- There are reports that no clear association was found between blue light at night and sleep quality.
- The evidence score is 53, and the reliability is moderate.
- This information is for those who want to know how blue-light-blocking glasses or nighttime device use affect sleep.
Blue light at night refers to light with a short wavelength and a bluish quality.
It is generally discussed in the context of light entering the eyes at night due to the use of digital devices.
A study has reported that no clear association was found between blue light at night and sleep quality (based on 3 studies, reliability moderate).
The first study behind this conclusion examined how the effects of light relate to sleep. It involved 24 participants with a healthy circadian (body clock) rhythm, who were exposed to light under specific conditions for 6.5 hours, from 5:30 p.m. to midnight.
This study was conducted as a randomized controlled trial (a highly reliable research method in which participants are randomly divided into groups to compare effects). As a result, no differences due to the light conditions were seen in melatonin (a hormone that promotes sleep) secretion levels, alertness (the state of consciousness and ease of directing attention), or sleep-related measurements. In other words, there are cases in which the effect of light does not show up in sleep.
Using blue-light-blocking glasses has not been shown to produce results that improve objective sleep quality.
This was a small-scale study conducted over a 14-day period involving 20 healthy adults (11 men, 9 women).
This study was also conducted as a randomized controlled trial (a highly reliable research method in which participants are randomly divided into groups to compare effects), but no changes due to glasses use were seen in objective indicators of sleep duration and quality (data measured numerically, such as sleep time and movement). In this small-scale study involving 20 healthy adults, no improvement in sleep from blue-light-blocking glasses was observed. In other words, using glasses does not necessarily mean that sleep-related measurements will improve.
Regarding blue light exposure after 9 p.m., effects on sleep and performance have been reported.
This study was conducted on young athletes. It investigated the effects of light during a specific time period.
As a result, there is a report that exposure to blue light after 9 p.m. negatively affects not only sleep quality but also athletic performance (movement and precision when engaging in physical activity) and cognitive function (brain functions such as thinking and judgment).
| Study | Design | Number of Participants | Duration | Main Result |
|---|---|---|---|---|
| Journal of Clinical Neurology (Seoul, Korea) (2020, PMID:32657060) | Randomized controlled trial (RCT) | 24 | Unknown | No clear association was found |
| Biology of Sport (2025, PMID:40656989) | Randomized controlled trial (RCT) | Unknown | Unknown | A possible negative effect was reported |
| Sleep Health (2021, PMID:33707105) | Randomized controlled trial (RCT) | 20 | 14 days | No clear association was found |
Across the 3 studies, a total of 44 participants were included. This includes 24 healthy subjects with an intermediate chronotype and 20 healthy adults (11 men, 9 women).
These studies targeted healthy adults and people with an intermediate chronotype. This can serve as a reference for checking whether your own situation matches these groups.
The number of studies analyzed here is 3.
All of the studies conducted used a randomized controlled trial (RCT) design.
While some reports found no clear association with sleep quality, others reported negative effects on sleep quality, athletic performance, and cognitive function — the results are divided.
What is the relationship between blue light at night and sleep quality?
Studies have reported that no clear association was found between blue light at night and sleep quality. This is based on 3 studies, with moderate reliability.
Do blue-light-blocking glasses help against blue light at night?
There is a study finding that blue-light-blocking glasses did not improve objective sleep duration or sleep quality in healthy adults. It has been shown that using blue-light-blocking glasses does not improve objective sleep indicators.
Does exposure to blue light after 9 p.m. have an effect?
There is a report that blue light exposure after 9 p.m. negatively affects sleep quality, athletic performance, and cognitive function. It has been shown that exposure to light after 9 p.m. may negatively affect these functions.
Regarding the relationship between blue light at night and sleep, while some reports found no clear association, others suggest that an effect may occur depending on the time of exposure. This information is based on 3 studies, and there are aspects that still require further examination, such as the limited number of participants. Why not check how your own lifestyle habits are affecting your sleep with a self-check?