It's pretty amazing to think about how much energy can be saved by such a simple, common-sense measure: By requiring shops and offices to turn off their lights at night, France will save the energy it takes to power 750,000 homes.

Effective July 1, all nonresidential buildings must shut off their lights an hour after the last worker leaves or by 1 a.m. each morning. They can't turn them on again until 7 a.m. or just before they open.

http://www.greenbiz.com/news/2013/02/15/france-simple-step-save-energy-shut-lights