The Life Spent in Darkness variable includes both night time and cloudy daytime hours. It’s a metric of your access to sunshine. Even if it’s not just a daytime or a winter measure, as a percentage, it’s an easily-compared measure of suffering and health threat. It’s hard to live in Goteborg because the winters are rainy and dark. Although it’s a dry winter in Winnipeg, it’s as hard to live in Winnipeg as it is to live in Portland, Oregon; the aggregate sun deprivation is the same.
However, the metric won’t capture the heightened difficulty of access to that sunshine on a short -19C February day, contrasted with Portlanders’ summertime full of sunshine. Now we know why almost all Canadians have chronic vitamin D deficiency, and associated diseases!