US 3872340 A
A high pressure sodium vapor lamp utilizing an alumina ceramic arc tube within an outer glass envelope is provided with a capacitive starting aid on the outside of the arc tube. The starting aid comprises a pair of thermally deformable bimetal arms whose ends embrace the arc tube at room temperature to provide a capacitive effect. The bimetal arms swing away from the arc tube when heated up under operating conditions in order to reduce the obstruction of light and prevent overheating of the arc tube wall.
Description (OCR text may contain errors)
United States Patent Collins [45 1 Mar. 18, 1975 HIGH TEMPERATURE LAMP STARTING AID Primary Examiner-Rudolph V. Rolinec Assistant Examiner-Darwin R. l-lostetter Attorney, Agent, or FirmErnest W. Legree; Lawrence R. Kempton; Frank L. Neuhauser  ABSTRACT A high pressure sodium vapor lamp utilizing an alumina ceramic arc tube within an outer glass envelope is provided with a capacitive starting aid on the outside of the arc tube. The starting aid comprises a pair of thermally deformable bimetal arms whose ends embrace the arc tube at room temperature to provide a capacitive effect. The bimetal arms swing away from the arc tube when heated up under operating conditions in order to reduce the obstruction of light and prevent overheating of the arc tube wall.
9 Claims, 6 Drawing Figures HIGH TEMPERATURE LAMP STARTING AID BACKGROUND OF THE INVENTION The invention relates to high pressure metal vapor lamps and more specifically high pressure sodium vapor lamps utilizing alumina ceramic envelopes. The invention is particularly concerned with means to facilitate the starting of such lamps.
High intensity sodium vapor lamps of the present kind are described in US. Pat. No. 3,248,590 Schmidt, entitled High Pressure Sodium Vapor Lamp. These lamps utilize a slender tubular envelope of light-transmissive refractory oxide material resistant to sodium at high temperatures, suitably high density polycrystalline alumina or synthetic sapphire. The filling comprises sodium along with a rare gas to facilitate starting, and mercury for improved efficiency. The ends of the alumina tube are sealed by suitable closure members affording connection to thermionic electrodes which may comprise a refractory metal structure activated by electron emissive material. The ceramic arc tube is generally supported within an outer vitreous envelope or jacket provided at one end with the usual screw base. The electrodes of the arc tube are connected to the terminals of the base, that is to shell and center contact, and the interenvelope space is usually evacuated in order to conserve heat.
The high pressure sodium vapor lamps which have been manufactured commercially up to the present time have generally followed the teachings of the Schmidt patent and used xenon as the starting gas. The goal has been maximum efficiency and the use of xenon provided an advantage in efficiency of percent or more over the lighter inert gas neon. The choice of xenon raised the starting voltage requirement and this was met by including in the ballast an electronic circuit which served as a source of short duration high voltage pulses. After the lamp is ignited, the voltage across it is reduced and a sensing circuit responds thereto and disables the starting pulse generator.
There are advantages to high pressure sodium vapor lamps which are easier starting than the conventional lamps even though they may be lower in efficiency, and the object of the invention is to provide an improved easy starting lamp of this kind.
It is well known that easier startingof a discharge lamp may be achieved through the Penning effect calling for a starting gas mixture comprising major and minor constituents. Penning mixtures are commonly used in mercury, fluorescent and low pressure sodium lamps. A suitable Penning mixture for a high pressure sodium lamp is a neon-l percent argon mixture. With such a starting fill, a starting aid in the form of an internal auxiliary starting electrode as used in high pressure mercury vapor lamps, or a conductive stripe painted on the outside of the lamp envelope as used with fluorescent lamps, is highly beneficial in further reducing the starting voltage. However the closure members or end caps used with ceramic lamp envelopes do not lend themselves well to the provision of auxiliary starting electrodes. Also the very high temperatures of ceramic envelopes may-create problems when conductors are applied or fastened to the outside.
SUMMARY OF THE INVENTION In accordance with my invention,'l have resolved the problem by a capacitive starting aid comprising a thermally deformable conductor which rests against the outside of the arc tube when it is cold and which is retracted when it is hot.
