光的非视觉效应在照明产品中的设计研究——以助眠情境为例

光的非视觉生物效应与人体健康密切相关，随着LED在室内照明中的广泛应用，LED照明与人体生理健康的关系也日益重要。心电图(ECG，electrocardiograph)是生理参数的主要表征之一。针对LED照明，以3种色温(3 000、5 000、6 500 K)、5种照度(300、500、750、1 000、1 500 lx)为主要变量，研究不同光照时长(10、20 min)下，老年人心电指标对光响应的情况。结果显示，照度、色温等光照参数的主效应对老年人的ECG无显著影响，但照度和色温的交互作用对老年人的ECG影响显著。其中，3 000 K和1 000 1x的交互作用对P波时间和T波时间影响最大；6 500 K和1 500 1x的交互作用影响最小；5 000 K和750 1x的交互作用对PR间期影响最大，6 500 K和500 1x的交互作用影响最小。但较短光照时长下，老年人的ECG变化不明显。因此，有必要探讨更长时间(1 h及以上)光照下，老年人的心电生理响应情况，从而为老年人健康照明参数的确定提供依据。

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, e.g. 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 scenarios rarely consider such individual effects. This review addresses recently identified links between individual traits, e.g. 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 i. why do certain individual traits differentially affect the influence of light on sleep and circadian rhythms; ii. What is the translational value of individual differences in light sensitivity in populations exposed to light at night, such as night shift workers; and iii. What is the magnitude of individual differences in light sensitivity in large 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.

Background — A growing body of research demonstrates that a substantial daily range of light exposure, characterized by ample daylight followed by darkness during sleep, is essential for human well-being. This encompasses crucial aspects like sleep quality, mood regulation, and cardiovascular and metabolic health. Objective — This study characterizes Circadian Light Hygiene (CLH) as an essential factor in maintaining health, well-being, and longevity in modern society. CLH involves adjusting the 24-hour light exposure dynamic range to support the natural sleep-wake cycle and circadian rhythms. Three major challenges to CLH negatively impacting human health are: 1) light pollution (light at night, or LAN), characterized by excessive evening and nighttime artificial light; 2) insufficient natural daylight; and 3) irregular light exposure patterns. These interacting challenges necessitate a systematic approach to measurement and analysis. Material and Methods — A systematic review of peer-reviewed literature published through October 30, 2024, examined the methodologies and health effects of circadian and seasonal aspects of light exposure. Conclusion — This review elucidates fundamental principles of circadian light hygiene, synthesizing existing literature and our research to assess the benefits of adequate daylight, the risks of light at night, and adverse outcomes stemming from diminished light exposure range, mistimed light exposure, and irregular patterns. Novel indices for quantifying and optimizing circadian light hygiene are introduced.

… circadian rhythm desynchrony and sleep disorders. To explore the effects of different lighting patterns on circadian rhythm and sleep… weeks with one lighting pattern per week. The static …

Summary 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.

Abstract 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.

We examined whether dynamically changing light across a scheduled 16‐h waking day influences sleepiness, cognitive performance, visual comfort, melatonin secretion, and sleep under controlled laboratory conditions in healthy men. Fourteen participants underwent a 49‐h laboratory protocol in a repeated‐measures study design. They spent the first 5 hours in the evening under standard lighting, followed by an 8‐h nocturnal sleep episode at habitual bedtimes. Thereafter, volunteers either woke up to static light or to a dynamic light that changed spectrum and intensity across the scheduled 16‐h waking day. Following an 8‐h nocturnal sleep episode, the volunteers spent another 11 hours either under static or dynamic light. Static light attenuated the evening rise in melatonin levels more compared to dynamic light as indexed by a significant reduction in the melatonin AUC prior to bedtime during static light only. Participants felt less vigilant in the evening during dynamic light. After dynamic light, sleep latency was significantly shorter in both the baseline and treatment night while sleep structure, sleep quality, cognitive performance, and visual comfort did not significantly differ. The study shows that dynamic changes in spectrum and intensity of light promote melatonin secretion and sleep initiation in healthy men.

Light is the primary circadian time cue, but there are large interindividual differences in how sensitive the circadian system is to light. Currently, it is not well understood how individual differences in light sensitivity interact with real-world light environments to determine sleep and circadian timing. We used a validated computational model to simulate sleep and circadian timing (predicted dim light melatonin onset) under realistic assumptions about light and work schedules. Simulations were repeated varying light sensitivity (translated to equivalent ED50 values for interpretability), as well as evening, morning, and daytime illuminances. Brighter evening light led to later predicted circadian and sleep timing, with this effect being amplified by high light sensitivity. Reducing evening light was particularly beneficial for those with high light sensitivity or a long circadian period. Brighter morning light was beneficial for individuals with a long circadian period, or those with both high light sensitivity and high evening light. However, bright morning light could be maladaptive in individuals with a short circadian period or those with low light sensitivity and low evening light. Brighter daytime light attenuated the delaying effects of evening artificial light across conditions, indicating that increasing daytime light was the most universally beneficial lighting intervention. Our results demonstrate how circadian light sensitivity can be used to tailor individual-level solutions that support optimal sleep and circadian timing.

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

Circadian adaptation to shifted sleep/wake schedules may be facilitated by optimizing the timing, intensity and spectral characteristics of light exposure, which is the principal time cue for mammalian circadian pacemaker, and possibly by strategically timing nonphotic time cues such as exercise. Therefore, circadian phase resetting by light and exercise was assessed in 44 healthy participants (22 females, mean age [±SD] 36.2 ± 9.2 years), who completed 8‐day inpatient experiments simulating night shiftwork, which included either an 8 h advance or 8 h delay in sleep/wake schedules. In the advance protocol (n = 18), schedules were shifted either gradually (1.6 h/day across 5 days) or abruptly (slam shift, 8 h in 1 day and maintained across 5 days). Both advance protocols included a dynamic lighting schedule (DLS) with 6.5 h exposure of blue‐enriched white light (704 melanopic equivalent daylight illuminance [melEDI] lux) during the day and dimmer blue‐depleted light (26 melEDI lux) for 2 h immediately before sleep on the shifted schedule. In the delay protocol (n = 26), schedules were only abruptly delayed but included four different lighting conditions: (1) 8 h continuous room‐light control; (2) 8 h continuous blue‐enriched light; (3) intermittent (7 × 15 min pulses/8 h) blue‐enriched light; (4) 8 h continuous blue‐enriched light plus moderate intensity exercise. In the room‐light control, participants received dimmer white light for 30 min before bedtime, whereas in the other three delay protocols participants received dimmer blue‐depleted light for 30 min before bedtime. Both the slam and gradual advance protocols induced similar shifts in circadian phase (3.28 h ± 0.37 vs. 2.88 h ± 0.31, respectively, p = .43) estimated by the change in the timing of timing of dim light melatonin onset. In the delay protocol, the continuous 8 h blue‐enriched exposure induced significantly larger shifts than the room light control (−6.59 h ± 0.43 vs. −4.74 h ± 0.62, respectively, p = .02). The intermittent exposure induced ~60% of the shift (−3.90 h ± 0.62) compared with 8 h blue‐enriched continuous light with only 25% of the exposure duration. The addition of exercise to the 8 h continuous blue‐enriched light did not result in significantly larger phase shifts (−6.59 h ± 0.43 vs. −6.41 h ± 0.69, p = .80). Collectively, our results demonstrate that, when attempting to adapt to an 8 h overnight work shift, delay shifts are more successful, particularly when accompanied by a DLS with high‐melanopic irradiance light stimulus during wake.

