Note: Descriptions are shown in the official language in which they were submitted.
This invention relates generally to a gas discharge
lamp and, more particularly, to an improved gas discharge
lamp in which a fluorescent material layer is formed on
the inner surface of a tube, and a discharge gas is
sealed within the tube.
Generally, in gas discharge lamp, a pair of elec-
trodes of mutually opposite polarities are mounted and
sealed in a cylindrical-shaped tube with a rare gas or
low mercury vapor pressure sealed therein. It is,
however, very difficult to mount and seal the electrodes
in the tube, due to the small diameter of the tube (e.g.
an inner diameter of less than 10 mm). Furthermore, a
longer sealing time is required, because both the
electrodes are sealed within the tube.
When, for example, a glow discharge is generated
within the tube, across a space separating the elec-
trodes, a low-level light emission occurs on fluorescent
material layer which is located behind each electrode,
that is, at the "tube end portion" side, away from each
electrode.
As a result, the effective light emission length
(electrode-to-electrode distance) becomes short, rela-
tive to the length of the tube. In order to obtain a
predetermined length of light emission, it has been
necessary to determine the light emission length to a
predetermined length. It is therefore necessary to
determine the length of the tube in accordance with the
effective light emission length.
Accordingly, demand has increased for a gas discharge lamp
having a simplified electrode sealing structure, as well as
for an increase in the effective light emission length in
relation to the tube length.
To this end U.S. Patent No. 4,645,979 discloses, in detail, a
gas discharge lamp with one of a pair of electrodes as an
external electrode and the other as an internal electrode.
This particular arrangement ensures a ready sealing mounting
in comparison with the case where both electrodes are mounted
and sealed in the tube. Since, in this case, the external
electrode is formed up to the end of the tube, the length
from the internal electrode to the external electrode, i.e.,
the effective light emission length, can be made longer.
In such gas discharge lamp, however, it is not difficult to
vary the effective light emission length. The electrodes are
externally taken out in the same direction from the tube.
That is, a connection means is required at the ends of the
tube to connect lead-in wires to an external power source,
requiring a cumbersome operation. Furthermore, a
predetermined spacing is required in such an operation.
The present invention
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provideSa gas discharge lamp which can decrease an
operation spacing for a connecting means to connect
electrodes to an external power source, without pro-
viding the electrodes one on each end side of that
tube.
A gas discharge lamp according to this invention
comprises a cylindrical-shaped tube having a discharge
gas therein and through which light is passed, an inter-
nal electrode provided at a tube end, and an external
electrode provided outside of the tube along an axis of
the tube, the internal and external electrodes respec-
tively having a portion provided near the tube end for
receiving energy to cause the discharge within the tube.
A gas discharge lamp apparatus according to another
embodiment of this invention comprises a gas discharge
lamp device including a cylindrical-shaped tube filled
a discharge gas therein and through which light is
passed, an internal electrode provided at a tube end,
an external electrode provided outside of the tube
along an axis of the tube, the internal and external
electrodes respectively having a portion provided near
the tube end, and a high frequency power source for
applying to the portions a high frequency power to
cause a gas discharge within the tube so that light is
directed.
These and other features and advantages of this
invention will become more apparent from the following
1;~9~
detailed description of exemplary embodiments as
illustrated in the accompanying drawings in which:
Fig. 1 is a general view showing a gas discharge
lamp according to a first embodiment of this invention;
Fig. 2 is a cross-sectional view, as taken along
line I-I line, showing the lamp of Fig. 1;
Fig. 3 is an outer, perspective view showing the
lamp of Fig. l;
Fig. 4 is a schematic view, generally showing
a gas discharge lamp according to a second embodiment of
this invention;
Fig. 5 is a cross-sectional view, as taken along
line II-II, showing the lamp of Fig. 4; and
Fig. 6 is a cross-sectional view, partly enlarged,
showing a third embodiment of this invention gas
discharge lamp of this invention.
A rare gas discharge lamp apparatus according to a
first embodiment of this invention will be explained
below by reference to Figs. 1 to 3.
In Fig. 1, discharge lamp 10 includes tube 12 of a
cylindrical configuration with each end closed. Tube 12
is made of a light-transmissive quartz glass or a hard
or soft glass and has, for example, internal diameter of
below 2 mm, or external diameter of below 3 mm.
A rare gas of at least one kind selected from the
group consisting of xenon, krypton, argon, neon, helium,
etc. is sealed into tube 12 with xenon as a principal
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component in which case a light output varies in pro-
portion to the rare gas pressure level.
Within tube 12, internal electrode 14 made of, for
example, nickel is provided at one end of the tube and
serves as one of a pair of electrodes. An emitter mate-
rial is coated on the surface of the internal electrode
1.2 mm in outer diameter to facilitate an electron emis-
sion. Internal electrode 14 is sealingly mounted by a
"pinch-sealing" method. Lead-in wire 16 which penetra-
tes through the end wall of tube 12 in a gas-tight
fashion is connected to internal electrode 14 and sealed
within tube 12.
