Definition:
Circadian rhythms are natural, internal processes that repeat roughly every 24 hours, regulating the timing of physiological and behavioural functions. They are driven by the suprachiasmatic nucleus (SCN) in the hypothalamus, which acts as the body’s master clock.
Why it matters:
Circadian rhythms influence sleep–wake cycles, hormone release, metabolism, immune response, and alertness. Misalignment between circadian rhythms and the environment can lead to poor sleep, reduced performance, and increased risk of chronic health conditions.
How they are regulated:
- Light is the strongest synchroniser (zeitgeber) of circadian rhythms.
- Specialised eye photoreceptors, especially ipRGCs, send light information to the SCN.
- The SCN coordinates peripheral clocks in organs and tissues across the body.
Relation to light measurement:
Metrics such as melanopic EDI or circadian stimulus are designed to describe how light impacts circadian rhythms. Spectral light dosimeters provide researchers, clinicians, and designers with accurate tools to quantify and optimise light exposure for circadian health.
Applications:
- Designing circadian-friendly lighting in offices, schools, hospitals, and aged care.
- Clinical studies of sleep and circadian rhythm disorders.
- Occupational health for shift workers and people with irregular schedules.
- Smart building systems supporting health and productivity.
Related terms: