Note: Descriptions are shown in the official language in which they were submitted.
97-1-071 -1- PATE~T APPLICATION
INCANDESCENT LAMP HAVING HARDGLASS
CAPSULE WITH EXTERNAL INFRARED REFLECTIVE
COATING AND OUTER JACKET ~ILL GAS COMPRISING HELIUM
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to electric incandescent lamps
and is directed more particularly to a tungsten-halogen
lamp.
Io 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 borosilicate and
aluminosilicate glasses. A suitable glass is discussed in
U.S. Patents Nos. 4,060,423 and 4,105,~26.
As the lamp wattage is increased and/or the size of the
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lamp envelope is decreased, the envelope wall temperature
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 level in
this manner can lead to failure of the halogen cycle, and
blackening of the envelope walls 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 i9 made from vitreous fused
silica (i.e., quartz) or a high silica content glass, such
S 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 difficule 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 layer 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
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reaching the atmosphere in the envelope. The halogen is
thus prevented from reacting with the alkaline ions of the
hardglass, leaving the halogen in a gaseous state. 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
lo 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 10, 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, issued 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 pentc,xide (Ta2Os)
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and cerium dioxide (CeO2), and the use of materials other
than silica, such as magnesia (MgO) and alumina (Al203). A
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
0 of titania and silica.
Unfortunately, when a reflective coating is used, and
the capsule is operated 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,
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.
'5 It had been thought that the above-mentioned insi e
coating of silicon dioxide, or the like, would solve the
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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
is needed, either in place of, or in addition to, the
interior barrier. It appears that the solution to the cost
problem in a tungsten-halogen capsule for a parabolic
reflector lamp, wherein the capsule is 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.
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 which reflects infrared energy back towards
the capsule filament, and wherein means are provided for
cooling the capsule wall to a temperature generally
coincident with the temperature of a conventional hardglass
capsule without an infrared reflective coating.
There i~ 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 hardglass tungsten-halogen
capsule is provided with an outside coating of infrared
reflective material and wherein there is provided means for
cooling the wall temperature of the capsule.
A further object of the invention is to provide a
parabolic reflector lamp including a tungsten-halogen
hardglass capsule disposed in an outer jacket comprising a
parabolic reflector means hermetically sealed around the
capsule.
A still further object of the invention i3 to provide
an incandescent lamp wherein a tungsten-halogen hardglass
capsule is provided with an outer coating of infrared
reflective material and an inqide coating of silicon
dioxide.
With the above and other objects in view, as will
hereinafter appear, a feature of the invention is the
provision of an incandeqcent lamp comprising a hermetically
sealed hardglass envelope, a first fill gaq including
halogen contained by the envelope, at least one tungsten
filament sealed in the envelope and supported by lead-in
wires, and an infrared reflective coating on an outside
surface of the envelope. An outer jacket encloses the
2S envelope, the outer jacket having therein a second fill gas
selected from a group of fill gases, the group consisting of
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(1) helium and (2) a mixture of helium and hydrogen
In accordance with a further feature of the invention,
the aforementioned outer jacket comprises a parabolic
reflector means 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 the aforementioned coating of silicon dioxide.
The above and other features of the invention,
including various novel details of construction and
0 combinations of parts, will now be more particularly
described with reference to the accompanying drawings and
pointed out in the claims. It will be under~tood that the
particular device embodying the invention i~ shown by way of
illustration only and not as a limitation of the invention.
The principles and features of thiq 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 it-~ novel features and advantages will be apparent.
In the drawings:
FIG. 1 i3 a sectional view of one form of incandescent
lamp illustrative of an embodiment of the inventioni and
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FIG. 2 iq a partly elevational and partly sectional
view showing the lamp 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 a
tungsten-halogen capsule 10 comprising a hermetically sealed
envelope 12 of hardglass, enclosing at least one tungsten
lo filament 14 supported by lead-in wires 16, 18. The filament
14 is electrically connected, through the lead-in wire 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, qhown 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
atmosphere in the envelope 12. As mentioned above, the
halogen is thereby prevented from reacting with the
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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 an infrared reflective
coating 40, such as a titania/silica coating, on an outer
surface 42 of the envelope. 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 maintain the filament temperature at a
filament 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 of
helium or a mixture of helium and hydrogen. When the second
fill gas is a mixture of helium and hydrogen, the hydrogen
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content is no more than about 10% of the mixture, by volume,
and preferably is less than about 10%, by volume. The
second fill ga9 mixture is under pressure in the outer
jacket 50 of no more than about 600 torr. The second fill
gas is a high thermal conductivity gas which cools the
hardglass capsule such that the capsule operates at about
the same temperature as a conventional hardglass capsule
without an infrared reflective coating.
There is thus provided an incandescent lamp and,
particularly, a parabolic reflector lamp, wherein a
hardglass tungsten-halogen capsule is provided with an outer
coating of infrared reflective material and wherein an outer
jacket hermetically encloses the capsule therein and
contains a fill gas of helium or a mixture of helium and
hydrogen and which conducts heat from the capsule
sufficiently to permit the use of hardglass as opposed to
quartz or ninety-six per cent silica glass.
There is further provided a lamp as described
immediately above and further provided with a capsule inner
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.
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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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