GB2092364A - Electric light source - Google Patents

Abstract

An electric light source is provided with an essentially axially symmetrically shaped bulb made of a light- transmitting material vacuum-tightly sealed by a lamp stem 2, a light emitter in the form of a tubular discharge vessel in the bulb 1, a lamp cap 3 electrically connected to the discharge tube 4 via he lamp stem 2 and mechanically and electrically connectible with an external lamp-holder, and metallic conductor supports 5, 6 extending from the stem 2 with ends electrically and mechanically connected to the discharge tube 4 which is filled with noble gas(es) and metallic additive(s) such as sodium, cadmium and/or mercury. As shown, the discharge tube 4 may be mounted transversely to the axis of the bulb 1, and preferably the maximum internal diameter of discharge tube 4 is 5.5 mm and the maximum diameter of the bulb 1 is 70 mm. <IMAGE>

Description

SPECIFICATION Electric light source The invention relates to an electric light source consisting of an envelope the shape of which has an essentially axial symmetry, and which is made of light-transmitting material vacuum-tightly sealed by a lamp stem, means arranged inside the envelope for emitting light under the effect of an electric current, a lamp cap joined to the envelope and electrically connectible via the stem to the lightemitting means as well as electrically and mechanically connectible to an external lampholder. In its essence, the invention is essentially identical with envelope, cap and step ofthewell-known, conventional general lighting incandescent lamps (the so-called GLS lamps) but proposes a novel structure for light sources which are very similar to such lamps.

The light-emitting means of the traditional light source is an incandescent coiled filament mechanically and electrically connected to the lamp stem to emit light when an electric current is passed through it. Although the luminous efficiency of these lamps is relatively low, due to their well-known pleasant colour and colour rendition as well as to their historically developed general application, they are generally the most widely applied light source, particularly for interior lighting.

High pressure sodium vapour lamps as light sources have become known more recently: their light-emitting means consists of a gas discharge vessel filled with a noble (inert) gas and metal additive(s), particularly sodium, cadmium and/or mercury with an operational internal vapour pressure of about 105Pa, the wall(s) of the discharge vessel being made of alumina. These lamps are increasingly applied for outdoor lighting, i.e. for illumination of streets and squares. They have the advantage of a very favourable luminous efficiency, which should justify their use in the light of everincreasing energy prices on the largest possible scale, to save electrical power. Their drawback is their colour rendition.The colour of light emitted by high pressure sodium vapour lamps is whitishyellow, which, though highly acceptable for public lighting, is not satisfactory for interior illumination.

For the latter a richer colour rentention is required, particularly if it is intended to substitute high pressure sodium vapour lamps, as energy efficient light sources, for the traditional and wellaccustomed incandescent lamps of impeccable colour rendition. A further problem arises from the fact that the discharge vessel of the hitherto known high pressure sodium vapour lamps is long. The ends of the tubes, which are long relative to their small diameter, and which may be made of alumina, ceramic material, sapphire, are hermetically closed by closing elements. Electrodes are disposed adjacent to the ends of the tube and are connected to electric current lead-in conductors leading into the interior of the discharge vessel through a hermetic seal.In the case of a known high pressure sodium vapour lamp with an output of 70 watts, the length of the discharge tube is 58 mm, its inner diameter is 3.5 mm, so the ratio of tube length to tube diameter is 16.5. It can readily be understood, therefore, that discharge vessels of such geometry, and particularly of such length, cannot be adapted or matched to the traditional incandescent lamps as regards their components, external dimensions and assembly.

Such matching or adaptation is made more difficult by other properties besides dimensional and structural differences between incandescent and high pressure sodium vapour lamps, as well as certain conflicting operational and physical parameters.

These difficulties become especially evident when known high pressure sodium lamps comprising known discharge vessels are used for interior or general lighting purposes, where in order to improve their colour rendition the discharge vessels are somewhat overloaded or are dimensioned for an operational vapour pressure that is higher than normal.

The higher operational internal pressure of high pressure sodium lamps is employed in an attempt two make their yellow colour whiter. The increased pressure, however, causes difficulties in re-starting, i.e. re-igniting the discharge. (If the lamps are operated from an A.C. supply, then at the end of the half-period of the mains supply the discharge always stops and has to re-start at the commencement of the next half-period.) The high pressure hinders the process of re-ignition of the discharge and this difficulty is increased by the fact that, due to the so-called wall-effect the ionised gas tends to recombination, i.e. neutralization.To overcome this drawback, it has been suggested to use tubes of larger internal diameter as a consequence of which the light generated in the gas is absorbed to a greater extent and the technological problems regarding production, hermetic seal, etc. become increasingly severe. On the other hand, overloading the discharge vessel causes a rise in the operating temperature which, combined with the increased internal pressure, reduce the reliability of the hermetic closure of the discharge vessel.

