US3885181A

US3885181A - Electric discharge lamps

Info

Publication number: US3885181A
Application number: US349003A
Authority: US
Inventors: Evan Herbert Nelson; Sydney Alfred Richard Rigden
Original assignee: General Electric Co PLC
Current assignee: Ledvance Ltd
Priority date: 1972-04-19
Filing date: 1973-04-09
Publication date: 1975-05-20
Anticipated expiration: 1992-05-20
Also published as: GB1401293A

Abstract

In a tubular high pressure electric discharge lamp, for example a high pressure sodium lamp, the conformation of the interior and/or exterior longitudinal surface of the tubular discharge envelope wall is such as to produce a non-circular cross-section of the interior and/or exterior of the envelope, the configuration of the envelope being such as to give an asymmetric polar distribution of the light emitted from the lamp as a whole. The envelope may be of uniform wall thickness, both the exterior and the interior being of similar non-circular cross-section, for example elliptical, ovate or substantially rectangular. Alternatively, the wall may be of varying thickness around the circumference, such that one or more optical elements, for example lenses, prisms or multiple prisms, are incorporated in the wall structure, the internal and external cross-sections of the tube thus being of different shape, and possibly one or the other being circular. The preferred material for the fabrication of the envelope is transparent crystalline corundum.

Description

United States Patent Nelson et al.

Sydney Alfred Richard Rigden, Hemel Hempstead, both of England [73] Assignee: The General Electric Company Limited, London, England [22] Filed: Apr. 9, 1973 [21] Appl. No.: 349,003

[30] Foreign Application Priority Data Apr. 19, 1972 United Kingdom 18095/72 [52] US. Cl 313/110; 220/21 R; 313/220; 313/221 [51] Int. Cl I101] 5/16; H01 17/16 H01j/61/33 [58] Field ofSearch 313/110, 111, 112, 220, 313/221, 284; 220/21 R, 2.2, 2.3

[56] References Cited UNITED STATES PATENTS 1,853,497 5/1932 Hall 313/111 2,362,171 11/1944 Swanson 313/110 2,482,421 9/1949 Lemmers 4 313/220 X 2,775,718 12/1956 Dubilier 313/220 X 3,119,040 1/1964 Gardiner et al..... 313/220 X 3,243,635 3/1966 Louden et al l 313/220 X 3,385,463 5/1968 Lange 313/220 UX A l 6 z r I [451 May 20, 1975 2/1969 Rigden et a1 313/284 10/1969 Zollweg et a1. 313/220 Primary Examiner-Alfred L. Brody Attorney, Agent, or Firm-Kirschstein, Kirschstein, Ottinger & Frank [57] ABSTRACT In a tubular high pressure electric discharge lamp, for example a high pressure sodium lamp, the con1ormation of the interior and/or exterior longitudinal surface of the tubular discharge envelope wall is such as to produce a non-circular cross-section of the interior and/or exterior of the envelope, the configuration of the envelope being such as to give an asymmetric polar distribution of the light emitted from the lamp as a whole. The envelope may be of uniform wall thickness, both the exterior and the interior being of similar non-circular cross-section, for example elliptical, ovate or substantially rectangular. Alternatively, the wall may be of varying thickness around the circumference, such that one or more optical elements, for example lenses, prisms or multiple prisms, are incorporated in the wall structure, the internal and external cross-sections of the tube thus being of different shape, and possibly one or the other being circular The preferred material for the fabrication of the envelope is transparent crystalline corundum.

10 Claims, 17 Drawing Figures ELECTRIC DISCHARGE LAMPS This invention relates to high pressure electric discharge lamps of the type comprising a tubular discharge envelope formed of light-transmissive material with a pair of electrodes disposed coaxially within said envelope and carried respectively by closure means closing each end of the envelope.

It is an object of the present invention to provide an improved form of discharge envelope for a lamp of this type, whereby the polar distribution of the light emitted by the lamp in operation can be controlled.

