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

Towards an evidence-based integrative lighting score: a proposed multi-level approach

Background: Human circadian clocks are synchronized daily with the external light-dark cycle and entrained to the 24-hour day. There is increasing evidence that a lack of synchronization and circadian entrainment can lead to adverse health effects. Beyond vision, light plays a critical role in modulating many so-called non-visual functions, including sleep-wake cycles, alertness, mood and endocrine functions. To assess (and potentially optimize) the impact of light on non-visual functions, it is necessary to know the exact 'dose' (i.e. spectral irradiance and exposure duration at eye level) of 24-hour light exposures, but also to include metadata about the lighting environment, individual needs and resources.

Problem statement: To address this problem, a new assessment tool is needed that uses existing metrics to provide metadata and information about light quality and quantity from all sources. In this commentary, we discuss the need to develop an evidence-based integrative lighting score that is tailored to specific audiences and lighting environments. We will summarize the most compelling evidence from the literature and outline a future plan for developing such a lighting score using internationally accepted metrics, stakeholder and user feedback.

Conclusion: We propose a weighting system that combines light qualities with physiological and behavioral effects, and the use of mathematical modelling for an output score. Such a scoring system will facilitate a holistic assessment of a lighting environment, integrating all available light sources.

Current Insights on the Photoprotective Mechanism of the Macular Carotenoids, Lutein and Zeaxanthin: Safety, Efficacy and Bio-Delivery

Ocular health has emerged as one of the major issues of global health concern with a decline in quality of life in an aging population, in particular and rise in the number of associated morbidities and mortalities. One of the chief reasons for vision impairment is oxidative damage inflicted to photoreceptors in rods and cone cells by blue light as well as UV radiation. The scenario has been aggravated by unprecedented rise in screen-time during the COVID and post-COVID era. Lutein and Zeaxanthin are oxygenated carotenoids with proven roles in augmentation of ocular health largely by virtue of their antioxidant properties and protective effects against photobleaching of retinal pigments, age-linked macular degeneration, cataract, and retinitis pigmentosa. These molecules are characterized by their characteristic yellow-orange colored pigmentation and are found in significant amounts in vegetables such as corn, spinach, broccoli, carrots as well as fish and eggs. Unique structural signatures including tetraterpenoid skeleton with extensive conjugation and the presence of hydroxyl groups at the end rings have made these molecules evolutionarily adapted to localize in the membrane of the photoreceptor cells and prevent their free radical induced peroxidation. Apart from the benefits imparted to ocular health, lutein and zeaxanthin are also known to improve cognitive function, cardiovascular physiology, and arrest the development of malignancy. Although abundant in many natural sources, bioavailability of these compounds is low owing to their long aliphatic backbones. Under the circumstances, there has been a concerted effort to develop vegetable oil-based carriers such as lipid nano-emulsions for therapeutic administration of carotenoids. This review presents a comprehensive update of the therapeutic potential of the carotenoids along with the challenges in achieving an optimized delivery tool for maximizing their effectiveness inside the body.

Acute effects of light during daytime on central aspects of attention and affect: A systematic review

Light regulates both image- and various non-image forming responses in humans, including acute effects on attention and affect. To advance the understanding of light's immediate effects, this systematic review describes the acute effects of monochromatic/narrow bandwidth and polychromatic white light during daytime on distinct aspects of attention (alertness, sustained attention, working memory, attentional control and flexibility), and measures of affect (self-report measures, performance-based tests, psychophysiological measures) in healthy, adult human subjects. Original, peer-reviewed (quasi-) experimental studies published between 2000 and May 2024 were included according to predefined inclusion and exclusion criteria. Study quality was assessed, and results were synthesized across aspects of attention and affect and grouped according to light interventions; monochromatic/narrowband-width or polychromatic white light (regular white, bright white, and white with high correlated color temperature (CCT)). Results from included studies (n = 62) showed that alertness and working memory were most affected by light. Electroencephalographic markers of alertness improved the most with exposure to narrow bandwidth long-wavelength light, regular white, and white light with high CCT. Self-reported alertness and measures of working memory improved the most with bright white light. Results from studies testing the acute effects on sustained attention and attentional control and flexibility were inconclusive. Performance-based and psychophysiological measures of affect were only influenced by narrow bandwidth long-wavelength light. Polychromatic white light exerted mixed effects on self-reported affect. Studies were strongly heterogeneous in terms of light stimuli characteristics and reporting of light stimuli and control of variables influencing light's acute effects.

Impact of COVID-19 pandemic on the circadian rhythm of cesarean section deliveries

Circadian rhythms synchronize all biological functions, enabling humans to foresee and respond better to periodic environmental changes. The coronavirus disease (COVID-19) lockdown regulations significantly changed the lighting conditions in pregnant women, leading to chronological disruption. This study aimed to investigate the impact of the COVID-19 on the circadian rhythm of cesarean deliveries. We investigated whether the circadian rhythm of cesarean section deliveries changed during the first year of the COVID-19 pandemic at a tertiary hospital in Van Province, eastern Turkey. We analyzed the distribution of birth times for 1476 cesarean deliveries performed between March 01, 2020 and January 20, 2021 (1st year of the COVID-19 pandemic) and compared this information with data from 1194 cesarean deliveries performed during a similar period in the previous year. The primary outcome was the change in the circadian rhythm of cesarean deliveries. Secondary outcomes included cesarean section (CS) delivery rates, indications for CS, 1st and 5th minutes Appearance (skin color), Pulse (heart rate), Grimace (reflex irritability), Activity (muscle tone), and Respiration scores, and anesthesia technique use rates. Regarding the time distribution of CS deliveries in the first year of the COVID-19 pandemic, the maximum number of cesarean deliveries (n = 234, 16%) occurred between 14:00 and 16:00 (P = .112). Cesarean deliveries in pre-COVID-19 group were most frequently performed between 10:00 and 12:00, at a rate of 18% (n = 216) (P = .001). In both groups, the time point at which CS deliveries were the least performed was 04:00 to 06:00, and the rates were different (n = 35, 2% and n = 14, 1%, respectively) (P = .022). A 4-hour phase shift was detected at the peak of the birth time in the first year of the COVID-19 pandemic compared to the previous year. These results suggest that the circadian rhythm of cesarean deliveries is affected by the pandemic.

The effects of multi-colour light filtering glasses on human brain wave activity

The prevalence of electronic screens in modern society has significantly increased our exposure to high-energy blue and violet light wavelengths. Accumulating evidence links this exposure to adverse visual and cognitive effects and sleep disturbances. To mitigate these effects, the optical industry has introduced a variety of filtering glasses. However, the scientific validation of these glasses has often been based on subjective reports and a narrow range of objective measures, casting doubt on their true efficacy. In this study, we used electroencephalography (EEG) to record brain wave activity to evaluate the effects of glasses that filter multiple wavelengths (blue, violet, indigo, and green) on human brain activity. Our results demonstrate that wearing these multi-colour light filtering glasses significantly reduces beta wave power (13-30 Hz) compared to control or no glasses. Prior research has associated a reduction in beta power with the calming of heightened mental states, such as anxiety. As such, our results suggest that wearing glasses such as the ones used in this study may also positively change mental states, for instance, by promoting relaxation. This investigation is innovative in applying neuroimaging techniques to confirm that light-filtering glasses can induce measurable changes in brain activity.

Enjoying art: an evolutionary perspective on the esthetic experience from emotion elicitors

The ubiquity of human art prompted evolutionary psychologists to explore its origins as a potential adaptation to the environment. Here we focus on emotionally charged art and posit that affective affordances embedded into some artworks play a pivotal role in explaining why these artworks are enjoyed from an evolutionary perspective. Such features, recurring in various art forms, are interpreted as cues to the emotional state of others, enabling art consumers to engage in empathetic experiences and vicarious emotions. We explore the adaptive value of deriving pleasure from vicarious emotions, while also addressing the seemingly counterintuitive enjoyment of artworks that evoke negative emotions. We discuss the appreciation of vicarious emotions irrespective of their valence and maintain this appreciation to hold adaptive significance for three key reasons. Firstly, it aids art consumers in refining their interpretational schemes of internal states, potentially enhancing emotional regulation skills. Secondly, it contributes to a deeper understanding of the emotions of others, thereby fostering emotional intelligence and empathy. Lastly, the enjoyment of affectively charged artworks reinforces social cohesion by harmonizing the emotions of group members. This perspective provides a comprehensive framework for understanding the evolutionary underpinnings of the human capacity for art appreciation and emotional engagement.

Seasonal and Annual Change in Physiological Ocular Growth of 7- to 11-Year-Old Norwegian Children

Purpose

To investigate seasonal and annual change in physiological eye growth in Norwegian school children.

Methods

Measurements of ocular biometry, non-cycloplegic spherical equivalent autorefraction (SER), and choroidal thickness (ChT) were obtained for 92 children (44 females) aged 7 to 11 years at four time points over a year (November 2019-November 2020). Seasons (3- and 5-month intervals) were classified as winter (November-January), winter-spring (January-June), and summer-autumn (June-November). Cycloplegic SER was obtained in January and used to group children. The seasonal and annual changes were tested with a linear mixed-effects model (P values were adjusted for multiple comparisons).

Results

All the children experienced annual ocular growth, irrespective of SER, but less so during the summer-autumn. The baseline SER was lower (P < 0.001), axial length (AL) was longer (P < 0.038), and choroids were thicker in 10- to 11-year-old than 7- to 8-year-old mild hyperopes (P = 0.002). Assuming mild hyperopes (n = 65) experience only physiological eye growth, modeling revealed seasonal and annual increases in AL across sex and age (P < 0.018), with less change during the summer-autumn than winter-spring. The 7- to 8-year-olds had a larger decrease annually and over winter-spring in SER (P ≤ 0.036) and in ChT over winter-spring than the 10- to 11-year-olds (P = 0.006).

Conclusions

There were significant seasonal and annual changes in AL in children who had physiological eye growth irrespective of age within this cohort. Annual changes in SER and seasonal choroidal thinning were only observed in 7- to 8-year-old children. This indicates continued emmetropization in 7- to 8-year-olds and a transition to maintaining emmetropia in 10- to 11-year-olds.

Recovery from shift work

One fifth of today's workforce is engaged in shift work and exposed to various mental and physical health risks including shift work disorder. Efficiently recovering from shift work through physical and mental interventions allows us to mitigate negative effects on health, enables a better work-life balance and enhances our overall wellbeing. The aim of this review is to provide a state-of-the-art overview of the available literature. The role of sleep timing and naps, light therapy and psychotherapy, diet and exercise in recovery from shift work is presented here. We further review the impact of shift schedules and social support on post-shift unwinding.

Associations between light exposure and sleep timing and sleepiness while awake in a sample of UK adults in everyday life

Experimental and interventional studies show that light can regulate sleep timing and sleepiness while awake by setting the phase of circadian rhythms and supporting alertness. The extent to which differences in light exposure explain variations in sleep and sleepiness within and between individuals in everyday life remains less clear. Here, we establish a method to address this deficit, incorporating an open-source wearable wrist-worn light logger (SpectraWear) and smartphone-based online data collection. We use it to simultaneously record longitudinal light exposure (in melanopic equivalent daylight illuminance), sleep timing, and subjective alertness over seven days in a convenience sample of 59 UK adults without externally imposed circadian challenge (e.g., shift work or jetlag). Participants reliably had strong daily rhythms in light exposure but frequently were exposed to less light during the daytime and more light in pre-bedtime and sleep episodes than recommended [T. M. Brown et al., PLoS Biol. 20, e3001571 (2022)]. Prior light exposure over several hours was associated with lower subjective sleepiness with, in particular, brighter light in the late sleep episode and after wake linked to reduced early morning sleepiness (sleep inertia). Higher pre-bedtime light exposure was associated with longer sleep onset latency. Early sleep timing was correlated with more reproducible and robust daily patterns of light exposure and higher daytime/lower night-time light exposure. Our study establishes a method for collecting longitudinal sleep and health/performance data in everyday life and provides evidence of associations between light exposure and important determinants of sleep health and performance.

Hilaire MA, Lockley SW, Rahman SA. Supplementation of ambient lighting with a task lamp improves daytime alertness and cognitive performance in sleep-restricted individuals

STUDY OBJECTIVES

We examined the impact of adding a single-high-melanopic-illuminance task lamp in an otherwise low-melanopic-illuminance environment on alertness, neurobehavioral performance, learning, and mood during an 8-h simulated workday.

METHODS

Sixteen healthy young adults [mean(±SD) age = 24.2 ± 2.9, 8F] participated in a 3-day inpatient study with two 8-h simulated workdays and were randomized to either ambient fluorescent room light (~30 melanopic EDI lux, 50 lux), or room light supplemented with a light emitting diode task lamp (~250 melanopic EDI lux, 210 lux) in a cross-over design. Alertness, mood, and cognitive performance were assessed throughout the light exposure and compared between conditions using linear mixed models.

RESULTS

The primary outcome measure of percentage correct responses on the addition task was significantly improved relative to baseline in the supplemented condition (3.15% ± 1.18%), compared to the ambient conditions (0.93% ± 1.1%; FDR-adj q = 0.005). Additionally, reaction time and attentional failures on the psychomotor vigilance tasks were significantly improved with exposure to supplemented compared to ambient lighting (all, FDR-adj q ≤ 0.030). Furthermore, subjective measures of sleepiness, alertness, happiness, health, mood, and motivation were also significantly better in the supplemented, compared to ambient conditions (all, FDR-adj q ≤ 0.036). There was no difference in mood disturbance, affect, declarative memory, or motor learning between the conditions (all, FDR-adj q ≥ 0.308).

