High Pressure Saturated Metal Vapor, Preferably Sodium Or Metal Halide Vapor Discharge Lamp

Abstract

The outer envelope is of thermally highly loadable material capable of witanding operating temperatures exceeding 500.degree. C, such as quartz glass. It surrounds the actual arc enclosing vessel, which is likewise of thermally highly loadable material, such as quartz glass. The spacing is so close that additional heating, by thermal radiation from the outer envelope results in increased vapor density in the arc since the metal vapors in metal halide vapor discharge lamps are essentially saturated during lamp operation. A suitable ratio of the inner diameter of the outer envelope to the outer diameter of the discharge vessel is 3:1 to 1.05:1; the diameter difference being smaller than 2 cm.

Description

The invention relates to a high pressure discharge lamp using an essentially saturated metal, or metal halide vapor, preferably a sodium vapor or a metal halide vapor discharge lamp with its discharge vessel, the so-called arc tube, hermetically sealed in an outer envelope.

In known lamps of this type the arc tube is enclosed in a single-ended ellipsoidal (see German Pat. No. 1,184,008) or single-ended cylindrical envelope of hard glass. The volume of the outer envelope is a multiple of the volume of the discharge vessel, and the ratio of diameter of outer envelope to diameter of arc tube is relatively large, for instance, in a metal halide vapor discharge lamp with a wattage input of 400 W, larger than six.

It is an object of the invention to improve lamps of the saturated metal and metal halide discharge type.

SUBJECT MATTER OF THE INVENTION:

The relative sizes of the envelope and arc tube are changed so that the ratio of inner diameter of the outer envelope to outer diameter of the arc tube is substantially less, that is from 3:1 to 1.05:1. The outer envelope is of thermally highly loadable material capable of withstanding a temperature exceeding 500.degree. C, such as quartz glass. It encloses the discharge vessel comparatively closely without however coming in contact with the latter. The discharge vessel, likewise, is of thermally highly loadable material. The temperature of the outer envelope is increased in operation; in consequence of heat radiation from the outer envelope, additional heating of the arc tube is effected and thus the vapor pressure increase in the discharge. This is of special advantage for high pressure sodium vapor and metal halide vapor lamps which, in operating condition, have essentially saturated metal or metal halide vapors, because in these lamps an increase in vapor density is additionally caused, apart from the increase in vapor pressure. With suitably selected additives the color quality of the light is additionally improved resulting in outstanding color rendition by the lamps when in use. In high pressure mercury vapor discharge lamps, without additives, an increase in vapor pressure would also be obtained by an increase of the wall temperature of the arc tube; however, no increase in vapor density is obtained, because the mercury vapor pressure in these lamps is unsaturated.

The outer envelope has to be made from a material which can be highly stressed thermally. A cylindrical tube of quartz glass is suitable. Photometrically, an envelope of sapphire would be even better. Costs make such material uneconomical; increasing the temperature of the arc tube beyond certain ranges does not proportionately increase light output.

Due to the small difference between outer diameter of arc tube and inner diameter of outer envelope which is generally less than 20 mm, the outer envelope is preferably made in double-ended form. The outer envelope is closed at each end by a pinch seal preferably of I-type cross-section, enveloping the lead-in wires. The bases of insulating material, for example, of a ceramic material, are so shaped that one of its ends is provided with a slotted cylindrical portion. The legs of the base resulting therefrom are closely embracing the flat mid-section of the pinch-seal. The lead-in wire is guided to the exterior by way of a contact pin passed through the base. Both bases of the outer envelope may be located in the direction of the lamp axis; or in order to obtain a reduction in lamp length, at least one of the bases of the outer envelope can be mounted at right angle to the lamp axis, an arrangement which is advantageous primarily in lamps of high wattage input, for example, 5 kW.

The inner wall surface of the outer envelope may be provided with an infrared (IR) radiation reflective coating of, for example, tin oxide; IR-radiation absorbing additives in the material of the outer envelope proved likewise suitable. Similar measures are also applicable for absorption of short-wave UV radiation and thus for suppression of objectionable formation of ozone, for example, coating with, or addition of TiO.sub.2.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic cross-sectional view of the structure of a 400 W metal halide vapor discharge lamp;

FIG. 2a is a graph showing the luminous efficiency (ordinate) of a 400 W discharge lamp containing dysprosium iodide plotted against temperature (.degree.C) and vapor pressure (Torr);

FIG. 2b shows a section of the color triangle wherein the chromaticity coordinates of the light are shown for a lamp either with quartz or glass envelope;

FIG. 3 is a schematic elevation of the structure of a 400 W high pressure sodium vapor discharge lamp;

FIG. 4 is a schematic view of a lamp having one base extending at right angle, and

FIG. 5 is a fragmentary cross-sectional view of a lamp base.

