Daylight in Tubes


WHEN the big fairs of New York and San Francisco opened two years ago with their bright prophecies of a brave new world, one of the first things that impressed the visitors was a glass wand which gave out a new kind of light. At the Flushing spectacle more than ten miles of these tubes produced a soft, diffused, yet powerful illumination unlike anything that had been seen before. Glowing in many colors, they flooded the streets and exhibits with hues unrivaled in purity and brilliance, and played a major part in creating the atmosphere of a futuristic wonderland.

What people saw was the public unveiling of the fluorescent light, the first radical departure in illumination since Edison’s invention of the filament electric bulb. Dazzled by the glittering parade of novelties, spectators dismissed the luminous tube as only another new toy for the decoration of fairs and carnivals. In this opinion they were not alone. Even many lighting experts who recognized the revolutionary nature of the new light believed that it would be used only for advertising and display, like the neon sign. All doubters were caught off balance, for in two short years fluorescent lighting has swept the country in a boom of amazing proportions. In defense factories, offices, shops, department stores, drugstores, restaurants, and fighting planes, the lamps are being installed as fast as they can be made. More than a million American establishments are now lighted by the World’s Fair toy, and if all these fluorescent tubes were joined together they would form an unbroken line of light from New York to San Francisco and back again.

And this is only one phase of the fluorescent boom. The active principle of the lamp has been adapted to a score of important uses. It has given pathologists a valuable new weapon in the study of disease; it saves the crops of Western potato farmers, detects mould and adulteration in foodstuffs, and guides bombed Londoners to air-raid shelters without violating blackout rules.

The new lamp uses a completely new method for converting electricity into light. It has no filament, like the ordinary light bulb. Mercury vapor in the tube gives off ultra-violet light when the current passes through it, and the ultraviolet, striking a chalk-like chemical coating with which the tube is lined, is converted into light suitable for illumination. It is pleasanter, cooler, easier on the eyes, and vastly more efficient than any other light ever invented for general use.

You may see the new light at work in the retail shops and cafés of almost any city or large town. Its quality is noticeable from the sidewalk, for every corner of the shop appears to be flooded with soft, evenly distributed light. Overhead in clusters, or perhaps fixed vertically on the walls, are the gleaming tubular fluorescent bars, often from two to four feet long and about an inch and a half in diameter. Sometimes the tubes are bare; sometimes they are partially shielded with grids made of glass or a translucent porcelain-like plastic. In either case you can look at the tubes without hurting your eyes. You will notice that, like Peter Pan, you have lost your shadow. This is because the sharp ‘point lighting’ of the ordinary bulb has been eliminated. The tube has ten times the surface area of a regular light bulb of the same wattage, so the light is spread out as evenly as melted butter on a piece of toast.

You may see these things with your own eyes, but if you speak to the proprietor he will tell you enthusiastically of other benefits. He will explain that he is getting more than twice as much light for the same amount of electricity, or, conversely, that he is getting just as much light for about half the current. Since standards of illumination have been increasing in recent years, the chances are that he has chosen the former course — however, the choice is his. And he will tell you that the new lamps are much cooler. Cool light is one of the Holy Grails of laboratory crusaders, and some investigators have even caged the firefly, that paragon of heatless light, in attempts to copy his production method. A fluorescent lighting system reduces lamp heat by about one half. Customers are more comfortable, and foods, flowers, and other perishable goods keep their freshness longer.

This peak of performance which the new lamp has reached overnight has long been the dream of engineers. For fifty years they have been making electric light by putting current through a wire and heating it until it glows. While this is incomparably better than light by kerosene or gas, even the newest gasfilled tungsten-filament lamp, the industry’s greatest achievement, is more of a furnace than a lamp. It turns 90 per cent of the current into unwanted heat and utilizes only 10 per cent to make the light we are paying for. Improvers of the filament lamp face a hurdle which cannot be surmounted, for further efforts to increase its yield of light would melt the tungsten. To make a more efficient lamp, laboratory research men had to start over again on an entirely different tack.

