I have experienced SADD for years and years. Some years it seems to be worse than others, for whatever reason.
I do have a light. I confess I don't use it religiously.
What seems to help me more than anything else is forcing myself (yeah, sometimes I really have to kick myself in the butt) to get outside in the daylight and go for a walk. That can frequently be a challenge around here: semi-rural, no sidewalks, mostly no shoulders on the roads; when there's a lot of snow it's a big issue.
I also fantasize about spring a lot.
Jane
Every human being must be viewed according to what it is good for; for none
of us, no not one, is perfect; and were we to love none who had
imperfections, this world would be a desert for our love.
--- Thomas Jefferson