GB2214364A

GB2214364A - Lamp holder for screw and bayonet lamps

Info

Publication number: GB2214364A
Application number: GB8829481A
Authority: GB
Inventors: Frank Putnam
Original assignee: TRANILAMP Ltd
Current assignee: TRANILAMP Ltd
Priority date: 1987-12-16
Filing date: 1988-12-16
Publication date: 1989-08-31
Also published as: GB8829481D0; GB8729335D0

Abstract

An electric lamp holder comprises a socket (4) for receiving interchangably a screw cap (6a) or a bayonet cap (6b), the socket having side wall formations (20) for engagement with the screw thread of a lamp screw cap as well as formations (24) for engagement with the radial projections of a lamp bayonet cap. Side wall formation (20) is in the form of a spring contact. <IMAGE>

Description

LAMP HOLDERS This invention relates to lamp holders for electric lamps.

The present use of both screw cap and bayonet cap lamps, although these cap forms are standardised, is inconvenient in many ways and can lead to difficulties for users. The invention is concerned with providing a lamp holder that is able to receive interchangeably a screw cap or a bayonet cap lamp.

According to the invention, there is provided an electric lamp holder comprising a socket for receiving the cap of a lamp, the socket being provided with spaced electrical contacts for the base and side of the cap respectively to connect the lamp operatively to a current source, the socket having respective side wall formations for engagement with the screw thread of a lamp screw cap and with the radial projections-of a lamp bayonet cap, at least one portion of the side walls of the socket being resiliently displaceable laterally outwards whereby to allow the insertion of either said screw cap or said bayonet cap to engage the inserted cap between said portion and an opposed portion of the socket.

Conveniently, said cap side contact is provided by or is carried on the resiliently displaceable portion or at least one of said portions, or on a rigid side wall portion or portions opposed thereto, in order to establish electrical continuity between the cap and said side contact. It is alternatively possible, however, to arrange that contact as a member projecting from the base of the socket to engage the outer edge region of an inserted lamp cap.

When said resiliently displaceable portion forms the cap side contact, for simplicity it may itself be in the form of a spring. Further simplification is possible if said side contact is formed with ridges and depressions for locating engagement with the cap screw thread.

The opposed side wall portions of the socket may both be resiliently displaceable away from each other or one may form a rigid part of the socket side walls.

Whether rigid or resiliently displaceable, they are preferably each provided with ridges and depressions for engaging a screw cap thread.

Slots to accommodate the projections of a bayonet cap can also be formed in rigid or resiliently displaceable wall portions of the socket. However, a simple and effective arrangement is achieved if the slots are formed in diametrically opposite rigid portions of the socket walls with said resilient side wall portion or portions located between these rigid portions.

One embodiment of the invention will be described by way of example with reference to the accompanying drawings, in which: Figs. 1 and 2 are diagrammatic sectional views of a lamp holder according to the invention, with a screw cap lamp and with a bayonet cap lamp respectively, and Figs. 3 and 4 illustrate modifications of the lamp holder of Figs. 1 and 2.

The lamp holder shown comprises a rigid body 2 of moulded plastics providing a cylindrical socket 4 in which a lamp cap 6a or 6b is received. Assembled into the body are metal strips 8,10 acting as electrical contacts. The first strip 8 comprises a cantilevered contact limb 12 that lies adjacent the bottom of the socket, and a tail 14 that projects out of the body to provide an external connection for a pressure clip or soldered joint (not shown). The second strip, of which there may be more than one, has a main part 16 extending over substantially the height of the socket and spaced from the adjacent side wall over most of its length, and a tail 18 projecting out of the body for an external connection, similarly to the first strip.

The main part of the second strip is formed with a series of transverse corrugations 20 or other projections at the same pitch as the thread of the screw cap 6a that can be fitted into the socket. The free end 22 of the strip is bent back against the rigid wall of the socket so that both ends of the main part 16 of the strip are supported by the body of the lamp holder.

Before insertion of a lamp cap, the corrugated main part 16 of the strip projects radially inwards somewhat further than is shown in the drawings. As the screw cap is entered into the socket and urges the portion 16 outwards, the corrugations therefore grip the cap to hold it firmly in place between the strip and the opposed side face of the socket and to make an electrical connection with the side wall of the cap. As the cap is screwed further into the socket its centre terminal makes contact with the free limb 12 of the first strip 8 which is then held by its resilience in electrical contact with the central end contact of the cap.

