Changing color and intensity of LED lighting across the day impacts on circadian melatonin rhythms and sleep in healthy men

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.

Ultradian sleep cycles: Frequency, duration, and associations with individual and environmental factors-A retrospective study

OBJECTIVE

Sleep varies between individuals in response to sleep-wake history and various environmental factors, including light and noise. Here we report on the intranight variation of the ultradian nonrapid eye movement-rapid eye movement (NREM-REM) sleep cycle in 369 participants who have contributed to different laboratory studies from 1994 to 2020 at the Centre for Chronobiology, Basel, Switzerland.

RESULTS

We observed a large interindividual variability in sleep cycle duration, including NREM and REM sleep episodes in healthy participants who were given an 8-hour sleep opportunity at habitual bedtime in controlled laboratory settings. The median sleep cycle duration was 96 minutes out of 6064 polysomnographically-recorded cycles. The number and duration of cycles were not normally distributed, and the distribution became narrower for NREM sleep and wider for REM sleep later in the night. The first cycle was consistently shorter than subsequent cycles, and moderate presleep light or nocturnal noise exposure had no significant effects on ultradian sleep cycle duration. Age and sex significantly affected NREM and REM sleep duration, with older individuals having longer NREM and shorter REM sleep particularly in the end of the night, and females having longer NREM sleep episodes. High sleep pressure (ie, sleep deprivation) and low sleep pressure (ie, multiple naps) altered ultradian sleep cycles, with high sleep pressure leading to longer NREM sleep in the first cycle, and low sleep pressure leading to longer REM sleep episodes. Positive correlations were observed between N2 and NREM duration, and between N1 and REM duration. Weak intrasleep REM sleep homeostasis was also evident in our data set.

CONCLUSIONS

We conclude that ultradian sleep cycles are endogenous biological rhythms modulated by age, sex, and sleep homeostasis, but not directly responsive to (moderate levels of) environmental cues in healthy good sleepers.

Investigating the effects of a blue-blocking software on the daily rhythm of sleep, melatonin, cortisol, positive and negative emotions

Since the use of light and electronic devices is inevitable, the use of blue light filters (in various light sources, electronic devices or optical devices including intraocular lenses) has been shown to improve sleep quality, especially in later hours of the day and during night time. In this study, we examine the effect of the blue light on sleep and wakefulness rhythms and positive and negative emotions. This randomized clinical trial was conducted with 80 AJA University of Medical Sciences employees who use computers at least 2 h a day. All subjects were employees of the discharge unit of Imam Reza Hospital, which is located next to AJA University. The subjects were divided into two groups of 40 people, blue light filter software intervention and sham treatment. Pittsburgh Sleep Quality Index (PSQI), Positive and Negative Affect Schedule (PANAS), Visual Function Questionnaire (VFQ), Epworth Sleepiness Scale (ESS) and salivary melatonin and cortisol levels were assessed for both groups before and 3 months after the intervention. Data analysis was performed using IBM SPSS statistics for windows, version 21.0 (Armonk, NY: IBM Corporation). P value ≤ 0.05 was considered as statistically significant. The results showed that the Pittsburgh sleep scale after the intervention was significantly lower in the intervention group than in the control group. After the intervention, the VFQ was significantly lower in the intervention group than in the control group (P = 0.018). There was no significant difference in the Epworth Sleepiness Scale (ESS) between the two study groups after the intervention (P = 0.370). There was no significant difference in Positive and Negative Affect Schedule (PANAS) in the two study groups after the intervention (P = 0.140). After the intervention, cortisol levels were significantly higher in the intervention group than in the control group (P = 0.006). Also, the amount of cortisol increased significantly in the intervention group (P = 0.028). The amount of melatonin decreased significantly in the intervention group (P = 0.034). The sleep quality score after the intervention was significantly lower in the intervention group than in the control group. This indicates better sleep quality in the intervention group. The results also show that the level of visual fatigue in the intervention group decreased significantly. However, no significant change was detected regarding positive and negative emotions. After the intervention, cortisol levels were significantly higher in the intervention group than the control group. In addition, cortisol levels increased significantly and melatonin levels decreased significantly in the intervention group during the course of study.

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.

