GB1579030A - High pressure electric discharge lamps - Google Patents
High pressure electric discharge lamps Download PDFInfo
- Publication number
- GB1579030A GB1579030A GB2635876A GB2635876A GB1579030A GB 1579030 A GB1579030 A GB 1579030A GB 2635876 A GB2635876 A GB 2635876A GB 2635876 A GB2635876 A GB 2635876A GB 1579030 A GB1579030 A GB 1579030A
- Authority
- GB
- United Kingdom
- Prior art keywords
- envelope
- discharge
- lamp
- electrodes
- pinch
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/04—Electrodes; Screens; Shields
- H01J61/06—Main electrodes
- H01J61/073—Main electrodes for high-pressure discharge lamps
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- Vessels And Coating Films For Discharge Lamps (AREA)
Description
(54) IMPROVEMENTS IN OR RELATING TO HIGH PRESSURE ELECTRIC
DISCHARGE LAMPS
(71) We, THE GENERAL ELECTRIC COM- PANY LIMITED, of 1 Stanhope Gate, London
W1A 1EH, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment::- This invention relates to high pressure electric discharge lamps of the type (hereinafter referred to as the type specified) comprising a tubular discharge envelope formed of fused silica and closed at each end by a pinch seal, a pair of tungsten electrodes between which an electric discharge passes in operation of the lamp, which electrodes are supported by the respective pinches so as to extend into the envelope and are attached to electrically conducting leads extending to the exteriors of the pinches, and, contained within the discharge envelope, a filling consisting of mercury, one or more metal halides, and a small amount of rare gas for facilitating starting of the discharge, the dimensions of the discharge envelope, and filling composition and pressure, being such that the discharge produced in operation is in the form of a constricted arc.A lamp of this type also includes an outer envelope of light-transmissive vitreous material within which the discharge envelope is mounted, one or both ends of which outer envelope is or are fitted with a cap or caps designed to be inserted into a lampholder or lampholders and incorporating terminals to which the leads from the electrodes are attached, for connection of the electrodes to a source of electric current supply for operation of the lamp. The invention is more particularly concerned with lamps of the type specified which are designed to be operated in such a position that the longitudinal axis of the discharge envelope is disposed horizontally. The term "high pressure" as used herein is to be understood to mean that the total vapour pressure developed within the discharge envelope in normal operation of the lamp is of the order of one atmosphere or higher.
It is desirable that the electrodes of a lamp of the type specified are activated by the provision of a quantity of electron emissive activator material. One preferred form of electrode for use in such lamps consists of a length of tungsten wire in the form of a coil with a linear extension which is sealed into the pinch so that the axis of the coil extends longitudinally into the discharge envelope, and possibly with a further linear extension from the inner end of the coil; a small amount of activator material, which is suitably a metal of low work function such as thorium, is preferably provided, and may be supported by the coil.
During operation of a lamp of the type specified in the horizontal position as aforesaid, the discharge arc is bowed upwards, as a result of the buoyancy of the hotter part of the vaporised filling of the discharge envelope, and we have found that, in the case of such a lamp having activated electrodes, during operation of the lamp the activator metal migrates to the inner ends of the elctrodes and collects on the upper surfaces of the electrode tips: consequently the discharge terminations, instead of becoming stabilised on the end surfaces of the electrode tips, tend to wander around the bodies of activator metal formed on the upper surfaces of the tips.
It is an object of the present invention to provide activated electrodes of improved construction, in a lamp of the type specified, whereby the stability of the discharge during normal operation of the lamp can be improved.
According to the invention, in a high pressure electric discharge lamp of the type specified which has activated electrodes and is designed to be operated with the longitudinal axis of the discharge envelope disposed horizontally, each of the said electrodes consists of a coil of tungsten wire with a linear portion of wire integral with and extending from each
end of the coil, the linear portion of wire at the outer end of each coil being sealed into a pinch so that the coils extend into opposite
ends of the discharge envelope, and each electrode being so shaped and disposed that at least the linear portion of wire extending from the inner end of each coil is located between the longitudinal axis of said envelope and a part of the wall of said envelope and is inclined towards the said axis, so that the tips of the two electrodes lie on a line substantially parallel to the said axis and between the said axis and the said part of the envelope wall.
It will be understood that the terms "outer end" and "inner end", as used herein with reference to the electrodes or the elctrode coils, mean respectively the end thereof which is sealed into or is adjacent to the pinch, and the end thereof which is remote from the pinch.
