Chapter III: Part 3

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.

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.

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.

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.

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.

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.

The mercury arc is peculiar in that it acts as an electric valve tending to let current flow through it only in one direction. Thus on alternating current, the current impulses will readily go through it in one direction, but the arc will go out in the other half cycle unless means are taken to prevent this. This is accomplished by having two terminals at one end of the tube, which are connected to choke coils, which in turn are connected to a single coil (auto) transformer. The alternating current supply mains are connected to wires tapping different parts of the coil of the auto transformer. The center of the coil of the auto transformer is connected through an induction coil to the other end of the tube. By this means the alternating current impulses are sent through the tube in one direction, one half cycle from one of the pairs of terminals of the tube, the other half cycle from the other terminal. Thus pulsating direct current, kept constant by the induction coil, flows through the tube, the pulsations overlapping each other by the magnetic action of the choke coils. This alternating current lamp is started by the high voltage discharge method. It has a 50-inch length of tube, consuming about 400 watts on 110 volts. Its efficiency is a little less than that of the direct current lamp.

The mercury arc is inherently for use on direct current, but by means of reactance coils, it can be operated on alternating current.]

THE LUMINOUS OR MAGNETITE ARC LAMP

About 1901 Dr. Charles P. Steinmetz, Schenectady, N. Y., studied the effect of metallic salts in the arc flame. Dr. Willis R. Whitney, also of Schenectady, and director of the research laboratory of the organization of which Dr. Steinmetz is the consulting engineer, followed with some further work along this line. The results of this work were incorporated in a commercial lamp called the magnetite arc lamp, through the efforts of C. A. B. Halvorson, Jr., at Lynn, Mass. The negative electrode consists of a pulverized mixture of magnetite (a variety of iron ore) and other substances packed tightly in an iron tube. The positive electrode is a piece of copper sheathed in iron to prevent oxidization of the copper. The arc flame gives a brilliant white light, and, similar to the mercury arc, is inherently limited to direct current. It burns in the open air at about 75 volts. The lamp is made for 4-ampere direct current series circuits and consumes about 310 watts and has an efficiency of about 11½ lumens per watt.

This has a negative electrode containing magnetite which produces a very luminous white flame in the arc stream.]

The negative (iron tube) electrode now has a life of about 350 hours. Later, a higher efficiency, 4-ampere electrode was made which has a shorter life but gives an efficiency of about 17 l-p-w, and a 6.6-ampere lamp was also made giving an efficiency of about 18 l-p-w using the regular electrode. This electrode in being consumed gives off fumes, so the lamp has a chimney through its body to carry them off. Some of the fumes condense, leaving a fine powder, iron oxide, in the form of rust. The consumption of the positive (copper) electrode is very slow, which is opposite to that of carbon arc lamps on direct current. The arc flame is brightest near the negative (iron tube) electrode and decreases in brilliancy and volume as it nears the positive (copper) electrode.

The method of control, entirely different from that of other arc lamps, was invented by Halvorson to meet the peculiarities of this arc.]

The peculiarities of the arc are such that Halvorson invented an entirely new principle of control. The electrodes are normally apart. In starting, they are drawn together by a starting magnet with sufficient force to dislodge the slag which forms on the negative electrode and which becomes an insulator when cold. Current then flows through the electrodes and through a series magnet which pulls up a solenoid breaking the circuit through the starting magnet. This allows the lower electrode to fall a fixed distance, about seven-eighths of an inch, drawing the arc, whose voltage is then about 72 volts. As the negative electrode is consumed, the length and voltage of the arc increases when a magnet, in shunt with the arc, becomes sufficiently energized to close the contacts in the circuit of the starting magnet causing the electrode to pick up and start off again.

MERCURY ARC RECTIFIER FOR MAGNETITE ARC LAMPS

The mercury arc converted the alternating constant current into direct current required by the magnetite lamp.]

