Plans to create a "smart" street lighting system in Leeds are nothing more than a "£5m dimmer switch", councillors have said.
The installation of "smart city" sensors for 86,000 LED street lights was agreed by the council in October.
The Labour-led Leeds City Council says the sensors would save electricity by dimming the LED lights without losing visibility.
But a Liberal Democrat councillor said "burglars will be rubbing their hands".
The tactic will save money on bills and would only be considered between 00:00-05:30, Labour said.
The sensor upgrade is part of a £30m four-year scheme to make about 92,000 street lights in the city more energy-efficient.
Leeds City Council previously said it could save about £3.4m a year, at current energy prices, after the programme is complete, the BBC's Local Democracy Reporting Service reported.
Carmel Harrison, a Liberal Democrat councillor, said: "This is a dim move and personally I am very angry that despite saving money with LEDs, Labour are going to spend £5m of our money to have the ability to make every street darker whenever they want.
"This is bad news for the elderly, women shift workers and public transport users. Burglars on the other hand will be rubbing their hands."
Stewart Golton, leader of the Liberal Democrat group, called it a "£5m dimmer switch".
Labour's Richard Lewis, portfolio holder for regeneration, transport and planning, responded: "The way LED lights work means we can easily dim areas when we need to, with very little impact on the actual visibility of an area which creates further savings.
"£5m spent on the ability to dim lights would still be a good investment."