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Vapor Lamps

light, lamp, current, tube, tubes and candle-power

VAPOR LAMPS, a form of lamp used in electric lighting in which a rarefied gas is ren dered luminous by the passage through it of an electric current. All other forms of artificial light now in practical use depend for their light ing properties upon the incandescence of a solid— either in the form of a filament of car bon or tungsten as in the ordinary glow lamp or of a rod of carbon as in the arc or of car bon in a finely divided state as in gas and kerosene lamps. The Hewitt vapor lamp, also known as the mercury vapor lamp, derives its light from the vapor of mercury, in which the passage of an electric current causes a high state of incandescence. The lamp is constructed of a glass tube having a metal sealing-in wire at each end. These wires lead the current to the electrodes, one or both of which are of mercury. The tubes are exhausted to a high degree on a vacuum pump and seated off. This prevents any escape of the vapor which fills the tube. Three types are made: a 20-inch tube operating on direct current; a 50-inch tube adapted for either direct or indirect current; and the quartz or high-pressure lamp, for di rect current only. One 330-watt Hewitt lamp will replace nine 32-candle-power incandescent lamps and give much more than twice the amount of light, using only one-third the cur rent. Or the same lamp will replace 12 16 candle-power incandescent lamps, giving over three times the light for one-half the current. The light may be employed to great advantage for purposes where considerable illumination is required and where the ordinary arc light is unsatisfactory on account of its sharp and heavy shadows and its flicker. The light given is bluish green in tint and is a strictly indus trial illuminant. In this field its advantages are visual acuity, low intrinsic brilliancy, natural shadows and subdued reflections. It is exten sively used in foundries and machine shops, varnishing and finishing plants, textile mills, printing plants, paper mills, clothing factories, etc. Another great field of application of the

lamp is for all sorts of photographic processes. The illumination being so diffused and the light composed to a great extent of the so-called •actinic° or chemically active rays it furnishes for this work, where there has never been a satisfactory artificial illuminant, a perfect ac tinic substitute for daylight. For the produc tion of a pure white imitation of average day light it is supplemented by other forms of lamps which add the colored rays missing from the Hewitt lamp. For each candle-power of the mercury light is added 0.57 candle-power of Welsbach; 0.54 candle-power of tungsten and 0.50 candle-power of carbon filament. The Moore light, also called the "vacuum tube° light, is a form of vapor lamp in which the rarefied gas used is either carbon dioxide or nitrogen. The nitrogen tubes give a warm yellow light which is soft as well as brilliant. They are extensively used in public rooms, banquet hallsrestaurants, etc. The New York office City post is illuminated with a mile of tkese tubes. The carbon dioxide tubes give a light whose spectrum approaches most nearly to that of diffused sunlight. Color matching may be done by this light as accurately as by daylight and hence this form of illuminant is invaluable in dye houses, which formerly had to shut down early in winter and altogether on dark days. In the latest forms of the Moore lamp an automatic mechanism is provided for feeding into the tubes from time to time the fresh gas necessary to replenish the amount which becomes inert and, therefore, non luminous. The neon tube is a form of lamp closely similar to the vapor lamps. It is dis tinctly a red light, lacking seriously the proper proportion of blue rays. It is useful in many decorative effects and when skilfully assorted with Hewitt lamps affords a perfect imitation of daylight at a lower cost than for any other electric light.