In the decades that followed, the industrialist, Samuel Eyde, known here as Uncle Sam, built just about everything that stands in Rjukan today. Managers got the houses with the most sunlight. Workers got apartments deeper in the valley. But all the housing was cutting edge for its day. There was indoor plumbing for everyone.

Mr. Eyde understood the yearning for sun, too. Back in 1913, one of his bookkeepers wrote to the local paper suggesting that a giant mirror might work. But instead, Mr. Eyde, who settled here because a waterfall nearby provided an easy means of generating electricity, built a cable car so his employees could go up the mountain to get some sunshine in the winter. The cable car still exists.

But the mirror enthusiasts wanted more. “We were a high-tech town 100 years ago,” Mr. Bergsland said, “and now we are using high tech to get some sun into our valley.

“Of course there were people here who said this is crazy,” he continued, “but a lot of people really liked the idea.”

And tourists have begun to trickle in, including from Oslo, about a three-hour drive away. Many of the businesses here report an uptick in income. If Rjukan becomes one of Unesco’s World Heritage sites next year, as it hopes, that should help, too.

Still, not everyone has embraced the mirrors. In this town of about 6,000 people, some 1,300 signed a petition to block the project. Some opponents, like Robert Jenbergsen, who is studying to become a teacher, have changed their minds. “I thought it would be a waste because we have a lot of bad weather here,” he said. “But when we got the sun, you could see the happiness it brought. We had never seen anything like that before. So, now I think it is great.”