- There are reports that morning light exposure may have a negative effect on sleep quality.
- The evidence score is 46, and reliability is considered low.
- This information is for people concerned about the timing and type of light exposure.
Morning light exposure refers to the light stimulus received through the eyes or skin.
It is treated in various contexts as one of the factors that regulates the cycle of sleep and the body clock.
Much research has been conducted on whether the timing of light exposure is appropriate for our bodies. As one example, there is a systematic review (a method that gathers and analyzes many studies together to derive a conclusion) published under the title "Systematic review of light exposure impact on human circadian rhythm." In other words, this is an attempt to grasp the overall picture by integrating various previous investigations, not just individual experimental results.
Research suggests that morning light exposure may have a negative effect on sleep quality. This study examined the body clock of adults mainly in their 20s and 30s. Specifically, it reports that exposure to light at the wrong timing may disrupt the human circadian rhythm (the body's mechanism, like a body clock, that repeats on a 24-hour cycle). In other words, a shift in the timing of light exposure in daily life may affect the body's rhythm.
There are also interesting research results regarding how one spends the evening. In a study of Americans with 1,508 participants, a survey was conducted on reading habits in the hours before bedtime. This study compares two patterns: reading a paper book, and reading a light-emitting eReader (electronic book).
The design of this study was carried out in a format called "other." This is a survey based on observation under specific conditions, differing from those conducted under strict conditions such as randomly dividing participants. As a result, it was shown that using an eReader tends to take longer to fall asleep compared with a paper book. It was also reported that nighttime sleepiness and melatonin secretion (the phenomenon by which the hormone that induces sleepiness is produced in the body) decreased. Furthermore, it was pointed out that the timing of the body clock may be delayed, and next-morning alertness levels may decrease. In other words, it can be said that how light is used before bed may affect subsequent sleep and the next day's activity.
There is also research targeting students regarding the light emitted from smartphone screens. The content concerns how the sleep state changes when the amount of blue light emitted from a smartphone at night is reduced.
This study showed an improvement in subjective sleep quality (the satisfaction and sensation of sleep as felt by the person themselves). Furthermore, there are reports of improvement also being seen in daytime activity levels. In other words, it can be said that paying attention to the nature of light during nighttime smartphone use may have a positive effect on how sleep is felt and on daytime activity.
| Study | Design | Number of Participants | Duration | Main Result |
|---|---|---|---|---|
| Chronobiology International (2019, PMID:30311830) | Systematic review | Unknown | Unknown | A possible negative effect was reported |
| Proceedings of the National Academy of Sciences of the United States of America (2015, PMID:25535358) | Other study design | 1508 people | Unknown | A possible negative effect was reported |
| Chronobiology International (2023, PMID:36744480) | Other study design | Unknown | Unknown | A positive effect was reported |
The subjects include American adults (mainly in their 20s and 30s) and students, totaling 1,508 people.
Because the research subjects are adults and students, this serves as material for considering it in comparison with your own lifestyle.
The research is based on data from 3 studies.
The study designs are a systematic review and other study designs, and no randomized controlled trial (RCT) has been conducted.
It has also been reported that there are contradictions in the results, and reliability is considered limited.
Is morning light exposure related to sleep quality?
Research has been reported suggesting that morning light exposure may have a negative effect on sleep quality. This result is based on data from 3 studies.
What format has research on morning light exposure taken?
Surveys using a systematic review and other study designs have been reported. The format of the study designs varies.
What is the reliability of research on morning light exposure like?
It is based on 3 reports, but reliability is considered limited. It has also been reported that there are contradictions in the results.
This article introduced 3 research reports on the effect that the timing and type of light have on sleep. There are reports suggesting that light exposure, including during the morning hours, may be related to the body clock and sleep quality, but the research also contains contradictions, and with an evidence score of 46, reliability is limited.
This information is merely a report based on research, and how it feels differs from person to person. If you are concerned about your own sleep condition, please also try the self-check assessment.