GB2346270A

GB2346270A - Soft start light fitting

Info

Publication number: GB2346270A
Application number: GB0011037A
Authority: GB
Inventors: Andrew David Walsh
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-09-02
Filing date: 1997-09-02
Publication date: 2000-08-02
Anticipated expiration: 2017-09-02
Also published as: GB0011037D0; GB9718457D0; GB2346270B; GB2329078A

Abstract

A light fitting comprises a generally cylindrical male plug portion (1) which is received in a standard bayonet light socket and a bayonet socket portion (5) which is arranged to receive a bayonet-type light bulb (8). The electrical connection between the terminals of the plug portion and bayonet socket portion includes a resistor (7) having a resistance of eg 20 to 40 ohms for a light fitting intended for use with a standard 240V, 60W tungsten filament bulb. The resistor has a resistance which is a significant proportion of the initial resistance of the bulb (when the filament of the latter is cold) and therefore substantially reduces the initial current to the bulb. When the bulb filament reaches its normal working temperature its resistance is many times that of the resistor which therefore only slightly reduces the steady-state power dissapation. Both these effects increase the life of the bulb. The fitting may alternatively be an Edison screw fitting, and the resistor may be a thermistor.

Description

Removable light fitting The present invention relates to a removable light fitting for providing a"soft start"to a filament lamp.

Relatively sophisticated"soft start"circuits are known from eg US 4,360,743, US 4,008,416 US 4,152,607, US 3,991, 343 and US 4, 355, 242 but these all employ gatecontrolled semiconductor switching devices and associated control circuitry which is too bulky to incorporate in a removable light fitting. These circuits are only disclosed in the context of a fixed lighting installation.

The above circuits have the further disadvantage that they generate radio interference as a result of chopping the mains waveform.

An object of the present invention is to provide a removable light fitting which overcomes at least some of the above disadvantages.

Accordingly the invention provides a removable light fitting for fitting a light bulb in a light socket, the fiting having a pair of first terminals arranged in use to contact the terminals of the light socket, a pair of second terminals arranged in use to contact the terminals of a light bulb and a resistive electrical connection in series between the first and second terminals which in use supplies current to the light bulb from the light socket, the electrical connection being arranged in use to reduce the initial flow of current to the light bulb.

Preferably the electrical connection comprises a series-connected resistance element which has a non-linear characteristic such that its resistance falls as the flow of current to the light bulb reduces. This feature reduces the power dissapation in the fitting during normal use, for a given reduction in the initial current.

For example the resistance element could be a thermistor having a negative temperature coefficient of resistance.

Preferably the electrical connection is arranged to conduct throughout each cycle of the mains waveform. This feature avoids the generation of radio interference which in some circumstances might otherwise need to be suppressed in order to comply with relevant legislation.

In one embodiment (for use with a bayonet socket) the pair of first terminals are located in a male portion arranged to fit a bayonet socket and the pair of second terminals are located in a bayonet socket portion of the light fitting.

In another embodiment (for use with an Edison screw socket) the pair of first terminals are located in a male portion arranged to fit an Edison screw socket and the pair of second terminals are located in an Edison screw socket portion of the light fitting.

The invention also encompasses a removable light fitting as defined above in combination with a light bulb, the initial resistance of the resistance element being from 1% to 10% (preferably 1% to 3%) of that of the light bulb at the rated current of the light bulb.

A preferred embodiment of the invention is described below by way of example only with reference to Figures 1 and 2 of the accompanying drawing, wherein: Figure 1 is a somewhat diagrammatic sketch perspective view of a bayonet light fitting in accordance with the invention, and Figure 2 is a somewhat diagrammatic sketch perspective view of an Edison screw light fitting in accordance with the invention.

Referring to Figure 1, the fitting shown comprises a generally cylindrical male plug portion 1 having diametrically opposite external pins 2 (only one of which is visible in the drawing) which are located and dimensioned to enable the fitting to be securely located in a standard bayonet light socket. A pair of first terminals 3,3'are located on the end face of portion 1 such that in use they contact the mains terminals in the light socket when the fitting is secured in the socket.

