Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ PHN 8239
~c~679S2
The invention relates to a method of ageing a
gas discharge lamp which is provided with a vacuum-tight sealed
light transmissive discharge vessel in which at least two
electrodes are disposed and which contains a gas filling.
Furthermore the invention relates to discharge lamps obtained
with such a method.
So-called ageing is a common practice in the manu-
facture of gas discharge lamps which takes place at the end
o~ the manufacturing process of the lamps when the discharge
vessel has already been sealed vacuum-tight and provided with
the electrodes and the desired gas filling. Prior to or after
ageing the discharge vessel may, if so desired be placed in an
outer bulb. Ageing conditions and stab11izes the operating
properties of the lamp. Particularly, ageing reduces the start-
ing voltage of the lamp to the desired level.
The prior art method of ageing of, for example,
high-pressure gas discharge lamps, consists of burning the lamp
either at the nominal operating voltage and lamp current or with
~ ~ a load larger than the load calculated for normal burning, for
a relatively long time, for example for 5 minutes ~o some hours,
(see United States Patent Specification 3,682,525 - William J.
` Knockel, et al - August 8, 1972.
A disadvantage of the prlor art methods of ageing
is the~length of~time of this manufacturing step. In general
~ thi~s is many timés~longer than the other manufacturing steps so
that ageing cannot be done at the rate of the machine which
PHN 8239
~79S2
produces the lamps. In particular ageing cannot be done on this
machine itself. Consequently it must be done in a separate
apparatus, for example a so-called ageing rack in which a plu-
rality of lamps can be processed simultaneously. This time-
consuming method is expensive and labour intensive.
United States Patent Specification 1,965,582 -
T.E. Foulke - July 10, 1934, discloses a method for producing
gas discharge lamps in which, as one of the manufacturing
steps, a high-frequency arc discharge of some amperes for ap-
proximately 30 seconds between the electrodes of the sealed
discharge vessel is mentioned. This high-frequency arc dis-
charge raises the electrodes to a high temperature and has for
its object to activate the electrodes. After this processing
of the electrodes the lamps must be aged for several minutes
more in order to obtain a low starting voltage.
The obiect of the invention is to provide a method
of ageing gas discharge lamps which does not have the disadvan~-
ages of the prior art methods and which can be performed in a
considerably shorter ~ime.
'l 20 A method according to the invention for ageing a
c gas discharge lamp which is provided with a vacuum-tight sealed~
light transmissive discharge vessel in which at least two elec-
trodes are disposed and which contains a gas filling, a discharge
being produced in the discharge vessel for a given period of
~, ~ 25 time, is characterized in that this discharge is a high-Frequency
glow discharge.
It has been found that maintaining a glow discharge
for a given period of time in the gas filling of the discharge
vessel of a gas discharge lamp whose starting voltage is too
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high, results in a considerable reduction in -the starting voltage
level of the lamp so that the effect aimed at by ageing is ob-
tained. As, in practice there are objections against producing
a d.c. or low frequency glow discharge in the gas filling of a
lamp a high-frequency glow discharge must be used in a method
according to the invention. Frequencies exceeding, for example,
lO0 Hz are eligible for use. Surprisingly it was found that
high-frequency ageing according to the invention by means of
a glow discharge -takes only very little time. If the discharge
is maintained for, for example, 0.1 sec. a considerable reduction
of the starting voltage is already obtained. Furthermore i-t was
found that ageing by means of high frequency are discharges is
indeed possible but that in order to achieve the desired effect
such an arc discharge must be maintained for substantlally the
same time as required for prior art ageing by means of normal
burning of the lamp.
A method according to the invention has the advantage
that it can be performed in a very short time so that ageing
may be done at a rate equal to or even greater than the rate
at which the machine produces the lamp. A further advantage is
that ageing according to the invention results in a saving of
energy compared to the prior art methods.
With a method according to the invention the fre-
quency of the glow discharge may be chosen within very wide
limits. The upper limit of the frequency is in practice only
determined by prevailing requirements as regards safety, radio
interference and such like. Preference is given to methods
according to the invention in which the frequency of the
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discharge has a value be-tween 1 kHz and 100 MHz, more in par-
ticular between 0.1 and 50 MHz. With these frequencies the best
results are obtained with simple equipment as regards reducing
the discharge voltage level within a short period of time.
The time during which -the discharge is maintained,
when ageing according to the invention, depends on the required
reduction in the discharge voltage, on the size of the discharge
lamp to be aged, and on the output of the high frequency genera-
tor to be used. In general it is possible to obtain the results
aimed at in time periods of 1 to 120 seconds. With a method accord-
ing to the invention these lengths of time are therefore
preferred.
