If you spend your days in an office, and put on your sunglasses to go outside, only to rush home to the dim confines of your air conditioned house, you are a potential sufferer or at least that is my experience. Depression is real. There are some excellent new therapies. The further north you live , the more likely you are to get the disease, because it is related to day light. Climate, season and weather affect mood, in addition to latitude, storms, cloud cover, and how much time you spend indoors under artificial light for whatever reason.
Some people are more sensitive to changes in light than others.
Doctors believe light has a biological effect on brain hormones and function. Treatment is based on the interaction of light with the eyes, not the skin. Typically the patient is directed to sit directly in front of the light once or twice a day, from 30 minutes for the brighter light boxes to a couple hours for the lights that are not quite as intense. The time required varies between different people. Opinions differ as to what kind of light and what intensity.