Note: Descriptions are shown in the official language in which they were submitted.
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UNSATURA~ED VAPOR HI~H PRESSURE SODIU~ LAMP GETTER MOUNTING
CROSS REFE~NCE TO OTHER APPLICATIONS
The following concurrently filed Canadian patent
applications relate to unsaturated vapor pressure type
high pressure sodium lamps and the fabrication thereof:
448,953-5; 448.916-1; 448,954-3; and 448,915-2.
TECHNICAL FIELD
This invention relates to unsaturated vapor high
pressure sodium lamps and more particularly to the
mounting of getters within the arc tube of an unsaturated
vapor high pressure sodium lamp.
BACKGROUND ART
In the field of high pressure sodium lamp6, it i8 a
common practice to provide an arc tube fill which
includes a large amount of sodium and mercury in order to
compensate for the undesired sodium lo~ses encountered.
These excess amounts of sodium and mercury re~ult in an
amalgam at the coolest points of the arc tube which
normally adjacent the electrodes at the ends of the arc
tube. As a result, undesired variations in source
voltage, color rendition and numerous other
characteristics are encountered.
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83-1-021 -2-
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In an effort to eliminate or at least reduce such undesired
effects, it has lon~ been known that a lamp wherein the amount of
sodium and mercury employed is only that which will becom~ totally
vaporized would provide the desired rasult. In other words, a high
pressure sodium lamp of the unsaturated vapor type wherein sodium
and mercury are introduced in only such an ~nount as to become
totally vaporiæed is a highly desirable structure insofar as
efficiency, cost of manufactur~ and enhanced lighting capability are
concerned.
Also, it has long been recognized that a principal cause of
undesired sodium loss in high presure sodium lamps is the presence
of oxygen in the gas fill of the arc tube. One known att~pt to
alleviate this undesired loss of sodium due to the presence of
oxyg~n is set forth in a concurrently filed Canadian patent
application, S~rial ~o. 448,953-5, of Philip J. White entitled
~'Unsaturated Vapor Pressure Type High Pressure Sodium Lamp",
assi~ned to the Assignee of the present application. Therein, a
getter in the form of a metal or metal alloy is located within an
elongated ceramic arc tube with the metal oxides of the getter
having a free energy of formation per mole of oxygen greater than
that of sodium oxide. In effect, the getter reacts with Eree oxygen
to inhibit the formation of compounds containing sodium and oxygen.
Although the above-described technique has been employed with
var~ing amounts of success, it has been found that the results do
leave something to be desired. ~ore specifically, it has be~n found
that intimate contact between the tubular ceramic envelope of the
arc tube and the oxygen-absorbing getter therein tends to cause an
undesired darkening of the ceramic envelope in the area of contact
with the getter material. Althou~h the exact cause of this
darkening condition of the ceramimc envelope is not thoroughly
understood, it is believed that a chemical reduction takes place
between the getter and the aluminum envelope whereat contact
therebetween is effected.
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~222274
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present inYention is to provide an improved
high pressure sodium lamp. Another object of the invention is to
enhance the arc tube of an unsaturated vapor high pressure sodium
lamp. A further object of the invention is the structure of an
unsaturated vapor high pressure sodium lamp.
These and other objects, advantages and capabilities are
achieved in one aspect of the invention by an arc tube having a
tubular ceramic envelope with an electrode sealed into each end of
the envelope, a dosing of sodium, mercury and rare gas within the
envelope and an oxygen-absorb;ng getter attached to at least one of
the electrodes within the ceramic envelope.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an elevational view of a preferred form of unsaturated
vapor high pressure sodium lamp; and
FI6. 2 is an exploded sectional view of an electrode formed for
enclosure within a ceramic envelope and having an oxygen-absor~ing
getter affixed thereto.
BEST MODE FOR CARRYING OUT THE INVENTION
For a better understanding of the present invention, together
with other and further objects, advantages and capabilities thereof, ,~
reference is made to the following disclosure and appended claims in
conjunction with the accompanying drawings.
Referring to the drawings, FIG. 1 illustrates an unsaturated
vapor high pressure sodium lamp having a hermetically sealed and
evacuated glass envelope 5 formed to fit into an ordinary screw-type
base member 7. A glass stem member 9 is sealed to the envelope
and projects therein. Electrical conductors, 11 and 13
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respectively, are sealed into and pass through the stem member 9 to
provide electrical connections from the interior to the exterior of
the glass envelope 5.
An electrically conductive support member 15 is affixed to one
5 of the electrical conductors 11 and has a pair of crossbars 17 and
19 affixed thereto at either end. Also, a plurality of spring-like
members 21 are affixed to the support member 15 and formed for
contact with the glass envelope 5. Moreover, a pair of getters 23
and 25 are attached to the support member 15 and serve to insure the
10 integrity of the evacuated envelope 5.
Disposed within the glass envelope 5 and supported by the
crossbars 17 and 19 is an arc tube 27. This arc tube 27, preferably
of a material such as polycrystalline alumina for example, includes
an electrode 29 and 31 at either end thereof. One electrode 29 is
15 affixed to and supported by the crossbar 17 while the other
electrode 31 is insulatingly supported by the other crossbar 19, but
electrically connected to the electrical conductor 13 passing -
through the stem member 9. Heat conserving elements 33 may be
wrapped about the arc tube 27 at each end thereof in the vicinity of
20 the electrodes 29 and 31 in order to reduce the heat differential
thereat from the center of the arc tube 27.
Referring more specifically to FIG. 2 wherein à getter 37 is
disposed within the arc tube 27 of FI5. 1, an electrode member 39 is
sealed into an apertured ceramic 41 which is, in turn, sealed into
25 the end of a tubular ceramic envelope of an arc tube. Similarly,
the opposite end of the tubular ceramic envelope is sealed in
substantially the ~same manner.
The electrode member 39 includes a shank portion 43 which has a
substantially circularly-wound cathode portion 45 telescoped
30 thereover and affixed thereto, as by welding for example. Also
affixed to the shank portion 43 intermediate the cathode portion 45
and the apertured ceramic 41 is the getter 37.
Preferably, the getter 37 is in the form of a suitable substrate
47, such as nickel plated iron, and a gettering material 49, such as
35 zirconium-aluminum powder, is sintered thereto. Thera~ter, the
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substrate 47 is affixed to or telescoped over the shank portion 43
of the electrode member 39. Although a preferred gettering material
is a zirconiu~-aluminum alloy known as ST-101~ available from SAES
Getters, Milan, Italy, other metals are equally applicable. For
example, metal alloys selected from the metal group consisting of
aluminum5 titanium, scandium, cerium, lanthanum, thoriu~, zirconium,
yttrium and other rare earth oxides are suitable getter;ng materials
for the above-described configurations.
Additionally, alternative methods of containing a getter
material within the ceramic envelope of the arc tube and separated
therefrom are appropriate. For example, a small tab containing a
gettering material could be affixed to the electrode or
alternatively, the getter material could be applied to the wound
cathode portion 45 of the electrode member 39. Obviously, other
configurations of a similar nature are appropriate to the structure
so long as the gettering material is separated from the ceramic
envelope of the arc tube.
While there has been shown and described what is at present
considered the preferred embodiments of the invention, it will be
- ~o obvious to those skilled in the art that various changes and
modifications may be made therein without departing from the
invention as defined by the appended claims.
