Lighting

Lighting provides safety in a number of places. At home and at work, good lighting helps us see things clearly and avoid accidents. Street lights and automobile lights help us travel safely. Signal lights guide motorists, airplane pilots, railroad engineers, and ship captains.

Companies and stores use lighted signs to identify themselves and to advertise their products. In addition, lighting adds beauty to homes and other buildings and to parks.

Good lighting helps the eyes work easily. Reading or working in poor light cannot damage the eyes. But it may cause fatigue or eyestrain and lead to dizziness, headaches, or sleepiness.

In the home, electric lamps and lighting fixtures provide light and safety for people walking from room to room or up and down stairs. Every room and passageway needs at least some general lighting so that things can be seen clearly enough to avoid accidents. Each area should have a light that can be turned on before entering.

Many activities require extra lighting in addition to general lighting. Bathrooms, for example, have special lighting that people use when putting on makeup or shaving. Bedrooms and living rooms have additional lighting for such activities as reading, studying, and sewing.

Interior designers use lighting to create various moods and to bring out the colors of walls and fabrics in a home. Incandescent lamps and warm white fluorescent lamps emphasize reds, yellows, and oranges (see Electric Light; Fluorescent Lamp). Cool white fluorescent lamps bring out blues and greens. Many people arrange spotlights or tinted lights to create interesting shadows. Others do so to draw attention to such objects as pictures or vases.

In offices, stores, and factories, proper lighting helps employees work efficiently and avoid costly accidents. Good lighting also provides a cheery atmosphere and reduces fatigue caused by eyestrain. In retail stores, proper lighting may help attract customers or bring out the best colors in merchandise.

Most offices and stores provide a large amount of general illumination, with additional lighting for such detailed jobs as repairing watches or making maps. Many factory jobs require more difficult eye work than do office jobs. Thus, factories need good lighting for safe, efficient work. The Illuminating Engineering Society (IES), a professional association of lighting engineers, recommends lighting standards for various types of industrial work. Some manufacturers, after improving their lighting to meet IES standards, found that their production increased more than 15 per cent. They also reported that employee accidents decreased by 50 per cent.

Improvement of lighting can also improve the quality of a company's products because employees may avoid errors that they otherwise might have made. One manufacturer reported that his customers rejected 50 per cent fewer of his firm's products after he improved the lighting in his plant.

On streets and highways, lighting helps people travel safely. Several cities have reduced night traffic accidents by improving their street lighting. Night accidents in some cities dropped as much as 50 per cent after street lighting was improved. Freeway lights can reduce traffic deaths and injuries on these highways as much as 50 per cent. Street lighting also helps to provide safety by discouraging criminals.

Decorative lights on buildings may reduce the necessity for street lighting. In some cities, lighting designers plan light so that it accents the architecture as it illuminates the streets and sidewalks.

For outdoor events. Floodlights illuminate baseball and football fields, golf courses, race tracks, swimming pools, tennis courts, and many other facilities for sports competition at night. Some sports, such as golf and swimming, require relatively little light. Others, including baseball and football, need much more light because they use larger fields and attract larger crowds. Additional lighting is required to televise outdoor events.

Outdoor lighting also allows such events as county or state fairs and open-air theater performances to be held at night. Country clubs, resorts, and homes use decorative lighting for night parties held outdoors.

Quantity of light needed for various activities depends on four factors: (1) the size of the things we are looking at, (2) the length of time we have to look at them, (3) the contrast between them and their background, and (4) our own seeing abilities. A watchmaker, who usually works with tiny parts, requires more light than a plumber, who connects large pipes. A person needs more light to read a road sign while speeding past in a car than while walking by. A tailor needs more light to sew black thread on black cloth than to sew white thread on black cloth. Older people generally need more light than young people to perform the same seeing tasks.

In the home, most people do not provide for the wide variety in the amount of light required for different activities. For example, a woman may use the same light for reading a newspaper and for hemming a black skirt with black thread. But her eyes need almost seven times as much light for this job as for reading.

Engineers use either the foot-candle or the lux to measure the amount of light that falls on a surface. The foot-candle is a unit in the customary system of measurement, and the lux is a metric unit. A sensitive instrument called a light meter records how much light a surface receives at that point. See Foot-Candle; Light Meter; Light.

Three factors determine how much light reaches any object: (1) the intensity (strength) of the light, (2) the distance of the object from the light source, and (3) the light distribution.

