CHAPTER XIX
MINIATURE LIGHTING
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
6 volts. 2 candle-power
6 volts. 4 candle-power
6 volts. 6 candle-power
6 volts. 8-10-12-16-20-24 candle-power
[Illustration: Fig. 282.—Miniature Tungsten Battery Lamp.]
To find the approximate amount of current drawn from a battery by a tungsten lamp, divide the candle-power by the voltage and the result will be the current in amperes. For example, a 6 v. 2 c. p. lamp will require, 2 divided by 6, or one-third of an ampere.
Six-volt tungsten lamp giving a light greater than six candle-power are only used on storage batteries and are employed principally for automobile lighting.
The filament of a tungsten lamp is much longer than that of a carbon lamp and is usually in the form of a spiral or helix, as shown in Figure 282.
The bases of battery lamps, the base being the lower portion of the lamp, which is made of brass and fits into a socket or receptacle, are made in three different styles: _miniature_, _candelabra_, and _Ediswan_.
[Illustration: Fig. 283.—Lamps fitted respectively with Miniature, Candelabra, and Ediswan Bases.]
The miniature and candelabra bases have a threaded brass shell on the outside and a small brass contact-button on the bottom. They are similar except in respect to size. The miniature base is smaller than the candelabra. The Ediswan base is a plain brass shell having two pins on the side and two contacts on the bottom. This type of base is only used in this country on automobiles. The miniature and the candelabra bases are standard for battery lighting. The miniature base has many advantages over the candelabra for the young experimenter, and should be adopted in making any of the apparatus described in this chapter. These three bases are shown in Figure 283.
[Illustration: Fig. 284.—Miniature Flat-Base Porcelain Receptacle.]
In order to form a good electrical connection between the lamp and the power wires some sort of a receptacle or socket is necessary. The most common arrangement for this purpose is the miniature flat-base porcelain receptacle shown in Figure 284. This type of receptacle is used in places where it can be permanently fastened in position with two small screws.
[Illustration: Fig. 285.—Weather-proof and Pin-Sockets.]
The devices shown in Figure 285 are known respectively as a porcelain weather-proof socket and a pin-socket. Sockets similar to the weather-proof socket are also made of wood. The weather-proof sockets are used in places where the light is to be exposed out-of-doors, as for instance on a porch. The small metal parts are sealed in the porcelain and entirely protected.
The pin-sockets and the wooden sockets are used principally on Christmas trees or in decorative outfits where lamps are hung in festoons. The flat-base receptacle, the pin-socket, and also the wooden socket will be found very useful in making the apparatus described farther on in this chapter.
*The Wires* used to carry the current in a miniature lighting system may be of the sort known as _annunciator_ or _office_ wire if the wires are to be run entirely indoors. The wire should not be smaller than No. 16 B. & S. gauge. When the wires are run outdoors, on a porch, or in some other place exposed to the weather, the wire used should be rubber-covered. Hanging lights or lights intended to be adjustable should be connected with "flexible conductor." This is made of a number of very fine wires braided together and insulated with silk. The wires used in a lighting system should not in any case be longer than it is necessary to have them. When a battery is connected to a system of wires it is found that the voltage at the end of the wires is much lower than at a point near the battery. This is called voltage "drop," and is much greater as the wires grow longer. A light placed at the end of two very long wires will not burn as brightly as it would if connected to the same battery by means of short wires.
*Switches* can be made by following the suggestions given in