Miniature lighting is a field of many interesting possibilities for the young experimenter. Any labor expended along this line will result in something far more useful from a practical standpoint than almost any of the other things described in this book. Miniature lights, operated from batteries, may be used in various ways; to light dark corners, hallways, or other places where a light is often temporarily wanted without the accompanying danger and nuisance of matches or kerosene lamps. Miniature lighting has only been made practical by the tungsten filament lamp. The filament, or wire inside the globe, which becomes hot and emits the light when the current is turned on, is made of _tungsten_ in a tungsten lamp. In the earlier lamps, it was made of carbon. The carbon lamp is now seldom used and is highly inefficient when compared to the tungsten. *A Carbon Lamp* consumes about three and one-half watts of current for each candle-power of light, whereas a small tungsten lamp uses only about one watt per candle-power small tungsten lamp uses only about one watt per candle-power. The tungsten lamp is therefore three times as efficient as a carbon lamp, and when used on a battery of equal voltage it is possible to obtain the same amount of light with one-third of the current that would be required by a carbon lamp. [Illustration: Fig. 281.—Miniature Carbon Battery Lamp.] Carbon lamps similar to that shown in Figure 281 are made in a number of different voltages. The lowest voltage that it is practically possible to make a carbon lamp for is three and one-half. A three-and-one-half volt carbon lamp is designed to be operated on small dry cells such as flashlight batteries. The E. M. F. of a dry cell is about one and one-half volts, but when three small dry cells of the flashlight type are connected in series and used to operate a lamp, their voltage "drops," and the available E. M. F. is only about three and one-half volts. Four-volt carbon lamps are intended to be operated on large dry batteries or wet cells because they do not lose their voltage as quickly as small dry cells. The table below gives the voltage and candle-power of the various small carbon lamps which are carried in stock by most electrical dealers or supply houses: *MINIATURE CARBON BATTERY LAMPS* 3.5 volts for flashlight batteries 4 volts. 2 candle-power 5.5 volts for flashlight batteries 6 volts. 2 candle-power 6 volts. 4 candle-power 8 volts. 4 candle-power 10 volts. 6 candle-power *Tungsten Lamps* are made for voltages as low as one and one-half, and will light on one cell of dry battery. The range of voltages is quite wide and varied. A few of the most common sizes are given below: *MINIATURE TUNGSTEN BATTERY LAMPS* 1.5 volts. for one dry cell 2.5 volts. for two-cell flashlight battery 2.8 volts. for two-cell flashlight battery 3.5 volts. for three-cell flashlight battery 3.8 volts. for three-cell flashlight battery 4 volts. 4 candle-power