High pressure sodium vapor lamp
suspended on wire.
New and old style street lights
Legii Bridge Prague
A
street light,
lamppost,
street lamp,
light standard, or
lamp standard is a raised source of
light on the edge of a
road, which
is turned on or lit at a certain time every night.
Modern lamps may also have light-sensitive
photocells to turn them on at
dusk, off at
dawn, or activate
automatically in dark
weather. In older
lighting this function would have been performed with the aid of a
solar dial. It is 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
Before
incandescent lamps,
gas lighting was employed in cities. 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 earliest of such street lamps were built
in the Arab Empire, especially in
Córdoba,
Spain
.S. P. Scott (1904), History of the Moorish
Empire in Europe, 3 vols, J. B. Lippincott Company,
Philadelphia and London.
F. B. Artz (1980), The Mind of the Middle Ages, Third
edition revised, University
of Chicago Press, pp 148-50.
(cf. References, 1001 Inventions)
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
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.
The first street in the UK to be lit by electric light was Mosley
Street, in Newcastle-upon-Tyne. The street was lit by Joseph Swan's
incandescent lamp in February, 1879.
The first in the
United States, and second overall, was the Public Square
road system in Cleveland, Ohio
, on April 29, 1879. Wabash, Indiana
holds the title of being the third electrically-lit
city in the world, which took place on February 2, 1880. Four
3,000 candlepower Brush arc lamps suspended over the courthouse
rendered the town square "as light as midday." Kimberley, South
Africa, was the first city in Africa to have electric street lights
- first lit on 1 September 1882.
In Latin America, San
Jose
, Costa
Rica
was the first city, the system was launched on
August 9, 1884, with 25 lamps powered by an hydroelectric plant
. Timişoara
, in present-day Romania
, was the
first city in mainland Europe to have electric public lighting on
the 12 of November 1884. 731 lamps were used.
In 1888 Tamworth
, New South
Wales
, Australia became the
first location in the Southern Hemisphere
to have electric street lighting, giving the city
the title of "First City of Light".
Arc lights had two major disadvantages. First, they emit an intense
and harsh light which, although useful at industrial sites like
dockyards, was discomforting in ordinary city streets. Second, they
are maintenance-intensive, as carbon electrodes burn away swiftly.
With the development of cheap, reliable and bright
incandescent light bulbs at the end
of the 19th century, they passed out of use for street lighting,
but remained in industrial use longer.
Incandescent lamps were primarily used for street lighting until
the advent of high-intensity discharge lamps. They were often
operated in high-voltage
series
circuits. Series circuits were popular since the higher voltage
in these circuits produced more light per watt consumed.
Furthermore, before the invention of photoelectric controls, a
single switch or clock could control all the lights in an entire
district.
To avoid having the entire system go dark if a single lamp burned
out, each street lamp was equipped with a device that ensured that
the circuit would remain intact. Early series street lights were
equipped with isolation transformers that would allow current to
pass across the transformer whether the bulb worked or not. Later
the
film cutout was invented. The film cutout was
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 voltage of the circuit (thousands of volts) to be
imposed across the insulating film, penetrating it (see
Ohm's law). In this way, the failed lamp was
bypassed and power restored to the rest of the district. The street
light circuit contained an automatic voltage regulator, preventing
the current from increasing as lamps burned out, preserving the
life of the remaining lamps. When the failed lamp was replaced, a
new piece of film was installed, once again separating the contacts
in the cutout. This system was recognizable by the large
porcelain insulator separating the lamp and
reflector from the mounting arm. This was necessary because the two
contacts in the lamp's base may have operated at several thousand
volts above ground/earth.