FIG. 1: the discharge vessel 1 of quartz glass is sealed at its opposite ends by a pinch seal 2, 3 each, through which the lead-in wires 4, 5 are passed in vacuum-tight manner. The filling of the lamp comprises, for example, 20 mg of Hg, 2.5 mg of Dy, 10 mg of HgJ.sub.2, 5.5 mg of TlJ and Ar at 30 torr in a volume of 16 cc. The end portions of the discharge vessel 1 are provided with a radiant-heat reflecting coating 6 of ZrO.sub.2. The ends of the lead-in wires 4, 5 extending outside the discharge vessel 1 are electrically connected with a disk 7 of metal, for example, of nickel or molybdenum. The disk 7 has at its periphery a plurality of supports 8 which are used as resilient mounting support of the discharge vessel 1 in the enclosing outer envelope 9 of quartz glass. The inner surface may be coated as schematically shown at 9', with an IR, or UV (or both) reflective coating. One conductor 10 or 11, respectively, is connected to the lead-in wires 4, 5 via disk 7, said conductors extending hermetically sealed, through the ends of the outer envelope by means of flat pinch seals 12 or 13. The ceramic bases 14, 15 are affixed to the pinch seals 12, 13. 16 denotes the getter material provided within the outer envelope. The outer envelope 9 may either be exhausted or filled with nitrogen or argon of about 700 torr cold pressure. Suitable dimensions for a 400 W lamp:

the inner diameter of outer envelope 9 is 27 mm;

the outer diameter of discharge vessel 1 is 22.5 mm

(so that the two vessels are spaced by distance of 2.25 mm);

Overall length of complete lamp:

about 20 cm.

If the lamp is operated in horizontal position with a wattage input of 400 W and an operating voltage of about 105 V, it has a luminous efficiency of about 70 lm/W. If operated in vertical position, the luminous efficiency is approx. 85 lm/W.

In a lamp having a wattage input of 5 kW, suitable dimensions are:

outer envelope 9 has an inner diameter of 50 mm;

the discharge vessel 1 and outer diameter of 35 mm

(so that the spacing between the two vessels is 7.5 mm);

Overall lamp length of 65-70 cm is reduced by passing one of the lead-in wires laterally out of the outer envelope

to about 50 cm.

The luminous efficiency of such a lamp is 90 lm/W in horizontal operating position.

The curve shown in FIG. 2a applies to 400 W lamps with a constant arc tube wall load of 10 W/cm.sup.2. Point A indicates the luminous efficiency .eta. for a lamp with an ellipsoidal outer envelope of glass, point B for a lamp with an outer envelope of quartz according to the invention. Left of dashed limit line G, glass may still be used (for thermal reasons) as the material for the outer envelope, whereas to the right of limit line G up to border line Q, quartz should be used. Beyond limit line Q, higher thermally loadable materials should be used which may, however, due to their cost, be uneconomical commercially. In the section of the color triangle shown in FIG. 2b, the displacement of the chromaticity coordinates towards Planck's curve which is replaced within this range by curve RD of the daylight phase representing reconstituted daylight is clearly seen. A displacement in that direction is desirable because the color and color rendition of a light source is thereby improved. Point A.sub.1 applies to a lamp with ellipsoidal outer envelope of glass, point B.sub.1 to a lamp with an outer envelope of quartz according to the invention. The border lines G and Q indicate -- similar to FIG. 2a -- the ranges of applicability of glass and quartz.

FIG. 3: the discharge vessel 17 of the high pressure sodium vapor discharge lamp is of light-transmissive alumina ceramic; its ends 18 and 19 are hermetically sealed in known manner. As is well known, the filling comprises sodium, mercury and a basic gas, for example, xenon or argon. The mounting support of the discharge vessel and the feed-through of the lead-in wires are similar to the embodiment of FIG. 1 and have been given the same reference numbers. The inner diameter of the outer envelope 9 is 20 mm, the outer diameter of the discharge vessel 17 is 9 mm, so that the two vessels are spaced a distance of 5.5 mm. The complete lamp has an overall length of about 20 cm. The wattage input of the lamp is 400 W, the luminous efficiency about 100 lm/W.