Light as a Modulator of Non-Image-Forming Brain Functions—Positive and Negative Impacts of Increasing Light Availability

Light use is rising steeply, mainly because of the advent of light-emitting diode (LED) devices. LEDs are frequently blue-enriched light sources and may have different impacts on the non-image forming (NIF) system, which is maximally sensitive to blue-wavelength light. Most importantly, the timing of LED device use is widespread, leading to novel light exposure patterns on the NIF system. The goal of this narrative review is to discuss the multiple aspects that we think should be accounted for when attempting to predict how this situation will affect the NIF impact of light on brain functions. We first cover both the image-forming and NIF pathways of the brain. We then detail our current understanding of the impact of light on human cognition, sleep, alertness, and mood. Finally, we discuss questions concerning the adoption of LED lighting and screens, which offer new opportunities to improve well-being, but also raise concerns about increasing light exposure, which may be detrimental to health, particularly in the evening.

Physiological consequences of space flight, including abnormal bone metabolism, space radiation injury, and circadian clock dysregulation: Implications of melatonin use and regulation as a countermeasure

Exposure to the space environment induces a number of pathophysiological outcomes in astronauts, including bone demineralization, sleep disorders, circadian clock dysregulation, cardiovascular and metabolic dysfunction, and reduced immune system function. A recent report describing experiments aboard the Space Shuttle mission, STS-132, showed that the level of melatonin, a hormone that provides the biochemical signal of darkness, was decreased during microgravity in an in vitro culture model. Additionally, abnormal lighting conditions in outer space, such as low light intensity in orbital spacecraft and the altered 24-h light-dark cycles, may result in the dysregulation of melatonin rhythms and the misalignment of the circadian clock from sleep and work schedules in astronauts. Studies on Earth have demonstrated that melatonin regulates various physiological functions including bone metabolism. These data suggest that the abnormal regulation of melatonin in outer space may contribute to pathophysiological conditions of astronauts. In addition, experiments with high-linear energy transfer radiation, a ground-based model of space radiation, showed that melatonin may serve as a protectant against space radiation. Gene expression profiling using an in vitro culture model exposed to space flight during the STS-132 mission, showed that space radiation alters the expression of DNA repair and oxidative stress response genes, indicating that melatonin counteracts the expression of these genes responsive to space radiation to promote cell survival. These findings implicate the use of exogenous melatonin and the regulation of endogenous melatonin as countermeasures for the physiological consequences of space flight.

Impact of Evening Light Exposures with Different Solid Angles on Circadian Melatonin Rhythms, Alertness, and Visual Comfort in an Automotive Setting

Future automotive interior lighting might have the potential to go beyond decorative purposes by influencing alertness, circadian physiology, and sleep. As the available space in the interior of an automobile for lighting applications is limited, understanding the impact of various luminous surface sizes on non-image-forming effects is fundamental in this field. In a laboratory study using a within-subject design, 18 participants were exposed to two bright light conditions with different solid angles and one dim light condition in a balanced, randomized order during the course of the evening. Our results demonstrate that both light conditions significantly increased subjective alertness and reduced salivary melatonin concentration but not cognitive performance compared to dim light. The solid angle of light exposure at constant corneal illuminance only affected visual comfort. While subjective alertness can be increased and melatonin can be attenuated with rather small luminaires, larger solid angles should be considered if visual comfort is a priority.

Electric lighting, adolescent sleep and circadian outcomes, and recommendations for improving light health

Light is a potent circadian entraining agent. For many people, daily light exposure is fundamentally dysregulated with reduced light during the day and increased light into the late evening. This lighting schedule promotes chronic disruption to circadian physiology resulting in a myriad of impairments. Developmental changes in sleep-wake physiology suggest that such light exposure patterns may be particularly disruptive for adolescents and further compounded by lifestyle factors such as early school start times. This narrative review describes evidence that reduced light exposure during the school day delays the circadian clock, and longer exposure durations to light-emitting electronic devices in the evening suppress melatonin. While home lighting in the evening can suppress melatonin secretion and delay circadian phase, the patterning of light exposure across the day and evening can have moderating effects. Photic countermeasures may be flexibly and scalably implemented to support sleep-wake health; including manipulations of light intensity, spectra, duration and delivery modality across multiple contexts. An integrative approach addressing physiology, attitudes, and behaviors will support optimization of light-driven sleep-wake outcomes in adolescents.

