Hypothesis

Combining evening amber-light blockade (wavelengths >590 nm) with a brief morning blue-light pulse (470 nm, 2–10 min) will produce a synergistic increase in nocturnal melatonin amplitude and improve metabolic rhythmicity greater than either intervention alone.

Rationale

Evening blue light suppresses melatonin via ipRGCs [1], while amber light removes this suppressive signal without affecting vision. Morning blue light advances the SCN and enhances melatonin secretion later in the day [4][5]. The ipRGC pathway shows separate melanopsin‑driven (blue‑sensitive) and cone‑driven (long‑wavelength) inputs to the SCN [6]; amber light preferentially stimulates long‑wavelength cones, providing a non‑suppressive daytime signal that may reinforce SCN amplitude when paired with a strong morning melanopsin signal.

We propose that the combined stimulus increases SCN firing robustness, leading to stronger sympathetic output to the pineal gland via the superior cervical ganglion, thereby raising melatonin synthesis amplitude and sharpening the circadian rhythm of downstream metabolic genes (e.g., Bmal1, Per2) in liver and muscle.

Predictions

1. Participants receiving both interventions will show a ≥25 % increase in area‑under‑the‑curve (AUC) of nocturnal melatonin compared with controls, and a ≥15 % greater increase than either single intervention.
2. The combined protocol will reduce fasting glucose and triglyceride variability by ≥10 % over 4 weeks, reflecting improved hepatic circadian metabolism.
3. Phase angle of activity (acrophase) will advance by ~0.5 h more than morning blue light alone, without altering total sleep time.

Experimental Design

• Recruit 120 healthy adults aged 30‑50, stratified by chronotype (mid‑sleep <02:30 vs >04:30).
• Randomize to four groups (n=30 each): (A) control (usual light), (B) evening amber‑blocking glasses only, (C) morning outdoor blue‑light pulse only, (D) both interventions.
• Intervention duration: 4 weeks.
• Measures: salivary melatonin every 30 min from 18:00 to 06:00 (AUC), continuous glucose monitoring, actigraphy for activity acrophase, and weekly questionnaires on sleep quality.
• Statistical analysis: two‑way ANOVA (time × group) with post‑hoc Tukey tests; significance set at p<0.05.

Falsifiability

If the combined group does not show a statistically significant greater melatonin AUC or metabolic improvement than the best single intervention, the hypothesis is falsified. Conversely, a significant synergistic effect supports the proposed mechanism of complementary ipRGC‑cone signaling enhancing SCN‑pineal coupling.