Human phase response curve to a single 6.5 h pulse of short-wavelength light.
Level 3 - non-randomized controlled study
Controlled laboratory physiological study evaluating phase shifts across timing points without a concurrent randomized comparator.
PubMed 23090946 · doi:10.1113/jphysiol.2012.239046
What was done
Eighteen healthy young adults (aged 18–30 years) were evaluated over 9–10 days in a time-free laboratory setting. Following three baseline days, baseline circadian phase was measured via dim light melatonin onset (DLMO) during a constant routine protocol. Participants then received a single 6.5-hour pulse of monochromatic short-wavelength light (480 nm; 11.8 μW cm⁻², 11.2 lux) administered through a modified Ganzfeld dome following pupil dilation (mydriasis). Circadian phase was reassessed during a second constant routine to map phase shifts across exposure timings and construct a phase response curve (PRC).
What was found
The 480 nm light pulse produced a conventional type 1 circadian phase response curve. Fitted maximum phase delays reached -2.6 hours and maximum phase advances reached 1.3 hours. Overall, the 11.2 lux blue-light PRC elicited approximately 75% of the phase-shifting response previously documented with 10,000 lux polychromatic white light using a similar protocol.
Why it matters
It demonstrates that human circadian phase shifting is highly sensitive to narrow-band short-wavelength light even at low photopic illuminance (11.2 lux), informing dosing parameters for clinical circadian interventions and fatigue countermeasures.
Limits
The sample was small (n = 18) and limited to healthy young adults. Delivery required pharmacological pupil dilation and a Ganzfeld dome, limiting direct generalizability to naturalistic light exposures. Comparisons to 10,000 lux white light were made against historical data rather than a concurrent randomized control group.
Cited by
- context Exposure to approximately 10,000 lux of bright blue-spectrum light can shift the human circadian rhythm by about 8 hours.