Note: Descriptions are shown in the official language in which they were submitted.
1~30149
LD 7763
1 --
MERCURY PRESSUPIZED INCANDESCENT L~P
BACKGROUND OF THE TNVENTION
This invention is related to an incandescent
lamp, and more particularly, to an incandescent lamp
housing a tungsten filament and containing an inert gas
along with the vaporizable metal mercury.
In typical operation of incandescent lamps over
an extended period of time, some of the tungsten of a
tungsten type filament evaporates and becomes deposited
on the-wall of the lamp. This deposition typically
causes darkening of the bulb wall which, in turn,
decreases the lumen output of the lamp thereby
decreasing the lumens per watt or efficacy of the lamp.
It is known that the darkening of the bulb wall caused
by the tungsten type filament may be substantially
reduced by providing a halogen gas type atmosphere
surrounding the tungsten-type filament so as to provide
a regenerative (transport) cycle which returns the
evaporated tungsten to the filament and keeps the bulb
walls clean and results in improved efficacy of the
incandescent lamp. '"~
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Incandescent la~ps utilizing a halogen
atmosphere are well-known and are described as such in
lU.S. Patent 2,883,571 of Fridrich et al, U.S. Patent
3,497,754 of P. D. Johnson and U. K. Patent
Specification 952,93~3 of J. N Bowtell and J. A. Moore.
Although the halogen atmosphere operates very
effectively as a transport agent it also has a
deleterious effect with regard to its reaction with the
inner leads supporting the tungsten filament within the
lamp. To avoid such a deleterious effect these inleads
are commonly formed of a relatively expensive material
such as molybdenum and tungsten. The halogen atmosphere
also has a drawback in that during the manufacturing
process of the halogen lamp safeguards need to be
accomplished to prevent gaseous impurities from entering
the confines of the lamp that would otherwise degrade
the tungsten-halogen regenerative cycle.
It is desired that the tungsten deposition rate
onto the walls of the incandescent type lamps be reduced
in order to eliminate the use of a halogen transport
agent so as to allow the use of less expensive inner
leads e.g., nickel, and nickel-plated iron and, also to
ease the manufacturing process of the incandescent type
lamp.
Accordingly, it is an object of the present
invention to provide a means whereby the bulb walls of
the incandescent type lamp remain clean without the use
of a halogen transport agent.
These and other objects of the present
invention will become apparent upon consideration of the
following description taken in conjunction with the
accompanying drawing.
SUMMARY OF THE INVENTION
In accordance with the present invention an
efficacy improved mercury pressurized incandescent lamp
is provided having an envelope containing a tungsten
filament, an inert gas, a predetermined amount of
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vaporizable mercury, and an oxygen getter.
The mercury pressurized incandescent lamp
comprises a light transmitting envelope having spatially
disposed therein the tungsten filament, the oxygen
getter, and contains an inert gas along with the vapor-
izable metal mercury. The inert gas has a fill
pressure of about slightly less than 1 atmosphere for
ease of manufacturing but can be greater than 1
atmosphere and is selected from the group consisting of
argon, nitrogen, krypton and xenon. The mercury
pressure is desired to be as high as possible to
suppress tungsten evaporation from the filament and is
determined by cold spot temperatures of the lamp. A
cold spot temperature of about 450 C or more is
necessary so as to advantageously obtain an operating
mercury pressure of five (5) atmospheres or more. The
oxygen getter is selected from the group consisting of
titanium, zirconium, tantalum, phosphorous and boron.
The features of this invention believed to be
novel as set forth with particularity in the appended
- claims. The invention, itself, however, both as to its
method and operation, together with further objects and
ldvantages thereof, may be best understood by referring
to the following description taXen in conjunction with
the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is the only drawing of the present
invention and illustrates an improved efficacy, mercury
pressurized light sources findinq application in various
incandescent type lamps.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1, illustrates a mercury pressurized
incandescent lamp 10 in accordance with one of the
embodiments of the present invention.
