Red Light Increases 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 to 4 p.m., or about 16 to 18 hours after an individual’s bedtime.
A new study from the Lighting Research Center (LRC) shows that exposure to certain wavelengths and levels of light has the potential to increase alertness during the post-lunch dip. The research was a collaboration between Mariana Figueiro, LRC Light and Health Program director and associate professor, and LRC doctoral student Levent Sahin.
The collaboration lays the groundwork for the possible use of tailored light exposures as a non-pharmacological intervention to increase alertness during the daytime. Figueiro has previously conducted studies that show that light has the potential to increase alertness at night. Exposure to more than 2500 lux of white light at night increases performance, elevates core body temperature, and increases heart rate.
In most studies to date, the alerting effects of light have been linked to its ability to suppress melatonin. However, results from another study led by Figueiro demonstrate that acute melatonin suppression is not needed for light to affect alertness during the nighttime. They showed that both short-wavelength (blue) and long-wavelength (red) lights increased measures of alertness but only short-wavelength light suppressed melatonin. Melatonin levels are typically lower during the daytime, and higher at night.
Figueiro and Sahin hypothesized that if light can impact alertness via pathways other than melatonin suppression, then certain wavelengths and levels of light might also increase alertness during the middle of the afternoon, close to the post-lunch dip hours.
Sahin, who has more than 10 years of experience in railway engineering, was interested in this study from a transportation safety perspective, and what the results could mean to the transportation industry. “Safety is a prerequisite and one of the most important quality indicators in the transportation industry,” said Sahin. “Our recent findings provided the scientifically valid underpinnings in approaching fatigue-related safety problems in 24-hour transportation operations.”