The Champs-Élysées. The lights of Paris add to its magic for tourists, but new rules may make French cities a little less bright.

PARIS — The City of Light is about to get dimmer. As of July, all shops and offices in France will have to shut off their lights at night, under a government decree issued on Wednesday.

The decree, from the Environment Ministry, is intended to save energy and “reduce the print of artificial lighting on the nocturnal environment.”

France is proud of its lights. Tourists cherish the Christmas illuminations on the Champs-Élysées, the 20,000 flashing bulbs on the Eiffel Tower and the bright, imaginative shop windows of large department stores like Printemps and Galeries Lafayette.

Major attractions like the Eiffel Tower will remain lighted, and local authorities can make exceptions for Christmas lighting and other celebrations. But France has decided to be “a pioneer” in preventing light pollution, said Delphine Batho, the environment minister.

The new law, she said in a statement, will also cut carbon dioxide emissions by 250,000 tons a year and save the equivalent of the annual consumption of 750,000 households. It is part of a series of government measures announced in December to improve energy efficiency and reduce waste.

Under the new law, the interior lights of nonresidential buildings will have to be turned off an hour after the last worker leaves, and lights on building facades and in shop windows will have to be extinguished by 1 a.m.

Ms. Batho also presented the decree as a matter of public health. Artificial lighting can damage sleep patterns, she said, and also “cause significant disruptions on ecosystems by changing communication between species, migrations, reproduction cycles or even the prey-predator relationships.”

From the context, it seemed as if she was referring to city wildlife, not to muggers and victims.