Note: Descriptions are shown in the official language in which they were submitted.
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TUNGSTEN HALOGEN LAMP ~ITH
LIGHT-SOURCE CAPSULE CONTAINMENT DEVICE
CROSS REFERENCES TO RELATED APPLICA~IONS
Canadian Patent Application, Ser~al No. 437,293-û, f~led
5 September 22, 1983 and assigned to the ass~gnee of th~s application,
contalns related sub~ect matter.
TECHN~CAL FIELD
This invention relates to double-enveloped tungsten halogen
incandescent lamps employing light-source capsule containment
devices.
BACKGR0UND ART
There is a small probability that a double-enveloped tungsten
halogen incandescent lamp will burst during operation of the lamp,
hereinafter called a "containment failure" of the lamp. When a lamp
containment failure occurs, the sequence of events internal to the
lamp is as follows. The tungsten halogen capsule bursts causing
fragments of glas~ or shards to be propel7ed against the outer
envelope; these shards shatter the outer envelope of the lamp. The
external result is that the lamp bursts. It is this type of lamp
Failure that is the subject of this disclosure.
~ ne type of containment failure which may occur in a lamp haYing
a single-ended light-source capsule is as follo~s. The capsule
ruptures near or in the press se~l. The rernainder ~r upper body of
the capsule remains intact~ Because of the release of substantial
pressure from within the capsule, the capsule body (sti!l referred
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to herein as a shard) is propelled away from the press seal toward
the outer envelope. The outer envelope is shattered by the impact
of the propelled capsule body.
The causes of these infrequ~ent lamp failures are varied and
5 unpredictable. There is no known way to eliminate the possibility
of such failures. Although occurrence of the failure is rare,
nevertheless it could present a safety hazard to a person in the
immediate vicinity of a lamp. Where such failures can be
anticipated, lamp manufacturers notify users by means of warnings on
lO packages and other descriptive materials and by suggested
precautions in specifications, This ha~ard may be avoided by
operating the lamp in a fixture designed to contain such a failure.
The requirement that the lamp be ooerated in a protective fixture is
frequently employed in commercial usage. However, this procedural
15 safeguard is less acceptable for consumer usage. For reasons of
safety, economy, and convenience in both commercial and consumer
usage, it may be desirable to incorporate a reliable containment
device as part o~ the larnp itself.
As used herein, the terms "light-source capsule" or "capsule~l
20 denote a tungsten halogen incandescent light~generating capsule of a
double-enveloped tungsten halogen lamp. This type of lamp, with
single-ended and double-ended capsules, has been suggested in the
prior art. U.S. Patent No. 3,l9~,625, by Danko, issued ~uly l3,
l965; ~o. 3,448,32l, by Shanks, issued June 3, l969; and No.
25 3,5l5,~30, by Walsh et al, issued June 2, l970, provide examples of
tungsten halogen lamps of both the single-ended and double-ended
capsule varieties.
The terms "efficacy" or "luminous efficacy" used herein are a
measure, expressed in lumens per watt, o~ the total lumi~ous flux
30 emitted by a light source over all wavelengths divided by the power
input of the source.
For a general reference on the tungsten halogen incandescent
lamp, see IES Lighting Handbook, l98l Reference Volume, Section 8.
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In U.S. Patent No. 4,281,274, issued July 28, 1981, by Bechard
et al, there is disclosed an enclosure of glass surrounding the arc
tube within the outer envelope of an arc discharge lamp. The
enclosure is suggested as being useful as a means to protect against
5 a containment failure of the lamp. While such enclosure may be
effective in containing some arç tube bursts, it has been ~ound that
in a substantial percentage of cases the enclosure itself is
shattered by the burst and containment failure of thP lamp ~ollows.
Thus, the glass enclosure device taught in the Bechard et al patent
10 offers only limited protection against lamp-containment failures,
and such protection is especially tenuous in lamps having
light-source capsules in which operating pressures may be as high as
20 atmospheres.
