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. 

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.

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.

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.

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.