In a preferred embodiment the starting aid comprises a pair of thermally deformable bimetal arms whose ends embrace the arc tube at room temperature to provide a capacitive'effect. After the lamp has started and as it becomes heated up to its normal operating temperature, the bimetal arms swing away from the arc tube in order to reduce the obstruction of light and prevent overheating of the arc tube wall.
BRIEF DESCRIPTION OF THE DRAWING In the drawing:
FIG. 1 is a side view of a high pressure sodium vapor discharge lamp embodying the invention in preferred form.
FIGS. 2a and 2b are plan section and end elevation views respectively of the capacitive starting aid in closed position.
FIGS. 3a and 3b are corresponding views of the capacitive starting aid in open position.
FIG. 4 is a plan section of a capacitive starting aid which is a variant in design.
DETAILED DESCRIPTION A high pressure sodium vapor lamp embodying the invention in preferred formis illustrated in FIG. 1. The lamp is of approximately watt rating which is a relatively small size in which easy starting is particularly desirable. The lamp 1 comprises an outer envelope 2 of glass to the neck of which is attached a standard mogul screw base 3. The outer envelope comprises a reentrant stem press 4 through which extend, in conventional fashion, a pair of relatively heavy lead-in conductors 5, 6 whose outer ends are connected to the screw shell 7 and eyelet 8 of the base.
The are tube-9 centrally located within the outer en-' velope comprises a length of polycrystalline alumina tubing. End closures consisting of metal caps 10, ll of niobium which matches the expansion coefficient of alumina ceramic are sealed to the ends of the tube by means of a glassy sealing composition. End cap 10 has a metal tube 12 sealed through it which serves as an exhaust and fill tubulation during manufacture of the lamp. The exhaust tube is sealed off at its-outer end and serves as a reservior in which excess sodium-mercury amalgam condenses during operation of the lamp, the illustrated lamp being intended for base-down operation. Electrode 13 within the lamp is attached to the inward projection of exhause tube 12 and a dummy exhaust tube 14 extending through metal end cap 11 supports the other electrode 15.
Exhaust tube 12 is connected by connector 16 and short support rod 17 to inlead conductor 6 which provides circuit continuity from a base terminal to electrode l3. Dummy exhaust tube 14 extends through a ring support 18 fastened to side rod 19 which provides lateral restraint while allowing axial expansion of the arc tube. A flexible metal strap 20 connects dummy exhaust tube 14 to side rod 19 which in turn is welded to inlead conductor 5, thereby assuring circuit continuity from the other base terminal toelectrodc IS. The distal end of side rod 19 is braced to inverted nipple 21 in the dome end of the envelope 2 by a clip 22 which engages it.
I have found that a lamp such as illustrated in FIG. 1 wherein the starting gas consists of neon with 1 percent argon has a starting voltage of approximately 300 volts rms in the absence of any capacitive starting aid.
- In a preferred embodiment of my invention, I provide a capacitive starting aid 23 consisting of a bifurcated strip of bimetal wrapping around side rod 19 and spotwelded thereto on opposite sides at 24, 25. The ends of the bimetal are curved at 26, 27 in order to embrace closely and wraparound the arc tube 9 to achieve good capacitive coupling thereto. The bimetal strip is commercially available material whereof the low expansion component is a nickel-iron alloy and the high expansion component is a nickel-chrome-steel alloy. Suitable dimensions for the bimetal strip material are 0.005 inch thickness by 0.150 inch width. FIGS. 2a and 2b show the starting air in rest position at room temperature with the bimetal arms embracing the arc tube. FIGS. 3a and 3b show the starting aid opened up at operating temperature wherein the arms are swung out and away from the arc tube as indicated at 26', 27
The starting aid illustrated causes the starting voltage to be reduced from about'300 volts to less than 180 volts. The starting aid is at the potential of the remote electrode and probably functions by acting as a capacitor in combination with the proximate electrode 13. A charging current flows from the starting aid through the arc tube wall to the proximate electrode which helps to ignite the lamp. The magnitude of charging current is dependent upon the area of the starting aid in close proximity to the arc tube wall and hence the need for appreciable width of the bimetal strip and close conformance of embrace of the arc tube.
