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Патент USA US2135284

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N_ov. 1, 1938.
>2,135,284
c. G. l-'oUND4
CATHODIC LAMP
AFiled Feb. 2e, 1938,
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TEMPERATURE
Inventor:
Clncto? G Found,
l-Iís Attorney
Patented Nov. 1, 1938 _
y2,135,234 „
UNITED STATES PATENT OFFICE
2,135,284
_
cA'rnoDro LAMP
Clifton G. Found, Schenectady, N. Y., assignor to
General Electric Company,` a _corporation of
New York
‘
Application February 26, 1938, Serial No. 192,808
3Claims. (CL 176-122)
'I'his application is a continuation-impart of
my application Serial No. 103,566, ñled October l,
1936.
-
,
'
.
My invention relates to a gas-filled or discharge
5 lamp of the so-called “cathodic” type _in which
light generation is largely Aconñned to a region
closely adjacent the cathode.
It is an object of the invention to provide an
electrode structure which will permit a greater
10 luminous output for a given size of cathodic lamp
than can be obtained with the structures hereto
fore employed. It is a further object to provide
a high intensity cathodic lamp in which the light
output is substantially insensitive to ambient tem
15 perature variations.
The novel features which I desire to protect
herein will be pointed out with particularity in
trons of low energy content as is more fully ex
plained in the following. The neon or other
inert gas, on the other hand, has been found to
serve a multiplicity of functions which add both
to the convenience of operation and the efficiency 5 .
of the lamp. Thus, besides facilitating the initia
tion of a discharge between the lamp electrodes
and the subsequent vaporization ofthe sodium,
the neon provides atoms which serve as a deflect
ing means to lengthen the total path of the mov- 10
ing electrons, which would otherwise proceed al
most directly through the ñeldof sparse sodium
atoms to the anode. 'I‘his increase in the aver
age path of travel of an individual electron greatly
enhances the -probability of vits encountering a l5
sodium atom in a light-emitting impact.
In addition to the two functions just described, the appended claims. The invention itself, how- . neon is capable of a further service which makes
ever, together with further objects and advan
20 tages thereof, may best be understood by refer
it particularly useful in the cathodic type of lamp.
It has been observed that the voltage drop in an 20
ence to the following specification taken in con >electron discharge tube having closely spaced
nection with the drawing, in which Fig. 1 is a electrodes is largely concentrated in a narrow
perspective view of a cathodic lamp embodying sheath around the cathode which sheath may be
my invention; and Figs. 2 and 3 are graphical less than 116 of a Acentimeter in thickness. It is
25 representations illustrating the improved charac
teristics which are realized by the use of the in
vention.
' The lamps with which -my invention deals are
of the >thermionic discharge type employing an
30 incandescible cathode and are conventionally con
structed so that the distance between the cathode
and the anode is comparable to the least dimen
sion of the envelope. As a result of such- con
struction substantially all of the utilizable light
35 energy is generated within a restricted radial dis
tance of the cathode. It is, therefore, convenient
to refer to such a light source as aV "cathodic”
lamp.
Cathodic lamps of the type with which my in
40 vention is particularly concerned comprise a
sealed envelope defining a discharge space which
contains suitable electrode structure, a vaporiza
ble substance such as sodium and an inert or non
condensable gas such as neon. It will be under
45 stood, however, that although sodium and neon
are particularly'referred to-in the following speci
' within this sheath that emittedelectrons receive 25y v
substantially all their energy, such energy being
conveniently expressedl by giving the number of
volts against which an electron of the given en
ergy content is capable of moving. . If the condi
tion of operation of the lamp is such that an elec- 30>
tron~ passing from the sheath with an energy con
tent above 16.5 volts collides with a, neon atom, lt
may either ionize the same or excite it to lumi
nosity, depending upon the exact energy values
involved. The impinglng electron will not, of 35'
course, be destroyed, but will continue its journey
with its energy reduced by an amount which rep
resents the ionization or excitation voltage of the
neon.
-
i
,
If such an electron of diminished energy, con- 40
veniently referred to as a secondary> electron, re
tains, as is very likely to be the case, an energy
of Vless than 5.1 volts and encounters a sodium
atom, it will not be able to ionize the latter. In
stead, a transfer of energy of, another type will 45
take place which is conventionally referred to as
This is- a.
phenomenon which requires an electron energy of
between 2.1 and 5.1 volts. _An excited sodium
iication, it is possible, and my invention contem- , an excitation of the- sodium atom.
plates, that equivalent materials such as I_nercury
or caesium may be substituted for the former while
50 >other inert gases such as argon or krypton may
be used instead ofv thelatter.
