CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2019/081294, filed on Nov. 14, 2019, which claims the benefit of Chinese International Patent Application No. PCT/CN2018/115727, filed on Nov. 15, 2018 and European Patent Application No. 19159012.4, filed on Feb. 25, 2019. These applications are hereby incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to lamps, and in particular to lamps having an electrical connector which fits to a socket by a coupling which involves rotation of the lamp relative to the socket.

BACKGROUND OF THE INVENTION

When fitting a lamp which has a screw connector to a socket, the action of screwing the connector to the socket will result in a torque between the different parts of the lamp. The torque will depend on the resistance offered by the socket, and will increase as the screw connection becomes tighter. When the screw connection has reached the end of its adjustment range (so that the socket resists all further relative rotation), all torque applied to the lamp will be exerted across components of the lamp.

The lamp screw connector and the lamp body are typically separate components. The screw connector is a metal body whereas the lamp body typically comprises a glass or plastic housing. It can happen that the torque applied by the user may cause a rupture between the screw connector and the lamp body, or result in breaking of the lamp body if it is fragile.

By way of example, the lamp body may be able to sustain a torque of up to 3 Nm. If a larger torque is applied across the lamp, such as 5 Nm, the lamp body may break.

It has been recognized that it would be desirable to prevent damage to a lamp when a large torque is applied. It is known to design the lamp to withstand a larger torque. However, this increases the cost of the lamp.

There remains a need for a lamp which provides protection against breakage in the event of a large torque being applied, but which does not increase significantly the cost of the design.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention, there is provided a lamp, comprising:

a lamp body which houses a light source;

an electrical connector for connecting the lamp to a socket by a rotational coupling; and

a clutch between the lamp body and the electrical connector for providing rotational coupling or else allowing rotational slippage between the lamp body and the electrical connector, in dependence on a torque applied between the lamp body and the electrical connector.

The clutch releases rotational engagement between the lamp body and the electrical connector in particular when the torque is too high. In this way, damage to the lamp body, or disconnection between the lamp body and the electrical connector, is avoided even if a large torque is applied. This may happen if a user inadvertently over tightens the connection between the lamp and the socket.

The clutch preferably allows rotational slippage only for a torque in one rotational direction.

Thus, the clutch provides protection to prevent over tightening, but still allows the lamp to be disconnected from the socket.

The one rotational direction is for example a clockwise direction of torque applied to the lamp body relative to the electrical connector. This is typically the rotational direction used to fit the lamp to the socket.

The clutch may comprise a first component which forms part of the electrical connector and a second component which forms part of the lamp body. The two components interface with each other to provide a controlled connection between the lamp body and the electrical connector.

The first component for example comprises a first, outer, annular tooth ring and the second component comprises a second, inner, annular tooth ring, wherein the second annular tooth ring is compressible to release engagement between teeth of the first and second annular tooth rings.

The compression takes place when the torque applied reaches a threshold. In particular, the torque is sufficient to overcome the frictional engagement between the teeth, so that the teeth slide relative to each other. This sliding is accompanied by compression of the inner annular tooth ring. For example, if the electrical connection is already tight, the electrical connector of the lamp will resist further rotation, thereby increasing the torque across the clutch. This torque makes the teeth ride over each other in the manner of a ratchet, with the riding accompanied by successive compressions of the inner annular tooth ring.

This provides a low cost ratchet type system. The teeth are preferably shaped so that they can only ride over each other in one direction of relative angular rotation.

The first annular tooth ring may have a continuous ring of teeth and the second annular tooth ring may have toothed regions and non-toothed regions.

The toothed and non-toothed regions are designed to provide a desired amount of total frictional engagement between the teeth, which in turn influences the torque level at which the ratchet function comes into play. Thus, the design of the second annular tooth ring may influence the threshold torque and thereby set the threshold to a level suitable for the particular lamp. The first annular tooth ring, which may form part of the electrical connector, may have a single design so that different lamp bodies can be designed to fit to a standard electrical connector design.

The second annular tooth ring for example comprises a cylinder having the teeth on an outer cylindrical surface and a set of slots extending parallel to the cylinder axis thereby to allow the compression. The slots enable the compression of the second tooth ring in a simple manner.

The second annular tooth ring may comprise a set of hooks for retaining the first annular tooth ring over the second annular tooth ring at a desired axial position. The first annular tooth ring is for example slid over the hooks of the second annular tooth ring, accompanied by compression of the second tooth ring, as part of the assembly. This provides a simple assembly procedure.

The electrical connector may comprise a male screw fitting.

This type of fitting involves a large period of rotational driving, and the user may not be aware when they are applying a torque that could cause damage. The invention may however be applied to other electrical connections which make use of a rotational adjustment, such as bayonet electrical couplings.

For a screw fitting, the electrical connector for example comprises a central conductive pin extending parallel to a connection direction of the electrical connector and forming a first electrical contact, and the lamp body comprises a first brush for making electrical contact with the pin in all rotational positions.

Thus, the angular position of the clutch does not alter the required electrical connection to the central contact of the male screw fitting.

The electrical connector may then comprise a conductive outer wall around the central pin and forming a second electrical contact, and the lamp body comprises a second brush for making electrical contact with an inner surface of the conductive outer wall in all rotational positions.

Thus, the angular position of the clutch does not alter the required electrical connection to the outer thread contact of the male screw fitting.

The lamp body for example houses a lighting driver and the first and second brushes comprise first and second power inputs to the lighting driver. The lighting driver may comprise a circuit board having a tab which projects into the electrical connector and which carries the first and second brushes.

This provides a compact arrangement in which the required electrical connections to allow for the clutch rotation are housed within the volume of the electrical connector.

The light source may comprise a LED or LED array.

The clutch is for example adapted to allow rotational slippage between the lamp body and the electrical connector when the torque applied between the lamp body and the electrical connector exceeds a threshold, wherein the threshold is in the range 2 Nm to 5 Nm.

By preventing torque to reach 5 Nm (or any other desired maximum in the range 2 Nm to 5 Nm) damage to the lamp body, or the connection between the lamp body and the electrical connector, is avoided.

The lamp body may have an outer diameter at least 4 times the outer diameter of the electrical connector. This type of lamp, with a large head, is particularly susceptible to damage because of the large torques that may result during fitting to a socket.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