According to the invention, in an electric discharge lamp of the type referred to, the conformation of the interior and/or exterior longitudinal surface of the tu bular discharge envelope wall is such as to produce a non-circular cross-section of the interior and/or exterior of the envelope, the resulting configuration of the envelope being such as to give, in operation, an asymmetric polar distribution of the light emitted from the lamp as a whole.

The envelope may be formed of a light-transmissive material conventionally used for the construction of the discharge envelopes of high pressure discharge lamps, such as fused silica or sintered polycrystalline alumina, but the preferred material is crystalline corundum, which is transparent and therefore has the obvious advantage of improved light transmissivity in comparison with that of the translucent polycrystalline alumina used hitherto especially for the discharge envelopes of high pressure sodium vapour lamps. Crystalline corundum is further advantageous for use for forming the envelopes of lamps in accordance with the invention, since it can readily be fabricated in the form of tubes of any desired predetermined cross-sectional size and configuration, by a known crystal growing technique comprising pulling from a melt film supported on a tubular member of appropriate cross section: a tube so produced may be monocrystalline or may consist of a few large crystals.

The interior and exterior surfaces of the tubular en velope wall may be of parallel conformation, so that the wall thickness is uniform, both the exterior and the interior of the tube being of similar non-circular crosssection, for example elliptical, ovate, or substantially rectangular, that is to say in the form of a rectangle with curved corners necessitated by the nature of the material employed for the construction of the tube. Alternatively, where the tube is formed of fused silica or crystalline corundum, the wall may be of varying thickness around the circumference of the tube, one or more optical elements such as lenses, prisms or multiple prisms being incorporated in the wall structure, the internal and external cross-sections of the tube thus differing in shape. and possibly one or the other being cir cular. Usually the configuration of the tube will be so designed that the maximum emission of light from the lamp in operation will be obtained from two opposite regions of the cross-section thereof, but if desired the maximum emission may be arranged to be derived from adjacent regions of the envelope, or from only a single relatively small portion of the circumference of the tube.

The advantage of a lamp in accordance with the invention is that asymmetrical polar distribution of the emitted light is automatically obtained therefrom, by virtue of the shape of the envelope. This feature is particularly advantageous for street light and similar space lighting applications, since asymmetrical light distribution in required directions can be obtained when the lamp is mounted in a fitting provided with minimal op' tical arrangements,

In an arrangement comprising, in combination, a fit ting and a lamp in accordance with the invention mounted therein, with the longitudinal axes of both the lamp and the fitting lying horizontally, as is usual in street lighting and similar installations, the lamp is preferably so arranged that those portions of the envelope wall from which the maximum emission of light is obtained in operation are disposed vertically, Thus where a trough-shaped fitting is employed, the said portions of the envelope wall will be disposed substantially parallel to the sides of the fitting, which may be provided with suitable optical means, such as reflectors or diffractors, for deflecting the light emitted through the said portions of the envelope wall into desired down ward directions. Such an arrangement gives improved efficiency of utilisation of the light emitted by the lamp, with the provision of only quite simple optical equipment in the fitting.

The discharge envelope may be closed at both ends by pinches (in the case ofa fused silica envelope) or by suitably shaped refractory metal closure members, in known manner. Niobium closure members are pre ferred for use with a polycrystalline or crystalline alumina envelope, since the thermal expansion characteristics of niobium substantially match those of alumina; moreover niobium is especially suitable for use in a high pressure sodium lamp, since it is resistant to attack by hot sodium vapour. Each metal closure member carries an electrode extending coaxially into the envelope and an external member for connection of the electrode to a source of electric current supply for operation of the lamp, one of these external members usually being an exhaust tube for use in evacuating the envelope and introducing the filling in manufacture of the lamp. The metal closure members may be in the form of discs, caps, or flanged recessed caps of the kind described in US, Pat. Specification No. 3,428,846, and may be sealed to the ends of an alumina tube in known manner, by means of a sealing glass or active alloy of suitable composition.

A lamp in accordance with the invention is mounted coaxially within a cylindrical glass outer jacket designed to maintain the discharge envelope at a suitable high temperature when the lamp is in operation, in conventional manner.

