INCANDESCENT LAMPS.

SUMMARY.

The commerical incandescent lamp consists essentially of a filament or wire, usually of either carbon or tungsten, inclosed in a glass bulb containing gas or exhausted to a vacuum. The filament is heated to a light-giving temperature by the passage of a

current.

In 1914 production of incandescent lamps in the United States amounted to about 90,000,000 lamps, valued at $17,350,000. In 1920 there were about 211,000,000 lamps sold in this country, of which over 95 per cent were of the tungsten filament type. The value of the output in 1919, according to the Census, was $57,647,000. Tungsten, glass, and brass are the chief raw materials used. The amount of tungsten used in the lamp industry is an extremely small part of the domestic consumption of that metal.

Lamps are produced by machinery of special design, in large quantities.

The great bulk of the output is from the factories of two large companies. One of these controls the patent on the process of producing the tungsten filament. Other firms are licensed and manufacture on a smaller scale. The principal licensees receive the benefit of all improvements made by the patentees.

Exports have increased rapidly, amounting to over $3,000,000 in 1921. This is not large in relation to the domestic output, since this country is by far the largest consumer of lamps. Exports are relatively large to Canada and Latin America, but the sale of American-made lamps in Europe is small.

In 1921 imports amounted to $430,569, probably not much more than 1 per cent of the domestic output. Nearly all the lamps imported were from Japan, and were mostly small decorative lamps, half of them of the carbon filament type. Import of the standard commercial lamps is controlled by the patentees.

Germany, Holland, Great Britain, and Japan are the chief foreign producers, the largest being Germany. The quality of the foreign product is comparable with that of the domestic, with the exception of the Japanese, which is often inferior. Methods of production and the organization of the industry are similar to those of the United States.

Since 1912 domestic prices have been considerably less than those prevailing in Great Britain. Japanese prices are understood to have been lower, but the quality is apparently not always dependable. German prices are not obtainable at present, but in the past have been low in the export markets.

The most important feature of the competitive situation is the patent control which covers the manufacture of the drawn tungsten filament, including more than 95 per cent of the lamps sold in the country. The American company owns plants or has affiliations in the principal producing countries. Competition of any consequence is met only in the small decorative or flashlight lamps, and that chiefly from Japan. Formerly this class of lamps came from Germany and Austria.

The incandescent electric lamp consists of a wire, called a "filament," inclosed in a glass bulb, and provided with terminals for conducting the current to the filament. The action of the current in passing through the resistance of the filament raises it to a high temperature, causing it to emit light. It is necessary that no air be in contact with the filament, as otherwise at the high temperature maintained it would be immediately oxidized. The bulb is therefore either exhausted or filled with an inert gas, nitrogen or argon. Even under these conditions it undergoes a slow disintegration, both by direct evaporation, the vapor being afterwards condensed on the glass, and by the action of minute amounts of water vapor, which act as vehicles, carrying the substance of the filament to the glass, depositing it, and returning to take up another amount. This action reduces the size of the filament, and also reduces the light by the black deposit formed on the inside of the glass. The efficiency of the lamp, or the amount of light obtained from a given consumption of electric current, depends on the temperature of the filament. The materials selected are therefore those which withstand the highest temperatures without melting or disintegrating. For many years carbon was employed, but about 1907 it was found that a filament could be produced from tungsten which could be operated at considerably higher temperatures without excessive loss, and which therefore would give a greater efficiency. In the smaller size lamps the bulb is exhausted to as high a vacuum as is obtainable, but in lamps above about 100 watts the bulb is filled with an inert gas, in which the filament evaporates more slowly; higher temperatures are thus permitted, and also higher efficiencies. The larger gas-filled lamps reach a degree of efficiency nearly twice that of the vacuum lamps. For the smaller sizes the advantage of the gas-filled bulb is offset by the increased conduction of heat away from the filament. In the smaller gas-filled lamps argon is used for the filler, on account of its low heat-conducting power, but in the larger sizes either nitrogen or a mixture of nitrogen and argon is used, since argon has a low electric insulating value. The filament, which is very thin and fragile. is supported in the bulb by a glass rod, sealed in the bulb, and carrying several heavy wires, to which the filament is attached. The terminals of the lamp are formed by a brass cap, in the form of a screw thread, and a small brass plate. Both of these are cemented to the base of the bulb and make contact with the terminals of the socket into which the lamp is screwed.