Impact of Upgraded Lighting on Falls in Care Home Residents

OBJECTIVES

Falls in care home residents have major health and economic implications. Given the impact of lighting on visual acuity, alertness, and sleep and their potential influence on falls, we aimed to assess the impact of upgraded lighting on the rate of falls in long-term care home residents.

DESIGN

An observational study of 2 pairs of care homes (4 sites total). One site from each pair was selected for solid-state lighting upgrade, and the other site served as a control.

SETTING AND PARTICIPANTS

Two pairs of care homes with 758 residents (126,479 resident-days; mean age (±SD) 81.0 ± 11.7 years; 57% female; 31% with dementia).

METHODS

One "experimental" site from each pair had solid-state lighting installed throughout the facility that changed in intensity and spectrum to increase short-wavelength (blue light) exposure during the day (6 am-6 pm) and decrease it overnight (6 pm-6 am). The control sites retained standard lighting with no change in intensity or spectrum throughout the day. The number of falls aggregated from medical records were assessed over an approximately 24-month interval. The primary comparison between the sites was the rate of falls per 1000 resident-days.

RESULTS

Before the lighting upgrade, the rate of falls was similar between experimental and control sites (6.94 vs 6.62 falls per 1000 resident-days, respectively; rate ratio [RR] 1.05; 95% CI 0.70-1.58; P = .82). Following the upgrade, falls were reduced by 43% at experimental sites compared with control sites (4.82 vs 8.44 falls per 1000 resident-days, respectively; RR 0.57; 95% CI 0.39-0.84; P = .004).

CONCLUSIONS AND IMPLICATIONS

Upgrading ambient lighting to incorporate higher intensity blue-enriched white light during the daytime and lower intensity overnight represents an effective, passive, low-cost, low-burden addition to current preventive strategies to reduce fall risk in long-term care settings.

Gut Microbiota Dysbiosis Induced by Decreasing Endogenous Melatonin Mediates the Pathogenesis of Alzheimer's Disease and Obesity

Lifestyle choices, external environment, aging, and other factors influence the synthesis of melatonin. Although the physiological functions of melatonin have been widely studied in relation to specific organs, the systemic effects of endogenous melatonin reduction has not been reported. This study evaluates the systemic changes and possible pathogenic risks in an endogenous melatonin reduction (EMR) mouse model deficient in the rate limiting enzyme in melatonin production, arylalkylamine N-acetyltransferase (Aanat) gene. Using this model, we identified a new relationship between melatonin, Alzheimer’s disease (AD), and gut microbiota. Systematic changes were evaluated using multi-omics analysis. Fecal microbiota transplantation (FMT) was performed to examine the role of gut microbiota in the pathogenic risks of EMR. EMR mice exhibited a pan-metabolic disorder, with significant transcriptome changes in 11 organs, serum metabolome alterations as well as microbiota dysbiosis. Microbiota dysbiosis was accompanied by increased gut permeability along with gut and systemic inflammation. Correlation analysis revealed that systemic inflammation may be related to the increase of Ruminiclostridium_5 relative abundance. 8-month-old EMR mice had AD-like phenotypes, including Iba-1 activation, A β protein deposition and decreased spatial memory ability. Moreover, EMR mice showed decreased anti stress ability, under high-fat diet, EMR mice had greater body weight and more obvious hepatic steatosis compared with WT group. FMT improved gut permeability, systemic inflammation, and AD-related phenotypes, while reducing obesity in EMR mice. Our findings suggest EMR causes systemic changes mediated by gut microbiota dysbiosis, which may be a pathogenic factor for AD and obesity, we further proved the gut microbiota is a potential target for the prevention and treatment of AD and obesity.

Impact of daytime spectral tuning on cognitive function

Light at night can improve alertness and cognition. Exposure to daytime light, however, has yielded less conclusive results. In addition to direct effects, daytime light may also mitigate the impact of nocturnal light exposure on alertness. To examine the impact of daytime lighting on daytime cognitive performance, and evening alertness, we studied nine healthy individuals using a within subject crossover design. On four visits, participants were exposed to one of four lighting conditions for 10 h (dim fluorescent, room fluorescent, broad-spectrum LED, standard white LED; the latter three conditions were matched for 100 lx) followed by an exposure to bright evening light. Cognitive performance, subjective and objective measures of alertness were regularly obtained. While daytime alertness was not impacted by light exposure, the broad-spectrum LED light improved several aspects of daytime cognition. The impact of evening light on alertness was not mitigated by the pre-exposure to different daytime lighting conditions. Results suggest that daytime exposure to white light with high melanopic efficacy has the potential to improve daytime cognitive function and that such improvements are likely to be direct rather than a consequence of light-induced changes in alertness.

