Lighting is a term that generally refers to artificial light—in most cases, electric light. We use artificial light both indoors and outdoors instead of—and in addition to—natural light from the sun. With lighting, we can use windowless areas of homes, hospitals, offices, schools, stores, and other buildings 24 hours a day. Lighting also enables us to use outdoor sports areas, such as baseball and football fields and tennis courts, at night.
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.
Vision depends on light, and 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.
How we use lighting
We use artificial lighting in four chief types of locations: (1) in the home; (2) in offices, stores, and factories; (3) on streets and highways; and (4) at outdoor events. Regardless of where lighting is used, people depend on it for general seeing and safety, for specific activities, and for decoration.
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 ). Cool white fluorescent lamps bring out blues and greens. Many people arrange spotlights or tinted lights to create interesting shadows. Others use accent lights 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 comfortable atmosphere and reduces fatigue caused by eyestrain. In retail stores, proper lighting may help attract customers or make merchandise look appealing.
Most offices and stores provide general illumination, with additional task lighting for such detailed jobs as repairing watches or making maps. Many factory jobs require more demanding eye work than do office jobs. Thus, factories require proper levels of lighting for safe, efficient work. In many countries, a professional association of lighting engineers, such as the Illuminating Engineering Society of North America, the Indian Society of Lighting Engineers, or the Institution of Lighting Engineers in the United Kingdom, recommends lighting standards for various types of work. Proper lighting in an office provides a comfortable level of general illumination without creating glare on computer screens. Good lighting design can improve the quality and quantity of a company’s work because employees may avoid errors that they otherwise might have made.
On streets and highways,
lighting helps people travel safely. Several cities have reduced night traffic accidents by improving their street lighting, some by as much as 50 percent. Freeway lights can reduce traffic deaths and injuries on these highways by a similar percentage. Street lighting also helps to provide safety and security 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 tennis 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.
What is good lighting
Good lighting allows the eyes to function comfortably and efficiently. The eyes need different amounts and types of light for different activities. As a result, lighting that may be suitable for some activities may be inadequate for others.
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 inch-pound 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 .
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. Watts tell the amount of electric power used by a lamp, not how much light it produces. For example, a 100-watt lamp may provide only a fourth as many lumens as a 100-watt fluorescent tube. Lamps (bulbs) sold in many countries are labeled with both watts and lumens.
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, most shades have white or near-white linings.
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 10 to 20 lumens per watt, whereas compact fluorescent lamps provide about 40 to 70 lumens per watt. A compact fluorescent lamp can be used to replace an incandescent lamp, and it fits into the same lamp socket. In addition, a compact fluorescent lamp usually lasts several times longer than a standard incandescent bulb.
Engineers and scientists are continually looking for ways to improve the efficiency of lamps. They have developed many types of lamps that are more efficient than incandescent lamps. High pressure sodium lamps, for example, often used in outdoor settings, can provide more than 100 lumens per watt. Light-emitting diodes (LED’s) can provide 50 to 100 lumens per watt. These devices, which are built much like computer chips, can be used in practically any application or setting. Both high pressure sodium lamps and LED’s also last much longer than incandescent 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.
Lighting devices
Many people use combinations of fluorescent and incandescent fixtures and portable lamps for attractive home lighting. Incandescent and fluorescent fixtures may be mounted on a wall or ceiling, recessed above the ceiling, or suspended from the ceiling. Suspended fixtures provide good general lighting for high-ceilinged halls or stairways. Recessed fixtures above sinks or other work areas furnish good lighting for various activities. Portable lamps give homes soft general lighting and provide extra lighting for such activities as sewing or studying. Ceiling-mounted track lights can be positioned to highlight special areas.
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.
Incandescent lamps are not typically used as a primary source of light in factories, offices, schools, and stores because they require a great deal of energy and produce much heat. However, lighting engineers sometimes prefer incandescent over fluorescent lamps because of their compact size, their flexibility of use, or their more familiar warm color. Many stores use incandescent lamps for decorative and accent lighting. In the 2010’s, expensive but versatile LED’s began widely replacing other light sources.
