As we adhere to strict physical distancing measures to slow the spread of COVID-19, most of us are also spending more time indoors. This means more time spent in a “biological cave” – although indoor lighting may appear appropriate, the intensity and temperature of the light might be inadequate considering the time of day. This can send confusing signals to our brain, negatively impacting our sleep, well-being, and health and thus throw our body’s circadian system into chaos.

The cycle of sleep and wakefulness is one of the key human behaviours. We spend about a third of our lives asleep and cannot survive without it. When asleep, our brain memorises and processes information. Our body clears toxins and repairs itself, allowing us to function properly when awake. Light is the most important external factor affecting sleep and plays a central role in regulating circadian rhythm, the body’s internal clock that signals when to be alert and when to rest. Light also affects the production of melatonin, an essential sleep-promoting hormone.

What are your circadian rhythms?

Our bodies have evolved over thousands of years to follow a natural 24-hour light-dark cycle. We naturally sleep when it gets dark and wake when the sun rises. Your sleep-wake circadian rhythm is an internal clock that runs constantly, cycling between alertness and sleepiness.

The hypothalamus controls each person’s circadian rhythm by receiving signals from the eyes that report when it’s daytime and nighttime and also controls the amount of melatonin released to correlate sleepiness with darkness and alertness with lightness. Drowsiness increases with rising melatonin levels, which is one way that this hormone facilitates sleep.

Our eye detects the light and dark cycle within our environment. This is so powerful that people who have very severe eye damage can find their body clock is thrown off, leading to sleep problems. We have 37 trillion cells in our body, each with its own time clock. For our bodies to sleep properly, it’s vital that each cell is properly synchronised. This is the function of the suprachiasmatic nucleus (SCN), a tiny area of the brain located within the hypothalamus.

“Light is this really strong time cue that’s used by the body to set the clock. As a result, it means that when we’re exposing ourselves to artificial light we’re actually pushing our clock forward and backward inappropriately.”

Stuart Peirson, a neuroscience professor and
circadian rhythm expert at Oxford University

Our circadian rhythms start to respond to light at around 100 lux, which is about the brightness of a dim room. Most office buildings are designed to have a light intensity of 300 to 500 lux, but that’s nothing compared to a bright sunny day with a light intensity 100-times that. Even on a cloudy day, the light intensity can be 1,000 lux.

Receiving light at the wrong time of day (light pollution) can disturb the circadian clock. Artificial light at night, from indoor lighting to electronic devices (e.g. computer or phone screens) suppresses the release of melatonin, essential for sleep. It can also lead the clock to synchronise to the artificial night light instead of daylight (in particular when the latter is in short supply), potentially delaying our sleep into the early morning hours.

The circannual clock

Similar to daily circadian rhythms, annual rhythms are controlled in part by exposure to earth’s light-dark cycle resulting from the 23.5° tilt of the earth on its axis, its daily rotation, and the annual orbit around the sun, as well as from climatic weather patterns.

Circannual rhythms have evolved as genetically programmed adaptive timing mechanisms to allow organisms to use favorable seasons to reproduce and grow, and survive through unfavorable seasons.

Why is it important to maintain a healthy circadian rhythm?

Sleep experts at the Stress Research Institute at Stockholm University have produced research that shows that more than one in ten Swedes have a sleep disorder. This is double the amount in Sweden 30 years ago. According to Helena Schiller, a PhD student at the Stress Research Institute, one of the reasons is the change in our way of life. “It’s about a 24-hour society that allows you to stay connected around the clock, and globalization that blurs day and night by allowing people to work with people in countries that are in a different time zone than ours.”

Lack of light is a primary cue that signals sleep. A healthy circadian rhythm and proper sleep are crucial not only for our mental well-being but also for our physical health, including our immune system functioning. Sleep not only reduces our risk for infection but can also improve outcomes once we are infected. This has been cleverly shown in experiments where participants were exposed to the rhinovirus, a common cold virus. Participants who reported less sleep had a greater chance of subsequently developing symptoms of the common cold.

An irregular circadian rhythm can have a negative effect on a person’s ability to sleep and function properly, and can result in a number of health problems, including mood disorders such as depression, anxiety, bipolar disorder, and seasonal affective disorder. Around 20.9 million Americans adults aged 18 and older have a mood disorder.

Misalignment of the circadian rhythm may also provoke anxiety. Most of the evidence on the relationship between mood problems and circadian rhythm comes from studies of shift workers, whose sleep periods are out of sync with their circadian rhythm. Multiple studies show an increased prevalence of depression in night-shift workers. One meta-analysis showed that night-shift workers are 40% more likely to develop depression than daytime workers. Conversely, circadian rhythm disturbances are common in people with depression, who often have changes in the pattern of their sleep, their hormone rhythms, and body temperature rhythms.

Depression as a mental illness which leads to medical issues and health disorders have a series of negative effects on an individual’s functions including feeling and thinking. It originates from genetic, hormonal or physiological factors, or it may be made by stressful environments or life conditions. Moreover, the disruption of circadian rhythms can contribute to the beginning of depression. Though the etiology of depression is complicated, circadian factors might have a significant effect in the process. As a disturbance of circadian rhythm could be due to lighting conditions and lifestyle in individuals who were exposed to a wide range of mood disorders including impulsivity, mania and depression.

