Morning light exposure plays key role in children’s sleep onset, study finds

In a recent study published in the Journal of Sleep Research, researchers discovered that the patterns of light exposure throughout the day and night significantly influence the sleep quality of children. The findings indicated that the timing and duration of bright light exposure, particularly in the morning and before bedtime, are crucial factors in determining sleep duration and the time it takes to fall asleep.

The motivation behind this new study was to explore further the impact of light exposure on sleep quality, given the increasing prevalence of sleep problems worldwide and their association with various health issues such as obesity, cardiovascular disease, and mental health disorders. Prior research has highlighted the role of chronic stress, air pollutants, and blue light exposure as potential risk factors for sleep problems. However, there remains a need for more research to identify additional modifiable risk factors that could inform preventive strategies.

“Experimental studies have shown an influence of light exposure on sleep in children, but in how far that translates to measurable effects under real life conditions was unclear. We measured light exposure and sleep in about 250 children over a week to answer this question,” explained study author Anke Huss, an associate professor in environmental epidemiology at Utrecht University.

To conduct their study, the researchers recruited 247 Dutch children aged between 11 and 13 years from the Adolescent Brain Cognitive Development (ABCD) Study. The participants were asked to wear a light meter, which recorded light intensity in lux every two seconds and logged these measurements as 10-second averages to preserve battery life.

The children wore these meters for a week to capture both their weekday and weekend sleep patterns. In addition to light exposure, sleep parameters such as sleep duration, efficiency, and sleep-onset delay were assessed using wrist-worn accelerometers (Actigraphs) and sleep diaries.

Free daily newsletter

An interesting association emerged, showing that earlier exposure to bright light in the day was linked to shorter delays in falling asleep. This suggests that early morning light plays a significant role in setting the body’s internal clock or circadian rhythm, affecting how quickly children fall asleep at night.

The duration of bright light exposure throughout the day also impacted sleep. Specifically, longer durations of exposure to bright daylight were associated with shorter sleep durations and faster sleep onset. Essentially, exposure to bright light in the morning may help signal to the body that it’s time to wake up and start the day, while longer periods of bright light during the day may help keep the circadian rhythm properly aligned, promoting healthier sleep patterns.

The effects of light intensity at night showed a clear negative impact on sleep duration. This finding is particularly relevant in the context of modern environments, where artificial lighting and screen time are prevalent, underscoring the importance of reducing bright light exposure during the evening to promote better sleep quality.

Additionally, the research found that higher light intensities before bedtime prolonged the time it took for children to fall asleep. This reinforces the idea that the light environment in the hours leading up to sleep is critical, with brighter light conditions being detrimental to the initiation of sleep.

These findings collectively underscore the importance of the natural light-dark cycle and suggest that aligning children’s light exposure patterns more closely with this cycle could improve sleep outcomes. Specifically, maximizing exposure to bright light during the morning and daytime while minimizing exposure to artificial light in the evening could enhance both the duration and quality of sleep.

“I had expected some effects of light on sleep, but the results were clearer than I had thought,” Huss told PsyPost. “It is not just light in the evening or at night, but the actual 24-hour light exposure profile that can affect sleep. If children experience sleeping problems, they could try influencing their light-dark exposure pattern.”

However, the study was not without its limitations. While actigraphy provides a non-intrusive way of assessing sleep patterns, it is not as accurate as polysomnography, the gold standard for sleep measurement. Additionally, the method of wearing the light meter may not have accurately reflected the actual light exposure at the eye level, potentially underestimating it.

“It is not a major caveat of the research we did, but it was a challenge to get 11/12-year-olds to fill in a diary of bedtimes and activities for a full week, every day,” Huss noted. “For a next time, we’d need to think about how we make it more fun to collect such data.

The researchers call for further studies to explore these associations in more detail, particularly to understand the impact of different types of light exposure (e.g., natural vs. artificial) and their timing (e.g., evening vs. morning) on sleep quality. They also highlight the need for research in different populations and settings to generalize their findings.

“I’m interested to see if we observe the same effects in adults, and across different parts in more northern or southern parts of Europe, with very different summer/winter light patterns,” Huss said. “Of course, further questions also pertain to e.g. blue light exposure.”

“The results of the study are interesting in the sense that light is an exposure we can influence quite easily, so it offers a lot of room for experimentation or prevention,” she added.

The study, “Associations of light exposure patterns with sleep among Dutch children: The ABCD cohort study,” was authored by Magdalini Stefanopoulou, Naomi Ruhé, Lützen Portengen, Luuk van Wel, Tanja G. M. Vrijkotte, Roel Vermeulen, and Anke Huss.