CONCLUSIONS

Our results show that supplementing ambient lighting with a high-melanopic-illuminance task lamp can improve daytime alertness and cognition. Therefore, high-melanopic-illuminance task lighting may be effective when incorporated into existing suboptimal lighting environments.

CLINICAL TRIALS

NCT04745312. Effect of Lighting Supplementation on Daytime Cognition. https://clinicaltrials.gov/ct2/show/NCT04745312.

Feasibility and Efficacy of Morning Light Therapy for Adults with Insomnia: A Pilot, Randomized, Open-Label, Two-Arm Study

Background and Objectives: Light therapy (LT) is used as an adjunctive treatment for sleep problems. This study evaluates the impact of LT on sleep quality and sleep-related parameters in patients with sleep disorders. Materials and Methods: We performed a pilot, randomized, open-label clinical trial. Fourteen patients aged 20-60 years with insomnia were randomized into the control and LT groups (1:1 ratio). The LT group was instructed to use a device that provides bright LT (6000 K, 380 lux, wavelength 480 nm) for at least 25 min before 09:00 a.m. for two weeks. A self-reported questionnaire was used to evaluate circadian preference, mood, and sleep-related parameters. We analyzed serum cortisol levels and clock genes' expression. Results: The Epworth Sleepiness Scale (ESS), insomnia severity index(ISI), and Pittsburgh Sleep Quality index(PSQI) were significantly improved within the LT group only after the two-week period. When comparing the two groups, only the change in ESS was significant (mean difference, control: -0.14 vs. LT: -1.43, p = 0.021) after adjusting for the baseline characteristics. There were no significant differences in serum cortisol or clock genes' expression. Conclusions: LT can improve daytime sleepiness in patients with sleep disorders; however, further well-designed studies are warranted to confirm its efficacy.

Shine light on sleep: Morning bright light improves nocturnal sleep and next morning alertness among college students

The relationship between daytime light, especially morning light and sleep, has not been well documented. People who work in an office spend most of their time indoors and thus have less access to high-level daylight. The current study employed a field intervention approach to investigate whether exposure to 1.5 h of bright electric light in the early morning for 1 workweek would benefit sleep among students who spent most of their time in an office at the university. Twelve students (24.92 ± 1.78 years) underwent a 2 workday baseline measurement and two inconsecutive 5 workday interventions (with 1 week washout) with morning bright light and regular office light (1000 lx, 6500 K vs. 300 lx, 4000 K, at eye level). The sleep outcomes were recorded with actigraphy and a sleep diary. In addition, self-ratings of daytime sleepiness, mood, mental fatigue, perceived effort, and next morning sleepiness were measured each workday. The results showed that exposure to morning bright light versus regular office light yielded a higher sleep efficiency (83.82% ± 1.60 vs. 80.35% ± 1.57, p = 0.02), a smaller fragmentation index (15.26% ± 1.31 vs. 17.18% ± 1.28, p = 0.05), and a shorter time in bed (7.12 ± 0.13 vs. 7.51 ± 0.12, p = 0.03). Meanwhile, an earlier sleep onset time, shorter sleep latency, and lower morning sleepiness were observed after a 5 workday morning bright light intervention compared with the baseline (ps <0.05), no such benefit was found for self-ratings (ps >0.05). These findings support existing evidence that morning bright light could function as an enhancer of sleep and alertness for office occupants.

The Updating and Individualizing of Sleep Hygiene Rules for Non-clinical Adult Populations

Sleep hygiene is essential for the prevention of somatic and mental disorders, including the prevention of sleep disorders. However, it does not typically address individual differences. The aim of this review is threefold: first, to outline the empirical evidence for particular components of sleep hygiene rules; second, to indicate the importance of individualized sleep hygiene application with regard to the varying degree of validity of sleep hygiene rules in the population; third, to highlight a new field of sleep hygiene, namely light hygiene. PubMed and Google Scholar were used to identify studies that were published between 2007 and 2022. A search was conducted for studies related to sleeping rules topics: sleep regularity, regular exercise, alcohol, caffeine, napping, relaxation and meditation, food intake and light exposure. In applying these sleep hygiene principles, it is essential to pay attention to individual variables such as age, genetic predisposition, health status, and substance (caffeine, alcohol) possible dependence.

Are We Ready to Implement Circadian Hygiene Interventions and Programs?

Circadian hygiene, a concept not to be confused with the notion of public or social hygiene, should be discussed among experts and society. Light-dark cycles and other possible synchronizers of the human circadian timing system affect ways of life, including sleeping, eating, working and physical activity. Some of these behaviors have also been investigated individually as synchronizers (e.g., eating times). Therefore, the knowledge held today about circadian rhythms, and their implications for health, allows future perspectives in this field to be mapped. The present article summarizes the latest knowledge on factors influencing circadian rhythms to discuss a perspective for the future of health promotion based on circadian hygiene. However, it is important to highlight that circadian hygiene is the product of an imbrication of individual and societal involvement. First, it is important to adopt practices and devise public health policies in line with circadian hygiene. Second, individual healthy habits require internal rhythms to be examined. Last, the research agenda on circadian hygiene can be developed on a public as well as individual level, raising the question as to how much society is willing to embrace this change.

Ecological factors are likely drivers of eye shape and colour pattern variations across anthropoid primates

External eye appearance across primate species is diverse in shape and colouration, yet we still lack an explanation for the drivers of such diversity. Here we quantify substantial interspecific variation in eye shape and colouration across 77 primate species representing all extant genera of anthropoid primates. We reassess a series of hypotheses aiming to explain ocular variation in horizontal elongation and in colouration across species. Heavier body weight and terrestrial locomotion are associated with elongated eye outlines. Species living closer to the equator present more pigmented conjunctivae, suggesting photoprotective functions. Irises become bluer in species living further away from the equator, adding to existing literature supporting a circadian clock function for bluer irises. These results shift the current focus from communicative, to ecological factors in driving variation in external eye appearance in anthropoid primates. They also highlight the possibility that similar ecological factors contributed to selection for blue eyes in ancestral human populations living in northern latitudes.

