Production of Light.—Artificial light is produced by heating some body to such a degree of temperature that it becomes incandescent. The color of light which a heated body gives off bears a certain relation to the degree of temperature. In producing artificial light the object is to obtain a temperature that will give off as large a per cent. as possible of those rays which are perceived by the sense of sight.

Nature of Illumination.—Until quite recently, artificial illumination was obtained through heat developed by chemical action, usually called combustion. Combustion is a process of oxidation, the chemical action being between the burning body and the oxygen of the air.

Materials of Light.—The materials of ordinary light are mainly carbon, with a certain degree of oxygen and hydrogen, and the process of combustion is one of rapid, even violent, oxidation of the carbon and hydrogen by the aid of the free oxygen of the air.

Phenomenon of Light.—Luminosity of light is due to the high temperature reached by the hydrogen and carbon, or hydrocarbons. The hydrogen has a greater affinity for oxygen than the carbon has, and consequently takes up the greater proportion of the oxygen surrounding the flame, producing intense heat, and separating the hydrocarbons which are in a state of dense vapor. Being intensely ignited in the hydrogen flame, the hydrocarbons become brightly luminous. Thus ordinary illumination has the disadvantage of extracting oxygen from the air, setting free carbonic acid gas and producing heat and certain products of combustion, which are calculated to vitiate the air of dwellings.

The Electric Light.—This light is not a product of combustion, but of an electric current passing through a resisting medium, as a gas, small wire, or carbon candle or filament. When a carbon filament is used it must be protected in a vacuum in a sealed glass globe. This is the so-called and familiar incandescent light. The electric arc light is produced by passing an electric current through carbon candles, whose tips are nearly touching. At the break a brilliant light appears. It is the favorite street and store light of our day.

Advantages of Electric Lights.—It is the cleanest of all lights. It produces no heat and has no effect on the gases of the air. It consumes no oxygen and gives off no impure compounds. With the discovery of how to make it economically it speedily succeeded all other kinds of light in large city houses and for street and area purposes.

Ordinary Lighting.—Sources of artificial light in common use are gas, mineral oils, solid and liquid fats, the latter employed in the form of candles and lamps.

Gas Light.—This is still largely used in cities and towns of some size. If properly made it is economic, cleanly and convenient, but otherwise its products of combustion are ruinous to furniture, books and health, and call for a thorough system of house ventilation.

A Ventilating Apparatus.—A ventilator for gas impurities consists of openings in the ceiling above chandeliers and burners leading into a tube of tin or zinc, which is carried beneath the floor of the room above and thence into a chimney or foul-air shaft.

Gas Lighting.—This common mode of lighting in cities and towns has its conveniences and dangers. Its greatest merit is convenience. It does not rank as an economic light. It can never be classed as a safe light.

Petroleum.—Petroleum, or kerosene, ranks next to gas as an illuminant. It was at first dangerous, but since the "flashing point" of kerosene has been ascertained, and laws have been enacted as to refining processes, the danger has been greatly reduced. Moreover, there has been a great improvement in lamps, so that now kerosene ranks as the favorite rural light.

Candles.—Candles as illuminants have been almost wholly superseded by gas and petroleum. Their use has little effect in determining the amount of air required for ventilation.

Effects of Combustion.—As regards the effects of combustion of lights upon ventilation, experiments have been made to determine the relative quantity of carbonic acid generated by different agents in producing uniform illumination. According to Douglas Galton, several kinds of lights were burned in given quantities of air, and the times at which the flames went out were carefully noted with the following effect:

        Colza oil ..................................... 71 minutes
        Tallow ........................................ 75 minutes
        Wax candles ................................... 79 minutes
        Spermaceti candles ............................ 83 minutes
        13-Oandle coal gas ............................ 98 minutes
        28-Candle cannel gas.......................... 152 minutes

It would appear from the above experiment, that coal gas required a longer time to vitiate the atmosphere of a room than any form of candles, or colza oil, which is an oil expressed from rape seed combined with other vegetable oils. According to Roth and Lex, petroleum produces a less quantity of carbonic acid than gas, the amount of light being equal. It must be taken into consideration that when candles and oil are used, a less illuminating effect is satisfactory, and therefore, in practice, the contamination of the air by these agents seldom ever reaches that produced by burning coal gas. When petroleum is burned in large quantity, there is, of course, the same necessity for providing a means of escape for the products of combustion as exists in the case of coal gas illumination.

Lights for Reading.—For writing or reading or other close work it is important that the light should be of sufficient quantity, steady and uniform, and so arranged that it shall come from a little above the eyes and from one side. For writing, it is usually arranged a little above the left front of the writer. When two lamps are used, they may be placed one on each side of the worker, so that the light shall come from above the level of the eyes.

Outlets for Products of Combustion.—The electric light, gas light and kerosene light hold the prominent place in lighting by reason of efficiency. With the moderate use of any of these illuminants there need usually exist no necessity for special outlets for removing the products of combustion, if the ordinary means of ventilation are properly applied. But where a large number of lights are required and are habitually employed, special provision should always be made for the escape of the resultants of combustion, and, preferably, such as will also afford channels of escape for the vitiated air of the room.

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Last Modified: Monday, 13-May-2013 15:31:47 EDT