Essex decided on this move last month after lighting costs soared by 65% to£3.9m. It will spend a one-off£1.8m on adaptations to deliver a£1m annual saving.
Rodney Bass (Con), cabinet member for highways and transportation, said: 'While it will clearly be appropriate for all night lighting to remain in certain areas, it is wasteful for this to be generally applied across the county.'
But Institution of Lighting Engineers (ILE) technical services manager, Dave Coatham, said: 'This a knee-jerk response to climate change and increases in energy costs, which could hit road safety and public security.
Mr Coatham said alternatives included altering the light level at which streetlights come on, dimming their output and the installation of more energy-efficient equipment.
There is also a concern motorists could collide with unlit streetlights. Even though they are switched off, they are still connected to the mains.
Joint guidance for councils is due next month from the ILE, the County Surveyors Society and the UK Lighting Board.