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.

Introduction: Sleep disturbance is a hallmark of Alzheimer’s disease and related dementias, and caregiver stress caused by patients’ nighttime wandering, injuries, and agitation are frequently at the root of decisions to move them to assisted living facilities, where typically dim institutional lighting can further exacerbate their sleep problems. This study explored the effects of a circadian-effective lighting intervention on actigraphic sleep measures and subjective assessments of sleep disturbance, depression, and sleep-disturbed behaviors. Methods: Fourteen older adult (≥60 years) participants (11 females, mean age = 84.1 [SD 8.9]), all diagnosed with moderate to severe dementia and sleep disturbance, were recruited from 3 assisted living and memory care facilities. Following a crossover, placebo-controlled design, 3 different lighting modes were used to deliver high levels of circadian stimulus to the participants’ eyes for two 8-week intervention periods in a counter balanced order with a 4-week washout between the study’s 2 conditions (dim light control vs. active intervention). Actigraphy and questionnaire data were collected over 7-day assessment periods that preceded (baseline weeks 1 and 9) and concluded (post-intervention week 9 and 22) the intervention periods. Actigraphic outcomes included sleep duration, sleep time, sleep efficiency, sleep start time, and sleep end time. Subjective assessments included the Cornell Scale for Depression in Dementia (CSDD), Pittsburgh Sleep Quality Index (PSQI), and Sleep Disorders Inventory (SDI) instruments. Results: Under the active condition, sleep duration significantly (p = 0.018) increased and sleep start time significantly (p = 0.012) advanced after the intervention compared to baseline. Also under the active condition, PSQI (p = 0.012), CSDD (p = 0.007), Sleep Disorders Inventory frequency (p = 0.015), and SDI severity (p = 0.015) scores were significantly lower after the intervention compared to baseline. Discussion: This study demonstrates that a circadian-effective lighting intervention delivering bright days and dark nights improves measures of sleep and mood in dementia patients living in controlled environments.

Abstract Study Objective Night work has detrimental impacts on sleep and performance, primarily due to misalignment between sleep–wake schedules and underlying circadian rhythms. This study tested whether circadian-informed lighting accelerated circadian phase delay, and thus adjustment to night work, compared to blue-depleted standard lighting under simulated submariner work conditions. Methods Nineteen healthy sleepers (12 males; mean ± SD aged 29 ± 10 years) participated in two separate 8-day visits approximately 1 month apart to receive, in random order, circadian-informed lighting (blue-enriched and dim, blue-depleted lighting at specific times) and standard lighting (dim, blue-depleted lighting). After an adaptation night (day 1), salivary dim-light melatonin onset (DLMO) assessment was undertaken from 18:00 to 02:00 on days 2–3. During days 3–7, participants completed simulated night work from 00:00 to 08:00 and a sleep period from 10:00 to 19:00. Post-condition DLMO assessment occurred from 21:00 to 13:00 on days 7–8. Ingestible capsules continuously sampled temperature to estimate daily core body temperature minimum (Tmin) time. Tmin and DLMO circadian delays were compared between conditions using mixed effects models. Results There were significant condition-by-day interactions in Tmin and DLMO delays (both p < .001). After four simulated night shifts, circadian-informed lighting produced a mean [95% CI] 5.6 [3.0 to 8.2] hours greater delay in Tmin timing and a 4.2 [3.0 to 5.5] hours greater delay in DLMO timing compared to standard lighting. Conclusions Circadian-informed lighting accelerates adjustment to shiftwork in a simulated submariner work environment. Circadian lighting interventions warrant consideration in any dimly lit and blue-depleted work environments where circadian adjustment is relevant to help enhance human performance, safety, and health.

The circadian rhythm, called Process C, regulates a wide range of biological processes in humans including sleep, metabolism, body temperature, and hormone secretion. Light is the dominant synchronizer of the circadian rhythm—it has been used to regulate the circadian phase to cope with jet-lag, shift work, and sleep disorder. The homeostatic oscillation of the sleep drive is called Process S. Process C and Process S together determine the sleep-wake cycle in what is known as the two-process model. This paper addresses the regulation of both Process C and Process S by scheduling light exposure and sleep based on numerical simulations of circadian rhythm and sleep mathematical models. This is a significant step beyond the existing literature that only considers the entrainment of Process C. Regulation of the two-process model poses several unique features and challenges: 1. Process S is non-smooth, i.e., the homeostatic dynamics are different in the sleep and wake regimes; 2. Light only indirectly affects Process S through Process C; 3. Light does not affect Process C during sleep. We consider two scenarios: optimizing light intensity as the control input with spontaneous (i.e., unscheduled) sleep/wake times and jointly optimizing the light intensity and the sleep/wake times, which allows limited delayed sleep and early waking as part of the decision variables. We solve the time-optimal entrainment problem for the two-process model for both scenarios using an extension of the gradient descent algorithm to non-smooth systems. To illustrate the efficacy of our time-optimal entrainment strategies, we consider two common use cases: transmeridian travelers and shift workers. For transmeridian travelers, joint optimization of the two-process model avoids the unrealistic long wake duration when only Process C is considered. The entrainment time also decreases when both the light input and the sleep schedule are optimized compared to when only the light input is optimized. For shift workers, we show that the entrainment time is significantly shortened by optimizing the night shift working light.

