Note: Descriptions are shown in the official language in which they were submitted.
CA 022l~088 l997-09-ll
PATENT APPLICATION
EXPRESS MAIL NO. TB862 878 808US
ATT'Y DOCKET NO.: 94-1-609
PAGE 2 OF 8
HIGH INTENSITY DISCHARGE LAMP WITH INTERMEDIATE PRESSURE
XENON FILL GAS
TECHNICAL FIELD
This invention relates to high intensity discharge lamps and more particularly to metal
halide lamps having improved lumen maintenance and good glow-to-arc characteristics
together with higher efficiencies.
BACKGROUND ART
Metal halide lamps generally include an amount of mercury and additionally need some
10 gas within the arc chamber in order to initiate the discharge. Typically, argon at
pressures from 40 millibars to 130 millibars is the gas and pressure range of choice.
Argon is a noble gas and does not react with the other chemicals or the lamp envelope. It
is the most abundant of the noble gases and is the least expensive. It is known that lamps
filled to the lower p.es~ules igrlite easier. Conversely, lamps filled to the higher pressures
15 are more difficult to ignite. Further, it has been observed that the electrodes in lamps
having the lower pressures sputter more, causing the lamp envelope to darken andshortening the lamp life. Electrodes in lamps having higher pressure, although being
harder to start, sputter less so the lamps experience better lumen m~intel-~nce. Thus,
argon pres~ule must be optimized for given applications.
Other noble gases, particularly xenon, have been utilized in metal halide arc discharge
lamps. However, it has not been known to use xenon as a low lJleS~I~re starting gas.
Because of its heavy atomic weight of 131, xenon at presau~s greater than one torr has
been used as a substitute for all or part of the mercury, see, for example, U.S. Patent No.
25 4,757,236. Such lamps can reach brilli~n~e quickly since there is less or no mercury to
vaporize during warm-up. Starting of these lamps, however, can be difficult, requiring
high voltage, low impedance igniters to initiate the discharge
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CA 0221~088 1997-09-ll
PATENT APPLICATION
EXPRESS MAIL NO. TB862 878 808US
ATT'Y DOCKET NO.: 94-1-609
PAGE 3 OF 8
DISCLOSURE OF INVENTION
It is, therefore, an object of the invention to obviate the disadvantages of the prior art.
5 It is another object of the invention to enhance the operation of metal halide discharge
lamps.
Yet another object of the invention is the provision of a metal halide discharge lamp that
is easy to start and has excellent lumen maintenance due to reduced electrode sputtering
10 causing darkening of the envelope.
These objects are accomplished, in one aspect of the invention, by the provision of a high
intensity arc discharge lamp which comprises an outer light tr~n~mi~ive envelope having
a light tr~n.~mi~ive arc discharge tube positioned therewithin. The arc discharge tube has
15 electrodes at opposite ends thereof and means are provided for electrical connection to the
electrodes. An arc generating and sustaining medium is provided within the arc tube, the
medium comprising a substantial amount of mercury, at least the iodides of sodium,
scandium and lithium, and xenon at a fill pressure at room temperature of between about
130 millibar to about 260 millibar.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of lamp which can utilize the invention, and
25 Fig. 2 is a graph of Lumen Output versus Time of lamps of the invention relative to prior
art controls.
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CA 0221~088 1997-09-ll
PATENT APPLICATION
EXPRESS MAIL NO. TB862 878 808US
ATT'Y DOCKET NO.: 94-1-609
PAGE40F8
BEST MODE FOR CARRYING OUT THE INVENTION
For a better understanding of the present invention, together with other and further
S objects, advantages and capabilities thereof, reference is made to the following disclosure
and appended claims taken in conjunction with the above-described drawings.
