How dark/bright are polar nights? During the polar night directly at the pole the Sun sets once and—after a period of twilight—stays down for months at a time.
The only sources of non-human-made light are the stars, the auroras, and the sunlight reflected by the moon.
Yet when I see various photos of, for example, Amundsen-Scott base during this period, the sky (and the ground illuminated by it) is often quite bright. Here is a timelapse of August, which should be way outside even the civil twilight for this period: https://youtu.be/cf14SL7m8Ys
Is there an issue with photo-sensitivity of the cameras?
Are these sources of illumination actually bright enough to turn the middle of the night into something more twilight-like (if not day-like) when perceived by a human eye? If so, how much of the polar night is actually dark, percentage-wise?
That's a timelaps video, most likely created from a sequence of photos. It's easy to choose sensitivity and ISO settings on normal cameras such that the night sky at the darkest night is over-exposed. The moon light looks like sunlight - as it simply is reflected sunlight.
E.g. see https://cloud.planetmaker.de/index.php/s/yJ7AXWG4dEC6csW - it's a an exposure of several seconds taken several hours after sunset in November in Kiruna, Sweden... the over-exposed part in the center are headlights of a car, the rest is illuminated by the nearly-full moon at that time.
As children of modern civilisation living in urban areas, we are simply not accustomed anymore to how bright even nights can be when you had sufficient time to adopt - and cameras can do that instantly. In arctic (or generally snowy) regions, the snow adds a lot to the overall brightness as it reflects the little available light at night extremely well.