Using Light Exposure to Combat the Post-Lunch Dip

Using Light Exposure to Combat the “Post-Lunch Dip”

Researchers at the Rensselaer Polytechnic Institute in the Lighting Research Center have discovered a way to combat the drowsy feeling often experienced in the afternoon (known as the “post-lunch dip”) using a novel method: exposure to visible light.

For years, researchers have known that exposure to certain wavelengths of visible light helps prevent production of melatonin, a chemical responsible for drowsiness. Short wavelength blue light striking the retina is known to suppress the production of melatonin, while long wavelength red light has no effect on melatonin production. The circadian rhythm, a 24 hour biological cycle responsible for regulating sleep, can be altered by varying your exposure to blue light during the hours immediately prior to sleep. Past research has shown that subjects who wore goggles that block blue light from their eyes in the hours before sleep, had significantly improved their sleep quality as well as their mood. New research has been conducted at RPI, evaluating the alerting effects of red and blue light exposure during daylight hours.

The team at RPI set out to determine if exposure to long wavelength red light, which is not associated with melatonin suppression, could also provide people with a feeling of alertness during daylight hours. Individuals were exposed to either blue or red light, at an illumination of 40 lux, for 48 minutes at a time. Lux is a unit of illuminance that can be measured using a device such as an illuminance meter. After the light exposure sessions, alpha, alpha theta, and theta brainwaves (which are associated with deep relaxation and sleepiness) were measured using an electroencephalogram (EEG). The result was that red light, which does not suppress melatonin production, is still effective in lowering the power of alpha, alpha theta, and theta brain waves. This indicates that the red light was able to increase alertness and decrease drowsiness in the test subjects. The research data shows that light can have an alerting effect during daylight hours even without suppressing the production of melatonin in the brain.

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