Chapter IX: Preface (9)

The cabinet used by Dr. Cleaves was large enough to contain a cot upon which the patient reclined. An arc-lamp was suspended at each of the two ends of the cabinet and a flood of light was obtained directly and by reflection from the white inside surfaces of the cabinet. By means of mirrors the light from the arcs could be concentrated upon any desired part of the patient.

Finsen, who in 1895 published his observations upon the stimulating action of light, is considered the pioneer in the use of so-called chemical rays in the treatment of disease. He had a circular room about thirty-seven feet in diameter, in which two powerful 100-ampere arc-lamps about six feet from the floor were suspended from the ceiling. Low partitions extended radially from the center, so that a number of patients could be treated simultaneously. The temperature of the room was normal, so that the treatment was essentially by radiant energy and not by heat. The chemical action upon the skin was said to be quite as strong as under sunlight. The exposures varied from ten minutes to an hour.

Light-baths containing incandescent filament lamps are also used. In some cases the lamp, sometimes having a blue bulb, is merely contained as a reflector and the light is applied locally as desired. Light-cabinets are also used, but in these there is considerable effect due to heat. The ultra-violet rays emitted by the small electric filament lamps used in these cabinets are of very low intensity and the bactericidal action of the light must be feeble. The glass bulbs do not transmit the extreme ultra-violet rays responsible for the production of ozone, or the middle ultra-violet rays which are effective in destroying animal tissue. The cabinets contain from twenty to one hundred incandescent filament lamps of the ordinary sizes, from 25 to 60 watts. In the days of the carbon filament lamp the 16-candle-power lamp was used. Certainly the heating effect has advantages in some cases over other methods of heating. The light-rays penetrate the tissue and are absorbed and transformed into heat. Other methods involve conduction of heat from the hot air or other hot applications. Of course, it is also contended that the light-rays are directly beneficial.

Light is also concentrated upon the body by means of lenses and mirrors. For this purpose the sun, the arc, the quartz mercury-arc, and the incandescent lamp have been used. Besides these, vacuum-tube discharges and sparks have been utilized as sources for radiant energy and "electrical" treatment. Röntgen rays and radium have also figured in recent years in the treatment of disease.

The quartz mercury-arc has been extensively used in the past decade for the treatment of skin diseases and there appears to be less uncertainty about the efficacy of radiant energy for the treatment of surface diseases than of others. Herod related that the Egyptians treated patients by exposure to direct sunlight and throughout the centuries and among all types of civilization sunlight has been recognized as having certain valuable healing or purifying properties. Finsen in his early experiments cured a case of lupus, a tuberculous skin disease, by means of the visible and near ultra-violet rays in sunlight. He demonstrated that these were the effective rays by using only the radiant energy which passed through a water-cell made by using a convex lens for each end of the cell and filling the intervening space with water. This was really a lens made of glass and water. The glass absorbed the ultra-violet rays of shorter wave-length and the water absorbed the infra-red rays. Thus he was able to concentrate upon the diseased skin radiant energy consisting of visible and near ultra-violet rays.

The encouraging results which Finsen obtained in the treatment of skin diseases led him to become independent of sunlight by equipping a special arc-lamp with quartz lenses. This gave him a powerful source of so-called chemical rays, which could be concentrated wherever desired. However, when science contributed the mercury-vapor arc, developments were immediately begun which aimed to utilize this artificial source of steady powerful ultra-violet rays in light-therapy. As a consequence, there are now available very compact quartz mercury-arcs designed especially for this purpose. Apparently their use has been very effective in curing many skin diseases. Certainly if radiant energy is effective, it has a great advantage over drugs. An authority has stated in regard to skin diseases that,

treatment with the ultra-violet rays, especially in conjunction
with the Röntgen rays, radium and mesothorium is that treatment
which in most instances holds rank as the first, and in many as
the only and often enough the most effective mode of handling
the disease.

Sterilization by means of the radiation from the quartz mercury-arc has been practised successfully for several years. Compact apparatus is in use for the sterilization of water for drinking, for surgical purposes, and for swimming-pools, and the claims made by the manufacturers of the apparatus apparently are substantiated. One type of apparatus withstands a pressure of one hundred pounds per square inch and may be connected in series with the water-main. The water supplied to the sterilizer should be clear and free of suspended matter, in order that the radiant energy may be effective. Such apparatus is capable of sterilizing any quantity of water up to a thousand gallons an hour, and the lamp is kept burning only when the water is flowing. It is especially useful in hotels, stores, factories, on ships, and in many industries where sterile water is needed.

Water is a vital necessity in every-day life, whether for drinking, cooking, or industrial purposes. It is recognized as a carrier of disease and the purification of water-supply in large cities is an important problem. Chlorination processes are in use which render the treated water disagreeable to the taste and filtration alone is looked upon with suspicion. The use of chemicals requires constant analysis, but it is contended that the bactericidal action of ultra-violet rays is so certain and complete that there is never any doubt as to the sterilization of the water if it is clear, or if it has been properly filtered before treating. The system of sterilization by ultra-violet rays is the natural way, for the sun's rays perform this function in nature. Apparatus for sterilization of water by means of ultra-violet rays is built for public plants in capacities up to ten million gallons per day and these units may be multiplied to meet the needs of the largest cities. Large mechanical filters are used in conjunction with these sterilizers, and thus mankind copies nature's way, for natural supplies of pure water have been filtered through sand and have been exposed to the rays of the sun which free it from germ life.