As the magnetite arc requires direct current for its operation, the obvious way to supply a direct constant current for series circuits is to rectify, by means of the mercury arc, the alternating current obtained from a constant current transformer. The terminals of the movable secondary coil of the constant current transformer are connected to the two arms of the rectifier tube. One end of the series circuit is connected to the center of the secondary coil. The other end of the series circuit is connected to a reactance which in turn is connected to the pool of mercury in the bottom of the rectifier tube. One-half of the cycle of the alternating current goes from the secondary coil to one arm of the rectifier tube through the mercury vapor, the mercury arc having already been started by a separate starting electrode. It then goes to the pool of mercury, through the reactance and through the series circuit. The other half cycle of alternating current goes to the other arm of the rectifier tube, through the mercury vapor, etc., and through the series circuit. Thus a pulsating direct current flows through the series circuit, the magnetic action of the reactance coil making the pulsations of current overlap each other, which prevents the mercury arc from going out.

INCANDESCENT LAMP DEVELOPMENTS, 1894–1904

With the development of a waterproof base in 1900, by the use of a waterproof cement instead of plaster of Paris to fasten the base to the bulb, porcelain at first and later glass being used to insulate the terminals of the base from each other, lamps could be exposed to the weather and give good results. Electric sign lighting therefore received a great stimulus, and lamps as low as 2 candlepower for 110 volts were designed for this purpose. Carbon lamps with concentrated filaments were also made for stereoptican and other focussing purposes. These lamps were made in sizes from 20 to 100 candlepower. The arc lamp was more desirable for larger units.

The dry battery was made in small units of 2, 3 and 5 cells, so that lamps of about ⅛ to 1 candlepower were made for 2½, 3½ and 6½ volts, for portable flashlights. It was not however until the tungsten filament was developed in 1907 that these flashlights became as popular as they now are. For ornamental lighting, lamps were supplied in round and tubular bulbs, usually frosted to soften the light.

This consisted of a tube about 1¾ inches in diameter and having a length up to 200 feet, in which air at about one thousandth part of atmospheric pressure was made to glow by a very high voltage alternating current.]

THE MOORE TUBE LIGHT

Geissler, a German, discovered sixty odd years ago, that a high voltage alternating current would cause a vacuum tube to glow. This light was similar to that obtained by Hawksbee over two hundred years ago. Geissler obtained his high voltage alternating current by a spark coil, which consisted of two coils of wire mounted on an iron core. Current from a primary battery passed through the primary coil, and this current was rapidly interrupted by a vibrator on the principle of an electric bell. This induced an alternating current of high voltage in the secondary coil as this coil had a great many more turns than the primary coil had. Scientists found that about 70 per cent of the electrical energy put into the Geissler tube was converted into the actual energy in the light given out.

In 1891 Mr. D. McFarlan Moore, an American, impressed with the fact that only one-half of one per cent of the electrical energy put into the carbon-incandescent lamp came out in the form of light, decided to investigate the possibilities of the vacuum tube. After several years of experiments and the making of many trial lamps, he finally, in 1904, made a lamp that was commercially used in considerable numbers.

As the carbon terminals inside the tube absorbed the very slight amount of gas in the tube, a feeder valve allowed gas to flow in the tube, regulating the pressure to within one ten thousandth part of an atmosphere above and below the normal extremely slight pressure required.]

The first installation of this form of lamp was in a hardware store in Newark, N. J. It consisted of a glass tube 1¾ inches in diameter and 180 feet long. Air, at a pressure of about one-thousand part of an atmosphere, was in the tube, from which was obtained a pale pink color. High voltage (about 16,000 volts) alternating current was supplied by a transformer to two carbon electrodes inside the ends of the tube. The air had to be maintained within one ten-thousandth part of atmospheric pressure above and below the normal of one-thousandth, and as the rarefied air in the tube combined chemically with the carbon electrodes, means had to be devised to maintain the air in the tube at this slight pressure as well as within the narrow limits required.

