In a single century science has converted the dimly lighted nights with\ntheir feeble flickering flames into artificial daytime. In this brief\nspan of years the production of light has advanced far from the\nprimitive flames in use at the beginning of the nineteenth century, but,\nas has been noted in another chapter, great improvements in\nlight-production are still possible. Nevertheless, the wonderful\ndevelopments in the last four decades, which created the arc-lamps, the\ngas-mantle, the mercury-vapor lamps, and the series of electric\nincandescent-filament lamps, have contributed much to the efficiency,\nsafety, health, and happiness of mankind.<\/p>\n\n\n\n\n\n\n\n
A hundred years ago civilization was more easily satisfied and an\nimprovement which furnished more light at the same cost was all that\ncould be desired. To-day light alone is not sufficient. Certain kinds of\nradiant energy are required for photography and other photochemical\nprocesses and a vast array of colored light is demanded for displays and\nfor effects upon the stage. Man now desires lights of various colors for\ntheir expressive effects. He is no longer satisfied with mere light in\nadequate quantities; he desires certain qualities. Furthermore, he no\nlonger finds it sufficient to be independent of daylight merely in\nquantity of light. In fact, he has demanded artificial daylight.<\/p>\n\n\n\n
Doubtless the future will see the production of efficient light of many\nqualities or colors, but to-day many of the demands must be met by\nmodifying the artificial illuminants which are available. Vision is\naccomplished entirely by the distinction of brightness and color. An\nimage of any scene or any object is focused upon the retina as a\nminiature map in light, shade, and color. Although the distinction of\nbrightness is a more important function in vision than the ability to\ndistinguish colors, color-vision is far more important in daily life\nthan is ordinarily appreciated. One may go through life color-blind\nwithout suffering any great inconvenience, but the divine gift of\ncolor-vision casts a magical drapery over all creation. Relatively few\nare conscious of the wonderful drapery of color, except for occasional\nmoments when the display is unusual. Nevertheless a study of vision in\nnearly all crafts reveals the fact that the distinction of colors plays\nan important part.<\/p>\n\n\n\n
In the purchase of food and wearing-apparel, in the decoration of homes\nand throughout the arts and industries, mankind depends a great deal\nupon the appearance of colors. He depends upon daylight in this respect\nand unconsciously often, when daylight fails, ceases work which depends\nupon the accurate distinction of colors. His color-vision evolved under\ndaylight; arts and industries developed under daylight; and all his\nassociations of color are based primarily upon daylight. For these\nreasons, adequate artificial illumination does not make mankind\nindependent of daylight in the practice of arts and crafts and in many\nminor activities. In quality or spectral character, the unmodified\nilluminants used for general lighting purposes differ from daylight and\ntherefore do not fully replace it. Noon sunlight contains all the\nspectral colors in approximately the same proportions, but this is not\ntrue of these artificial illuminants. For these reasons there is a\ndemand for artificial daylight.<\/p>\n\n\n\n
The “vacuum” tube affords a possibility of an extensive variety of\nilluminants differing widely in spectral character or color. Every gas\nwhen excited to luminescence by an electric discharge in the “vacuum”\ntube (containing the gas at a low pressure) emits light of a\ncharacteristic quality or color. By varying the gas a variety of\nilluminants can be obtained, but this means of light-production has not\nbeen developed to a sufficiently practicable state to be satisfactory\nfor general lighting. Nitrogen yields a pinkish light and the nitrogen\ntube as developed by Dr. Moore was installed to some extent a few years\nago. Neon yields an orange light and has been used in a few cases for\ndisplays. Carbon dioxide furnishes a white light similar to daylight and\nsmall tubes containing this gas are in use to-day where accurate\ndiscrimination of color is essential.<\/p>\n\n\n\n
The flame-arcs afford a means of obtaining a variety of illuminants\ndiffering in spectral character or color. By impregnating the carbons\nwith various chemical compounds the color of the flame can be widely\naltered. The white flame-arc obtained by the use of rare-earth compounds\nin the carbons provides an illuminant closely approximating average\ndaylight. By using various substances besides carbon for the\nelectrodes, illuminants differing in spectral character can be\nobtained. These are usually rich in ultra-violet rays and therefore have\ntheir best applications in processes demanding this kind of radiant\nenergy. The arc-lamp is limited in its application by its unsteadiness,\nits bulkiness, and the impracticability of subdividing it into\nlight-sources of a great range of luminous intensities.<\/p>\n","protected":false},"excerpt":{"rendered":"
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 … <\/p>\n