I look at the bipolar map as shown in the attachment below, and if I imagine the sun making a circle around the south pole as it is proposed that it does in the winter in the bipolar model described further up in this thread, there is a point on Dec. 21st when the sun is on the opposite side of the south pole from all of the continents in the northern hemisphere. At that distance, and again according to this model where the sun's light only reaches a certain distance on the flat earth (as described by Tom Bishop: "There is another mechanism which pushes the sun lower than it actually is, and limits its total visibility, and is a separate topic from this thread, and which there is evidence for. If this mechanism did not exist day and night could not exist, and the sun would be at all times above the surface of the earth."), then it would seem that none of the light would reach the northern hemisphere. Again in circling the south pole, the sun would be on the other side of the pole from all of the continents in the north, as shown in position B for at least part of every 24 hour day/night cycle.
This would result in the entire northern hemisphere being dark at the same time. That never happens even in the dead of winter. It is dark at the north pole for months at a time, but if you plot the positions of the sun as it circles the south pole, then at its closest position to the north pole, it would be at point A in the version of the map that is attached below. At its furthest position from the north pole it would be at position B, again in the attached image.
If at point A, the north pole is in total darkness, then at point B, all of the northern hemisphere (and even actually most of the land masses in the southern hemisphere would all be in darkness at the same time. This does not ever happen. It is never nighttime in the entire northern hemisphere at the same time.
To check this compare the distance from point A to the north pole, with the distances from all of the continents to point B. If the sun at point A does not light up the north pole, then the sun at point B would not light up most of the land masses on earth with the exception of the southern tips of South America, Africa and Australia. Everything else would be dark at that time of the day.
When has it ever been dark at the same time of the day in every city of North America, Europe, Asia and northern Africa and northern South America? Really? Nighttime in Honolulu, Los Angeles, New York, London, Paris, Cairo, New Delhi, Bangkok, Beijing, Tokyo and everywhere in between all at the same moment in time? That simply does not happen, ever. These cities span 18 time zones! When is it ever dark across 18 time zones at the temperate latitudes and also at the equator?
There is no path of the sun over a bipolar flat earth that can match the simplest patterns of daylight we observe every day in the winter in the northern hemisphere, where it is always daylight somewhere in the northern hemisphere, and is never simultaneously dark everywhere above the equator.