An aim of the invention is to provide a light source to substitute or replace traditional general lighting service (GLS) lamps which light source is of increased luminous efficiency, is energy-saving and, in respect of colour rendition and other optical parameters, is the equal of traditional incandescent lamps and which may be produced by retaining as much as possible of the technology and equipment of traditional incandescent lamp manufacture.

The invention is based on the surprising discovery that if the length of the tube of the discharge vessel is considerably reduced in relation of its diameter and at the same time a discharge vessel with relatively small internal diameter is used, then a light source can be created which, despite increased pressure in the discharge vessel and its inevitable overload, not only emits a suitably coloured light (because, due to the short distance between the discharge plasma and the tube wall, the absorption of the light generated is minimal), but also resuits in better conditions for production and greater reliability, compared with known discharge vessels. We have discovered that these favourable effects may be achieved best when the length of the tube of the discharge vessel is at most nine times its diameter.

The aim of the invention is sought to be achieved by the development of an electric light source provided with an envelope of essentially axially symmetrical shape made of a light-transmitting material and hermetically closed by being sealed to a lamp stem, means arranged inside the envelope for emitting light under the effect of an electric current, a lamp cap united with the lamp envelope, electrically connected through the lamp stem to the light emitting means and mechanically and electrically connectible to an exterior lamp-holder, and according to the invention, metallically conducting supports are arranged on the lamp stem, to the ends of which supports an essentially tubular discharge vessel constituting the light-emitting means and containing noble gases and filling material, particularly sodium, cadmium and/or mercury, is mechanically and electrically connected.

The electric light source according to the invention may readily be manufactured by traditional incandescent lamp manufacturing machinery, its assembly may be automated and it requires essentially the same components as GLS lamps except for the incandescent coiled filament which is replaced by a tubular discharge vessel of suitable dimensions.

From the point of view of manufacture, it is particularly advantageous if the length of the tubular discharge vessel of the light source is smaller than the maximum dimension of the segment of the bulb envelope between the lamp cap and the discharge vessel measured perpendicularly to the axis of symmetry.

In the light source according to the invention, the maximum internal diameter of the tube of the discharge vessel of the light source made of an alumina ceramic or sapphire is expediently selected so as not to exceed 5.5 mm. In this way extremely advantageous light sources of at most 100 W power consumption may be produced, wherein the bulb diameter does not exceed 70 mm. A further advantage is that a tube with such dimensions can be produced with great geometric dimensional accuracy, which is also favourable from the point of view of the vacuum-tightness of the sealing of the ends of the tube, whereby to improve the reliability and increase the longevity of the light source, despite the greater operational internal pressure and overload.

In the light source according to the invention, the distance between the centres of the electrodes and the ends of the tubular discharge vessel is 5 - 10 mm, depending on the output of the lamp, so that a correlation is derived or derivable between the length of arc formed between the tips of the electrodes and the interval diameter of the tube from the above-mentioned ratio of the length of the tube to its diameter.

The light source according to the invention, similarly to the general lighting service incandescent lamps that they are to replace, may be produced in various ways depending on the requirements of the field of their respective application, e.g. at least partly frosted, colour-coated, or with a coating providing selective spectral radiation transmission, particularly with external bulbs provided with light and/or heat-reflective coating.

It is generally known that the operation of gasdischarge lamps requires ballasts or series resistances for current limiting, occasionally for supplying ignition impulses or ignition enhancing and promoting. Various embodiments of the light source according to the invention may expediently be developed as so-called 'compact' lamps provided with current limiting and, if need be, impuisegenerating units of rotationally symmetrical shape which are expediently fitted to the neck of the bulb and/or to the lamp cap, either formed integrally into the lamps or mountable on and electricallyconnecti- ble with the lamps. The units may comprise a high frequency converter having semi-conductor eie- ments of which at least certain structural and circuit elements may be arranged in the lamp cap.

The invention is further described purely by way of preferred embodiments illustrated in the accompanying drawings, wherein: Figure 1 is a diagrammatic view of a light source according to the invention with a traditional pearshaped bulb; Figure 2 is a diagrammatic view of a light source according to the invention with a mushroom-shaped bulb as generally used for crypton gas-filled incandescent lamps; Figure 3 is a diagrammatic view of a light source according to the invention, showing the initial stage of the 'sealing-in' operation together with the relative arrangement of the lamp components, and Figure 4 is a diagrammatic view of a light source according to the invention, but without a lamp cap after sealing-in evacuation.

Electric light sources according to the invention may advantageously be manufactured with the traditional bulb envelopes used in the manufacture of incandescent lamps, e.g. pear-like bulbs, i.e. bulbs with a spherical dome (Figure 1) or with mushroomshaped bulbs developed for crypton gas-filled lamps (Figure 2). A glass bulb 1 of rotationally symmetrical shape is fitted to a lamp cap 3 which in the given case is of the screw-type, a lamp stem 2 being sealed into the bulb 1 in the traditional manner. Atubular discharge vessel 4 is mechanically and electrically connected to the lamp stem 2. Support wires 5 and 6 are hermetically sealed in the known way into the stem 2, the ends of the supports 5 and 6 disposed in the interior of the bulb 1 being connected electrically via the current lead-in wires 43, 44 and mechanically by straps 41, 42 to the tubular discharge vessel 4.

