Hypothesis

Extending evening darkness duration—defined as reducing illuminance to <5 lux for at least 4 hours before habitual bedtime—combined with morning bright light exposure (≥10,000 lux for 30 min) will produce greater advances in circadian phase, larger reductions in sleep onset latency, and improved overnight cognitive consolidation than using blue‑light blocking glasses (BBGs) alone.

Mechanistic Rationale

Evening light suppresses melatonin via melanopsin‑containing ipRGCs that project to the suprachiasmatic nucleus (SCN) and to the locus coeruleus (LC), increasing norepinephrine tone and cortical arousal [[https://www.health.harvard.edu/healthy-aging-and-longevity/blue-light-has-a-dark-side]]. While BBGs filter the 460‑480 nm band, they do not attenuate overall photon flux; residual light in the green‑red spectrum can still activate ipRGCs at high intensities [[https://pmc.ncbi.nlm.nih.gov/articles/PMC6449639/]]. Prolonged darkness lowers the baseline firing rate of ipRGCs, decreasing tonic LC‑driven norepinephrine release, which in turn reduces high‑frequency EEG activity (beta/gamma) associated with cortical arousal [[https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2022.943108/full]]. Consequently, melatonin onset occurs earlier and with greater amplitude, facilitating faster sleep initiation and enhancing spindle‑dependent memory consolidation.

Testable Predictions

1. Participants receiving the darkness + morning light protocol will show a mean advance in dim‑light melatonin onset (DLMO) of ≥45 min compared with BBG‑only controls (p<0.01).
2. Sleep onset latency will be reduced by ≥15 min in the protocol group versus ≤5 min change in BBG group (p<0.01).
3. Overnight improvement in a paired‑associate learning task will correlate positively with increase in melatonin amplitude (r≥0.4).
4. EEG power in the beta band (15‑25 Hz) during the hour before sleep will be significantly lower in the protocol group (p<0.05).

Methods Outline

• Recruit 60 healthy adults (age 18‑35) with habitual bedtime 23:00‑01:00.
• Randomize to three arms (n=20 each): (A) BBGs worn from 20:00 to bedtime; (B) darkness protocol: ambient light <5 lux from 20:00 to bedtime, verified with photometers; (C) Control: usual indoor lighting.
• All arms receive morning bright light (10,000 lux, 30 min) at 07:00 for 7 days.
• Collect saliva for DLMO on day 1 and day 8, polysomnography on night 8, and EEG spectral analysis pre‑sleep.
• Administer a memory consolidation task before sleep and after wake.
• Statistical analysis via mixed‑effects models with arm, time, and arm × time interaction.

If the darkness + morning light arm fails to outperform BBGs on DLMO advance, sleep latency, or cognitive gain, the hypothesis is falsified.