Spectral dependency of the human pupillary light reflex. Influences of pre-adaptation and chronotype

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Summary

The pupillary constriction response follows L+M-cone sensitivity when light stimuli are continuous, but ipRGC and short-wavelength influences emerge under discontinuous stimulation, after brief (1-second) stimuli, and when chronotype and time of day interact. These findings highlight that lighting design relying on simple cone-based pupil models may misrepresent non-visual photoreceptor contributions, especially in circadian-sensitive applications where stimulus timing and individual chronotype matter.

Key Findings

Normalized pupillary constriction (nPC) aligns with L+M-cone sensitivity under continuous light series, but not under discontinuous (dark-interrupted) protocols.
Mesopic illuminance weighting provided the best overall prediction of pupillary constriction compared to photopic or other illuminance measures.
Subjects of differing chronotypes showed heightened or lowered short-wavelength sensitivity depending on their time of preference, consistent with ipRGC modulation.
Post-illumination pupil reflex (PIPR) revealed ipRGC influence specifically when prior stimulus duration was 1 second; at 15–30 seconds, shorter wavelengths than expected became more prominent.
Sex influenced nPC magnitude but showed no interaction with wavelength sensitivity.
Study included 83 healthy participants across 9 experimental protocols and 150 stimulation series; data analyzed with generalized additive mixed models (GAMM).

Categories

The Science of Light: Investigates the spectral dependency of the pupillary light reflex, examining the roles of ipRGCs, rods, and cones under mesopic conditions and how chronotype modulates wavelength sensitivity.

Sleep & Circadian Health: Reveals that chronotype interacts with time of day to alter short-wavelength (ipRGC-mediated) sensitivity, suggesting a potential feedback mechanism for reinforcing individual circadian preferences.