Light at night
Pooled observational studies link more light at night to more sleep disturbance, obesity, depression and type 2 diabetes. In one trial, a single night of room light during sleep raised next-morning insulin resistance. Eye masks improved rated sleep in hospital patients. Blue-light filtering glasses gave inconsistent results on sleep and did not change eye strain.
Checked 2026-11-13
- Status
- A daily life factor, not a product. Blue-light filtering glasses and sleep masks are sold as consumer products.
- Also called
- artificial light at night, ALAN, light pollution, bedroom light, sleeping with the light on, sleeping with the TV on, night light, nightlight, blue light, screen light before bed, light-emitting devices at night, dark bedroom, eye mask, sleep mask, blue-light blocking glasses, blue-blocking glasses, amber glasses
- Studied for
- sleep, falling asleep faster, melatonin, mood, depression, weight control, blood sugar, diabetes prevention, less eye strain from screens
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Shown to help1
Reported risks8
- ModerateLinked to 27% more sleep disturbance in people with the most light at night in one meta-analysis of observational studies.How often is not known
- ModerateLinked to 14% higher odds of obesity with the most light at night in one meta-analysis. In women, sleeping with a light or television on predicted weight gain.How often is not known
- ModerateLinked to 22% higher odds of depression with more light at night in one meta-analysis. In older adults, bedroom light of 5 lux or more predicted new depressive symptoms.How often is not known
- ModerateLinked to more diabetes with light at night in one meta-analysis and one cohort that measured light with wrist sensors, with risk rising as nights got brighter.How often is not known
- ModerateLinked to 8% to 10% more breast cancer in women with higher indoor or outdoor light at night in one meta-analysis. Data on other cancers were too few.How often is not known
- LimitedOne small trial found a single night of sleeping in room light raised next-morning insulin resistance by about 15% and night heart rate, against sleeping in dim light.How often is not known
- LimitedOne laboratory study found reading on a light-emitting e-reader before bed delayed sleep and the body clock and lowered next-morning alertness, against a printed book.How often is not known
- LimitedLimited evidence: trials reported infrequent side effects of blue-light filtering glasses, including headache, discomfort, lower mood and more depressive symptoms.How often is not known
What it was studied for, and what was found
Shown to help1
Eye masks for sleep in hospital
Shown to improve rated sleep quality in intensive care patients using eye masks, alone or with earplugs, in three reviews. Earplugs alone did not change sleep quality.
Compared with control groups in randomized trials the abstract does not describe [1]; control groups, including routine care, in randomized and nonrandomized studies [2]; comparison conditions the abstract does not describe [3]
The numbers and sources
- Effect
- Earplugs and eye masks together or apart improved self-reported sleep quality (SMD 1.44, 95% CI 0.80 to 2.09). Eye masks alone had a large effect (1.56, 95% CI 1.08 to 2.05), both together the largest (2.08, 95% CI 0.95 to 3.21), and earplugs alone none (0.07, 95% CI -0.50 to 0.64) [1]. Eye masks and earplugs improved sleep questionnaire scores, and polysomnography showed more total sleep time, higher sleep efficiency, more REM sleep and fewer awakenings and arousals [2]. Most of 19 studies showed better subjective sleep quality, while objective measures were not consistently improved [3].
- Population
- 797 adult ICU patients in 13 randomized trials [1]. 2,687 participants in 35 studies, 21 pooled [2]. 1,379 participants in 19 ICU and non-ICU studies [3].
- Sources
- [1], [2], [3]
- Caveats
- Patients in intensive care, where light and noise at night are far above home levels. Masks cannot be blinded, and sleep quality was mostly self-rated with tools that varied between studies [3].
Mixed results1
Blue-light filtering glasses in the evening
Mixed results: three reviews of blue-light filtering glasses found sleep improved in some trials and not others, with no change in objectively measured sleep against clear lenses.
