Note: Descriptions are shown in the official language in which they were submitted.
LD-7061
The invention relates to jacketed discharge lamps of
the kind wherein the inner arc tube transmits ultraviolet
radiation which is normally absorbed by the glass outer
jacket.
Some common types of high intensity discharge lamps
used for general lighting comprise a quartz or fused silica
arc tube enclosed within a glass outer jacket fitted with
a screw base at one end. In high pressure mercury vapor
lamps the arc tube contains a filling of mercury, whereas
in high pressure metal halide lamps, the arc tube contains
; a filling of mercury and metal halides. In both kinds,
` the arc tube transmits ultraviolet radiation which is
harmlessly absorbed by the glass outer envelope, or even
gainfully absorbed by a phosphor coating on the other
envelope.
Most commonly the outer envelope remains intact to
the end, and lamp life is ended by other factors. However
it does happen occasionally that the outer envelope or
glass jacket is shattered and the arc tube remains intact
so that the lamp continues to operate. In this mode of
operation, the ultraviolet radiation from the arc tube
is not intercepted and may create a safety hazard.
A solution proposed to this problem by U.S. Patent
No. 4,039,893 dated August 2, 1977 f Eugene K. Corbley,
titled "Discharge Lamp Having Disconnect Effective Upon
Jacket Failure" and assigned like this application, utilizes
a mechanical disconnect located in the outer envelope.
The disconnect comprises conductors which are part of the
arc tube supporting frame and which are held in engagement
by the outer envelope. Upon fracture of the outer envelope,
spring pressure forces the conductors apart whereupon the
circuit is opened and the arc tube is disabled. While this
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arrangement is effective and achieves its intended purpose,
a reliable, simpler and more economical solution is de-
sired.
The object of the invention is to provide a jacketed
discharge lamp which includes improved means for mechanic-
- ally disconnecting the arc tube in the event the outer
envelope is shattered, in order to prevent release of
ultraviolet radiation.
In accordance with our invention, a springy conductor
is connected to one of a pair of inleads, either a current
inlead into the outer envelope or an inlead to an electrode
of the arc tube, and is pressed by engagement with the outer
; envelope into a connection with the other of the pair. The
connection with the other inlead of the pair is opened
. when the outer envelope is shattered.
- In a preferred embodiment, a jacketed discharge lamp
includes within the outer envelope a mechanical dis-
connect or switch means comprising a springy conductor
fastened to a side rod which supports the arc tube and
serves as a connector to one of the current inleads into the
outer envelope. The springy conductor is compressed bet-
ween the outer envelope and a contact attached to an arc
tube inlead to provide circuit continuity from the current
` inlead to the arc tube inlead. Upon fracture of the outer
envelope, the springy conductor expands and straightens
out, thereby opening the circuit and disabling the arc
tube.
In the drawing:
FIG. l shows a high pressure metal vapor lamp embody-
ing the invention;
FIG. 2 is a pictorial detail of the mechanical dis-
connect opened upon outer envelope fracture.
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Referring to the drawing and more particularly to FIG.
1, there is shown a high pressure mercury vapor lamp 1
embodying the invention in preferred form. It comprises a
glass outer envelope or jacket 2 of ellipsoidal shape
having a neck 3 to the end of which is attached a screw
type base 4. The neck 3 is closed by a re-entrant stem 5
having a press portion through which extend relatively
stiff current inlead wires 6, 7. The current inleads are
connected exteriorly to the contact surfaces of the base,
namely the insulated center contact or eyelet 8 and the
base shell 9.
Inner arc tube 11 is made of fused silica, commonly
' referred to as quartz, and encloses a charge of mercury and
- an inert starting gas, suitably argon at a pressure of about
20 torr. In a metal halide lamp, the filling would in-
clude additionally small quantities of one or more metal-
lic halides, for instance sodium and scandium iodides. The
arc tube is provided at opposite ends with a pair of main
discharge supporting electrodes 12, 13 to which connections
are made by ribbon type inleads 14 sealed through the
flattened ends of the tube. A fine tungsten wire 15
sealed into the arc tube at the stem end serves as an
auxiliary starting electrode and is connected through a
current limiting resistor 16 to inlead 6 by way of side
rod 17. The side rod is welded to inlead 6 at the stem
end and extends to an anchoring dimple 18 at the dome end
of the envelope which it engages by an encircling clip 19.
The arc tube is attached to the mount frame by clamping its
flat ends 20 between strap clips 21, 22 which are welded
to side rod 17, the lower clip being additionally welded to
reverted portion 17a of the side rod. Electrode 12 is con-
~- nected to current inlead 7 by conductor 23.
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The arc discharge through mercury vapor at a pressure
exceeding one atmosphere generates both visible and ultra-
violet radiation which is transmitted by fused silica arc
tube 11. However, outer envelope 2 is of glass which does
not transmit ultraviolet radiation. When the outer envelope
7;~ is clear, the ultraviolet radiation is merely harmlessly
absorbed. In so-called deluxe mercury lamps, the outer
~,' envelope is coated internally with a phosphor layer and in
such case the ultraviolet radiation is absorbed and con-
. .
verted into visible light including red which improves the
- color rendition of the lamp. The space within outer envelope
- 2 may be either evacuated or filled with an inactive gas
such as nitrogen.
It is possible for the jacket to be broken away and
the arc tube to remain intact. For instance when a con-
ventional lamp is operated base-up, it happens occasionally
that the jacket upon being struck by a ball or projectile
shatters and falls off without breaking the arc tube or the
connections thereto. The lamp may continue to operate in
this fashion until the inleads to the arc tube are oxidized
and burned through. This may take several hours and in
the meantime the ultraviolet radiation from the arc tube
is freely radiated and may create a safety hazard.
Our invention eliminates the foregoing possibility
by a mechanical disconnect or switch means in the inter-
envelope space which turns off the arc tube instantaneously.
It comprises springy conductor 24 which is formed into a
loop and spot welded at 25 to side rod 17 in such manner
as to extend between dimple 18 in the jacket and the
lower end of the arc tube. When the lamp mount is sealed
into the outer envelope, the lower branch of the loop is
pressed upward by the dimple and causes the upper branch to
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bear against silver-plated contact button 26 which is at-
tached by crimping to the inlead of electrode 13. A
small cup 27 attached to the lower branch of the loop
` functions as a centering device engaging the conical part
of the dimple and serves to stabilize and hold the spring
loop in place. A disk or contact plate 28 is attached
to the upper branch of the loop and forms a contact sur-
face which securely engages contact 26. The disk assures
that the engagement with contact 26 is maintained despite
the flexing of mount parts during shipment and handling.
As illustrated in FIG. 1, the circuit from the side rod to
electrode 13 is completed through loop 24 and remains closed
so long as the outer envelope is intact.
Should the jacket or outer envelope be shattered, the
pressure exerted by dimple 18 is removed from the lower
branch of the loop. The loop now expands, the branches
~- start to straighten out, and disk 28 moves away from con-
tact 26, thereby opening the circuit, as illustrated in
FIG. 2. Desirably, loop conductor 24 has sufficient re-
; 20 siliency to force dimple 18 out of clip 19 should the
weight of the fractured jacket itself be insufficeint
to do so. Thus a broken connection is assured which dis-
ables the lamp immediately. Clip 19 limits the extent
to which loop conductor 24 straightens out. This is
desirable during manufacture of the lamp in order to
facilitate engagement of dimple 18 by cup 27 during as-
sembly of the arc tube mount into the outer envelope.
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