As the days become shorter and shorter many people – up to 30% – report noticeable changes in energy.  10% of those with less energy would qualify for a diagnosis of depression between October and March.  Less daylight equals less energy and a lower mood which are symptoms of Seasonal Affective Disorder (SAD).  Worsening of mood as the sun rises later and sets earlier are related to our circadian rhythms.  Circadian rhythms are controlled by our brains and related to exposure to light.