Compared with non-blue-light filtering lenses [4]; visually identical clear-lens glasses worn at the same time [5]; control conditions the abstract does not describe [6]
The numbers and sources
- Effect
- Six trials gave inconsistent findings on sleep quality, three showing improvement and three no difference, with very low certainty of evidence [4]. In three double-blind crossover trials, the glasses did not change time to fall asleep (-4.86 minutes, 95% CI -20.23 to 10.52), total sleep time (8.75 minutes, 95% CI -35.31 to 52.82), sleep efficiency or wake after sleep onset, measured by wrist actigraphy [5]. A review of 16 randomized trials and other reports found substantial evidence of shorter time to fall asleep in people with sleep disorders, jet lag or variable shift schedules [6].
- Population
- 148 participants in 6 trials of sleep, within 17 trials overall [4]. 49 adults in 3 crossover trials [5]. 453 patients in 16 randomized trials, plus uncontrolled studies and case reports [6].
- Sources
- [4], [5], [6]
- Caveats
- Trials were small and short, and most were at high risk of bias [4]. The positive review was not a meta-analysis and included uncontrolled studies [6]. Populations ranged from healthy adults to people with insomnia, mania and depression.
Amounts studied
Cohorts measured light at night in three ways: outdoor light at night from satellite images, self-reported light in the bedroom (no light, a nightlight, light outside the room, or a light or television on in the room), and light sensors worn or placed in the bedroom [7][8][9][10]. One cohort used 5 lux in the bedroom as its cut point [9], and another ranked a week of wrist light sensor data into percentiles [10].
The laboratory trial compared overhead room light at 100 lux with dim light under 3 lux during one night of sleep [11]. The e-reader study compared reading on a light-emitting device with reading a printed book in the hours before bed [12]. Glasses trials lasted from under a day to five weeks [4], and one crossover trial used amber lenses for 2 hours before bed [5].
Risks
Reported risks8
Light at night linked to sleep disturbance
Linked to 27% more sleep disturbance in people with the most light at night in one meta-analysis of observational studies.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Against low or no light at night, the highest exposure group had more sleep disturbance (pooled prevalence ratio 1.27, 95% CI 1.12 to 1.45). The certainty of the evidence was rated high, although most studies had a high risk of bias in how exposure was assessed [7].
- Population
- 765,838 participants in 15 studies, 691,851 in the 10 pooled [7].
- Sources
- [7]
- Caveats
- Observational. Outdoor light from satellites does not measure light in the bedroom. People who sleep poorly may turn on lights, which is reverse causation.
Light at night linked to weight gain and obesity
Linked to 14% higher odds of obesity with the most light at night in one meta-analysis. In women, sleeping with a light or television on predicted weight gain.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- The highest exposure group had higher odds of obesity (OR 1.14, 95% CI 1.07 to 1.22) and overweight (OR 1.07, 95% CI 1.00 to 1.15) than the lowest, in adults and adolescents, and not significantly in Europe [13]. Against no light, sleeping with a television or light on in the room was linked to gaining 5 kg or more (RR 1.17, 95% CI 1.08 to 1.27), new overweight (RR 1.22) and new obesity (RR 1.33, 95% CI 1.13 to 1.57) over about 5.7 years [8].
- Population
- 867,647 participants in 13 studies, 9 cross-sectional and 4 cohorts [13]. 43,722 US women aged 35 to 74 without cancer or heart disease [8].
- Sources
- [13], [8]
- Caveats
- Observational. Heterogeneity was very high (I² 92.5%) [13]. Weight was self-reported at follow-up, and the results held after adjusting for sleep length, diet and activity, but other habits may differ in people who sleep with the television on [8].
Light at night linked to depression
Linked to 22% higher odds of depression with more light at night in one meta-analysis. In older adults, bedroom light of 5 lux or more predicted new depressive symptoms.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Higher light at night was linked to higher odds of depression (OR 1.224, 95% CI 1.176 to 1.275) [14]. Older adults whose measured bedroom light averaged 5 lux or more had more new depressive symptoms than those in darker rooms (HR 1.72, 95% CI 1.03 to 2.89, adjusted for sleep and health) [9].
- Population
- 8 observational studies [14]. 863 adults with a mean age of 71.5 in Nara, Japan, followed a median 24 months [9].
- Sources
- [14], [9]
- Caveats
- Observational with few studies and moderate to high heterogeneity [14]. People with poor sleep or low mood may leave lights on, which is reverse causation.