Preferably the outer end linear portion of each electrode is sealed into the pinch at a location offset from the centre of the pinch, the longitudinal axes of the coils being aligned with one another and with the said outer end portions, and lying substantially parallel to the longitudinal axis of the discharge envelope and at such a distance therefrom that the coils and the inclined inner end portions of the electrodes lie wholly between the said envelope axis and the said part of the envelope wall.
However, several alternative arrangements of the electrodes might be used: for example, each electrode may be bent into three sections forming angles with one another, the coil being included either in the innermost section and aligned with the inclined inner end portion or included in an oppositely inclined central section, and the outer end linear portion of the electrode being sealed into the centre of the pinch or, if desired, in an offcentre position such that the outer and inner ends of the electrode are situated on the same or opposite sides of the longitudinal axis of the discharge envelope.In another alternative arrangement, the outer end linear portion of each electrode which is sealed into the pinch may be inclined at an angle to the longitudinal axis of the pinch and the discharge envelope, the coil being aligned with said outer end portion and thus inclined to said axis in an opposite direction to that of the inner end linear portion of the electrode.
For operation, a lamp in accordance with the invention must be mounted in a lampholder or pair of lampholders in such a position that the longitudinal axis of the discharge envelope is disposed horizontally, and must be so orientated that the inner end linear portions of the electrodes lie below the longitudinal axis of the discharge envelope and are inclined upwards.
The upturned inner end linear portions of the electrodes are preferably inclined at such an angle that they constitute extensions of the arc of a circle formed by the discharge when it is bowed upwards in operation of the lamp.
This ensures that the activator material collects on the end surfaces of the elctrode tips, and hence that the discharge terminations are stabilised on the said end surfaces. Considerable improvement in the stability of the discharge is obtained, however, even if the inner linear portions of the electrodes are inclined upwards at a slightly different angle from that of the ends of the discharge arc.
Additional advantages are derived from the offcentre location of the inner ends of the electrodes of a lamp in accordance with the invention. Thus since the electrode tips are located below the longitudinal axis of the discharge envelope, when the lamp is in the correct horizontal operating position, the upward bowing of the discharge in operation does not cause the discharge to approach as closely to the upper part of the discharge envelope wall as is the case when the electrodes are wholly coaxial with the envelope, as in a conventional lamp of the type specified, so that overheating of the upper part of the envelope wall is avoided or reduced.At the same time the lower part of the envelope wall is raised to a higher temperature than in a conventional lamp as aforesaid, so that the temperature difference between the upper and lower portions of the envelope wall is reduced: reduction of this temperature difference is desirable, to enable a relatively high vapour pressure to be maintained in the envelope, with resulting high luminous efficacy of the lamp, and also to prevent condensation of metal halides of the filling on the central region of the lower part of the envelope wall.
In the case of a lamp containing a sodium halide as a constituent of the filling, an additional advantage arises from the location of the electrodes, and hence the discharge in operation, nearer to the lower part of the discharge envelope wall: thus the volume of the region of the discharge envelope which is predominantly occupied by thermally excited sodium ions during operation of the lamp, namely the region between the discharge and the upper part of the envelope wall, is increased, and this also results in an increase in the luminous efficacy of the lamp.
Furthermore, it is possible to employ a higher filling pressure than is usual in lamps of the type specified, without increasing the risk of the upper part of the discharge envelope wall becoming overheated: thus lamps in accordance with the invention may be operated at pressures up to at least ten atmospheres.It is also possible to employ a discharge envelope of internal diameter 2 to 3 millimetres larger than is suitable for a lamp of similar power dissipation but having axially disposed electrodes, since the disposition of the electrode tips below the envelope axis prevents any significant reduction in the operating temperature of the lower part of the envelope wall: an increased discharge envelope diameter is advantageous in that it permits the lamp to be run at a higher loading without risk of overheating of the envelope wall, and also, when a sodium halide is present, in the provision of an increased volume of the envelope occupied by thermally excited sodium ions in operation.
The electron emissive material employed for activating the electrodes may be metallic thorium, or any other suitable material, having similar electron emissive properties.
The activator material may be initially supported by the electrode coils, or alternatively may be introduced into the discharge envelope as part of the filling: in the latter case the activator is rapidly deposited on the electrodes during the initial operation of the lamp.