How to Design Lighting for Health and Well-being

The benefits of electric lighting soon ensued as night shift work was introduced. By the end of the 20th century, technology provided people with additional sources of night-time light, including television, computer screens, e-readers, smartphones, and tablet computers. Today, >80% of humans and 99% of those living in the US or Europe experience significant night-time light pollution.

To promote a healthy sleep-wake schedule, architects strive to direct as much natural light into spaces as possible. To do this, you can install skylights and floor-to-ceiling windows, especially in large community areas such as the front lobby, cafeteria, and lounge. Architects can also help you site the building so that these community spaces get the greatest amount of direct sunlight when the highest number of visitors enter the space.

However, not every building or home can be designed with floor-to-ceiling windows and skylights. Budget constraints, privacy considerations, and other factors might make it impossible to direct enough natural light into the building. In such cases, artificial lighting is used instead.

Thanks to advancements in color tuning and lighting control technology, it is now possible to imitate the complex nature of daylight indoors.

Lighting control systems can mirror the variations in intensity and color that are intrinsic in the sun’s daily cycle and deliver these different types of light at the right time of the day. Lighting controls pave the way for interior spaces that support the internal clock of the human body, offering a healthier and less disruptive alternative to the traditional built environment.

Natural daylight is a dynamic light source. Over the course of the day, it transitions through different intensities and colors. Beginning in the morning, the natural light level builds in intensity toward its noontime high, and the color temperature moves quickly from a warm, orange-yellow at dawn to a cooler, crisper blue-white. In the afternoon, the intensity of the light from the sun wanes until sunset, and the color temperature warms from a cool white into the richer yellow glow of dusk.

A circadian lighting system is, in essence, an artificial ‘sunrise to sunset’ that travels through illuminance levels and color spectrums from a warm color spectrum (1,400K) to brighter, cooler (6,500K and upwards) and back again.

Studies have suggested that blue light is an especially powerful melatonin suppressant. Melanopsin, the pigment that helps eye cells assess light brightness, is particularly sensitive to shorter, cooler wavelengths like blue light, which some research says means blue light may affect the body more dramatically than other hues. One highly cited study from 2014 showed that using a blue-light-emitting iPad before bed suppresses melatonin, while reading a traditional book does not. IPad readers started producing melatonin 1.5 hours later than usual the next day.

There can be important differences between types of artificial light as well. Some types have more illuminance and brightness. That said, even light that appears to have the same brightness may, in reality, have a different wavelength, changing how it’s perceived by the eye and brain.

Tailoring Lighting Throughout the Home or Office

If you don’t have access to daylight, studies have also found that working under “blue-enriched” light bulbs that are at 5,000K and up actually increases work performance by supporting mental acuity, vitality and alertness while reducing fatigue and daytime sleepiness. Researchers at the University of Greenwich, Felderman and Keatinge, found in a two-month study that the workers they put under “blue-enriched light bulbs” reported feeling “happier, more alert and had less eye strain.”

Other benefits of blue light include lowering melatonin, which is created in our glands and basically puts us to sleep. This lower level of melatonin keeps people alert in the same way coffee does.

With so many brainpower benefits, blue or cooler light should be kept in brainstorming rooms where you want people to feel invigorated and excited to share their ideas, according to Felderman and Keatinge.

On the other hand, since warmer tones tend to create a sense of comfort, use this kind of lighting in more intimate settings where you want to feel calm and relaxed, perhaps in a meeting room for an office setting or the family room at your home.

Tips on how to choose your lighting system:

DIODES: The chipset used in the fixture must replicate the sun spectrum of light during the day to release energy and cortisol then almost eliminate all blue light at night while providing a warm amber glow to promote melatonin growth.

OPERATING SYSTEM: Your system needs to be simple to program, use and maintain both using an automated schedule and manual controls that override the automated system. If app based, the app needs to be intuitive and simple to adjust schedules. The system must allow for remote access for troubleshooting and repairs off site by a qualified support team.

COST: Everyone wishes they had an open budget, but reality is we all want quality at a reasonable cost. Many systems are too complex which raises their cost.

In many ways, light can be considered a drug, having the potential for both beneficial and deleterious effects. These conflicting effects can occur concurrently, and in a single individual and context. If circadian lighting can be used to manipulate a brain on a biological level, then we must be extremely cautious with how it is used.

It’s clear that, in trying to influence the physiology of people through light, there’s the possibility that we could lose sight of the simple objective of lighting: to create attractive and comfortable spaces that benefit people and improve the built environment for society as a whole.

Focusing on wellbeing is about understanding light’s impact on a space and how it can enhance a space either aesthetically, emotionally, and physiologically.

Aesthetic: creating spaces we want to use and be in.

Emotional: understanding the intrinsic, personal, and emotive relationships we have with light.

Physiological: the impact of the light on the functions of our body. And the importance of our perception on these functions.