Some specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which FIG. I shows, in part-sectional elevation, a lamp in accordance with the invention having a discharge enve lope of elliptical cross-section,

FIG. 2 is a section drawn on the line Il-ll of FIG. I, and

FIGS. 3 to 17 show, in cross-section, various alternative configurations of discharge envelopes for lamps in accordance with the invention.

The lamp shown in FIG. I is a high pressure sodium vapour discharge lamp comprising an envelope 1 formed of transparent crystalline corundum tubing of elliptical cross-section and uniform wall thickness, as shown by the transverse section constituting FIG. 2. The envelope is closed by niobium

sheet end caps

2, 3,

which are sealed to the ends of the corundum tube by means of a zirconium-titamum-vanadium alloy; the cap 2 carries an electrode 4 and a connection tag 6. brazed to the interior and exterior surfaces respectively of the cap, and a second electrode is supported by an exhaust tube 7, which is inserted through an aperture in the cap 3 and is brazed to the exterior of the cap. The electrodes are silicated tungsten rods carrying on their inner ends small quantities of electron emissive material retained by coils of tungsten wire; and the tag 6 and exhaust tube 7 are of niobium; all brazes are effected with titanium.

In a specific example of a lamp of the form shown in FIGS. 1 and 2, the tubular envelope 1 is 100 mm long and has a uniform wall thickness of 0.8 mm, and the internal cross-section of the tube has a major axis of 7 mm and a minor axis of 5 mm, in length. The electrodes are l mm in diameter and 12 mm long, the part of the exhaust tube 7 extending within the envelope constituting part of the length of the electrode 5. The lamp has a filling of sodium, mercury, and xenon at a pressure of 30 Torr at room temperature.

The lamp envelopes shown in cross-section in FIGS. 3 and 4 also have walls, 8 and 9 respectively, of uniform thickness, the envelope of FIG. 3 being of ovate section and that of FIG. 4 of rectangular section. FIGS. 5, 6 and 7 show envelopes of generally rectangular section, with optical elements built into the two longer sides of the wall in each case: thus in FIG. 5 the longer sides 10, ll of the rectangle are Ienticular, in FIG. 6 they are in the form of

prisms

12, 13, and in FIG. 7 each of the longer sides is formed with

multiple prisms

14, 15 on the exterior. In the case of the envelope shown in FIG. 8 the bore is of square cross-section, and the exterior is of elliptical cross-section, so that the wall is formed with two relatively

thick lenses

16, 17 on two opposite sides of the square bore, the other two

sides

18, 19 of the wall also being lenticular but thinner.

The envelopes shown in FIGS. 9, 10, 11 and 12 all have circular cylindrical bores with variously shaped exteriors so that optical elements are formed in the walls. Thus in FIG. 9 the exterior of the envelope is of elliptical section and in FIG. 10 it is of substantially rectangular section, so that in each of these cases the wall incorporates a pair of thick lenses, 20, 21 and 22, 23 respectively, in two opposite regions. The envelopes of FIGS. 11 and 12 have exteriors respectively of gen erally elliptical and generally rectangular section, but with

multiple prisms

24, 25 and 26, 27 respectively formed on the exteriors of two opposite sides. In FIGS. 11 and 12 the multiple prisms are shown on the two shorter sides of the ellipse and the rectangle respectively, but it will be appreciated that they could alternatively be formed on the longer sides, the shorter sides then being lenticular.

The envelopes of FIGS. 13 and 14 both have bores of elliptical cross-section; in the case of FIG. 13 the exterior of the envelope is of circular section, so that the wall incorporates

lenses

28, 29, and in the case of FIG. 14 the exterior is of generally circular section with

mul tiple prisms

30, 31 formed in two opposite regions of the wall.

FIGS. 15, 16 and 17 all show envelopes with multiple prisms formed on the internal surface of the wall. The envelope of FIG. is of elliptical section, with internal

multiple prisms

32, 33 formed in the longer sides of the wall; the envelope of FIG. 16 is of rectangular section with internal

multiple prisms

34, 35 formed in the longer sides of the wall; and the envelope of FIG. 17 is of circular section with internal

multiple prisms

36, 37 formed in two opposite regions of the Wall.

