A street light, is a lighting source on the edge of a roadway, walkway, street and other public area, which will be turned on during night and off at dawn. Some modern street lights also have light-sensitive photocells to turn the lights on at dusk, off at dawn. Street light usually have high pole to distribute lighting to large area.
History
The earliest street lights were used by Greek and Roman civilizations, where light primarily served the purpose of security, both to protect the wanderer from tripping over something on the path as well as keeping the potential robbers at bay. At that time oil street lights were used predominantly as they provided a long-lasting and moderate flame. The Romans had a word 'laternarius', which was a term for a slave responsible for lighting up the oil street lamps in front of their villas. This task continued to be kept for a special person as far as up to Middle Ages where the so-called 'link boys' escorted people from one place to another through the murky winding streets of medieval towns.
The first electric street lighting employed arc lamps, initially the 'Electric candle', 'Jablotchkoff candle' or 'Yablochkov candle' developed by the Russian Pavel Yablochkov in 1875. This was a carbon arc lamp employing alternating current, which ensured that both electrodes were consumed at equal rates. Yablochkov candles were first used to light the Grands Magasins du Louvre, Paris where 80 were deployed—improvement which was one of the reasons why Paris earned its "City of Lights" nickname. 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 Friedrich von Hefner-Alteneck of Siemens & Halske. The United States was quick in adopting arc lighting, and by 1890 over 130,000 were in operation in the US, commonly installed in exceptionally tall moonlight towers.
New street lighting technologies, such as LED or induction lights, emit a white light that provides high levels of scotopic lumens allowing street lights with lower wattages and lower photopic lumens to replace existing street lights. However, there have been no formal specifications written around Photopic/Scotopic adjustments for different types of light sources, causing many municipalities and street departments to hold back on implementation of these new technologies until the standards are updated.
Measurement
Two very similar measurement systems were created to bridge the scotopic and photopic luminous efficiency functions, creating a Unified System of Photometry. This new measurement has been well-received because the reliance on V(λ) alone for characterizing night-time light illuminations requires more electric energy. The cost-savings potential of using a new way to measure mesopic lighting scenarios is tremendous. Outdoor Site-Lighting Performance (OSP) is a method for predicting and measuring three different aspects of light pollution: glow, trespass and glare. Using this method, lighting specifiers can quantify the performance of existing and planned lighting designs and applications to minimize excessive or obtrusive light leaving the boundaries of a property.
Advantages
Major advantages of street lighting includes: prevention of accidents and increase in safety. Studies have shown that darkness results in a large number of crashes and fatalities, especially those involving pedestrians; pedestrian fatalities are 3 to 6.75 times more likely in the dark than in daylight. Street lighting has been found to reduce pedestrian crashes by approximately 50%. Furthermore, lighted intersections and highway interchanges tend to have fewer crashes than unlighted intersections and interchanges. Towns, cities, and villages use the unique locations provided by lampposts to hang decorative or commemorative banners. Many communities in the U.S. use lampposts as a tool for fund raising via lamppost banner sponsorship programs first designed by a U.S. based lamppost banner manufacturer.
Disadvantages
Dangers
There are two optical phenomena that need to be recognized in street light installations. The loss of night vision because of the accommodation reflex of drivers' eyes is the greatest danger. As drivers emerge from an unlighted area into a pool of light from a street light their pupils quickly constrict to adjust to the brighter light, but as they leave the pool of light the dilation of their pupils to adjust to the dimmer light is much slower, so they are driving with impaired vision. As a person gets older the eye's recovery speed gets slower, so driving time and distance under impaired vision increases. Oncoming headlights are more visible against a black background than a grey one. The contrast creates greater awareness of the oncoming vehicle. Stray voltage is also a concern in many cities. Stray voltage can accidentally electrify lampposts and has the potential to injure or kill anyone who comes into contact with the post. Some cities have employed the Electrified Cover Safeguard(TM) technology which sounds an alarm and flashes a light, to warn the public, when a lampost becomes dangerously electrified. There are also physical dangers. Street light stanchions (lampposts) pose a collision risk to motorists and pedestrians, particularly those affected by poor eyesight or under the influence of alcohol. This can be reduced by designing them to break away when hit (frangible or collapsible supports), protecting them by guardrails, or marking the lower portions to increase their visibility. High winds or accumulated metal fatigue also occasionally topple street lights.
Light pollution
In urban areas light pollution can hide the stars and interfere with astronomy and the migration of many bird species. 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 metal halide 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. Full cutoff streetlights also reduce light pollution by reducing the amount of light that is directed at the sky which also improves the luminous efficiency of the light.
Main manufacturers
Australia
GEC (General Electric)
Osram Sylvania
Philips
Rexel
Thorn Lighting
Westinghouse
North America
American Electric Lighting (formerly ITT, later Thomas & Betts), USA.
Cooper Lighting division of Cooper Industries, USA.
General Electric, USA.
Osram Sylvania, USA.
LED Roadway Lighting Ltd, Canada
Westinghouse Lighting Corporation (formerly Angelo Brothers) division of the new Westinghouse Electric, USA.
Europe
Osram, Germany.
Philips, the Netherlands.
Siemens, Germany.
Svetlina AD, Bulgaria.
Tungsram, Hungary
Thorn Lighting formerly Europhane,United Kingdom
GEC,United Kingdom
Philips,United Kingdom
Asia
Matsushita Electric Industrial Co., Japan
Sanyo, Japan
External links
- An enthusiast's guide to street lighting - including many close-up photographs of UK street lighting equipment, as well as information on installations through the ages. (UK)
- Example Installation of Integrated Renewable Power in Street Lighting, An example of a street lighting system with integrated solar and wind generator from
- Australian Street Lights (an enthusiast site).
- New Streetlights - LED streetlight news in North America.
- Transportation Lighting at the Lighting Research Center