Restriction of blue light in the evening

The evening light environment in hospitals can be designed to produce less disruptive effects on the circadian system and improve sleep

Type of study:

Number of citations: 49

Year: 2020

Authors: D. Vethe, Jan Scott, M. Engstrøm, Ø. Salvesen, T. Sand, A. Olsen, G. Morken, H. Heglum, K. Kjørstad, P. Faaland, C. L. Vestergaard, K. Langsrud, H. Kallestad

Journal: Sleep

Journal ranking: Q1

Key takeaways: Evening blue-depleted lighting in hospitals can improve sleep quality and reduce circadian disruption without serious side effects.

Abstract: Abstract Study Objectives Blue-depleted lighting reduces the disruptive effects of evening artificial light on the circadian system in laboratory experiments, but this has not yet been shown in naturalistic settings. The aim of the current study was to test the effects of residing in an evening blue-depleted light environment on melatonin levels, sleep, neurocognitive arousal, sleepiness, and potential side effects. Methods The study was undertaken in a new psychiatric hospital unit where dynamic light sources were installed. All light sources in all rooms were blue-depleted in one half of the unit between 06:30 pm and 07:00 am (melanopic lux range: 7–21, melanopic equivalent daylight illuminance [M-EDI] range: 6–19, photopic lux range: 55–124), whereas the other had standard lighting (melanopic lux range: 30–70, M-EDI range: 27–63, photopic lux range: 64–136), but was otherwise identical. A total of 12 healthy adults resided for 5 days in each light environment (LE) in a randomized cross-over trial. Results Melatonin levels were less suppressed in the blue-depleted LE (15%) compared with the normal LE (45%; p = 0.011). Dim light melatonin onset was phase-advanced more (1:20 h) after residing in the blue-depleted LE than after the normal LE (0:46 h; p = 0.008). Total sleep time was 8.1 min longer (p = 0.032), rapid eye movement sleep 13.9 min longer (p < 0.001), and neurocognitive arousal was lower (p = 0.042) in the blue-depleted LE. There were no significant differences in subjective sleepiness (p = 0.16) or side effects (p = 0.09). Conclusions It is possible to create an evening LE that has an impact on the circadian system and sleep without serious side effects. This demonstrates the feasibility and potential benefits of designing buildings or hospital units according to chronobiological principles and provide a basis for studies in both nonclinical and clinical populations.

The bright and dark side of blue-enriched light on sleep and activity in older adults.

Type of study: rct

Number of citations: 0

Year: 2025

Authors: Débora Barroggi Constantino, K. Lederle, B. Middleton, V. Revell, Tracey L Sletten, Peter Williams, Debra J. Skene, D. R. van der Veen

Journal: GeroScience

Journal ranking: Q1

Key takeaways: Morning blue-enriched light improves rest-activity rhythm stability and decreases sleep fragmentation in older adults, while evening light exposure increases sleep latency and lowers sleep efficiency.

Abstract: Low indoor light in urban housing can disrupt health and wellbeing, especially in older adults who experience reduced light sensitivity and sleep/circadian disruptions with natural aging. While controlled studies suggest that enhancing indoor lighting may alleviate the negative effects of reduced light sensitivity, evidence for this to be effective in the real world is lacking. This study investigates the effects of two light conditions on actigraphic rest-activity rhythms and subjective sleep in healthy older adults (≥ 60 years) living at home. Two photon-matched lights were compared; a control white light (4000 K) and a blue-enriched white light (17000 K) at two different intensities (300-450 lx and 1100-1200 lx respectively). Participants (n = 36, 25 female) completed an 11-week randomized, cross-over study, comprising 1 week of baseline, 3 weeks of self-administered light exposure (2 h in the morning and 2 h in the evening), and 2 weeks of washout for each light condition. Participants completed sleep diaries, wore a wrist actigraph and a light sensor necklace, and collected urine to measure 6-sulphatoxymelatonin. Longer duration of morning blue-enriched light significantly improved rest-activity rhythm stability and decreased sleep fragmentation. More time spent above 2500 lx increased actigraphy amplitude, daytime activity, and advanced bedtime. Evening light exposure, however, increased sleep latency and lowered sleep efficiency. Our findings show morning blue-enriched light is beneficial whereas evening light should be avoided. Optimal timing of self-administered light interventions thus may offer a promising strategy to improve sleep and rest-activity rhythms in older adults in real-world settings.

Evening light environments can be designed to consolidate and increase the duration of REM-sleep

Type of study:

Number of citations: 15

Year: 2022

Authors: D. Vethe, H. Drews, J. Scott, M. Engstrøm, H. Heglum, J. Grønli, J. Wisor, T. Sand, S. Lydersen, K. Kjørstad, P. Faaland, C. L. Vestergaard, K. Langsrud, H. Kallestad

Journal: Scientific Reports

Journal ranking: Q1

Key takeaways: Evening blue-depleted light environments (BDLEs) can consolidate and increase the duration of REM sleep, potentially benefiting individuals with fragmented REM sleep disorders.

Effect of evening blue light blocking glasses on subjective and objective sleep in healthy adults: A randomized control trial.

Type of study: rct

Number of citations: 15

Year: 2021

Authors: Jeremy A. Bigalke, Ian M Greenlund, Jennifer R Nicevski, J. Carter

Journal: Sleep health

Journal ranking: Q1

Key takeaways: Blue light blocking glasses did not improve objective sleep time or quality in healthy adults, despite reducing subjective sleep onset and awakenings.

Strategies to decrease social jetlag: Reducing evening blue light advances sleep and melatonin

Type of study: non-rct experimental

Number of citations: 54

Year: 2018

Authors: G. Zerbini, T. Kantermann, M. Merrow

Journal: European Journal of Neuroscience

Journal ranking: Q2

Key takeaways: Reducing evening blue light exposure can advance melatonin secretion and sleep onset, helping late chronotypes better cope with early social schedules.

Abstract: The timing of sleep is under the control of the circadian clock, which uses light to entrain to the external light‐dark cycle. A combination of genetic, physiological and environmental factors produces individual differences in chronotype (entrained phase as manifest in sleep timing). A mismatch between circadian and societal (e.g., work) clocks leads to a condition called social jetlag, which is characterized by changing sleep times over work and free days and accumulation of sleep debt. Social jetlag, which is prevalent in late chronotypes, has been related to several health issues. One way to reduce social jetlag would be to advance the circadian clock via modifications of the light environment. We thus performed two intervention field studies to describe methods for decreasing social jetlag. One study decreased evening light exposure (via blue‐light‐blocking glasses) and the other used increased morning light (via the use of curtains). We measured behaviour as well as melatonin; the latter in order to validate that behaviour was consistent with this neuroendocrinological phase marker of the circadian clock. We found that a decrease in evening blue light exposure led to an advance in melatonin and sleep onset on workdays. Increased morning light exposure advanced neither melatonin secretion nor sleep timing. Neither protocol led to a significant change in social jetlag. Despite this, our findings show that controlling light exposure at home can be effective in advancing melatonin secretion and sleep, thereby helping late chronotypes to better cope with early social schedules.

