Light Exposure and Circadian Rhythm Regulation

Human physiology and behaviour are governed by an intrinsic near-24-hour timing system, the circadian rhythm, which synchronises internal processes with the external light–dark cycle. Light acts as the principal zeitgeber, or time cue, by influencing specialised photoreceptors in the retina that convey information to the suprachiasmatic nucleus of the hypothalamus. Beyond image formation, these non-visual pathways regulate hormone secretion (notably melatonin), sleep–wake timing, alertness and metabolic functions. Both the intensity and spectral quality of light—particularly short-wavelength (‘blue’) components—determine the strength of these effects, while timing of exposure dictates advance or delay of the internal clock. Modern lifestyles, featuring reduced daylight exposure indoors and elevated evening illumination from screens and artificial lighting, can lead to circadian misalignment with consequences for sleep health, mood and long-term disease risk. Emerging wearable sensors and real-world interventions have heightened understanding of how personalised light exposure patterns shape daily physiology and suggest strategies to optimise environmental lighting for public health.

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Light Exposure and Circadian Rhythm Regulation publication trend

The graph below shows the total number of articles in light exposure and circadian rhythm regulation across all publications each year (not limited to Nature Index journals).

Technical terms

Circadian rhythm: Endogenous near-24-hour cycle governing physiological and behavioural functions.

Zeitgeber: External cue, especially light, that synchronises biological clocks to the environment.

Melanopsin: Photopigment in intrinsically photosensitive retinal ganglion cells, maximally sensitive to short-wavelength light, mediating non-visual effects.

Equivalent daylight illuminance: Measure of light weighted by melanopic sensitivity, reflecting biological impact.

Phase shift: Adjustment of the timing of the internal clock forward (advance) or backward (delay) in response to light exposure.

References

1. Associations between light exposure and sleep timing and sleepiness while awake in a sample of UK adults in everyday life. Proceedings of the National Academy of Sciences of the United States of America (2023).
2. Are we still in the dark? A systematic review on personal daily light exposure, sleep-wake rhythm, and mood in healthy adults from the general population. Sleep Health (2021).
3. The Light-Dosimeter: A new device to help advance research on the non-visual responses to light. Lighting Research & Technology (2023).