The invention relates to an illumination unit comprising a discharge lamp and a housing with a first and a second housing part which support the discharge lamp and a lamp cap, respectively, a supply unit for the discharge lamp being accommodated in said second housing part and electrically connected to contacts at the lamp cap, which housing parts are fastened to one another by means of cooperating coupling members comprising a first and a second coupling member.

Such an illumination unit is commercially available. The illumination unit is designed for use in locations where originally incandescent lamps were used. In the ensuing description, the word "lamp" is used for indicating a discharge lamp. In the known illumination unit, the lamp has a discharge vessel provided with a filling of mercury and a rare gas. The discharge vessel comprises four parallel tubes which are closed at the ends and which are in mutual communication through fused bridges. The first housing part comprises a cap-shaped element in which the lamp is fixed with cement and which has a circumferential rim which is accommodated in the second housing part. The circumferential rim is provided with first coupling members in the form of studs pointing radially outwards which enter further coupling members formed by recesses in the rim of the second housing part.

At the end of lamp life, it is desirable to separate the discharge vessel as well as possible from other components of the illumination unit, such as the supply unit, in order to limit the quantity of waste containing mercury. This is comparatively difficult in the known illumination unit. An assembly of a lamp and an adaptor is known per se in which the adaptor can be accommodated in a holder for incandescent lamps and in which the lamp is provided with a plug with contact pins cooperating with a contact socket of the adaptor. Mutually cooperating retention means are also present for coupling the lamp detachably to the adaptor. Such an assembly, however, has the disadvantage that it is comparatively voluminous in comparison with the illumination unit mentioned earlier because much space is required for the contact pins and the retention means. As a result, the assembly is not suitable for replacing an incandescent lamp in many cases.

It is an object of the invention to provide an illumination unit of the kind described in the opening paragraph whose discharge lamp can be separated comparatively easily from other components of the illumination unit at the end of lamp life, while the illumination unit can nevertheless be comparatively compact.

According to the invention, the illumination unit is for this purpose characterized in that at least the second coupling member is integral with a breakable connection for eliminating the cooperation between the first coupling member and the second coupling member. A breakable connection is understood to mean in the present description and claims a connection which remains intact during normal use of the illumination unit but which may be easily broken if so desired. In the lamp according to the invention, the first housing part can be separated from the second housing part comparatively easily in that the breakable connection of the second coupling member is broken. The first housing part with the lamp is irreversibly detached from the second housing part with the supply unit thereby. The first housing part with the lamp and the second housing part with the supply may then be separately processed. Since the separation of the housing parts of the illumination unit cannot be followed by a renewed fastening thereof, the electrical and mechanical connections can be comparatively simple and occupy little space. The illumination unit may be comparatively compact as a result. A practical embodiment is characterized in that the second coupling member forms part of a band-shaped element which extends around the first and the second housing part and which has a first circumferential edge which faces the discharge lamp. The connection between the first and the second housing part is lost when the band-shaped element is broken. Since the band-shaped element extends around the housing parts, it is readily accessible. It is sufficient to cut through the band-shaped part. The housing parts may then be separated from one another.

An attractive modification of this embodiment is characterized in that the band-shaped element is provided with a tag and has a weakened zone at at least one side of said tag. This has the advantage that tools are unnecessary for detaching the housing parts. The weakened zone is, for example, a comparatively thin and/or perforated region. Another practical embodiment is characterized in that the first and the second coupling member each form part of a respective housing part, the second coupling member being connected to the associated housing part by means of a weakened zone, and in that the first housing part after removal of the second coupling member is movable relative to the second housing part in a direction transverse to the direction from the first to the second

3 housing part. The first and the second housing part can be separated in that the second coupling member is detached from the associated housing part along the weakened zone, after which the first housing part can be shifted from the second housing part.

In an embodiment, the lamp is coupled to the supply unit, for example inductively, for example by means of concentric coils. An attractive embodiment of the illumination unit according to the invention is characterized in that current supply conductors from the supply unit to the lamp each have a weakened zone which is recessed in the second housing part. It is realised in a simple manner thereby that the current supply conductors break off in a location inaccessible to the consumer when the housing parts are separated from one another.

