We often hear that getting enough daylight is important for our health. But there is another side to the story that is just as important: darkness. In today's world, darkness has become increasingly rare. Our evenings are filled with bright LED lighting, televisions, smartphones, tablets and illuminated streets. While these technologies have made modern life more convenient, they have also dramatically changed the light environment our bodies evolved in. Photo by Maeghan Smulders on Unsplash Just as bright light during the day tells your body to be awake and alert, darkness in the evening signals that it is time to prepare for sleep. Without sufficient darkness, your biological clock struggles to distinguish day from night. Darkness is the other half of good light Our bodies evolved under a simple daily pattern: bright days and dark nights. For thousands of years, the setting sun naturally reduced the amount of light reaching our eyes. This gradual transition triggered biological changes that prepared the body for sleep and overnight recovery. Today, many people spend the day in relatively dim indoor lighting before moving into brightly lit homes in the evening. In other words, we often experience the exact opposite of what our biology expects. Good light is therefore not only about getting enough light during the day. It is equally about protecting darkness at night. Your biological clock depends on darkness Your circadian rhythm is your body's internal 24-hour clock. It regulates nearly every aspect of your physiology, including: sleep and wakefulness, hormone production, body temperature, metabolism, cognitive performance and mood. The strongest environmental cue that keeps this clock synchronised is light. As evening approaches and light levels fall, spheres, specialised light-sensitive cells in the eye signal the brain that night is approaching. This allows the body to begin preparing for sleep. When evening remains bright, this process is delayed. Evening light tells your brain it is still daytime Your brain cannot tell the time by looking at a clock. Instead, it relies on light. Bright evening light sends the message that daytime is continuing. As a result, your body delays many of the processes that normally occur before sleep. This can leave you feeling alert when you would rather feel sleepy, making it more difficult to unwind at the end of the day. Over time, repeated exposure to bright evenings may contribute to a mismatch between your biological clock and your daily schedule. How dark should your evenings be? For optimal circadian health, it is recommended to begin reducing light exposure approximately three hours before bedtime. Aim to keep light levels below 10 lux during this period whenever practical. The goal is not complete darkness throughout the evening, but a gradual reduction in light that signals the end of the day. Protect your nights as well Darkness remains important after you have fallen asleep. If you wake during the night, try to keep light exposure below 1 lux whenever possible. Avoid checking your phone, and if light is necessary, use only the dimmest illumination required for safety.

Most people think of indoor lighting as something that simply helps us see. But good indoor lighting does much more than illuminate a room. The quality, intensity and timing of light have a profound effect on your circadian rhythm, sleep, energy levels, mood, productivity and overall health. Modern life means we spend around 90% of our time indoors, often under lighting that is too dim during the day and far too bright in the evening. As a result, many people experience poor sleep, fatigue and difficulty concentrating without realising that their lighting environment may be part of the problem. Photo by Yuri Efremov on Unsplash Creating healthy indoor lighting does not necessarily require expensive technology. By following a few evidence-based principles, you can support your biological clock and create a healthier home or workplace. Why indoor lighting matters Your circadian rhythm is your body's internal 24-hour clock. It regulates your sleep-wake cycle, alertness, hormone production, metabolism, immune function and many other biological processes. The strongest signal that keeps this clock synchronised is light. Unfortunately, typical indoor lighting often provides only 100 to 300 lux at eye level during the day, far below what our biological clock expects. Meanwhile, our evenings are often filled with bright lighting, televisions and smartphones that tell the brain it is still daytime. The goal of healthy indoor lighting is simple: Bright days Dark evenings Very dark nights Start your morning with bright light The first hour after waking is one of the most important moments for your circadian rhythm. As soon as you wake up, open the curtains and expose your eyes to at least 500 lux of daylight. This tells your brain that the day has started, helping to regulate the production of cortisol and melatonin at the appropriate times. Whenever possible, step outside for a few minutes, as natural daylight is usually much brighter than indoor lighting. Sit near a window during the day Natural daylight changes continuously throughout the day, providing the ideal light signal for your biological clock. When working indoors, try to sit as close to a window as possible. Even on cloudy days, daylight near a window is often significantly brighter than artificial lighting deeper inside a building. If you have the option, position your desk so that daylight reaches your eyes without causing glare on your screen. The closer you are to a window, the more your body benefits from the changing intensity and spectrum of natural daylight. Use at least 500 lux when daylight is insufficient Not every building has large windows, and during winter there may simply not be enough daylight available. When natural daylight is insufficient, use electric lighting that provides at least 500 lux at eye level. This