Safety and Security
The lighting up of streets by electricity has brought a sense of security and wellbeing to our cities, towns and villages for over 125 years. The first ever electric streetlights in Britain were brought into operation in the 1870s in Holborn Viaduct and The Thames Embankment, London. By 1881, there were thousands. Today there are over 7.5 million streetlights in the UK, all of which require maintenance and upkeep.
The most recent studies have proved that well placed and well maintained street lighting can reduce crime not only at night, as you would expect, but during the day as well. It is suggested that the improved lighting helps to bring about a community pride and sense of ownership as well as the more direct effect of increased surveillance of offenders.
However street lighting is not only used to affect crime rates. Floodlighting of historic buildings and monuments can also enhance the image of an area, and so instil a sense of civic pride. Road safety is one of the main uses for street lighting, especially on dual carriageways, trunk roads and motorways. Lighting on motorways reduces the stress on drivers and therefore reduces the likelihood of accidents.
The lighting of road junctions and roundabouts can decrease the number of road traffic accidents at these locations. Pedestrian Crossing lighting further lowers the risk to the general public, as does lighting of traffic calming measures.
Types of street lighting
There are many types of street lighting, from the familiar orange glow of Low Pressure Sodium discharge lamps - which have been around since the 1930s, and are still one of the most efficient light sources to date - to the near-daylight quality of the more recent Metal Halide group of lamps. Like all discharge lamps these work via the principle of passing an electric current through a gas to excite the gas molecules to produce light.
The addition of different metals within the gas mix will give the light source its colour (Sodium for orange, Mercury for white). There are older street lights which use the good old Tungsten filament bulb, more commonly found in your front room. New technology has brought us the compact fluorescent lamp for lower energy consumption and the LED street light which has a maintenance-free lifespan of at least 10 years.
Nearly every residential street light runs on full mains voltage, supplied by the local electricity board, via its own connection into the local electricity grid. Some older systems run on what is commonly known as 5th Core - this system employs the use of one central control point inside an electricity sub-station to switch whole roads or areas of street lighting on and off. Most new dual carriageways that are lit use a ‘private cable' system which means that the local electricity board install their power supply into a ‘Feeder Pillar' at the side of the road and from there local authority-owned power cables supply the individual lighting units.
Inside the lighting unit they use transformers to change and in many cases step up the voltage to more than the mains 220v. The solar or wind powered street light is also available for areas where it is impossible or uneconomical to provide mains electricity.
Streetlight luminaries design has moved forward with the times, from the mirrored butterfly lantern in the 1920s to today's weather proof, dust-sealed high pressure discharge lamp luminaries which can prolong lamp life. Light pollution can also be a problem which can be minimised by using flat glass aspect lanterns which direct the light to where it is needed, that is, the road surface and not spill it to the side of rear of the unit.
From time switch to photocell and group control, from all-night operation to part night operation, there are nearly as many ways to control street lights as there are types of light source. Most lighting schemes use photo-cells to control the switching of the lights. These come in two basic types: all-night lighting which as its name suggests switches the light on at dusk but off again at dawn. Part night lighting will switch on at dusk but off at midnight and so save power and then on again at 5.30am, if it is dark enough, to light the winter mornings.
Some street light controls can even report themselves out of light via radio signals or direct down the power supply cable. Again new technology has made its mark by producing timers which can be computer programmed years in advance, to operate units such as school flashing signs, which can now tell what day of the year it is so they only operate on school days and turn off during weekends and holidays without an operator.
Maintenance
Most urban street lighting is the responsibility of the local authority to keep in working order. Motorway and trunk roads lighting is the responsibility of the Highways Agency, Scottish Executive or Welsh Assembly Government. Maintenance is carried out employing a range of methods and maintenance contractors. There are two types of standard maintenance programme: Reactive Maintenance and Preventative Maintenance.
Reactive Maintenance
Scouting of outages: Nearly all contracts include a night time scout of all lighting to ascertain which units are faulty. This is done fortnightly or monthly depending what time of year it is. They are carried out by teams of night time scouts pounding our pavements and driving our roads in all weathers taking note of any streetlight which is out of light or defective, that is, dim, flashing or misaligned.
Repair of outages: The detail of the night scout is passed to the repair team whose job it is to get the unit back into lighting within a given timescale or report back to the local authority what is required to do so. This may entail the simple operation of replacing a fuse or re-setting a time switch, but it may involve replacing the whole unit. Skilled and competent operatives carry out this work whatever the weather.
Emergency response: In any urban area the likelihood of a street lighting unit being damaged, either by vehicle impact or vandalism is high. All local authorities who have street lighting in their care provide a 24 hour, 365 day a year emergency response to reports made by the general public. This could be anything from a lighting column access door missing to a complete lighting unit knocked down in a road traffic accident. Any damage should be reported as soon as possible to minimise the risk to the public.
Preventative Maintenance
Bulk Lamp Change: Discharge lighting of most types will slowly decline in light output over time. Faults are more likely to occur the older the lamp, so bulk lamp change programmes (the wholesale change of all lamps by type or geographic area) are used to make sure a lamp is changed before it gets to the end of its burning life. This is normally three to four years, although some lamps are changed sooner.
Cleaning: Cleaning can prolong the life of a lighting unit as a build-up of traffic grime can diminish the light output of even the newest lamp. This is normally programmed alongside the bulk lamp change or annually along with a visual inspection of the lighting unit. The cleaning of lit traffic signs and bollards may be carried out on a higher frequency.
Electrical Testing: As in the home, electrical safety is of paramount concern to the responsible body, so a programme of electrical testing is carried out where each lighting column is tested every six years as a minimum. These results will show if a columns protective device, that is, the fuse, will operate correctly and within a given timescale if required to do so. The results of these tests are also used to direct the use of maintenance budgets to upgrade and replace units and so keep everyone safe.
Structural testing: Structural testing is used in much the same way as electrical testing, as a guide in the decision about where capital investment should be made into the lighting infrastructure. The lighting column itself can also be made of steel, aluminium, cast-iron, fibre glass and even wood, so periodic testing can also prevent structural failures which can put the public at risk.
Structural testing employs the use of ultrasonics to detect problems above and below ground level as well as a detailed visual inspection. Steel columns are vulnerable to external acid attack, especially canine urine, as well as wind and rain, which cause rust. Concrete columns are vulnerable to impact damage and frost. Once the outer layer is broken the steel reinforcement is exposed and rust can cause more damage and further cracking. Fibre-glass columns can be prone to impact damage and ultraviolet derogation.
Protective Coatings: Painting is a way of prolonging the life of lighting columns. If the material that a column is made from is protected from the elements, then the life expectancy will increase. There are many ways of doing this, but the most common is galvanising the steel of a column at the time of manufacture, then further painting systems are used to increase the protection. Although more expensive, the use of stainless steel and aluminium columns is on the increase. These do not require painting but can have a design life of up to 70 years as opposed to 20 to 30 years for normal galvanised/painted steel.
Capital Investment Schemes: Capital schemes are the local authority's way of upgrading and replacing lighting units which have come to the end of their design life. This may be a lantern replacement scheme or a complete column renewal for an entire street including a computer aided re-design of lighting levels to meet current British and European standards.
