Note: Descriptions are shown in the official language in which they were submitted.
97-l-070 -l- PATENT APPLICATION
INCANDESCENT LAMP HAVING TUNGSTEN-HALOGEN
CAPSULE WITH TITANIA/SILICA EXTERNAL INFRARED REFLECTIVE
COATING AND OXYGEN-FILLED OUTER JACKET
BACKGROUND OF THE INVENTION
l. Field of the Invention
The invention relates to electric incandescent lamps
and is directed more particularly to a tungsten-halogen
lamp.
2. Description of the Prior Art
Tungsten-halogen lamps are well known in the art and
may include a hardglass envelope having a pair of lead-in
wires. A tungsten filament extends between the internal
termination of the lead-in wires. The envelope is
hermetically sealed, typically by a press seal. The
envelope is filled with an inert gas, and one or more
halogens (i.e., iodine, bromine, chlorine and fluorine).
The hardglass is a material having a linear coefficient of
thermal expansion of from about 30 to 50 X 10-7 in/in/~C,
having softening temperatures from about 750~C to about
1020~C, and having a strain point of about 650~C to about
760~C. Exemplary of such materials are the borosLlicate and
aluminosilicate glasses. A suitable glass is discussed in
U.S. Patents Nos. 4,060,423 and 4,105,826.
As the lamp wattage is increased and/or the size of the
lamp envelope is decreased, the envelope wall temperature
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increases, causing some of the alkaline ions of the
hardglass (i.e., barium, strontium and calcium ions) to
diffuse to the inner surface of the glass and/or outgas into
the lamp where they interact with the halogen gas. The
result is a condensation of the reacted halogen gas on inner
walls of the lamp, which reduces the available halogen level
in the lamp. Sufficient depletion of the halogen content in
this manner can lead to failure of the halogen cycle, and
blackening of the envelope wall, due to deposited tungsten.
In view of the limitations of using hardglass for the
envelope of a tungsten halogen incandescent lamp, the
envelope of such lamps sometimes i8 made from vitreous fused
silica (i.e., quartz) or a high silica content glass, such
as one composed of ninety-six per cent silica. However,
quartz and ninety-six per cent silica glass are difficult to
process and therefore relatively expensive. Also, lamps
made of quartz require a moly foil seal which is also
somewhat more difficult and expensive to fabricate.
To prevent the reaction of halogen with the lamp
envelope and to alleviate the need to use quartz or 96~
silica glass, it is known to provide a tungsten-halogen
incandescent lamp with an internal barrier layer of silicon
dioxide (SiO2). The coating forms a continuous and glassy
barrier on the inner surface of the lamp envelope which
prevents alkaline ions of the hardglass of the envelope from
reaching the atmosphere in the envelope. The halogen is
thus prevented from reacting with the alkaline ions of the
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hardglass, leaving the halogen in a gaseous stat:e. In U.S.
Patent No. 5,473,226 issued December 5, 1995 to Mark D.
Beschle et al, the silicon dioxide coating is discussed in
detail.
It is also known to provide a tungsten-halogen
incandescent lamp envelope with an external coating of
infrared ray reflection material to make use of the usually
wasted infrared energy emitted by incandescent lamps. The
infrared ray reflection film transmits visible rays and
reflects infrared rays back to the filament, thereby
decreasing the energy needed to maintain the filament at its
operating temperature.
In U.S. Patent No. 4,160, 929, issued July l0, 1979 to
Luke Thorington et al, there is disclosed an external
coating comprising three layers, including a first layer of
titanium dioxide (TiO2), a second layer of silver (Ag), and
a third layer of titanium dioxide.
In U.S. Patent No. 4,524,410, isgued June 18, 1985 to
Akira Kawakatsu et al, there is discussed an envelope
external coating comprising three layers, including a first
layer of titanium dioxide (TiO2), a second layer of silica
(SiO2) and a third layer of titanium dioxide. There is also
discussed the use of materials other than titanium dioxide,
such as zirconium dioxide (ZrO2), tantalum pentoxide (Ta2Os)
and cerium dioxide (CeO2), and the use of materials other
than silica, such as magnesia (MgO) and alumina (Al203). A
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single layered film of titanium dioxide is further
suggested.
