Intermittent Morning Bright Light Pulses Yield Greater Circadian Phase Advance Than Continuous Exposure via Melanopsin Regeneration

Hypothesis: In individuals with delayed sleep‑phase syndrome, splitting a prescribed morning bright‑light dose into two short pulses separated by a recovery interval produces a larger advance of the circadian rhythm than delivering the same total light as a single continuous block. The underlying mechanism relies on the bistable nature of melanopsin in intrinsically photosensitive retinal ganglion cells (ipRGCs). After photon absorption, melanopsin transitions to a meta‑stable state that cannot capture additional photons until it regenerates to the ground state via thermal relaxation or interaction with chromophore. Continuous illumination therefore leads to progressive bleaching and a diminishing return on photon capture. Intermittent pulses allow melanopsin to partially regenerate during the dark interval, maintaining a higher effective sensitivity across the session and thus generating a stronger downstream signal to the suprachiasmatic nucleus (SCN). This should translate into an earlier dim‑light melatonin onset (DLMO) and an earlier sleep midpoint compared with continuous exposure of equal total irradiance.

Prediction: Participants receiving two 15‑minute pulses of 1000 lux melanopic EDI at 07:00 and 08:30 will show a mean DLMO advance of at least 20 minutes greater than those receiving a single 30‑minute pulse of 1000 lux at 07:00, after one week of daily exposure. The pulse group will also exhibit a larger shift in actigraphy‑derived sleep midpoint (≥15 minutes) and higher sleep efficiency (>85 %) than the continuous group, while subjective sleepiness (Karolinska Sleepiness Scale) will be lower in the evening.

Test: Randomized crossover trial with 30 adults (age 18‑35) diagnosed with delayed sleep‑phase syndrome (DLMO >02:00). Each condition lasts seven days with a three‑day washout. Morning light delivered via calibrated LED panels; melanopic EDI verified with a spectroradiometer. Saliva samples collected hourly from 18:00 to 00:00 to assess DLMO. Wrist actigraphy records sleep timing and efficiency. Statistical analysis uses paired t‑tests for DLMO and sleep midpoint, and ANOVA for sleep efficiency and sleepiness scores. A significant advantage for the pulse condition would support the hypothesis; a null or opposite result would falsify the claim that intermittent morning light yields a greater circadian advance via melanopsin regeneration.