Five years ago, Nokia engineer Antti Aunio was trying to brighten up his flat to deal with seasonal affective disorder, known as winter depression and a common problem in northern Finland with its dark and long winters.

His childhood friend Juuso Nissila, a scientist who had studied the impact of lights on animals, had another suggestion: instead of getting new lamps that promise to lighten your mood, why not make a device that sends light straight to your brain?

That’s how Aunio quit Nokia and joined Nissila in starting up Valkee, which now sells earplugs which send bright lights to the brain through ear canals.

On Wednesday, Valkee and scientists from the University of Oulu presented results of two small clinical trials to a science conference in Budapest, saying the earplugs can effectively prevent and treat winter depression.

Around 15-20 percent of central Europeans suffer from the winter disorder. In Valkee’s hometown of Oulu in northern Finland, there is less than four hours of daylight during the depths of winter.