Daytime Exposure to Bright Light, as Compared to Dim Light, Decreases Sleepiness and Improves Psychomotor Vigilance Performance

Oct 24, 2003Sleep

Daytime bright light reduces sleepiness and improves attention compared to dim light

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Abstract

Bright light exposure significantly reduced subjective sleepiness and improved performance on psychomotor vigilance tasks after sleep restriction.

Exposure to bright light (1,000 lux) decreased subjective sleepiness compared to dim light (< 5 lux).
Participants exposed to bright light showed fewer incidences of slow eye movements (SEMs).
Psychomotor vigilance task (PVT) performance improved with bright light exposure relative to dim light.
No significant effect of bright light on salivary melatonin levels was observed.
A positive correlation existed between PVT reaction times and subjective sleepiness for both light conditions.
Changes in SEMs did not significantly correlate with subjective sleepiness or PVT performance.

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STUDY OBJECTIVES: This study examined the effects of bright light exposure, as compared to dim light, on daytime subjective sleepiness, incidences of slow eye movements (SEMs), and psychomotor vigilance task (PVT) performance following 2 nights of sleep restriction.

DESIGN: The study had a mixed factorial design with 2 independent variables: light condition (bright light, 1,000 lux; dim light, < 5 lux) and time of day. The dependent variables were subjective sleepiness, PVT performance, incidences of SEMs, and salivary melatonin levels.

SETTING: Sleep research laboratory at Monash University.

PARTICIPANTS: Sixteen healthy adults (10 women and 6 men) aged 18 to 35 years (mean age 25 years, 3 months).

INTERVENTIONS: Following 2 nights of sleep restriction (5 hours each night), participants were exposed to modified constant routine conditions. Eight participants were exposed to bright light from noon until 5:00 pm. Outside the bright light exposure period (9:00 am to noon, 5:00 pm to 9:00 pm) light levels were maintained at less than 5 lux. A second group of 8 participants served as controls for the bright light exposure and were exposed to dim light throughout the entire protocol.

MEASUREMENTS AND RESULTS: Bright light exposure reduced subjective sleepiness, decreased SEMs, and improved PVT performance compared to dim light. Bright lights had no effect on salivary melatonin. A significant positive correlation between PVT reaction times and subjective sleepiness was observed for both groups. Changes in SEMs did not correlate significantly with either subjective sleepiness or PVT performance.

CONCLUSIONS: Daytime bright light exposure can reduce the impact of sleep loss on sleepiness levels and performance, as compared to dim light. These effects appear to be mediated by mechanisms that are separate from melatonin suppression. The results may assist in the development of treatments for daytime sleepiness.

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Daytime Exposure to Bright Light, as Compared to Dim Light, Decreases Sleepiness and Improves Psychomotor Vigilance Performance

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