The impact of wavelength on acute non-visual responses to light: A systematic review and meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of experimental laboratory trials
PubMed 37364848 · doi:10.1016/j.brainres.2023.148470
What was done
Authors conducted a systematic review of 36 studies and a meta-analysis of 17 studies to evaluate the acute effects of different narrowband light wavelengths, exposure timing, and intensity on subjective and objective measures of alertness (including cognitive performance and neurophysiological brain activity).
What was found
Short-wavelength light (~460–480 nm, λmax: 470/475 nm) significantly improved subjective alertness, cognitive function, and neurological brain activities at night for up to ~6 hours (0.4 < |Hedges's g| < 0.6, p < 0.05), but showed virtually no effect during the day outside of the early morning. Long-wavelength light (~600–640 nm, λmax: ~630 nm) showed little effect at night, but significantly enhanced alertness measures during the day at lower irradiance over ~1 hour, particularly under homeostatic sleep drive (0.5 < |Hedges's g| < 0.8, p < 0.05).
Why it matters
This review shows that non-visual alerting responses depend strongly on time of day and wavelength, demonstrating that melanopic illuminance alone does not fully capture daytime alerting effects.
Limits
The abstract does not report the total participant sample size, demographics, heterogeneity statistics, or risk of bias assessments. Exposure protocols, intensities, and specific outcome measures varied across the analyzed studies.
Cited by
- supports Blue light around 480 nanometers stimulates intrinsically photosensitive retinal ganglion cells, which signal the suprachiasmatic nucleus and the pineal gland to release melatonin roughly 12 to 14 hours later.