Light of both high and low melanopic illuminance improves alertness and attention during daytime.
Level 2 - randomized trial
Controlled experimental laboratory trial in humans
PubMed 41286402 · doi:10.1038/s41598-025-29154-4
What was done
Healthy young adults (n = 39; mean age 21.7 ± 2.6 years, 61.5% female) completed the Psychomotor Vigilance Task (PVT) three times during a morning window (09:00–11:00) across four artificial lighting conditions: short-wavelength blue light (high melanopic illuminance), long-wavelength red light (low melanopic illuminance), bright white light with high correlated color temperature, and dim white light as a control. Evaluated outcomes included mean reaction time (RT), attention lapses, intra-individual RT variability, and optimum response capability (fastest 10% RTs).
What was found
The abstract reports directions of effect without numerical values (such as reaction times in milliseconds, lapse frequencies, effect sizes, or p-values). Relative to dim light, both short-wavelength and long-wavelength light significantly decreased lapses and accelerated mean RT. Long-wavelength light also significantly enhanced optimum response capability. Bright white light produced no significant changes on any PVT parameter, light condition did not significantly affect RT variability, and short-wavelength light was not superior to long-wavelength light.
Why it matters
This study demonstrates that alerting effects during daytime hours are not exclusive to high-melanopic or blue-enriched light, indicating that low-melanopic red light can also acutely improve sustained attention.
Limits
The sample was small (n = 39) and restricted to healthy young adults, limiting generalizability to other age groups or clinical populations. The abstract provides no numeric values, effect sizes, confidence intervals, or exact p-values. Testing was restricted to an acute two-hour morning window, precluding conclusions about sustained effects throughout the day.
Cited by
- supports Bright light exposure in the morning, especially from sunlight, increases daytime mood, focus, alertness, and improves sleep quality later that night.