Alerting effects of light in healthy individuals: a systematic review and meta-analysis

Light plays an essential role in psychobiological and psychophysiological processes, such as alertness. The alerting effect is influenced by light characteristics and the timing of interventions. This meta-analysis is the first to systematically review the effect of light intervention on alertness and to discuss the optimal protocol for light intervention. In this meta-analysis, registered at PROSPERO (Registration ID: CRD42020181485), we conducted a systematic search of the Web of Science, PubMed, and PsycINFO databases for studies published in English prior to August 2021. The outcomes included both subjective and objective alertness. Subgroup analyses considered a variety of factors, such as wavelength, correlated color temperature (CCT), light illuminance, and timing of interventions (daytime, night-time, or all day). Twenty-seven crossover studies and two parallel-group studies were included in this meta-analysis, with a total of 1210 healthy participants (636 (52%) male, mean age 25.62 years). The results revealed that light intervention had a positive effect on both subjective alertness (standardized mean difference (SMD) = –0.28, 95% confidence interval (CI): –0.49 to –0.06, P = 0.01) and objective alertness in healthy subjects (SMD = –0.34, 95% CI: –0.68 to –0.01, P = 0.04). The subgroup analysis revealed that cold light was better than warm light in improving subjective alertness (SMD = –0.37, 95% CI: –0.65 to –0.10, P = 0.007, I² = 26%) and objective alertness (SMD = –0.36, 95% CI: –0.66 to –0.07, P = 0.02, I² = 0). Both daytime (SMD = –0.22, 95% CI: –0.37 to –0.07, P = 0.005, I² = 74%) and night-time (SMD = –0.32, 95% CI: –0.61 to –0.02, P = 0.04, I² = 0) light exposure improved subjective alertness. The results of this meta-analysis and systematic review indicate that light exposure is associated with significant improvement in subjective and objective alertness. In addition, light exposure with a higher CCT was more effective in improving alertness than light exposure with a lower CCT. Our results also suggest that both daytime and night-time light exposure can improve subjective alertness.

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

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 Effect of Light Therapy on Electroencephalographic Sleep in Sleep and Circadian Rhythm Disorders: A Scoping Review

Light therapy is used to treat sleep and circadian rhythm disorders, yet there are limited studies on whether light therapy impacts electroencephalographic (EEG) activity during sleep. Therefore, we aimed to provide an overview of research studies that examined the effects of light therapy on sleep macro- and micro-architecture in populations with sleep and circadian rhythm disorders. We searched for randomized controlled trials that used light therapy and included EEG sleep measures using MEDLINE, PubMed, CINAHL, PsycINFO and Cochrane Central Register of Controlled Trials databases. Five articles met the inclusion criteria of patients with either insomnia or delayed sleep−wake phase disorder (DSWPD). These trials reported sleep macro-architecture outcomes using EEG or polysomnography. Three insomnia trials showed no effect of the timing or intensity of light therapy on total sleep time, wake after sleep onset, sleep efficiency and sleep stage duration compared to controls. Only one insomnia trial reported significantly higher sleep efficiency after evening light therapy (>4000 lx between 21:00−23:00 h) compared with afternoon light therapy (>4000 lx between 15:00−17:00 h). In the only DSWPD trial, six multiple sleep latency tests were conducted across the day (09:00 and 19:00 h) and bright light (2500 lx) significantly lengthened sleep latency in the morning (09:00 and 11:00 h) compared to control light (300 lx). None of the five trials reported any sleep micro-architecture measures. Overall, there was limited research about the effect of light therapy on EEG sleep measures, and studies were confined to patients with insomnia and DSWPD only. More research is needed to better understand whether lighting interventions in clinical populations affect sleep macro- and micro-architecture and objective sleep timing and quality.

[Chronobiological interventions for prevention and treatment of delirium in critically ill patients]

Circadian body and behavior rhythms serve to coordinate and maintain the physiological processes in the human body. A disruption of these rhythms frequently occurs in intensive care patients and can be the cause for the development of delirium. This review article discusses the underlying pathophysiological mechanisms and develops a chronobiologically oriented prevention and treatment approach for delirium in the context of intensive care medicine.

Take the Right Seat: The Influence of Occupancy Schemes on Performance Indicators of Lighting in Open Plan Offices

Work processes and sociological structures can differ significantly between organizations. These organizational aspects determine user behavior, which in turn exerts considerable influence on the key performance indicators of artificial lighting systems. Accordingly, the use of generalized assumptions about user behavior in the building design phase can lead to large discrepancies between design and operation. In the following work, the possible influences of different occupancy schemes, an essential aspect of user behavior and shaped by the organization, on energy demand and workplace-related daylight dose are evaluated. For this purpose, calculations are made based on real measurement data of an open-plan office with zoned lighting. Multi-level calculation models are used to determine improved user distributions in the room to ensure optimization according to the desired target criteria. The results show that occupancy schemes have a significant impact on energy demand, contributing significantly to overall building performance, but only slightly to workplace-related light exposure rates in terms of total daily light dose. A correlated influence on the target criteria could not be demonstrated, but given the minor influence on daily light dose, the optimization of planning and operation can be focused on energy efficiency.

Optimized office lighting advances melatonin phase and peripheral heat loss prior bedtime

Improving indoor lighting conditions at the workplace has the potential to support proper circadian entrainment of hormonal rhythms, sleep, and well-being. We tested the effects of optimized dynamic daylight and electric lighting on circadian phase of melatonin, cortisol and skin temperatures in office workers. We equipped one office room with an automated controller for blinds and electric lighting, optimized for dynamic lighting (= Test room), and a second room without any automated control (= Reference room). Young healthy participants (n = 34) spent five consecutive workdays in each room, where individual light exposure data, skin temperatures and saliva samples for melatonin and cortisol assessments were collected. Vertical illuminance in the Test room was 1177 ± 562 photopic lux (mean  ± SD) , which was 320 lux higher than in the Reference room (p < 0.01). Melanopic equivalent daylight (D65) illuminance was 931 ± 484 melanopic lux in the Test room and 730 ± 390 melanopic lux in the Reference room (p < 0.01). Individual light exposures resulted in a 50 min earlier time of half-maximum accumulated illuminance in the Test than the Reference room (p < 0.05). The melatonin secretion onset and peripheral heat loss in the evening occurred significantly earlier with respect to habitual sleeptime in the Test compared to the Reference room (p < 0.05). Our findings suggest that optimized dynamic workplace lighting has the potential to promote earlier melatonin onset and peripheral heat loss prior bedtime, which may be beneficial for persons with a delayed circadian timing system.

Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults

Ocular light exposure has important influences on human health and well-being through modulation of circadian rhythms and sleep, as well as neuroendocrine and cognitive functions. Prevailing patterns of light exposure do not optimally engage these actions for many individuals, but advances in our understanding of the underpinning mechanisms and emerging lighting technologies now present opportunities to adjust lighting to promote optimal physical and mental health and performance. A newly developed, international standard provides a SI-compliant way of quantifying the influence of light on the intrinsically photosensitive, melanopsin-expressing, retinal neurons that mediate these effects. The present report provides recommendations for lighting, based on an expert scientific consensus and expressed in an easily measured quantity (melanopic equivalent daylight illuminance (melaponic EDI)) defined within this standard. The recommendations are supported by detailed analysis of the sensitivity of human circadian, neuroendocrine, and alerting responses to ocular light and provide a straightforward framework to inform lighting design and practice.

