Daytime Exposure to Bright Light Decreases Sleepiness and Improves Neurobehavioral Performance

By Dr. Gregg D. Jacobs

Excessive sleepiness can result from sleep deprivation, circadian rhythms disturbances due to shift work, sleep apnea, and insomnia. Some studies have reported that nocturnal exposure to bright light has an alerting effect on humans and reduces subjective sleepiness. However, other studies have failed to confirm these findings. Additionally, the potential for bright light to be used during the day to improve alertness and performance has not been systematically investigated.

In a recent study published in the journal Sleep (26, 2003:695-670), researchers from Australia and the United Kingdom examined the effects of daytime bright light (1,000 lux) compared to dim light (<5 lux) on subjective and objective measures of sleepiness. They recruited healthy, young eight hour sleepers who maintained a normal sleep schedule for nine days and then were sleep restricted to five hours of sleep for two nights before being exposed to bright or dim light. The light exposure took place for five hours (noon to 5:00 pm) while a battery of testes were given to subjects.

The researchers found that afternoon bright light exposure for about five hours reduced subjective sleepiness, improved neurobehavioral performance on tests of psychomotor vigilance and reaction time, and reduced slow eye movements (a physiological measure of drowsiness) compared to dim light.

The results of this study suggest that bright light exposure during the day counters the adverse effects of sleep restriction on sleepiness and performance. These findings may assist in the developments of treatments for daytime sleepiness caused by sleep loss from voluntary sleep restriction, shift work, and insomnia. Although naps and caffeine are both recognized as effective strategies for reducing sleepiness, light may as- or more- effective for reducing the effects of sleep restriction.