They found the answer in fluorescent light, in which no such hurdle exists. Its superiority can be easily shown. Expressed in terms of lumens per watt (amount of light delivered per unit of electric current) today’s fluorescent tube ranks about 40 as against 12 or 13 for the common 60-watt household bulb. Its laboratory efficiency has already been stepped up to 60 and better, and the sky appears to be the limit. Engineers see no reason why fluorescent lamps cannot be made that are eight times as efficient as the best tungsten lamp on the market.


In a laboratory at Nela Park, Cleveland, — the General Electric Company’s ‘University of Light,’ — Mr. George Inman, who had a lot to do with making the new lamp, showed me a speckled rock which looked like a piece of cottage cheese heavily sprinkled with black sage. Mr. Inman darkened the room, and placed the rock beneath a lamp which radiated invisible ultra-violet. The stone was transformed into a blazing ball of greenish-white light. I was looking at a piece of willemite, a fluorescent substance found in abundance in many parts of the country.

‘ Fluorescent ‘ is now a familiar word to anyone who reads the advertisements, but two years ago it meant little to people outside the research plants and technical schools. A great number of materials which we see about us every day will ‘fluoresce,’ or glow, when exposed to ultra-violet light. For three centuries something has been known of this strange ability. As long ago as 1602 an Italian cobbler who dabbled in the black arts came back from the mountains with a stone that emitted a fierce glow under daylight. His neighbors crossed themselves and avoided him. Now we know that the stone must have been composed of a fluorescent material which reacted to the ultra-violet band in the sun’s spectrum.

Many able scientists worked on the problem without finding the true explanation. Then ninety years ago the eminent physicist Sir G. G. Stokes picked up the loose threads and tied them together for all time by means of a simple experiment. Using a piece of quartz to break up the rays of the sun into its various wave lengths, he took a test tube filled with a solution of quinine sulphate — which was known to behave strangely under daylight — and moved it slowly down the rainbow spectrum. When he reached the ultra-violet range, a ghostlike gleam of blue light shot across the tube. He had found that the curious light-changing quality of the chemical was attuned to ultra-violet; that it had the ability to absorb light of one wave length and pour it out in another. He christened this ability ‘fluorescence.’

Like many other pioneer scientists, Stokes had no idea that his discovery was of any practical use. After he pointed the way, there was still a great deal to do before fluorescence could be used for anything except a subject for scientific papers. Investigators in Germany, France, England, and the United States compiled long lists of fluorescent minerals and plant substances, and experimented with light to find out what wave lengths were most effective in exciting them.

Finally someone hit upon the idea of caging ultra-violet light and a fluorescent material inside a glass tube and thus making a new kind of lamp. Many people had a finger in the pie. The first fluorescent tubes were seen in Holland in the mid-thirties, but they were highvoltage lamps unsuitable for general use. It remained for American engineers to bring practical fluorescent lighting to the public.

In Cleveland, George Inman ground his willemite to powder, and picked out the useless black spots by hand. He and his fellow workers mixed the white powder with an adhesive, and sprayed a thin coating on the inside of a glass tube. Electric terminals were placed in the ends of the tube, and it was filled with mercury vapor, which acted as a conductor and closed the circuit when the current was turned on. This provided a rich source of ultra-violet. It was transformed by the excited willemite into a wave length suitable for illumination, and soft fluorescent light poured forth from the tube. It was a crude affair, but gave promise.

Meanwhile in Salem, Massachusetts, James L. Cox, a young Cornell graduate, was working on the same problem in the interests of the Hygrade Sylvania Corporation. For his work in treating fluorescent powders to yield the greatest amount of light, Mr. Cox was honored last year by the National Association of Manufacturers as an inventor whose work has ‘materially affected the lives of Americans.’ And a Worcester Tech student, Edward C. Dench, who spent a summer vacation working in the Westinghouse laboratories, got an idea for a more efficient starting switch.

