The polar night in Lapland is not complete darkness; it's more like twilight, lasting a few hours between the "nights." If you want to shoot mostly night scenes, then the polar night is not an issue. Otherwise, it might be a bit challenging, especially in the areas where polar night lasts for weeks. Cloud coverage during the polar night means "complete" darkness around the clock. You will get most hues during the last days of the polar night as the sun is already close to the horizon.