Vol.2 Light entering the eyes and sleep quality
Blue light is something we hear about frequently today. When a large amount of blue light enters the eyes at night, it can have a negative impact on sleep rhythms. How does the light entering the eyes affect sleep quality? | ![]() |
Melatonin, a hormone that induces sleepiness
We fall asleep at night and wake up in the morning because our body rhythms are controlled by our internal clocks. Melatonin, which is secreted by the brain, synchronizes the body’s internal clock with the 24-hour rotation of the Earth. Melatonin induces sleepiness in the brain Its secretion begins 14 hours after sunlight enters the eye. We regulate our internal clock by getting sunlight into our eyes in the morning to regulate the secretion of melatonin.
Blue light is a wake-up call
Blue light is emitted at a wavelength of 380–500 nm, which is close to that of ultraviolet light in visible light. It is a strong light that is not absorbed by the cornea or lens, rather directly reaching the retina at the back of the eye. Computers and smartphones, especially those using light-emitting diodes (LED), emit significant amounts of light.
Our bodies switch to a state suitable for daytime activities by allowing sunlight, which is rich in blue light, to enter the eyes in the morning. However, if a computer screen is operated late at night, the blue light emitted from the screen stimulates the eyes to perceive that it is daytime, and the secretion of melatonin is suppressed. Thus, blue light disrupts the body’s internal clock, which is one of the factors that reduce sleep quality.
However, blue light is not harmful to human health. Awareness of the amount and duration of light entering the eyes does not adversely affect sleep. As mentioned earlier, in the morning, letting sunlight, including blue light, enter your eyes will help you wake up. At night, it would be better to avoid exposure to blue light two hours before bedtime so that one can sleep comfortably.
Be aware of the light that enters your eyes and try to have a good night’s sleep and a perfect morning!
References
“Kisho-jutsu (The art of waking up)” by Naofumi KAJIMURA, Kawade Shobo Shin-sha
“The Art of Sound Sleep” by Yoshihiko KOGA, “Media Factory
“Melatonin” by Reiter, Russel J., translated by Toshiko OGAQA, Kodan-sha
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