Hypothesis

Combining morning bright light exposure with evening blue‑light filtering yields a greater reduction in sleep onset latency than either intervention alone.

Mechanistic Rationale

Morning light activates ipRGCs, advancing the circadian phase and increasing melatonin amplitude[2]. This advance enhances homeostatic sleep drive by aligning the timing of adenosine accumulation with the biological night. Evening blue‑light filtering reduces melatonin suppression[1], preserving nocturnal melatonin signaling. Together, they potentiate adenosine‑mediated sleep pressure in the basal forebrain, a mechanism not captured when each strategy is tested in isolation.

Testable Predictions

1. Participants receiving both interventions will show a ≥15 minute greater decrease in SOL compared to morning‑light‑only or filter‑only groups.
2. Salivary melatonin onset will occur earlier and reach higher peak concentrations in the combined group.
3. Adenosine levels measured via microdialysis in a subset (or proxy via CSF) will be elevated during the early sleep period only in the combined condition.
4. Cognitive reaction time improvements will correlate with SOL reduction, replicating the daylight‑cognition link[9].

Experimental Design

A three‑arm, crossover RCT with 60 adults experiencing SOL >20 minutes. Each arm lasts two weeks with a one‑week washout: (A) morning bright light (>3000 lux, blue‑enriched, 30 min upon waking), (B) evening blue‑light filtering glasses (<500 nm block) from 19:00 to bedtime, (C) both A and B. Sleep latency measured nightly via actigraphy and sleep diaries; melatonin sampled hourly 20:00‑02:00; adenosine assessed via PET tracer or CSF in a subsample. Cognitive PVT administered each morning.

Potential Outcomes and Interpretation

If the combined condition produces the predicted synergistic SOL reduction and biomarker changes, the hypothesis is supported, indicating that ipRGC‑driven circadian advance and evening melatonin preservation converge on adenosinergic sleep pressure. Failure to observe added benefit would falsify the hypothesis, suggesting that morning light and evening filtering act via independent pathways with ceiling effects on sleep latency.