^
It is a function of the sodium or-equivalent
vaporizable material to provide a source of sub
stantial numbers of atoms which may be brought
55 to a state of light radiation by impact with elec
atom is, generally speaking, capable of two further' 50
changes in condition; it may, if undisturbed for
a brief period, return to its natural state, such
return being accompanied with the production of
light, or it may be converted into ‘a sodium ion by »
a further impact with an electron having energy 56
2
2,135,284
coiled or straight, coated with an electron emis
of 3 or more volts. 'I'his latter conversion not~
only fails to result in the production of light, but
sive substance such as an alkaline earth metal
Ialso eliminates' an excited sodium atom.- - This
Y form ,of ionization by successive impacts with sec
oxide and supplied with heating current through,
suitable lead-in connections I 9 and 20. This fila
ondary electrons is conventionally referred as cu
mulative ionization. It tends to increase rapidly
with increasing concentrations of excited atoms.
In view of the above it is obviously desirable
ment is supported more or less resiliently at its
upper end by a bent metal ribbon I3 which in
turn is mounted on a pair of vertical supports I5
for the most efiicient production of light that all
_and I6. These latter elements are coated with a
heat-resisting material, such as alumina, for the
purpose of preventing their'destruction during
used in producing from unexcited sodium atoms the operation of the device. For reasons to be
a maximum .number of ' excited sodium- atoms shortly explained, I consider that the anode. and
which, as before explained, are av potential source cathode should have opposed, discharge-receiving
of light. Correlatively, the concentration or >surfaces of as great a longitudinal extent as the
dimensions of the envelope permit. With a tubu
15 “crowding” of excited sodium atoms should be
lar envelope construction such as that shown, the '
kept so low that cumulative ionization is sub
electrodes should extend lengthwise of the enve
stantvially avoided.A
'
lope for a distance substantially greater than the
, With the aboveprinciples in view it is believed
that the nature of my invention now may be tube diameter and preferably commensurate with
its length. For energizing the lamp, I have in 20
clearly understood.
.
g
dicated an elementary circuit comprising a main
Referring to Fig. '1, I have illustrated an elon
gated sealed envelope I terminating at its base transformer 22, a filament transformer 23 and a
»
in a reentrant stem 2 provided with a press 3. current. limiting resistor 24.
10 available- secondary electron energy should be
A filling of a ñxed gas such as neon is provided
By analogy with accepted usage in other types .
in the envelope I and a quantity of sodium, or
other vaporizable material, is deposited on the
of discharge lamps it has heretofore been deemed 25
most advantageous, both for electron generation
and for conservation of heating energy, to con
struct-the cathode member of a cathodic lamp in
the form of a concentrated electron source, such
as a closely coiled wire helix; I have found, 30
however, that by using an elongated configura
wall of the tube as shown at 4.
` Observations indicate that actual generation of
light in a cathodic lamp takes place within a re
stricted radial distance of the cathode defined by
the range within which substantially all second
ary-electron energy will be absorbed. In the case v tion such as that specified above, a greater lumi
of a sodium lamp, in normal operation, the entire nous output may be obtained than has hereto
fore been deemed possible with lamps of the type
tube may> appear to be filled with a diffused so
dium glow.
This is because sodium resonance _
radiation, actually generated within the re
stricted region only, is continually absorbed and
reemitted by. sodium atoms in the outlying space.
Luminous emission from the tube is thus viewed
40 externally as though it were taking place from
the outer portion of 'the lamp.
The dimensions of the region of light genera
tion are determined in part by the concentration
of excitable atoms which in turn depends on the
45 ratio of neon pressure to sodium pressure.
The
optimum condition which can be obtained is
that at which the light generating region is co
extensive with the volume of the bulb. It is not
practical to assign an exact value for the best
50
neon pressure to be employed, but this factor may ~
be determined experimentally for any given tube
construction. I have obtained most satisfactory
resultsvwith a pressure of neon in the neighbor
hood of 400 microns of `mercury and a pressure
55 of sodium of the order -oi’ magnitude of one
_micron.
In order to prevent gradual condensation of
the s_odiuminto the relatively cold' base of the
tube a mica disk 6 is provided which effectively
60 divides the base froml the main body of the en
velope. Through this disk lead-in wires are
passed which at one end are sealed into the mem
ber 3 and at the other end serve to support the
various electrodes. The anode 5 is shown as>
comprising a coiled ribbon ofsuitable metal, for
example, nickel,.forming a helix which has its
axis substantially coincident with the major- axis "
of the envelope I.> >This anode is supported from
the press 3 by a pair of conducting .rods 8 and 9,
70 of whichfthe latter is provided with van external
connection to permit a suitable potential to be
impressed on the anode.