The effect of reducing blue light from smartphone screen on subjective quality of sleep among students

Type of study: non-rct experimental

Number of citations: 14

Year: 2023

Authors: Pavle J. Randjelović, N. Stojanović, I. Ilić, Dragan Vučković

Journal: Chronobiology International

Journal ranking: Q2

Key takeaways: Reducing blue light emission from smartphone screens at night significantly improves subjective sleep quality and daytime functioning in medical students aged 20-22.

Abstract: ABSTRACT The exposure of humans to artificial light at night (ALAN) with predominant blue part of the visible spectrum is strongly influencing circadian rhythm and sleep through melanopsin-containing retinal ganglion cells (RGC). We hypothesized that reducing the amount of emitted blue light from screens of mobile phones during the night will increase sleep quality in our student population. The aim of the work was to investigate the effect of reducing blue light from smartphone screen during the night on subjective quality of sleep among students of medicine. The target population was students of medicine aged 20 to 22 years old of both sexes. The primary outcome of the study was subjective sleep quality, assessed by the Serbian version of the Pittsburgh Sleep Quality Index (PSQI). The mean total PSQI score before intervention was 6.83 ± 2.73 (bad), while after the intervention the same score was statistically significant reduced to 3.93 ± 1.68 (good) with large effect size. The study has shown that a reduction of blue light emission from LED backlight screens of mobile phones during the night leads to improved subjective quality of sleep in students, as well as improvement in daytime functioning and going to sleep.

Effect of the Combined Use of Morning Blue-Enriched Lighting and Night Blue-Suppressed Lighting (MENS) on Sleep Quality

Type of study: rct

Number of citations: 2

Year: 2023

Authors: Wankiun Lee, K. Jung

Journal: Journal of Sleep Medicine

Journal ranking: brak

Key takeaways: The combined use of morning blue-enriched and night blue-suppressed lighting (MENS) significantly improves sleep quality, with 480-nm blue light effectively reducing sleep latency.

Abstract: Objectives: Previous studies have shown that exposure to blue-enriched light in the morning or blue-suppressed light in the evening may positively affect sleep. In this study, we aimed to investigate the effect of combination of morning blue-enriched and night blue-suppressed lighting (MENS) on sleep quality. Methods: Thirty workers were recruited. After one-week baseline evaluation, the participants were randomly assigned to either an experimental or a control group. Both were exposed to light in the morning and evening for two weeks. The experimental group used a lighting device emitting 480-nm wavelength maximized light in the morning and minimized light in the evening, while the control group used 450-nm wavelength light in the same way. The final evaluation was conducted using questionnaires and sleep diaries. Results: Both groups showed statistically significant improvements in seven out of nine sleep quality measures (p<0.05). The experimental group showed improvement in sleep latency and sleep fragmentation compared to that in the control group (p=0.017). The control group showed improvement in wake after sleep onset. The ratio of participants who showed improvement and transitioned from abnormal to normal values was significantly higher in the experimental group for sleep latency (p=0.046) and in the control group for fatigue (p=0.012). Conclusions: The findings suggest that the use of MENS significantly improves sleep quality. Although the difference in the improvement effect between different wavelengths of blue light was not substantial, the use of 480-nm blue light appears to be effective in reducing sleep latency.

Interventions to reduce short-wavelength (“blue”) light exposure at night and their effects on sleep: A systematic review and meta-analysis

Type of study: meta-analysis

Number of citations: 30

Year: 2020

Authors: A. Shechter, K. Quispe, Jennifer S Mizhquiri Barbecho, Cody Slater, L. Falzon

Journal: Sleep Advances: A Journal of the Sleep Research Society

Journal ranking: brak

Key takeaways: Wearing color-tinted lenses to filter short-wavelength light exposure before bedtime may improve sleep, particularly in individuals with insomnia, bipolar disorder, delayed sleep phase syndrome, or ADHD.

Abstract: Abstract The sleep-wake and circadian cycles are influenced by light, particularly in the short-wavelength portion of the visible spectrum. Most personal light-emitting electronic devices are enriched in this so-called “blue” light. Exposure to these devices in the evening can disturb sleep. Interventions to reduce short-wavelength light exposure before bedtime may reduce adverse effects on sleep. We conducted a systematic review and meta-analysis to examine the effect of wearing color-tinted lenses (e.g. orange or amber) in frames to filter short-wavelength light exposure to the eye before nocturnal sleep. Outcomes were self-reported or objective measures of nocturnal sleep. Relatively few (k = 12) studies have been done. Study findings were inconsistent, with some showing benefit and others showing no effect of intervention. Meta-analyses yielded a small-to-medium magnitude combined effect size for sleep efficiency (Hedge’s g = 0.31; 95% CI: −0.05, 0.66; I2 = 38.16%; k = 7), and a small-to-medium combined effect size for total sleep time (Hedge’s g = 0.32; 95% CI: 0.01, 0.63; I2 = 12.07%; k = 6). For self-report measures, meta-analysis yielded a large magnitude combined effects size for Pittsburgh Sleep Quality Index ratings (Hedge’s g = −1.25; 95% CI: −2.39, −0.11; I2 = 36.35%; k = 3) and a medium combined effect size for total sleep time (Hedge’s g = 0.51; 95% CI: 0.18, 0.84; I2 = 0%; k = 3), Overall, there is some, albeit mixed, evidence that this approach can improve sleep, particularly in individuals with insomnia, bipolar disorder, delayed sleep phase syndrome, or attention-deficit hyperactive disorder. Considering the ubiquitousness of short-wavelength-enriched light sources, future controlled studies to examine the efficacy of this approach to improve sleep are warranted. Systematic review registration: PROSPERO 2018 CRD42018105854.

Effects of pre-bedtime blue-light exposure on ratio of deep sleep in healthy young men.

Type of study: non-rct experimental

Number of citations: 23

Year: 2021

Authors: M. Ishizawa, T. Uchiumi, M. Takahata, M. Yamaki, Toshiaki Sato

Journal: Sleep medicine

Journal ranking: Q1

Key takeaways: Pre-bedtime blue-light exposure significantly reduces the ratio of deep sleep in healthy young men, negatively affecting sleep quality.

Managing Blue Light Exposure: Impacts on Sleep Quality and Circadian Health

Type of study: systematic review

Number of citations: 0

Year: 2024

Authors: Alicja Grzelak

Journal: Quality in Sport

Journal ranking: brak

Key takeaways: Prolonged blue light exposure disrupts circadian rhythms and sleep quality, leading to mood disorders, cognitive decline, and metabolic imbalances, but preventive measures can mitigate these negative effects.

Abstract: Introduction: Blue light, a high-energy visible light emitted from natural and artificial sources, plays a crucial role in regulating circadian rhythms and sleep quality. While essential for maintaining alertness and synchronizing the biological clock, excessive exposure, especially during evening hours, disrupts melatonin production, adversely impacting sleep and overall health. Purpose of Work: This paper investigates the effects of blue light exposure on circadian rhythms and sleep quality, aiming to evaluate its biological mechanisms and health implications. Additionally, it explores evidence-based preventive measures to mitigate its negative impacts. State of Knowledge: Research reveals that prolonged blue light exposure delays sleep onset, shortens sleep duration, and impairs sleep efficiency by suppressing melatonin secretion. Disrupted circadian rhythms are linked to mood disorders, cognitive decline, and metabolic imbalances. Preventive strategies, including blue light-blocking glasses, screen filters, optimized lighting environments, and adherence to healthy screen-time habits, demonstrate effectiveness but require further validation in diverse populations. Material and methods: This study employed a systematic literature review approach, comprising a comprehensive search across scientific databases such as PubMed and Google Scholar, followed by a screening process to identify relevant studies for further investigation. Summary: Blue light exposure significantly influences circadian rhythms and sleep quality, with implications for mental and physical health. Preventive measures, when adopted consistently, offer promising solutions to mitigate adverse effects. Continued research is necessary to refine these strategies and ensure widespread applicability in an increasingly digital world.

