UNIVERSAL LAMP HOLDER

BACKGROUND OF THE INVENTION

THIS invention relates to a universal lamp holder which can accommodate both Edison screw and bayonet cap lamps.

Conventional lamps or light bulbs are generally provided with either a bayonet cap or an Edison screw cap at one end, defining contacts which mate with complemental contacts in a matching lamp holder to connect the lamp filament (or other light emitting element) to an electrical source. Each type of cap is generally incompatible with lamp holders designed for the other type of cap, so that where fuminaires are provided with Edison screw lamp holders, only lamps with a matching Edison screw cap can be installed in them. Likewise, where luminaires have bayonet lamp holders, only lamps with a matching bayonet cap can be used.

Because both types of lamp are commonplace, it is often the case that in a given building there may be luminaires with lamp holders of both kinds, requiring both types of lamp to be kept in stock. Conversely, when purchasing replacement lamps, a user may not know whether to obtain Edison screw or bayonet cap lamps, as the type of lamp holder cannot readily be determined without removing the lamp from the lamp holder first.

It would be advantageous to provide a lamp holder which could accommodate lamps fitted with either an Edison screw cap or a bayonet cap.

SUMMARY OF THE INVENTION

According to the invention there is provided a lamp holder usable with either a screw cap famp or a bayonet cap lamp, the lamp holder comprising:

a body defining a cavity shaped to receive either a screw cap or a bayonet cap of a lamp, the body defining respective locating formations for retaining the screw cap or the bayonet cap within the cavity; and

first and second sets of electrical contacts disposed within the cavity, the first set of contacts comprising a pair of spaced apart contact members arranged to make contact with complementai spaced apart contacts on an end of a bayonet cap lamp, the second set of contacts comprising an inner contact member arranged to make contact with a central contact of an screw cap lamp, and an outer contact member arranged to engage a threaded outer contact of said screw cap lamp, at least one contact member of the first and second sets of contacts being moveable relative to at least one other contact member so that insertion of either a screw cap lamp or a bayonet cap lamp causes only the appropriate set of contacts to engage the contacts of the lamp cap.

The outer contact member of the second set of contacts may comprise a threaded metallic insert shaped to engage a threaded portion of a screw cap of a lamp inserted into the lamp holder.

Alternatively, the outer contact member of the second set of contacts may comprise a conductive finger arranged to engage the threaded portion of a screw cap of a lamp inserted into the lamp holder.

Preferably, the cavity in the body has an outer portion which is threaded to receive an Edison screw cap, and an inner portion having a diameter

sfightly larger than the diameter of a bayonet cap to receive the bayonet cap slidably.

The cavity may define a stop in a form of a step or shoulder for limiting the extent to which the Edison screw cap can extend into the cavity towards the contacts.

In one embodiment, the inner contact member of the second set of contacts is located centrally between the contact members of the first set of contacts.

For example, the inner contact member may be an upstanding pin mounted on a contact carrier which is movable axially in the cavity and biased towards an outer portion of the cavity.

Preferably, the contact carrier has at least one portion shaped to be engaged by a bayonet cap when the bayonet cap is inserted into the lamp holder, so that the contact carrier is moved axially in the cavity and the inner contact member of the second set of contacts is maintained apart from the bayonet cap as the bayonet cap is inserted.

The contact members of the first set of contacts may be upstanding pins which extend through apertures in the contact carrier to engage the contacts of a bayonet cap.

In another embodiment, the contact members of the second set of contacts are conductive fingers, one of which serves as a contact member of both the first and second set of contacts.

This embodiment may include a body movable axially in the cavity and biased towards an outer portion of the cavity, with the other of the contact members of the first set of contacts being a conductive finger which is resiliently biased towards an outer wall of the body, and which is engaged

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by the body to move the finger inwardly so that it can engage a contact of a bayonet cap when the bayonet cap is inserted into the lamp holder.

!n a preferred embodiment, the body comprises polybutylene terephthalate (PBT) or polyethylene terephthalate (PET).

The body may be provided with an Edison screw cap or a bayonet cap fitting at one end thereof for insertion into a conventional lamp holder socket.