Some sterilizers of this character are used at the place where a supply of pure water is desired or at a point where water is bottled for use in various parts of a factory, hospital, store, or office building. These were used in some American hospitals during the recent war, where they supplied sterilized water for drinking and for the antiseptic bathing of wounds. In warfare the water supply is exceedingly important. For example, the Japanese in their campaign in Manchuria boiled the water to be used for drinking purposes. The mortality of armies in many previous wars was often much greater from preventable diseases than from bullets, but the Japanese in their war with Russia reversed the mortality statistics. Of a total mortality of 81,000 more than 60,000 died of casualties in battle.

The sterilization of water for swimming-pools is coming into vogue. Heretofore it was the common practice to circulate the water through a filter, in order to remove the impurities imparted to it by the bathers and to return it to the pool. It is insisted by the adherents of sterilization that filtration of this sort is likely to leave harmful bacteria in the water. Sterilizers in which ultra-violet rays are the active rays are now in use for this purpose, being connected beyond the outflow from the filter. The effectiveness of the apparatus has been established by the usual method of counting the bacteria. Near the outlet of the ordinary filter a count revealed many thousand bacteria per cubic inch of water and among these there were bacteria of intestinal origin. Then a sterilizer was installed in which the effective elements were two quartz mercury-lamps which consumed 2.2 amperes each at 220 volts. A count of bacteria in the water leaving the sterilizer showed that these organisms had been reduced to 5 per cent. and finally to a smaller percentage of their original value, and that all those of intestinal origin had been destroyed. In fact, the water which was returned to the pool was better than that which most persons drink. Radiant energy possesses advantages which are unequaled by other bactericidal agents, in that it does not contaminate or change the properties of the water in any way. It does its work of destroying bacteria and leaves the water otherwise unchanged.

These glimpses of the use of the radiant energy as a means of regaining and retaining good health suggest greater possibilities when the facts become thoroughly established and correlated. The sun is of primary importance to mankind, but it serves in so many ways that it is naturally a compromise. It cannot supply just the desired radiant energy for one purpose and at the same time serve for another purpose in the best manner. It is obscured on cloudy days and disappears nightly. These absences are beneficial to some processes, but man in the highly organized activity of present civilization desires radiant energy of various qualities available at any time. In this respect artificial light is superior to the sun and is being improved continually.

XXI

MODIFYING ARTIFICIAL LIGHT

In a single century science has converted the dimly lighted nights with their feeble flickering flames into artificial daytime. In this brief span of years the production of light has advanced far from the primitive flames in use at the beginning of the nineteenth century, but, as has been noted in another chapter, great improvements in light-production are still possible. Nevertheless, the wonderful developments in the last four decades, which created the arc-lamps, the gas-mantle, the mercury-vapor lamps, and the series of electric incandescent-filament lamps, have contributed much to the efficiency, safety, health, and happiness of mankind.

A hundred years ago civilization was more easily satisfied and an improvement which furnished more light at the same cost was all that could be desired. To-day light alone is not sufficient. Certain kinds of radiant energy are required for photography and other photochemical processes and a vast array of colored light is demanded for displays and for effects upon the stage. Man now desires lights of various colors for their expressive effects. He is no longer satisfied with mere light in adequate quantities; he desires certain qualities. Furthermore, he no longer finds it sufficient to be independent of daylight merely in quantity of light. In fact, he has demanded artificial daylight.

Doubtless the future will see the production of efficient light of many qualities or colors, but to-day many of the demands must be met by modifying the artificial illuminants which are available. Vision is accomplished entirely by the distinction of brightness and color. An image of any scene or any object is focused upon the retina as a miniature map in light, shade, and color. Although the distinction of brightness is a more important function in vision than the ability to distinguish colors, color-vision is far more important in daily life than is ordinarily appreciated. One may go through life color-blind without suffering any great inconvenience, but the divine gift of color-vision casts a magical drapery over all creation. Relatively few are conscious of the wonderful drapery of color, except for occasional moments when the display is unusual. Nevertheless a study of vision in nearly all crafts reveals the fact that the distinction of colors plays an important part.

In the purchase of food and wearing-apparel, in the decoration of homes and throughout the arts and industries, mankind depends a great deal upon the appearance of colors. He depends upon daylight in this respect and unconsciously often, when daylight fails, ceases work which depends upon the accurate distinction of colors. His color-vision evolved under daylight; arts and industries developed under daylight; and all his associations of color are based primarily upon daylight. For these reasons, adequate artificial illumination does not make mankind independent of daylight in the practice of arts and crafts and in many minor activities. In quality or spectral character, the unmodified illuminants used for general lighting purposes differ from daylight and therefore do not fully replace it. Noon sunlight contains all the spectral colors in approximately the same proportions, but this is not true of these artificial illuminants. For these reasons there is a demand for artificial daylight.

The "vacuum" tube affords a possibility of an extensive variety of illuminants differing widely in spectral character or color. Every gas when excited to luminescence by an electric discharge in the "vacuum" tube (containing the gas at a low pressure) emits light of a characteristic quality or color. By varying the gas a variety of illuminants can be obtained, but this means of light-production has not been developed to a sufficiently practicable state to be satisfactory for general lighting. Nitrogen yields a pinkish light and the nitrogen tube as developed by Dr. Moore was installed to some extent a few years ago. Neon yields an orange light and has been used in a few cases for displays. Carbon dioxide furnishes a white light similar to daylight and small tubes containing this gas are in use to-day where accurate discrimination of color is essential.