helps provide a stronger daytime signal to your circadian rhythm and supports concentration, alertness and productivity. Many offices, schools and homes are illuminated far below this level, even though brighter daytime lighting can make a significant difference to how people feel and perform. Healthy indoor lighting provides the right amount of light at the right time and, where possible, reflects the changing characteristics of natural daylight. Dim the lights three hours before bedtime Healthy lighting is not only about getting enough light during the day, it is equally important to reduce light exposure in the evening. Approximately three hours before bedtime, begin lowering your light levels to below 10 lux whenever possible. This allows your body to begin producing melatonin, the hormone that prepares you for sleep. Creating a darker evening environment helps your body recognise that bedtime is approaching. Keep nights as dark as possible \During the night, darkness is just as important as daylight is during the day. If you need to get out of bed, try to keep light exposure below 1 lux whenever possible. Bright lighting during the night can interrupt melatonin production and signal to your brain that it is daytime. Avoid checking your phone if you wake during the night, as even short exposure to bright screens can affect your biological clock. If night lighting is necessary, choose the dimmest light possible and avoid looking directly at it. For decades, lighting design focused primarily on visual comfort and energy efficiency. Today, we know that healthy indoor lighting also plays a crucial role in supporting our circadian rhythm, sleep quality, mental wellbeing, productivity and long-term health. The perfect indoor lighting environment does not need to be complicated. By creating bright mornings, well-lit days, dim evenings and dark nights, you give your biological clock the signals it has evolved to expect. Good light is not simply about seeing better, it is about helping your body function at its best, every day.

When most people think about lighting, they think about vision. We switch on a lamp to read a book, illuminate a workspace or make a room feel cosy. For more than a century, lighting has been designed primarily to help us see better. But science has revealed that light does far more than illuminate our surroundings. It also tells our body when to be awake and when to prepare for sleep. In other words, good light isn't only about seeing better, it's also about sleeping better. Photo by Shadrina Izzati on Unsplash Light is the body's most powerful clock Every cell in your body follows a roughly 24-hour rhythm, known as the circadian rhythm.This internal timing system regulates much more than sleep. It influences alertness, hormone production, body temperature, metabolism, digestion and even your mood and energy. To stay synchronised with the outside world, your biological clock depends on one signal above all others: Light. Every morning, the light entering your eyes tells your brain that a new day has begun. As daylight increases, your body becomes more alert. As evening falls and light levels decrease, the opposite happens and the dim light shows your body it’s time to prepare for a restful night's sleep. Your eyes don't just see, they tell time For many years, scientists believed the eye had only one purpose: vision. Research over the past two decades has shown that the eye has another crucial role beyond vision. Specialised light-sensitive cells in the retina, scientifically known as ipRGCs, continuously measure the timing and spectrum composition of light around us. For simplicity, we call these cells ‘spheres’. These cells don't create images. Instead, they send information directly to the brain's master biological clock, allowing your body to distinguish between day and night. Every glance out of a window, every walk outdoors and the kind of light in which you spent every evening influences this system. Bright days and dark nights lead to better nights Healthy sleep begins with the light your eyes receive during the day. Receiving plenty of bright daylight during the morning and throughout the day strengthens your biological clock. A well-synchronised clock makes it easier to become alert during the day and sleepy at night. Spend at least two hours a day in daylight or under electric lighting that provides at least 500 lux at eye level. During the three hours before bedtime, keep light levels below 10 lux. At night, keep light levels below 1 lux and avoid screens whenever possible. Sleep doesn't begin when you get into bed. It begins with the light your eyes receive throughout the day. Modern life has reversed nature Humans evolved under an environment with bright daylight, gradually darkening evenings and dark nights. Modern life often looks very different. Many of us spend our days indoors under relatively dim lighting before returning home to brightly lit living rooms, televisions, smartphones and tablets. From the perspective of our biological clock, this sends mixed messages. Our days are often too dim, while our evenings are too bright.This weaker distinction between day and night can make it more difficult for the body to recognise when it should be awake and when it should prepare for sleep. The strongest circadian rhythm comes from creating a clear contrast: Bright days. Dark nights. Good light means the right light at the right time The benefits of good light and a well-aligned circadian rhythm include: better sleep, more energy, a more positive mood, sharper concentration, and better overall health. Does this lighting support human health? Offices, schools, hospitals, care homes and homes themselves are beginning to recognise that lighting should support not only visual performance, but also sleep, wellbeing and long-term health. This shift marks a new era in lighting design, one where human biology becomes just as important as energy efficiency or aesthetics.