Blue-Enriched Morning Light as a Countermeasure to Light at the Wrong Time: Effects on Cognition, Sleepiness, Sleep, and Circadian Phase

Type of study: non-rct experimental

Number of citations: 90

Year: 2017

Authors: M. Münch, C. Nowozin, J. Regente, F. Bes, J. de Zeeuw, Sven Hädel, A. Wahnschaffe, D. Kunz

Journal: Neuropsychobiology

Journal ranking: Q1

Key takeaways: Bright blue-enriched morning light can stabilize circadian phase and counteract the detrimental effects of inadequate daytime and evening lighting, improving cognitive performance and reaction times.

Abstract: Light during the day and darkness at night are crucial factors for proper entrainment of the human circadian system to the solar 24-h day. However, modern life and work styles have led to much more time spent indoors, often with lower daytime and higher evening/nighttime light intensity from electrical lighting than outdoors. Whether this has long-term consequences for human health is being currently investigated. We tested if bright blue-enriched morning light over several days could counteract the detrimental effects of inadequate daytime and evening lighting. In a seminaturalistic, within-between subject study design, 18 young participants were exposed to different lighting conditions on 3 evenings (blue-enriched, bright orange, or dim light), after exposure to 2 lighting conditions (mixed blue-enriched light and control light, for 3 days each) in the mornings. Subjective sleepiness, reaction times, salivary melatonin concentrations, and nighttime sleep were assessed. Exposure to the blue-enriched morning lighting showed acute wake-promoting effects and faster reaction times than with control lighting. Some of these effects persisted until the evening, and performance improved over several days. The magnitude of circadian phase shifts induced by combinations of 3 different evening and 2 morning lighting conditions were significantly smaller with the blue-enriched morning light. During the night, participants had longer total sleep times after orange light exposure than after blue light exposure in the evening. Our results indicate that bright blue-enriched morning light stabilizes circadian phase, and it could be an effective counterstrategy for poor lighting during the day and also light exposure at the wrong time, such as in the late evening.

Daytime Exposure to Blue-Enriched Light Counters the Effects of Sleep Restriction on Cortisol, Testosterone, Alpha-Amylase and Executive Processes

Type of study: rct

Number of citations: 12

Year: 2020

Authors: B. Faraut, T. Andrillon, C. Drogou, C. Gauriau, Alexandre Dubois, Aurélie Servonnet, P. van Beers, M. Guillard, D. Gomez-Mérino, F. Sauvet, M. Chennaoui, D. Léger

Journal: Frontiers in Neuroscience

Journal ranking: Q2

Key takeaways: Daytime exposure to blue-enriched light can counteract the negative effects of sleep restriction on physiological markers and cognitive performance.

Abstract: Sleep debt is becoming a better acknowledged cause of physiological stress and neurobehavioral deficits with major public-health concerns. We investigated whether exposure to blue light during daytime could be an efficient countermeasure to limit sleep restriction’s impact on relevant behavioral (stress, sleepiness, sustained attention, and memory performance) and physiological (saliva cortisol, testosterone, and alpha-amylase) markers. Our semi-ecological, crossover, randomized design included 17 young men that underwent two sleep-restricted nights (3 h each) followed or not by blue light exposure (30-min-long sessions at 100 lux repeated four times throughout the day). Behavioral and physiological measurements were performed in the lab but outside these periods the participants kept following their usual routine. After sleep restriction, morning cortisol and testosterone, and afternoon alpha-amylase levels decreased. In parallel, subjective ratings of stress and sleepiness increased while performance on the sustained attention and memory tasks deteriorated. In contrast, after periods of blue light exposure, all these parameters were largely restored to baseline levels, despite an identical sleep restriction procedure, although this restorative effect was reduced for the memory task. Our findings suggest that even short exposure to blue light could trigger persistent beneficial effects throughout the day and could be potentially efficient in real-life settings.

Acute exposure to evening blue‐enriched light impacts on human sleep

Type of study: non-rct experimental

Number of citations: 248

Year: 2013

Authors: S. Chellappa, R. Steiner, P. Oelhafen, Dieter Lang, T. Götz, Julia Krebs, C. Cajochen

Journal: Journal of Sleep Research

Journal ranking: Q1

Key takeaways: Exposure to blue-enriched polychromatic light at low room light levels impacts homeostatic sleep regulation, with reduced frontal slow wave activity during the first non-rapid eye movement episode.

Abstract: Light in the short wavelength range (blue light: 446–483 nm) elicits direct effects on human melatonin secretion, alertness and cognitive performance via non‐image‐forming photoreceptors. However, the impact of blue‐enriched polychromatic light on human sleep architecture and sleep electroencephalographic activity remains fairly unknown. In this study we investigated sleep structure and sleep electroencephalographic characteristics of 30 healthy young participants (16 men, 14 women; age range 20–31 years) following 2 h of evening light exposure to polychromatic light at 6500 K, 2500 K and 3000 K. Sleep structure across the first three non‐rapid eye movement non‐rapid eye movement – rapid eye movement sleep cycles did not differ significantly with respect to the light conditions. All‐night non‐rapid eye movement sleep electroencephalographic power density indicated that exposure to light at 6500 K resulted in a tendency for less frontal non‐rapid eye movement electroencephalographic power density, compared to light at 2500 K and 3000 K. The dynamics of non‐rapid eye movement electroencephalographic slow wave activity (2.0–4.0 Hz), a functional index of homeostatic sleep pressure, were such that slow wave activity was reduced significantly during the first sleep cycle after light at 6500 K compared to light at 2500 K and 3000 K, particularly in the frontal derivation. Our data suggest that exposure to blue‐enriched polychromatic light at relatively low room light levels impacts upon homeostatic sleep regulation, as indexed by reduction in frontal slow wave activity during the first non‐rapid eye movement episode.

Sex differences in light sensitivity impact on brightness perception, vigilant attention and sleep in humans

Type of study: non-rct experimental

Number of citations: 86

Year: 2017

Authors: S. Chellappa, R. Steiner, P. Oelhafen, C. Cajochen

Journal: Scientific Reports

Journal ranking: Q1

Key takeaways: Men show a stronger response to blue-enriched light in the late evening, leading to increased vigilant attention and faster reaction times in sustained attention tasks.

0316 A Case Report: Comparing Sleep with and without blue light blockers

Type of study: case report

Number of citations: 0

Year: 2023

Authors: Sanket Meghpara, Dana Awad, Rijesh Niraula, L. Delrosso, L. Keenan, Karl Van Gundy

Journal: SLEEP

Journal ranking: Q1

Key takeaways: Wearing blue light blockers all day may improve morning alertness, but there were no statistically significant differences in sleep parameters between non-blue light blocking and blue light blocking eyewear.

