 36 is composed of ZrCo.

When the lamp 10 is being manufactured, after the outer vessel 12 has been closed off (the outer vessel 12 is evacuated and then sealed in the region of its tip), the getter material 32 is activated by targeted heating. In the course of this, the ZrCo material 36 becomes active and binds some of the oxygen that is still present in the interior of the vessel 12. The possible materials for the material 36 and the procedure for activating it are lcnown per se to the man skilled in the art and therefore do not require any further elucidation here.

The outer vessel of the lamp 10 is approx. 5 cm long and has a diameter of approx. 1.4 cm. In this way, the burner 14, which has a diameter of approx. 1 cm in the central region, can be arranged at a distance from the walls of the outer vessel 12. The lamp 10 is used by plugging it into an appropriate socket, usually one having a reflector. The projecting contacts 38 are used as male pins when this is done.

The lamp 10 is operated at voltages of 10-24 volts and consumes powers of 20-100 W. Of the light emitted by the incandescent filament 18, the infrared part is reflected back onto the filament 18 by the layer 24. The visible part emerges through the wall of the outer vessel 12 (except for the light-impermeable cap 30) and is used for lighting purposes.

Despite the high temperatures in operation of more than 500°C, there is, in the sealing regions 20, no oxidation of the strips 22 of molybdenum due to the absence of oxygen in the interior of the outer vessel 12.