As of 1 September 2026, Bruno Smets has stepped down as Treasurer and Board member of the Good Light Group Foundation. He is succeeded by Kees van Meerten. Bruno was one of the co-founders of the Good Light Group Foundation in 2019 and has played an important role in the Foundation’s development over the past seven years. We are very grateful for his commitment, support and contribution from the very beginning. Kees brings extensive experience in the lighting industry as well as in trade associations. He has already been involved in several Good Light Group Board meetings over recent months. We are pleased that Kees has agreed to take over Bruno’s responsibilities as Treasurer and Board member and look forward to working with him. We thank Bruno warmly for everything he has contributed to the Good Light Group and welcome Kees to the Board.

Following his recent retirement from the Board, we are pleased that Bruno Smets will remain closely involved with the Good Light Group Foundation as an Advisor. Bruno will focus specifically on the socio-economic benefits of good light: helping us better understand and communicate the wider value that good light can bring to people, organisations and society. As a co-founder of the Foundation and our Treasurer since 2019, Bruno brings valuable experience and continuity to this new role. We look forward to continuing our work together.

Take a moment to think about your average day. You wake up in your home, travel to school or work, spend the day in an office or classroom, return home, eat dinner and relax in front of the television before going to bed. For many people, this means spending 90% of the day indoors. From an evolutionary perspective, that's a remarkable change. For hundreds of thousands of years, humans evolved almost entirely outdoors. Our bodies, brains and biological clock developed under the ever-changing rhythm of natural daylight. Yet within just a few generations, we have become an indoor species. Our homes and workplaces have become more comfortable and efficient, but our biology has not adapted to this new environment. Our need for daylight remains much the same as it has always been. How did we become an indoor generation? Our ancestors spent most of their lives outside. They hunted, gathered food, farmed and travelled under the open sky. Their days were governed by sunrise and sunset, exposing them to bright daylight during waking hours and darkness at night. Today, life is very different. Many of us work behind a desk, study in classrooms, commute by car and spend our evenings watching television or using digital devices. Technology has allowed us to work, communicate and entertain ourselves without ever going outside. Ironically, the more advanced our society has become, the less natural daylight many of us experience. Indoor light is much dimmer than daylight One of the biggest misconceptions about lighting is that indoor enviroenments are bright enough. For vision, they usually are. For your biological clock,they are often not. A well-lit office typically provides around 300 to 500 lux on the desk. The amount of light actually reaching your eyes is often lower, particularly if the lighting is indirect or you are sitting away from a window. Now compare that with daylight: A cloudy day outdoors can easily provide 10,000 lux. A sunny day often exceeds 100,000 lux. Even sitting near a window can expose you to several times more light than sitting deeper inside the same room. The difference is enormous. Our biological clock evolved under daylight conditions that are often 20 to 200 times brighter than what many people experience during the day. Why this matters for your body Your biological clock relies on strong daytime light to know when it's daytime. When the light during the day indoors is too dim, the brain receives a weaker or no signal. As a result, the distinction between day and night for your body becomes less clear. This can affect many aspects of health, such as your sleep quality, daytime alertness, mood and energy levels. Your biological clock starts running behind the time of day. We make evenings too bright The problem doesn't stop there. While our days are often too dim, our evenings have become much brighter than they were throughout most of human history. LED lighting, televisions, smartphones and tablets allow us to continue exposing our eyes to biologically active light long after sunset. This creates exactly the opposite pattern from what nature intended, days that are too dim and nights that are too bright. For our biological clock, this weak contrast can make it harder to know when to be alert and when to prepare for sleep. We weren't designed for indoor daylight Our visual system and biological clock evolved under a highly dynamic lighting environment. Every day, nature provided bright mornings, extremely bright midday