adopted about 1888, was to dip it in a hydrocarbon liquid before
carbonizing. Another, more generally adopted in 1893 was a process
originally invented by Sawyer, one of the Americans who had attempted
to “sub-divide the electric light” in 1878–79. This process consisted
of passing current through a carbonized filament in an atmosphere of
hydrocarbon vapor. The hot filament decomposed the vapor, depositing
graphite on the filament. The graphite coated filament improved it so
it could operate at 3½ lumens per watt (initial efficiency). Lamps of
20, 24, 32 and 50 candlepower were developed for 110-volt circuits.
Lamps in various sizes from 12 to 36 cp were made for use on storage
batteries having various numbers of cells and giving a voltage of
from 20 to 40 volts. Miniature lamps of from ½ to 2 cp for use on dry
batteries of from 2½ to 5½ volts, and 3 to 6 cp on 5½ to 12 volts, were
also made. These could also be connected in series on 110 volts for
festoons. Very small lamps of ½ cp of 2 to 4 volts for use in dentistry
and surgery were made available. These miniature lamps had no bases,
wires being used to connect them to the circuit.
[Illustration: STANDARD EDISON LAMP, 1894.
This lamp had a “treated” cellulose filament, permitting an efficiency
of 3½ lumens per watt which has never been exceeded in a carbon
lamp. This lamp is in the exhibit of Edison lamps in the Smithsonian
Institution.]
Lamps for 220-volt circuits were developed as this voltage was
desirable for power purposes, electric motors being used, and a few
lamps were needed on such circuits. They are less efficient and more
expensive than 110-volt lamps, their use being justified however
only when it is uneconomical to have a separate 110-volt circuit for
lighting. The lamps were made in sizes from 16 to 50 candlepower.
[Illustration:
Edison. Thomson-Houston. Westinghouse. Brush-Swan.
Edi-Swan Edi-Swan United States. Hawkeye.
(single contact). (double contact).
Ft. Wayne Jenny. Mather or Perkins. Loomis.
Schaeffer or National. Indianapolis Jenny. Siemens & Halske.
VARIOUS STANDARD BASES IN USE, 1892.]
[Illustration: THOMSON-HOUSTON SOCKET.]
[Illustration: WESTINGHOUSE SOCKET.]
Electric street railway systems used a voltage in the neighborhood of
550, and lamps were designed to burn five in series on this voltage.
These lamps were different from the standard 110-volt lamps although
they were made for about this voltage. As they were burned in series,
the lamps were selected to operate at a definite current instead of
at a definite voltage, so that the lamps when burned in series would
operate at the proper temperature to give proper life results. Such
lamps would therefore vary considerably in individual volts, and
hence would not give good service if burned on 110-volt circuits. The
candelabra screw base and socket and the miniature screw base and
socket were later developed. Ornamental candelabra base lamps were made
for use direct on 110 volts, smaller sizes being operated in series
on this voltage. The former gave about 10 cp, the latter in various
sizes from 4 to 8 cp. The miniature screw base lamps were for low volt
lighting.
[Illustration:
Thomson-Houston. Westinghouse.
ADAPTERS FOR EDISON SCREW SOCKETS, 1892.
Next to the Edison base, the Thomson-Houston and Westinghouse bases
were the most popular. By use of these adapters, Edison base lamps
could be used in T-H and Westinghouse sockets.]
The various manufacturers of lamps in nearly every instance made bases
that were very different from one another. No less than fourteen
different standard bases and sockets came into commercial use.
These were known as, Brush-Swan, Edison, Edi-Swan (double contact),
Edi-Swan (single contact), Fort Wayne Jenny, Hawkeye, Indianapolis
Jenny, Loomis, Mather or Perkins, Schaeffer or National, Siemens &
Halske, Thomson-Houston, United States and Westinghouse. In addition
there were later larger sized bases made for use on series circuits.