Fluorescent material layer 18 is formed on the inner
surface of tube 12 such that the thickness of the film
varies along the axis of the tube, for the reason set
forth below.
That is, if the fluorescent material layer is uni-
formly formed within tube 12 throughout the length of
the tube, a luminance level becomes high at a position,
for example, substantially two-thirds the whole length
of the tube as viewed from internal electrode 14. In
such a luminance distribution, the luminance level is
decreased frGm the aforementioned position toward the
end of tube 12.
For this reason, the thickness of fluorescent
material layer 18 is so set as to obtain a transmittance
of 25 to 40~. That is, the thickness of fluorescent
1~937~
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material layer 18 is decreased at the position sub-
stantially two-thirds the whole length of the tube
as viewed from internal electrode 14 so that the
transmittance exceeds 40%. In this case the thickness
of fluorescent material layer 18 is gradually increased
toward the end of the tube.
External electrode 20 is intimately attached to the
outer side portion of tube 12 and serves as the other
electrode. That is, external electrode 20 is formed
from end to end across the whole length of the tube,
that is, in a direction in which lead-in wire 16 to
internal electrode 14 extends, to provide a band of a
substantially uniform width along the axis of the tube.
External electrode 20 is formed of an electroconductive
coating film which is obtained by coating, for example,
a copper/carbon blend paste on the surface portion of
the tube and sintering it.
Light shielding film 22 is formed on the external
surface of tube 12 with an opening, such as slit 24,
formed opposite to band-like external electrode 20 to
allow passage of a predetermined quantity of light.
Stated in more detail, light shielding film 22 is formed
over the whole surface of tube 12 except for slit 24,
that is, over the outer tube surface including the outer
surface of external electrode 20, with the width of slit
24 formed substantially uniformly across the whole
length of the tube.
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In tube 12, first receiving end film 14a is formed
on the outer surface portion of that tube end portion
with internal electrode 14 sealed within the tube, that
is, on the outer surface of light shielding film 22.
First receiving end film 14a is formed of an electrocon-
ductive paste, such as silver--epoxy resin. First
receiving end film 14a is connected to lead-in wire 16
which is connected to internal electrode 14.
Second receiving end film 20a is formed on the
outer surface of tube 12 in an axially spaced-apart
relation to first receiving end film 14a. Second
receiving end film 20a is also formed of an electro-
conductive paste, such as silver-epoxy resin and circum-
ferentially so provided in the axially spaced-apart
relation to first receiving end film 14a as to have
a predetermined width. Second receiving end film 20a is
formed on the outer surface of light shielding film 22,
not on slit 24, and connected to external electrode 20.
Internal electrode 14 and external electrode 20 are
connected to high frequency power source 28 through
first receiving end film 14a and second receiving end
film 20a and directly and through current-limiting capa-
citor 26, respectively. High frequency power source 28
is comprised of inverter circuit 30, frequency generat-
ing section 40 and power source 50.
Inverter circuit 30 is of such a push-pull type
that transformer 32 has its primary winding connected to
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the collectors of switching transistors 34a and 34b and
its secondary winding connected to discharge lamp 10.
Switching transistors 34a and 34b have their emitters
connected to each other with a common junction coupled
to a negative terminal (-) of variable D.C. power
source 50 in the power source and their base-to-emitter
circuits connected to a series circuit of resistors 36a
and 36b.
Switching transistors 34a and 34b have their bases
connected to I.C. 42 (e.g. TL494, Texas Instruments Inc)
which, together with variable capacitor 44 and variable
resistor 46, provides a frequency generating circuit.
Variable capacitor 44 and variable resistor 46 are
grounded.
I.C. 42 is connected to both the terminals of D.C.
power source 50 to supply the voltage of D.C. power sup-
ply 50. D.C. power source 50 has its positive terminal
(+) connected to a predetermined location on the primary
winding side of transformer 32 through coke coil 38.
In the gas discharge lamp, a high frequency power
is supplied from D.C. power source 50 through first and
second receiving ends 14a and 20a and through push-pull
inverter 30 to internal electrode 14 and external
electrode 20. At this time, the frequency employed is
set to a proper value (20 to 45 KHz in this embodiment)
by frequency generating section 40 comprised of I.C. 42,
variable capacitor 44 and variable resistor 46.
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g
When current is supplied to internal electrode 14
and external electrode 20, the direct current is con-
verted to an alternating current with the aforemen-
tioned proper frequency through push-pull inverter 30.