Since these beginnings, the lamp has been steadily improved. Rocks are no longer ground up to make the powder. Other methods have been found to produce purer materials, and scores of fluorescent powders have been developed which will react under ultra-violet to produce whatever color of light is desired. In the laboratories of General Electric, Westinghouse, and Hygrade Sylvania — the leading manufacturers of the lamp — they will show you half a dozen bottles all containing powder that is white under ordinary light. Pour out a sample from each bottle and turn on the ultra-violet, and the little mounds become torches of vivid green, blue, yellow, and so on. Light of various colors can be obtained simply by mixing the fluorescent powders. Powders that fluoresce pink, buff, and blue will yield a white light, and by altering the recipe you can get a ‘ daylight’ which consumes only one third of the current used by an incandescent daylight bulb. Before these new lamps were invented, colored light was produced by staining the bulb or using a colored screen, and as much as 90 per cent of the light was lost in the process. Fluorescent colored light is colored to begin with — the wasteful middleman has been fired. This was one reason for the immediate popularity of the lamp in display lighting.

In the lamp’s early days, engineers noticed a curious optical illusion when objects were in motion beneath a single tube. If you waved your hand rapidly, you seemed to have an extra finger, and sometimes a wheel revolving at a high rate appeared to stand still. This was because the light in the tube actually went out 120 times a second, owing to the rapid alternation of the current. This flicker was corrected by installing the tubes in pairs, with the two currents ‘out of step’ with each other.

The infant invention was hardly out of its diapers when it was snatched from the laboratory and set to work. In the summer of 1937, Bassett Jones, lighting director of New York’s projected World of Tomorrow, went to Nela Park, Cleveland, and asked, ‘What’s new in lighting?’ He saw the glowing tubes, and nothing else would do. Orders were quickly placed with all firms which were making the tubes, and research men put on overalls to turn them out. Every fluorescent light which spectators saw at the opening of the fair was a laboratory product.

By degrees the industry moved into the factory. Two million of the tubes were sold that year. Since then, new plants have been built and new production machines designed. Now assembly lines are running day and night to fill the estimated 1941 demand for 20,000,000 fluorescent lamps.


The new lamp came along just in time to light the new defense plants, where it provides the best illumination ever discovered for close mechanical work. Twenty-six miles of fluorescent tubes have just been installed in the big new factory of the Vega Airplane Company at Burbank, California. Workers in the new Chrysler tank factory, the Packard Rolls-Royce plane-motor plant, and the Bell Aircraft, Republic Aviation, and Curtiss-Wright factories, to name only a few, are speeding production and saving their eyes under its soft, powerful glow.

When the country launched the big armament drive, it was common knowledge that most factories were too dimly lighted for fast, accurate work. The average illumination was about five footcandles, which is hardly one hundredth of the light you get when you sit under a tree reading on a bright day. For many years authorities had been crusading for better light, but the heavy cost of wiring for more current had blocked their efforts. Now the government called for 35 to 60 foot-candles of light in plants which it financed. The fluorescent lamp, giving more than double the amount of light for the current, made this possible. To the machine operator it is like bringing a piece of the noonday sky indoors.

Big textile plants in New England and the South are rapidly changing to fluorescent lighting. In one typical factory, the plant engineer had added all the bulbs which the wiring would take, and the light was still so dim that eye trouble was an occupational ailment among the machine operators. Fluorescent lights were installed which doubled the amount of illumination without increasing the load on the wiring. The light bill remained the same, and the cost of the change was about one third what the factory would have paid for rewiring.

These are a few of the reasons why the new lamp is rapidly becoming standard equipment in large American plants. The lamp’s auxiliary devices make fluorescent lighting more expensive to install than the ordinary filamentbulb system, so it is still of chief interest to establishments that use a great deal of light, and in places where light of a special quality is needed. Art museums, for instance, have tried for years to duplicate artificially the north light under which painters work, and which should fall on the paintings if we are to see them as artists meant them to be seen. Now Pittsburgh’s Carnegie Institute has solved the problem with fluorescent light.

The new light has spread through the nation’s retail shops with the speed of an epidemic. Its coolness reduces the cost of air-conditioning in modern restaurants, ‘five and ten’ stores, offices, and trains. Drugstore proprietors all tell the same story of better light and current economy. Many of them report slashes in the light bill of 30 per cent or better. Since they remain open long hours and often burn lights in the daytime, this saving usually pays off an installation cost of $300 or so inside of a year.

