I fall into depression every winter, but intend to get by without meds.
That may well be seasonal affective disorder (SAD), also called winter depression, which is caused by lack of light. Light sensors in the retina (called retinal ganglion cells) detect ambient light levels, and signal to the brain. In people with SAD, once the ambient light levels fall below a certain point, low mood and depression occurs.
The remedy is simple: use artificial light to increase ambient light levels in your eyes. SAD can be eliminated simply by 30 minutes daily exposure to bright light at around 10,000 lux (or equivalently, 5,000 lux for one hour a day, or 2,500 lux for two hours a day, etc). You can buy SAD lamps which will provide 10,000 lux of light (but you have to sit close to these lamps, because the lux level falls off the further you are away from them).
On eBay, you can buy cheap light meters that measure ambient lux level for around £10. These are very useful tools in ensuring that your eyes are exposed to sufficient lux levels in the winter in your home.
For my own SAD, what I do is shine several spotlight lamps onto the white wall behind my computer monitor. That way, while you are using the computer, you are getting lots of bright light into the peripheries of your vision.
I use my light meter to measure the lux level at the location where my eyes are positioned when I am using the computer, to ensure that the light entering my eyes is at a sufficient lux level.