Improvements in Electric Incandescent Lamps.
Year: 1898

page_text: Date of Application, 10th May, 1898-Accepted, 18th June, 1898
Improvements in Electric Incandescent Lamps.
I, WILLIAM JOSHUA PHELPS, of Elmwood, Peoria County, State of Illinois, United
States of America, Gentleman, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
In the electric incandescent lamp of familiar construction, no means is provided
for varying the intensity of individual lamps from the maximum candle power for
which they have been designed. Various methods have been proposed, from time to
time, for accomplishing such regulation, and have been made the subject of letters
patent.
Considerable groups of lamps, as in threatres, are modulated by varying the
effective voltage of the electric supply through adjustable resistance inserted in the
circuit and it has been proposed to apply the same method to the individual lamp, a
small rheostat being formed as a part of the lamp socket. Other inventors have
proposed to employ several circuits differing in electro-motive force and either to
arrange a lamp to be burned on any of the circuits or to provide a multiplicity of
lamps, on the several circuits, so that a light of the desired intensity may at any
time be selected.
Again, it has been suggested that several filaments of different candle power be
mounted in one vacuum bulb in connection with means for turning on the current
to any one filament or to several at once.
Finally, it has been proposed to mount two filaments in one vacuum bulb under
the control of a commutating switch arranged to burn either filament alone,
both in parallel or both in series, thereby securing three different intensities of
illumination.
The qualities of the incandescent filament are such that white light, coincident
with reasonable durability is only secured through an exceedingly small range of
electro-motive force which is the critical voltage for which the filament is designed-
more voltage causes the lamp to blacken and if continued, to burn out, while less
than the critical voltage causes the filament to emit a yellow and then a red light
growing more dim down to the point of no light. Modulation of one incandescent
filament by varying the effective voltage is, therefore, attended with the disadvantage
that the lamp is burned (at anything less than maximum intensity) with poor color
and low efficiency.
On the other hand, a multiplicity of lamps or of filaments in parallel in one bulb
is relatively expensive and has the disadvantage that the least intensity practical at
the usual voltages, is as great as eight or ten candle power.
This invention is intended to secure an economical incandescent lamp in which
widely differing intensities may be obtained without materially changing the quality
or color of the light emitted. It is a further object to provide a modulating incan-
descent lamp of such form that it may be used without a socket of special construction,
but which may be used interchangeably with ordinary lamps.
The nature of the improvements will appear in detail from the description follow-
ing, and will be more particularly pointed out by claims at the conclusion thereof.

page_text: designation throughout.
Figure 1 is an elevation of my improved lamp with Edison type hase.
Figs. 2 and 3 are enlarged vertical sections of the lamp base and a portion of an
Edison socket, respectively showing the lamp in the two positions of least and greatest
intensities.
Figs. 4, 5 and 6 are enlarged perspective views showing parts of the lamp base.
Fig. 7 shows in enlarged vertical section an alternative construction for the parts
illustrated in Figs. 4, 5 and 6.
Fig. 8 is an enlarged perspective view of the shunting spring which forms part of
Fig. 7.
Figs. 9 and 10 show two enlarged vertical sections of a lamp base so constructed
that the current turned off during the change from the position of greatest to that
of least intensity and vice versa.
Fig. 11 is a plan view partly in section, looking at the top of Fig. 9.
Fig. 12 is a plan view looking at the bottom of the lamp-base shown in Fig. 10.
Fig. 13 is an enlarged vertical section of a Thomson-Houston lamp-base, and part
of a Thomson-Houston socket, showing my improvement as applied to this type of
lamp-base.
Fig. 14 is a perspective view of the contact ring which forms part of Fig. 13.
Figs. 15, 16, 17 and 18 show diagramatically various embodiments of my invention
illustrating features which form the subjects of the claims.
Referring now to Fig. 1, A is the glass bulb of an incandescent lamp, B the metal
screw base of familiar Edison type, E the incandescing filament, and H and G the
leading-in wires, sealed into the glass neck P. F is an auxiliary filament connected
to G and to the extra leading-in wire I. K is a disc of insulating material (prefer-
ably porcelain) to which the shunting spring is secured by a tubular rivet C.
