TECHNICAL FIELD
[0001] The present invention relates, in general. to metal halide discharge lamps and more
particularly to metal halide discharge lamps configured to prevent breakage of the
lamp's outer envelope by reducing shard dispersion upon an arc tube fracture.
BACKGROUND OF THE INVENTION
[0002] The high pressure discharge lamps of the invention operate by vaporizing mercury
and selected metal halides and often are simply called metal halide lamps. High wattage
metal halide lamps which achieve relatively high efficacy are known in the art. However,
these high wattage lamps are too large for general illuminating purposes in a home
or the like. Intermediate wattage metal halide lamps which can be used for some general
illuminating purposes are known but their efficacy is low when compared with lamps
of large sizes.
[0003] Through the recent development of miniature arc tubes, lamp designers have been able
to achieve acceptable efficacies in smaller sizes of metal halide discharge lamps
to justify its use as a replacement for the standard incandescent lamp. However, the
remote possibility of a minor dispersion of glass shards resulting from a fracture
of the pressurized light-source capsule (e.g., arc tube) contained within the lamp
is a substantial impediment in the path of developing a feasible replacement in the
industrial or commercial market. Although occurrence of such a fracture is rare, nevertheless.
it could present a safety hazard to a person or object in the immediate vicinity of
the lamp (i.e., food preparation). Therefore, it would be desirable to devise a simple
method that would allow for the safe use of such a lamp in an open fixture. An arc
discharge lamp which substantially eliminates the problem of shard dispersion upon
the fracture of the light-source capsule would constitute an advancement in the art.
[0004] Methods have been suggested to improve the ability of tungsten halogen and arc discharge
lamps to withstand a fracture of the inner light-source capsule. In one example, the
shards are restricted from impacting with the outer envelope through the use of a
cylindrical body disposed about the arc tube. U.S. Patent 4.281.274. issued July 28,
1981 to Bechard et al. The problem with the arrangement described in Bechard et al
is that the structure for mounting both the arc tube and the particular cylindrical
body is complex and requires welding several parts together. This leads to increased
cost and manufacturing difficulties during the process of making such a lamp.
[0005] It is believed, therefore, that an electric lamp that provides for a simple and inexpensive
means for mounting an arc tube and preventing shard dispersion upon an arc tube fracture,
and would also overcome the other disadvantages associated with the prior art devices
mentioned above, would constitute a significant advancement in the art.
DISCLOSURE OF THE INVENTION
[0006] It is, therefore, a primary objective of this invention to overcome the disadvantages
of the prior art devices such as mentioned above.
[0007] It is another object of this invention to provide an electric lamp which will substantially
eliminate the possibility of minor shard dispersion upon fracture of a pressurized
light-source capsule that is simple and inexpensive to manufacture.
[0008] Another object of this invention is to provide means for supporting a light-source
capsule and containment means about the capsule which will cause little or no loss
of luminous efficacy in lamps utilizing such means.
[0009] In accordance with one aspect of the present invention. there is provided an improved
metal halide discharge lamp of the type having an outer envelope, a stem member located
within the outer envelope having a pair of electrical conductors extending therefrom
and a frame means located within the outer envelope and supported by one of the electrical
conductors. The lamp also includes an arc tube, supported by and electrically coupled
to the frame means, having a chemical fill including a sodium halide. The arc tube
has a pair of electrical leads sealed into and passing through at least one end thereof
to provide a pair of electrodes therein. A cylindrical member is also included in
the lamp which is supported by the frame means and surrounds the arc tube. The improvement
in the lamp lies with the frame means which comprises a single wire member, having
a particular configuration, which supports the arc tube within the lamp and fixedly
maintains the cylindrical member about the arc tube. The frame means extends along
an axis substantially parallel to the longitudinal axis of the lamp.
BRIEF DESCRIPTION OF THE DRAWING
[0010] The FIGURE illustrates one embodiment of the metal halide lamp made in accordance
with the teachings of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0011] 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 in conjunction with the above described drawing.
