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A blog by Timo Partonen From November to January, if your exposure to daylight is of 1 hour or longer per day, it is likely that you will not have depressive symptoms during that period of the year. Compared to the conditions where your exposure of less than 1 hour per day, the odds of having depressive symptoms will be 0.72 on average, yielding the confidence interval from 0.60 to 0.82. If you have children younger than 12 years of age at home, it is even more likely that you will not have depressive symptoms from November to January, if your exposure to daylight is of 1 hour or longer per day. These findings, of the total of 23,581 observations, were derived from 10,430 persons living in Sweden (Raza et al. 2024). Self-reports were corroborated by the all-wavelength readouts of solar radiation, with a horizontal resolution of 11 km × 11 km and a temporal resolution of 1 hour. The individual readouts demonstrated that the greater the exposure to solar radiation in residential neighborhood was, the less frequent the depressive symptoms were. I think that this is good news. Because, first, I see that they are generalizable to people living in high latitude regions, and second, they open a way to adapt to climate change. Photo by brooklyn  on Unsplash In high latitude regions, the seasonal variation in natural light is an essential characteristic of the climate. As climate change is already quickly warming up the Arctic and subarctic regions, there will be significant changes in solar radiation as well. Solar radiation is projected, e.g., in northern Finland by the end of this century, to increase by about 5% in summertime and to decrease by 10% to 20% in wintertime. From the perspective of public health, the outcome is likely to turn out negative, if left unnoticed. On the one hand, less solar radiation in wintertime will turn the morning hours darker, which tends to result in greater than usual delays of the circadian pacemaker. It is thereafter likely that sleep disturbance as well as depressive symptoms together with carbohydrate craving in the evening hours will emerge more frequently than as usual. On the other hand, more solar radiation in summertime will turn the evening hours lighter, which leads to greater than usual delays of the circadian pacemaker as well. As a result, more frequent sleep disturbance is likely, such as among 1962 individuals of a cohort of the general population being exposed to greater solar radiation in their residential neighborhood during the past year (Elovainio et al.  2022). Albeit winter depression has been studied for decades and associated with low exposure to daylight, the influence of global radiation on depression remains rather unexplored. There are some reports though. A study from the Netherlands (Sarran et al.  2017), with the total of 23,197 assessments of depressive symptoms weekly during the winter months over six years, included 291 patients having winter depression and living in and near Groningen. It suggested that forecasting sunshine duration or cloud cover might improve the possibilities of early intervention. Another study from Finland (Komulainen et al.  2022) demonstrated that 1845 individuals of a population-based cohort being exposed to greater solar radiation in their residential neighborhood during the past year were less likely to report suicidal thoughts. To adapt to slowly emerging impacts of climate change, we need to rethink, (a) how to design new and renovate old buildings to let daylight come in from outside, (b) how to time artificial light exposures during the day to align with the circadian pacemaker, and (c) how to spend our time in daylight. Future is now, is not it.   Further reading Elovainio M, Komulainen K, Lipsanen J, Partonen T, Pesonen AK, Pulkki-Råback L, Paunio T, Kähönen M, Vahtera J, Virtanen M, Ruuhela R, Hakulinen C, Raitakari O. Long-term cumulative light exposure from the natural environment and sleep: a cohort study. J Sleep Res 2022; 31: e13511. https://doi.org/10.1111/jsr.13511 Komulainen K, Hakulinen C, Lipsanen J, Partonen T, Pulkki-Råback L, Kähönen M, Virtanen M, Ruuhela R, Raitakari O, Elovainio M. Associations of long-term solar insolation with specific depressive symptoms: evidence from a prospective cohort study. J Psychiatr Res 2022; 151: 606–610. https://doi.org/10.1016/j.jpsychires.2022.05.038 Raza A, Partonen T, Hanson LM, Asp M, Engström E, Westerlund H, Halonen JI. Daylight during winters and symptoms of depression and sleep problems: a within-individual analysis. Environ Int 2024; 183: 108413. https://doi.org/10.1016/j.envint.2023.108413 Sarran C, Albers C, Sachon P, Meesters Y. Meteorological analysis of symptom data for people with seasonal affective disorder. Psychiatry Res 2017; 257: 501–505. https://doi.org/10.1016/j.psychres.2017.08.019

