Light Yesterday and Tomorrow Page 82

the life is lengthened by increasing the filament resistance.

The rise in efficiency, and the sustained emission of more lumens has also been accompanied by steadily dropping lamp prices. Herein occurs a shining example of millions of dollars of research expenditures returning constant dividends to lamp users! A 60-watt tungsten-filament lamp retailed for $1.75 in 1907; today a vastly improved lamp, producing 835 lumens compared with the older lamp’s 474, retails for 12 cents. During this period the price declined steadily — to 45 cents in 1913, 36 cents in 1917, 25 cents in 1927, and to 15 cents in 1937 — and all this while light output, usability, ruggedness, and good looks were multiplying manyfold!

Lamp Manufacture — A Vital Factor in Progress

The lamp industry is unusual in that its machines cannot be bought on the open market; they are custom-built by lamp-company specialists. Thus, advances in the mechanics of lampmaking assume the same importance as lamp design. The many magnificently integrated and almost super-human lampmaking machines, which incorporate the crystallized thinking of many scientists throughout these fifty years, have contributed to the low price, stability, and uniformity.

The wide disparity between early lampmaking and that of today is illustrated by the fact that now a single great machine turns out in just two hours a volume equivalent to the entire daily output of the Westinghouse plant of 1900. And then less than a dozen varieties of filament lamps were regularly manufactured — mostly the 16 and 32 candlepower sizes. Today there are from 5000 to 6000 varieties.

In succession, developments enabled faster and better production. Machines were devised to produce flares mechanically from pre-cut lengths of tubing; stem production and sealing gradually became automatic processes; the laborious and often inconsistent hand work was gradually eliminated — the accuracy of a good watch was inbuilt on a volume basis!

As the incandescent lamp and electrical distribution systems progressed, it became increasingly clear that standardization was to be an essential step from the standpoint of both manufacturer and consumer. Early lamps were individual units, largely handmade, with no assurance of uniformity.

One curious difficulty came with voltage ratings. Early lamps were photometered at fixed candlepowers, and marked for corresponding voltages. Often three voltages were marked on the bulb label, the user and the utility company endeavoring to get together on a common one. Eventually candlepower ratings grew meaningless since this rating of intensity was not constant for all directions; hence watts (for input) or lumens (for output) were substituted.

The first “standard” voltage was fixed at 50 to 55 volts; later this was raised to 110 or 115 volts, and then to 120. Here in the main it has held for the past decade. Higher voltages for incandescent lamps would involve less rugged filaments and lower efficiencies; lower voltages would require heavier amperages and more copper and iron in the wiring systems.

Another troublesome feature of early lamps was that each manufacturer had a different base and socket, with the result that many lamps were carried in stock unbased, and later fitted with whatever type the customer needed. The standardization of bases about 1908 not only minimized possible sales obstacles, but also accelerated mechanization of the industry. Indeed it is a tribute to the lighting industry that each day some two million standard lamps are sold, each fitting into any regular socket.

Soon after World War I, lamp manufacture was further improved by the combination of two steps — exhaust and sealing — into a machine sometimes known as the Sealex. Automatic stem-making and filament-mounting machines came into being soon after. Meanwhile giant strides were being taken in another phase of lamp making — glass fabrication. Hand glass blowing, always a bottleneck in lamp construction, was gradually replaced by automatic bulb-blowing machines. Bulb design itself, however, with the exception of the introduction of the tipless bulb made possible by the new method of exhaustion through the lamp stem (inside the base), has changed but little since 1913. Ever-increasing requirements have, however, led to some 15 different kinds of glass, plus many coloring, frosting, and ceramic treatments.