[0012] As used herein, the term "light-source capsule" denotes: an arc tube of an arc discharge
lamp, or any light emitting capsule within the outer envelope of the lamp wherein
the light-source capsule operates at a pressure other than atmospheric and the possibility
of minor shard dispersion upon fracture of the light-source capsule exists.
[0013] Referring now to the drawing with greater particularity. the FIGURE shows a metal
halide lamp 10 made in accordance with the teachings of the present invention. Metal
halide discharge lamp 10 includes an evacuated outer envelope 12, which is hermetically
sealed to a glass stem member 14, and an external base 16. Base 16 is formed for easy
connection to an electrical source and is affixed to the hermetically sealed stem
member 14 and outer envelope 12. A pair of electrical conductors 18 and 20 are sealed
into and pass through stem member 14 and are electrically connected to base 16. external
of outer envelope 12, to provide access for energization of discharge lamp 10.
[0014] Within evacuated outer envelope 12 and affixed to electrical conductor 20 is an electrically
conductive frame means 22. Frame means 22 extends along an axis substantially parallel
to the longitudinal axis of discharge lamp 10 and includes a circular portion 24,
in operative contact with an uppermost portion 23 of outer envelope 12. a helical
portion 25 and a substantially straight portion 26. Circular portion 24, in conjunction
with the uppermost portion 23, and stem member 14 serve the dual function of maintaining
frame means 22 in proper alignment and resisting deformation due to external shock
to discharge lamp 10.
[0015] Disposed within outer envelope 12 is a cylindrical member 36, which may be in the
form of a quartz sleeve or shield, which is supported by frame means 22. Also supported
by frame means 22 and contained within quartz shield 36 is an arc tube 28. Arc tube
28 has a chemical fill including a sodium halide and electrodes 29 and 30-at one end
thereof. Moreover, electrode 29 is mechanically and electrically connected to frame
means 22 through an electrical lead 32 while electrode 30 is affixed to an electrical
lead 34 which passes above a portion of cylindrical member 36 and is electrically
and mechanically connected to electrical connector 18 by a connector wire 40. Wire
40 is preferably made of molybdenum. Cylindrical member 36 is located within and is
supported by helical portion 25 of frame means 22. Cylindrical member 36 is secured
in frame means 22 by a bend 21 and a small nickel wire 38 which is welded to the upper
most part of said straight portion 26 of frame means 22. A small kink or bend in the
uppermost part of straight portion 26 may be substituted for wire 38 in securing cylindrical
member 36 in position.
[0016] The purpose of the present invention is to provide a simple and inexpensive means
for maintaining the cylindrical member about the arc tube and mounting the arc tube
within the lamp without both a reduction in lamp performance and damage to the outer
envelope. Three conditions had to be met in order to arrive at a solution to the aforementioned
problem. Firstly, the particular cylindrical member to be used, which is a transparent
shield or quartz tube, had to be securely held in place in such a manner so that it
did not come in contact with the arc tube. Secondly, proper distances had to be maintained
between the electrical conductors of opposite electrical potential. Thirdly, the arc
tube and the cylindrical member had to be held securely in their proper positions
during regular handling. Any breach of the above conditions would have reduced lamp
performance, shortened lamp life and would not have provided a permanent solution
to preventing outer envelope damage due to an arc tube fracture.
[0017] In the present invention the solution to the aforementioned problem was a cylindrical
member 36 positioned about arc tube 28, in the form of quartz shield, in conjunction
with frame means 22 within outer envelope 12. A single wire member is used to form
frame means 22, thereby eliminating the need for welding together several wires in
order to form the frame structure that supports quartz shield 36 and arc tube 28 itself.
As illustrated in the FIGURE, arc tube 28 is parallel and substantially concentric
to both quartz shield 36 and helical portion 25 of frame means 22. Lead 32 is electrically
coupled to frame means 22 and lead 34 is electrically coupled to conductor 18, in
stem member 14, by connector wire 40.