Apart from the already disclosed advantages of considerably increased luminous efficiency, color improvement and outstanding color rendition, further advantages of the lamps according to the invention are obvious. In addition to the reduced costs of manufacture -- most marked in lamps of lower wattage input -- the lamps are perfectly suited for use in reflectors due to their base construction ensuring good adjustability. Because of the small dimensions, high intensity discharge lamps of this type are well suited for use in conjunction with search lights, headlights, projectors and the like. Incorporation into lighting fixtures intended for halogen incandescent lamps is likewise possible. The double-ended structure permits ignition of the lamp even under hot operating conditions by means of ignition devices with high starting pulses (30 kV) which is impossible in case of single-ended lamps due to the possibility of spurious arc-over caused by the small spacings at the base, lamp socket and fixture.

FIG. 4 shows a 5 kW lamp with conventional cylindrical seals having an outer envelope 9, and in-line base 20 and a base 21 at the other end of the lamp extending at right angle with respect to the center line or axis C of the lamp. Of course, if desired, and as required by design of the fixture with which the lamp is to be used, both bases 20, 21 can be of the angle type.

FIG. 5 is a cross-sectional view taken along lines V--V of FIG. 3 of a base and the lamp foot. The press 12 of the lamp is an I cross-section, with a foil type electrode lead 10 embedded and sealed therein. Two legs 22, 23 of a slotted base portion 14 embrace the I-shaped press.

Claims

We claim:

1. High pressure metal vapor discharge lamp with saturated vapor in operating condition of the lamp comprising:

a discharge vessel (1) of thermally highly loadable material permitting an operating temperature exceeding 500.degree. C confining an arc-type discharge and forming an arc enclosing tube, and having a wall load exceeding 10 W/cm.sup.2 ;

a double ended cylindrical outer envelope (9) of thermally highly loadable material permitting an operating temperature exceeding 500.degree. C and enclosing said discharge vessel;

the spacing between the inner diameter of the outer envelope (9) and the outer diameter of the discharge vessel (1) being defined by a ratio of from 3:1 to 1.05:1 to provide radiation of heat from the discharge within the discharge vessel (1) to the outer envelope (9) and radiation back of such heat towards the discharge vessel (1) to additionally heat said vessel to the extent that vapor density is additionally increased apart from the increase in vapor pressure.

2. Lamp as claimed in claim 1 wherein the difference between outer diameter of the arc tube and inner diameter of the outer envelope is less than 20 mm.

3. Lamp as claimed in claim 1 wherein a pinch seal (12, 13) is provided at each end of the outer envelope, said pinch seal being of I-shape in cross-section.

4. Lamp as claimed in claim 3 including a substantially cylindrical base of insulating material with slotted end portion constituting two opposed legs (22, 23) which closely embrace the flat mid-section of the pinch seal.

5. Lamp as claimed in claim 1 wherein the two bases of the outer envelope are extending in the direction of the lamp axis.

6. Lamp as claimed in claim 1 wherein at least one of the bases of the outer envelope is mounted at right angle to the lamp axis.

7. Lamp as claimed in claim 1 wherein the inner wall surface of the outer envelope (9) is provided with an infrared reflecting coating (9').

8. Lamp as claimed in claim 1 wherein the material of the outer envelope comprises IR-absorbing additives.

9. Lamp as claimed in claim 1 wherein the outer envelope (9) is provided with a coating reducing UV-radiation (9').

10. Lamp as claimed in claim 1 wherein the material of the outer envelope comprises UV-absorbing additives.

11. Lamp as claimed in claim 1 for 400 W input, wherein the discharge vessel has an outer diameter of about 21/4 cm and the outer envelope has an inner diameter of between 21/2 to 3 cm.

12. Lamp as claimed in claim 1 for 5 kW input, wherein the discharge vessel has an outer diameter of about 31/2 cm and the outer envelope has an inner diameter of about 5 cm.

13. Lamp as claimed in claim 1, wherein the discharge vessel contains halides of metal.

14. Lamp as claimed in claim 1, wherein the discharge vessel contains sodium.

15. Lamp as claimed in claim 14 for 400 W input, wherein the discharge vessel has an outer diameter of up to about 1 cm and the outer envelope an inner diameter of about 2 cm.

16. Lamp as claimed in claim 1, wherein the material of the outer envelope (9) is quartz glass.

17. Lamp as claimed in claim 1, wherein the material of the discharge vessel (1) is quartz glass.

18. Lamp as claimed in claim 1, wherein the material of the discharge vessel is light-transmissive alumina ceramic.