The carbon lamp is still used to some extent in situations subject to rough usage and high breakage, since it is lower in price; it is also used where electric power is very cheap, since, although wasteful of power, the cost of renewing lamps is lower.

The incandescent electric lamp, on account of its high efficiency and great convenience, has been rapidly superseding both the gas and the arc lamp. It has practically displaced the arc for interior

lighting, and largely for street lighting, and is invading other fields of the arc, such as motion-picture projection. It is also displacing gas and oil lamps as electric distribution lines are extended.

DOMESTIC PRODUCTION.

In 1914 the production of incandescent lamps amounted to $17,350,385, of which 74,434,059 lamps, valued at $11,886,354, were of the standard tungsten type. In 1919 the census reported the production of incandescent lamps at $57,647,000. In 1920 there were sold in the United States approximately 202,000,000 tungsten lamps for general illumination, about 9,000,000 carbon lamps, about 211,000,000 standard lamps,' and probably about 50,000,000 miniature and other special lamps.

Materials.-Lamp filaments are fine-drawn tungsten wire, but although incandescent lamps are manufactured by millions, the filaments are so small, usually two or three thousandths of an inch in diameter or smaller, that the total amount of tungsten used for this purpose is insignificant. The domestic supply of tungsten ore has never been sufficient to supply the demand of the country and it has had to be imported. But since the quantities required by the lamp industry are so small, the supply of tungsten presents no difficulties. The materials used for the manufacture of the glass bulbs include sand, soda ash, and lime, and are in ample supply. In the bulbs of the gas-filled lamps argon and nitrogen gases are used, both of which are extracted from the atmosphere.

Equipment. Electric lamps are made almost wholly by special equipment, the most of which has been developed by the American lamp manufacturers.

Methods of production. The production of the tungsten filament is an extended operation, to which much research has been devoted. Pure tungstic oxide is first extracted in powder form from the concentrated ore, and is then formed under great pressure into ingots about one-quarter inch square and 6 inches long. These are heated in the electric furnace to a high temperature, in an atmosphere of hydrogen, welded together, and swaged down till a rod is formed about three-hundredths of an inch in diameter and 30 feet long. This rod is now drawn down at a red heat through successive diamond. dies, until it reaches the form of a wire of very small diameter, which is ductile and fairly strong. A machine inserts the anchor wires at the top of the stem which supports the filament, and the whole stem with the filament attached is inserted into the bulb and sealed automatically. A tubing machine then melts a small hole in the bulb and seals on a short length of glass tube, after which the lamps pass to an oven, and, while hot, pipe connections in communication with rotary air pumps descend over the tube and the air is exhausted. the lamps are to be of the gas-filled type the necessary amount of the gas is then admitted, and the tube is melted off and the aperture is sealed. The brass base is then cemented on and the lamp is complete. Practically the whole process is carried on by special automatic machines.

If

The bulbs are machine blown in molds. Dutch lamps are exhausted by a somewhat more careful process; the air pump is sealed to the bulb, and a slightly different form of pump is used, one which

Report of lamp committee, forty-fourth annual convention, N. E. L. A., May, 1921.

is said to give a better vacuum, and consequently a higher grade lamp, although it involves more labor.

The bulbs may be of clear glass, or may be frosted by an acid or sand-blast process in order to reduce the glare from the filament. Gas-filled lamps of high intensity are sometimes covered with a light enamel for the same purpose. For colored lamps a colored glass may be used, or to reduce the expense the lamps may be dipped in a color bath after completion. Many decorative lamps for the lighting of Christmas trees are blown in fancy shapes, and colored by hand. Organization. By far the greater part of the incandescent lamps produced in the United States are made by two companies. The patents on the drawn tungsten filaments, which are in practically exclusive use for commercial purposes, are controlled by one company, which manufactures lamps, and also licenses other manufacturers. Its lamp division is a consolidation of more than 20 concerns. many of which are operated as separate works. The trade-mark "Mazda" has been adopted by the company to designate the lamps manufactured under its patents, and the manufacturers licensed to use this trade-mark receive the benefit of any improvement originated by the patentee or any of the licensees. Over such licensees the patentees exercise a somewhat parental supervision, furnishing instruction in cases where a manufacturer does not appear to be able to produce lamps of the required standard. In addition to the licensees, there are a number of other smaller concerns which manufacture tungsten drawn-wire lamps, but do not receive any engineering assistance from the larger firm. The patentee does not assume responsibility for the quality of the lamps made by these concerns. and the Mazda trade-mark is not used by them. There are also a few small firms making miniature lamps.