light, gradually dimmer afternoons, warm sunsets and dark nights. Indoors, many people experience almost the opposite: similar light levels all day and very little variation in intensity or spectrum. Our eyes, and especially the spheres (ipRGCs) in the retinae of our eyes, which regulate the biological clock, expect a much stronger daily rhythm than most indoor environments provide. Getting outside doesn't mean spending hours outdoors The good news is that you don't have to spend your entire day outside to make a meaningful difference. Small habits can significantly increase your daily light exposure. Follow our Six Steps to Good Light here. These six steps help strengthen your circadian rhythm and reinforce the natural distinction between day and night.

We often talk about getting “enough light” during the day. But what does enough actually mean? Is the light in your home or office bright enough? Is sitting near a window enough? And does everyone need the same amount of light? The answer depends on several factors, including the time of day, where the light is measured and, importantly, your age. Photo by Beth Macdonald on Unsplash First things first: what is lux? Lux is a measure of how much light falls on a surface. One lux equals one lumen per square metre. When we talk about light for health and your biological clock, however, the amount of light on your desk isn’t necessarily what matters most. Your body responds to the light that reaches your eyes. That is why we recommend measuring light vertically at eye level, facing the direction you normally look. An office might have 500 lux on a desk, for example, while the amount of light reaching your eyes could be considerably lower. How much light do you need during the day? As a practical rule of thumb, younger adults should aim for at least 500 lux at eye level during the day. This might sound like a lot, especially compared with many indoor environments, but it is still relatively dim compared with being outdoors. Even an overcast day outside can provide thousands of lux. Bright daytime light helps tell your biological clock that it is daytime. This supports the daily rhythm that regulates alertness during the day and prepares the body for sleep at night. If you can, spend plenty of time outdoors and sit or work close to a window during the day. When there is not enough daylight available, use electric lighting that provides sufficient light at eye level. As we age, we need more light Our light requirements change as we get older. As the eye ages, the lens becomes less transparent and the pupil tends to become smaller. As a result, less light reaches the retina. This means an older person may need considerably more light than a younger person to receive a similar amount of light at the eye. As a practical guideline, older adults should aim for around 1,000 lux at eye level during the day. So while approximately 500 lux may be suitable for a younger person, an older person may benefit from roughly twice that amount. This becomes particularly important because older adults often spend more time indoors, where light levels can already be much lower than outside. light indoors is not the same as daylight Our perception can be misleading. A room can feel perfectly bright while providing relatively little light to the eyes. Typical indoor lighting is much dimmer than natural daylight. While an indoor environment may provide a few hundred lux, outdoor daylight can easily reach several thousand or even tens of thousands of lux. This is one reason why simply switching on a ceiling light is not always enough. During the day, make daylight your first choice. Go outside regularly, open the curtains and position yourself close to a window. If daylight is limited, particularly during dark winter months, supplement it with good electric lighting. More during the day, less in the evening Getting the right amount of light is not just about brightness. Timing matters too. During the day, your body needs plenty of light. In the evening, it needs the opposite. A simple daily light rhythm could look like this: Younger adults during the day: aim for at least 500 lux at eye level Older adults during the day: aim for around 1,000 lux at eye level Three hours before bedtime: keep light levels below 10 lux During the night: keep light levels below 1 lux and avoid screens whenever possible In other words: bright days and dark nights. Check your own light levels Want to know how much light actually reaches your eyes? Measure the light vertically at eye level using a lux meter. You can also use a lux meter app on your phone to get an indication, although smartphone apps are not always accurate and can overestimate light levels. Try measuring in different places: at your desk, next to a window, in the middle of the room and outside. You might be surprised by just how big the differences are.