Spaceflight exposes crewmembers to circadian misalignment and sleep loss, which impair cognition and increase the risk of errors and accidents. We compared the effects of an experimental dynamic lighting schedule (DLS) with a standard static lighting schedule (SLS) on circadian phase, self‐reported sleep and cognition during a 45‐day simulated space mission. Sixteen participants (mean age [±SD] 37.4 ± 6.7 years; 5 F; n = 8/lighting condition) were studied in four‐person teams at the NASA Human Exploration Research Analog. Participants were scheduled to sleep 8 h/night on two weekend nights, 5 h/night on five weekday nights, repeated for six 7‐day cycles, with scheduled waketime fixed at 7:00 a.m. Compared to the SLS where illuminance and spectrum remained constant during wake (~4000K), DLS increased the illuminance and short‐wavelength (blue) content of white light (~6000K) approximately threefold in the main workspace (Level 1), until 3 h before bedtime when illuminance was reduced by ~96% and the blue content also reduced throughout (~4000K × 2 h, ~3000K × 1 h) until bedtime. The average (±SE) urinary 6‐sulphatoxymelatonin (aMT6s) acrophase time was significantly later in the SLS (6.22 ± 0.34 h) compared to the DLS (4.76 ± 0.53 h) and more variable in SLS compared to DLS (37.2 ± 3.6 min vs. 28.2 ± 2.4 min, respectively, p = .04). Compared to DLS, self‐reported sleep was more frequently misaligned relative to circadian phase in SLS RR: 6.75, 95% CI 1.55–29.36, p = .01), but neither self‐reported sleep duration nor latency to sleep was different between lighting conditions. Accuracy in the abstract matching and matrix reasoning tests were significantly better in DLS compared to SLS (false discovery rate‐adjusted p ≤ .04). Overall, DLS alleviated the drift in circadian phase typically observed in space analog studies and reduced the prevalence of self‐reported sleep episodes occurring at an adverse circadian phase. Our results support incorporating DLS in future missions, which may facilitate appropriate circadian alignment and reduce the risk of sleep disruption.

Bright light therapy is an effective treatment option for seasonal and non-seasonal affective disorders. However up to now, no study has investigated effects of dynamic bedroom lighting in hospitalized patients with major depression. A bedroom lighting system, which automatically delivered artificial dawn and dusk and blue-depleted nighttime lighting (DD-N lighting) was installed in a psychiatric ward. Patients with moderate to severe depression were randomly assigned to stay in bedrooms with the new lighting or standard lighting system. Patients wore wrist actimeters during the first two treatment weeks. Additionally, hospitalization duration and daily psychotropic medication were retrieved from patients’ medical charts. Data from thirty patients, recorded over a period of two weeks, were analyzed. Patients under DD-N lighting generally woke up earlier (+ 20 min), slept longer (week 1: + 11 min; week 2: + 27 min) and showed higher sleep efficiency (+ 2.4%) and shorter periods of nighttime awakenings (− 15 min). In the second treatment week, patients started sleep and the most active 10-h period earlier (− 33 min and − 64 min, respectively). This pilot study gives first evidence that depressed patients’ sleep and circadian rest/activity system may benefit from bedroom lighting when starting inpatient treatment.

This study investigated the effects of two whole-day ambient lighting interventions applied in living rooms on the objective and subjective sleep quality in older adults. Both lighting …

The aim of this systematic review was to investigate the effects of combined melatonin and bright light therapies on improved sleep and circadian outcomes. We conducted a systematic review that resulted in a total of eight papers meeting criteria. Four papers investigated the effectiveness of combined therapy in inducing a circadian phase shift on healthy participants. Combined therapy outperformed single light and melatonin therapies in phase advancing, but not in delaying, dim light melatonin onset (DLMO). The other four papers investigated the effect of combined therapy on sleep outcomes. Two of them were performed in elderly populations suffering from cognitive decline and two in delayed sleep-wake phase disorder (DSWPD) patients. While combined therapy was more beneficial than single therapy in elderly populations it did not show any benefit in DSWPD patients. The reported adverse effects of melatonin in elderly populations must be carefully considered. Future studies should investigate the separate and combined effect of melatonin and bright light on sleep and circadian outcomes in different target populations.

Significance Ambient nighttime light exposure is implicated as a risk factor for adverse health outcomes, including cardiometabolic disease. However, the effects of nighttime light exposure during sleep on cardiometabolic outcomes and the related mechanisms are unclear. This laboratory study shows that, in healthy adults, one night of moderate (100 lx) light exposure during sleep increases nighttime heart rate, decreases heart rate variability (higher sympathovagal balance), and increases next-morning insulin resistance when compared to sleep in a dimly lit (<3 lx) environment. Moreover, a positive relationship between higher sympathovagal balance and insulin levels suggests that sympathetic activation may play a role in the observed light-induced changes in insulin sensitivity.

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.

International standard CIE S 026:2018 provides lighting professionals and field researchers in chronobiology with a method to characterize light exposures with respect to non-visual photoreception and responses. This standard defines five spectral sensitivity functions that describe optical radiation for its ability to stimulate each of the five α-opic retinal photoreceptor classes that contribute to the non-visual effects of light in humans via intrinsically-photosensitive retinal ganglion cells (ipRGCs). The CIE also recently published an open-access α-opic toolbox that calculates all the quantities and ratios of the α-opic metrology in the photometric, radiometric and photon systems, based on either a measured (user-defined) spectrum or selected illuminants (A, D65, E, FL11, LED-B3) built into the toolbox. For a wide variety of ecologically-valid conditions, the melanopsin-based photoreception of ipRGCs has been shown to account for the spectral sensitivity of non-visual responses, from shifting the timing of nocturnal sleep and melatonin secretion to regulating steady-state pupil diameter. Recent findings continue to confirm that the photopigment melanopsin also plays a role in visual responses, and that melanopsin-based photoreception may have a significant influence on brightness perception and aspects of spatial vision. Although knowledge concerning the extent to which rods and cones interact with ipRGCs in driving non-visual effects is still growing, a CIE position statement recently used melanopic equivalent daylight (D65) illuminance in preliminary guidance on applying “proper light at the proper time” to manipulate non-visual responses. Further guidance on this approach is awaited from the participants of the 2nd International Workshop on Circadian and Neurophysiological Photometry (in Manchester, August 2019). The new α-opic metrology of CIE S 026 enables traceable measurements and a formal, quantitative specification of personal light exposures, photic interventions and lighting designs. Here, we apply this metrology to everyday light sources including a natural daylight time series, a range of LED lighting products and, using the toobox, to a smartphone display screen. This collection of examples suggests ways in which variations in the melanopic content of light over the day can be adopted in strategies that use light to support human health and well-being.

