Electric Light

The source of light has always been important to humans. In addition, the convenience of producing light simply by flicking on a switch proved to be one of the main benefits brought by the age of electricity. By the early 1800's electric batteries had become readily available. As a result many more scientists and inventors began to study the effects of electricity. Of particular interest was the fact that a strong electrical current could make a wire glow red hot, or even white-hot. Meaning it was possible to create light from electricity. However, using a strong current meant that the batteries would quickly run down. A thin wire needed less current to make it glow brightly, but the wire tended to burn out quite quickly. So many years pass before the incandescent or glowing, electric became economically feasible and practical.

An alternate way of producing light from electricity was to connect the supply of two carbon rods whose ends almost connected. A bright arc of light was created between the two rods, but again a high current was needed. By the 1850's electric arc, street lamps had appeared in many towns and cities. By this time powerful electricity generators had been developed, so the production of heavy current over a long period was no longer a problem. Nevertheless, the incandescent lamp was to prove more suitable for use in the home.

Suitable incandescent lamps were developed independently in 1879 by Thomas Edison (1847-1931)in the U.S. and in 1878 by Sir Joseph Swan (1828-1914) in England. Edison's, first, commercially produced lamps had a filament of carbonized paper, while Swans used carbonized cotton. In both cases, the filament was encased in a glass bulb in which most of the air had been removed. With little oxygen in the bulb, the filament could glow brightly for many hours without burning out. But in 1880, Edison and Swan teamed up to produce the world's first "practical" light bulb.

The modern incandescent electric light bulb has a filament of fine coiled tungsten wire. In an evacuated bulb, atoms of the filament would gradually break away and form a coating on the glass. To reduce this effect the bulb is filled with a mixture of argon and nitrogen gases. As in the early-evacuated bulbs, the absence of oxygen prevents the thin filament from burning out quickly.

Most domestic lamps are designed to last approximately 1000 hours. Their life can be extended by making them run at a lower temperature, but this would make the light a reddish color. Also, a larger proportion of the electricity consumed would be converted into heat instead of light. As it is, a modern incandescent lamp converts only approximately 10% of the electricity into light. So it is not considered worthwhile to further reduce efficiency in order to extend its life.

Some incandescent lamps used for photography operate at an extremely high temperature. They are much more efficient than ordinary lamps and produce an intense white light. However, the high operating temperature of the photography lamps restricts the life to only about one or two hours.

Vapor lamps such as fluorescent tubes have greater efficiency, but also are more expense to manufacture. However, they have a longer life than most incandescent lamps and are widely used in stores, offices, and street lighting.