GB2294806A

GB2294806A - A filament lamp

Info

Publication number: GB2294806A
Application number: GB9420880A
Authority: GB
Inventors: Michael John Furnell
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-10-17
Filing date: 1994-10-17
Publication date: 1996-05-08
Also published as: GB9420880D0

Abstract

A filament lamp has an envelope (10) constructed in two parts, one part (10a) being fixed with respect to the screw connector (11) and the other (10b) forming a removable cap via which the filament (20) may be removed and replaced. For this purpose, rigid terminals (25, 26) attached to the filament are releasably retained in a socket member (30). A multi-filament embodiment is also described. <IMAGE>

Description

Improvements in and Relating to Lamps The present invention relates to lamps, in particular lamps of the kind having a wire filament, typically tungsten, surrounded by a transparent or translucent envelope and electrical connection means for connecting the ends of the filament to an external source of electrical power.

It is well known that the weakest part of this type of lamp is the tungsten filament. The filament has a limited life and once worn out, usually through evaporation of the tungsten itself, the whole lamp has to be discarded.

It would therefore be advantageous to provide a lamp whose filament alone could be replaced to avoid the need to replace the whole lamp when the filament has.worn out.

The present invention provides a lamp comprising at least one wire filament having first and second terminals, a transparent or semi-transparent envelope surrounding the filament and connector means for electrically connecting the filament to a source of power outside the envelope, the connector means including means for releasably retaining the terminals of the filament and at least part of the envelope being removable from the remainder of the lamp to enable removal of the filament from the connector means.

Although it is possible, in accordance with this invention, for the whole of the envelope to be removable from the connector/filament assembly, preferably the envelope is provided in two parts, one fixed with respect to the connector means and one removable. The two parts may be screwed together.

Preferably the envelope is in the well known bulb shape having a generally spherical portion and a narrow neck portion from which the connector means lead to the outside of the envelope. With this shape, the removable part of the envelope may comprise a hemispherical cap portion.

The means for releasably retaining the terminals of the filament may be in the form of a socket having respective channels for receiving the terminals. The channels may include resilient means, such as springs, for gripping the terminals. The socket may be provided in a stem extending into the envelope, for example in the case of the classic bulb shape the stem would extend from the neck portion into the hemispherical portion. The stem may house flexible wires extending from the socket to the external connector means, such as a screw threaded connector or bayonet-type fitting.

In a development of the invention, several filaments are provided in the same envelope, preferably connected to common first and second terminals. The filaments may be mounted on a circuit board and may produce different coloured lights for example. In any of the embodiments of the invention the filaments may each be provided with an individual sealed envelope. This may provide additional protection for the delicate filament during replacement and may contain fluorescent gas, eg.

halogen gas.

The envelopes may be made from a plastics material such as polycarbonate.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a vertical part cross-section of a first embodiment of lamp according to the invention; Figure 2 is a view corresponding to Figure 1 showing the filament removed; Figure 3 is a vertical part cross-section of a second embodiment of lamp according to the invention; Figure 4 is a view corresponding to Figure 3 showing the filament group removed; Figure 5 is a vertical part cross-section of a third embodiment of lamp according to the invention; and Figure 6 is a vertical part cross-section view taken perpendicular to the view of Figure 5.

Referring firstly to Figures 1 and 2, a first lamp according to the invention comprises a transparent envelope 10 secured to a conventional screw connector 11 by which the lamp can be connected to a mating screw-threaded socket for the supply of power. The envelope 10 is constructed in two parts, namely a removable cap portion iOa and a main body portion 1Ob which is fixed which respect to the screw connector 11.

The envelope is made from transparent LEXAN(tm) high impact u.v stabilised polycarbonate, available from General Electric Corporation of America. The envelope is made in the traditional lamp shape comprising a generally spherical portion and a narrow neck portion which connects the spherical portion to the screw connector. Thus, the cap iOa is generally hemispherical in shape. The facing circular edges of the cap portion iOa and the main body portion 1Ob have mating screw threads arranged so that the cap portion can be secured with respect to the main body portion in approximately 4 revolution.

The envelope 10 is attached to the screw connector 11 via a circular collet 12 which is likewise fabricated from LEXAN(tm) polycarbonate material. The collet 12 is preferably made in two halves for ease of manufacture and extends along the neck portion of the envelope 10. The collet includes an annular shoulder 12a against which a turned under portion of the envelope 10 abuts. The collet and envelope portion 1Ob are fixed together, for example with adhesive. The collet also includes transverse holes which simply act as locating points in the assembly of the lamp. The screw connector 11 is suitably adhered to the collet 12. The collet 12 also includes vanes 13 which extend from the collet to the neck portion of the envelope 10 to strengthen the structure in the region of the neck portion. Preferably there are four vanes in total.

A stem 14 extends through a central hole in the collet 12 towards the spherical portion of the envelope 10.

The stem has the form of a tube whose external diameter is slightly smaller than the internal diameter of the collet 12 so that it fits snugly in the collet. A small abutment 14a protruding from the stem 14 determines the axial location of the stem 14 within the collet 12.

The stem supports a filament unit generally designated by numeral 15. The filament unit includes a tungsten filament 20 housed in a sealed envelope 21 containing halogen gas. The sealed envelope 21 may again be made from polycarbonate material. Wires 22,23 passing from the filament 20 out of the sealed envelope 21 are attached to more rigid conductive metal connections encased in moulded polycarbonate indicated at 24. Stiff wire connections 25,26 extend from polycarbonate moulding 24.