Light plays a crucial role in affecting the melatonin secretion process, and consequently the sleep–wake cycle. Research has demonstrated that the main characteristics of lighting affecting the so-called circadian rhythms are spectrum, light levels, spatial pattern and temporal pattern (i.e., duration of exposure, timing and previous exposure history). Considering that today people spend most of their time in indoor environments, the light dose they receive strictly depends on the characteristics of the spaces where they live: location and orientation of the building, dimensions of the windows, presence of external obstructions, geometric characteristics of the space, optical properties of walls and furniture. Understanding the interaction mechanism between light and architecture is fundamental to design non-visually comfortable spaces. The goal of the paper is to deepen this complex issue. It is divided into two parts: a brief historical excursus about the relationship between lighting practice and architecture throughout the centuries and a review of the available research works about the topic. The analysis demonstrates that despite the efforts of the research, numerous open questions still remain, and they are mostly due to the lack of a shared and clear method to evaluate the effects of lighting on circadian rhythm regulation.

… non-visual channel, affecting emotions, sleep quality, alertness and even health. The indoor luminous environment of buildings where people spend more and more time is divided into …

… This section describes and summarizes the effects of lighting on elderly sleep, presenting a review of 21 relevant studies [13, 14, 29,30,31,32,33,34,35,36,37,38,39,40, 44,45,46,47,48,…

… effects of … non-visual and visual outcomes before sleep remain unclear. To address this issue, we conducted a human-factor experiment to compare five smartphone-based evening light …

… human visual function, visible light has non-visual biological and psychological effects. The non-visual effects of light affect a human's health, well-being, activity and sleep. Comfortable …

Physiological effects of light exposure in humans are diverse. Among them, the circadian rhythm phase shift effect in order to maintain a 24-h cycle of the biological clock is referred to as non-visual effects of light collectively with melatonin suppression and pupillary light reflex. The non-visual effects of light may differ depending on age, and clarifying age-related differences in the non-visual effects of light is important for providing appropriate light environments for people of different ages. Therefore, in various research fields, including physiological anthropology, many studies on the effects of age on non-visual functions have been carried out in older people, children and adolescents by comparing the effects with young adults. However, whether the non-visual effects of light vary depending on age and, if so, what factors contribute to the differences have remained unclear. In this review, results of past and recent studies on age-related differences in the non-visual effects of light are presented and discussed in order to provide clues for answering the question of whether non-visual effects of light actually vary depending on age. Some studies, especially studies focusing on older people, have shown age-related differences in non-visual functions including differences in melatonin suppression, circadian phase shift and pupillary light reflex, while other studies have shown no differences. Studies showing age-related differences in the non-visual effects of light have suspected senile constriction and crystalline lens opacity as factors contributing to the differences, while studies showing no age-related differences have suspected the presence of a compensatory mechanism. Some studies in children and adolescents have shown that children’s non-visual functions may be highly sensitive to light, but the studies comparing with other age groups seem to have been limited. In order to study age-related differences in non-visual effects in detail, comparative studies should be conducted using subjects having a wide range of ages and with as much control as possible for intensity, wavelength component, duration, circadian timing, illumination method of light exposure, and other factors (mydriasis or non-mydriasis, cataracts or not in the older adults, etc.).

Abstract Since the discovery of non-visual effect of light, consequences on human psychology and physiology have been investigated; however, effects on cognition of exposure to different spectral composition have been partially explored. Aim of this paper is an overview on researches developed in this field to compare general approaches and measurements protocols: the scarce knowledge of the physiological mechanisms, as well as the lack of shared methods, techniques, tools and procedures represent the weak point of this research. The impact of different procedures and experimental settings on results is shown, evidencing the need for scientifically consistent and internationally agreed procedures.

With the growing interest in designing circadian-effective lighting, it is becoming increasingly important to determine how different lighting designs aimed at supporting circadian entrainment might also affect visual performance, preference, discomfort glare and lighting power density (LPD). These outcome measures were simultaneously examined in a controlled setting at night. Four ceiling lighting configurations, using combinations of direct and indirect lighting, were implemented along with one design that utilised local lighting. Every design delivered the same high level of circadian-effective lighting to participants. Saliva samples were obtained to measure nocturnal melatonin suppression. Two visual performance computer tasks together with subjective assessments of sleepiness, discomfort glare and preference were administered to participants. LPDs were determined. None of the lighting configurations created unacceptable levels of discomfort glare, and only one was above the required maximum allowable LPD. Lighting configuration had no differential effect on nocturnal melatonin suppression, visual performance and sleepiness. While the results show that a wide range of lighting approaches can meet visual, non-visual and energy objectives, the majority of participants preferred the local lighting over the ceiling-mounted lighting.

… exposure during the evening can delay circadian phase, suppress melatonin, and promote alertness, while daytime exposure strengthens circadian alignment and improves sleep …

Light simultaneously induces visual and non-visual effects. Although the differences in the spectral sensitivity of intrinsic photosensitive retinal ganglion cells induce opposing influences on physiological responses, it is difficult to independently measure only non-visual effects. Therefore, the reported effects of light color on physiological responses are inconsistent. This study aimed to clarify the visual and non-visual effects of light color on physiological responses. Three different conditions were employed to construct a lighting environment in which light colors were difficult to perceive due to chromatic adaptation and change blindness: constant white light (baseline condition), a gradual transition from white to blue light, and a gradual transition from white to red light. The physiological responses (brain activity, heart rate variability, and electrodermal activity) of 21 participants were measured with and without light color perception. The results suggested that blue light causes more non-visual effects compared to red light as blue light induces brain activation in some regions of the PFC (p < 0.05) and increases sweating, although the differences were not statistically significant. A mean comparison suggested that the visual effects of blue light showed tendencies toward a calming role for the prefrontal cortex and inhibition of sweating, but the differences were not statistically significant. Another mean comparison suggested that the visual effects of red light tended to enhance sweating, but the differences were not statistically significant. Visual and non-visual effects did not cause significant differences in heart rate variability. Additionally, a mean comparison did not reveal any significant tendencies.