With a method according to the invention it is
possible to connect a high-frequency voltage source to the
electrodes of the discharge lamp so that the high-frequency
glow discharge in the gas filling of the discharge vessel is
maintained via the electrodes. However, preference is given to
a me-thod according to the invention in which the high-frequency
glow discharge is fed from a high frequency voltage source
which comprises two high-frequency electrodes and in which the
electrical coupling between these high-frequency electrodes and
the gas filling in the discharge vessel takes place via the wall
of the discharge vessel. Operating the glow discharge in this ;~
manner, also called electrodeless discharge, has the advantage
that it is easy to mechanize the method because the lamps need
not make direct contact with the high-frequency electrodes.
Furthermore, in this manner blackening of the discharge vessel
which may occur to a slight degree when apply]ng the high-
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: frequency voltage via the electrodes of the lamp is practically
excluded.
With a method in which the above-described electrode-
less discharge is used, the high-frequency electrodes may be in
the shape of two metal brackets or clamps which are placed
interspaced around the discharge vessel of the lamps. However,
preference is given to a method according to the invention in
which at least one of the high-frequency electrodes is in the
form of a metal plate and the other high -frequency electrode is
arranged a-t such a distance from this plate that the lamp can
be passed between these two electrodes. The o-ther high-frequency
electrode may, for example, also be a metal plate which is
arranged parallel with the first electrode. This preferred em-
, bodiment of the method has the advantage that a large plurality
of lamps can be placed simultaneously between the high-frequency
electrodes. In this method it is also possible to pass the lamps
continuously between the electrodes at a desired rate, for
example equal to the production rate of the lamp machine, the
dimensions of the electrodes having been chosen such that the
period of time the lamps remain between these elec-trodes is of
a length which is suitable for ageing.
Pre~erence is given to a method in which high-
,~ pressure mercury vapour discharge lamps are aged. When producing
j this kind of lamps, large number of lamps are frequently ob- `;
tained which initially have too high a starting voltage. With a
method according -to the invention the starting voltage level of
~` these lamps can be brought ln a simple manner and in a short
time to the desired value.
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The invention will now be further explained with
reference to two embodiments.
High-pressure mercury vapour discharge lamps, in-
-tended, for connection during operation to a voltage of 220 volts
and for consuming a power of 80 W, are produced in a customary
manner, starting from quartz glass tubes having an outside
diameter of approximately 10 mm and an inside diameter of appro-
ximately 8 mm. An electrode is disposed at both ends of these
tubes (distance between the tops of the electrodes approximately
22 mm) and sealed vacuum-tight by means of a pinch seal. The
discharge vessels formed in this way, which are still connected
to the environment by means of an exhaust tube, are thereafter
degassed and evacuated. Thereafter the gas filling, consisting
of a quantity of mercury which fully evaporates during operation
lS of the lamp and also of argon to a pressure of some dozens of -
torr is passed into the discharge vessel whereafter the discharge
vessel is sealed off. The discharge vessels thus obtained are
manufactured into lamps by placing them in a glass outer bulb
which is either evacuated or filled with inert gas. There lamps
must satisfy the requirement that they ignite when a voltage of
not more -than 180 V is applied. If no further measures are taken,
the majority of the lamps do not satisfy this requirement. In -
accordance with the invention the discharge vessels (prior to
being built into the outer bulb) are aged by generating a high
frequency glow discharge in the gas filling. To that end two
metal brackéts are applied around the discharge vessel at a
mutual spacing of approximately 1 cm. The output terminals of a
high frequency voltage generator (1 MHz; 1250 V) are connected
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to these brackets which causes an electrodeless glow discharge
(current strength some dozens of mA) in the discharge vessel.
The power dissipated in this glow discharge is low so that the
; gas filling in the discharge vessel is only heated a little and
the discharge takes place in rare gas having a low pressure. The
glow discharge is maintained for 30 seconds. It was found that
nearly all discharge vessels which were aged in this manner
started at voltages below 170V. So far it has only been possible
to obtain a similar result with -these discharge lamps by burning
the lamps for 6 minutes at 1.5 times the nominal operating
current.
Substantially the same result can be achieved with
the above described discharge tubes which are intended for 80 W
lamps by passing the discharge tubes continuously between two
parallel disposed metal plates (dimensions 10 x 10 cms). At any
moment approximately 6 discharge tubes are present between the
plates and each tube stays approximately 10 seconds between the
plates. A high-frequency voltage (80 MHz) is appIied to the plates -
so that a glow discharge (current strength approximately lO0 mA)
is generated in the Cischarge vessels.
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