Every living organism on earth follows internal 24-hour cycles known as circadian rhythms. From a flower opening at dawn to a surge of human alertness in the mid-morning, these rhythms are deeply embedded in our biology. They regulate countless processes, from gene expression and metabolism to behaviour and sleep. In mammals, the central pacemaker of this system is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN synchronises peripheral clocks that exist in nearly all tissues through neural, hormonal and behavioural signals. Light, especially short-wavelength, blue-white light detected by specialised retinal cells in the eye, serves as the primary environmental cue that entrains the SCN with the Earth’s natural day-night cycle. When our exposure to light and darkness is disrupted, so too are our circadian rhythms. Spending too much time indoors, working night shifts, travelling across time zones or being exposed to artificial light at night can all interfere with this delicate system. Such disruption can lead to a range of metabolic, cognitive and physiological effects. Increasingly, research is showing how circadian misalignment contributes to disease risk, and how understanding temporal biology can guide both medical treatment and lifestyle choices. The circadian clock is therefore not simply a passive timer but a fundamental regulatory system that keeps our internal physiology in tune with the external environment. This short blog is inspired by the book On the Essential Principles and Practice of Circadian Biology: A Road Map  by Roelof A. Hut and William J. Schwartz.

In this episode of the Happier with Light podcast, Lard talks with Jan Denneman, Chairman of the Good Light Group. Jan shares why the organisation was founded and how everything it does is based on science. More than thirty scientific advisors and experts in fields such as chronobiology, neurophysiology, sleep, psychiatry and light, support the group in shaping its message and grounding every insight in solid research. Jan reminds us of something that is often overlooked: most of us think about light only in terms of what we can see. If we can read, work or move around comfortably indoors, we assume the lighting is fine. But that is where the problem begins. Our eyes can perform perfectly well under dim conditions, even when it’s almost dark, while our brains actually need much more light during the day to stay alert, balanced and healthy. Inside our eyes are special light-sensitive cells, the spheres, that send signals not just to the visual part of the brain but also to our internal biological clock and to areas that affect our mood and energy. These cells act as an inner sundial, constantly telling the brain what time of day it is. Based on that information, our brain adjusts hormone levels, deciding when we should feel awake and when it’s time to wind down. The trouble is that indoor light levels are usually far too low, leaving this inner sundial without proper guidance. As a result, many people suffer from sleep problems, low energy and poor concentration. The solution, however, is surprisingly simple. Spend at least two hours a day outdoors, ideally with half an hour in the morning light. When that isn’t possible, sit near a window or use modern LED lighting that mimics natural daylight. Throughout the day, our eyes need at least 500 lux of light to stay in sync with our biological rhythms. Yet most indoor spaces provide only 50 to 100 lux, which is far too little. If we truly want to support human health and wellbeing, we need to rethink how we illuminate our homes, offices and schools. Setting lighting standards to deliver at least 500 lux at eye level would make a real difference. It would allow even those who spend most of their time indoors to experience the benefits of good light — light that not only helps us see, but helps us to live a healthier, better life. Listen on Spotify

Light affects how we sleep, feel, and perform – yet public awareness of its impact remains limited. The Light for Public Health  initiative aims to make evidence-based knowledge on light and health both accessible and actionable, thus turning scientific insight into public benefit. “Light isn’t just for vision – it is a key signal for human biology,” says Manuel Spitschan, research group leader at the Max Planck Institute for Biological Cybernetics and professor at the Technical University of Munich, who chairs Light for Public Health initiative. “By bringing light and health experts together, we can make healthier light an integral part of global health policy and everyday life.” To mark its launch, the initiative has published 26 foundational statements outlining up-to-date expert consensus on how light exposure influences human physiology and behavior. These statements have now been published as an open-access article in the journal BMJ Public Health  and have been translated into 18 languages. The Light for Public Health initiative has emerged from the Ladenburg Roundtable “Light for health and well-being”, a forum for interdisciplinary research dialogue held in April 2024. It is supported by the Light for Public Health Consortium, a network of international experts serving as its scientific advisory body. Participating organizations are: the International Commission on Illumination (Vienna, Austria) the Society for Light, Rhythms and Circadian Health (Philadelphia, PA, USA) the Daylight Academy (Zurich, Switzerland) the Good Light Group (Eindhoven, The Netherlands) the Center for Environmental Therapeutics (New York, USA). Together, they represent leading global scientific institutions advancing healthy light exposure in public health strategies, built environments, and daily life. Foundational statements and further information: www.lightforpublichealth.org

