Red Light Can Increase Workplace Alertness During "Post-Lunch Dip"

Acute or chronic sleep deprivation resulting in increased feelings of fatigue is one of the leading causes of

workplace incidents and related injuries. More incidents and performance failures, such as automobile accidents, occur in the mid-afternoon hours known as the “post-lunch dip.” The post-lunch dip typically occurs from 2-4 p.m., or about 16-18 hours after an individual's bedtime from the previous night.

A new study from the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute shows that exposure to certain wavelengths and levels of light has the potential to increase alertness during the post-lunch dip.

During the study, participants experienced two experimental lighting conditions in addition to darkness; long-wavelength “red” light and short-wavelength “blue” light. Participant alertness was measured by electroencephalogram (EEG) and subjective sleepiness (KSS scale).

The researchers found that, compared to remaining in darkness, exposure to red light in the middle of the afternoon significantly reduces power in the alpha, alpha theta, and theta ranges. Because high power in these frequency ranges has been associated with sleepiness, these results suggest that red light positively affects measures of alertness not only at night, but also during the day.

Red light also seemed to be a more potent stimulus for modulating brain activities associated with daytime alertness than blue light, although they did not find any significant differences in measures of alertness after exposure to red and blue lights. This suggests that blue light, especially higher levels of blue light, could still increase alertness in the afternoon.

Photo: David Castillo Dominici








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