Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
LD10,109
DISCHARGE LAMP WITH SURROUNDING SHROUD AND
METHOD OF MAKING SyCH LAMP
CROSS-REFERENCE TO RELATED APPLICATIOM
This application is related to earliex Application
S.N.157,360 Hansler et al, filed February 18, 1988, and
assigned to the assignee of the present invention, which
earlier application is incorporated by re~erence in the
pressnt application.
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This invention relates to a discharge-type lamp
that includes an inner envP}ope and a shroud joined to
the inner envelope and bounding a space surrounding the
inner envelope. The invention also relates to a method
of making such a lamp, particularly to a method o~
joining the shroud to the envelope.
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BACXG~OUND
In the aforesaid Application S.N. 157,360, Hansler
et al there is disclosed and claimed a metal-halide type
discharge lamp that includes a quartz inner envelope and
a tubular glass shroud surrounding the inner envelope
and spaced therefrom along a portion of the shroud
length. The tubular glass shroud is sealed at
predeterm~ned locations along its length to the inner
envelope, and the space between the shroud and the inner
envelope is evacuated or gas filled so that this space
constitutes a sealed chambPr. The shroud and the sealed
chamber serve a number o~ impcrtant functions, which are
pointed out and discussed in tha a~oresaid application.
Generally speaking, one of these functions is to make
the temperature of the inner envelope higher and more
uniform, and another is to keep the shroud relatively
cool in comparison to the inner envelope. The
significance of th~se functions is discussed hereinafter
and also in more detail in the afores~id earlier
application.
The ability to accomplish the results desired from
the shroud and the vacuum chambar or gas chamber depends
materially upon the nature of the joints or seals
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formed between the shroud and the inner envelope. For
example, if we assume that (i) the inner envelope is of
quartz and comprises an enlarged central region and
tubular portions extending therefrom and (ii) the shroud
is made of quartz tubing of inside diameter larger than
that of the enlarged central region, which tubing i5
simply shrunk down upon these tubular portions of the
inner envelope to form the two seals, then each seal
will be constituted by a very thick region of quartz
surroundinq a substantial length of the tubular portion.
To make such a seal requires a relatively large amount
o~ heat applied for a.relatively long time, followed by
a relatively long cooling period; and, as a result, the
thermal characteristics of this region are susceptibla
to being significantly changed by slight variations in
the process of making the seals. These changes in
thermal characteristics can detrimentally af~ect lamp
performance. ~oreover, the large amount of heat and the
relatively long times involved in making such a seal can
produce conditions that weaken, and possibly crack, the
tubular inner-envelope portion at the sealO
Another disadvantage of making the shroud-to-inner
en~elope seals by simply shrinking down the shroud about
the tubular portions of the inner env~lope, as above
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LDlo,los
described r is that using this approach will usually
result in each of these shroud seals being located
closely adjacent one of the foil seals of the lamp.
These foil seals are used for providing a seal for the
conductive inleads extending through the quartz of the
inner envelope. If the shroud seal is closely adjacent
the foil seal, there is an increased likelihood that the
heat used for making the shroud seal will adversely
affect the foil seal, possibly cracking the vitreous
material in the foil seal region and possibly even
causing a leak to develop in this r~gion.
Simply locating the shroud~to-inner envelope seals
at locations spaced further outwardly along the tubular
portions of the inner envelope from the foil seals is
not a satisfactory solution to these problems because
the heat for making the shroud seals can cause oxidation
of the nearby conductive inleads, and, moreover, this
approach results in undesirably increasing the overall
length of the lamp.
OBJECTS
An object o~ this invention is to provide a
discharge lamp of this general type in which a high
quality seal between the inner env210pe and the
surrounding shroud can be quickly made with very little
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heat.
Another object is to construct a lamp of this
general type in such a manner that the inner envelope-
to-shroud seals are located remote from the foil seals
yet without adding materially to the overall length of
the lamp.
Another object is to provide a discharge lamp of
this general type in which ths inner envelope-to-shroud
seals are made in such a manner that the thermal
characteristics of the lamp in the region of these se~ls
are relatively unaffected by slight variations in the
process of making the seals.
Still another object is to provide an improved
method for making a vacuum-tight seal or gas tight seal
between the inner vitreous envelope of a metal halide
discharge lamp and the surrounding shroud of vitreous
material.
