What are the common misunderstandings about how bright a bedroom should be?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
"Should I sleep in total darkness, or is a small night light fine?" is asked all over the world. In Japanese homes the standard ceiling light has a built-in night-light setting, the small orange bulb called the *mame-denkyū* (豆電球, "bean bulb"), and how to use it is a common question.
In numbers
| Situation | Guide | Basis |
|---|---|---|
| 1–2 hours before bed | Dim the lights (indirect lighting, warm colour). Avoid phone and PC screens, or dim them | Sleep Guide 2023 |
| Bedroom (while asleep) | As dark as possible. If needed, a weak warm-coloured light at floor level (a few lux) | Same as above |
| Morning | Open the curtains after getting up and take in the light. Even on a cloudy day, outdoors is several thousand lux | Same as above |
| Typical indoor lighting | 300–500 lux (living room); offices about 750 lux (JIS Z9110) | JIS |
| Night light (mame-denkyū) | 1 to a few lux (varies by product) | — |
- Bluish-white light ("daylight colour", a high colour temperature) is generally described as promoting wakefulness, while warm light ("bulb colour") has a smaller effect. Use warm "bulb colour" lighting in the bedroom (on Japanese bulb packaging: 電球色, *denkyū-shoku*).
- Light at night is known to suppress melatonin (a hormone involved in sleep), and several studies find that the habit of sleeping in a bright room lowers sleep quality.
- For older people who get up to use the toilet at night, a weak light at floor level prevents falls better than total darkness, so a warm-coloured light with a motion sensor is practical.
[Verify] Check the statements on light in the Sleep Guide 2023, and the illuminance standards in JIS Z9110.
Misunderstanding 1｜Once you get used to a bright room, it makes no difference
Brightness acts on the body clock; it is generally described as not a matter of getting used to it. Even if you sleep, the sleep is shallower.
Misunderstanding 2｜A night light is dim, so it is no problem
A weak, warm-coloured light at floor level is generally described as having little effect. Avoid white light near the face or from the ceiling.
Misunderstanding 3｜If you dim the screen, a phone is fine right before bed
The problem is not only brightness but the wakefulness caused by the content. Staying off screens for the hour before bed is the sleep guide's basic position (see our article on phones before bed).
Misunderstanding 4｜In the morning, it is better to wake slowly in a dark room
Morning light is the strongest signal for setting the body clock. Opening the curtains, sleeping with them slightly open, or a dawn-simulating light alarm (*hikari mezamashi*) are the everyday tricks people in Japan use.
Misunderstanding 5｜Blackout curtains are always the right answer
They are effective at blocking city light at night, but they also block the morning light, so many people open them at their wake-up time or combine them with timer-driven curtains or a light alarm.
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Sources
- Ministry of Health, Labour and Welfare, *Sleep Guide for Health Promotion 2023* [健康づくりのための睡眠ガイド2023]
https://www.mhlw.go.jp/content/10904750/001181265.pdf
- Japanese Industrial Standards Committee (JISC), JIS Z9110 *General rules of recommended lighting levels* [照明基準総則]
https://www.jisc.go.jp/
- Ministry of Health, Labour and Welfare, e-Healthnet, *The body clock and light* [体内時計と光]
https://www.e-healthnet.mhlw.go.jp/information/heart/k-02-002.html
⚠️ 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.
About this article
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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