The above terminals 3,3'are electrically connected to a pair of second terminals 4,4' respectively which lie in a bayonet socket portion 5 of the fitting which is provided with L-shaped slots 6,6'in its cylindrical wall and arranged to receive a bayonet-type light bulb with the terminals of the bulb held in contact with terminals 4,4' respectively.

The electrical connection between the first and second terminals includes a resistor 7 having a resistance of eg 20 to 40 ohms for a light fitting intended for use with a standard 240V, 60W tungsten filament bulb. The resistance of the filament of such a bulb is typically about 70 ohms when cold, so the resistor reduces the initial current by about 22% to about 36%. When the bulb 8 reaches its normal working temperature its resistance rises to about 960 ohms so the power dissapated in resistor 7 is only about 1.2W to 2.4W in the steady state condition. This power dissapation is easily achievable in a resistor sufficiently small to fit in a light fitting.

Furthermore the reduction in the steady-state current through the light bulb is only about 2% to 4%, which should not unduly affect the colour temperature and yet should result in a significant increase in the useful life of the bulb.

Figure 2 shows a similar arrangement for use with an Edison screw light socket.

Corresponding parts are indicated by primed reference numerals. The fitting differs from that of Figure 1 in that the pair of first terminals 9 and 10 are connected to a pair of second terminals 12 and 11 respecively, terminal 9 being a central outer terminal arranged to contact the corresponding terminal of an Edison screw light socket (not shown) and terminal 12 being a spring terminal in contact with the central terminal 13 of bulb 8'. The fitting has an interior threaded shell 11 into which the threaded portion of the bulb 8'is screwed and shell 11 is electrically connected (by means not shown) to a metal exterior threaded portion 10 of the fitting which is arranged to be screwed into the corresponding threaded shell of the Edison screw light socket (not shown).

In both embodiments the outer part of the cylindrical portion of the fitting which accommodates the bulb 8 or 8'is made of plastic or other suitable insulating material.

In a further embodiment the male portion of the fitting could be of the bayonet type and the female portion could be of the Edison screw type, or vice versa.

If necessary a thermistor having a negative temperature coefficient or a varistor (eg a 250V 130J varistor, RS No 238946 obtainable from RadioSpares) could be used instead of or in addition to the resistor, in order to increase the ratio of the initial series resistance to the steady state series resistance, ie to limit the initial current to a greater extent for a given limitation on the steady state current.

Claims

Claims 1. A removable light fitting for fitting a light bulb in a light socket, the fiting having a pair of first terminals arranged in use to contact the terminals of the light socket, a pair of second terminals arranged in use to contact the terminals of a light bulb and a resistive electrical connection in series between the first and second terminals which in use supplies current to the light bulb from the light socket, the electrical connection being arranged in use to reduce the initial flow of current to the light bulb.
2. A removable light fitting as claimed in claim 1 wherein the electrical connection comprises a series-connected resistance element which has a non-linear characteristic such that its resistance falls as the flow of current to the light bulb reduces.
3. A removable light fitting as claimed in claim 2 wherein the resistance of the resistance element is temperature-sensitive.
4. A removable light fitting as claimed in any preceding claim wherein the electrical connection is arranged to conduct throughout each cycle of the mains waveform.
5. A removable light fitting as claimed in any preceding claim wherein the pair of first terminals are located in a male portion arranged to fit a bayonet socket and the pair of second terminals are located in a bayonet socket portion of the light fitting.
6. A removable light fitting as claimed in any of claims 1 to 4 wherein the pair of first terminals are located in a male portion arranged to fit an Edison screw socket and the pair of second terminals are located in an Edison screw socket portion of the light fitting.
7. A removable light fitting substantially as described hereinabove with reference to Figure 1 or Figure 2 of the accompanying drawing.
8. A removable light fitting as claimed in any preceding claim in combination with a light bulb, the initial resistance of the resistance element being from 1% to 10% of that of the light bulb at the rated current of the light bulb.
9. A combination as claimed in any of claim 8 wherein said initial resistance is from 1% to 3% of that of the light bulb at the rated current of the light bulb.