FIELD OF THE INVENTION

This invention relates to a unit of a lamp and a reflector. The unit comprises: a reflector body provided with a reflective portion having a concave reflective surface and defining an optical axis and, as an integral part of the reflector body, provided with a neck-shaped portion having an opening surrounding the optical axis, an electric discharge lamp provided with a lamp vessel having a gastight discharge space in which an electric element is arranged on the optical axis, the discharge space being closed by a first and a second seal facing each other, through which first and second seal a first and a second electric current conductor, respectively, extend from the electric element to the exterior; a ceramic lamp cap fixed to a side of the neck-shaped portion facing away from the reflective portion and having an aperture surrounding the optical axis, the lamp cap being provided with at least one electric contact to which at least one current conductor is electrically connected; the lamp vessel being fixed by means of an adhesive compound in the neck- shaped portion via its first seal and with the discharge space positioned in the reflective portion, and a ring provided around the first seal for counteracting the flow of the adhesive compound from the neck-shaped portion into the reflective portion during manufacture of the unit.

BACKGROUND OF THE INVENTION

Such a unit is known from EP-595412. Units of this type may be used for projection purposes, for example, film or slide projection, but also in projection TV devices. If the light generated by the lamp is to be efficiently used, it is necessary to have a clean, reflective surface which is as large as possible. In particular, this applies to a most relevant part of the reflective surface which is located relatively close to the electric element, namely, the reflective surface close to the neck-shaped portion. During a manufacturing fixation step, the lamp vessel is fixed in the neck-shaped portion of the reflector body by means of an adhesive compound, for example, cement. If no counteractive measures are taken during said fixation step, there is a great risk that cement flows from the neck-shaped portion onto the reflective surface located close to the neck- shaped portion, thus reducing the size of the most relevant part of the reflective surface. Furthermore, if the cement flows too far over a part of the first seal, i.e. that part of the first seal which is located in the reflective portion, there is an increased risk of explosion of the lamp. To counteract these risks in the known unit, a ring is provided which narrows the opening of the neck- shaped portion for a significant part at a transition area where the neck-shaped portion merges into the reflective portion. Said ring is held in position by an internally narrowed portion of the neck-shaped portion adjacent the transition area. The known unit has the drawback that manufacture of the reflector is rather complicated because of the narrowed portion in the neck-shaped portion. It has the further drawback that provision of an antenna to facilitate (re-)ignition of the lamp in the known unit is relatively difficult to realize as both the cavity and the antenna, which should be around the cavity, are located inside the cement.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a unit of the type described in the opening paragraph, in which at least one of the above-mentioned drawbacks is counteracted. To this end, the unit is characterized in that the aperture of the ceramic lamp cap is narrower than the opening in the neck-shaped portion so that the ceramic lamp to functions as a seat for the ring. During the manufacturing process, in particular during positioning of the lamp in the neck and its fixation by means of the adhesive compound, for example, cement, the ring may be temporarily kept in position until the adhesive compound has hardened and does not readily flow anymore. The ring narrows a passage from the lamp cap to the neck- shaped portion and thus to the reflective portion, so that the passage is blocked for a readily flowing mass like the adhesive compound. A reduction of the reflective surface, in particular of its most relevant part, and a decreased efficiency of the unit due to flow of the adhesive compound onto the reflective surface is thus counteracted. Furthermore, as the flow of the adhesive compound is counteracted, the risk of presence of the adhesive compound on the first seal is reduced, thus also reducing the risk of explosion of the lamp vessel. Moreover, manufacture of the reflector body is simplified as special manufacturing steps to obtain the internal narrowed portion in the neck of the known reflector body are no longer required. The ring is preferably made of a heat-resistant material, for example, hard glass, quartz glass, stainless steel, or, for example, heat-resistant foil (Kapton). In another embodiment, a kind of automatic positioning of the ring may be realized. To this end, the unit is characterized in that the first seal has a first and a second sealed portion between which a cavity is present, and in that the first seal has a flared portion at the location of the cavity, the ring having only limited freedom in the axial direction between the flared portion and the ceramic cap. By keeping the lamp positioned in the reflective portion, the ring is kept in position substantially automatically. In a preferred embodiment, the unit is characterized in that the ring is positioned adjacent the flared portion so that an opening in the ring through which the first seal extends is substantially closed by the flared portion. This further reduces the risk of flow of adhesive compound onto the reflective surface.

Alternatively and/or additionally to the above-mentioned automatic positioning of the ring, the unit is characterized in that a spiral is provided around the first seal, which spiral exerts resilient pressure on the ring in an axial direction towards the ceramic lamp cap due to the ring being jammed in between the ceramic lamp cap and the wall of the discharge space of the lamp vessel. The spiral may be made of any resilient, material resistant to high temperatures in the range of 300 ⁰ C to about 600 ⁰ C, for example, high temperature-resistant metals such as, for example, molybdenum, tungsten, kanthal, chromium, tantalum, etc., or hard/quartz glass fibers. The unit preferably has a construction wherein the spiral is made of electrically conducting material and simultaneously functions as an external antenna. The antenna facilitates (re-)ignition of the lamp. This construction offers the advantage that the ring and the antenna are combined to one constructive part. For optimal functioning as an antenna, the spiral should be located at least at the location of the cavity.