We claim:

1. A high pressure electric discharge lamp comprising a tubular discharge envelope formed of transparent crystalline corundum, with a pair of electrodes disposed coaxially within said envelope and carried respectively by closure means closing each end of the en velope, wherein at least one of the interior and exterior longitudinal surfaces of the tubular discharge envelope wall is of nonuniform conformation around the circumference such that in any cross-section of the envelope the distance of said surface from the longitudinal axis of the envelope is less in at least one region of the cross section than in the remainder of the cross-section, the cross-sectional conformation of the envelope wall being uniform throughout the length of the envelope, whereby the polar distribution of light emitted from the lamp as a whole, in operation of the lamp, is nonuniform around the circumference of th. envelope.

2. A lamp according to claim 1 wherein the interior and exterior surfaces of the envelope wall are of paral lel conformation, so that the wall thickness is uniform and both the exterior and interior of the envelope are of similar cross-sectional conformation.

3. A lamp according to claim 2 wherein the cross section of the envelope has one of the shapes consisting of an ellipse, an ovoid, and substantially a rectangle, whereby the maximum emission of light from the lamp in operation is obtained from two opposite regions in said cross-section.

4. A lamp according to claim I wherein the interior and exterior surfaces of the envelope are of different conformation, so that in the cross-section of the envelope the wall is ofvarying thickness and at least one optical element is incorporated in the wall structure.

5. A lamp according to claim 4 wherein at least one lens is incorporated in the envelope wall structure.

6. A lamp according to claim 5 wherein a lens is incorporated in each of two opposite sides of the envelope wall, whereby the maximum emission of light from the lamp in operation is obtained from the two opposite regions in the cross-section of the envelope which comprise said lenses.

7. A lamp according to claim 4 wherein at least one prism is incorporated in the envelope wall structure.

8. A lamp according to claim 7 wherein a prism is incorporated in each of two opposite sides of the envelope wall, whereby the maximum emission of light from the lamp in operation is obtained from the two opposite regions in the cross-section of the envelope which comprise said prisms.

9. A lamp according to claim 4 wherein at least one multiple prism is incorporated in the envelope wall structure.

10. A lamp according to claim 9 wherein a multiple prism is incorporated in each of two opposite sides of the envelope wall, whereby the maximum emission of light from the lamp in operation is obtained from the two opposite regions in the cross-section of the enve lope which comprise said multiple prisms.

Claims

1. A high pressure electric discharge lamp comprising a tubular discharge envelope formed of transparent crystalline corundum, with a pair of electrodes disposed coaxially within said envelope and carried respectively by closure means closing each end of the envelope, wherein at least one of the interior and exterior longitudinal surfaces of the tubular discharge envelope wall is of nonuniform conformation around the circumference such that in any cross-section of the envelope the distance of said surface from the longitudinal axis of the envelope is less in at least one region of the cross-section than in the remainder of the cross-section, the cross-sectional conformation of the envelope wall being uniform throughout the length of the envelope, whereby the polar distribution of light emitted from the lamp as a whole, in operation of the lamp, is non-uniform around the circumference of the envelope.

2. A lamp according to claim 1 wherein the interior and exterior surfaces of the envelope wall are of parallel conformation, so that the wall thickness is uniform and both the exterior and interior of the envelope are of similar cross-sectional conformation.

3. A lamp according to claim 2 wherein the cross-section of the envelope has one of the shapes consisting of an ellipse, an ovoid, and substantially a rectangle, whereby the maximum emission of light from the lamp in operation is obtained from two opposite regions in said cross-section.

4. A lamp according to claim 1 wherein the interior and exterior surfaces of the envelope are of different conformation, so that in the cross-section of the envelope the wall is of varying thickness and at least one optical element is incorporated in the wall structure.

10. A lamp according to claim 9 wherein a multiple prism is incorporated in each of two opposite sides of the envelope wall, whereby the maximum emission of light from the lamp in operation is obtained from the two opposite regions in the cross-section of the envelope which comprise said multiple prisms.