Light Yesterday and Tomorrow Page 85

planted a less reliable thermal device for lamp starting. This starter automatically connects the electrodes of a fluorescent lamp in series for preheating before the arc is struck, thereby lengthening lamp life. This simple device has aided materially in the standardization of all starters.

Recent Vapor-Lamp Developments

Within the last year, a fluorescent-mercury lamp has been devised that combines the excellent efficiency of high-pressure mercury lamps with the more flattering warm color of fluorescent light, but with greater wattage in a more compact bulb. A special phosphor, which, unlike previous compounds, can function well above 150 degrees F, transforms some of the excess ultraviolet radiation to visible pink, with subsequent improvement in the usually red-deficient color.

Other metallic vapors, used alone or combined with mercury, provide illumination for special purposes. One example is the experimental, short-arc cadmium-mercury lamp being studied for motion-picture and television studios. Its five to ten kilowatts produce powerful light, rich in all three primary colors, and from an arc only half an inch long.

Vapor lamps for special color effects also have proved feasible. They utilize zinc, cadmium, tellurium and thallium vapors and produce colors ranging from green to gold to deep pink. Caesium-vapor lamps have also been used for the unusual purpose of confidential signaling with an invisible beam.

Another recently developed mercury lamp is filled with krypton and produces a brilliant flash of light some 17 millionths of a second in duration from a timed condenser discharge. This cigarette-sized quartz tube is the key unit in a runway approach-lighting system that can penetrate several hundred feet of dense fog to guide pilots to safe landings.

Today we have a whole new family of lamps that exist for purposes other than illumination — those that can kill disease bacteria and spores of fungi, others that produce healthful erythema or tan, or tenderize meats and preserve foods.

Outstanding among these is the Sterilamp. A low-pressure mercury-vapor device, it generates ultraviolet wavelengths in the narrowly limited wave-band fatal to bacteria, viruses, and the propagation of mold. Developed as a practical lamp about 1936, by the late Dr. Harvey C. Rentschler, it made possible the first convenient, effective and economical method of controlling these air-borne bacteria, viruses, and mold spores. These lamps are of numerous shapes and sizes, including one of golfball size for use inside a domestic refrigerator, and a 30-inch cold-cathode tube for hospitals, offices, and homes.

Two major types of lamps now provide year-round body tan without going outdoors. The newest is a fluorescent sun lamp that emits about five times the total ultraviolet volume (E vitons) of the RS screw-in bulb sun lamp. Utilizing a special phosphor and resembling an ordinary fluorescent lamp except for its small output of visible light, the fluorescent sun lamp was designed primarily for group irradiation of human beings and animals. For individual indoor suntanning, the older RS type, a medium-pressure sun lamp, remains in favor.

The Search for Metals

The dependence of nearly all the newer electric illuminants upon metal vapors made it mandatory that Westinghouse scientists appraise even the rarest metals. It was a search for an incandescent filament material better than tungsten, for example, that accounted for one of the outstanding contributions of the Westinghouse Lamp Division in World War II. In their lamp investigations, Westinghouse scientists had made samples of pure uranium as far back as May, 1922, so they were well equipped to supply the initial samples of pure uranium for the first experimental atomic-energy pile at Chicago in 1942. During the course of the experiments Westinghouse supplied more than 65 tons of U238 and reduced the cost of pure uranium from $750 to $7.34 per pound. And this despite the fact that uranium had previously been made only in the laboratory and at the rate of only a few grams at a time! Thus does lamp research have far-reaching influences.

A golden thread of romance and adventure runs through the tapestry of lighting history. Promises of new materials, newer methods, and still newer uses beckon workers on to widening fields. New language terms, new measuring instruments, even the changes in man’s treatment of his eyes and his life, all grow apace as radiant energy becomes more abundant. No Aladdin ever received more wealth from any lamp!

The Long Vistas Ahead

During these past five decades since the days of open electric-arc lamps and fish-tail gas burners, man’s ingenuity has successively evolved and improved the carbon-filament incandescent electric lamp, the metalized-carbon lamp, some few tantalum and similar wire-filament illuminants, and then the tungsten-filament lamps with improved alloys, coiled in the heat-retaining atmosphere of an inert gas. All but the last are obsolete. Undoubtedly others will be born — and pass.

In volume usage three major types of electric light sources remain — the perfected tungsten-filament lamp, the high-intensity mercury-vapor lamp (plus sodium and neon and a few other less-popular ionized vapor or gas sources), and the rapidly developing fluorescent lamp. These three are expected