Intensity. Scientists measure the intensity of light coming from any source in units called lumens. Until 1971, lamps (bulbs) were marked only with their number of watts. Watts tell the amount of electricity used by a lamp, not how much light it produces. For example, two 50-watt lamps supply fewer lumens than one 100-watt lamp. A 100-watt lamp may provide only a fourth as many lumens as a 100-watt fluorescent tube. In 1971, the United States Federal Trade Commission (FTC) issued a ruling requiring that lamp cartons be marked with both lumens and watts.

Distance. According to a principle known as the inverse square law, the amount of light an object receives depends on its distance from the source. An object placed 2 feet from a lamp receives only a fourth as much light as when it is placed 1 foot from the lamp.

Distribution. Dark colors absorb light, and so dark carpets, ceilings, curtains, furniture, or walls may limit the amount of light in rooms. But pale-colored walls and furnishings reflect light back into a room.

A lamp shade distributes the light from a bare bulb and shields the bulb from direct view. The shade directs light downward toward the seeing task and upward to help light the room. Opaque shades send all the light up and down, but translucent shades transmit some light to the room. Colored shades tend to color the light. For this reason, shades with white or near white linings should be used.

Efficient use of lighting can conserve energy. Different types of lighting can provide different amounts of light while using the same amount of energy. For example, incandescent lamps provide about 20 lumens per watt, while fluorescent lamps provide 70 lumens per watt.

Engineers and scientists are continually looking for ways to improve the efficiency of lamps. They have developed vapor lamps with improved efficiencies over incandescent lamps. For example, mercury vapor lamps provide 50 lumens per watt, metal halide lamps provide 90 lumens per watt, and high pressure sodium lamps provide 110 lumens per watt. Vapor lamps also last longer than incandescent lamps. Scientists are also producing improved, more compact fluorescent lamps.

Lighting problems may occur even if enough light has been provided for an activity. For example, a bright light that shines, or is reflected, directly into the eyes causes glare, which can cause discomfort. Severe glare, such as that caused by the headlights of some cars, may be temporarily blinding. Lamps and fixtures that diffuse (scatter) the light tend to produce more comfortable illumination. Indirect lighting, in which all the light from the source is reflected from ceilings and walls, produces completely glare-free and comfortable lighting.

An unshaded clear glass bulb gives off harsh, undiffused, glaring light. Lamps with frosted, or white, bulbs and tubes give some diffusion, but still should be shielded or positioned so they do not shine directly in a person's field of vision. A globe or diffusion bowl can be used to conceal the bulb and help scatter and soften the light.

Even if a light source does not cause glare directly, other surfaces, such as glossy finishes on walls, furniture, and paper, may produce reflected glare. Sharp color contrasts on work surfaces, such as white paper on a dark blotter, may also cause discomfort. At first, the color contrast helps the eyes see the objects. However, in time the color contrast strains the eyes, which must refocus each time they move from a light surface to a dark surface.

Sharp contrasts in the brightness of lighting can also cause eyestrain. For this reason, a person should not watch television in a completely dark room or study by the light of a single intense lamp. To avoid harsh contrasts, the eyes need general lighting in addition to the light from the television screen or the lamp.

Portable lamps give homes soft general lighting, and extra lighting for such activities as sewing or studying. The Better Light Better Sight Bureau (BLBS), a nonprofit educational organization, sets minimum standards for performance, quality, and safety of study lamps. The organization provides BLBS tags, which the manufacturer attaches to approved lamps.

In homes and small offices, lighting designers may conceal fluorescent tubes behind faceboards mounted at the edges of the walls or ceiling. Such structural lighting provides soft indirect light and draws attention to the walls and draperies. Structural lighting on two opposite walls of a square room makes the lighted walls seem farther apart than the unlighted ones. When mounted on a low ceiling, structural lights give the illusion of greater height in the room.

Most factories, large offices, schools, and stores use fluorescent or vapor fixtures for general lighting. Fluorescent lights produce as much as three times, and vapor lamps produce up to six times, the light per watt of electricity as do incandescent lamps. Thus, for the same amount of light, fluorescent or vapor lamps cost less to burn. They also produce less heat. However, lighting engineers sometimes prefer incandescent lamps because of their compact size, flexibility of use, or their more familiar warm color. Many stores use a combination of fluorescent or vapor fixtures for general lighting and incandescent lamps for decorative and accent lighting.

Contributor: William Hand Allen, M.S., Former Electrical Engineer, Rockwell International.

Related articles include:

Candela; Electric Light; Fluorescent Lamp; Light.

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