Inside the suprachiasmatic nucleus (SCN) of your brain, which is part of your hypothalamus, resides your master biological clock. Based on signals of light and darkness, your SCN tells your pineal gland when it’s time to secrete melatonin, and when to turn it off.
Your melatonin level inversely rises and falls with light and darkness, and both your physical and mental health is intricately tied to this rhythm of light and dark.
When it’s dark, your melatonin levels increase, which is why you may feel tired when the sun starts to set. Conversely, when you’re exposed to bright artificial lighting at night, including blue light emitted from TVs and electronic screens, you may have trouble falling asleep due to suppressed melatonin levels.
Many sleep problems can be resolved by making sure you avoid blue light exposure after sunset and sleep in total darkness.
Interestingly, being exposed to very dim light during sleep — even if it does not noticeably seem to impair your sleep — may also affect your brain function and cognition during the day.
Minute Amounts of Light During Sleep Can Affect Cognition
I’ve been a long-time advocate of sleeping in TOTAL darkness, and an interesting study1 published in Scientific Reports highlights the importance of this recommendation — not just for solid sleep, but also for cognitive health.
In this study, 20 healthy men slept in a laboratory shrouded in complete darkness for two nights in a row. On the third night, they were exposed to a dim light of either 5 or 10 lux while sleeping.
To get an idea of how dim a light intensity of 5 or 10 lux is, 1 lux is equal to the brightness of a surface illuminated by one candle, placed 1 meter (3.28 feet) away from the surface. Twilight is just below 11 lux, whereas an object illuminated by the light of the full moon is about one-tenth of a lux.2
After the second and third nights, the participants performed working memory tests (so-called n-back tests) while undergoing functional magnetic resonance imaging (fMRI). The goal was to evaluate the effects of dim light exposure during sleep on functional brain activation during a working memory task the next day.
When sleeping under 10 lux light conditions, there was decreased activation in the right inferior frontal gyrus, an area of your brain involved in response inhibition, attentional control and the detection of relevant cues when performing a task.3
Exposure to 5-lux light had no statistically significant effect on the participants’ brain activity. In other words, past a certain point of very dim light, nighttime light exposure can have a direct influence on your brain function, specifically your cognition and working memory.
Nighttime Light — A Hazardous ‘Pollutant’
According to the authors of this study:
“Nighttime light is now considered to be one of the fastest growing pollutants, and the invasion of artificial light into previously unlit areas is threatening the soundness of human health and sleep.
Nighttime artificial lighting in cities is divided into three types: sky glow, trespass and glow. Light trespass refers to unwanted direct lighting of an area, and it occurs when unwanted light spills over into another property or dwelling and causes sleep interference, negative influence on one’s well-being …
Several studies have also shown that light pollution and shift work are tentative risk factors for cardiovascular disease, breast cancer, ovarian cancer, gastrointestinal disease and metabolic syndrome …”
Fortunately, the detrimental effects of nighttime light pollution are starting to gain recognition, and some countries have even adopted regulations to reduce nighttime light in residential areas.
Guidelines issued by the Commission Internationale de l’Eclairage (CIE), Illuminating Engineering Society of North America (IESNA) and Institution of Lighting Engineers (ILE), have an upper brightness limit for light trespass of 2, 3 and 5 lux in in residential areas respectively.
Chronic Exposure to Light During Sleep May Cause Pronounced Effects on Cognition
The study in question was done to investigate whether these limits are sufficient to reduce sleep and cognitive problems associated with nighttime light pollution.
While limits of 5 lux or less appear sufficient, they discovered that exposure to 10 lux may produce adverse brain effects even if there are no subjective, outward symptoms of impairment. As noted by the authors:
“This study is meaningful because it is the first to scientifically identify the effect of the dim light at night on human brain function and cognition. It is noteworthy that the brain activation was altered after only a single night of light exposure.
This suggests that the chronic exposure to the light at night for many nights might have caused more pronounced effects on the brain and cognition … The interesting finding in the 10 lux group … was the discrepancy between the n-back task and fMRI results.
The decrease of the brain activation in fMRI in the frontal lobe without significant finding in the n-back task of 10 lux group suggests that the absence of evidence of subjective or objective cognitive dysfunction does not necessarily mean that the brain is functioning normally.
This indicates that certain exposure to dim light might influence brain function for cognition even if there is no significant impairment in subjective symptoms (or even in an objective neurocognitive function test).”
Read more: http://articles.mercola.com/sites/articles/archive/2016/12/22/dim-light-exposure-during-sleep-harmful-effects.aspx?utm_source=dnl&utm_medium=email&utm_content=art1&utm_campaign=20161222Z3&et_cid=DM128792&et_rid=1807927855