The effect of light on human physiology as well as its non-image forming effects have been known for several years. An important milestone in understanding the non-visual effects of light was the discovery of a new type of photoreceptor namely the intrinsically photosensitive retinal ganglion cells, or ipRGCs which play a vital role in the human circadian system. The non-visual effects of light are the following: regulation of melatonin secretion, circadian entrainment and modification of body temperature. With the advent of solid-state lighting, it is possible to precisely regulate the spectral power distribution of artificial lighting, so as to favour the human circadian rhythm. The scope of this paper is to present a conceptual methodology for the evaluation of artificial lighting systems with regards to visual, circadian effects and their energy consumption. In other words, this paper aims to outline an assessment process for lighting designers by elaborating not only on the visual aspects of each lighting system but also the melanopic effects and its energy efficiency.

… The participants had to indicate their current sleep-alertness … positive role in improving non-visual functions compared to low … had no noticeable effect in influencing non-visual functions …

Abstract Light environment is an important part of the office environment. Aside from visual effects, light also has non-visual effects, for example, on mood, alertness, and performance. Although essential for healthy light design, current office lighting rarely considers non-visual effects. The evaluation of non-visual light environment is predominantly based on two physiological models: the equivalent melanopic lux (EML) and circadian stimulus (CS) models. EML is similar to visual illuminance but the spectral sensitivity function is non-visually converted. CS indicates the percentage of melatonin suppression and is more complex as it considers the interaction between different photoreceptors. Model comparison and spectral analysis of field measurements are required to verify the applicability of these models. Therefore, this study conducted field evaluations of non-visual effects in several typical office environments with different window orientations, then compared the calculation differences between EML and CS models. Errors in the spectral approximation calculations were also analyzed. According to the analysis of 571 measured data sets, no workstation with existing layout met the non-visual standards under overcast conditions. EML and CS models are similar in office indoor environment compliance evaluation, but CS model gets more reasonable results at high eye-level illuminance. Moreover, daylight irradiances were effectively approximated by the CIE standard illuminants D50 and D55. The conclusions of this study can be used as guidelines for interior design, field evaluations, and daylight simulations of the non-visual effects of light in office environments.

With the inherent sleep and wake cycle regulated by natural sunlight, the human body has evolved over millennia to be active during the day and to rest at night. However, maintaining an optimal 24 h cycle has become increasingly problematic in modern society as more people spend the majority of the day indoors. Many research groups have reported that inadequate artificial lighting interferes with melatonin production and disrupts the circadian rhythm. This study considered biological functions for light-emitting diodes (LEDs) of next-generation illumination, and LED packages and spectra suitable for both daytime and nighttime applications were designed. The prepared daytime human-centric (HC)-LEDs had a melanopic/photopic (M/P) ratio that was up to 26% higher than that of conventional (c)-LEDs, whereas the nighttime HC-LEDs exhibited up to a 26% lower M/P ratio compared to the c-LEDs. Nevertheless, because the HC-LED is designed to have almost the same color coordinates as the c-LED having the same correlated-color temperature (CCT), there is no change in the perceived color. To substantiate the biological effect, melatonin level data were obtained from 22 voluntary participants in c- and HC-LED lighting environments. In the HC-LED lighting environment, melatonin was suppressed by 21.9% after waking, and nocturnal melatonin secretion was increased by up to 12.2%. As human-centric lighting, our HC-LEDs are expected to become an essential element for modern life, where people spend most of their time indoors.

… The lighting field has seen tremendous growth in basic and … more than 20 years, but lighting design for occupants in isolated, … pre-sleep lighting intervention on melatonin, alertness and …

… This figure is included to provide lighting designers and practitioners with some first-order practical guidance on how to adjust CCT and illuminance as to reach a particular melanopic …

Exposure to light during overtime work at night in confined spaces may disrupt the normal circadian clock, affect hormone secretion, sleep quality and performance, thereby posing great risks to the physical and mental health of night workers. Integrative lighting should be adopted to reduce the disturbance of normal physiological rhythm, while meeting the visual requirements of work. Through adjustable LED (CCT 6000 K/2700 K) and different vertical illuminance, five lighting patterns with different circadian stimuli (CS = 0.60, 0.30. 0.20, 0.10 and 0.05) were conducted, respectively, in a sleep lab using a within-subject design. Each lighting pattern lasted for 5 h every night. Eight healthy adults were recruited to complete the night work and their salivary melatonin, Karolinska sleepiness scale (KSS), Psychomotor Vigilance Task (PVT) and sleep quality were tested. The results showed that subjective sleepiness and melatonin concentration increased rapidly under low intervention (CS = 0.05) with the best sleep quality, while they decreased in high intervention (CS = 0.60) at night and led to significantly higher levels of sleepiness the next morning (p < 0.05). For the PVT, the middle intervention (CS = 0.30) showed the lowest response time and least errors (p < 0.05), suggesting that appropriate illuminance can improve visual performance. To reduce biorhythm disruptions, lower lighting stimulation is preferred during night work. For difficult visual tasks, high illuminances may not improve visual performance; just a slight increase in the existing lighting levels is adequate. Lighting interventions have a clear impact on sleep improvement and work capacity for those working overtime, and they may be translatable to other shift work scenarios.

Evening residential illumination possesses the capacity to impair sleep quality via the suppression of endogenous melatonin production, a process largely driven by short-wavelength (blue) light. In this investigation, we characterized the light emissions from 52 distinct examples across three common lamp technologies: light-emitting diodes (LED), incandescent, and compact fluorescent (CFL) lamps. To estimate the differential circadian impact of these sources, we determined the Melatonin Suppression Value (MSV), melanopic illuminance, and photopic illuminance for each. Our findings reveal that “cool” white LED (median 12.3% MSV) and “cool” white CFL (12.1% MSV) lamps induce considerably greater melatonin suppression than “warm” white LED (3.6%), “warm” white CFL (2.6%), or traditional incandescent (1.5%) lamps. As potential countermeasures, we examined the efficacy of tunable Correlated Color Temperature (CCT) lamps and “blue-light–filtering” (BLF) lenses. The four tunable LED lamps demonstrated a profound ability to mitigate circadian disruption, reducing estimated melatonin suppression from 10% at a 5700 K (cool white) setting to 0.1% at 2100 K (warm white). An analysis of eight BLF lenses identified variable performance; while six had moderate impacts compared to uncorrected vision, their benefit was limited relative to standard clear lenses. Only two BLF lenses, distinguished by a “brown” tint, proved highly effective, reducing estimated suppression to below 0.3%. These results suggest that cool white CFL and LED lamps may exert a greater disruptive influence on sleep physiology than other lamp types. Conversely, tunable lamps adjusted to warm settings and “brown”-tinted BLF lenses represent beneficial strategies for ameliorating this effect. (Detailed measurement methodologies are available in a previously published study, with supplementary calculations provided separately).

