GB2096755A

GB2096755A - Lamp bulb mounting

Info

Publication number: GB2096755A
Application number: GB8111657A
Authority: GB
Original assignee: KEELER OPTICAL PRODUCTS Ltd
Current assignee: KEELER OPTICAL PRODUCTS Ltd
Priority date: 1981-04-13
Filing date: 1981-04-13
Publication date: 1982-10-20
Also published as: JPS57180072A; DE3213593A1

Abstract

An incandescent lamp bulb, intended primarily for otoscopes, ophthalmoscopes and similar instruments, has a lamp envelope 1 mounted in a metal tube 6 with an air gap 12. The envelope is located only by an elastomeric ring 13 and the conical end of the tube. The internal surface of the tube is bright metal plated. This plating, the air gap, and the small area of contact with the surroundings ensure that the envelope, which is preferably a halogen-containing envelope, runs hot. The conical tube end has slots 11 such that the tube end can be deformed in order to centre the filament 3 accurately in the bulb body. <IMAGE>

Description

SPECIFICATION Lamp bulb This invention relates to electric lamp bulbs, in particular miniature incandescent bulbs used for example in otoscopes and similar instruments.

Bulbs for otoscopes, ophthalmoscopes and the like must have very accurately placed filaments in order to ensure that the instrument in which they are used gives an accurately defined and aligned light beam.

Existing miniature incandescent bulbs for otoscopes and ophthalmoscopes have a glass envelope held either in a metal body by a cement filler, or retained within the metal body itself. Such a construction makes adjustment of the position of the filament relative to the body (which is what locates the bulb in the instrument) difficult.

Adjustment can be effected if the glass envelope is first mounted with plaster in an inner metal tube, which can then be adjusted within the lamp body before being fixed in position by a cement filler. This procedure is very cumbersome and time consuming.

A major disadvantage of the conventional bulbs described above is that the cement filler allows high heat transfer from the glass envelope. This means that tungsten/halogen bulbs cannot be used effectively, because such bulbs only operate effectively if the envelope temperature is above 2500C to prevent condensation of tungsten evaporated from the filament. Although bulbs mounted in cement can reach a suitable operating temperature, the time taken to do this is often longer than the time for which the instrument is used, so that in practice the correct operating temperature is often not reached. The life of halogen bulbs is therefore reduced and their light intensity is also reduced if the correct operating temperature is not reached.

According to the present invention, a miniature incandescent bulb comprises a glass envelope containing a filament, and a body containing the envelope, which body includes a preferably metal enclosure which directly or indirectly locates the envelope but is spaced from the envelope throughout substantially the entire extent of the envelope and the enclosure. The enclosure preferably has an end region which engages the end region of the envelope and is flexible to allow adjustment of the envelope in the body.

The gap between the envelope and the enclosure contains substantially static air which provides excellent thermal insulation and allows a tungsten/haiogen bulb to reach its correct operating temperature very rapidly. At the same time, the flexible end allows precise alignment of the bulb filament after assembly, by the simple application of pressure to the end of the enclosure.

Preferably, the internal surface of the enclosure is bright plated, so that reflected energy further increases the envelope temperature.

Although the increased envelope temperature and rapid envelope heating which arise from the construction according to the invention are particularly advantageous for a halogen bulb, it is also possible to use a miniature vacuum-filled envelope. The high envelope temperature does not have significant deleterious effects and indeed reduces condensation of tungsten on the envelope thereby increasing the life of the bulb.

The body may be constructed to allow longitudinal adjustment of the envelope, for correct pre-focussing, particularly when the envelope is not of the lens-ended type. For example, the enclosure may comprise telescopically adjustable parts of which one part contains the envelope and another part serves to locate the bulb in an instrument.

In the accompanying drawings, which illustrate the invention by way of example: Figure 1 is an end view of an otoscope bulb embodying the invention, Figure 2 is a cross section on the line X-X of Figure 1, Figure 3 schematically illustrates the adjustment of the bulb, Figure 4 is a view similar to Figure 2, of an ophthalmoscope bulb.

The illustrated bulb has a conventional miniature bulb envelope 1 with a lens end 2, containing a transverse filament 3 connected to leads 4, 5.

The envelope is mounted in a body which comprises an enclosing brass tube 6, a nylon insert 7 and a silver-plated brass rivet 8. The filament leads are trapped between the tube 6, the rivet 8 and the nylon insert 7 so that the brass tube and rivet serve as contacts.

To locate the bulb body in an otoscope, the rear end of the tube 6 has an annular flange 9, and a pair of diametrically opposed chrome steel balls 10 spot welded on the tube.

