Why the dimmer way is smarter for street lighting
Local authorities under pressure to trim their street lighting costs would do well to look to controlled LED solutions, rather than simply switch off, in however considered a fashion, writes Nick Martindale
The tragic case of the off-duty soldier who died on Christmas Day in a road accident in Somerset in an area where street lights had been turned off reignited the controversy over the decision by some local authorities to switch off street lighting to save money.
Northamptonshire County Council in particular has come under fire after turning off half of the county’s 66,000 street lights, a move which even prompted a group of vigilante electricians to start a campaign to re-ignite the lights under cover of darkness.
A spokesman for the council defended the decision, pointing out that it needs to trim costs by £73 million in 2011-12 alone and estimating the move will save about £2 million.
“Turning off roughly half the lights did not mean turning off every other light in an ad hoc way,” says the spokesman. “Careful consideration was given to which lights were turned off and which ones were left on.
“We looked at different criteria in the assessment, including crime figures, accident rates and proximity to complex junctions and a priority list was developed in conjunction with the police and road safety officers.”
Northamptonshire is certainly not the only council to have taken such steps – and has since unveiled plans to overhaul its existing lighting stock.
But the move has disappointed many in the lighting industry, who feel councils are missing an opportunity to embrace new technology, which could deliver far greater savings in the long run, as well as enhance public safety.
In particular, the emergence of LEDs as a viable alternative to traditional street lighting presents opportunities not only to use more energy-efficient luminaires but also to reduce the amount of time for which they need to be switched on, says Nigel Parry, professional services manager at the Institute of Lighting Professionals.
“Traditionally we have had lighting-up time a good half-hour before it was needed, because the lamps took between 15 and 20 minutes to warm up,” he says. “With LEDs, it’s instant, so you can switch on a lot later.
You could save 100-200 hours a year per lighting column. With 7.5 million street lights in the UK, the savings soon add up.”
Because LEDs can be easily controlled, they can also be set to dim at certain parts of the day, enabling councils to react to peak or low-usage periods.
“Solid state technology can have in-built astronomic clocks and daylight sensors, in addition to circuits to set dimming levels,” says David Fear, technical director at Siteco UK, part of Osram. “It would be possible for an in-built clock to check for time and daylight presence before switching on or off.”
Remote-control technology can also enable lighting operators to monitor and control individual networks of luminaires from a laptop, helping councils to respond to the particular needs of a given situation.
“Users can create profiles that can dim lighting at a time of day or night to suit, therefore offsetting daylight saving areas and geographical locations,” says Richard Adelsberg, marketing manager at Harvard Engineering.
“This can also be used to cover sporting and live entertainment to ensure the safety of the public at the beginning and the end of events, particularly late at night.”
Further, the use of such control technologies could enable councils to avoid situations where luminaires are designed to function at a level that will still be satisfactory after a period of four or five years, meaning they are effectively over-lit for the first two or three years.
“Remote monitoring systems now give you the opportunity to apply a responsible maintenance regime over all lighting,” says Dave Franks, service development manager for public lighting at Westminster City Council. “You’re not even dimming at this stage; just removing unnecessary light. From day one you can get a 20-25 per cent energy saving and across four years you increase your energy slightly to keep that light the same.”
Further down the line, greater use could be made of motion- detected systems, where areas are lit when vehicles or people approach, and dimmed back down afterwards. This is already being used in some public spaces.
“If you were going to put light into an area where you have significant footfall there are systems being developed which generate energy when people step on paving slabs and you can then store that energy in batteries. This could then be used to illuminate signage,” says Franks.
“I don’t believe it would work for street lighting yet, because the technology is not advanced enough. But maybe it could be in five to ten year’s time.”
The use of solar-powered luminaires is also developing nicely, adds Franks. Westminster already boasts a number of solar- powered bollards, which Franks says have saved considerable sums of money.
The irony is that those councils that have taken the easy option of simply turning lights off could end up losing out financially in the long term. Estimates vary as to the payback period for installing LEDs and controls, but range between five and seven years.
Implementing a more intelligent approach to lighting could also lead to other benefits, which fit in with councils’ wider objectives, suggests Stephen Lisk, director of One Eighty Light.
“Part of how we design our towns and cities is around pedestrianising high streets and getting people walking and cycling, and out of their cars,” he says.
“LEDs are a great solution to lighting footpaths, pedestrian walkways, bus stops or cycle ways and encouraging people to get onto their bikes.”
Moving with the Times
The London Borough of Richmond is making use of an intelligent lighting system, which detects movement to illuminate a footpath running alongside the River Thames.
The Warren is a footpath that is well used by the public and is also home to many species of wildlife, including a significant number of bats, which had been deterred from their natural behavior by ultra-violet emissions from the previous lighting set-up.
Using Philips’s standalone LumiMotion detectors, the luminaires alongside the footpath can increase from 10 per cent to 100 per cent to ensure individuals using the path have sufficient light to see where they are going and feel safe, before dimming down once the area is cleared.
The council estimates the new system will reduce the footpath’s energy costs by 80 per cent, as well as cutting lighting spill by 50 per cent by ensuring light remains focused on the path itself.
Northhamptonshire County-Council’s long-term strategy
Northamptonshire County Council has come in for its fair share of criticism recently, after turning off about half of its street lights, while continuing to floodlight its own headquarters.
But the council has announced plans to upgrade its entire lighting stock - including street lights, illuminated signs and bollards - over the next five years under a Private Finance initiative contract with building contractor Balfour Beatty.
New street lighting luminaires will use LEDs, transforming the traditional yellow glow into stronger white light, while using 40 per cent less energy compared with the existing scheme.
“Under the scheme, Balfour Beatty will replace the lamp units and electronics of all street lights and replace lighting columns where necessary,” says a council spokesman. “It is anticipated people will also see a real difference in the quality of the lighting and that light pollution will be greatly diminished.”
the contract came into force in October 2011 and will last 25 years.
Westminster goes Wireless
With a wide variety of spaces used intensively at different times of day, Westminster City Council took the decision to install a wireless system that would enable it to remotely manage individual or groups of luminaires in accordance with usage.
“You design for the worst-case scenario on the streets - 6pm on a December evening at rush hour and where footfall and vehicle traffic flows are the highest,” says Dave Franks, service development manager (public lighting) at Westminster City Council. “But that environment might be totally different at 10pm at night. You have to understand your environment and have a policy that backs it up.”
Using the leafnut system from harvard engineering, the council has been able to dim street lights in residential areas by 25 per cent in the small hours, as well as reducing light levels on major road networks.
The new scheme has cut energy usage by 30 per cent and the council hopes it will generate further savings in its carbon reduction bill.