Spectrophotometric properties of commercially available blue blockers across multiple lighting conditions

Lenses that filter short-wavelength ("blue") light are commercially marketed to improve sleep and circadian health. Despite their widespread use, minimal data are available regarding their comparative efficacy in curtailing blue light exposure while maintaining visibility. Fifty commercial lenses were evaluated using five light sources: a blue LED array, a computer tablet display, an incandescent lamp, a fluorescent overhead luminaire, and sunlight. Absolute irradiance was measured at baseline and for each lens across the visual spectrum (380-780 nm), which allowed calculation of percent transmission. Transmission specificity was also calculated to determine whether light transmission was predominantly circadian-proficient (455-560 nm) or non-proficient (380-454 nm and 561-780 nm). Lenses were grouped by tint and metrics were compared between groups. Red-tinted lenses exhibited the lowest transmission of circadian-proficient light, while reflective blue lenses had the highest transmission. Orange-tinted lenses transmitted similar circadian-proficient light as red-tinted lenses but transmitted more non-circadian-proficient light, resulting in higher transmission specificity. Orange-tinted lenses had the highest transmission specificity while limiting biologically active light exposure in ordinary lighting conditions. Glasses incorporating these lenses currently have the greatest potential to support circadian sleep-wake rhythms.

Current Insights into Optimal Lighting for Promoting Sleep and Circadian Health: Brighter Days and the Importance of Sunlight in the Built Environment

This perspective considers the possibility that daytime's intrusion into night made possible by electric lighting may not be as pernicious to sleep and circadian health as the encroachment of nighttime into day wrought by 20th century architectural practices that have left many people estranged from sunlight.

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.

Optimising metameric spectra for integrative lighting to modulate the circadian system without affecting visual appearance

Smart integrative lighting systems aim to support human health and wellbeing by capitalising on the light-induced effects on circadian rhythms, sleep, and cognitive functions, while optimising the light's visual aspects like colour fidelity, visual comfort, visual preference, and visibility. Metameric spectral tuning could be an instrument to solve potential conflicts between the visual preferences of users with respect to illuminance and chromaticity and the circadian consequences of the light exposure, as metamers can selectively modulate melanopsin-based photoreception without affecting visual properties such as chromaticity or illuminance. This work uses a 6-, 8- and 11-channel LED luminaire with fixed illuminance of 250 lx to systematically investigate the metameric tuning range in melanopic equivalent daylight illuminance (EDI) and melanopic daylight efficacy ratio (melanopic DER) for 561 chromaticity coordinates as optimisation targets (2700 K to 7443 K ± Duv 0 to 0.048), while applying colour fidelity index Rf criteria from the TM-30-20 Annex E recommendations (i.e. Rf [Formula: see text] 85, Rf,h1 [Formula: see text] 85). Our results reveal that the melanopic tuning range increases with rising CCT to a maximum tuning range in melanopic DER of 0.24 (CCT: 6702 K, Duv: 0.003), 0.29 (CCT: 7443 K, Duv: 0) and 0.30 (CCT: 6702, Duv: 0.006), depending on the luminaire's channel number of 6, 8 or 11, respectively. This allows to vary the melanopic EDI from 212.5-227.5 lx up to 275-300 lx without changes in the photopic illuminance (250 lx) or chromaticity ([Formula: see text] [Formula: see text] 0.0014). The highest metameric melanopic Michelson contrast for the 6-, 8- and 11-channel luminaire is 0.16, 0.18 and 0.18, which is accomplished at a CCT of 3017 K (Duv: - 0.018), 3456 K (Duv: 0.009) and 3456 K (Duv: 0.009), respectively. By optimising ~ 490,000 multi-channel LED spectra, we identified chromaticity regions in the CIExy colour space that are of particular interest to control the melanopic efficacy with metameric spectral tuning.