This was accomplished by a piece of carbon through which the air could seep, but if covered with mercury would make a tight seal. As the air pressure became low, an increased current would flow through the tube, the normal being about a tenth of an ampere. This accordingly increased the current flowing through the primary coil of the transformer. In series with the primary coil was an electro-magnet which lifted, as the current increased, a bundle of iron wires mounted in a glass tube which floated in mercury. The glass tube, rising, lowered the height of the mercury, uncovering a carbon rod cemented in a tube connecting the main tube with the open air. Thus air could seep through this carbon rod until the proper amount was fed into the main tube. When the current came back to normal the electro-magnet lowered the floating glass tube which raised the height of the mercury and covered the carbon rod, thus shutting off the further supply of air.

As there was a constant loss of about 400 watts in the transformer, and an additional loss of about 250 watts in the two electrodes, the total consumption of the 180-foot tube was about 2250 watts. Nitrogen gas gave a yellow light, which was more efficient and so was later used. On account of the fixed losses in the transformer and electrodes the longer tubes were more efficient, though they were made in various sizes of from 40 to 200 feet. The 200-foot tube, with nitrogen, had an efficiency of about 10 lumens per watt. Nitrogen gas was supplied to the tube by removing the oxygen from the air used. This was accomplished by passing the air over phosphorous which absorbed the oxygen.

Carbon dioxide gas (CO_{2}) gave a pure white light but at about half the efficiency of nitrogen. The gas was obtained by allowing hydrochloric acid to come in contact with lumps of marble (calcium carbonate) which set free carbon dioxide and water vapor. The latter was absorbed by passing the gas through lumps of calcium chloride. The carbon dioxide tube on account of its daylight color value, made an excellent light under which accurate color matching could be done. A short tube is made for this purpose and this is the only use which the Moore tube now has, owing to the more efficient and simpler tungsten filament incandescent lamp.

THE OSMIUM LAMP

Dr. Auer von Welsbach, the German scientist who had produced the Welsbach gas mantle, invented an incandescent electric lamp having a filament of the metal osmium. It was commercially introduced in Europe in 1905 and a few were sold, but it was never marketed in this country. It was generally made for 55 volts, two lamps to burn in series on 110-volt circuits, gave about 25 candlepower and had an initial efficiency of about 5½ lumens per watt. It had a very fair maintenance of candlepower during its life, having an average efficiency of about 5 l-p-w. Osmium is a very rare and expensive metal, usually found associated with platinum, and is therefore very difficult to obtain. Burnt out lamps were therefore bought back in order to obtain a supply of osmium. It is also a very brittle metal, so that the lamps were extremely fragile.

This incandescent lamp was used in Europe for a few years, but was impractical to manufacture in large quantities as osmium is rarer and more expensive than platinum.]

THE GEM LAMP

Dr. Willis R. Whitney, of Schenectady, N. Y., had invented an electrical resistance furnace. This consisted of a hollow carbon tube, packed in sand, through which a very heavy current could be passed. This heated the tube to a very high temperature, the sand preventing the tube from oxidizing, so that whatever was put inside the tube could be heated to a very high heat. Among his various experiments, he heated some carbon filaments and found that the high temperature changed their resistance “characteristic” from negative to positive. The ordinary carbon filament has a resistance when hot that is less than when it is cold, which was reversed after heating it to the high temperature Dr. Whitney was able to obtain. These filaments were made into lamps for 110-volt service and it was found that they could be operated at an efficiency of 4 lumens per watt. The lamps also blackened less than the regular carbon lamp throughout their life.

This incandescent lamp had a graphitized carbon filament obtained by the heat of an electric furnace, so that it could be operated at 25 per cent higher efficiency than the regular carbon lamp. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.]

This lamp was put on the market in 1905 and was called the Gem or metallized carbon filament lamp as such a carbon filament had a resistance characteristic similar to metals. At first it had two single hair pin filaments in series which in 1909 were changed to a single loop filament like the carbon lamp.

