On my trip the furthest south I went was London--and that ain't south, boys and girls! Even in London it wouldn't get completely dark at night. It was strange, seeing light outside at 1 am.
Reykjavik, so close to the Arctic Circle you can almost throw a stone to it from there, didn't even put on airs about darkness. Yes, the sun was below the horizon for 4 hours, but it was still like early morning in the sky. In fact, this web site says it was no darker than "civil twilight" during the night; the US Naval Observatory defines that as
Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under good atmospheric conditions in the absence of moonlight or other illumination. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities.London got to "astronomical twilight", whereas Sacramento gets to "night".
I left home on June 19th and flew up over the Arctic Circle on my way to London. It was completely bright the entire flight, as we were so high up and so far north that the sun was visible at all times. Throughout the entire trip the darkest the sky got was "twilight", and there was still plenty of light out. When we landed in Sacramento late Thursday night it was actually dark out. It was the first time I'd seen darkness in 3 weeks.