A glow discharge corresponding to a lamp current of
below 20 mA occurs across internal electrode 14 and
external electrode 20 within tube 12 with the use of the
aforementioned high frequency current. As a result of
such glow discharge, fluorescent material layer 18 is
excited by a resonance line of the rare gas within tube
12 to produce visible light. The visible light is
emitted as a narrow beam pattern to the outside of tube
12 through slit 24.
Upon the occurrence of the aforementioned glow
discharge the current density is decreased at a location
remote from internal electrode 14 and external electrode
20. Since, however, fluorescent material layer 18 is so
set as to obtain a transmittance of 25 to 40~ as already
set out above, the luminance level is increased in a
location remote from the aforementioned electrodes.
Even in the location nearer to internal electrode
14 and external electrode 20 the thickness of fluorescent
material layer 18 is likewise so set as to obtain a
transmittance of 25 to 40% and, even if electrons coming
from internal electrode 14 never have a distance adequate
to be accelerated, the luminance level is increased.
Furthermore, at the location substantially
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two-thirds the whole distance of tube 12 as viewed from
internal electrode 14 the thickness of fluorescent
material layer 18 is so set as to obtain a transmittance
of over 40% and the luminance level is decreased at
that location.
As a result, the luminance level is relatively
increased at each end portion of tube 12 and decreased
at the location substantially two-thirds the whole
length of tube 12 as viewed from internal electrode 14.
By so doing, the luminance distribution tends to be made
uniform as a whole within tube 12.
According to this invention, since the terminal or
lead-in wire (the connecting means as the receiving end)
of the internal electrode sealed within the tube and
that of the external electrode extend from the same end
of the tube, the lamp of this invention can reduce the
operation spacing of said connecting means to one half
that required in the conventional lamp.
From this it follows that light external emitted
from tube 12 is restricted to only a light beam which is
transmitted through slit 24. For this reason, the illu-
mination light is directional in nature and is oriented
only in the direction in which slit 24 is formed. Since
the width of slit 24 can be made smaller than the
diameter of tube 12, the illumination light can be
transmitted, as a very narrow beam, through slit 24.
The outline of the illumination light becomes much
lZ93765
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sharper relative to the background becomes of the illu-
mination of the light only through slit 24.
In the case of cylindrical-shaped discharge lamp
10, external electrode 20 is formed up to the end of
tube 12 and thus the emission length of discharge lamp
10 corresponds to a distance from internal electrode 14
to the end of tube 12, offering a longer effective
emission length. This means that it is not necessary to
increase the length of the tube per se.
In discharge lamp 10, if the aforementioned high
frequency power is adequately high, leakage current
tends to flow b ~ween external electrode 20 and a dis-
charge space wi/thin tube 12, allowing the capacitor's
function to adequately reach the end of the tube. If,
on the other hand, the aforementioned frequency power
becomes lower, then the light emission length becomes
shorter due to the failure of the capacitor's function
to reach the end of the tube. It is therefore, pos-
sible to freely vary the light emission length if the
aforementioned frequency power is made variable.
Where, for example, the voltage of variable D.C.
power source 50 is varied or where the capacitance or
resistance of variable capacitor 44 or variable resistor
46, respectively, in the frequency generating circuit is
varied to cause a variation in frequency involved, then
the aforementioned high frequency power varies in either
case, causing a variation in a flow of leakage current
1;~93~6S
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between externa] electrode 20 and the discharge space
within tube 12. Therefore, the capacitor's function and
thus the light emission length vary.
A rare gas discharge lamp according to a second
embodiment of this invention will be explained below by
reference to Figs. 4 and 5 jointly.
In Figs. 4 and 5, the internal arrangement of dis-
charge lamp 10' is the same as the first embodiment.
That is, discharge lamp 10' includes tube 12 having
fluorescent material layer 18 formed in the inner sur-
face thereof. The thickness of fluorescent material
layer 18 varies along the axis of tube 12 for the same
reason as set forth in connection with the aforemen-
tioned first embodiment. Further explanation is, there-
fore, omitted.
The second embodiment is the same as the afore-
mentioned embodiment with respect to the constituents of
rare gas sealed within tube 12, gas pressure, internal
electrode 14 provided within the tube at one end of the
tube and lead-in wire 16.
External electrode 20' is formed on the whole outer
surface of tube 12 except for slit 24 formed along the
axis of tube 12. External electrode 20' is made of a
light shielding material, such as carbon, and that outer
surface portion of the tube not covered by external
electrode 20', that is to say, slit 24' provides an
opening through which light is emitted.
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Internal electrode 14 and external electrode 20'
are connected to high frequency power source 28 directly
and through current-limiting capacitor 26, respectively.
High frequency power source 28 is comprised of push-pull
inverter 30, frequency generating section 40 and power
source 50. That is, high frequency power source 28 is
the same as that of the aforementioned embodiment.
Further explanation is, therefore, omitted.