Ergonomic lighting considerations for the home office workplace

BACKGROUND: The COVID-19 pandemic has resulted in a large increase in the use of the home office environment. Compared to traditional commercial offices, home offices typically have more variable lighting conditions that can affect the worker’s performance and well-being. OBJECTIVE: To review and discuss various lighting sources and their ergonomic impacts on the population of office employees now working from home. Specifically addressing the impacts of electronic light from screens, daylight, and task lighting’s impact on health and well-being in the frame of the COVID-19 pandemic. METHODS: Over 75 ergonomic and lighting literature publications covering various work environments were reviewed, with a focus on the health effects of screen light, daylight, and task light. RESULTS: Resulting from the literature review, design recommendations regarding the safety and health of home office lighting conditions are discussed. CONCLUSION: As COVID-19 continues to encourage remote working, individuals will be exposed to daylight and screen light in different ways compared to a traditional office environment. The impact of these different lighting conditions should be further studied to understand best design and well-being practices.

Effects of Daytime Electric Light Exposure on Human Alertness and Higher Cognitive Functions: A Systematic Review

This paper reports the results of a systematic review conducted on articles examining the effects of daytime electric light exposure on alertness and higher cognitive functions. For this, we selected 59 quantitative research articles from 11 online databases. The review protocol was registered with PROSPERO (CRD42020157603). The results showed that both short-wavelength dominant light exposure and higher intensity white light exposure induced alertness. However, those influences depended on factors like the participants' homeostatic sleep drive and the time of day the participants received the light exposure. The relationship between light exposure and higher cognitive functions was not as straightforward as the alerting effect. The optimal light property for higher cognitive functions was reported dependent on other factors, such as task complexity and properties of control light. Among the studies with short-wavelength dominant light exposure, ten studies (morning: 3; afternoon: 7) reported beneficial effects on simple task performances (reaction time), and four studies (morning: 3; afternoon: 1) on complex task performances. Four studies with higher intensity white light exposure (morning: 3; afternoon: 1) reported beneficial effects on simple task performance and nine studies (morning: 5; afternoon: 4) on complex task performance. Short-wavelength dominant light exposure with higher light intensity induced a beneficial effect on alertness and simple task performances. However, those effects did not hold for complex task performances. The results indicate the need for further studies to understand the influence of short-wavelength dominant light exposure with higher illuminance on alertness and higher cognitive functions.

[Light Therapy for Prevention of Delirium in Critically Ill Patients: What's the Evidence?]

Circadian dysrhythmia affects the majority of ICU patients and has far-reaching effects on organ functioning. At the level of the central nervous system, circadian misalignment facilitates executive cognitive dysfunction and the development of ICU delirium. The pathophysiological mechanisms, especially in the cohort of critically ill patients, appear to be complex, multilayered and far from understood. Results from preliminary research indicate that multidimensional, patient-specific chronotherapeutic concepts developed specifically for the ICU setting may help improve the healing process of patients. Circadian lighting therapy might be a promising intervention in this context.

Temporal Dynamics of Subjective and Objective Alertness During Exposure to Bright Light in the Afternoon for 5 h

Light can induce an alertness response in humans. The effects of exposure to bright light vs. dim light on the levels of alertness during the day, especially in the afternoon, as reported in the literature, are inconsistent. This study employed a multiple measurement strategy to explore the temporal variations in the effects of exposure to bright light vs. regular office light (1,200 lx vs. 200 lx at eye level, 6,500 K) on the alertness of participants for 5 h in the afternoon. In this study, 20 healthy adults (11 female; mean age 23.25 ± 2.3 years) underwent the Karolinska sleepiness scale (KSS), the auditory psychomotor vigilance test (PVT), and the waking electroencephalogram (EEG) test for two levels of light intervention. The results yielded a relatively lower relative delta power and a relatively higher beta power for the 1,200 lx condition in comparison with the 200 lx condition. However, the light conditions elicited no statistically significant differences in the KSS scores and performance with respect to the PVT. The results suggested that exposure to bright light for 5 h in the afternoon could enhance physiological arousal while exerting insignificant effects on subjective feelings and performance abilities relating to the alertness of the participants.

Assessment of the Light Exposures of Shift-working Nurses in London and Dortmund in Relation to Recommendations for Sleep and Circadian Health

Shift work causes disruption to circadian physiological processes in the human body, and desynchronization from the natural day-and-night rhythm. Circadian disruption is thought to explain the associations between shift work and various long-term diseases; light is an unrivalled synchronizer (or Zeitgeber) of circadian processes and inappropriate light exposure plausibly plays a critical role in the development of health impairments. As published measurement data on the actual light environments encountered by shift workers are sparse, nurses working in two hospitals in London (UK) and Dortmund (Germany) wore light-logging dosimetry devices to measure personal light exposures continuously over a week in three different seasons. The study identifies and quantifies several of the characteristics of light exposure related to different working patterns in winter, spring, and summer, and quantifies interindividual variations. These data enable informed design of light exposure interventions or changes to shifts to reduce unwanted effects of disruptive light exposure profiles.

Diversity in Primate External Eye Morphology: Previously Undescribed Traits and Their Potential Adaptive Value

Comparative examinations of external eye morphology in primates initially focused on communicative functions of the eye. Subsequent work has failed to find consistent associations between specific eye morphologies and communicative functions. In this article, we review the field of primate external eye morphology and inspect publicly available and unpublished photographs. We identify and describe five commonly occurring traits that have not received attention so far. We cross-examined the clinical and psychological literature to propose potential adaptive functions. These potential adaptive functions include communicative functions, but also photoregulatory functions and photoprotective functions.

Reply to Bracke et al. Comment on "Prayag et al. Light Modulation of Human Clocks, Wake, and Sleep. Clocks&Sleep 2019, 1, 193-208"

We thank Bracke and colleagues [...].

Crystalline lens transmittance spectra and pupil sizes as factors affecting light-induced melatonin suppression in children and adults

PURPOSE

To investigate the contributions of ocular crystalline lens transmittance spectra and pupil size on age-related differences in the magnitude of light-induced melatonin suppression at night. The first aim was to demonstrate that spectral lens transmittance in children can be measured in vivo with a Purkinje image-based system. The second aim was to test the hypothesis that the magnitude of melatonin suppression in children is enhanced by larger pupils and higher lens transmittance of short wavelengths.

METHODS

Fourteen healthy children and 14 healthy adults participated in this study. The experiment was conducted for two nights in our laboratory. On the first night, the participants spent time under dim light conditions (<10 lux) until one hour after their habitual bedtime (BT+1.0). On the second night, the participants spent time under dim light conditions until 30 min before their habitual bedtime (BT-0.5). They were then exposed to LED light for 90 min up to BT+1.0. Individual pupil sizes were measured between BT and BT+1.0 for both conditions. Lens transmittance spectra were measured in vivo using the Purkinje image-based system during the daytime. Non-visual photoreception was calculated from lens transmittance and pupil size. This was taken as an index of the influence of age-related ocular changes on the non-visual photopigment melanopsin.

RESULTS

Measured lens transmittance in children was found to be higher than for adults, especially in the short wavelength region (p < 0.001). Pupil size in children was significantly larger than that of adults under both dim (p = 0.003) and light (p < 0.001) conditions. Children's non-visual photoreception was 1.48 times greater than that of adults, which was very similar to the finding that melatonin suppression was 1.52 times greater in children (n = 9) than adults (n = 9).