The body may provided with a removable mounting fitting having a threaded mounting formation therein.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a sectional isometric view of a first embodiment of a universal lamp holder according to the invention;

Figure 2 is a pictorial view of a moveable contact carrier of the lamp holder;

Figure 3 is a sectional side view of the iamp holder of Figure 1 with a bayonet cap lamp inserted;

Figure 4 is a similar view to that of Figure 3, showing an Edison screw cap lamp inserted in the lamp holder;

Figure 5 is a sectional side view of a second embodiment of a universal lamp holder according to the invention;

Figure 6 is a sectional side view of the iamp holder of Figure 5 with an Edison screw cap lamp inserted in the lamp holder;

Figure 7 is a sectional side view of the lamp holder of Figure 5 with a bayonet cap lamp inserted in the lamp hoider;

Figure 8 is a pictorial view showing the lower end of a lamp holder according to the invention and a clip-on mounting fitting;

Figure 9 shows the mounting fitting fitted to the lamp holder;

Figures 10 and 11 show embodiments of the lamp hoider provided with Edison screw cap and bayonet cap connectors, respectively;

Figure 12 is a sectional side view of a third embodiment of a universal lamp holder according to the invention;

Figure 13 is a sectional side view of the lamp holder of Figure 12 with a bayonet cap lamp inserted in the lamp holder;

Figure 14 is a sectional side view of the lamp holder of Figure 12 with an Edison screw cap lamp inserted in the lamp holder; and

Figure 15 is a pictorial view of a contact carrier body of the lamp holder of Figures 12 to 14.

DESCRIPTION OF EMBODIMENTS

Figure 1 shows a partial sectional isometric view of a universal lamp holder according to the invention. The lamp holder is designed to accept light bulbs or lamps having either an Edison screw cap or a conventional bayonet cap.

Edison screw caps have a threaded metallic cap body which defines a first contact, and a raised central second contact at an extreme end of the cap body. A conventional lamp holder for an Edison screw cap comprises a

threaded metallic body (or a body with a threaded metallic insert) and a central contact which may or may not be spring loaded. The lamp or bulb is screwed into the lamp holder until the central contact of the cap makes contact with the central contact of the lamp holder, with the threaded body or insert serving both to retain the lamp and to make electrical contact with the metallic body of the lamp cap.

In the case of a lamp having a bayonet cap, the cap body is cylindrical with opposed pins extending transversely from the body, and a pair of spaced apart contact pads are provided on the end surface of the cap. The lamp holder defines a cylindrical cavity with generally L-shaped slots formed in the side walls to receive the pins of the cap with an initial axial movement followed by a rotational movement to lock the pins in position. A pair of contact pins, which are generally spring loaded, are arranged to make contact with the spaced apart contact pads on the end of the bayonet cap when it is locked into position in the lamp holder.

Referring now to Figure 1 , the universal lamp holder of the invention is seen to comprise a body 10 defining a cylindrical cavity 12 which is sized to receive either a bayonet cap or an Edison screw cap of a lamp. The body 10 will typically be moulded from a suitable non-conductive and heat resistant plastics material. For example, the lamp holder socket can be formed from polyester material, as used for conventional lamp holders. Preferably, the lamp holder body is formed from polybutylene terephthalate (PBT) or from polyethylene terephthalate (PET) material. Other suitable materials can also be used. For example, the lamp holder body could be formed from porcelain or another highly heat resistant material.

An upper or outer portion 14 of the lamp holder socket has a somewhat wider internal diameter than an inner portion 16 and is provided with a threaded metallic insert 18, the thread being complemental to the thread on an Edison screw cap. Typically, the threaded insert is formed from brass or another suitable conductive metal, in an alternative embodiment of the lamp holder, the outer portion 14 of the lamp holder may be provided with a

thread formed in the non-conductive material of the lamp holder body, with a contact member in the form of a conductive tongue or finger extending adjacent the thread to engage the threaded portion of a screw cap, instead of a threaded insert.

The internal diameter of the inner portion 16 of the socket corresponds to the outer diameter of the end portion of a bayonet cap, which can be accommodated snugly therein. Below the threaded insert 18, where the internal diameter of the inner portion 16 of the lamp holder reduces, a circular step or shoulder 66 is defined.

A pair of axially extending grooves or slots 20 are defined by the body 10, extending through the conductive insert 18 and the wall 22 of the body defining the inner region 16 thereof. At its innermost end, each slot 20 is contiguous with a circumferential slot 24 extending at right angles to the slot 20, and the slot 24 is in turn contiguous with a slot 26 which extends for a short distance in the direction of the outer end of the socket. The sets of slots 20, 24 and 26 accommodate the pins of a bayonet cap lamp, allowing the lamp to be inserted axially into the socket, rotated, and retained in position by the slot 26 under the urging of spring-loaded contacts (see below).

Located centrally within the socket is a bridge member 28 which extends diametrally and on which a pair of contact pins 30 and 32 are supported. The pins 30 and 32 are mounted in respective sleeves 34 and 36 which are fixed to the bridge member 28, with the pins 30 and 32 being spring loaded for axial movement in the sleeves. The pins 30 and 32 form a first set of contacts.