Bulbs are supplied chiefly by two large glass works. There are also one or two smaller glass companies making lamp bulbs.

Incandescent lamps are sold by the large manufacturers on consignment through agents, who are compensated on the basis of a discount list graded according to the amount of sales made to consumers or to other agents. The larger agents supply the smaller on the same terms as the manufacturers, and prices are carefully controlled, both to subagents and to the consumers, by the contractof agency.

Geographical distribution.-New Jersey, Ohio, Pennsylvania, and Connecticut are large producers; lamps are also made in New York. Illinois, Rhode Island, and Missouri.

History of the industry.--Although many years ago, as early as 1845, light was obtained from wires heated to incandescence by electric currents from batteries, the invention of the practical lamp was made by Edison in 1879, when he produced the carbon filament. Several materials were used for carbonizing to produce the filament, among them bristol board and bamboo. Later the filament was squirted out through an aperture from a colloidal solution, and allowed to dry, and then carbonized by heat. A great advance was made about 1907, when the metal filament was developed. Several of the semirare metals were tried; osmium was used commercially to some extent and tantalum came into considerable use about 1910. Along with these types the tungsten lamp was being developed using the squirted filament controlled by German and Austrian patents, but the earlier types were fragile and easily broken. In 1911

the process of drawing metallic tungsten wire was invented, and from this time the progress of the metal filament was rapid. In 1914 the gas filled lamp was brought out, allowing the use of higher temperatures, and consequently higher degrees of efficiency-in some cases twice as high as those formerly obtained. At the present time. tungsten lamps form more than 95 per cent of the total lamp production of the United States.

Domestic production and consumption. In 1914 there were 88,526,114 standard incandescent lamps of tungsten and carbon filament produced in the United States, valued at $13,283,926, according to data from the United States Census; in 1919 there were 224,713,466 and the value of the output was $48,459,987. Other types of lamps made in the two years were valued at $4,066,459 and $9,187,913, respectively. Sales of standard lamps, or lamps other than miniature and decorative lamps, were reported by the National Electric Lamp Association for 1914 as approximately 100,000,000. Sales have increased rapidly and uniformly since that year and in 1920 amounted to 211,000,000. Production of small lamps for decorative purposes and for vehicle lighting has also increased rapidly in this period, owing to the extension of electric automobile and train lighting, and for Christmas tree and other decorative uses. In 1915 sales of this class of lamps were reported at over 1,000,000, and in 1918 were estimated at about 50,000,000. Production of all classes is sufficient to supply the domestic demand.

Exports.-Exports have not been large in relation to production, although they have shown a rapid increase, from somewhat over $600,000 in 1913 to over $3,000,000 in 1921; while the greater part of the exports have been to Canada and Latin America there have also been increases in the exports to Italy and Australia. Exports to most European countries is almost negligible. Before the war there was keen competition in the South American markets from Holland, and especially from Germany, which controlled the greater part of the South American trade. Since the war, American manufacturers have made great gains in South America and Australia at the expense of Germany and Great Britain. International trade. agreements largely prevent competition between American and British manufacturers in home and export markets.

FOREIGN PRODUCTION.

Great Britain.-British production of incandescent lamps in 1913 is estimated at 25,000,000, and at 30,000,000 in 1919. The industry is controlled by a strong combination, including a dozen or more of the largest firms, and was based originally on the American patents on the drawn wire filament. Although these patents have been adjudged invalid in the British courts, the association founded upon them has lost little of its power. This association is estimated to control between 90 and 95 per cent of the British output, and fixes prices rigidly, both to consumers and agents. There are a number of nonassociated firms, of much smaller size, which are practically excluded from the retail trade by agreements enforced by the association, which prohibit retailers from selling any but association lamps. These agreements also exclude to a great extent the impor

Report of British Committee on Trusts, on the Electric Lamp Industry. Cd. No. 622, 1920.