GB1558509A

GB1558509A - High pressure mercury vapour discharge lamp for horizontaloperating position

Info

Publication number: GB1558509A
Application number: GB3358376A
Authority: GB
Original assignee: Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
Current assignee: Osram GmbH
Priority date: 1975-08-12
Filing date: 1976-08-12
Publication date: 1980-01-03
Also published as: FR2321186B3; DE2535922A1; FR2321186A1

Description

(54) HIGH PRESSURE MERCURY VAPOUR DISCHARGE LAMP FOR HORlZONTAL OPERATING POSITION (71) We, PATENT-TREUHAND GESELL SCHAFT FUR ELEKTRISCHE GLUHLAMPEN m.b.H., of 1 Hellabrunner Strasse, 8 Munchen 90, Federal Republic of Germany, a German body corporate, 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 statement: The invention relates to an elongate high pressure mercury vapour discharge lamp for a horizontal operating position. One such lamp comprises an arc tube, preferably of quartz glass, with an electrode each of metal which does not melt easily sealed into the respective end thereof. The spacing of the electrodes from one another is larger than the arc tube diameter. Each electrode is connected to a hermetic seal.

As an additive filling to the mercury, the arc tube contains metal halides and a rare gas and is encompassed by an outer envelope.

It is well known to seal the dischargesustaining main electrodes of such lamps, extending in the longitudinal axis of the lamp, centrally at the ends. Sometimes, the main electrodes are positioned off the longitudinal lamp axis for structural reasons to provide space for auxiliary electrodes such as, for example, starting electrodes. In such a case, however, either the tips of the main electrodes are positioned on the longitudinal lamp axis (DT-PS 1184 008; DT-OS 1 539 547) or, the electrodes are sealed into the lamp ends offset relative to each other such, that the line of connection between the electrode tips traverses the lamp centre (FR-PS 1 359 979).In spite of orienting the electrodes along the longitudinal lamp axis, the discharge arc is deflected in the horizontal operating position upwardly of the longitudinal lamp axis, due to convection. As a consequence, the temperature distribution around the arc tube wall is highly irregular and lamp life is impaired by the excessive heating up of the upper bulb wall.

it is however desirable to keep the temperature differences on the arc tube wall as small as possible, since then the average temperature in the arc tube can be chosen higher. A higher temperature is moreover desirable in order to obtain as high an evaporation of the metal halides as possible where these are present, to get higher luminous efficiency of the lamp. In order to place the arc in a position in which it is spaced equally far from all parts of inner wall surface of the arc tube, it has been proposed to influence the arc respectively by external magnetic fields (DT-PS 1 098 607; DT-PS 1 012 688). In another solution, the shape of the arc tube had been adapted to the shape of the arc (JA-Utility Model sup3499; DT-OS 2 432 210).Said embodiments, however, are both technically and economically too expensive.

The present invention seeks to provide a lamp with a temperature distribution across the arc tube wall as uniform as possible, and of as high a temperature as possible in the coolest spot thereof. It is intended to obtain a low colour temperature of the discharge with at the same time a high luminous efficiency and good colour rendering characteristics.

According to the invention there is provided an elongate high pressure mercury vapour discharge lamp for horizontal operation comprising an arc tube and main electrodes mounted at respective ends of the arc tube with their ends facing the discharge being positioned below the longitudinal axis of the lamp in the operative position of the lamp.

Preferably the arc tube is quartz glass.

The electrodes may be of refractory metal projecting into the arc tube and may be spaced from one another a distance larger than the arc tube diameter, hermetic seals being respectively connected with each one of the electrodes, and the arc tube may be encompassed by an outer envelope. As an additive filling to the mercury, metal halides and a rare gas may be used.

The electrodes may be sealed into the arc tube with their ends facing the discharge in downwardly inclined position, the angle of inclination amounting to from 10 to 45" relative to the longitudinal lamp axis. Instead of sealing the electrode in inclined positions, it is also possible to bend the electrode support rod downwardly, and to a}ig:l the electrode end parallel to but spaced from the longitudinal lamp axis or, to mount the electrode, its support and the seal below the longitudinal lamp axis. The inner end of the electrode may be positioned eccentrically of the longitudinal axis of the lamp by at least 1/3 prefereably 1/2 of the arc tube radius.Due to the position of the electrode tips according to the invention, the arc spots come to lie below the longitudinal axis of the lamp. The position of the electrode tips is preferably determined such as to provide as small an average deviation of arc path from the longitudinal lamp axis as possible, so that the temperature of the arc tube is in all places as uniform as possible. With this arc path it is at the same time achieved, that the arc comes to lie closer to the non-evaporated portion of any metal halides present in saturation during operation of the lamp, whereby said metal halides are more intensely heated and thus a larger amount of them is evaporated. As a result of the higher vapour density of the metal halides, a higher luminous efficiency is obtained.At the same time the colour temperature is reduced and the colour rendering characteristics are improved. The metal halides best suited for the lamp according to the invention are the halides of the rare earth metals. By "rare earth metals" in this specification and claims is intended not only the lanthanides of atomic numbers 57 to 71 but also Yttrium and Scandium. Tungsten may be used as the electrode material which is preferably activated with up to 5% by weight of oxide of the rare earth metals instead of with thorium oxide, for instance, with from 1 to 3% by weight of dysprosium oxide.