In the gas discharge lamp, a high frequency power
is supplied from D.C. power source 50 through push-pull
inverter 30 to internal electrode 14 and external
electrode 20'. Upon the supply of current to internal
electrode 14 and external electrode 20' a glow discharge
corresponding to a lamp current of below 20 mA is pro-
duced across internal electrode and external electrode
20'. As a result, fluorescent material layer 18 is
excited by a resonance line of a rare gas within tube 12
to produce visible light. The visible light is exter-
nally emitted from within the tube through slit 24'.
In the second embodiment, the lead-in wires are
also provided in the same direction of the tube, per-
mitting the spacing of the connecting means to be halved
as in the first embodiment when compared with the con-
ventional lamp, and external electrode 20' covering the
outer surface of tube 12 serves also as a light shield-
ing film, ensuring a simpler structure than in the case
where the light shielding film and external electrode
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are formed in separate steps. It is also easier to form
the light shielding film.
The light emitting from within tube 12 is
restricted only to light which has been transmitted
through slit 24'. The illumination light is directional
in nature, that is, is oriented only in the direction in
which slit 24' is formed. Since the width of slit 24'
is smaller than the diameter of tube 12, the illumina-
tion light is emitted as a very narrow light beam
through slit 24'.
The aforementioned gas discharge lamp is of such
a type that a rare gas only is used. This rare gas
discharge lamp utilizes the negative glow section of the
glow discharge, offering such an advantage that the
light output is not temperture-dependent.
The aforementioned gas discharge lamp does not
need to be restricted only to the glow discharge and may
be applied to an arc discharge in which case the inter-
nal electrode is partially thickened so that a hot
cathode is inserted therein.
The material to be sealed within the tube is not
restricted only to the rare gas and this invention can
equally be used as a low mercury vapor pressure discharge
lamp. In a practical lamp using Hg sealed therein, for
example, a very small amount of Hg of about 0.1 mg may
be sealed at an argon pressure of 3 Torrs within the
same tube as the rare gas discharge lamp.
1;~93~5
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The fluorescent material layer is not necessarily
required, because a special gas for emitting visible
light may be sealed within the gas discharge lamp. For
example, argon, neon and helium emit pink, orange and
red purple color visible light, respectively. Further-
more, a low mercury vapor pressure discharge lamp pro-
duces visible light as an ultraviolet lamp of a narrow
beam pattern source.
Fig. 6 shows another variant of a combination of
internal and external electrodes and external power
source of a third embodiment with one end portion shown
enlarged. Tube 12 has fluorescent material layer 18 in
the inner surface thereof and external electrode 20 on
the outer surface portion thereof. External electrode
20 is obtained by bonding, for example, carbon phenol or
silver-epoxy resin on the outer surface of tube 12 in a
band-like fashion in the axial direction of the tube and
sintering it. In this case, electrode 20 has a predeter-
mined width along substantially the whole length of
the tube. The resultant structure is covered by light
shielding film 22 except at a location where slit 24 is
formed. External electrode 20 is connected at one end
to lead-in wire 20c in the axial direction of the tube.
Lead-in wire 20c is comprised of a covered cord and has
its inner conductor jointed by soldering or silver-epoxy
resin to one end of external electrode 20 at the loca-
tion of connection portion 20b.
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- 16 -
Recess 60 is formed as a mode at that location of
tube 12 where lead-in wire 20c is taken out. Recess 60
provided a circumferentially continued groove, but it
may be formed as one circumferential portion only.
In tube 12, insulating shrinkable tube 62 is fitted
over recess 60 and connection portion 20b between exter-
nal electrode 20 and lead-in wire 20c. Shrinkable tube
is of a heat shrinkable type, such as vinylchloride or
polyester, and intimately fitted over the base portion
of the tube, that is, over connection portion 20b and
lead-in wire 20c. In this way, connection portion 20b
between external electrode 20 and lead-in wire 20c, as
well as recess 60, are covered by shrinkable tube 62.
On the other hand, internal electrode 14 is sealed
within the tube and brought out of the tube through
lead-in wire 16.
In this embodiment, the other component parts, as
well as the operation, are the same as in the aforemen-
tioned first and second embodiments and any further
explanation is, therefore, omitted.
In the third embodiment, a connection space at the
receiving end can be reduced to one half that required in
the conventional lamp. Since the base portion of lead-
in wire 20c are firmly attached to tube 12 by shrinkable
tube 62, even if any displacement of lead-in wire 20c
relative to tube 12 occurs, for example, in a direction
as indicated by an arrow in Fig. 6, it never propagates
1~937~iS
over connection portion 20b and thus no stress is pro-
duced in connection section 20b, thus preventing a
breakage of lead-in wire 20c.
Since shrinkable tube 62 is engaged with recess 60
at the end portion of tube 12, there is no possibility
that is will slip out of tube 12.
