I agree about SAD. A full spectrum light used first thing in the morning is very helpful. Be sure and open your curtains and/or blinds when you get up so lights gets to your brain. You don't want to keep your house dark all day as that makes SAD worse.

Another thing that has been linked to SAD is low melatonin levels. I've noticed how much less depressed I am in the winter if I take melatonin before bed.