The flame-arcs afford a means of obtaining a variety of illuminants differing in spectral character or color. By impregnating the carbons with various chemical compounds the color of the flame can be widely altered. The white flame-arc obtained by the use of rare-earth compounds in the carbons provides an illuminant closely approximating average daylight. By using various substances besides carbon for the electrodes, illuminants differing in spectral character can be obtained. These are usually rich in ultra-violet rays and therefore have their best applications in processes demanding this kind of radiant energy. The arc-lamp is limited in its application by its unsteadiness, its bulkiness, and the impracticability of subdividing it into light-sources of a great range of luminous intensities.

The most extensive applications of artificial daylight have been made by means of the electric incandescent filament lamp, equipped with a colored glass which alters the light to the same quality as daylight. The light from the electric filament lamp is richer in yellow, orange, and red rays than daylight, and by knowing the spectral character of the two illuminants and the spectral characteristics of colored glasses in which various chemicals have been incorporated, it is possible to develop a colored glass which will filter out of the excess of yellow, orange, and red rays so that the transmitted light is of the same spectral character as daylight. Thousands of such artificial daylight units are now in use in the industries, in stores, in laboratories, in dye-works, in print-shops, and in many other places. Currency and Liberty Bonds have been made under artificial daylight and such units are in use in banks for the detection of counterfeit currency. The diamond expert detects the color of jewels and the microscopist is certain of the colors of his stains under artificial daylight. The dyer mixes his dyes for the coloring of tons of valuable silk and the artist paints under this artificial light. These are only a few of a vast number of applications of artificial daylight, but they illustrate that mankind is independent of natural light in another respect.

There are various kinds of daylight, two of which are fairly constant in spectral character. These are noon sunlight and north skylight. The former may be said to be white light and its spectrum indicates the presence of visible radiant energy of all wave-lengths in approximately equal proportions. North skylight contains an excess of violet, blue, and blue-green rays and as a consequence is a bluish white. Noon sunlight on a clear day is fairly constant in spectral character, but north skylight varies somewhat depending upon the absence or presence of clouds and upon the character of the clouds. If large areas of sunlit clouds are present, the light is largely reflected sunlight. If the sky is overcast, the north skylight is a result of a mixture of sunlight and blue skylight filtered through the clouds and is slightly bluish. If the sky is clear, the light varies from light blue to deep blue.

The daylight which enters buildings is often considerably altered in color by reflection from other buildings and from vegetation, and after it enters a room it is sometimes modified by reflection from colored surroundings. It may be commonly noted that the light reflected from green grass through a window to the upper part of a room is very much tinted with green and the light reflected from a yellow brick building is tinted yellow. Besides these alterations, sunlight varies in color from the yellow or red of dawn through white at noon to orange or red at sunset. Throughout the day the amount of light from the sky does not change nearly as much as the amount of sunlight, so there is a continual variation in the proportion of direct sunlight and skylight reaching the earth. This is further varied by the changing position of the sun. For example, at a north window in which the direct sunlight may not enter throughout the day, the amount of sunlight which enters by reflection from adjacent buildings and other objects may vary greatly. Thus it is seen that daylight not only varies in quantity but also in quality, and an artificial daylight, which is based upon an extensive analysis, has the advantage of being constant in quantity and quality as well as correct in quality. Modern artificial-daylight units which have been scientifically developed not only make mankind independent of daylight in the discrimination of colors but they are superior to daylight.

Although there are many expert colorists who require an accurate artificial daylight, there are vast fields of lighting where a less accurate daylight quality is necessary. The average eyes are not sufficiently skilled for the finest discrimination of colors and therefore the Mazda "daylight" lamp supplies the less exacting requirements of color matching. It is a compromise between quality and efficiency of light and serves the purpose so well that millions of these lamps have found applications in stores, offices, and industries. In order to make an accurate artificial north skylight for color-work by means of colored glass, from 75 to 85 per cent. of the light from a tungsten lamp must be filtered out. This absorption in a broad sense increases the efficiency of the light, for the fraction that remains is now satisfactory, whereas the original light is virtually useless for accurate color-discrimination. About one third of the original light is absorbed by the bulb of the tungsten "daylight" lamp, with a resultant light which is an approximation to average daylight.

Old illuminants such as that emitted by the candle and oil-lamp were used for centuries in interiors. All these illuminants were of a warm yellow color. Even the earlier modern illuminants were not very different in color, so it is not surprising that there is a deeply rooted desire for artificial light in the home and in similar interiors of a warm yellow color simulating that of old illuminants. The psychological effect of warmth and cheerfulness due to such illuminants or colors is well established. Artificial light in the home symbolizes independence of nature and protection from the elements and there is a firm desire to counteract the increasing whiteness of modern illuminants by means of shades of a warm tint. The white light is excellent for the kitchen, laundry, and bath-room, and for reading-lamps, but the warm yellow light is best suited for making cozy and cheerful the environment of the interiors in which mankind relaxes. An illuminant of this character can be obtained efficiently by using a properly tinted bulb on tungsten filament lamps. By absorbing about one fourth to one third of the light (depending upon the temperature of the filament) the color of the candle flame may be simulated by means of a tungsten filament lamp. Some persons are still using the carbon-filament lamp despite its low efficiency, because they desire to retain the warmth of tint of the older illuminants. However, light from a tungsten lamp may be filtered to obtain the same quality of light as is emitted by the carbon filament lamp by absorbing from one fifth to one fourth of the light. The luminous efficiency of the tungsten lamp equipped with such a tinted bulb is still about twice as great as that of the carbon-filament lamp. Thus the high efficiency of the modern illuminants is utilized to advantage even though their color is maintained the same as the old illuminants.