The forward end of the tube is conically tapered, with a central circular aperture. The end of the tapered part of tube, forming the rim of this aperture, touches the periphery of the lens end of the envelope 1. This tapered region has two or more radial slots 11 so that the tapered region has a certain amount of flexibility. In the illustrated bulb, there are two such slots, aligned with the transverse filament 3, in a plane at 450 to that defined by the balls 10.

Except at the tip of the envelope and the tube 6, there is a radial air gap 12 between the envelope and the tube.

Towards the rear of the envelope 1, a ring 13 of an elastomer (for example a silicone or nitrile rubber) rests against the tip of the plastics insert 7 and forms a resilient seat for the glass envelope.

An ophthalmoscope bulb is generally similar but has a single locating pin instead of the locating balls 10, and incorporates a dome-ended envelope instead of a lens-ended envelope (see Figure 4).

The assembly procedure is very simple. The glass envelope is fitted into the enclosing tube 6, followed by the elastomer ring 13, the plastics insert 7 and the rivet 8. Alternatively, some of the inner components could be pre-assembled before being inserted in the enclosing tube 6. The frusto conical internal surface of the tube end, engaging the end 2 of the envelope, automatically centres the envelope in the tube. It is only necessary to ensure that the filament is aligned approximately with the slots 11 in the tube end. The plastics insert and the rivet can be secured in any convenient way or can be a simple push fit. The plastics insert is preferably slotted longitudinally to facilitate push-fitting.

This ease of assembly and automatic centering of the envelope are in marked contrast to conventional miniature bulbs in which the envelope is secured by solid cement, which form of construction makes centering impossible or very tedious.

For some purposes, the filament will be sufficiently accurately located in the lamp by the simple assembly procedure described above.

However, if particularly accurate centering of the filament is required, an off-centre filament can be centered by deformation of the slotted end of the tube 6.

Figure 3 shows an arrangement for aligning the bulb filament. The assembled bulb is mounted facing a square target 14 and the position of the light spot formed by the bulb on the target is observed. If this is off centre, an alignment tool 1 5 with a concave seat in its end is forced against one side of the tapered end of the bulb, for example at an angle of 450 to the bulb axis. This slightly deforms the tip of the enclosing tube 6 and the envelope pivots on the elastomer ring 1 3, so that the light beam is centered on the target. In general, it is only necessary to adjust the envelope in the direction transverse to the filament When the filament has been centered, optimum performance in an instrument is ensured by accurate seating of the bulb in the instrument by means of the flange 9 and the balls 10 (or pin).

Alternatively the tapered end of the enclosing tube may have four slots intersecting at 900. The slotted end can then be deformed to centre the filament in two orthogonal planes, whereas the illustrated bulb only allows such centering in one plane.

Figure 4 shows an ophthalmoscope bulb, with means for adjusting focussing. The bulb body tube is in two telescopic parts 6a, 6b. The rear part 6a has a locating pin 1 6 to fit a standard ophthalmoscope. The front part 6b fits inside the rear part and contains a dome-ended envelope 17, located at the rear by a high-temperature plastics disk 18 in the tube front part 6b and seated against the elastomer ring 13. The plastics insert 7 has a rebate 1 9 in which the rear end of the tube front part 6b can slide, to adjust the distance of the filament 3 from the locating flange 9 and pin 16 so as to position the filament correctly relative to the optical system of an ophthalmoscope. After this adjustment, the tube parts 6a, 6b are fixed using a locking compound for example.

The gap 12 around the envelope, as well as allowing for movement to centre the filament, form#s an excellent heat insulator. The air in this gap remains substantially static. The slots 1 1 are made as short as is compatible with the flexibility required to centre the filament, so as to minimise air flow inside the enclosing tube 6. As can be seen in Figure 2, these slots extend only slightly beyond the conical end part of the tube. In practice, the rate of loss of heat in a bulb embodying the invention can be as little as 2% of that in a bulb in which the envelope is fixed by cement. The very small area of physical contact between the glass envelope and its enclosure minimises heat loss by conduction. Heat loss by radiation is minimised by bright plating the internal surface of the brass tube 6.

The retention of heat inside the enclosing tube provides an excellent working environment for halogen filled bulb envelopes, which require an envelope wall temperature above 2500C for the halogen working cycle to operate correctly. A halogen-filled envelope mounted as shown in the drawings has double the life of a similar envelope mounted in cement or in full contact with a metal body wall.Since the light output is indirectly a function of the working temperature, the light intensity is also improved in the present bulb compared with a bulb having a cemented envelope: Furthermore, the low heat loss ensures that the correct working temperature of the envelope is reached much sooner than in a bulb with a cemented envelope or an envelope in contact with the body wall: in the bulb shown in Figure 2 the working temperature can be reached in about 30 seconds whereas cemented bulbs take several minutes to reach the correct operating temperature, which may well be longer than the time for which the bulb is switched on for examination of a- patient.

