A sunny day in midsummer further south generates about 80,000 lux. Sometimes called winter depression, or SAD disease, symptoms of seasonal affective disorder can occur year around, even in a bright sunny climate. 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.