Referring now to the drawings with greater particularity, there is shown in Fig. 1 a metal
halide arc discharge lamp 10 including a lamp envelope 12 and an arc discharge tube 14
10 mounted within the envelope by mounting frame 16. The arc tube 14, which preferably is
fused silica or polycrystalline alumina, may be positioned within a shroud 20 which can
also be supported by the mounting frame 16. Electrical energy is coupled to theelectrodes (not shown, but which are preferably 2% thoriated tungsten rods having a
diameter of 0.43 mm and provided with short coiled coil overwinds, as is known) of arc
tube 14 through a base 22, a lamp stem 24 and electrical leads 26 and 28. The arc tube 14
contains an arc generating and s.lct~ining medium characterized generally as a chemical
fill or dose of materials to provide light when an arc is initiated therein, as will be
explained hereinafter. The shroud 20 comprises a cylindrical tube of light tr~n~mi~ive,
heat resistant material such as quartz.
As noted, in this particular instance, the mounting frame 16 supports both the arc tube
and the shroud within the lamp envelope 12. The mounting frame 16 includes a metal
support rod 30 attached to lamp stem 24 by a strap 31. The support rod engages an
inward projection 32 in the upper end of the lamp envelope 12. The support rod 30 in its
25 central portion is parallel to a central axis of the arc tube 14 and shroud 20. The
mounting means 16 further includes an upper clip 40 and a lower clip 42 which secure
both arc tube 14 and shroud 20 to support rod 30. The clips 40 and 42 are attached to the
support rod 30, preferably by welding.
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CA 0221~088 1997-09-ll
PATENT APPLICATION
EXPRESS MAIL NO. TB862 878 808US
ATT'Y DOCKET NO.: 94-1-609
PAGE 5 OF 8
Referring now to Fig. 2, the graph depicted shows the results of tests comparing xenon
and argon cont~ining fills. The test comprised four groups each cont~ining four 100 watt
metal halide lamps. As noted above, the arc tubes were fused silica and the thoriated
tungsten electrodes were provided with molybdenum electrical feedthroughs, as is5 known. The arc length was 14 mm. The arc tubes had a volume of 1.4 cc and the lamps
were dosed with 12 mg of mercury, 0.13 mg of pure scandium metal and 10 mg of the
iodides of sodium, scandium and lithium in a molar ratio of 24: 1 :2.5. The lamp of plot A
contained xenon at a fill pressure of 260 millibar; the lamp of plot B contained xenon at a
fill pressure of 130 millibar; the lamps of plots C and D represented a control. The lamp
10 of plot C contained argon at a fill pressure of 260 millibar and the lamp of plot D
contained argon at a fill pressure of 130 millibar.
As is readily appalellt, the xenon filled lamps exhibited superior lumens as compared to
the argon filled lamps . At 9000 hours the 260 millibar group (plot A) was still averaging
6400 lumens whereas both argon groups were less than 3500 lumens.
The lamps were operated with standard ANSI M90 ballasts using standard 100 watt
igmtors.
20 After the lamps had aged for fifteen min~ltes, measurements were taken of the glow-to-arc
transition times for both electrodes, the peak-to-peak voltage just after the transition to
arc, the voltage at peak current (also just after the transition to arc), and the re-ignition
spike, a high voltage pulse occurring at current zero crossing during the first minute or so
of warm-up. No differences were found in glow-to-arc transition times between gases or
25 fill pressures. However, it was found that both xenon and the higher fill pressures
reduced peak-to-peak voltage and the voltage at peak current by as much as 45 volts.
Also, both xenon and the higher pressures were observed to reduce re-ignition voltage by
49 and 59 volts respectively. It is believed that these lower voltages reduce the electrode
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CA 0221~088 1997-09-ll
PATENT APPLICATION
EXPRESS MAIL NO. TB862 878 808US
ATT'Y DOCKET NO.: 94-1-609
PAGE60F8
sputtering and thereby contribute to the better maintenance of the high pressure xenon
group.
While there have been shown and described what are at present considered the preferred
5 embodiments of the invention, it will be a~ ar~ 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 by the appended claims.
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