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Encyclopedia > Lamppost
A roadway light in front of a red sky at night
A roadway light in front of a red sky at night

A street light or street lamp, also known as a light standard or lamp standard, 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 dusk and off at sunrise, or activate automatically in dark weather. It is also not uncommon for street lights to be on posts which have wires strung between them (telephone poles or electrical poles). Download high resolution version (1600x1200, 397 KB)streetlight during the evening in front of a bright orange horizont Source: Image*After This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... Download high resolution version (1600x1200, 397 KB)streetlight during the evening in front of a bright orange horizont Source: Image*After This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... A typical rural county road in Indiana, USA, where traffic drives on the right. ... Composite satellite image showing the progress of a hurricane weather system approaching the East Coast of the United States Weather comprises all the various phenomena that occur in the atmosphere of a planet. ... A telegraph post, telegraph pole or telephone pole is a post or pole upon which telephone network equipment is situated. ...

Contents


History of street lighting

Today, street lighting is most commonly achieved using high-intensity discharge lamps, often sodium vapor lamps. Such lamps provide the greatest amount of illumination for the least consumption of electricity. High-intensity discharge (HID) lamps include the types of electrical lights: mercury vapor, metal halide, high-pressure sodium and less common, xenon short-arc lamps. ... A sodium vapor lamp is a gas discharge lamp which uses sodium in an excited state to produce light. ...


Before the advent of high-intensity discharge lamps, street light circuits used incandescent 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 (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. An incandescent light bulb and its glowing filament. ... Left: Series / Right: Parallel Arrows indicate direction of current flow. ... Open circuit can mean:- In electronics, where there is nothing connected to a load and no current can flow. ... In electricity, current refers to electric current, which is the flow of electric charge. ... Ohms law, named after its discoverer Georg Ohm [1], states that the potential difference or Voltage drop V between the ends of a conductor and the current I flowing through the conductor are proportional at a given temperature: The equation yields the proportionality constant R, which is the electrical... Section of a string of Christmas lights Christmas lights (also sometimes called fairy lights or twinkle lights) are strands of electric lights used to decorate homes and Christmas trees during the holiday season. ... A rare Dresden porcelain figurine Porcelain is a type of hard ceramic material fired at a higher temperature than that used to fire glazed earthenware and stoneware pottery. ...


And 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. Gas lighting is the process of burning piped natural gas or coal gas for illumination. ... A lamplighter, historically, was an employee of a town who lit gas streetlights, generally by means of a wick on a long pole. ...


Desirability of street lights

Many residents favor street lights in their neighborhood and around town because they believe it makes it easier to navigate at night, and their proponents claim they also help reduce crime. A variety of studies have supported this view but at least one indicated that it had little or no effect.


Disadvantages

The major criticisms of street lighting are that it can actually cause accidents if misused, and can cause light pollution. This composite satellite photograph of the earth at night demonstrates how much of the worlds light is projected into space, rather than on its intended target. ...


Dangers of street lights

There are two optical phenomena that need to be recognized when considering installing a street light.

  • The loss of night vision because of the accommodation reflex of the driver's eyes is the greatest danger. As he emerges from an unlighted area into a pool of light from a street light, his pupil quickly constricts to adjust to the brighter light, but as he leaves the pool of light, the pupil's dilation to adjust to the dimmer light is much slower, so the driver is speeding down the road with impared vision. As a person get older, the eye's recovery speed gets slower so his driving time and distance under impaired vision also increases.
  • Oncoming headlights are more visible to a driver if they are against a black background than a grey one. The contrast creates a greater awareness of the oncoming vehicle.

Night-vision is seeing in the dark. ... Human eye The Accommodation Reflex is a reflex action of the eye, in response to focusing on a near object, then looking at distant object (and vice versa). ... The human eye The pupil is the central transparent area (showing as black). ...

Light pollution

In urban areas light pollution can hide the stars and interfere with astronomy. In settings near astronomical telescopes and observatories, low pressure sodium lamps may be used. These lamps are advantageous over other lamps such as mercury and halogen lamps because low pressure sodium lamps emit lower intensity, monochromatic light. Observatories can filter the sodium wavelength out of their observations and virtually eliminate the interference from nearby urban lighting. This composite satellite photograph of the earth at night demonstrates how much of the worlds light is projected into space, rather than on its intended target. ... Astrometry: the study of the position of objects in the sky and their changes of position. ... 50 cm refracting telescope at Nice Observatory. ... Observatory of Strasbourg An observatory is a location used for observing terrestrial and/or celestial events. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ... General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery white Atomic mass 200. ... The halogens are a chemical series. ... Something which is monochromatic has a single color. ... The wavelength is the distance between repeating units of a wave pattern. ...


