Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a low pressure
discharge lamp having an inner tube to restrict a discharge
pa-th in an outer bulb forming a discharge space.
The presen-t invention will be illustrated by wa~
of the accompanying drawings in which:
Figure 1 is an exploded perspective view of a con-
ventional low pressure discharge lamp;
Figure 2 is an exploded perspective view of an
embodimen-t of the low pressure discharge lamp according to
the present inven-tion;
Figure 3 is a diagram showing the first stage of
preparation of an inner tube shown in Figure 2;
Figure 4 is a diagram showing the second stage of
preparation oE the inner tube in Figure 2;
Figure 5 is a diagram showing the final s-tage of
prepara-tion of the inner tube in Figure 2;
Figure 6 is an e~ploded perspective view of ano-ther
embodiment of the low pressure discharge lamp according to
the present invention;
Figure 7 is a cross sectional view partly omitted
of the other embodiment of the discharge lamp of the presen-t
invention;
Figure 8 is a cross sec-tional view of an important
part of still another embodiment of the present invention;
Figure 9 is a cross sectional view showing modifica-
tion of the embodimen-t in Figure 8; and
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~ igure 10 is a cross sectional view of a separat~
enlbodiment of the discharge lamp of the present invention.
A variety of proposals have been made on this kind
oE discharge lamp to substitute it for an incandescent lamp
because the discharge lamp allows its size-reduction into a
compact form. The discharge lamp disclosed in Japanese Un-
e~amined Patent Publication No. 44956/1982 is shown in Fig-
ure 1 as an example, in which there are provided two elec-
trodes 3, 3 passing through an end plate 2 closing -the lower
opening portion of an ou-ter bulb 1, extending in the outer
bulb 1 and each one end oE inner tubes 4, formed into a U-
shape, is fitted to each projection 11 through which each
of -the electrodes 3 passes, on account of which cross-talk
discharge possibly occurring between the electrodes 3 is
preven-ted~ The other open end of -the inner tubes 4 is in
contact with the upper surface of the end plate 2 and near
each of the open ends, a recess 5 for causing bridge of
electric discharge is formed. On the other hand, the inner
-tubes 4 are held by a pressing plate 10 fi-tted to the upper
end of a supporting rod 9 secured to the end plate 2 so that
bo-th -the open ends are in contact with the end pla-te 2. The
inner wall o~ the inner tubes 4 is coated wi-th a layer of
fluorescent material.
In the discharge lamp having the cons-truction de-
scribed above, since the supporting rod 9 and the pressiny
pla-te 10, both needed to secure the inner tubes 4 are incor-
porated in the lamp as additional par-ts, there are problems
of increasing the number of parts; causing additional man-
agement for these parts, complicated structure of the lamp
and increasing manufacturing steps.
The present invention eliminates the disadvan-tage
of the conventional discharge lamp and provides a low
pressure discharge lamp having double tube structure compris-
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incJ an ou-ter bulb and at least one inner tube, in ~Afhich
each open end part at the side of covering an electrode of
the inner tube is bonded with an adhesive to an end plate
at a position facing the outer bulb and the other open end
par-t, which does no-t cover the electrode, of the inner -tube
is made in contac-t with the end pla-te thereby eliminating
problems of complicated management of par-ts; complicated
manufacturing steps and increase in weight of the discharge
lamp, all resulting from use of additional parts to secure
-the inner tube.
The present inven-tion fur-ther provides a low
pressure discharge lamp having double tube structure, in
which an outer bulb, at least one inner tube and a fine
pipe for air discharge are bonded with an adhesive on a sur-
face of an end plate facing the outer bulb whereby manu-
facturing work can be simplified, damage of parts -to be
bonded or bonding portions can be prevented and reliability
on air -tight can be increased.
According to one aspec-t thereof the present inven-
tion provides a low pressure discharge lamp of double tube
; structure comprising an outer bulb containing therein a
sealed gas and having one,end closed by an end plate and at
least one inner tube supported by an end plate to communi-
ca ~ fa W i. th -the interior of said outer bulb; receiving -therein
e.lectrodes and restricting an electric di.scharging path, characterized
in that the ends, receiving therein said electrodes, of said inner
tube are bonded with an adhesive on the surface on the side facing
sa:~d outer bulb of said end plate and a par-t of each enfd other than
sai.d ends of sai.d i.nner l-ube is in contact-to and supporte(lhy said
e~ld l):late.