All modern illuminants emit radiant energy, which does not affect the ordinary photographic plate. This superfluous visible energy merely contributes toward glare or a superabundance of light in photographic studios. A glass has been developed which transmits virtually all the rays that affect the ordinary photographic plate and greatly reduces the accompanying inactive rays. Such a glass is naturally blue in color, because it must transmit the blue, violet, and near ultra-violet rays. Its density has been so determined for use in bulbs for the high-efficiency tungsten lamps that the resultant light appears approximately the color of skylight without sacrificing an appreciable amount of the value of the radiant energy for ordinary photography. This glass, it is seen, transmits the so-called chemical rays and is useful in other activities where these rays alone are desired. It is used in light-therapy and in some other activities in which the chemical effects of these rays are utilized.

In the photographic dark-room a deep red light is safe for all emulsions excepting the panchromatic, and lamps of this character are standard products. An orange light is safe for many printing papers. Panchromatic plates and films are usually developed in the dark where extreme safety is desired, but a very weak deep red light is not unsafe if used cautiously. However, many photographic emulsions of this character are not very sensitive to green rays, so a green light has been used for this purpose.

A variety of colored lights are in demand for theatrical effects, displays, spectacular lighting, signaling, etc., and there are many superficial colorings available for this purpose. Few of these show any appreciable degree of permanency. Permanent superficial colorings have recently been developed, but these are secret processes unavailable for the market. For this reason colored glass is the only medium generally available where permanency is desired. For permanent lighting effects, signal glasses, colored caps, and sheets of colored glass may be used. Tints may be obtained by means of colored reflectors. Other colored media are dyes in lacquers and in varnishes, colored inks, colored textiles, and colored pigments.

Inasmuch as colored glass enters into the development of permanent devices, it may be of interest to discuss briefly the effects of various metallic compounds which are used in glass. The exact color produced by these compounds, which are often oxides, varies slightly with the composition of the glass and method of manufacture, but this phase is only of technical interest. The coloring substances in glass may be divided into two groups. The first and largest group consists of those in which the coloring matter is in true solution; that is, the coloring is produced in the same manner as the coloring of water in which a chemical salt is dissolved. In the second group the coloring substances are present in a finely divided or colloidal state; that is, the coloring is due to the presence of particles in mechanical suspension. In general, the lighter elements do not tend to produce colored glasses, but the heavier elements in so far as they can be incorporated into glass tend to produce intense colors. Of course, there are exceptions to this general statement.

The alkali metals, such as sodium, potassium, and lithium, do not color glass appreciably, but they have indirect effects upon the colors produced by manganese, nickel, selenium, and some other elements. Gold in sufficient amounts produces a red in glass and in low concentration a beautiful rose. It is present in the colloidal state. In the manufacture of "gold" red glass, the glass when first cooled shows no color, but on reheating the rich ruby color develops. The glass is then cooled slowly. The gold is left in a colloidal state. Copper when added to a glass produces two colors, blue-green and red. The blue-green color, which varies in different kinds of glasses, results when the copper is fully oxidized, and the red by preventing oxidation by the presence of a reducing agent. This red may be developed by reheating as in the case of making gold ruby glass. Selenium produces orange and red colors in glass.

Silver when applied to the surface of glass produces a beautiful yellow color and it has been widely used in this manner. It has little coloring effect in glass, because it is so readily reduced, resulting in a metallic black. Uranium produces a canary yellow in soda and potash-lime glasses, which fluoresce, and these glasses may be used in the detection of ultra-violet rays. The color is topaz in lead glass. Both sulphur and carbon are used in the manufacture of pale yellow glasses. Antimony has a weak effect, but in the presence of much lead it is used for making opaque or translucent yellow glasses. Chromium produces a green color, which is reddish in lead glass, and yellowish in soda, and potash-lime glasses.

Iron imparts a green or bluish green color to glass. It is usually present as an impurity in the ingredients of glass and its color is neutralized by adding some manganese, which produces a purple color complementary to the bluish green. This accounts for the manganese purple which develops from colorless glass exposed to ultra-violet rays. Iron is used in "bottle green" glass. Its color is greenish blue in potash-lime glass, bluish green in soda-lime glass, and yellowish green in lead glass.

Cobalt is widely used in the production of blue glasses. It produces a violet-blue in potash-lime and soda-lime glasses and a blue in lead glasses. It appears blue, but it transmits deep red rays. For this reason when used in conjunction with a deep red glass, a filter for only the deepest red rays is obtained. Nickel produces an amethyst color in potash-lime glass, a reddish brown in soda-lime glass, and a purple in lead glass. Manganese is used largely as a "decolorizing" agent in counteracting the blue-green of iron. It produces an amethyst color in potash-lime glass and reddish violet in soda-lime and lead glasses.