Still another object is to provide, ~or making a
shroud-to-inner en~alope se~l of this type, an improved
method that enables the seal to be made quickly and with
very little heat.
Still another object is to make a shroud-to-innsr
envelope seal by a method that results in such seal
being located relatively remote from any other seals in
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LDlo,109the lamp, e.g., from any foil seal at the same end of
the lamp.
Another object is to provide an improved method
for making a lamp of this general type that readily
lends itself to being performed with automated
equipment.
SUMM~RY
In carrying out our invention in one form, we
provide (i) an innex envelope comprising a hollow
bulbous portion and two tubular portions of vitreous
material extending from the bulbous portion and (ii) a
tubular shroud of vitreous material surrounding the
bulbous portion and said tubular portions. In each of
the tubular portions of the inner envelope, we form a
disk-shaped enlargement by first heating a localized
region of the tubular portion to its softening point and
then subjecting this softened localized region to a
compressive force (i) that is abruptly applied along the
length of said tubular portion and (ii) that drives the
soPtened vitreous material radially outward into a disk
formation. We then place the tubular shroud over the
inn~r envelope so that each o~ the disk-shaped
enlargements is positioned in alignment with a
predetermined portion of the shroud and with the outer
periphery of the enlargement closely adjacent but
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slightly spaced from the inner periphery of said
predetermined shroud portion, thus forming an unsealed
chamber between the shroud and the inner envelope and
between the disk-shaped enlargements. We then form a
first seal between the inner periphery of one of said
predetermined portions of the shroud and the outer
periphery of the aligned disk-shaped enlargement by
heating and thereby softening said one predetermined
shroud portion and then collapsing this shroud portion
about the outer periphery of the aligned enlargement.
We form a second seal between the inner periphery of the
other o~ said predetermined shroud portions and the
outer periphery of the disk-shaped enlargement aligned
therewith.
In one embodiment of the invention, we evacuate
the above-defined chamber to a hard vacuum. In another
embodiment, we fill the chamber with a suitable gaseous
filler.
In still another e~bodiment, w~ provide the above-
defined disk-shaped enlarqement in only one of the
tubular portions of the inner envelope, omitting the
disk-shaped enlargement from the other tubular portion
and forming a conventional seal between the other
tubular portion and the surrounding portion o~ the
shroud aligned therewith.
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BRIEF DESCRIPTION OF FIGURES
For a better understanding of the invention,
reference may be had to the following detailed
description taken in connection with accompanying
drawings, wherein:
Fig. 1 is a sectional view of a metal-halide
disrharge lamp embodying one form of the present
invention. This lamp comprises an inner envelope of
vitreous material and a tubular shroud of vitreous
material surrounding the inner envelope.
Fig. 2 is a schematic illustration of one st~p
used in making the inner envelope portion of the lamp of
Fig. 1.
Fig. 3 shows the inner envelope portion of Fig. 2
after the fabrication steps depicted in Fig. 2 have been
completed.
Fig. 4 illustrates the manufacture of an arc tube
incorporating the inner envelope of Fig. 3.
Fig. 5 illustrates so~e of the method steps that
are used for incorporating the shroud of Fig. 1 into the
metal-halide lamp.
Fig. 6 is a sectional view of a metal-halide lamp
embodying a modified ~orm of the invention.
Fig. 7 is a sectional view of a vehirle
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head lamp that utilizes as its light source the lamp of
Figs. 1-5.
Fig. 8 is a simplified sectional view of another
modified form of the invention.
DETAILED DESC~IPTION OF EMOBIDMENTS
Referring now to Fig. 1, there ic shown a metal-
halide type of discharge lamp 10 that comprises an inner
envelope i2 of a light-transmitting vitreous material,
preferably quartz. The inner envelope 12 comprises a
bulbous central portion 14 and two tubular portions 16
and 18 integral with the central portion 14 and
projecting in opposite directions therefrom.