So great is the demand for the new lamps in factories and stores that the industry has had little time to think of other uses, but fluorescent lighting in the home, still in the experimental stage, offers fascinating possibilities. Some pioneers have already installed these lamps in bathrooms, game rooms, and kitchens, and at the head of their beds. Their coolness and lack of glare make them popular over sinks and kitchen worktables. The tubes last about 2500 hours, compared with about 1000 hours for the filament bulb. Replacement is a simple matter of lifting the tube from the fixture and dropping in a new one — like changing a window shade. Since the lamps take a second or two to light up after the switch is turned, they are less convenient for quick use in passageways than in rooms where light is needed for longer periods.

Because they are slenderer than filament bulbs, the tubes are more practical for built-in lighting. They are so cool that they can be safely installed behind the tops of window draperies, and a number of people are using them in this manner, not only in modern interiors, but in period living rooms. Their strong, unobtrusive glow, reflected against the ceiling, provides excellent light for entertainment, card playing, and so on, but portable fluorescent lamps that would look well in the average living room have not yet been developed. Most American rooms are designed for circular ‘spot lighting.’ Just as early automobiles looked like buggies, home lighting fixtures are still under the influence of the tallow candle.

The use of the new lamps in homes will depend mainly upon the quality of the light and the fitness of the tube in decorative schemes. Since few home lights are used more than 800 hours a year, fluorescent fixtures would take a long time to pay for themselves out of savings in the light bill. They will save money in other ways, however. Home air-conditioning is becoming more prevalent every year, and, as we have seen, cool fluorescent light reduces its cost. And in old houses where more light is needed the new lamp will give double the quantity without the expense and annoyance of rewiring.

The effect of fluorescent light upon colors is slightly different from the familiar color distortions caused by the filament light bulb. The ordinary bulb is overrich in yellow and red, while the new lamp has an extra supply of blue and green. For this reason, navy blue and black are easily distinguished under fluorescent light, while under the filament bulb they look much the same. The old yellow light tends to conceal scorching caused by ironing, while the new light warns the housewife immediately. On the other hand, the yellow of butter takes on a faintly greenish tinge under fluorescent lamps. A new ‘soft white’ fluorescent tube, to which a little red has been added, helps to correct this distortion, and in a ‘model house’ in the Westinghouse laboratories engineers and decorators are experimenting with foods, fabrics, and fluorescence with a view to producing a light which will satisfy the most fastidious homeowner. They are also working on fluorescent floor lamps and table lamps, and turning out a wider variety of tubes of all sizes to fill all needs.

Sizes now run all the way from giant tubes five feet long to tubes of six inches no thicker than your finger. These pygmies are being used to light the instrument boards of the newest fighting planes. The fluorescent mixture is painted on the indicators and numerals of the dials, and the pale beam of ultraviolet kicks it into vivid life. The dials are easier to read, and the reduced glare inside the cockpit helps the pilot’s vision and conceals his position from the enemy.


The recent discoveries about fluorescence which made the lamp possible have stimulated the invention of scores of devices using the same basic principles. The powder need not be confined in a glass tube — it is excited by ultra-violet at a distance of many feet. It can be mixed with paints, lacquers, and dyes without losing this special sensitivity. English ‘twilight engineers’ mark the entrances of subways and bomb shelters with fluorescent paint, and during a blackout the markings glow under a lamp which sheds invisible ultra-violet. At army field headquarters, a fine powder is dusted on military maps so that generals can read them in the dark with the aid of a small portable ‘invisible lamp.’

Fluorescent paint is used in outdoor advertising to make the same billboard carry a double message. There is an effective billboard in Cleveland that under ordinary light shows a line of rooftops and the words, ‘How about coal next winter?’ When the lights go out at intervals, invisible light excites fluorescent paint, showing a Christmas card design of roofs piled with gleaming snow and a sky full of flakes. Night clubs use the same technique. At a turn of a switch, walls that are ordinarily blank blossom forth with romantic pictures of tropical scenes.