Should We Re-think Regulations and Standards for Lighting at Workplaces? A Practice Review on Existing Lighting Recommendations

Nowadays lighting projects often include temporal variations of the light, both spectrally and in terms of intensity to consider non-visual effects of light on people. However, as of today there are no specific regulations. Compliance with common lighting standards that address visual aspects of light, often means that only little non-visually effective light reaches the eye. In this practice review we confront existing regulations and standards on visual lighting aspects with new recommendations on non-visual aspects and highlight conflicts among them. We conclude with lighting recommendations that address both aspects.

Tackling Heterogeneous Color Registration: Binning Color Sensors

Intelligent systems for interior lighting strive to balance economical, ecological, and health-related needs. For this purpose, they rely on sensors to assess and respond to the current room conditions. With an augmented demand for more dedicated control, the number of sensors used in parallel increases considerably. In this context, the present work focuses on optical sensors with three spectral channels used to capture color-related information of the illumination conditions such as their chromaticities and correlated color temperatures. One major drawback of these devices, in particular with regard to intelligent lighting control, is that even same-type color sensors show production related differences in their color registration. Standard methods for color correction are either impractical for large-scale production or they result in large colorimetric errors. Therefore, this article shows the feasibility of a novel sensor binning approach using the sensor responses to a single white light source for cluster assignment. A cluster specific color correction is shown to significantly reduce the registered color differences for a selection of test stimuli to values in the range of 0.003–0.008 Δu′v′, which enables the wide use of such sensors in practice and, at the same time, requires minimal additional effort in sensor commissioning.

Individual differences in light sensitivity affect sleep and circadian rhythms

Artificial lighting is omnipresent in contemporary society with disruptive consequences for human sleep and circadian rhythms because of overexposure to light, particularly in the evening/night hours. Recent evidence shows large individual variations in circadian photosensitivity, such as melatonin suppression, due to artificial light exposure. Despite the emerging body of research indicating that the effects of light on sleep and circadian rhythms vary dramatically across individuals, recommendations for appropriate light exposure in real-life settings rarely consider such individual effects. This review addresses recently identified links among individual traits, for example, age, sex, chronotype, genetic haplotypes, and the effects of evening/night light on sleep and circadian hallmarks, based on human laboratory and field studies. Target biological mechanisms for individual differences in light sensitivity include differences occurring within the retina and downstream, such as the central circadian clock. This review also highlights that there are wide gaps of uncertainty, despite the growing awareness that individual differences shape the effects of evening/night light on sleep and circadian physiology. These include (1) why do certain individual traits differentially affect the influence of light on sleep and circadian rhythms; (2) what is the translational value of individual differences in light sensitivity in populations typically exposed to light at night, such as night shift workers; and (3) what is the magnitude of individual differences in light sensitivity in population-based studies? Collectively, the current findings provide strong support for considering individual differences when defining optimal lighting specifications, thus allowing for personalized lighting solutions that promote quality of life and health.

Melanopic Limits of Metamer Spectral Optimisation in Multi-Channel Smart Lighting Systems

Modern indoor lighting faces the challenge of finding an appropriate balance between energy consumption, legal requirements, visual performance, and the circadian effectiveness of a spectrum. Multi-channel LED luminaires have the option of keeping image-forming metrics steady while varying the melanopic radiance through metamer spectra for non-visual purposes. Here, we propose the theoretical concept of an automated smart lighting system that is designed to satisfy the user’s visual preference through neural networks while triggering the non-visual pathway via metamers. To quantify the melanopic limits of metamers at a steady chromaticity point, we have used 561 chromaticity coordinates along the Planckian locus (2700 K to 7443 K, ±Duv 0 to 0.048) as optimisation targets and generated the spectra by using a 6-channel, 8-channel, and 11-channel LED combination at three different luminance levels. We have found that in a best-case scenario, the melanopic radiance can be varied up to 65% while keeping the chromaticity coordinates constant (Δu′v′≤7.05×10−5) by using metamer spectra. The highest melanopic metamer contrast can be reached near the Planckian locus between 3292 and 4717 K within a Duv range of −0.009 to 0.006. Additionally, we publish over 1.2 million optimised spectra generated by multichannel LED luminaires as an open-source dataset along with this work.