These are the principal coloring ingredients used in the manufacture of colored glass. The staining of glass is done under lower temperatures, so that a greater variety of chemical compounds may be used. The resulting colors of metals and metallic oxides dissolved in glass depend not only upon the nature of the metal used, but also partly upon the stage of oxidation, the composition of the glass and even upon the temperature of the fusion.

In developing a glass filter the effects of the various coloring elements are determined spectrally and the various elements are varied in proper proportions until the glass of desired spectral transmission is obtained. It is seen that the coloring elements are limited and the combination of these is further limited by chemical considerations. In combining various colored glasses or various coloring elements in the same glass the "subtractive" method of color-mixture is utilized. For example, if a green glass is desired, yellowish green chromium glass may be used as a basis. By the addition of some blue-green due to copper, the yellow rays may be further subdued so that the resulting color is green.

The primary colors for this method of color-mixture are the same as those of the painter in mixing pigments--namely, purple, yellow, and blue-green. Various colors may be obtained by superposing or intimately mixing the colors. The resulting transmission (reflection in the case of reflecting media such as pigments) are those colors commonly transmitted by all the components of a mixture. Thus,

Purple and yellow = red
Yellow and blue-green = green
Blue-green and purple = blue

The colors produced by adding lights are based not on the "subtractive" method but on the actual addition of colors. These primaries are red, green, and blue and it will be noted that they are the complementaries of the "subtractive" primaries. By the use of red, green, and blue lights in various proportions, all colors may be obtained in varying degrees of purity. The chief mixtures of two of the "additive" primaries produce the "subtractive" primaries. Thus,

Red and blue = purple
Red and green = yellow
Green and blue = blue-green

Although the coloring media which are permanent under the action of light, heat, and moisture are relatively few, by a knowledge of their spectral characteristics and other principles of color the expert is able to produce many permanent colors for lighting effects. The additive and subtractive methods are chiefly involved, but there is another method which is an "averaging" additive one. For example, if a warm tint of yellow is desired and only a dense yellow glass is available, the yellow glass may be cut into small pieces and arranged upon a colorless glass in checker-board fashion. Thus a great deal of uncolored light which is transmitted by the filter is slightly tinted by the yellow light passing through the pieces of yellow glass. If this light is properly mixed by a diffusing glass the effect is satisfactory. These are the principal means of obtaining colored light by means of filters and by mixing colored lights. By using these in conjunction with the array of light-sources available it is possible to meet most of the growing demands. Of course, the ideal solution is to make the colored light directly at the light-source, and doubtless future developments which now appear remote or even impossible will supply such colored illuminants. In the meantime, much is being accomplished with the means available.

XXII

SPECTACULAR LIGHTING

Artificial light is a natural agency for producing spectacular effects. It is readily controlled and altered in color and the brightness which it lends to displays outdoors at night renders them extremely conspicuous against the darkness of the sky. It surpasses other decorative media by the extreme range of values which may be obtained. The decorator and painter are limited by a range of values from black to white pigments, which ordinarily represents an extreme contrast of about one to thirty. The brightnesses due to light may vary from darkness to those of the light-sources themselves. The decorator deals with secondary light--that is, light reflected by more or less diffusely reflecting objects. The lighting expert has at his command not only this secondary light but the primary light of the sources. Lighting effects everywhere attract attention and even the modern merchant testifies that adequate lighting in his store is of advertising value. In all the field of spectacular lighting the superiority of artificial light over natural light is demonstrated.

Light is a universal medium with which to attract attention and to enthrall mankind. The civilizations of all ages have realized this natural power of light. It has played a part in the festivals and triumphal processions from time immemorial and is still the most important feature of many celebrations. In the early festivals fires, candles, and oil-lamps were used and fireworks were invented for the purpose. Even to-day the pyrotechnical displays against the dark depths of the night sky hold mankind spellbound. But these evanescent notes of light have been improved upon by more permanent displays on a huge scale. Thirty years before the first practical installation of gas-lighting an exhibition of "Philosophical Fireworks" produced by the combustion of inflammable gases was given in several cities of England.

It is a long step from the array of flickering gas-flames with which the fronts of the buildings of the Soho works were illuminated a century ago to the wonderful lighting effects a century later at the Panama-Pacific Exposition. Some who saw that original display of gas-jets totaling a few hundred candle-power described it as an "occasion of extraordinary splendour." What would they have said of the modern spectacular lighting at the Exposition where Ryan used in a single effect forty-eight large search-lights aggregating 2,600,000,000 beam candle-power! No other comparison exemplifies more strikingly the progress of artificial lighting in the hundred years which have elapsed since it began to be developed.

The nature of the light-sources in the first half of the nineteenth century did not encourage spectacular or display lighting. In fact, this phase of lighting chiefly developed along with electric lamps. Of course, occasionally some temporary effect was attempted as in the case of illuminating the dome of St. Paul's Cathedral in London in 1872, but continued operation of the display was not entertained. In the case of lighting this dome a large number of ship's lanterns were used, but the result was unsatisfactory. After this unsuccessful attempt at lighting St. Paul's, a suggestion was made of "flooding it with electric light projected from various quarters." Spectacular lighting outdoors really began in earnest in the dawn of the twentieth century.