- _
Concentrically arranged within the anode -I
provide a thermionic or incandescible cathode- II
-75 comprising an elongated metal ñlament, either
in question. This unexpected result I attribute 35
to the fact that a more advantageous distribu
tion of emitted electrons is obtained. »In other
words, while the total number of electronsmay
be unchanged, any unit volume of gas adjacent
the cathode is subject to relatively less-`electr„on 40
bombardment. Consequently, excitation of sodi
um atoms is disposed over so great a space that
cumulative ionization as above defined is sub
stantially prevented up to very high discharge
currents.
This means, of course, that a much 45
greater amount of energy can-be utilized in light
production- without cumulativeionization becom
ing the predominant energy absorbing factor.
When the ratio of neon to sodium pressure also
is so chosen that the region of secondary energy 50
absorption extends radially as far as the wall of
the envelope, optimum operating conditions exist.
- In previously constructed lamps of the type in
question a maximum of light output has been
obtained at a sodium' pressure such that less 55
than all the secondary electron energy is ab
sorbed. Any increase in pressure above the criti
cal value magniñes cumulative ionization to
such an extent that a net loss rather than a net
gain in light output is realized. As a conse 60
quence of this enforced suboptimal mode of
operation changes in sodium pressure produced
by variations _in ambient temperature cause cor- '
responding ‘changes in light generation. My
present invention, however, makes it possible to 65
use current densities adequate to vaporize more
than enough sodium to absorb all the secondary
electron energy while avoiding :excessive cumu
lative ionization. As a result constant luminous
output is obtained which output is independent 70
of ambient temperature variations.
-
Referring to Fig. 2, I have provided curves
illustrating the relative importance of the vari
ous factors referred to in the foregoing. The'
coordinates chosen are such that .the curves 75
2,185,284
show the variation in luminous output with
changes in are current for different operating
conditions.
'I'he lower curve, indicated as curve A, com
prises the output characteristic of a cathodic
lamp of known type in which the cathodev com
prises a relatively concentrated coil. It will be
seen that While the luminous output increases
linearly with cu'rrent up to a value of about 11/2
10 amperes, above that value -the curve iiattens
out to such an extent that little or no gain is
realized by increasing the current input.
'I'he curve B shows the improvement obtained'
in the operation of a cathodic lamp of identical
construction with that of curve A by carefully
selecting an optimum ratio of neon to sodium
pressure -which in the instance chosen operated
at such temperature that the sodium;~ vapor
pressure was approximately one micron. How
20 ever, in spite of thefact that a considerable in-`
crease in luminous output is .realized by the
a certain point.
However, with an extended cathode such as.
characterizes my invention, excessive cumula
tive ionization will not set in until an amount of
sodium vapor is present in excess of that re
quired to utilize all available secondary electron
energy in the excitation of light. ï When a com->
pletely adequate supplyl of vaporized sodium is
present, a further increas'e in temperature and 10
in sodium vapor pressure obviously cannot'in
crease the light generation. Consequently" Aa
range of temperature exists in which constant
light output will obtain at least up to the point
where even the extended nature of the cathode
cannot prevent excessive cumulative ionization
from occurring. 'I'his range comprises, for ex
ample, the yregion from y to z on curve E of Fig.
`3. The point y indicates the temperature re-_
quired to vaporize the least amount of sodium
sufficient to produce maximum,A light excitation,
i. e., 'to permit full utilization of available elec
curs at currents materially in excess of 5 am
tron energy.
peres.
represents the temperature vat which excessive
cumulative ionization begins to occur.
'
whichv this curve was obtained the envelope and
other structural parts were of precisely the same-
'I'he point z, on the‘other'hand,
It is obvious that if the lamp can be operated so
that its normal temperature of operation corre
sponds to the point l0 on curve E, the light output
of the lamp may be substantially insensitive lto_
dimensions as were employed in connection with
curves A and B. However, as a result of the
variations in ambient temperature (at least as
long as such variations do not carry the oper
ating temperature of the lamp above z or »below
increased gaseous volume traversed by the emit
ted electrons, a current intensity corresponding
il).
to'an ar'c current of 10 amperes was employedwithout producing any manifestation of satura
tion due to cumulative ionization. A luminous
tained by selectingthe proportions and heat in 35
sulation of the lamp such that at the preferred
operating currents, i. e. for discharge currents
_corresponding to the range of emcient operation
ofthe lamp, the temperature of the lamp will
output Iof approximately 10,000 lumens was ob
tained in a lamp having a volumetric content of
approximately 450 cubic centimeters and using
a power» input of. approximately.- 200 watts. To
the best of my knowledge this is the first time
that an output of this magnitude has been at
tained in a cathodic, lamp irrespective of the
45
than' a net, gain in light output is realized above
change indicated a definite saturation eiïect oc
The curve C represents the results obtained by
using( an electrode arrangement such as is shown>
in Fig. 1 in connection with an optimal neon
pressure of about 400 microns. In the tests Irom>
40
3
input employed.
