Your sleep and wake cycles follow your “circadian rhythm”. The Latin word “circa” means “one” and “diem” means “day”, so circadian translates to “one day”. This one-day cycle initiates when your eyes first take in light in the morning.
The light passes through your eyes to your hypothalamus, a group of brain cells behind the optic nerves. The hypothalamus acts as your body’s hormonal hub – when your hypothalamus “sees” the morning light, it signals the start of its daily hormone production schedule. At set times throughout the day, it releases hormones that control your energy levels, digestion, blood pressure, immune system, fat burning and more. Inconsistent and inadequate sleep will throw off that schedule.
Sunlight taken in through our eyes and skin when you’re outdoors helps regulate production of cortisol, serotonin, and melatonin – all essential hormones for a good night’s sleep (and a better mood tomorrow). Daylight is 100 times more powerful than indoor lighting. Even on a cloudy day, you get 10 times more light outdoors than inside (source, p.11).