We are pleased to announce that Roger Sexton has become an Advisor to the Good Light Group. After several years as a member of our Board, Roger continues to support the Good Light Group, with a particular focus on technical marketing, industry relations and partnerships.

Our Chairman Jan Denneman wrote the commentary of LED professional Review #116. This issue is focussing on the good light. In his commentary he explores why good light could become the next major growth story for the lighting industry. After decades of innovation focused on energy efficiency, LEDs, digital controls and intelligent lighting systems, the industry is entering a new phase. Increasing scientific evidence shows that light affects much more than our ability to see: it can influence our sleep, alertness, wellbeing and performance. With people spending almost 90% of their lives indoors, the quality of indoor light represents an important opportunity. Good light builds on the essential principles of visual comfort, aesthetics and energy efficiency, while adding another dimension: creating indoor environments that work in harmony with human biology. Rather than focusing on a single metric or technology, good light brings together daylight, electric lighting, architecture, controls and user behaviour to better support people throughout the day and night. As Jan explains, this shift could redefine the value of lighting: from infrastructure that simply helps us see to an environmental factor that actively supports health, wellbeing and human performance. At the same time, it creates opportunities for new lighting solutions, products and services, laying the foundation for sustainable growth across the lighting industry. Read the full commentary

If you've searched for ways to improve your sleep, you've almost certainly come across blue-light-blocking glasses. They come in all shapes and colours, from almost clear lenses to bright orange or deep red ones, all promising better sleep, less eye strain and improved wellbeing.But do they really work?The answer is more nuanced than many advertisements suggest. Photo by nacer eddine on Unsplash Why light colour matters Our eyes do much more than allow us to see. They also contain specialised light-sensitive cells, which we call spheres, that communicate directly with the brain's biological clock, located in the suprachiasmatic nucleus (SCN). These cells are particularly sensitive to short-wavelength (blue) light. During the daytime, this is exactly what we need. Exposure to bright, blue-enriched daylight helps keep us alert, improves mood, supports cognitive performance and strengthens the alignment of our circadian rhythm. In the evening, however, the situation changes. If we continue exposing ourselves to bright, blue-rich light from LED lighting, televisions, computers or smartphones, our brain may interpret this as daytime. This can delay the body;s preparation for sleep. The goal in the evening is therefore not to avoid all light, but to reduce the amount of biologically stimulating light reaching the eyes. Dim the lights and choose a warmer light tone. Do blue-light-blocking glasses really work? Yes, but only under the right circumstances. Blue-light-blocking glasses can reduce the amount of short-wavelength light reaching the retina. Research has shown that wearing them during the three hours before bedtime may help some people fall asleep more easily, particularly when they are exposed to bright artificial light during the evening. However, they are not a substitute for good lighting habits. If you're sitting in a brightly lit room with hundreds of lux reaching your eyes, simply wearing lightly tinted glasses may have only a limited effect. Likewise, wearing blue-blocking glasses during the day is generally not advisable, as daytime exposure to blue-rich daylight is essential for maintaining a healthy circadian rhythm. Different glasses Clear or lightly yellow lenses Many glasses marketed for computer use have nearly transparent or slightly yellow lenses. These usually block only a small percentage of blue light. They may slightly reduce glare or visual discomfort for some users, but they generally have little effect on circadian timing. For sleep improvement, their impact is likely to be modest. Amber or orange lenses Amber and orange lenses block a much larger portion of blue wavelengths. These are considerably more effective at reducing circadian stimulation during the evening and are commonly used in scientific research investigating evening light exposure. Wearing them for approximately three hours before bedtime may help support the body's natural transition into the biological night, particularly when exposure to bright indoor lighting or screens cannot be avoided. Deep orange or red lenses The darkest orange or red lenses block almost all blue light and often a significant part of the green spectrum as well. These provide the strongest reduction in circadian stimulation and are sometimes used by shift workers, people with circadian rhythm disorders or individuals who are particularly sensitive to evening light. However, they also significantly alter colour perception and are generally unnecessary for most people. Are they better than reducing screen time? No. For most healthy people, the priority should be achieving a strong contrast between day and night. That means: Plenty of bright daylight during the morning and afternoon. Bright indoor lighting when needed during the day. Dim, warm lighting in the evening. Avoiding unnecessary screen use during the last three hours before bed or switching your screens to night mode. Darkness during sleep. Blue-light-blocking glasses are best viewed as a practical tool for situations where reducing evening light exposure isn't possible, for example, if work requires computer use or if you are travelling. For most people, getting plenty of daylight in the morning is likely to be more important for healthy sleep than simply blocking blue light at night. Rather than asking, "Should I buy blue-light glasses?", a better question is: "Am I getting enough bright light during the day, and am I allowing my evenings to become progressively darker?"