Rivet C is insulated from the shunting spring D by the washer M and is preferably
clinched on the under side of K. The free end of the shunting spring D carries a
round disc D¹ which is slightly concavo-convex as shown in order. to more readily
engage the various styles of central contact used by the several makers of Edison
type sockets.
In Figs. 2 and 3, the bulb A and filaments E and F are broken away and the re-
maining parts as hereinbefore described and designated, are shown in vertical section,
the scale being enlarged to secure greater clearness. Part of the porcelain core of an
Edison socket is shown at N to which are attached the central contact O, the screw
shell L and the outer shell 23 which is insulated from L by the bushing L³ of fibre
or other suitable insulating material. The leading-in wires are electrically connected
as shown at H¹, I¹ and G¹; H to screw B, I (through a hole in K) to shunting
spring D, and G to the head of tubular rivet C being passed through the rivet and
secured in a small groove (shown at G¹, Fig. 6). The glass bulb is secured to the
base B by means of the customary plaster of Paris filling shown at J. Figs. 4, 5 and 6
respectively show enlarged perspective views of the porcelain disc K, the shunting
spring D and the tubular rivet. C.
The alternative construction shown in Figs. 7 and 8 is intended to enable the
advantages of this invention to be realized with the smallest possible change in the
design of the common Edison type base. The parts K and C are substantially
the insulating disc and central contact used by several manufacturers. The shunting
spring D, in this case is secured to disc K, concentric with C (but separated from it)
by means of the prongs 26 which are passed through holes in K and clinched.
Thus the addition of the part shown in Fig. 8 to the ordinary Edison type lamp-base
will fit it to be used in connection with my bi-filament lamp. If the parts are in
the position shown in Fig. 2 and the contact O be connected to one pole of an electric
circuit, current will flow to shunting spring D and thence by leading-in wire I to
the auxiliary filament F, thence through the main filament E, the leading-in
wire H and the screw B to the shell L which is connected to the opposite pole

page_text: of the circuit. The auxiliary filament will now glow with a small white light and
the main filament will be black or only dull red.
If now the globe A be turned toward the right so as to drive the screw B into the
socket shell the shunting spring D will be pressed down against the rivet C and
the parts will then assume the relation shown in Fig. 3. In this position current
flows from central contact O to disc D¹ and thence by the path of least resistance,
to rivet C, leading-in wire G, and main filament E, returning by leading-in wire H,
screw B, and shell L, which is connected to the opposite pole of the circuit. The
main filament, now being subjected to the maximum electro-motive force, burns
with full incandescence passing the normal current for which it has been designed.
Owing to the fact that the resistance of the filament increases with the decrease
of current, it may be desirable in order to avoid straining the auxiliary filament, to
turn out the main filament and allow it to cool before connecting the two in series.
This is accomplished by the means shown in Figs. 9 and 10. B is the screw-base of
Edison type, K is an insulating disc (preferably porcelain) fixed in one end of same,
Cand S are two flat rings secured on either side of K by means of the screws U and V
which are separated from the ring C by the insulating bushings M, M. The
screw U is drilled to permit the passage of leading-in wire I. X is a square rod of
metal passing through disc K and having on one end the light spring R and on the
other end the cap T secured by screw D. The stiff spiral spring W forces the parts
into the position shown in Fig. 9. In this position the screw D, being against the
central contact of an Edison socket 0, current passes through X to R and thence
through ring S, tubular screw U and leading-in wire I to both filaments burning
in series. On screwing the lamp further into its socket, spring R leaves the ring S,
thereby breaking the circuit, but a further movement establishes the circuit again as
shown in Fig. 10. Current now passes from screw D to cap T and ring C, thence by
leading-in wire G (through a hole in disc K) to the main filament burning alone.
The current returns in either case by leading-in wire H to serew-base B.
If now the lamp be partly unscrewed from the socket, it is evident from the
construction that the cap T will leave the ring C before the spring R can touch the
ring S. Thus the main filament will be turned out (and will quickly cool thereby
reaching the condition of greatest resistance) before being connected to the circuit
in series with the auxiliary filament. The sections shown in Figs. 9 and 10 are at
right angles to each other and approximately double size. Fig. 11 is a plan view
looking at the top of the lamp with the cap T and spring W removed. The
screws U and V and the ring C are shown together with a section of rod X. Leading-
in wire G is soldered to ring C at the point G and leading-in wire I is soldered to
the screw U (in electrical connection with ring S) at the point I¹. Fig. 12 is a plan
view looking at the bottom of Fig. 10 with the glass bulb and plaster of Paris
filling entirely removed. Spring R, ring S and screws U and V are shown and rod X
is indicated by the dotted lines.