In another preferred embodiment, the unit is characterized in that the antenna is electrically connected to the second current conductor. A passive serial antenna having a simple structure, which is easy to provide, and operating in a very reliable manner is thus realized.

The electric element may be an incandescent body, for example, in an inert gas comprising a halogen, or a pair of electrodes in an ionizable gas. In an alternative embodiment of the unit, the current conductor is passed from the second end portion through the reflective portion to the exterior where it is connected to a contact member. The two contact members may then be at a comparatively large distance from one another, so that there is a very small risk of flash-over between these members. A preferred embodiment of the unit is characterized in that the aperture in the ceramic lamp cap has a stepped profile in which a first part of the aperture adjacent the neck- shaped portion has a diameter Di which is larger than an inner diameter D _r of the opening in the neck- shaped portion, while a second part of the aperture remote from the neck- shaped portion has a diameter D _s which is smaller than the diameter D _r of the opening in the neck- shaped portion. This has the advantage that the most relevant part of the reflective surface of the reflective portion is increased because it allows the neck- shaped portion of the reflector body to have a relatively small inner diameter. For auto-positioning of the ring in the axial direction, the ring is preferably clamped between the stepped profile of the ceramic lamp cap and the neck-shaped portion of the reflector body. Manufacture of the unit is thus simplified. In a unit comprising an electric discharge lamp, for example, a high-pressure discharge lamp, for example, a lamp having a filling of rare gas and metal halides, or a lamp having a filling of rare gas, mercury and halogen, and operating at a very high pressure, for example, approximately 200 bar or more, it is favorable when the reflector has means at its exterior for accommodating a low- voltage/high- voltage converter, for example, a recess suitable for this purpose. Conductors carrying a high voltage may then be very short. Furthermore, it is convenient when the reflector is shut off by a transparent plate, which is then provided at a light exit window opposite the neck portion and transverse to the optical axis. Flammable objects can thereby be prevented from coming into contact with hot portions of the lamp, thus also reducing the risk involved in an explosion of the lamp vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the electric lamp and reflector unit according to the invention are shown in the drawing, in which: Fig. 1 shows a prior-art unit in an axial section,

Fig. 2 shows, in an axial section, an embodiment of the unit according to the invention, and

Fig. 3 shows a detail of another embodiment of the first seal in the neck of the reflector in an axial section; Fig. 4 shows a detail of another embodiment of the unit according to the invention.

DESCRIPTION OF EMBODIMENTS In Fig. 1, the electric lamp and reflector unit has a reflector body 1 which is provided with a reflective portion 2 having a reflective surface 3 with an optical axis 4 and, integral therewith, a hollow neck-shaped portion 5 surrounding the optical axis. The unit also comprises an electric lamp 10 which is provided with a light-transmitting lamp vessel 11, which is sealed in a gastight manner and has a discharge space 12 accommodating an electric element 13. The lamp vessel has a first and a second end portion 14, 15 with a respective seal. The electric lamp 10 is fixed in the reflector body 1 by means of cement 19. Internally, the neck-shaped portion 5 has a narrowed portion 6 which merges into the reflective surface 3. A ring 58 is provided adjacent the narrowed portion 6 and around the first end portion 14 of the electric lamp 10 inside the neck-shaped portion 5 of the reflector body 1. The ring abuts the narrowed portion 6 of the neck-shaped portion 5 and surrounds the first end portion with a small clearance.

In Fig. 2, the electric lamp and reflector unit has a molded reflector body 1 which is provided with a reflective portion 2 having a concave, for example, paraboloidally curved reflective surface 3 defining an optical axis 4 and, integral with the reflective portion, a hollow neck-shaped portion 5 surrounding the optical axis. In an alternative embodiment, however, this surface may be curved, for example, ellipsoidally. The Figure shows a reflector body made of glass and having a metal layer, for example, an aluminum layer serving as a mirror. Alternatively, however, the reflector body may be made of, for example, glass- ceramic, ceramic, metal or synthetic resin. The unit also comprises an electric lamp 10 which is provided with a light-transmitting lamp vessel 11, for example, made of quartz glass, i.e. glass with an SiO2 content of at least 95% by weight, which is sealed in a gastight manner and has a discharge space 12 accommodating an electric element 13, here a pair of electrodes. The lamp vessel has a first and a second seal 14, 15 facing each other, while a respective first and second current conductor 16, 17 extends through each seal and is connected to the electric element 13 and issues from the lamp vessel 11 to the exterior. The second current conductor is electrically connected to a second metal wire 37a which extends alongside the lamp vessel and through the neck-shaped portion and is connected to a second electric contact 21a provided on a lamp cap 20. The lamp shown is a high-pressure mercury gas discharge lamp which has a pressure of approximately 200 bar or more during operation. Besides mercury, the lamp vessel contains a rare gas, for example, argon, and bromine. The electric lamp 10, which has a power consumption of approximately IOOW to approximately 450W, is fixed in the reflector body 1 by means of cement 19 as shown in the Figure, with the first seal 14 inside the neck- shaped portion 5, the discharge space 12 inside the reflecting portion 2, and the electric element 13 on the optical axis 4.