The outer envelope may be designed such as to encompass the arc tube relatively closely, and in this case it may be made of quartz glass. The ratio of inner diameter of the outer envelope to outer diameter of the arc tube may be less than 2:1 preferably from 1.7 to 1.1. The space between arc tube and outer envelope may be suitably exhausted.

With the lamp design as above, it is possible to increase the vapour pressure of the metal halides without diminishing the size of the arc tube-which would lead to reduced useful life and thus to a reduction in the colour temperature. When using the particularly suitable halides of the rare earth metals, the colour temperature obtained may now be only from 4000 K to 4500 K instead of 6000 K, with a luminous efficiency of 80 Im/W. The colour rendering index R may be increased from 86 to 93.

The invention will now be described in greater detail, by way of example, with reference to the drawing, the single figure of which shows, schematically, one embodiment of the invention.

The cylindrical arc tube 1 of quartz glass, as shown in the drawing, has an inner diameter of from 15 to 16 mm; the volume is 6 cubic centimeters. Mounted at each end of the arc tube is an electrode 2 and 3, respectively, of tungsten, preferably activated with from 1 to 3% by weight of dysprosium oxide (Dy2O2). The electrodes 2 and 3 are sealed in inclined position with an angle of inclination of about 20 relative to the longitudinal lamp axis. The electrode tips 4 and 5 come to lie about 4 mm below the longitudinal lamp axis. The electrodes are spaced a distance of 25 mm. The electrodes 2 and 3 are connected to the leads 8 and 9, respectively, by means of foil seals 6 and 7. 10 indicates the arc path.Each end of the arc tube is provided with a heat-radiation absorbing or reflecting coating 11 or 12, respectively, or zirconium dioxide extending in inclined downward position from the top. The under side of the arc tube 1 is likewise provided with a longitudinal strip 13 of Zoo2. The width of the strip is from 2 to 25 mm, preferably from 8 to 12 mm, depending on the desired temperature distribution in the discharge space. he arc tube 1 is encompassed by an outer envelope 14 of quartz glass with an inner diameter of 21 mm. The outer envelope is exhausted. The filling of arc tube 1 comprises a starting gas such as, argon at 30 torr, 10 mg Hg, 1/3 mg each of Dy, Ho and Tm, 4 mg Hg 12, 1 mg TII and 1 mg CsI for stabilization of the arc. The structural data and fill quantities apply to a lamp with a wattage input of 250 W, with about 3 A of lamp current and 100 V operating voltage. The luminous efficiency is from 70 to 80 lm/W; the colour temperature is about 4300K.

Due to its aforementioned characteristics.

the lamp can be employed for interior lighting as well as for street lighting.

It will of course be appreciated that the provision of the offset electrodes is not limited to the above described lamp but may be used in other lamps, such as those described in our copending application No.

33582/76. (Serial no. 1558508).

WHAT WE CLAIM IS:- 1. An elongate high pressure mercury vapour discharge lamp for horizontal oper

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

additive filling to the mercury, metal halides and a rare gas may be used.

The electrodes may be sealed into the arc tube with their ends facing the discharge in downwardly inclined position, the angle of inclination amounting to from 10 to 45" relative to the longitudinal lamp axis. Instead of sealing the electrode in inclined positions, it is also possible to bend the electrode support rod downwardly, and to a}ig:l the electrode end parallel to but spaced from the longitudinal lamp axis or, to mount the electrode, its support and the seal below the longitudinal lamp axis. The inner end of the electrode may be positioned eccentrically of the longitudinal axis of the lamp by at least 1/3 prefereably 1/2 of the arc tube radius.Due to the position of the electrode tips according to the invention, the arc spots come to lie below the longitudinal axis of the lamp. The position of the electrode tips is preferably determined such as to provide as small an average deviation of arc path from the longitudinal lamp axis as possible, so that the temperature of the arc tube is in all places as uniform as possible. With this arc path it is at the same time achieved, that the arc comes to lie closer to the non-evaporated portion of any metal halides present in saturation during operation of the lamp, whereby said metal halides are more intensely heated and thus a larger amount of them is evaporated. As a result of the higher vapour density of the metal halides, a higher luminous efficiency is obtained.At the same time the colour temperature is reduced and the colour rendering characteristics are improved. The metal halides best suited for the lamp according to the invention are the halides of the rare earth metals. By "rare earth metals" in this specification and claims is intended not only the lanthanides of atomic numbers 57 to 71 but also Yttrium and Scandium. Tungsten may be used as the electrode material which is preferably activated with up to 5% by weight of oxide of the rare earth metals instead of with thorium oxide, for instance, with from 1 to 3% by weight of dysprosium oxide.

