Alternate lights will go out in some areas under the plan
A council is planning to switch off more than a third of its 14,000 street lights for a full year in an attempt to save money and energy.
Powys Council's annual street lighting bill is about £500,000, but that is set to rise by £175,000, officials say.
The authority said the soaring costs, coupled with a tight budget, had forced it to adopt a "radical approach".
Areas covered by CCTV, pedestrian crossings and trunk roads will not be affected by the switch off.
If councillors vote in favour of the project next Tuesday then 5,000 lights will be switched off in June. That will rise to 6,400 in the next financial year.
However, areas under threat of reduced lighting have not yet been identified.
A rural county covering about a quarter of the area of Wales
There is one person in every 10 acres (four hectares)
The economy is based on agriculture and tourism
Placed end to end, Powys' street lights would stretch from Llandrindod Wells to Glasgow
Some councils in England, such as Buckinghamshire, Essex, Hampshire and Hertfordshire are already trialling similar schemes.
Powys Council said a 36% rise in its street lighting bill had forced it to consider the option.
But it said the plan was good for the environment as it would cut its carbon footprint by up to 1,100 tonnes a year, and reduce night sky pollution.
Executive director for organisation and regeneration Jeremy Patterson said: "The council is responsible for more than 14,000 street lights on county roads and is facing a £175,000 increase in energy costs on top of a £50,000 budget cut.
"We had considered moving to part-night lighting to tackle the budget problem, but the scale of energy cost increases and time required to carry out the work has meant a taking a more radical approach.
"The only option we have is to switch off around 5,000 lights (36% of stock) for a full year to meet the targets in 2008/2009.
"This would rise to 6,400 (45% of stock) in 2009/2010."
Mr Patterson said alternate lights would be switched off under the authority's plamns.
But the charity Help the Aged fear the move could affect the elderly, and it called on the council to consult the public before a decision is made.
A spokesman said: "We hope that there will be a full consultation with residents before a decision is reached on this proposal and that what is deemed acceptable levels of lighting considers the differing needs of all sectors of the local community."