Claims
- 1. In a high pressure sodium discharge reflector lamp, comprising a sealed outer lamp envelope having a reentrant stem and an axis of symmetry through said stem and defining a lamp centerline, a high pressure sodium discharge device comprising an elongate body having a pair of terminals each extending from a respective end of said elongate body for receiving thereacross an electrical potential to energize said discharge device to emit light, and mounting means for mounting said discharge device within said sealed envelope on the lamp centerline and for defining a conductive circuit to said pair of terminals to permit energization of said discharge device, the improvement comprising:
- said sealed outer envelope containing a quantity of rare gas such that the pressure of said rare gas is approximately one atmosphere when the lamp is at its operating temperature; and
- said mounting means comprising a pair of upstanding support conductors extending from said stem, one shorter and one longer than the other, and extending generally parallel to said lamp axis, transverse conductive links connected between said support conductors and said discharge device terminals for mounting said discharge device on the lamp centerline and establishing a conductive path for energizing said discharge device, and means for increasing the electrical breakdown voltage between said pair of support conductors to avoid electrical breakdown through said rare gas in said outer envelope when said discharge device is energized during lamp operation.
- 2. In a high pressure sodium discharge lamp according to claim 1, one of said support conductors comprising a straight length of wire extending from said stem, and said means for increasing the electrical breakdown voltage comprising a sleeve of non-conductive material covering a substantial length of said one support conductor.
- 3. In a high pressure sodium discharge lamp according to claim 2, wherein said sleeve of non-conductive material is a glass sleeve sealed to said stem and extending from said stem with said one support conductor extending through said sleeve and into said stem.
- 4. In a high pressure sodium discharge lamp according to claim 1, the shorter of said support conductors comprising a straight length of wire extending from said stem, and the longer of said support conductors comprising a length of wire bent in the form of a sequence of straight segments extending end to end generally parallel to said lamp centerline, said longer support wire comprising
- a first segment extending from said stem parallel to said shorter support conductor;
- a second segment perpendicular to said first segment and extending away from said shorter support conductor,
- a third segment parallel to said shorter support conductor,
- a fourth segment extending away from the imaginary plane defined by said shorter support conductor and said first, second and third segments of said longer support conductor and extending away from said stem,
- a fifth portion parallel to said lamp centerline and extending away from said stem, and
- a sixth portion extending back toward the line of direction of said third portion.
- 5. In a high pressure sodium discharge lamp according to claim 4, said longer support wire further comprising
- a seventh portion extending along the line of direction of said third portion; and
- a getter support mounted on said seventh portion of said longer support wire remote from said discharge device.
- 6. In a high pressure sodium discharge lamp according to claim 1, said transverse conductive links are each comprised of a length of wire having a circular cross and respective end portions wound substantially around one of said terminals and one of said support conductors for defining a connecting link free of protrusions and mounting said discharge device on said support conductors.
- 7. In a high pressure sodium discharge lamp having an outer envelope, a high pressure sodium discharge device disposed in said outer envelope, and mounting means for mounting said discharge device within said outer envelope and for defining a conductive circuit to said discharge device to permit energization of said discharge device, the improvement comprising:
- a metallic reflective layer disposed on a portion of said outer envelope for reflecting and imparting directivity to light emitted from said discharge device;
- a rare gas atmosphere within said outer envelope having a fill pressure at room temperature of the order of one atmosphere; and
- said mounting means having first and second conductors which define said conductive circuit to said discharge device, a first of said conductors to said discharge device, and a second of said conductors following a non-linear path spaced from said first conductor for establishing an electrical breakdown voltage through said rare gas atmosphere between said conductors above a certain value and spaced from said reflective layer for establishing the electrical breakdown voltage through said rare gas atmosphere between said second conductor and said reflective layer above said certain value.
- 8. In a high pressure sodium discharge lamp according to claim 7, the shorter of said support conductors comprising a straight length of wire extending from said stem, and the longer of said support conductors comprising a length of wire bent in the form of a sequence of straight segments extending end to end generally parallel to said lamp centerline, said longer support wire comprising
- a first segment extending from said stem parallel to said shorter support conductor;
- a second segment perpendicular to said first segment and extending away from said shorter support conductor,
- a third segment parallel to said shorter support conductor,
- a fourth segment extending away from the imaginary plane defined by said shorter support conductor and said first, second and third segments of said longer support conductor and extending away from said stem,
- a fifth portion parallel to said lamp centerline and extending away from said stem, and
- a sixth portion extending back toward the line of direction of said third portion.
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation of application Ser. No. 212,818, filed June 29, 1988, now abandoned.
The copending application filed concurrently with this application Ser. No. 212,803 entitled High Pressure Sodium Discharge Lamp Having Gas Filled Outer Envelope of Ray G. Gibson, III and Joseph Steven Droho discloses and claims an HPS lamp having a gas filled outer envelope with structure for preventing electrical breakdown through the gas atmosphere of the outer envelope.