The outer envelope may be designed such as to encompass the arc tube relatively closely, and in this case it may be made of quartz glass. The ratio of inner diameter of the outer envelope to outer diameter of the arc tube may be less than 2:1 preferably from 1.7 to 1.1. The space between arc tube and outer envelope may be suitably exhausted.

With the lamp design as above, it is possible to increase the vapour pressure of the metal halides without diminishing the size of the arc tube-which would lead to reduced useful life and thus to a reduction in the colour temperature. When using the particularly suitable halides of the rare earth metals, the colour temperature obtained may now be only from 4000 K to 4500 K instead of 6000 K, with a luminous efficiency of 80 Im/W. The colour rendering index R may be increased from 86 to 93.

The invention will now be described in greater detail, by way of example, with reference to the drawing, the single figure of which shows, schematically, one embodiment of the invention.

The cylindrical arc tube 1 of quartz glass, as shown in the drawing, has an inner diameter of from 15 to 16 mm; the volume is 6 cubic centimeters. Mounted at each end of the arc tube is an electrode 2 and 3, respectively, of tungsten, preferably activated with from 1 to 3% by weight of dysprosium oxide (Dy2O2). The electrodes 2 and 3 are sealed in inclined position with an angle of inclination of about 20 relative to the longitudinal lamp axis. The electrode tips 4 and 5 come to lie about 4 mm below the longitudinal lamp axis. The electrodes are spaced a distance of 25 mm. The electrodes 2 and 3 are connected to the leads 8 and 9, respectively, by means of foil seals 6 and 7. 10 indicates the arc path.Each end of the arc tube is provided with a heat-radiation absorbing or reflecting coating 11 or 12, respectively, or zirconium dioxide extending in inclined downward position from the top. The under side of the arc tube 1 is likewise provided with a longitudinal strip 13 of Zoo2. The width of the strip is from 2 to 25 mm, preferably from 8 to 12 mm, depending on the desired temperature distribution in the discharge space. he arc tube 1 is encompassed by an outer envelope 14 of quartz glass with an inner diameter of 21 mm. The outer envelope is exhausted. The filling of arc tube 1 comprises a starting gas such as, argon at 30 torr, 10 mg Hg, 1/3 mg each of Dy, Ho and Tm, 4 mg Hg 12, 1 mg TII and 1 mg CsI for stabilization of the arc.The structural data and fill quantities apply to a lamp with a wattage input of 250 W, with about 3 A of lamp current and 100 V operating voltage. The luminous efficiency is from 70 to 80 lm/W; the colour temperature is about 4300K.

Due to its aforementioned characteristics.

the lamp can be employed for interior lighting as well as for street lighting.

It will of course be appreciated that the provision of the offset electrodes is not limited to the above described lamp but may be used in other lamps, such as those described in our copending application No.

33582/76. (Serial no. 1558508).

WHAT WE CLAIM IS:- 1. An elongate high pressure mercury vapour discharge lamp for horizontal oper

ation comprising an arc tube and main electrodes mounted at respective ends of the arc tube with their ends facing the discharge being positioned below the longitudinal axis of the lamp in the operative position of the lamp.
2. A lamp as claimed in claim 1, wherein the arc tube is quartz glass.
3. A lamp as claimed in claim 1 or 2, wherein the electrodes are of refractory metal projecting into the arc tube and spaced from one another a distance larger than the arc tube intenlal diameter, hermetic seals being respectively connected with each one of the electrodes, and the arc tube is encompassed by an outer envelope.
4. A lamp as claimed in any one of claims 1 to 3, wherein as an additional filling to the mercury, metal halides and a rare gas are used.
5. A lamp as claimed in any one of claims 1 to 4, wherein the electrodes are sealed into the arc tube with their end portions facing the discharge in a downwardly inclined position.
6. A lamp as claimed in claim 5, wherein the electrodes are downwardly inclined through an angle of from 10 to 450.
7. A lamp as claimed in any one of claims 1 to 4, wherein the electrode support rod located in central position at the lamp end, is downwardly bent and that the electrode end is orientated parallel to but spaced from the longitudinal axis of the lamp.
8. A lamp as claimed in any one of claims 1 to 4, wherein the electrode, its support and the seal are positioned below the longitudinal axis of the lamp.
9. A lamp as claimed in any one of claims 1 to 8, wherein the inner end of the electrode is positioned eccentrically of the longitudinal axis of the lamp by at least 1/3 of the arc tube radius.
10. A lamp as claimed in claim 4 or any claim appendant directly or indirectly thereto, wherein the added halides are halides of the rare earth metals.
11. A lamp as claimed in any one of claims 1 to 12, wherein the electrode material comprises tungsten with up to 5% by weight of rare earth metal oxide.
12. A lamp as claimed in claim 11, wherein the rare earth metal oxide is dysprosium oxide.
13. A lamp as claimed in claim 2 or any claim appendent directly or indirectly thereto, wherein the outer envelope is made of quartz glass and that the ratio of inner diameter of the outer envelope to outer diameter of the arc tube is less than 2:1.
14. A lamp as claimed in claim 13, wherein the said ratio is from 1:7 to 1:1.