DISCLOSURE OF THE INVENTION
It is, therefore, an object of this invention to obviate the
deficiencies in the prior art.
It is another object of this invention to improve the operating
safety characteristics of tungsten halogen lamps.
These objects are accomplished, in one aspect of the invention,
by the provision of a double-enveloped tungsten halogen incandescent
lamp having a light-source capsule containment device. The lamp
comprises an outer envelope, a light-source capsule, a stem, a
containment mesh, and mesh-mounting means. The light-source capsule
is mounted within the outer envelope on the stem. The containment
2~ mesh is mounted operatively via the mesh-mounting means within the
outer envelope such that it substantially surrounds the light-source
capsule. ~he containment mesh has a minimal ef~ect on the e~ficacy
of the lamp. The flare of the stem is hermetically sealed to the
outer en~elope. -
In the event of a containment failure of the lamp, the ~
containment mesh restricts shards of the light-source capsule from
shattering the outer envelope.
.
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These objects are further accornplished, in another aspect o~ the
invention, by the provision of a dcuble-enveloped tungsten halogen
incandescent lamp having a light-source capsule containment
device. The lamp comprises an outer envelope, a light-source
capsule, a stem, a containment mesh, mesh-mounting means, and
collision-absorbing means. The light-source capsule is
single-ended, such capsule comprising a top and opposed base, with
the base including a press seal. The light-source capsule is
mounted within the outer envelope on the stem. The containment rnesh
is mounted operatively via the mesh-mounting means within the outer
envelope such that it substantially surrounds the light-source
capsule. The containment mesh has a minimal effect on the efficacy
of the lamp. The collision-absorbing means is mounted within the
outer envelope above the top of the light-source capsule. ~rhe flare
of the stem is hermetically sealed to the outer envelope.
In the event of a containment failure of the lamp, the
containment mesh restricts shards of the light-source capsule from
shattering the outer envelope. The outer ~envelope may be further
protected from being shattered by the collision-absorbing means
which absorbs and dissipates the energy of impact in the event the
light-source capsule or a substantial part thereof and the
containment mesh are propelled against the outer envelope
imrnediately following the burst of the light-source capsule.
Lamps with light-source capsule containment devices constructed
in accordance with the foregoing description will exhibit
substantially improved operating safety characteristics when
compared to lamps of the prior art.
.
BRIEF DESCRIPrION OF DRAWINGS
FIG. 1 is an elevational view of a tungsten halogen lamp
employing an embodiment of the invention, with some parts broken
away for clarity,
.
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FIG. 2 is an elevational view of a single-ended light-source
capsule illustrating an alternate embodiment of the invention3 with
parts broken away for clarity;
FIG. 3 is an elevational view of a single-ended light-source
5 capsule illustrating another embodiment of the invention, wikh
certain parts omitted for clarity;
FIG. 4 is an elevational view of a double-ended light-source
capsule employing an embodiment of the invention, with certain parts
omitted for clarity;
FIG. 5 is an enlaryed, partial, pictorial view of an embodiment
of a knitted containment mesh, and
FIG. 6 is an enlarged partial, pictorial, view of an embodiment
of a rigid containment mesh or screen.
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 taken in conjunction with the above-described drawings.
Referring to the drawings with greater particularity, FIG. l
shows a double-enveloped tungsten halogen incandescent lamp lO
having a light-source capsule containment device 12. Lamp lO
comprises outer envelope 14, light-source capsule 16, stem 18,
containment mesh 20, and mesh mounting means 22. Capsule 16 is
mounted on stem 18 by means of stiff lead-in wires 23 which protrude
from stem 18. In this embodiment, mesh 20 comprises knitted metal
.~
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wire which forms a cylindrical sleeve which is closed at mesh top
26. Mesh 20 encloses capsule 16 laterally and about capsule-top
2~. Mesh 20 may be formed into such a closed cylindrical sleeve by
means of being knitted, self-welded, clamped, etc. More than cne
method may be used in the construction of containment mesh 20, such
as knittiny the mesh into a cylindrical sleeve and closing mesh-top
26 by welding or clamping. Mounting means 22 for containment mesh
20 comprises anchoring pins 29. Mesh 20, in sleeve formD is mounted
by slipping the open end of the sleeve over capsule 16 and a portion
of stem 18 such that anchoring pins 29 fit through respective
stitches of mesh 20. Anchoring pins 29 should be inserted into
stitches of mesh 20 which are sufficiently distant from the edge of
the fabric so that the fabric ~ill not tear in the event a force is
exerted on mesh 20 in the direction of arrow 30. The distance
between mesh-top 26 and outer envelope 14, as shown by distance d in
the dra~ing, is greater than the maximum stretch of mesh 20 in the
direction of arrow 30. The flare of stem 18, not sho~n in the
drawing, is hermetically sealed to outer envelope 14.