Surrounding the inner envelope 12 is a tubular
shroud 20, also of a Yitreous material, preferably
quartz. This shroud 20 has an enlarged central portion
22 disposed about the central portion 14 of the inner
envelope. Projecting from this enlarged central portion
22 are two tubular portions 24 and 26 respectively
surrounding the tubular por~ions 16 and 18 o~ the inner
envelope. Joining the shroud 20 to the inner envelop~
are two disk members 30 and 32 also of ~uartz. As will
be explained in more detail, these disk mem~ers 30 and
32 are integral with the tubular portions 16 and 18 of
the inner envelope and are joined at their respective
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LD10,109outer peripheries to the surrounding regions of the
shroud 20 to form vacuum-tight annular seals 33 and 35
between the disk members and the shroud.
The tubular shroud 20 is spaced from the inner
envelope 12 in the region between the two disk members
and 32, thus providing a sealed chamber 36
surrounding the inner envelope 12 and having an exterior
wall defined by shroud 20 and end walls defined by disk
members 30 and 32. In one form of this invention, this
sealed cha~ber 36 is ev~cuated to a hard vacuum during
fabrication of the lamp in a manner that will soon be
described~ Preferably, thi~ chamber includes a suitable
getter 38 that is used in a conventional manner to
assist in maintaininq the hard YacuUm in the chamber.
Within the inner envelope 12 are two spaced-apart
electrodes 40 and 42 between which an electric arc is
developed in a conventional manner to ser~e as a light
source. The electrodes are preferably of tungsten or a
mixture of tungsten and ~%-3% thorium oxide~ The
electrodes include rod portions 44 and 46, respectively,
that extend outwardly from the gap between the
electrodes into the tubular portions 16 and 18 of the
inner envelope. At the outer end of rod portion 44
there is a foil member 47, preferably of molybdenum,
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joined to the rod portion 44; and extending outwardly
from the foil member there is an inlead 48, preferably
of molybdenum, that is joined at its inner end to the
foil member. The foil member 47, the inlead 48, and the
rod portion 44 of the electrode are of a conventional
form, and they are joined together in a conventional
manner. The surrounding vitreous material o~ the
envelope portion 16, while hot and softened, is
collapsed about the foil, rod, and inlead structure in a
conventional manner (such as disclosed, ~or ex~mple, in
U.S. Patent 4,891,551 - Ahlgren et al) to form a leak-
proof seal between the foil member and th~ surrounding
vitreous material. At the opposite, or right-hand, end
of the arc tube there is a foil member 52 joined to an
inlead 50 and to the rod portion 46 of electrode 42.
These components are of the same fo~m and composition as
those at the left-hand end of the arc tube and are
mounted within the surrounding vitreous material in the
same way, a seal being present between the foil m mber
and the surrounding vitreous material. The above-
described inleads 48 and 50 and their associated foil
members s~rve in a conventional manner to carry electric
current to and from the arc, or discharge, that is
present between the electrodes when the lamp is on.
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In one embodiment of the invention, the central
portion 14 of the inner envelope 12 contains a fill
containing mercury, a metal halide, and in some cases
xenon gas. The operating pressure of the fill is in the
range of about 2 to about 65 atmospheres. This fill is
dsscribed in more detail and is claimed in the aforesaid
Application S.N. 157,360. Typically, one of the
principal components of the fill is sodium iodine.
As further pointed in Application S.N. 157,360,
the evacuated chamber 36 acts to produce an improved
wall temperature of the inner envelope 12 by
substantially eliminating the effects of gas conduction
and convection in th~ region surrounding the inner
envrlope. The presence o~ the evacuated chamber makes
this wall temperature higher and more uniform. This
results in more metal halide being vaporized and
maintained in the arcing region, which improves the
ef~iciency of the lamp and the color of the emitted
light. In metal-halide lamp~ operating at low frequency,
there is a catephoresis effect that tends to sweep the
metal halides into th~ end regions of the bulb (1~, but
in the illustrated lamp this effect is largely cancelled
out by the higher temperatures produced in these end
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regions by the presenc~ of the evacuated chamber 36 and
its thermal insulating effect.
This thermal insulating effect enables us, through
proper choice of the size of the shroud, to operate a
shroud of reasonable size at a sufficiently low
temperature that its electronic conductivity remains
very low. Maintaining thi~ low electronic conductivity
allows any sodium ions which diffuse through the inner
envelope and evaporate to settle on the inside wall of
the shroud without being electrically neutralized by
wall conduction. It is believed that this enables the
settled sodium ions to produce a strong electrical field
which opposes the motion of subsequent migrating sodium
ions, thereby reducing any further related sodium loss.
