Daily light exposure differences between extreme chronotypes persist after alignment to habitual sleep timing

Extreme chronotypes show different near-eye melanopic daylight exposure timing, with an evening-to-morning exposure ratio of 0.16 pre-MSFsc and 14.0 post-MSFsc in 140 participants.

• Why it matters: If early and late chronotypes receive light at different clock times, it may sustain circadian timing extremes; this study tests whether photoperiod alters those exposure patterns.
• What they did: Using near-eye melanopic equivalent daylight illuminance from 778 participant-days (35,949 half-hour observations) across seven countries, the authors modeled quartiles of MSFsc with cyclic generalized additive mixed models.
• The result: The exposure timing differences persisted after aligning to habitual sleep timing, with post-MSFsc ratio increasing by 2.59 (95% CI 1.06–6.34) across civil photoperiods, while pre-MSFsc contrast was not significantly moderated.

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