Moulded into the lamp holder body, at diametrically opposite positions offset from the second strip 10, are slots 24 of angled form for a conventional bayonet-type connection. The screw cap lamp can thus be replaced by the bayonet cap lamp 6b, and the slots 24 will retain this second type of lamp cap within the holder. The main part 16 of the second strip 10 is urged radially outwards by the insertion of the lampXcap and the cap is therefore held firmly between the strip and the opposed side wall of the socket, although in this case the corrugations 20 play no part in securing the lamp in place.

As with the screw cap, the bottom electrical contact is established between the centre terminal of the cap and the first strip 8 to complete the circuit through the lamp, and the resilience of the strip 8 pushes the lamp cap up to lock the bayonet-type connection.

Many modifications are possible within the scope of the invention. For example, to hold a screw cap more securely, a portion of the socket side wall opposed to said main part 16 of the second strip can also be corrugated or have other projections to engage the cap screw thread. In the simplest case, such projections will be moulded into the rigid side wall region 26 of the socket diametrically opposite the sprung part 16 of the second strip, but other configurations may be used and in particular the screw cap can be held between side wall members that are analogous to the strip part 16 and are each resiliently displaceable away from each other. It is also possible for the lamp cap side wall contact to be rigidly fixed in place, either type of lamp cap being urged against it by a resiliently displaceable element that does not provide part of the electrical circuit.

Fig. 3 shows a further alternative in which the outer contact is provided by a coil spring 28 at the bottom of the socket only slightly smaller than the socket in diameter, and the corrugated projection 30 is formed from an electrically non-conductive strip. As in the previous examples the required resilience can be provided by this strip and/or another opposed part within the socket and there can be a number of such strips spaced around the socket side walls.

It will be understood that in these arrangements employing combinations of rigid and resiliently displaceable side wall engagements, either or each may be profiled to mesh with a screw cap thread, although in general the provision of a spring-form electrical contact with a thread-engaging profile will give the required result in the simplest and most economical manner.

The bottom contact can also take other forms. As Fig. 4 illustrates, it is possible to mount a coil spring 32 on the metal strip 8 to connect resiliently with the centre contact of the lamp cap. It is also possible to use a unitary wire contact between the lamp cap centre contact and the external connection.

Other modifications are also possible within the scope of the invention. For example, other forms of spring, such as a resilient pad, e.g. of plastics, can be employed to engage the lamp cap to push it up in the socket for locking a bayonet-type connection. The centre contact can project through such a pad and be movable with it but would not be required to apply a force to push the lamp cap upwards.

Claims

1. An electric lamp holder comprising a socket for receiving the cap of a lamp, the socket being provided with spaced electrical contacts for the base and side of the cap respectively to connect the lamp operatively to a current source, the socket having respective side wall formations for engagement with the screw thread of a lamp screw cap and with the radial projections of a lamp bayonet cap, at least a portion of the side walls of the socket being resiliently displaceable laterally outwards whereby to allow the insertion of either said screw cap or said bayonet cap to engage the inserted cap between said portion and an opposed portion of the socket.

2. A holder according to claim 1 wherein said cap side contact is provided by or is carried on the or at least one said resiliently displaceable portion or on a rigid sidewall portion or portions opposed thereto.

3. A holder according to claim 2 wherein said cap side contact is in the form of a resiliently displaceable spring.

4. A holder according to claim 1 wherein said cap side contact is provided by a member projecting from the base of the socket to engage the outer edge region of an inserted lamp cap.

5. An electric lamp holder according to any one of the preceding claims wherein one or both of said opposed side wall portions are provided with ridges and depressions for locating engagement with the cap screw thread.

6. An electric lamp holder according to claim 5 wherein said cap side contact is formed with ridges and depressions for locating engagement with the cap screw thread

7. An electric lamp holder according to any one of the preceding claims wherein said opposed side wall portions of the socket are both resiliently displaceable away from each other.

8. An electric lamp holder according to claim 7 wherein slots for engagement with the projections of a bayonet cap are formed in diametrically opposite rigid portions of the socket wall with said resilient side wall portion or portions being located between said rigid portions

9. An electric lamp holder constructed and arranged substantially as described herein with reference to the accompanying drawings.