When the sun doesn´t reach above the horizon during the midwinter, we call it polar night.
This phenomenon occur above the northern polar circle which means that we experience it in Kiruna during a period in the winter. The period called the Midwinter night falls on the day of Winter solstice, the 21st of December. This is when the sun does not rise above the horizon. The 4th of January is usually when we can see the sun again for the first time.Thanks to the white snow that reflects the sun rays we still have some daylight a couple of hours each day.
The polar night starts in the northern hemisphere during the autumnal equinox around the 23d of September, culminate around the 21th of December and finally ends at the vernal equinox.