The pinch seal closing each end of the discharge envelope of a lamp of the invention is suitably of the type comprising a strip of molybdenum foil embedded in the pinch, the electrode and a lead wire extending to the exterior of the pinch being attached respectively to the inner and outer ends of the foil, for example by welding.When the electrodes are sealed into the pinches in off-centre locations the molybdenum foils are preferably relatively wide, that is to say of greater width than those usually employed in seals of this type, in order to give a robust seal construction with the offset electrodes, preferably each foil being located so that the long edge of the foil which is uppermost, when the lamp is in the correct horizontal operating position as aforesaid, lies on or near the longitudinal axis of the pinch, and the electrode and lead wire being attached to the foil respectively near the lower long edge and near the upper long edge thereof.
The relative proximity of at least parts
of the electrodes to the part of the discharge envelope wall which is lowermost when the lamp is in the operating position can cause overheating of this part of the wall in the regions nearest to the inclined inner end portions of the electrodes. According to another preferred feature of the invention therefore, these regions of the envelope wall are formed with outward protuberances, so that the distance between each inclined electrode portion and the region of the wall adjacent thereto is increased.
The outer envelope of a lamp in accordance with the invention is preferably of the doubleended type, in which the lead from each electrode is sealed through the end of the outer envelope adjacent to that electrode, and each end of the outer envelope is fitted with a cap incorporating a terminal to which the lead sealed through that end is attached.
Furthermore, the outer envelope suitably is of tubular form and is fitted with a pair of bipin caps of the type generally employed for tubular low pressure fluorescent discharge lamps, one pin on each cap constituting a said terminal. Bipin caps are advantageous since the pins can be employed, in conjunction with appropriately orientated lamp-holders, for ensuring specific location of the lamp in the correct horizontal operating position, the pins of course being correctly aligned in relation to the orientation of the discharge envelope within the outer envelope.If desired, one or both of the lamp caps may be provided with addtional locating means arranged to cooperate with complementary locating means incorporated in one or both of the lamp holders, such locating means being designed to ensure correct orientation of the lamp, that is to say to prevent the possibility of the lamp being inserted into the lampholders in the upside-down position.
The outer envelope may contain a suitable gas filling if desired.
Also if desired, the interior surface of the outer envelope wall may be wholly or partially coated with an infra-red reflecting lighttransmissive film, for example of tin oxide or indium oxide, to raise the overall temperature attained by the discharge envelope in operation of the lamp, and to assist in reducing differences in operating temperature between different parts of the discharge envelope.
A specific form of lamp in accordance with the invention is shown, in elevation, in the drawing accompanying the Provisional Specification, and will now be described by way of example.
The lamp shown in the drawing, in the correct horizontal operating position, comprises a tubular discharge envelope 1 of fused silica enclosed within a double-ended tubular glass outer envelope 2 having a bipin cap 3 fitted over each end. The discharge envelope contains a filling of mercury, rare gas, and one or more metal iodides, and is closed at each end by a pinch 4, into which is sealed an assembly consisting of a wide molybdenum foil strip 5, located substantially in the lower half of the pinch, a molbydenum lead wire 6 welded to the outer end, and near to the upper edge, of the molybdenum foil, and an electrode in accordance with the invention welded to the inner end, and near to the lower edge, of the foil.Each electrode consists of a tungsten wire coil 7, with an outer linear extension 8 sealed into the pinch and attached to the foil 5, and an inner linear extension 9 bent so as to be inclined upward towards the longitudinal axis of the tube 1. Protuberances 10 are formed in those regions of the lowermost part of the discharge envelope wall which are most closely adjacent to the inclined electrode portions 9.
Each of the lead wires 6 is welded to one end of a bent nickel strip 11, the other end of which is welded to a stout nickel wire 12, which is sealed through a pinched foot tube 13 closing the adjacent end of the outer envelope 2 and is connected to a pin 14, these pins constituting the lamp terminals. The assemblies of wires 4, strips 11 and wires 12 thus constitute both the conducting leads for connecting the electrodes to an electric current supply, and the means of supporting the discharge envelope 1 within the outer envelope 2: the bends 15 in the nickel strips 11 accommodate expansion of the lead assemblies due to heating in operation of the lamp. Each of the caps 3 carries a pair of pins 14, which are aligned in a horizontal plane at right angles to the vertical plane of the pinches 4: hence only one pin of each pair is visible in the drawing.
