Electric Lights

87. Kinds of Electric Lamps in Use. The electric lamps on the market now are either tungsten (also called Mazda) or metallized carbon (called gem carbon) lamps. Of all lighting appliances, electric lamps and systems are most easily cared for. If properly selected, they make an excellent light from the standpoint of hygiene. It is important for every one to know enough about lighting to be able to select proper kinds and sizes of lamps.

88. Electrical Measurements. A volt is the unit of electric pressure which compares with the pound as the unit of water pressure.

An ampere is the unit of electricity flowing thru a wire which compares to the gallon as the unit of water per minute flowing thru a pipe.

A watt is the unit of electrical power. It is determined by multiplying the volts by the amperes.

A kilowatt equals 1000 watts.

A kilowatt hour equals 1000 watt-hours.

A watt-hour is the amount of energy needed by a device which uses one watt and is operated for one hour. For example, a 25-watt lamp uses 25 watts, and if it is operated one hour, it uses 25-watt hours of electricity.

The cost of burning an electric lamp is the number of watts marked on the lamp multiplied by the hours the lamp is burned, and then translated into kilowatt hours and multiplied by the price per kilowatt hour.

89. Carbon Lamps. Few carbon lamps are being made now, but they may still be obtained in some stores. The carbon lamp can be distinguished from Mazda lamps (Fig. 45) by the appearance of the filament. The carbon lamp gives about 0.40 candles of light per watt of electricity consumed. Carbon lamps burn, making a yellow or reddish light, and consume fully twice as much current as Mazda lamps of the same candle power.

90. Mazda or Tungsten Lamps. Tungsten lamps are the ones in common use. They give 0.80 to 1.00 candle of light to one watt of electricity used. They have a filament of tungsten and may now be used in any position. Less electricity is required to bring tungsten to a glowing white heat than other materials used in lamps.

To compare the brightness of two lamps, do not look at the filament, but hold pieces of white material like paper at an equal distance from each lamp and compare the brightness of the surfaces; or put an opaque object in front of the light and let a shadow be cast on another object. The brighter light will cast a heavier shadow.

When substituting a new tungsten lamp for a carbon lamp, select one about one-half the number of watts, unless more light is wanted. In houses, it is a common practice to substitute a 40-watt Mazda for a 50-watt gem carbon lamp, thus saving ten watts per hour and getting more light.

91. Selecting Lamps for a Room. There are so many possibilities for the use of electricity in lighting a house, that it becomes a fine art. When buying lights for a room, consider (1) the size of the room, (2) the use of the room, and (3) the color of walls, floors, ceilings, furnishings and decorations. For lighting purposes, lamps may be obtained ranging from 10 or less to more than 100-candle power.

There are colored, transparent and frosted globes. There are reflectors and shades of various colors and patterns. To obtain the same degree of illumination, smaller lamps are needed in small rooms than in large ones.

92. Effect of Color Schemes Upon Illumination. The color of the walls and furnishings makes a difference in the candle power required to give a certain amount of light. Those colors which absorb the most light require the higher candle power, and those reflecting the highest per cent of light require the lower candle power.

The frosted globes absorb some light, they diffuse the rest of it. They dispense with the annoyance of glare from lamps, and are useful in places where the full intensity of the lamps is not required.

The light absorbed by different colors varies considerably, as shown by the accompanying table:

TABLE SHOWING ABSORPTION OF LIGHT

93. Distribution of Light. Light in rooms for general use should be distributed as evenly as possible thruout the entire room. Avoid excessive contrasts of brightness and darkness. Have the lamps shaded to diffuse the light so that no one need look directly at the filament. When working by a light, do not put the lamp very close to the material, as this produces too strong contrasts of light and dark, or, when reading, it produces too much reflection from the white parts of the paper, which is trying on the eyes.

Direct lighting means that the rays from the lamp go directly into the room (Fig. 45). Indirect lighting means that the rays are all directed toward a reflecting surface such as the ceiling (Fig. 46). From here they are reflected, giving an even amount of light to other parts of the room. When directed toward the ceiling, they make it the brightest part of the room.

A semi-indirect light avoids this difficulty (Fig. 47).

In diffused lighting, the lamp is covered, as by frosting, so that the rays of light are broken up and so scattered that no direct ray shines into the eyes, and there is no bright spot of light in the room.

When costs must be limited, certain decorative effects must be weighed for their value, some being more expensive than others.

City lighting plants can provide current for any number of lamps in a house if it is properly wired. If more lamps are attached than the wiring will carry, and all are turned on, the fuses will burn out.

Electric plants for private homes (see Sec. 271) usually furnish current of a different voltage from city electric plants, so special equipment and lamps must be used with small plants.

Inquire of the company who installed the wiring or electric system, how many lights and other devices can be attached and for what voltage they should be made.