By Rebekah Mullaney
From the April 2017 Issue
Americans spend more than 90% of their time indoors, yet little attention has been given to understanding how light affects health in the built environment. A team of researchers at the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute in Troy, NY, is working to change that. The research team, led by Dr. Mariana Figueiro, Light and Health Program Director at the LRC and Professor of Architecture at Rensselaer, recently conducted one of the first studies to measure circadian light exposures in office workers and to relate those measures to mood and sleep outcomes. “Light is as essential to our daily health as the air we breathe and the food we eat. Yet, healthy light is in short supply in our work environments where the traditional emphasis is on light for vision,” said Dr. Figueiro.
All living organisms on Earth exhibit circadian rhythms—biological cycles that repeat approximately every 24 hours. In humans, light is the main stimulus that helps the circadian clock (and thus circadian rhythms) to remain synchronized with the 24 hour day. Research has shown that a lack of synchrony, known as “circadian disruption,” can lead to decrements in physiological functions, neurobehavioral performance, and sleep, and increase the risk of developing more serious conditions such as cardiovascular disease, diabetes, and certain forms of cancer.
Office lighting is typically designed for the human visual system, not the circadian system. Lighting for the circadian system employs lighting design objectives that differ from those typically used in traditional architectural lighting design. An ideal office lighting system for day shift workers provides cool, high light levels during the workday, especially in the morning, from 8:00 a.m. to noon. Many lighting systems currently installed in office buildings provide too little circadian-effective light during the workday, which can lead to circadian disruption, as described earlier.
The U.S. General Services Administration (GSA) awarded a contract to the LRC in 2013, to study the correlation of lighting with health and well-being, to assess the building occupant experience of light, and to identify health outcomes linked with measured light exposure in federal buildings. More than 100 participants took part in the LRC study at five office buildings managed by the GSA. Sites included the GSA Central Office in Washington, DC; the Edith Green-Wendell Wyatt Federal Building in Portland, OR; the Federal Center South Building in Seattle, WA (pictured here); the Wayne N. Aspinall Federal Building and U.S. Courthouse in Grand Junction, CO; and the GSA Regional Office Building in Washington, DC.
Each study participant wore a Daysimeter (see inset photo above), a research tool developed by the LRC, which is used to measure the amount of circadian stimulus (CS) a person actually receives, along with their activity patterns, over an extended period of time, in this case, for one week. CS is the calculated effectiveness of light’s impact on the circadian system, ranging from zero (the threshold for circadian system activation) to 0.7 (response saturation). LRC researchers also collected data on the participants’ sleep and mood.
Dr. Figueiro and her team found that office workers receiving a morning CS of at least 0.3 exhibited greater circadian entrainment, were able to fall asleep more quickly at bedtime, and experienced better quality sleep than those receiving a morning CS of 0.15 or less. Participants receiving high CS throughout the entire workday also experienced better sleep quality and felt less depressed compared to those receiving low CS.
One important insight from the study is that even in buildings designed to maximize daylight availability indoors, CS exposures were typically not delivered at the desired level. This can be attributed to factors such as desk location and orientation, window shade position, weather patterns, and daylight availability due to the changing seasons. Thus, electric lighting should be used to supplement daylight to ensure that every office worker receives enough CS during the daytime to support circadian health.
Even if a particular building provides ideal circadian-effective lighting, too much light after work, such as using a backlit tablet or e-reader before bedtime, can lead to circadian disruption. In 2012, Dr. Figueiro’s research team published a study showing that two hours of exposure to light from self-luminous electronic devices can suppress melatonin by approximately 23%. Stimulating the human circadian system to this level may delay sleep in those using the devices prior to bedtime.
Last year, the LRC research team took the project a step further. Applying the results of the previous studies, the team developed and installed experimental desktop and overhead lighting, providing a CS of 0.3 or greater, for 36 participants at two additional sites: the White River Junction VA Medical Center in Vermont, and the Turner-Fairbank Highway Research Center, near Washington, DC. Daysimeters were again used to measure personal circadian light exposure and activity patterns. The research team also collected data on the participants’ sleepiness and energy levels. Preliminary results revealed that participants reported feeling less sleepy and more energized after receiving the lighting intervention.
In a project funded by the GSA and the U.S. Department of State, the LRC is performing similar studies at U.S. embassies in Reykjavík, Iceland and Riga, Latvia.
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