Note: Descriptions are shown in the official language in which they were submitted.
35'i'~6
srNGLE-~NDED METAL HALIDE DISC~RGE LAMPS AND
PR~CESS OF M~NUFACTURE
CROSS REFERENCE TO OTHER APPLICA~IONS
The following concurrently filed Canadian patent applications
relate to single-ended metal halide discharge lamps and the
~abrication thereof: g55.934-~; ~55,933-~; 455,932-1; and
455,9~5-5.
TECHN r CAL FIELD
This inven~ion relates to single-ended me-tal halide discharge
lamps and the manufacture of such lamps and more paLticularly to
single-ended meta~ halide discharge lamps having a stabili~ed arc
and an envelope formed for isothermal operation.
BAC~GROU~D OF q'HE INVENTION
rn the field of projectors. optical lens systems and similar
applications requiring a relatively intense source of light, it has
been a common practice tO employ a light source in the form of a
tungsten lamp. Although tungsten or tungsten halogen lamps do have
certain desirable features such as low cost~ desirable color
features enhancing skin tones and do not require a special power
source, several undesirable features are unfortunately also
present. For example, structures employing a tungsten source do not
generate enough blue light, ~end to undesiLably generate large
amounts of heat which necessitates expensive and cumbeLsome cooling
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devices located adjacent the light source, and ten~ to exhibit a
relatively short life such as an operatlonal period of about 10 to
20 hours. Thus, it is not uncommon to replace the li~ht source each
time the appa~atus is employed. Obviously, such inconvenience and
e2pense leaves much to be desired. ~oreover, screen illuminatlon is
limited due to the inability to increase surface luminance much
beyond 3400 K while the mechanical body structure ls rigid leading
to destruction during operation by chemical means and by vibration
or shock.
An improvement over the above-described system is provided by
the use of metal halide discharge lamps as a light sourcs. For
e2ample, a common form of high pressure metal halide discharge lamp
is disclosed in U.S. Patent No. 4,161,672. Thereln, a double-ended
arc tube or an arc tube having electrodes sealed into diametrically
opposite ends is employed in conjunction with an evacuated or noble
gas filled outer envelope. However, it has been found that such
structures are relatively expensive to manufacture and are obviously
not appropriate for use in projectors or other optlc lens-type
appartus.
As to single-ended metal halide arc discharge lamps, U.S. Patent
Nos. 4,302,699; 4,308,483; 4,320,322; 4,321,501 and 4,321,504 all
dlsclose variations in structure or flll suitable to a particular
application. However, any one or all of the above-mentioned patents
leave something to be deslred lnsofar as stabllity of the arc and
lsothermal uniformity of the dlscharge lamp are concerned.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present lnventlon is to provide an Improved
single-ended high intensity discharge lamp. Another object of the
invention is to enhance the capabilitles of single ended hlgh
intenslty discharge lamps. Still another object of the inventlon ls
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to provide a single-ended high intensity discharge lamp having an
improved structural configuration. A further ob~ect of the
invention is to provide an improved process for manufacturing
sin~le-ended hi~h intensity discharge lamps.
-5 ~ ~ These and other objects, advantages and cspabilities are
achieved in one aspect of the invention by a slngle-ended high
pressure hi~h intensity discharge lamp having a pair of electrodes
each including a metal rod with a spherical ball on the end thereof
sealed into and passing through one end of sn elliptical-shaped
envelope of fused silica containing a metal-bearln~ mercury fill
therein.
In another aspect of the invention, a process for manufacturlng
single-ended metal halide discharge lamps is provided wherein a pair
of electrodes each ha~ing a spherical ball on the end o~ a metal rod
are sealed into one end of an elliptical-shaped fused slllca
envelope, and the envelope is filled with unsaturated metal-be~ring
mercury.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of one embodiment of a
sln~le-ended hi8h intensity dlscharge lamp of the inventiOD
FIG. 2 is a diagrammatic illustration of the discharge and
convect1On gas flow for Yertlcal operation of the dischar~e lamp of
FIG. l;
FIG. 3 is another illustration of the dlscharge lamp of FIG. 1
showing the approximate electric field lines of force between the
electrodes of the lamp; and
FIG. 4 is a photograph, 100 X enlargement, of an electrode of
the embodiment of FIG. 1.