The lamp 10 has an envelope 12 which may be
comprised of a relatively thick, about 1.0 mm.,
translucent glass material. The envelope 12 may be
'i~8~)14~
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formed of glass tubing with an outer diameter in the
range of about 5 mm to about 10 mm. The envelope 12 may
be of a ~180 type low sodium, high temperature glass
r available from the General Electric Glass Department of
Cleveland, Ohio, and permits high wall temperatures
necessary to vaporize the mercury and also
advantageously provide high operating pressures.
The light transmissive envelope 12, shown in
FIG. 1, has spatially disposed therein, in a transverse
manner, a tungsten filament 14. The filament 14 may
also be arranged to be disposed in a coaxial manner
within the envelope 12. Further, the lamp 10 shown in
FIG. 1 as being of a single-ended arrangement with both
inner leads 16 and 18 extending out of the same end of
envelope 12, may also be arranged as a double-ended lamp
wherein inner leads 16 and 18 extend out of opposite
ends of envelope 12.
The parameter of the filament 14, such as the
number of turns of tungsten wire, the pitch ratio of the
turns, the length and wire size, are all preselected in
according with the excitation voltage desired to operate
the lamp 10. The filament 14, shown in FIG 1, is
connected across the pair of inner leads 16 and 18 which
enter, extend through and exit out of a pinch seal
region 20 of the envelope 12.
The inner leads 16 and 18 are formed of a
relatively inexpensive material such as nickel, and
nickel-plated iron. As discussed in the "Background"
section of the present invention, the use of these
30 relatively inexpensive inner leads in the lamp 10 is
advantageous over prior art tungsten lamps having a
halogen gas which require relatively expensive materials
inner leads such as molybdenum and tungsten. These
relatively expensive inner leads are necessitated by the
use of a halogen gas within the envelope as a transport
agent to return evaporated tungsten back to the
filament. Further~ the halogen gas necessitates
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safeguards during the related manufacturing process so
as to prevent gaseous impurites from entering the
c:onfines of the related lamp which would otherwise
r clegrade the performance of the tungsten-halogen
regenerative cycle.
The present invention negates the need of these
expensive inner leads and eases the manufacturing
process of related lamp by eliminatin~ the use of a
halogen additive and instead provides a vaporizable
metal mercury operated at a relatively high pressure as
the transport agent of lamp 10.
The light transmissive envelope contains an
inert gas, a vaporizable metal mercury and an oxygen
getter. The inert gas has a fill pressure of slightly
less than one atmosphere, more particularly, it is the
range of about 600 torr to about 700 torr, for ease of
manufacturing and is selected from the group consisting
of argon, krypton, xenon, and nitrogen. The lamp may
contain a pressure of inert gas in excess of 1
atmosphere for higher total pressure during operation.
The mercury pressure within the lamp is desired
to be as high as possible and is determined by the cold
spot temperatures of the lamp. A cold spot temperature
in excess of 450 C is desired so as to obtain an
operating mercury pressure of five (5) atmospheres or
25 more. The cold spot temperatures are occurring within
the envelope 12 at locations remote from the operating
filament such as those locations in the upper and lower
regions of the envelope 12. For an envelope with a
volume of lcc and a cold spot temperature of 450C, 16.7
mg of mercury produces an operating pressure of five (5)
atmospheres, and for the same envelope having a cold spot
temperature of 510~C, 31 mg of mercury produces an
operating pressure of ten (10) atmospheres. The amount
of mercury within the lamp should also be such that it is
completely vaporized during operation so that there is no
condensed liquid mercury present that would otherwise
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result in a potential arcing problem between the inner
leads of the lamp.
Further, the envelope 12 contains an oxygen
getter 22 selected from the group consisting of titanium,
zirconium, tantalum, phosphorus and boron. If an oxygen
getter 22 is selected from the group consisting of
titanium, zirconium, tantalum, and boron it may be in the
form of a pad affixed to either or both of the inner
leads, so long as it is connected within the confines of
the envelope 12, and is shown in FIG. 1 as being affixed
to inner lead 18. If phosphorus is selected as the
oxygen getter 22, it may be placed into the envelope in
the form of a slurry added onto the filament 14.