Although some of the first attempts at spectacular lighting outdoors were made with search-lights, spectacular lighting did not become generally popular until the appearance of incandescent filament lamps of reasonable efficiency and cost. The effects were obtained primarily by the use of small electric filament lamps draped in festoons or installed along the outlines and other principal lines of buildings and monuments. The effect was almost wholly that of light, for the glare from the visible lamps obscured the buildings or other objects. The method is still used because it is simple and the effects may be permanently installed without requiring any attention excepting to replace burned-out lamps. However, the method has limitations from an artistic point of view because the artistic effects of painting, sculpture, and architecture cannot be combined with it very effectively. For example, the details of a monument or of a building cannot be seen distinctly enough to be appreciated. The effect is merely that of outlines or lines and patterns of points of light and is usually glaring.

The next step was to conceal these lamps behind the cornices or other projections or in nooks constructed the purpose. Light now began to mold and to paint the objects. The structures began to be visible; at least the important cornices and other details were no longer mere outlines. The introduction of the drawn-wire tungsten lamp is responsible for an innovation in spectacular lighting of this sort, for now it became possible to make concentrated light-sources so essential to projectors. Furthermore, these lighting units require very little attention after once being located. With the introduction of electric-filament lamps of this character small projectors came into use, and by means of concentrated beams of light whole buildings and monuments could be flooded with light from remote positions. The effects obtained by concealing lamps behind cornices had demonstrated that the lighting of the surfaces was the object to be realized in most cases, and when small projectors not requiring constant attention became available, a great impetus was given to flood-lighting.

When France gave to this country the Bartholdi Statue of Liberty there was no thought of having this emblem visible at night excepting for the torch held the hand of Liberty. This torch was modified at the time of the erection of the statue to accommodate the lamps available, with the result that it was merely a lantern containing a number of electric lamps. At night it was a speck of light more feeble than many surrounding shore lights. The statue had been lighted during festivals with festoons and outlines of lamps, but in 1915, when the freedom of the generous donor of the statue appeared to be at stake, a movement was begun which culminated in a fund for flood-lighting Liberty. The broad foundation of the statue made the lighting comparatively easy by means of banks of incandescent filament search-lights. About 225 of these units were used with a total beam candle-power of about 20,000,000. The original idea of an imitation flame for the torch was restored by building this from pieces of yellow cathedral glass of three densities. About six hundred pieces of glass were used, the upper ones being generally of the lighter tints and the lower ones of the darker tints. A lighthouse lens was placed in this lantern so that an intense beam of light would radiate from it. The flood-lighted Statue of Liberty is now visible by night as well as by day and it has a double significance at night, for light also symbolizes independence.

Just as the Statue of Liberty stands alone in the New York Harbor so does the Woolworth Building reign supreme on lower Manhattan. Liberty proclaims independence from the bondage of man and the Woolworth Tower stands majestically in defiance of the elements as a symbol of man's growing independence of nature. This building with its cream terra-cotta surface and intricate architectural details touched here and there with buff, blue, green, red, and gold, rises 792 feet or sixty stories above the street and typifies the American spirit of conceiving and of executing great undertakings. In it are blended art, utility, and majesty. Viewed by multitudes during the day, it is a valuable advertisement for the name which stands for a national institution. But by day it shares attention with its surroundings. If lighted at night it would stand virtually alone against the dark sky and the investment would not be wholly idle during the evening hours.

Mr. H. H. Magdsick, who designed the lighting for Liberty, planned the lighting for the Woolworth Tower, which rises 407 feet or thirty-one stories above the main building. Five hundred and fifty projectors containing tungsten filament lamps were distributed about the base of the tower and among some of the architectural details. The main architectural features of the mansard roof extending from the fifty-third to the fifty-seventh floor, the observation balcony at the fifty-eighth and the lantern structures at the fifty-ninth and sixtieth floors are covered with gold-leaf. By proper placing of the projectors a glittering effect is obtained from these gold surfaces. The crowning features of the lighting effect are the lanterns in the crest of the spire. Twenty-four 1000-watt tungsten lamps were placed behind crystal diffusing glass, which transmits the light predominantly in a horizontal direction. Thus at long distances, from which the architectural details cannot be distinguished, the brilliant crowning light is visible. An automatic dimmer was devised so that the effect of a huge varying flame was obtained. At close range, owing to the nature of the glass panels, this portion is not much brighter than the remainder of the surfaces. When the artificial lighting is in operation the tower becomes a majestic spire of light and this magnificent Gothic structure projecting defiantly into the depths of darkness is in more than one sense a torch of modern civilization.

Many prominent buildings and monuments have burst forth in a flood of light, and their beauty and symbolism have been appreciated at night by many persons who do not notice them by day. Not only are the beautiful structures of man lighted permanently but many temporary effects are devised. Artificial lighting effects have become a prominent part in outdoor festivals, pageants, and theatricals. Candles have been associated with Christmas trees ever since the latter came into use and naturally artificial light has been a feature in the community Christmas trees which have come into vogue in recent years. The Municipal Christmas Tree in Chicago in 1916 was ninety feet high and was lighted with projectors. Thousands of gems taken from the Tower of Jewels at the San Francisco Exposition added life and sparkle to that of the other decorations.