These and other aspects of the illumination unit according to the invention will be explained in more detail with reference to the drawings, in which Figs. 1A and IB show an embodiment in elevation and in longitudinal section, respectively,

Figs. 2A and 2B show the housing parts of the illumination unit of Figs. 1A and IB after they have been separated, in elevation and in longitudinal section, respectively, Figs. 3A, 4A and 5A are elevations of a further embodiment, the housing parts of this embodiment after the second coupling member has been detached and the first housing part has been partly shifted relative to the second housing part, and the housing parts of this embodiment after they have been separated from one another, respectively, and

Figs. 3B, 4B, 5B show an elevation taken on the line III in Fig. 3A, on the line IV in Fig. 4A, and on the line V in Fig. 5A, respectively.

Figs. 1A and IB show an illumination unit which comprises a discharge lamp 10 and a housing 20 with a first and a second housing part 30, 40. The first housing part 30 constructed as a cap-shaped element supports the discharge lamp 10. The discharge lamp 10 is fastened to the first housing part 30 with cement 31. Alternatively, the discharge lamp may be accommodated in the first housing part 30, for example, by clamping means. The second housing part 40 supports a lamp cap 41. A supply unit 42 for the lamp 10 is accommodated in the second housing part 40 and is connected to electrical contacts 43a, 43b

of the lamp cap 41. The first and the second housing part 30, 40 are fastened to one another by means of cooperating coupling members 32, 51, 52, 44, comprising a first coupling member 32 and a second coupling member 51.

At least the second coupling member 51 is integral with a breakable connection 50 for eliminating the cooperation between the first coupling member 32 and the second coupling member 51.

In this case, the first and the second housing part 30, 40 are fastened to one another by a band-shaped element 50 which extends around the first housing part 30 and the second housing part 40 and which has a circumferential edge 53 which faces the discharge lamp 10. The second coupling member 51 is formed by studs on the band-shaped element 50 which point radially inwards and which grip into- a first coupling member 32 formed by recesses in the cap-shaped element 30. Opposite said studs, there are further studs which form a further second coupling member 52 and which grip into recesses in the second housing part 40, the latter recesses forming a further first coupling member 44. In the embodiment shown, the housing 20 and the band-shaped element 50 are made of polybutylene terephthalate. Alternative suitable materials are, for example, polycarbonate, polythene, polypropylene, and polyamide.

The band-shaped element 50 in the embodiment shown is provided with a tag 54. The band-shaped element 50 has a weakened zone 34 at at least one side of this tag. Here the band-shaped element has weakened zones 55 on either side of the tag 54. The weakened zones 55 are constructed, for example, as perforated strips or locally thinned portions of the band-shaped element 50. When the band-shaped element 50 is torn loose along the weakened zones 55 by means of the tag 54, the first housing part 30 and the second housing part 40 are no longer fastened to one another. The first housing part 30 may then be pulled away from the second housing part 40 as shown in Figs. 2 A and 2B.

The discharge lamp is connected to the supply unit 42 via current supply conductors 11a to lid. The current supply conductors 11a to l id each have a weakened zone 12a to 12d which is recessed in the second housing part 40.

In the embodiment shown in Figs. 3A to 5B, components corresponding to those in Figs. 1A to 2B have reference numerals which are 100 higher. In the embodiment shown in Figs. 3A and 3B, the first housing part 130 is fastened to the second 140 by means of two ridges 145 on an internal surface 146 of the second housing part 140 which each enter a groove 133 of the first housing part 130 (see Fig. 4A). The ridges 145 run in a direction transverse to the direction from the first to the second housing part 130, 140. In the

embodiment shown, the ridges 145 run mutually parallel. Alternatively, the ridges may run in a direction away from the second coupling member towards one another, for example in an arc shape. Furthermore, the parts 130, 140 are fastened to one another by means of wall portions 147, 148 of the second housing part 140 which lie opposite the ends of the ridges 145 and which block a displacement of the first housing part 130 along the ridges 145. One

^■ of the wall portions 148 forms part of the second housing part 140 via a weakened zone 149 and forms a second coupling member 148. The second coupling member 148 is provided with a tag 148a to facilitate breaking-off of the coupling member 148. The first coupling member 134 is formed by a surface of the first housing part 130 which abuts against the second coupling member 148.

In Fig. 4A, the second coupling member 148 has been broken off from the second housing part 140 along the weakened zone 149. Fig. 4B shows how subsequently the first housing part 130 has been partly moved from the second housing part 140. In Figs. 5A and 5B, the first and the second housing part 130, 140 have been separated.