The stem 14 houses a socket member 30 which receives the wire connections 25,26 and electrically connects them to flexible insulated leads 31,32 which extend from the socket member 30. The socket member includes respective channels for receiving the connections 25,26 and, as with conventional electrical sockets, the channels preferably house spring connectors which not only make good electrical contact with the connections 25,26 but also help to ensure that the wire connections are firmly gripped so that the filament unit 15 cannot fall out of the socket member 30.

The flexible insulated leads are connected to the screw connector as in a standard light bulb.

It should be noted that the screw connector 11 may be readily replaced by a bayonet connector if desired and in fact a bayonet connector 41 is illustrated in Figure 2.

Figures 3 and 4 show an alternative to the lamp of Figures 1 and 2 which include several tungsten filaments connected in parallel. Like parts to those in Figures 1 and 2 are indicated by the same reference numerals, increased by 100. Figure 3 shows a version with a bayonet connector 141 and Figure 4 shows a version with a screw connector 111.

The lamp of Figure 3 and 4 includes ten tungsten filaments 151-160 housed in respective envelopes 161-170.

In order to accommodate these extra filaments, the stem 114 is shorter than the stem 14 of the first embodiment. The stem 114 houses a socket member 130 which is identical to the socket member 30 of Figures 1 and 2. Currently available encased filaments sometimes known as "seeds" for this application are incandescent rather than fluorescent but halogen-filled fluorescent envelopes may be used.

The socket member 130 receives two.rigid wire connectors 125 and 126 which are connected to the filaments 151-160. Each filament envelope 161-170 has two conductive wires extending from it which extend from the filament itself. These wires are relatively flexible but hold their shape once formed. Two relatively rigid wires 172,173 (Fig.

4) extend from the wire connections 125,126 in the direction away from socket member 130. The wires which extend from the filament envelopes are connected respectively to the relatively rigid wires 173 and 172 to result in a parallel connection of all ten filaments as shown.

The whole assembly of the ten filaments is removable, and hence replaceable, by unscrewing the cap portion 110a and removing the wire connections 125,126 from the socket member 130.

For extra stability the wire connections 125,126 are held spaced from each other by a plastics (eg.

polycarbonate) moulding indicated at 180 (Fig. 4).

Figures 5 and 6 show a modification of the embodiment of the invention shown in Figures 3 and 4 in which the flexible wires and wires 171,172 are replaced by a circuit board. Parts in Figures 5 and 6 which correspond to parts in Figures 3 and 4 are indicated by the same reference numerals, increased by 100. The lamps of Figures 5 and 6 both include a screw connector 211 but it will be appreciated that this could be readily replaced by a bayonet connector.

The filament envelopes 261-270 of Figures 5 and 6 are identical to those of Figures 3 and 4 and all include a tungsten filament and wires extending outside the envelope from the filament.

A printed circuit board 290 is attached to the rigid wire connections 225 and 226 which have been described above and the wires extending from the filament envelopes are soldered to the printed conductors 295 on the circuit board 290 in such a way that they are all connected in parallel across connectors 225,226. Figure 5 shows just one possible conductor configuration. Preferably the filaments are arranged five on each side of the board 290.

Preferably the board is rectangular and has a rectangular hole at its centre. The use of a board makes the multiple filament assembly easier to handle and hence easier to remove for replacement.

With all of the embodiments of the invention, the envelope 10, 110 or 210 may be clear or coloured transparent material and may even be translucent, depending on the desired application. Where halogen-filled envelopes are used, a transformer would be needed for mains operations.

It will be appreciated that all of the described embodiments of the invention are intended for use with standard screw thread or bayonet-type lamp holders although the invention is not limited to such applications.

Claims

Claims:

1. A lamp comprising at least one wire filament having first and second terminals, a transparent or semi-transparent envelope surrounding the filament and connector means for electrically connecting the filament to a source of power outside the envelope, the connector means including means for releasably retaining the terminals of the filament and at least part of the envelope being removable from the remainder of the lamp to enable removal of the filament from the connector means.

2. A lamp as claimed in claim 1 in which the envelope comprises two parts, one of which is fixed with respect to the connector means and the other of which is removable.

3. A lamp as claimed in claim 2 in which the two parts of the envelope have mating screw threads by means of which they may be assembled.

4. A lamp as claimed in claim 1, 2 or.3 in which the envelope has a generally spherical portion merging with a neck portion attached to the connector means.

5. A lamp as claimed in claim 4 in which a hemispherical portion of the envelope is removable.

6. A lamp as claimed in any preceding claim in which the means for releasably retaining the terminals comprises socket means for receiving the terminals of the filament.

7. A lamp as claimed in claim 6 in which the socket means includes resilient means for gripping the terminals.

8. A lamp as claimed in any preceding claim in which the means for releasably retaining the terminals is provided in a stem extending into the envelope.

9. A lamp as claimed in any preceding claim comprising a plurality of filaments connected to common first and second terminals.

10. A lamp as claimed in claim 9 in which the filaments are connected in parallel.

11. A lamp as claimed in claim 9 or 10 in which the filaments are mounted on a circuit board from which said first and second terminals extend.

12. A lamp as claimed in any preceding claim in which the or each filament is surrounded by an additional sealed envelope.

13. A lamp as claimed in any preceding claim in which the envelope is made from plastics material.

14. A lamp substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

15. A lamp substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.

16. A lamp substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.