For the operation of lamp 10, it is necessary to
eliminate or minimize the transport of tungsten from the
filament to the bulb wall by the well-known water cycle,
and this can be accomplished by the addition of the known
getters such as titanium, zirconium, tantalum,
phosphorous and boron. In general, these getters are
added in milligram quantities which is a function of the
volu~e of the lamp 10. For the lamps contemplated by the
present invention, the amount of getter is desired to be
in the range of 0.1 milligrams to 1.0 milligram.
The incandescent lamp 10 of the present
invention containing the high pressure of mercury in the
envelope 12 reduces the occurrences of arcing between the
inner leads which may renders the lamp 10 inoperable.
These arcing conditions, without the benefits of the
present invention, are most prominent when the lamp is
operated with voltage excitation in excess of 120 volts
and reduces as the operating voltage is lowered to a
value of about 10 volts. The arcing problem particularly
noticed at the higher voltages, may be reduced by the
selection of the relatively heavy inert gases of krypton
and xenon along with the addition of nitrogen. The
present invention of lamp 10 also containing the high
pressure of mercury suppresses the evaporation of
1~30149
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tungsten from the filament and thus reduces the rate of
wall blackening of the envelope 12.
In our initial investigation, an attempt to
r calculate the evaporation rate of tungsten, or more
particularly, the arrival rate of the evaporated tungsten
from the filament at the walls of the mercury
pressured lamp, revealed that an unusual situation
exists in such a lamp in that the mercury ingredient
which acts as buffer gas was heavier than the dilute
species of tungsten which evaporates from the filament.
As a result of our lamp test findings, we were
unable to determine, by a light transmission technique,
the approximate rate of tungsten evaporation in this
environment. The contribution of concentration or
thermal diffusion to the tungsten transport from the
filament to the walls of the envelope is related to the
temperature difference between the energized filament
and the walls of the envelope. The contribution and the
sign~ positive or negative contribution, of the
transport due to thermal diffusion was unknown initially.
After further investigation, we determined that
because mercury, which is heavier than the tungsten
material being evaporated, was acting as a buffer gas
and up-gradient transport was apparently taking place.
The up-gradient transport was unexpected in that a
down-gradient transport of tungsten from the hot
filament to the cold wall, was expected which would
otherwise increase the deposition rate of the evaporated
tungsten to the walls of the envelope. ~owever, the
3~ unique mercury-tungsten interaction decreased the rate
of arrival of the evaporated tungsten at the walls of
the envelope 12.
We further recognized that in the mercury
pressurized lamps of our invention not having a halogen
additive, an effective oxygen getter, such as those
previously described, further reduces the transport of
tungsten from the filament to the wall of the envelope
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otherwise occurring by a water cycle transfer created by
oxygen bearing impurities, specifically water (H2O) or
carbon dioxide (CO2) that may have entered the
confines of envelope 12.
The combination of mercury-tungsten interaction
and the oxygen getter both of the present invention
reduces the deposition rate of the evaporated tungsten
at the wall of the envelope 12 and thereby prolongs the
life of lamp 10 with regard to its efficient operation.
In the practice of our invention two (2) lamps
havin~ ar~on and mercury, in amounts previously
described and an oxygen getter were tested. In
contemplation of the testing, it was our expectation
that the lamps to be tested which were processed to
minimize oxygen contamination, and accordingly, the
water cycle transfer, would experience blackening of the
walls of the envelope a~ter a period of approximately 50
hours. To our surprise the lamps were successfuly
operated for a period of over 700 hours without
experiencing any visible blackening of the walls of the
inner envelope.
It should now be appreciated that the present
invention provides a mercury pressurized incandescent
lamp that provides for means to reduce or even eliminate
the wall blackening of the incandescent lamp without the
need of a halogen gas.