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_4
BEST MODE FOR CARRYING OUT THE INYENTION
For a better understanding of the present inventlon, together
with other and further objects, advantages and capabilltles thereof,
"~ ~
- reference ls made to the ~ollowing dlsclosure and appended clalms ln
connection wlth the accompanying drawings.
Re~errlng to the drawlngs, FIG. 1 illustrates a low wattage
metal halide lamp having a body portlon 5 oÇ a materlal such as
fused silica. This fused sllica body portion 5 ls formed to provlde
an elllptlcal-shaped lnterior portlon 7 having a ma~or and minor
diametrlcal measurement, "X" and "Y" respectlvely, in a ratio of
about 2:1. Moreover, the elllptlcal-shaped interior portlon 7
preferably has a helght "Z" substantially equal to the mlnor
dimenslonal measurement "Y~.
Sealed lnto one end o~ and passing through the body portlon 5 ls
15 a palr of electrodes 9 and 11. Each of the electrodes 9 and 11
includes a metal rod 13 with a spherlcal ball 15 on the end thereof
wlthln the elllptlcal-shaped lnterior portlon 7. Preferably, the
electrodes 9 and 11 are posltioned wlthin the elllptlcal-shaped
lnterlor portion 7 in a manner such that the end o~ the spherlcal
20 balls 15 o~ the electrodes 9 and 11 15 substantlally equally spaced
from the interlor portlon 7 lnsofar as the ma~or and mlnor axes "~"
and "Y" and slso substantlQlly at the mldpolnt of the height "Z".
~lso, a metal-bearing mercury fill ls disposed withln the
elllptical-shaped interior portlon 7. For example, mercury dosed
25~ with a metal hallde such as sodlum and scandlum along wlth argon ls
an approprlate flll for a low wattage metal hallde dlscharge lamp.
Speciflcally, ~ S0-watt discharge lamp having an elllptical-shaped
lnterlor portlon 7 wlth a volume o~ about .1 Cm3 was ~111Qd with
about 3.0 mgms of mercury, 1.9 mgms of sodlum and scandium ln a
molar ratlo of about 20:1 and argon at a pressure of about 200
D-83-1-058 ~ ~ ~ S 7 i~
torr. Oper~tional testin~ provided an initial lumen output of about
3100 lumens with a lumen maintenance of about 84% after 160 hours o~
operational life.
Referring more speciÇically to the above-described
elllptical-shaped lnterior portion 7, FIG. 2 of the drawin~s
illustrates the electrodes 9 and 11 each having a spherical ball 15
thereon and spaced along the major a~is "X" and substantlally equal
dlstance from the walls 17 of the interior portlon 7. As can
readily be seen, the body portion S is preferably vertlcally
positloned such that the spherical balls 15 are located one above
the other. As a result, a ~as flow pattern ls provlded, as
lndlcated by the arrows, wherein cool ~as tends to flow down the
outslde wall 17 of the interior portion 7 and is drawn into the
elliptical-shaped arc or plasma column 22 at the bottom electrode
11. The spherical ball 15 of the bottom electrode 11 provldes a
spherical extension, which will be explained hereinaEter, and~ in
turn, produces gas flow pinching or a venturi action 20 at the arc
terminus of the spherical ball 15 of the bottom electrode 11. In
thls manner, arc terminus wanderln~ is minimlzed. Also, the gas
atoms are heated in the plasma column 22, and the upper electrode 9
acts as a deflector which spreads the hot gases reaching the top of
the body portion 5 of the elliptical-shaped arc tube. Moreover,
infrared measurements oÇ the temperature oÇ the wall 17 during
operation of the arc tube lndicate less than a 20~ te~perature
variation at a wall temperature of about 1100~ C. Thus, the
above-described elliptical-shaped interior portion 7 and the
elliptical-shaped arc 22 provlde a convection current flow; 21 of
FIG. 2, which is substantially uniform and free from undesired
turbulence such that arc stability, which is particularly lmportant
in projectors and lens systems, ls provided.
'7 ~
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Additionally, lt has been noted that the above-described arc
tends to wander about the contact re~lon of the spherical balls 15
initlally. Howsver, lt has been Eound that the employlng of a
seasoning step in the manufacturing process tends to cause
deYelopment of protuberances 24 of (FIG. 4) on each one of the bQlls
15. As a result, the protuberances 24tend to minimize the arc gap
between the spherical balls 15 of the electrodes g and 11 and force
the arc to have centrally located terminatlon points on each of the
electrodes ~ and 11.
