Log in
After returning home and before going to bed, it can be quite difficult to stay away from your smartphone, PC, or TV. Many people, especially when they can't fall asleep right away, tend to reach for their smartphones. This behavior, however, actually hinders your sleep even further. Let's take a closer look at the details.
Using your smartphone before bed is counterproductive
It's easy to find yourself using electronic devices like smartphones and PCs for work, leisure, or personal matters right up until bedtime, but it's best to resist the urge to look at electronic devices that emit blue light before sleep. Also, it's recommended to keep the room dim and use indirect lighting to reduce the overall illumination.
Reasons why blue light should be avoided
Exposure to strong blue light (when the human retina perceives light with a wavelength of about 470nm) suppresses the secretion of "melatonin," known as the sleep hormone, and shifts the body into an awake state.
Incidentally, visible light wavelengths (visible light: approx. 400-800nm) (※1) become longer as they approach red (infrared) and shorter as they approach purple (ultraviolet). Blue light (bluish light) is a short wavelength light with high energy, making it easy to reach the retina.
On the other hand, light closer to red (long-wavelength, warm-toned light) is easily absorbed by the cornea and lens, making it less likely to reach the retina. Furthermore, the human retina has three photoreceptor cells (cone cells, rod cells, and melanopsin-expressing retinal ganglion cells). When strong blue light reaches the melanopsin-expressing retinal ganglion cells, the function of suppressing melatonin secretion, the sleep hormone, is activated, which in turn hinders sleep. In animals, blue light itself has been confirmed to have an awakening effect.
While fluorescent lamps and sunlight also contain blue light and emit a wide range of wavelengths, LEDs, which are used in many electronic devices, have a very high proportion of blue light. Therefore, electronic devices that use LEDs should be avoided as much as possible before bedtime.
Depending on how it's used, light can be both a poison and a cure for sleep. In other words, it can promote both wakefulness and sleep.
During the day or when you want to ward off sleepiness, exposure to strong light, including LEDs, makes you more alert and active. For example, during night sports, the lights are dazzlingly bright, which, in addition to simply making things brighter, helps both athletes and spectators become more alert.
What's important is the time and timing of light exposure. In particular, strong light can disrupt the body's rhythm, so it's crucial to use it wisely. Nearly 10 years ago, many railway companies, including JR companies, installed blue lights (blue light) at the ends of station platforms and at level crossings as a suicide prevention measure. Blue light may have not only an awakening effect but also an antidepressant effect.
If using electronic devices, use the blue light OFF function as much as possible
Many phones and computers have a function to reduce blue light (night mode). If you haven't used it before, check it out. Even if it's not built-in by default, you can use free apps.
Common bad habits
Using a smartphone at close range for extended periods in a completely dark room after turning off the lights before bed is very bad for sleep, so we recommend that anyone with this habit stop today. This is because it enhances the impact of blue light. Even though you are about to sleep, this behavior amplifies the stimulation of the sympathetic nervous system by blue light, putting you in an awakened state and making it difficult to fall asleep for a while.
Furthermore, prolonged use, due to the intensity of blue light, can easily lead to retinal damage (damage to the macula at the center of the retina, potentially increasing the risk of age-related macular degeneration) (※2) and eye strain (eye fatigue and dry eyes) (※3). Therefore, it is ideal to take regular breaks and gradually reduce usage as bedtime approaches.
The effects of light exposure vary depending on timing, illuminance/wavelength, and duration. Exposing yourself to blue light at night is the worst timing, and playing games or sending/receiving emails on your smartphone will further excite your brain and make it even harder to fall asleep.
Japan's overly bright lighting
Compared to America, Japan's lighting in places like restaurants and hotels seems considerably brighter, even at night. In homes, while Japan often uses fluorescent lights and ceiling lights to brighten the entire room, it is said that in America, orange-toned indirect lighting is often used instead of fluorescent lights or ceiling lights.
This is believed to be because Americans have a stronger perception that "home is a place for family gatherings and relaxation," and people of Caucasian descent have relatively lighter eye pigment, making them more sensitive to light. If possible, creating a relaxing lighting environment after returning home, allowing your body to naturally transition towards sleep, can be effective for getting a good night's rest.
Also, while some people leave the bedside light on when sleeping, it is recommended to turn off the lights and darken the room. This is because even typical night light (approximately 10 lux) is believed to inhibit melatonin synthesis and secretion. Instead of a bedside light that shines directly into your eyes, why not try using a small footlight or similar alternative?
【References】
※1:Blue Light Research Society, What is Blue Light?
※2:Biological effects of blocking blue and other visible light on the mouse retina.
※3:Effect of Blue Light-Reducing Eye Glasses on Critical Flicker Frequency.
