The positions you worked out in summer were correct in summer. By January they describe a different apartment, and the plants standing in them have not moved.
This is the single cheapest maintenance job in the whole subject, it takes about twenty minutes once a year, and almost nobody does it.
What actually changes
Four things, and none of them requires a source to notice.
The days get shorter. Fewer hours of light per day, regardless of what any position's band is at noon.
The heating comes on. Which introduces warm, dry positions that did not exist in August, in the exact places furniture tends to be: beside radiators, above vents, near heaters.
The glass gets cold. A windowsill that was the best position in the apartment in July becomes the coldest surface in the room on a January night, while remaining the brightest by day.
You change the room. Curtains get closed earlier and opened later. Things get moved. In a small apartment, winter arrangements are genuinely different from summer ones.
The result is that your light and temperature map is not the one you planned around, and the plants are still standing where the old map put them.
Do the survey again
The same walk you did originally, with the University of Illinois Extension's bands in hand: Bright is an east or west window directly in front or a south window up to 5 feet away; Medium is a north window directly in front, an east or west window a few feet away, or a south window 3 to 10 feet away; Low is a north window a few feet away, an east or west window 3 to 10 feet away, or a south window 15 to 20 feet away.
Walk it in winter, in the afternoon, with the curtains as they actually are. That last part matters more than people expect: a curtain half-drawn all season changes a position's band, and it is invisible if you do the survey mentally rather than physically.
The room-by-room survey is the full version, and the winter run is faster because you already know the shape of the apartment.
The three moves that usually come out of it
Toward the window. The most common. A plant that was comfortably in a band in summer may be a band down in winter, and moving it a couple of feet closer recovers most of that. Per the table above, a couple of feet is a real change.
Away from a heat source. A radiator under a windowsill converts the best light position in the room into a warm, dry one. That is a real conflict and it is worth resolving deliberately rather than leaving a plant sitting in it all season. What a radiator does to a plant beside it covers that position.
Off the cold glass. A plant touching or nearly touching a window in winter is in a different microclimate from the same plant a hand's width back. What happens beside a cold window in winter covers the trade, and the useful part is that a small move usually settles it without losing the light.
Notice that the second and third moves pull against the first. The winter position is frequently a compromise between light, heat and cold glass, which is exactly why it deserves a deliberate decision rather than inertia.
Read the plants, not the calendar
Iowa State University Extension gives two signals, and although they were written about plants outdoors they are the same two indoors.
Leaning or stretching toward the light: the plant wants a brighter spot, so move it toward the window.
Burning or discoloration: too much light, so move it back.
In winter the first is the one you will see. A plant that was upright in September and reaching by December is telling you its band changed, and that is the most reliable instrument you have.
The winter answer this page is not giving
The obvious response to less light is to add some.
Supplemental lighting is a different specialty and is not this site's subject. It is covered properly by people who deal with fixtures and run times, and it deserves that treatment rather than a paragraph here.
What is worth saying from a placement point of view: do the rearrangement first. It is free, it takes twenty minutes, and it frequently solves enough of the problem that the question does not arise. Buying equipment to compensate for a plant standing in the wrong place is an expensive way to avoid moving it.
Two other things that change, and are not mine
Winter changes how much water a plant uses and how the air around it behaves. Both are real, both matter, and both belong to the people who cover care properly. They are worth reading about separately, because a plant that is repositioned correctly and treated as though it were still August is only half sorted.
Put the summer map back in spring
The whole point of doing this deliberately is that it reverses.
Make a note of what you moved and from where. Two lines in your phone. In spring you undo it, and the plant goes back to the position that was right for it in the season it was chosen for.
Without the note, the winter arrangement quietly becomes the permanent one, and by the following July everything is in a compromise position that nobody chose.
If you have pets
Winter rearrangements usually mean plants come down off sills and into rooms, which puts them within reach. Check anything you relocate, by botanical name, against the ASPCA's toxic and non-toxic plants database.
Frequently Asked Questions
Do houseplants really need moving for winter?
The positions themselves change, so yes, the arrangement is worth redoing. Four things shift without any of them needing a source: the days get shorter, the heating comes on and creates warm dry spots that did not exist in August, the glass gets cold at night while staying the brightest surface by day, and you change the room by closing curtains earlier and opening them later. The plants are still standing where the old map put them.
How do I redo the survey?
The same walk, with the University of Illinois Extension's bands in hand, but done in winter, in the afternoon, with the curtains as they actually are. That last part matters more than people expect, because a curtain half-drawn all season changes a position's band and it is invisible if you do the survey in your head rather than on your feet.
Which moves usually come out of a winter survey?
Three, and two of them pull against the first. Toward the window, because a plant comfortably in a band in summer may be a band down now and a couple of feet is a real change on the Illinois table. Away from a heat source, since a radiator under a sill turns the best light position in the room into a warm dry one. And off the cold glass, because a plant nearly touching a window in winter is in a different microclimate from the same plant a hand's width back. The winter position is frequently a compromise.
How do I tell whether a plant needs moving?
Read the plant. Iowa State University Extension gives two signals: leaning or stretching towards the light means find a spot with brighter light, and burning or discoloration means the light is too intense. In winter the first is the one you will see, and a plant that was upright in September and reaching by December is telling you its band changed.
Should I buy a light instead of moving things around?
Do the rearrangement first. Supplemental lighting is a different specialty and is not covered here, but from a placement point of view the move is free, takes about twenty minutes, and often solves enough of the problem that the question does not arise. Also write down what you moved and from where, because without that note the winter arrangement quietly becomes the permanent one.
The part worth remembering
The apartment you mapped in summer is not the apartment your plants are standing in now. Shorter days, heating on, cold glass, curtains drawn.
Redo the survey once in winter and once in spring, write down what you moved, and move it back. It costs twenty minutes twice a year and it is the difference between plants that hold through the winter and plants you replace in March.