The discovery of intrinsically photosensitive retinal ganglion cells in the eye and their interaction with melatonin has shown that light has significant effects beyond vision. The present study compared the effect of an integrative lighting system, providing low-intensity melanopic illuminance with the effect of an ordinary, qualitatively equivalent, electric lighting system. The study utilised a 2 × 7 randomised mixed experimental design. The sample consisted of 13 women and 11 men. Salivary melatonin secretion and subjectively perceived sleepiness in the evening were measured every half hour during 3 hours of light exposure. The chronobiologic typology (stability and amplitude) and trait-like negative and positive affect were measured once and analysed as covariates. The results showed a general increasing linear effect for both melatonin and sleepiness. A significant nonlinear effect of time was present in the group exposed to integrative lighting, indicating delayed melatonin secretion. The findings were stable across all levels of the examined covariates. These results confirm that the integrative lighting system produces effects beyond vision under otherwise ordinary lighting conditions. Furthermore, the results corroborate research suggesting that melatonin secretion and sleepiness may not be directly linked. The integrative lighting system provides new opportunities to develop indoor electric lighting resembling daylight.

Neuroscience and biological evidence emphasizes the profound influence of natural light on human health, offering benefits such as reducing fatigue, heightened alertness in healthcare providers, and improving patient outcomes. The objective of this review is to identify scientific studies and research to evaluate and report evidence of indoor lighting conditions’ influence on health outcomes, which can be used to develop lighting designs that align circadian rhythms in healthcare settings. A comprehensive search was conducted to identify rigorous empirical studies focused on the link between interior lighting conditions with health outcomes in the healthcare environment. For a comprehensive review of the existing literature, a four-phased methodology was employed including literature search, screening, and selection. Literature appraisals were conducted to determine the relevance and quality of evidence for each study identified. In addition, using a thematic analysis, patterns were identified, analyzed, and interpreted within the literature review. Accordingly, the results were organized into two main groups interventional human subjects and simulation-based studies. Despite evidence that natural light influences human health and happiness, a synthesis of reviewed studies suggests that the evidence for the benefits of artificial lighting in healthcare settings is less conclusive, with potential factors including variations in lighting design, inconsistent implementation of lighting interventions, and differing sample populations across studies. We conclude with an executive summary suggesting that future research should use standardized metrics and methods to focus on bridging the gap between theoretical understanding and practical application in lighting design for healthcare environments. Collaboration among architects, designers, lighting experts, and healthcare professionals can address these factors contributing to building a stronger evidence-based design for the benefits of artificial lighting in healthcare settings.

A better understanding of the spatial sensitivity of the human circadian system to photic stimulation can provide practical solutions for optimized circadian light exposures. Two psychophysical experiments, involving 25 adult participants in Experiment 1 (mean age = 34.0 years [SD 15.5]; 13 females) and 15 adult participants in Experiment 2 (mean age = 43.0 years [SD 12.6]; 12 females), were designed to investigate whether varying only the spatial distribution of luminous stimuli in the environment while maintaining a constant spectrally weighted irradiance at the eye could influence nocturnal melatonin suppression. Two spatial distributions were employed, one where the luminous stimulus was presented On-axis (along the line of sight) and one where two luminous stimuli were both presented Off-axis (laterally displaced at center by 14°). Two narrowband LED light sources, blue (λmax = 451 nm) for first experiment and green (λmax = 522 nm) for second experiment, were used in both the On-axis and the Off-axis spatial distributions. The blue luminous stimulus targeting the fovea and parafovea (On-axis) was about three times more effective for suppressing melatonin than the photometrically and spectrally matched stimulus targeting the more peripheral retina (Off-axis). The green luminous stimulus targeting the fovea and parafovea (On-axis) was about two times more effective for suppressing melatonin than the photometrically and spectrally matched stimulus targeting the more peripheral retina (Off-axis).

Light‐induced melatonin suppression data from 29 peer‐reviewed publications was analysed by means of a machine‐learning approach to establish which light exposure characteristics (ie photopic illuminance, five α‐opic equivalent daylight illuminances [EDIs], duration and timing of the light exposure, and the dichotomous variables pharmacological pupil dilation and narrowband light source) are the main determinants of melatonin suppression. Melatonin suppression in the data set was dominated by four light exposure characteristics: (1) melanopic EDI, (2) light exposure duration, (3) pupil dilation and (4) S‐cone‐opic EDI. A logistic model was used to evaluate the influence of each of these parameters on the melatonin suppression response. The final logistic model was only based on the first three parameters, since melanopic EDI was the best single (photoreceptor) predictor that was only outperformed by S‐cone‐opic EDI for (photopic) illuminances below 21 lux. This confirms and extends findings on the importance of the metric melanopic EDI for predicting biological effects of light in integrative (human‐centric) lighting applications. The model provides initial and general guidance to lighting practitioners on how to combine spectrum, duration and amount of light exposure when controlling non‐visual responses to light, especially melatonin suppression. The model is a starting tool for developing hypotheses on photoreceptors’ contributions to light's non‐visual responses and helps identifying areas where more data are needed, like on the S‐cone contribution at low illuminances.

… the evening can significantly suppress melatonin secretion, … modes in maintaining evening melatonin production. The study … had significantly higher melatonin production than those in …

At its best, human-centric lighting considers the visual and non-visual effects of light in support of positive human outcomes. At its worst, it is a marketing phrase used to healthwash lighting products or lighting design solutions. There is no doubt that environmental lighting contributes to human health, but how might one practice human-centric lighting given both the credible potential and the implausible hype? Marketing literature is filled with promises. Technical lighting societies have summarized the science but have not yet offered design guidance. Meanwhile, designers are in the middle, attempting to distinguish credible knowledge from that which is dubious to make design decisions that affect people directly. This article is intended to: (1) empower the reader with fundamental understandings of ways in which light affects health; (2) provide a process for human-centric lighting design that can dovetail with the decision-making process that is already a part of a designer's workflow.