Luna Park, Coney Island, studded with 60,000 incandescent filament lamps

THE NEW FLOOD LIGHTING CONTRASTED WITH THE OLD OUTLINE LIGHTING]

After the close of the recent war artificial light played a prominent part throughout the country in the joyful festivals. A jeweled arch erected in New York in honor of the returning soldiers rivaled some of the spectacles of the Panama-Pacific Exposition. The arch hung like a gigantic curtain of jewels between two obelisks, which rose to a height of eighty feet and were surmounted by jeweled forms in the shape of sunbursts. Approximately thirty thousand jewels glittered in the beams of batteries of arc-projectors. Many of the signs and devices which played a part in the "Welcome Home" movement were of striking nature and of a character to indicate permanency. The equipment of a large building consisted of more than five thousand 10-watt lamps, the entire building being outlined with stars consisting of eleven lamps each. The "Brighten Up" campaign spread throughout the country. The lighting and installation of signs and special patriotic displays, the flooding of streets and shop-windows with light without stint, produced an inspiring and uplifting effect which did much to restore cheerfulness and optimism. A glowing example was set in Washington, where the flood-lighting of the Capitol, discontinued shortly after our entrance into the war, was resumed.

In Chicago a "Victory Way" was established, with street-lighting posts on both sides of the street equipped with red, white, and blue globes surmounted by a golden goddess of Victory. One hundred and seventy-five projectors were installed along the way on the roofs and in the windows of office buildings. A brilliant, scintillating "Altar of Victory" was erected at the center of the Way. It was composed of two enormous candelabra erected one on each side of a platform ninety feet high. These were studded with jewels and supported a curtain of jewels suspended from the altar. In the center of the curtain was a huge jeweled eagle bearing the Allied flags. This was illuminated by arc-projectors which delivered 200,000,000 beam candle-power. In addition to these there were many smaller projectors. In the top of each candelabra six large red-and-orange lamps were installed in reflectors. These illuminated live steam which issued from the top. Surmounting the whole was a huge luminous fan formed by beams from large arc search-lights. These are only a few of the many lighting effects which welcomed the returning soldiers, but they illustrate how much modern civilization depends upon artificial light for expressing its feelings and emotions. Throughout all these festivals light silently symbolized happiness, freedom, and advancement.

Projectors were used on a large scale in several cases before the advent of the concentrated filament lamp. W. D'A. Ryan, the leader in spectacular lighting, lighted the Niagara Falls in 1907 with batteries of arc-projectors aggregating 1,115,000,000-beam candle-power. In 1908 he used thirty arc-projectors to flood the Singer Tower in New York with light and projected light to the flag on top by means of a search-light thirty inches in diameter. Many flags waved throughout the war in the beams of search-lights, symbolizing a patriotism fully aroused. The search-light beam as it bores through the atmosphere at night is usually faintly bright, owing to the small amount of fog, dust, and smoke in the air. By providing more "substance" in the atmosphere, the beams are made to appear brighter. Following this reasoning, Ryan developed his scintillator consisting of a battery of search-light beams projected upward through clouds of steam which provided an artificial fog. This was first displayed at the Hudson-Fulton celebration with a battery of arc search-lights totaling 1,000,000,000-candle-power.

All these effects despite their magnitude were dwarfed by those at the Panama-Pacific Exposition, and inasmuch as this up to the present time represents the crowning achievement in spectacular lighting, some of the details worked out by Ryan may be of interest. In general, the lighting effects departed from the bizarre outline lighting in which glaring light-sources studded the structures. The radiant grandeur and beauty of flood-lighting from concealed light-sources was the key-note of the lighting. In this manner wonderful effects were obtained, which not only appealed to the eye and to the artistic sensibility but which were free from glare. By means of flood-lighting and relief-lighting from concealed light-sources the third dimension or depth was obtained and the architectural details and colorings were preserved. A great many different kinds of devices and lamps were used to make the night effects superior in grandeur to those of daytime. The Zone or amusement section was lighted with bare lamps in the older manner and the glaring bizarre effects contrasted the spectacular lighting of the past with the illumination of the future.

In another section the visitor was greeted with a gorgeous display of carnival spirit. Beautifully colored heraldic shields on which were written the early history of the Pacific coast were illuminated by groups of luminous arc-lamps on standards varying from twenty-five to fifty-five feet in height. The Tower of Jewels with more than a hundred thousand dangling gems was flood-lighted, and the myriads of minute reflected images of light-sources glittering against the dark sky produced an effect surpassing the dreams of imagination. Shadows and high-lights of striking contrasts or of elusive colors greeted the visitor on every hand. Individual isolated effects of light were to be found here and there. Fire hissed from the mouths of serpents and cast the spell of mobile light over the composite Spanish-Gothic-Oriental setting. A colored beam of a search-light played here and there. Mysterious vapors rising from caldrons were in reality illuminated steam. Symbolic fountain groups did not escape the magic touch of the lighting wizard.

In the Court of the Universe great areas were illuminated by two fountains rising about a hundred feet above the sunken gardens. One of these symbolized the setting sun, the other the rising sun. The shaft and ball at the crest of each fountain were glazed with heavy opal glass imitating travertine marble and in these were installed incandescent lamps of a total candle-power of 500,000. The balustrade seventy feet above the sunken gardens was surmounted by nearly two hundred incandescent filament search-lights. Light was everywhere, either varying in color into a harmonious scene or changing in light and shadow to mold the architecture and sculpture. The enormous glass dome of the Palace of Horticulture was converted into an astronomical sphere by projecting images upon it in such a manner that spots of light revolved; rings and comets which appeared at the horizon passed on their way through the heavens, changing in color and disappearing again at the horizon. All these effects and many more were mirrored in the waters of the lagoons and the whole was a Wonderland indeed.