Light at night linked to type 2 diabetes
Linked to more diabetes with light at night in one meta-analysis and one cohort that measured light with wrist sensors, with risk rising as nights got brighter.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Light pollution was linked to higher odds of diabetes (OR 1.31), and indoor light more strongly (OR 1.66, 95% CI 1.15 to 2.39) [15]. Against people with the darkest nights, diabetes risk rose with brighter night light: HR 1.29 at the 50th to 70th percentiles, 1.39 at the 70th to 90th and 1.53 (95% CI 1.32 to 1.77) at the top 10% [10].
- Population
- 6 studies [15]. 84,790 UK Biobank participants who wore light sensors for a week, 1,997 cases over about 7.9 years [10].
- Sources
- [15], [10]
- Caveats
- Observational with few pooled studies [15]. The cohort adjusted for lifestyle and genetic risk, but light was measured for only one week [10].
Room light during sleep raised next-morning insulin resistance
One small trial found a single night of sleeping in room light raised next-morning insulin resistance by about 15% and night heart rate, against sleeping in dim light.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- After one night with overhead room light at 100 lux, HOMA-IR rose about 15%, against a 4% fall after a second dim night (p = 0.018). Early insulin response to a glucose drink rose, heart rate during sleep was higher and heart rate variability lower. Melatonin levels did not differ [11].
- Population
- 20 young adults randomized to room light (n = 10) or dim light under 3 lux (n = 10) in a sleep laboratory [11].
- Sources
- [11]
- Caveats
- One night, 20 people. Glucose levels stayed similar in both groups, and whether repeated nights change health was not tested [11].
Screen light before bed and sleep
One laboratory study found reading on a light-emitting e-reader before bed delayed sleep and the body clock and lowered next-morning alertness, against a printed book.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Against reading a printed book, reading a light-emitting e-book in the hours before bed led to taking longer to fall asleep, less evening sleepiness, less melatonin, later circadian timing and lower alertness the next morning [12].
- Population
- Adults reading in a controlled laboratory setting. The abstract does not give the head count [12].
- Sources
- [12]
- Caveats
- One small laboratory study with several hours of reading at a set brightness. Screen use at home varies in time, brightness and content, and the screen-time page covers its other effects.
Light at night linked to breast cancer
Linked to 8% to 10% more breast cancer in women with higher indoor or outdoor light at night in one meta-analysis. Data on other cancers were too few.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Higher indoor light at night (summary RR 1.08, 95% CI 1.01 to 1.15) and outdoor light at night (RR 1.10, 95% CI 1.04 to 1.15) were linked to breast cancer. Removing one low-quality study did not change the result [16].
- Population
- 19 breast cancer studies within 26 case-control and cohort studies of adults [16].
- Sources
- [16]
- Caveats
- Observational, and half the studies were case-control, where recall of past light exposure can be biased. Night shift work, a separate exposure, has its own page.
Side effects of blue-light filtering glasses
Limited evidence: trials reported infrequent side effects of blue-light filtering glasses, including headache, discomfort, lower mood and more depressive symptoms.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Nine trials reported on device-related adverse events and three described any. Events with blue-light filtering lenses were infrequent and included increased depressive symptoms, headache, discomfort wearing the glasses and lower mood. Clear lenses brought occasional discomfort and raised mood [4].
- Population
- 333 participants in 9 randomized trials [4].
- Sources
- [4]
- Caveats
- Adverse events were not consistently reported, and the certainty was low [4].
Claims tested and not found
- That blue-light filtering glasses reduce eye strain from screens. Trials found no difference in visual fatigue scores against regular lenses (MD 9.76, 95% CI -33.95 to 53.47, 120 participants) [4], and an earlier review found no difference in eyestrain symptoms [17].
- That blue-blocking glasses help people fall asleep faster, measured objectively. In three double-blind crossover trials, time to fall asleep did not change against clear lenses (-4.86 minutes, 95% CI -20.23 to 10.52) [5].
- That light during sleep acts by lowering melatonin. In the room light trial, melatonin levels were similar in both groups while insulin resistance rose [11].