The straps 41, 42 encompass the tube of the discharge vessel 4, the tube being arranged trans tersely to the longitudinal axis of the bulb 1, i.e. to the complete lamp.

The supports 5 and 6 must be made of a thicker, more rigid material than in the traditional incandescent lamp.

In an embodiment of the invention the inside diameter of the discharge vessel 4 formed by a tube made of an alumina ceramic or sapphire is 3.5 mm and the length of the tube is 24 mm. The maximum width h of the current lead wires 43, 44 including their portions protruding from the ends of the discharge vessel 4, and including the horizontal joining elements at the ends of the supports 5 and 6 is 31 mm, measured perpendicularly to the longitudinal axis of the bulb 1, or of the lamp, (Figure 3).

Since the inside diameterdofthe neck of the bulb B for a traditional 40 watt incandescent lamp is 32 mm, the mounted stem 2 may easily be placed into the region of the neck of the bulb B, marked by A in Figure 3, it can thereafter readily be sealed together with the lamp stem 2 as the first step of conventional lamp assembly operation, by heating and rotation, the so-called 'sealing-in'. As the next steps of the assembly process performed on traditional lamp production machinery, the interior of the closed bulb B is pumped out (evacuated) and, if desired, filled with an inert gas via the exhaust tube E; after the closing of the exhaust tube E, the so-called 'tippingoff', there is obtained an intermediate product shown in Figure 4 which is thereafter provided with a lamp cap 3 to result in the finished light source according to the invention.

In the embodiment described, purely by way of example, the distance between the electrodes placed into the ends of a n an alumina-ceramic discharge tube 4 with a length of 24 mm and internal diameter of 3.5 mm is 16 mm. The discharge vessel 4 is filled with xenon gas and a sodium-cadmium alloy containing 8% sodium. The electric current consumption of this light source is 35 watt, its luminous flux is 2300 lumens, therefore the luminous efficiency of this light source is approximately four times better that that of a 40 watt general lighting serve incandescent lamp of identical external appearance.

Maintaining the same internal structure but reducing the interelectrodal distance in the discharge vessel 4to 12 mm light sources according to the invention have also been produced which emit practically white light at a slightly higher current consumption.

Within the scope of protection of the accompanying claims, numerous other light sources according to the invention may be developed in addition to the described embodiments by way of example by varying the dimensions of the discharge vessel, the mode of sealing the tube and the current lead-in wires, the filling, sealing the bulb as well as the preparation of the bulb, the type of cap and the optical and electric parameters of the light source.

Claims (11)

1. An electric light source comprising an envelope the shape of which displays an essentially axial symmetry, made of light-transmitting material and vacuum-tightly sealed to a lamp stem, light emitting means arranged in the envelope and effective to emit light under the effect of an electric current, a lamp cap electrically and mechanically connectible to an external lamp-holder and electrically connected to the light-emitting means, wherein metallically conductive supports are arranged on the lamp stem and are mechanically and electrically connected at their end regions to an essentially tubular discharge vessel constituting the lightemitting means, the discharge vessel containing a noble gas and a fill.

2. An electric light source according to claim 1 wherein said fill includes sodium and/or cadmium and/or mercury.

3. An electric light source according to claim 1 or 2 wherein the length of the tube of the tubular discharge vessel is at most nine times the internal diameter of the tube.

4. An electric light source according to any preceding claim wherein the discharge vessel is arranged either coaxially with or transversely to the axis of symmetry of the envelope.

5. An electric light source according to any preceding claim wherein the length of the tubular discharge vessel is smaller than maximum dimension of the envelope segment measured between the lamp cap and the discharge vessel perpendicularly to the axis of symmetry of the envelope.

6. An electric light source according to any preceding claim wherein the envelope is at least partially frosted and/or colour coated and/or is provided with a coating for the selective spectral transmission of the light emitted from the discharge vessel.

7. An electric light source according to any preceding claim wherein a portion of the surface of the envelope is provided with a light and/or heatreflecting coating.

8. An electric light source according to any preceding claim wherein a ballast, preferably of rotationally symmetrical shape, is connected to the cap and is preferably at least partly disposed in the cap, said ballast being effective as a current-iimited and/or a starter for the discharge.

9. An electric light source according to claim 8 wherein the ballast is provided with a high frequency converter.

10. An electric light source according to any preceding claim wherein the envelope is bulbshaped with a maximum diameter of substantially 70 mm, electric power consumption of 100 watts maximum and the maximum internal diameter of the discharge vessel is substantially 5.5 mm.

11. An electric light source substantially as herein described with reference to and as shown in the accompanying drawings.