ARTIFICIAL ILLUMINATION Use of Systems of Illumination.— Artificial light is the third most im portant of the necessities of civiliza tion, taking rank after the items of clothing and shelter. A comparative statement of the annual value of illu mination in the United States shows the following results: Acetylene (esti mated), about $11,000,000; illumina ting gas, $60,000,000; kerosene, $133, 000,000; electricity, $150,000,000; or total of $360,000,000, being about $4 for every man, woman, and child in the United States. Probably 10 per cent of the light thus generated is wasted through misuse and ignorance, which would amount to forty cents per capita for the entire population of the country, or a total of $36,000, 000. Including all items pertaining to the lighting industry, it is probable that the grand total of expenditure would reach annually $500,000,000.
Cost of Lighting Systems.—An av erage period for the burning of arti ficial light per twenty-four hours is perhaps from 6 to 10 P.M., or about four hours. A careful comparison of the cost of different systems of light ing shows that each twenty-four can dle power of light produced from gas at $1 a thousand with a Welsbach burner, or from gasoline gas with a Welsbach burner, would be fi cent for four hours, or about $2.46 a year;
the•same candle power produced from acetylene would be for four hours, or $5.85 a year; from kerosene, 9-fi cents a day, or $8.76 a year. From gas at $1 per thousand without a Welsbach burner, 3 cents a day, or $10.95 a year; from incandescent elec tric lamps, 5 cents a day, or $18.25 a year. But of course allowance must be made for varying prices and other local conditions.
Effect of Artificial Light on Health. —It is not commonly known that most ordinary lights vitiate the atmosphere of living rooms to t greater extent than does the breathing of several per sons. The incandescent electric light has a great advantage in this respect, as it is inclosed in a vacuum, and so consumes no oxygen and gives off very •little heat. The next least injurious form of lighting is the Welsbach burn er with any illuminating gas, which consumes about the same amount of air as three persons. The ordinary gas jet without the Welsbach burner vitiates the air about as rapidly as the breathing of five persons; the common oil lamp, about the same as that of eight persons; and the ordinary tal low candle is equal to the breath of twelve persons in the amount of at mospheric oxygen it consumes.