Referring to Fig. 13, B is a metal shell in one end of which is secured the disc K
of insulating material (preferably indurated fibre or other similar composition). The
dise K surrounds the nut C to which the leading-in wire I is soldered at the point I¹
and carries the flat spring Q to which the leading-in wire H is soldered at the
point H¹. A portion of the vacuum bulb is shown at A secured to B by the plaster
of Paris filling J. The flat spring Z is secured to the under side of disc K in
such a position as to make contact with the central post 0 of a Thomson-Houston
socket when screwed into nut C. Spring Z carries a prong at one end which
projects through disc K and connects with leading-in wire G at the point G¹.
The springs Q are arranged in a circle concentric with, but insulated from,
the nut C. N, L and 23 are portions of a Thomson-Houston socket together with the
post O.
If now this base be screwed into a Thomson-Houston socket until springs Q
touch the annular contact plate L which forms one pole of the socket, the current
will pass from springs Q and leading-in wire H through both filaments in series
to the leading-in wire I and nut C. The auxiliary filament will then be alight,

page_text: .
On screwing the lamp still further into its socket, the springs Q will be bent
down and the contact post 0 of the socket will touch the spring Z. The auxiliary
filament will then be shunted by the superior path offered by leading-in wire G
and spring Z and the main filament will then burn with full candle power.
Fig. 14 is a perspective view of the annular spring contact shown in section at Q-Q,
Fig. 13.
In the form of lamp shown in Fig. 1, the auxiliary filament has usually a smaller
cross-section than the main filament so that the amount of current which will bring
the auxiliary filament up to white incandescence is insufficient to make the main fila-
ment luminous or, at most, more than red-hot. The design is such that the cold resist -
ance of the main filament E (or its resistance when warmed much below the temperature
of white incandescence) when added to the hot resistance of the auxiliary filament F,
is just sufficient to pass the normal current, required by the auxiliary filament, when
both filaments in series are subjected to the electro-motive force for which the lamp
has been designed.
The design may be varied through a great many combinations, according to the
length and cross-section of the filaments. The auxiliary filament may be a very short
length of the most attenuated carbon thread which it is practical to make, or it may be
of the same cross-section as the main filament and only smaller in length, or it may
be a thick filament of greater cross-section than the main filament but too low
resistance to be independently connected to the circuit.
In the embodiment of my invention I prefer that the sections of incandescing
material shall be formed as separate filaments since I believe that commercially this
will be the most successful manner of producing the sections, but I do not wish the
broad features of this invention to be understood as restricted to a lamp in which the
sections of incandescing material are necessarily formed separate from each other or
as two separate and distinct filaments. I should regard as the embodiment of this
invention a lamp in which a single continuous length of incandescing material is
separated into two sections by means of an extra electric connection located at some
point between its two ends. I have shown such a lamp in Fig. 15 where the continuous
length of incandescing material E, E¹ is separated into two unequal sections by the
extra connection G. The section E is of too low resistance to be independently sub-
jected to the full voltage of the circuit and is not burned alone but when current is
passed through both sections in series from the leading-in wire H to the leading-in
wire I the added resistance of the section E¹ reduces the current below the amount
sufficient to bring the section E to full incandescence. When current passes from
leading-in wire H to leading-in wire G, section E¹ being shunted, the section E glows
with full candle power.
In like manner, Fig. 16 shows a main filament E, an auxiliary filament F and
three leading-in wires I, H, G. In this form of lamp the auxiliary filament is of
greater cross section than the main filament and when connected in series therewith
serves as a dark and dead resistance to reduce the current below that amount which
is required to bring filament E to full incandescence.
Fig. 17 shows a form of lamp in which the main and auxiliary filaments are
permanently connected in series. The object in this form is to provide a lamp of
small candle power which may be used upon the standard commercial circuits of say
50 or 110 volts. The filament E acts as a dead resistance to modify the effective
voltage for the filament F which then glows with a small but relatively white
light.
