For me I feel the answer is yes, sunlight can make a difference. My diagnosis up north was major depression. When I moved to Florida I had my first hospitalization for mania. Diagnosis is now bipolar 1. And I rapid to ultra rapid cycle. I blame the sun for the drastic change in my mood swings. Not completely. I m sure other stuff is going on.

And looking back at my decades long deep depressions, a lot of it may have been mixed episodes.

My depression would deepen in the winter months. But I never experienced stability or mania/hypomania up north.

North being both New Hampshire and Pennsylvania.