LRC Research Collaboration With GSA Finds Morning Blue Light and Afternoon Red Light Promote Entrainment and Increase Alertness in Office Workers

Researchers from the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute and the U.S. General Services Administration (GSA) recently published the latest in a series of studies exploring how light impacts alertness during the day and sleep quality at night in daytime office workers.

The study field tested a novel luminaire developed by the LRC to promote circadian entrainment and alertness in the office environment. Nineteen participants from three U.S. Department of State office buildings in Washington, D.C., completed the 3-week study. The luminaires, mounted near the participants’ computer monitors provided: (1) morning saturated blue light delivering a circadian stimulus (CS) of 0.4, (2) midday polychromatic white light delivering a CS of 0.3, and (3) afternoon saturated red light delivering a CS close to zero. Objective and subjective measures of rest–activity, sleep, vitality, and alertness were used to evaluate the lighting interventions.

Results show that participants exhibited more consolidated rest–activity patterns, indicating better circadian entrainment, and woke up earlier during the intervention compared to baseline. The morning blue light appears to have advanced participants’ circadian phase, causing participants to wake up earlier in the morning. The afternoon red light elicited an acute alerting response close to the post-lunch dip (around 3 p.m.), reducing subjective sleepiness and increasing subjective vitality and energy.

These field results are the first to demonstrate that red light in combination with ambient white light provides an effective alerting stimulus, and support the inference that light exposures, when properly applied, can promote circadian entrainment and increase alertness.

The research paper, “Light, entrainment and alertness: A case study in offices” was published earlier this month in the journal Lighting Research & Technology. Authors include Mariana Figueiro, Mark Rea, Levent Sahin, and Charles Roohan from the LRC.

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