CONCLUSIONS

Our Purkinje image-based system can measure children's lens transmittance spectra in vivo. Lens transmittance and pupil size may contribute to differences in melatonin suppression between primary school children and middle-aged adults.

Daytime Exposure to Short Wavelength-Enriched Light Improves Cognitive Performance in Sleep-Restricted College-Aged Adults

We tested the effect of daytime indoor light exposure with varying melanopic strength on cognitive performance in college-aged students who maintained an enforced nightly sleep opportunity of 7 h (i.e., nightly sleep duration no longer than 7 h) for 1 week immediately preceding the day of light exposure. Participants (n = 39; mean age ± SD = 24.5 ± 3.2 years; 21 F) were randomized to an 8 h daytime exposure to one of four white light conditions of equal photopic illuminance (~50 lux at eye level in the vertical plane) but different melanopic illuminance [24–45 melanopic-EDI lux (melEDI)] generated by varying correlated color temperatures [3000K (low-melEDI) or 5000K (high-melEDI)] and spectra [conventional or daylight-like]. Accuracy on a 2-min addition task was 5% better in the daylight-like high-melEDI condition (highest melEDI) compared to the conventional low-melEDI condition (lowest melEDI; p < 0.01). Performance speed on the motor sequence learning task was 3.2 times faster (p < 0.05) during the daylight-like high-melEDI condition compared to the conventional low-melEDI. Subjective sleepiness was 1.5 times lower in the conventional high-melEDI condition compared to the conventional low-melEDI condition, but levels were similar between conventional low- and daylight-like high-melEDI conditions. These results demonstrate that exposure to high-melanopic (short wavelength-enriched) white light improves processing speed, working memory, and procedural learning on a motor sequence task in modestly sleep restricted young adults, and have important implications for optimizing lighting conditions in schools, colleges, and other built environments.

Time for Novel Strategies to Mitigate Cardiometabolic Risk in Shift Workers

Circadian disruption induced by shift work is robustly associated with obesity, diabetes, and cardiovascular disease in humans. Less well-known are the mechanisms underlying these associations, and the effectiveness of strategies to reduce cardiometabolic risk in the shift work population. In this review, the different ways in which shift work can deteriorate cardiometabolic health, and how to use this information to reflect on various risk-mitigating strategies, is discussed. While individual strategies appear promising in animal studies, the multifactorial disease risk in shift workers likely requires a multidisciplinary approach. Therefore, the need for individually-tailored combined lifestyle interventions, that could be essential in reducing cardiometabolic disorders in the large population of shift workers in our 24/7 society, is argued.

Dramatically altered environmental lighting conditions in women with high-risk pregnancy during hospitalization

The maternal circadian time structure is incredibly important in the entrainment and programing of the fetal and newborn circadian time structure. Natural sunlight is the primary environmental time cue for entrainment of circadian rhythms, but high-risk pregnant women spend most of their time indoors with artificial light sources and extremely low levels of natural light both during the day and night. Because the daily level, timing, duration of light exposure and its spectral properties are important in maintaining the normal circadian physiology in humans, we aimed to evaluate the environmental lighting conditions in high-risk pregnant women admitted to hospital for long-term stay. About 30 patients were included in the study. Exposed illuminance, color temperature and effective circadian radiation dose were measured and recorded every 10 s by light dosimeters attached to the patients' clothing. We documented the illuminance of 29 pregnant women on 235 inpatient days. Median (IQR) measured illuminance was 70 (28-173) lux in the morning, 124 (63-241) lux in the afternoon, 19 (6-53) lux in the evening and 0 (0-0) lux at the night. Median illuminance for the 235 inpatient days of assessment was below the recommended EU standard of 100 lux-60.5% of the mornings and 42.7% of the afternoons. The women confined to indoor locations rarely achieved an illuminances more than 300 lux in the morning and in the afternoon. Compared to women with outdoor mobility, those confined indoors have a significantly lower illuminance and color temperature, both in the morning and in the afternoon. Our study presents the first information about the dramatically altered environmental lighting conditions experienced by high-risk pregnant women during their hospital stay. Their exposure to light while in the hospital is significantly lower than exposure to natural daylight levels and below the recommended EU standard.

Effects of altered photoperiod due to COVID-19 lockdown on pregnant women and their fetuses

Maternal circadian rhythms provide highly important input into the entrainment and programming of fetal and newborn circadian rhythms. The light-dark cycle is an important regulator of the internal biological clock. Even though pregnant women spend a greater part of the day at home during the latter stages of pregnancy, natural light exposure is crucial for the fetus. The current recommended COVID-19 lockdown might dramatically alter normal environmental lighting conditions of pregnant women, resulting in exposure to extremely low levels of natural daylight and high-intensity artificial light sources during both day and night. This article summarizes the potential effects on pregnant woman and their fetuses due to prolonged exposure to altered photoperiod and as consequence altered circadian system, known as chronodisruption, that may result from the COVID-19 lockdown.

The Role of Daylight for Humans: Gaps in Current Knowledge

Daylight stems solely from direct, scattered and reflected sunlight, and undergoes dynamic changes in irradiance and spectral power composition due to latitude, time of day, time of year and the nature of the physical environment (reflections, buildings and vegetation). Humans and their ancestors evolved under these natural day/night cycles over millions of years. Electric light, a relatively recent invention, interacts and competes with the natural light-dark cycle to impact human biology. What are the consequences of living in industrialised urban areas with much less daylight and more use of electric light, throughout the day (and at night), on general health and quality of life? In this workshop report, we have classified key gaps of knowledge in daylight research into three main groups: (I) uncertainty as to daylight quantity and quality needed for "optimal" physiological and psychological functioning, (II) lack of consensus on practical measurement and assessment methods and tools for monitoring real (day) light exposure across multiple time scales, and (III) insufficient integration and exchange of daylight knowledge bases from different disciplines. Crucial short and long-term objectives to fill these gaps are proposed.

Structure of Rhythms of Blood Pressure, Heart Rate, Excretion of Electrolytes, and Secretion of Melatonin in Normotensive and Spontaneously Hypertensive Rats Maintained under Conditions of Prolonged Daylight Duration

We studied the structure of rhythms of BP, HR (by telemetric monitoring), electrolyte excretion (by capillary electrophoresis), and products of epiphyseal melatonin (by the urinary concentration of 6-sulfatoxymelatonin measured by ELISA) in normotensive Wistar-Kyoto rats and spontaneously hypertensive SHR rats maintained at 16/8 h and 20/4 h light-dark regimes. In Wister-Kyoto rats exposed to prolonged daylight, we observed changes in the amplitude, rhythm power (% of rhythm), and range of oscillations of systolic BP; HR mezor decreased. In SHR rats, mezor of HR also decreased, but other parameters of rhythms remained unchanged. Changes in electrolyte excretion were opposite in normo- and hypertensive rats. Under conditions of 20/4 h light-dark regime, daytime melatonin production tended to increase in normotensive rats and significantly increased in SHR rats. At the same time, nighttime melatonin production did not change in both normotensive and hypertensive animals. As the secretion of melatonin has similar features in animals of both lines, we can say that the epiphyseal component of the "biological clock" is not the only component of the functional system that determines the response of the studied rhythms to an increase in the duration of light exposure.

Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates

Artificial light at night (ALAN) is increasing exponentially worldwide, accelerated by the transition to new efficient lighting technologies. However, ALAN and resulting light pollution can cause unintended physiological consequences. In vertebrates, production of melatonin—the “hormone of darkness” and a key player in circadian regulation—can be suppressed by ALAN. In this paper, we provide an overview of research on melatonin and ALAN in vertebrates. We discuss how ALAN disrupts natural photic environments, its effect on melatonin and circadian rhythms, and different photoreceptor systems across vertebrate taxa. We then present the results of a systematic review in which we identified studies on melatonin under typical light-polluted conditions in fishes, amphibians, reptiles, birds, and mammals, including humans. Melatonin is suppressed by extremely low light intensities in many vertebrates, ranging from 0.01–0.03 lx for fishes and rodents to 6 lx for sensitive humans. Even lower, wavelength-dependent intensities are implied by some studies and require rigorous testing in ecological contexts. In many studies, melatonin suppression occurs at the minimum light levels tested, and, in better-studied groups, melatonin suppression is reported to occur at lower light levels. We identify major research gaps and conclude that, for most groups, crucial information is lacking. No studies were identified for amphibians and reptiles and long-term impacts of low-level ALAN exposure are unknown. Given the high sensitivity of vertebrate melatonin production to ALAN and the paucity of available information, it is crucial to research impacts of ALAN further in order to inform effective mitigation strategies for human health and the wellbeing and fitness of vertebrates in natural ecosystems.

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

The widespread use of electric light and electronic devices has resulted in an excessive exposure to light during the late-evening and at night. This late light exposure acutely suppresses melatonin and sleepiness and delays the circadian clock. Here we investigate whether the acute effects of late-evening light exposure on our physiology and sleepiness are reduced when this light exposure is preceded by early evening bright light. Twelve healthy young females were included in a randomised crossover study. All participants underwent three evening (18:30-00:30) sessions during which melatonin, subjective sleepiness, body temperature and skin blood flow were measured under different light conditions: (A) dim light, (B) dim light with a late-evening (22:30-23:30) light exposure of 750 lx, 4000 K, and (C) the same late-evening light exposure, but now preceded by early-evening bright light exposure (18.30-21.00; 1200 lx, 4000 K). Late-evening light exposure reduced melatonin levels and subjective sleepiness and resulted in larger skin temperature gradients as compared to dim. Interestingly, these effects were reduced when the late-evening light was preceded by an early evening 2.5-hour bright light exposure. Thus daytime and early-evening exposure to bright light can mitigate some of the sleep-disruptive consequences of light exposure in the later evening.

Living in Biological Darkness: Objective Sleepiness and the Pupillary Light Responses Are Affected by Different Metameric Lighting Conditions during Daytime

Nighttime melatonin suppression is the most commonly used method to indirectly quantify acute nonvisual light effects. Since light is the principal zeitgeber in humans, there is a need to assess its strength during daytime as well. This is especially important since humans evolved under natural daylight but now often spend their time indoors under artificial light, resulting in a different quality and quantity of light. We tested whether the pupillary light response (PLR) could be used as a marker for nonvisual light effects during daytime. We also recorded the wake electroencephalogram to objectively determine changes in daytime sleepiness between different illuminance levels and/or spectral compositions of light. In total, 72 participants visited the laboratory 4 times for 3-h light exposures. All participants underwent a dim-light condition and either 3 metameric daytime light exposures with different spectral compositions of polychromatic white light (100 photopic lux, peak wavelengths at 435 nm or 480 nm, enriched with longer wavelengths of light) or 3 different illuminances (200, 600, and 1200 photopic lux) with 1 metameric lighting condition (peak wavelength at 435 nm or 480 nm; 24 participants each). The results show that the PLR was sensitive to both spectral differences between metameric lighting conditions and different illuminances in a dose-responsive manner, depending on melanopic irradiance. Objective sleepiness was significantly reduced, depending on melanopic irradiance, at low illuminance (100 lux) and showed fewer differences at higher illuminance. Since many people are exposed to such low illuminance for most of their day—living in biological darkness—our results imply that optimizing the light spectrum could be important to improve daytime alertness. Our results suggest the PLR as a noninvasive physiological marker for ambient light exposure effects during daytime. These findings may be applied to assess light-dependent zeitgeber strength and evaluate lighting improvements at workplaces, schools, hospitals, and homes.

Light Modulation of Human Clocks, Wake, and Sleep

Light, through its non-imaging forming effects, plays a dominant role on a myriad of physiological functions, including the human sleep–wake cycle. The non-image forming effects of light heavily rely on specific properties such as intensity, duration, timing, pattern, and wavelengths. Here, we address how specific properties of light influence sleep and wakefulness in humans through acute effects, e.g., on alertness, and/or effects on the circadian timing system. Of critical relevance, we discuss how different characteristics of light exposure across the 24-h day can lead to changes in sleep–wake timing, sleep propensity, sleep architecture, and sleep and wake electroencephalogram (EEG) power spectra. Ultimately, knowledge on how light affects sleep and wakefulness can improve light settings at home and at the workplace to improve health and well-being and optimize treatments of chronobiological disorders.

Awakening effects of blue-enriched morning light exposure on university students' physiological and subjective responses

We investigated physiological and subjective responses to morning light exposure of commercially available LED lighting with different correlated colour temperatures to predict how LED-based smart lighting employed in future learning environments will impact students. The classical markers of the circadian system (melatonin and cortisol), as well as the subjective perception of sleepiness, mood, and visual comfort, were compared. Fifteen university students underwent an hour of morning light exposure to both warm (3,500 K) and blue-enriched (6,500 K) white lights at recommended illuminance levels for classrooms and lecture halls (500 lux). The decline of melatonin levels was significantly greater after the exposure to blue-enriched white light. Exposure to blue-enriched white light significantly improved subjective perception of alertness, mood, and visual comfort. With regard to cortisol, we did not find a significant difference in the cortisol decrement between the two light conditions. Our findings suggest that the sensitivity of physiological and subjective responses to white LED light is blue-shifted. These findings, extending the already known effects of short-wavelength light on human physiology, reveal interesting practical implications. Blue-enriched LED light seems to be a simple yet effective potential countermeasure for morning drowsiness and dozing off in class, particularly in schools with insufficient daylight.