The scintillator consisted of 48 arc search-lights three feet in diameter totaling 2,600,000,000 beam candle-power. The lighting units were equipped with colored screens and the beams which radiated upward were supplied with an artificial fog by means of steam generated by a modern express locomotive. The latter was so arranged that the wheels could be driven at a speed of sixty miles per hour under brake, thereby emitting great volumes of steam and smoke, which when illuminated with various colors produced a magnificent spectacle. Over three hundred scintillator effects were worked out and this feature of fireless fireworks was widely varied. The aurora borealis and other effects created by this battery of search-lights extended for many miles. The many effects regularly available were augmented on special occasions and it is safe to state that this apparatus built upon a huge scale provided a flexibility of fireless fireworks never attained even with small-scale devices.

The lighting of the exposition can barely be touched upon in a few paragraphs and it would be difficult to describe in words even if space were unlimited. It represented the power of light to beautify and to awe. It showed the feebleness of the decorator's media in comparison with light pulsating with life. It consisted of a great variety of direct, masked, concealed, and projected effects, but these were blended harmoniously with one another and with the decorative and architectural details of the structures. It was a crowning achievement of a century of public lighting which began with Murdock's initial display of a hundred flickering gas-jets. It demonstrated the powers of science in the production of light and of genius and imagination in the utilization of light. It was a silent but pulsating display of grandeur dwarfing into insignificance the aurora borealis in its most resplendent moments.

XXIII

THE EXPRESSIVENESS OF LIGHT

From an esthetic or, more broadly, a psychological point of view no medium rivals light in expressiveness. Not only is light allied with man's most important sense but throughout long ages of associations and uses mankind has bestowed upon it many attributes. In fact, it is possible that light, color, and darkness possess certain fundamentally innate powers; at least, they have acquired expressive and impressive powers through the many associations in mythology, religion, nature, and common usage. Besides these attributes, light possesses a great advantage over the media of decoration in obtaining brightness and color effects. For example, the landscape artist cannot reproduce the range of values or brightnesses in most of nature's scenes, for if black is used to represent a deep shadow, white is not bright enough to represent the value of the sky. In fact, the range of brightnesses represented by the deep shadow and the sky extends far beyond the range represented by black and white pigments. The extreme contrast ordinarily available by means of artist's colors is about thirty to one, but the sky is a thousand times brighter than a shadow, a sunlit cloud is thousands of times brighter than the deep shadows of woods, and the sun is millions of times brighter than the shadows in a landscape.

The range of brightnesses obtainable by means of light extends from darkness or black throughout the range represented by pigments under equal illumination and beyond these through the enormous range obtainable by unequal illumination of surfaces to the brightnesses of the light-sources themselves. In the matter of purity of colors, light surpasses reflecting media, for it is easy to obtain approximately pure hues by means of light and to obtain pure spectral hues by resorting to the spectrum of light. It is impossible to obtain pure hues by means of pigments or of other reflecting media. These advantages of light are very evident on turning to spectacular lighting effects, and even the lighting of interiors illustrates a potentiality in light superior to other media. For example, in a modern interior in which concealed lighting produces brilliantly illuminated areas above a cornice and dark shadows on the under side, the range in values is often much greater than that represented by black and white, and still there remains the possibility of employing the light-sources themselves in extending the scale of brightness. Superposing color upon the whole it is obvious that the combination of "primary" light with reflected light possesses much greater potentiality than the latter alone. This potentiality of light is best realized if lighting is regarded as "painting with light" in a manner analogous to the decorator's painting with pigments, etc.

The expressive possibilities of lighting find extensive applications in relation to painting, sculpture, and architecture. A painting is an expression of light and the sculptor's product finally depends upon lighting for its effectiveness. Lighting is the master painter and sculptor. It may affect the values of a painting to some extent and it is a great influence upon the colors. It molds the model from which the sculptor works and it molds the completed work. The direction, distribution, and quality of light influence the appearance of all objects and groups of them. Aside from the modeling of ornament, the light and shade effects of relatively large areas in an interior such as walls and ceiling, the contrasts in the brightnesses of alcoves with that of the main interior, and the shadows under cornices, beams, and arches are expressions of light.

The decorator is able to produce a certain mood in a given interior by varying the distribution of values and the choice of colors and the lighting artist is able to do likewise, but the latter is even able to alter the mood produced by the decorator. For example, a large interior flooded with light from concealed sources has the airiness and extensiveness of outdoors. If lighted solely by means of sources concealed in an upper cornice, the ceiling may be bright and the walls may be relatively dark by contrast. Such a lighting effect may produce a feeling of being hemmed in by the walls without a roof. If the room is lighted by means of chandeliers hung low and equipped with shades in such a manner that the lower portions of the walls may be light while the upper portions of the interior may be ill defined, the feeling produced may be that of being hemmed in by crowding darkness. Thus lighting is productive of moods and illusions ranging from the mystery of crowding darkness to the extensiveness of outdoors.