Summary
This systematic review of 12 studies (337 participants) demonstrates that bright light exposure—especially with strong short-wavelength (blue/green) components—during late night or early morning significantly elevates cortisol secretion compared to dim light, while long-wavelength (red) light produces smaller effects. Lighting designers and facility managers should carefully control spectral composition and intensity in bedrooms, classrooms, and device screens, particularly during morning and nighttime periods, to avoid unintended disruption of HPA axis rhythms.
Key Findings
- Bright light of any colour during late night or early morning induced significant increases in cortisol relative to time-matched dim light conditions (across 12 studies, n=337).
- Short-wavelength (blue/green) dominant light in the early morning typically produced greater cortisol increases than long-wavelength (red) dominant light, consistent with ipRGC/melanopsin-driven circadian entrainment.
- Cortisol circadian regulation shows wavelength sensitivity analogous to the well-established spectral sensitivity of melatonin suppression.
- Review identified only 12 eligible studies from 3,418 screened, highlighting a significant gap in controlled research on light wavelength and HPA axis function.
Categories
Sleep & Circadian Health: Reviews how light wavelength and intensity entrain cortisol rhythms via the SCN and HPA axis, paralleling melatonin's known light sensitivity.
The Science of Light: Systematically examines spectral power distribution and luminance effects on neuroendocrine (cortisol) secretion, informing lighting standards and spectral design choices.
Student Learning: Identifies classroom lighting as a key constructed environment where short-wavelength light exposure warrants careful management due to cortisol effects.
Author(s)
I Robertson-Dixon, MJ Murphy, SG Crewther, N Riddell
Publication Year
2023
Number of Citations
1
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