STREET lights in Derby could be dimmed or turned off completely at night to help the environment and save thousands of pounds a year.

Derby City Council is considering spending £3m on a control system which would allow it to change the lighting levels in areas at certain times.

It estimates it could save £137,000 and 839 tonnes of carbon dioxide a year through measures including dimming lights by up to 25% between 8pm and midnight and by 50% from midnight to 5.30am.

Councillor Bob Troup, cabinet member for housing and the environment, said that newer street lights were actually using more electricity than the older ones.

He said: "This is because of increased lighting levels and the quality of lights – despite the lights being more efficient.

"So we are looking at ways of reducing that and the option of putting in a fully controllable system to dim lights or increase intensity as we think fit."

And he said the council had not ruled out turning off lights completely in some small roads.

Street lights in Derby currently cost £783,000 a year to power and are giving off 5,641 tonnes of carbon emissions each year – the equivalent of 1,070 4x4 cars.

The authority has signed up to reduce its carbon emissions by 25% by 2012 and says dimming or switching off lights is the only way of significantly reducing its energy consumption.

The council estimates the savings – including 1.6 M kWh of electricity per year – could be achieved through 70% of lights in the city being dimmed by 25% from 8pm to midnight and by 50% from midnight to 5.30am and a further 20% of all lights being dimmed by 25% from 8pm to 5.30am.

But officers said these estimates were to give an indication of potential savings and were not a definite proposal.

Mr Troup added that by using the management system, it would allow the council to be flexible so it could respond to issues about crime and road safety should they arise.

"If there were problems with security in an area we could have increased levels of lighting there and if we had a particular event on, for example in a park at night, we could increase lighting levels there," he said.

And he added if the system was bought, the council would consult with police and other groups to see which areas could suit having lower levels of light, such as smaller back streets. The council would then trial changes in certain areas after taking into account crime levels and recommendations from police.

At the moment there are 26,417 street lights in the city.

Of those 10,434 have been installed under the private finance agreement between Balfour Beatty and Derby City Council, known as Lighting Derby.

The Lighting Derby agreement was launched in 2007 and will see Balfour Beatty replace and maintain thousands of lighting columns.

Over the entire 25-year contract, 25,190 lights will have been installed.

The majority installed so far have been replacements – 8,965 – with the remaining 1,469 being additional lights.

Some residents fear for safety if lights are dimmed.

George Hawksworth, of Spondon Neighbourhood Watch, said: "The reason for putting in these new lights was to deter break-ins and burglaries and things like that. If they dimmed them here we wouldn't be happy.

"They may turn lights down in an area that doesn't have problems but then it attracts crime because people know it has low lighting."