Related
Sources
- Fang CS, Wang HH, Wang RH, et al. Effect of earplugs and eye masks on the sleep quality of intensive care unit patients: A systematic review and meta-analysis. Journal of Advanced Nursing. 2021. https://doi.org/10.1111/jan.14914
- Karimi L, Rahimi-Bashar F, Mohammadi SM, et al. The Efficacy of Eye Masks and Earplugs Interventions for Sleep Promotion in Critically Ill Patients: A Systematic Review and Meta-Analysis. Frontiers in Psychiatry. 2021. https://doi.org/10.3389/fpsyt.2021.791342
- Locihová H, Axmann K, Padyšáková H, Fejfar J. Effect of the use of earplugs and eye mask on the quality of sleep in intensive care patients: a systematic review. Journal of Sleep Research. 2018. https://doi.org/10.1111/jsr.12607
- Singh S, Keller PR, Busija L, et al. Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults. Cochrane Database of Systematic Reviews. 2023. https://doi.org/10.1002/14651858.CD013244.pub2
- Luna-Rangel FA, Gonzalez-Bedolla B, Salazar-Ortega MJ, et al. Efficacy of blue-light blocking glasses on actigraphic sleep outcomes: a systematic review and meta-analysis of randomized controlled crossover trials. Frontiers in Neurology. 2025. https://doi.org/10.3389/fneur.2025.1699303
- Hester L, Dang D, Barker CJ, et al. Evening wear of blue-blocking glasses for sleep and mood disorders: a systematic review. Chronobiology International. 2021. https://doi.org/10.1080/07420528.2021.1930029
- Kretzschmar J, Rath N, Starke KR, Seidler A, Freiberg A. The effect of exposure to artificial light at night (ALAN) on sleep disturbance: a systematic review and meta-analysis. Environmental Research. 2026. https://doi.org/10.1016/j.envres.2026.123689
- Park YM, White AJ, Jackson CL, Weinberg CR, Sandler DP. Association of Exposure to Artificial Light at Night While Sleeping With Risk of Obesity in Women. JAMA Internal Medicine. 2019. https://doi.org/10.1001/jamainternmed.2019.0571
- Obayashi K, Saeki K, Kurumatani N. Bedroom Light Exposure at Night and the Incidence of Depressive Symptoms: A Longitudinal Study of the HEIJO-KYO Cohort. American Journal of Epidemiology. 2018. https://doi.org/10.1093/aje/kwx290
- Windred DP, Burns AC, Rutter MK, et al. Personal light exposure patterns and incidence of type 2 diabetes: analysis of 13 million hours of light sensor data and 670,000 person-years of prospective observation. The Lancet Regional Health Europe. 2024. https://doi.org/10.1016/j.lanepe.2024.100943
- Mason IC, Grimaldi D, Reid KJ, et al. Light exposure during sleep impairs cardiometabolic function. Proceedings of the National Academy of Sciences. 2022. https://doi.org/10.1073/pnas.2113290119
- Chang AM, Aeschbach D, Duffy JF, Czeisler CA. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences. 2015. https://doi.org/10.1073/pnas.1418490112
- Tang W, Dong S, Li Y. Impact of artificial light at night on obesity and overweight: a systematic review and meta-analysis. BMC Public Health. 2025. https://doi.org/10.1186/s12889-025-25883-3
- Li X, Li S, Geng Q, et al. Light at night exposure and risk of depression: a meta-analysis of observational studies. Journal of Global Health. 2025. https://doi.org/10.7189/jogh.15.04304
- Zhang M, Xie Y, Hu D, et al. Light pollution and risk of diabetes: a systematic review and meta-analysis of observational studies. Frontiers in Public Health. 2026. https://doi.org/10.3389/fpubh.2026.1709841
- Ma S, Alsabawi Y, El-Serag HB, Thrift AP. Exposure to Light at Night and Risk of Cancer: A Systematic Review, Meta-Analysis, and Data Synthesis. Cancers. 2024. https://doi.org/10.3390/cancers16152653
- Lawrenson JG, Hull CC, Downie LE. The effect of blue-light blocking spectacle lenses on visual performance, macular health and the sleep-wake cycle: a systematic review of the literature. Ophthalmic and Physiological Optics. 2017. https://doi.org/10.1111/opo.12406