With insights from IALD, WELL, DLA, and leading researchers, this webinar explores daylight-like conditions indoors and their impact on health, design, and circadian well-being. With an increasing evidence base that properties of daylight can positively affect people’s health and well-being, time has come to address the challenge of daylight-like conditions indoors. At present, many people spend time in spaces lit with electric lighting – at work places and in classrooms. How to design the built environment with appropriate light exposure in mind is the topic of a recent white paper by the the International Association of Lighting Designers (IALD) . During this webinar their findings will be presented and commented and contextualized by researchers and practitioners selected by the Daylight Academy, the International WELL Building Institute and the Society of Light, Rhythms and Circadian Health. Introduction by Lisa Wu Light and Human Health: Insights from Hospital Rooms An introduction to the importance of light and human health, with a focus on the hospital room. This introduction will showcase findings from two studies by Lisa and her colleagues, highlighting the important role of light in the hospital environment.  Watch the introduction Lighting Design for Health, Wellbeing and Quality of Light, A Holistic Approach by Kevan Shaw This presentation covers the content of the similarly titled IALD white paper . It covers the current thinking on non visual effects of light and provides some practical guidance on how to incorporate this in the lighting design process. It also includes some more recent information and case studies showing how Integrative Lighting is being applied in real projects. Watch the lecture Panel discussion Panel discussion and the Q&A with the experts: Johannes Zauner Luisa Brotas Nathan Stodola Watch the panel discussion

The CPD covers Designing Lighting to Promote Better Sleep. It involves an in-depth look at what sleep is, what circadian rhythms are and light’s entrainment of them, the effect of circadian disruption on sleep and the knock-on negative effects of sleep deprivation for general health. Connected with above, shortcomings of many indoor lit environments are discussed, followed by a look at lighting recommendations which can go a long way toward solving these shortcomings. The presentation then moves from the academic to the practicable and shows what an integrative (ie looking at visual and non-visual needs) lighting design process looks like. An example of putting healthy lighting design into practice wraps up the course. More info

It’s almost the time of the year again, the day in autumn when the clocks turn back to natural time. Every year, millions of people groan, lose sleep, and wonder, why are we still changing our clocks to daylight saving time in the summer? The seasonal clock change is one of those traditions that perhaps made sense once upon a time but no longer serves us. In fact, modern science is increasingly clear: switching the clocks twice a year disrupts our health, our productivity, and even our safety. It’s time, literally, to stop the time shift and stay aligned with natural time. The clock change at the end of October, which returns us to natural time, is necessary, and from now on we should never switch again to the unnatural daylight saving time. What is natural time? Natural time (standard time) is the rhythm that best matches the solar day — when the sun reaches its highest point around noon, and our biological clocks follow light and darkness as nature intended. Our bodies run on circadian rhythms, internal 24-hour cycles that control sleep, hormones, mood, alertness and more. These rhythms are set primarily by sunlight. When our social clock (the clock on the wall) doesn’t match the solar clock (what the sun says), our rhythms falls out of sync, also known as a jet lag. Standard time keeps us closest to the sun’s natural rhythm. Daylight Saving Time pushes us artificially ahead, a full hour of social jet lag that lasts for months. Energy savings, the original reason for daylight savings time , are negligible today, while the costs to our health are undeniable.   In short, permanent natural time is healthier, safer, and more humane.

Start:  November 2025 Location:  Online What are the goals of this course? The course will provide a comprehensive understanding of the role of daylight in human behaviour, molecular biology, psychophysiology, neuroendocrinology and clinical applications The course will highlight the importance of daylight in the built environment for office users, schoolchildren or the elderly in care homes The course will inform about: personal light exposure behaviour and consequences, the impact of light on mental health The course integrates topics covering the biological effects of daylight from various fields such as architecture, chronobiology, lighting design, medicine and psychology. This opens up theoretical and, above all, practical applications for improving public health. The course is open to all. The course will be held online at 3pm (CET). Duration is 45 Min plus 15 Min Q&A   Visit the iHCDP website for more details or send an email to mirjam.muench@unibas.ch (course coordinator), if you are interested in participating.