The lamp cap 20, here made of ceramic material such as, for example, steatite, with a first electric contact 21 to which a current conductor 16 is connected, is fixed by means of cement 29 to the neck-shaped portion 5 of the reflector body 1. The ceramic lamp cap has an aperture 23 around the optical axis 4, which aperture is narrower than an opening 24 in the neck- shaped portion, so that a seat 25 is formed. A ring 58 adjacent the ceramic lamp cap and around the first seal 14 of the electric lamp 10 is present in the neck- shaped portion. The ring, which is made of, for example, stainless steel, abuts the seat 25 of the ceramic lamp cap and surrounds the first seal with a small clearance of, for example, 0.5 mm all round. The ring is kept in position by a spirally shaped antenna 35 which is provided around the first seal and is electrically connected to the second current conductor. The antenna is compressed in between the ring and a wall 9 of the discharge space, so that it exerts an axially directed pressure on the ring towards the ceramic lamp cap and keeps it positioned there.

The reflector body 1 shown is shut off by a transparent plate 30. In this case, the plate is fixed with cement 39 but may be alternatively mounted by other means, for example, a flanged metal ring. The reflective portion 2 has a substantially cylindrical end portion 7 adjacent the transparent plate 30, which increases the volume of the reflective portion without substantially increasing the diameter of the unit.

Fig. 3 (not drawn to scale) shows a first seal 14 in a neck-shaped portion 5 of a reflector body 1, the seal 14 incorporating an electric conductor 16 in the form of a foil 16a, in a plan view, which connects a first electrode 34 to a metal wire 37 projecting from the first seal to the exterior, which first seal has a first gastight portion 14a and a second gastight portion 14b between which a gas-filled cavity 31 is present. The cavity comprises at least a gaseous constituent of the filling, for example, argon.

At the area of the cavity, the first seal has a flared portion 41 around which an external antenna 35 is provided, the antenna being squeezed in between a wall 9 of the discharge space 12 and a ring 58. The first seal 14 constitutes a collapsed seal, but may be alternatively a pinched seal. The foil 16a is a Mo-strip having knife edges. The metal wire 37 is secured by means of, for example, welding to one end 16b of the strip 16a via a wire part 16d of the current conductor 16 and projects to the exterior from the seal and from the discharge vessel. The electrode rod 34 is secured to a further end 16c of strip 16a via this strip 16a. A discharge extends between the electrodes in the operating condition of the lamp. In the embodiment described, a very reliable passive antenna is thus realized in an extremely simple manner.

A ring 58 is provided around the first seal and rests on a ceramic lamp cap 20 which is fixed at a rear side 36 of the neck-shaped portion 5 of the reflector body 1. The ring 58 substantially shuts off an opening 38 in the neck- shaped portion and counteracts the flow of cement 19 into the neck-shaped portion and thus onto the reflective surface 3. The antenna 35 simultaneously functions as a metal spring which exerts an axial pressure on the ring 58 towards the ceramic lamp cap 20, where it is thus fixed and kept in position. Furthermore, the ring 58 surrounds the first seal of the lamp vessel adjacent the flared portion 41 of the first seal 14, so that a clearance 42 between the opening in the ring and the first seal of the lamp vessel is substantially shut off and flow of cement 19 through said opening in the ring is prevented. The ceramic lamp cap has only one electric contact (not shown), as the second metal wire (reference numeral 37a in Fig.2) does not extend through the neck-shaped portion but is led elsewhere to the exterior via the reflective portion 2 (not shown). Fig. 4 shows a detail similar to that shown in Fig. 3 (not drawn to scale), in which all technical features are the same as those shown in Fig. 3, except for the construction of the ceramic lamp cap 20. The ceramic lamp cap 20 is provided with a stepped profile 61, indicated by the circle. As a result, the ceramic lamp cap has a first part 62 of the aperture 23 adjacent the neck- shaped portion 5 of the reflector body 1, and a second part 63 of the aperture distant from said neck-shaped portion. The first part 62 has an inner diameter Di which is larger than an inner diameter D _r of the neck-shaped portion of the reflector body. The second part 63 has an inner diameter D _s which is smaller than the inner diameter D _r of the neck- shaped portion of the reflector body. The ring 58 fits with ample spacing within the first part 62 so as to allow adjustment transversal to the optical axis 4, which is necessary for alignment of the lamp vessel 11 in the reflective portion 2 of the reflector body, but the ring is too large to fit in the second part 63. The ring 58 is pressed against the stepped profile 61 by the antenna 35.

It should be noted that the protective scope of the invention is not limited to the embodiments described. Any reference sign placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements other than those stated in the claims. Use of the indefinite article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.