Abstract: Blue light filtered eyewear is popular. Studies have looked at the effect of using blue light blockers in the evening but data is lacking on the effect of wearing blue light blockers (BLB) through the day. In this study we compared the effects of wearing BLB all day, on sleep and daytime sleepiness. This is a single case report. A 32 year male wore an Actiwatch Pro and collected sleep diaries for 18 days. On days 1-9, non-blue light blocking eyewear (NBLB) were used all day. On days 10-18, BLB were used all day. Karolinska Sleepiness Scale (KSS) and Stanford Sleepiness Scale (SSS) during morning, afternoon and before sleep were recorded. IBM SPSS v. 29.0.0 is used for descriptive analysis, Pearson correlation and T-test comparison. White light exposure was not statistically different from BLB and NBLB. Data measured in minutes. Mean and standard deviation of in-bed duration with NBLB was 477.89±66.17 and with BLB was 518.06±53.06 (p=0.087). Sleep time with NBLB was 431.89±52.05 and with BLB was 471.72±48.49 (p=0.056). Wake After Sleep Onset (WASO) with NBLB was 43.78±18.63 and with BLB 46.33±14.25 (p=0.374). Percent Sleep with NBLB was 90.96±2.83% and with BLB was 91.09±2.29 (p=0.459). KSS scores for morning on NBLB was 1.75±1.035 and 1.00±0 with BLB (p= 0.023), afternoon NBLB 4.13±1.25, BLB 3.67±0.87 (p=0.194), before sleep NBLB 8.5±1.41 and 8.56±0.53 with BLB (p=0.457). SSS scores for morning on NBLB was 1.63±0.744 and 1.00±0 with BLB (p= 0.012), afternoon NBLB 3.38±1.06, BLB 3.56±0.88 (p=0.353), before sleep NBLB 7.00±1.41 and 7.89±0.60 with BLB (p=0.053). There was a strong correlation between white light exposure and increased WASO (Pearson 0.514) and strong negative correlation (Pearson -0.535) between white light exposure and percent of sleep duration. Although there were no statistically significant differences between the sleep parameters between NBLB and BLB, we found a strong correlation between sleep time and white light exposure and negative correlation. When using BLB morning alertness was better.

Early evening light mitigates sleep compromising physiological and alerting responses to subsequent late evening light

Type of study: rct

Number of citations: 50

Year: 2019

Authors: Marije te Kulve, L. Schlangen, W. D. van Marken Lichtenbelt

Journal: Scientific Reports

Journal ranking: Q1

Key takeaways: Early evening bright light exposure can reduce the sleep-disruptive consequences of late-evening light exposure, reducing melatonin levels and subjective sleepiness.

Two hours of evening reading on a self-luminous tablet vs. reading a physical book does not alter sleep after daytime bright light exposure.

Type of study: non-rct experimental

Number of citations: 70

Year: 2016

Authors: Frida H. Rångtell, Emelie Ekstrand, Linnea Rapp, Anna Lagermalm, Lisanne Liethof, Marcela Olaya Búcaro, D. Lingfors, J. Broman, H. Schiöth, C. Benedict

Journal: Sleep medicine

Journal ranking: Q1

Key takeaways: Reading on a self-luminous tablet in the evening does not alter sleep parameters or melatonin levels when combined with daytime bright light exposure.

The effect of evening light on circadian-related outcomes: A systematic review.

Type of study: systematic review

Number of citations: 11

Year: 2022

Authors: Marie-Josée Cyr, Despina Z. Artenie, Alain Al Bikaii, D. Borsook, Jay A. Olson

Journal: Sleep medicine reviews

Journal ranking: Q1

Key takeaways: Evening light exposure before night shifts can improve sleep quality, memory, and work performance, but its effects on mood are uncertain.

Abstract: Bright light exposure at night can help workers adapt to their shift schedules, but there has been relatively little research on evening light. We conducted a systematic review of studies that manipulated light exposure in the evening (broadly defined as 16:00-22:00) before real or simulated night shifts. Across the five eligible studies, evening light produced phase delays in melatonin, body temperature, and sleep propensity; it also improved sleep quality, sleep duration, memory, and work performance. There were mixed effects for mood, no changes in sleepiness, and no negative effects. The confidence in these results ranged from moderate for physiological markers of circadian phase delays to very low for mood. Future studies should compare the relative effectiveness and safety of evening versus night-time light exposure. Overall, the benefits of evening light for shift workers are tentative yet promising.

The influence of blue light on sleep, performance and wellbeing in young adults: A systematic review

Type of study: systematic review

Number of citations: 64

Year: 2022

Authors: M. I. Silvani, R. Werder, C. Perret

Journal: Frontiers in Physiology

Journal ranking: Q2

Key takeaways: Blue light exposure can positively affect cognitive performance, alertness, and reaction time, but may negatively impact sleep quality and duration, potentially worsening athletes' physical and cognitive performance and recovery.

Abstract: Introduction: Blue light from electronic devices has a bad reputation. It has a wavelength which may influence our circadian rhythm and cause bad sleep. But there are other aspects of blue light exposure which are often overlooked, for example, it may influence performance and wellbeing. However, few resources summarize its effects systematically. Therefore, the goal of this systematic review was to distil the present evidence on blue light exposure and its influence on sleep, performance and wellbeing and discuss its significance for athletes. Methods: The databases that were searched were Cochrane, Embase, Pubmed, Scopus, and Virtual Health Library. The studies included investigated the influence of blue light exposure on either sleep, performance, wellbeing or a combination of those parameters on healthy humans. Quality assessment was done based on the quantitative assessment tool “QualSyst.” Results: Summarizing the influence of blue light exposure, the following results were found (expressed as proportion to the number of studies investigating the particular parameter): Fifty percent of studies found tiredness to be decreased. One fifth of studies found sleep quality to be decreased and one third found sleep duration to be decreased. Half of the studies found sleep efficacy to be decreased and slightly less than half found sleep latency to be increased. More than one half of the studies found cognitive performance to be increased. Slightly more than two thirds found alertness to be increased and reaction time to be decreased. Slightly less than half of the studies found wellbeing to be increased. Conclusion: Blue light exposure can positively affect cognitive performance, alertness, and reaction time. This might benefit sports reliant on team-work and decision-making and may help prevent injury. Blue light might also have negative effects such as the decrease in sleep quality and sleep duration, which might worsen an athlete’s physical and cognitive performance and recovery. Further research should explore if blue light can improve sleep, performance and wellbeing to significantly benefit athletic performance.

The Effects of Pre-bedtime Blue-Light Exposure on Subjective Sleep Quality, Attention, and Work Efficiency in Men Students: A Pilot Study

Type of study:

Number of citations: 0

Year: 2024

Authors: T. Uchiumi, M. Ishizawa, M. Takahata, Michiyasu Yamaki, Toshiaki Sato

Journal: Sleep and Vigilance

Journal ranking: Q4

Key takeaways: Pre-bedtime blue-light exposure negatively affects deep sleep ratio, sustained attention, and work efficiency in young men without sleep disorders.

