New LRC Study Tests the Impact of Circadian Light on Alertness in Office Workers

In response to these findings, the LRC team theorized that supplemental electric lighting could be used to ensure that office workers receive enough light during the day—and put their theory to the test in this new study, installing circadian-effective lighting for 68 participants at two additional U.S. federal government office sites and two U.S. embassies, and evaluating whether the lighting intervention would reduce sleepiness and increase alertness, vitality, and energy. The U.S. embassy sites, in Reykjavík, Iceland and Riga, Latvia, near the Arctic, experience a dramatic reduction in daylight hours and extended darkness in winter. The federal government office sites, the White River Junction VA Medical Center in Vermont, and the Turner-Fairbank Highway Research Center, near Washington, D.C., also experience a reduction in daylight hours during winter, although not quite so severe as that experienced near the Arctic circle.

A scholarly article detailing the study’s results has just been published in the peer-reviewed journal Lighting Research and Technology. The LRC is one of the few groups actually conducting light and health research out in the field.

“We are supporting this type of research so we can learn more about the connections between lighting and health,” said Bryan Steverson, Program Advisor with GSA’s Office of Federal High-Performance Buildings. “The data from this research will help support our efforts in developing new lighting practices that can optimize health benefits for federal employees working in our buildings.”

Overhead lighting donated by CREE and desktop lamps designed by the LRC provided circadian-effective light during the two-day intervention. The study participants completed questionnaires inquiring about their sleep habits, stress, and subjective feelings of vitality and energy. A pendant-mounted personal circadian-effective light measuring device called a Daysimeter, also designed by LRC researchers, was used to record participant-specific circadian stimulus (CS) exposures during the baseline and the intervention days.

As part of a long-term research effort exploring light’s effects on the circadian system, LRC researchers developed the CS metric, which is based on light’s ability to acutely suppress the production of melatonin. This metric has been applied in lab and field studies with the participation of diverse subject populations in settings ranging from middle schools to eldercare facilities, and even including U.S. Navy submarines.

The study’s results showed that the office workers received significantly higher amounts of CS while at work during the two intervention days compared to a baseline assessment day that preceded the intervention. The office workers’ self-reported sleepiness scores were significantly reduced during the intervention days and, as hypothesized, they also reported feeling significantly more vital, energetic, and alert during that time. What is particularly remarkable is that the four independent office buildings all showed the same trends. These results demonstrated that lighting systems delivering a high amount of circadian-effective light, especially early in the workday, can reduce sleepiness in office workers while also improving their mood and alertness.

The circadian system keeps people synchronized with the 24-hour day by regulating internal biological cycles that repeat themselves on a daily basis, such as digestion, the release of hormones, the control of core body temperature, and the timing of alertness and sleepiness. The patterns of light and dark received by our eyes are the major synchronizer of the circadian system’s master clock to our local position on Earth. Without the cues provided by these light–dark patterns, the numerous physiological and behavioral systems that help to ensure our wellbeing, if not survival, become asynchronous with each other and the environment. Research has associated such asynchrony with a number of mental and physical health problems, particularly including elevated risk for metabolic diseases such as obesity, diabetes, and cancer. In addition to light’s synchronizing effect and of particular interest in this study, light can also have an acute alerting effect, similar to that provided by a cup of coffee, at any time of day or night.

Although this study did not measure evening light exposures, which can be just as important as daytime exposures because the circadian system is synchronized by the comprehensive 24-hour light–dark patterns received at the eye, these results nonetheless confirm findings from a wide range of previous LRC lab studies. Namely, that “high” light levels delivered to the eye during the day will (a) better align circadian rhythms to a day-active and night-sleeping pattern and (b) increase alertness during working hours. These promising empirical results from the field, backed up by more basic research, justify further investigations of the impact of retinal light exposure on the neurophysiology of the brain and, perhaps more importantly, a reexamination of current lighting standards that are based solely on office illumination for visibility and comfort.

For addinional information, please visit www.lrc.rpi.edu or contact the principal investigator Dr. Mariana Figueiro at figuem@rpi.edu