Courtesy of the New York Public Library

When Paul LeClerc, the president of the New York Public Library, was preparing to unveil his Beaux-Arts Fifth Avenue beauty after a $50 million, three-year renovation, he knew that he would need to show it in literally the best light possible. So he went to Paris to consult François Jousse, who was then City Hall’s chief engineer for “doctrine, expertise and technical control” — something like the lighting director of the City of Light. Mr. Jousse took Mr. LeClerc on tours of Paris by night, showing him lighting canisters, electrical wiring and spotlight colors of the city’s monuments, official buildings, bridges and boulevards.

Along the way, Mr. Jousse revealed a secret about the Petit Palais, a Beaux-Arts wonder in its own right that becomes one of the city’s most beautiful buildings at night. The trick was hiding spotlights in the tops of streetlamps as part of the building’s restoration several years ago. Mr. LeClerc was so seduced by the idea that he persuaded the mayor of New York to ask the mayor of Paris to send Jousse to New York for consultations. He would have loved to have lighted up the library himself, but he spoke not a word of English and chained-smoked foul-smelling cigarillos. But Mr. Jousse’s adornment of the Petit Palais nonetheless served as a model for the library. And on May 23, the glow of Paris will come to Fifth Avenue. To celebrate the 100th anniversary of the Fifth Avenue building, the library will be lighted up, its columns, arches and majestic lions bathed in warm white for the first time in its history.

“This is one of the greatest Beaux-Arts buildings in America, and it’s going to be as gorgeous as any building in Paris at night,” Mr. LeClerc said. “We’ll flip the switch and knock everybody’s socks off.”

The lighting is the climax of the renovation, which included the restoration of the roof, sculptures and bronze window frames; the cleaning of all of the building’s white marble; and the carving by hand of more than 2,000 new pieces of marble for the facade by master stone-carvers.

Luiz Felipe Castro/Getty Images

To light the exterior, the library chose the lighting consultant Claude R. Engle, who had lighted, among other structures, I. M. Pei’s pyramid at the Louvre and the Pompidou Center in Paris; the viaduct in the French city of Millau; the World Trade Center; the World Bank headquarters; and the Bilbao Metro system. The company’s goal was to illuminate the library’s facade at an angle, which shows subtlety of detail, rather than to deliver a solid white mass. Mr. Engle mounted lights on 22-foot-high posts on the north and south sides of the plaza and on some of the highest street lights across Fifth Avenue. A stronger beam will shine on the top of the south facade, with light fading as it hits bottom — not unlike the south face of Notre Dame in Paris.

“We didn’t want a floodlit castle on the hill that had no life in it,” said Claude R. Engle Jr., who worked with his father on the project. “We didn’t want to turn the library into a mausoleum. A glow had to come from within, like the glow of a person’s eyes.”

For Mr. LeClerc, a scholar of Voltaire and the 18th-century French enlightenment, who will end his 18-year tenure at the helm of the library at the end of June, the lighting project is both a fitting and a sentimental farewell. “A student of the Enlightenment who runs a library inspired by the Enlightenment seeks to bring the lighting he’s seen in Paris to New York,” he said. “It’s perfect.”