Located centrally, between the pins 30 and 32, is a central contact pin 38 which serves as the first contact of a second set of contacts (the second contact of the second set comprising the threaded insert 18). The contact pin 38 is mounted on a contact carrier member 40 (see Figure 2) which comprises a disk shaped base 42 and a pair of curved upstanding walls 44

and 46 separated by gaps. The gaps are sized to receive the bridge member 28 and to allow the contact carrier member 40 to move axially relative to the bridge member.

The contact carrier member 40 is retained in a compartment 48 below the bridge member and is biased upwardly by a pair of coil springs 50 and 52 into engagement with the underside of the bridge member. In this configuration, the tip of the central pin 38 extends beyond the ends of the pins 30 and 32, as seen in Figure 1. Thus, if a !amp with an Edison screw cap is screwed into the lamp holder, the central contact 54 of the cap will make contact with the tip of the pin 38, while the threaded portion 56 of the cap makes contact with the threaded insert 18. The pin 38 and the contact carrier 40 are moved downwardly by a short distance as the central contact of the lamp is screwed into position. However, as can be seen from Figure 4, the pins 30 and 32 remain well clear of the screw cap in this configuration. Also as shown in Figure 4, the conically tapered outer end portion of the screw cap abuts the step or shoulder 66 when the lamp is fully screwed into position in the lamp holder, limiting the extent to which the screw cap can extend into the holder and preventing it from coming into contact with the pins 30 and 32.

If a lamp with a bayonet cap is inserted into the lamp holder, so that the pins 58 on the bayonet cap 60 are engaged with the slots 26 to locate the bulb in the lamp holder, the end surface 68 of the bayonet cap engages the upper edges of the upstanding walls 44 and 46 as the cap is inserted, forcing the contact carrier member 40 downwardly and retracting the pin 38, as shown in Figure 3. The contact pads 62 and 64 at the outer end of the bayonet cap 60 engage the pins 30 and 32, while the pin 38 is well clear of the bayonet cap. The outer diameter of the bayonet cap 60 is slightly less than the inner diameter of the inner portion 16 of the lamp holder, enabling the bayonet cap to slide in and out of the lamp holder easily, without being restricted by the step or shoulder 66.

Referring now to Figure 5, an alternative embodiment of the lamp holder is shown, which has a somewhat simplified design compared with the embodiment of Figure 1. The embodiment of Figure 5 comprises a body 100 defining a cavity 102 which is sized to receive a lamp having either a bayonet cap or an Edison screw cap, and the internal wal! of the body defining the cavity 102 is threaded complementally to an Edison screw. The outer wail of the body 100 is formed with an L shaped slot 150 which functions similarly to the slots 20, 24 and 26 of the first embodiment.

The second embodiment includes a cup shaped body 104 (essentially similar to the cup shaped body 206 of Figure 15) which can slide axially in a cylindrical cavity 106 defined in an inner portion of the body 100, below a shoulder 108. The cup shaped body 104 has a flat, disc shaped base 110 and an upstanding side wail 112 which is circular in plan. A coil spring 114 between the body 104 and an end wall 116 of the body 100 biases the cup shaped body upwardly towards the position shown in Figure 5. The cup shaped body has a pair of opposed openings 118 and 120 formed in it, which allow contact fingers to extend therethrough as described below.

A pair of contact members 122 and 124 which can be formed from beryllium copper or another suitable conductive material are located in respective recesses 126 and 128 near the lower end of the body 100, and can be connected to flexible conductors 130 and 132 as illustrated, or to other contacts (see below). The contact members 122 and 124 are formed from strips that are bent into the illustrated shapes. Variations in the illustrated shapes are possible.

The contact member 122 has a first end portion which extends into the upper, threaded portion of the body 100, just past the shoulder 108, and is there kinked outwardly at about 45 degrees to define a contact finger 152 which is located so that it can make electrical contact with the outer, threaded portion of an Edison screw cap when the latter is screwed into the body 100.

A second end portion of the contact member 122 extends through the aperture 118 in the cup shaped body 104, with an elbow portion 134 which is biased outwardly towards the outer wall of the body 100, and defines a first contact finger 136 in the tower portion of the cavity 106. The second contact member 124 extends through the aperture 120 in the cup shaped body and defines a second contact finger 138 adjacent to the first. As best seen in Figure 5, the tip of the second contact finger 138 extends further towards the open end of the body 100 than the tip of the first contact finger 136, that is, their tips are axially displaced relative to one another with reference to a central axis of the lamp holder body 100.

