The country with the lowest levels of UV radiation exposure is Iceland. Some key reasons why Iceland has very low UV levels include:
High latitude: Iceland's location just outside the Arctic Circle means the sun's UV rays have to traverse more atmosphere compared to equatorial regions.
Cloud cover: Iceland has a very high prevalence of cloud cover, especially in fall, winter and spring seasons. Clouds reflect a significant portion of UV rays back into space.
Short summer season: Iceland also has long dark winters with few hours of sunlight, and a short summer season when the sun shines. This limits overall UV exposure.
Ozone layer: Iceland is under the thicker mid-latitude ozone layer, which absorbs more incoming UV radiation than over the equator.
Snow cover in winter: ice and snow reflect up to 80% of UV rays, preventing absorption at ground level. Much of Iceland is covered in ice and snow for a third of the year.