The light pollution also disrupts the natural growing cycle of plants.


Safety

A common misconception is that merely installing street lights will automatically make streets safer and lower crime, so political pressure can be a major factor in installation of street lights. Untrained officials often innocently assume that if some is good, more must be better, and so install the brightest lights they can. But misuse of street lights can cause accidents, and crime lighting is an entirely different type of lighting than used for automobile navigation.


Purposes of street lights

Decorative omnidirectional beacon lights on a standard. Beacon lights can also be on an arm with a downward reflector.
Decorative omnidirectional beacon lights on a standard. Beacon lights can also be on an arm with a downward reflector.

There are three distinct main uses of street lights, each requiring different types of lights and placement. Incorrect misuse of the different types of lights can make the situation worse by compromising visibility or safety. Download high resolution version (426x640, 93 KB)Sreet lights (waterfront, San Francisco) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Download high resolution version (426x640, 93 KB)Sreet lights (waterfront, San Francisco) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...


Beacon lights

A modest steady light at the intersection of two roads is an aid to navigation because it helps a driver see the location of a side road as he comes closer to it and he can adjust his braking and know exactly where to turn if he intends to leave the main road or see if someone is at the intersection. A beacon light's function is to say "here I am" and even a dim light provides enough contrast against the dark night to serve the purpose. To prevent the dangers caused by a car driving through a pool of light, a beacon light must never shine onto the main road, and not brightly onto the side road. In residential areas, this is usually the only appropriate lighting, and it has the bonus side effect of providing spill lighting onto any sidewalk there for the benefit of pedestrians.


Roadway lights

Street lights are not normally intended to light up the driving route (Rationale being headlights are preferred for that), but to disclose signs and hazards outside of the headlights' normal view. Because of the dangers discussed above, roadway lights are properly used only sparingly and only when a particular situation justifies increasing the risk. This usually involves an intersection with several turning movements and much signage — situations where the driver must take in much information quickly that is not within the beam of his headlights. In situations like that (A freeway junction or exit ramp) the intersection may receive lighting so that the driver can quickly see all the hazards, and in a well-designed plan there will be gradually increasing lighting for a quarter-minute or so both before the intersection and gradually decreasing lighting after it. The main stretches of a highway remain unlighted to preserve the driver's night vision and increase the visibility of oncoming headlights. If there is a sharp curve where the headlights will not illuminate the road ahead, a roadway light on the outside of the curve is often justified. A headlight or headlamp is a light, usually attached to the front of a vehicle such as a car, with the purpose of illuminating the road ahead during periods of low visibility, such as night or precipitation. ...


If it is desired to truly light a roadway, perhaps because it carries heavy volumes of fast multilane traffic, then to avoid the dangers caused by casual placement of street lights, it should not be lit intermittantly, as this requires repeated eye reajustment which implies eyestrain and temporary blindness when entering and leaving light pools. In this case the system is instead designed to eliminate the need for headlights. This is usually achieved with bright lights placed on high poles at close regular intervals so that there is a consistent light level all along the route. The lighting goes from curb to curb.


Security lighting

A sodium vapor light. This type is often used as crime lighting.
Enlarge
A sodium vapor light. This type is often used as crime lighting.

Crime, or security, lighting is similar to high-intensity lighting on a busy major street, with no pools of light and dark, but with the lighted area extending onto peoples property, at least to their front door. This requires a different type of fixture and lens. The increased glare experienced by drivers going through the area might be considered a trade-off for the increased security being sought. This is what would normally be used along sidewalks in dense areas of major cities. Often unappreciated is that the light from a full moon is actually brighter than even most crime lighting. It has been suggested that this article or section be merged with Lighting. ... File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...


See also

The use of street lighting was first recorded in London in 1417 when Sir Henry Barton, the mayor, ordered lanterns with lights to be hanged out on the winter evenings between Hallowtide and Candlemasse. ... The following is a list of some of the most common streetlighting fixtures. ...

External links

  • Home Office Research Study 251 (PDF)
  • The influence of street lighting on crime and fear of crime (PDF)
  • Gaslight Lamp in Berlin (Germany)

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