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Good Light: Understanding Individual Differences in Light Sensitivity and the Human Circadian Clock

William J. Schwartz, MD

This study explores why different people have different reactions to light, especially how it affects their sleep-wake patterns. The research focuses on the genetic factors that influence these differences.

Photo by Dewang Gupta on Unsplash

Circadian Clock and Light

  • Our circadian clock is an internal system that regulates sleep and wakefulness based on environmental light and dark cycles.

  • Light characteristics such as wavelength, intensity, and exposure patterns help synchronize this clock to the natural day-night cycle.


  • Chronotype refers to individual sleep patterns, ranging from early risers ("larks") to night owls, with many variations in between.

  • Light exposure significantly influences chronotype, but individuals react differently to the same light conditions.

Biological Mechanisms

  • Biological processes, including how our eyes process light and send signals to the brain, contribute to these individual differences.

  • The study looks into genetic factors that might explain why people have different light sensitivities.

The Study

  • Researchers used data from 280,897 people in the UK BioBank to investigate the genetic basis of light sensitivity.

  • They identified a new genetic locus on the ARL14EP gene, which may influence how sensitive someone is to light and could be related to retinal development.


  • People with greater light sensitivity tend to have a later chronotype, meaning they are more likely to be night owls.

  • This might be linked to modern lighting patterns where there is less natural daylight exposure and more artificial light at night.

Implications and Future Research

  • While there are some limitations to the study, it marks a significant step toward understanding the genetic basis of light sensitivity.

  • The ultimate goal is to develop personalized light exposure recommendations, termed "Good Light" regimens, to optimize individual circadian rhythms.

This research is a promising start in understanding how genetics influence our response to light and how this affects our sleep patterns. Future work could lead to personalized advice on light exposure to improve sleep and overall health.

Burns AC, Phillips AJK, Rutter MK, Saxena R, Cain SW, Lane JM. Genome-wide gene by environment study of time spent in daylight and chronotype identifies emerging genetic architecture underlying light sensitivity. Sleep, Volume 46, Issue 3, March 2023, zsac287. 



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