These were called the Bernstein, Heisler, Large Edison, Municipal
Bernstein, Municipal Edison, Thomson-Houston (alternating circuit) and
Thomson-Houston (arc circuit). Some of these bases disappeared from
use and in 1900 the proportion in the United States was about 70 per
cent Edison, 15 per cent Westinghouse, 10 per cent Thomson-Houston
and 5 per cent for all the others remaining. A campaign was started
to standardize the Edison base, adapters being sold at cost for the
Westinghouse and Thomson-Houston sockets so that Edison base lamps
could be used. In a few years the desired results were obtained so that
now there are no other sockets in the United States but the Edison
screw type for standard lighting service. This applies also to all
other countries in the world except England where the bayonet form of
base and socket is still popular.
[Illustration:
Bernstein. Heisler. Thomson-Houston
(alternating current).
Thomson-Houston Municipal Edison. Municipal Bernstein.
(arc circuit).
VARIOUS SERIES BASES IN USE, 1892.
The above six bases have been superseded by the “Large Edison,” now
called the Mogul Screw base.]
THE EDISON “MUNICIPAL” STREET LIGHTING SYSTEM
[Illustration: EDISON “MUNICIPAL” SYSTEM, 1885.
High voltage direct current was generated, several circuits operating
in multiple, three ampere lamps burning in series on each circuit.
Photograph courtesy of Association of Edison Illuminating Companies.]
The arc lamp could not practically be made in a unit smaller than
the so-called “1200 candlepower” (6.6 ampere) or “half” size, which
really gave about 350 spherical candlepower. A demand therefore arose
for a small street lighting unit, and Edison designed his “Municipal”
street lighting system to fill this requirement. His experience in the
making of dynamos enabled him to make a direct current bipolar constant
potential machine that would deliver 1000 volts which later was
increased to 1200 volts. They were first made in two sizes having an
output of 12 and 30 amperes respectively. Incandescent lamps were made
for 3 amperes in several sizes from 16 to 50 candlepower. These lamps
were burned in series on the 1200-volt direct current system. Thus the
12-ampere machine had a capacity for four series circuits, each taking
3 amperes, the series circuits being connected in multiple across the
1200 volts. The number of lamps on each series circuit depended upon
their size, as the voltage of each lamp was different for each size,
being about 1½ volts per cp.
A popular size was the 32-candlepower unit, which therefore required
about 45 volts and hence at 3 amperes consumed about 135 watts.
Allowing 5 per cent loss in the wires of each circuit, there was
therefore 1140 of the 1200 volts left for the lamps. Hence about 25
32-candlepower or 50 16-candlepower lamps could be put on each series
circuit. Different sizes of lamps could also be put on the same
circuit, the number depending upon the aggregate voltage of the lamps.
[Illustration: EDISON MUNICIPAL LAMP, 1885.
Inside the base was an arrangement by which the lamp was automatically
short circuited when it burned out.]
A device was put in the base of each lamp to short circuit the lamp
when it burned out so as to prevent all the other lamps on that circuit
from going out. This device consisted of a piece of wire put inside
the lamp bulb between the two ends of the filament. Connected to this
wire was a very thin wire inside the base which held a piece of metal
compressed against a spring. The spring was connected to one terminal
of the base. Should the lamp burn out, current would jump from the
filament to the wire in the bulb, and the current then flowed through
the thin wire to the other terminal of the base. The thin wire was
melted by the current, and the spring pushed the piece of metal up
short circuiting the terminals of the base. This scheme was later
simplified by omitting the wire, spring, etc., and substituting a piece
of metal which was prevented from short circuiting the terminals of
the base by a thin piece of paper. When the lamp burned out the entire
1200 volts was impressed across this piece of paper, puncturing it and
so short circuiting the base terminals. Should one or more lamps go
out on a circuit, the increase in current above the normal 3 amperes
was prevented by an adjustable resistance, or an extra lot of lamps
which could be turned on one at a time, connected to each circuit and
located in the power station under the control of the operator. This
system disappeared from use with the advent of the constant current
transformer.
THE SHUNT BOX SYSTEM FOR SERIES INCANDESCENT LAMPS
[Illustration: SHUNT BOX SYSTEM, 1887.
Lamps were burned in series on a high voltage alternating current, and
when a lamp burned out all the current then went through its “shunt
box,” a reactance coil in multiple with each lamp.]
Soon after the commercial development of the alternating current
constant potential system, a scheme was developed to permit the use
of lamps in series on such circuits without the necessity for short
circuiting a lamp should it burn out. A reactance, called a “shunt box”
and consisting of a coil of wire wound on an iron core, was connected
across each lamp. The shunt box consumed but little current while the
lamp was burning. Should one lamp go out, the entire current would
flow through its shunt box and so maintain the current approximately
constant. It had the difficulty, however, that if several lamps went
out, the current would be materially increased tending to burn out the
remaining lamps on the circuit. This system also disappeared from use
with the development of the constant current transformer.
THE ENCLOSED ARC LAMP
Up to 1893 the carbons of an arc lamp operated in the open air, so
that they were rapidly consumed, lasting from eight to sixteen hours
depending on their length and thickness. Louis B. Marks, an American,
found that by placing a tight fitting globe about the arc, the life
of the carbons was increased ten to twelve times. This was due to the
restricted amount of oxygen of the air in the presence of the hot
carbon tips and thus retarded their consumption. The amount of light
was somewhat decreased, but this was more than offset by the lesser
expense of trimming which also justified the use of more expensive
better quality carbons. Satisfactory operation required that the arc
voltage be increased to about 80 volts.
[Illustration: ENCLOSED ARC LAMP, 1893.
Enclosing the arc lengthened the life of the carbons, thereby greatly
reducing the cost of maintenance.]
This lamp rapidly displaced the series open arc. An enclosed arc lamp
for use on 110-volt constant potential circuits was also developed. A
resistance was put in series with the arc for use on 110-volt direct
current circuits, to act as a ballast in order to prevent the arc from
taking too much current and also to use up the difference between the
arc voltage (80) and the line voltage (110). On alternating current, a
reactance was used in place of the resistance.
The efficiencies in lumens per watt of these arcs (with clear
glassware), all of which have now disappeared from the market, were
about as follows:
6.6 ampere 510 watt direct current (D.C.) series arc, 8¼ l-p-w.
5.0 ampere 550 watt direct current multiple (110-volt) arc, 4½ l-p-w.
7.5 ampere 540 watt alternating current (A.C.) multiple (110-volt)
arc, 4¼ l-p-w.
[Illustration: OPEN FLAME ARC LAMP, 1898.
Certain salts impregnated in the carbons produced a brilliantly
luminous flame in the arc stream which enormously increased the
efficiency of the lamp.]
[Illustration: ENCLOSED FLAME ARC LAMP, 1908.
By condensing the smoke from the arc in a cooling chamber it was
practical to enclose the flame arc, thereby increasing the life of the
carbons.]
The reason for the big difference in efficiency between the series
and multiple direct-current arc is that in the latter a large amount
of electrical energy (watts) is lost in the ballast resistance. While
there is a considerable difference between the inherent efficiencies
of the D. C. and A. C. arcs themselves, this difference is reduced in
the multiple D. C. and A. C. arc lamps as more watts are lost in the
resistance ballast of the multiple D. C. lamp than are lost in the
reactance ballast of the multiple A. C. lamp.
This reactance gives the A. C. lamp what is called a “power-factor.”
The product of the amperes (7.5) times the volts (110) does not give
the true wattage (540) of the lamp, so that the actual volt-amperes
(825) has to be multiplied by a power factor, in this case about 65
per cent, to obtain the actual power (watts) consumed. The reason
is that the instantaneous varying values of the alternating current
and pressure, if multiplied and averaged throughout the complete
alternating cycle, do not equal the average amperes (measured by an
ammeter) multiplied by the average voltage (measured by a volt-meter).
That is, the maximum value of the current flowing (amperes) does not
occur at the same instant that the maximum pressure (voltage) is on the
circuit.
THE FLAME ARC LAMP
About 1844 Bunsen investigated the effect of introducing various
chemicals in the carbon arc. Nothing was done, however, until Bremer,
a German, experimented with various salts impregnated in the carbon
electrodes. In 1898 he produced the so-called flame arc, which
consisted of carbons impregnated with calcium fluoride. This gave a
brilliant yellow light most of which came from the arc flame, and
practically none from the carbon tips. The arc operated in the open air
and produced smoke which condensed into a white powder.
The two carbons were inclined downward at about a 30-degree angle with
each other, and were of small diameter but long, 18 to 30 inches,
having a life of about 12 to 15 hours. The tips of the carbons
projected through an inverted earthenware cup, called the “economizer,”
the white powder condensing on this and acting not only as an excellent
reflector but making a dead air space above the arc. The arc was
maintained at the tips of the carbons by an electro-magnet whose
magnetic field “blew” the arc down.
Two flame arc lamps were burned in series on 110-volt circuits. They
consumed 550 watts each, giving an efficiency of about 35 lumens per
watt on direct current. On alternating current the efficiency was about
30 l-p-w. By use of barium salts impregnated in the carbons, a white
light was obtained, giving an efficiency of about 18 l-p-w on direct
current and about 15½ on alternating current. These figures cover lamps
equipped with clear glassware. Using strontium salts in the carbons,
a red light was obtained at a considerably lower efficiency, such
arcs on account of their color being used only to a limited extent for
advertising purposes.
[Illustration: CONSTANT CURRENT TRANSFORMER, 1900.
This converted alternating current of constant voltage into constant
current, for use on series circuits.]
These arcs were remarkably efficient but their maintenance expense was
high. Later, about 1908, enclosed flame arcs with vertical carbons were
made which increased the life of the carbons, the smoke being condensed
in cooling chambers. However, their maintenance expense was still high.
They have now disappeared from the market, having been displaced by the
very efficient gas-filled tungsten filament incandescent lamp which
appeared in 1913.
THE CONSTANT CURRENT TRANSFORMER FOR SERIES CIRCUITS
About 1900 the constant current transformer was developed by Elihu
Thomson. This transforms current taken from a constant potential
alternating current circuit into a constant alternating current for
series circuits, whose voltage varies with the load on the circuit.
The transformer has two separate coils; the primary being stationary
and connected to the constant potential circuit and the secondary
being movable and connected to the series circuit. The weight of the
secondary coil is slightly underbalanced by a counter weight. Current
flowing in the primary induces current in the secondary, the two coils
repelling each other. The strength of the repelling force depends
upon the amount of current flowing in the two coils. The core of the
transformer is so designed that the central part, which the two coils
surround, is magnetically more powerful close to the primary coil than
it is further away.
When the two coils are close together a higher voltage is induced in
the secondary than if the later were further away from the primary
coil. In starting, the two coils are pulled apart by hand to prevent
too large a current flowing in the series circuit. The secondary
coil is allowed to gradually fall and will come to rest at a point
where the voltage induced in it produces the normal current in the
series circuit, the repelling force between the two coils holding the
secondary at this point. Should the load in the series circuit change
for any reason, the current in the series circuit would also change,
thus changing the force repelling the two coils. The secondary would
therefore move until the current in the series circuit again becomes
normal. The action is therefore automatic, and the actual current
in the series circuit can be adjusted within limits to the desired
amount, by varying the counterweight. A dash pot is used to prevent the
secondary coil from oscillating (pumping) too much.
In the constant current transformer, the series circuit is insulated
from the constant potential circuit. This has many advantages. A
similar device, called an automatic regulating reactance was developed
which is slightly less expensive, but it does not have the advantage of
insulating the two circuits from each other.
ENCLOSED SERIES ALTERNATING CURRENT ARC LAMPS
The simplicity of the constant current transformer soon drove the
constant direct-current dynamo from the market. An enclosed arc lamp
was therefore developed for use on alternating constant current. Two
sizes of lamps were made; one for 6.6 amperes consuming 450 watts
and having an efficiency of about 4½ lumens per watt, and the other
7.5 amperes, 480 watts and 5 l-p-w (clear glassware). These lamps
soon superseded the direct current series arcs. They have now been
superseded by the more efficient magnetite arc and tungsten filament
incandescent lamps.
SERIES INCANDESCENT LAMPS ON CONSTANT CURRENT TRANSFORMERS
Series incandescent lamps were made for use on constant current
transformers superseding the “Municipal” and “Shunt Box” systems. The
large Edison, now called the Mogul Screw base, was adopted and the
short circuiting film cut-out was removed from the base and placed
between prongs attached to the socket.
[Illustration:
Holder. Socket. Holder and socket.
SERIES INCANDESCENT LAMP SOCKET WITH FILM CUTOUT, 1900.
The “Large Edison,” now called Mogul Screw, base was standardized and
the short circuiting device put on the socket terminals.]
The transformers made for the two sizes of arc lamps, produced 6.6
and 7.5 amperes and incandescent lamps, in various sizes from 16 to
50 cp, were made for these currents so that the incandescent lamps
could be operated on the same circuit with the arc lamps. The carbon
series incandescent lamp, however, was more efficient if made for lower
currents, so 3½-, 4- and 5½-ampere constant current transformers were
made for incandescent lamps designed for these amperes. Later, however,
with the advent of the tungsten filament, the 6.6-ampere series
tungsten lamp was made the standard, as it was slightly more efficient
than the lower current lamps, and was made in sizes from 32 to 400 cp.
When the more efficient gas-filled tungsten lamps were developed, the
sizes were further increased; the standard 6.6-ampere lamps now made
are from 60 to 2500 cp.
THE NERNST LAMP
Dr. Walther Nernst, of Germany, investigating the rare earths used in
the Welsbach mantle, developed an electric lamp having a burner, or
“glower” as it was called, consisting of a mixture of these oxides. The
main ingredient was zirconia, and the glower operated in the open air.
It is a non-conductor when cold, so had to be heated before current
would flow through it. This was accomplished by an electric heating
coil, made of platinum wire, located just above the glower. As the
glower became heated and current flowed through it, the heater was
automatically disconnected by an electro-magnet cut-out.
[Illustration: NERNST LAMP, 1900.
The burners consisted mainly of zirconium oxide which had to be heated
before current could go through them.]
The resistance of the glower decreases with increase in current, so a
steadying resistance was put in series with it. This consisted of an
iron wire mounted in a bulb filled with hydrogen gas and was called
a “ballast.” Iron has the property of increasing in resistance with
increase in current flowing through it, this increase being very
marked between certain temperatures at which the ballast was operated.
The lamp was put on the American market in 1900 for use on 220-volt
alternating current circuits. The glower consumed 0.4 ampere. One, two,
three, four and six glower lamps were made, consuming 88, 196, 274, 392
and 528 watts respectively. As most of the light is thrown downward,
their light output was generally given in mean lower hemispherical
candlepower. The multiple glower lamps were more efficient than the
single glower, owing to the heat radiated from one glower to another.
Their efficiencies, depending on the size, were from about 3½ to 5
lumens per watt, and their average candlepower throughout life was
about 80 per cent of initial. The lamp disappeared from the market
about 1912.
[Illustration: DIAGRAM OF NERNST LAMP.]
THE COOPER-HEWITT LAMP
In 1860 Way discovered that if an electric circuit was opened between
mercury contacts a brilliant greenish colored arc was produced.
Mercury was an expensive metal and as the carbon arc seemed to give
the most desirable results, nothing further was done for many years
until Dr. Peter Cooper Hewitt, an American, began experimenting with
it. He finally produced an arc in vacuum in a one-inch glass tube
about 50 inches long for 110 volts direct current circuits, which was
commercialized in 1901. The tube hangs at about 15 degrees from the
horizontal. The lower end contains a small quantity of mercury. The
terminals are at each end of the tube, and the arc was first started
by tilting the tube by hand so that a thin stream of mercury bridged
the two terminals. Current immediately vaporized the mercury, starting
the arc. A resistance is put in series with the arc to maintain the
current constant on direct current constant voltage circuits. Automatic
starting devices were later developed, one of which consisted of an
electro-magnet that tilted the lamp, and the other of an induction coil
giving a high voltage which, in discharging, started the arc.
[Illustration: COOPER-HEWITT MERCURY VAPOR ARC LAMP, 1901.
This gives a very efficient light, practically devoid of red but of
high actinic value, so useful in photography.]
This lamp is particularly useful in photography on account of the
high actinic value of its light. Its light is very diffused and is
practically devoid of red rays, so that red objects appear black in its
light. The lamp consumes 3½ amperes at 110 volts direct current (385
watts) having an efficiency of about 12½ lumens per watt.