Effects of a chronic reduction of short-wavelength light input on melatonin and sleep patterns in humans: Evidence for adaptation

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Summary

After two weeks of chronically reduced blue light exposure via orange contact lenses, the human non-visual light system adapted by increasing its sensitivity to melatonin suppression, normalizing the response to levels seen under full-spectrum light. This suggests that long-term changes in spectral lighting environments — such as those caused by aging lenses or intentional blue-light filtering — may be partially compensated by adaptive mechanisms, complicating predictions about circadian disruption from spectral interventions.

Key Findings

Acute exposure to reduced short-wavelength light (via soft orange contact lenses) decreased melatonin suppression, as expected.
After 2 weeks of chronic reduced blue light exposure (n=15 young healthy subjects), melatonin suppression sensitivity increased, normalizing the response to match that of full polychromatic light.
No significant differences were found in dim light melatonin onset (DLMO) or amplitude of melatonin rhythms after chronic SOCL wear.
Sleep parameters showed limited effects, suggesting the circadian system compensates for chronic spectral reduction without major sleep disruption.
Results indicate the non-visual (melanopsin-driven) system can adapt to chronic changes in spectral light composition, warranting caution in assuming linear or persistent effects of blue light reduction.