Have you ever noticed how different the world looks at sunrise compared to midday or sunset? In the early morning, daylight has a warm, golden glow. Around noon, it appears bright and crisp. As evening approaches, the light becomes soft, orange and eventually fades into darkness. Photo by Sasha Freemind on Unsplash These changes are more than beautiful scenery. They are powerful biological signals that have shaped human physiology for millions of years throughout our evolution. Our bodies have evolved under the predictable daily rhythm of the sun, and our biological clock still relies on these changing light conditions to regulate sleep, alertness, mood, hormone production and overall health. Understanding how the light spectrum changes throughout the day helps explain why timing matters just as much as the amount of light we receive. What is the light spectrum? Visible light consists of many different wavelengths, each perceived as a different colour. The spectrum ranges from shorter wavelengths, which we see as blue and violet, to longer wavelengths, which appear yellow, orange and red. Sunlight contains all of these colours, but their proportions change throughout the day. Our eyes use this information from the spectrum not only for vision but also to inform the brain about the time of day. Specialised light-sensitive cells in the retina, called intrinsically photosensitive retinal ganglion cells (ipRGCs), or as we call them: spheres, communicate directly with the brain's master biological clock, helping regulate circadian rhythms. Sunrise: A gentle wake-up call Just before and after sunrise, sunlight travels through a thick layer of the Earth's atmosphere. During this journey, much of the shorter blue wavelengths are scattered, allowing more longer wavelengths, reds, oranges and warm yellows, to dominate what we see. Sunrise is an important signal for the biological clock. Even relatively low levels of natural daylight are far brighter than typical indoor lighting and begin preparing the body for the day ahead. As the sun rises, the intensity increases rapidly and more blue wavelengths become available, helping promote alertness. Morning: Building biological momentum As the sun climbs higher, daylight becomes brighter and richer in shorter wavelengths. This combination of increasing light intensity and greater blue content tells the brain that daytime has fully arrived. For this reason, spending time outdoors in the morning is one of the most effective ways to strengthen your biological clock. Midday: Nature's strongest light Around midday, sunlight reaches its highest intensity. The sun is high in the sky, meaning its light passes through less atmosphere. As a result, the full spectrum reaches the Earth's surface with relatively little filtering and is rich in blue light. Even on cloudy days, outdoor light often provides many times more illumination than a well-lit office. The brightness of midday light plays a crucial role in reinforcing the difference between biological day and biological night. Afternoon: A gradual transition As afternoon progresses, the sun slowly moves lower. The spectrum begins shifting again as sunlight passes through more atmosphere. The proportion of blue light gradually decreases while warmer colours become increasingly prominent. At the same time, overall light intensity starts to decline. This gradual change acts as a natural transition, allowing the body to begin preparing for the evening without an abrupt shift. Sunset: Preparing for night During sunset, the atmosphere filters out much of the shorter blue wavelengths.The remaining sunlight appears rich in orange and red tones, creating the warm colours often associated with the "golden hour." This warmer spectrum, combined with rapidly decreasing light intensity, signals to the brain that daytime is ending. As darkness approaches, this stimulates the body to prepare for sleep. The transition from bright days to dim evenings is one of the most consistent environmental signals our circadian system has evolved to recognise. Night: Darkness is part of the spectrum tooAlthough we often think about daylight, darkness is equally important. For thousands of generations, humans experienced nights illuminated only by moonlight, starlight and fire, all relatively dim light sources with very limited biological impact compared to modern lighting. Today's homes often remain brightly illuminated well into the evening using LED