Daylight variability throughout the day makes it an ideal light source for the stimulation of humans’ circadian systems. However, the key criteria, including proper quantity, quality, and hours of access to daylight, are not always present inside the built environment. Therefore, artificial light is necessary to complement the human’s visual and non-visual needs for light. Architectural design parameters, such as window area, orientation, glazing material, and surface reflectance alter the characteristics of both daylight and artificial light inside buildings. These parameters and their impact on lighting design should be considered from the early design stages to attain a circadian-effective design. In response to this need, a design approach called Human-Centric Lighting (HCL) was introduced. HCL places humans, and their visual and non-visual needs, in the center of the design process. It manipulates the light-related factors, such as spectrum and intensity, within the built environment for circadian benefits. The effect of HCL on lighting energy efficiency is still not clear. This paper reviews essential architectural design parameters and their impacts on circadian lighting design, considers the HCL design process and explores the most widely used circadian lighting metrics and standards.

ABSTRACT The use of daylight in the built environment is often preferred to artificial light sources as its successful application can provide visual comfort and satisfaction along with the potential for significant energy savings. Exposure to daylight is also the primary source for stimulus that establishes a healthy day/night cycle in all living organisms. This is known as circadian rhythm. Newly discovered photoreceptors (intrinsically photosensitive retinal ganglion cells – ipRGC) within the mammalian eye, including humans, are specifically linked to the portion of the brain responsible for maintaining a healthy circadian rhythm. This discovery has led to a new subject area in the field of lighting design focused on controlling the spectrum of light that these photoreceptors are sensitive to. Currently, work in the field of circadian lighting design is concentrated on the use of artificial light sources for circadian stimulus. This is largely due to the advent of the widespread use of LED technology, which has proven that it can be a significant source of light that can delay or advance the circadian clock. The use of daylight to provide circadian stimulus has been a given in this field of design, however, there has not been very much research into how the built environment affects our ability to effectively receive this stimulus from daylight. In this research, the groundwork is established to start to create a set of guidelines to help architects and designers maximize the potential for daylight to provide circadian stimulus at the earliest stages of a project. This is accomplished through a series of lighting simulations that explore and test various architectural parameters that affect daylight-driven circadian lighting, with simultaneous consideration given to photopic lighting availability and visual comfort. The architectural parameters tested in this study included window head height, building orientation, shading devices, visual obstructions to the sky, and room depth. The results show that informed design decisions could maximize circadian potential in a given space, while achieving visually satisfactory luminous environments.

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.

ABSTRACT Light is the main environmental signal synchronizing circadian rhythms to the 24-hour light-dark cycle. Recent research has identified significant inter-individual variability in the sensitivity of the circadian system to light as measured by, among other indicators, melatonin suppression in response to light. These inter-individual differences in light sensitivity could result in differential vulnerability to circadian disruption and related impacts on health. A growing body of experimental evidence points to specific factors which are associated with variability in the melatonin suppression response; however, no review to date has summarized this research to present a comprehensive summary of current knowledge. The aim of this review is to provide an overview of the state of this evidence, which to date spans demographic, environmental, health-related, and genetic characteristics. Overall, we find that there is evidence of inter-individual differences for the majority of the characteristics examined, although research on many factors remains limited. Knowledge of individual factors that are linked to light sensitivity could inform improved lighting personalization, as well as the use of measures of light sensitivity to determine disease phenotypes and treatment recommendations.

… for biophilic design. On the other hand, for human centric lighting the Equivalent Melatonin … corresponding human centric lighting metrics in order to create a lighting design guide for …

Proper lighting adjustments can reduce energy consumption in buildings, particularly by supporting thermal comfort and minimizing reliance on heating and cooling systems. This study explores the impact of office lighting on sleepiness and melatonin levels, contributing to a broader understanding of lighting’s impacts on human health and wellbeing. Twenty participants were exposed to various lighting conditions over five consecutive working days, with repeated measurements providing insights into the influence of artificial lighting on sleepiness and daily melatonin fluctuations. Results showed that lighting conditions did not significantly affect sleepiness during the experimental period (8:40–15:15). While no immediate melatonin response was observed, longer-term exposure to warm white light for two days resulted in lower melatonin levels at 20:00 and bedtime compared to one-day exposure. Morning melatonin levels decreased throughout the experiment, likely due to the absence of daylight in the office setting.

The global phenomenon of population aging presents a significant challenge, affecting both the increasing number of older individuals and their duration of living with disability. Tailored care services are crucial for improving the quality of life of older adults, particularly those with disabilities residing in nursing homes. However, ensuring personalized care and mitigating the risks associated with institutionalization are essential in optimizing care quality. One particular challenge in nursing homes is maintaining residents' personal routines and addressing sleep disturbances linked to neurodegenerative disorders. Non-pharmacological interventions are increasingly recognized as preventive and management strategies for behavioral and psychiatric symptoms in nursing home residents. Sleep disruptions, such as reduced duration and increased nocturnal awakenings, are prevalent among nursing home residents. Excessive nocturnal lighting and frequent caregiver interventions contribute to these disturbances. This study aimed to investigate the impact of implementing smart humancentric lighting on the sleep efficiency of nursing home residents. Data from pressure sensors embedded in mattresses were collected to assess sleep efficiency. The findings suggest that smart humancentric lighting can significantly reduce sleep disturbances and improve sleep quality in nursing home residents. Future research should delve into specific symptoms, care burden, and psychotropic agent utilization to validate the effectiveness of this intervention.

… and sleep duration, sleep timing, and sleep quality across … light exposure and its influence on sleep behaviors. So, it … in sleep duration was associated with lower sleep quality, we …

Over the past 300 years, scientific observations have revealed the significant influence of circadian rhythms on various human functions, including sleep, digestion, and immune system regulation. Access to natural daylight is crucial for maintaining these rhythms, but modern lifestyles often limit its availability. Despite its importance, there is a lack of a comprehensive design framework to assist designers. This study proposes an architectural design framework based on the review of literature, lighting-related codes and standards, and available design and analysis tools that guides the creation of lighting systems supporting healthy circadian rhythms. The framework outlines key decision-making stages, incorporates relevant knowledge, and promotes the integration of dynamic lighting techniques into building design. The proposed framework was presented to a group of design professionals as a focus group and their feedback on the relevance and usability of the tool was obtained through a survey (n = 10). By empowering designers with practical tools and processes, this research bridges the gap between scientific understanding and design implementation, ensuring informed decisions that positively impact human health. This research contributes to the ongoing pursuit of creating lighting environments that support healthy circadian rhythms and promote human well-being.

