Daily Light Exposure Patterns Reveal Phase and Period of the Human Circadian Clock

Abstract

Light is the most potent time cue that synchronizes (entrains) the circadian pacemaker to the 24-h solar cycle. This entrainment process is an interplay between an individual’s daily light perception and intrinsic pacemaker period under free-running conditions. Establishing individual estimates of circadian phase and period can be time-consuming. We show that circadian phase can be accurately predicted (SD = 1.1 h for dim light melatonin onset, DLMO) using 9 days of ambulatory light and activity data as an input to Kronauer’s limit-cycle model for the human circadian system. This approach also yields an estimated circadian period of 24.2 h (SD = 0.2 h), with longer periods resulting in later DLMOs. A larger amount of daylight exposure resulted in an earlier DLMO. Individuals with a long circadian period also showed shorter intervals between DLMO and sleep timing. When a field-based estimation of tau can be validated under laboratory studies in a wide variety of individuals, the proposed methods may prove to be essential tools for individualized chronotherapy and light treatment for shift work and jetlag applications. These methods may improve our understanding of fundamental properties of human circadian rhythms under daily living conditions.

The flexible clock: predictive and reactive homeostasis, energy balance and the circadian regulation of sleep–wake timing

“…This line of investigation might eventually bear relevant insights for targeted treatment of humans who are facing frequent disruptions of their daily routines (e.g. shift work, traveling time zones, irregular lifestyles) or who have reduced exposure to natural light-dark cycles (Woelders et al, 2017).…”

Optimal Lighting Conditions for Office Workers from the Perspective of Non-visual Effects

“…Therefore, it has been hypothesized that lighting conditions normally seen in an office, which involve constant intensity and color temperature, would make the rhythm vague [8]. In this study, the amplitude of rhythm was evaluated by temporal changes in rectal temperature during sleep; circadian phase advance due to daytime lighting conditions was assessed via dim light melatonin onset (DLMO); and sleep architecture was evaluated by PSG [2].…”

Light effects on circadian and homeostatic regulation: alertness increases independent of time awake

“…Dim light (<10 lux) has been standard procedure since the first FD experiment was performed in 13 . Apart from model calculations 15 , this is the first study we know that shows that short FD protocols can also be used for disentangling effects of bright light gated by wake duration related variation and circadian processes. During FD paradigms, concentrations of the nocturnal hormone melatonin have regularly been used as output measures of SCN rhythmicity.…”

“…Earlier model simulations indicated that FD protocols with limited amount of cycles may typically overestimate circadian period at high light intensities 15 , and should therefore not be over-interpreted. Subjective alerting effects of light depend on homeostatic control.…”

“…This is partially caused by relative coordination of the circadian system with the sleep-wake pattern and synchronous light-dark cycle. However, examination of the parameter space of the human circadian pacemaker indicated the possibility to run a FD design at various light intensities without major effects of relative coordination 15 . To investigate the contribution of both circadian and wake duration related variation to alerting effects of light, we conducted such an FD experiment in humans under both low and high light intensities.…”