[0018] In one particular embodiment. a 40-watt lamp required the use of a quartz shield
which had a wall thickness of about one millimeter in order to prevent the dispersion
of shards and ultimate breakage of the outer envelope. The frame means was partially
formed in a helix in order to allow the quartz shield to be inserted freely and pushed
up to touch the bend in the frame means (see the FIGURE). The length of the frame
means was about 95 millimeters (mm). The helical portion was about 30 mm in length
and had an average diameter of about 20 mm. In addition, the length of the quartz
shield was about 38 mm and the diameter was about 19 mm.
[0019] In laboratory tests of the 40-watt metal halide lamp, purposely induced fractures
of arc tube 28in the lamps proved that quartz shield 36, with the one millimeter wall
thickness. was sufficient to prevent glass shards from damaging outer envelope 12.
Cylindrical member 36 may also be made of other materials suitable for withstanding
shard impact (i.e., hard glass). Additional testing showed that the use of quartz
tubing and the helical frame had a negligible effect on lamp performance and lamp
life. Other similar type lamps can be made shard-dispersion-proof by varying the diameter
of the helical frame and the thickness of the quartz shield.
[0020] Thus. there has been shown and described an improved metal halide lamp that provides
frame means therein for mounting an arc tube and fixedly maintaining a cylindrical
member about the arc tube which will prevent shard dispersion upon a fracture of the
arc tube itself. More particularly, frame means is provided in the form of a single
wire member, which is parallel to the longitudinal axis of the lamp, that will serve
to support the arc tube and the cylindrical member about the arc tube. thereby simplifying
and lowering the cost of making such a lamp.
[0021] While there have been shown what are at present to be the preferred embodiments of
the invention, it will be apparent to those skilled in the art that various changes
and modifications can be made herein without departing from the scope of the invention
as defined in the appended claims.
1. An improved metal halide discharge lamp of the type having an outer envelope, a
stem member located within said outer envelope having a pair of electrical conductors
extending therefrom, frame means located within said outer envelope and supported
by one of said electrical conductors, an arc tube supported by and electrically coupled
to said frame means having a chemical fill including a sodium halide. said arc tube
having a pair of electrical leads sealed into and passing through at least one end
thereof to provide a pair of electrodes therein and a cylindrical member supported
by said frame means and surrounding said arc tube, the improvement wherein said frame
means comprises:
a single wire member, having a particular configuration. which supports said arc tube
within said lamp and fixedly maintains said cylindrical member about said arc tube,
said frame means extending along an axis substantially parallel to the longitudinal
axis of said lamp.
2. The improvement according to Claim 1 wherein said particular configuration of said
frame means comprises a small circular portion. a helical portion and a substantially
straight portion, said circular portion being in operative contact with said outer
envelope and said straight portion having means for securing said cylindrical member
in position.
3. The improvement according to Claim 2 wherein said means for securing said cylindrical
member includes a small wire welded to said straight portion of said frame means.
4. The improvement according to Claim 1 wherein said cylindrical member is a quartz
sleeve that prevents shard dispersion upon a fracture of said arc tube.
5. The improvement according to Claim 4 wherein said quartz shield has a wall thickness
of about 1 millimeter for a 40-watt lamp.
6. The improvement according to Claim 4 wherein said arc tube is parallel and substantially
concentric to said quartz shield and said helical portion of said frame means, one
of said electrical leads of said arc tube is electrically coupled to said frame means
and other of said electrical leads is electrically coupled to an electrical conductor
in said stem member by a connector wire.
7. The improvement according to Claim 3 wherein said small wire is made of nickel.
8. The improvement according to Claim 6 wherein said connector wire is made of molybdenum.
9. The improvement according to Claim 1 wherein said cylindrical member is a hardglass
sleeve.