For the evacuated chamber 36 to function
consistently in the desired manner summarized above, it
is important to construct the joints between the outer
shroud (20) and the tubular portions (16 and 18) of the
inner Pnvelope in such a manner that the thermal
characteristics o~ the la~p in the region of these
joints are consistent and predictable from one lamp to
another. If these joints had required for their
fabrication high heat inputs maintained for long times,
then small variations in the process for making the~
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LD10,109
co~lld produce undesirable large variations in the
thermal characteristics of these regions of the lamp.
We have developed a method for making these joints which
can be performed with relatively little heat applied for
relatively short times, thus materially reducing these
undesirable variations.
The first step in our method is illustrated in
Fig. 2, where the tubular blank 60 from which the inner
envelope is formed is shown mounted within a convent-
ional glass lathe schematically illustrated at 61. This
lathe comprises a headstock 62 and a collet chuck 64 for
mounting the left~hand end of the tubular blank on the
headstock so that the left-hand end is fixed again~t
axial motion but i5 rotatable about the central
longitudinal axis 66 of the blank 60. The lathe further
comprises a tailstock 72 and a collet chuck 73 for
mounting the right-hand end of the blank 60. During
lathe operation, the tailstock and the heads~ock are
rotatably driven in synchrsnism about a common
longitudinal axis coinciding'with axis 66 by the same
drive mechanism, ~hereby rotating the blank 60 about its
longitudinal axis 66. In a conventional manner, the
tails~ock is alss sui~ably mounted for selective
movement parallel to this longitudinal axis 66, as
indicated by the arrow 79.
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LD10,109
Positioned adjacen~ the left-hand tubular portion
16 of the blank 60 is a burner 80 that is adapted to
develop a flame 82 that can be directed as shown against
an axially -localized region ~3 of the tubular portion
16. While the blank 60 is being slowly turned about its
axis 66 by the lathe, the flame 82 heats the axially~
localiæed region 83 about the entire periphery of the
tubular portion 83 until the quartz in this region 83
has reached its softening point. The tailstock remains
stationary during such heating; but when the quartz in
region 83 is sufficiently softened, the tailstock is
abruptly moved a short distance to the lPft, as
indicated by arrow 79. This abrupt leftward motion
causes compressive force to be applied to the softened
region 83 in a direction along the axis 66, and such
force has the effect of driving the softened quartz in
this region 83 radially outward about the entire
periphery of the tubular portion 16, thereby producing
the disk formation shown at 30 in Fig. 3. These heating
and force-applying steps (so~etimes rsferred to herein
as an upsetting op~ration~ can be readily controlled to
consistently produce a disk formation of a pred~termined
outer diameter and a predetermined thickness along the
length of axis 66.
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LD10,109
The operations of the immediately-prsceding
paragraph are repeated with the burner in a position 86
sAown in Fig. 2, thereby producing a second disk-shaped
enlargement, shown at 32 in Fig. 3. The outer diameter
of the disk-shaped enlargements 30 and 32 should not
exceed the outer diameter of the arc chamber 14 so that
the diameter of the shroud tube, which is later slipped
over the arc chamber, may be minimized.
A~ a next step, the two electrodes 40 and 42 and
their inlead structures are installed by first suitably
positioning each of these electrodes and inlead
structures as shown in Fig. 4. Then the surrounding
quartz (in region 90) is heated to its softening point
and is collapsed about the conductive structure. The
result is a sturdy mount for the inlead and the
electrode and a good leak-proof seal between the foil
memb~r 47 or 52 and the surrounding quartz. This
sealing of the foil member and mounting of the
electr~des and inleads is a conventional operation,
which is disclosed in grea~e~ detail in the aforesaid
U.S. Patent 4,8~1,551 - Ahlgren et al, assigned to the
assignee of the present invention. Th~ fill, described
hereinabove, that is present in the arc chamber 14 of
the lamp assembly of Fig. 1 is installed in a
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LD10,109
conventional manner after one of the foil seals is made
as above described but before the other foil seal is
made.
