Note: Descriptions are shown in the official language in which they were submitted.
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24,514
LIGHT-SOURCE CAPSULE CONTAINMENT
DEVICE AND LAMP EMPLOYING SUCH DEVICE
CROSS REFERENCE TO RELATED APPLICATION
Canadian patent application serial number 437,015-5 filed
concurrently herewith and assigned to the assignee of this
application, contains related subject matter.
TECHNICAL FIELD
This invention relates to light-source capsule containment
devices and electric lamps employing such devices.
BACKG~OUND ART
There is a small probability that a metal halide lamp or a
tungsten halogen 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 arc tube or tungsten halogen capsule bursts
causing fragments of glass or shards to be propelled against the
outer envelope; these shards shatter the outer envelope of the
lamp. The external result ;s that the lamp bursts. It is this type
of lamp failure that is the subject of this disclosure.
The causes of these infrequent lamp failures are varied and
unpredictable. there is no know 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. ~here such failures can be
anticipated, lamp manufacturers notify users by means of warnings on
packages and other descriptive materials and by suggested
precautions in specifications. This hazard may be avoided by
operating the lamp in a fixture designed to contain such a failure.
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The requirement that the lamp be operated in a protective fixture is
frequently employed in commercial usage. However, this procedural
safeguard is less acceptable for consumer usage. For reasons of
safety, economy, and convenience in both commercial and consumer
5 usage, it may be desirable to incorporate a reliable containment
device as part of the lamp itself.
As used herein, the term "light-source capsule" denotes an arc
tube of an arc discharge lamp, a halogen capsùle of a tungsten
halogen lamp, or any light-emitting capsule within the outer
envelope of a lamp where the possibility of a lamp-containment
failure exists.
The terms "efficacy" or "luminous efficacy" used herein are a
measure expressed in lumens per watt of the total luminous flux
emitted by a light source over all wavelengths divided by the power
15 input of the source.
In U.S. Pat. No. 4,281,274, issued July 28, 1981, by Bechard et
al, there is disclosed an enclosure of glass surrounding the arc
tube wi$hin the outer envelope of an arc discharge lamp. The
enclosure is suggested as being useful as a means to protect against
20 a containment failure of the lamp. While such enclosure may be
effective in containing some arc tube bursts, it has been found that
in a substantial percentage of cases the enclosure itself is
shattered by the burst and containment failure of the lamp follows.
Thus, the glass enclosure device taught in the Bechard et al patent
2~ 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 or 30 atmospheres.
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DISCLOSURE OF THE INVE~ITION
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
5 safety characteristics of arc discharge lamps.
Another object of this invention is 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 light-source capsule containment device
10 comprising a shield, containment means, and mounting means. The
shield has a light-transmissive body enclosing a cavity. The body
of the shield has at least one opening in it. The containment means
substantially contains shards of the shield. The containment means
has a minimal effect on the transmissiveness of the shield. The
15 mounting means provides for mounting the oontainment means
operatively with respect to the shield.
These objects are further accomplished, in another aspect of the
invention, by the proYiSion of a lamp having a light-source capsule
containment device. Such 1amp comprises an outer envelope, a
20 light-source capsule, a stem, a shield, containment means, and
mounting means. The light-source capsule is mounted on the stem
within the outer envèlope. The shield has a light-transmissive body
which encloses a cavity. The body of the shield has at least one
opening in it. The shield is mounted such that the light-source
~5 capsule is substantially contained within the cavity of the shield.
The containment means substantially restricts shards of the shield
and shards of the light-source capsule from colliding with and ~
shattering the outer envelope in the event the light-source capsule
bursts and causes the shattering of the shield. The containment
30 means preferably has a minimal effect on the efficacy of the lamp.
The mounting means provides for operatively mounting the containment
means ~ith respect to the shield.
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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 DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view of one embodiment of a light-source
capsule containment device,
FIG. 2 is a perspective view of a second embodiment of a
light-source capsule containment device;
FIG. 3 is an elevational view of an arc discharge lamp employing
an embodiment of the invention;
FIG. 4 is an enlarged partial view of one embodiment of
containment means; and
FIG. 5 is an enlarged partial view of an alternate embodiment of
15 contaiment means.
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 ~isclosure and appended
20 claims taken in conjunction with the above-described drawings.
Referring to the drawings with greater particularity, FIG. 1~
shows a light-source capsule containment device 2 comprising shield
1, containment means 3, and mounting means 5. Shield-l is a
light-transmissive cylinder. Containment means 3 is a loosely woven
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wire mesh 4 which is wrapped around and substantially surrounds
shield 1. Mesh 4 may be sewn or constructed such that the mesh
forms a continuous cylinder around the exterior of shield 1.
Mounting means 5 comprises two metal straps 6 which secure mesh 4 to
5 shield 1. Metal straps 6 may be bound by appropriate means, such as
welding or clamping.
FIG. 2 shows an alternate embodiment of light-source capsule
containment device 2 comprising shield 9, containment means 11, and
mounting means 13. Shield 9 comprises light-transmissive cylinder
10 15 and dome 17 fused into a single light-transmissive body. There
is a circular opening 19 at the base of shield 9. Containment means
11 is a loosely-woven wire mesh 12 which surrounds shield 9
laterally and about dome 17. Mesh 12 may be sewn or constructed
such that the mesh forms a continuous enclosure around the exterior
15 of shield 9 everywhere except in the vicinity of opening 19.