In 1905 the rating of incandescent lamps was changed from a candlepower to a wattage basis. The ordinary 16-candlepower carbon lamp consumed 50 watts and was so rated. The 50-watt Gem lamp gave 20 candlepower, both candlepower ratings being their mean candlepower in a horizontal direction. The Gem lamp was made for 110-volt circuits in sizes from 40 to 250 watts. The 50-watt size was the most popular, many millions of which were made before the lamp disappeared from use in 1918. The lamp was not quite as strong as the carbon lamp. Some Gem lamps for series circuits were also made, but these were soon superseded by the tungsten-filament lamp which appeared in 1907.

THE TANTALUM LAMP

The tantalum filament could be operated at 50 per cent greater efficiency than that of the regular carbon incandescent lamp. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.]

Dr. Werner von Bolton, a German physicist, made an investigation of various materials to see if any of them were more suitable than carbon for an incandescent-lamp filament. After experimenting with various metals, tantalum was tried. Tantalum had been known to science for about a hundred years. Von Bolton finally obtained some of the pure metal and found it to be ductile so that it could be drawn out into a wire. As it had a low specific resistance, the wire filament had to be much longer and thinner than the carbon filament. A great number of experimental lamps were made so that it was not until 1906 that the lamp was put on the market in this country. It had an initial efficiency of 5 lumens per watt and a good maintenance of candle power throughout its life, having an average efficiency of about 4¼ l-p-w. The usual sizes of lamps were 40 and 80 watts giving about 20 and 40 candlepower respectively. It was not quite as strong as the carbon lamp, and on alternating current the wire crystallized more rapidly, so that it broke more easily, giving a shorter life than on direct current. It disappeared from use in 1913.

INVENTION OF THE TUNGSTEN LAMP

Alexander Just and Franz Hanaman in 1902 were laboratory assistants to the Professor of Chemistry in the Technical High School in Vienna. Just was spending his spare time in another laboratory in Vienna, attempting to develop a boron incandescent lamp. In August of that year he engaged Hanaman to aid him in his work. They conceived the idea of making a lamp with a filament of tungsten and for two years worked on both lamps. The boron lamp turned out to be a failure. Their means were limited; Hanaman’s total income was $44 per month and Just’s was slightly more than this. In 1903 they took out a German patent on a tungsten filament, but the process they described was a failure because it produced a filament containing both carbon and tungsten. The carbon readily evaporated and quickly blackened the bulb when they attempted to operate the filament at an efficiency higher than that possible with the ordinary carbon filament. Finally in the latter part of the next year (1904) they were able to get rid of the carbon and produced a pure tungsten filament.

Tungsten had been known to chemists for many years by its compounds, its oxides and its alloys with steel, but the properties of the pure metal were practically unknown. It is an extremely hard and brittle metal and it was impossible at that time to draw it into a wire. Just and Hanaman’s process of making a pure tungsten filament consisted of taking tungsten oxide in the form of an extremely fine powder, reducing this to pure tungsten powder by heating it while hydrogen gas passed over it. The gas combined with the oxygen of the oxide, forming water vapor which was carried off, leaving the tungsten behind.

The tungsten powder was mixed with an organic binding material, and the paste was forced by very high pressure through a hole drilled in a diamond. This diamond die was necessary because tungsten, being so hard a substance, would quickly wear away any other kind of die. The thread formed was cut into proper lengths, bent the shape of a hair pin and the ends fastened to clamps. Current was passed through the hair pin in the presence of hydrogen gas and water vapor. The current heated the hair pin, carbonized the organic binding material in it, the carbon then combining with the moist hydrogen gas, leaving the tungsten particles behind. These particles were sintered together by the heat, forming the tungsten filament. Patents were applied for in various countries, the one in the United States on July 6, 1905.

The two laboratory assistants in 1905 finally succeeded in getting their invention taken up by a Hungarian lamp manufacturer. By the end of the year lamps were made that were a striking success for they could be operated at an efficiency of 8 lumens per watt. They were put on the American market in 1907, the first lamp put out being the 100-watt size for 110-volt circuits. This was done by mounting several hair pin loops in series to get the requisite resistance, tungsten having a low specific resistance. The issue of the American patent was delayed owing to an interference between four different parties, each claiming to be the inventor. After prolonged hearings, one application having been found to be fraudulent, the patent was finally granted to Just and Hanaman on February 27, 1912.

