Nov 30, 2020

What is Circadian Lighting and How Does it Work?

Category: Illumination
People spend more time indoors than ever before — in fact, a 2001 study by UC Berkley and the EPA reported that we spend 87% of our time indoors.
People spend more time indoors than ever before — in fact, a 2001 study by UC Berkley and the EPA reported that we spend 87% of our time indoors.

Guest Blog: Bios Lighting

Circadian lighting is a term that has gained popularity in recent years – you may have also heard it referred to as ‘human-centric lighting’ or ‘tunable lighting’ or mentioned in the context of biophilia. While these are more often used as buzzwords, circadian lighting is an area of real research, science, and innovation.

The term “circadian rhythm” refers to functions within the body that occur approximately every 24-hours. The word ‘circadian’ comes from Latin with ‘circa’ meaning ‘around’ and ‘diēm’ meaning ‘day’. While circadian lighting is a relatively new term, circadian rhythms have been observed for centuries in both plants and animals.

Circadian lighting refers to lighting that is designed to have a biological impact on the human circadian system. Circadian lighting sends signals to the master clock in the brain, telling our bodies when it is daytime and when it is night and what functions to perform at various times of the day. A healthy circadian rhythm is associated with improved long-term health and helps promote better sleep at night, allowing our brains to repair our bodies as well as our minds.

The goal of circadian lighting is to provide sufficient light signals to the brain to help reinforce the natural light/dark signals we would receive from the sun if we spent more of our time outdoors. A simple mantra to help capture the goal of circadian lighting is, “brighter days and darker nights”. Circadian lighting should provide a strong daytime light signal, telling our brain that it is daytime and to perform all the functions it needs to during the day. At night, we want to reduce that daytime light signal to help our bodies wind down, telling our brain to perform nighttime functions.

Light and Circadian Rhythms

Humans are light-seeking creatures. We have evolved to rely on sunlight as the primary signal that helps regulate the master-clock in our brains. This master-clock controls all kinds of biological functions – from gene expression to daily hormone production in our bodies.

In order for our bodies to receive a meaningful circadian light signal, light must enter the eye so it can be transmitted to the master clock in the brain. Every day our bodies prioritize certain biological functions at different times of day — Did you know that every cell in our body has its own clock?! That means every cell in your body relies on the master-clock to help regulate when they are active and when they should rest.

Ideally, we would spend our days in the sunshine and our nights under the stars. When we receive good daytime light signals the master-clock in our brain is able to tell our bodies to perform all kinds of functions – regulate body temperature, blood pressure, regulate our metabolism, help us to feel alert, and much more. In the evening, after sunset, our bodies should also receive proper darkness signals or lower light signals. This tells the master-clock that the day has ended and to begin nighttime functions – melatonin production, changes to body temperature, metabolism, cortisol levels, and much more.

For many people, their only exposure to light during the day is from artificial lighting in our workplace, classrooms, or home. These lighting conditions may be sufficient to allow us to see and perform tasks, but research has shown that they are woefully insufficient at providing the daytime circadian light signals our bodies need. Sustained exposure to this type of low-quality light can have long-term adverse effects like low mood, fatigue, lack of concentration, and poor sleep.

Additionally, rather than winding down under the stars, we remain very active in the night and often spend evenings hours under the same lighting conditions we had during the day.

Ironically, the artificial light that was too dim for daytime circadian stimulation is now too bright to allow our bodies to wind down. We find ourselves living in this perpetual state of circadian limbo – where our days are too dim to clearly signal the master-clock for the daytime tasks and our nights are too bright to signal the master-clock to begin nighttime tasks.

The Problem: Chronic Indoor Lifestyle

People spend more time indoors than ever before — in fact, a 2001 study by UC Berkley and the EPA reported that we spend 87% of our time indoors3. If we think back in human history, we evolved into our natural surroundings – waking with the sun and going to sleep soon after sunset. Fast forward to today — we no longer maintain this critical connection to the sun or daylight and are spending the vast majority of our time under artificial lighting.

From a lighting perspective, we know our biology relies heavily on our relationship with the sun to repair our bodies and our minds. In fact, daylight is the strongest signal our bodies can receive to help regulate our circadian rhythms and send signals to our brain telling our bodies when to perform different functions.

Spending most of our time indoors means that we no longer receive this critical light signal and research shows that traditional indoor lighting does not provide the light signals our bodies need for healthy circadian rhythms.

Is Circadian Lighting Real?

Yes! There is a special photopigment in the eye – melanopsin – which communicates directly with the master clock in the brain. Melanopsin is most sensitive to 490nm – which translates to the “sky-blue” region of the visible spectrum – and transmits non-visual information to the master clock in our brains. Lighting that doesn’t target this region of the visible spectrum simply will not be as effective at targeting melanopsin or providing a circadian signal to the brain4.

Circadian Lighting and Productivity

Lighting to optimize circadian health continues to gain popularity and many businesses are interested in circadian lighting as a means of and understanding whether happier, more energized workers result in increased productivity. From a business standpoint, the benefits of circadian lighting go beyond wellness and offer a new way to increase employee retention rates and harness a more productive and motivated workforce.

Some studies suggest circadian lighting can promote productivity in the workplace, citing an increase in people’s energy and vitality – particularly at the start and middle of the day1. Research continues to look at methods for bringing key aspects of daylight indoors and how that might have a beneficial effect on memory recall and other tasks.

Circadian Lighting and Wellness

Wellness is becoming more of a central theme in the design and a critical part of each of our daily routines. We know that subtle changes in lifestyle can allow us to feel better, which has a significant ripple effect on our overall feelings of well-being. Circadian lighting is one way we can design better spaces to create subtle, yet meaningful change in our lifestyle. With true circadian lighting, our bodies are getting better daytime light signals which can help improve sleep, mood, and our overall sense of well-being.

Circadian lighting sends signals to our internal master clock which regulates all kinds of hormone production, telling our bodies when and what to do during the day and even at night while we sleep. Sending strong light signals to the master clock promotes better sleep, reduced fatigue, and increased concentration which all contribute to how motivated we feel2.

Together, BIOS and Lumileds are bringing their expertise in the science of circadian lighting and LED design and manufacturing to the human-centric lighting ecosystem. Early in the coming year, new LEDs will be available that open up exciting opportunities for luminaire manufacturers and others to provide true circadian lighting.


1. Figueiro PhD, M., Steverson, B., Heerwagen PhD, J. and Rea PhD, M., (2017). Circadian Light And Its Impact On Alertness In Office Workers: A Field Study. [online] <>

2. Court, MBA., A., Pearson, Prof., A. and Frewin, Prof., D., (2010). The Effects Of Exposure To Natural Light In The Workplace On The Health And Productivity Of Office Workers: A Systematic Review Protocol. [online] Walters Kluwer. <>

3. Klepeis NE, Nelson WC, Ott WR, et al. The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants.J Expo Anal Environ Epidemiol 2001;11:231-52.<>

4. Lucas, R. J., Peirson, S. N., Berson, D. M., Brown, T. M., Cooper, H. M., Czeisler, C. A., … Brainard, G. C. (2014). Measuring and using light in the melanopsin age.Trends in Neurosciences, 37(1), 1–9. doi: 10.1016/j.tins.2013.10.004.<>