Energy-saving street lamps are to be installed in every street in Westminster after a successful trial.
The lamps were successfully tested last month
They could save £20,000 each year if all 15,000 street lights were replaced, Westminster City Council said.
The local authority said it will spend £15m fitting the Furyo Lanterns, meaning it would take 750 years for the savings to pay for the scheme.
The lamps were trialled in Harrow Road and saved, on an average day, enough energy to light a house for two days.
They reflect light in a much stronger way which means that low wattage bulbs can be used.
According to the council they helped cut carbon emissions in Harrow Road by 0.28 tonnes over three weeks.
To bolster the amount of energy saved, solar microchips are installed to detect levels of light and switch on the light when it starts to get dark rather than being on a timer.
The cost of installing the lamps will depend on the condition of the street lamps being replaced and could cost between £800 and £2,000 each, a council spokesman said.
Responding to the fact the scheme would take 750 years for the council to recoup the savings, the spokesman said it was not just a money saving measure but to save energy as well.
Councillor Alan Bradley said: "Westminster Council is proud to be installing these new lanterns.
"By doing so, our main aim is to save energy and reduce our carbon footprint during a time when global warming is becoming an increasing threat to our way of life."
Embankment Gardens will be the next area to have the lanterns fitted. There is no fixed timetable for installing the lamps across the borough of Westminster.