Modern Actigraphy Sheds New Light on Sleep Health

By Lindsey Nolen

Given the prevalence of natural and artificial light sources in today’s environment, measuring an individual’s light exposure has become increasingly relevant for understanding the impacts of light on sleep health and overall well-being. 

For example, a study using activity and light data from the GT3X+ ActiGraph, which included more than 11,000 people, found that men spend about 52% more time in bright light than women.1 The study also found that men tend to have earlier first daily timing for bright light exposure, with women’s exposure occurring approximately 30 minutes later.1

“In adults, time spent outdoors during workdays appeared to explain some, but not all, of the sex difference in the amount of time spent in bright light. These findings suggest that occupational factors may be playing a role in these sex differences, in addition to other factors,” says investigator Danielle A. Wallace, MPH, PhD, a research fellow in sleep epidemiology at Harvard Medical School’s Division of Sleep Medicine, in a release.

A separate study from Flinders University analyzed about 13 million hours of light sensor data captured using an Axivity AX3, and it linked personal light exposure with an individual’s risk of type 2 diabetes. “Our findings suggest that reducing your light exposure at night and maintaining a dark environment may be an easy and cheap way to prevent or delay the development of diabetes,” says senior author Andrew Phillips, PhD, Matthew Flinders Fellow in the College of Medicine and Public Health, in a release.2

As a sleep specialist, you’ve probably shared similar sleep hygiene tips with patients being treated for any number of sleep disorders: encouraging bright light exposure in the morning and discouraging blue-light exposure from smartphones and other screens near bedtime. But how do sleep specialists objectively track whether patients’ personal light exposures are helping or hindering their health outcomes? Some sleep specialists find actigraphy devices a viable solution for 24/7 activity and light monitoring.

Light Sensors in Modern Actigraphy Devices

New actigraphs combine ​​multiple data streams, creating a more complete picture of sleep patterns and environmental influences. Advancements in light sensors have enhanced the ability to detect and analyze light exposure. 

Paul Raymond, MD, medical director of Anchorage Sleep Center in Alaska, uses light sensor data to differentiate between types of nighttime exposures. The ability to detect different light intensities helps him determine if a patient is experiencing light from, say, the bedroom lights being on (a high-intensity light source) versus from, say, electronic device usage (a low-intensity light source). He uses this information when discussing behaviors with patients, particularly to identify the source of light intrusions during the night. 

Behavioral sleep medicine practitioner Jesse Cook, PhD, echoes the sentiment that light data collected via actigraph “can be extremely helpful clinically for multiple reasons.” He says, “It provides key information about the timing of sleep and wake behavior, which is useful for circadian characterization. It can also help identify unhelpful light exposure and electronic use prior to bedtime and during the sleep period.”

Limitations to Measuring Light via Actigraph

Challenges to accurate light measurement also exist, particularly when considering device placement.

“Any actigraphy system is usually worn on the wrist like a watch, and the light sensor might be covered by clothing, especially during winter,” says Tinta Visser, head of product management at sleep diagnostic device manufacturer SOMNOmedics. “For the most accurate measure of light and the influence of light on circadian rhythm, the light sensor should sit at eye level.”

Integrating smartphone usage detection may ultimately overcome some of the limitations. “Simply providing information on phone usage to users is probably unlikely to be helpful,” says Cook, also a postdoctoral fellow at the University of Wisconsin-Madison. “Rather, providing the information in context with other parameters related to their goals, such as increasing sleep duration or quality, can strengthen the likelihood of improved and maintained health-focused behavior.”

In the future, Cook would like to see actigraphs and other light-sensing devices provide light exposure summaries to enhance the data’s utility. “Presenting the data in more digestible visualizations can help better identify key patterns in wake behavior that influence sleep and overall well-being, perhaps displaying distributions of average light exposure across the hours of the day on days with reported good and poor sleep quality to help foster insight for clients on what behaviors are most important for them in efforts to prioritize healthy sleep,” he says.

Behavioral sleep medicine practitioner Michael Nadorff, PhD, a professor of psychology at Mississippi State University, says, “From my perspective, it is less about sensor capabilities and accuracy than it is how many devices, including many affordable devices, now have sensors and algorithms that are good enough that they can be used for research. This is huge and opens up this valuable data source to many more clinicians, patients, and researchers who may not have huge grants. 

“For much of our research…a sensor has to meet a certain threshold of reliability and validity, and anything more precise than that is great, but also not required. What I am seeing is many more devices hitting that threshold where we can use them, and that is really the advance.”

Additional Actigraph Sensors

Better light sensing is just one area in which modern actigraphs have advanced beyond detecting movement.

Behavioral sleep medicine practitioner Michael A. Grandner, PhD, MTR, DBSM, says, “Most of the current devices include photoplethysmography sensors that may detect heart rate. In addition, other sensors (like for skin temperature) are becoming more common.” Sensors are smaller and more efficient, and innovations “seem to be more software-based,” he says.

Tom Kazlausky, president of Ambulatory Monitoring Inc, which is beta testing its newest actigraph, the Sleep Watch 2.0, says, “These channels open the door for more accurate and detailed sleep (four-stage) scoring, as well as insights into O2 saturation, respiratory rates, and, with the help of AI, other biomarkers.”

SOMNOmedics’ SOMNOwatch eco offers a wide range of applications: it monitors the sleep-wake rhythm, detects periodic leg movements, and analyzes tremors. 

At SOMNOmedics, its newest actigraph, the SOMNOwatch eco, has applications like periodic limb movement (PLM) detection and tremor analysis, which are enabled by an adjustable sample rate of up to 256 Hz, according to Visser. “The power of measuring patient activity is underestimated by many,” Visser says. “It is a useful and objective tool for gathering information on the circadian rhythm, insomnia, and other sleep disorders, like PLM. It can also be used in many other areas, such as rehabilitation and psychiatry, in case of sleep misperception.”

“As the benefits of actigraphy monitoring are acknowledged for developing treatment protocols, it is our hope providers and insurance companies will see the benefit of such an easy tool that can provide robust data for patient care,” Visser adds.

Kazlausky is excited about the future. “Low-power, solid-state sensors are getting smaller and more accurate. Implantable devices, ingestible sensors, and recording biomarkers no one has yet considered seem to be within reach,” he says. “Even light sensors the size of a freckle powered by body heat might even come to pass, and researchers would finally get accurate measures of light incident to the eye.”

References

1. Wallace, DA. Light exposure differs by sex in the US, with females receiving less bright light. npj Biol Timing Sleep. 2024.
2. Windred DP, Burns AC, Rutter MK, et al. Personal light exposure patterns and incidence of type 2 diabetes: analysis of 13 million hours of light sensor data and 670,000 person-years of prospective observation. Lancet Reg Health Eur. 2024;42:100943.

Top photo: Ambulatory Monitoring’s SleepWatch 2.0 actigraph, currently in beta testing, will have light tracking, Bluetooth connections, cloud software, a photoplethysmography sensor, and a touchscreen with a scroll wheel.

Further Reading for You:

Source