lighting that contains substantial amounts of blue light. This creates an environment that no longer resembles the natural progression from day to night. Instead of experiencing a gradual reduction in light intensity, many people effectively extend their biological daytime by several hours. What modern lighting gets wrong Modern indoor lighting is remarkably consistent. Many offices, homes and public spaces use the same lighting throughout the entire day, often with similar brightness and colour temperature from morning until bedtime. This is very different from the dynamic lighting environment humans evolved under. This weak distinction between day and night can reduce circadian contrast and make it more difficult for the body to know when to be alert and when to prepare for sleep. The body's response depends on the entire daily light history, not just a single moment. Six steps to good light While we cannot always work outside, we can design our environments to better reflect the natural rhythm of daylight. Give your eyes a few minutes of bright daylight in the morning. This signals to your body that the day has begun. Spend at least two hours outdoors during the day, especially in the morning. Sit as close to a window as possible during the day. Not enough daylight? Use electric lighting that provides at least 500 lux at eye level. Keep light levels below 10 lux three hours before bedtime. Dim the lights, close the curtains, avoid bright screens, and switch your phone to night mode. Keep light levels below 1 lux at night, even when getting out of bed, and avoid screens whenever possible. These simple changes help recreate the natural contrast between biological day and biological night.

Most people think our eyes exist for one purpose: to help us see. In reality, our eyes have another equally important job. Besides creating vision, they constantly measure the light around us to help regulate our biological clock, hormones, alertness, mood and sleep. To do this, the retina contains three different types of light-sensitive cells. Two are responsible for vision: rods and cones. The third type, known scientifically as intrinsically photosensitive retinal ganglion cells (ipRGCs), but which we’ll simply call spheres, doesn't contribute to vision. Instead, it helps our body understand when it is day and when it is night. Rods: Seeing in the dark Rods are the most sensitive light receptors in the eye. They allow us to see when light levels are very low, such as at dusk, under moonlight or in a dimly lit room. Rods are excellent at detecting brightness and movement, but they cannot distinguish colours. That's why the world appears almost black and white at night. You have around 120 million rods in each eye, making them the most numerous light-detecting cells in the retina. Their job is simple: help you see when there isn't much light. Cones: Seeing colour and detail Cones take over when there is plenty of light. They allow us to perceive colours, read text, recognise faces and appreciate fine details. Humans have three types of cones, each responding most strongly to different parts of the visible spectrum: S-cones are most sensitive to shorter (blue) wavelengths. M-cones respond primarily to middle (green) wavelengths. L-cones respond mainly to longer (red) wavelengths. Your brain combines information from these three cone types to create the rich colour vision we experience every day. There are approximately 6 million cones in each eye, concentrated mainly in the centre of the retina where visual acuity is highest. Spheres: Your body's light sensors Then there are the spheres. Unlike rods and cones, spheres don't help you recognise faces, read books or distinguish colours. Instead, they measure the overall lighting environment and send that information directly to the brain's master biological clock, located in the suprachiasmatic nucleus (SCN). You could think of them as your body's built-in light meter. Their primary task is to let the body know: Is it morning or evening? Is it bright enough to be daytime? Should you stay alert? Is it time to get ready for sleep? Rather than creating vision, spheres help synchronise your body's daily rhythms with the outside world. A well-synchronised circadian rhythm helps you sleep better during the night, have more energy during the day and brighten up your mood. This is why it’s so important to spend time outdoors during the day so your spheres can do their job.