Improvements in Incandescent Electric Lamps.
Year: 1899

page_text: Date of Application, 18th Mar., 1899-Accepted, 22nd Apr., 1899
Improvements in Incandescent Electric Lamps.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Edwin W. Rice,
Jr., residing at Schenectady, in the County of Schenectady, State of New York,
United States of America, Electrical Engineer), and in what manner the same is
to be performed to be particularly described and ascertained in and by the
following statement;―
The present invention relates to electric lights, and its specific embodiment is
in a new form of electric lamp especially adapted to high-voltage circuits. It
has particular advantages in an alternating circuit, inasmuch as the conducting
body is of such a size that after it comes to incandescence, the particular frequency
of the circuit is of comparatively little importance; thus the lamp is especially
useful with those installations in which current of low frequency is generated, it
being well understood that this form of alternating current has certain advantages
in some cases. In general, the invention comprises not only a new form of lamp,
but the particular method and means of operating it to advantage. The light
giving body which is preferably enclosed in a sealed globe, such as is common in
incandescent lights, is one which at ordinary temperatures is a non-conductor, but
which at high temperatures becomes a conductor of electricity.
"
As such a substance does not take current when cold, it is necessary to " start
the lamp by external heat. This may be accomplished by exposing it to the action
of a heating conductor of high resistance, which may be coiled about the incan-
descing body, or may be embedded in it. In either case, it is preferable to so
arrange the lamp that after the healing conductor has raised the temperature of
the normally non-conducting medium to such a point that the latter becomes a
conductor, the former is cut out. This may be done in various ways, some of
which are shown in the accompanying drawings. A. thermostat may be employed,
which will act by the rise in temperature of the incandescing body, or (and this
is the preferred construction), a relay device may be employed which, when a
sufficient current passes through the normal non-conductor, will open the circuit
of the heating conductor.
There are a number of substances which are suitable for the incandescing body;
porcelain is one of these, and clay in its various forms may be used. Magnesium
oxide or magnesia is another substance. In practice it has been found that the
substances which have the lowest melting point become conductors at the lowest
temperature, while those which are extremely refractory become conductors only
at a very high temperature.
The accompanying drawings show some ways of carrying out the invention:-
Fig. 1 is a side elevation of a lamp in which it is embodied, Fig. 2 is a similar
view of the lamp, in which a thermostat is used, Fig. 3 is a section on the
line 33 of Fig. 2, looking down, Fig. 4 is a perspective detail of a modification
and Fig. 5 is a diagram of circuits.