This study presents a literature review on human centric lighting, utilizing solid-state lighting and switchable glazing, which has immense potential to create comfortable and productive environments. Windows and shading devices of a building are the essential components that allow natural daylight to enter indoors, thereby maintaining a relationship between the interior and exterior environments. Artificial light sources are always integrated with natural light to provide the right lighting environment. Achieving a balance between natural and artificial light is crucial; the efficiency depends on how effectively artificial light is combined with daylight. This paper explores the benefits of intelligent solid-state lighting and switchable glazing technology in creating a comfortable and energy-efficient environment. Lighting metrics for assessing circadian entrainment and algorithms for optimizing visual and thermal comfort along with energy efficiency are the main topics of concern. By optimizing lighting and temperature control, workplaces can increase productivity and promote circadian entrainment. This review considers papers mainly from 2004 to 2023, challenges and problems in implementation, along with future directions are also considered. If the right spectrally controllable source is designed by giving a suitable light exposure for the right duration, it is possible to achieve comfort, health, and energy efficiency. This integrative lighting solution provides new and innovative ways to enhance our daily lives. Climate-responsive algorithms seem more reliable for switchable glazing; overall circadian performance improves when mixed with natural light.

… In this chapter, we will explore how human- centric lighting (HCL) can help improve our health and … move into sleep more smoothly and makes their sleep better. Humancentric lighting is …

Human centric lighting is an umbrella concept which covers human health and well-being in general. As the conventional lighting techniques are based on horizontal workplane illuminance, it drives from the vertical eye level illuminance and its spectral distribution triggering the non-visual effects on humans. That is named as melanopic illuminance consequently. Its metrics have taken their place in lighting design literature and applications, with emergence of related standards subsequently. This literature overview contributes about the understanding the meaning human centric lighting due to transition from visual to non-visual effects of light, and how they direct recent research through light's impacts on human performance, emotions health and well-being, and relations to energy saving even. The shift from the concept of human centric lighting to circadian lighting design is obvious in very current studies.

This paper discusses the rise of human-centric lighting and its current status in lighting. We summarise the human benefits associated with light and lighting and show that human-centric lighting has sound motivations, despite being tainted by misleading marketing claims. The phrase integrative lighting avoids the hype and encapsulates what lighting aspires to be. Embodied in these concepts are some things old and some things new. The old is twofold. First, without diminishing the value of lighting products, the core ingredient for good human outcomes is good design, driven by a design team. Second, light is still for vision, and lighting for visibility, visual comfort and visual amenity is as important as ever. Complementing the old is new awareness and responsibility for how light and lighting influence non-visual responses in humans. Circadian, neuroendocrine and neurobehavioural responses are important for human health and should be considered on-par with visual responses. This awareness leads toward lighting design solutions with increased contrast between day and night. The parties responsible for addressing non-visual responses to light and lighting are evolving. Architects, lighting professionals, lighting equipment manufacturers, medical professionals, building owners and individuals all have a stake, but who should drive decisions and in what proportion?

… for recognizing how light influences sleep, mood and overall health. From the 1960s through the 1980s, research into the psychological impact of lighting showed that bright, cool light …

… concerns determining how the principles of Human Centric Lighting can be translated into the practice … Users of spaces equipped with HCL systems report improved sleep quality, better …

Indoor lighting plays a crucial role in shaping occupant comfort, health, and productivity, as they spend 90% of their time indoors. While intensive research on adaptive lighting technologies is ongoing, most current strategies are still primarily based on static standards and subjective questionnaires, which may not reliably capture dynamic human responses to real-time changes in lighting conditions. Also, current strategies often address only a few parameters, such as illuminance and colour temperature, and overlook how variations in lighting influence actual human behaviour. This paper presents a comprehensive review of the literature spanning the non-visual effects of light. It highlights persistent methodological shortcomings, i) particularly the narrow parameter focus, ii) methodological constraints like reliance on invasive sensing, static comfort models, and laboratory-based studies with limited ecological validity and iii) difficulty with integration with control systems. The paper further examines the limitations of relying solely on subjective lighting evaluations for occupant-responsive lighting control. A living lab study was conducted in a university environment (n = 81), where illuminance levels were measured across nine spatial zones and compared with occupants' self-reported satisfaction, perceived control, and productivity using Likert-scale surveys. Results showed weak and inconsistent relationships between measured illuminance and subjective responses. The zone with the highest illuminance also reported the highest dissatisfaction, indicating a mismatch between objective lighting levels and perceived comfort. Response clustering, adaptation effects, and contextual confounding factors further limited the sensitivity and reliability of subjective assessments. The findings highlight the importance of integrating non-invasive behavioural and physiological sensing modalities with qualitative assessments when evaluating indoor lighting environments. Therefore, the paper proposes a structured methodological framework that employs non-invasive behavioural and physiological drivers, such as eye-tracking metrics, heart rate and heart-rate variability, facial expression analysis, and posture and movement patterns to capture real-time occupant responses under static and dynamic lighting conditions. The framework is designed to support transparent, closed-loop lighting adaptation while maintaining user override and practical deployability.

… lighting design strategies. Although the dataset 34 used did not permit personalized lighting … the development of personalized light environment models and advance human-centric 745 …

Sleep is vital for maintaining cognitive function, facilitating metabolic waste removal, and supporting memory consolidation. However, modern societal demands, particularly shift work, often disrupt natural sleep patterns. This can induce excessive sleepiness among shift workers in critical sectors such as healthcare and transportation and increase the risk of accidents. The primary contributors to this issue are misalignments of circadian rhythms and enforced sleep-wake schedules. Regulating circadian rhythms that are tied to alertness can be regarded as a control problem with control inputs in the form of light and sleep schedules. In this paper, we address the problem of optimizing alertness by optimizing light and sleep schedules to improve the cognitive performance of shift workers. A key tool in our approach is a mathematical model that relates the control input variables (sleep and lighting schedules) to the dynamics of the circadian clock and sleep. In the sleep and circadian modeling literature, the newer physiology-based model shows better accuracy in predicting the alertness of shift workers than the phenomenology-based model, but the dynamics of physiological-based model have differential equations with different time scales, which pose challenges in optimization. To overcome the challenge, we propose a hybrid version of the PR model by applying singular perturbation techniques to reduce the system to a non-stiff, differentiable hybrid system. This reformulation facilitates the application of the calculus of variation and the gradient descent method to find the optimal light and sleep schedules that maximize the subjective alertness of shift worker. Our approach is validated through numerical simulations, and the simulation results demonstrate improved alertness compared to other existing schedules.