Sui.tably, said innex tube compri.sf-s a
p.l.uralit.y of li.gh-t transmitting tubes each having
at least one opening communi.cated with said
bnlb and said tubes are con-
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nected by melt-bonding at a part of the edge portion of
said opening.
In ano-ther aspect thereof the presen-t invention
provides a low pressure discharge lamp of double tube struc-
ture comprising an outer bulb containing therein a sealed
gas and having one end closed and at least one inner tube
supported by an end pla-te to communicate with the interior
of said outer bulb; receiving therein electrodes and re-
stricting an electric discharging path, characterized inthat the ends, receiving therein said electrodes, of said
inner tube are bonded with an adhesive on the surface on
the side facing said outer bulb of said end plate and said
outer bulb and a fine tube for air discharge are bonded
with an adhesive in said end plate at positions facing said
: ollter bulb.
: .~uitably, said inner tube, outer bulb ancl fi.ne
tube for air discharge are bonded with an adhesive at
respecti.ve grooves formed in said end plate. Preferably,
a flange is fvrmed in si.ad fine tube for air di.scharge at
its end portion extending to said outer bulb. Desirably,
said electrodes are bonded with an adhesive on said end
plate through respective electrode supporters.
An emhodi.men-t of -the present invention will be
described wi.th reference to Figure 2.
A reference numeral 1 designates a cyli.ndrical
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outer bulb made of glass having a domed top and an opened
bottom and numeral 2 refers -to an end plate made of metal
or ceramics for closing the opened bottom of -the ou-ter bulb
1 to make it in air tight condition. There is enclosed a
medium for discharge consisting of a predetermined amount
of mercury and a rare gas such as argon in a sealed space
formed by the end plate 2 and the ou-ter bulb 1. Numerals
3, 3 designates electrodes both being seal-bonded to the end
plate 2 to ex-tend in-to the outer bulb 1 and a numeral 4 in-
dica~es an inner tube made of glass which is -to be arranged
in -the outer bulb 1 to restrict a discharge path. The inner
tube 4 is formed in one piece by melt-bonding each of legs
of two glass tubes bended to be a U-shape. Namely, free
ends of -the inner tube 4 are bonded with an adhesive of
ylass frit 8 to a
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surface of the end plate 2 in an air-tight fashion to
respectively cover the electrodes 3, 3 so that no
cross-talk electric discharge takes place between t'ne
electrodes 3, 3. On the other hand, the other ends of
the inner tube 4 is bridged by forming t'nerebetween a
connecting part 6 by melt-bonding the vicinity of the
open ends ~ of the two U-shaped glass tubes so that the
end part thus connected is brought to in contact with`the
surface of the end plate 2. A substantially
semi-circular opening 5 formed by obliquely cutting the
glass tube from its open end is provided in each side
portion of the glass tubes facing each other.
Simple explanation will be made as to assembling work
for the embodiment shown in Figure 2.
First of all, an adhesive 8 is applied to a
predetermined por~ion on the end plate 2.
U-shaped glass tubes placed in juxta-position each
other are made in one piece by means of the connecting
part 6. Thus formed single inner tube 4 is set up on the
2~ surface of the end plate 2 with its four lower surfaces
without any supporting aid. Then, the outer bulb 1 is
sealed by the end plate 2.
In the assembling work as above-mentioned, it is
unnecessary to use a jig for supporting the inner tube
for the purpose of bonding the inner tube 4 to the end
plate 2 with the adhesive of glass frit 8, as required in
the conventional processes to secure an inner tube 4
. 6 --
consisting of a single U-shaped glass tub~, whereby the
assembling work can be remarXably simplified. Further,
since the four lower surfaces of the inner tube 4 of the
present invention are all in contact with the end plate
surface, the inner tube 4 stands in a stable manner even
though an impact force is applied to the assembly or a
incomplete lamp in the later stage of the assembling wor~
or in the transportation of the lamp.