In a specific example of a lamp of the form described above with reference to the drawing, the discharge envelope 1 has an internal diameter of 12 to 13 mm, the molybdenum foils 5 are 5 mm wide, the electrode coils 7 are positioned with their axes 2 mm from the interior surface of the adjacent straight parts of the discharge envelope wall, and the maximum depth of the protuberances 10 is 2 mm; the inner electrode portions 9 are inclined upwards at an angle of 35 :t5 to the horizontal, the tips thereof being 3 mm below the longitudinal axis ofthe discharge envelope, and the horizontal length of the discharge path between the tips is 15 mm.The discharge envelope filling consists of 40 mg of mercury, 20 mg of sodium iodide, 10 mg of scandium tri-iodide, and xenon or argon at a room temperature pressure of 35 torr, together with 2 mgms thorium metal as activator for the electrodes. The outer envelope 2 is 20 cm long and has an internal diameter of 35 mm, and contains a filling of nitrogen at a pressure of 200 torr at room temperature. In normal operation this lamp dissipates 175 watts at a tube voltage of 110 volts, and has a luminous efficacy of 85 lumens per watt.
WHAT WE CLAIM IS:- 1. A high pressure electric discharge lamp of the type specified which has activated electrodes and is designed to be operated with the longitudinal axis of the discharge envelope disposed horizontally, wherein each of the said electrodes consists of a coil of tungsten wire with a linear portion of wire integral with and extending from each end of the coil, the linear portion of wire at the outer end of each coil being sealed into a pinch so that the coils extend into opposite ends ofthe discharge envelope, and each electrode being so shaped and disposed that at least the linear portion of wire extending from the inner end of each coil is located between the longitudinal axis of said envelope and a part of the wall of said envelope and is inclined towards the said axis, so that the tips of the two electrodes lie on a line substantially parallel to said axis and between the said axis and the said part of the envelope wall.
2. A lamp according to Claim 1, wherein the said outer end linear portion of each electrode is sealed into the pinch at a location offset from the centre of the pinch, the longitudinal axes of the coils being aligned with one another and with the said outer end portions, and lying substantially parallel to the longitudinal axis of the discharge envelope and at such a distance therefrom that the coils and the inclined inner end portions of the electrodes lie wholly between the said envelope axis and the said part of the envelope wall.
3. A lamp according to Claim 1 or 2, wherein the said inner linear end portions of the electrodes are inclined at such an angle that they constitute extensions of the arc of a circle formed by the discharge when it is bowed upwards in operation of the lamp.
4. A lamp according to Claim 2, wherein the pinch seal closing each end of the discharge envelope includes a relatively wide (as hereinbefore defined) strip of molybdenum foil to which the electrode and a lead wire extending to the exterior of the pinch are attached, and the said foil is embedded in the pinch at such a location that one long edge of the foil lies on or near the longitudinal axis of the pinch, the lead wire and the electrode being attached to the foil respectively near the said edge and near the opposite long edge thereof.
5. A lamp according to any preceding
Claim, wherein the regions of the discharge envelope wall adjacent to the inclined inner end portions of the electrodes are formed with outward protuberances.
6. A high pressure electric discharge lamp according to Claim 1, substantially as hereinbefore described with reference to the drawing accompanying the Provisional Spcification.
7. An arrangement including a lamp according to any preceding Claim and a lampholder or pair of lampholders in which the lamp is mounted in such a position that the longitudinal axis of the discharge envelope is disposed horizontally, wherein the lamp is so orientated that the inner end linear portions of the electrodes lie below the longitudinal axis of the discharge envelope and are inclined upwards.