When an Edison screw cap buib is inserted into the lamp holder, as shown in Figure 6, the central contact of the cap contacts the finger 138, while the threaded outer portion of the cap contacts the first end portion of the contact member 122. The tip of the finger 136 is clear of both the central contact and the outer portion of the cap, as iflustrated.

When a bayonet cap bulb is inserted into the lamp holder, as shown in Figure 7, the end surface of the bayonet cap engages the upper edge of the upstanding side wall 1 12 of the cup shaped body 104 as the cap is inserted, forcing the cup shaped body downwardly against the urging of the spring 114.

The upper portion of the side wall 112 above the aperture 1 18 slides over the elbow 134 in the first contact member 122 and displaces it inwardly from the position shown in Figure 5 to the position shown in Figure 7, moving the contact finger 136 into a position in which it can engage one of the contacts at the bottom of the bayonet cap, while the contact finger 138 engages the other contact. The side wall defining the upper portion of the aperture 1 18 is formed with a tapered or inclined surface 140 to facilitate sliding of the side wall over the elbow 134.

Thus, it can be seen that the functionality of the two embodiments of the lamp holder is very similar.

Figure 8 shows the lower end portion of the lamp holder body 100, and it can be seen that a pair of opposed apertures 142 and 144 are formed at the end of the body. A threaded cup shaped mounting fitting 146 is provided with a pair of hooked fingers 148 which can clip into the apertures 142 and 144 to retain the fitting 146 snugly on the end of the lamp holder body as shown in Figure 9. This allows the lamp holder to be screwed onto a conventionally threaded mounting stem of a table or standard iamp, for example.

Figures 10 and 11 show versions of the lamp holder in which the body 100 is formed with either an Edison screw-type fitting 152 or a bayonet-type fitting 154 at its lower end, respectively, so that the lamp holder can be inserted into a conventional lamp holder or light fitting of the appropriate type, and thus converts the conventional fitting into a universal fitting.

A further embodiment of the lamp holder is shown in Figures 12 to 15. This embodiment includes aspects of both the first and second embodiments. A lamp holder body 200 defines a cavity 202 which is sized to receive a lamp having either a bayonet cap or an Edison screw cap, and the internal wall of the body defining the cavity 202 is threaded complementaily to an Edison screw. The outer wall of the body 200 is formed with an L shaped slot 204, similar to the slot 150 of the second embodiment.

The third embodiment includes a cup shaped body 206 which can slide axially in a cylindrical cavity 208 defined in an inner portion of the body 200, below a shoulder 210. The cup shaped body 206 has a flat, disc shaped base 212 and an upstanding side wall 214 which is circular in plan. A coil spring 216 between the base 212 of the cup shaped body 206 and an end wall 218 of the body 200 biases the cup shaped body upwardly towards the position shown in Figure 12. The cup shaped body has a pair of opposed openings 220 and 222 formed in it, which allow contact pins to extend therethrough as described below. The cup shaped body also has a pair of opposed catch members 224 and 226 which are elongate and have

outwardly extending hooks or teeth 228, as shown in Figure 15. When the cup shaped body is inserted into the lamp holder body into the cavity 208, the catch members can bend resiliency inwardly until the teeth 228 snap into compiemental slots in the wall of the body 206, permitting axial movement of the cup shaped member in the body but retaining it in the body.

In this embodiment, a central upstanding contact pin 230 is carried by the cup shaped body 206, while a pair of fixed pins 238 and 240 with spring loaded tips 242 and 244 are fixed to the body 200. The pin 230 is connected by a flexible conductor 246 to the pin 240, and a contact finger 248, similar to the contact finger 152 of the second embodiment, is connected to the pin 238.

It can be seen from Figure 13 that the tips 242 and 244 of the pins 238 and 240 make contact with the contact pads at the base of a bayonet cap lamp, with the central pin 230 on the cup shaped body being moved on the cup shaped body 206 as the bayonet cap is inserted into the lamp holder, keeping this pin out of contact with the bayonet cap. When an Edison screw cap is inserted into the lamp holder, as shown in Figure 14, the contact finger 248 and the central pin 230 are active.

From the above description, it will be appreciated that a universal famp holder is provided which accommodates both conventional bayonet cap and Edison screw cap lamps, in a manner which requires no special skill or knowledge on the part of a user of the device. Either type of lamp can be inserted normally and will function correctly.

It will be appreciated that variations of the described lamp holder are possible, with the main requirement being that insertion of a lamp having different types of cap must, in at least one case, cause relative movement of the contacts in the lamp holder to avoid interference between the different sets of contacts and the respective lamp caps.