The copending application filed concurrently with this application Ser. No. 212,811 entitled High Pressure Sodium Discharge Reflector Lamp of Ray G. Gibson, III discloses and claims a reflector lamp having an HPS discharge device and having a gas filled outer envelope in order to avoid implosion or explosion if the outer envelope should break.
The present invention relates to high pressure sodium vapor high intensity discharge lamps, and more particularly to the support structure for a high pressure sodium discharge light source within the lamp.
High pressure sodium discharge lamps are comprised of a discharge device mounted in an evacuated outer envelope. The discharge device is typically a ceramic discharge vessel comprised of alumina or sapphire and having conductive terminals for receiving an operating voltage. The conductive terminals are niobium which is used because its coefficient of thermal expansion matches that of alumina and because it is resistant to sodium vapor. Titanium solder is used in connections to the niobium.
The outer envelope is evacuated in order to thermally isolate the discharge device, and to avoid reactions of any gas within the outer envelope with the discharge device. Nitrogen, which is used in the outer envelope of other types of high intensity discharge lamps, cannot be used in high pressure sodium lamps because of its reactivity with niobium and titanium at high temperature.
The evacuated outer envelope of high pressure sodium lamps must be strong and able to withstand severe mechanical impacts without breaking. If the lamp outer envelope were to break, it would implode scattering glass fragments and create a safety hazard.
It has been the practice to manufacture high pressure sodium lamps with evacuated outer envelopes, and to make those envelopes sufficiently strong to avoid breakage. However, high envelope strength is not feasible in the case of many reflector lamps. Reflector lamp envelopes have a large face that merges with the envelope side walls at an edge portion having a small radius of curvature. The atmospheric pressure acting on the evacuated envelope causes high stress concentrations in the edge portion and makes it susceptible to breakage. Moreover, reflector lamps have thin blown glass envelopes and cannot be strengthened by making them substantially thicker. Incandescent reflector lamps having blown glass envelopes uniformly contain a fill gas with an internal pressure of about one atmosphere. With the inner and outer pressures acting on the envelope being approximately equal, no implosion will occur if the envelope breaks and there is less apt to be flying glass fragments.
There has been some consideration of gas filled high pressure sodium lamps. U.S. Pat. No. 3,932,781 issued to Jozef C.I. Peeters et al discloses a high pressure sodium lamp having an outer envelope that is gas filled to inhibit evaporation of the alumina discharge tube. This reduces the deposition of alumina on the outer envelope and the attendant reduction in light output. The results of experiments involving such a lamp are also disclosed in the article by R.J. Campbell et al, "Evaporation studies of the sintered aluminum oxide discharge tubes used in high pressure sodium (HPS) lamps", Journal of the IES, July 1980, pages 233-239.
The introduction of a fill gas into the outer envelope of a high pressure sodium discharge lamp presents the problem of voltage breakdown through the gas. These lamps have closely spaced metal parts having a potential difference of around 4000 volts during lamp operation. In the high vacuum of conventional high pressure sodium lamps electrical breakdown between the lamp parts was not a problem. A fill gas has the potential of ionizing and providing a conductive path between the internal lamp parts at the different potentials and electrical breakdown can occur.
Accordingly, it is an object of the invention to provide a high pressure sodium discharge lamp having a gas filled outer envelope in which electrical breakdown through the fill gas is prevented.
It is another object of the invention to provide support structure for the discharge device of a lamp that will operate in a rare gas atmosphere without electrical breakdown through the rare gas.
According to the invention a high pressure sodium lamp is comprised of an outer envelope containing a rare gas at a pressure of approximately one atmosphere. A metallic reflective layer is disposed on a portion of the outer envelope for defining a reflector. Mounting means mounts the discharge device of the lamp within the outer envelope and is comprised of a pair of conductors for providing a conductive path to the discharge device. The pair of conductors are configured to have a breakdown voltage between them greater than a certain value, and to maintain the breakdown voltage between the conductors and the metallic reflector greater than the certain value.
US Referenced Citations (7)
Foreign Referenced Citations (7)
| Number |
Date |
Country |
| 59-175548 |
Oct 1984 |
JPX |
| 62-131460 |
Jun 1987 |
JPX |
| 63-26939 |
Feb 1988 |
JPX |
| 63-40245 |
Feb 1988 |
JPX |
| 1585041 |
Feb 1981 |
GBX |
| 2097179 |
Oct 1982 |
GBX |
| 2145557 |
Mar 1985 |
GBX |
Continuations (1)
|
Number |
Date |
Country |
| Parent |
212818 |
Jun 1988 |
|
Patent Grant
4963791
