Psychophysiological effects of a brief nocturnal light exposure.
Level 3 - non-randomized controlled study
Repeated measures within-subject laboratory trial (randomization not specified)
What was done
Ten participants took part in a repeated measures laboratory study across five weekend sessions (18:00 to 06:00 h). Between 02:00 and 03:00 h, participants were exposed to a 60-minute light pulse under one of five conditions: full-spectrum light at 1000, 500, or 30 lux, or green light at 1000 or 500 lux. Outside of the pulse, ambient room lighting was maintained at 30 lux white light. Salivary melatonin, oral temperature, cognitive performance, and subjective mood were sampled across each session.
What was found
The abstract reports no numerical values, effect sizes, or confidence intervals. All experimental light conditions significantly suppressed salivary melatonin immediately following the 60-minute pulse, but suppression did not persist after light cessation. Light exposure had no statistically significant effect on oral temperature, cognitive performance, or subjective mood, though non-significant positive trends were observed.
Why it matters
The findings demonstrate that while brief nocturnal exposure to moderate-intensity green or full-spectrum light acutely suppresses melatonin secretion, this biological response does not reliably translate to immediate functional gains in alertness, mood, or cognitive performance.
Limits
The sample size was very small (n = 10), limiting statistical power. The abstract provides no exact numerical data, and it does not report whether the condition order was counterbalanced or randomized. Participant demographics (e.g., age, sex, habitual sleep schedules) and sleep status during non-testing hours are not described.
Cited by
- context Turning on bathroom lights in the middle of the night signals morning to the brain and halts melatonin production.