Effects of light on human circadian rhythms
Related Experiment Video
Updated: Oct 19, 2026

Inducing Daytime Circadian Phase Shifts Using Chemogenetic and Spectral Approaches
Published on: June 12, 2026
D J Skene1, S W Lockley, K Thapan
1School of Biological Sciences, University of Surrey, Guildford, UK. d.skene@surrey.ac.uk
Abstract:
Blind subjects with defective retinal processing provide a good model to study the effects of light (or absence of light) on the human circadian system. The circadian rhythms (melatonin, cortisol, timing of sleep/wake) of individuals with different degrees of light perception (n = 67) have been studied. Blind subjects with some degree of light perception (LP) mainly have normally entrained circadian rhythms, whereas subjects with no conscious light perception (NPL) are more likely to exhibit disturbed circadian rhythms. All subjects who were bilaterally enucleated showed free running melatonin and cortisol rhythms. Studies assessing the light-induced suppression of melatonin show the response to be intensity and wavelength dependent. In contrast to ocular light exposure, extraocular light failed to suppress night-time melatonin. Thus, ocular light appears to be the predominant time cue and major determinant of circadian rhythm type. Optimisation of the light for entrainment (intensity, duration, wavelength, time of administration) requires further study.
Related Concept Videos
Circadian Rhythms and Gene Regulation
Biological Clocks and Seasonal Responses
Chronopharmacokinetics: Circadian Rhythms and Influence on Drug Response
The time of drug administration is an important factor to consider, as it can influence the toxic dose of a drug. For example, a study conducted by Prins et al. in 1997 examined the effects of the timing of...
Management of Insomnia
Understanding Sleep
The circadian rhythm, a nearly 24-hour cycle, is deeply influenced by environmental light cues. Light exposure directly affects the hypothalamus, which in turn regulates...
Insufficient Sleep and Sleep Deprivation
Sleep deprivation is a more severe form of sleep loss...