While I have shown and described as one embodiment of this invention a lamp
with one auxiliary filament and one main filament, it is to be understood that I do
not confine myself to the use of two filaments and the shunting spring adapted
thereto, because two or more auxiliary filaments and one inain filament, or one
auxiliary filament and two or more main filaments (each adapted to the full voltage)
may be located within one vacuum globe and fitted with connections to shunt the
same in or out of circuit by the progressive longitudinal movement of the lamp in
screwing the same in or out of its socket or support. I have shown a three-filament

page_text: lamp in Fig. 18 in which the current passes first to the shunting spring, reading-in
wire G and the thin auxiliary filament F from whence the current is led through the
filament E¹, the filament E and the leading-in wire H. Filaments E and E¹ now
serve as relatively dark and dead resistance. If the lamp be further screwed into a
socket the spring D will be pressed into contact with spring 61 shunting out the
filament F. The resistance of filament F being now removed, the flow of current
through filaments E and E¹ in series is sufficient to cause the latter to glow. If now
the lamp be screwed into its socket to the utmost extent, spring D and with it
spring 61 will be pressed into contact with the central button Cand current will now
pass directly to filament E and leading-in wire H which is connected to the other
pole of the circuit. The resistance of E is such that, the other filaments being
withdrawn, sufficient current is passed to produce full incandescence.
I am conscious that the use of two or more incandescent filaments connected in
series or in parallel, within the exhausted globe of one incandescent lamp is not new;
therefore I do not broadly claim such structures. This invention consists in a novel
construction of the lamp-base whereby a multi-filament lamp may be used inter-
changeably with ordinary lamps in the sockets or supports commonly provided, and
in the advantageous use of one or more filaments as relatively dark resistance to
modify the current for one or more other filaments within the same vacuum.
'
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what
I claim is
1. An electric incandescent lamp comprising a vacuum bulb, two sections of
incandescing material, one of said sections serving as a resistance to modify the
current for the other section when in series therewith, but being of too low resistance
to be independently subjected to the full voltage of the electric supply, and connec-
tions whereby current may be passed to both sections in series or through the section
of higher resistance alone, but not through the section of lower resistance alone.
2. An incandescent lamp comprising an exhausted transparent bulb, two or more
incandescent filaments with electrical connections to each filament and a shunting or
disconnecting device so arranged that current can at will be caused to flow through
two or more of the filaments in series or through one of the filaments alone, said
change in current flow being effected by a longitudinal movement of the lamp in its
socket.
3. In constant potential electric lighting, the combination with a vacuum bulb, of
two or more filaments or sections the relative resistance of which is such that when
current is passed to two or more of the filaments in series, one at least of said
filaments glows while one at least of said filaments serves as a relatively dark and
dead resistance to modify the current, a base or part adapted to screw into a socket,
or support, and mechanism for shunting or disconnecting one or more of the fila-
ments, actuated by the longitudinal movement of the lamp in its socket effected in
screwing the same into place.
4. An electric incandescent lamp comprising two filaments or sections of incan-
descing material and a movable shunt or bridge piece adapted to shunt one of the
filaments and actuated by the longitudinal movement of the lamp in its socket
effected in screwing the saine into position, said filaments being connected together in
series with one end of each filament in permanent connection with an electrical ter-
minal of the lamp.
5. An electric incandescent lamp comprising an exhausted globe, a main incan-
descing filament adapted to withstand the full electro-motive force of the electric
circuit for which the lamp has been designed, an auxiliary filament having too little
resistance to be directly connected to such circuit, three conducting wires leading
from the filaments (one end of each filament being electrically connected within the
vacuum) a base containing the terminals of the conducting wires normally insulated
from each other and a rod or part situated on or within the base and actuated by the
progressive longitudinal movement effected in screwing the base into a socket or

page_text: support; in the normal position, the said rod or part carries the electric current to the
main and auxiliary filaments in series when partly screwed into a socket ;- when
screwed in somewhat further the circuit is broken and when screwed into the socket
to the utmost extent the current is turned through the main filament burning alone.
Dated at Chicago, Cook County, Illinois, United States of America, this 22nd 5
day of April. A.D) 1898
WILLIAM JOSHUA PHELPS,
F. Wise Howorth,
,i
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.