Safety Beacons/ Lights

A street light, street lamp, light standard or lamp standard, is a raised source of light on the edge of a road, turned on or lit at a certain time every night. more...

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Modern lamps may also have light-sensitive photocells to turn them on at dusk and off at dawn, or activate automatically in dark weather. It is also not uncommon for street lights to be on posts which have wires strung between them, such as on telephone poles or utility poles.

History of street lighting

Further information: History of street lighting in the United States

Before incandescent 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 automatically strike the flame when the gas supply was activated.

The first electric street lighting employed arc lamps, initially the 'Electric candle', 'Jablochoff candle' or 'Yablochkov candle' developed by the Russian Pavel Yablochkov in 1875. This was a carbon arc lamp employing alternating current, which ensured that the electrodes burnt down at the same rate. Yablochkov candles were first used to light the Grand Magasins de Louvre, Paris where 80 were deployed. Soon after, experimental arrays of arc lamps were used to light Holborn Viaduct and the Thames Embankment in London - the first electric street lighting in Britain. More than 4,000 were in use by 1881, though by then an improved differential arc lamp had been developed by Friederich von Hefner‑Alteneck of Siemens & Halske. The United States was swift in adopting arc lighting, and by 1890 over 130,000 were in operation in the US, commonly installed in exceptionally tall moonlight towers.

Ultimately, however, arc lights suffered from two major disadvantages. Firstly they emitted an extremely intense and harsh light which, although useful at industrial sites like dockyards, was discomforting in the context of ordinary city streets. Second, they required a high level of maintenance, as the carbon electrodes burned away quite swiftly. With the development of cheap, reliable - and bright - incandescent light bulbs in the closing years of the 19th century, they swiftly passed out of use for street lighting, though they were retained in industrial use for rather longer.

Incandescent lamps, continued to be used for street lighting until the advent of high-intensity discharge lamps, 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 (an open circuit), the current through the string became zero, causing the entire voltage of the street lighting circuit (thousands of volts) to be imposed across the insulating film in the cutout, rupturing it (see Ohm's law). In this way, the failed lamp was bypassed and illumination restored to the rest of the street. (This is the same principle used in Christmas tree lights.) 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 recognizable 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.

Read more at Wikipedia.org