Street light
A street light or street lamp, also known as a light normal or lamp normal, is a raised light on the edge of a road, turned on or lit at a certain time every night. Modern lamps may also have light-sensitive photocells to turn them on at twilight and off at sunrise, or turn on automatically in dark weather. It is also not uncommon for street lights to be on posts which have wires strung between them.
History of street lighting
Today, street lighting is most usually achieved using high-intensity discharge lamps, often sodium vapor lamps. Such lamps supply the greatest amount of illumination for the least burning up of electricity.
Before the advent of high-intensity discharge lamps, street light circuits used radiant light bulbs. These were often operated as high-voltage series circuits. To avoid the problem of the entire street going dark if a single lamp burned out, each individual street-lamp was equipped with a film cutout; a small disk of insulating film that separated two contacts connected to the two wires leading to the lamp. If the lamp failed, the entire voltage of the street lighting circuit was imposed across the insulating film in the cutout, causing it to rupture. In this way, the failed lamp was bypassed and enlightenment restored to the rest of the street. The circuit usually contained an automatic device to regulate the electrical current flowing in the circuit, preventing the current from rising as additional lamps burned out and thus preserving the life of the remaining lamps. When the failed lamp was finally changed, a new piece of film was also installed, once again separating the electrical contacts in the cutout. This style of street lighting was identifiable by the large porcelain insulator that separated the lamp and reflector from the light's mounting arm; the insulator was necessary because the two contacts in the lamp's base may have routinely operated at a potential of several thousands of volts above ground/earth.
And before shining lamps, gas lighting was employed. The earliest lamps required that a lamplighter tour the town at dusk, lighting each of the lamps, but later designs employed ignition devices that would routinely strike the flame when the gas supply was activated.
History of street lighting
Today, street lighting is most usually achieved using high-intensity discharge lamps, often sodium vapor lamps. Such lamps supply the greatest amount of illumination for the least burning up of electricity.
Before the advent of high-intensity discharge lamps, street light circuits used radiant light bulbs. These were often operated as high-voltage series circuits. To avoid the problem of the entire street going dark if a single lamp burned out, each individual street-lamp was equipped with a film cutout; a small disk of insulating film that separated two contacts connected to the two wires leading to the lamp. If the lamp failed, the entire voltage of the street lighting circuit was imposed across the insulating film in the cutout, causing it to rupture. In this way, the failed lamp was bypassed and enlightenment restored to the rest of the street. The circuit usually contained an automatic device to regulate the electrical current flowing in the circuit, preventing the current from rising as additional lamps burned out and thus preserving the life of the remaining lamps. When the failed lamp was finally changed, a new piece of film was also installed, once again separating the electrical contacts in the cutout. This style of street lighting was identifiable by the large porcelain insulator that separated the lamp and reflector from the light's mounting arm; the insulator was necessary because the two contacts in the lamp's base may have routinely operated at a potential of several thousands of volts above ground/earth.
And before shining lamps, gas lighting was employed. The earliest lamps required that a lamplighter tour the town at dusk, lighting each of the lamps, but later designs employed ignition devices that would routinely strike the flame when the gas supply was activated.
posted by Best-Mature at 1:02 AM
0 Comments:
Post a Comment
<< Home