Abstract: BackgroundAlthough exposure to blue light in the evening has been shown to affect sleep, its effects on alertness and work efficiency the next day are not fully understood.ObjectiveThis study aimed to investigate the effects of pre-bedtime blue-light exposure on subjective sleep quality, attention, and work efficiency.MethodsThirteen young men (aged 20–23 years) without sleep disorders participated in two sessions, in which they were exposed to either incandescent light or blue light 1 h before bedtime. On the next morning, participants underwent assessments of subjective sleep quality, attention, and work efficiency. Objective parameters during sleep were measured using a mat-type sleep meter (sleep scan, SL- 504; TANITA Corp., Japan).ResultsBlue-light exposure significantly decreased the ratio of time spent in deep sleep (p < 0.05), reaction times (i.e., attention) during the second half of the 10-min session (p < 0.01), and work efficiency (p < 0.05).ConclusionThe present study suggests that blue-light exposure before bedtime leads to a decrease in the ratio of deep sleep and negative effects on sustained attention and work efficiency.

Clinical benefits of modifying the evening light environment in an acute psychiatric unit: A single-centre, two-arm, parallel-group, pragmatic effectiveness randomised controlled trial

Type of study: rct

Number of citations: 0

Year: 2024

Authors: H. Kallestad, K. Langsrud, M. R. Simpson, C. L. Vestergaard, D. Vethe, K. Kjørstad, P. Faaland, S. Lydersen, Gunnar Morken, Ingvild Ulsaker-Janke, S. Saksvik, Jan Scott

Journal: PLOS Medicine

Journal ranking: Q1

Key takeaways: Modifying the evening light environment in acute psychiatric hospitals can have clinically significant benefits without increasing side effects, reducing patient satisfaction, or requiring additional clinical staff.

Abstract: Background: The impact of light exposure on mental health is increasingly recognized. Modifying inpatient evening light exposure may be a low-intensity intervention for mental disorders, but few randomized controlled trials (RCTs) exist. We report a large-scale pragmatic effectiveness RCT exploring whether individuals with acute psychiatric illnesses experience additional benefits from admission to an inpatient ward where changes in the evening light exposure are integrated into the therapeutic environment. Methods and findings: All adults admitted for acute inpatient psychiatric care over eight months were randomly allocated to a ward with a blue-depleted evening light environment or a ward with standard light environment. Baseline and outcome data from individuals who provided deferred informed consent were used to analyze the primary outcome measure (differences in duration of hospitalization) and secondary measures (differences in key clinical outcomes). The Intent to Treat sample comprised 476 individuals (mean age 37; 41% were male). There were no differences in the mean duration of hospitalization (6.7 vs. 7.1 days). Inpatients exposed to the blue-depleted evening light showed higher improvement during admission (Clinical Global Impressions scale-Improvement: 0.28, 95% CI: 0.02 to 0.54; p=0.035, Number Needed to Treat for clinically meaningful improvement (NNT): 12); lower illness severity at discharge (Clinical Global Impressions Scale-Severity: -0.18, 95% CI: -0.34 to -0.02; p=0.029, NNT for mild severity at discharge: 7); and lower levels of aggressive behaviour (Broset Violence Checklist difference in predicted serious events per 100 days: -2.98; 95% CI: -4.98 to -0.99; p=0.003, NNT: 9). Incidents of harm to self or others, side effects, and patient satisfaction did not differ between the lighting conditions. Conclusions: Modifying the evening light environment in acute psychiatric hospitals according to chronobiological principles does not change duration of hospitalizations, but can have clinically significant benefits without increasing side effects, reducing patient satisfaction or requiring additional clinical staff.

Non-visual effects of indoor light environment on humans: A review✰

Type of study: systematic review

Number of citations: 76

Year: 2020

Authors: Hui Xiao, Huiling Cai, Xuefeng Li

Journal: Physiology & Behavior

Journal ranking: Q2

Key takeaways: High illuminance and correlated color temperature at night can suppress melatonin and stimulate positive mood, while high illuminance during daytime can increase subjective alertness and positively affect mood.

Blue-enriched white light in the workplace improves self-reported alertness, performance and sleep quality.

Type of study: non-rct experimental

Number of citations: 538

Year: 2008

Authors: A. Viola, L. James, L. Schlangen, D. Dijk

Journal: Scandinavian journal of work, environment & health

Journal ranking: Q1

Key takeaways: Exposure to blue-enriched white light during daytime work hours improves subjective alertness, performance, and reduces evening fatigue in office workers.

Abstract: OBJECTIVES Specifications and standards for lighting installations in occupational settings are based on the spectral sensitivity of the classical visual system and do not take into account the recently discovered melanopsin-based, blue-light-sensitive photoreceptive system. The authors investigated the effects of exposure to blue-enriched white light during daytime workhours in an office setting. METHODS The experiment was conducted on 104 white-collar workers on two office floors. After baseline assessments under existing lighting conditions, every participant was exposed to two new lighting conditions, each lasting 4 weeks. One consisted of blue-enriched white light (17 000 K) and the other of white light (4000 K). The order was balanced between the floors. Questionnaire and rating scales were used to assess alertness, mood, sleep quality, performance, mental effort, headache and eye strain, and mood throughout the 8-week intervention. RESULTS Altogether 94 participants [mean age 36.4 (SD 10.2) years] were included in the analysis. Compared with white light (4000 K), blue-enriched white light (17 000 K) improved the subjective measures of alertness (P<0.0001), positive mood (P=0.0001), performance (P<0.0001), evening fatigue (P=0.0001), irritability (P=0.004), concentration (P<0.0001), and eye discomfort (P=0.002). Daytime sleepiness was reduced (P=0.0001), and the quality of subjective nocturnal sleep (P=0.016) was improved under blue-enriched white light. When the participants' expectation about the effect of the light treatments was entered into the analysis as a covariate, significant effects persisted for performance, alertness, evening fatigue, irritability, difficulty focusing, concentrating, and blurred vision. CONCLUSIONS Exposure to blue-enriched white light during daytime workhours improves subjective alertness, performance, and evening fatigue.

Workplace lighting for improving alertness and mood in daytime workers.

Type of study: meta-analysis

Number of citations: 47

Year: 2018

Authors: D. Pachito, Á. Éckeli, Ahmed Desouky, M. Corbett, T. Partonen, S. Rajaratnam, R. Riera

Journal: The Cochrane database of systematic reviews

Journal ranking: Q1

Key takeaways: High CCT light may improve alertness in daytime workers, but no studies compared mood effects with standard illumination.