When the arms of the starting aidswing away from the arc tube, blockage of light is reduced to a small fraction of that occurring upon engagement and, of course, harmful overheating of the bimetal material is avoided. Reaction between the starter and the arc tube wall is avoided. Also thermal etching of the arc tube wall which can occur when energy reflected from the starter raises the arc tube temperature enough to cause increased vaporization of the ceramic material, is avoided. Overheating of the arc tube wall can also occur as a result of deflection of the arc toward the wall by the capacitive effect of the starting aid and this is avoided when the arms swing away from the arc tube.
FIG. 4 illustrates another capacitive starting aid 30 embodying the invention. It comprises a bifurcated and reverted strip of bimetal wrapping around side rod 19 and spot-welded thereto on opposite sides at 31, 32. The arms of the strip are curved back on themselves at 33, 34 and redirected towards the tube 19. The ends are curved at 35, 36 to wrap around the arc tube to achieve good capacitive coupling thereto. This construction permits a greater throw of the ends 35, 36 than the construction .shown in FIGS. 2 and 3. It may also be used to accommodate thicker bimetal strip material, for instance 0.10 inch thick material which has less flexure for a given change in temperature than the thinner 0.005 inch thick material utilized in FIGS. 2 and 3.
Although the capacitive starting aid has been shown as operating in a plane transverse to the arc tube axis, that is not essential and the arms could be arranged to operate in a plane including the axis of the are tube or at any angle thereto.
What I claim as new and desire to secure by Letters Patent of the United States is:
l. A high pressure metal vapor lamp comprising: a tubular light-transmitting envelope having thermionic electrodes sealed into its ends and containing a charge of vaporizable metal and inert starting gas;
and a capacitive starting aid comprising a thermally deformable metal member electrically connected to one electrode, said member having an end disposed to lie against the envelope at room temperature in order to facilitate starting by capacitive effect, and adapted to move away from said are tube when heated by the operation of said lamp.
2. A lamp as in claim 1 wherein the starting aid comprises a pair of arms of bimetal strip attached to a frame part and having their ends embracing and wrapping around the arc tube at room temperature and swinging away therefrom when heated.
3. A lamp as in claim 2 wherein the envelope is alumina ceramic and the vaporizable metal comprises sodium and mercury.
4. A lamp as in claim 3 wherein the inert starting gas is a neon-argon mixture.
5. A high pressure metal vapor lamp comprising:
an outervitreous envelope domed at one end and having a base attached to the other end, and a pair of inleads sealed into said envelope and connected to said base;
an arc tube having electrodes sealed therein and containing a charge of vaporizable metal and inert starting gas;
a mounting frame within said envelope comprising a side rod extending from one inlead towards the dome end of said envelope, and a short support rod extending from the other inlead, said electrodes being connected one to the side rod and the other to the support rod; 7
and a capacitive starting aid comprising a thermally deformable metal member fastened to said side rod, said member having an end disposed to lie against the arc tube wall at room temperature in order to facilitate starting by capacitive effect, and adapted to move away from said are tube when heated by the operation of said lamp.
6. A lamp as in claim 5 wherein the starting aid comprises a pair of arms of bimetal strip attached to said side rod and having their ends embracing and wrapping around the arc tube at room temperature and swinging away therefrom when heated.
7. A lamp as in claim 5 wherein the arc tube is alumina ceramic and the vaporizable metal comprises sodium and mercury.
8. A lamp as in claim 5 wherein the arc tube is alumina ceramic and the vaporizable metal comprises sodium and mercury and wherein the starting aid comprises a pair of arms of bimetal strip attached to said side rod and having their ends embracing and wrapping around the arc tube at room temperature and swinging away therefrom when heated.
9. A lamp as in claim 8 wherein the inert starting gas is a neon-argon mixture.