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.