0 Although not completely understood, it ls believed that the
above-described protuberances 24 of (FIG. 4) are o a size which
depends upon the local materlal properties and the field stren~th
and eas flow properties. Moreover, the growth formation also
appears to be a function of the electrode size and temperature.
Thus, the lower the operating temperature the lon~er the seasoning
time requirad.
As a specific example, a 0.017-inch tungsten rod having a ball
15 thereon of about 0.025-inch was operated in a 100-watt metal
halide filled dlscharge lamp drawing about 1.6 amperes of current.
After about 15 minutes of "seasoning" at normal operational
conditions, it was found that ths arc stabillzed and one or more
protuberances appeared on the surface of the spherical balls 15 o~
the electrodes 9 and 11. Thus, the surface brea~up into platelets
and formatlon o~ the protuberances on the spheroid balls 15 inhiblts
any wanderlng of the arc and enhances the llght source.
Additionally, it is to be noted that an arc source, such as a
metal halide discharge lamp, provldes not only higher luminance but
also hl~her efflcacy than a tungsten source. Also, 8 mPtal halide
dlscharge lamp provides a point source relatlve to a tungsten
source. Speciflcally, a 100-watt metal halide dlscharge lamp
exihibits a plssma having a minlmum lumlnance intermediate the
spherical balls 15 and a maximum luminance at or near the spherical
S'i~
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balls 15. ~oreover, the plasma column is normally about 1 to 2 mm
in diameter and about 3 mm ln length. However, a tun~sten source ls
about 2.5 mm in diameter and 8 mm ln length with the luminance
varyln~ ln a sinusoidal manner over the len~th of the tungsten
~;~ source.
Following is a table, Table I, showing a comparison ln
lumlnance, efficacy and size of a tungsten source, a high pressure
xenon source and a metal halide lamp source:
TABLE I
0 Size Theoretlcal
Luminance Efficacy (Len~th ~Throu~hPut
(Cd~mm) (Lumens~Watt) Diam.)(Lumens)
Tungsten 30 33 8 2 2.5 1980
(300 Watts)
Xenon 150 20 2.2 g 5 ~00
(150 Watts)
Metal Halide
Lamp 75 65 3 ~ } 1300
~100 WBttS)
As can readily be seen, the tungsten source at 300 watts
provldes about 33 lumens per watt as compared with 65 L/W for a
100-watt metal halide lamp. Also, tests in a 35 mm projectlon
system lndicate an output of about 10,000 ~umens from the 300-watt
tungsten source is equivalent to that of the 6,500 lumens from the
100-watt metal halide lamp source. The lon~ wavelenth radlatlon snd
th~ m~sdlrected visible light of the tungsten source tends to be
absorbed as heat by the fllm of a pro~ector. Thus, 15 has been
found that the tun~sten lamp ~enerates about 270 watts of heat as
compared to about 90 watts or about lJ3 thereof by the metal hallde
lsmp snd sssoclated power supply.
~5~7~L6
D-83-1-05B
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Further, the ~enon source shows a relatively high luminance
capability but a relatively low efficacy capability. Thus, n lumen
output of the xenon source which ls comparable to that provided by a
100-watt metal halide lamp would necessitate a xenon source of about
200 watts in order to compensate for a relatively poor ef~lcacy
capability. ~oreover, a xenon source has a relatively small
diameter, about 0.5 mm in the example, as compared with a metal
halide lamp, about 1.0 mm, which greatly and undesirably reduces the
tolerances or variations in positioned location of the arc source
0 when employed with a reflector in a projection system. In other
words, positional adjustment of an arc source in a xenon lamp is
much more critical than in a metal halide discharge lamp system.
Accordin~ly, a sin~le-ended metal halide discharge lamp has been
provided wherein electrodes are disposed within an elliptical-shaped
interior portion of a fused silica envelope. This elliptical-shaped
envelope interior, in conjunction with an elliptical-shaped arc
therein, provides a substantially isothermal operational conditlon
of the fused silic8 envelope forming the discharge lamp. Moreover,
lt has been found possible to provide a stabilized arc which is
particularly important in the operatlon of pro~ector and optic lens
apparatus.
While there has been shown and described what is at present
considered the preerred embodiments of the invention, it will be
obvlous to those skilled in the art that various changes and
modlflcations may be made therein without departing from the
invention as defined by the appended clalms.