The original 100 watt tungsten lamp was nearly three times as efficient as the carbon lamp, but its “pressed” filament was very fragile. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.]

This “pressed” tungsten filament was quite fragile, but on account of its relatively high efficiency compared with other incandescent lamps, it immediately became popular. Soon after its introduction it became possible to make finer filaments so that lamps for 60, 40 and then 25 watts for 110-volt circuits were made available. Sizes up to 500 watts were also made which soon began to displace the enclosed carbon arc lamp. Lamps were also made for series circuits in sizes from 32 to 400 candlepower. These promptly displaced the carbon and Gem series lamps. The high efficiency of the tungsten filament was a great stimulus to flashlights which are now sold by the millions each year. The lighting of railroad cars, Pullmans and coaches, with tungsten lamps obtaining their current from storage batteries, soon superseded the gas light formerly used. In some cases, a dynamo, run by a belt from the car axle, kept these batteries charged.

Scientists had declared it impossible to change tungsten from a brittle to ductile metal. This, however, was accomplished by Dr. Coolidge, and drawn tungsten wire made the lamp very sturdy. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.]

DRAWN TUNGSTEN WIRE

After several years of patient experiment, Dr. William D. Coolidge in the research laboratory of a large electrical manufacturing company at Schenectady, N. Y., invented a process for making tungsten ductile, a patent for which was obtained in December, 1913. Tungsten had heretofore been known as a very brittle metal, but by means of this process it became possible to draw it into wire. This greatly simplified the manufacture of lamps and enormously improved their strength. Such lamps were commercially introduced in 1911.

With drawn tungsten wire it was easier to coil and therefore concentrate the filament as required by focusing types of lamps. The automobile headlight lamp was among the first of these, which in 1912 started the commercial use of electric light on cars in place of oil and acetylene gas. On street railway cars the use of tungsten lamps, made possible on this severe service by the greater sturdiness of the drawn wire, greatly improved their lighting. Furthermore, as the voltage on street railway systems is subject to great changes, the candlepower of the tungsten filament has the advantage of varying but about half as much as that of the carbon lamp on fluctuating voltage.

The mercury arc if enclosed in quartz glass can be operated at much higher temperature and therefore greater efficiency. The light is still deficient in red but gives a considerable amount of ultra-violet rays which kill bacteria and are very dangerous to the eye. They can, however, be absorbed by a glass globe. The lamp is not used as an illuminant in this country, but is valuable for use in the purification of water.]

THE QUARTZ MERCURY VAPOR ARC LAMP

By putting a mercury arc in a tube made of quartz instead of glass, it can be operated at a much higher temperature and thereby obtain a greater efficiency. Such a lamp, however, is still largely deficient in red rays, and it gives out a considerable amount of ultra-violet rays. These ultra-violet rays will kill bacteria and the lamp is being used to a certain extent for such purpose as in the purification of water. These rays are very dangerous to the eyes, but they are absorbed by glass, so as an illuminant, a glass globe must be used on the lamp. These lamps appeared in Europe about 1912 but were never used to any extent in this country as an illuminant. They have an efficiency of about 26 lumens per watt. Quartz is very difficult to work, so the cost of a quartz tube is very great. The ordinary bunsen gas flame is used with glass, but quartz will only become soft in an oxy-hydrogen or oxy-acetylene flame.

By operating a coiled filament in an inert gas, Dr. Langmuir was able to greatly increase its efficiency, the gain in light by the higher temperature permissible, more than offsetting the loss of heat by convection of the gas. This lamp is in the exhibit of Edison lamps in the Smithsonian Institution.]

THE GAS-FILLED TUNGSTEN LAMP

The higher the temperature at which an incandescent lamp filament can 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.

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.

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.