In the event capsule 16 bursts, mesh 20 will absorb and contain
a substantial portion of the energy emanating from such burst. In
particular, mesh 20 will restrict shards of capsule 16 from
shattering outer envelope 14. If capsule 16 fractures such that a
substantial portion of capsule 16 is propelled in the direction of
arrow 30, mesh 2Q will contain capsule 16 and prevent it from
shattering outer envelope 14 because mesh 20 is anchored to stem 18
and distance d exceeds the maximum possible extension of mesh 20.
Thus, the protection against a containment failure of a tungsten
halogen lamp has been significantly improved.
In some embodiments, containment mesh 20 is knitted. In other
embodiments, containment mesh 20 may be rigid. In some embod;ments,
the knitted mesh may be preferred because of its superior
energy-containing capability, in other embodiments, the ri~id mesh
may be preferred because of its tractability~
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It is desirable tha~ the mesh be as light-transmissive as
possible so that there will be a minimal effect on the efficacy of
the lamp. A certain percentage of li ht will be reflected by the
mesh on the light's first pass through the capsule. A portion of
the reflected light will be unobstructed by the mesh on the
reflected light's subsequent pass or passes through the capsule.
Thus, the net reduction in luminous efficacy is less than would be
expected by estimating the percentage of the area of the capsule
covered by the mesh. In all observed cases, efficacy was reduced by
less than 7% due to the presence of the mesh. This efficacy loss
can be reduced to less than 6% by electropolishing the mesh.
Because of the partial diffusion caused by the mesh, there is
reduced glare from the lamp.
The mesh size, i.e., the number of stitches per inch, should be
selected such that the mesh will contain shards with mass larye
enough to be likely to cause a rupture of the outer envelope in the
event of a burst of the light-source capsule. The selection of mesh
si7e is dependent on many factors, such as the type of lamp, the
properties of the light-source capsule, the atmosphere within the
capsule, the type of mesh, the diameter and tensile strength of the
- strand or strands in the mesh, etc.
In embodiments where a wire mesh is employed, there is the
possibility of an electrical short circuit caused by contact of the
wire mesh with both lead-in wires. Where this possibility is a
concern, one or both lead-in wires can be insulated by means of a
dielectric sleeve or coating; also, one or both lead-in wires may
contain a f~se as an additional precaution.
In the embodiment shown in FIG. 19 containment mesh 20 is
mounted to stem 18 by means of anchoring pins 29. In some
embodiments, a single anchoring pin or clamp may suffice. Another
feasible mounting means would be to wrap a strap tightly around mesh
20 and stem 18. Stiil another mounting means may be to weld or
clamp the mesh to one or both lead-in wires 23 provided one or both
lead-;n wires 23 have been properly insul~ted against the
possibility of an electrical short circuit.
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The selection of construction material for the containment mesh
is heavily influenced by the environment within the outer envelope
during operation of the lamp and immediately follDwing a burst of
the light-source capsule. During lamp operation, the temperature
about the mesh may be in excess of 200 C. Stainless-steel wire
with a high chromium content is a preferred material for the
construction of the mesh and mounting strap or straps because o~ its
superior high-temperature properties, relatively low coefficient of
thermal expansion~ good resistance to oxidation and corrosion, and
high tensile strength.
