The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
Practical Electricity And House Wiring
Dictionary Of Common Devices
Lamps.—The electric lamp bulb is probably the most commonly known electrical device; it is a simple contrivance. The main part of any lamp is its filament, which consists of a coil of wire made of the metal, tungsten, which experiment has shown can be heated to an exceedingly high temperature without melting. The lamp is so designed that when electricity flows through this wire or filament, it raises its temperature to nearly 5,000° F.; the heat causes light. If the filament were heated in open air, its life would be extremely short, so the filament is enclosed in a glass bulb from which all air has been removed and a chemically inert gas like argon or nitrogen introduced in place of it. Leads from the two ends of the filament are brought out of the bottom of the bulb, and could be connected directly to the wires of the house wiring system, but for convenience in replacement, they are connected to a base which is cemented to the bulb. The glass part is the bulb; the complete device is a "lamp."
The ordinary household variety of lamp gives about 1,000 hours of useful life. From 7% to 11% of the electricity used is converted into light; the remainder is wasted as heat. Nevertheless, even where electric power is relatively expensive, the electric lamp is by long odds the cheapest form of light known, in terms of cost per candlepower-hour. It is significant that today's lamps are twice as efficient, convert twice as much of the electricity consumed into light, as the best lamps in existence thirty years ago. At the expense of much shorter life, the efficiency of lamps can be greatly increased, and today's lamps represent the lowest over-all cost, considering both the cost of the lamp and the cost of the electric power to operate it (a 60-watt lamp today costs 11c, during 1,000 hours of life consumes 60 kilowatt-hours
of power costing from $1.20 to $3.00). It would not be difficult to manufacture lamps which would convert 25% of the power used into light, but their life would be hopelessly short.
Lest these figures cause any apprehension regarding the efficiency of other electrical devices and machines, let it be stated that most other devices are nearer 90% to 99 % efficient; that is, only 1% to 10% of the power used is not productive of the purpose intended.
Sockets.—Any device (with usually, but not always a threaded lamp-holding shell) into which a lamp can be quickly inserted, is known as a socket. Figs. 6 and 7 show a picture and a cross-section of a variety of socket known as a "cleat receptacle." It consists of a porcelain or bakelite insulating block, a threaded screw-shell of metal, a center metal contact (of course carefully insulated from the screwshell) and two terminals for later attachment of wires.