Invisible fluorescent dye is used for identification in cases where an obvious marking might be objectionable. A research scientist was once showing me some fluorescent chemicals under invisible light in his laboratory when I noticed that across his white shirt front ‘B-15’ was stamped in large blue symbols. When we left the laboratory, it was gone. He explained that his laundry marked garments with a fluorescent dye, since many people dislike indelible-ink markings. The man who makes up the packages sorts the garments under invisible light. A Chicago hospital, after a lawsuit in which it was charged that babies had been shuffled, took to marking them with a harmless fluorescent dye, and can now settle any dispute with ultra-violet.

The fact that different inks and glues fluoresce differently under the invisible light provides a new weapon for the detection of forgery, alteration of documents, and tampering with the mail. If a letter is pried open and glued up again, the new adhesive betrays itself unmistakably. An Ohio firm advertises an inexpensive fluorescence kit — a package of powder and a small ‘ invisible lamp ‘ — for the detection of petty thieves or saboteurs. If cash or merchandise has been disappearing, or if machines are being damaged, you dust them with the inconspicuous powder. No matter how long the guilty person scrubs his hands, beneath the light they will blaze with a telltale green.

Fluorescence has many uses in agriculture, and in determining the contents and the freshness of foods. Butter and margarine may look alike under daylight, but margarine glows with a strong blue under invisible ultra-violet. Fresh eggs have a reddish fluorescence, but after ten days the color begins to change through reddish brown to blue. Eggs that have been dipped in preservative are easily spotted by their changed fluorescence color. The lilac fluorescence of fresh walnuts changes to yellow as they age. Fluorescence betrays the presence of chicory in coffee, horse fat in lard, and refined oil in supposedly virgin olive oil. Put honey beneath ultra-violet light, and with a little training you can tell by the nature of the fluorescence what flower the bees fed on.

Fungus infections and other plant diseases are now detected at government experiment stations by their fluorescence. Ring rot has long been a serious problem of the Western potato farmer. When he cut up his seed potatoes for planting, the occasional infected spot was hard to see, and sometimes his entire crop was blighted because he spread the infection with his knife. Professor R. B. Harvey of the University of Minnesota observed that the fluorescence color of ring rot is bright green, and worked out a technique which many farmers used with success last spring. When they did their cutting beneath ultra-violet, it was easy to throw out the diseased potato and dip the knife in a disinfectant.

New horizons in the study of disease have been opened up by pioneer explorers in fluorescence. Last year an audience of New York physicians sat spell-bound as Dr. Hans Popper, pathologist of Cook County Hospital, Chicago, told of his work with the fluorescent microscope. The new instrument is hailed by such an authority as Dr. Paul Klemperer of Mt. Sinai Hospital as the first major step in the study of cell structure in the last half century. Since Ehrlich’s time, pathologists have stained sections of tissue with dyes to make them visible under the microscope. In its day this was a great advance, but scientists have always had to make allowance for changes in appearance caused by the chemical action of the dyes. With the new microscope, the specimen is flooded with invisible ultra-violet, and its fluorescence colors create a more vivid, clear-cut picture than research men have ever seen before.

It has been found that all species of bacteria have characteristic fluorescence colors. The tuberculosis germ glows in yellowish rose, the ‘A-type’ typhoid germ in violet-tinged yellow, and the ‘B-type’ in greenish yellow. Cancerous tissue fluoresces with a purplish-pearly hue, in contrast with healthy tissue, which appears almost black. Dr. Popper has been experimenting with Vitamin A, which is important in the prevention of night blindness. He feeds the vitamins to rats, and studies specimens from their livers beneath the new microscope. The vitamin’s green fluorescence color enables him to trace its course, and reveals facts about its behavior which are of value in treatment.

The new microscope has just begun its career, and the same may be said of the lamp and of all other developments in the fluorescent field. Many able men are testing the fluorescence of hundreds of materials, experimenting with different wave lengths of ultra-violet, and trying out new mechanisms to unite them for all manner of tasks. The development stands today about where aviation stood when Orville Wright took off at Kitty Hawk.