The most common form of electric lighting at the present time is the incandescent lamp. It consists of a slender filament of some highly resisting material prepared from carbonized paper or bamboo and enclosed in a glass bulb. The ends of the filament are connected to platinum or lead wires fused in the glass. One of the wires is connected with the base of the socket, and the other with its rim. The intervening space is filled with white cement, which is a non-conductor. An attachment is placed on the socket by which the current enters and leaves the lamp. The air is exhausted from the bulb as completely as possible, and the exhaustion tube sealed off. When the electricity passes through the filament, it glows on account of the great resistance, but because of the lack of air does not burn. The glowing particles of the filament give off the illuminating rays. The way in which the light is distributed from the lamp depends upon the form in which the filament is bent.
When certain metals with a very high melting point, such as tungsten, osmium, etc., are made into fine wires or filaments, they possess remarkable endurance and a high degree of efficiency.