Lights at some of Italy's most famous monuments including the Colosseum, the Trevi Fountain and St Peter's Basilica will be turned off at 18.00 Friday for the fifth annual energy-saving day.
Tourists at St Mark's Square in Venice and the Duomo in Milan will also find themselves in the dark during the voluntary black-out, which will last from several minutes to an hour and a half.
The Chamber of Deputies, the Senate and government ministries are among other buildings where light switches will be flicked, as well as at schools and museums across the country.
Italian fuels giant ENI, the principal sponsor of the initiative, and a host of other businesses will also take part in a bid to beat last year's record, when 400 megawatts were saved - equivalent to the consumption of seven million light bulbs.
Organisers say cities across the globe including London, Barcelona, Brussels, Vienna and Athens will join the initiative.