Today, street lighting commonly uses
high-intensity discharge
lamps, often HPS
high
pressure sodium lamps. Such lamps provide the greatest amount
of
photopic illumination for the least
consumption of electricity. However when
scotopic/
photopic light
calculations are used, it can been seen how inappropriate HPS lamps
are for night lighting. White light sources have been shown to
double driver peripheral vision and increase driver brake reaction
time at least 25%. When S/P light calculations are used, HPS lamp
performance needs to be reduced by a minimum value of 75%. This is
now a standard design criteria for Australian roads.
New street lighting technologies, such as
LED or
inductionlights, 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.
Disadvantages
The major criticisms of street lighting are that it can actually
cause accidents if misused, and cause
light pollution.
Dangers of street lights
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 light poles
and has the potential to injure or kill anyone who comes into
contact with the pole. Some cities have employed the Electrified
Cover Safeguard technology which sounds an alarm and flashes a
light, to warn the public, when a pole becomes dangerously
electrified.
There are also physical dangers. Street light stanchions (poles)
pose a collision risk to motorists. 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. 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.
The light pollution also disrupts the natural growing cycle of
plants.
Purposes of street lights
There are three distinct main uses of street lights, each requiring
different types of lights and placement. Misuse of the different
types of lights can make the situation worse by compromising
visibility or safety.
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 vehicles or pedestrians. 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. On Interstate
highways this purpose is commonly served by placing reflectors at
the sides of the road.
Roadway lights
Street lights are not normally intended to illuminate the driving
route (
headlights are preferred), but to
reveal signs and hazards outside of the headlights' beam . Because
of the dangers discussed above, roadway lights are properly used
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 drivers must
take in much information quickly that is not in the headlights'
beam. In these situations (A freeway junction or exit ramp) the
intersection may be lit so that drivers can quickly see all
hazards, and a well designed plan will have gradually increasing
lighting for approximately a quarter of a minute before the
intersection and gradually decreasing lighting after it. The main
stretches of highways remain unlighted to preserve the driver's
night vision and increase the visibility of oncoming headlights. If
there is a sharp curve where headlights will not illuminate the
road, a light on the outside of the curve is often justified.
If it is desired to light a roadway (perhaps due to heavy and fast
multilane traffic), to avoid the dangers of casual placement of
street lights it should not be lit intermittently, as this requires
repeated eye reajustment which implies
eyestrain and temporary blindness when entering
and leaving light pools. In this case the system is 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 consistent light along the route. The lighting goes
from curb to curb.
Research a few years ago suggested that by comparison to other
countries, more pedestrians are hit by motor vehicles at night in
Britain. The theory behind this was that Britain almost
exclusively, used low pressure sodium street lighting, (LPS);
unlike the rest of the world that use mercury vapour gas discharge
lighting . This was most noticeable when flying in from Europe at
night and seeing a warm orange glow when approaching Britain. LPS
lighting, being monochromatic, shows pedestrians as shadowy forms,
unlike other forms of street lighting. In recognition of this,
pedestrian crossings are now lit by additional "white" lighting,
and sodium lighting is being replaced by modern types.
Security lighting
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 people's
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 increased security. This is what
would normally be used along sidewalks in dense areas of cities.
Often unappreciated is that the light from a
full moon is brighter than most security
lighting.
NEMA wattage labels
Many Street lights have a
NEMA
wattage label, these labels are for work crews to identify the
wattage of the lamp, the labels are in three different colours Red,
Blue and Yellow to represent different types of
lamps.Image:NemaTag.jpg|A 250 Watt HPS NEMA wattage lable.
Main manufacturers of street lanterns and/or bulbs
Australia
America
Europe
A historical Slovakian lamppost.
German streetlight at night.
- Osram, Germany.
- Philips, the Netherlands.
- Industria, the Netherlands.
- Schreder, Belgium.
- Siemens, Germany.
- Svetlina AD, Bulgaria.
- Aura Light, Sweden.
- AEC Illuminazione, Italy.
- Tungsram, Hungary
- Art Metal, Poland.
- Innolumis, Netherlands.
United Kingdom
Asia
See also
References
External links