Light is the most important external factor affecting sleep. While most people intuitively know that it’s easier to sleep when it’s dark, the link between light and sleep goes much deeper.

Light plays a central role in regulating circadian rhythm, the body’s internal clock that signals when to be alert and when to rest. Light also affects the production of melatonin, an essential sleep-promoting hormone.

While human biology evolved with sleep following the daily patterns of sunlight and darkness, ubiquitous electricity makes 24/7 illumination possible. From streetlights to office lighting to cell phones, artificial light is a constant part of modern life, brightening homes and the nighttime sky.

Daily light exposure, including the type of light we see as well as when and how long we’re exposed to it, has a critical effect on sleep. Learning about the complex links between light and sleep allows you to set up your bedroom to be more conducive to consistent, high-quality sleep.

Article Source: https://www.sleepfoundation.org/bedroom-environment/light-and-sleep#what-types-of-light-affect-sleep--2