Mounting means 13 comprises a metal strap 14. Mesh 12 may be
securely mounted to shield 9 with s~rap 14. `-Strap 14 may be bound
by appropriate means, such as welding or clamping.
FIG 3 shows a lamp 8 with light-source containment device 2.
Lamp 8 comprises outer envelope 21, light-source capsule 23, stem
25, shield 1, containment means 3, and mounting means 5. In the
embodiment of FIG. 3, lamp 8 is an arc discharge lamp and
light-source capsule 23 is a double-ended arc tube 24. Containment
25 device 2, comprising shield 1, containment means 3, and mounting
means 5, is the identical embodiment shown in FIG. 1 above.
Containment device 2 is mechanically mounted within outer envelope
21 to lamp mount 33 by means of support wires 31 such that
containment device 2 substantially surrounds arc tube 24 laterally.
30 Strap 10, being the closer of the two straps of mounting means 5 to
lamp mount 33~ is rigidly fastened to support wires 31. Support
wires 31 are rigidly fastened to lamp mount 33. Lamp mount 33 i3
mounted on stem 25. Rigid mechanical fastening may be accomplished
by welding, clamping, or other suitable--means.
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In the event arc tube 24 bursts, shield 1 will absorb a
substantial portion of the shards and energy emanating from such
burst. Frequently, shield 1 will be shattered by the effects of the
burst. At this point, mesh 4 is critical, Mesh 4 ~ill
substantially restrict shards of shield 1 and shards of arc tube 24
from shattering outer envelope 21. Thus, the protection against the
possibility of a lamp-containment failure has been significantly
improved.
FIG. 4 shows an enlarged partial view of mesh 4. The stitching
of the mesh is approximately square. As shown in the diagram,
distance x is size of the stitch.
FIG. 5 shows an enlarged partial view of another embodiment of
containment means 3 comprising a rigid mesh 35. This type of mesh
or screen is well known.
In the embodiments of the invention shown~in FIGS. 1, 2, and 3,
the containment means is exterior to the shield. There are other
embodiments where the containment means may be imbedded in the
shield.
In some embodiments, the containment means is a loosely woven
wire mesh. In other embodiments, the containment means may be a
rigid mesh. In some embodiments, the loosely woven mesh may be
preferred because of its superior energy-containing capability. In
other embodiments, the rigid mesh may be preferred because of its
tractability or greater transmissiveness.
It is desirable that the mesh be nighly transmissiYe of visible
light so that there will be a minimal effect on the efficacy of the
lamp. A certain percentage of light will be reflected by the mesh
on the light's first pass through the shield. A portion of the
reflected light will be unobstructed by the mesh on the reflected
light's subsequent pass or passes through the shield. Thus, the net
reduction in luminous efficacy is less than would be expected by
estimating the percentage of the area of the shield coYered by the
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mesh. In all observed cases, efficacy was reduced by less than 5%
due to the presence of the Mesh. Because of the partial diffusion
caused by the mesh, lamps with mesh-containment devices tend to have
less glare.
The selection of construction materials for the shield and
containment means is heavily influenced by the environment within
the outer envelope during operation of the lamp and immediately
following a burst of the light-source capsule. During lamp
operation, the ambient temperature about the shield and contaiment
means Inay be in excess of 300 C. Upon the burst of the
light-source capsule, the ambient pressure about the shield and
containment means may be in the neighborhood of 30 atmospheres.
Because of their excellent h;gh-temperature properties and
transmissiveness, quartz, fused silica, Pyrex, and hard glass would
be suitable materials for the construction of the shield.
Stainless-steel wire with a high chromium content is a preferred
material for the construction of the conta;nment mesh and mounting
strap or straps because of its superior high-temperature properties,
relatively low coefficient of thermal expansion, good resistance to
oxidation and corrosion, and high tensile strength.
In embodiments employing a containment mesh, the mesh size,
i.e., the number of stitches per inch, should be selected such that
the mesh will contain shards with mass large enough to be likely to
cause a rupture of the outer envelope in the event of a burst of the
light-source capsule. Thus, the selection of mesh size 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 wire in the mesh, etc.
In FIG. 3, there is shown an arc discharge lamp having a
double-ended arc tube and a cylindrical containment device. There
are equally feasible embodiments where arc discharge lamps with~
double-ended arc tubes employ domed containment devices like the
device shown in FIG. 2. There are also feasible embodiments where
arc discharge lamps with single-ended arc tubes employ domed
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con-tainment devices. All o~ the benefits and variations of
embodiments that have been disclosed with respect to arc discharge
lamps apply with equal effectiveness and validity to tungsten
halogen lamps and more generally to any electric lamps having a
light-source capsule within an outer envelope where the possibility
of lamp-containment failure exists~
Several example lamps were constructed. Each lamp employed a
quartz shield. ~he containment means was a loosely woven wire mesh
surrounding the shield. Mesh sizes ranged from 8 to 20 stitches per
inch. The mesh was constructed of stainless-steel wire having a
diameter of approximately .005 inches. The mounting means comprised
one or two stainless-steel straps.
In some embodiments of the invention, the mounting means for
securing the containment means to the shield may be inherent in the
shield or containment means. One example is an embodiment wherein
the containment means is imbedded in the shield. Another example is
an embodiment wherein the containment means is secured to the shield-
by means of elastic or adhesive forces exerted by the containment
means itself.
Thus, there is provided a light-source capsule containment
device and a lamp employing such a device which provide
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 that uarious changes and
modifications can be made herein without departing from the scope of
the invention as defined by the appended claims.
