Lighting, articifial illumination. Lighting is used indoors and out for both useful and decorative purposes. Lighting illuminates areas used for work, study, and recreation; roads and streets; and airports. It is used for advertising signs and displays and to achieve dramatic effects as in the theater.
Proper lighting in the home, store, office, salesroom, or shop prevents eye-strain and helps reduce accidents. The chief requirements for proper lighting are sufficient light, proper placement of fixtures to prevent shadows, and elimination of both direct and reflected glare. Glare makes seeing difficult and occurs when some areas are much brighter or darker than others.
The amount of lighting needed in a room depends on the room's use. Stronger light is needed for study and close work than for conversation or watching television. Lighting engineers calculate the level of lighting in units called lumens. As an example, for areas designed for writing and studying, they recommend around 70 lumens per square foot (753 lumens per square meter), whereas for general lighting less than one-half that amount is needed. (A 100-watt incandescent bulb provides approximately 1,700 lumens; a 30-watt fluorescent tube, up to 1,800 lumens.) For rooms where detailed work (such as drafting) is done, lighting engineers recommend up to 200 lumens per square foot (2,153 lumens per square meter).
To help avoid glare, engineers recommend room walls with a light, dull finish. In general, ceilings should reflect 75 per cent of the light they receive; upper walls, more than 50 per cent; and lower walls, more than 33 per cent.
Floodlights are used to illuminate large areas such as railway yards, parking lots, recreation areas, and sports stadiums. The lights are generally mounted on tall poles spaced to provide uniform illumination and to avoid shadows.
Mercury-vapor, sodium-vapor, or fluorescent lamps are used for most street lighting. These lamps consume less electrical power than incandescent lamps to produce the same amount of light. Vapor lamps are very effective in fog; fluorescent lamps produce little glare.
Ample lighting of intersections, expressway exits and entrances, underpasses, and heavily traveled streets greatly reduces traffic accidents at night and adequate lighting of streets and other public places is a strong deterrent to nighttime crime.
Advertising displays often make dramatic use of lighting, sometimes combining incandescent and electric discharge lamps of various colors. Some buildings, statues, and sculptures are decoratively illuminated for nighttime viewing.
For thousands of years, lighting was limited to campfires, which served also to provide heat. The first torches were burning sticks snatched from the fire for use as weapons against wild beasts. Crude oil-burning lamps carved from stone and fitted with wicks were used as early as 3000 B.C. Many refinements were later added by the Greeks and Romans.
Candles, introduced about 1150 A.D., and oil lamps were the chief means of lighting until the 1860's, by which time gas lamps had come into general use. Electric lighting came into widespread use during the last two decades of the 19th century.