Light + Health, Research

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

In 2017, the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute published a study showing that office workers who receive a robust dose of circadian-effective light experience better sleep, and lower levels of depression and stress, than those who spend their days in dim or low light levels.

The team of LRC researchers, led by Dr. Mariana Figueiro and sponsored by the U.S. General Services Administration, measured existing light levels for 109 participants at five federal office buildings designed to maximize daylight availability indoors. The research team found that even in open offices with many, large windows, office workers were not receiving enough light to stimulate their circadian system during the day, due to factors such as season, cloud cover, desk orientation, and window shade position.

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.

LRC-designed task lights delivered sufficient light to the eye at least one hour per morning during a two-day study at four Federal office buildings, resulting in self-reported scores reflected improved mood and vitality. Image courtesy of the Lighting Research Center.

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.

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.

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.

author avatar
Craig DiLouie


Light + Building 2024
LEDucation 2024
LightSPEC West
Click For More


Colonial Electric – Inside Sales -Remote.