Incidentally 7 since the inner tube supporting rod as
shown in Figure 1 is not required because the inner tube
4 is attached by bonding operation, the number of parts
needed can be reduced, hence -the number of the
manufacturing steps can be reduced and accordingly,
management for the parts is easy and manufacturing
process is simplified.
The supporting rod 9 and the pressing plate lO used
in the conventional lamp as shown in Figure l have been
made oE metal. In the discharge lamp of this kind which
is required to reduce its weight for the purpose of
substituting the discharge lamp for an incandescent lamp,
if the supporting rod 9 and the pressing plate 10 can be
eliminated, the total weight of the lamp can be reduced.
In the next place, a method of preparation of the
inner tube 4 of the embodiment shown in Figure 2 will be
described~ The inner tube 4 is prepared according to
steps as shown in Figure 3. Two glass tubes A, A each
- having a U-shaped portion are placed in juxta-position
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with respect to two legs Al, Al and A~, A2 facing each
other and with their open ends directing upwards; the
upper portions of the respective legs A2, A2 are
simultaneously heated by a burner C from the open end to
the just lower portion to cause them to be molten; after
a short time period, a part of the top of the respective
legs A2, A2 deforms due to wind pressure of the flame
from the burner C to Eorm a semi-circular opening 5 as if
cut obliquely from the open end and a mass of molten
glass 52 is formed at the peripheral portion 51 of the
opening 5 as shown in Figure 4 (The molten glass mass is
formed at the lower part of the peripheral portion in
view of Figures 3 to 5, but at the upper part when the
inner tube 4 is set up on the end pla.te 2.); the molten
glass mass of both the glass tubes A, A are brought into
contact each other; then, the glass tubes A, A are
slightly apart from each other to form a connecting part
6; thus the preparation of the inner tube 4 is completed
(Figure 5). It is advantageous that a fluorescent layer
7 to be coated on the inner wall of the inner tube 4 is
formed after the preparation of the inner tube 4 because
the connecting part 6 can be easily formed. In the
discharge lamp of the present invention, since the
connecting part 6 is formed at the same time of the
formation of the opening 5 as a recess to cause a brid~e
of electric discharge when the inner tube 4 is to be
prepared, the number oE steps for heating and annealing
the glass tube are reduced.
The shape of the opening 5 to be formed in the inner
tube 4 is not limited to a semi-circular one whicn is
formed by obliquely cutting the leg from the open end,
but can be a circular shape which may be formed at the
intermediate of the leg of the inner tube 4. In this
case, the circular opening 5 can be obtained by blowing a
flame oli~uely from the outside at a high temperature
such as oxygen gas flame to a position where an opening
is to be formed in the leg.
The shape of the inner tube 4 is variab-le; for
example, the inner tube is formed in such a manner that a
glass tube in a U-shape is again subjected to bending
operation into a saddle shape to form a plurality of
U-shaped portions. Then, the electrodes are covered by
the respective ends of the glass tube and the lower side
surfaces of the plurality of U-shaped portions are
brought into contact with the end plate.
~ It is considered that in addition to the inner tube
bonded to the end plate with an adhesive, the outer bulb
and the fine tube for air discharge are also bonded to
the end plate with an adhesive.~ In this case, bonding
operations are carried out by putting an adhesive of
glass frit in either a molded form or paste on
predetermined portions; putting a body to be bonded such
as an outer bulb on the glass frit or directly putting
_ 9 _
the body on, for example, the end plate, followed by
coating a paste-like glass frit around the contacting
area of the body, and then applying heat to the glass
frit until the glass frit reaches a predetermined
tempera-ture for melt-bonding.
In the discharge lamp having many portions to be
bonded with an adhesive such as glass frit, it is
essential to reduce the number of bonding operations to
simplify manufacturing work. Further, when the inner
tube, the outer bulb and the fine tube for air discharge
are separately bonded, a part having been bonaed or
bonding portion may be broken- or air-tight property may
be impaired due to thermal stress caused by application
of heat in the bonding operations conducted later.