The present bulb is also resistant to mechanical shock and vibration, because of the cushioning or damping effect provided by the elastomer ring 13.

The high envelope temperature is also advantageous for vacuum-filled bulbs, as it reduces condensation of filament metal on the envelope.

The internal surface of the enclosing tube can be bright plated with nickel, gold, or any other suitable reflective coating.

Claims

1. An incandescent lamp bulb comprising a filament containing envelope mounted in an enclosing body, the body being spaced from the envelope by an air gap throughout substantially the whole extent of the envelope.

2. An incandescent lamp bulb comprising a filament-containing envelope mounted in an enclosing body provided with means for locating the bulb in use, the body being deformable whereby the position of the envelope relative to the bulb locating means is adjustable.

3. A lamp bulb as claimed in Claim 2, in which the envelope has a predetermined light-emitting region and the body positively locates the envelope at the periphery of the said region by a deformable portion or portions of the body.

4. A lamp bulb as claimed in Claim 2 or 3, in which the body is spaced from the envelope by an air gap throughout substantially the whole extent of the envelope.

5. A lamp bulb as claimed in Claim 2, in which the envelope is an elongate convex-ended envelope, and the body is a tube laterally spaced from the envelope and provided with inwardly directed deformable portions which locate the envelope at the convex end thereof.

6. A lamp bulb as claimed in Claim 5, including resilient means locating in the tube the region of the envelope remote from the lens end.

7. A lamp bulb as claimed in Claim 5 or 6 in which the tube has a tapered end region encircling the lens end region of the envelope, and longitudinal slots in the tube end region defining said deformable portions.

8. A lamp bulb as claimed in Claim 7, having only two said deformable portions defined by diametrically opposed slots, the filament being substantially coplanar with the slots.

9. A lamp bulb as claimed in Claim 7 having four said deformable portions defined by intersecting slots.

10. A lamp bulb as claimed in Claim 1 or any of Claims 4 to 9 in which the internal surface of the body is highly reflective.

1 1. A lamp bulb as claimed in any of Claims 1 to 10 in which the envelope is a halogen containing envelope.

12. A lamp bulb as claimed in any of Claims 1 to 11 in which the body comprises a first portion containing the envelope, and a second portion provided with means for locating the bulb in use, said portions providing for adjustment of the envelope relative to the bulb-locating means.

13. A method of making an incandescent lamp bulb in which a filament-containing envelope is placed in an enclosing body which locates the envelope and includes means for locating the bulb in use, and the body is deformed to adjust the position of the envelope relative to the bulblocating means to provide a predetermined distribution of light.

14. An incandescent lamp bulb substantially as herein described with reference to Figs. 1 and 2 or Fig. 4 of the accompanying drawings.

New claims or amendments to claims filed on 5.6.82 Superseded claims New or amended claims:~ CLAIMS

1. An incandescent lamp bulb comprising a filament contained in an envelope which is mounted in an enclosing body, with leads extending through the envelope from the filament to external contact-forming means of the enclosing body, characterised in that the body is spaced from the envelope by an air gap throughout substantially the whole extent of the envelope.

2. An incandescent lamp bulb comprising a filament contained in an envelope which is mounted in an enclosing body provided with means for locating the bulb in use, with leads extending through the envelope from the filament to external contact-forming means of the enclosing body, characterised in that the body is deformable whereby the position of the envelope relative to the bulb locating means is adjustable.

5. A lamp bulb as claimed in claim 2, in which the envelope is an elongate convex-ended or lens ended envelope, and the body comprises a tube laterally spaced from the envelope and provided with inwardly directed deformable portions which locate the envelope at the convex end or lens end thereof.

6. A lamp bulb as claimed in claim 5, including resilient means locating in the tube a region of the envelope remote from the convex end or lens end.

7. A lamp bulb as claimed in claim 5 or 6, in which the tube has a tapered end region encircling the convex end or lens end of the envelope, and longitudinal slots in the tube end region defining said deformable portions.

9. A lamp bulb as claimed in claim 7, having four said deformable portions defined by intersecting slots.

10. A lamp bulb as claimed in any preceding claim in which the internal surface of the body is highly reflective.

11. A lamp bulb as claimed in any of claims 1 to 10 in which the envelope contains a halogen

12. A lamp bulb as claimed in any of claims 1 to 11 in which the body comprises a first portion containing the envelope, and a second portion provided with means for locating the bulb in use, relative adjustment of said portions providing for adjustment of the envelope relative to the bulb locating means.

13. A method of making an incandescent lamp bulb comprising the steps of placing a filament containing envelope is placed in an enclosing body which locates the envelope and which includes means for locating the bulb in use, leads extending through the envelope from the filament are connected to external contacts of the body, and deforming the body to adjust the position of the envelope relative to the buib-locating means to provide a predetermined distribution of light