In U.S. Patent No. 5,422,534, issued June 6, 1995 to
Frederick W. Dynys, there is disclosed a reflective coating
for incandescent lamps, the coating including alternating
layers of titania, tantala and silica.
It is known also to use a coating of alternating layers
of titania and silica.
Unfortunately, when a reflective coating is used on a
capsule in a parabolic reflector lamp, the capsule wall
temperature can exceed the use temperature range for most
hard glass formulations. When the capsule wall sustains
high temperatures for long periods of time, the halogen in
the capsule reacts with the capsule wall, leading to a
reduction in the available halogen content, thus causing the
halogen cycle to fail. Accordingly, quartz envelopes are
frequently used in combination with the infrared reflective
coatings in parabolic reflector lamps, making the infrared
conserving products very expensive and less cost effective
than they might otherwise be. To reduce the cost of the
lamp substantially, it appears necessary that the capsule
envelope be of hardglass rather than quartz.
It had been thought that the above-mentioned inside
coating of silicon dioxide, or the like, would solve the
problem by eliminating the halogen reaction with the
hardglass capsule wall. While the interior barrier layer
appears to have merit, it is clear that a further safeguard
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is needed, either in place of, or in addition to, the
interior barrier. It appears that the solution to the cost
and halogen cycle failure problems in a tungsten-halogen
capsule for a parabolic reflector lamp, wherein the capsule
i9 provided with a infrared reflective outer coating, is to
provide a hardglass capsule and means to cool the capsule to
an operational temperature consistent with the operational
temperature of a hardglass capsule without the infrared
reflective coating. It has been found that filling the
outer jacket with helium provides the necessary cooling
effect; however, the helium fill may have the deleterious
effect of reducing the titania layer on the capsule
exterior. This reduction can result in a 1088 of visible
transmission of the coating.
S Accordingly, there is a need to provide an incandescent
lamp, and in particular, a parabolic reflector lamp, wherein
a hardglass tungsten-halogen capsule is provided with an
outer coating of titania-silica and wherein the visible
light transmission is not degraded by reduction of the
titania.
There is further a need to provide a lamp as described
immediately above, wherein the outer coating may be used in
conjunction with the aforesaid silicon dioxide inner
coating.
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SUMMARY OF THE INVENTION
An object of the invention is, therefore, to provide an
incandescent lamp wherein a tungsten-halogen capsule is
provided with an outside coating of titania-silica and
wherein visible light transmission is not degraded by
reduction of the titania in the outside coating.
A further object of the invention is to provide an
incandescent lamp wherein a hardglass tungsten-halogen
capsule is provided with an outside coating of titania-
silica.
A further object of the invention is to provide aparabolic reflector lamp including a tungsten-halogen
capsule disposed in an outer jacket comprising a parabolic
reflector hermetically sealed around the capsule.
A still further object of the invention is to provide
an incandescent lamp wherein a tungsten-halogen capsule is
provided with an outside coating of titania-silica and an
inside coating of silicon dioxide.
With the above and other objects in view, as will
hereinafter appear, there is provided an incandescent lamp
comprising a hermetically sealed envelope, a first fill gas
including halogen contained by the envelope, at least one
tungsten filament sealed in the envelope and supported by
lead-in wires, and a titania/silica infrared reflective
coating on an outside surface of the envelope. An outer
jacket encloses the envelope, the outer jacket having
therein a second fill gas at a pressure of no more than
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about 600 torr, the fill gas consisting of a mixture of
helium and oxygen.
In accordance with a further feature of the invention,
the capsule is of hardglass.
In accordance with a further feature of the invention
the aforementioned outer jacket comprises a parabolic
reflector hermetically sealed about the envelope.
In accordance with a still further feature of the
invention, there is provided on an inside surface of the
envelope a coating of silicon dioxide.
The above and other features of the invention,
including various novel details of construction and
combinations of parts, will now be more particularly
described with reference to the accompanying drawings and
pointed out in the claims. It will be understood that the
particular device embodying the invention is shown by way of
illustration only and not as a limitation of the invention.
The principles and features of this invention may be
employed in various and numerous embodiments without
departing from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference is made to the accompanying drawings in which
is shown an illustrative embodiment of the invention, from
which its novel features and advantages will be apparent.