As measures to solve such drawback, there is another
embodiment of the present invention which will be
described with referece to Figure 6 and 7. In Figure 6,
the same reference numerals as in Figure 2 designate the
same or corresponding parts and therefore~ the
description is omitted~
Figure 6 shows a discharge lamp in which there are
provided two inner tubes 4, 4 each having an upper open
end and the lower end bonded to the end plate 2 with an
adhesive 8 such as glass frit and each enlosing therein
an electrode 3. The reference numeral l~ designates a
fine tube for air discharge which has one end
communicated with the interior of the outer bulb l for
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the purpose of evacuation of air. The fine tube 12 is
fitted into an insertion hole 21 for fine tube formed in
the end plate 2 as shown in Figure 7.
The construction of the end plate 2 will be described
in more detail with reference to Figure 7.
The insertion hole 21 for fine tube is provided
between the electrodP 3, 3 in the end plate 2 and a
recess 22 having relatively large diameter is formed in
the surface at the side of the electrodes-, of the end
plate 2. Annular grooves 23 are formed around the
electrodes 3 in the end plate 2 so as to have a diameter
corresponding to the inner tube 4. Separate annular
grooves 24 are formed near the edge of the end plate 2 on
the same side as the annular grooves 23 as above-
mentionPd so as to have a diameter corresponding to the
outer bulb 1. In these grooves 22, 23 and 24, the
adhesive 8 of glass frit is applied.
Assembling operations for the discharge lamp having
the construction described above will be explained.
First of all, the adhesive 8 of paste-like glass frit
is applied to each of the grooves 22, 23 and 24 in the
end plate 2. The fine tube 7 for air discharge is
inserted into the insertion hole 21 for fine tube. The
inner tube 4 is put on the glass frit 8 in the groove 23.
In the same manner, the outer bulb 1 is put on the
adhesive 8 in the groove 24. Thus combined product is
subject to preliminary drying and then it i5 passed
through a heat oven to cause melt-bonding of 'che adhesive
8 of glass frit followed by solidification; thus, the
bonding operation is completed.
Since the grooves 22, 23 and 24 to which the outer
bulb 1, the inner tube ~ and the fine tube 12 for air
discharge are bonded are all provided on the single
surface of the end plate 2, which is covered by the outer
bulb 1, the assembling work such as application of the
adhesive ~ of glass frit~ putting or inserting the outer
bulb (1), the inner tube 4 and the ~ine tube 12 and so on
are all carried out on the same surface side without
requirement of necessity of separate operations for the
outer bulb (1) or the inner tube 4 etc. In this way, the
assembling operation is simplified.
It is known that when a glass frit as an adhesive is
heated, it becomes molten state to exhibit fluidity. In
the present invention, however, since the grooves 22, 23,
24 to which the glass frit is applied are formed in the
same surface of the end plate 2, there is no risk of
flowing the glass frit from any of grooves 22, 23, 24.
In the embodiment, it is unnecessary to separately
carry out bonding operations on account o~ which a part
having been bonded is not damaged due to thermal stress
caused by bonding operations to the other part and
excellent mechanical strength and air-tight property can
be obtained.
25~
Description will b~ made as to another embodiment of
the present invention.
Although the fine tube 7 for air disc'narge of
generally cylindrical shape is used in the embodiment as
shown in Figures 6 and 7, it can be one which has an
external flange 121 at one end of the fine tube whic'n
extends in the outer bulb 1 as shown in Figures 8 and 9.
This structure of the fine tube 12 eliminates an
auxiliary means to support the fine tube 12 for air
discharge.
For a separate embodiment of the construction for the
electrodes 3, 3 and the end p-late 2, it is possible, as
shown in Figure 10, to provide supporters 31, 31 made of
glass or ceramics to support the electrodes 3, 3 and bond
the supporters 31, 31 with the glass frit on the end
plate surface facing the outer bulb as with the other
elements. Further, it is always unnecessary to apply the
glass frit in -the grooves 22, 23, 24 as shown in Figure
10 .
Use of the glass frit as an adhesive is made not only
in paste form as described above but also in a
predetermined molded form to a part or the entire portion
of the end plate 2.
In the embodiments shown in Figures 6 to 10, it is,
2~ of course, possible to use the inner tube 4 in which two
U-shaped glass tubes are combined into one piece as shown
in Figure 2, or in which a single U-shaped tube is bent
into a saddle form.
