Daytime exposure to bright light, as compared to dim light, decreases sleepiness and improves psychomotor vigilance performance.
OBJECTIVE
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.


METHODS
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.


METHODS
Sleep research laboratory at Monash University.


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


METHODS
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.


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.
School of Psychology, Psychiatry and Psychological Medicine, Monash University, Victoria, Australia. Billie-Jo.Phipps-Nelson@med.monash.edu.au
Jo
J
Phipps-Nelson
Jennifer R
JR
Redman
Derk-Jan
DJ
Dijk
Shantha M W
SM
Rajaratnam
D000293:Adolescent; D000328:Adult; D001143:Arousal / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D006970:Disorders of Excessive Somnolence / Q000628:therapy*; D004569:Electroencephalography; D004585:Electrooculography; D005133:Eye Movements / Q000502:physiology; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000032:analysis; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time; D012463:Saliva / Q000737:chemistry; D014851:Wakefulness / Q000502:physiology
D008550:Melatonin