Abstract: BACKGROUND Exposure to light plays a crucial role in biological processes, influencing mood and alertness. Daytime workers may be exposed to insufficient or inappropriate light during daytime, leading to mood disturbances and decreases in levels of alertness. OBJECTIVES To assess the effectiveness and safety of lighting interventions to improve alertness and mood in daytime workers. SEARCH METHODS We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, seven other databases; ClinicalTrials.gov and the World Health Organization trials portal up to January 2018. SELECTION CRITERIA We included randomised controlled trials (RCTs), and non-randomised controlled before-after trials (CBAs) that employed a cross-over or parallel-group design, focusing on any type of lighting interventions applied for daytime workers. DATA COLLECTION AND ANALYSIS Two review authors independently screened references in two stages, extracted outcome data and assessed risk of bias. We used standardised mean differences (SMDs) and 95% confidence intervals (CI) to pool data from different questionnaires and scales assessing the same outcome across different studies. We combined clinically homogeneous studies in a meta-analysis. We used the GRADE system to rate quality of evidence. MAIN RESULTS The search yielded 2844 references. After screening titles and abstracts, we considered 34 full text articles for inclusion. We scrutinised reports against the eligibility criteria, resulting in the inclusion of five studies (three RCTs and two CBAs) with 282 participants altogether. These studies evaluated four types of comparisons: cool-white light, technically known as high correlated colour temperature (CCT) light versus standard illumination; different proportions of indirect and direct light; individually applied blue-enriched light versus no treatment; and individually applied morning bright light versus afternoon bright light for subsyndromal seasonal affective disorder.We found no studies comparing one level of illuminance versus another.We found two CBA studies (163 participants) comparing high CCT light with standard illumination. By pooling their results via meta-analysis we found that high CCT light may improve alertness (SMD -0.69, 95% CI -1.28 to -0.10; Columbia Jet Lag Scale and the Karolinska Sleepiness Scale) when compared to standard illumination. In one of the two CBA studies with 94 participants there was no difference in positive mood (mean difference (MD) 2.08, 95% CI -0.1 to 4.26) or negative mood (MD -0.45, 95% CI -1.84 to 0.94) assessed using the Positive and Negative Affect Schedule (PANAS) scale. High CCT light may have fewer adverse events than standard lighting (one CBA; 94 participants). Both studies were sponsored by the industry. We graded the quality of evidence as very low.We found no studies comparing light of a particular illuminance and light spectrum or CCT versus another combination of illuminance and light spectrum or CCT.We found no studies comparing daylight versus artificial light.We found one RCT (64 participants) comparing the effects of different proportions of direct and indirect light: 100% direct lighting, 70% direct lighting plus 30% indirect lighting, 30% direct lighting plus 70% indirect lighting and 100% indirect lighting. There was no substantial difference in mood, as assessed by the Beck Depression Inventory, or in adverse events, such as ocular, reading or concentration problems, in the short or medium term. We graded the quality of evidence as low.We found two RCTs comparing individually administered light versus no treatment. According to one RCT with 25 participants, blue-enriched light individually applied for 30 minutes a day may enhance alertness (MD -3.30, 95% CI -6.28 to -0.32; Epworth Sleepiness Scale) and may improve mood (MD -4.8, 95% CI -9.46 to -0.14; Beck Depression Inventory). We graded the quality of evidence as very low. One RCT with 30 participants compared individually applied morning bright light versus afternoon bright light for subsyndromal seasonal affective disorder. There was no substantial difference in alertness levels (MD 7.00, 95% CI -10.18 to 24.18), seasonal affective disorder symptoms (RR 1.60, 95% CI 0.81, 3.20; number of participants presenting with a decrease of at least 50% in SIGH-SAD scores) or frequency of adverse events (RR 0.53, 95% CI 0.26 to 1.07). Among all participants, 57% had a reduction of at least 50% in their SIGH-SAD score. We graded the quality of evidence as low.Publication bias could not be assessed for any of these comparisons. AUTHORS' CONCLUSIONS There is very low-quality evidence based on two CBA studies that high CCT light may improve alertness, but not mood, in daytime workers. There is very low-quality evidence based on one CBA study that high CCT light may also cause less irritability, eye discomfort and headache than standard illumination. There is low-quality evidence based on one RCT that different proportions of direct and indirect light in the workplace do not affect alertness or mood. There is very low-quality evidence based on one RCT that individually applied blue-enriched light improves both alertness and mood. There is low-quality evidence based on one RCT that individually administered bright light during the afternoon is as effective as morning exposure for improving alertness and mood in subsyndromal seasonal affective disorder.

Dark Matters

Type of study: literature review

Number of citations: 0

Year: 2025

Authors: Randy J Nelson

Journal:

Journal ranking: brak

Key takeaways: Curtailing blue light exposure at night and maximizing it in the morning can improve health and well-being by optimizing circadian rhythms and reducing risks for obesity, depression, and other issues.

Abstract: One feature of modern life that may have negative consequences for our health is exposure to light levels that are not aligned with the solar days. This book reviews the scientific literature on the role of appropriately timed light exposure and concludes that it seems prudent to curtail exposure to blue light during the night and maximize exposure to blue light during the morning. Circadian rhythms require short wavelength (blue) light early during the day to optimize their temporal regulation. Experiencing light at night or insufficient light during the day can lead to a host of problems such as obesity, major depression, bipolar depressive disorder, seasonal affective disorder, sleep disorders, common problems with learning and memory, Alzheimer’s disease and other forms of dementia, sundowning syndrome, cancer, heart disease, hypertension, heart attacks, and strokes. Even sustained exposure to the equivalent of a child’s night light can impact everything from how well our brains function every day to how well our bodies recover from injury. Lack of bright light during the day can compromise mood, accelerate cancer growth, and impair cognition. This book introduces the importance of light and circadian rhythms and examines the role of light and body weight; the relationship between appropriately timed light exposure and mood; the role of light on sleep; the interaction among light exposure, cognition, and memory; and the importance of appropriate exposure to light to reduce risk for cancer and cardiovascular disease. Finally, it describes strategies to reduce disruptions to circadian rhythms to improve health and well-being.

Evening blue light exposure during adolescence induces avoidance behaviors and rewires medial amygdala circuit

Type of study:

Number of citations: 0

Year: 2025

Authors: Pablo Bonilla, David McBride, Alexandria Shanks, Janhvi Kartik, Ashita Bhan, Alessandra Porcu

Journal: bioRxiv

Journal ranking: brak

Key takeaways: Evening blue light exposure during adolescence increases avoidance behaviors and alters the medial amygdala's functions, potentially increasing the risk of affective disorders.

Abstract: Adolescents are being increasingly exposed to artificial blue light from electronic devices, raising concerns about its effects on brain development and mental health. The medial amygdala (MeA), a brain region critical for emotional regulation, is light-sensitive, yet how evening blue light during puberty influences its circuitry and behavior remains unknown. Using a light cycle disruption paradigm, we found that adolescent mice exposed to evening blue light displayed increased avoidance behaviors compared to those exposed to darkness or reduced blue light conditions. Single-nuclei RNA sequencing revealed altered cell-type composition and disrupted synaptic communication pathways in the MeA. In vivo calcium imaging showed increased activity in MeA somatostatin neurons during avoidance behaviors, while chemogenetic inhibition of these neurons reduced these behaviors. Our findings identify the MeA as a key integrator of emotional responses to environmental blue light, suggesting evening blue light exposure during puberty as a potential risk factor for affective disorders. Teaser Evening blue light exposure during adolescence alters medial amygdala functions, leading to anxiety-like behaviors.

Lactic acid contributes to the emergence of depression-like behaviors triggered by blue light exposure during sleep.

Type of study: non-rct experimental

Number of citations: 1

Year: 2025

Authors: Yinhan Li, Xinhui Zou, Ying Ma, Jiaqi Cheng, Xiangmin Yu, Wenya Shao, Fuli Zheng, Zhenkun Guo, Guangxia Yu, Siying Wu, Huangyuan Li, Hong Hu

Journal: Ecotoxicology and environmental safety

Journal ranking: Q1

Key takeaways: Excessive exposure to high-blue light-content artificial light at night is linked to increased depressive symptoms, with lactic acid levels playing a role in these behaviors.

Preliminary Results: The Impact of Smartphone Use and Short-Wavelength Light during the Evening on Circadian Rhythm, Sleep and Alertness

Type of study: non-rct experimental

Number of citations: 46

Year: 2021

Authors: C. Höhn, S. R. Schmid, C. Plamberger, Kathrin Bothe, M. Angerer, G. Gruber, Belinda Pletzer, K. Hoedlmoser

Journal: Clocks & Sleep

Journal ranking: Q3

Key takeaways: Smartphone use before bedtime increases short-wavelength light exposure, negatively affects circadian rhythm, sleepiness, and alertness in the morning, but using a blue light filter partially reduces these negative effects.

Abstract: Smartphone usage strongly increased in the last decade, especially before bedtime. There is growing evidence that short-wavelength light affects hormonal secretion, thermoregulation, sleep and alertness. Whether blue light filters can attenuate these negative effects is still not clear. Therefore, here, we present preliminary data of 14 male participants (21.93 ± 2.17 years), who spent three nights in the sleep laboratory, reading 90 min either on a smartphone (1) with or (2) without a blue light filter, or (3) on printed material before bedtime. Subjective sleepiness was decreased during reading on a smartphone, but no effects were present on evening objective alertness in a GO/NOGO task. Cortisol was elevated in the morning after reading on the smartphone without a filter, which resulted in a reduced cortisol awakening response. Evening melatonin and nightly vasodilation (i.e., distal-proximal skin temperature gradient) were increased after reading on printed material. Early slow wave sleep/activity and objective alertness in the morning were only reduced after reading without a filter. These results indicate that short-wavelength light affects not only circadian rhythm and evening sleepiness but causes further effects on sleep physiology and alertness in the morning. Using a blue light filter in the evening partially reduces these negative effects.

A randomized, double-blind, placebo-controlled trial of blue wavelength light exposure on sleep and recovery of brain structure, function, and cognition following mild traumatic brain injury

Type of study: rct

Number of citations: 71

Year: 2019

Authors: William D S Killgore, J. Vanuk, Bradley R Shane, Mareen Weber, Sahil Bajaj

Journal: Neurobiology of Disease

Journal ranking: Q1

Key takeaways: Blue light exposure improves sleep timing, reduces daytime sleepiness, and enhances cognitive function in adults recovering from mild traumatic brain injury.

Exposure to Blue Light Increases Subsequent Functional Activation of the Prefrontal Cortex During Performance of a Working Memory Task.

Type of study: non-rct experimental

Number of citations: 83

Year: 2016

Authors: A. Alkozei, Ryan Smith, D. Pisner, J. Vanuk, Sarah M Berryhill, Andrew Fridman, Bradley R Shane, Sara A Knight, W. Killgore

Journal: Sleep

Journal ranking: Q1

Key takeaways: Short exposure to blue light improves working memory performance and leads to temporary brain changes in prefrontal regions associated with executive functions.

Abstract: STUDY OBJECTIVES Prolonged exposure to blue wavelength light has been shown to have an alerting effect, and enhances performance on cognitive tasks. A small number of studies have also shown that relatively short exposure to blue light leads to changes in functional brain responses during the period of exposure. The extent to which blue light continues to affect brain functioning during a cognitively challenging task after cessation of longer periods of exposure (i.e., roughly 30 minutes or longer), however, has not been fully investigated. METHODS A total of 35 healthy participants (18 female) were exposed to either blue (469 nm) (n = 17) or amber (578 nm) (n = 18) wavelength light for 30 minutes in a darkened room, followed immediately by functional magnetic resonance imaging (fMRI) while undergoing a working memory task (N-back task). RESULTS Participants in the blue light condition were faster in their responses on the N-back task and showed increased activation in the dorsolateral (DLPFC) and ventrolateral (VLPFC) prefrontal cortex compared to those in the amber control light condition. Furthermore, greater activation within the VLPFC was correlated with faster N-back response times. CONCLUSIONS This is the first study to suggest that a relatively brief, single exposure to blue light has a subsequent beneficial effect on working memory performance, even after cessation of exposure, and leads to temporarily persisting functional brain changes within prefrontal brain regions associated with executive functions. These findings may have broader implication for using blue-enriched light in a variety of work settings where alertness and quick decision-making are important.

Aging reduces the stimulating effect of blue light on cognitive brain functions.

Type of study: non-rct experimental

Number of citations: 59

Year: 2014

Authors: Véronique Daneault, M. Hébert, G. Albouy, J. Doyon, M. Dumont, J. Carrier, G. Vandewalle

Journal: Sleep

Journal ranking: Q1

Key takeaways: Blue light's stimulating effect on cognitive brain functions diminishes with age in areas involved in visual functions and alertness regulation.

Abstract: STUDY OBJECTIVES Light exposure, particularly blue light, is being recognized as a potent mean to stimulate alertness and cognition in young individuals. Aging is associated with changes in alertness regulation and cognition. Whether the effect of light on cognitive brain function changes with aging is unknown, however. DESIGN Cross-sectional study. SETTING Functional Neuroimaging Unit, University of Montreal Geriatric Institute. PARTICIPANTS Sixteen younger (23 ± 4.1 y) and 14 older (61 ± 4.5 y) healthy participants were recruited in the current study. INTERVENTION Blue light administration. MEASUREMENTS We used functional magnetic resonance imaging to record brain responses to an auditory working memory task in young and older healthy individuals, alternatively maintained in darkness or exposed to blue light. RESULTS Results show that the older brain remains capable of showing sustained responses to light in several brain areas. However, compared to young individuals, the effect of blue light is decreased in the pulvinar, amygdala, and tegmentum as well as in the insular, prefrontal, and occipital cortices in elderly individuals. CONCLUSION The effect of blue light on brain responses diminishes with aging in areas typically involved in visual functions and in key regions for alertness regulation and higher executive processes. Our findings provide the first indications that the effect of light on cognition may be reduced in healthy aging.

Daily Morning Blue Light Therapy for Post-mTBI Sleep Disruption: Effects on Brain Structure and Function

Type of study: rct

Number of citations: 19

Year: 2021

Authors: A. Raikes, N. Dailey, Brittany Forbeck, A. Alkozei, William D S Killgore

Journal: Frontiers in Neurology

Journal ranking: Q2

Key takeaways: Daily morning blue light therapy improves self-reported daytime sleepiness in individuals recovering from mild traumatic brain injuries by increasing gray matter volume and functional connectivity in sleep regulation and cognitive networks.