Several example lamps of the type shown in FIG. 1 were
constructéd. Mesh sizes ranged from 7 to 20 stitches per inch.
Each containment mesh was knitted into a cylindrical sleeve ~rom a
single strand of stainless-steel wire having a diameter of .005
inches. Closure of the top of the mesh was accomplished by welding a
strap o~ nickel across the mesh top. The light-source capsules were
sealed into A 21 bulbs such that the distance between the top of the
mesh and the outer envelope was approximately one-half inch.
Internal capsule pressures were approximately 7-10 atmospheres when
20 the lamp was cold; operating capsule pressures were in the 15-20
atmospheres range.
FIG. 2 shows an elevational view of light-source capsule 16,
containment mesh 20, and mesh-mounting means 32. In this
embodiment, mesh 20 is mounted directly on capsule 16 by means of
strap 33 which is tightly wrapped around mesh 20 and press seal 28
of capsule 16. Alternate mounting means would be to clamp mesh 20
together below capsule-base 34 or to clamp mesh 20 to one or both
lead-in wjreS ~3. If either of ~he alternate mesh-mounting means
are employed, one or both lead_jn wires 23 should be insulated with
30 a dielectric sleeve or coating in order to prevent a possible
electrical short circuit caused by the wire mesh coming in co~tact
~ith both lead-in wires 23.
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In FIG~ 3, mesh 20 is mounted directly on capsule 16 by means of
elastic or frictional forces exerted against the body of capsule 16
by mesh 20 itself. W;th the frictional mounting means, mesh 20 may
not be anchored sufficiently to insure against the possibility of a
5 substantial portion of capsule 16 and mesh 20 being propelled in the
direction of arrow 30 and ;mpacting with the outer envelope of the
lamp. If this collision should occur, collision-absorbing means 36
acts as a cushion and prevents the shattering of the outer
envelope. In this embodiment, collis;on-absorbing means 36 is a
10 slightly crumpled portion of mesh 20 positioned above capsule-top 24.
In FIG. 4~ a double-ended light-source capsule 38 has
containment ~esh 20 secured thereto by mesh-mounting means 22. In
this embodiment, containment mesh 20 is a knitted cylindrical sleeve
21, and mesh-mounting means 22 comprises straps 43 which are tightly
15 wrapped around sleeve 21 and press seals 44 of capsule 3~.
FIG. 5 is an enlarged, partial, pictorial view of an embodiment
of a knitted con$ainment mesh 20. The stitch is approximately
square, as shown by approximately equal horizontal and vertical
distances x on the diagram. This type of mesh may be knitted from a
single strand 46 of wire or other suitable material~
FI&. 6 is an enlarged partial, pictorial view of an embodiment
of a screen or rigid containment mesh 20 which may be preferred in
certain embodiments of the invention. The stitch is approximately
square, as shown by approximately equal hori~ontal and vertical
distances y on the diagram. This type of mesh generally is
constructed from a plurality of strands of wire or strands of other
suitable material as shown by vertical strands 4R and hori~ontal
stran~s 50 in the diagram.
In another alternate embodiment of the inYention, the
containment mesh may be imbedded in the walls of ~he light-source
capsule.
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When light-source capsules in lamps like those described in FIG
1 were purposely induced to burst, an additional benefit of the
presence of the containment mesh ~as noted. The usual loud report,
which may be quite startling if unanticipated, was absent. The
capsules burst almost in total silence. It is believed that the
absence of the loud report may be explained by the fact that the
burst of the capsule was contained within the outer envelope. The
atmosphere within the outer envelope was near vacuum, and the sound
of the burst does not propagate through the vacuum.
Thus, there is provided a double-enveloped tungsten halogen
incandescent lamp having a light-source capsule containment device
which provides substantially improved operational safety
characteristics.
While there have been shown and described what are at present
considered to be the preferred embodiments of the invention, it will
be apparent to those skilled in the art t~lat various changes and
modifications can be made herein without departing from the scope o~
the invention as defined by the appended claims.
