Light plays a bigger role in our daily biological rhythms and health than many of us realize. All life on earth depends on photosynthesis in plants and trees, affecting food supply, climate, erosion, air pollution and the ozone layer. Plants and trees are the earth’s lungs; in one year, a mature tree will absorb more than 48 pounds of carbon dioxide from the atmosphere while producing oxygen so that we can breathe. But light also impacts our biological clock which has implications for our physical and mental health. Our daily and nightly biological rhythms are entrained to beneficial blue light (roughly 460 to 490 nm). Exposure to this light in the morning raises our dopamine levels and suppresses melatonin (our sleep hormone). As evening approaches and the light fades in our environment, these wavelengths decline in natural light allowing our melatonin levels to rise so that we fall into a deep sleep and stay asleep. Our daily cycles of melatonin production normalize circadian rhythm, reinforcing a stable sleep-wake schedule. When our circadian rhythm is thrown off, it affects everything from normal eye development in the young eye to our metabolic and heart health and more recently has been linked to cognitive decline and even dementia and Alzheimer’s.

According to research, there are two aspects of light to consider relative to healthy sleep, one is melatonin suppression preventing normal sleep regulation and second low ambient light during sleep keeps our fight or flight stress response on. When we sleep in a room with as little as 100 lux (light enough to see but not to read) our sympathetic arm of the autonomic nervous system responsible for the body’s fight or flight response remains active. The fight or flight response is supposed to cool down during sleep as the body moves into a parasympathetic state, when the body’s heart rate and respiration decrease. According to recent research, changes in cardiovascular function suggests the small amount of light exposure while sleeping was enough to shift the nervous system to a more activated and alert state. “It’s almost like the brain and the heart knew that the lights were on, although the individual was sleeping,” says Zee in the “Light Exposure During Sleep Impairs Cardiometabolic Function” research paper. So we not only need to protect our eyes from being exposed to the wavelengths that suppress melatonin within two to three hours before bedtime (think digital device… put them in dark mode) but also, we must ensure that the room we sleep in is dark enough. Reportedly up to 40 percent of us sleep with a bedside lamp on or with a light on in the bedroom and/or keep the television on.

I think back to the old black and white movies, and the stars always wore sleep masks to bed; whatever their reason for donning a sleep mask, it is a message that applies now if we want a good night’s sleep.

Deborah Kotob
Pro to Pro Director
[email protected]