Abstract: Background: Mild traumatic brain injuries (mTBIs) are associated with novel or worsened sleep disruption. Several studies indicate that daily morning blue light therapy (BLT) is effective for reducing post-mTBI daytime sleepiness and fatigue. Studies demonstrating changes in brain structure and function following BLT are limited. The present study's purpose is to identify the effect of daily morning BLT on brain structure and functional connectivity and the association between these changes and self-reported change in post-mTBI daytime sleepiness. Methods: A total of 62 individuals recovering from a mTBI were recruited from two US cities to participate in a double-blind placebo-controlled trial. Eligible individuals were randomly assigned to undergo 6 weeks of 30 min daily morning blue or placebo amber light therapy (ALT). Prior to and following treatment all individuals completed a comprehensive battery that included the Epworth Sleepiness Scale as a measure of self-reported daytime sleepiness. All individuals underwent a multimodal neuroimaging battery that included anatomical and resting-state functional magnetic resonance imaging. Atlas-based regional change in gray matter volume (GMV) and region-to-region functional connectivity from baseline to post-treatment were the primary endpoints for this study. Results: After adjusting for pre-treatment GMV, individuals receiving BLT had greater GMV than those receiving amber light in 15 regions of interest, including the right thalamus and bilateral prefrontal and orbitofrontal cortices. Improved daytime sleepiness was associated with greater GMV in 74 ROIs, covering many of the same general regions. Likewise, BLT was associated with increased functional connectivity between the thalamus and both prefrontal and orbitofrontal cortices. Improved daytime sleepiness was associated with increased functional connectivity between attention and cognitive control networks as well as decreased connectivity between visual, motor, and attention networks (all FDR corrected p < 0.05). Conclusions: Following daily morning BLT, moderate to large increases in both gray matter volume and functional connectivity were observed in areas and networks previously associated with both sleep regulation and daytime cognitive function, alertness, and attention. Additionally, these findings were associated with improvements in self-reported daytime sleepiness. Further work is needed to identify the personal characteristics that may selectively identify individuals recovering from a mTBI for whom BLT may be optimally beneficial.

Improved cognitive morning performance in healthy older adults following blue-enriched light exposure on the previous evening

Type of study: rct

Number of citations: 27

Year: 2018

Authors: K. Scheuermaier, M. Münch, J. Ronda, J. Duffy

Journal: Behavioural Brain Research

Journal ranking: Q2

Key takeaways: Exposure to blue-enriched white light in the evening significantly improves working memory performance and objective alertness in older adults, without affecting sleep or circadian timing.

Evening exposure to a light-emitting diodes (LED)-backlit computer screen affects circadian physiology and cognitive performance.

Type of study: non-rct experimental

Number of citations: 623

Year: 2011

Authors: C. Cajochen, S. Frey, D. Anders, Jakub Späti, Matthias Bues, A. Pross, R. Mager, A. Wirz-Justice, O. Stefani

Journal: Journal of applied physiology

Journal ranking: Q1

Key takeaways: Evening exposure to LED-backlit computer screens suppresses melatonin production and enhances cognitive performance, but may disrupt circadian physiology.

Abstract: Many people spend an increasing amount of time in front of computer screens equipped with light-emitting diodes (LED) with a short wavelength (blue range). Thus we investigated the repercussions on melatonin (a marker of the circadian clock), alertness, and cognitive performance levels in 13 young male volunteers under controlled laboratory conditions in a balanced crossover design. A 5-h evening exposure to a white LED-backlit screen with more than twice as much 464 nm light emission {irradiance of 0,241 Watt/(steradian × m(2)) [W/(sr × m(2))], 2.1 × 10(13) photons/(cm(2) × s), in the wavelength range of 454 and 474 nm} than a white non-LED-backlit screen [irradiance of 0,099 W/(sr × m(2)), 0.7 × 10(13) photons/(cm(2) × s), in the wavelength range of 454 and 474 nm] elicited a significant suppression of the evening rise in endogenous melatonin and subjective as well as objective sleepiness, as indexed by a reduced incidence of slow eye movements and EEG low-frequency activity (1-7 Hz) in frontal brain regions. Concomitantly, sustained attention, as determined by the GO/NOGO task; working memory/attention, as assessed by "explicit timing"; and declarative memory performance in a word-learning paradigm were significantly enhanced in the LED-backlit screen compared with the non-LED condition. Screen quality and visual comfort were rated the same in both screen conditions, whereas the non-LED screen tended to be considered brighter. Our data indicate that the spectral profile of light emitted by computer screens impacts on circadian physiology, alertness, and cognitive performance levels. The challenge will be to design a computer screen with a spectral profile that can be individually programmed to add timed, essential light information to the circadian system in humans.

Morning and Evening Blue-Enriched Light Exposure Alters Metabolic Function in Normal Weight Adults

Type of study: rct

Number of citations: 77

Year: 2016

Authors: Ivy N Cheung, P. Zee, Dov M. Shalman, R. Malkani, Joseph Kang, K. Reid

Journal: PLoS ONE

Journal ranking: Q1

Key takeaways: Blue-enriched light exposure acutely alters glucose metabolism and reduces sleepiness, suggesting a role of environmental light exposure in regulating metabolism.

Abstract: Increasing evidence points to associations between light-dark exposure patterns, feeding behavior, and metabolism. This study aimed to determine the acute effects of 3 hours of morning versus evening blue-enriched light exposure compared to dim light on hunger, metabolic function, and physiological arousal. Nineteen healthy adults completed this 4-day inpatient protocol under dim light conditions (<20lux). Participants were randomized to 3 hours of blue-enriched light exposure on Day 3 starting either 0.5 hours after wake (n = 9; morning group) or 10.5 hours after wake (n = 10; evening group). All participants remained in dim light on Day 2 to serve as their baseline. Subjective hunger and sleepiness scales were collected hourly. Blood was sampled at 30-minute intervals for 4 hours in association with the light exposure period for glucose, insulin, cortisol, leptin, and ghrelin. Homeostatic model assessment of insulin resistance (HOMA-IR) and area under the curve (AUC) for insulin, glucose, HOMA-IR and cortisol were calculated. Comparisons relative to baseline were done using t-tests and repeated measures ANOVAs. In both the morning and evening groups, insulin total area, HOMA-IR, and HOMA-IR AUC were increased and subjective sleepiness was reduced with blue-enriched light compared to dim light. The evening group, but not the morning group, had significantly higher glucose peak value during blue-enriched light exposure compared to dim light. There were no other significant differences between the morning or the evening groups in response to blue-enriched light exposure. Blue-enriched light exposure acutely alters glucose metabolism and sleepiness, however the mechanisms behind this relationship and its impacts on hunger and appetite regulation remain unclear. These results provide further support for a role of environmental light exposure in the regulation of metabolism.

The influence of light exposure and chronotype on working memory in humans.

Type of study: non-rct experimental

Number of citations: 6

Year: 2021

Authors: B. Kossowski, Dawid Droździel, Katarzyna Rode, J. Michałowski, K. Jankowski, M. Wypych, A. Wolska, A. Marchewka

Journal: Acta neurobiologiae experimentalis

Journal ranking: Q3

Key takeaways: Exposure to blue, green, and red light does not affect working memory performance in individuals with extreme morning or evening chronotype, but may increase brain activity in prefrontal areas.

Abstract: Here we examine how exposure to blue (peaking at λ=470 nm), green (peaking at λ=505 nm) and red (peaking at λ=630 nm) light affects subsequent working memory performance measured with visual N-back tasks and associated functional brain responses in participants with extreme morning and extreme evening chronotype. We used within-subjects experimental manipulation on carefully selected samples and state of the art equipment for light exposure. The results show no differences between extreme morning-type and evening-type individuals in N-back task performance. We also did not replicate the alerting effect of exposure to blue wavelength light, supposedly enhancing performance on cognitive tasks. However, we found higher brain activity in the morning hours for extreme morning in comparison to extreme evening chronotype in several frontal areas of the precentral gyrus, middle and superior frontal gyri and in the occipital gyrus. This may indicate increased strategic or attentional recruitment of prefrontal areas, implicated in compensating working memory load in the morning type.