Daytime light, sleep and mood
The Lighting Research Center examined people staying home or quarantining indoors during the COVID-19 pandemic to determine how different levels of light exposure affected their sleep and mood.
The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute is investigating the impacts of working from home or quarantining indoors due to the COVID-19 pandemic on individual daily light exposures, and how this may be affecting sleep quality and psychological health. In May 2020, the LRC invited people who had been staying home due to the pandemic to complete a short survey about their sleep, mood, and daily light exposure.
A total of 708 people responded to the survey. LRC researchers analyzed the data to understand how daily indoor light exposure, time spent outside, and time of day spent outside affected sleep quality, sleep-related impairment, anxiety, stress, depression, and mood. Of the survey respondents, only those who were unemployed and staying at home, or employed and working from home were included in the analysis, approximately 600 people, total.
The results revealed that daily indoor light exposure and time spent outside had a major impact on all survey outcomes, including sleep disturbances, sleep-related impairment, anxiety, stress, depression, and mood. Compared to people with “somewhat dim” to “very dim” indoor lighting, people with “somewhat bright” to “very bright” lighting, including having windows without (or with open) curtains or shades, or having several lights turned on, reported:
Fewer sleep disturbances
Less anxiety and depression
Feeling less tired or less irritable
Feeling generally happier and more positive
Less sleep-related impairment
“Sleep quality and mood significantly improved when people spent the majority of their time in a brighter, compared to dimmer, location in their homes,” said LRC researcher Charles Jarboe, who led the study. “If you can add a little more light to your space during the day — one extra lamp, or open your window shades, for example, it could help you feel better, and improve your sleep.”
Another especially important factor was the amount of time spent outdoors. The survey results revealed that people who spent one to two hours outdoors each day reported feeling significantly less anxiety, stress, and depression, and reported that they slept better than those who spent less than 30 minutes outdoors each day. The impact leveled off after two hours, however. Morning light provided the greatest benefits.
“Our results show that just one hour spent outdoors each day can help you feel your best, and can help you sleep better at night,” said LRC Director Dr. Mariana Figueiro, one of the world’s leading experts in the area of light and health.
The survey results also revealed slightly higher than average overall scores for anxiety. Given the extraordinary nature of the current times, there are many factors that contribute to psychological and emotional health outcomes that are more severe than in normal circumstances. The higher scores for anxiety may be a reflection of this. However, for all outcome measures, the strong trends exist that one would normally expect in relation to overall light exposures and time spent outside during the day, indicating that our daily habits and establishment of a robust 24-hour light–dark pattern has a significant impact on our health and wellbeing, even during trying times.
It is also worthy of note that a potential benefit of working or quarantining at home is that individuals can have more control over their environment, such as setting up their workspace facing an open window. Individuals can also benefit from flexibility in their work schedule, and can choose to work or take breaks outside, which may not be an option when working at the office. These factors can increase daily light exposure, which has many benefits, as revealed in the survey.
How Does Light Impact Sleep?
Light has to enter the eye to be effective for circadian entrainment. People in modern society usually spend more than 90% of their time indoors, yet lighting in the built environment, especially in homes, is typically not bright enough to stimulate the circadian clock. Typical indoor lighting provides less than 100 lux at the eye, whereas being outside on a sunny day will provide anywhere from 1,000 to 3,000 lux on a cloudy morning to as much as 100,000 lux at the eye on a bright sunny day.
We now know that most people are not getting enough light during the day. Unfortunately, too little light during the day is compounded by too much light at night. Many people use luminous electronic devices like smartphones and tablets in the evening or stay up late working on the computer. Light from these screens makes the brain think it’s time to wake up, just as you’re getting ready for bed.
Disruption of the 24-hour rhythm of light and dark affects every one of our biological systems from DNA repair in single cells to melatonin production by the pineal gland in the brain. Circadian disruption is most obviously linked with disruption of rest–activity patterns, which can cause sleepiness during the day and insomnia at night—but is also linked with increased risk for diabetes, obesity, cardiovascular disease and certain types of cancer.
Underwriters Laboratories (UL) recently published a Design Guideline explaining how electric lighting can be specified during the day to support circadian entrainment for occupants of commercial, industrial and educational facilities. Some of these design guidelines may be adopted to home offices so that those working at home get more daytime light.
Using the Power of Light to Sleep Better & Feel Better.
Good sleep is essential for good health, and may even have a protective effect against coronavirus, because a healthy, regular sleep pattern promotes a strong immune system. Dr. Figueiro recommends the following tips to help you sleep better and feel better every day.
Seek light during the day, especially in the morning.
If the sky is clear and the sun is shining, go for a 30-minute walk or run every morning at the same time. Morning light provides the most health benefits.
If you must stay indoors during the daytime, work facing the windows. Open the window curtains or shades to let in daylight.
If you don’t have a window in your workspace, add more fixtures. For example, if you have one table lamp near your desk, add three additional ones. Don’t forget to turn the extra lights off in the evening, mimicking sunset.
In the evening, use warm, low-level, dim lighting and turn off your screens one to two hours before bedtime. The intense glow from an electronic screen can make it harder for you to fall asleep.