'
‘
~
A further advantage attendant upon the use
of an extended rather than a concentrated cath
ode consists in the‘ possibility of making a cath
odio -lamp which is substantially insensitive to
50 variations in ambient temperature.
l
Where a concentrated cathode is employed,
a continuous variation of luminous output with
temperature occurs, as is indicated, for example,
by curve D in Fig. 3._ In this curve a condition
55 of constant current operation is assumed, the
As a practical matter, this result can be ob
be maintained at a point corresponding to the 40
point O. The determination of this point for a
given lamp is a matter which will oil‘er little dith
culty for one`skil1ed in the art. Ordinarily, the
maintenance of the requisitev temperature will
require the .use of some type of heat conservator
in connection’ with thejdischarge envelope so as
to achieve the proper relationship between the
energy supplied to the discharge and that dissi
pated fromthe envelope. Such a conservator
.f may, for example, take the form of a transparent
vacuum jacket such as is indicated at 25 in Fig. 1.
The form of lamp which I have described is
exemplary only and it will be understood that
various modiñcations o_f 'structure may be used.
For example, the anode may be constituted of'a 55
screen-like mesh rather than a spiral ribbon
changing the proportions or insulation of the- -as illustrated and the cath°ode may lcomprise an
discharge envelope. 'I'he rising portion of the, velongated helical structure rather than a straight
curve to the left of the point X Vis due to the ñlament such as that shown in Fig, 1. I aim in
60
the >appended -claims to cover all such variations 60
increase with temperature of _the number ofso
dium atoms .available for light excitation. 4The of form and use as fall within the> true spirit and
_ ,
decreasing portion of the curve, on the other scope. of the foregoing disclosure._
What I claim as new and desire to secure‘by
- hand, I consider to be due to the destruction
Letters Patent of the United States is:
_
of excited sodium atoms- by .cumulative ioniza
1. A cathodic lamp- comprising _an envelope
tion. With a concentrated cathode, the concen
tration of excitedsodium atoms in the vicinity of .- which encloses a discharge-Supporting gas. a
temperature being varied, for’.example, by
the cathode increases extremely rapidly with
rising sodium pressure. Consequently cumula
vaporizable light-producing substance, and a pair
of cooperating electrodes having mutually facing
great enough to nullify thev favorable effect of
discharge-receiving surfaces of as great longi
tudinal extent as the major dimension of the
the increased availability of sodium atoms even
before enough atoms are provided to make it
lation of the envelope .'being such that at dis
charge ‘currents within the range of eillcient op
70 tive ionization adjacent to the cathode becomes
theoretically possible to utilize all available elec~ '
75 tronv energy.v For this reason a net'loss rather
envelope permits, the proportions and heat insu
eration of the lamp the amount of said substance
maintained inthe vapor phase is appreciably
4
2,185,284
place, whereby the luminous output of said lamp
above the least amount suflicient for maximum
light excitation at 'such currents but below the
is substantially insensitive to variations in am
value at which excessive cumulative ionization
bient temperature.
3. A cathodic lamp comprising an elongated
takes place, whereby the luminous output of the
lamp is substantially insensitive to variations in tubular envelope enclosing an inert gas, a quan
- tity of sodium and concentrically arranged dis
ambient temperature.
charge electrodes having opposed discharge-re
2.` A cathodic lamp including an elongated tu
ceiving surfaces which extend longitudinally of
bular envelope which encloses a discharge-sup
porting gas, a vaporizable light-producing sub
10 stance, and a vpair of cooperating electrodes hav-`
- ing mutually facing discharge-receiving surfaces
which extend longitudinally of the envelope a
distance substantially greater than the diameter
thereof, the proportions and heat insulation of
the' envelope being such that at discharge cur
rents within the range of emcient operation of
the lamp the amount of said substance main
tained in the vapor phase is appreciably above
the leastamount sumcient for maximum light
20 excitation at such currents but below the value
at which excessive cumulative ionization takes
the envelope a distance substantially greater than
the diameter thereof, the proportions and heat
insulation of the envelope being such as to main-v
tain in the vapor phase during operation of the
lamp a quantity of sodium intermediate between
the least amount suflicient for maximum light ex
citation at the operating current of the lamp and. 15
the amount at which cumulative ionization be
comes excessive, whereby the luminous output of
the lamp is substantiallyv independent of vari
ations in ambient temperature.
'
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cm'roN G. FOUND.
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