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (7)
- **WARNING** start of CLMS field may overlap end of DESC **.2 and is connected to a pin 14, these pins constituting the lamp terminals. The assemblies of wires 4, strips 11 and wires 12 thus constitute both the conducting leads for connecting the electrodes to an electric current supply, and the means of supporting the discharge envelope 1 within the outer envelope 2: the bends 15 in the nickel strips 11 accommodate expansion of the lead assemblies due to heating in operation of the lamp. Each of the caps 3 carries a pair of pins 14, which are aligned in a horizontal plane at right angles to the vertical plane of the pinches 4: hence only one pin of each pair is visible in the drawing.In a specific example of a lamp of the form described above with reference to the drawing, the discharge envelope 1 has an internal diameter of 12 to 13 mm, the molybdenum foils 5 are 5 mm wide, the electrode coils 7 are positioned with their axes 2 mm from the interior surface of the adjacent straight parts of the discharge envelope wall, and the maximum depth of the protuberances 10 is 2 mm; the inner electrode portions 9 are inclined upwards at an angle of 35 :t5 to the horizontal, the tips thereof being 3 mm below the longitudinal axis ofthe discharge envelope, and the horizontal length of the discharge path between the tips is 15 mm.The discharge envelope filling consists of 40 mg of mercury, 20 mg of sodium iodide, 10 mg of scandium tri-iodide, and xenon or argon at a room temperature pressure of 35 torr, together with 2 mgms thorium metal as activator for the electrodes. The outer envelope 2 is 20 cm long and has an internal diameter of 35 mm, and contains a filling of nitrogen at a pressure of 200 torr at room temperature. In normal operation this lamp dissipates 175 watts at a tube voltage of 110 volts, and has a luminous efficacy of 85 lumens per watt.WHAT WE CLAIM IS:- 1. A high pressure electric discharge lamp of the type specified which has activated electrodes and is designed to be operated with the longitudinal axis of the discharge envelope disposed horizontally, wherein each of the said electrodes consists of a coil of tungsten wire with a linear portion of wire integral with and extending from each end of the coil, the linear portion of wire at the outer end of each coil being sealed into a pinch so that the coils extend into opposite ends ofthe discharge envelope, and each electrode being so shaped and disposed that at least the linear portion of wire extending from the inner end of each coil is located between the longitudinal axis of said envelope and a part of the wall of said envelope and is inclined towards the said axis, so that the tips of the two electrodes lie on a line substantially parallel to said axis and between the said axis and the said part of the envelope wall.
- 2. A lamp according to Claim 1, wherein the said outer end linear portion of each electrode is sealed into the pinch at a location offset from the centre of the pinch, the longitudinal axes of the coils being aligned with one another and with the said outer end portions, and lying substantially parallel to the longitudinal axis of the discharge envelope and at such a distance therefrom that the coils and the inclined inner end portions of the electrodes lie wholly between the said envelope axis and the said part of the envelope wall.
- 3. A lamp according to Claim 1 or 2, wherein the said inner linear end portions of the electrodes are inclined at such an angle that they constitute extensions of the arc of a circle formed by the discharge when it is bowed upwards in operation of the lamp.
- 4. A lamp according to Claim 2, wherein the pinch seal closing each end of the discharge envelope includes a relatively wide (as hereinbefore defined) strip of molybdenum foil to which the electrode and a lead wire extending to the exterior of the pinch are attached, and the said foil is embedded in the pinch at such a location that one long edge of the foil lies on or near the longitudinal axis of the pinch, the lead wire and the electrode being attached to the foil respectively near the said edge and near the opposite long edge thereof.
- 5. A lamp according to any preceding Claim, wherein the regions of the discharge envelope wall adjacent to the inclined inner end portions of the electrodes are formed with outward protuberances.
- 6. A high pressure electric discharge lamp according to Claim 1, substantially as hereinbefore described with reference to the drawing accompanying the Provisional Spcification.
- 7. An arrangement including a lamp according to any preceding Claim and a lampholder or pair of lampholders in which the lamp is mounted in such a position that the longitudinal axis of the discharge envelope is disposed horizontally, wherein the lamp is so orientated that the inner end linear portions of the electrodes lie below the longitudinal axis of the discharge envelope and are inclined upwards.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2635876A GB1579030A (en) | 1977-06-23 | 1977-06-23 | High pressure electric discharge lamps |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB2635876A GB1579030A (en) | 1977-06-23 | 1977-06-23 | High pressure electric discharge lamps |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1579030A true GB1579030A (en) | 1980-11-12 |
Family
ID=10242424
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB2635876A Expired GB1579030A (en) | 1977-06-23 | 1977-06-23 | High pressure electric discharge lamps |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB1579030A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5055740A (en) * | 1987-02-25 | 1991-10-08 | Venture Lighting Interntional, Inc. | Horizontal burning metal halide lamp |
-
1977
- 1977-06-23 GB GB2635876A patent/GB1579030A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5055740A (en) * | 1987-02-25 | 1991-10-08 | Venture Lighting Interntional, Inc. | Horizontal burning metal halide lamp |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |