be operated, the more efficient it becomes. The limit in temperature is
reached when the material begins to evaporate rapidly, which blackens
the bulb. The filament becoming thinner more quickly, thus rupturing
sooner, shortens the life. If, therefore, the evaporating temperature
can by some means be slightly raised, the efficiency will be greatly
improved. This was accomplished by Dr. Irving Langmuir in the research
laboratories at Schenectady, N. Y., by operating a tungsten filament
in an inert gas. Nitrogen was first used. The gas circulating in the
bulb has the disadvantage of conducting heat away from the filament
so that the filament was coiled. This presented a smaller surface to
the currents of gas and thereby reduced this loss. The lamps were
commercially introduced in 1913 and a patent was granted in April, 1916.
[Illustration: GAS FILLED TUNGSTEN LAMP, 1923.
This is the form of the lamp as at present made. For 110-volt circuits
the sizes range from 50 to 1000 watts.]
An increased amount of electrical energy is required in these lamps
to offset the heat being conducted away by the gas. This heat loss is
minimized in a vacuum lamp, the filament tending to stay hot on the
principle of the vacuum bottle. This loss in a gas filled lamp becomes
relatively great in a filament of small diameter, as the surface in
proportion to the volume of the filament increases with decreasing
diameters. Hence there is a point where the gain in temperature is
offset by the heat loss. The first lamps made were of 750 and 1000
watts for 110-volt circuits. Later 500- and then 400-watt lamps were
made. The use of argon gas, which has a poorer heat conductivity than
nitrogen, made it possible to produce smaller lamps, 50-watt gas-filled
lamps for 110-volt circuits now being the smallest available. In the
present state of the art, a vacuum lamp is more efficient than a
gas-filled lamp having a filament smaller than one consuming about half
an ampere. Thus gas-filled lamps are not now practicable much below 100
watts for 220 volts, 50 watts for 110 volts, 25 watts for 60 volts, 15
watts for 30 volts, etc.
From the foregoing it will be seen that the efficiency of these lamps
depends largely on the diameter of the filament. There are other
considerations, which also apply to vacuum lamps, that affect the
efficiency. Some of these are: the number of anchors used, as they
conduct heat away; in very low voltage lamps having short filaments the
relative amount of heat conducted away by the leading-in wires becomes
of increasing importance, etc. The 1000-watt lamp for 110-volt circuits
is now made for nearly 20½ lumens per watt; the 50-watt lamp a little
over 10 l-p-w.
The advent of the tungsten filament and especially the gas-filled
lamp sounded the doom of all other electric illuminants except the
magnetite and mercury arc lamps. All other incandescent lamps have now
practically disappeared. The flame arc as well as the enclosed carbon
arc lamp are hardly ever seen. The simplicity of the incandescent
lamp, its cleanliness, low first cost, low maintenance cost and high
efficiency of the tungsten filament have been the main reasons for its
popularity.
TYPES AND SIZES OF TUNGSTEN LAMPS NOW MADE
There are about two hundred different types and sizes of tungsten
filament lamps now standard for various kinds of lighting service. For
110-volt service, lamps are made in sizes from 10 to 1000 watts. Of
the smaller sizes, some are made in round and tubular-shaped bulbs for
ornamental lighting. In addition there are the candelabra lamps used
in ornamental fixtures. Twenty-five- to five hundred-watt lamps are
made with bulbs of special blue glass to cut out the excess of red and
yellow rays and thus produce a light approximating daylight.
For 220-volt service lamps are made in sizes of from 25 to 1000 watts.
For sign lighting service, 5-watt lamps of low voltage are made for
use on a transformer located near the sign to reduce the 110 volts
alternating current to that required by the lamps. Lamps are made from
5 to 100 watts for 30-volt service, such as is found in train lighting
and in gas engine driven dynamo sets used in rural homes beyond the
reach of central station systems. Concentrated filament lamps are
made for stereopticon and motion picture projection, floodlighting,
etc., in sizes from 100 to 1000 watts, for street railway headlights
in sizes below 100 watts and for locomotive headlights in sizes from
100 to 250 watts. For series circuits, used in street lighting, lamps
are made from 60 to 2500 candlepower. Miniature lamps cover those for
flashlight, automobile, Christmas-tree, surgical and dental services,
etc. They range, depending on the service, from ½ to 21 candlepower,
and in voltage from 2½ to 24.
[Illustration: STANDARD TUNGSTEN LAMPS, 1923.
This illustrates some of the two hundred different lamps regularly
made.]
STANDARD VOLTAGES
Mention has been made of 110-volt service, 220-volt service, etc.
In the days of the carbon incandescent lamp it was impossible to
manufacture all lamps for an exact predetermined voltage. The popular
voltage was 110, so lighting companies were requested in a number of
instances to adjust their service to some voltage other than 110. They
were thus able to utilize the odd voltage lamps manufactured, and this
produced a demand for lamps of various voltages from 100 to 130. Arc
lamps had a resistance (reactance on alternating current) that was
adjustable for voltages between 100 and 130.
Similarly a demand was created for lamps of individual voltages of
from 200 to 260. The 200- to 260-volt range has simmered down to
220, 230, 240 and 250 volts. These lamps are not as efficient as the
110-volt type and their demand is considerably less, as the 110-volt
class of service for lighting is, with the exception of England,
almost universal. Thus 110-volt service means 100 to 130 volts in
contra-distinction to 200 to 260 volts, etc. The drawn tungsten wire
filament made it possible to accurately predetermine the voltage of
the lamp, so now that the carbon incandescent lamp is a thing of the
past, there is no need for so many different voltages. Several years
ago standard voltages of 110, 115 and 120 were recommended for adoption
by all the electrical societies in the United States, and practically
all central stations have now changed their service to one of these
voltages.
COST OF INCANDESCENT ELECTRIC LIGHT
In the early ’80’s current was expensive, costing a consumer on the
average about twenty cents per kilowatt hour. The cost has gradually
come down and the general average rate for which current is sold for
lighting purposes is now about 4½ cents. During the period 1880 to 1905
the average efficiency of carbon lamps throughout their life increased
from about one to over 2¾ lumens per watt and their list price
decreased from one dollar to twenty cents. The average amount of light
obtained for one cent at first was about five candlepower hours and in
1904 it was increased to over thirty-six at the average rate then in
effect. The next year with the more efficient Gem lamp 44 candle-hours
could be had for one cent. In 1906 the amount was increased to 50 with
the tantalum lamp and with the tungsten lamp in 1907, even at its high
price of $1.50, the amount was further increased to 63. Since then
the average cost of current has been reduced but slightly, but the
efficiency of the tungsten lamp has materially increased and its cost
reduced so that it is now possible to obtain, with the ordinary 40-watt
lamp 170 candle-hours for a cent. If the gas-filled tungsten lamp were
used the amount of light now obtained for a cent would depend upon the
size, which, for the 1000-watt lamp, would be 382 candle-hours.
STATISTICS REGARDING THE PRESENT DEMAND FOR LAMPS
In the United States there are about 350 million incandescent and
about two hundred thousand magnetite arc lamps now (1923) in use.
They are increasing about 10 per cent each year. The annual demand
for incandescent lamps for renewals and new installations is over 200
millions, exclusive of miniature lamps. The use of incandescent lamps
in all other countries put together is about equal that in the U. S.
The average candlepower of standard lighting lamps has increased from
16, which prevailed during the period prior to 1905, to over 60. The
average wattage has not varied much during the past twenty-odd years,
the average lamp now consuming about 55 watts. This indicates that the
public is utilizing the improvement in lamp efficiency by increased
illumination. The present most popular lamp is the 40-watt size which
represents 20 per cent of the total demand. Second in demand is the
25-watt at 18 per cent and third, the 50-watt at 15 per cent of the
total in numbers. While the aggregate demand of all the gas-filled
tungsten lamps is a little over 20 per cent in numbers, they represent,
on account of their greater efficiency and wattage, over half the
amount of total candlepower used. In the United States about 85 per
cent of all lamps are for the 110-volt range. About 5 per cent for 220
volts, 2 per cent for street series lighting, 3 per cent for street
railway and 5 per cent for trainlighting and miscellaneous classes of
service.
SELECTED BIBLIOGRAPHY
ALGLAVE AND BOULARD, “The Electric Light,” translated by T.
O’Connor Sloane, edited by C. M. Lungren, D. Appleton & Co.,
New York, 1884.
BARHAM, G. BASIL, “The Development of the Incandescent Electric
Lamp,” Scott Greenwood & Son, London, 1912.
DREDGE, JAMES, “Electric Illumination,” 2 vols., John Wiley & Sons,
New York, 1882.
DURGIN, WILLIAM A., “Electricity--Its History and Development,”
A. C. McClurg & Co., Chicago, 1912.
DYER & MARTIN, “Edison, His Life and Inventions,” 2 vols., Harper &
Bros., New York, 1910.
GUILLEMIN, AMEDEE, “Electricity and Magnetism,” edited by Silvanus
P. Thompson, McMillan & Co., London, 1891.
HOUSTON, EDWIN J., “Electricity One Hundred Years ago and To-day,”
The W. J. Johnston Co., New York, 1894.
HOUSTON AND KENNELLY, “Electric Arc Lighting,” McGraw Publishing
Co., New York, 1906.
HUTCHINSON, ROLLIN W., JR., “High Efficiency Electrical Illuminants
and Illumination,” John Wiley & Sons, New York, 1911.
MAIER, JULIUS, “Arc and Glow Lamps,” Whittaker & Co., London, 1886.
POPE, FRANKLIN LEONARD, “Evolution of the Electric Incandescent
Lamp,” Boschen & Wefer, New York, 1894.
SOLOMON, MAURICE, “Electric Lamps,” D. Van Nostrand Co., New York,
1908.
Transcriber’s Notes
Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in the original book; otherwise they
were not changed.
Simple typographical errors were corrected; unbalanced quotation
marks were remedied when the change was obvious, and otherwise left
unbalanced.
Illustrations in this eBook have been positioned between paragraphs. In
versions of this eBook that support hyperlinks, the page references in
the List of Illustrations lead to the corresponding illustrations.
“Allesandro Volta” was printed that way.