The replacement of Dunedin's ageing streetlight stock with energy efficient lights is expected to cost the city about $6 million.
The cost will be funded initially from loans, but council staff expect the cost of servicing the debt will be ''more than'' offset by savings in maintenance and electricity bills.
Council transportation operations programme engineer Michael Harrison said some high-level work had been done on what it would cost to replace the city's 14,000 streetlights with longer-lasting, more efficient technology units, probably LED lights.
The plan was to replace the lights over a four-year period, starting from 2015-16, but prudent budget planning meant funding had to be included in outlying years' budget lines now.
This would also allow the council to meet this year's deadline to apply for New Zealand Transport Agency subsidies.
Staff estimated new lights could save the council up to $400,000 a year in replacement and electricity costs.The savings would start in the 2021-22 year, after a recovery period from taking the loan.
Council roading maintenance engineer Peter Standring said the extra capital expenditure would be part of the council's operational expenditure.
The exact type of lights were yet to be chosen, but would likely be some sort of low-spill LED lighting with built-in extras, such as dimmers or light sensors on selected lights.
The city's streetlight stock is 20 to 25 years old.
While the bulbs in a quarter of the lights were replaced each year, the glass housings for the bulbs were reaching the end of their life and would need to be replaced in the next few years, Mr Standring said.
Street lighting costs the city about $1 million a year for electricity and about $400,000 in bulb replacement and light maintenance.