As a next step, the tubular shroud 20 is installed
as shown in Fig. 5. This shroud is positioned about the
inner envelope of Fig. 4 so that predetermined portions
92 and 94 thereof are in alignment with the disk-shaped
enlargements 30 and 32, respectively. Each of the disk-
shaped enlargements has been fo~med by the operation of
FigO 2 in such a manner that its outer diameter is
almost, but not quite, as large as the internal diameter
of the shroud 20 in the aligned regions 92 or 94.
Accordingly, there is a small clearance space about the
outer periphery of each of the enlargements that allows
the shroud 20 to be readily positioned in the desired
position shown.
After the shroud 20 has been so positioned, the
region 92 of the shroud is heated by flame 95 derived
~rom a ring-~ype burner 95 that surrounds the region 32.
After a relatively short time, the quartz of region 92
reaches its softening point and begins to contract under
the influence o~ surface tension. This causes the
softened region 92 to collapse about the outer periphery
of the aligned disk-shaped enlargement 30, which,
because of its proximity, has also been heated by flame
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LD10,109
9S. When the softened shroud region 92 collapses about
the outer periphery of the disk-shaped enlargement 30,
an excellent seal is formed between shroud region 92 and
the enlargement 30 ahout the entire outer periphery of
the enlargement.
After the first seal is made at 92, the space 36
between the shroud 20 and the inner envelope 12 and
between the disk-shaped enlargements 30 and 32 i~
evacuated. This is done by evacuating this space 36
with a suitable vacuum pump (not shown), which draws the
contents of this space out through tAe small clearance
space 97 surrounding the other disk-shaped enlargement
32. (The intake o~ the pump is connected in a
conventional manner between the tubular portion 18 of
the inner envelope and the surrounding tubular portion
26 of the shroud in a location above the enlargement
32.) While such evacuation is taking place, the walls
of space 36 are suitably heated to help drive off
absorbed gases. In a preferred form of the evacuation
proce s, we alternately pump the space 36 and flush it
with an inert gas, such as argon or nitrogen. The
flushing gas is introduced through the clearance space
97 in the intervals between the pumping periods.
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LD10,109
After space 36 has been evacuated in this manner
to a hard vacuum, a seal is made between the outer
periphery of the disk-shaped enlargement 32 and the
surrounding region 94 of the shroud 20. This seal is
made in essentially the same manner as was used for
makin~ the first seal (at 92). More specifically, the
shroud region 94 is heated to soften it, thereby causing
it to collapse about the outer periphery of the disk-
shaped enlargement and form a seal therewith. Because a
vacuum is then present in the chamber 36 and also in the
region above enlargement 32, there is a pressure
differential on opposite sides of the shroud wall which
promotes such collapse of the shroud about disk-shaped
enlargement 32.
To assure that a hard vacuum is developed and
maintained within the chamber 36, we provide, in one
form of the invention, a suitable getter 38 within
chamber 36. This getter is introduced, preferably,
before the shroud is assembled over the inner envelope.
In one form of the invention,~the getter comprises chips
of zirconium-titanium alloy dispersed about the inner
wall of the shroud This material is a good getter for
hydrogen.
The locations (83 and 86 of Fig. 2~ chosen ~or
forming the disk-shaped ~nlargements 30 and 32 are such
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that the enlargements ~o not interfere with sealing the
foils 47 and 52 within the tubular portions 16 and 18 of
the inner envelope 12. More specifically, the chosen
locations 83 and 86 are spaced axially outward from the
location of the foils. But this axial spacing is kept
sufficiently small so that the presence of the
enlargements does not add materially to the overall
length of the shrouded lamp.
A significant feature of our shroud-to-inner
envelope seals is that each seal is relatively remote
~rom the foil seal at the same end o~ the envelope. In
this respect, note in.Fig. 1 that the shroud-to-inner
envelope seal at each end of ths lamp is located
radially-outward of the foil seal at the same end of the
lamp by a distance approximately equal to the radial
dimension R of the associated disk-shaped enlargement 30
or 32. This remoteness of the shroud seal from the foil
seal is advantageous because it materially reduces the
chances that the foil seal will b~ detrimentally
affected by the heak involved in making the shroud seal.
It should also be noted that this remoteness between the
two seals is achieved without materially increasing the
overall length of the lamp since much of the separation
between the two seals is in a radial direction rather
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than an axial direction. Some axial separation is,
however,required so that the foil seal is located
outside the axial boundaries of the associated disk-
shaped enlargement.
