According to a 2019 survey by the Taiwan Sleep Medicine Association, 10% of Taiwan's population suffers from long-term insomnia. Insomnia seems to be an epidemic of the 21st century. However, recent scientific discoveries suggest that "embracing darkness" is the key to unlocking health and longevity. This is because when you turn off the lights, shut down the computer, and listen to the TV in the evening, the brain detoxifies, cells repair, and the secretion of important hormones occurs in the dark. This process helps you feel relaxed and rejuvenated, and when you wake up the next day, you'll feel refreshed and full of energy.
Professor Zhou Zhuohui from the Department of Materials Science and Engineering at Tsinghua University conveys this new health concept in the book Embracing Darkness, using scientific research and data to show that lighting up at night is a harmful habit. Below are key highlights from the book:
The Harmful Effects of Sleeping with Lights On
Increasing medical research confirms that sleeping with lights on can cause various harms and negatively affect health. These harms might occur the following day or even decades later, but our bodies will pay a huge price. On the other hand, sleeping in darkness brings countless benefits. More importantly, if you can turn off the lights early and sleep in a completely dark environment, not only will you sleep deeply, but you'll also wake up feeling energized!
Turn Off the Lights Early to Receive Sleep Signals
In the evening, creating an atmosphere conducive to sleep can include dimming the lights, turning off unnecessary lights, playing soothing music, or doing simple stretching exercises to help the body relax. This allows your body to receive sleep signals earlier and also improves sleep quality.
Research on Light Exposure and Melatonin Secretion
Joshua Gooley, Assistant Professor at Duke-NUS Medical School in Singapore, conducted a study with 116 healthy volunteers aged 18 to 30. The study compared their melatonin secretion after exposure to different light levels. The results showed that participants exposed to bright indoor light (less than 200 lux) from dusk until bedtime had their melatonin production suppressed, with a 90-minute reduction in the duration of melatonin secretion compared to those exposed to dim light (less than 3 lux).
One important finding was that light exposure before bedtime reduced melatonin secretion by 71%. This means that turning off the lights just before sleep shortens the time and amount of melatonin produced, making it harder to fall asleep. On the other hand, turning off unnecessary lights earlier can promote melatonin secretion and help induce sleep.
The Relationship Between Light and Melatonin Secretion
In another study by Iveta Herichova, Associate Professor at Comenius University in Slovakia, researchers showed a graph of the relationship between melatonin secretion and time. The graph showed that from 7 p.m. to 9 p.m., melatonin secretion increased by 13% to 27%. If this data applies to humans, it suggests that turning off lights before bedtime would help increase melatonin secretion. From 9 p.m. to 1 a.m., melatonin levels would peak, and it would maintain that peak until 5 a.m., just like in humans.
Daylight and Darkness
Numerous studies have concluded that turning off the lights before bed can prevent melatonin secretion from being delayed. If you sleep with lights on, it will suppress melatonin secretion even more. It's important to note that light exposure affects children's melatonin secretion more than adults.
Furthermore, the brighter the light at night, the more it suppresses melatonin production. Specifically, blue light or high color temperature light before or during sleep is the most disruptive to melatonin secretion. However, low-intensity light, like candlelight (under 2000K), has no such effect.
Interestingly, exposure to bright light (900-2700 lux) during the day can promote stable melatonin secretion in the evening. In contrast, insufficient daylight, such as being indoors in a shopping mall, can easily affect melatonin production at night. In short, bright light during the day and dark nights are both healthy habits.
The Importance of Darkness at Night
This explains a lot. If we don't turn off the lights or dim them, the brain cannot secrete melatonin, the natural sleep aid. Without melatonin, the body cannot relax, making it difficult to sleep. What's worse is that light causes the secretion of "waking hormones" like cortisol, keeping us highly alert and making it almost impossible to feel sleepy.
Luckily, after I developed the habit of turning off the lights earlier in the evening, I was able to fall asleep more easily. At first, I would dim the lights around 9 p.m. and found it to be quite comfortable. Later, I started dimming them at 8 p.m. with just two small lamps. Now, after dinner, by about 7 p.m., I turn on only one small light. Not only have I saved on electricity bills, but more importantly, I have saved my eyes, improved my sleep, and enhanced my health. In this kind of environment, I can sleep 7 to 8 hours every night and wake up refreshed, making it a common and enjoyable experience.