ELECTRIC LIGHTING. Illumination pro duced by the conversion of electrical energy into light, practically always through the agency of either arc or incandescent lamps. The electrical energy, or electric current, is produced by dy namos (see DYNAMO-ELECTRIC MACHINERY), driven most frequently by either steam-engines or water-power, and sometimes by other forms of mechanical power, such as wind. The dynamos maw produce direct or alternating current, of either high or low potential, which is brought to the lamps throueh a system of wires. The are light is produced whenan electric current passes across a space between two rods or pencils of car bon which have been in contact and then slightly separated. (See ELECTRIC Ant%) In the mean descent lamp an electric current passes through a carbon filament mounted in a glass bulb, from which the air has been exhausted. The carbon filament offers considerable resistance to the cur rent. so that the energy of the latter is trans formed into heat. When the carbon is sufficiently heated it becomes incandescent and emits light.
The are lamp was the first to be developed, and while its inception dates from the very beginning of the nineteenth its general use for lighting was only during the last twenty years of that century and preceded that of the Mean descent lamp by only a few years. In 1862 one lamp of this kind was installed in a lighthouse at Dungeness. Supplied with current from a cumbrous Holmes magneto-electrie machine, this light was in use for many years, and is credited with being the first electric lamp in regular ser vice. I dynamo of 1870 marked an era in electrical development, yet there were but two electric-light exhibits at the Centennial Exhibi tion at Philadelphia in 1876. Only 2:3 years later
the revised list of electric lighting exhibits at the Paris Exposition included 200 entries. In 187S Paul .lablochkoff's 'electric candle' made a sell sation. lle placed his two carbons side by side. vertically, with baked kaolin between and did away with the carbon feed-mechanism. It was only an ingenious arrangement which did not come into use. In the same year, however. Charles E. Brush. of Cleveland, Ohio, devised a complete system of arc electric lighting, including a special form of dynamo and lamps arranged in series. About the same time the Thomson Houston system was developed, as well as a number of others.
The Edison incandescent lamp was first exhib ited in 1S79 in Edison's laboratory, at :Menlo Park. N. J.. and three yea FA la ter. at t he Pearl Street Edison lighting-station in New York. the first incandescent plant was put in operation. Of the previous attempts at incandescent lamps the most promising was one describes] in 1S15 in a British patent to an American named Starr, who died when only 25 years old. In ISs5 or 1SS6 occurred the first use of a transformer (q.v., also see below I. Notable developments of more re cent years have supplying both arc and in candescent lights from the same dynamo and wire system, using the inclosed are lamp. and the employment of rotary converters to change alternating to direct currents. or the reverse. These various improvements, give great flexibility to the generation, distribution, and use of electric current for light or power, so that almost any local condition may be met with ease.