Festoon lamp

Abstract

 The filament 3 is attached to leads 4 and 5 which are joined at one end by an insulating bead 6. This forms a self-supporting filament mount with the lead 5 extending from the bead 6 arround the filament 3 in a generally heli- calor angled path to minimize obstruction of the emitted light. A free end 7 of the lead 5, extending beyond the filament 3, passes through one end of the bulb 1 to form one terminal. At the other end a press seal is formed in which the end of the lead 5 is embedded while the lead 4 passes through to form a second terminal of the lamp.

Description

[0001] The present invention relates to double ended tubular lamps of the type referred to as "Festoon" lamps.

[0002] Such lamps have a generally tubular envelope with a lead wire sealed through each end of the lamp envelope and a longitudinal filament connected between the lead wire parallel to the envelope axis. In the known method of manufacture of such lamps the filament and lead wire mount arrangement is inserted into a pre-shaped tubular bulb with reduced diameter portions at each end. One lead wire is bent to allow it to seat on one of the open ends of the bulb so as to support the filament in position while the other end of the bulb is sealed onto the other lead wire. The bent lead wire is sealed into the bulb by butt sealing an exhaust tube onto the open end of the bulb and after exhausting and, if required, gas filling this tube is sealed by tipping off. In this method of manufacture the positioning of the filament along the centre line of the bulb depends critically on the size of the bulb, which is difficult to control accurately.

[0003] In accordance with the present invention there is provided a method of manufacturing a festoon lamp wherein a filament mount is formed in which one of two leads to which the ends of the filament are attached extends to the opposite end of the filament and is there joined to the other lead by an insulating bead, the filament mount is positioned inside a tubular envelope, and one end of the envelope is pinch sealed about the two leads on the side of the insulating bead remote from the filament.

[0004] Preferably the other end of the envelope is sealed about the said one lead which emerges from the said other end but in the finished lamp does not emerge from the said pinch seal. In this way the two leads form electrical connections to the filament at opposite ends of the lamp and the said one lead provides additional mechanical support for the filament by reason of being embedded in the said pinch seal.

[0005] Preferably the filament mount is formed with the outer ends. of the leads at approximately the same distance from the insulating bead and after formation of the pinch seal the end of the said one lead outside the seal is cut off. The two leads- facilitate handling of the filament mount while it is being positioned in the envelope and the seal is being formed. The filament mount is self-supporting and can be positioned accurately within the envelope without relying on accuracy of the dimensions of the envelope and the mount. The pinch seal formed about the leads improves control of lateral positioning.

[0006] Preferably the said one lead follows a generally helical or angled path around the filament to minimize interruption of the light from the filament in any one direction.

[0007] Conveniently an exhaust tube is incorporated in the pinch seal. It can be located between the two leads.

[0008] It will be appreciated that the use of the method in accordance with the invention can result in a lamp having a generally tubular envelope, a longitudinal filament mounted within the envelope between two leads which at one end of the filament are joined by an insulating bead and embedded in a pinch seal of the envelope, one of the leads being attached to the end of the filament remote from the bead and extending through the end of the envelope remote from the pinch seal.

[0009] A lamp and method of manufacturing the lamp according to the present invention will now be described by way of example and with reference to the accompanying drawings, in which:-

Figure 1 shows a filament mount construction for the lamp; and

Figure 2 shows a lamp incorporating the filament mount structure of Figure 1.

[0010] Referring to the drawings, the lamp shown is of the type commonly referred to as a "Festoon" lamp and has a generally tubular envelope 1 with contact caps 2 (shown in dotted outline in Figure 2) at each end of an elongate filament 3 disposed along the axis of the envelope.

[0011] As shown in Figure 1, the filament 3 and dumet lead wires 4, 5 are pre-assembled as a rigid unitary filament mount construction. The lead wires 4 and 5 are joined at one end of the filament by an insulating glass bead 6 and are connected to opposite ends of the filament by mechanical or welded joints between the tungsten filament wire and the dumet leads. The lead wire 5 which connects to the end of the filament remote from the glass bead 6 has a free end 7 extending away from the filament and is-cranked to follow a generally helical path between this end and the glass bead so as not to obscure the filament in any one direction.

[0012] The lamp is assembled by first inserting the filament mount construction into a straight-sided glass tube with an exhaust tube 8 positioned between the lead wires 4, 5. The free end 7 of the lead wire 5 protrudes from one end of the glass tube and is sealed by heating that end of the tube and working it so that the glass forms a hermetic seal with the dumet. The other end of the tube is sealed by a pinch seal technique in which the glass is heated to a suitable temperature and then pressed onto the two lead wires 4, 5 and the exhaust tube 8 by two opposing jaws.

[0013] After exhausting and then gas filling the sealed bulb, the exhaust tube is tipped off. The part of the lead wire 5 which extends outside the pinch seal is cropped off and conventional contact caps 2 are secured to the ends of the bulb and connected to the lead wires.

[0014] This method of manufacture is simpler and quicker than that previously used and involves less material waste, while giving a more accurate positioning of the filament in the lamp.

Claims

1. A-method of manufacturing a festoon lamp wherein a filament mount is formed in which one of two leads- to which the ends of the filament are attached extends to the opposite end of the filament and is there joined to the other lead by an insulating bead, the filament mount is positioned inside a tubular envelope, and one end of the envelope is pinch sealed about the two leads on the side of the insulating bead remote from the filament.

2. A method as claimed in claim 1 in which the other end of the envelope is sealed about the said one lead such that the lead emerges from the said other end to form an electrical connection for the lamp whereas the said one lead does not project outside the pinch seal.

3. A method as claimed in claim 2 in which the filament is formed with the outer end of the leads at approximately the equal distances from the insulating bead and after formation of the pinch seal the end of the said one lead outside the pinch seal is cut off.

4. A method as claimed in claim 1, 2 or 3 in which the said one lead follows an angled path around the filament.

5. A method as claimed in any of the preceding claims in which an exhaust tube is incorporated in the pinch seal between the two leads.

6. A method of manufacturing a festoon lamp substantially as described with reference to the accompanying drawing.

7. A festoon lamp produced by the method of any one of the preceding claims.

8. A lamp having a generally tubular envelope, a longitudinal filament mounted within the envelope between two leads which at one end of the filament are joined by an insulating bead and embedded in a pinch seal of the envelope, one of the leads being attached to the end of the filament remote from the bead and extending through the end of the envelope remote from the pinch seal.

9. A lamp as claimed in claim 8 in which the said one lead follows an angled path around the filament..

Drawing