It is no coincidence that our mood improves in the summer. The anticipation of holidays, the sea, and more frequent nearby excursions can certainly fill us with positive emotions. However, these are not the only factors that contribute to peace of mind; the increased sunlight also plays a unique role.

According to researchers at Harvard-affiliated Brigham and Women’s Hospital, exposure to the sun can improve a person’s mood, leading to more restful nights. Specifically, in their study examining data from more than 6,600 participants from 2011 to 2014, they found that participants who spent more time in bright light had more regular sleep patterns. This regularity in sleep was associated with fewer symptoms of depression and lower odds of mild or severe depression.

“Consistent, regular sleep has broad implications for our health,” said co-author Dr. Susan Redline, the Peter C. Farrell Professor of Sleep Medicine at Harvard Medical School and senior physician in Brigham’s Division of Sleep and Circadian Disorders. “Future studies examining bright light therapy should not overlook the role that sleep regularity may play in influencing mood and depressive symptoms,” she adds.

The research team investigated whether exposure to bright light (at a level generally equivalent to daylight exposure) was associated with depressive symptoms, and if so, whether the sleep regularity index (a measure of the consistency of daily sleep schedules) explains this association. Bright lighting and sleep regularity were measured with a portable device worn on the wrist.