In the drawings:
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FIG. 1 is a sectional view of one form of incandescent
capsule illustrative of an embodiment of the invention; and
FIG. 2 is a partly elevational and partly sectional
view showing the capsule of FIG. 1 in combination with an
outer jacket comprising a parabolic reflector.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, it will be seen that an
illustrative embodiment of the invention includes tungsten-
halogen capsule 10 comprising a hermetically sealed envelope
12, preferably of hardglass, but alternatively of quartz, or
96~ silica glass, enclosing at least one tungsten filament
14 supported by lead-in wires 16, 13. The filament 14 is
electrically connected, through the lead-in wires 16, 18 to
a pair of contact pins 20, 22 which project from the
envelope 12. The hermetic seal of the envelope is effected
by a press seal 24. The envelope 12 is further provided
with a tubulation 26, shown tipped-off in the drawings,
through which air is exhausted, in manufacture of the
capsule 10, and an inert first fill gas including one or
more halogens (i.e., iodine, bromine, chlorine and fluorine)
is introduced.
The envelope 12 preferably, but not necessarily, is
provided with an inner barrier layer 30 on an inside surface
32 of the envelope 12, the barrier layer 30 preferably
comprising silicon dioxide. The barrier layer 30 prevents
the alkaline ions of the hardglass from reaching the
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atmosphere in the envelope 12, the halogen thereby being
prevented from reacting with the hardglass alkaline ions,
permitting the halogen to remain in a gaseous state and
continue a tungsten-halogen regenerative cycle, well known
in the art.
The envelope 12 is provided with a titania/silica
infrared reflective coating 40 on an outer surface 42 of the
ènvelope. The coating 40 permits passage therethrough of
visible light and reflects infrared energy back towards the
filament 14 such that less electrical energy is required to
malntain the filament temperature at an operative level.
Referring to FIG. 2, it will be seen that the
illustrative lamp includes an outer jacket 50 hermetically
enclosing the capsule 10. Illustrated in FIG. 2 is outer
jacket 50 in the form of a parabolic reflector 52. The
reflector 52 forms a cavity 54 and includes a forward
concave reflecting portion 56 and a rear neck portion 58
adjacent thereto. A skirted portion 60 of a lamp base 62 is
secured to the rear neck portion 58 of reflector 52. A lamp
base portion 64 includes a threaded metal shell 66 and a
metal eyelet 68. Contact pins 20, 22 are electrically
connected to the threaded metal shell 66 and the metal
eyelet 68, respectively. A lens 70 is hermetically sealed
to the reflecting portion 56.
The outer jacket 50 contains a second fill gas
including oxygen. The second fill gas is a mixture of
helium and oxygen, wherein the oxygen content is about 2% to
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about 20% of the mixture, by volume, and preferably is
around 5~ by volume. The second fill gas mixture is under
pressure in the outer jacket 50 of no more than about 600
torr. The second fill gas insures that oxygen is present
contiguous to the titania/silica outer capsule coating 40 to
maintain the oxidation state of the coating 40 such that the
coating 40 retains the proper visible light transmission and
infrared light reflectance characteristics. The second fill
gas also conducts heat away from the capsule 10, thereby
operating to cool the capsule to an acceptable operating
temperature.
While the use of a hardglass capsule is preferred for
cost reasons, it has been found beneficial to provide the
oxygen-containing fill gas in quartz and 96~ glass capsules
in parabolic reflectors to insure proper visible light
transmission.
There is thus provided an incandescent lamp and,
particularly, a parabolic reflector lamp, wherein the
tungsten-halogen capsule is provided with an outer coating
of titania/silica and wherein an outer jacket hermetically
encloses the capsule therein and contains a fill gas
including oxygen which conducts heat from the capsule and
which maintains the oxidation state of the outer coating
such that the transmission of visible light from the capsule
is maintained and not degraded.
There is further provided a lamp as described
immediately above and further provided with a capsule inner
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coating of silica dioxide to prevent the alkaline ions of a
hardglass capsule from reacting with the halogen content of
the capsule fill gas, to permit the halogen to remain in a
gaseous state and react appropriately with the tungsten in a
regenerative manner.
It is to be understood that the present invention is by
no means limited to the particular construction herein
disclosed and/or shown in the drawings, but also comprises
any modifications or equivalents within the scope of the
claims.
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