Another significant advantage of our shroud-to-
inner envelope seals is that they can be made with
relatively little heat applied for only a short ti~e.
In this respect, it should be noted that because the
disk-shaped enlar~ements 30 and 32 extend radially
outward almost completely to the inner periphery of the
tubular form of the shroud, as best shown in Fig. 5,
only a slight displacement of the shroud radially
inwardly is required in order to move the shroud
material into contact with the portion of the inner
envelope to which it sealed. B~cause the amount of this
displace~ent is so small, very little heat and time is
required to effect it, and thus the chances are
substantially reduced that the lamp matrrial in the
vicinity of such seal will be detrimentally affected by
the heat of the s~al-making operation. This reduced
heating cooperates with the remoteness features of the
immediately-preceding paragraph further to protect the
foil seals from any detrimental effects of the shroud-
sealing operation.
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Moreover, because we are able to make the shroud-
to-inner envelope seals without requiring large amounts
of heat and time, we have found that the process
parameters are not critical. Minor variations in these
parameters can be tolerated without significantly
affecting the quality or characteristics oP the
resulting seal and the nearby lamp material. '7
Another significant advantage of our lamp and our
method of making it is that the lamp can be readily and
quickly made with automated equipmsnt. For example,
formation of the disk-shaped enlargements (30 and 32) is
effected with the simple heating and force-application
steps depicted in Fig. 2. Such steps are readily
performed on the same machine (lathe 61~ that was used
for forming the bulbous central portion 14 of the inner
envelope, which central portion 14 is pxeferably formed
in a conventional manner ~y heating the starting tubular
blank in this region and blowing the heat-softened
quartz radially outward. Wh~le the blank is on this
same machine and in the same position, the disk-shaped
enlargements 30 and 32 are introduced, as above
described. In addition, the seals between the shroud
and the inner envelope are made by simple and brieP
heating operations (Fig.5), which cause the heat
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softened regions of the shroud to collapse the short
distances required to effect high-quality seals to the
disk-shaped enlargements 30 and 32.
While the embodiment of Figs. 1-5 includes disk-
shaped enlargements (30 and 32) provided at both ends of
the lamp for making the shroud-to-inner envelope seals,
some of the advantages of our invention can still be
realized if an enlargement of this character is provided
only at one end of the lamp. At the other end of such a
lamp, the seal between the shroud and the inner envelope
can be made in a conventional manner, for example, by
allowing the heat-softened portion of the tubular shroud
to shrink down to the tuhular portion of the inner
envelope that it seals to. Such a lamp is illustrated
in Fig. 6, where this conventional seal, designated 100,
is shown at the left-hand end of the lamp. To
facilitate the making of seal 100, the tubular portion
24 of the shroud on the let hand end of the shroud is
made only slightly larger than the left-hand-end tubular
portion 16 of the inner env~lope. The shroud is then
slipped onto the inner envelope from the left hand end
of the inner envelope 50 that the larger diameter end of
the shroud slips over the bulbous portion 14 of the
inner envelope and the disk enlargement 32. Then the
seal 100 is made in a conventional manner.
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One type of lamp where the approach of Fig. 6 is
useful is one in which a surface of the shroud is coated
with a reflective material to form a reflector which can
be located close to the lamp. Such reflective material
is indicated at 102 in Fig. 6. At the right-hand side
of this lamp the shroud-to-inner envelope seal is the
same as in Fig. 1. At the left-hand side of the lamp,
the conventional seal 100 of the immediately-preceding
paragraph is present.
In a preferred embodiment of the lamp, the inner
envelope and the shroud are both of identical quartz~
But our invention in its broader aspects contemplates
the use of other vitreous material capable of
withstanding the high temperatures developed by
operation of the arc tube. It is usually very desirable
to use the same material for the shroud and the inner
envelope to avoid cracking or sealing problems that
might arise because of differ nt coefficients of thermal
expansion of two different fusedotogether materials.
