Intermittent exposure to bright light during the day counteracts sleepiness and may improve attention span, according to data presented today in Seattle by a Japanese research team at SLEEP 2009, the annual meeting of the Associated Professional Sleep Societies.

"I have been consulting and studying the circadian sleep-wake disorders for more than 20 years," Dr. Toshiharu Takahashi, from Hosei University in Tokyo, told Reuters Health. "One of our goals is to reduce the sleepiness of many shift-workers," such as those working in the airline industry.

The team's current research involved 10 healthy young volunteers, 18 to 24 years of age, who kept to their usual sleep-wake patterns 7 days prior to the experiments, which were conducted on 2 separate days. On the first day, the subjects were exposed to ordinary room light (less than 200 lux); on the second day, the subjects were exposed to bright light (more than 3000 lux.)

Under the two light conditions, sleepiness was determined every 2 hours using the Multiple Sleep Latency Test and by subjective reports from the study participants. Attention was determined by performance testing and by measuring P300, "an auditory event-related potential that reflects cognitive function," the researchers explain in their meeting abstract.

Compared with normal room lighting, bright light exposure was associated with decreased sleepiness, increased amplitude of P300, and improvement in performance testing, Takahashi said, explaining that selective attention is faster under bright light conditions than under ordinary light conditions.

The only adverse effect reported involved "one subject who complained about the dazzle at first, but she got used to the bright light within 30 minutes."

Their next step, the researcher noted, will be to study the intensity, timing and length of exposure to bright light... "and the influence of bright light exposure on sleep after the experimental day."