page_text: A is a lamp bulb, of ordinary form,. B, B are leading in wires, C is the heating
conductor, which may be a platinum wire, but is preferably of carbon or some
other refractory, high resistance conductor, and D is the incandescing body, which
as already stated, may be of magnesia or porcelain, or other substance possessing
similar properties.
The heating conductor is coiled around, or embedded in, an incandescing body,
as shown in the drawings. When current is first admitted to the lamp it flows
only in the heating conductor C, but as this conductor gradually heats the body D,
that body begins to take current and to give out light; so that ultimately the cur-
rent taken by the conductor C may form only a very small portion of that passing
through the lamp.
A device for cutting out the heating conductor C when the body D is heated to
a sufficient temperature, is shown in Figs. 2 and 3. The thermostat F', consisting
of two strips of metal of different expansion co-efficients, normally occupies the
position shown in full lines in Fig. Current entering the lamp passes to the
wires B and B in multiple: The wire B is connected to the body D, and the
wile. Bis connected to one end of the heating conductor C. The wire B' is con-
nected to the body D and to the other end of the heating conductor C, and serves
to connect these two substances to the other terminal of the lamp.
When. current is first admitted to the lamp it passes through the wire B and
the conductor C, but, as the temperature of the lamp rises, the thermostat
finally open-circuits the conductor B³, so that all of the current passes through
the body D, which has now become a conductor.
In Fig. 4 another method of accomplishing the same result is shown. In this
form a relay or electro-magnet G is provided, with a spring contact G¹ and a con-
tact g to which one end of the wire Bs is attached. When current is first turned
on, it passes by way of the wire B2 and wire C to wire B. As the temperature of
the refractory body D. rises, its conductivity increases and current begins to pass
through it and through the coils of the magnet G. When the current reaches
sufficient intensity for the magnet to pull down the spring contact G¹ the circuit of
the coil C is interrupted and current passes only by the refractory body D.
Though we have shown our improved lamp provided with a globe in which a
vacuum may be maintained, it will be understood that we do not limit ourselves
to this arrangement, for in some cases it seems preferable to omit the globe, or,
if the globe is present, to open the lamp to the atmosphere at one or more points.
Referring to Fig. 5, G is a constant potential" generator of alternating or
direct current, and H; H are lines extending therefrom. A,A are the lamps
connected in multiple with the mains. It will be seen that in series with each
lamp there is connected a resistance R. This is for the purpose of steadying the
currents. The resistance of the conductor D decreases as the temperature rises,
and the decrease of resistance serves to admit more current. This action is likely
to fuse the substanco D, no matter how refractory it may be, unless the steadying
resistance is inserted.
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same is
to be performed, we declare that what we claim is:-
1-In an electric lamp, the combination of an incandescing body composed of a
material which is a non-conductor at ordinary temperatures and becomes conduct-
ing only at high temperatures, a heating device for rendering said body conduct-
ing, the same consisting of a normally conducting body in contact with said incan-
descing body, means for generating heat within said normally conducting body,
of such intensity as to act by its transfer to said. incandescing body to render the
latter an electrical conductor, and means for discontinuing the generation of heat
in said normally conducting body when the temperature of said incandescing body
has been raised sufficiently to render it conducting.
2-In an electric lamp, the combination of an incandescing body composed of
5

page_text: a material which is a non-conductor at ordinary temperatures and becomes
conducting only at high temperatures, a heating device for rendering
said body conducting, the same consisting of a refractory normally con-
duoting body in contact with said incandescing body, means for generating
heat within said normally conducting body, of such intensity as to act by its
transfer to said incandescing body, to render the latter an electrical conductor,
and means for discontinuing the generation of heat in said normally conducting
body when the temperature of said incandescing body has been raised sufficiently
to render it conducting.
3-In an electric lamp, the combination of an incandescent body composed of a
material which is a non-conductor at ordinary temperatures and becomes conduct-
ing only at high temperatures, a heating device for rendering said body conduct-
ing, the same consisting of a normally conducting body encompassing or
embedded in said incandescing body, and means for generating heat within said
normally conducting body of such intensity as to act by its transfer to said incan-
descing body to render the latter an electrical conductor.
4-In an electric lamp, the combination of an incandescing body composed of a
material which is a non-conductor at ordinary temperatures and becomes conduct-
ing only at high temperatures, a heating device for rendering said body conduct-
ing, the same consisting of a normally conducting body coiled about said
incandescing body, and means for generating heat within said normally conducting
body of such intensity as to act by its transfer to said incandescing body to render
the latter an electrical conductor.
5-The combination of an incandescent lamp the light-giving member of which
is a non-conductor at ordinary temperatures and a conductor at high temperatures,
and a steadying resistance in series with the lamp.
6-In an electric lamp, the combination of a light-giving member formed of a
material which is a non-conductor at ordinary temperatures and a conductor at
high temperatures, a heating resistance receiving energy from the same source as
the light-giving member, and means for automatically cutting said resistance out
of circuit when said light-giving member becomes operative.
7-In an electric lamp, the combination of a light giving member formed of a
material which is a non-conductor at ordinary temperatures and a conductor at
high temperatures, a heating resistance receiving energy from the same source
as the light giving member and an electro-magnetic device for automatically
cutting said resistance out of circuit when said light-giving member becomes
operative.
8-In an electric lamp, a light-giving member formed of a material which is a
non-conductor at ordinary temperatures, and a conductor at high temperatures,
in combination with a coiled resistance filament in heat-conducting relation
therewith.
Dated 17th day of March 1800.