But minor differences in the'two materials can often be
tolerated. For example, in another embodiment of our
invention, we utilize for the shroud quartz which has
been heated with a high electric field applied thereto
to remove any traces of sodium which can increase
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electronic conductivity. Such high resistance quarkz is
available from General Electric Company as its sodium-
free quartz. This high resistance quartz can be sealed
to an inner envelope of ordinary quartz without
encountering significant problems of differential
thermal expansion. The presence of such high resistance
quartz in the shroud is believed to help block sodium
loss through the inn~r envelope.
The lamps described hereinabove are especially
suited for forward lighting applications in a vehicle,
such as an automobile, truck, bus, van or tractor. The
aforesaid Application S.N. 157,360 - Hansler et al
discloges several different ways in which a lamp of this
general type is utilized for such forward lighting, and
the present lamps are utilizable in the sam~ ways. For
example, referring to Fig. 7 o~ the present application,
our lamp is shown at 10 within an automobile headlamp
110~ This headlamp comprises a reflector 112, a lens
member 114 at the front of the reflector, and lamp 10 in
the space between the reflec~or and the lens.
The reflector 112 has a rear section 118 having
mounted thereon a connector 120 with rearwardly-
projecting prongs 122 and 124 capable of being connected
to an external electrical source of the vehicle. The
reflector 112 has a focal point 126 on the axis 128 of
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LDlo,109
the headlamp. The light source 10 is predeterminedly
positioned within the reflector 112 so that its mid-
portion approximately coincides with the focal point 126
of the reflector. In the embodiment illustrated in Fig.
7, the light source 10 is oriented with its longitudinal
axis extending vertically and in a transverse manner
relative to the axis 128 of the headlamp.
In one embodiment, the reflector 112 has a
parabolic shape with a focal length in the range of
about 6 mm to about 35 mm, with a preferred range of
about 8 mm to about 30 mm. The lens 114, which is
suitably mated to the front portion of,the reflector, is
of a transparent material, such as glass or a suitable
plastic. The lens has a rear face preferably formed of
prism members.
The light source 10 is connected to the rear
section of the reflector 112 by means of rel tively
heavy support wires 134 and 136 each having one end
connected to one of the inleads 48 or 50 of the light
source and its other end connected to one of the prongs
122 or 124. The light source 10 is energized via an
electrical circuit that extends in series through the
prongs and the support wires.
While in the lamps described hereinabove, the
chamber 36 between ~he inner envelope and the shroud is
~J ~ 3
27
LD10,109
evacuated to a hard vacuum, it should be un~erstood that
our invention in its broader aspects comprehends lamps
of essentially the same structure as shown in Figs. 1
and 6 except including in the chamber 36 a gas having
appropriate properties. For example, in certain lamps it
is desirable that a predetermined portion of the heat
developed by operation of the arcing tube be transferred
across the chamber 36 by conduction or convection rather
than primarily by radiation, as when a hard vacuum is
present. With this consideration in mind, the chamber
36 can be filled with one of the fsllowing gases or
mixtures thereof: argon, krypton, xenon, nitrogen, air,
helium, and hydrogen. Typical charging pressures are in
the range of 0 to 1500 torr.
While in making the lamp of Fig. 1 we prefer to
evacuate (or fill) the chamber 36 through one of the
seal locations (e.g.,35) before a seal is made at this
location, our invention in its broader aspects
comprehends the use of a separate sealable tube (such as
shown in Fig. 8 at 105~ extending into this chamber
through which the cha~ber may be evacuated and/or
filled. When such a separate tube i5 used, we complete
the seals at 33 and 35 before evacuting (or filling~ the
chamber through the separate tube. Then the separate
tube 105 is pinched off or otherwise sealed in a
,
2 ~ 3
28
LD10,109
conventional manner to seal the chamber 36.
While we prefer to form the disk-shaped
enlargements 30 and 32 before the electrodes 40, 42 and
their inlead structures are incorporated in the arc
tube, the invention in its broader aspects contemplates
forming these enlargements after the ele~trod2s and
their inlead structures are incorporated and before the
shroud 20 is installedO
~ hile we have shown and described partic~lar
embodiments of our invention, it will be obvious to
those skilled in the art ~hat various change and
modifications may be made without departing from our
invention in its broader aspects; and we, therefore,
intend herein to cover all such changes and
modifications as fall within the true spirit and scope
of our in~ention.
, ' , ~ ', ' ~. : .,