Research progress about the effect and prevention of blue light on eyes

In recent years, people have become increasingly attentive to light pollution influences on their eyes. In the visible spectrum, short-wave blue light with wavelength between 415 nm and 455 nm is closely related to eye light damage. This high energy blue light passes through the cornea and lens to the retina causing diseases such as dry eye, cataract, age-related macular degeneration, even stimulating the brain, inhibiting melatonin secretion, and enhancing adrenocortical hormone production, which will destroy the hormonal balance and directly affect sleep quality. Therefore, the effect of Blu-rays on ocular is becoming an important concern for the future. We describe blue light's effects on eye tissues, summarize the research on eye injury and its physical prevention and medical treatment.

Morning boost on individuals' psychophysiological wellbeing indicators with supportive, dynamic lighting in windowless open-plan workplace in Malaysia

Workplace architectural lighting conditions that are biologically dim during the day are causing healthy individuals to experience light-induced health and performance-related problems. Dynamic lighting was reported beneficial in supporting individuals’ psychological behavior and physiological responses during work period in Europe. It has yet to be investigated in workplaces with minimal/no natural daylight contribution in tropical Malaysia. Hence, an exploratory experimental study was initiated in an experimental windowless open-plan workplace in Universiti Putra Malaysia, Serdang. The aim was to identify dynamic lighting configurations that were more supportive of a morning boosting effect than the control constant lighting, to support dayshift individuals’ psychophysiological wellbeing indicators during the peak morning work period. The immediate impact of a 2-hour morning exposure to overhead white LED (6500 K) with different horizontal illuminance levels and oscillations (lighting patterns) were investigated on physiological indicator limited to urinary 6-sulfatoxymelatonin, and psychological indicators for alertness, mood, visual comfort, cognitive and visual task performance. Not all of the investigated dynamic lighting configurations were supportive of a morning boost. Only configurations 500_{increased to}750 and 500_{increased to}1000 lx therapeutically supported most of the indicators. Both these configurations suppressed urinary 6-sulfatoxymelatonin, and improved alertness, cognitive performance, positive affect, and visual comfort better than ‘visit 1: 500_constant500’ lx (control). The increasing oscillation was observed more beneficial for the morning boost in tropical Malaysia, which is in reverse to that specified in the human rhythmic dynamic lighting protocol developed by researchers from the Netherlands for application during winter. The findings from this study present the feasibility of dynamic architectural lighting acting as an environmental therapeutic solution in supporting the individuals’ psychophysiological wellbeing indicators in windowless open-plan workplace in tropical Malaysia. Further investigations on the two prospective configurations are recommended to determine the better supportive one for the morning boosting effect in Malaysia.

Impact of long-term daylight deprivation on retinal light sensitivity, circadian rhythms and sleep during the Antarctic winter

Long-term daylight deprivation such as during the Antarctic winter has been shown to lead to delayed sleep timing and sleep fragmentation. We aimed at testing whether retinal sensitivity, sleep and circadian rest-activity will change during long-term daylight deprivation on two Antarctic bases (Concordia and Halley VI) in a total of 25 healthy crew members (mean age: 34 ± 11y; 7f). The pupil responses to different light stimuli were used to assess retinal sensitivity changes. Rest-activity cycles were continuously monitored by activity watches. Overall, our data showed increased pupil responses under scotopic (mainly rod-dependent), photopic (mainly L-/M-cone dependent) as well as bright-blue light (mainly melanopsin-dependent) conditions during the time without direct sunlight. Circadian rhythm analysis revealed a significant decay of intra-daily stability, indicating more fragmented rest-activity rhythms during the dark period. Sleep and wake times (as assessed from rest-activity recordings) were significantly delayed after the first month without sunlight (p < 0.05). Our results suggest that during long-term daylight deprivation, retinal sensitivity to blue light increases, whereas circadian rhythm stability decreases and sleep-wake timing is delayed.

Effects of blue- and red-enriched light on attention and sleep in typically developing adolescents

Differential effects of blue- and red-enriched light on attention and sleep have been primarily described in adults. In our cross-over study in typically developing adolescents (11-17 years old), we found attention enhancing effects of blue- compared to red-enriched light in the morning (high intensity of ca. 1000 lx, short duration: <1 h) in two of three attention tasks: e.g. better performance in math tests and reduced reaction time variability in a computerized attention test. In our pilot study, actigraphy measures of sleep indicated slight benefits for red- compared to blue-enriched light in the evening: tendencies toward a lower number of phases with movement activity after sleep onset in the complete sample and shorter sleep onset latency in a subgroup with later evening exposure times. These findings point to the relevance of light concepts regarding attention and sleep in typically developing adolescents. Such concepts should be developed and tested further in attention demanding contexts (at school) and for therapeutic purposes in adolescents with impaired attention or impaired circadian rhythms.

Light, Alertness, and Alerting Effects of White Light: A Literature Overview

Light is known to elicit non-image-forming responses, such as effects on alertness. This has been reported especially during light exposure at night. Nighttime results might not be translatable to the day. This article aims to provide an overview of (1) neural mechanisms regulating alertness, (2) ways of measuring and quantifying alertness, and (3) the current literature specifically regarding effects of different intensities of white light on various measures and correlates of alertness during the daytime. In general, the present literature provides inconclusive results on alerting effects of the intensity of white light during daytime, particularly for objective measures and correlates of alertness. However, the various research paradigms employed in earlier studies differed substantially, and most studies tested only a limited set of lighting conditions. Therefore, the alerting potential of exposure to more intense white light should be investigated in a systematic, dose-dependent manner with multiple correlates of alertness and within one experimental paradigm over the course of day.

Spectral Tuning of White Light Allows for Strong Reduction in Melatonin Suppression without Changing Illumination Level or Color Temperature

Studies with monochromatic light stimuli have shown that the action spectrum for melatonin suppression exhibits its highest sensitivity at short wavelengths, around 460 to 480 nm. Other studies have demonstrated that filtering out the short wavelengths from white light reduces melatonin suppression. However, this filtering of short wavelengths was generally confounded with reduced light intensity and/or changes in color temperature. Moreover, it changed the appearance from white light to yellow/orange, rendering it unusable for many practical applications. Here, we show that selectively tuning a polychromatic white light spectrum, compensating for the reduction in spectral power between 450 and 500 nm by enhancing power at even shorter wavelengths, can produce greatly different effects on melatonin production, without changes in illuminance or color temperature. On different evenings, 15 participants were exposed to 3 h of white light with either low or high power between 450 and 500 nm, and the effects on salivary melatonin levels and alertness were compared with those during a dim light baseline. Exposure to the spectrum with low power between 450 and 500 nm, but high power at even shorter wavelengths, did not suppress melatonin compared with dim light, despite a large difference in illuminance (175 vs. <5 lux). In contrast, exposure to the spectrum with high power between 450 and 500 nm (also 175 lux) resulted in almost 50% melatonin suppression. For alertness, no significant differences between the 3 conditions were observed. These results open up new opportunities for lighting applications that allow for the use of electrical lighting without disturbance of melatonin production.