Together with the  Society for Light, Rhythms, and Circadian  Health (SLRCH) , the  Daylight Academy (DLA) , the  International Association of Lighting Designers  (IALD) and  Luger Research (LR) , we are organising and presenting the ‘deLIGHTed Talks’ lecture series. The lectures are free to attend. SAVE THE DATE: 3 November 2025 (3 PM CET) Register here With insights from IALD, WELL, DLA, and leading researchers, this webinar explores daylight-like conditions indoors and their impact on health, design, and circadian well-being. Join the discussion and gain perspectives from science, practice, and international thought leaders. ​ With an increasing evidence base that properties of daylight can positively affect people’s health and well-being, time has come to address the challenge of daylight-like conditions indoors. At present, many people spend time in spaces lit with electric lighting – at work places and in classrooms. How to design the built environment with appropriate light exposure in mind is the topic of a recent white paper by the the International Association of Lighting Designers (IALD). More info

Good light changes lives. A peer-reviewed study “ Biodynamic lighting effects on the sleep pattern of people with dementia ” reports that good light, either daylight or light that compensates for a lack of daylight, has a substantially positive influence on people with dementia. The results are both humane and practical: better sleep at night, greater alertness by day, and less restlessness overall. What the research found Under good light conditions, residents experienced: Less night-time wandering: average episodes fell from 11 to 5 per night. More night-time rest: time spent lying quietly in bed increased by 77 minutes on average. Fewer daytime naps: episodes fell from 16 to 7 per day. Across two biodynamic lighting conditions (A1, A2) compared with normal lighting (B1, B2), there was a clear decrease in both night-time bed exits and daytime dozing. Photo by Kampus Production How the light was delivered To achieve a therapeutic dose of light, the programme provided 1,000 lux measured vertically at eye level (120 cm). In practice, this was delivered by positioning three Sparckel  luminaires in strategic locations within a larger shared living room with more than 18 residents. The set-up was freestanding and plug-and-play, making it straightforward to apply in real-world care settings.   Why dynamic good light matters Good light is the right light at the right time. Specialised daylight detectors in the eye connect to the part of the brain that houses the biological clock. This clock regulates daily bodily rhythms like sleep, alertness, mood and digestion. These detectors require bright light during the day and dim light in the evening to keep time accurately. This is especially important for people with dementia, who rely even more on a stable biological clock.   ‘We launched a good light pilot in the summer in the living room at Wilhelmina van Sonsbeeck (a nursing home in the Netherlands). During the pilot, we observed that residents slept through the night again, felt fit and active during the day, and were in a better mood; night-time restlessness decreased by about 60%. The extra lighting was appreciated by residents, families and staff alike. The results were astonishing,’ — Engeline Plaggenmarsch, Location Director, IJsselheem   Evidence from everyday care homes Three students conducted complementary research at Zorgboog Helmond and Liessel, studying 48 residents with dementia in small-scale residential settings. Across three observational sub-studies, they found: Sleep–wake cycle:  a significant decrease in daytime sleepiness, with greater daytime alertness and longer night-time sleep. Restlessness:  a significant decrease in non-aggressive physical behaviours such as general restlessness, repetitive actions and aimless wandering. Mood:  a significant reduction in apathy, reflected in improved motivation and engagement. Source: https://sparckel.com/nl/fontys-onderzoek-daglicht-is-gunstig-bij-dementie/ https://sparckel.com/nl/ongezellige-verlichting-zorgt-voor-topsfeer-in-zwols-zorghuis-voor-mensen-met-dementie/

In this episode we’ll be focusing on how to measure light. To guide us through this topic, we’ve invited Hedy Lee from UPRtek, a specialist in spectral measurement devices, which are amazing tools for everyone creating light or seeking hight-quality lighting products. UPRtek is dedicated to helping people explore light and colour through advanced technology. When LED lighting first entered the market, it also brought with it challenges around colour accuracy and light safety. In response, UPRtek developed practical, laboratory-grade spectral measurement devices, making it far easier to assess light quality without relying on complex lab equipment. Join us and discover how to measure good light and why it matters. Listen on Spotify

We are very pleased to announce that Lawrence Lin has joined our board as a new member! Lawrence is an innovative LED & lighting expert, with strong connections in China and across global networks. He has 27 years' experience in the LED and Lighting industry and is the founder & CEO of Lighting Recipe Studio as well as Senior Advisor to Zumtobel Group APAC. He succesfully led the acquisition of LEDVANCE GmBH, formerly SYLVANIA general lighting in USC and OSRAM general lighting global. Lawrence rebuild LEDVANCE into one of the most profitable global lighting player, achieving great results in both consumer and professional applications. “I am very pleased to welcome Lawrence to our Board. His broad experience in lighting, entrepreneurship in promoting human-centric light, and extensive Asian network will be invaluable in advancing the mission of the Good Light Group,” says Jan Denneman, Chair of the Board. Lawrence Lin