Six volt lamps of more than six candle-power are best operated on storage batteries because the current required is too great for dry cells to give efficient service in such a case. The tungsten lamps made for automobiles are ideal for miniature lighting plants operated by storage batteries. The list below shows some of the sizes on a current of six to eight volts. The bases are made of brass and come in four different styles, miniature, candelabra, single Ediswan and double Ediswan. The single and double Ediswan are used on automobiles because the construction of the base and the socket or the receptacle into which it fits is such that the lamp cannot jar loose. [Illustration: FIG. 155.—Miniature Sockets of the types known as "Flat Base Porcelain," "Pin" and "Weatherproof."] The candelabra base is probably the type best adapted to miniature lighting elsewhere than on an automobile. The letter "G" and the number in the first column indicates the size of the glass globe or bulb of the lamps. You can compute the approximate amount of current drawn from a battery by a tungsten lamp, by dividing the candle-power by the voltage. The result is the current in amperes. For example, a 6 volt, 12 candle-power lamp will consume 12 divided by 6, or 2 amperes. [Illustration: FIG. 156.—Connections for a 2.8 Volt Lamp.] Storage batteries are rated by their output in *ampere hours*. An ampere hour is the amount of current represented by one ampere flowing for one hour. A forty ampere hour cell will deliver one ampere for forty hours, 4 amperes for ten hours or 5 amperes for eight hours. The ampere hour capacity of a storage cell divided by the amount of current being used will determine how long that current can be drawn before recharging is necessary. The maximum amount of current it is safe to draw from a storage cell without impairing its life and efficiency is the maximum current which that cell can deliver continuously for eight hours. In order to determine this current simply divide the manufacturer’s rating of the battery in ampere hours by eight. The answer is the maximum current you should require from the battery if you wish to obtain good service from it. For example, the maximum safe discharge rate of a 40 ampere hour battery is 40 divided by 8 or 5 amperes. [Illustration: FIG. 157.—A Miniature Base Tungsten Filament Battery Lamp for small lighting.] The method of computing the current required by a lamp and the method for determining the maximum safe discharge rate of a battery will enable you to figure the size of the smallest battery it is desirable to use in a lighting plant.