Value Village ／ Health
This answer is a draft. It stays unpublished until legal review and source verification are complete.
"The light from the screen is bad for you" is one of the best-known pieces of sleep advice in the world. Far fewer people, in Japan or elsewhere, know what the Japanese government's own sleep guideline actually says. Its advice goes one step further than the light.
The Ministry of Health, Labour and Welfare (MHLW) published the *Sleep Guide for Health Promotion 2023* (健康づくりのための睡眠ガイド2023). As conditions for good sleep, it lists not looking at bright screens before bed, not bringing smartphones or tablets into the bedroom, and keeping the bedroom as dark as possible.
[Verify] The above was confirmed through secondary sources. Check the wording of the original text.
Several studies confirm that strong light at night affects the body clock and sleepiness. However, studies disagree on how much difference a screen-level brightness makes. Outdoor daylight reaches tens of thousands of lux; indoor lighting is a few hundred lux; a screen is weaker still.
We are not yet at the stage where "phone light disturbs sleep" can be stated as a hard number.
Changing the colour of the screen does not help if the content is stimulating and pushes your bedtime later. The guideline says "do not bring it in" because, as we read it, changing behaviour is more reliable than changing light.
Many people use their phone as an alarm clock. A rule you cannot follow is worth nothing. Simply placing the phone out of arm's reach reduces the number of times your hand drifts towards it without thinking.
An interruption after you have fallen asleep cuts directly into your sleep. Switching off notifications works, reliably.
A work email, a message that could turn into an argument, a video you want to see the end of. If the content sets your mind working, falling asleep becomes harder whatever the light.
Many factors affect sleep. If you keep failing to sleep to the point where it disrupts your daily life, see a doctor (in Japan, a general internal-medicine clinic, 内科 *naika*, is a normal first stop and is covered by health insurance).
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https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/kenkou/suimin/index.html
https://www.e-healthnet.mhlw.go.jp/information/heart/k-02-001.html
https://www.ncnp.go.jp/nimh/sleep/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
This article is not meant to diagnose or manage any specific medical condition. If you are worried about your health, see a doctor rather than relying on your own judgement.
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